An auditory periphery model for improving narrow-band noise recognition rate of underwater targets

The recognition rate of the auditory periphery features decreases when the model is used to identify underwater targets in practice. To solve this problem, an improved method based on Gammatone filter bank is proposed. Firstly, after the reason of the decreasing of the recognition results is analyzed,the mechanism of multichannel data acquisition in acoustic engineering may narrow down signal frequency range, which leads to time-frequency features distortion. Secondly, the Gammatone filter bank is implemented to simulate frequency decomposition characteristics of human ear basilar membrane. Since the class information of the underwater noise signal is mostly contained in low frequency range, the auditory features of the conventional model are interpolated and the channel number of the filter bank and the central frequency of each frequency band are adjusted accordingly to obtain a 27-dimensional feature vector of the narrow-band target signal. The adjusted model may reflect the target's timefrequency feature more precisely. Finally, the performance of the auditory features is tested by a Neural Network classifier. The experiment results show that the modified auditory model is more effective than the conventional ones. The major information contained in broadband signals is reserved and the classification ability for real targets is further enhanced. The recognition results are increased from 82.59% to 88.80%. The modified auditory features effectively improve the recognition rate for underwater target radiated noise signals.     

Above-Threshold Dissociation of HD+ in Femtosecond Laser Field

The above-threshold dissociation （ATD） of the HD＋ molecular ion in femtosecond laser field is investigated theoretically. The energy-dependent distribution of the dissociated fragments is calculated using an asymptoticflow expression in the momentum space. The calculations show that the ATD of HD＋ is sensitive to the initial vibrational level of ground electronic state. Multiphoton ATDs can be observed in the dissociation processes. The dynamics phenomena are interpreted by using the concept of light-dressed potential.     

不用固定规范的微扰论

本文建议从趋向平衡的Langevin方程出发,建立量子场论的微扰展开.文中证明了这种表述可用于规范理论,无需固定规范就能正确算出规范不变的量.文中还给出了简单例子的计算细节,并讨论了Langevin方程的微扰解趋向平衡的速率.     

硅晶体中单个位错的运动

本文利用化学浸蚀方法,在400—900℃的温度范围内,在0.35—13kg·mm^{-2的应力条件下,测量了硅晶体中单个位错的运动速度。实验结果表明,位错运动速度V(τ,T)作为温度(T)和分解切应力(τ)的函数,满足如下方程:V(τ,T)=Aτme-Q/(KT)。式中m=1.02—1.49,Q=1.96—2.07eV。最后,把实验结果与扩展位错的弯结模型作了比较。 关键词：}     

A new approach to variable selection in least squares problems

The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l₁ bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms.     

MXenes复合材料的发展:界面调控及结构设计

MXenes作为一类新兴的二维材料, 因具有独特的亲水性、 优异的力学性能、 丰富的表面官能团、 高导电率、 光热以及光电效应等性能而成为研究热点, 广泛应用在电磁屏蔽、 电化学储能、 生物医药、 分离、 传感器和海水淡化等领域. 虽然MXenes具有这些优异的性能, 但是其存在的与疏水性高分子相容性差、 带负电的官能团阻碍电解质运输及易氧化等问题限制了其实际应用. 近年来, 通过对MXenes进行界面调控以解决其固有缺陷, 并在此基础上对MXenes进行针对性的结构设计以提升界面稳定性, 其性能得到了进一步提升. 本文对MXenes复合材料发展过程中在界面调控和结构设计方面的研究进展进行总结, 并重点介绍了MXenes的结构和性质及MXenes在复合材料中的界面调控手段, 对MXenes复合材料的结构设计进行了阐述, 并对MXenes复合材料的发展前景进行了展望.     

激光粒度分析技术在药物研究和质量控制中的应用进展

近年来,激光粒度分析技术广泛应用于药物的质量研究和质量控制领域.从激光散射测定粒度的原理、仪器的一般要求和影响测试结果的因素、方法验证的要求以及该技术在药物领域中最新应用等方面进行综述,为激光粒度分析技术在药物中的应用开发提供有益的参考.     

Bound states of schrödinger equations with electromagnetic fields and vanishing potentials

We study the bound states to nonlinear Schrödinger equations with electro-magnetic fields $\text{i}h\frac{?\psi }{?t}={(\frac{h}{i}?-A(x))}^2\psi +V(x)\psi -K(x){|}^{p-1}\psi =0,\text{on}{?}_{+}\times {?}^N$. Let $G(x)={[V(x)]}^{\frac{p+1}{p-1}-\frac{N}{2}}{[K(x)]}^{-\frac{2}{p-1}}$ and suppose that G(x) has k local minimum points. For h > 0 small, we find multi-bump bound states ψh(x,t) = _e^?lEt/^h_Uh(χ) with Uh concentrating at the local minimum points of G(x) simultaneously as h → 0. The potentials V(x) and K(x) are allowed to be either compactly supported or unbounded at infinity.     

超支化高分子结构和聚集态研究的新进展

超支化高分子上具有大量的活性末端基,对这些末端基的修饰和功能化会使其聚集态结构发生变化.文中针对超支化高分子所具有的独特结构和性能特点,概述了超支化高分子的构象结构和聚集态结构的研究现状,系统讨论了超支化高分子的支化度、分子量分布、空间尺度、玻璃化转变温度和特性粘度等分子结构参数,并在此基础上介绍了超支化高分子的物理化学性质和分析表征方法,同时综述了国内外学者在该领域的贡献,展望了该领域的研究进程和发展前景.     

聚乙二醇-b-聚对苯二甲酸丁二醇酯嵌段共聚物降解行为的研究

研究了系列PEG-b-PBT嵌段共聚物在pH=7.4磷酸盐缓冲溶液中和37℃条件下的体外降解行为.同时观察了水解降解过程中系列共聚物溶胀率、失重、特性粘度、结晶度和表面形态等方面的变化.实验结果表明,嵌段共聚物的组成直接影响其水解降解性能,共聚物的溶胀率和失重率随聚醚组分含量而增大;通过调节共聚物的组分比可以达到调节降解速率的目的.此外研究还表明,共聚物最初的降解主要发生在软段和硬段相联的酯键上.