跨膜浓度梯度对渗透压囊泡循环活性的调控

本文通过分析囊泡在膨胀状态与孔隙状态的动力学行为,揭示调控膨胀拉伸能与孔隙势能的内在物理参量.建立递推微分方程的分析模型,该模型提供了膨胀-破裂循环特征量膨胀系数在各个循环中初始跨膜浓度梯度依赖性的定量信息.研究得出,通过增加初始跨膜浓度梯度,可加快膨胀系数增长速率(循环数为1时,初始跨膜浓度梯度增加3倍,膨胀系数增长速率增加2.65倍);随着循环数的增多,膨胀系数的增长由线性转变为非线性.此外,初始跨膜浓度梯度与循环次数密切相关,我们的模型计算预测增加初始跨膜浓度梯度可实现循环次数的增多.研究结果为靶组织以可编程方式释放活性生物治疗剂的发展提供了具有实际意义的理论依据.     

Express Method for Determination of Low Value of Trans-membrane Potential of Living Cells with Fluorescence Probe: Application on Haemocytes at Immune Responses

The method for measurement of trans-membrane potential of cell membrane was evaluated for the case of low potential value using fluorescence probe 4-(4-dimethylaminostyryl)-1-methylpyridinium, DSM. The method is based on comparative titration of cells with probe in buffers containing Na(+) or K(+). The apparent trans-membrane potential obtained with this way is a result of K(+)-Na(+) pump activity. The presented approach allowed measuring the low value of potential with 1-2?mV of accuracy without additional calibration procedures. The method was applied for investigation of potential of cell membrane of haemocytes of Galleria mellonella larvae. The value of potential of intact insect's haemocytes was found in the range from -10 to -20?mV. The change of potential value of haemocytes was investigated under model immune response and natural envenomation and parasitizing. The obtained deviations of cell membrane potential were in good correlation with changes of activity of main immune reactions, described in literature and obtained by us earlier.     

Coarse-grained model of entropic allostery

Many signaling functions in molecular biology require proteins to bind to substrates such as DNA in response to environmental signals such as the simultaneous binding to a small molecule. Examples are repressor proteins which may transmit information via a conformational change in response to the ligand binding. An alternative entropic mechanism of "allostery" suggests that the inducer ligand changes the intramolecular vibrational entropy, not just the mean static structure. We present a quantitative, coarse-grained model of entropic allostery, which suggests design rules for internal cohesive potentials in proteins employing this effect. It also addresses the issue of how the signal information to bind or unbind is transmitted through the protein. The model may be applicable to a wide range of repressors and also to signaling in trans-membrane proteins.     

Neuron model with conductance-resistance symmetry

This paper is to derive a mathematical model for neuron by imposing only a principle of symmetry that two modelers must obtain the same model when one models the conductances of ion channels and the other models the channels' resistances. Conductance-voltage characteristics for ion transport channels and protein gating channels are both derived. They are expressed as products of maximal conductances and opening probabilities for both types of channel. It gives an explanation to the role of spontaneous firing of individual channel pores and to the origin of leak current. The model has a better fit to a classical data than the Hodgkin-Huxley model does. It can also be reduced to a 2-dimensional model qualitatively similar to the FitzHugh-Nagumo equation and be expanded to a model of three ion channels capable of spike bursts.     

随机海洋声信道下的噪声场时空相关函数

本文把传播的随机时变网络模型用于水声信道,建立了噪声辐射场的时空相关函数的一般表示式。讨论了时变、多径、色散水声信道下噪声场时空相关函数的时变、起伏与衰落。     

Molecular dynamics study of biomembrane/local anesthetics interactions

It is still controversial how local anesthetics (LAs) act upon the nervous system and how the membrane contributes to this process, since probably the most important active site of the LAs is located in the sodium channels, a trans-membrane protein. An important role of the bio-membrane would be the stabilization and orientation of local anesthetics molecules, reducing their translational and rotational degrees of freedom, which could reinforce the mechanisms which interrupt the nervous impulse. This study aims to perform a computational analysis of the LAs behaviour in the membrane, and the effect of the water/membrane interface on their stabilization and orientation. Analysis by molecular dynamics (MD) showed that the charged form of these drugs are oriented at the interface, while the neutral form can easily cross the interface, entering the membrane, in agreement with the most recent experimental results in the literature. In contrast, it is here suggested that benzocaine (BZC), which exists only in its uncharged form in physiological media, behaves like the charged anesthetics, remaining stabilized and oriented at the interface. This could explain the similar anesthetic effect of BZC and the charged forms of tetracaine (TTC) and lidocaine (LDC).     

Reduction of the Many-Body Problem and the Unified Theory for Nuclear Reaction

We reduce the many-body problem to a multi-channel few-body problem by the AGS method. The channels may be chosen according to the problem under consideration and the reduction is formally exact. For the nuclear reaction we may choose some one-body channels to represent compound nucleus and choose some two- or more-body channels to represent open reaction channels. We then apply formal collision theory to this multi-channel system. Direct reaction, resonant reaction and their interference emerge. There are also distortions of ingoing and outgoing waves in compound nucleus formation and decay respectively. The omission of all but one open channel leads to the optical model, and an incomplete consideration of the open channels may lead to a multi-channel generalization of the optical model. Nonnucleon degrees of freedom as well as relativity may be included in principle. The reaction induced by particles other than nuclei may be considered on the same footing.     

An overview of shadowed fading wireless channels in terms of a cascaded approach

Wireless channels suffer from short term fading and shadowing simultaneously. While simple models of short term fading are based on the Nakagami-m distribution, short term fading can also be described as a cascading process allowing the modeling of wireless channels having worse fading than what exists in Nakagami-m channels. Shadowing, on the other hand, has been traditionally modeled as a lognormal process, making the analysis of shadowed fading channels cumbersome. Taking note of the fact that the lognormal density arises out of a multiplicative process, it was shown that shadowing can also be modeled as a cascading process. Utilizing such a vision of shadowing, this work provides an overview of a unified cascaded approach to model wireless channels when short term fading and shadowing are simultaneously present. The degradation in such shadowed fading channels is estimated in terms of error rates and outage probabilities. Results are compared to those of the exact model based on lognormal density as well as random number simulation. Analysis demonstrates that error rates and outage probabilities obtained using the exact model (lognormal model for shadowing) agree very well with those obtained through the composite cascaded model as well as random number simulations.     

Structure and properties of confined sodium nitrite

We study the lateral and transverse diffusion of amphiphiles in two-component bilayer membranes, using a coarse-grained model for amphiphilic molecules and combined Monte Carlo-Molecular Dynamics simulations. Membrane structural properties, such as the mean thickness, are also measured. The dependence of such properties on membrane composition, inter-molecular interactions, and amphiphile stiffness is determined. In particular, we show that addition of shorter amphiphiles drives the model membrane towards a more fluid state, with increased amphiphile lateral diffusion rates. These results can be understood in the framework of a simple free-volume model. Furthermore, we observe an increase in the trans-membrane diffusion when the interaction energy of amphiphiles with their neighboring molecules is decreased. Received: 6 December 2002 / Accepted: 17 April 2003 / Published online: 27 May 2003 RID="a" ID="a"e-mail: imparato@mpikg-golm.mpg.de RID="b" ID="b"e-mail: shillcock@mpikg-golm.mpg.de RID="c" ID="c"e-mail: lipowsky@mpikg-golm.mpg.de     

Quantum walk under coherence non-generating channels

We investigate the probability distribution of the quantum walk under coherence non-generating channels. We definea model called generalized classical walk with memory. Under certain conditions, generalized classical random walk withmemory can degrade into classical random walk and classical random walk with memory. Based on its various spreadingspeed, the model may be a useful tool for building algorithms. Furthermore, the model may be useful for measuring thequantumness of quantum walk. The probability distributions of quantum walks are generalized classical random walkswith memory under a class of coherence non-generating channels. Therefore, we can simulate classical random walkand classical random walk with memory by coherence non-generating channels. Also, we find that for another class ofcoherence non-generating channels, the probability distributions are influenced by the coherence in the initial state of thecoin. Nevertheless, the influence degrades as the number of steps increases. Our results could be helpful to explore therelationship between coherence and quantum walk.     

Debye-Waller factor in atom-surface scattering: Elastic and inelastic channels

Explicit expressions for the Debye-Waller factor for the elastic and one-phonon channels are presented to lowest order in the phonon displacement, using a hard wall model to represent the atom-surface interaction. The periodicity of the crystal is accounted for; thus we explicitly generalize to all elastic channels the reflectance result found by Garcia et al. within the plane-surface model, and we include the contribution of the umklapp processes to the inelastic channels. We show how for high incident energy of the atom all Debye-Waller factors reduce to the standard result.     

Resonant widths, line intensities and lineshapes for MQDT models with two or more open channels

Approximate analytical formulae describing the energy variation of line intensities, autoionization widths and lineshape asymmetries, are derived for a Phase-Shifted Multichannel Quantum Defect Theory model composed of two closed interacting channels coupled to two effective continua. This is accomplished by putting the two compatibility equation solutions, for the common phase shifts of the two open channels, in such a form so the resonant behavior is attributed to one of them, the other accounting for an energy dependent background. Then, the well-known procedures for the simpler case where only one continuum is considered are applied, using only the resonant solution. The method is quite general and applicable to any MQDT model with two or more open channels. The resulting analytical formulae are tested on experimental spectra of Sr, Ba and Cu and it is shown that they are valid as long as: i) The resonances are non-overlapping, ii) The direct closed channel coupling is much stronger than the indirect one through the continua and (when excitation matrix elements are involved) iii) The open channels excitation strength is smaller or at least comparable to the closed channels one. Received: 26 May 1998 / Accepted: 1st July 1998     

Reinforcement learning for performance improvement in cooperative spectrum sensing

Cognitive radio (CR) can provide a promising solution to the spectrum scarcity issue for upcoming wireless communication technologies. Cooperative spectrum sensing (CSS) is generally adopted to improve spectrum utilization and minimize interference to primary users (PUs). The performance of CSS is significantly affected by imperfect reporting channels, and it is an easy target for Byzantine attackers. This paper studies CSS under imperfect reporting channels and Byzantine attacks. We have considered centralized CSS with a hard combining fusion rule. The binary symmetric channel (BSC) is used to model the imperfect reporting channels, and a centralized independent probabilistic small scale attack model is chosen to model Byzantine attackers. We first analyze the traditional CSS (T-CSS) under the imperfect reporting channel and the Byzantine attack. The performance of T-CSS is found to be greatly affected in the considered scenarios. We propose a reinforcement learning-based algorithm to detect cooperating secondary users (CSUs) experiencing weak reporting channels and Byzantine attackers. Generally, in literature, the detected malicious users (MUs) are removed to improve the performance. However, in case there are CSUs with weak reporting channels, the genuine CSUs may be detected as Byzantine attackers and hence removed. To overcome this issue, we propose a weighted sum-based CSS (WS-CSS) algorithm that can improve the CSS performance under weak reporting channels and attacks from Byzantine attackers. It is demonstrated using plots that the proposed WS-CSS algorithm significantly improves the CSS performance.     

激光诱导等离子体加工石英微通道机理研究

利用调Q的Nd: YAG激光器输出的纳秒激光脉冲诱导等离子体加工石英微通道, 显微镜下观察微通道深度可达4 mm, 通道周围没有发现热裂纹, 围绕通道内壁产生了固化层. 研究了纳秒脉冲下固体材料损伤的电离机理. 波长为1064 nm, 光强不很强的纳秒脉冲作用时, 光学击穿中等离子体的形成主要是雪崩电离的结果, 利用雪崩击穿的阈值理论得到了等离子体形成模型, 求出了等离子体形成范围, 理论模型结果与实验结果基本相符.最后基于激光支持的爆轰波模型, 利用流体力学理论求出了等离子体的温度、 速度、 压强等特征参数, 并分析了微通道的特点.高温高压的等离子体烧蚀出石英微通道, 等离子通过后, 在冲击波压力作用下微通道内壁熔化的 石英凝固形成固化层.     

Statistical model of current-coupled ion channels in nerve membranes

A statistical model of a driven system is developed. Its microscopic elements are the ion channels through a nerve membrane. Their conductances are stochastically switching under the competing influences of thermal noise and local membrane voltage. A current flow through the membrane induces a coupling between the channels via the electrolytes surrounding the membrane. The long range of the coupling permits a generalized mean field theory for the stationary membrane current as a function of the applied electrode voltage. We derive analytically the macroscopic conductance-voltage-temperature relation for the spatially uniform current state. It shows analogues of first and second order phase transitions. The critical temperature diverges at a finite coupling strength. The theory fits sodium conductance characteristics measured on nerve axon membranes from various species by a variation of only the coupling strength. This supports the hypothesis that this simplest possible model for sodium channels is universal for all species.The work of this author was partially supported by the Deutsche Forschungsgemeinschaft     

“Orthogonalized” sparsity enhanced mismatch models for wireless heterogeneous networks

Performance of MIMO precoder for heterogeneous networks can be hindered by a lack of accurate channel state information. The sparsity enhanced mismatch model (SEMM) has been proposed recently to account for the channel estimate mismatch problem by exploiting the inherent sparse characteristics of MIMO interference channels. When (single user-MIMO) SU-MIMO precoder design takes into account the SEMM, it was shown to have better transmission performance compared to the conventional norm ball mismatch model (NBMM) in a single-user multi-victims scenario. However, when communicating and interference channels are highly correlated, which can happen frequently in ultra-dense heterogeneous networks, performance of the SEMM precoder degrades and in some cases, underperforms the NBMM precoder. An “orthogonalized” SEMM (OSEMM) is proposed herein to modify the SEMM such that it is better suited for correlated channels. The concept of orthogonalization of channels is not new but this work uses it to enhance the SEMM, which creates synergy between transmission performance and robustness toward channel mismatch error. Two variants of the OSEMM are proposed, namely the OSEMM-LQ and OSEMM-SVD, to modify the basis expansion model that is an integral part of the SEMM. The resulting mismatch model influences the design of the SU-MIMO precoder that aims to maximize certain transmission criterion. Even though SU-MIMO precoding is considered, a new channel correlation definition, which acts as a metric for the OSEMM, is given that allows for user selection in a multiuser scenario such that optimal performance can be attained for the targeted user. Analytical and simulation results are given that highlight the difference in performance between the two variants of the OSEMM.     

Model of a magma flow during the Great Tolbachik Fissure Eruption (Kamchatka)

A model of magma flow-up through a set of fissure channels during the Great Tolbachik Fissure Eruption observed in Kamchatka in 1975 is suggested. The model is based on the assumption that the magmatic liquid flowing through fissure channels in the lithosphere experiences the Brinkman hydrodynamic resistance. Relationships between the depth of a magmatic source, time of magma flow-up to the Earth’s surface, and velocity of the magma flow through fissure channels to the Earth’s surface are derived.     

Parametrizing the line shapes of near-threshold resonances

A parametrization is proposed for the line shapes of near-threshold resonances, which is based on the model of coupled channels and can include an arbitrary number of elastic and inelastic channels and bare poles. The proposed parametrization satisfies the requirements imposed by unitarity and analyticity, and is convenient for the data analysis embracing all available experimental information. The model parameters are physically meaningful, and their values can be found using different theoretical schemes.     

Production cross sections of the superheavy nucleus 117 based on the dinuclear system model

Within the framework of the dinuclear system model,the capture of two colliding nuclei,and the formation and de-excitation process of a compound nucleus are described by using an empirical coupled channel model,solving the master equation numerically and the statistical evaporation model,respectively.In the process of heavy-ion capture and fusion to synthesize superheavy nuclei,the barrier distribution func-tion is introduced and averaging collision orientations are considered.Based on this model,the production cross sections of the cold fusion system 76-82Se+209Bi and the hot fusion systems 55Mn+238U,51V-+244Pu,59 Co+232 Th,48 Ca+247-249 Bk and 45 Sc+246-248 Cm are calculated.The isotopic dependence of the largest production cross sections is analyzed briefly,and the optimal projectile-target combination and excitation energy of the ln-4n evaporation channels are proposed.It is shown that the hot fusion systems 48Ca+247 249Bk in the3n evaporation channels and 45Sc+248Cm in the 2n-4n channels are optimal for synthesizing the superheavy element 117.