遗传算法BP神经网络的预报研究和应用

针对目前 BP神经网络在实际气象预报应用中 ,网络结构难以确定以及网络极易陷入局部解问题 ,用遗传算法优化神经网络的连接权和网络结构 ,并在遗传进化过程中采取保留最佳个体的方法 ,建立基于遗传算法的 BP网络模型 ,并以广西的月降水量进行实例分析 ,计算结果表明 ,该方法预报精度高、而且稳定 .     

Parameter study of sound propagation between city canyons with a coupled FDTD-PE model

A parameter study is performed for the case of two-dimensional sound propagation from a (source) city canyon to a nearby, identical (receiver) city canyon. Focus was on sound pressure levels, relative to the free field, in the shielded canyon. An accurate and efficient coupled FDTD-PE model was applied, exploiting symmetry of the source and receiver canyon. With the proposed calculation method, simulations were necessary in only half the sound propagation domain. The shielding in the receiver canyon in case of a coherent line source was compared to the shielding by an incoherent line source, by means of sound propagation calculations in a number of 2D cross-sections through source and receiver. It was found that the shielding is rather insensitive to the width-height ratio of the canyons. The presence of diffusely reflecting façades and balconies lead to an important increase in shielding compared to flat façades. Rigid façades yield significantly lower shielding compared to partly reflecting façades. Effects of a moving atmosphere were modeled in detail. Shielding decreases significantly in case of downwind sound propagation when comparing to sound propagation in a non-moving atmosphere. Refraction is the most important effect in the latter. In case of upwind sound propagation, turbulent scattering plays an important role and the shielding is similar to the one of a non-moving atmosphere for the parameters used in this paper. The combination of effects, as is shown by some examples, is in general not a simple addition of the separate effects.     

Asymptotic Stability for a Class of Neutral Systems with Discrete and Distributed Time Delays

In this note, the asymptotic stability for a class of neutral systems with discrete time and distributed time delays is considered. Delay-dependent criteria are proposed to guarantee the stability for such systems. Some numerical examples are given to illustrate that our results are less conservative than previous results.     

自然对流边界层中湍流的发生

自然对流边界层中从层流到湍流的转捩经历了浮力振型、无摩擦振型和黏性振型的三重流动不稳定性相继产生的前转捩过程,以及近壁迅速出现强湍流源,随之平缓地向自模拟的湍流边界层过渡的热转捩过程.浮力振型在修正Grashof数G>40时开始失稳并成为主要振型,在振幅分布中3种振型的临界层位置处出现3个峰值;在G>100时浮力振型消失,无摩擦振型失稳并成为主要振型,振幅分布中在近壁区还出现黏性振型的峰值;在G>170时无摩擦振型经非线性演化在外层形成较弱的湍流,但内层黏性应力仍远高于湍流应力,振幅分布中仅有与黏性振型相应的峰值,在频谱中黏性振型的基频、第一、第二、第三阶亚谐频随G的增加相继出现,此时黏性不稳定波的高频成分已转化为湍流,但低频成分仍按线性规律增长,直至湍流惯性子区开始形成;至G>800时黏性振型消失,并在G=850附近时近壁区出现强湍流源,湍流应力、湍能产生项和近壁湍流热流率剧增.在热转捩后期,湍流应力和湍能产生项明显下降,流动在内外层趋于平衡.     

Critical Reynolds number in plasma flows on a stabilized plasmatron section

A technique for determining the criterion of transition from the laminar to the turbulent flow regime on a stabilized plasmatron channel section is proposed. The technique uses experimental data and the methods of numerical simulation of plasma flows. A criterial generalization of the experimental data which for the first time makes it possible to establish the boundary of transition from the laminar to the turbulent flow regime on a stabilized plasmatron channel section is proposed. The experimental results are in good agreement with the theoretical dependences derived in the study. A curve (analog of the neutral curve) separating the domains of existence of laminar and turbulent plasma flows in a cylindrical channel is constructed in the space of the plasmatron working parameters.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, 2004, pp. 49–61. Original Russian Text Copyright © 2004 by Sinkevich and Chikunov.     

Interactions of DNA with graphene and sensing applications of graphene field-effect transistor devices: A review

Graphene field-effect transistors (GFET) have emerged as powerful detection platforms enabled by the advent of chemical vapor deposition (CVD) production of the unique atomically thin 2D material on a large scale. DNA aptamers, short target-specific oligonucleotides, are excellent sensor moieties for GFETs due to their strong affinity to graphene, relatively short chain-length, selectivity, and a high degree of analyte variability. However, the interaction between DNA and graphene is not fully understood, leading to questions about the structure of surface-bound DNA, including the morphology of DNA nanostructures and the nature of the electronic response seen from analyte binding. This review critically evaluates recent insights into the nature of the DNA graphene interaction and its affect on sensor viability for DNA, small molecules, and proteins with respect to previously established sensing methods. We first discuss the sorption of DNA to graphene to introduce the interactions and forces acting in DNA based GFET devices and how these forces can potentially affect the performance of increasingly popular DNA aptamers and even future DNA nanostructures as sensor substrates. Next, we discuss the novel use of GFETs to detect DNA and the underlying electronic phenomena that are typically used as benchmarks for characterizing the analyte response of these devices. Finally, we address the use of DNA aptamers to increase the selectivity of GFET sensors for small molecules and proteins and compare them with other, state of the art, detection methods.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part I

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the “conventional” detectors). The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods.     

Mathematical Models for Studying Environment Pollution Risks

The problem of longterm ecological prediction by means of mathematical modeling with available factual data on climate dynamics is discussed. The technique of quantitative estimates of risk/vulnerability on the basis of forward and inverse modeling and methods of the sensitivity theory is described. Examples of the calculated risk domains for Lake Baikal are given.     

Development of resonance‐enhanced multiphoton ionization SNMS for state‐selective detection of sputtered atoms under low‐energy ion irradiation

An instrument for a sputtered neutral mass spectrometry with a quadrupole mass spectrometer (QMS) by resonance‐enhanced multiphton ionization method is developed to study sputtered neutrals emission phenomena under ion irradiation in a low‐energy region. We have prepared a pulsed primary ion beam and an ion counting system, and have optimized the operation parameter including a sample bias, energy analyzer voltages, pulsed timing of laser and ion beam, etc. A yield ratio of the lowest‐lying excited state a⁵S₂ to the ground state a⁷S₃ for sputtered Cr atoms has been measured as a function of incident energy of Ar⁺ and O₂⁺ down to 600 eV using a polycrystalline Cr sample. The yield ratio has become a constant value for the Ar⁺ incidence, while it has exponentially increased below 1 keV for the O₂⁺ incidence. It is found that the internal energy distribution of sputtered Cr atoms has been significantly influenced by oxygen density at the surface. Copyright © 2011 John Wiley & Sons, Ltd.