What is attenuation? 

Attenuation

Attenuation is a measure of how much of the sugar in the wort has been fermented by the yeast.

In home brewing, we usually deal with apparent attenuation:

apparent attenuation = ( ( OG in points - FG in points ) / OG in points ) x 100

Apparent attenuation is different (higher) than the actual attenuation, because the alcohol produced during fermentation is lighter than water, and throws the reading off.

The apparent attenuation you will get on a given batch depends on a number of factors, including the types of grains/extracts used, mash temperature (if brewing all-grain), and the strain of yeast. Typically, apparent attenuation will range from 65 to 80%. Beers with a lower apparent attenuation will be sweeter, fuller-bodied, and lower in alcohol. Higher apparent attenuation will result in a drier, thinner, higher alcohol brew.

Example:

What is the apparent attenuation of a beer with an OG of 1.055 and a FG of 1.016?

( 55 - 16 ) / 55 x 100 = 71%

Answered by M P , an ibibo Master, at 3:36 PM on October 07, 2008

Attenuation is a reduction in signal strength over distance.First strip the jacket from the cable, being very careful not to cut into the individual conductors. It is wise to take a few practice tries to make sure you are not stripping too deep before you end up cutting too much off.

Answered by Sharad Singh , an ibibo Master, at 5:40 PM on September 24, 2008

Attenuation is a reduction in signal strength over distance.

Each cable standard will list an acceptable amount of attenuation which a cable may allow over a given distance. This is usually measured in decibels.

Cables with better protection against attenuation may enable higher speeds or longer distances, subject to the limitations of network timing.

Attenuation is also referred to as loss.

Attenuation coefficient

Attenuation coefficients are used to quantify different media according to how strongly the transmitted ultrasound amplitude decreases as a function of frequency. The attenuation coefficient (α) can be used to determine total attenuation in dB/cm in the medium using the following formula:

\mathrm{Attenuatio n[dB]} = \alpha\mathrm{[dB/(MHz*cm)]}\c dot\mathit{l}\mathrm{[cm]}\cdo t\mathrm{f[MHz]}

As this equation shows, besides the medium length and attenuation coefficient, attenuation is also linearly dependent on the frequency of the incident ultrasound beam. Attenuation coefficients vary widely for different media. In biomedical ultrasound imaging however, biological materials and water are the most commonly used media. The attenuation coefficients of common biological materials at a frequency of 1 MHz are listed below:[2]
Material α(dB / MHz * cm)
Lung 41
Bone 20
Kidney 1.0
Liver 0.94
Fat 0.63
Blood 0.18
Brain 0.85
Water 0.0022

There are two general ways of acoustic energy losses: absorption and scattering, for instance light scattering.[4] Ultrasound propagation through homogeneous media is associated only with absorption and can be characterised with absorption coefficient only. Propagation through heterogeneous media requires taking into account scattering.

Answered by jaivir , an ibibo Master, at 7:01 PM on September 11, 2008

well suparna!
Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances. The extent of attenuation is usually expressed in units called decibels (dBs).

If Ps is the signal power at the transmitting end (source) of a communications circuit and Pd is the signal power at the receiving end (destination), then Ps > Pd. The power attenuation Ap in decibels is given by the formula:

Ap = 10 log10(Ps/Pd)

Attenuation can also be expressed in terms of voltage. If Av is the voltage attenuation in decibels, Vs is the source signal voltage, and Vd is the destination signal voltage, then:

Av = 20 log10(Vs/Vd)

In conventional and fiber optic cables, attenuation is specified in terms of the number of decibels per foot, 1,000 feet, kilometer, or mile. The less the attenuation per unit distance, the more efficient the cable. When it is necessary to transmit signals over long distances via cable, one or more repeaters can be inserted along the length of the cable. The repeaters boost the signal strength to overcome attenuation. This greatly increases the maximum attainable range of communication.

for more inf check http://searchnetworking.techtarget. com/sDefinition/0,,sid7_gci211613,0 0.html

Answered by raj u , an ibibo Master, at 1:07 PM on September 09, 2008

well, Attenuation, expressed in dB per unit length, is the sum of the power loss along the length of the cable. Coupling Loss is the difference between the power that is contained in the cable and the transmitted power received by a dipole antenna located a fixed distance away.

Answered by Romi , an ibibo Master, at 10:12 AM on September 09, 2008

well;
Attenuation is the weakening of a radar beam as it moves downstream due to some of the energy being lost to scattering and absorption. The further a radar beam moves downstream the more dust, hydrometeors, etc. the radar beam will have to pass through. Because of attenuation, storms close to the radar are better sampled than storms far from the radar site. Beam spreading and attenuation both combine to produce a much poorer sampling of storms far from the radar. Attenuation is higher when the radar beam has the flow through a large number of hydrometeors. Storms and precipitation close to the radar degrade the radar energy before it reaches storms further from the radar. Smaller wavelength radar beams attenuate more rapidly than long wavelength radar. Because of this, most television station radars (C-band) have a shorter range of high clarity compared to the WSR-88D radar (S-band).

Answered by Kishore , an ibibo Master, at 8:36 AM on September 09, 2008

Suparna reduction of signal strength during transmission. Attenuation is the opposite of amplification, and is normal when a signal is sent from one point to another. If the signal attenuates too much, it becomes unintelligible, which is why most networks require repeaters at regular intervals. Attenuation is measured in decibels.

One area of research in which attenuation figures strongly is in ultrasound physics. Attenuation in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced.

Answered by Keshto Patel , an ibibo Master, at 8:47 PM on September 08, 2008

As light travels along an optical fibre it is gradually scattered or absorbed by the glass, even though the glass is by far the most transparent type we have. Therefore the light becomes weaker and weaker – this is called attenuation.

When the light is attenuated the signal deteriorates so that it may not be recognised when it arrives at the receiver. It has to be ‘boosted’ by a repeater or amplifier. A repeater adds energy to the signal to make it strong enough to arrive and be decoded.

Answered by Nagendra , an ibibo Master, at 8:28 PM on September 08, 2008

Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a medium, or by increments calculated in electronic circuitry or set by variable controls. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question.

One area of research in which attenuation figures strongly is in ultrasound physics. Attenuation in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced. By knowing the attenuation that an ultrasound beam experiences travelling through a medium, one can adjust the input signal amplitude to compensate for any loss of energy at the desired imaging depth.[2]

* Ultrasound attenuation measurement in heterogeneous systems, like emulsions or colloids yields information on particle size distribution. There is ISO standard on this technique.[3]

* Ultrasound attenuation can be used for extensional rheology measurement. There are acoustic rheometers that employ Stokes' law for measuring extensional viscosity and volume viscosity.

[edit] Attenuation coefficient

Attenuation coefficients are used to quantify different media according to how strongly the transmitted ultrasound amplitude decreases as a function of frequency. The attenuation coefficient (α) can be used to determine total attenuation in dB/cm in the medium using the following formula:

\mathrm{Attenuatio n[dB]} = \alpha\mathrm{[dB/(MHz*cm)]}\c dot\mathit{l}\mathrm{[cm]}\cdo t\mathrm{f[MHz]}

As this equation shows, besides the medium length and attenuation coefficient, attenuation is also linearly dependent on the frequency of the incident ultrasound beam. Attenuation coefficients vary widely for different media. In biomedical ultrasound imaging however, biological materials and water are the most commonly used media. The attenuation coefficients of common biological materials at a frequency of 1 MHz are listed below:[2]
Material α(dB / MHz * cm)
Lung 41
Bone 20
Kidney 1.0
Liver 0.94
Fat 0.63
Blood 0.18
Brain 0.85
Water 0.0022

There are two general ways of acoustic energy losses: absorption and scattering, for instance light scattering.[4] Ultrasound propagation through homogeneous media is associated only with absorption and can be characterised with absorption coefficient only. Propagation through heterogeneous media requires taking into account scattering.

for details,please visit:
http://en.wikipedia.or g/wiki/Attenuation_(electromag netic_radiation)

Answered by Anju Singh , an ibibo Master, at 8:27 PM on September 08, 2008