An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 7 Search : acoustic
  صدایی، صداییک   
sedâyi, sedâyik

Fr.: acoustique   

Pertaining to the sense of hearing, or to → sound waves.


acoustic peak
  ستیغ ِ صداییک   
setiq-e sedâyik

Fr.: pic acoustique   

One of several peaks appearing in the → CMB angular power spectrum of the → cosmic microwave background radiation which are ripples left by acoustic oscillations of the plasma-radiation fluid in the early Universe (→ baryon acoustic oscillations). When the Universe was small and very hot, the free electron density was so high that photons could not propagate freely without being scattered by electrons. Ionized matter, electrons and radiation formed a single fluid, with the inertia provided by the baryons and the radiation pressure given by the photons.

acoustic; → peak.

acoustic pressure
  فشار ِ صدا   
fešâr-e sedâ

Fr.: pression acoustique   

Same as → sound pressure.

acoustic; → pressure.

acoustic wave
  موج ِ صدایی   
mowj-e sedâyi

Fr.: onde acoustique, ~ sonore   

A type of → longitudinal wave that consists of mechanical → vibrations of small → amplitude propagated in an → elastic medium. Acoustic waves exhibit phenomena like → diffraction, → reflection, and → interference, but not → polarization. Also called → sonic and → sound waves. See also → acoustic wave equation. The branch of physics concerned with the properties of sonic waves is called → acoustics.

acoustic; → wave.

acoustic wave equation
  هموگش ِ موج ِ صدایی   
hamugeš-e mowj-e sedâyi

Fr.: équation de l'onde acoustique   

A → differential equation that describes the time evolution of the → scalar potential of the field φ. It is expressed by: ∇2φ = (1/c2)∂2φ/∂t2, where c is → velocity of → longitudinal waves and ∇2 is the → Laplacian operator.

acoustic; → wave; → equation.

  صداییک، صداشناسی   
sedâyik, sedâšenâsi

Fr.: acoustique   

1) The study of sound, especially of its generation, propagation, and reception.
2) Those qualities of an enclosure that together determine its character with respect to distinct hearing.

From Fr. acoustique, from Gk. akoustikos "pertaining to hearing," from akoustos "heard, audible," from akouein "to hear," from copulative prefix a- + koein "to mark, perceive, hear," from PIE root *(s)keu- "to notice, observe."

Sedâyik from sedâ "sound" + Pers. suffix -ik, → -ics. Sedâ is most probably Persian, since it exists also in Indo-Aryan languages: Skt. (late Vedic): sabda "articulate sound, noise," Pali and Prakriti: sadda "sound, noise," Sindhi: sadu, sado "shout, call," Gujrâti sad "call, voice, echo," Marathi: sad "shouting to," Konkani sad "sound," Sinhali: sada "sound." Therefore, sadâ in Arabic "reverbrating noise, echo" may be borrowed from Persian, or a coincidence. Note that for the author of the classical Persian dictionary Borhân-e Qâte' (India, 1652 A.D.), the Arabic term is a loanword from Persian.

phone; →phonetics.

baryon acoustic oscillation (BAO)
  نوش ِ صداییک ِ باریونی   
naveš-e sedâyik-e bâryoni

Fr.: oscillation acoustique baryonique   

In cosmology, one of a series of peaks and troughs that are present in the power spectrum of matter fluctuations after the → recombination era, and on large scales. At the time of the Big Bang, and for about 380,000 years afterwards, Universe was ionized and photons and baryons were tightly coupled. Acoustic oscillations arose from perturbations in the primordial plasma due to the competition between gravitational attraction and gas+photons pressure. After the epoch of recombination, these oscillations froze and imprinted their signatures in both the → CMB and matter distribution. In the case of the photons, the acoustic mode history is manifested as the high-contrast Doppler peaks in the temperature anisotropies. As for baryons, they were in a similar state, and when mixed with the non-oscillating → cold dark matter perturbations, they left a small residual imprint in the clustering of matter on very large scales, ~100 h-1Mpc (h being the → Hubble constant in units of 100 km s-1 Mpc-1). The phenomenon of BAOs, recently discovered using the Sloan Digital Sky Survey data, is a confirmation of the current model of cosmology. Like → Type Ia supernovae, BAOs provide a → standard candle for determining cosmic distances. The measurement of BAOs is therefore a powerful new technique for probing how → dark energy has affected the expansion of the Universe (see, e.g., Eisenstein 2005, New Astronomy Reviews 49, 360; Percival et al. 2010, MNRAS 401, 2148).

baryon; → acoustic; → oscillation.