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Acronym: IGM
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intergalactic medium
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tter in the universe was mostly in the form of neutral hydrogen and helium atoms. However, observations of galaxies today seem to indicate that most of the volume of the intergalactic medium (IGM) consists of ionized material (since there are few absorption lines due to hydrogen atoms). This implies a period of reionization during which some of the material of the universe was broken into |
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Acronym: CBI
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Cosmic Background Imager
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ments of the fluctuations with higher accuracy over the next three years, including the Very Small Array, Degree Angular Scale Interferometer (DASI), and the Cosmic Background Imager (CBI). DASI made the first detection of the polarization of the CMB and the CBI provided the first E-mode polarization spectrum with compelling evidence that it is out of phase with the T-mode spectrum. |
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Acronym: DFT
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discrete Fourier transform
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to last version by Luckas-bot</comment> <text xml:space="preserve"> A '''fast Fourier transform''' ('''FFT''') is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse. There are many distinct FFT algorithms involving a wide range of mathematics, from simple complex-number arithmetic to group theory and number theory; this |
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Acronym: LPC
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linear predictive coding
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ing|signal]] are estimated as a linear function of previous samples. In digital signal processing, linear prediction is often called linear predictive coding (LPC) and can thus be viewed as a subset of filter theory. In system analysis (a subfield of mathematics), linear prediction can be viewed as a part of [[mathematical model|mathematical modelli |
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Acronym: AC
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alternating current
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tween ''A'' and ''B'' and the voltage between ''B'' and ''C''. The various voltages in a circuit can be computed using Kirchhoff's circuit laws. When talking about alternating current (AC) there is a difference between instantaneous voltage and average voltage. Instantaneous voltages can be added as for direct current (DC), but average voltages can be meaningfully added only when t |
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Acronym: AC
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Alternating current
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lead to a lethal electric shock under certain circumstances. Electrical safety is discussed in the articles on high voltage and electric shock. ==See also== *Alternating current (AC) *Direct current (DC) *Electric potential *Electrical measurements *Electrochemical potential *Fermi level *Mains electricity (an article about domestic power supply volt |
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Acronym: THD
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Total harmonic distortion
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distortion may be expressed in terms of the relative strength of individual components, in decibels, or the Root Mean Square of all harmonic components: Total harmonic distortion (THD), as a percentage. The level at which harmonic distortion becomes audible is not generally agreed upon; in the past a THD figure of 0.1% was considered the magic figure to aim for. Harmonic distortion |
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Acronym: MER
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modulation error ratio
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noise levels in a digital system can be expressed using SNR, it is more common to use Eb/N0|E b /N o , the energy per bit per noise power spectral density. The modulation error ratio (MER) is a measure of the SNR in a digitally modulated signal. === Fixed point === For ''n''-bit integers with equal distance between quantization levels ([[Quantization (signal processing)|unifo |
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Acronym: NF
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noise figure
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aving a 50 Ω input impedance, connected to an Antenna (radio)|antenna with a 50 Ω radiation resistance would be scaled by the noise figure (NF), shown as follows: : P_\mathrm{receiver noise} (dB) = P_\mathrm{resistor noise} (dB) + 10\ \log_{10}(10^{NF/10}-1) or : P_\mathrm{receiver noise} = P_\mathrm{resistor noise} (10^{NF/10}-1). |
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Acronym: FTC
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Federal Trade Commission
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uments/audio/amplifier_power.html epanorama.net/Amplifier power ] In the US on May 3, 1974, the Amplifier Rule CFR 16 Part 432 (39 FR 15387) was instated by the Federal Trade Commission (FTC) requiring audio power and distortion ratings for home entertainment equipment to be measured in a defined manner with power stated in RMS terms. (See more in the section '''Standards''' at the end of |
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Acronym: FFT
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fast Fourier transform
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ly one (or zero) numbers, but to amortize the overhead of recursion one would normally use a larger base case. The equivalent of cascade summation is used in many fast Fourier transform (FFT) algorithms, and is responsible for the logarithmic growth of roundoff errors in those FFTs. S. G. Johnson and M. Frigo, "[http://cnx.org/content/m16336/latest/ Implementing FFTs in practice], in |
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Acronym: PDB
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Protein Data Bank
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r sets of structures as well as in the production of "all-to-all" comparison databases that measure the divergence between every pair of structures present in the Protein Data Bank (PDB). Such databases are used to classify proteins by their fold. [[Image:Ssap-vectors.png|frame|Illustration of the atom-to-atom vectors calculated in SSAP. From these vectors a s |
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Acronym: PPM
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Prediction by Partial Matching
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e terms of the GNU general public license |accessdate=2007-07-10 |}} ==Algorithm== PAQ uses a context mixing algorithm. Context mixing is related to Prediction by Partial Matching (PPM) in that the compressor is divided into a predictor and an arithmetic coder, but differs in that the next-symbol prediction is computed using a weighed combination of probability estimates from a |
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Acronym: SLM
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Scanning laser microscope
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'Vertical scanning'': * Interferometry * Confocal microscopy * Focus variation * Confocal chromatic aberration ''Horizonal scanning'': * Scanning laser microscope (SLM) * Structured Light 3D Scanner|Structured light scanning ===Choose of the right measurement instrument=== Because of every instrument has advantages and disadvantages the operator must choose |
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Acronym: DC
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Direct Current
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rent power]] in an electrical circuit, equal to the product of voltage and electrical_current|current. It is equal to the electrical power measured in watts for Direct Current (DC) circuits. The apparent power may differ from the real power for Alternating Current (AC) circuits, where voltage and current may be out of phase. The real power is equal to the apparent power |
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Acronym: DPF
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displacement power factor
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is the fundamental component of the current and I_{\mbox{rms}} is the total current - both are root mean square-values. The result when multiplied with the displacement power factor (DPF) is the true power factor or just power factor (PF): : \mbox{PF} = \mbox{DPF} {I_{\mbox{1,rms}} \over I_{\mbox{rms}}} == See also == * Power factor ==External links== *[http:/ |
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Acronym: LES
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Large eddy simulation
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ysics of turbulence. Also, direct numerical simulations are useful in the development of turbulence models for practical applications, such as sub-grid scale models for Large eddy simulation (LES) and models for methods that solve the Reynolds-averaged Navier-Stokes equations (RANS). This is done by means of "a priori" tests, in which the input data for the model is taken from a |
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Acronym: CNR
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carrier to noise ratio
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er|analog-to-digital coversion]] and compression, peak signal-to-noise ratio (PSNR) in image and video coding, Eb/N0|''E'' b /''N'' 0 in digital transmission, carrier to noise ratio (CNR) before the detector in carrier-modulated systems, and noise figure in cascaded amplifiers. In communication systems, the noise is an error or undesired disturbance of a useful information |
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Acronym: AWGN
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additive white Gaussian noise
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plitude of the signal has very nearly a Gaussian probability density function. A communication system affected by thermal noise is often modelled as an additive white Gaussian noise (AWGN) channel. The root mean square (RMS) voltage due to thermal noise v_n , generated in a resistance ''R'' (ohms) over bandwidth Δ''f'' (hertz), is given by : v_{n} = \sqrt{ 4 k_B T |
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Acronym: SPL
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sound pressure level
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ured using a hydrophone, which is the underwater equivalent of a microphone. A hydrophone measures pressure fluctuations, and these are usually converted to sound pressure level (SPL), which is a logarithmic measure of the mean square acoustic pressure. Measurements are usually reported in one of three forms :- * RMS acoustic pressure in micropascals ( |
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Acronym: SPR
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surface plasmon resonance
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ated in greater detail in reference . ==Experimental applications== The excitation of surface plasmons is frequently used in an experimental technique known as surface plasmon resonance (SPR). In SPR, the maximum excitation of surface plasmons are detected by monitoring the reflected power from a prism coupler as a function of incident angle or wavelength. This technique can be used t |
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