SUMMARY / RELATED TOPICS

Transponder

In telecommunication, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a portmanteau of responder, it is variously abbreviated as XPDR, XPNDR, TPDR or TP. In air navigation or radio frequency identification, a flight transponder is an automated transceiver in an aircraft that emits a coded identifying signal in response to an interrogating received signal. In a communications satellite, a satellite transponder receives signals over a range of uplink frequencies from a satellite ground station; the transponder amplifies them, re-transmits them on a different set of downlink frequencies to receivers on Earth without changing the content of the received signal or signals. A communications satellite’s channels are called transponders because each is a separate transceiver or repeater. With digital video data compression and multiplexing, several video and audio channels may travel through a single transponder on a single wideband carrier. Original analog video only has one channel per transponder, with subcarriers for audio and automatic transmission identification service.

Non-multiplexed radio stations can travel in single channel per carrier mode, with multiple carriers per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, or using landlines to send it to an earth station for multiplexing with other stations. In optical fiber communications, a transponder is the element that sends and receives the optical signal from a fiber. A transponder is characterized by its data rate and the maximum distance the signal can travel; the term "transponder" can apply to different items with important functional differences, mentioned across academic and commercial literature: according to one description, a transponder and transceiver are both functionally similar devices that convert a full-duplex electrical signal into a full-duplex optical signal. The difference between the two is that transceivers interface electrically with the host system using a serial interface, whereas transponders use a parallel interface to do so.

In this view, transponders provide easier-to-handle lower-rate parallel signals, but are bulkier and consume more power than transceivers. According to another description, transceivers are limited to providing an electrical-optical function only, whereas transponders convert an optical signal at one wavelength to an optical signal at another wavelength; as such, transponders can be considered as two transceivers placed back-to-back. This view seems to be held by e.g. Fujitsu; as a result, difference in transponder functionality might influence the functional description of related optical modules like transceivers and muxponders. Another type of transponder occurs in identification friend or foe systems in military aviation and in air traffic control secondary surveillance radar systems for general aviation and commercial aviation. Primary radar works best with large all-metal aircraft, but not so well on small, composite aircraft, its range is limited by terrain and rain or snow and detects unwanted objects such as automobiles and trees.

Furthermore, it cannot always estimate the altitude of an aircraft. Secondary radar overcomes these limitations but it depends on a transponder in the aircraft to respond to interrogations from the ground station to make the plane more visible. Depending on the type of interrogation, the transponder sends back a transponder code or altitude information to help air traffic controllers to identify the aircraft and to maintain separation between planes. Another mode called Mode S is designed to help avoiding over-interrogation of the transponder and to allow automatic collision avoidance. Mode S transponders are backward compatible with Modes A and C. Mode S is mandatory in controlled airspace in many countries; some countries have required, or are moving toward requiring, that all aircraft be equipped with Mode S in uncontrolled airspace. However, in the field of general aviation there have been objections to these moves, because of the cost, limited benefit to the users in uncontrolled airspace, and, in the case of balloons and gliders, the power requirements during long flights.

Transponders are used on some military aircraft to ensure ground personnel can verify the functionality of a missile’s flight termination system prior to launch. Such radar enhancing transponders are needed as the enclosed weapon bays on modern aircraft interfere with prelaunch, flight termination system verification performed by range safety personnel during training test launches; the transponders re-radiates the signals allowing for much longer communication distances. The International Maritime Organization's International Convention for the Safety of Life at Sea requires the Automatic Identification System to be fitted aboard international voyaging ships with 300 or more gross tonnage, all passenger ships regardless of size. Although AIS transmitters/receivers are called transponders they transmit autonomously, although coast stations can interrogate class B transponders on smaller vessels for additional information. In addition, navigational aids have transponders called RACON designed to make them stand out on a ship's radar screen.

Many modern automobiles have keys with transponders hidden inside the plastic head of the key. The user of the car may not be aware that the transponder is there, because there are no button

You're Gonna Get It!

You're Gonna Get It! is the second album by Tom Petty and the Heartbreakers, released in 1978. The album was to be titled Terminal Romance, it peaked at No. 23 on the Billboard Top LPs & Tapes chart in 1978. Many reviewers rated You're Gonna Get It! A notch lower than the band's moderately well-received debut album; some reviews such as in Rolling Stone at the time noted the "impressive stylistic cohesiveness" between the two. It did chart higher, than its predecessor. All tracks are written except where noted. Tom Petty & the Heartbreakers Tom Petty – electric guitar, acoustic guitar, twelve-string guitar, rhythm guitar, vocals Mike Campbell – electric guitar, acoustic guitar, twelve string guitar, lead guitar, accordion Benmont Tenchpiano, Hammond organ, backing vocals Ron Blairbass guitar, acoustic guitar, sound effects, backing vocals Stan Lynchdrums, backing vocalsAdditional musicians Phil Seymour – backing vocals on "Magnolia" Noah Shark – percussionProduction Denny Cordell – producer Tom Petty – producer Max Reese – engineer Noah Shark – producer, engineer

Nuclear receptor coregulators

Nuclear receptor coregulators are a class of transcription coregulators that have been shown to be involved in any aspect of signaling by any member of the nuclear receptor superfamily. A comprehensive database of nuclear receptor coregulators can be found at the Nuclear Receptor Signaling Atlas website; the ability of nuclear receptors to alternate between activation and repression in response to specific molecular cues, is now known to be attributable in large part to a diverse group of cellular factors, collectively termed coregulators and including coactivators and corepressors. The study of nuclear receptors owed a debt to decades of historical endocrinology and pathology, prior to their discovery there was a wealth of empirical evidence that suggested their existence. Coregulators, in contrast, have been the subject of a rapid accumulation of functional and mechanistic data, yet to be consolidated into an integrated picture of their biological functions. While this article refers to the historical terms "coactivator" and "corepressor," this distinction is less clear than was at first thought, it is now known that cell type, cell signaling state and promoter identity can influence the direction of action of any given coregulator.

Coregulators are incorrectly referred to as cofactors, which are small, non-protein molecules required by an enzyme for full activity, e.g. NAD+; as far back as the early 1970s, receptor-associated nonhistone proteins were known to support the function of nuclear receptors. In the early 1990s, some investigators such as Keith Yamamoto had suggested a role for non-DNA nuclear acceptor molecules. A biochemical strategy designed in Myles Brown's laboratory provided the first direct evidence of ligand-dependent recruitment by nuclear receptors of ancillary molecules; the yeast two-hybrid protein-protein interaction assay led to the identification of an array of receptor-interacting factors in David Moore's laboratory and RIP140 repressive protein was discovered in Malcolm Parker's laboratory. The stage was now set for the cloning of the coactivators; the first authentic, common nuclear receptor coactivator was steroid receptor coactivator 1, or SRC-1, first cloned in Bert O’Malley's laboratory. SRC-1 and two related proteins, GRIP-1, cloned first by Michael Stallcup, ACTR/p/CIP identified in Ron Evans and Geoff Rosenfeld's lab, together make up the SRC/NCOA family of coactivators.

The SRC family is defined by the presence in the N-terminus of beta-HLH motifs. Malcolm Parker's laboratory was the first to show that a recurring structural feature of many coactivators is an alpha-helical LXXLL motif, or nuclear receptor box, present from a single to several copies in many coactivators, implicated in their ligand-dependent recruitment by the receptor AF-2; the SRC coactivator family, for example, has a conserved cluster of NR boxes located in the central region of each member of the family. Coactivators can be categorized based upon their varied functional properties. To name a few, classes of coactivators include: Acetyltransferases, such as members of the Src/NCOA family Ubiquitin ligases, such as E6-AP ATP-coupled chromatin remodeling complexes, such as the SWI/SNF/BRG-1 complex Protein methylases, such as CARM-1 and PRMT-1 RNA transcripts, such as SRA1 Cell cycle regulators such as cdc 25B RNA helicases such as p72 And members of the TRAP/DRIP mediator complex, which foster direct contact with components of the basal transcription machinery Transcriptional repression by corepressors is in many ways conceptually comparable to the mediation of receptor transcriptional activation by coactivators, but has an opposite outcome.

Recruitment of corepressors occurring in the absence of ligand, depends on a critical conformation of the receptor AF-2 domain, as well as upon nuclear receptor box-like helical motifs in the corepressor. Moreover, corepressors themselves recruit ancillary enzyme activities which help to establish or maintain the repressive state at their target promoters. Early cell transfection experiments had shown that discrete regions of certain receptors, such as thyroid hormone receptor, were sufficient to repress, or silence, reporter genes when fused to DNA-binding domains of heterologous transcription factors, suggesting that specific cellular factors – or corepressors - might bind to these regions and silence receptors in cells. Again, using the yeast two-hybrid screen, two corepressors were isolated in rapid succession, nuclear receptor corepressor, or NCoR, in Geoff Rosenfeld's laboratory, silencing mediator of retinoid and thyroid receptors, or SMRT, by Ron Evans. Alignment of the two proteins indicated that they had a common domain structure, suggesting parallels in their mode of action.

Mitch Lazar's group has shown that inactive nuclear receptors recruit corepressors in part through amphipathic helical peptides called CoRNR boxes, which are similar to the coactivator nuclear receptor boxes. In addition to these structural analogies and coactivators have common functional themes; the acetylation state of nucleosomes on a promoter is related to the rate of transcription of the gene. Histone acetylase coactivators increase the rate of acetylation, opening the nucleosome to transcription factors. Other histone modifications have opposite effects on transcription; the physiological role of SRC/p160s, CBP/p300 and other coactivators has been implied by knockout studie