遗传算法在散射介质光输运逆问题研究中的应用

建立了一个散射介质模型,在用蒙特卡罗方法成功模拟介质中光输运过程的基础上,用遗传算法有效地解决了因蒙特卡罗方法模拟结果的离散性和统计性使其在利用传统化方法进行逆问题研究时存在的困难,从而较好地实现了对散射介质模型的单个光学特性参数的重构和多参数的联合重构,同时还深入地讨论了遗传算法在过程中的作用机理。     

On the mechanism of xylan pyrolysis by combined experimental and computational approaches

Pyrolysis is the initial stage of biomass combustion, whereas, the pyrolysis mechanism of biomass, especially the hemicellulose component, is still not well elucidated. Herein, a common hemicellulose polysaccharide, xylan, was investigated to reveal the evolution of volatiles and solid residue through combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) techniques. Quantum chemistry calculation was also conducted to analyze the primary xylan pyrolysis mechanism by using a long-chain xylan model which was built based on the structural characterization of xylan. The experimental results indicated that the functional groups in solid-phase evolved intensively during the main weight loss zone (200–350 °C), leading to the violent release of volatiles. The decomposition of branches, especially the arabinose unit, was prior to that of the backbone, with relatively low energy barriers and high rate constants. The initial enhancement of CO vibration in solid-phase above 200 °C derived from the formation of the furanose unit. Both dehydration and breakage of glycosidic bonds were responsible for the formation of CC bond in solid-phase from 300 °C. The cracking of the 4-O-Me group resulted in the release of aldehydes to gas-phase in the main weight loss zone (200–350 °C). The scission of the whole 4-O-MeGlc unit and/or the rupture of the uronic acid group led to the gas-phase CO bond formation.     

Second-order variational analysis in second-order cone programming

Mathematical Programming - The paper conducts a second-order variational analysis for an important class of nonpolyhedral conic programs generated by the so-called second-order/Lorentz/ice-cream...     

Likelihood Inferences for High-Dimensional Factor Analysis of Time Series With Applications in Finance

This article investigates likelihood inferences for high-dimensional factor analysis of time series data. We develop a matrix decomposition technique to obtain expressions of the likelihood functions and its derivatives. With such expressions, the traditional delta method that relies heavily on score function and Hessian matrix can be extended to high-dimensional cases. We establish asymptotic theories, including consistency and asymptotic normality. Moreover, fast computational algorithms are developed for estimation. Applications to high-dimensional stock price data and portfolio analysis are discussed. The technical proofs of the asymptotic results and the computer codes are available online.     

Reconfigurable computing for Monte Carlo simulations: Results and prospects of the Janus project

We describe Janus, a massively parallel FPGA-based computer optimized for the simulation of spin glasses, theoretical models for the behavior of glassy materials. FPGAs (as compared to GPUs or many-core processors) provide a complementary approach to massively parallel computing. In particular, our model problem is formulated in terms of binary variables, and floating-point operations can be (almost) completely avoided. The FPGA architecture allows us to run many independent threads with almost no latencies in memory access, thus updating up to 1024 spins per cycle. We describe Janus in detail and we summarize the physics results obtained in four years of operation of this machine; we discuss two types of physics applications: long simulations on very large systems (which try to mimic and provide understanding about the experimental non-equilibrium dynamics), and low-temperature equilibrium simulations using an artificial parallel tempering dynamics. The time scale of our non-equilibrium simulations spans eleven orders of magnitude (from picoseconds to a tenth of a second). On the other hand, our equilibrium simulations are unprecedented both because of the low temperatures reached and for the large systems that we have brought to equilibrium. A finite-time scaling ansatz emerges from the detailed comparison of the two sets of simulations. Janus has made it possible to perform spin-glass simulations that would take several decades on more conventional architectures. The paper ends with an assessment of the potential of possible future versions of the Janus architecture, based on state-of-the-art technology.     

Photoluminescence of Turkish purple jade (turkiyenite)

The purple-colored unique gem material is only found in the Harmanc?k (Bursa) region of the western Anatolia (Turkey). Therefore, it is specially called “Turkish purple jade or turkiyenite” on the worldwide gem market. Even though its jadeite implication is the principal constituent, the material cannot be considered as a single jadeite mineral since other implications are quartz, orthoclase, epidote, chloritoid and phlogopite minerals.Even if the analytical methods are used to characterize and identify the Turkish purple jade samples in detail, the luminescence spectra, especially photoluminescence features regarding to composite mineral implications of the material are important because of the existence the numerous characteristic broad and intensive luminescence bands in the samples. We can state that the UV-irradiation luminescence centers as photoluminescence (PL) are due to the overall signals in the Turkish purple jade samples. Accordingly, the distinctive photoluminescence peaks at 743, 717, 698, 484, 465 and 442 nm in PL-2D (counter diagram and sections) and PL-3D (sequence spectra) ranging between 300 and 900 nm of wavelengths, and between 220 and 340 K of temperatures are observed.Finally, photoluminescence features of the heterogeneous-structured material cannot be simply attributed to any chemical impurities, since the jade mass has numerous heterogeneous mineral constituents instead of a single jadeite mineral. Six different mineral implications and chemical impurities in the material composition display complex and individual all kind of luminescence features. Therefore, photoluminescence as well as radioluminescence, cathodoluminescence and thermoluminescence spectra provide positive identification regarding to the provenance (geographic origin) of the original Turkish purple jade (turkiyenite).