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An assessment of the factors involved in effective attenuation coefficient of the compensator material for the treatment with 6MV photons using An assessment of the factors involved in effective attenuation coefficient of the compensator material for the treatment with 6MV photons using intensity modulated radiation therapy method  [cached]
Abbas Haghparast,Bijan Hashemi,Mohammad Taghi Eivazi
Koomesh , 2011,
Abstract: Introduction : One of the intensity modulated radiation therapy (IMRT) methods is based on using compensators. The most important factor in designing a compensator is the accurate calculation of its thickness to achieve the intensity modulation of interest. To achieve that, the exact attenuation coefficient of compensator materials must be calculated. However, there are several parameters that are effective in calculating the attenuation coefficient of compensator materials . In this research, the effects of dosimeter and phantom type as well as irradiation dose and measurement depth in the calculation of this compensator characteristic were assessed. Materials and Methods : Using two types of dosimeters (RK & FC65G) and phantoms (RFA300plus & SP34), the effects of radiation dose and measured depth on the estimation of the effective attenuation coefficient was investigated for a 6MV linear accelerator. The value of applied radiation dose was 100, 200, 300 and 400 cGy, and the measured depths were 2, 5, 10, 15 and 20 cm. The measurements were carried out at the reference field size (10×10 cm2) and for a thickness of 1 cm of the compensator. Results: The results indicated that radiation dose has no significant effect in calculating the effective attenuation coefficient of compensator materials. However, altering measured depth from 2 to 20 cm resulted in a change of more than 5% in the calculations. In addition, the type of the dosimeter and phantom used in this study had no significant effect on the calculations. Conclusion: Based on these findings, it is recommended that for more accurate estimation of the effective attenuation coefficient of a compensator material, it is necessary to measure the attenuation coefficient at different depths of the treatment field.
Effective x-ray attenuation coefficient measurements from two full field digital mammography systems for data calibration applications
John J Heine, Jerry A Thomas
BioMedical Engineering OnLine , 2008, DOI: 10.1186/1475-925x-7-13
Abstract: Logarithmic response calibration curves and effective x-ray attenuation coefficients were measured from two full field digital mammography (FFDM) systems with breast tissue equivalent phantom imaging and compared. Normalization methods were studied to assess the possibility of reducing the amount of calibration data collection. The percent glandular calibration map functional form was investigated. Spatial variations in the calibration data were used to assess the uncertainty in the calibration application by applying error propagation analyses.Logarithmic response curves are well approximated as linear. Measured effective x-ray attenuation coefficients are characteristic quantities independent of the imaging system and are in agreement with those predicted numerically. Calibration data collection can be reduced by applying a simple normalization technique. The calibration map is well approximated as linear. Intrasystem calibration variation was on the order of four percent, which was approximately half of the intersystem variation.FFDM systems provide a quantitative output, and the calibration quantities presented here may be used for data acquired on similar FFDM systems.Early detection is a key element in reducing breast cancer mortality [1]. Mammography screening is an essential surveillance component for early detection [2]. Similarly, there is interest in developing total cancer care methods in clinical practice so that disease screening and treatment can be tailored to the patient [3]. The development of accurate breast cancer risk models may play an important role in designing risk based cancer control strategies. Because breast density is a significant breast cancer risk factor [4], it may be useful to include it in the clinical setting for risk assessment. The Gail breast cancer risk model is used for intervention studies and counseling [5] but does not include breast density beyond research purposes. There is a critical need to incorporate all available i
Entrainment coefficient and effective mass for conduction neutrons in neutron star crust: simple microscopic models  [PDF]
Brandon Carter,Nicolas Chamel,Pawel Haensel
Physics , 2004, DOI: 10.1016/j.nuclphysa.2004.11.006
Abstract: In the inner crust of a neutron star, at densities above the ``drip'' threshold, unbound ``conduction'' neutrons can move freely past through the ionic lattice formed by the nuclei. The relative current density $n^i= n \bar v^i$ of such conduction neutrons will be related to the corresponding mean particle momentum $p_i$ by a proportionality relation of the form $n^i= {\cal K}p^i$ in terms of a physically well defined mobility coefficient $\cal K$ whose value in this context has not been calculated before. Using methods from ordinary solid state and nuclear physics, a simple quantum mechanical treatment based on the independent particle approximation, is used here to formulate $\cal K$ as the phase space integral of the relevant group velocity over the neutron Fermi surface. The result can be described as an ``entrainment'' that changes the ordinary neutron mass m to a macroscopic effective mass per neutron that will be given -- subject to adoption of a convention specifying the precise number density n of the neutrons that are considered to be ``free'' -- by $m_\star=n/{\cal K}$. The numerical evaluation of the mobility coefficient is carried out for nuclear configurations of the ``lasagna'' and ``spaghetti'' type that may be relevant at the base of the crust. Extrapolation to the middle layers of the inner crust leads to the unexpected prediction that $m_\star$ will become very large compared with m.
Influences of effective gain length and attenuation coefficient on output energy of stimulated Brillouin scattering in water
水的衰减系数及有效增益长度对受激布里渊散射输出能量的影响

He Xing-Dao,Xia Jian,Shi Jiu-Lin,Liu Juan,Li Shu-Jing,Liu Jian-An,Fang Wei,
何兴道
,夏健,史久林,刘娟,李淑静,刘建安,方伟

物理学报 , 2011,
Abstract: In this paper, the effects of attenuation coefficient and effective gain length on output energy of stimulated Brillouin scattering (SBS) in water are investigated theoretically and experimentally. The experimental results indicate that the smaller the attenuation coefficient, the higher the output energy of SBS is. When the energy of incident laser is very high and the effective gain length is long enough, the SBS may obtain high enough energy thereby reach an extremely strong peak power due to the pulse compression; once it exceeds the threshold of SRS or second-order SBS, the SBS is able to excite an SRS or a second-order SBS as a new source and consumes a part of its own energy. Therefore, the longer the effective gain length, the lower the output energy of SBS is.
On the attenuation coefficient of monomode periodic waveguides  [PDF]
Alexandre Baron,Simon Mazoyer,Wojciech Smigaj,Philippe Lalanne
Physics , 2011, DOI: 10.1103/PhysRevLett.107.153901
Abstract: It is widely accepted that, on ensemble average, the transmission T of guided modes decays exponentially with the waveguide length L due to small imperfections, leading to the important figure of merit defined as the attenuation-rate coefficient alpha = -/L. In this letter, we evidence that the exponential-damping law is not valid in general for periodic monomode waveguides, especially as the group velocity decreases. This result that contradicts common beliefs and experimental practices aiming at measuring alpha is supported by a theoretical study of light transport in the limit of very small imperfections, and by numerical results obtained for two waveguide geometries that offer contrasted damping behaviours.
Effect of atmospheric environment on the attenuation coefficient of light in water  [PDF]
Juan Liu,Jiulin Shi,Yijun Tang,Kaixing Zhu,Yuan Ge,Xuegang Chen,Xingdao He,Dahe Liu
Physics , 2014,
Abstract: The attenuation coefficient of 532 nm light in water under different atmospheric conditions was investigated. Measurements were made over a two-year period at the same location and show that the attenuation coefficient is significantly influenced by the atmospheric environment. It is lowest when the atmospheric pressure is high and temperature is low, and is highest when the atmospheric pressure is low and temperature is high. The maximum attenuation coefficient of pure water in these studies was about three times the minimum value. The mechanism of the phenomena is discussed. These results are also important in underwater acoustics.
Simple parameterization of nuclear attenuation data
Akopov, N.;Grigoryan, L.;Akopov, Z.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevC.76.065203
Abstract: Based on the nuclear attenuation data obtained by the HERMES experiment on nitrogen and krypton nuclei, it is shown that the nuclear attenuation $R_M^{h}$ can be parametrised in a form of a linear polynomial $P_1=a_{11}$ + $\tau a_{12}$, where $\tau$ is the formation time, which depends on the energy of the virtual photon $\nu$ and fraction of that energy $z$ carried by the final hadron. Three widely known parameterizations for $\tau$ were used for the performed fit. The fit parameters $a_{11}$ and $a_{12}$ do not depend on $\nu$ and $z$.
Improving Rain Attenuation Estimation: Modelling of Effective Path Length Using Ku-Band Measurements at a Tropical Location
Arpita Adhikari;Saurabh Das;Aniruddha Bhattacharya;Animesh Maitra
PIER B , 2011, DOI: 10.2528/PIERB11072503
Abstract: Rain attenuation is an important aspect of signal propagation above 10 GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modified by incorporating an effective slant path model. The effective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007-2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.
Effective radiation attenuation calibration for breast density: compression thickness influences and correction
John J Heine, Ke Cao, Jerry A Thomas
BioMedical Engineering OnLine , 2010, DOI: 10.1186/1475-925x-9-73
Abstract: A thickness correction was developed and evaluated using a fully specified two-component surrogate breast model. A previously developed calibration approach based on effective radiation attenuation coefficient measurements was used in the analysis. Water and oil were used to construct phantoms to replicate the deformable properties of the breast. Phantoms consisting of measured proportions of water and oil were used to estimate calibration errors without correction, evaluate the thickness correction, and investigate the reproducibility of the various calibration representations under compression thickness variations.The average thickness uncertainty due to compression paddle warp was characterized to within 0.5 mm. The relative calibration error was reduced to 7% from 48-68% with the correction. The normalized effective radiation attenuation coefficient (planar) representation was reproducible under intra-sample compression thickness variations compared with calibrated volume measures.Incorporating this thickness correction into the rigid breast tissue equivalent calibration method should improve the calibration accuracy of mammograms for risk assessments using the reproducible planar calibration measure.Breast density is a significant breast cancer risk factor [1-3]. When estimating breast density from mammograms, the breast is considered as a two-component model consisting of adipose and fibroglandular (abbreviated as glandular hereafter) tissue to varying degrees. One method of measuring breast density uses binary labeling resulting in areas of radiographically dense tissue (glandular tissue) or adipose (non-dense) tissue. Breast density is then estimated as the ratio of the radiographically dense area to the total breast area (dense + adipose) [4-6]. Binary labeling techniques have repeatedly produced a measure that correlates well with breast cancer [2] without considering inter-image acquisition technique differences.Recent work has focused on calibration to c
Simple characters and coefficient systems on the building  [PDF]
Paul Broussous,Peter Schneider
Mathematics , 2014,
Abstract: Let F be a non-archimedean local field and G be the group GL(N,F). Let \pi be a smooth complex representation of G lying in the Bernstein block B(\pi) of some simple type in the sense of Bushnell and Kutzko. Refining the approach of the second author and U. Stuhler, we canonically attach to \pi a subset X_\pi of the Bruhat-Tits building X of G, as well as a G-equivariant coefficient system C[\pi ] on X_\pi. Roughly speaking the coefficient system is obtained by taking isotypic components of \pi according to some representations constructed from the Bushnell and Kutzko type of \pi . We conjecture that when \pi has central character, the augmented chain complex associate to C[\pi ] is a projective resolution of \pi in the category B(\pi). Moreover we reduce this conjecture to a technical lemma of representation theoretic nature. We prove this lemma when \pi is an irreducible discrete series of G. We then attach to any irreducible discrete series \pi of G an explicit pseudo-coefficient f_\pi and obtain a Lefschetz type formula for the value of the Harish-Chandra character of \pi at a regular elliptic element. In contrast to that obtained by U. Stuhler and the second author, this formula allows explicit character value computations.
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