On 5 June 2008, Secretary of Defense Robert Gates, accepted the resignations of both the Secretary of the Air Force, Michael Wynne, and the Chief of Staff of the United States Air Force, General T. Michael Moseley. Gates in effect fired both men for "systemic issues associated with declining Air Force nuclear mission focus and performance." This followed an investigation into two embarrassing incidents involving mishandling of nuclear weapons: specifically a nuclear weapons incident aboard a B-52 flight between Minot AFB and Barksdale AFB, and an accidental shipment of nuclear weapons components to Taiwan. The resignations were also the culmination of disputes between the Air Force leadership, populated primarily by non-nuclear background fighter pilots, versus Gates. To put more emphasis on nuclear assets, the USAF established the nuclear-focused Air Force Global Strike Command on 24 October 2008.


What Secretary of the Air Force resigned in 2008?


Where did the US Air Force accidentally ship a component of Nuclear Weapons?


What US Chief of Staff of the US Air Force also resigned in June of 2008?


When was the Air Force Global Strike Command formed?


Why was the USAF forced to ground some of its squadrons in 2013?

Due to the Budget sequestration in 2013, the USAF was forced to ground many of its squadrons. The Commander of Air Combat Command, General Mike Hostage indicated that the USAF must reduce its F-15 and F-16 fleets and eliminate platforms like the A-10 in order to focus on a fifth-generation jet fighter future. In response to squadron groundings and flight time reductions, many Air Force pilots have opted to resign from active duty and enter the Air Force Reserve and Air National Guard while pursuing careers in the commercial airlines where they can find flight hours on more modern aircraft.


Who was the Commander of Air Combat Command in 2013?


Why have many US Air Force pilots opted to resign from active service?


Where have many of these US Air Force pilots chosen to find employment instead?


What is one of the concerns of the Air Force?

Specific concerns include a compounded inability for the Air Force to replace its aging fleet, and an overall reduction of strength and readiness. The USAF attempted to make these adjustments by primarily cutting the Air National Guard and Air Force Reserve aircraft fleets and their associated manpower, but Congress reversed this initiative and the majority of the lost manpower will come from the active forces. However, Congress did allow for $208 million of reprogramming from fleet modernization to enable some portion of the third of the grounded fleet to resume operations.


How did the USAF try to make these adjustments to help with strength and readiness of its fleet?


How much money did Congress give to the USAF to enable them to replace some of the grounded fleet?


Who is the Department of the Air Force managed by?

The Department of the Air Force is one of three military departments within the Department of Defense, and is managed by the civilian Secretary of the Air Force, under the authority, direction, and control of the Secretary of Defense. The senior officials in the Office of the Secretary are the Under Secretary of the Air Force, four Assistant Secretaries of the Air Force and the General Counsel, all of whom are appointed by the President with the advice and consent of the Senate. The senior uniformed leadership in the Air Staff is made up of the Chief of Staff of the Air Force and the Vice Chief of Staff of the Air Force.


Who does the Secretary of the Air Force report to?


Who appoints the top positions in the USAF, including the Assistant Secretaries and General Council?


Upon whom does the President call on for support in his appointments to the USAF?


Who does the senior leadership roles in the USAF include?


Who directs the Secretary of the Air Force during operational missions?

The organizational structure as shown above is responsible for the peacetime organization, equipping, and training of aerospace units for operational missions. When required to support operational missions, the Secretary of Defense (SECDEF) directs the Secretary of the Air Force (SECAF) to execute a Change in Operational Control (CHOP) of these units from their administrative alignment to the operational command of a Regional Combatant Commander (CCDR). In the case of AFSPC, AFSOC, PACAF, and USAFE units, forces are normally employed in-place under their existing CCDR. Likewise, AMC forces operating in support roles retain their componency to USTRANSCOM unless chopped to a Regional CCDR.


What does the abbreviation CHOP stand for?


Who does the AMC forces usually retain their componency to?


Who is in charge of these Change in Operational Control missions?


What are "Chopped" units called in the USAF?

"Chopped" units are referred to as forces. The top-level structure of these forces is the Air and Space Expeditionary Task Force (AETF). The AETF is the Air Force presentation of forces to a CCDR for the employment of Air Power. Each CCDR is supported by a standing Component Numbered Air Force (C-NAF) to provide planning and execution of aerospace forces in support of CCDR requirements. Each C-NAF consists of a Commander, Air Force Forces (COMAFFOR) and AFFOR/A-staff, and an Air Operations Center (AOC). As needed to support multiple Joint Force Commanders (JFC) in the COCOM's Area of Responsibility (AOR), the C-NAF may deploy Air Component Coordinate Elements (ACCE) to liaise with the JFC. If the Air Force possesses the preponderance of air forces in a JFC's area of operations, the COMAFFOR will also serve as the Joint Forces Air Component Commander (JFACC).


What is the top level structure of these Chopped forces in the USAF?


Who does the C-NAFF coordinate with on ACEE missions?


AFSCs range from officer specialties such as pilot, combat systems officer, missile launch officer, intelligence officer, aircraft maintenance officer, judge advocate general (JAG), medical doctor, nurse or other fields, to various enlisted specialties. The latter range from flight combat operations such as a gunner, to working in a dining facility to ensure that members are properly fed. There are additional occupational fields such as computer specialties, mechanic specialties, enlisted aircrew, communication systems, cyberspace operations, avionics technicians, medical specialties, civil engineering, public affairs, hospitality, law, drug counseling, mail operations, security forces, and search and rescue specialties.


What is one of the many types of AFSC employed by the USAF?


What is an example of an occupational field position in the USAF?


What does the abbreviation EOD stand for in the USAF?

Beyond combat flight crew personnel, perhaps the most dangerous USAF jobs are Explosive Ordnance Disposal (EOD), Combat rescue officer, Pararescue, Security Forces, Combat Control, Combat Weather, Tactical Air Control Party, and AFOSI agents, who deploy with infantry and special operations units who disarm bombs, rescue downed or isolated personnel, call in air strikes and set up landing zones in forward locations. Most of these are enlisted positions augmented by a smaller number of commissioned officers. Other career fields that have seen increasing exposure to combat include civil engineers, vehicle operators, and Air Force Office of Special Investigations (AFOSI) personnel.


What is one of the most dangerous jobs for USAF personnel?


What do some of these special missions in the USAF who deploy with the infantry do?


What are these enlisted positions in the USAF complimented by?


What other career fields have seen an increase in active combat missions?


How long is the training for Explosive Ordnance Disposal in the USAF?

Training programs vary in length; for example, 3M0X1 (Services) has 31 days of tech school training, while 3E8X1 (Explosive Ordnance Disposal) is one year of training with a preliminary school and a main school consisting of over 10 separate divisions, sometimes taking students close to two years to complete. Officer technical training conducted by Second Air Force can also vary by AFSC, while flight training for aeronautically-rated officers conducted by AETC's Nineteenth Air Force can last well in excess of one year.


What USAF tech school has 31 days of training?


Who conducts the training for Technical Officers in the USAF?


How long does the flight training for the AETC's Nineteenth Air Force last?


What groups is the USAF rank divided amoung?

USAF rank is divided between enlisted airmen, non-commissioned officers, and commissioned officers, and ranges from the enlisted Airman Basic (E-1) to the commissioned officer rank of General (O-10). Enlisted promotions are granted based on a combination of test scores, years of experience, and selection board approval while officer promotions are based on time-in-grade and a promotion selection board. Promotions among enlisted personnel and non-commissioned officers are generally designated by increasing numbers of insignia chevrons. Commissioned officer rank is designated by bars, oak leaves, a silver eagle, and anywhere from one to four stars (one to five stars in war-time).[citation needed]


How are Enlisted promotions in the USAF decided?


How are Officer promotions within the USAF decided?


How is a Commissioned Officer's rank shown?


Air Force officer promotions are governed by the Defense Officer Personnel Management Act of 1980 and its companion Reserve Officer Personnel Management Act (ROPMA) for officers in the Air Force Reserve and the Air National Guard. DOPMA also establishes limits on the number of officers that can serve at any given time in the Air Force. Currently, promotion from second lieutenant to first lieutenant is virtually guaranteed after two years of satisfactory service. The promotion from first lieutenant to captain is competitive after successfully completing another two years of service, with a selection rate varying between 99% and 100%. Promotion to major through major general is through a formal selection board process, while promotions to lieutenant general and general are contingent upon nomination to specific general officer positions and subject to U.S. Senate approval.


What are Air Force Officer promotions overseen by?


How long does it usually take to be promoted from second to first lieutenant in the USAF?


Who establishes limits on the amount of Air Force officers?


What promotion in the USAF is governed by a formal selection process?


Where is an officer's record in the USAF reviewed for a promotion?

During the board process an officer's record is reviewed by a selection board at the Air Force Personnel Center at Randolph Air Force Base in San Antonio, Texas. At the 10 to 11 year mark, captains will take part in a selection board to major. If not selected, they will meet a follow-on board to determine if they will be allowed to remain in the Air Force. Promotion from major to lieutenant colonel is similar and occurs approximately between the thirteen year (for officers who were promoted to major early "below the zone") and the fifteen year mark, where a certain percentage of majors will be selected below zone (i.e., "early"), in zone (i.e., "on time") or above zone (i.e., "late") for promotion to lieutenant colonel. This process will repeat at the 16 year mark (for officers previously promoted early to major and lieutenant colonel) to the 21 year mark for promotion to full colonel.


What state is the Randolph Air Force Base located in?


When does promotion from major to lieutenant colonel in the USAF typically occur?


The promotion process repeats when for officers promoted early in the USAF?


What section in the US Code for the Secretary of the Air Force allows for the appointment of warrant officers?

Although provision is made in Title 10 of the United States Code for the Secretary of the Air Force to appoint warrant officers, the Air Force does not currently use warrant officer grades, and is the only one of the U.S. Armed Services not to do so. The Air Force inherited warrant officer ranks from the Army at its inception in 1947, but their place in the Air Force structure was never made clear.[citation needed] When the Congress authorized the creation of two new senior enlisted ranks in 1958, Air Force officials privately concluded that these two new "super grades" could fill all Air Force needs then performed at the warrant officer level, although this was not publicly acknowledged until years later.[citation needed] The Air Force stopped appointing warrant officers in 1959, the same year the first promotions were made to the new top enlisted grade, Chief Master Sergeant. Most of the existing Air Force warrant officers entered the commissioned officer ranks during the 1960s, but small numbers continued to exist in the warrant officer grades for the next 21 years.


When did the USAF inherit warrant officer ranks from the Army?


When did Congress authorize the creation of two new senior officer grades?


When did the USAF stop appointing warrant officers?


What is the newest top enlisted grade in the USAF?


What is the lowest pay grade in the USAF?

Enlisted members of the USAF have pay grades from E-1 (entry level) to E-9 (senior enlisted). While all USAF military personnel are referred to as Airmen, the term also refers to the pay grades of E-1 through E-4, which are below the level of non-commissioned officers (NCOs). Above the pay grade of E-4 (i.e., pay grades E-5 through E-9) all ranks fall into the category of NCO and are further subdivided into "NCOs" (pay grades E-5 and E-6) and "Senior NCOs" (pay grades E-7 through E-9); the term "Junior NCO" is sometimes used to refer to staff sergeants and technical sergeants (pay grades E-5 and E-6).


What is the highest pay grade in the USAF?


What pay grades are included in the USAF for Senior NCOs?


What does junior NCO refer to in the USAF pay grade system?


When does NCO status happen in all other branches of the US Military?

The USAF is the only branch of the U.S. military where NCO status is achieved when an enlisted person reaches the pay grade of E-5. In all other branches, NCO status is generally achieved at the pay grade of E-4 (e.g., a Corporal in the Army and Marine Corps, Petty Officer Third Class in the Navy and Coast Guard). The Air Force mirrored the Army from 1976 to 1991 with an E-4 being either a Senior Airman wearing three stripes without a star or a Sergeant (referred to as "Buck Sergeant"), which was noted by the presence of the central star and considered an NCO. Despite not being an NCO, a Senior Airman who has completed Airman Leadership School can be a supervisor according to the AFI 36-2618.


What must a Senior Airman do to become a supervisor in the USAF?


What rank is NCO status achieved in the US Army?


Where was the Uxbridge Blue dress uniform developed?

The first USAF dress uniform, in 1947, was dubbed and patented "Uxbridge Blue" after "Uxbridge 1683 Blue", developed at the former Bachman-Uxbridge Worsted Company. The current Service Dress Uniform, which was adopted in 1993 and standardized in 1995, consists of a three-button, pocketless coat, similar to that of a men's "sport jacket" (with silver "U.S." pins on the lapels, with a silver ring surrounding on those of enlisted members), matching trousers, and either a service cap or flight cap, all in Shade 1620, "Air Force Blue" (a darker purplish-blue). This is worn with a light blue shirt (Shade 1550) and Shade 1620 herringbone patterned necktie. Enlisted members wear sleeve insignia on both the jacket and shirt, while officers wear metal rank insignia pinned onto the coat, and Air Force Blue slide-on epaulet loops on the shirt. USAF personnel assigned to Base Honor Guard duties wear, for certain occasions, a modified version of the standard service dress uniform, but with silver trim on the sleeves and trousers, with the addition of a ceremonial belt (if necessary), wheel cap with silver trim and Hap Arnold Device, and a silver aiguillette placed on the left shoulder seam and all devices and accoutrement.


When was the first USAF dress uniform introduced?


When was the current USAF dress uniform standardized?


Where does an officer in the USAF wear their rank insignia?


What is worn by USAF members to indicate a billet assignment?

In addition to basic uniform clothing, various badges are used by the USAF to indicate a billet assignment or qualification-level for a given assignment. Badges can also be used as merit-based or service-based awards. Over time, various badges have been discontinued and are no longer distributed. Authorized badges include the Shields of USAF Fire Protection, and Security Forces, and the Missile Badge (or "pocket rocket"), which is earned after working in a missile system maintenance or missile operations capacity for at least one year.


What else can Badges be used to designate in the USAF?


What is one of the types of Authorized Badges in the USAF?


When is the special "pocket rocket" badge given to USAF personnel working in a missile system operation?


USAF Officers can be commissioned after graduation from what school?

Officers may be commissioned upon graduation from the United States Air Force Academy, upon graduation from another college or university through the Air Force Reserve Officer Training Corps (AFROTC) program, or through the Air Force Officer Training School (OTS). OTS, previously located at Lackland AFB, Texas until 1993 and located at Maxwell Air Force Base in Montgomery, Alabama since 1993, in turn encompasses two separate commissioning programs: Basic Officer Training (BOT), which is for line-officer candidates of the active-duty Air Force and the U.S. Air Force Reserve; and the Academy of Military Science (AMS), which is for line-officer candidates of the Air National Guard. (The term "line officer" derives from the concept of the line of battle and refers to an officer whose role falls somewhere within the "Line of the Air", meaning combat or combat-support operations within the scope of legitimate combatants as defined by the Geneva Conventions.)


What is another program that allows officers to become commissioned in the USAF?


Where is the OTS in the US currently located?


How many commissioning programs does the OTS offer the USAF?


What does the Air Force provide for officers of direct to non-line positions?

The Air Force also provides Commissioned Officer Training (COT) for officers of all three components who are direct-commissioned to non-line positions due to their credentials in medicine, law, religion, biological sciences, or healthcare administration. Originally viewed as a "knife and fork school" that covered little beyond basic wear of the uniform, COT in recent years has been fully integrated into the OTS program and today encompasses extensive coursework as well as field exercises in leadership, confidence, fitness, and deployed-environment operations.


What fields of study in the COT are included in this area of the USAF?


What is an example of the coursework now offered in the COT in the USAF?


What is the more strict program that the USAF adopted in 2010 called?

The US Air Force Fitness Test (AFFT) is designed to test the abdominal circumference, muscular strength/endurance and cardiovascular respiratory fitness of airmen in the USAF. As part of the Fit to Fight program, the USAF adopted a more stringent physical fitness assessment; the new fitness program was put into effect on 1 June 2010. The annual ergo-cycle test which the USAF had used for several years had been replaced in 2004. In the AFFT, Airmen are given a score based on performance consisting of four components: waist circumference, the sit-up, the push-up, and a 1.5-mile (2.4 km) run. Airmen can potentially earn a score of 100, with the run counting as 60%, waist circumference as 20%, and both strength test counting as 10% each. A passing score is 75 points. Effective 1 July 2010, the AFFT is administered by the base Fitness Assessment Cell (FAC), and is required twice a year. Personnel may test once a year if he or she earns a score above a 90%. Additionally, only meeting the minimum standards on each one of these tests will not get you a passing score of 75%, and failing any one component will result in a failure for the entire test.


What test is designed to test the fitness of airmen in the USAF?


How long is the run that the USAF airmen are tested on for the fitness program?


What is a passing score on the US Air Force Fitness Test?


What score must an airman get on the US Air Force Fitness test to be able to opt out of one of the mandatory twice a year retests?


What are the ground-attack aircraft in the USAF usually deployed in support for?

The ground-attack aircraft of the USAF are designed to attack targets on the ground and are often deployed as close air support for, and in proximity to, U.S. ground forces. The proximity to friendly forces require precision strikes from these aircraft that are not possible with bomber aircraft listed below. They are typically deployed as close air support to ground forces, their role is tactical rather than strategic, operating at the front of the battle rather than against targets deeper in the enemy's rear.


What does the closeness to friendly troops require of these US Air Force aircraft?


What part of a battle line are the precision strike aircraft of the USAF deployed?


What type of aircraft is not appropriate to be used in close proximity of US ground troops?


What are most attack aircraft in the US Air Force designed to do?

In the US Air Force, the distinction between bombers, fighters that are actually fighter-bombers, and attack aircraft has become blurred. Many attack aircraft, even ones that look like fighters, are optimized to drop bombs, with very little ability to engage in aerial combat. Many fighter aircraft, such as the F-16, are often used as 'bomb trucks', despite being designed for aerial combat. Perhaps the one meaningful distinction at present is the question of range: a bomber is generally a long-range aircraft capable of striking targets deep within enemy territory, whereas fighter bombers and attack aircraft are limited to 'theater' missions in and around the immediate area of battlefield combat. Even that distinction is muddied by the availability of aerial refueling, which greatly increases the potential radius of combat operations. The US, Russia, and the People's Republic of China operate strategic bombers.


What type of USAF aircraft is designed for long range airstrike attacks?


What types of aircraft are typically limited to close proximity of battlefield conflict by the USAF?


What increases the radius of combat missions by the US Air Force?


What countries utilize strategic bomber aircraft in their missions?


When did the B-2A aircraft enter into service of the US Air Force?

The service's B-2A aircraft entered service in the 1990s, its B-1B aircraft in the 1980s and its current B-52H aircraft in the early 1960s. The B-52 Stratofortress airframe design is over 60 years old and the B-52H aircraft currently in the active inventory were all built between 1960 and 1962. The B-52H is scheduled to remain in service for another 30 years, which would keep the airframe in service for nearly 90 years, an unprecedented length of service for any aircraft. The B-21 is projected to replace the B-52 and parts of the B-1B force by the mid-2020s.


When did the USAF introduce the B-1B aircraft?


What aircraft in the USAF was introduced in the 1960s?


How long is the B-52H scheduled to remain in service of the USAF?


What aircraft is scheduled to replace the B-52 in the USAF?


What type of aircraft is used to deliver troops and weapons to military operations?

Cargo and transport aircraft are typically used to deliver troops, weapons and other military equipment by a variety of methods to any area of military operations around the world, usually outside of the commercial flight routes in uncontrolled airspace. The workhorses of the USAF Air Mobility Command are the C-130 Hercules, C-17 Globemaster III, and C-5 Galaxy. These aircraft are largely defined in terms of their range capability as strategic airlift (C-5), strategic/tactical (C-17), and tactical (C-130) airlift to reflect the needs of the land forces they most often support. The CV-22 is used by the Air Force for the U.S. Special Operations Command (USSOCOM). It conducts long-range, special operations missions, and is equipped with extra fuel tanks and terrain-following radar. Some aircraft serve specialized transportation roles such as executive/embassy support (C-12), Antarctic Support (LC-130H), and USSOCOM support (C-27J, C-145A, and C-146A). The WC-130H aircraft are former weather reconnaissance aircraft, now reverted to the transport mission.


What aircraft are considered the workhorses of the US Air Force?


The CV-22 aircraft is used by what section of the USAF?


What aircraft offers Antarctic Support to the US Air Force?


What did the USAF use the WC-130H aircraft for before they converted them for transport missions?


What is the purpose of electronic warfare?

The purpose of electronic warfare is to deny the opponent an advantage in the EMS and ensure friendly, unimpeded access to the EM spectrum portion of the information environment. Electronic warfare aircraft are used to keep airspaces friendly, and send critical information to anyone who needs it. They are often called "The Eye in the Sky." The roles of the aircraft vary greatly among the different variants to include Electronic Warfare/Jamming (EC-130H), Psychological Operations/Communications (EC-130J), Airborne Early Warning and Control (E-3), Airborne Command Post (E-4B), ground targeting radar (E-8C), range control (E-9A), and communications relay (E-11A)


What nickname is given to Electronic warfare aircraft?


What does the USAF use Electronic warfare aircraft for?


What is the EC-130H used for by the US Air Force?


What does the USAF use the E-4B aircraft for?


What is the primary function of the USAF fighter aircraft?

The fighter aircraft of the USAF are small, fast, and maneuverable military aircraft primarily used for air-to-air combat. Many of these fighters have secondary ground-attack capabilities, and some are dual-roled as fighter-bombers (e.g., the F-16 Fighting Falcon); the term "fighter" is also sometimes used colloquially for dedicated ground-attack aircraft. Other missions include interception of bombers and other fighters, reconnaissance, and patrol. The F-16 is currently used by the USAF Air Demonstration squadron, the Thunderbirds, while a small number of both man-rated and non-man-rated F-4 Phantom II are retained as QF-4 aircraft for use as Full Scale Aerial Targets (FSAT) or as part of the USAF Heritage Flight program. These extant QF-4 aircraft are being replaced in the FSAT role by early model F-16 aircraft converted to QF-16 configuration. The USAF has 2,025 fighters in service as of September 2012.


What is the name of a type of dual purpose fighter-bomber aircraft used by the US Air Force?


What aircraft is used by the US Air Demonstration group The Thunderbirds?


What kind of aircraft is utilized by the USAF in Full Scale Aerial Targets?


What are the QF-4 aircraft being replaced by the US Air Force?


What kind of aircraft is the USAF's KC-135?

The USAF's KC-135 and KC-10 aerial refueling aircraft are based on civilian jets. The USAF aircraft are equipped primarily for providing the fuel via a tail-mounted refueling boom, and can be equipped with "probe and drogue" refueling systems. Air-to-air refueling is extensively used in large-scale operations and also used in normal operations; fighters, bombers, and cargo aircraft rely heavily on the lesser-known "tanker" aircraft. This makes these aircraft an essential part of the Air Force's global mobility and the U.S. force projection. The KC-46A Pegasus is undergoing testing and is projected to be delivered to USAF units starting in 2017.


How does the aerial refueling aircraft supply fuel during flight?


When is air-to-air refueling primarily used by the US Air Force?


What aircraft will be available for use by the US Air Force in 2017?


What US Secretary of Defense accepted resignations of top US Air Force officials in June of 2009?

In response to the 2007 United States Air Force nuclear weapons incident, Secretary of Defense Robert Gates accepted in June 2009 the resignations of Secretary of the Air Force Michael Wynne and the Chief of Staff of the Air Force General T. Michael Moseley. Moseley's successor, General Norton A. Schwartz, a former tactical airlift and special operations pilot was the first officer appointed to that position who did not have a background as a fighter or bomber pilot. The Washington Post reported in 2010 that General Schwartz began to dismantle the rigid class system of the USAF, particularly in the officer corps.


What US Secretary of the Air Force resigned following a nuclear weapons problem ?


Who was appointed to the Chief of Staff of the Air Force following Mosley's resignation?


What newspaper reported on Schwartz's dismantlement of the US Air Force's class system?


What author wrote about the US Air Force egalitarian culture?

Daniel L. Magruder, Jr defines USAF culture as a combination of the rigorous application of advanced technology, individualism and progressive airpower theory. Major General Charles J. Dunlap, Jr. adds that the U.S. Air Force's culture also includes an egalitarianism bred from officers perceiving themselves as their service's principal "warriors" working with small groups of enlisted airmen either as the service crew or the onboard crew of their aircraft. Air Force officers have never felt they needed the formal social "distance" from their enlisted force that is common in the other U.S. armed services. Although the paradigm is changing, for most of its history, the Air Force, completely unlike its sister services, has been an organization in which mostly its officers fought, not its enlisted force, the latter being primarily a rear echelon support force. When the enlisted force did go into harm's way, such as members of multi-crewed aircraft, the close comradeship of shared risk in tight quarters created traditions that shaped a somewhat different kind of officer/enlisted relationship than exists elsewhere in the military.


How does the US Air Force differ from other branches of the military?


How have the enlisted forces of the US Air Force been seen?


What is the reason for the shortage of UAV operators in the US Air Force?

Cultural and career issues in the U.S. Air Force have been cited as one of the reasons for the shortfall in needed UAV operators. In spite of an urgent need for UAVs or drones to provide round the clock coverage for American troops during the Iraq War, the USAF did not establish a new career field for piloting them until the last year of that war and in 2014 changed its RPA training syllabus again, in the face of large aircraft losses in training, and in response to a GAO report critical of handling of drone programs. Paul Scharre has reported that the cultural divide between the USAF and US Army has kept both services from adopting each other's drone handing innovations.


During what war the the USAF establish a new career field for piloting UAVs and drones?


Why did the USAF change its training methods on UAVs in 2014?


What branch of the US Military does a cultural divide prevent the US Air Force from adopting their drone protocols?


Where did some of the US Air Force traditions come from?

Many of the U.S. Air Force's formal and informal traditions are an amalgamation of those taken from the Royal Air Force (e.g., dining-ins/mess nights) or the experiences of its predecessor organizations such as the U.S. Army Air Service, U.S. Army Air Corps and the U.S. Army Air Forces. Some of these traditions range from "Friday Name Tags" in flying units to an annual "Mustache Month." The use of "challenge coins" is a recent innovation that was adopted from the U.S. Army while another cultural tradition unique to the Air Force is the "roof stomp", practiced by Air Force members to welcome a new commander or to commemorate another event, such as a retirement.


What traditions does the US Air Force have?


What organization did the US Air Force adopt "Challenge Coins" from?


What does the roof stomp tradition signify in the US Air Force?


What was a recent US Air Force recruiting slogan?

The United States Air Force has had numerous recruiting slogans including "No One Comes Close" and Uno Ab Alto ("One From On High"). For many years, the U.S. Air Force used "Aim High" as its recruiting slogan; more recently, they have used "Cross into the Blue", "We've been waiting for you" and "Do Something Amazing", "Above All", and the newest one, as of 7 October 2010, considered a call and response, "Aim high" followed with the response, "Fly-Fight-Win" Each wing, group, or squadron usually has its own slogan(s). Information and logos can usually be found on the wing, group, or squadron websites.


What does the USAF slogan Uno Ab Alto mean?


What is the most recent US Air Force recruitment slogan in October 2010?


Where can individual each USAF wing, group or squadrons individual motto be found?


What type of atmosphere can LED lighting be used?

Recent developments in LEDs permit them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes and lighted wallpaper. As of 2015[update], LEDs powerful enough for room lighting remain somewhat more expensive, and require more precise current and heat management, than compact fluorescent lamp sources of comparable output.


What is an advantage to using LED lighting over the normal light sources?


Why are some people hesitant to use LED lighting?


What was the nationality of the man who discovered Electroluminescence?

Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Soviet inventor Oleg Losev reported creation of the first LED in 1927. His research was distributed in Soviet, German and British scientific journals, but no practical use was made of the discovery for several decades. Kurt Lehovec, Carl Accardo and Edward Jamgochian, explained these first light-emitting diodes in 1951 using an apparatus employing SiC crystals with a current source of battery or pulse generator and with a comparison to a variant, pure, crystal in 1953.


LED lighting is the end result of what phenomenon?


When was Electroluminescence discovered?


Who is the Soviet man that created the first LED?


What type of detector did H.J. Round use to help him in his discovery?


What year was it discovered that early LED instruments could be used for non-radio communication?

In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer Braunstein".. had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier, and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." This setup presaged the use of LEDs for optical communication applications.


Who discovered non-radio uses for early LED devices?


The current in non-radio communication had to go through what type of component?


What other component was needed to detect the first current of a non-radio signal?


What final device was needed to hear the signal from the initial GaAs diode?


In what state what near-infrared light emission discovered?

In September 1961, while working at Texas Instruments in Dallas, Texas, James R. Biard and Gary Pittman discovered near-infrared (900 nm) light emission from a tunnel diode they had constructed on a GaAs substrate. By October 1961, they had demonstrated efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically-isolated semiconductor photodetector. On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias. After establishing the priority of their work based on engineering notebooks predating submissions from G.E. Labs, RCA Research Labs, IBM Research Labs, Bell Labs, and Lincoln Lab at MIT, the U.S. patent office issued the two inventors the patent for the GaAs infrared (IR) light-emitting diode (U.S. Patent US3293513), the first practical LED. Immediately after filing the patent, Texas Instruments (TI) began a project to manufacture infrared diodes. In October 1962, TI announced the first LED commercial product (the SNX-100), which employed a pure GaAs crystal to emit a 890 nm light output. In October 1963, TI announced the first commercial hemispherical LED, the SNX-110.


What type of diode was used to help discover near-infrared light emission?


In what year was the patent filed for the Semiconductor Radiant Diode?


The two inventors of the first practical diode were employed by what famous company?


At what global company was the first visible-spectrum LED developed?

The first visible-spectrum (red) LED was developed in 1962 by Nick Holonyak, Jr., while working at General Electric Company. Holonyak first reported his LED in the journal Applied Physics Letters on the December 1, 1962. M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall created the first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.


What GE employee developed the visible-spectrum LED?


What color is associated with the visible-spectrum LED?


What color LED was later created in 1972?


What graduate student of Holonyak created the yellow LED?


What was the first commercial uses of LEDs?

The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, as well as watches (see list of signal uses). Until 1968, visible and infrared LEDs were extremely costly, in the order of US$200 per unit, and so had little practical use. The Monsanto Company was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide (GaAsP) in 1968 to produce red LEDs suitable for indicators. Hewlett Packard (HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and appeared in appliances and equipment. In the 1970s commercially successful LED devices at less than five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor. The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. These methods continue to be used by LED producers.


What was one use of early LED light in products?


What modern company introduced LEDs in 1968?


In what decade were production costs greatly reduced for LEDs to enable successful commercial uses?


What color LED was demonstrated in 1994?

The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994 and was based on InGaN. In parallel, Isamu Akasaki and Hiroshi Amano in Nagoya were working on developing the important GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN. Nakamura, Akasaki and Amano were awarded the 2014 Nobel prize in physics for their work. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using indium tin oxide (ITO) on (AlGaInP/GaAs).


What did Nakamura, Akasaki, and Amano receive for their work?


Who investigated the efficiency of high-brightness LED at Cardiff University in 1995?


What substance did Barbieri use in his work with high-brightness LED?


What LED quickly followed the blue LEDs?

The attainment of high efficiency in blue LEDs was quickly followed by the development of the first white LED. In this device a Y 3Al 5O 12:Ce (known as "YAG") phosphor coating on the emitter absorbs some of the blue emission and produces yellow light through fluorescence. The combination of that yellow with remaining blue light appears white to the eye. However using different phosphors (fluorescent materials) it also became possible to instead produce green and red light through fluorescence. The resulting mixture of red, green and blue is not only perceived by humans as white light but is superior for illumination in terms of color rendering, whereas one cannot appreciate the color of red or green objects illuminated only by the yellow (and remaining blue) wavelengths from the YAG phosphor.


What does the YAG phosphor coating produce?


What converts absorbed light energy into an electric current?

A P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called electroluminescence, which can be defined as the emission of light from a semi-conductor under the influence of an electric field. The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes will be lesser than the energy levels of the electrons. Some portion of the energy must be dissipated in order to recombine the electrons and the holes. This energy is emitted in the form of heat and light.


What is the phenomenon where a P-N junction emits light when an electrical current is applied to it?


Where are the free electrons located in the production of electroluminescence?


Whose energy levels are lower than the electrons in the electroluminescence process?


Why is some energy in the electroluminescence process emitted as heat and light?


In what year was a new type of blue LED produced?

In September 2003, a new type of blue LED was demonstrated by Cree that consumes 24 mW at 20 milliamperes (mA). This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006, they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Nichia Corporation has developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA. Cree's XLamp XM-L LEDs, commercially available in 2011, produce 100 lm/W at their full power of 10 W, and up to 160 lm/W at around 2 W input power. In 2012, Cree announced a white LED giving 254 lm/W, and 303 lm/W in March 2014. Practical general lighting needs high-power LEDs, of one watt or more. Typical operating currents for such devices begin at 350 mA.


Who demonstrated in 2003 the new type of blue LED?


How much more efficient as standard incandescents was the white LED commercially available in 2003?


What is the typical operating current for high-power LEDs?


The most common symptom of LED (and diode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can also occur. Early red LEDs were notable for their short service life. With the development of high-power LEDs the devices are subjected to higher junction temperatures and higher current densities than traditional devices. This causes stress on the material and may cause early light-output degradation. To quantitatively classify useful lifetime in a standardized manner it has been suggested to use L70 or L50, which are the runtimes (typically given in thousands of hours) at which a given LED reaches 70% and 50% of initial light output, respectively.


What could cause early light-output degradation in LEDs?


What is a classification used in LED lighting to describe how much usefulness it will receive?


LED efficacy is inversely proportional to what?

Since LED efficacy is inversely proportional to operating temperature, LED technology is well suited for supermarket freezer lighting. Because LEDs produce less waste heat than incandescent lamps, their use in freezers can save on refrigeration costs as well. However, they may be more susceptible to frost and snow buildup than incandescent lamps, so some LED lighting systems have been designed with an added heating circuit. Additionally, research has developed heat sink technologies that will transfer heat produced within the junction to appropriate areas of the light fixture.


LEDs produce less waste heat than what other device?


What is LED lighting more susceptible to than incandescent light?


What students developed the first blue-violet LED?

The first blue-violet LED using magnesium-doped gallium nitride was made at Stanford University in 1972 by Herb Maruska and Wally Rhines, doctoral students in materials science and engineering. At the time Maruska was on leave from RCA Laboratories, where he collaborated with Jacques Pankove on related work. In 1971, the year after Maruska left for Stanford, his RCA colleagues Pankove and Ed Miller demonstrated the first blue electroluminescence from zinc-doped gallium nitride, though the subsequent device Pankove and Miller built, the first actual gallium nitride light-emitting diode, emitted green light. In 1974 the U.S. Patent Office awarded Maruska, Rhines and Stanford professor David Stevenson a patent for their work in 1972 (U.S. Patent US3819974 A) and today magnesium-doping of gallium nitride continues to be the basis for all commercial blue LEDs and laser diodes. These devices built in the early 1970s had too little light output to be of practical use and research into gallium nitride devices slowed. In August 1989, Cree introduced the first commercially available blue LED based on the indirect bandgap semiconductor, silicon carbide (SiC). SiC LEDs had very low efficiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum.[citation needed]


The first blue-violet LED was developed at what University?


When was the first blue-violet LED developed?


What substance helped demonstrate the first blue electroluminescence?


In what decade were breakthroughs made that brought in the modern era of GaN-based optoelectronic devices?

In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, Dr. Moustakas at Boston University patented a method for producing high-brightness blue LEDs using a new two-step process. Two years later, in 1993, high-brightness blue LEDs were demonstrated again by Shuji Nakamura of Nichia Corporation using a gallium nitride growth process similar to Dr. Moustakas's. Both Dr. Moustakas and Mr. Nakamura were issued separate patents, which confused the issue of who was the original inventor (partly because although Dr. Moustakas invented his first, Dr. Nakamura filed first).[citation needed] This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like BlueRay, as well as allowing the bright high resolution screens of modern tablets and phones.[citation needed]


Who first patented a method to produce high-brightness blue LEDs?


Who first invented a method to produce high-brightness blue LEDs?


What technology was made possible by high-power blue light sources?


What is one modern gadget that benefits from high-power blue LED lighting?


What Nobel Prize did Nakamura, Amano, and Akasaki receive in 2014?

Nakamura was awarded the 2006 Millennium Technology Prize for his invention. Nakamura, Hiroshi Amano and Isamu Akasaki were awarded the Nobel Prize in Physics in 2014 for the invention of the blue LED. In 2015, a US court ruled that three companies (i.e. the litigants who had not previously settled out of court) that had licensed Mr. Nakamura's patents for production in the United States had infringed Dr. Moustakas's prior patent, and order them to pay licensing fees of not less than 13 million USD.


What award did Nakamura receive in 2006 for his invention?


How many companies did a judge say infringed on Dr. Moustakas's prior blue light patent in 2015?


What was the fine given to the three companies?


By the late 1990s, blue LEDs became widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If un-alloyed GaN is used in this case to form the active quantum well layers, the device will emit near-ultraviolet light with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications.[citation needed]


How can light emission be varied from violet to amber?


What LEDs are more efficient when produced from the InGaN/GaN systems than without?


With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies. Shorter-wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 240 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LED emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices. UV-C wavelengths were obtained in laboratories using aluminium nitride (210 nm), boron nitride (215 nm) and diamond (235 nm).


What sort of LEDs are becoming more available on the market?


What is the range of wavelengths for cheap UV LEDs?


Shorter wavelength diodes provide wavelengths as low as what?


What UV wavelengths are found in sterilization devices?


What colors are used to form white light?

White light can be formed by mixing differently colored lights; the most common method is to use red, green, and blue (RGB). Hence the method is called multi-color white LEDs (sometimes referred to as RGB LEDs). Because these need electronic circuits to control the blending and diffusion of different colors, and because the individual color LEDs typically have slightly different emission patterns (leading to variation of the color depending on direction) even if they are made as a single unit, these are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors, and in principle, this mechanism also has higher quantum efficiency in producing white light.[citation needed]


What is the method called that mixes red, green, and blue colors to form white light?


What does the multi-color white LED method need to produce the end result?


What is another name to reference the multi-color white LED method?


What is a factor that may be different in the various types of multi-color white LEDs?

There are several types of multi-color white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different methods, include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency will mean lower color rendering, presenting a trade-off between the luminous efficacy and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.


Higher efficiency in multi-color white LEDs may mean what?


What is one type of multi-color white LED?


What type has the best luminous efficacy?


What luminous efficacy does trichromatic white LEDs have?


Multi-color LEDs offer what else besides the formation of white light?

Multi-color LEDs offer not merely another means to form white light but a new means to form light of different colors. Most perceivable colors can be formed by mixing different amounts of three primary colors. This allows precise dynamic color control. As more effort is devoted to investigating this method, multi-color LEDs should have profound influence on the fundamental method that we use to produce and control light color. However, before this type of LED can play a role on the market, several technical problems must be solved. These include that this type of LED's emission power decays exponentially with rising temperature, resulting in a substantial change in color stability. Such problems inhibit and may preclude industrial use. Thus, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists.


What problem must be solved before multi-color LEDs can play a role in the market?


What problem results when rising temperatures decays power?


What method involves coating LEDs of one color with phosphors of different colors?

This method involves coating LEDs of one color (mostly blue LEDs made of InGaN) with phosphors of different colors to form white light; the resultant LEDs are called phosphor-based or phosphor-converted white LEDs (pcLEDs). A fraction of the blue light undergoes the Stokes shift being transformed from shorter wavelengths to longer. Depending on the color of the original LED, phosphors of different colors can be employed. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively raising the color rendering index (CRI) value of a given LED.


In pcLEDs method, a fraction of what light is used?


What shift does blue light undergo in the pcLEDs method?


The different colors of phosphors that can be used is based on what?


What broadens the emitted spectrum in a pcLEDs method?


What do phosphor-based LEDs luminous efficacies depend on?

Phosphor-based LED efficiency losses are due to the heat loss from the Stokes shift and also other phosphor-related degradation issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function). Due to the simplicity of manufacturing the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.


What is the most popular method for making high-intensity white LEDs?


Why is efficiency sometimes lost in phosphor-based LEDs?


What are some of the luminous efficacies of yellow phosphor based white LED compared to blue?


What type of emitter is used in phosphor-based white LED methods?


What can improve the efficiency of LED-based white light?

Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stoke shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself account typically for another 10% to 30% of efficiency loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor. Conformal coating process is frequently used to address the issue of varying phosphor thickness.


What is the most efficient yellow phosphor?


What is the percentage of stoke shift loss in YAG phosphor?


What area are scientists looking into regarding phosphor LED development?


What is one method that can raise the efficiency of phosphor-based LEDs?


White LEDs can also be made by coating near-ultraviolet (NUV) LEDs with a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.


What are near-ultraviolet LEDs coated with to create white LED?


What device also works in a similar way as NUV LEDs?


The method of coating NUVs less efficient than what other LEDs?


What is being used to produce white LEDs?

A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate in relatively small 100- or 150-mm wafer sizes. The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It is predicted that by 2020, 40% of all GaN LEDs will be made with GaN-on-Si. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant. LED companies shifting from using sapphire to silicon should be a minimal investment.


What size are the wafers used to create white LEDs?


By using silicon wafers, what is being avoided?


What needs to be used to reflect light that would otherwise be wasted?


By what year will% of all GaN LEDs be made with gallium-nitride-on-silicon wafers?


What nanocrystals possess unique optical properties?

Quantum dots (QD) are semiconductor nanocrystals that possess unique optical properties. Their emission color can be tuned from the visible throughout the infrared spectrum. This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering than white LEDs since the emission spectrum is much narrower, characteristic of quantum confined states. There are two types of schemes for QD excitation. One uses photo excitation with a primary light source LED (typically blue or UV LEDs are used). The other is direct electrical excitation first demonstrated by Alivisatos et al.


Quantum Dot LEDs can do what special skill?


The narrowing of the emission spectrum in Quantum Dot LEDs allows them to do what?


How many types of schemes are there in Quantum Dot LED excitation?


What is one scheme of Quantum Dot excitation?

The structure of QD-LEDs used for the electrical-excitation scheme is similar to basic design of OLEDs. A layer of quantum dots is sandwiched between layers of electron-transporting and hole-transporting materials. An applied electric field causes electrons and holes to move into the quantum dot layer and recombine forming an exciton that excites a QD. This scheme is commonly studied for quantum dot display. The tunability of emission wavelengths and narrow bandwidth is also beneficial as excitation sources for fluorescence imaging. Fluorescence near-field scanning optical microscopy (NSOM) utilizing an integrated QD-LED has been demonstrated.


What is one material used in electrical-excitation?


During the electrical-excitation scheme, what moves into the quantum dot layer?


A Quantum Dot LED has been used in what?


How many lumens can some high-power LEDs emit?

High-power LEDs (HP-LEDs) or high-output LEDs (HO-LEDs) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can emit over a thousand lumens. LED power densities up to 300 W/cm2 have been achieved. Since overheating is destructive, the HP-LEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HP-LED is not removed, the device will fail in seconds. One HP-LED can often replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp.


Up to how many densities have been achieved with LED power?


Why must High-power LEDs be mounted on a heat sink?


What will happen if the heat from a high-power LED is not removed?


What company has developed LEDs that can operate on AC power?

LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half-cycle, part of the LED emits light and part is dark, and this is reversed during the next half-cycle. The efficacy of this type of HP-LED is typically 40 lm/W. A large number of LED elements in series may be able to operate directly from line voltage. In 2009, Seoul Semiconductor released a high DC voltage LED, named as 'Acrich MJT', capable of being driven from AC power with a simple controlling circuit. The low-power dissipation of these LEDs affords them more flexibility than the original AC LED design.


What is the efficacy of an AC powered HP-LED?


When did Seoul Semiconductor release the first high DC voltage LED?


What is so good about ac powered HP-LEDs?


What did Seoul Semiconductor name their ac powered HP-LED?


What type of LEDs are available in seven-segment format?

Alphanumeric LEDs are available in seven-segment, starburst and dot-matrix format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Dot-matrix displays typically use 5x7 pixels per character. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but rising use of liquid crystal displays, with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.


What is another format that Alphanumeric LEDs are available in?


Which alphanumeric LED display can display all letters?


What type of pixels does a dot matrix display use?


What has reduced the popularity of numeric LED displays?


Digital-RGB LEDs are RGB LEDs that contain their own "smart" control electronics. In addition to power and ground, these provide connections for data-in, data-out, and sometimes a clock or strobe signal. These are connected in a daisy chain, with the data in of the first LED sourced by a microprocessor, which can control the brightness and color of each LED independently of the others. They are used where a combination of maximum control and minimum visible electronics are needed such as strings for Christmas and LED matrices. Some even have refresh rates in the kHz range, allowing for basic video applications.


How are Digital-RGB LED strobe signals connected?


What object sources the data in of the first LED of a digital rgb LED?


The microprocessor does what in a digital RGB LED?


What is one example of where Digital RGB LED lights are used?


An LED filament consists of multiple LED dice connected in series on a common longitudinal substrate that form a thin rod reminiscent of a traditional incandescent filament. These are being used as a low cost decorative alternative for traditional light bulbs that are being phased out in many countries. The filaments require a rather high voltage to light to nominal brightness, allowing them to work efficiently and simply with mains voltages. Often a simple rectifier and capacitive current limiting are employed to create a low-cost replacement for a traditional light bulb without the complexity of creating a low voltage, high current converter which is required by single die LEDs. Usually they are packaged in a sealed enclosure with a shape similar to lamps they were designed to replace (e.g. a bulb), and filled with inert nitrogen or carbon dioxide gas to remove heat efficiently.


What type of voltage is needed for LED filaments?


What helps LED filaments remain low cost?


The current–voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can cause a large change in current. If the applied voltage exceeds the LED's forward voltage drop by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Since most common power sources (batteries, mains) are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor. However, the high resistance of three-volt coin cells combined with the high differential resistance of nitride-based LEDs makes it possible to power such an LED from such a coin cell without an external resistor.


What is a solution to preventing an LED failure?


What can cause a large change in current in LEDs?


What feature do most LED fixtures need to have?


The vast majority of devices containing LEDs are "safe under all conditions of normal use", and so are classified as "Class 1 LED product"/"LED Klasse 1". At present, only a few LEDs—extremely bright LEDs that also have a tightly focused viewing angle of 8° or less—could, in theory, cause temporary blindness, and so are classified as "Class 2". The opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) of 2010, on the health issues concerning LEDs, suggested banning public use of lamps which were in the moderate Risk Group 2, especially those with a high blue component in places frequented by children. In general, laser safety regulations—and the "Class 1", "Class 2", etc. system—also apply to LEDs.


What does being a Class 1 LED product mean?


What type of LED can possibly cause blindness?


Which government advocated the banning of Class 2 LEDs?


What class are extremely bright LEDs listed as?


While LEDs have the advantage over fluorescent lamps that they do not contain mercury, they may contain other hazardous metals such as lead and arsenic. Regarding the toxicity of LEDs when treated as waste, a study published in 2011 stated: "According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb [lead] at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5). However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), lead (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous."


What substance does fluorescent lamps contain?


Which LEDs are considered dangerous by a 2011 study?


According to a California study, what harmful metal is in most LEDs?


What LEDs are considered safer than any other?


What type of light is ideal for traffic signals?

One-color light is well suited for traffic lights and signals, exit signs, emergency vehicle lighting, ships' navigation lights or lanterns (chromacity and luminance standards being set under the Convention on the International Regulations for Preventing Collisions at Sea 1972, Annex I and the CIE) and LED-based Christmas lights. In cold climates, LED traffic lights may remain snow-covered. Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.


In what year were luminescence standards set?


What color LEDs are used when night vision is important?


What is an example of a night vision needed area?


What is another use for one-color light?


Because of their high output, LED lights are very useful where?

Because of their long life, fast switching times, and their ability to be seen in broad daylight due to their high output and focus, LEDs have been used in brake lights for cars' high-mounted brake lights, trucks, and buses, and in turn signals for some time, but many vehicles now use LEDs for their rear light clusters. The use in brakes improves safety, due to a great reduction in the time needed to light fully, or faster rise time, up to 0.5 second faster[citation needed] than an incandescent bulb. This gives drivers behind more time to react. In a dual intensity circuit (rear markers and brakes) if the LEDs are not pulsed at a fast enough frequency, they can create a phantom array, where ghost images of the LED will appear if the eyes quickly scan across the array. White LED headlamps are starting to be used. Using LEDs has styling advantages because LEDs can form much thinner lights than incandescent lamps with parabolic reflectors.


Why are LED lights sought after for various applications?


LED brake lights are how many times faster than incandescent ones?


What color LEDs are now starting to be used more?


What types of light can LEDs form better than incandescent?


Where are infrared LEDs used in everday life?

Assistive listening devices in many theaters and similar spaces use arrays of infrared LEDs to send sound to listeners' receivers. Light-emitting diodes (as well as semiconductor lasers) are used to send data over many types of fiber optic cable, from digital audio over TOSLINK cables to the very high bandwidth fiber links that form the Internet backbone. For some time, computers were commonly equipped with IrDA interfaces, which allowed them to send and receive data to nearby machines via infrared.


LEDs can send data over what type of cable?


What type of fiber forms the backbone of the internet?


In what country does one kilowatt-hour of electricity causes 1.34 pounds of CO 2 emission?

In the US, one kilowatt-hour (3.6 MJ) of electricity currently causes an average 1.34 pounds (610 g) of CO 2 emission. Assuming the average light bulb is on for 10 hours a day, a 40-watt bulb will cause 196 pounds (89 kg) of CO 2 emission per year. The 6-watt LED equivalent will only cause 30 pounds (14 kg) of CO 2 over the same time span. A building’s carbon footprint from lighting can therefore be reduced by 85% by exchanging all incandescent bulbs for new LEDs if a building previously used only incandescent bulbs.


How much CO2 emission would a 40-watt light bulb produce after 10 hours?


A 6-watt LED left on for 10 hours a day will emit how much CO 2?


How much can a building's carbon footprint be reduced by switching to LEDs?


LEDs are often used for what type of systems?

Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used for this purpose, and this is likely to remain one of their major uses until the price drops low enough to make signaling and illumination uses more widespread. Barcode scanners are the most common example of machine vision, and many low cost products use red LEDs instead of lasers. Optical computer mice are an example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:


Why are LEDs preferred for machine vision systems?


What can help make LEDs more widely used?


What is the most common example of a machine vision system?


Where are some LEDs in machine vision systems found?


The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and free space optics communications. This includes remote controls, such as for TVs, VCRs, and LED Computers, where infrared LEDs are often used. Opto-isolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between two circuits. This is especially useful in medical equipment where the signals from a low-voltage sensor circuit (usually battery-powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or monitoring device operating at potentially dangerous voltages. An optoisolator also allows information to be transferred between circuits not sharing a common ground potential.


What is an example of a device that uses free space optic communications?


In what common household item can you find infrared LEDs?


What video game console uses infrared LEDs?

Many sensor systems rely on light as the signal source. LEDs are often ideal as a light source due to the requirements of the sensors. LEDs are used as motion sensors, for example in optical computer mice. The Nintendo Wii's sensor bar uses infrared LEDs. Pulse oximeters use them for measuring oxygen saturation. Some flatbed scanners use arrays of RGB LEDs rather than the typical cold-cathode fluorescent lamp as the light source. Having independent control of three illuminated colors allows the scanner to calibrate itself for more accurate color balance, and there is no need for warm-up. Further, its sensors only need be monochromatic, since at any one time the page being scanned is only lit by one color of light. Since LEDs can also be used as photodiodes, they can be used for both photo emission and detection. This could be used, for example, in a touchscreen that registers reflected light from a finger or stylus. Many materials and biological systems are sensitive to, or dependent on, light. Grow lights use LEDs to increase photosynthesis in plants, and bacteria and viruses can be removed from water and other substances using UV LEDs for sterilization.


What device uses infrared LEDs to measure oxygen saturation?


Some flatbed scanners use what type of LED?


By using LEDs, scanners do not have to what?


LEDs have also been used as a medium-quality voltage reference in electronic circuits. The forward voltage drop (e.g. about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee. Nitride-based LEDs have a fairly steep I/V curve and are useless for this purpose. Although LED forward voltage is far more current-dependent than a Zener diode, Zener diodes with breakdown voltages below 3 V are not widely available.


What LED has the flattest I/V curve above the knee?


LED forward voltage is more current-dependent than what diode?


Zener diodes below what voltage are not widely available?


What is a group of endothermic vertebrates characterised by feathers and toothless beaked jaws?

Birds (Aves) are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. They rank as the class of tetrapods with the most living species, at approximately ten thousand, with more than half of these being passerines, sometimes known as perching birds or, less accurately, as songbirds.


What are the last surviving dinosaurs, according o the fossil record?

The fossil record indicates that birds are the last surviving dinosaurs, having evolved from feathered ancestors within the theropod group of saurischian dinosaurs. True birds first appeared during the Cretaceous period, around 100 million years ago. DNA-based evidence finds that birds diversified dramatically around the time of the Cretaceous–Paleogene extinction event that killed off all other dinosaurs. Birds in South America survived this event and then migrated to other parts of the world via multiple land bridges while diversifying during periods of global cooling. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period. Many of these early "stem-birds", such as Archaeopteryx, were not yet capable of fully powered flight, and many retained primitive characteristics like toothy jaws in place of beaks, and long bony tails.


What makes birds uniquely adapted for flight?

Birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinct moas and elephant birds. Wings, which evolved from forelimbs, give most birds the ability to fly, although further speciation has led to some flightless birds, including ratites, penguins, and diverse endemic island species of birds. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly the aforementioned flightless penguins, and also members of the duck family, have also evolved for swimming. Birds, specifically Darwin's finches, played an important part in the inception of Darwin's theory of evolution by natural selection.


What type of bird particularly played an important part in the inception of Darwin's theory of evolution by natural selection?


Which part of the bird developed from forelimbs?


Which type of birds are among the most intelligent animals?

Some birds, especially corvids and parrots, are among the most intelligent animals; several bird species make and use tools, and many social species pass on knowledge across generations, which is considered a form of culture. Many species annually migrate great distances. Birds are social, communicating with visual signals, calls, and bird songs, and participating in such social behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have polygynous ("many females") or, rarely, polyandrous ("many males") breeding systems. Birds produce offspring by laying eggs which are fertilized through sexual reproduction. They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilized, though unfertilized eggs do not produce offspring.


Many species of birds are economically important. Domesticated and undomesticated birds (poultry and game) are important sources of eggs, meat, and feathers. Songbirds, parrots, and other species are popular as pets. Guano (bird excrement) is harvested for use as a fertilizer. Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry.


What is harvested for use as fertilizer?


How many species of birds have become extinct as a result of human activity?


Besides Aves, what group contains the only living representatives of the reptile clade Archosauria?

Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica. However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and is used by many scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils, and assigning them, instead, to the Avialae, in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.


Who defined Aves to include only the crown group of the set of modern birds?


What evidence leads most scientists to accept that birds are a specialized subgroup of theropod dinosaurs?

Based on fossil and biological evidence, most scientists accept that birds are a specialized subgroup of theropod dinosaurs, and more specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids, among others. As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod feathered dinosaurs, contribute to this ambiguity.


What is a group of theropods which include dromaeosaurs and oviraptorids?


Recent discoveries in what country demonstrate many small theropod feathered dinosaurs.


What are the closest relatives of the deinonychosaurs?

The consensus view in contemporary paleontology is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids. Together, these form a group called Paraves. Some basal members of this group, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were omnivores.


What are the closest relatives of flying theropods?


Dromaeosaurids and troodontids are members of what group?


What is known as one of the first transitional fossils to be found?

The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics: teeth, clawed fingers, and a long, lizard-like tail, as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor.


What was the first fossil to display both clearly traditional reptilian characteristics?


Fossils with teeth, clawed fingers and a long lizard-like tail have what type of characteristics?


The Oxfordian stage is also known as what?

The earliest known avialan fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi, Xiaotingia zhengi, and Aurornis xui. The well-known early avialan, Archaeopteryx, dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering.


How long ago was the late Jurassic period?


What may have been used in aerial maneuvering?


Avian species such as Anchiornis huxleyi and Xiaotingia zhengi are from which time period?


During which time period did avialans diversify into a wide variety of forms?

Avialans diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). While the earliest forms, such as Archaeopteryx and Jeholornis, retained the long bony tails of their ancestors, the tails of more advanced avialans were shortened with the advent of the pygostyle bone in the group Pygostylia. In the late Cretaceous, around 95 million years ago, the ancestor of all modern birds also evolved a better sense of smell.


Which forms retained the long bony tails of their ancestors?


When did the ancestor of all modern birds evolve a better sense of smell?


How long ago was the late Cretaceous period?


What were the first large, diverse lineage of short-tailed avialans to evolve?

The first large, diverse lineage of short-tailed avialans to evolve were the enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the Mesozoic era.


Because of the construction of their shoulder bones, what were the enantiornithes called?


What was the dominant group of avialans during the Cretaceous period?


What group became the first avialans to develop true pygostyle and a fully mobile fan of tail feathers?

Many species of the second major avialan lineage to diversify, the Euornithes (meaning "true birds", because they include the ancestors of modern birds), were semi-aquatic and specialized in eating fish and other small aquatic organisms. Unlike the enantiornithes, which dominated land-based and arboreal habitats, most early euornithes lacked perching adaptations and seem to have included shorebird-like species, waders, and swimming and diving species. The later included the superficially gull-like Ichthyornis, the Hesperornithiformes, which became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic. The early euornithes also saw the development of many traits associated with modern birds, like strongly keeled breastbones, toothless, beaked portions of their jaws (though most non-avian euornithes retained teeth in other parts of the jaws). Euornithes also included the first avialans to develop true pygostyle and a fully mobile fan of tail feathers, which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight.


What may have replaced the "hind wing" as the primary mode of aerial maneuverability?


All modern birds lie within which crown group?

All modern birds lie within the crown group Aves (alternately Neornithes), which has two subdivisions: the Palaeognathae, which includes the flightless ratites (such as the ostriches) and the weak-flying tinamous, and the extremely diverse Neognathae, containing all other birds. These two subdivisions are often given the rank of superorder, although Livezey and Zusi assigned them "cohort" rank. Depending on the taxonomic viewpoint, the number of known living bird species varies anywhere from 9,800 to 10,050.


The two subdivisions of what group include Palaeognathae and Neognathae?


What is the number range of living bird species?


What was the earliest divergence within the Neognathes?

The earliest divergence within the Neognathes was that of the Galloanserae, the superorder containing the Anseriformes (ducks, geese, swans and screamers) and the Galliformes (the pheasants, grouse, and their allies, together with the mound builders and the guans and their allies). The earliest fossil remains of true birds come from the possible galliform Austinornis lentus, dated to about 85 million years ago, but the dates for the actual splits are much debated by scientists. The Aves are agreed to have evolved in the Cretaceous, and the split between the Galloanseri from other Neognathes occurred before the Cretaceous–Paleogene extinction event, but there are different opinions about whether the radiation of the remaining Neognathes occurred before or after the extinction of the other dinosaurs. This disagreement is in part caused by a divergence in the evidence; molecular dating suggests a Cretaceous radiation, while fossil evidence supports a Cenozoic radiation. Attempts to reconcile the molecular and fossil evidence have proved controversial, but recent results show that all the extant groups of birds originated from only a small handful of species that survived the Cretaceous–Paleogene extinction.


What is the superorder containing the Anseriformes?


Ducks, geese, swans and screamers are part of which group?


The pheasants, grouse and their allies form which group?


Sibley and Ahlquist' Phylogeny and Classification of Birds is a landmark work on the classification of what animals?

The classification of birds is a contentious issue. Sibley and Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds, although it is frequently debated and constantly revised. Most evidence seems to suggest the assignment of orders is accurate, but scientists disagree about the relationships between the orders themselves; evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders. The most recent effort is drawn above and is based on whole genome sequencing of 48 representative species.


Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the snow petrel's breeding colonies up to 440 kilometres (270 mi) inland in Antarctica. The highest bird diversity occurs in tropical regions. It was earlier thought that this high diversity was the result of higher speciation rates in the tropics, however recent studies found higher speciation rates in the high latitudes that were offset by greater extinction rates than in the tropics. Several families of birds have adapted to life both on the world's oceans and in them, with some seabird species coming ashore only to breed and some penguins have been recorded diving up to 300 metres (980 ft).


Highest bird diversity occurs in which regions?


Some penguins have been recording diving up to how many feet?


Some seabird species only come ashore for what purpose?


The ring-necked pheasant has been introduced as what kind of bird?

Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate; the ring-necked pheasant, for example, has been introduced around the world as a game bird. Others have been accidental, such as the establishment of wild monk parakeets in several North American cities after their escape from captivity. Some species, including cattle egret, yellow-headed caracara and galah, have spread naturally far beyond their original ranges as agricultural practices created suitable new habitat.


Why have some species spread naturally far beyond their original ranges?


Where have many birds established breeding populations?


What consists of very lightweight bones?

The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system. The skull bones in adults are fused and do not show cranial sutures. The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae. The last few are fused with the pelvis to form the synsacrum. The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.


What are large air-filled cavities that connect to the respiratory system?


What is formed when vertebrae are fused with the pelvis?


What is it called when a bird's kidneys extract nitrogenous waste from their bloodstream and secrete it as uric acid?

Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid instead of urea or ammonia through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with feces as a semisolid waste. However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. They also excrete creatine, rather than creatinine like mammals. This material, as well as the output of the intestines, emerges from the bird's cloaca. The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets. Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves. The length is thought to be related to sperm competition. When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth. Most birds are highly adapted for rapid digestion to aid with flight. Some migratory birds have adapted to use protein from many parts of their bodies, including protein from the intestines, as additional energy during migration.


Which bid has a urinary bladder or external urethral opening?


What is a multi-purpose opening on birds?


Upon inhalation, what percentage of fresh air bypasses the lungs and flows directly into a posterior air sac?

Birds have one of the most complex respiratory systems of all animal groups. Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs. When the bird exhales, the used air flows out of the lung and the stored fresh air from the posterior air sac is simultaneously forced into the lungs. Thus, a bird's lungs receive a constant supply of fresh air during both inhalation and exhalation. Sound production is achieved using the syrinx, a muscular chamber incorporating multiple tympanic membranes which diverges from the lower end of the trachea; the trachea being elongated in some species, increasing the volume of vocalizations and the perception of the bird's size.


Where does the other 25 percent of fresh air go?


Sound production is achieved using what muscular chamber?


Which animal has one of the most complex respiratory system of all animal groups?


The avian circulatory system is driven by what?

The avian circulatory system is driven by a four-chambered, myogenic heart contained in a fibrous pericardial sac. This pericardial sac is filled with a serous fluid for lubrication. The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium. The sinoatrial node uses calcium to cause a depolarizing signal transduction pathway from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The avian heart also consists of muscular arches that are made up of thick bundles of muscular layers. Much like a mammalian heart, the avian heart is composed of endocardial, myocardial and epicardial layers. The atrium walls tend to be thinner than the ventricle walls, due to the intense ventricular contraction used to pump oxygenated blood throughout the body. Avian hearts are generally larger than mammalian hearts when compared to body mass. This adaptation allows more blood to be pumped to meet the high metabolic need associated with flight.