An Etymological Dictionary of Astronomy and Astrophysics

According to the → de Broglie hypothesis, which has been verified by experiments, every → particle of matter, whatever its nature, has a characteristic → wavelength
associated with its wavelike quantum aspect. The de Broglie equation gives the equivalent wavelength of a moving particle: λ = h/mv, where h is → Planck’s constant, m the mass of the particle, and v its velocity.

See also: → de Broglie wavelength, → Davisson-Germer experiment.

Etymology (EN): Named after Louis Victor de Broglie (1892-1987), French physicist, creator of a new field in physics, wave mechanics, who won the Nobel prize in physics in 1929. → equation

According to the → de Broglie hypothesis, which has been verified by experiments, every → particle of matter, whatever its nature, has a characteristic → wavelength
associated with its wavelike quantum aspect. The de Broglie equation gives the equivalent wavelength of a moving particle: λ = h/mv, where h is → Planck’s constant, m the mass of the particle, and v its velocity.

See also: → de Broglie wavelength, → Davisson-Germer experiment.

Etymology (EN): Named after Louis Victor de Broglie (1892-1987), French physicist, creator of a new field in physics, wave mechanics, who won the Nobel prize in physics in 1929. → equation

The suggestion by Louis de Broglie in 1924 whereby if → electromagnetic waves possess particle properties (→ particle nature), then it might be reasonable to suppose that material particles, such as → electrons, should possess wave properties (→ wave nature). The de Broglie hypothesis was based on the intuitive feeling that nature seems to have strong attachment to symmetry. In other words,
if radiation has particle-like properties, then material particles should possess wave-like properties. At the time no direct experimental evidence was present for the validity of this suggestion. The first confirmation of de Broglie’s hypothesis was provided by the → Davisson-Germer experiment. See also → wave-particle duality;

See also: → de Broglie equation; → hypothesis.

The suggestion by Louis de Broglie in 1924 whereby if → electromagnetic waves possess particle properties (→ particle nature), then it might be reasonable to suppose that material particles, such as → electrons, should possess wave properties (→ wave nature). The de Broglie hypothesis was based on the intuitive feeling that nature seems to have strong attachment to symmetry. In other words,
if radiation has particle-like properties, then material particles should possess wave-like properties. At the time no direct experimental evidence was present for the validity of this suggestion. The first confirmation of de Broglie’s hypothesis was provided by the → Davisson-Germer experiment. See also → wave-particle duality;

See also: → de Broglie equation; → hypothesis.

The wavelength of the wave associated with a → particle as given by the → de Broglie equation.

See also: → de Broglie equation; → wavelength.

The wavelength of the wave associated with a → particle as given by the → de Broglie equation.

See also: → de Broglie equation; → wavelength.

A solution to → Einstein’s field equations of → general relativity which contains no ordinary matter (Ω_M = 0) or radiation (Ω_R = 0), is → Euclidean (k = 0), but has a → cosmological constant (Ω_Λ > 0). The Universe expands exponentially forever. This solution was the first model expanding of → expanding Universe. See also → empty Universe, → Milne Universe.

See also: After the Dutch mathematician and physicist Willem de Sitter (1872-1934) who worked out the model in 1917; → universe.

A solution to → Einstein’s field equations of → general relativity which contains no ordinary matter (Ω_M = 0) or radiation (Ω_R = 0), is → Euclidean (k = 0), but has a → cosmological constant (Ω_Λ > 0). The Universe expands exponentially forever. This solution was the first model expanding of → expanding Universe. See also → empty Universe, → Milne Universe.

See also: After the Dutch mathematician and physicist Willem de Sitter (1872-1934) who worked out the model in 1917; → universe.

A mathematical expression describing the → surface brightness profile of a typical → elliptical galaxy,
whereby the projected luminosity distribution varies as exp(-R)^1/4.

See also: → de Vaucouleurs radius; → law.

A mathematical expression describing the → surface brightness profile of a typical → elliptical galaxy,
whereby the projected luminosity distribution varies as exp(-R)^1/4.

See also: → de Vaucouleurs radius; → law.

An → isophotal radius of a galaxy, where the → surface brightness in the B band falls to 25 mag arcsec^-2.

See also: After the French-born American astronomer Gérard de Vaucouleurs (1918-1995); → radius.

An → isophotal radius of a galaxy, where the → surface brightness in the B band falls to 25 mag arcsec^-2.

See also: After the French-born American astronomer Gérard de Vaucouleurs (1918-1995); → radius.

A widely used scheme for classifying galaxies which is an extension to the → Hubble sequence Hubble sequence. De Vaucouleurs introduced a more elaborate classification system for spiral galaxies (→ spiral galaxy) based on three morphological characteristics:

1. Bars. Galaxies are divided on the basis of the presence or absence of a nuclear → stellar bar. SA denotes spiral galaxies without bars, complementing Hubble’s use of SB for → barred spirals. De Vaucouleurs also defined an intermediate class, SAB, containing weakly barred spirals. → Lenticular galaxies are also classified as unbarred (SA0) or barred (SB0), with the notation S0 reserved for those galaxies for which it is impossible to tell if a bar is present or not.
   

2. Rings. Galaxies possessing ring-like structures are denoted (r), those without rings (s), and transition galaxies (rs).
   

3. Spiral arms. These are divided into the following subclasses: Sd (SBd), that is diffuse, broken arms made up of individual stellar clusters and nebulae; very faint central → bulge;

Sm (SBm): irregular in appearance; no bulge component; and Im, that is highly irregular galaxy.

Galaxies in the classes Sm and Im are termed the → Magellanic spirals and irregulars, respectively. The → Large Magellanic Cloud is of type SBm, while the → Small Magellanic Cloud is an irregular (Im).

See also: → de Vaucouleurs radius; → system.

A widely used scheme for classifying galaxies which is an extension to the → Hubble sequence Hubble sequence. De Vaucouleurs introduced a more elaborate classification system for spiral galaxies (→ spiral galaxy) based on three morphological characteristics:

1. Bars. Galaxies are divided on the basis of the presence or absence of a nuclear → stellar bar. SA denotes spiral galaxies without bars, complementing Hubble’s use of SB for → barred spirals. De Vaucouleurs also defined an intermediate class, SAB, containing weakly barred spirals. → Lenticular galaxies are also classified as unbarred (SA0) or barred (SB0), with the notation S0 reserved for those galaxies for which it is impossible to tell if a bar is present or not.
   

2. Rings. Galaxies possessing ring-like structures are denoted (r), those without rings (s), and transition galaxies (rs).
   

3. Spiral arms. These are divided into the following subclasses: Sd (SBd), that is diffuse, broken arms made up of individual stellar clusters and nebulae; very faint central → bulge;

Sm (SBm): irregular in appearance; no bulge component; and Im, that is highly irregular galaxy.

Galaxies in the classes Sm and Im are termed the → Magellanic spirals and irregulars, respectively. The → Large Magellanic Cloud is of type SBm, while the → Small Magellanic Cloud is an irregular (Im).

See also: → de Vaucouleurs radius; → system.

A prefix occurring in loanwords from L. to indicate:

1. Opposition, reversal: decentralize, decode, deactivate, de-emphasis.
   
2. Removal from: dethrone.
   
3. Reduction, degradation: declass, devalue.
   
4. reversal: detract, detect.
   
5. Derivation from: derive, deverbative.

Etymology (EN): M.E., from O.Fr. de-, des-, partly from L. de- “from, down, away,” and partly from L. → dis-.

Etymology (PE): Prefix vâ- denoting “reversal, opposition; separation; repetition; open; off; away,” variant of bâz-, from Mid.Pers. abâz-, apâc-; O.Pers. apa- [pref.] “away, from;” Av. apa- [pref.] “away, from,”
apaš [adv.] “toward the back;” cf. Skt. ápāñc “situated behind.”
Foru- “down, downward; below; beneath,” Mid.Pers. frôt “down, downward,” O.Pers. fravata “forward, downward,” Skt. pravát- “a sloping path, the slope of a mountain.”

A prefix occurring in loanwords from L. to indicate:

1. Opposition, reversal: decentralize, decode, deactivate, de-emphasis.
   
2. Removal from: dethrone.
   
3. Reduction, degradation: declass, devalue.
   
4. reversal: detract, detect.
   
5. Derivation from: derive, deverbative.

Etymology (EN): M.E., from O.Fr. de-, des-, partly from L. de- “from, down, away,” and partly from L. → dis-.

Etymology (PE): Prefix vâ- denoting “reversal, opposition; separation; repetition; open; off; away,” variant of bâz-, from Mid.Pers. abâz-, apâc-; O.Pers. apa- [pref.] “away, from;” Av. apa- [pref.] “away, from,”
apaš [adv.] “toward the back;” cf. Skt. ápāñc “situated behind.”
Foru- “down, downward; below; beneath,” Mid.Pers. frôt “down, downward,” O.Pers. fravata “forward, downward,” Skt. pravát- “a sloping path, the slope of a mountain.”

Transition from an excited energy state to a lower energy level, as in spectral line formation or particle emission from an atomic nucleus.

See also: From → de- + → excitation.

Transition from an excited energy state to a lower energy level, as in spectral line formation or particle emission from an atomic nucleus.

See also: From → de- + → excitation.

To cause a spacecraft to leave its operational orbit to enter a descent phase or to change course.

See also: From → de- + → orbit.

To cause a spacecraft to leave its operational orbit to enter a descent phase or to change course.

See also: From → de- + → orbit.

Of a spacecraft, the act or process of departing from an operational orbit. → de-orbit.

See also: Noun form of → de-orbit.

Of a spacecraft, the act or process of departing from an operational orbit. → de-orbit.

See also: Noun form of → de-orbit.

A method for estimating the real orientation of a field and/or related velocities/separations from two-dimensional images.

See also: → de-; → projection.

A method for estimating the real orientation of a field and/or related velocities/separations from two-dimensional images.

See also: → de-; → projection.

To correct the intensity or flux of a spectral line by eliminating the → reddening effect of → interstellar dust.

Etymology (EN): De-redden, from → de- + redden verb of
→ red.

Etymology (PE): Vâsorxidan, from vâ-, → de-, + sorxidan verb of sorx, → red.

To correct the intensity or flux of a spectral line by eliminating the → reddening effect of → interstellar dust.

Etymology (EN): De-redden, from → de- + redden verb of
→ red.

Etymology (PE): Vâsorxidan, from vâ-, → de-, + sorxidan verb of sorx, → red.

A magnitude which has been corrected for the interstellar reddening.

Etymology (EN): De-reddened, p.p. of → de-redden;
→ magnitude.

Etymology (PE): Borz, → magnitude; vâsorxidé p.p. of vâsorxidan, → de-redden.

A magnitude which has been corrected for the interstellar reddening.

Etymology (EN): De-reddened, p.p. of → de-redden;
→ magnitude.

Etymology (PE): Borz, → magnitude; vâsorxidé p.p. of vâsorxidan, → de-redden.

The process that de-reddens. The state of being de-reddened.

See also: Verbal noun of → de-redden.

The process that de-reddens. The state of being de-reddened.

See also: Verbal noun of → de-redden.

To cause to be → inactive; remove the → effectiveness of (Dictionary.com).

See also: → de-; → activate.

To cause to be → inactive; remove the → effectiveness of (Dictionary.com).

See also: → de-; → activate.

1. Deprived of life.
   

2. No longer producing or functioning. → dead pixel.

Etymology (EN): M.E. deed, O.E. dead “dead;” cf. O.S. dod, Dan. død, Swed. död, Du. dood, O.H.G. tot, Ger. tot; PIE *dhou-toz-, from base *dheu- “to die.”

Etymology (PE): Mordé “dead,” p.p. of mordan, mir- “to die,” → death.

1. Deprived of life.
   

2. No longer producing or functioning. → dead pixel.

Etymology (EN): M.E. deed, O.E. dead “dead;” cf. O.S. dod, Dan. død, Swed. död, Du. dood, O.H.G. tot, Ger. tot; PIE *dhou-toz-, from base *dheu- “to die.”

Etymology (PE): Mordé “dead,” p.p. of mordan, mir- “to die,” → death.

Of a → CCD detector, a pixel that is not sufficiently active.

See also: → dead; → pixel.

Of a → CCD detector, a pixel that is not sufficiently active.

See also: → dead; → pixel.

The time by which something must be finished or submitted; the latest time for finishing something (Dictionary.com).

Etymology (EN): Historically, during the American Civil War, the term referred to a physical line or boundary beyond which prisoners were shot; → dead; → line.

Etymology (PE): Ruzband, literally “day lock, that which blocks date,” from ruz, → day, + band, → bond; cf. Ger. Stichtag, Anmeldeschluss, Einsendeschluss and Fr. date de clôture.

The time by which something must be finished or submitted; the latest time for finishing something (Dictionary.com).

Etymology (EN): Historically, during the American Civil War, the term referred to a physical line or boundary beyond which prisoners were shot; → dead; → line.

Etymology (PE): Ruzband, literally “day lock, that which blocks date,” from ruz, → day, + band, → bond; cf. Ger. Stichtag, Anmeldeschluss, Einsendeschluss and Fr. date de clôture.

The act of dying; the end of life.

Etymology (EN): M.E. deeth, O.E. deað (cf. O.S. doth, O.Fris. dath, Du. dood, O.H.G. tod, Ger. Tod, O.N. dauði, Dan. død, Swed. död, Goth. dauþas “death”), from dheu- “to die” + -thuz “-th;”

Etymology (PE): Marg “death,” from Mid.Pers. marg “death;” Av. mahrka- “death,” mərəxš- “ruin;” related to Mod.Pers. mordan (present stem mir-) “to die;” Mid.Pers. murdan
“to die;” O.Pers. mrt- “to die,” amriyta “dies,” martiya- “(mortal) man” (Mod.Pers. mard “man”); Av. mərəta- “died;” cf. Skt. mar- “to die,” mrti- “death,” marc- “to damage, hurt, injure;” PIE base *mor-/*mr- “to die.” Cognates in other IE languages: Gk. emorten “died,” ambrotos “immortal;”
L. morior “I die,” mortuus “dead” (Fr. mourir “to die,” mort “dead”); Arm. merani- “to die;” O.C.S. mrutvu “dead;” O.Ir. marb; Welsh marw “died;” O.E. morþ “murder;” Lith. mirtis.

The act of dying; the end of life.

Etymology (EN): M.E. deeth, O.E. deað (cf. O.S. doth, O.Fris. dath, Du. dood, O.H.G. tod, Ger. Tod, O.N. dauði, Dan. død, Swed. död, Goth. dauþas “death”), from dheu- “to die” + -thuz “-th;”

Etymology (PE): Marg “death,” from Mid.Pers. marg “death;” Av. mahrka- “death,” mərəxš- “ruin;” related to Mod.Pers. mordan (present stem mir-) “to die;” Mid.Pers. murdan
“to die;” O.Pers. mrt- “to die,” amriyta “dies,” martiya- “(mortal) man” (Mod.Pers. mard “man”); Av. mərəta- “died;” cf. Skt. mar- “to die,” mrti- “death,” marc- “to damage, hurt, injure;” PIE base *mor-/*mr- “to die.” Cognates in other IE languages: Gk. emorten “died,” ambrotos “immortal;”
L. morior “I die,” mortuus “dead” (Fr. mourir “to die,” mort “dead”); Arm. merani- “to die;” O.C.S. mrutvu “dead;” O.Ir. marb; Welsh marw “died;” O.E. morþ “murder;” Lith. mirtis.

1a) A → discussion, as of a public question in an assembly, involving opposing viewpoints.

1b) A formal contest in which the affirmative and negative sides of a proposition are advocated by opposing speakers.

2. To engage in argument or discussion, as in a legislative or public assembly (Dictionary.com).

Etymology (EN): M.E. debaten, from O.Fr. debatre, literally “to fight,” from → de- “down, completely,” + batre “to beat,” → beat.

Etymology (PE): Vâzat, from vâ-, → de-, + zat- (Baluci žat-) variant of zad-, zadan “to strike, beat”, → beat.

1a) A → discussion, as of a public question in an assembly, involving opposing viewpoints.

1b) A formal contest in which the affirmative and negative sides of a proposition are advocated by opposing speakers.

2. To engage in argument or discussion, as in a legislative or public assembly (Dictionary.com).

Etymology (EN): M.E. debaten, from O.Fr. debatre, literally “to fight,” from → de- “down, completely,” + batre “to beat,” → beat.

Etymology (PE): Vâzat, from vâ-, → de-, + zat- (Baluci žat-) variant of zad-, zadan “to strike, beat”, → beat.

To substract the → bias from a flat-field or science frame obtained using an electronic detector.

Etymology (EN): Debias, from → de- + → bias.

Etymology (PE): Varak zodudan, from varak→ bias + zodudan “to polish, clean,” Mid.Pers. uzdātan, Av. uzdā-, from uz-, → ex-, + dā- “make, create.”

To substract the → bias from a flat-field or science frame obtained using an electronic detector.

Etymology (EN): Debias, from → de- + → bias.

Etymology (PE): Varak zodudan, from varak→ bias + zodudan “to polish, clean,” Mid.Pers. uzdātan, Av. uzdā-, from uz-, → ex-, + dā- “make, create.”

The process of removing the → bias from a → flat-field or science → frame. → debias

See also: Verbal noun of → debias.

The process of removing the → bias from a → flat-field or science → frame. → debias

See also: Verbal noun of → debias.

In → spectroscopy, to → resolve a → blend into its constituent → spectral lines.

Etymology (EN): Deblend, from → de- + → blend.

Etymology (PE): Tuham, → blend, + zodudan “to polish, clean,” Mid.Pers. uzdātan, Av. uzdā-, from uz-,
→ ex-, + dā- “make, create.”

In → spectroscopy, to → resolve a → blend into its constituent → spectral lines.

Etymology (EN): Deblend, from → de- + → blend.

Etymology (PE): Tuham, → blend, + zodudan “to polish, clean,” Mid.Pers. uzdātan, Av. uzdā-, from uz-,
→ ex-, + dā- “make, create.”

The process or state of separating or resolving into constituent → spectral lines.

See also: Verbal noun of deblend, from → de- + → blend.

The process or state of separating or resolving into constituent → spectral lines.

See also: Verbal noun of deblend, from → de- + → blend.

To → increase the → spatial resolution or the clearness of an → image. Same as → sharpen. See also → deconvolve.

Etymology (EN): Deblur, from → de- + → blur.

Etymology (PE): Tigidan “to sharpen,” from tig “sharp,” variants tiz, tež, tej, tij, tiq, Mid.Pers. tigr, têz, têž “sharp,” O.Pers. tigra- “pointed,”
tigra.xauda- “pointed helmet (epithet of Scythians),” Av. tiγra- “pointed,” tiγray- “arrow,” tiži.arštay- “with the pointed spear,” cf. Skt. tikta- “sharp, pungent, bitter,” tejas- “sharpness, edge, point or top of a flame;” PIE base *st(e)ig- “to stick; pointed.” Cognates in other IE languages: Gk. stizein “to prick, puncture,” stigma “mark made by a pointed instrument,” L. in-stigare “to goad,” O.H.G. stehhan, Ger. stechen “to stab, prick,” Du. stecken, O.E. sticca “rod, twig, spoon,” E. stick.

To → increase the → spatial resolution or the clearness of an → image. Same as → sharpen. See also → deconvolve.

Etymology (EN): Deblur, from → de- + → blur.

Etymology (PE): Tigidan “to sharpen,” from tig “sharp,” variants tiz, tež, tej, tij, tiq, Mid.Pers. tigr, têz, têž “sharp,” O.Pers. tigra- “pointed,”
tigra.xauda- “pointed helmet (epithet of Scythians),” Av. tiγra- “pointed,” tiγray- “arrow,” tiži.arštay- “with the pointed spear,” cf. Skt. tikta- “sharp, pungent, bitter,” tejas- “sharpness, edge, point or top of a flame;” PIE base *st(e)ig- “to stick; pointed.” Cognates in other IE languages: Gk. stizein “to prick, puncture,” stigma “mark made by a pointed instrument,” L. in-stigare “to goad,” O.H.G. stehhan, Ger. stechen “to stab, prick,” Du. stecken, O.E. sticca “rod, twig, spoon,” E. stick.

The process or state of making an image sharper. → deblur; same as sharpening. → deconvolution.

See also: Verbal noun of → deblur.

The process or state of making an image sharper. → deblur; same as sharpening. → deconvolution.

See also: Verbal noun of → deblur.

The remains of anything broken down or destroyed; rubble; ruins.
Astro.: → debris disk; → orbital debris.
Geology: An accumulation of loose fragments of rock.

Etymology (EN): From Fr. débris, from M.Fr. débriser “break down, crush,” from O.Fr. debrisier, → de- + brisier “to break,” from L.L. brisare.

Etymology (PE): Tifâl, from tif “rubbish, sweepings, debris” + -al relation suffix → -al.

The remains of anything broken down or destroyed; rubble; ruins.
Astro.: → debris disk; → orbital debris.
Geology: An accumulation of loose fragments of rock.

Etymology (EN): From Fr. débris, from M.Fr. débriser “break down, crush,” from O.Fr. debrisier, → de- + brisier “to break,” from L.L. brisare.

Etymology (PE): Tifâl, from tif “rubbish, sweepings, debris” + -al relation suffix → -al.

A disk developing around a star after the dissipation of the → protoplanetary disk of gas and dust whose material was used in the formation of planets during the first 10 million years. The resulting debris disk is mainly composed of residual → planetesimals
analogous to → asteroids, → comets, and → Kuiper Belt Objects in the Solar System. Their mutual collisions produce observable → dust emission in a belt encompassing the planetary system.

See also: → debris; → disk.

A disk developing around a star after the dissipation of the → protoplanetary disk of gas and dust whose material was used in the formation of planets during the first 10 million years. The resulting debris disk is mainly composed of residual → planetesimals
analogous to → asteroids, → comets, and → Kuiper Belt Objects in the Solar System. Their mutual collisions produce observable → dust emission in a belt encompassing the planetary system.

See also: → debris; → disk.

A → unit of electric → dipole moments, equal to 10^-18 → CGS units or 3.336 x 10^-30 → coulomb meter.

Etymology (EN): After Peter Joseph Wilhelm Debye (1884-1966), Dutch-born American, who made important studies in the conductivity of electricity by salt solutions and in the heat capacity of solids. He received the 1936 Nobel Prize in chemistry for his work on the structure of molecules.

A → unit of electric → dipole moments, equal to 10^-18 → CGS units or 3.336 x 10^-30 → coulomb meter.

Etymology (EN): After Peter Joseph Wilhelm Debye (1884-1966), Dutch-born American, who made important studies in the conductivity of electricity by salt solutions and in the heat capacity of solids. He received the 1936 Nobel Prize in chemistry for his work on the structure of molecules.

The → Debye model at → low  → temperatures, where the → specific heat is proportional to the cube of the → absolute temperature, i.e. C_V ∝ T³.

See also: → debye; → law.

The → Debye model at → low  → temperatures, where the → specific heat is proportional to the cube of the → absolute temperature, i.e. C_V ∝ T³.

See also: → debye; → law.

A characteristic length scale in a → plasma, determined by the temperature and number density of the charged particles. The Debye length (in cm) is given by the expression:
λ_D = 743(T_e/n_e)^1/2, where T_e is the electron temperature in → electron-volts
and n_e is the electron density in cm^-3. Particles which pass each other at distances smaller than the Debye length interact directly. Outside the Debye length particle interactions are dominated by collective effects. In typical laboratory plasmas the Debye length is small compared with the plasma dimension, so that collective effects are important.

See also: → debye (D); → length.

A characteristic length scale in a → plasma, determined by the temperature and number density of the charged particles. The Debye length (in cm) is given by the expression:
λ_D = 743(T_e/n_e)^1/2, where T_e is the electron temperature in → electron-volts
and n_e is the electron density in cm^-3. Particles which pass each other at distances smaller than the Debye length interact directly. Outside the Debye length particle interactions are dominated by collective effects. In typical laboratory plasmas the Debye length is small compared with the plasma dimension, so that collective effects are important.

See also: → debye (D); → length.

An extension of the → Einstein model accounting for → specific heats, based on the concept of → elastic waves in → crystals. In this model specific heat is given by: C_V = 9R[(4/x²)∫ y²/(e^y - 1)dy - x/(e^x - 1)], integrating from 0 to x, where R is the → gas constant, k is → Boltzmann’s constant, x = hν_max/k, and y = hν/k. The parameter T_D = hν_max/k is the characteristic → Debye temperature of the crystal. At low temperatures the specific heat prediction by this model is in good agreement with observations (→ Debye law),
in contrast to Einstein’s model.

See also: → debye; → temperature.

An extension of the → Einstein model accounting for → specific heats, based on the concept of → elastic waves in → crystals. In this model specific heat is given by: C_V = 9R[(4/x²)∫ y²/(e^y - 1)dy - x/(e^x - 1)], integrating from 0 to x, where R is the → gas constant, k is → Boltzmann’s constant, x = hν_max/k, and y = hν/k. The parameter T_D = hν_max/k is the characteristic → Debye temperature of the crystal. At low temperatures the specific heat prediction by this model is in good agreement with observations (→ Debye law),
in contrast to Einstein’s model.

See also: → debye; → temperature.

The characteristic → temperature of the → crystal as given by the → Debye model of → specific heats.

See also: → debye; → temperature.

The characteristic → temperature of the → crystal as given by the → Debye model of → specific heats.

See also: → debye; → temperature.

Prefix meaning “ten” and “ten times” used in terms belonging to the metric system.

Etymology (EN): From Fr. déca-, from L. deca-, dec-, from Gk. deka “ten;”
cf. Av. dasa “ten,” Mod.Pers. dah “ten,” Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Etymology (PE): Dekâ-, from Fr. as above.

Prefix meaning “ten” and “ten times” used in terms belonging to the metric system.

Etymology (EN): From Fr. déca-, from L. deca-, dec-, from Gk. deka “ten;”
cf. Av. dasa “ten,” Mod.Pers. dah “ten,” Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Etymology (PE): Dekâ-, from Fr. as above.

A ten-sided → polygon. A decagon that is equilateral and equiangular is called a regular decagon. Each angle of a regular decagon is 144°. The central angle subtending any side is 36°. The ratio of the radius to the side of a regular decagon forms the → golden ratio.

See also: → deca-; → -gon.

A ten-sided → polygon. A decagon that is equilateral and equiangular is called a regular decagon. Each angle of a regular decagon is 144°. The central angle subtending any side is 36°. The ratio of the radius to the side of a regular decagon forms the → golden ratio.

See also: → deca-; → -gon.

1a) To become decomposed.

1b) Of a radioactive nucleus, to disintegrate spontaneously into one or more different nuclei, accompanied by the emission of → alpha particles, → beta particles, → positrons, and/or → gamma rays.

2a) Decomposition.

2b) The → transition of a system from an → excited state to a less excited one. Radiative decay refers to the process when the energy difference between the states is taken away by radiation. Likewise, collisional decay is when the energy difference is removed by a target during a collision.

2c) Of a spacecraft, a gradual decrease in the radius of its orbit over time, caused by aerodynamic drag of the atmosphere and other forces. The rate of orbit decay rises as the spacecraft falls and encounters increasing atmospheric density, eventually resulting in reentry.
→ alpha decay; → beta decay; → dark matter decay; → decay chain; → decay constant; → decay mode; → decay product; → decay time; → inverse beta decay; → Ohmic decay time; → orbit decay; → radioactive decay; → turbulence decay.

Etymology (EN): From O.Fr. decair, from V.L. *decadere “to fall off,” from L. cadere “to fall,” PIE base *kad- “to fall” (cf. Pers. Gilaki katan “to fall,” ba.ka.tam “I fell,” dakatan “to fall (in a marsh, in a pit),” vakatan “to fall from tiredness, be exhausted,” fakatan “to fall from (lose) reputation,” Pers. Laki: katen “to fall,” kat “he fell,” beko “fall!,” Pers. Tabari: dakətə “fallen,” dakətən “to crash down,” dakət.gu “stray cow,” Arm. chacnum “to fall”).

Etymology (PE): Tabâhidan, verbal form of tabâhi, noun form of tabâh “spoiled, ruined, destroyed,” Mid.Pers. tapâh “spoiled, destroyed.” Maybe related to Mod.Pers. tâb “affliction, pain, torment; heat, burning,” tab “fever,” tâbidan, tâftan “to shine,” tafsidan “to become hot,” Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth,” cf.
Skt. tap- “to spoil, injure, damage; to suffer; to heat, be/become hot,” tapati “burns,” L. tepere “to be warm,” tepidus “warm,” PIE base *tep- “warm.”

1a) To become decomposed.

1b) Of a radioactive nucleus, to disintegrate spontaneously into one or more different nuclei, accompanied by the emission of → alpha particles, → beta particles, → positrons, and/or → gamma rays.

2a) Decomposition.

2b) The → transition of a system from an → excited state to a less excited one. Radiative decay refers to the process when the energy difference between the states is taken away by radiation. Likewise, collisional decay is when the energy difference is removed by a target during a collision.

2c) Of a spacecraft, a gradual decrease in the radius of its orbit over time, caused by aerodynamic drag of the atmosphere and other forces. The rate of orbit decay rises as the spacecraft falls and encounters increasing atmospheric density, eventually resulting in reentry.
→ alpha decay; → beta decay; → dark matter decay; → decay chain; → decay constant; → decay mode; → decay product; → decay time; → inverse beta decay; → Ohmic decay time; → orbit decay; → radioactive decay; → turbulence decay.

Etymology (EN): From O.Fr. decair, from V.L. *decadere “to fall off,” from L. cadere “to fall,” PIE base *kad- “to fall” (cf. Pers. Gilaki katan “to fall,” ba.ka.tam “I fell,” dakatan “to fall (in a marsh, in a pit),” vakatan “to fall from tiredness, be exhausted,” fakatan “to fall from (lose) reputation,” Pers. Laki: katen “to fall,” kat “he fell,” beko “fall!,” Pers. Tabari: dakətə “fallen,” dakətən “to crash down,” dakət.gu “stray cow,” Arm. chacnum “to fall”).

Etymology (PE): Tabâhidan, verbal form of tabâhi, noun form of tabâh “spoiled, ruined, destroyed,” Mid.Pers. tapâh “spoiled, destroyed.” Maybe related to Mod.Pers. tâb “affliction, pain, torment; heat, burning,” tab “fever,” tâbidan, tâftan “to shine,” tafsidan “to become hot,” Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth,” cf.
Skt. tap- “to spoil, injure, damage; to suffer; to heat, be/become hot,” tapati “burns,” L. tepere “to be warm,” tepidus “warm,” PIE base *tep- “warm.”

A series of nuclear decays produced by successive → daughter products, when the daughters are themselves → radioactive. For example, the decay chain N₁→ N₂→ N₃→ … in which the parent nuclide N₁ decays to the daughter N₂, which in turn decays to N₃. Each → radionuclide in the decay chain can → branch to more than one daughter.

See also: → decay; → chain.

A series of nuclear decays produced by successive → daughter products, when the daughters are themselves → radioactive. For example, the decay chain N₁→ N₂→ N₃→ … in which the parent nuclide N₁ decays to the daughter N₂, which in turn decays to N₃. Each → radionuclide in the decay chain can → branch to more than one daughter.

See also: → decay; → chain.

A constant of proportionality occurring in the formula expressing spontaneous → decay of → radionuclides. The number of atoms decaying is given by N = N₀e^-kt, where N₀ is the number of nuclei in the given volume of the substance at instant t = 0, N is the number of nuclei at t, and k is decay constant. Decay constant is related to → half-life by τ = ln2/k, roughly 0.693/k.

See also: → decay; → constant.

A constant of proportionality occurring in the formula expressing spontaneous → decay of → radionuclides. The number of atoms decaying is given by N = N₀e^-kt, where N₀ is the number of nuclei in the given volume of the substance at instant t = 0, N is the number of nuclei at t, and k is decay constant. Decay constant is related to → half-life by τ = ln2/k, roughly 0.693/k.

See also: → decay; → constant.

A possible type of decay of a → radionuclide or → elementary particle.
In general, a given particle may decay by more than one decay mode. Usually the number of decay modes is one or two. There are, however, → nuclides
which have many decay modes; for example the nuclide ¹¹Li has seven decay modes.

See also: → decay; → mode.

A possible type of decay of a → radionuclide or → elementary particle.
In general, a given particle may decay by more than one decay mode. Usually the number of decay modes is one or two. There are, however, → nuclides
which have many decay modes; for example the nuclide ¹¹Li has seven decay modes.

See also: → decay; → mode.

A → stable nuclide or → radioactive nuclide formed by the → disintegration of a → radioactive isotope, either directly or as a result of a → decay chain. Also called → daughter product. For example, the decay product of ²³⁸U is ²⁰⁶Pb, after passing through the following chain:

²³⁸U → ²³⁴Th (4.5 billion yr) → ²³⁴Pa (24 days) → ²³⁴U (1 min) → ²³⁰Th (245,000 yr) → ²²⁶Ra (76,000 yr) → ²²²Rn (1,600 yr) → ²¹⁸Po (3.8 d) → ²¹⁴Pb (3 m) → ²¹⁴Bi (27 m) → ²¹⁴Po (160 microseconds) → ²¹⁰Pb (22 yr) → ²¹⁰Bi (5 d) → ²¹⁰Po (138 d) → ²⁰⁶Pb.

See also: → decay; → product.

A → stable nuclide or → radioactive nuclide formed by the → disintegration of a → radioactive isotope, either directly or as a result of a → decay chain. Also called → daughter product. For example, the decay product of ²³⁸U is ²⁰⁶Pb, after passing through the following chain:

²³⁸U → ²³⁴Th (4.5 billion yr) → ²³⁴Pa (24 days) → ²³⁴U (1 min) → ²³⁰Th (245,000 yr) → ²²⁶Ra (76,000 yr) → ²²²Rn (1,600 yr) → ²¹⁸Po (3.8 d) → ²¹⁴Pb (3 m) → ²¹⁴Bi (27 m) → ²¹⁴Po (160 microseconds) → ²¹⁰Pb (22 yr) → ²¹⁰Bi (5 d) → ²¹⁰Po (138 d) → ²⁰⁶Pb.

See also: → decay; → product.

The time required for the amplitude of a vibrating system to decrease to 1/e of its initial value.
Of an orbiting object, its lifetime in a non stable orbit.

See also: → decay; → time.

The time required for the amplitude of a vibrating system to decrease to 1/e of its initial value.
Of an orbiting object, its lifetime in a non stable orbit.

See also: → decay; → time.

(v.intr.) To slow down. (v.tr.) To decrease the velocity of.

Etymology (EN): From → de- + (ac)celerate, from
→ accelerate.

Etymology (PE): Vâšetâbidan, from vâ-→ de- + šetâbidan, → accelerate.

(v.intr.) To slow down. (v.tr.) To decrease the velocity of.

Etymology (EN): From → de- + (ac)celerate, from
→ accelerate.

Etymology (PE): Vâšetâbidan, from vâ-→ de- + šetâbidan, → accelerate.

The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration.

See also: Verbal noun of decelerate.

The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration.

See also: Verbal noun of decelerate.

A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by:
q(t) = -R(t)R ^..(t)/R ^.2(t), where R(t) represents the size of the Universe at time t. See also
→ expansion parameter; compare with → acceleration parameter.

See also: → deceleration;
→ parameter.

A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by:
q(t) = -R(t)R ^..(t)/R ^.2(t), where R(t) represents the size of the Universe at time t. See also
→ expansion parameter; compare with → acceleration parameter.

See also: → deceleration;
→ parameter.

Prefix used in the metric system to mean on-tenth.

Etymology (EN): From Fr. déci-, from L. decimus “tenth,” from decem “ten,” cf. Av. dasa “ten,” Mod.Pers. dah “ten,” Gk. deka, Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Etymology (PE): Desi-, from Fr. déci-, as above.

Prefix used in the metric system to mean on-tenth.

Etymology (EN): From Fr. déci-, from L. decimus “tenth,” from decem “ten,” cf. Av. dasa “ten,” Mod.Pers. dah “ten,” Gk. deka, Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Etymology (PE): Desi-, from Fr. déci-, as above.

A dimensionless unit used to express relative difference in power or intensity, usually between two acoustic or electric signals. It is defined as n [dB] = 10 log (P₁/P₀),
with → natural logarithm. One decibel equals one-tenth of a → bel (B).

See also: → deci-; → bel (B).

A dimensionless unit used to express relative difference in power or intensity, usually between two acoustic or electric signals. It is defined as n [dB] = 10 log (P₁/P₀),
with → natural logarithm. One decibel equals one-tenth of a → bel (B).

See also: → deci-; → bel (B).

To make a choice or come to a conclusion about something. → decision, → rule of decision.

Etymology (EN): M.E. deciden, from O.Fr. decider, from L. decidere “to decide, determine,” literally “to cut off,” from → de-“off” + caedere “to cut, chop, beat, hew.”

Etymology (PE): Vâsunidan, from vâ- “off, away,” → de-,

• sun “to cut;” cf. Kurd. Soriani su, sun “to sharpen, whet;” Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun “to sharpen, whet;” Mod.Pers. sân “whetstone,” variants fasân, afsân, awsân; Av. si-, sā- “to cut;” cf. Skt. śā- “to sharpen, whet;” + -idan infinitive suffix.

To make a choice or come to a conclusion about something. → decision, → rule of decision.

Etymology (EN): M.E. deciden, from O.Fr. decider, from L. decidere “to decide, determine,” literally “to cut off,” from → de-“off” + caedere “to cut, chop, beat, hew.”

Etymology (PE): Vâsunidan, from vâ- “off, away,” → de-,

• sun “to cut;” cf. Kurd. Soriani su, sun “to sharpen, whet;” Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun “to sharpen, whet;” Mod.Pers. sân “whetstone,” variants fasân, afsân, awsân; Av. si-, sā- “to cut;” cf. Skt. śā- “to sharpen, whet;” + -idan infinitive suffix.

Someone who decides, or something that allows to determine.

See also: → decide; → -er.

Someone who decides, or something that allows to determine.

See also: → decide; → -er.

Referring to or based in the number 10; relating to tens or tenths.

Etymology (EN): M.L. decimalis “of tithes or tenths,” from L. decimus “tenth,” from decem, → ten.

Etymology (PE): Dahi , of or relating to dah, → ten; dahdahi literally “ten by ten.”

Referring to or based in the number 10; relating to tens or tenths.

Etymology (EN): M.L. decimalis “of tithes or tenths,” from L. decimus “tenth,” from decem, → ten.

Etymology (PE): Dahi , of or relating to dah, → ten; dahdahi literally “ten by ten.”

A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.

See also: → decimal; → fraction.

A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.

See also: → decimal; → fraction.

→ common logarithm.

See also: → decimal; → logarithm.

→ common logarithm.

See also: → decimal; → logarithm.

A system of numerals for representing real numbers that uses the → base 10. It includes the digits from 0 through 9.

See also: → decimal; → system.

A system of numerals for representing real numbers that uses the → base 10. It includes the digits from 0 through 9.

See also: → decimal; → system.

The position of a digit to the right of a → decimal point written in decimal notation. In 0.032, for example, 0 is the first decimal place, 3 is the second decimal place, and 2 is the third decimal place.

Etymology (EN): → decimal; → place.

Etymology (PE): Raqam, → digit; pas, → after; jodâgar, momayez, → decimal point.

The position of a digit to the right of a → decimal point written in decimal notation. In 0.032, for example, 0 is the first decimal place, 3 is the second decimal place, and 2 is the third decimal place.

Etymology (EN): → decimal; → place.

Etymology (PE): Raqam, → digit; pas, → after; jodâgar, momayez, → decimal point.

A symbol (usually a point or dot) used to separate the integer part from the fractional part of a → decimal number.

Etymology (EN): → decimal; → point.

Etymology (PE): Jodâgar, → separator.
Momayez, from Ar. mumaiyiz “distinguisher, discerner, separator.”

A symbol (usually a point or dot) used to separate the integer part from the fractional part of a → decimal number.

Etymology (EN): → decimal; → point.

Etymology (PE): Jodâgar, → separator.
Momayez, from Ar. mumaiyiz “distinguisher, discerner, separator.”

A representation of a real number between 0 and 1, as written a = d₁d₂d₃ …, where each d_i is one of the digits 0, 1, 2, …, 9. This means that a = d₁ x 10^-1 + d₂ x 10^-2 + d₃ x 10^-3+ …

See also: → decimal; → representation.

A representation of a real number between 0 and 1, as written a = d₁d₂d₃ …, where each d_i is one of the digits 0, 1, 2, …, 9. This means that a = d₁ x 10^-1 + d₂ x 10^-2 + d₃ x 10^-3+ …

See also: → decimal; → representation.

same as → decimal number system.

See also: → decimal; → number; → system.

same as → decimal number system.

See also: → decimal; → number; → system.

An electromagnetic radio wave having wavelengths between 10 cm and 1m, corresponding to a frequency between 300 and 3,000 Mega Hertz. It is naturally emitted by various astronomical objects.

Etymology (EN): Decimetric, from → deci- + from Fr. métrique, → metric; → wave.

Etymology (PE): Mowj, → wave; desimetri, from décimétrique, as above.

An electromagnetic radio wave having wavelengths between 10 cm and 1m, corresponding to a frequency between 300 and 3,000 Mega Hertz. It is naturally emitted by various astronomical objects.

Etymology (EN): Decimetric, from → deci- + from Fr. métrique, → metric; → wave.

Etymology (PE): Mowj, → wave; desimetri, from décimétrique, as above.

The act or process of deciding. → rule of decision.

See also: Verbal noun of → decide.

The act or process of deciding. → rule of decision.

See also: Verbal noun of → decide.

Having the power or quality of deciding; putting an end to controversy; crucial or most important (Dictionary.com).

See also: → decide; → -ive.

Having the power or quality of deciding; putting an end to controversy; crucial or most important (Dictionary.com).

See also: → decide; → -ive.

To speak aloud in an oratorical manner; make a formal speech (Dictionary.com).

See also: → de-; → claim.

To speak aloud in an oratorical manner; make a formal speech (Dictionary.com).

See also: → de-; → claim.

The act of declaring; announcement.

2. Something that is announced or proclaimed.

See also: Verbal noun of → declare.

The act of declaring; announcement.

2. Something that is announced or proclaimed.

See also: Verbal noun of → declare.

1. To make known or state clearly, especially in explicit or formal terms.
   

2. To announce officially; proclaim (Dictionary.com).

Etymology (EN): M.E. declaren, from O.Fr. declarer “explain, elucidate,” from L. declarare “make clear, reveal, disclose, announce,” from → de- intensive prefix + clarare “clarify,” from clarus, → clear.

Etymology (PE): From Kurd. (Sorani) rûnâk, runâg “clear, bright,” rûn “bright, clear,” rûn kirdin “to explain,” variants of rowšanâ, rowšan, rušanâ, → bright, → day.

1. To make known or state clearly, especially in explicit or formal terms.
   

2. To announce officially; proclaim (Dictionary.com).

Etymology (EN): M.E. declaren, from O.Fr. declarer “explain, elucidate,” from L. declarare “make clear, reveal, disclose, announce,” from → de- intensive prefix + clarare “clarify,” from clarus, → clear.

Etymology (PE): From Kurd. (Sorani) rûnâk, runâg “clear, bright,” rûn “bright, clear,” rûn kirdin “to explain,” variants of rowšanâ, rowšan, rušanâ, → bright, → day.

The → inflection of nouns, pronouns, or adjectives for case, number, and gender.

Etymology (EN): M.E. declenson, declynson (with suffix later assimilated to -sion), from O.Fr. declinaison, from L. declinatio,
→ declination

Etymology (PE): → declination.

The → inflection of nouns, pronouns, or adjectives for case, number, and gender.

Etymology (EN): M.E. declenson, declynson (with suffix later assimilated to -sion), from O.Fr. declinaison, from L. declinatio,
→ declination

Etymology (PE): → declination.

1. Angular distance (symbol δ) from the celestial equator. One of the coordinates, with → right ascension, that defines the position of a heavenly body in the equator system. Declination is measured positively (+) north or negatively (-) south of the celestial equator from 0° to 90°.
   
2. Angle between geographic North and magnetic North (symbol D).

See also: Verbal noun of → decline; → -tion.

1. Angular distance (symbol δ) from the celestial equator. One of the coordinates, with → right ascension, that defines the position of a heavenly body in the equator system. Declination is measured positively (+) north or negatively (-) south of the celestial equator from 0° to 90°.
   
2. Angle between geographic North and magnetic North (symbol D).

See also: Verbal noun of → decline; → -tion.

The axis to which the telescope tube is fastened in an → equatorial mounting.

See also: → declination; → axis.

The axis to which the telescope tube is fastened in an → equatorial mounting.

See also: → declination; → axis.

For a telescope with an → equatorial mounting, a graduated circle attached to the → declination axis that shows the → declination to which the telescope is pointing.

See also: → declination; → circle.

For a telescope with an → equatorial mounting, a graduated circle attached to the → declination axis that shows the → declination to which the telescope is pointing.

See also: → declination; → circle.

1a) To bend down; slope downward; descend.

1b) Grammar: To → inflect according to the various cases of a noun, adjective, or pronoun.

2. The process of declining; a downward movement; gradual loss or deterioration.

Etymology (EN): M.E. declinen, from O.Fr. decliner “to sink, decline, degenerate, turn aside,” from declinare
“to turn away, inflect,” from → de- + clinare “to bend,” cf. Gk. klinein “to cause to slope, slant, incline,” Skt. sri- “to lean,” O.Pers. θray-, Av. sray- “to lean,” Mod.Pers. kil “bent, inclined, slant,” PIE base *klei- “to lean, incline” from which is also derived
(Ger. lehnen, E. lean).

Etymology (PE): Vâkil, from prefix vâ- “away” + kil “bent, crooked, inclined” [Dehxodâ], Mid.Pers. xwahl “bent, crooked” (Mod.Pers. dialectal/colloquial variants kowleh, cowleh, cowl, caval, xohl, xohal, hol), cf. Skt. kûla- “slope, declivity;” PIE base *klei-, as above. → inclination

1a) To bend down; slope downward; descend.

1b) Grammar: To → inflect according to the various cases of a noun, adjective, or pronoun.

2. The process of declining; a downward movement; gradual loss or deterioration.

Etymology (EN): M.E. declinen, from O.Fr. decliner “to sink, decline, degenerate, turn aside,” from declinare
“to turn away, inflect,” from → de- + clinare “to bend,” cf. Gk. klinein “to cause to slope, slant, incline,” Skt. sri- “to lean,” O.Pers. θray-, Av. sray- “to lean,” Mod.Pers. kil “bent, inclined, slant,” PIE base *klei- “to lean, incline” from which is also derived
(Ger. lehnen, E. lean).

Etymology (PE): Vâkil, from prefix vâ- “away” + kil “bent, crooked, inclined” [Dehxodâ], Mid.Pers. xwahl “bent, crooked” (Mod.Pers. dialectal/colloquial variants kowleh, cowleh, cowl, caval, xohl, xohal, hol), cf. Skt. kûla- “slope, declivity;” PIE base *klei-, as above. → inclination

To convert encoded symbols so that they can be used by the computer or understood by a person. See also → encode and → decrypt.

Etymology (EN): → de-; → code.

Etymology (PE): Vâramzidan, from vâ-, → de-. Ramz bardâštan, from ramz, → code,

• bardâštan “to remove, to take,” from bar- “on; up; upon; in; into; at; forth; with,” → on-, + dâštan “to have; to hold; to posses,” → property.

To convert encoded symbols so that they can be used by the computer or understood by a person. See also → encode and → decrypt.

Etymology (EN): → de-; → code.

Etymology (PE): Vâramzidan, from vâ-, → de-. Ramz bardâštan, from ramz, → code,

• bardâštan “to remove, to take,” from bar- “on; up; upon; in; into; at; forth; with,” → on-, + dâštan “to have; to hold; to posses,” → property.

An electronic device that converts audio or video signals into a different form that can be heard or seen correctly.

See also: → decode; → -er.

An electronic device that converts audio or video signals into a different form that can be heard or seen correctly.

See also: → decode; → -er.

The process of translating data or a message from a code into the original language or form. See also → encoding and → decryption.

See also: → decode; → -ing.

The process of translating data or a message from a code into the original language or form. See also → encoding and → decryption.

See also: → decode; → -ing.

Of a physical force or entity or chemical substance, to separate or break into constituent parts or elements.

See also: From → de- + → compose.

Of a physical force or entity or chemical substance, to separate or break into constituent parts or elements.

See also: From → de- + → compose.

The process or the state of breaking down a physical entity or an organic material.

See also: From → de- + → composition.

The process or the state of breaking down a physical entity or an organic material.

See also: From → de- + → composition.

To cause to undergo → decompression.

See also: → de- + → compress.

To cause to undergo → decompression.

See also: → de- + → compress.

1. A gradual decrease in surrounding → pressure, especially the controlled decrease in pressure that divers undergo after working in deep water or breathing compressed air.
   
2. Computers: The restoration of compressed electronic data to their full size.

See also: → de- + → compression.

1. A gradual decrease in surrounding → pressure, especially the controlled decrease in pressure that divers undergo after working in deep water or breathing compressed air.
   
2. Computers: The restoration of compressed electronic data to their full size.

See also: → de- + → compression.

A mathematical operation that allows to restore the original input signal, such as an astronomical image or spectrum, to its state before being affected by the → atmospheric turbulence and the → transfer function of the instrument. → convolution.

See also: From → de- + → convolution.

A mathematical operation that allows to restore the original input signal, such as an astronomical image or spectrum, to its state before being affected by the → atmospheric turbulence and the → transfer function of the instrument. → convolution.

See also: From → de- + → convolution.

An algorithm used to improve the resolution of an image particularly when the convolving function is well defined. Also called deconvolution code.

See also: → deconvolution; → algorithm.

An algorithm used to improve the resolution of an image particularly when the convolving function is well defined. Also called deconvolution code.

See also: → deconvolution; → algorithm.

Verbal form of → deconvolution.

See also: From → de- + → convolve.

Verbal form of → deconvolution.

See also: From → de- + → convolve.

1. To separate or detach; to cause to become disconnected or divergent.
   

2. Electronics: To reduce or eliminate the coupling of (one circuit or part to another).
   

3. Physics: To decrease or eliminate the shock waves of a nuclear explosion by having it take place underground.

See also: → de- + → couple.

1. To separate or detach; to cause to become disconnected or divergent.
   

2. Electronics: To reduce or eliminate the coupling of (one circuit or part to another).
   

3. Physics: To decrease or eliminate the shock waves of a nuclear explosion by having it take place underground.

See also: → de- + → couple.

Cosmology: In the early history of the Universe, separation of matter and radiation due to their non-interaction. At a redshift of 1000, that is about 400,000 years after the Big Bang, the temperature would have cooled to the point (4000 degrees Kelvin) where electrons and nuclei can recombine and form neutral hydrogen atoms. Since atoms do not scatter the radiation appreciably, free electrons were lacking, and the Universe became transparent to radiation. Same as → recombination.
See also → decoupling era.

See also: Verbal noun of decouple, from → de- + → couple + → -ing.

Cosmology: In the early history of the Universe, separation of matter and radiation due to their non-interaction. At a redshift of 1000, that is about 400,000 years after the Big Bang, the temperature would have cooled to the point (4000 degrees Kelvin) where electrons and nuclei can recombine and form neutral hydrogen atoms. Since atoms do not scatter the radiation appreciably, free electrons were lacking, and the Universe became transparent to radiation. Same as → recombination.
See also → decoupling era.

See also: Verbal noun of decouple, from → de- + → couple + → -ing.

The era some 400,000 years after the → Big Bang, when the cosmic → blackbody radiation was last scattered by the matter. → decoupling.
Same as → recombination era and → last scattering epoch.

See also: → decoupling; → era.

The era some 400,000 years after the → Big Bang, when the cosmic → blackbody radiation was last scattered by the matter. → decoupling.
Same as → recombination era and → last scattering epoch.

See also: → decoupling; → era.

1. (v.tr.) To cause to diminish, to make less. (v.intr.) To diminish or lessen in extent, quantity, power, etc.
   

2. The act or process of decreasing; condition of being decreased. → Forbush decrease.

Etymology (EN): Decrease, from M.E. decres (n.), decresen, from
O.Fr. descreistre, from L. decrescere, from → de- + crescere “to grow,” → crescent.

Etymology (PE): Kâstan, kâh-, from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen,” Av. kasu- “small, little” (Mod.Pers. keh), Proto-Iranian *kas- “to be small, diminish, lessen;” kâheš verbal noun from kâhidan.

1. (v.tr.) To cause to diminish, to make less. (v.intr.) To diminish or lessen in extent, quantity, power, etc.
   

2. The act or process of decreasing; condition of being decreased. → Forbush decrease.

Etymology (EN): Decrease, from M.E. decres (n.), decresen, from
O.Fr. descreistre, from L. decrescere, from → de- + crescere “to grow,” → crescent.

Etymology (PE): Kâstan, kâh-, from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen,” Av. kasu- “small, little” (Mod.Pers. keh), Proto-Iranian *kas- “to be small, diminish, lessen;” kâheš verbal noun from kâhidan.

1. The amount lost in the process of decreasing.
   

2. Math.: The quantity by which a variable is decreased. A negative → increment.
   

3. Physics: 1) The ratio of the amplitude of an oscillation to that of its succeeding oscillation in an underdamped vibrating system. 2) The intensity ratio of a series of spectral lines of the same nature, such as
   → Balmer decrement.

Etymology (EN): L decrementum, from decre(tus), → decrease + -mentum noun suffix -ment.

Etymology (PE): Kâheh, from kâh- present stem of kâhidan, → decrease + noun suffix -é.

1. The amount lost in the process of decreasing.
   

2. Math.: The quantity by which a variable is decreased. A negative → increment.
   

3. Physics: 1) The ratio of the amplitude of an oscillation to that of its succeeding oscillation in an underdamped vibrating system. 2) The intensity ratio of a series of spectral lines of the same nature, such as
   → Balmer decrement.

Etymology (EN): L decrementum, from decre(tus), → decrease + -mentum noun suffix -ment.

Etymology (PE): Kâheh, from kâh- present stem of kâhidan, → decrease + noun suffix -é.

A physical process that is contrary to accretion, referring to the outward direction of the mass flow from a star to its environment.

See also: From → de- “reversal, removal,” + -cretion, from L. accretionem (nom. accretio, gen. accretionis) “a growing larger,” from stem of accrescere, → accretion.

A physical process that is contrary to accretion, referring to the outward direction of the mass flow from a star to its environment.

See also: From → de- “reversal, removal,” + -cretion, from L. accretionem (nom. accretio, gen. accretionis) “a growing larger,” from stem of accrescere, → accretion.

A disk that would form around a star when the star injects matter into a close orbit. This is in contrast to an → accretion disk, which transfers matter from outside to the star. The mass gets injected into the decretion disk by a not yet well-known mechanism, most probably a combination of → non-radial pulsation, fast rotation, and possibly small-scale → magnetic fields. See also → viscous decretion disk.

See also: → decretion; → disk.

A disk that would form around a star when the star injects matter into a close orbit. This is in contrast to an → accretion disk, which transfers matter from outside to the star. The mass gets injected into the decretion disk by a not yet well-known mechanism, most probably a combination of → non-radial pulsation, fast rotation, and possibly small-scale → magnetic fields. See also → viscous decretion disk.

See also: → decretion; → disk.

Make crypted data or information intelligible. See also → encrypt and → decode.

See also: → de- + crypt, → encrypt.

Make crypted data or information intelligible. See also → encrypt and → decode.

See also: → de- + crypt, → encrypt.

The process of restoring encrypted data back to the original information. See also → encryption and → decoding.

See also: → decrypt; → -tion.

The process of restoring encrypted data back to the original information. See also → encryption and → decoding.

See also: → decrypt; → -tion.

To derive as a conclusion from facts or premises.

Etymology (EN): L. deducere “to lead down, derive,” from → de- “down” + ducere “to lead.”

Etymology (PE): Foruhâxtan, foruhâzidan, from foru- “down,” → de- + Mid.Pers. hâxtan, hâzidan “to lead, guide, persuade,” Av. hak-, hacaiti “to attach oneself to, to join,” cf. Skt. sacate “accompanies, follows,” Gk. hepesthai “to follow,” L. sequi “to follow;” PIE *sekw- “to follow.”

To derive as a conclusion from facts or premises.

Etymology (EN): L. deducere “to lead down, derive,” from → de- “down” + ducere “to lead.”

Etymology (PE): Foruhâxtan, foruhâzidan, from foru- “down,” → de- + Mid.Pers. hâxtan, hâzidan “to lead, guide, persuade,” Av. hak-, hacaiti “to attach oneself to, to join,” cf. Skt. sacate “accompanies, follows,” Gk. hepesthai “to follow,” L. sequi “to follow;” PIE *sekw- “to follow.”

1. The act or process of deducting; something that is or may be deduced.
   

2. A process of reasoning in which a conclusion
   is derived from the premises presented without a need for additional information. → deductive reasoning.

See also: Verbal noun from → deduce.

1. The act or process of deducting; something that is or may be deduced.
   

2. A process of reasoning in which a conclusion
   is derived from the premises presented without a need for additional information. → deductive reasoning.

See also: Verbal noun from → deduce.

Of or relating to → deduction.

See also: From deduct, → deduce, + → -ive.

Of or relating to → deduction.

See also: From deduct, → deduce, + → -ive.

Reasoning from the → general to the → particular (or from → cause to → effect).

See also: → deductive; → reasoning.

Reasoning from the → general to the → particular (or from → cause to → effect).

See also: → deductive; → reasoning.

1a) General: Extending well inward from an outer surface or back from an edge.

1b) Great in measure; intense. → deep exposure.

1c) Of colors, dark and vivid.

2. The deep part of a body of water, especially an area of the ocean floor having a depth greater than 5400 meters (Dictionary.com).

Etymology (EN): O.E. deop, from P.Gmc. *deupaz, from PIE *d(e)u- “deep, hollow.”

Etymology (PE): Žarf “deep;” variants Gilaki jalf, julf, jal; Tabari jol, jal, jul; Baluci jahl, johl; Kermâni jarr “deep;” Mid.Pers. zufr; Av. jafra- “deep.”
Gowd, probably ultimately from PIE root *g^wādh- “to sink, submerge;” cf. Av. vigāθô- “ravines, gorges;”
Skt. gādha- “depth; shallow;” Gk. bessa “gorge, ravine.”

1a) General: Extending well inward from an outer surface or back from an edge.

1b) Great in measure; intense. → deep exposure.

1c) Of colors, dark and vivid.

2. The deep part of a body of water, especially an area of the ocean floor having a depth greater than 5400 meters (Dictionary.com).

Etymology (EN): O.E. deop, from P.Gmc. *deupaz, from PIE *d(e)u- “deep, hollow.”

Etymology (PE): Žarf “deep;” variants Gilaki jalf, julf, jal; Tabari jol, jal, jul; Baluci jahl, johl; Kermâni jarr “deep;” Mid.Pers. zufr; Av. jafra- “deep.”
Gowd, probably ultimately from PIE root *g^wādh- “to sink, submerge;” cf. Av. vigāθô- “ravines, gorges;”
Skt. gādha- “depth; shallow;” Gk. bessa “gorge, ravine.”

An exposure in which the detector shutter remains open for a relatively long time in order to bring out the weaker features of the observed object. In practice a deep exposure with a CCD detector is usually obtained from co-addition of shorter exposures.

See also: → deep; → exposure.

An exposure in which the detector shutter remains open for a relatively long time in order to bring out the weaker features of the observed object. In practice a deep exposure with a CCD detector is usually obtained from co-addition of shorter exposures.

See also: → deep; → exposure.

An area on the sky whose image is obtained with a deep exposure, such as → Hubble Deep Field.

See also: → deep; → field.

An area on the sky whose image is obtained with a deep exposure, such as → Hubble Deep Field.

See also: → deep; → field.

An image obtained using a deep exposure to reveal the weak features of the object.

See also: → deep; → image.

An image obtained using a deep exposure to reveal the weak features of the object.

See also: → deep; → image.

The time-scale of geologic processes which is millions or billions of years in contrast to the few thousand years claimed by supporters of the → creationism.

The concept of “deep time” was first described in 1788 by the Scottish geologist James Hutton (1726-1797) in the Transactions of the Royal Society of Edinburgh. The term was coined by the American author John McPhee (1931-).

See also: → deep; → time.

The time-scale of geologic processes which is millions or billions of years in contrast to the few thousand years claimed by supporters of the → creationism.

The concept of “deep time” was first described in 1788 by the Scottish geologist James Hutton (1726-1797) in the Transactions of the Royal Society of Edinburgh. The term was coined by the American author John McPhee (1931-).

See also: → deep; → time.

1. Failure to act; inaction or neglect; failure to meet financial obligations.
   

   2. Lack; want; absence. See also → deficiency, → lack, → shortage.
      

   3. Computers: A selection automatically used by a program when none is specified by the user. → by default.

Etymology (EN): M.E. defau(l)te, O.Fr. defaute “fault, defect, failure,” from V.L. *defallita “a deficiency or failure,” p.p. of *defallere, from L. → de- “away” + fallere “to deceive, to cheat; to put wrong, to lead astray.”

Etymology (PE): Nâbun, literally “not-being, non-existence,” from nâ- negation prefix, → non-, + (Kurd.) bun “to be,” variants (Gazi, Yarani, Gurani, Semnâni) bu-, classical Pers. bov-, budan “to be, → exist.”

1. Failure to act; inaction or neglect; failure to meet financial obligations.
   

   2. Lack; want; absence. See also → deficiency, → lack, → shortage.
      

   3. Computers: A selection automatically used by a program when none is specified by the user. → by default.

Etymology (EN): M.E. defau(l)te, O.Fr. defaute “fault, defect, failure,” from V.L. *defallita “a deficiency or failure,” p.p. of *defallere, from L. → de- “away” + fallere “to deceive, to cheat; to put wrong, to lead astray.”

Etymology (PE): Nâbun, literally “not-being, non-existence,” from nâ- negation prefix, → non-, + (Kurd.) bun “to be,” variants (Gazi, Yarani, Gurani, Semnâni) bu-, classical Pers. bov-, budan “to be, → exist.”

General: Something or a lack of something that results in incompleteness, inadequacy, or imperfection.
Crystals: A discontinuity in the arrangement of atoms, ions, or electrons.
Cosmology: → cosmic defect.

Etymology (EN): From L. defectus “failure,” from p.p. of deficere “to fail, desert,” from → de- “down, away” + facere “to do,” (cf. Fr. faire, Sp. hacer), from PIE base *dhe- “to put, to do” (cf. Av. dadaiti “he puts,” Skt. dadhati “puts, places,” Hitt. dai- “to place,” Gk. tithenai “to put.”

Etymology (PE): Âk “defect, blemish;” Mid.Pers. ak, âk “evil, harm;” Av. aka- “bad, wicked;” cf. Skt. aka- “pain , trouble.”
Kâst “loss,” from kâstan, kâhidan “to decrease, lessen, diminish,” from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen;” keh “small, little, slender;”
Av. kasu- “small, little;” Proto-Iranian *kas- “to be small, diminish, lessen.”

General: Something or a lack of something that results in incompleteness, inadequacy, or imperfection.
Crystals: A discontinuity in the arrangement of atoms, ions, or electrons.
Cosmology: → cosmic defect.

Etymology (EN): From L. defectus “failure,” from p.p. of deficere “to fail, desert,” from → de- “down, away” + facere “to do,” (cf. Fr. faire, Sp. hacer), from PIE base *dhe- “to put, to do” (cf. Av. dadaiti “he puts,” Skt. dadhati “puts, places,” Hitt. dai- “to place,” Gk. tithenai “to put.”

Etymology (PE): Âk “defect, blemish;” Mid.Pers. ak, âk “evil, harm;” Av. aka- “bad, wicked;” cf. Skt. aka- “pain , trouble.”
Kâst “loss,” from kâstan, kâhidan “to decrease, lessen, diminish,” from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen;” keh “small, little, slender;”
Av. kasu- “small, little;” Proto-Iranian *kas- “to be small, diminish, lessen.”

1. To ward off attack from; guard against assault or injury.
   

   2. To maintain by argument, evidence, etc.; uphold (Dictionary.com).

Etymology (EN): From → de- “from, away,” + -fendere “to strike, push,” → offend.

Etymology (PE): Padâfandidan, from padâfand, from prefix pad- “contrary to; against; opposing,” → counter-,

• âfand “strife, war,” → offend.

1. To ward off attack from; guard against assault or injury.
   

   2. To maintain by argument, evidence, etc.; uphold (Dictionary.com).

Etymology (EN): From → de- “from, away,” + -fendere “to strike, push,” → offend.

Etymology (PE): Padâfandidan, from padâfand, from prefix pad- “contrary to; against; opposing,” → counter-,

• âfand “strife, war,” → offend.

A person who defends someone or something.

See also: → defend; → -er.

A person who defends someone or something.

See also: → defend; → -er.

1. Resistance against attack; protection.
   

   2. The defending of a cause or the like by speech, argument, etc. (Dictionary.com).

See also: Noun from → defend.

1. Resistance against attack; protection.
   

   2. The defending of a cause or the like by speech, argument, etc. (Dictionary.com).

See also: Noun from → defend.

1. Serving to defend; protective; of or relating to defense.
   

   2. A position or attitude of defense (Dictionary.com).

See also: → defense; → -ive.

1. Serving to defend; protective; of or relating to defense.
   

   2. A position or attitude of defense (Dictionary.com).

See also: → defense; → -ive.

In Ptolemy’s geocentric model, the circle around the Earth in which the center of the → epicycle of a body was thought to move.

Etymology (EN): Deferent, from L. deferent-, pr.p. of deferre “to carry from or down, transfer” from → de- + ferre “to carry, bear,” from PIE *bher- “to bear, to carry, to take” (cf. O.Pers./Av. bar- “to bear, carry,” barəθre “to bear” (infinitive), Mod.Pers. bordan, bar- “to carry,”
Skt. bharati “he carries,” Gk. pherein “to carry”).

Etymology (PE): Falak-e hâmel, from Ar. falak “heaven; orbit, sphere” + hamil “carrier.”

In Ptolemy’s geocentric model, the circle around the Earth in which the center of the → epicycle of a body was thought to move.

Etymology (EN): Deferent, from L. deferent-, pr.p. of deferre “to carry from or down, transfer” from → de- + ferre “to carry, bear,” from PIE *bher- “to bear, to carry, to take” (cf. O.Pers./Av. bar- “to bear, carry,” barəθre “to bear” (infinitive), Mod.Pers. bordan, bar- “to carry,”
Skt. bharati “he carries,” Gk. pherein “to carry”).

Etymology (PE): Falak-e hâmel, from Ar. falak “heaven; orbit, sphere” + hamil “carrier.”

In a CCD detector, phenomenon caused by charge traps or potential pockets, which prevent electrons from being released to the adjacent pixel; eventually the electrons may be released in a subsequent cycle.

Etymology (EN): Differed, p.p. of differ, from O.Fr. différer, from L. differre “set apart, put off, delay,” also “be different, differ,” → differ; → charge.

Etymology (PE): Bâr→ charge; bâzdâšté “prevented,” p.p. of bâzdâštan, from preventive suffix bâz- + dâštan “to hold, have, maintain,” Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maitain, keep in mind,” Skt. dhar- “to hold, keep, preserve,” dharma- “law,”
Gk. thronos “elevated seat, throne,” L. firmus “firm, stable,” Lith. daryti “to make,” PIE *dher- “to hold, support.”

In a CCD detector, phenomenon caused by charge traps or potential pockets, which prevent electrons from being released to the adjacent pixel; eventually the electrons may be released in a subsequent cycle.

Etymology (EN): Differed, p.p. of differ, from O.Fr. différer, from L. differre “set apart, put off, delay,” also “be different, differ,” → differ; → charge.

Etymology (PE): Bâr→ charge; bâzdâšté “prevented,” p.p. of bâzdâštan, from preventive suffix bâz- + dâštan “to hold, have, maintain,” Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maitain, keep in mind,” Skt. dhar- “to hold, keep, preserve,” dharma- “law,”
Gk. thronos “elevated seat, throne,” L. firmus “firm, stable,” Lith. daryti “to make,” PIE *dher- “to hold, support.”

See also: Noun from → deficient.

See also: Noun from → deficient.

1. Lacking some element or characteristic; defective.
   

   2. Insufficient; inadequate.

Etymology (EN): From L. deficientem, pr.p. of deficere “to desert, fail,” from → de- “down, away” + facere “to do, perform” + -ency a noun suffix, equivalent to → -ence.

Etymology (PE): Maxeš, from (Dehxodâ) max “missing; vanished; annihilated,” variant (Nâyini) mak “missing;” maybe ultimately from Proto-Ir. *maiH- “to fade, damage, to harm;” cf. Av. (+ *ui-) vīmiti- “loss, destruction;” O.Pers. mīθah- “damage, harm;” Mid.Pers. myh-g’r “damage, harm;” Sogdian ‘’m’yk “dirt, mixture,” ‘myq “taint, infection;” Ossetic mynæg, minæg “weak, dim, fading;” Skt. mayⁱ “to damage, to lessen;” Gk. minytho “to diminish, to lessen;” L. minuoere “to diminish, to lessen,” minor “smaller, less;” PIE root *meiH- “to lessen, diminish” (Cheung 2007).

1. Lacking some element or characteristic; defective.
   

   2. Insufficient; inadequate.

Etymology (EN): From L. deficientem, pr.p. of deficere “to desert, fail,” from → de- “down, away” + facere “to do, perform” + -ency a noun suffix, equivalent to → -ence.

Etymology (PE): Maxeš, from (Dehxodâ) max “missing; vanished; annihilated,” variant (Nâyini) mak “missing;” maybe ultimately from Proto-Ir. *maiH- “to fade, damage, to harm;” cf. Av. (+ *ui-) vīmiti- “loss, destruction;” O.Pers. mīθah- “damage, harm;” Mid.Pers. myh-g’r “damage, harm;” Sogdian ‘’m’yk “dirt, mixture,” ‘myq “taint, infection;” Ossetic mynæg, minæg “weak, dim, fading;” Skt. mayⁱ “to damage, to lessen;” Gk. minytho “to diminish, to lessen;” L. minuoere “to diminish, to lessen,” minor “smaller, less;” PIE root *meiH- “to lessen, diminish” (Cheung 2007).

1. To state or set forth the meaning of (a word, concept, etc.).
   

2. To explain or identify the nature or essential qualities of.
   

3. To fix or mark the boundaries or extent of.

Etymology (EN): From O.Fr. définir “to end, determine,” from L. definire “to limit, determine, explain,” from → de- + finire “to bound, limit,” from finis “boundary.”

Etymology (PE): Hedâridan, infinitive from Semnâni hedâr “boundary (between pieces of lands),” Tabari hedâri “boundary, border,” may be related to
Av. haêtav- “dam, dike,” Skt. setu- “a ridge of earth, bank, dike, dam, bridge.”

1. To state or set forth the meaning of (a word, concept, etc.).
   

2. To explain or identify the nature or essential qualities of.
   

3. To fix or mark the boundaries or extent of.

Etymology (EN): From O.Fr. définir “to end, determine,” from L. definire “to limit, determine, explain,” from → de- + finire “to bound, limit,” from finis “boundary.”

Etymology (PE): Hedâridan, infinitive from Semnâni hedâr “boundary (between pieces of lands),” Tabari hedâri “boundary, border,” may be related to
Av. haêtav- “dam, dike,” Skt. setu- “a ridge of earth, bank, dike, dam, bridge.”

1. Clearly characterized or fixed.
   

2. Showing clearly the outline or profile or boundary.
   

3. Computer science: A variable having received a value prior to a given point in a program.

See also: P.p. of → define.

1. Clearly characterized or fixed.
   

2. Showing clearly the outline or profile or boundary.
   

3. Computer science: A variable having received a value prior to a given point in a program.

See also: P.p. of → define.

Clearly defined or determined; having fixed limits. → definite integral.

Etymology (EN): From L. definitus “limited, precise,” p.p. of definire,
→ define.

Etymology (PE): Hedârmand from hedâr, stem of hedârdan, → define, + -mand possession suffix.

Clearly defined or determined; having fixed limits. → definite integral.

Etymology (EN): From L. definitus “limited, precise,” p.p. of definire,
→ define.

Etymology (PE): Hedârmand from hedâr, stem of hedârdan, → define, + -mand possession suffix.

An integral with upper and lower limits.

See also: → definite; → integral.

An integral with upper and lower limits.

See also: → definite; → integral.

1. The act or process of establishing some value or condition with precision.
   

2. The formal statement of the meaning or significance of a word, concept, etc.
   

3. Optics: The clarity, fidelity, sharpness, and brilliancy of an image formed by an optical system.

See also: Verbal noun of → define.

1. The act or process of establishing some value or condition with precision.
   

2. The formal statement of the meaning or significance of a word, concept, etc.
   

3. Optics: The clarity, fidelity, sharpness, and brilliancy of an image formed by an optical system.

See also: Verbal noun of → define.

Most reliable or complete (as of a text, author, criticism, study, judgement, or the like) that serves as a standard or reference point.

Etymology (EN): M.E., from O.Fr., from L. definitivus, from definit(us)→ definite + -ivus a suffix of adjectives.

Etymology (PE): Hedârâ, adj., from hedâr present stem of hedâridan→ define + adj. suffix -â.

Most reliable or complete (as of a text, author, criticism, study, judgement, or the like) that serves as a standard or reference point.

Etymology (EN): M.E., from O.Fr., from L. definitivus, from definit(us)→ definite + -ivus a suffix of adjectives.

Etymology (PE): Hedârâ, adj., from hedâr present stem of hedâridan→ define + adj. suffix -â.

To burn suddenly and violently with great heat and intense light. → deflagration.

Etymology (EN): From L. deflagratus, p.p. of deflagrare “to burn down,” from → de- + flag(rare) “to blaze, glow, burn” (L. fulgur “lightning;” PIE *bhleg- “to shine;” cf. Gk. phlegein “to burn, scorch,” Skt. bhárgas- “radiance, lustre, splendour,” O.E. blæc “black”) + -atus “-ate”

Etymology (PE): Taškaftidan, from taš “fire,” variant of âtaš→ fire + kaftidan “to explode,” → explode.

To burn suddenly and violently with great heat and intense light. → deflagration.

Etymology (EN): From L. deflagratus, p.p. of deflagrare “to burn down,” from → de- + flag(rare) “to blaze, glow, burn” (L. fulgur “lightning;” PIE *bhleg- “to shine;” cf. Gk. phlegein “to burn, scorch,” Skt. bhárgas- “radiance, lustre, splendour,” O.E. blæc “black”) + -atus “-ate”

Etymology (PE): Taškaftidan, from taš “fire,” variant of âtaš→ fire + kaftidan “to explode,” → explode.

A rapid → chemical reaction in which the → output of → heat is enough to enable the reaction to proceed and be accelerated without input of heat from another source. The effect of a true deflagration under confinement is an → explosion.
See also: → detonation; → explosion.

See also: Verbal noun of → deflagrate.

A rapid → chemical reaction in which the → output of → heat is enough to enable the reaction to proceed and be accelerated without input of heat from another source. The effect of a true deflagration under confinement is an → explosion.
See also: → detonation; → explosion.

See also: Verbal noun of → deflagrate.

To bend or turn aside; turn from a true course or straight line.

Etymology (EN): From L. deflectere “to bend down, turn aside,” from → de- “away” + flectere “to bend, turn.”

Etymology (PE): Vâcaftidan, vâcaftan, from vâcaft, from vâ- “away,” → de- + caft “bent, curved, crooked,” variants cafté, jafté, jaftâ.

To bend or turn aside; turn from a true course or straight line.

Etymology (EN): From L. deflectere “to bend down, turn aside,” from → de- “away” + flectere “to bend, turn.”

Etymology (PE): Vâcaftidan, vâcaftan, from vâcaft, from vâ- “away,” → de- + caft “bent, curved, crooked,” variants cafté, jafté, jaftâ.

The act or state of deflecting or the state of being deflected. Amount of deviation.
Electronics: In a cathode-ray tube, the bending, by a magnetic field, of the beam of electrons after the focused beam leaves the electron gun.

See also: Verbal noun of → deflect.

The act or state of deflecting or the state of being deflected. Amount of deviation.
Electronics: In a cathode-ray tube, the bending, by a magnetic field, of the beam of electrons after the focused beam leaves the electron gun.

See also: Verbal noun of → deflect.

1. The angle by which a light ray is curved by the gravitational field of a massive body. Einstein’s general relativity predicts that a light ray which tangentially grazes the surface of the Sun is deflected by 1’’.7. This result was confirmed in 1919 when the apparent angular shift of stars close to the limb of the Sun was measured during a total solar eclipse.
   
2. In a cathode-ray tube, the angle through which the beam is bent, vertically, horizontally, or diagonally.

See also: → deflection; → angle.

1. The angle by which a light ray is curved by the gravitational field of a massive body. Einstein’s general relativity predicts that a light ray which tangentially grazes the surface of the Sun is deflected by 1’’.7. This result was confirmed in 1919 when the apparent angular shift of stars close to the limb of the Sun was measured during a total solar eclipse.
   
2. In a cathode-ray tube, the angle through which the beam is bent, vertically, horizontally, or diagonally.

See also: → deflection; → angle.

The bending of a light ray under the gravitational effect of a massive body. → deflection angle.

See also: → deflection; → light.

The bending of a light ray under the gravitational effect of a massive body. → deflection angle.

See also: → deflection; → light.

To cause to deviate from accurate focus.

See also: → vâ- + → focus.

To cause to deviate from accurate focus.

See also: → vâ- + → focus.

1. To undergo → deformation.
   

2. To change the form or shape of. → deformable, → deformed, → deformation.

Etymology (EN): From O.Fr. déformer, from L. deformare “to disfigure,” from → de- + → form.

Etymology (PE): Vâdisidan, vâdisândan infinitive from vâdis, from vâ-, → de-, + dis, → form.

1. To undergo → deformation.
   

2. To change the form or shape of. → deformable, → deformed, → deformation.

Etymology (EN): From O.Fr. déformer, from L. deformare “to disfigure,” from → de- + → form.

Etymology (PE): Vâdisidan, vâdisândan infinitive from vâdis, from vâ-, → de-, + dis, → form.

Capable of being → deformed. → deformable mirror

See also: → deform + → -able.

Capable of being → deformed. → deformable mirror

See also: → deform + → -able.

A very thin mirror whose shape can be changed by the force applied by many small pistons behind the mirror. Such a mirror is used in the → adaptive optics technique to correct the → wavefront affected by the → atmospheric turbulence. See also → tip-tilt mirror.

See also: → deformable; → mirror.

A very thin mirror whose shape can be changed by the force applied by many small pistons behind the mirror. Such a mirror is used in the → adaptive optics technique to correct the → wavefront affected by the → atmospheric turbulence. See also → tip-tilt mirror.

See also: → deformable; → mirror.

Altering in the size or shape of a body. See also → deformable.

See also: Verbal noun of → deform.

Altering in the size or shape of a body. See also → deformable.

See also: Verbal noun of → deform.

Having the → form → changed.

See also: Past participle of → deform.

Having the → form → changed.

See also: Past participle of → deform.

1. No longer in effect or use; not operating or functioning.
   

2. No longer in existence; dead; extinct.

Etymology (EN): M.E., from O.Fr. defunct or directly from L defunctus “dead,” literally “off-duty,” from p.p. of defungi “to discharge, finish,” from → de- “off, completely” + fungi “perform or discharge duty,” from PIE root *bheug- “to enjoy” (cognates: Latin fructus).

Etymology (PE): Nâkâr, “disabled” (Dehxodâ), leterally “not working,” from negation prefix nâ-, → un-, + kâr, kardan,
→ work

1. No longer in effect or use; not operating or functioning.
   

2. No longer in existence; dead; extinct.

Etymology (EN): M.E., from O.Fr. defunct or directly from L defunctus “dead,” literally “off-duty,” from p.p. of defungi “to discharge, finish,” from → de- “off, completely” + fungi “perform or discharge duty,” from PIE root *bheug- “to enjoy” (cognates: Latin fructus).

Etymology (PE): Nâkâr, “disabled” (Dehxodâ), leterally “not working,” from negation prefix nâ-, → un-, + kâr, kardan,
→ work

A comet that has lost its ability to emit dust and gas and no longer displays the classic cometary features of a nebulous coma and a tail, or a destroyed comet. Comet Pigott The asteroid (944) Hidalgo is considered by some to be a defunct comet because of its unusual orbit. Another case is the asteroid Phaethon.

See also: → defunct; → comet.

A comet that has lost its ability to emit dust and gas and no longer displays the classic cometary features of a nebulous coma and a tail, or a destroyed comet. Comet Pigott The asteroid (944) Hidalgo is considered by some to be a defunct comet because of its unusual orbit. Another case is the asteroid Phaethon.

See also: → defunct; → comet.

The process of producing a quantifiable result in a → fuzzy logic system, given → fuzzy sets and corresponding → membership functions.
Defuzzification is the last step in a fuzzy logic system. After → fuzzy inferencing,
the overall result is a → fuzzy value. This result should be defuzzified to obtain a final → crisp value.

See also: Verbal noun of → defuzzify; → -tion.

The process of producing a quantifiable result in a → fuzzy logic system, given → fuzzy sets and corresponding → membership functions.
Defuzzification is the last step in a fuzzy logic system. After → fuzzy inferencing,
the overall result is a → fuzzy value. This result should be defuzzified to obtain a final → crisp value.

See also: Verbal noun of → defuzzify; → -tion.

To transform a → fuzzy set to a → crisp set in a → fuzzy logic system.

See also: → de-; → fuzzy; → -fy.

To transform a → fuzzy set to a → crisp set in a → fuzzy logic system.

See also: → de-; → fuzzy; → -fy.

1. General: Degenerate state or character. Reverting to an earlier, simpler, state.
   

2. Math.: Limiting case in which a class of object changes its nature so as to belong to another, usually simpler, class.
   

3. Physics: In quatum mechanics, the condition in which two or more different → wave functions of a system correspond to the same energy. In the case of atomic energy levels, the degeneracy can be removed, for example, by applying an electric field to the atom.
   

State or charcater of → degenerate matter.

Etymology (EN): From degener(ate), → degenerate, + -acy suffix of nouns of quality and state.

Etymology (PE): Vâgeni, from vâgen, → degenerate, + noun suffix -i.

1. General: Degenerate state or character. Reverting to an earlier, simpler, state.
   

2. Math.: Limiting case in which a class of object changes its nature so as to belong to another, usually simpler, class.
   

3. Physics: In quatum mechanics, the condition in which two or more different → wave functions of a system correspond to the same energy. In the case of atomic energy levels, the degeneracy can be removed, for example, by applying an electric field to the atom.
   

State or charcater of → degenerate matter.

Etymology (EN): From degener(ate), → degenerate, + -acy suffix of nouns of quality and state.

Etymology (PE): Vâgeni, from vâgen, → degenerate, + noun suffix -i.

Pressure in a degenerate electron or neutron gas. → degenerate matter.

See also: → degeneracy; → pressure.

Pressure in a degenerate electron or neutron gas. → degenerate matter.

See also: → degeneracy; → pressure.

Characterized by or associated with → degeneracy.

Etymology (EN): L. degeneratus, p.p. of degenerare “depart from one’s kind, fall from ancestral quality,” from → de- + gener-, stem of
genus “race, stock, kind,” gignere “to beget,” cf. with Gk. genos “race, kind,” gonos “birth, offspring,” from PIE base *gen-/*gon-/*gn- “to produce, beget, be born,” cf. Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born,” zana- “race” (in sruuô.zana- “belonging to the race of the horned ones”), O.Pers. zana- “tribe” (in paru-zana- “consisting of many tribes”),
Skt. janati “begets, bears,” jana- “creature, human being, race, tribe, people.”

Etymology (PE): Vâgen, from vâ-, → de-, + gen “kind,” (as in hamgen “of the same kind, like each other; friend, partner,” from ham- “together,” → com- + gen “kind,” O.Pers./Av. zana- “race; tribe,” cognate with L. genus, as above). Alternatively, gen may be a variant of Mid./Mod.Pers. gôn/gun “kind, type; manner; color, skin color,” from Av. gaona- “hair, hair color, color.”

Characterized by or associated with → degeneracy.

Etymology (EN): L. degeneratus, p.p. of degenerare “depart from one’s kind, fall from ancestral quality,” from → de- + gener-, stem of
genus “race, stock, kind,” gignere “to beget,” cf. with Gk. genos “race, kind,” gonos “birth, offspring,” from PIE base *gen-/*gon-/*gn- “to produce, beget, be born,” cf. Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born,” zana- “race” (in sruuô.zana- “belonging to the race of the horned ones”), O.Pers. zana- “tribe” (in paru-zana- “consisting of many tribes”),
Skt. janati “begets, bears,” jana- “creature, human being, race, tribe, people.”

Etymology (PE): Vâgen, from vâ-, → de-, + gen “kind,” (as in hamgen “of the same kind, like each other; friend, partner,” from ham- “together,” → com- + gen “kind,” O.Pers./Av. zana- “race; tribe,” cognate with L. genus, as above). Alternatively, gen may be a variant of Mid./Mod.Pers. gôn/gun “kind, type; manner; color, skin color,” from Av. gaona- “hair, hair color, color.”

Same as → white dwarf.

See also: → degenerate; → dwarf.

Same as → white dwarf.

See also: → degenerate; → dwarf.

Highly compressed matter in which the normal atomic structure has broken down and which, because of quantum-mechanical effects, exerts a pressure that is independent of temperature. Bodies with masses less than → Chandrasekhar’s limit (1.4 solar masses) are supported by electron → degeneracy pressure and have densities of about 10⁶ kg/m³. In collapsed stars of mass above 1.4 solar masses, gravity will overwhelm electron degeneracy and further collapse ensues. Electrons combine with protons to form neutrons, so producing a → neutron star. Because neutrons, like electrons, are
→ fermions and therefore subject to the → Pauli exclusion principle, at high enough densities, about 10¹⁴ kg/m³, neutron degeneracy pressure prevents further collapse of the star. For masses larger than 2-3 solar masses, even neutron degeneracy cannot prevent further collapse, and a → black hole is formed.

See also: → degenerate; → matter.

Highly compressed matter in which the normal atomic structure has broken down and which, because of quantum-mechanical effects, exerts a pressure that is independent of temperature. Bodies with masses less than → Chandrasekhar’s limit (1.4 solar masses) are supported by electron → degeneracy pressure and have densities of about 10⁶ kg/m³. In collapsed stars of mass above 1.4 solar masses, gravity will overwhelm electron degeneracy and further collapse ensues. Electrons combine with protons to form neutrons, so producing a → neutron star. Because neutrons, like electrons, are
→ fermions and therefore subject to the → Pauli exclusion principle, at high enough densities, about 10¹⁴ kg/m³, neutron degeneracy pressure prevents further collapse of the star. For masses larger than 2-3 solar masses, even neutron degeneracy cannot prevent further collapse, and a → black hole is formed.

See also: → degenerate; → matter.

1. To lower in dignity or estimation; bring into contempt.
   

2. To lower in character or quality; debase.
   

3. Chemistry: Of a compound, especially an organic hydrocarbon, to break down (Dictionary.com).

See also: → de-; → grade.

1. To lower in dignity or estimation; bring into contempt.
   

2. To lower in character or quality; debase.
   

3. Chemistry: Of a compound, especially an organic hydrocarbon, to break down (Dictionary.com).

See also: → de-; → grade.

1. Subdivision of an interval in a scale of measurement.
   

2. Geometry: Measure of angle, the 360th part of a circle.
   

3. Math.: Rank of an equation or expression as determined by the sum of the exponents of the variables.

Etymology (EN): From O.Fr. degré, from V.L. *degradus “a step,” from L.L. degredare, from L. → de- “down” + gradus “step.”

Etymology (PE): Darajé, from Ar. darajat “step, ladder.”

1. Subdivision of an interval in a scale of measurement.
   

2. Geometry: Measure of angle, the 360th part of a circle.
   

3. Math.: Rank of an equation or expression as determined by the sum of the exponents of the variables.

Etymology (EN): From O.Fr. degré, from V.L. *degradus “a step,” from L.L. degredare, from L. → de- “down” + gradus “step.”

Etymology (PE): Darajé, from Ar. darajat “step, ladder.”

The extent of → coherence of an → electromagnetic wave, as indicated by a → dimensionless number.

Since interference takes place when waves are → coherent, using a → Young’s experiment, the degree of coherence
is measured from the → fringe  → visibility, V. It is defined as the ratio V = (I_max - I_min) / (I_max + I_min), where I_max is the intensity at a maximum of the → interference pattern, and I_min is the intensity at a minimum of the interference pattern.

The electromagnetic wave is considered to be highly coherent when the degree of coherence is about 1, incoherent for nearly zero values, and partially coherent for values between 0 and 1.

See also: → degree; → coherence.

The extent of → coherence of an → electromagnetic wave, as indicated by a → dimensionless number.

Since interference takes place when waves are → coherent, using a → Young’s experiment, the degree of coherence
is measured from the → fringe  → visibility, V. It is defined as the ratio V = (I_max - I_min) / (I_max + I_min), where I_max is the intensity at a maximum of the → interference pattern, and I_min is the intensity at a minimum of the interference pattern.

The electromagnetic wave is considered to be highly coherent when the degree of coherence is about 1, incoherent for nearly zero values, and partially coherent for values between 0 and 1.

See also: → degree; → coherence.

Of a → mechanical system, the number of → independent variables needed to describe its configuration.

See also: → degree; → freedom.