神经系统的简并性与序空间编码分析

Edelman提出了神经系统中存在简并现象,但并未说明简并在神经系统中的具体形式和作用.文中从序空间理论出发,以神经回路为讨论基础,具体讨论了双耳定向的神经回路中可能出现的简并网络,以及各种网络被简并的方法.把简并现象的讨论和编码的讨论结合起来,对神经网络中的简并现象有了一个具体的认识.文中虽然是由纯理论推导的结果,但所得回路包含了被广泛承认的Jeffress模型,因此也间接证明了该理论也有一定的生物学基础. 关键词： 简并 神经编码 序空间 双耳声源定向     

等离子体四波混频透射放大理论

研究了寻常波在磁化等离子体中四波混频透射放大理论，得到了简并和非简并时的精确解析解，其结果适用于非磁化等离子体中的电磁波四波混频． 关键词：     

二维准晶顶角模型的电子性质

本文研究构造在Penrose晶格上的顶角模型的电子性质。对有对称心的Penrose晶格,引入一相似变换,将紧束缚哈密顿量约化成分块对角的形式,以此化简了本征能量和本征态的数值计算,并且根据这一约化确定约三分之二的能量本征态是双重简并的,而另外三分之一的态是非简并的。用Household方法和改进的Dean方法数值求解了本征能量和本征态,并用二阶矩,反参加比和波函数空间分布等方法研究了电子态的局域性质,发现三种类型的电子态(延展态、中间态和局域态)共存于二维准晶中。此外,还对能谱中的高简并态进行了研究。 关键词：     

脉冲控制量子系统的哈密顿量约化

探索了脉冲控制的含近简并能级的有限维量子系统的哈密顿量的约化．由一个非简并基态能级和几个近简并激发态能级组成的量子系统被一个短脉冲控制,目标是控制所有激发态的布居数之和．考虑了两个可以看成等价二能级系统的例子,当脉冲强度比较弱时,得到了原始系统和约化系统的简单关系;当脉冲强度比较强时,对于只含一个频率的脉冲,一阶近似的关系也是存在的．     

一种可能的简并谱NNS分布

利用随机矩阵理论,通过对一特殊情形的简并谱展开研究,得到了简并谱一种可能的最小相邻间距NNS分布函数．研究表明,由于简并的存在,简并谱不仅可分解成随机谱和规则谱两个子谱,同时还影响其规则谱,使规则谱的能级斥力减少．     

微扰计算中表象的选择

本文证明了：在能量为定值的简并空间中，微扰Ｈ’在表象（Ｈ０，Ａ，Ｂ）中的矩阵对角的充要条件为时易式［Ｈ’，Ａ］和［Ｈ’，Ｂ］在该简并空间中的矩阵 为零。此充要条件可作为微扰计算中选择表象的依 据     

Oh型分子三重简并态Hamiltonian算符的研究

本文应用群论原理及不可约张量性质，详细推导了Ｏｈ型分子三重简并态Ａｍａｔ－Ｎｉｅｌｓｅｎ方案中精确到四级的Ｈａｍｉｌｔｏｎｉａｎ算符，为Ｏｈ型分子精细结构理论和光谱的进一步研究做了数学上的准备。     

光折变晶体中高速调制光简并四波混频特性的研究

本文对光折变晶体中高速调制光简并四波混频过程的特性进行了理论分析、给出了在Ce:SBN晶体中进行的实验结果;并指出,光折变晶体中的简并四波混频可应用于消空间畸变的时域编码通信和双向时域信息的传输、放大。     

消除简并双光子过程中二能级原子的消相干性

研究了置于外部环境(热库)中的二能级原子在外加驱动场时原子的消相干问题.得到简并双光子过程中原子约化密度算符非对角元.在二能级原子的消相干被消除的情况下,讨论外加驱动场的特性. 关键词： 简并双光子过程 二能级原子 消相干性     

C60外价简并轨道电子相关性质的DFT研究

用密度泛函理论(DFT)方法研究C60分子的外价能量简并轨道的动量分布、空间电子密度分布等基本性质.取DFT理论中的B3LYP方法在6-311 G的基组上分析了C60分子最外层5个简并轨道(Hu)的动量分布及轨道电子的密度分布,并进行相关分析.     

“Hopf/homoclinic”簇放电和“SubHopf/homoclinic"簇放电之间的同步

以修正过的Morris-Lecar神经元模型为例,讨论了“Hopf/homoclinic”簇放电和“SubHopf/homoclinic"簇放电之间的同步行为.首先,分别考察了同一拓扑类型的两个耦合簇放电神经元的同步行为,发现“Hopf/homoclinic”簇放电比“SubHopf/homoclinic”簇放电达到膜电位完全同步所需要的耦合强度小,即前者比后者更容易达到膜电位完全同步.其次,对这两个不同拓扑类型的簇放电神经元的耦合同步行为进行了讨论.通过数值分析发现随着耦合强度的增加,两种不同类型的簇放电首先达到簇放电同步,然后当耦合强度足够大时甚至可以达到膜电位完全同步,并且同步后的放电类型更接近容易同步的簇放电类型,即“Hopf/homoclinic”簇放电.然而令人奇怪的是此时慢变量并没有达到完全同步,而是相位同步;慢变量之间呈现为一种线性关系.这一点和现有文献的结果截然不同.     

Pressure-driven "molecular metal" to "atomic metal" transition in crystalline Ga

We present the ultrasonic study of gallium (Ga I) under high pressure up to 1.7 GPa, including the measurements of the density and elastic properties during phase transitions to Ga II and to a liquid state. The observed large drop of both bulk and shear moduli (by 30% and 55%, correspondingly) during the phase transition to Ga II, as well as the increase of the Poisson's ratio from typically "covalent" ( approximately 0.22) to "metallic" ( approximately 0.32) values, experimentally testifies to the coexistence of a molecular and metallic behavior in Ga I and to the disappearance of the "covalency" during the transition to Ga II. A high value of the pressure derivative of the bulk modulus for Ga I and the increase in the Poisson's ratio can be associated with the weakening of the covalency in compressed Ga I and considered as a precursor of the transition to normal metal.     

Observation of "Stick" and "Handle" intermediates along the fullerene road

The hypothesis that fullerenes grow in a carbon plasma by the addition of C2 units (the "fullerene road") has been widely acclaimed as the most plausible mechanism for formation of larger fullerenes including C60 and C70. Calculations suggest that the association of C2 with fullerenes proceeds through two classes of intermediates, "sticks" and "handles." Here we report the observation of these species using high-resolution ion-mobility measurements for C(n) cations generated by laser vaporization of graphite and laser desorption of C60. Sticks with up to eight-atom chains have also been found.     

Dissociation of perceptual judgments of "what" and "where" in an ambiguous auditory scene

Whenever an acoustic scene contains a mixture of sources, listeners must segregate the mixture in order to compute source content and/or location. Some past studies have explored whether perceived location depends on which sound elements are perceived within a source. However, no direct comparisons have been made of "what" and "where" judgments for the same sound mixtures using the same listeners. The current study tested if the sound elements making up an auditory object predict that object's perceived location. Listeners were presented with an auditory scene containing competing "target" and "captor" sources, each of which could logically contain a "promiscuous" tone complex. In separate blocks, the same listeners matched the perceived spectro-temporal content ("what") and location ("where") of the target. Generally, as the captor intensity decreased, the promiscuous complex contributed more to both what and where judgments of the target. However judgments did not agree either quantitatively or qualitatively. For some subjects, the promiscuous complex consistently contributed more to the spectro-temporal content of the target than to its location while for some it consistently contributed more to target location. These results show a dissociation between the perceived spectro-temporal content of an auditory object and where that object is perceived.     

Melting of "porous" vortex matter

Bitter decoration and magneto-optical studies reveal that in heavy-ion irradiated superconductors, a "porous" vortex matter is formed when vortices outnumber columnar defects. In this state ordered vortex crystallites are embedded in the "pores" of a rigid matrix of vortices pinned on columnar defects. The crystallites melt through a first-order transition while the matrix remains solid. The melting temperature increases with density of columnar defects and eventually turns into a continuous transition. At high temperatures a sharp kink in the melting line is found, signaling an abrupt change from crystallite melting to melting of the rigid matrix.     

基尔霍夫定律中的“独立回路”

对电路理论基尔霍夫定律中“独立回路”概念进行讨论,提出较为合理的独立回路的概念,并运用线性代数、几何方法、拓扑图论等方法,分别对平面电路网络和立体电路网络进行讨论,证明在此规定下基尔霍夫方程的独立性和解的确定性.     

Model basis states for photons and "empty waves"

From the perspective of physical realism (PR), a photon is a localized entity that carries energy and momentum, and which is surrounded by a wave packet (anempty wave) that is devoid of observable energy or momentum. In creating quantized PR basis states for a photon wave packet, three requirements must be met:(1) The basis states must each carry the frequency of the wave;(2) They must closely resemble the photon, so that e.g. they scatter in the same manner from an optical mirror;(3) They must have infinitesimal energy, linear momentum, and angular momentum. An essentially zero-energy "empty wave" quantum-a "zeron"-is defined which meets these requirements. It is created as an asymmetric single-particle (or single-antiparticle) excitation of the vacuum state, with the "particle" (or "antiparticle") and its associated "hole" (or "antihole") forming a rotational bound state. The photon is reproduced as a symmetric particle-antiparticle excitation of the vacuum state, with the "particle" and "antiparticle" also forming a rotational bound state. The relativistic transformation problem is discussed. A key point in this development is the deduction of the correct equation of motion for a "hole" state in an external electrostatic field.     

"Work-Hardenable" ductile bulk metallic glass

Usually, monolithic bulk metallic glasses undergo inhomogeneous plastic deformation and exhibit poor ductility (< 1%) at room temperature. We present a new class of bulk metallic glass, which exhibits high strength of up to 2265 MPa together with extensive "work hardening" and large ductility of 18%. Significant increase in the flow stress was observed during deformation. The "work-hardening" capability and ductility of this class of metallic glass is attributed to a unique structure correlated with atomic-scale inhomogeneity, leading to an inherent capability of extensive shear band formation, interactions, and multiplication of shear bands.     

粗糙波面中心点亮度比像质评价准则

建立了兼含粗糙与波面像差影响的中心点亮度比公式及其像质评价准则，根据粗糙波面中心点亮度比的大小，把像质标准划分为“极佳”“良好”和“不理想”等三个等级，粗糙度公差范围为λ／２０～λ／８０。