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Sergio De NicolaRenato Fedele Margarita A. Man'koVladimir I. Man'ko 《Physics letters. A》2011,375(6):961-965
A novel approach, based on Fresnel tomography, to determine the entropy of two-dimensional optical Laguerre-Gaussian beams is presented and discussed. Numerical evaluations of the entropy distribution in the phase space associated with Laguerre-Gauss modes are presented. It is shown that the concept of Fresnel entropy provides a general criterion for studying and characterizing the vorticity of Laguerre-Gauss modes. 相似文献
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Regioselectivity of nucleophilic aromatic photosubstitution has been shown experimentally to depend upon activation energies of the competing transition states. Computational means of determining relative activation energies were sought, therefore, in order to predict regioselectivity. Optimization of the three triplet transition states of 2-chloro-4-nitroanisole with hydroxide ion gave energies of insufficient accuracy to predict regioselectivity. Computed enthalpy changes from the first triplet transition state to the triplet σ-complexes correlated precisely with the experimental activation energies. This exemplifies the Bell–Evans–Polanyi Principle, and it provides an accurate means of assessing regioselectivity. 相似文献
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设计合成了5种新型正电子发射断层显像剂[O-(2-[18F]氟乙基)-L-酪氨酸的前体化合物:N-叔丁氧羰基-O-(2-甲磺酰/对硝基苯磺酰)-氧乙基-L-酪氨酸甲酯(9a,11a)和N-叔丁氧羰基-O-(2-甲磺酰/对甲苯磺酰/对硝基苯磺酰)-氧乙基-L-酪氨酸叔丁酯(9b,10b,11b)。 这些化合物以L-酪氨酸为原料,先与甲醇发生酯化反应或与乙酸叔丁酯进行酯交换,再用叔丁氧羰基保护氨基,最后以碳酸钾为碱、18-冠-6为相转移催化剂与乙二醇的磺酸酯在丙酮溶液中加热回流形成目标化合物,总收率为30%~67%。 相似文献
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建立了被动多轴差分吸收光谱层析系统,实现烟羽气体的时空浓度分布测量,分别采用传统的同步迭代重建算法(SIRT)和改进的SIRT对测量数据进行了重建分析,克服了一些实际测试中不能获
取大量投影数据或投影分布不均匀、存在噪声的问题,精确地重建出大气痕量气体的二维空间分布.在不同的模型及评价指标下,通过数值模拟对两种重建算法的效果进行比较,改变改进的SIRT算法中的松弛因子,在5500次的迭代过程中,指标d从0.435降到了0.044,指标r从0.376降到了0.044,改进的SIRT算法具有更好的重建效果.外场重建试验中成功重建了大气痕量气体的二维空间. 相似文献
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Fast parallel algorithm for three-dimensional distance-driven model in iterative computed tomography reconstruction 下载免费PDF全文
The projection matrix model is used to describe the physical relationship between reconstructed object and projection.Such a model has a strong influence on projection and backprojection,two vital operations in iterative computed tomographic reconstruction.The distance-driven model(DDM) is a state-of-the-art technology that simulates forward and back projections.This model has a low computational complexity and a relatively high spatial resolution;however,it includes only a few methods in a parallel operation with a matched model scheme.This study introduces a fast and parallelizable algorithm to improve the traditional DDM for computing the parallel projection and backprojection operations.Our proposed model has been implemented on a GPU(graphic processing unit) platform and has achieved satisfactory computational efficiency with no approximation.The runtime for the projection and backprojection operations with our model is approximately 4.5 s and 10.5 s per loop,respectively,with an image size of 256×256×256 and 360 projections with a size of 512×512.We compare several general algorithms that have been proposed for maximizing GPU efficiency by using the unmatched projection/backprojection models in a parallel computation.The imaging resolution is not sacrificed and remains accurate during computed tomographic reconstruction. 相似文献
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Based on the acoustic radiation theory of a dipole source,the influence of the transducer reception pattern is studied for magnetoacoustic tomography with magnetic induction(MAT-MI).Numerical studies are conducted to simulate acoustic pressures,waveforms,and reconstructed images with unidirectional,omnidirectional,and strong directional transducers.With the analyses of equivalent and projection sources,the influences of the model dimension and the layer effect are qualitatively analyzed to evaluate the performance of MAT-MI.Three-dimensional simulation studies show that the strong directional transducer with a large radius can reduce the influences of equivalent sources,projection sources,and the layer effect effectively,resulting in enhanced pressure and improved image contrast,which is beneficial for boundary pressure extraction in conductivity reconstruction.The reconstructed conductivity contrast images present the conductivity boundaries as stripes with different contrasts and polarities,representing the values and directions of the conductivity changes of the scanned layer.The favorable results provide solid evidence for transducer selection and suggest potential practical applications of MAT-MI in biomedical imaging. 相似文献
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Artur Czerwinski 《理论物理通讯》2021,73(8):85101
In this article, we introduce a framework for entanglement quantification of photon pairs represented by two-qubit Werner states. The measurement scheme is based on the symmetric informationally complete POVM. To make the framework realistic, we impose the Poisson noise on the measured two-photon coincidences. For various settings, numerical simulations were performed to evaluate the efficiency of the framework. 相似文献