GPS Operational ConstellationThe system ofover 20 more-or-less evenly spaced, orbiting satellites some of which are spares, equipped with atomic clocks, in the Global Positioning System
Trang 1Fiber Optics Illustrated Dictionary
also being extended to include a set of commonly
used office productivity tools
One of the more interesting aspects of GNOME is
thatitcan be internationalized in order to make it
possible for developers around the globe to create
applications in the language syntax that is most
com-fortable for them One of the secondary goals of the
GNOME project is to make GNOME developer tools
and documentation available in every known world
language (an ambitious goal but likely to result in a
rich choice of options even if it is not literally
achieved) GNOME also takes into consideration the
maximizing ofaccessibility for people with
disabili-ties, through the GNOME Accessibility Project http:/
/www.gnome.org/
GNSSSee Global Navigation Satellite System
GNUAcronym for "GNU's Not Unix!" AUnix
work-alike developed under the aegis ofRichard Stallman
of the Free Software Foundation (FSF) See Free
Software Foundation, GNOME
GNUas A GNU family of assemblers used to write
software code for a variety ofobject file formats The
original GNU assembler for the Digital Equipment
Corporation (DEC) VAX system was written by Dean
Elsner Many subsequent programmers and even
some commercial vendors have enhanced and
main-tained the software See Free Software Foundation
GNUC compiler GCC A C compiler supporting
ANSI standard C, C++, and Objective C The GNU
C library includes ANSI C, Unix, and POSIX
func-tions
GNUEmacs Apowerful, extensible, scriptable
dis-play editor distributed by Berkeley programmers with
BSD, and by many other distributors and
commer-cial vendors Emacs is so powerful and so well liked
by power editor users, many have half seriously
re-ferred to it as an operating system
The first Emacs was written in 1975 by Richard
Stallman GNU Emacs, which was enhanced by
Stallman with true LISP integrated into the editor, was
introduced in the mid-1980s GNU Emacs is widely
available on Unix systems
GNUgrapbics Aset ofgraphics utilities for plotting
scientific data, with support for GNU plot files on
various systems and output devices, including
Post-Script, The X Window System, and Tektronix
de-vices
GNU'sBulletin Asemiannual newsletter about
vari-ous GNU projects, produced and distributed by the
Free Software Foundation
go local A command to instruct software to connect
to a local connection (usually in the same room or
vicinity), usually through a serial null modem interface
GO-MVIPGlobal Organization for Multi-Vendor
Integration Protocol GO-MVIP is a nonprofit trade
association which took over the development and
promotion of MVIP in 1994, in order to assure its
development and maintenance as a practical, robust
common integration standard GO-MVIP seeks to
continue to develop and establish the design
specifi-cations for further versions ofMVIP See MVIP
http://www.mvip.org/
Satellite Sensing Systems
An artistsconception ofan EROS meteorological satellite system, which was essentially the conceptfor the GOES satellites This April1961drawing indi-cates thefield ofview and orientation ofthe proposed AEROS geostationary satellite {NOAA In Space Col-lection image.]
An example of a visible image from the GOES 8 satellite on16July 2001 with a line drawing ofNorth America and parts ofCentral and South America su-perimposed to aid in locating geographical features [NOAA FSL image.]
GOESGeostationary Operational Environmental Satellite A geosynchronous satellite system provid-ing environmental monitorprovid-ing data to various gov-ernmental organizations and the public GOES sys-tems began broadcasting, as we know it today, in
1974, having evolved out of early SMS weather sat-ellite systems Almost a dozen satsat-ellites were launched between the early 1968 magnetometer and infrared sensor-equipped satellites and the more so-phisticated multisensor satellites of the late 1990s With each launch, adjustments and improvements have been made to the systems Vertical temperature and moisture sensors were added to GOES-4, and additional signal relay capabilities were added to later GOES systems The original GOES satellites were spin controlled, meaning that they used the physics
of spinning to maintain attitude control Since the
Trang 28, the configuration has changed to a
three-axis-sta-bilized system Ihis configuration changed not only
attitude control, but also the means by which the
sors were installed and operated Doppler radar
sen-sors were added to the more recent satellites and have
become an indispensable aspect of creating and
in-terpreting weather maps The Pacific GOES has been
used for operating the Pan-Pacific Educational and
Cultural Experiments (PEACESAI) to enhance
medical, cultural, and educational resources in the
Pacific island nations
GOES data is available to the Command and Data
Acquisition Station, the National Weather Service, the
Forecast Systems Laboratory (FSL) of the National
Oceanic and Atmospheric Administration (NOAA),
and many others NOAA handles the operations of
the satellites GOES sensors provide continuous
weather monitoring along with infonnation that can
be used to estimate rainfall during more violent
stonns (e.g., hurricanes) and snow accumulations and
cover Ice flows on large bodies ofwater can also be
monitored with GOES data Even the weather in
space, in terms of various magnetic and energy
particles, is monitored by GOES sensors
The GOES Space Environment Monitor (SEM)
mis-sion provides a better understanding ofspace weather
through the National Space Weather Program Space
weather forecasts aid not only in probe, shuttle, and
satellite missions, but also in providing valuable
cos-mological infonnation to physicists and astronomers
Satellite images with a variety ofcharacteristics
(vis-ible, infrared, water vapor, etc.) from GOES sensors
are available through the Forecast Systems
Labora-tory
goldA malleable, metallic chemical element with
high conductivity, which makes it useful for
special-ized electrical applications Gold contacts are often
found on sensitive electronics connectors in the
com-puter and video industries Copper and silver are also
good conductors, with copper being the most widely
used for electrical installations
GOLDSee Global Online Directory
gold disk, gold disc1 The master or final copy of a
product (software, music CD, laserdisc, etc.) from
which mass production replicas are made 2 A
spe-ciallimited edition distribution Collectors' edition
Gold disc music CDs sometimes are marketed as
higher quality pressings with special inserts and
spe-cial tracks that may not be included on a regular copy
of the CD
gold number, custom number, vanity number A
phone number specifically selected so that it is easy
to remember, particularly ifthe letters associated with
the number spell out a word or other mnemonic
There is typically an extra fee associated with
get-ting a gold number Sometimes people get lucky, and
their number just happens to be easy to remember or
to spell something interesting
Goldstone Deep Space Communication Complex
One ofthe complexes ofthe NASA Deep Space
Net-work (DSN) that provides radio communications for
for radio astronomy and radar observations of our solar system and the universe beyond Other com-plexes in the Network are located in Madrid, Spain, and Canberra, Australia See Deep Space Network Deep Space Communication Complex
Large beam waveguide parabolic antennas at the Goldstone Deep Space Communication Complex in the Mojave Desert in Goldstone, California The 34-meter dishes are used for astronomical research and radio space communications [NASAIJPL image,
1990.J
GOMESee Global Ozone Monitoring Experiment GOME Data ProcessorGDP A ground segment system designed to process data from the satellite-based Global Ozone Monitoring Experiment (GOME) Raw data is processed by the GDP into Levellradianceslreflectances and Level 2 trace gas quantities data that are made available to interested
parties A number of images and otherdatasets are also available, some of which may be downloaded
by FIP The GDP was jointly designed and developed
by Gennan, Dutch, and U.S organizations and is ad-ministrated by the European Space Agency (ESA) Processing is handled at the DFD, the German Re-mote-Sensing Data Center See Global Ozone Moni-toring Experiment
GOMSSee Geostationary Operational Meteorologi-cal Satellite
goniometerA detection instrument that can be set
at a range ofangles, sometimes in selected increments (or with optional heads), to assess the different pat-terns oflight scattered from a sample The results are useful in industrial analysis ofmaterials such as poly-mers and particulate composites Fiber optics enable the probing surface to be separate from the rest ofthe electronics Goniometers may be built into spectrom-eters although some newer fiber optic spectromspectrom-eters don't require traditional goniometers
Gooch, Daniel(1816-1889)AnEnglish locomotive engineer and businessman who aided in the installa-tion ofthe fITst successful permanent telegraph cable link between North America and the British Isles At
a relatively young age, Gooch was appointed the lo-comotive superintendent of the Great Western Rail-way (GWR) In 1840, Gooch contacted gifted engi-neering designer Isambard K BruneI about design-ing an engine works for GWR (this association be-tween the two talented engineers was to take an in-teresting tum more than a decade later) Using new
Trang 3Fiber Optics Illustrated Dictionary
technology and the results of experiments in
atmo-spheric resistance, Gooch designed locomotives that
could travel at faster speeds than previous models
He was also a supporter of wide gauge technology,
despite the trend to smaller gauges Gooch designed
morethan300 locomotives in his career as an engineer
In the 1860s, Gooch resigned his position with GWR
to put his efforts into telegraphic communications He
became Chairman ofthe Telegraph Construction and
Maintenance Company and a director of the
Anglo-American Company In the meantime, BruneI had
been designing the Great Eastern (originally the
Leviathon) The Great Eastern was purchased by
Gooch and his colleagues for cable laying and was
instrumental in laying the first transatlantic
commu-nications cable, the feat that Gooch is best known for,
despite his many other accomplishments See Great
Eastern
good condition In many rating systems, a product
with minimal abrasions from wear and tear, and
mechanisms that are in good working order Good
condition does not describe the age ofthe product or
its remaining useful life Often intermediary between
fair conditionandexcellentorlike newcondition
goodputAgeneric measurement ofnetwork data
suc-cessfully received, effective throughput; in contrast,
discarded cells, or transmitted cells in a congested
link, are called badput See cell rate, throughput
Goodwin, Hannibal (1822-1900)AnAmerican
min-ister and inventor who created celluloid film in 1885
and received a patent for rollable film in 1887 For
many years, motion picture films were known as
celluloids, and individual animation frames used to
create frame-by-frame animation are still known by
the abbreviated formcells.
gopher The command for initiating a Gopher client
on a text-based system is "gopher" (all lower case),
and "xgopher" is a similar client command that works
with The X Window System See Gopher
Gopher Adocument system developed by P Lindner,
M McCahill, B.Alberti, F.Anklesaria, andD Torrey
at the University of Minnesota in the early 1990s to
provide a local campus information server The
Go-pher service quickly grew to become a worldwide
resource It is a client/server distributed document
delivery system, i.e., a means oflocating information
on the Internet through a simple menu-like text
terface (or graphical Gopher client) or ofsending
in-formation through electronic mail.Itis also possible
to set bookmarks, Gopher information locations that
are frequently used Links to various Gopher servers
together comprise a virtual community known as
Gopherspace The Gopher text menu interface is
be-ing superseded by graphical Web interfaces See
Veronica, RFC 1436
Gopherspace The Gopher document system is
com-posed of many widely distributed document
reposi-tories and Internet services in Cyberspace Hence, the
Gopher facilities online are called "Gopherspace" by
many their users See Gopher
GORIZONT A Russian geostationary
telecommu-nications satellite launched in 1996
GoS grade of service A phrase to describe service levels, which usually are individually defined on an industry basis See class of service
GOS See Global Observing System
GOSIP Government Open Systems Interconnection Profile AU.S government version of the Open Sys-tems Interconnection system which is required in many government data network installations Gosling, James Gosling is best known for his con-tributions to the Java programming language, devel-oped at Sun Microsystems, Inc He was associated with Bill Joy, Mike Sheradin, and Patrick Naughton
on Project Stealth in 1991 Project Stealth's goal was
to develop a distributed network in which the vari-ous electronic devices could intercommunicate See Java; Joy, William
Goubau 1958 Wave-Guiding Patent
This selection of diagrams from Goubauspatent accompanies his description of a method for trans-mitting a substantially cylindrical wave beam by
re-setting the cross-sectional amplitude and phase dis-tribution ofthe beam at intervals that are large com-pared to the beam radius Goubau further describes a mechanism to phase-correct elements intercepting the beam to effect repetitions of the cross-sectional am-plitude and phase distribution, as desired The dia-gram illustrates some ofthe phase-correcting lenses for accomplishing his goals.
Goubau, Georg Johann Ernst Apioneer researcher into hollow optical waveguides utilizing lenses as a
Trang 4plication for an invention to transmit electromagnetic
wave beams, in November 1958 (U.S #3,101,472)
In 1961, he coauthored "On the~idedpropagation
of electromagnetic wave beams' in IEEE
Transac-tionsand continued lens guide research with a
num-ber ofscientists through the 1960s See Dicke, Ronum-bert
Gould, Gordon (1920- ) An American engineer,
Gould has been involved in maser/laser technology
since the late 1950s Gould studied optics at Yale
Uni-versity and later began a Ph.D in physics at
Colum-bia University, where Charles Townes was a professor
Townes had been conducting historic research on
masers (microwave amplification) since the early
1950s.In1957, Townes and Gould discussed the
con-cept of using light amplification rather than
micro-wave amplification for developing lasers
Gould was an ambitious student who wanted to earn
a patent for a historic invention After discussions
with Towne about patent application procedures, he
left graduate school to work for TRG, worked on a
prototype and filed a patent, in 1959 The patent was
initially denied due to the earlier patent of lasers
de-veloped by Townes and Schawlow because Gould,
at the time, could not produce substantive written or
prototypic proof of lasers invented in 1958 But,
af-ter a subsequent legal battle, some ofthe claims were
accepted and a patent was awarded in 1977 giving
him rights to royalties for certain laser technologies
In1967 Gould accepted a professorship at the
Poly-technic Institute of New York where he established
and promoted laser research Gould supports
educa-tion in optics See Dicke, Robert; laser; laser history
Gouy, Louis-Georges(1854-1926) AFrench
physi-cist and educator who described thermal motion in
ions in support of molecular theories that applied to
an electrical double layer associated with planar
sur-faces, now called the Gouy-Chapman theory The
theory, while flawed in some of its assumptions,
ap-plies reasonably well for certain aqueous solutions,
but does not hold up as well for small distances and
high surface potentials (e.g., edges)
Gouy balanceAninstrument for assessing the
mag-netization ofaparamagnetic substance (one with
un-paired electrons) as compared to the gravitational
at-traction of a counterweight, named after
Louis-Georges Gouy.Inother words, a device for
determin-ing magnetic susceptibility Differences in apparent
mass of a sample may be assessed in and out of a
magnetic field The number ofunpaired electrons of
a sample may be determined as the force with which
a paramagnetic compound is attracted to the magnet
is related to the number ofunpaired electrons and can
be compared with substanced with known parameters
A Gouy balance utilizes large magnets mounted
sta-tionary opposite a movable sample Contemporary
replacements for the Gouy balance do it the other way
around, with movable magnets balanced on either
side of a stationary sample
Gouy phase shiftA shift in the Gaussian mode that
occurs when the beam passes through a focal point
(sometimes called the beam waist), named after
as a means to split and statistically observe radiant energy characteristics and has been described as a mechanism for accelerating fast pulses However, ob-servation of the phenomenon was mainly of math-ematical interest until the late 1990s, when systems were designed capable oftransmitting in the terahertz (THz) frequencies-yielding beams that could be as-sessed for both amplitude and phase This enables the Gouy phase shift to be more readily observed and in-terferometrically plotted See tilt locking
Government Emergency Telecommunications ServiceGETS.Aservice of the U.s National
Com-~~i:~t~t~f:~~::!~!~;~1~;~:~;~:~ ~~ I. works by authorized users GETS provides
emer-gency access and processing in local and long-dis-tance telephone networks through a dialing plan and personal identification number (PIN) GETS services are provided through major long-distance networks, local networks, and leased networks through a uni-versal access number and common telephone devices (desk phone, cell, phone, fax line, etc.) Once authen-ticated through the PIN, the caller receives special handling that may include priority and/or enhanced routing See National Communications System
http://gets.ncs.gov/
Government Information Locator ServiceGILS
An ISO standard metadata scheme for describing government information resources with the intent of streamlining the management of information for ef-ficient search and retrieval GILS is an open, cost-effective, scalable data standard to facilitate the search for collections ofinformation and specific in-formation within a collection GILS extensions allow specific categories of data to be managed and searched GILS is based on the ISO 23950 search standard and can be approached in somewhat the same way as information searching may be ap-proached in a reference library See Dublin Core, In-ternational Development Markup Language
http://www.access.gpo.gov/su_docs/gils/index.html GPFSee general protection fault
GPRSSee General Packet Radio Service
GPSSee Global Positioning System
GPS Control SegmentA general overall category ofthe GPS system which comprises a main tracking station, in Schriever (formerly Falcon) Air Force Base, Colorado, and subsidiary tracking stations worldwide as part of the U.S Department of Defense's Global Positioning System The tracking stations take the signals from the satellites and incor-porate them into orbital models that are further used
to compute precise, individual, orbital data and clock
corrections Portions of this orbital ephemeris are
sent via radio transmissions to GPS receivers See GPS Space Segment, GPS User Segment
GPS Navigation DataSatellites in the Global Posi-tioning System (GPS) send out two microwave car-rier signals, one of which provides navigation infor-mation in the form of a series of time-lagged data
Trang 5Fiber Optics Illustrated Dictionary
frames sent over a specific time period Subframes
are also included for checking data integrity The
sat-ellites are equipped with atomic clocks, and clock
data parameters are sent and related to GPS time
Orbits are described by transmitting regularly updated
ephemeris data See Global Positioning System,
Uni-versal Coordinated Time
GPS Operational ConstellationThe system ofover
20 more-or-less evenly spaced, orbiting satellites
(some of which are spares), equipped with atomic
clocks, in the Global Positioning System (GPS) Space
Segment These satellites orbit the Earth twice a day
at about 11,000 miles altitude, transmitting
informa-tion used in the U.S Department of Defense's
Glo-bal Positioning System The orbital planes are
in-clined at about55degrees in relation to Earth's
equa-torial plane From anyone point on Earth, it is
gen-erally possible to locate between five and eight
sat-ellites, four or five ofwhich are typically used to
com-pute location and timing information The satellites
transmit two microwave carrier signals; theL1
fre-quencies carry the navigation message (with data
de-scribing the orbit and clock parameters) and SPS code
signals, and the L2 frequencies monitor ionospheric
delay ofPPS receivers See Global Positioning
Sys-tem
GPS receiver/displayA fixed or mobile Global
Po-sitioning System (GPS) device that interprets GPS
information and computes graphics, text, locations,
maps, or other displays that provide the user
infor-mation about position, time, and sometimes
veloc-ity A graphical display of latitude and longitude is
common Receivers vary from room-sized systems
to small handheld units from $180 up to hundreds of
thousands of dollars GPS consoles are used by
sur-veyors, have been combined with map databases to
provide car consoles, and have also been incorporated
into 'smart cars' that can steer themselves It is not
unrealistic to predict that someday small GPS
sys-tems will be designed into wristwatch-style personal
locators for travellers, sales representatives, hikers,
et a1 See Global Positioning System, Intelligent
Ve-hicle Highway System
GPS Space SegmentA general overall category of
the GPS system that consists of GPS satellites
de-ployed and administered by the U.S Department of
Defense as part ofits Global Positioning System See
GPS Control Segment, GPS User Segment
GPS translatorA Global Positioning System
trans-lating capability to support technologies that require
precise positioning and trajectory tracking data This
type of data is of importance to missiles and rockets
and other high-velocity acceleration devices
Trans-lator GPS systems support midcourse corrections,
safety operations, and downrange tracking They are
a cost-effective option to certain radar tracking
sys-tems and a higher-accuracy option to portable GPS
receiver systems
A vehicle or interceptor device installed with a GPS
translator captures the GPS signals, translates them
to an appropriate communications frequency, and
transmits them to a ground-based station for further
processing The use of ground-based stations also makes it possible to store the data in larger storage media for subsequent playback and analysis, a capabil-ity that is impractical in most on-site GPSdevices.
IEC is a commercial vendor of GPS translators that has been providing and developing the technology since the 1980s It has supplied translator systems to both the U.S Navy and the U.S Air Force IEC has recently introduced a family of digital GPS transla-tors that can support encryption for greater security, and it is developing a smaller, more powerful Trans-lated GPS Range System (TGRS), in cooperation with the Air Force
GPS User SegmentAgeneral overall category ofthe GPS system that includes GPS receivers and users ofthe U.S Department ofDefense's Global Position-ing System See GPS Control Segment, GPS Space Segment
Grade 1 to 5 twisted pairSee twisted pair cable Grade B signalAradio-frequency broadcasting sig-nal defined by the Federal Communications Commis-sion (FCC) It is a measure of the strength of a tele-vision broadcasting station's signal at a specific lo-cation The purpose of the rating is to define mini-mumacceptable standards ofquality for viewing pur-poses in the context of defining whether a specific subscriber is served or unserved by the signal When the Satellite Home Viewer Improvement Act (SHVIA) was passed in 1999, it included a require-ment that the FCC re-evaluate the Grade B signal standard to determine if it should be changed or re-placed with something else for determining whether
a household is unserved (unable to receive a signal
of an acceptable level) Since it is impractical to go out and measure radio signal strengths in the vicin-ity of every subscriber in the U.S., the FCC created a computer model for satellite companies and televi-sion stations to predict whether a given household is served or unserved This computer model went through several versions in order to include the ef-fects of buildings, terrain, and land cover variations that could impede radio-frequency signals Ifthe pre-dicted model is under dispute, a person may request
a waiver from local TV stations serving the area If the waiver is granted, the person becomes eligible to receive distant signals
If the parties cannot agree whether a subscriber is served or unserved, the American Radio Relay League (ARRL) has been designated as an indepen-dent, neutral entity for arbitrating and designating the party, with input from the satellite provider andTV station, to conduct a field test of signal strength grade ofserviceGoS Aservice level indicator evalu-ated on an industry basis according to the type of ser-vice provided In some industries a hierarchical cat-egory scale is applied to various levels or definitions
of service In telecommunications, grade of service
is typically described in statistical terms related to the speed and probability ofconnecting, and the charac-teristics of the connection, etc See class of service, quality of service
graded indexGI Adesignation for a fiber waveguide
Trang 6tain wavelengths altered by the deliberate inclusion
of dopant materials in the fiber Thus, undesirable
effects such as dispersion can be mitigated in
multi-mode fibers (especially those for longer distances) by
selectively controlling the speeds at which the light
beams travel within certain portions of the fiber
Beams that reflect in the lightguide at steeper angles
normally would take longer to traverse the distance
than beams that have a "straight shot" through the
guide However, by gradually changing the index of
refraction of the lightguide out towards the outer
di-ameters to enable faster propagation in this region, it
is possible to compensate for the longer travel path
GI fiber operates in the O-band region around 1300
nm See dispersion, light speed, stepped index
gradientGradual change in elevation, color, or
tex-ture along an axis Gradual blend or transition See
gradient fill
gradient fiUAcommon feature ofpaint programs that
allows the user to fill a defined area with graduated
tones ranging from one specified color or shade of
gray to another The number of colors in the palette
and the two end-tones selected will affect the
smooth-ness and visual appeal of the transition, with more
tones generally creating a more pleasing effect
Ra-dial fills can be used to simulate 3D surface areas, as
lighter areas appear as highlights
Graham ActA U.S 1921 act in which telephone
companies were granted exemptions to the provisions
of the Shennan Antitrust Act.Itenabled AT&T,
es-pecially, to expand and exert further monopolistic
control over the telephone networks See the
Kings-bury Commitment, Modified Final Judgment
Gramme, Zenobe Theophile(1826-1901) A
Bel-gian engineer who emigrated to France, Gramme
de-veloped a direct current (DC) generator, featuring a
ring armature in 1869 and 1870 Together with
Hippolyte Fontaine, Gramme opened a factory called
Societe des Machines Magneto-Electriques Gramme
In1873, at the Vienna Exposition, it was noticed by
a mechanic that an electrical connection from another
generator could power the armature of the first
gen-erator, thus exhibiting the characteristics of a motor
It was an important historical advancement in
indus-trial and transportation technologies
grandfather clauseA previously existing object,
structure, statute, ownership right, or policy that may
continue despite subsequent restrictions or
regula-tions that would prevent its creation or continuance
A grandfather clause grants a type ofpardon, special
permission, or immunity For example, military
sur-plus purchased by a civilian in the 1960s may be
regu-lated in the 1990s such that similar items may not be
purchasable by current civilians (such as radiation
bunkers) If the ownership is protected by a
grandfa-ther clause, when restrictions are imposed or
rein-stated, current civilian owners might not have to give
up the property (but also may not be able to sell it,
except perhaps back to the government)
Building codes are often subject to grandfather
clauses Ifyou purchase a house built in 1920, it may
regulations as current structures
Voting and immigration laws have certain grandfa-ther clauses Immigrants to the country prior to a cer-tain date do not require the same documents and eli-gibility requirements as later immigrants
Intelecommunications, phones and various electronic components built or installed before a certain date may not have to meet all current Federal Communi-cations Commission (FCC) regulations
grandfathered inInstated or installed before certain restrictions or regulations were put in place that would otherwise prevent creation, installation, or operation
;~:~;:~~~!~~~:~~~~~:;n::;'k:~~~~~~ *~: •
graphechon can store an electrical charge pattern, similar to the functioning of an iconoscope, and re-cover the pattern at different scanning rates
graphic equalizerA component providing a set of controls for adjusting the tonal qualities at several fre-quencies in an audio system, usually a music system The equalizer is not a stand-alone component; it works in conjunction with other components such as receivers, phonographs, tape players, CD players, etc
It frequently has a series ofvertical analog sliders for making individual adjustments
Graphical Kernel SystemGKS An official standard for 2D graphics in the mid-1980s, evolved from the Core A 3D extension was subsequently developed, and GKS-3D became a standard in 1988 See Core, PHIGS
graphical user interfaceGUI Away of facilitating communication between a human and a device, usu-ally a computing machine, by presenting the infor-mation in the form ofvisual metaphors Agraphical user interface works in conjunction with a variety of physical input devices, including speech recognition hardware, mice, keyboards, stylus pens, touchscreens, and joysticks They provide a means to select and control the various visual elements, which commonly include menus, drag bars, buttons, icons, and window gadgets Video games like Pong were early electronic adaptations of simple GUIs Many ofthe earliest ap-plied GUI ideas in general use today were developed
at Xerox PARC and incorporated by Apple Computer into the Macintosh operating system
graphics acceleratorA chip or circuit board inte-grated into a computer system to relieve the CPU of some of the functions related to the processing and display of graphics Graphics tend to be computing intensive, and sharing the load can significantly speed the display and refresh ofimages Graphics accelera-tors are often sold as peripheral cards that can be plugged into a slot See graphics coprocessor
graphics controller, graphics display processor Specialized computer hardware to improve raster displays by taking some of the load from the CPU Graphics controllers can speed up scan conversion, and the composition, display, and movement of graphics images and primitives See cathode-ray tube, frame buffer
Trang 7Fiber Optics Illustrated Dictionary
graphics coprocessor Achip designed to speed
com-puter graphics composition, display, or refresh by
sharing the load with the system CPU Coprocessors
are sometimes designed for very specific tasks, such
as updating a screen, or storing and displaying
graph-ics primitives, hardware sprites, and the like Unlike
graphics accelerators, which are often sold to
con-sumers as optional system-enhancing peripherals,
graphics coprocessors are more commonly sold
in-tegrated into the system, often on the motherboard
See graphics accelerator
Standardized Recording/Playback Fonnats
VHS
Super-VHS
Hi-8mm
CD+G
laserdisc
The variety ofstandardized recording andplayback
media for graphics and multimedia products is
in-creasing Some ofthe more common formats
support-ing both images and sound are shown here It may be
that DVD-relatedformats, which hold more
informa-tion in less space, will eventually supersede most or
all ofthe above technologies.
graphics device interface GO! Physical and virtual
connections between graphics hardware components
and the computer CPU Since graphics applications
tend to be CPU intensive, it is very common for other
graphics hardware (accelerator cards, frame buffers,
blitters, etc.) to be incorporated into a system to
fa-cilitate the fast creation, display, and refresh of
im-ages on a variety of output devices
graphics engine The part ofa computer architecture
supporting the graphics functions ofthe machine,
par-ticularly graphics composition, buffering, display,
and fast refresh Graphics engines are typically
de-signed to handle many of the functions in hardware,
so there is a minimum of on-the-spot software
cal-culations Enhanced graphics standards and
graph-ics engines are being developed to support features
such as realtime animation; hardware pan, zoom,
compression/decompression; instant
resolution-switching; and video signal support
Graphics Environment Manager GEM One ofthe
first graphical user interfaces (Gills) developed by
Gary Kildall's Digital Research, the same company
that created the popular CP1M text-based operating system in the 1970s GEM was fIrst demonstrated publicly at the COMDEX computer industry trade show in 1983 and shipped a few months later The interface greatly resembled the Macintosh interface that Apple had developed after observing develop-ment research at the Xerox PARC laboratories GEM did not become widely distributed, with the excep-tion ofproviding a front-end to Xerox's Ventura Pub-lisher, a desktop publishing programming that was widely used for documentation page layout on Intel-based microcomputers in the later 1980s
GraphicsInterchan~eFormat GIF (GIF ought to
be pronounced "gif given that the G stands for
"graphics," but its author apparently uses "jif.") GIF
is a proprietary raster graphics format introduced by CompuServe, Inc in 1987 It is an 8-bit graphics for-mat developed with the patented Lempel-Ziv-Welch (LZW) compression, whose implementation requires
a royalty agreement from Unisys Corporation The level of compression varies with the type of image and number of colors, but 3 or 4 times compression ratios are common on a typical color image Due to patent issues, CompuServe agreed in 1994 to secure
a license agreement to distribute the LZW technol-ogy and issued the Graphics Interchange Format De-veloper Agreement to provide software deDe-velopers permissions under CompuServe's software license agreement with Unisys
GIF is particularly suitable for images that have a small number ofdistinct colors, as opposed to images that have a great variety of subtle color changes It also handles line art, grayscale images (through color palette gray matching), and sharp color boundaries better than formats optimized for other characteris-tics Because GIF is a 256-color fonnat rather than a 24-bit color format ( 1.6 million colors), 24-bit im-ages will be dithered and adjusted and may not fully satisfy the needs of the user
GIP will support transparency, which is sometimes desired in order for a background image to be dis-played behind the GIF image or through parts of the GIP image as though there were holes Transparency
is often used by Web designers to produce special ef-fects in Web pages, such as buttons with irregularly shaped edges
GIF is one of the three most common graphics for-mats supported by World Wide Web browsers, the other two being PNG and JPEG PNG is an open, nonproprietary format, developed to supersede GIP
In January1995,CompuServe announced theGIF24
project for designing a replacement format for the original 8-bit GIP, and a month later officially an-nounced that Portable Network Graphics (PNG) would be used as the basis for GIF24
Support for GIF users is provided on the CompuServe Graphics Support Forum (GO GRAPHSUPPORT) See Lempel-Ziv-Welch, Portable Network Graphics graphics library GL The writing of graphics rou-tines for computers is time intensive and specialized For that reason, many companies decide to purchase graphics libraries rather than to write their own These
Trang 8used graphics primitives and actions (lines, circles,
dots, fills, patterns, etc.) that can be dynamically
called from the graphics library or compiled and
linked into the software executables as needed
graphics mode Asetting on dual-display mode
sys-tems (typically older IBM-compatibles) that permits
the access and display of individually addressable
pixels for the rendering ofimages andgraphics
char-acters.Some systems distinguish between text and
graphics modes and will display only in one mode or
the other With faster processors, the trend is toward
the more flexible graphics modes, with graphics
char-acters This frees the user from having to select a
mode and switch between them
Graticule Examples
[
[
Graticules are overlay templates used for a wide
variety ofalignment and calibration purposes,
espe-cially in scientific viewing and measuring instnlments,
video titling and the evaluation ofvideo images They
are also used to display and analyze field positions in
videotapes ofteam sports.
graticuiegraphical reticule 1 A diagnostic and
mea-surement overlay screen used with cathode-ray tubes
(CRTs) The screen is calibrated and placed on the
front of the tube, with the tube image showing
through so the relationship ofthe displayed image to
the screen can be observed A graticule may also be
used with a spectrum analyzer, for analyzing
band-width, with the analyzer calibrated to a specified
num-ber of graticule units 2 A microscopic component
incorporated into some eyepieces that provides an
ar-rayed reference field for observation and count
esti-mates of fibrous or particulate specimens (e.g.,
as-bestos fibers).Inthis context, it is often called a
reti-cule It is useful in fabrication, contamination
test-ing, and quality assurance 3 A reference grid or
out-line image superimposed over a still or moving
im-age to aid in analyzing or understanding the imim-age
or making sure it is within certain tolerances (e.g.,
the correct aspect ratio) This is especially useful for
mapping, video element alignment (to avoid
undes-ired clipping of titles or images), and video transfer
to other media with the increasing variety of
differ-picture-in-picture, etc.) A graticule is the same ba-sic concept as a reticule, but is more often used to assess recorded images, as in cartography or video,
as opposed to real specimens as might be viewed with scientific devices, especially microscopes and tele-scopes See graticule library, reticule
graticuie library Aset ofpredesigned graticules for use as reference, calibration, or counting templates for superimposing over an image or text A simple example of a graticule is a reticular grid on a piece
of mylar that is placed over a picture to provide ref-erence marks for hand copying the picture More so-r:£:~~~~~{~~~~~~~:;r~~~~:~images or magnified viewing fields For example, a •
graticule with reference marks for scale and for indi-cating the outlines ofan antarctic icefield as it looked
in 1970, could be superimposed over as~tellite im-age of the icefield as it looks today User-designed graticule templates could be included as part of a graticule library database for custom applications
or future use See graticule
grating Aseries of narrow ordered slits or grooves specifically designed and oriented so they reflect elec-tromagnetic waves in a spread or concentrated pat-tern in a desired direction For some types of grat-ings, the period of the grating (the distance from one facet to the next) can be "tuned" to selectively admit
or reflect optical wavelengths Other types of grat-ings depend upon the shape of the corrugations to control light in a particular diffraction order Thus, gratings are useful as filtering mechanisms Antenna reflectors sometimes incorporate grating designs
Gratings have existed for centuries for a wide vari-ety of purposes However, most grating components intended for use in scientific instruments have been developed since 1900 Diffraction gratings as they are used in modern components have been manufactured
in a number of ways since the 1960s They are now regularly incorporated into fiber optic filament and semiconductor components to act as lightwave filters Gratings can be produced mechanically in a variety
of materials or photographically in layered films A photographicinterference gratingis a recording ofa stationary interference fringe field (sometimes called
a holographic grating)
Since gratings are often fabricated on thin films with fine tolerances and densities, it is necessary to match the light source with the structure It may be neces-sary to lower the light intensity or increase the thick-ness of the grating and associated component layers
in order to prevent the light (which is often laser light) from melting the grating See blazed grating, Bragg grating, diffraction, echelle grating, Fresnel lens, in-terference grating, ruled grating
grating arrowIn scientific and engineering diagrams illustrating grating components with asymmetric cor-rugations, an indication ofthe orientation ofthe grat-ing For example, in a sawtooth-shaped grating (e.g.,
a blazed grating), the arrow would be oriented from
Trang 9Fiber Optics Illustrated Dictionary
the peak to the more distant trough (the one farthest
from and connected to that peak) along the grating
normal (typically illustrated along the horizontal[X]
axis)
grating equationInthe context of diffraction
grat-ings, an equation that enables the ordered angles of
reflected incident light to be calculated and modeled
Thus, sine =sine+mA.ld with q representing the
light source's incident angle upon a diffraction
grat-ing, at a wavelength of! and a grating period (the
dis-tance from one corrugation to the next) ofd, q,
rep-resents the diffraction angle such that the sin of the
diffraction angle is equal to the sin of the angle of
in-cidence plus the incident wavelength divided by the
grating period The structure of diffraction gratings
and their effectiveness is in part due to the "tuning"
of the angles to interact in desirable ways with
spe-cific wavelengths See diffraction, grating, Wood
anomaly
grating, fiber optic Aseries ofgrooves in a fiber optic
filament intended to control the propagation oflight
as it passes through the grating For example, a
grat-ing can help control the direction of the lightwave,
the wavelength(s) ofthe propagated light, or both The
grating is "etched" or "written" into the fiber and the
fiber may be strained at the time the grating is
Wl;t-ten Multiple overlapping gratings may be used to
further condition the propagating lightwave Long-period gratings may provide phase-matched coupling from transfering power from one optical mode to another within a fiber (e.g., between guid-ing and claddguid-ing modes) Permanent long-period gratings are typically laser written through an ampli-tude mask Adjustable long-period gratings may be mechanically written through pressure that produces nonpermanent microbends
Fiber gratings are used in sensors, scientific instru-ments, and fiber optic communication networks See Bragg grating, grating
gravity cell, crowfoot cell A type of voltaic wet cell suitable for providing small currents at a constant electromotive force It derives its name from the way the lower and upper chemical solutions (e.g., copper sulphate over zinc sulphate) align themselves in re-lation to each other
Gray, Elisha(1835-190I) A physicist and inventor who developed many early telegraph technologies at about the same time Alexander Graham Bell was working to develop a harmonic telegraph Gray was mechanically apt and had publicly demonstrated an early version ofa harmonic telegraph, a device to send tones over wire, before Bell applied for a patent for his version Gray filed a caveat for a patent the same day as Bell filed for the patent on what is now
Mechanically Impressed Adjustable Grating
LI:CU-i-i~:j~~
. , lIel 0 9 1
r'~'~~'~"'AAO"""~
elastic 1 - - - - 1
A long-period adjustable grating designed by L Mollenauer ofLucent Technologies, Inc pmvides an alternative
to pemJanent gratings.
Instead ofwriting the grating into the stlucture ofa single-mode jiber; as is traditional, the fiber is impressed into
an external mechanical grating ''form'' to inlfVduce microbends into thejiber that cause the pmpagating light to be conditioned for certain specified wavelengths In other words, only selected wavelengths will escape the jiltering process and continue pmpagating along the transmission path By inlfVducing a series ofimpressed gratings into the path selectivity can befurther controlled With this type ofconfiguration, dynamic changes in the wavelength selec-tivity and gain equalization are possible This may be practicalfor many situations where small grating periods (the distance between cO/rugations) are not required.
Trang 10speaking telegraph at the time.
In 1867, Gray developed a new telegraph relay
in-strument In collaboration with his partner, Enos M
Barton, Gray organized the Western Electric
Manu-facturing Company in 1869 and expanded by
buy-ing out the Ottawa, Illinois Western Union offices
Late in 1873, Gray reports having noticed different
vibratory properties in human tissue (an idea
pio-neered by Meucci) and described the placing ofa
gal-vanometer in the circuit with a microphone for
trans-mitting human speech through wires This
observa-tion resulted in a patent applicaobserva-tion that was not
ac-cepted until three years later as Gray had to
substi-tute animal tissue for human to satisfy the Patent
Of-fice Gray filed a patent similar to Bell's only hours
after Bell, and his company was later purchased by
Bell
In the 1880s, telegraphs that would transmit
hand-writing were developed and Gray patented a
telau-tographwhich could lift the pen between letters
per-mitting more natural characters to be transcribed, and
sold the rights to a company founded with his name
See telephone history
Gray, Stephen (1666-1736) An English
experi-menter who authored an article for Philosophical
Transactionsin 1720, describing various
investiga-tions of attractive properties and light-producing
properties of various "electrics." He discovered that
a substance electrified by friction could pass this
property to another substance He enlarged on the
prior work of Gilbert, demonstrating that Gilbert's
"non-electrics" could conduct electricity from one
body to another and could be electrified if insulated
with a conductor
His association with the Royal Society of London
indicates that he was likely familiar with the work
and writings ofF Hauksbee, and he continued some
ofthe interesting lines ofinquiry first investigated by
Hauksbee
In the late 1720s, Gray began a fruitful collaboration
with Granville Wheler, a member of the Royal
Soci-ety Gray and Wheler were to discover that substances
could be roughly divided into additional substances
that readily conducted "electric virtues" and those that
did not See inductance
Gray&BartonAtelecommunications company
es-tablished by Elisha Gray and Enos Barton in 1869
when Elisha Gray bought out George Shawk's
inter-est in the partnership The physical facility was an
electric shop abandoned by the Western Union
Tele-graph Company In 1872, it became Western
Elec-tric Company, which supplied components to the
Western Union Telegraph Company and later became
an exclusive manufacturer for the Bell System See
Graybar Electric Company, Inc.; Western Electric
Company
gray market productOne of several types of
prod-ucts that are not fully endorsed by the manufacturer
Examples include a product sold by an unauthorized
distributor; a product that might be second rate in
some way, which nonnally wouldn't be sold by
repu-ingnew
Gray Telephone Pay Station CompanyAcompany fonned to commercialize the rotary payphones that were common from about 1930 to the 1960s Graybar Electric Company, Inc.A spinoff of the Western Electric Company in 1925, this company handled electrical distribution The name derives from the original founders ofthe Gray&Barton com-pany, founded by Elisha Gray and Enos Barton in
1869 In 1928-1929, the employees purchased the company from Western Electric Company, and it is still one of the largest employee-owned companies
in the United States Graybar Electric continues to
do business after more than sixty years, globally sup-plying almost a million different electrical and tele-communications products See Gray&Barton, West-ern Electric Company
graylineThe region in any particular place where the Sun is rising or setting This infonnation is of inter-est to those trying to detennine a radio signal trans-missions path using the characteristics ofthe Earth's ionosphere to help propagate the signal There are software programs containing extensive databases of thousands of cities, designed to generate a grayline chart and display a world clock to assist amateur and professional radio operators in sending and receiv-ing radio communications Some grayline generators also include azimuth projection maps (Great Circle maps) which can help the user detennine where ra-dio signals may be arriving from different parts of the world, depending upon location and time of day See ionosphere
grayscaleVisual infonnation represented in shades ofgray, i.e., with no color In computing tenns, many
people confuse the terms monochrome and grayscale.
Monochrome refers to one active color, whether it be white, black, green, or amber Many older computer monitors were monochrome monitors Grayscale re-fers to two or more (typically 16 to 64) shades ofgray typically ranging between white and black Grayscale monitors are less expensive than color and are very suitable for desktop publishing and other black and white and grayscale print-related applications grayscale monitorAmonitor capable of displaying
a variety oflevels oflight intensities (usually between
16 and 64), which are perceived as shades of gray grazing incidenceAnangle that is perpendicular or
nearly perpendicular to a reference surface's normal
such that an incident wave within the grazing inci-dence tolerances is reflected off the surface For re-flection at very low grazing angles that are almost parallel to the surface in an internal resonating cav-ity, a very highly reflective surface and short high-energy wavelengths (e.g., X-rays) are generally re-quired However, external resonators/reflectors have been used with wavelengths in the optical region Assemblies with two adjacent dielectric materials with different indexes ofrefraction may exploit graz-ing angles to achieve total internal or external reflec-tance, depending upon the relationship ofthe conduc-tive materials