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Welcome to IFF, formerly the Illinois Facilities Fund.IFF conducts research to guide and improve public policy.Site Design: tanagram partners Programming: Thirdwave, LLC.This page was last modified 00:40, 7 January 2008.All text is available under the terms of the GNU Free Documentation License.It has been suggested that this article or section be merged into Logical biconditional.This article does not cite any references or sources.Thus, either both statements are true, or both are false.In writing, common alternative phrases to "if and only if" include iff, Q is necessary and sufficient for P, P is equivalent to Q, P precisely if Q, P precisely (or exactly) when Q, P exactly in case Q, and P just in case Q.The difference between if, only if, and iff
3.Another term for this logical connective is exclusive nor.Proving this pair of statements sometimes leads to a more natural proof, since there are not obvious conditions in which one would infer a biconditional directly.Kelley's 1955 book General Topology.Its invention is often credited to the mathematician Paul Halmos, but in his autobiography he states that he borrowed it from puzzlers.If the pudding is a custard, then Madison will eat it)
Madison will eat pudding only if the pudding is a custard.If Madison is eating pudding, then it must be a custard)
Madison will eat pudding if and only if (iff) the pudding is a custard.AND If Madison is eating pudding, then it must be a custard.Analysis
Sentence (1) states only that Madison will eat custard pudding.All we know for certain is that she will eat custard pudding.Sentence (2) states that the only pudding Madison will eat is a custard.Sentence (3), however, makes it quite clear that Madison will eat custard pudding and custard pudding only.She will not eat any other type of pudding.Philosophical interpretation
A sentence that is composed of two other sentences joined by "iff" is called a biconditional."Iff" joins two sentences to form a new sentence.The biconditional "A iff B" uses the sentences A and B, describing a relation between the states of affairs A and B describe.Certainly it is the case that when A is logically equivalent to B, "A iff B" is true.But the converse does not hold.Quine's Mathematical Logic, Section 5.Not B implies not A means A implies B, so then we get two way implication.Definitions
In philosophy and logic, "iff" is used to indicate definitions, since definitions are supposed to be universally quantified biconditionals.Some authors, nevertheless, explicitly indicate that the "if" of a definition means "iff"!The statement "(A iff B)" is equivalent to the statement "(not A or B) and (not B or A)," and is also equivalent to the statement "(not A and not B) or (A and B)."The elements of X are all and only the elements of Y is used to mean: "for any z in the domain of discourse, z is in X if and only if z is in Y."This page was last modified 14:28, 21 January 2008.Iff manufacturers products include all kinds of lighting suspensions, FROM simple telescopic posts to studio pantographs, lighting hoists, brackets and suspensions for ceiling.IFF offers a comprehensive range of lighting suspensions for a variety of applications from television and film production studios to auditoriums, conference and presentation halls to schools and churches, taking in a other architectural uses along the way.Iff lighting manufacturers products include all kinds of lighting suspensions, simple telescopic posts to studio pantographs, lighting hoists, brackets and suspensions for ceiling.Depending on the situation and the tactical decisions that must be made, this characterization will be at least, but may not be limited to, "friend," "enemy," or "neutral."In addition to distinguishing friend from foe for weapons employment, the Navy requires secure, jam resistant Identification Friend or Foe (IFF) systems for battle group air defense management and air traffic control.The cooperative combat identification capability in surface ships is provided by the Mark XIIA Interrogation Friend of Foe (IFF) system, a challenge and reply (or "Q and A") system.AWACS IFF system received codes from aircraft that weren't always processed correctly.There was also a chance the codes could get garbled, which made it more difficult to identify the aircraft as friend or foe.By 1997 a new system had an improved reliability to correctly identifying the codes and improves the ability to determine the location of an aircraft under surveillance, which will help ensure IFF operators give accurate IFF information to higher headquarters or other aircraft.By 1999 a serious problem existed in the field due to IFF test sets not being available or not working properly.The solution was to increase the rate of return of unserviceable test sets to Tobyhanna Army Depot (TYAD).Conway believes that the word originated with P.Oxford,
England: Clarendon Press, p.The system is
further broken down into four modes of operation, two for both military and civilian
aircraft and two strictly for military use.Each mode of operation elicits a specific type of information from the aircraft that is
being challenged.Mode 1, which has 64 reply codes, is used in military air traffic
control to determine what type of aircraft is answering or what type of mission it is on.There are 4096 possible reply codes in this mode.Mode C challenges thus receiving continuous identity and
altitude data from the controlled aircraft.After takeoff, the aircraft soon leaves the departure zone.At this time, the pilot is
instructed via radio to contact a specific enroute controller on a specific radio
frequency.On a transcontinental
flight, the aircraft passes through dozens of such zones until it is handed over to the
approach controller at its destination.A, it is eight microseconds; and, in Mode C, it is 21 microseconds.The airborne
transponder contains circuitry that discriminates between these various timings and
automatically sends back the desired reply.The total number of reply code combinations therefore, is 4,096.The reply codes are
entered by means of four code wheels on the transponder control unit.The reply pulses
generated by the transponder are decoded by the interrogating system and are typically
displayed as needed on the primary radar scope near the blip that represents the aircraft
that has been challenged.Thus, the aircraft controller can monitor the track of each
aircraft through his zone and know its identity, altitude and position at all times.A: Throughout time, it has always been important to know who one's friends are.Nowhere has this been more obvious than in military conflicts, where for centuries, flags,
banners, insignia and uniforms have allowed adversaries to distinguish their cohorts from
others who might have less friendly intentions.That system worked for millennia as long as conflicts were more or less face to face
and visual identification was possible.But about 50 years ago, just as World War II
began, the widespread use of aircraft caused a dramatic and inexorable change.Now threats
could approach with great swiftness.So by the time the visual identification was
possible, it was often too late to prevent destruction.And while battle forces were once
drawn up on opposing sides of some geographic line, the new battle zones quickly became
chaotic mixtures of friendly and hostile forces with many isolated units operating
autonomously.The earliest forms of radar were then emerging and, although it seemed to offer a
solution to the problem, a major drawback soon became evident.It is ironic that the tragic events that occurred
at Pearl Harbor might have been changed had the radar been able to identify as well as
detect.Diamond Head saw the incoming armada, but it was dismissed
as a flight of American aircraft coming in from the mainland.It was then realized that by
rolling over at a predetermined signal the Germans were changing the polarization of the
radar reflections picked up by their own ground radars.It incorporated the basic structure of all cooperative IFF systems that followed:
a challenge or question (the coded radio message) and a specific response (the roll over
that caused a change in the reflected radar signal).Both British and American forces were working to develop a viable identification system
as well.That first German maneuver, which was soon superseded by others, was a passive
system in that the returned signal was still just a reflection of the radar energy sent
from the ground.This is the basic method now used in
all modern cooperative IFF systems.About 1940 an active system, designated the Mk I, was put into service.It used a
receiver aboard each aircraft that broke into oscillation and acted as a transmitter when
it received a radar signal.Because of the variety of radar frequencies used, it had to be
mechanically tuned across the radar bands in order to be triggered by any radar that was
illuminating it.This mechanical tuning requirement and other factors limited its
performance.This greatly increased the strength of the return signal and
the return range.Litton's
history started when the company began making IFF components in 1951.The
interrogator system is frequently associated with a primary radar installation, but it may
also be installed aboard a ship or another airplane.The interrogation code or challenge,
as it is called, is received by an electronic system known as a transponder that is aboard
the target aircraft.If the transponder receives the proper electronic code from an
interrogator, it automatically transmits the requested identification back to the
interrogating radar.How is civilian air traffic control different than military identification?By the 1960's civilian air traffic in the United States had increased so much
that air traffic controllers began to have their own identity crisis.Consequently, a system
similar to and compatible with, military IFF systems was authorized and introduced by the
civilian air traffic control authorities.Since civilian air traffic control deals only
(hopefully) with friendly aircraft, it is more properly called the Air Traffic Control
Radar Beacon System.In the present IFF system, the beam of interrogation signals sweeps the
horizon in synchronism with the primary radar beam and all aircraft transponders that are
reached by that beam are triggered to respond whether they are of immediate interest to
the air controllers or not.As air traffic densities increase, the situation becomes even
more severe.To reverse this trend, the FAA has authorized the development of a new system
designated Mode S to be implemented for commercial carriers.The system uses the standard IFF frequencies of 1030 and
1090 megahertz, but both the challenge and reply formats are more complexly coded than in
the current beacon system.In particular, each user aircraft will be assigned a permanent
Mode S address which will share with no other (more than 16 million addresses will be
available).Upon the aircraft's entrance into a Mode S control zone, the address will be
automatically elicited by the ground control station and entered into a central computer.Military identification is also being investigated for change.The system was designated Mk XV.In Europe, the NATO countries also participated
in a parallel program dubbed NIS (NATO Identification System).Interest in a new waveform which can also provide data transfer similar to Mode S is
still a priority.The NATO nations are continuing in defining a new waveform dubbed Mk
XIIA which will use spread spectrum techniques to provide improvements in jamming and
garble performance.The original reason for IFF systems came about was to identify friendly
forces in a battlefield environment.For that reason, it is essential that hostile forces
not be able to use the system to identify themselves as friendly even if the physical IFF
equipment should fall into their hands.Litton supplies military IFF equipment, including
the most advanced encryption systems, that prevent unauthorized use.The challenge itself is encrypted at the interrogator by a separate
device that uses various mathematical algorithms to put it in a secure form.The
transponder routes the ensuing challenge to a separate device that uses the inverse
algorithms to decode the challenge.In effect, each challenge is telling the transponder
to respond in a certain way.If the transponder cannot decipher the challenge, it will not
be able to respond in the proper way and thus will not be identified as a friend.New Constructs, LLCPlunkett's Chemicals, Coatings and Plastics Industry Trends and Statistics 2008...PEG Ratio (5 yr expected):1.Quotes delayed, except where indicated otherwise.Quotes and other information supplied by independent providers identified on the Yahoo!Financials data provided by Edgar Online.Historical chart data and daily updates provided by Commodity Systems, Inc.Fund summary, fund performance and Morningstar Index data provided by Morningstar.Analyst estimates data provided by Thomson Financial Network.All data povided by Thomson Financial Network is based solely upon research information provided by third party analysts.All information provided "as is" for informational purposes only, not intended for trading purposes or advice.
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