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91.
Optimization of L‐shell X‐ray fluorescence detection of lead in bone phantoms using synchrotron radiation 下载免费PDF全文
Closely related toxicity and retention mechanisms of lead (Pb) in the human body involve the bone tissues where Pb can accumulate and reside on a time scale ranging from years to tens of years. In vivo measurements of bone Pb can, therefore, play an important role in a comprehensive health risk assessment of Pb exposure. In vivo L‐shell X‐ray fluorescence (LXRF) measurement of bone Pb was first demonstrated over 4 decades ago. Implementation of the method, however, encountered challenges associated with low sensitivity and calibration procedure. In this study, the LXRF measurement was optimized by varying the incident photon energy and the excitation‐detection geometry. The Canadian Light Source synchrotron radiation was used to compare 2 different excitation‐detection geometries of 90° and 135° using 3 different X‐ray photon energies: 15.8, 16.6, and 17.5 keV. These energies optimized excitation of the L3 subshell of Pb and simulated the most intense K‐shell emissions of zirconium, niobium, and molybdenum, respectively. Five rectangular plaster‐of‐Paris bone phantoms with Pb concentrations of 0, 7, 17, 26, and 34 μg/g, and one rectangular 3.1‐mm‐thick resin phantom mimicked the X‐ray attenuation properties of human bone and soft tissue, respectively. Optimal LXRF detection was obtained by the 15.8‐keV energy and the 90° and 135° geometries for the bare bone and the bone and soft tissue phantoms, respectively. 相似文献
92.
Zs. Podolyák G.F. Farrelly P.H. Regan A.B. Garnsworthy S.J. Steer M. Górska J. Benlliure E. Casarejos S. Pietri J. Gerl H.J. Wollersheim R. Kumar F. Molina A. Algora N. Alkhomashi G. Benzoni A. Blazhev P. Boutachkov A.M. Bruce L. Caceres I.J. Cullen A.M. Denis Bacelar P. Doornenbal M.E. Estevez Y. Fujita W. Gelletly H. Geissel H. Grawe J. Gr?bosz R. Hoischen I. Kojouharov S. Lalkovski Z. Liu K.H. Maier C. Mihai D. Mücher B. Rubio H. Schaffner A. Tamii S. Tashenov J.J. Valiente-Dobón P.M. Walker P.J. Woods 《Physics letters. [Part B]》2009
93.
Mihai Ciucu 《Discrete Mathematics》2007,307(15):1957-1960
The even Aztec diamond ADn is known to have precisely four times more spanning trees than the odd Aztec diamond ODn—this was conjectured by Stanley and first proved by Knuth. We present a short combinatorial proof of this fact in the case of odd n. Our proof works also for the more general case of odd-by-odd Aztec rectangles. 相似文献
94.
One describes, using a detailed analysis of Atiyah-Hirzebruch spectral sequence, the tuples of cohomology classes on a compact,
complex manifold, corresponding to the Chern classes of a complex vector bundle of stable rank. This classification becomes
more effective on generalized flag manifolds, where the Lie algebra formalism and concrete integrability conditions describe
in constructive terms the Chern classes of a vector bundle.
Since deceased. 相似文献
95.
Mihai Tibăr 《Israel Journal of Mathematics》2007,157(1):309-322
We study the vanishing neighbourhood of non-isolated singularities of functions on singular spaces by associating a general
linear function. We use the carrousel monodromy in order to show how to get a better control over the attaching of thimbles.
For one-dimensional singularities, we prove obstructions to integer (co)homology groups and to the eigenspaces of the monodromy
via monodromies of nearby sections. Our standpoint allows one to find, in certain cases, the structure of the Milnor fibre
up to the homotopy type. 相似文献
96.
José Seade Mihai Tibăr Alberto Verjovsky 《Bulletin of the Brazilian Mathematical Society》2005,36(2):275-283
Using a geometric approach, we determine the relations between the local Euler obstruction Euf of a holomorphic function f and several generalizations of the Milnor number for functions on singular spaces.
*This work was partially supported by CNRS-CONACYT (12409) Cooperation Program. The first and third named authors partially
supported by CONACYT grant G36357-E and DGPA (UNAM) grant IN 101 401. 相似文献
97.
In this paper we discuss the problem of verifying and computing optimal controls of systems whose dynamics is governed by
differential systems with a discontinuous right-hand side. In our work, we are motivated by optimal control of mechanical
systems with Coulomb friction, which exhibit such a right-hand side. Notwithstanding the impressive development of nonsmooth
and set-valued analysis, these systems have not been closely studied either computationally or analytically. We show that
even when the solution crosses and does not stay on the discontinuity, differentiating the results of a simulation gives gradients
that have errors of a size independent of the stepsize. This means that the strategy of “optimize the discretization” will
usually fail for problems of this kind. We approximate the discontinuous right-hand side for the differential equations or
inclusions by a smooth right-hand side. For these smoothed approximations, we show that the resulting gradients approach the
true gradients provided that the start and end points of the trajectory do not lie on the discontinuity and that Euler’s method
is used where the step size is “sufficiently small” in comparison with the smoothing parameter. Numerical results are presented
for a crude model of car racing that involves Coulomb friction and slip showing that this approach is practical and can handle
problems of moderate complexity. 相似文献
98.
Miles Lubin J. A. Julian Hall Cosmin G. Petra Mihai Anitescu 《Computational Optimization and Applications》2013,55(3):571-596
We present a parallelization of the revised simplex method for large extensive forms of two-stage stochastic linear programming (LP) problems. These problems have been considered too large to solve with the simplex method; instead, decomposition approaches based on Benders decomposition or, more recently, interior-point methods are generally used. However, these approaches do not provide optimal basic solutions, which allow for efficient hot-starts (e.g., in a branch-and-bound context) and can provide important sensitivity information. Our approach exploits the dual block-angular structure of these problems inside the linear algebra of the revised simplex method in a manner suitable for high-performance distributed-memory clusters or supercomputers. While this paper focuses on stochastic LPs, the work is applicable to all problems with a dual block-angular structure. Our implementation is competitive in serial with highly efficient sparsity-exploiting simplex codes and achieves significant relative speed-ups when run in parallel. Additionally, very large problems with hundreds of millions of variables have been successfully solved to optimality. This is the largest-scale parallel sparsity-exploiting revised simplex implementation that has been developed to date and the first truly distributed solver. It is built on novel analysis of the linear algebra for dual block-angular LP problems when solved by using the revised simplex method and a novel parallel scheme for applying product-form updates. 相似文献
99.
Mihai Todica Traian Stefan Diana Trandafir Simion Simon 《Central European Journal of Physics》2013,11(7):928-935
The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were investigated by ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signal appears only for irradiated samples and it is associated with the breaking of the polymeric chain, followed by local reorganization of the polymeric segments and the apparition of the unpaired electrons and free radicals. The intensity of the signal decreases with the concentration of TiO2, indicating a shielding effect of the dopand. That the modification of local order of the polymeric chains has been modified after irradiation is confirmed by XRD method. 相似文献
100.
A. Younes M. Younes H. Sayah M. Bilici A. Samuila L. Dascalescu 《Journal of Electrostatics》2013,71(1):84-91
Corona-electrostatic separation is a multi-variable process that has been thoroughly studied in connection with its various applications in the recycling industry. The aim of the present paper is to point out one parasitic phenomenon that adversely affects the efficiency of the separation: the sparks generated at the passage of conductive particles through the electric field zone. The experiments were carried out on a laboratory roll-type corona electrostatic separators, and the sparks were generated by introducing 16 calibrated copper pins in 40-g samples of granular insulating material (PVC; typical granule size: 1.5 mm) that were fed at a constant rate onto the surface of the grounded rotating roll electrode. The distribution of the PVC granules in the 14 boxes of the collector was altered by the occurrence of the spark discharges, as they were accompanied by the annealing of the electric field between the electrodes. The numerical simulation of insulating granules charging and movement under the action of the electric field enabled a better understanding of the interactions between the spark discharges and the other factors that influence their trajectories and affect the efficiency of the separation: roll-speed, particle size and ambient humidity. The particle dynamics equations were solved using an iterative scheme by using the electric field calculated in any point with the commercial software TRICOMP. The good agreement between the predictions made by these simulations and the experimental findings confirms the ability of the mathematical model to reflect the complexity of the physical phenomena. 相似文献