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51.
52.
Participating media with an inhomogeneous index of refraction make light follow curved paths. Simulating this in a global
illumination environment has usually been neglected due to the complexity of the calculations involved, sacrificing accurate
physical simulations for efficient visual results.
This paper aims to simulate non-linear media in a more reasonable time than previous works without losing physical correctness.
Accuracy is achieved by solving the Eikonal equation of geometrical optics, which describes the path followed by a light beam
that traverses a non-linear medium. This equation is used in the context of a photon mapping extension. 相似文献
53.
54.
JC López Pacios L Parra Muntaner MC Pi?eiro Fernández SC Gómez Cisneros E Sánchez Sánchez JA Rivas Escudero FJ Madrid García J García Alonso 《Canadian Metallurgical Quarterly》1998,51(4):331-333
The occurrence of secondary hypogonadism is a common finding in males who seek help with erectile dysfunction, although the relationship to diminished testosterone is unclear. Two possibilities exist regarding both the genesis and maintenance of the hypogonadotropic hypogonadal state. First, a defect in hypothalamic function, resulting in downregulation as well as in alterations of anterior pituitary function; second, estradiol inhibition of gonadotropin release, both of which result in decreased testosterone production. As testosterone levels decrease and estradiol levels increase, the ratio of free testosterone to estradiol reaches a critical point and the estrogenic gonadotropin suppressive effects predominate. This ratio may signal the biological point of no return and could become one of the criteria for defining the separation of the transitional hypogonadal state from the final 'end stage' hypogonadotropic hypogonadal state. As the aging process continues, there is a relative accumulation of fatty tissue, and aromatization accelerates the conversion of testosterone to estradiol. This additional secondary estradiol inhibition results in the maintenance of the testosterone deficient state, and the aging process continues uncontested. 相似文献
55.
Muñoz-Montoro A. J. Suarez-Dou D. Cortina R. Canadas-Quesada F. J. Combarro E. F. 《The Journal of supercomputing》2021,77(8):8135-8150
The Journal of Supercomputing - In this paper, we propose a parallel source separation system designed to extract heart and lung sounds from single-channel mixtures. The proposed system is based on... 相似文献
56.
The Journal of Supercomputing - DNA methylation analysis has become an important topic in the study of human health. DNA methylation analysis requires not only a specific treatment of DNA samples... 相似文献
57.
针对基于PC机和专用运动控制卡的传统数控系统的不足,提出了ARM微处理器(S3C2440)和数字信号处理芯片DSP(TMSC6713)双CPU主从式结构硬件平台,嵌入式Linux操作系统软件平台构建嵌入式运动控制器的方法;分别介绍了此嵌入式运动控制器主从控制板的硬件结构设计;软件方面,在Linux2.6内核环境下设计了FPGA的驱动程序,并给出了基于MiniGUI的人机界面设计以及DSP软件实现的程序结构框架;测试结果表明,该运动控制器工作可靠、运算能力强、结构灵活,精度达到1μm,在实践中有一定的借鉴意义。 相似文献
58.
Design sensitivity analysis of flexible multibody systems is important in optimizing the performance of mechanical systems.
The choice of coordinates to describe the motion of multibody systems has a great influence on the efficiency and accuracy
of both the dynamic and sensitivity analysis. In the flexible multibody system dynamics, both the floating frame of reference
formulation (FFRF) and absolute nodal coordinate formulation (ANCF) are frequently utilized to describe flexibility, however,
only the former has been used in design sensitivity analysis. In this article, ANCF, which has been recently developed and
focuses on modeling of beams and plates in large deformation problems, is extended into design sensitivity analysis of flexible
multibody systems. The Motion equations of a constrained flexible multibody system are expressed as a set of index-3 differential
algebraic equations (DAEs), in which the element elastic forces are defined using nonlinear strain-displacement relations.
Both the direct differentiation method and adjoint variable method are performed to do sensitivity analysis and the related
dynamic and sensitivity equations are integrated with HHT-I3 algorithm. In this paper, a new method to deduce system sensitivity
equations is proposed. With this approach, the system sensitivity equations are constructed by assembling the element sensitivity
equations with the help of invariant matrices, which results in the advantage that the complex symbolic differentiation of
the dynamic equations is avoided when the flexible multibody system model is changed. Besides that, the dynamic and sensitivity
equations formed with the proposed method can be efficiently integrated using HHT-I3 method, which makes the efficiency of
the direct differentiation method comparable to that of the adjoint variable method when the number of design variables is
not extremely large. All these improvements greatly enhance the application value of the direct differentiation method in
the engineering optimization of the ANCF-based flexible multibody systems. 相似文献
59.
The perovskite-type oxide PrCoO3 has been studied by means of X-ray photoelectron spectroscopy (XPS), reduction in H2 and X-ray diffraction. Two types of oxygen were detected: lattice oxygen (binding energy = 528.4 eV) and adsorbed oxygen (binding energy = 530.9 eV). The increase in relative intensity of the peak corresponding to the latter species after reduction of PrCo03 to 3e– per molecule is assigned to the formation of hydroxyl groups. Temperature-programmed reduction (TPR) results showed two reduction steps: to 1 e– per molecule (Co3.1 Co2+) at 475 to 635 K, and to 3e– per molecule (Co21 Co0) at 725 to 815 K. Reduction in the first and second steps occurs according to the contracting sphere model and the nucleation mechanism, respectively. Reduction of Co3+ to Co2+ causes minimal structural changes in the perovskite. Reduction to 3e– per molecule yielded Pr2O3 and metallic cobalt. After this reduction and reoxidation at 973 K, the perovskite structure was regained. By XPS and TPR it was shown that PrCo03 is more easily reducible than LaCo03. It is concluded that the cation in the A position of the structure plays a significant role in the bulk and surface properties of LnCo03 (Ln, lanthanide elements) oxides. 相似文献
60.
Victor Sosa J. A. Azamar-Barrios J. L. Peña L. Francisco Garfias A. I. Oliva P. Quintana 《Journal of Materials Science》1992,27(22):6131-6133
Synthesis of ceramic YBa2Cu3O7– by solid-state reaction was performed under different conditions. Different values of cooling rate and oxygen flow were used, and no significant influence on superconducting characteristics of the samples was observed. A major influence on their mechanical properties was found. 相似文献