Transcript m called Sabine 16

• Attenuation
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Optical fiber - Mechanisms of attenuation
1
Empirical research has shown that
attenuation in optical fiber is caused
primarily by both scattering and
absorption.
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Particle size distribution - Acoustic spectroscopy or ultrasound attenuation
spectroscopy
1
The resulting ultrasound attenuation
frequency spectra are the raw data for
calculating particle size distribution
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Alzheimer's disease research - Metal-protein interaction attenuation
PBT2 is an 8-hydroxy quinoline that
removes copper and zinc from
cerebrospinal fluid, which are held to be
necessary catalysts for amyloid beta
aggregation. This drug has been in a
Phase II trial for early Alzheimers and
which has reported preliminarily promising,
but not detailed, results.
1
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Ultrasound attenuation spectroscopy
1
'Ultrasound attenuation spectroscopy'
is a method for characterizing
properties of fluids and dispersed
particles. It is also known as 'acoustic
spectroscopy'
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Ultrasound attenuation spectroscopy
1
There is an international standard for
this method. ISO 20998-1:2006
Measurement and characterization of
particles by acoustic methodsDukhin,
A.S. and Goetz, P.J. Ultrasound for
characterizing colloids, Elsevier, 2002
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Ultrasound attenuation spectroscopy
1
Measurement of attenuation coefficient
versus ultrasound frequency yields raw
data for further calculation of various
system properties. Such raw data are
often used in the calculation of the
particle size distribution in
heterogeneous systems such as
emulsions and colloids. In the case of
acoustic rheometers, the raw data are
converted into extensional viscosity or
volume viscosity.
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Ultrasound attenuation spectroscopy
1
Instruments that employ ultrasound
attenuation spectroscopy are referred
to as Acoustic spectrometers.
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Attenuation (electromagnetic radiation)
In physics, 'attenuation' (in some
contexts also called 'extinction') is the
gradual loss in intensity of any kind of
flux through a medium. For instance,
sunlight is attenuated by dark glasses,
X-rays are attenuated by lead, and
light and sound are attenuated by
water.
1
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Attenuation (electromagnetic radiation)
In electrical engineering and
telecommunications, attenuation affects
the propagation of waves and signals in
electrical circuits, in optical fibers, and in
air (radio waves).
1
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Attenuation (electromagnetic radiation) - Background
In many cases, attenuation is an
exponential function of the path length
through the medium. In chemical
spectroscopy, this is known as the
Beer-Lambert law.
1
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Attenuation (electromagnetic radiation) - Background
In engineering, 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.Essentials of Ultrasound Physics,
James A. Zagzebski, Mosby Inc., 1996.
1
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Attenuation (electromagnetic radiation) - Background
Attenuation also occurs in
earthquakes; when the seismic waves
move farther away from the epicenter,
they grow smaller as they are
attenuated by the Earth|ground.
1
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Attenuation (electromagnetic radiation) - Ultrasound
By knowing the attenuation that an
ultrasound beam experiences traveling
through a medium, one can adjust the
input signal amplitude to compensate
for any loss of energy at the desired
imaging depth.Diagnostic Ultrasound,
Stewart C
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Attenuation (electromagnetic radiation) - Ultrasound
1
*Ultrasound attenuation measurement
in heterogeneous systems, like
emulsions or colloids, yields
information on particle size
distribution. There is an ISO standard
on this technique.ISO 20998-1:2006
Measurement and characterization of
particles by acoustic methods
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Attenuation (electromagnetic radiation) - Ultrasound
1
*Ultrasound attenuation can be used
for extensional rheology
measurement. There are acoustic
rheometers that employ Stokes' law
for measuring extensional viscosity
and volume viscosity.
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Attenuation (electromagnetic radiation) - Ultrasound
1
Wave equations which take acoustic
attenuation into account can be
written on a fractional derivative
form, see the article on acoustic
attenuation or e.g. the survey paper.S.
P. Näsholm and S. Holm, On a
Fractional Zener Elastic Wave
Equation, Fract. Calc. Appl. Anal. Vol.
16, No 1 (2013), pp. 26-50, DOI:
10.2478/s13540-013--0003-1
[http://arxiv.org/abs/1212.4024 Link
to e-print]
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Attenuation (electromagnetic radiation) - Attenuation coefficient
1
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 (\alpha) can be used to
determine total attenuation in
decibel|dB in the medium using the
following formula:
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Attenuation (electromagnetic radiation) - Attenuation coefficient
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
1
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Attenuation (electromagnetic radiation) - Attenuation coefficient
1
There are two general ways of acoustic
energy losses: absorption
(acoustics)|absorption and scattering, for
instance light scattering.Bohren,C. F. and
Huffman, D.R. Absorption and Scattering
of Light by Small Particles, Wiley, (1983),
isbn= 0-471-29340-7
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Attenuation (electromagnetic radiation) - Attenuation coefficient
Ultrasound propagation through
Homogeneous
(chemistry)|homogeneous media is
associated only with absorption and can
be characterized with absorption
coefficient only. Propagation through
heterogeneous media requires taking
into account scattering.Dukhin, A.S. and
Goetz, P.J. Ultrasound for characterizing
colloids, Elsevier, 2002 Fractional
derivative wave equations can be
applied for modeling of lossy acoustical
wave propagation, see also acoustic
attenuation and Ref.
1
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Attenuation (electromagnetic radiation) - Light attenuation in water
1
Shortwave radiation emitted from the
sun wavelengths in the visible
spectrum of light that range from
360nm (violet) to 750nm (red). When
the sun’s radiation reaches the seasurface, the shortwave radiation is
attenuated by the water, and the
intensity of light decreases
exponentially with water depth. The
intensity of light at depth can be
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Attenuation (electromagnetic radiation) - Light attenuation in water
In clear open waters, visible light is
absorbed at the longest wavelengths first.
Thus, red, orange, and yellow
wavelengths are absorbed at higher water
depths, and blue and violet wavelengths
reach the deepest in the water column.
Because the blue and violet wavelengths
are absorbed last compared to the other
wavelengths, open ocean waters appear
deep-blue to the eye.
1
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Attenuation (electromagnetic radiation) - Light attenuation in water
1
In near-shore (coastal) waters, sea water
contains more phytoplankton than the very
clear central ocean waters
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Attenuation (electromagnetic radiation) - Earthquake
The energy with which an earthquake
affects a location depends on the running
distance. The attenuation in the signal of
ground motion intensity plays an important
role in the assessment of possible strong
groundshaking. A seismic wave loses
energy as it propagates through the earth
(attenuation). This phenomenon is tied in
to the Dispersive mass transfer|dispersion
of the seismic energy with the distance.
1
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Attenuation (electromagnetic radiation) - Earthquake
1
* geometric dispersion caused by distribution
of the seismic energy to greater volumes
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Attenuation (electromagnetic radiation) - Electromagnetic
1
Attenuation decreases the intensity of
electromagnetic radiation due to
absorption (electromagnetic
radiation)|absorption or scattering of
photons. Attenuation does not include
the decrease in intensity due to
inverse-square law geometric
spreading. Therefore, calculation of
the total change in intensity involves
both the inverse-square law and an
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Attenuation (electromagnetic radiation) - Electromagnetic
1
The primary causes of attenuation in
matter are the photoelectric effect,
compton scattering, and, for photon
energies of above 1.022 MeV, pair
production.
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Attenuation (electromagnetic radiation) - Radiography
1
See Attenuation coefficient.
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Oncolytic virus - Attenuation
1
Attenuation involves deleting viral genes,
or gene regions, to eliminate viral
functions that are expendable in tumour
cells, but not in normal cells, thus making
the virus safer and more tumour-specific
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Oncolytic virus - Attenuation
The enzymes thymidine kinase and
ribonucleotide reductase in cells are
responsible for DNA replication|DNA
synthesis and are only expressed in cells
which are actively replicating. These
enzymes also exist in the genomes of certain
viruses (E.g. HSV, vaccinia) and allow viral
replication in G0 phase|quiescent(nonreplicating) cells, so if they are inactivated by
mutation the virus will only be able to
replicate in proliferating cells, such as cancer
cells.
1
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Fiber-optic communication - Attenuation
1
Other forms of attenuation are caused by
physical stresses to the fiber, microscopic
fluctuations in density, and imperfect
splicing techniques.
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Radiography - Theory of X-ray attenuation
1
X-ray photons used for medical purposes
are formed by an event involving an
electron, while gamma ray photons are
formed from an interaction with the
nucleus of an atom.Radiation Detection
and Measurement 3rd Edition,
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Radiography - Theory of X-ray attenuation
1
Glenn F. Knoll : Chapter 1, Page 1:
John Wiley Sons; 3rd Edition (26
January 21615461651: ISBN 0-47107338-5 In general, medical
radiography is done using X-rays
formed in an X-ray tube. Nuclear
medicine typically involves gamma
rays.
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Radiography - Theory of X-ray attenuation
1
The types of electromagnetic radiation
of most interest to radiography are Xray and gamma radiation. This radiation
is much more energy|energetic than the
more familiar types such as radio
waves and visible light. It is this
relatively high energy which makes
gamma rays useful in radiography but
potentially hazardous to living
organisms.
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Radiography - Theory of X-ray attenuation
1
The radiation is produced by X-ray tubes,
high energy X-ray equipment or natural
radioactive elements, such as radium and
radon, and artificially produced radioactive
isotopes of elements, such as
Cobalt#Isotopes|cobalt-60 and
Iridium#Isotopes|iridium-192
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Radiography - Theory of X-ray attenuation
1
Gamma rays are
indirectly ionizing
radiation
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Radiography - Theory of X-ray attenuation
1
For the range of energies commonly
used in radiography, the interaction
between gamma rays and electrons
occurs in two ways
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Radiography - Theory of X-ray attenuation
1
In both of these effects the emergent
electrons lose their kinetic energy by
ionizing surrounding atoms. The
density of ions so generated is a
measure of the energy delivered to the
material by the gamma rays.
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Radiography - Theory of X-ray attenuation
The most common means of
measuring the variations in a beam of
radiation is by observing its effect on
a photographic film. This effect is the
same as that of light, and the more
intense the radiation is, the more it
darkens, or Exposure
(photography)|exposes, the film.
Other methods are in use, such as the
ionizing effect measured
1
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Weather radar - Attenuation
Microwaves used in weather radars
can be absorbed by rain, depending
on the wavelength used. For 10 cm
radars, this attenuation is negligible.
That is the reason why countries with
high water content storms are using
10cm wavelength, for example the US
NEXRAD. The cost of a larger antenna,
klystron and other related equipment
is offset by this benefit.
1
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Weather radar - Attenuation
1
For a 5cm radar, absorption becomes
important in heavy rain and this
attenuation leads to underestimation of
echoes in and beyond a strong
thunderstorm
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Weather radar - Attenuation
Shorter wavelengths are even more
attenuated and are only useful on short
range radar. Many television stations in
the United States have 3cm radars to
cover their audience area. Knowing their
limitations and using them with the local
NEXRAD can supplement the data
available to a meteorologist.
1
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Transparency (optics) - Mechanisms of attenuation
1
Light leakage due to bending, splices,
connectors, or other outside forces are
other factors resulting in attenuation.
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Contrast media - X-ray attenuation
1
Iodine and barium are the most common
types of contrast medium for enhancing xray-based imaging methods
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Compliance (physiology) - Natural factors of attenuation of the reduction on
arterial compliance
A study concluded that arterial
compliance, which diminishes with
menopause, was significantly
improved with red clover isoflavones
1
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Compliance (physiology) - Natural factors of attenuation of the reduction on arterial
compliance
Another study concluded that one
important measure of arterial health,
systemic arterial compliance, was
significantly improved in perimenopausal
and menopausal women taking soy
isoflavones to about the same extent as is
achieved with conventional hormone
replacement therapy.
1
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Attenuation coefficient
1
:For attenuation coefficient as it applies to
electromagnetic theory and
telecommunications see Attenuation
constant|propagation constant. For the
mass attenuation coefficient, see the
article mass attenuation coefficient.
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Attenuation coefficient
1
Attenuation coefficient is
measured using units of
reciprocal length.
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Attenuation coefficient
1
The attenuation coefficient is also called
'linear attenuation coefficient', 'pencil
beam|narrow beam attenuation
coefficient'. Although all four terms are
often used interchangeably, they can
occasionally have a subtle distinction, as
explained #Attenuation versus
absorption|below.
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Attenuation coefficient - Overview
1
The attenuation coefficient describes
the extent to which the intensity of an
energy beam is reduced as it passes
through a specific material. This
might be a beam of electromagnetic
radiation or sound.
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Attenuation coefficient - Overview
*It is used in the context of X-rays or
Gamma rays, where it is represented
using the symbol \mu, and measured in
cm−1.
1
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Attenuation coefficient - Overview
1
*It is used in the context of neutrons and
nuclear reactors, where it called
macroscopic cross section (although
actually it is not a section dimensionally
speaking) being represented using the
symbol \Sigma, and measured in m−1.
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Attenuation coefficient - Overview
*It is also used for modeling visible
spectrum|solar and infrared radiative
transfer in the atmosphere, albeit usually
denoted with another symbol (given the
standard use of \mu = \cos(\theta) for slant
paths).
1
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Attenuation coefficient - Overview
1
*In the case of ultrasound attenuation it
is usually denoted as \alpha and
measured in dB/cm/MHz.ISO 209981:2006 Measurement and
characterization of particles by
acoustic methodsDukhin, A.S. and
Goetz, P.J. Ultrasound for
characterizing colloids, Elsevier, 2002
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Attenuation coefficient - Overview
1
*The attenuation coefficient is widely
used in acoustics for characterizing
particle size distribution. A common
unit in this contexts is inverse metres,
and the most common symbol is the
Greek letter \alpha.
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Attenuation coefficient - Overview
1
*It is also used in acoustics for quantifying
how well a wall in a building absorbs
sound. Wallace Sabine was a pioneer of
this concept. A unit named in his honor is
the sabin: the absorption by a slab of
perfectly absorptive material (the same
amount of sound loss as if there were a 1square-metre window). Note that the sabin
is not a unit of attenuation coefficient;
rather, it is the unit of a related quantity.
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Attenuation coefficient - Overview
Generally, for electromagnetic
radiation, the higher the energy of the
incident photons and the less dense
the material in question, the lower the
corresponding linear attenuation
coefficient will be.
1
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Attenuation coefficient - Definitions and formulae
The measured intensity I of
transmitted through a layer of
material with thickness z is related to
the incident intensity I_0 according to
the inverse exponential power law that
is usually referred to as Beer–Lambert
law:
1
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Attenuation coefficient - Definitions and formulae
where z denotes the path length. The
attenuation coefficient is \alpha (z'). If it is
uniform, the situation is referred to as
linear attenuation and the law simplifies:
1
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Attenuation coefficient - Definitions and formulae
1
The Half Value Layer (HVL) signifies
the thickness of a material required to
reduce the intensity of the emergent
radiation to half its incident
magnitude. It is from these equations
that engineers decide how much
protection is needed for safety from
potentially harmful radiation. The
attenuation factor of a material is
obtained by the ratio of the emergent
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Attenuation coefficient - Definitions and formulae
The linear attenuation coefficient and
mass attenuation coefficient are related
such that the mass attenuation coefficient
is simply \alpha/\rho, where \rho is the
density in g/cm3. When this coefficient is
used in the Beer-Lambert law, then mass
thickness (defined as the mass per unit
area) replaces the product of length times
density.
1
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Attenuation coefficient - Definitions and formulae
1
The linear attenuation coefficient is also
inversely related to mean free path.
Moreover, it is very closely related to the
absorption cross section.
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Attenuation coefficient - Attenuation versus absorption
1
The terms attenuation coefficient and
absorption coefficient are generally
used interchangeably. However, in
certain situations they are
distinguished, as follows. Bohren,C. F.
and Huffman, D.R. Absorption and
Scattering of Light by Small Particles,
Wiley, (1983), isbn= 0-471-29340-7
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Attenuation coefficient - Attenuation versus absorption
When a narrow (Collimated
light|collimated) beam of light passes
through a substance, the beam will lose
intensity due to two processes: The light
can be absorbed by the substance, or the
light can be scattering|scattered (i.e., the
photons can change direction) by the
substance
1
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Attenuation coefficient - Attenuation versus absorption
1
In this context, the absorption coefficient
measures how quickly the beam would
lose intensity due to the absorption alone,
while attenuation coefficient measures the
total loss of narrow-beam intensity,
including scattering as well. Narrow-beam
attenuation coefficient always
unambiguously refers to the latter. The
attenuation coefficient is always larger
than the absorption coefficient, although
they are equal in the idealized case of no
scattering.
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Fibre optic - Mechanisms of attenuation
Empirical research has shown that
attenuation in optical fiber is caused
primarily by both scattering and absorption
(electromagnetic radiation)|absorption
1
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Stokes' law (sound attenuation)
1
'Stokes law of sound attenuation' is a
formula for the attenuation of sound in
a Newtonian fluid, such as water or
air, due to the fluid's viscosity. It
states that the amplitude of a plane
wave decreases exponential
decay|exponentially with distance
traveled, at a rate \alpha given by
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Stokes' law (sound attenuation)
where \eta is the dynamic
viscosity|dynamic viscosity coefficient
of the fluid, \omega is the sound's
frequency, \rho is the fluid density, and
V is the sound speed|speed of sound in
the medium:Stokes, G.G. On the
theories of the internal friction in fluids
in motion, and of the equilibrium and
motion of elastic solids, Transaction of
the Cambridge Philosophical Society,
1
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Stokes' law (sound attenuation)
The law and its derivation were
published in 1845 by physicist George
Gabriel Stokes|G. G. Stokes, who also
developed the well-known Stokes' law
for the friction force in fluid motion.
1
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Stokes' law (sound attenuation) - Interpretation
1
Stokes' law applies to sound propagation
in an isotropic and homogeneous
Newtonian medium. Consider a plane
sinusoidal pressure wave that has
amplitude A_0 at some point. After
traveling a distance d from that point, its
amplitude A(d) will be
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Stokes' law (sound attenuation) - Interpretation
1
In the International System of Units (SI), it
is expressed in neper per metre|meter or
simply Multiplicative inverse|reciprocal of
meter (\mathrm^). That is, if \alpha = 1
\mathrm^, the wave's amplitude decreases
by a factor of 1/e for each meter traveled.
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Stokes' law (sound attenuation) - Importance of volume viscosity
1
The law is amended to include a contribution by
the volume viscosity \eta^\mathrm:
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Stokes' law (sound attenuation) - Importance of volume viscosity
1
The volume viscosity coefficient is
relevant when the fluid's
compressibility cannot be ignored,
such as in the case of ultrasound in
water.Happel, J
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Stokes' law (sound attenuation) - Modification for very high frequencies
Stokes's law is actually an asymptotic
approximation for low frequencies of a more
general formula:
1
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Stokes' law (sound attenuation) - Modification for very high frequencies
1
where the relaxation
time \tau is given by:
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Stokes' law (sound attenuation) - Modification for very high frequencies
1
The relaxation time is about 10^ \mathrm
(one picosecond), corresponding to a
frequency of about 1000 GHz. Thus
Stokes' law is adequate for most practical
situations.
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Attenuation to crosstalk ratio
1
In order for a signal to be received with an
acceptable bit error rate, the attenuation
and the crosstalk must both be minimized
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Attenuation to crosstalk ratio
Positive ACR calculations mean that
transmitted signal strength is stronger
than that of near-end
crosstalk.[http://inetco.com.vn/list.aspx
?cat=014], De-Mystifying Cabling
Specifications - Important Definitions
1
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RG-6 - Attenuation/signal loss
1
Cables attenuate the signal proportional
with the length. Attenuation of higher
frequency signals is greater than for
frequencies down to about 7 MHz. Below
7 MHz the loss of RG-6 coaxial cables
with a solid copper center conductor
continues to decrease; however, the loss
of RG-6 with a copper clad steel center
conductor increases below 7 MHz
because of skin effect.
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Acoustic attenuation
1
Acoustic attenuation in a lossy medium
plays an important role in many scientific
researches and engineering fields, such
as medical ultrasonography, vibration and
noise reduction.
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
Many experimental and field
measurements show that the acoustic
attenuation coefficient of a wide range
of Viscoelasticity|viscoelastic
materials, such as soft tissue,
polymers, soil and porous rock, can
be expressed as the following power
law with respect to frequency:Szabo T
1
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
1
S., 1986, “Frequency dependence of
ultrasound attenuation and
backscatter in breast tissue,”
Ultrasound Med
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
695-703, DOI:
10.1016/j.ultrasmedbio.2013.09.033
[http://arxiv.org/abs/1306.6507 Link to eprint] for a recent paper which
compares fractional wave equations
which model power-law attenuation
1
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
The phenomenon of attenuation
obeying a frequency power-law may
be described using a causal wave
equation, derived from a fractional
constitutive equation between stress
and strain. This wave equation
incorporates fractional time
derivatives:
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
1
See alsoS. Holm and S. P. Näsholm, A
causal and fractional all-frequency
wave equation for lossy media,
Journal of the Acoustical Society of
America, Volume 130, Issue 4, pp.
2195-2201 (October 2011) and the
references therein.
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
1
Holm, Linking multiple relaxation, powerlaw attenuation, and fractional wave
equations, Journal of the Acoustical
Society of America, Volume 130, Issue 5,
pp
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Acoustic attenuation - Power-law frequency-dependent acoustic attenuation
1
For frequency band-limited waves, Ref.S. P.
Näsholm: Model-based discrete relaxation
process representation of band-limited
power-law attenuation. J. Acoust. Soc. Am.
Vol. 133, Issue 3, pp. 1742-1750 (2013) DOI:
10.1121/1.4789001
[http://arxiv.org/abs/1301.5256 Link to e-print]
describes a model-based method to attain
causal power-law attenuation using a set of
discrete relaxation mechanisms within the
Nachman et al. framework.
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Attenuator (genetics) - Small-molecule-mediated attenuation (riboswitches)
1
Riboswitch sequences (in the mRNA
leader transcript) bind molecules
such as amino acids, nucleotides,
sugars, vitamins, metal ions and other
small ligands which cause a
conformational change in the mRNA.
Most of these attenuators are
inhibitory and are employed by genes
for biosynthetic enzymes or
transporters whose expression is
inversely related to the concentration
of their corresponding metabolites.
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Attenuator (genetics) - Protein-mediated attenuation
1
Protein-RNA interactions may prevent or
stabilize the formation of an anti-terminator
structure.
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Attenuator (genetics) - Ribosome-mediated attenuation
1
'In this situation RNA polymerase' is
dependent on (lagging) ribosome
activity; if the ribosome pauses due to
insufficient charged tRNA then the
anti-terminator structure is favoured.
The canonical attenuator example of
Attenuator (genetics)#Mechanism in
the trp operon|the trp operon uses
this mechanism in E. coli.
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Attenuator (genetics) - Other operons controlled by attenuation
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The discovery of this type of mechanism to
control the expression of genes in a
biosynthetic operon lead to its rediscovery
in a wide variety of such operons for which
repressors had never been discovered.
For example:
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Attenuator (genetics) - Attenuation in eukaryotes
Research conducted on microRNA
processing showed an evidence of
attenuation process in Eukaryotes. After
co-transcriptional endonucleolitical
cleavage by Drosha 5'- 3' exonuclease
XRN2 may terminate further transcription
by torpedo mechanism.
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Attenuation (disambiguation)
1
'Attenuation' is the gradual loss in intensity of
any kind of flux through a medium, including:
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Attenuation (disambiguation)
* Acoustic
attenuation, the loss
of sound energy in a
viscous medium
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Attenuation (disambiguation)
* Anelastic attenuation factor, a way to
describe attenuation of seismic energy in the
earth
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Attenuation (disambiguation)
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'Attenuation' may also refer to:
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Attenuation (disambiguation)
1
* Attenuation (brewing), the percent of
sugar converted to alcohol and carbon
dioxide by the yeast in brewing
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Attenuation (disambiguation)
1
* Attenuation coefficient, a basic quantity
used in calculations of the penetration of
materials by quantum particles or other
energy beams
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Attenuation (disambiguation)
1
* Mass attenuation coefficient, a
measurement of how strongly a
chemical species or substance
absorbs or scatters light at a given
wavelength, per unit mass
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Attenuation (disambiguation)
1
* Regression dilution, a cause of
statistical bias
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Attenuation (disambiguation)
1
* The process of producing an attenuated vaccine
by reducing the virulence of a pathogen
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Attenuation (disambiguation)
1
* Attenuation constant, the
real part of the propagation
constant
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Attenuation (disambiguation)
1
* Attenuator (genetics), form
of regulation in prokaryotic
cells.
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Projectional radiography - X-ray attenuation
Conversely, areas on the image
receptor that receive the least
radiation (portions of the remnant
beam experience the most
attenuation) will be less exposed and
will be processed as being lighter
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Attenuation length
In physics, the 'attenuation length' or
'absorption length' is the distance \lambda
into a material when the probability has
dropped to 1/e that a Elementary
particle|particle has not been Absorption
(electromagnetic radiation)|absorbed.
Alternatively, if there is a beam of particles
incident on the material, the attenuation
length is the distance where the intensity
(physics)|intensity of the beam has dropped
to 1/e, or about 63% of the particles have
been stopped.
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Attenuation length
1
Mathematically, the probability of finding a
particle at depth x into the material is
calculated by Beer-Lambert law:
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Doppler weather radar - Attenuation
Microwaves used in weather radars
can be absorbed by rain, depending
on the wavelength used. For 10cm
radars, this attenuation is negligible.
That is the reason why countries with
high water content storms are using
10cm wavelength, for example the US
NEXRAD. The cost of a larger antenna,
klystron and other related equipment
is offset by this benefit.
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Laser beam profiler - Attenuation techniques
Since CCD sensors are highly
sensitive, attenuation is almost always
needed for proper beam profiling. For
example, 40 dB (neutral density|ND 4
or 10−4) of attenuation is typical for a
milliwatt HeNe laser. Proper
attenuation has the following
properties:
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Laser beam profiler - Attenuation techniques
1
* It does not result in multiple reflections leaving a
ghost image on the CCD sensor
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Laser beam profiler - Attenuation techniques
1
* It does not result in interference fringes
due to reflections between parallel
surfaces or diffraction by defects
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Laser beam profiler - Attenuation techniques
1
* It does not distort the wavefront and will
be an optical element with sufficient optical
flatness (less than one tenth of a
wavelength) and homogeneity
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Laser beam profiler - Attenuation techniques
1
* It can handle the required optical
power
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Laser beam profiler - Attenuation techniques
For laser beam profiling with CCD
sensors, typically two types of
attenuators are used: neutral density
filters, and wedges or thick optical
flats.
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Pure tone audiometry - Cross hearing and interaural attenuation
1
When sound is applied to one ear the
contralateral cochlea can also be
stimulated to varying degrees, via
vibrations through the bone of the skull
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Pure tone audiometry - Cross hearing and interaural attenuation
1
A reduction or loss of energy occurs
with cross hearing, which is referred to
as interaural attenuation (IA) or
transcranial transmission loss. IA
varies with transducer type. It varies
from 40 dB to 80 dB with supra-aural
headphones. However, with insert
earphones it is in the region of 55 dB.
The use of insert earphones reduces
the need for masking, due to the
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Pure tone audiometry - Cross hearing and interaural attenuation
1
Air conduction results in isolation, give little
information regarding the type of hearing loss
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Mass attenuation coefficient
1
The 'mass attenuation coefficient' is a
measurement of how strongly a
chemical species or substance
absorbance|absorbs or
scattering|scatters light at a given
wavelength, per unit mass. In addition
to visible light, mass attenuation
coefficients can be defined for other
electromagnetic radiation (such as Xrays), sound, or any other beam that
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Mass attenuation coefficient
The mass attenuation coefficient is
also called 'mass absorption
coefficient' or 'mass extinction
coefficient'. Although all three terms
are usually used interchangeably, they
can occasionally have a subtle
distinction, as explained #Attenuation
versus absorption|below.
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Mass attenuation coefficient
1
The mass extinction coefficient should not
be confused with the different definition of
index of refraction|extinction coefficient
used more commonly in physics, namely
the imaginary part of the complex index of
refraction (which is unitless). In fact, they
have a straightforward but nontrivial
relationship; see Mathematical
descriptions of opacity.
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Mass attenuation coefficient - Defining equations
The defining equation for the mass
attenuation coefficient is essentially a
different way to write the Beer-Lambert
law. The Beer-Lambert law is normally
written
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Mass attenuation coefficient - Defining equations
:I is the intensity of
the beam at distance
\ell into the
substance,
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Mass attenuation coefficient - Defining equations
:e is e (mathematical
constant)|Euler's number, about
2.718,
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Mass attenuation coefficient - Defining equations
1
:\mu is the attenuation coefficient.
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Mass attenuation coefficient - Defining equations
When discussing the mass
attenuation coefficient, this equation
is rewritten
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Mass attenuation coefficient - Defining equations
1
:\rho is the density, (\mu/\rho) is the mass
attenuation coefficient and \rho \ell is the
area density known also as mass
thickness.
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Mass attenuation coefficient - Defining equations
1
In accordance with the above, the mass
attenuation coefficient is equal to the
attenuation coefficient divided by the
density.
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Mass attenuation coefficient - In solutions
In chemistry, mass attenuation
coefficients are often used for a
chemical species dissolved in a
solution. In that case, the mass
attenuation coefficient is defined by
the same equation, except that the
density is the density of only that one
chemical species, and the attenuation
is the attenuation due to only that one
chemical species. The actual
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Mass attenuation coefficient - In solutions
where each term in the sum is the
mass attenuation coefficient and
density of a different component of the
solution (the solvent must also be
included). This is a convenient
concept because the mass attenuation
coefficient of a species is
approximately independent of its
concentration (as long as BeerLambert law#Prerequisites|certain
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Mass attenuation coefficient - In solutions
1
A closely related concept is molar absorptivity. They
are quantitatively related by:
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Mass attenuation coefficient - In solutions
:(Mass attenuation
coefficient)×(Molar mass) =
(Molar absorptivity).
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Mass attenuation coefficient - Units
The attenuation coefficient has units of
inverse-length, while density has units of
mass per volume. Since the mass
attenuation coefficient is the ratio of these
two, we find that it has units of (lengthsquared) per mass. The SI unit is m2kg-1.
Other common units include cm2g-1 (the
most common unit for X-ray mass
attenuation coefficients) and mL×g-1cm-1
(sometimes used in solution chemistry).
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Mass attenuation coefficient - Mass attenuation coefficients for X-rays
Tables of photon 'mass attenuation
coefficients' are essential in
radiological physics, radiography (for
medical and security purposes),
dosimetry, diffraction, interferometry,
crystallography and other branches of
physics. The photons can be in form of
x-ray, gamma-ray, and
bremsstrahlung.
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Mass attenuation coefficient - Mass attenuation coefficients for X-rays
The values of mass attenuation
coefficients are dependent upon the
absorption (electromagnetic
radiation)|absorption and scattering of the
incident ray|incident radiation caused by
several different mechanisms such as:
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Mass attenuation coefficient - Mass attenuation coefficients for X-rays
1
*Pair production - electron-positron production in the
fields of the nucleus and atomic electrons
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Mass attenuation coefficient - Mass attenuation coefficients for X-rays
1
The actual values have been thoroughly
examined and are available to the general
public through three databases run by
National Institute of Standards and
Technology (NIST):
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Mass attenuation coefficient - Calculating the composition of a solution
1
If several known chemicals are dissolved
in a single solution, the concentrations of
each can be calculated using a light
absorption analysis. First, the mass
attenuation coefficients of each individual
solute or solvent, ideally across a broad
spectrum of wavelengths, must be
measured or looked up. Second, the
attenuation coefficient of the actual
solution must be measured. Finally, using
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Mass attenuation coefficient - Calculating the composition of a solution
the spectrum can be fitted using
\rho_1,\rho_2,\ldots as adjustable
parameters. (Remember, \mu and each
(\mu/\rho)_i are functions of wavelength.)
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Mass attenuation coefficient - Calculating the composition of a solution
If there are N solutes or solvents, this
procedure requires at least N measured
wavelengths to create a solvable system
of simultaneous equations, although using
more wavelengths gives more reliable
data.
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Mass attenuation coefficient - Attenuation versus absorption
The terms mass attenuation
coefficient, mass absorption
coefficient, and mass extinction
coefficient are almost always used
interchangeably. However, in certain
situations they are distinguished, as
follows.
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Mass attenuation coefficient - Attenuation versus absorption
1
When a narrow (collimated) beam of light
passes through a substance, the beam will
lose intensity due to two processes: The
light can be absorbed by the substance, or
the light can be scattering|scattered (i.e.,
the photons can change direction) by the
substance
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Mass attenuation coefficient - Attenuation versus absorption
In this context, the mass absorption
coefficient measures how quickly the
beam would lose intensity due to the
absorption alone, while mass attenuation
coefficient measures the total loss of
narrow-beam intensity, including scattering
as well. The mass extinction coefficient
can be either.
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