Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 57 for “"attenuation coefficient"”.
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Measurement of ultrasonic wave mode transition in unidirectional graphite/epoxy composites
… with theory. To show this mode transition, an attenuation study was performed. The attenuation coefficient, measured in units of reciprocal time, does not appear to depend on the wave vector orientation and the wave type (quasi-transverse and quasi-longitudinal waves) at 5 MHz frequency. But …
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Backscatter And Attenuation Properties Of Mammalian Brain Tissues
… brain tissues focusing on backscatter and attenuation. Orientation dependence and spatial averaging of data were analyzed using the same method resulting from insertion of tissue sample between a transducer and a reference reflector. Apparent Backscatter Transfer Function (ABTF) at 1 to 10 …
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Effects of high intensity focused ultrasound on the intervertebral disc
… to the nerve or muscle could be found. The attenuation coefficient in bovine annulus fibrosus was found to be in the range of 1.1 to 1.3 dB cm-1 MHz-1 and the absorption coefficient 0.4 to 0.7 dB cm-1 MHz-1, which is approximately half of the attenuation coefficient. This indicates that a …
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Effects of an External Field and Dissipation on Decoherence
… heat bath by calculating its contribution to the attenuation coefficient, which is a measure of decoherence in coordinate space and involves directly observable probability distributions. It is found that, while non-random external force does not result in decoherence, a random external force can …
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First limit from a surface run of a 10 liter Dark Matter Time Projection Chamber
… detector is used to measure the mean energy and attenuation coefficient of electrons propagating in CF4.
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Propagation of zero sound in liquid He3
… * As the temperature was increased, the sound attenuation increased, went through a max.imum, and then decreased. At low temperatures, the attenuation was proportional to T~,(2 but independent of frequency, and at higher temperatures it was proportional to W 2/T*2, where w is the angular …
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Elastic stretchable optical fibers
… of their light guiding properties. The fibers' attenuation coefficient was determined to be 0.021 ± 0.003 dB/mm, which is 2 orders of magnitude higher than for standard optical glass fibers. The high attenuation coefficient is likely due to scattering of light by air inclusions incorporated …
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Effect of myofibril length and tissue constituents on acoustic propagation properties of muscle
The ultrasonic speed and attenuation coefficient of three muscle samples were measured in-vitro as a function of temperature and frequency. The sarcomere length of each of these samples was also determined. The three muscle groups were bovine longissimus dorsi, psoas major and lobster extensor. …
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Measurement of optical properties of molten salts and metallic compounds for advanced solar and nuclear systems
… concentrated solar thermal system. The attenuation coefficient of light in a binary nitrate salt mixture (KNO 3-NaNO3 40-60 wt%) was measured over the wavelength range 833-2500 nm and the temperature range 300-400°C. This salt is the leading candidate for the first generation of a …
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Exploring light transmission through ice-snow cover and water in lakes
… used to estimate water clarity and irradiance attenuation in the water column is the attenuation coefficient, which quantifies the exponential decrease of irradiance with depth. Although the attenuation coefficient can be determined from irradiance profiles measured with radiometers, their high …
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Development of a method for automating effective patient diameter estimation for digital radiography
… the image receptor. Values of effective linear attenuation coefficient are estimated from Monte Carlo simulations. Monte Carlo simulations were created for two x-ray systems. The simulations were optimised and thoroughly validated to ensure that any result obtained is accurate. The validation …
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Ultrasonic Characterization of Human Coronary Arteries and Atherosclerotic Plaques
… atherosclerotic plaque is quite substantial. The attenuation coefficient of coronary artery tissues and atherosclerotic plaques was measured across the wide bandwidth 22 to 105 MHz. It was shown that, in the axial orientation, the attenuation coefficient is lower in the media layer than in the …
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Topics in transport phenomena near the critical point
… and Swift for the estimation of, transport coefficients near the critical point is applied to the calculation of the electrical conductivity near the superconducting transition and to the calculation of the attenuation coefficient for longitudinal sound waves near the magnetic transition. …
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Using X-ray Imaging Techniques to Determine Density of Foods
… for evaluation of food density. The x-ray attenuation through materials is dependent on the chemical composition and is proportional to density as described by the Beer-Lambert's law. This relationship forms the hypothesis of this study. The proposed experiments were conducted to verify and …
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Using wave attenuation techniques for monitoring of stress levels
… for investigating stress in rocks is the attenuation coefficient. Attenuation has been observed to be more sensitive to stress changes than wave velocity; however, the measurement of attenuation is more difficult than that of wave velocity. In this study, the mechanism of sonic attenuation …
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An Experimental re-evaluation of Photon Mass Attenuation Coefficients
Photon mass attenuation coefficients are indispensable input parameters for use in several disciplines. They are of value for medical diagnostics, radiation therapy, material science, etc. Currently, photon mass attenuation coefficients derived from model calculations are widely used. This project …
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Oblique-incidence fiber-optic reflectometry for measuring absorption and scattering in turbid media
… measuring the absorption and reduced scattering coefficients, $\mu\sb{a}$ and $\mu\sb{s}\sp\prime ,$ of semi-infinite turbid media. Obliquely incident light produces a spatial distribution of diffuse reflectance that is not centered about the point of light entry. The shift in the center of …
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Statistical correlation as a tool in propagation studies
… correlating dB values of the satellite signal attenuation and polarization isolation with dBZ values of radar backscatter from each of 128 range gates. In it, Pearson product moment correlation coefficients are calculated for attenuation and backscatter and for isolation and backscatter. When …
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Optical and chemical properties of molten salt mixtures for use in high temperature power systems
… was the objective of this Thesis. The light attenuation coefficient of two reagent grade molten salt mixtures (KNO 3 - NaNO 3, 40- 60 wt% and NaCI-KCI, 50-50 wt%) was measured and characterized over the wavelength range 400nm- 800nm and for different operating temperature ranges: 250*C-5000C …
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Modeling and characterization of a monoenergetic gamma-ray imaging system for active interrogation applications
… acquisition techniques, based on differences in attenuation coefficient as a function of energy, are developed and characterized for material-specific radiography. It is found that the monoenergetic sources offer better material specificity and higher contrast. Finally, tomographic image …
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