Pseudo Real-Time Method for Monitoring of the Limiting Anisotropy in Membranes

Data acquisition and analysis of the time-resolved fluorescence anisotropy is typically a time consuming process preventing usage of this experimental method for monitoring of time-dependent phenomena. We describe a method for pseudo real-time monitoring of the limiting fluorescence anisotropy r(infinity) allowing to track changes of the membrane order occurring on the time scale of minutes. Principle and performance of the method is demonstrated in the time domain with the time-correlated single photon counting detection. DMPC liposomes stained with 1,6-diphenyl-1,3,5-hexatriene (DPH) have been used to test influence of the diffusion membrane potential on the membrane order during the temperature-induced phase transition in DMPC membranes. It has been found that the transmembrane field of the order of -70 mV increases the phase transition temperature by about 1.5 degrees C-2 degrees C. It is proposed that the full advantage of the method can be utilized with a gated detection, which besides a faster data acquisition brings additional advantage of excitation light suppression. The method can be also used for imaging.     

一种新型真空型紫外成像探测器

针对紫外告警的关键元器件——紫外探测器，简述了紫外告警的特点及发展，紫外辐射的大气传输特性和紫外探测器的发展。详细介绍了一种新型响应波段为105nm～300nm的真空型紫外成像探测器，其光电阴极具有“日盲性”，管型采用近贴聚焦结构，从而使得弥散和像差得以减小。探测器读出系统有光耦合读出和电耦合读出2种读出方法：光耦合读出系统能实时响应；电耦合读出灵敏度高，分辨力强，探测距离远。采用自动门控BSP电源，可实现大动态范围探测，并对光电阴极和微通道板起到保护作用。     

A single server queue with gated processor-sharing discipline

In this paper we consider a single server queue in which arrivals occur according to a Poisson process and each customer's service time is exponentially distributed. The server works according to the gated process-sharing discipline. In this discipline, the server provides service to a batch of at mostm customers at a time. Once a batch of customers begins service, no other waiting customer can receive service until all members of the batch have completed their service. For this queue, we derive performance characteristics, such as waiting time distribution, queue length distribution etc. For this queue, it is possible to obtain the mean conditional response time for a customer whose service time is known. This conditional response time is a nonlinear function (as opposed to the linear case for the ordinary processor-sharing queue). A special case of the queue (wherem=) has an interesting and unusual solution. For this special case, the size of the batch for service is a Markov chain whose steady state distribution can be explicitly written down. Apart from the contribution to the theory of Markov chains and queues, the model may be applicable to scheduling of computer and communication systems.     

Femtosecond time-resolved two-photon photoemission studies of electron dynamics in metals

Electron-hole excitation and relaxation in the bulk, at interfaces, and surfaces of solid state materials play a key role in a variety of physical and chemical phenomena that are important for surface photochemistry, particle-surface interactions, and device physics. Information on charge carrier relaxation in metals can be obtained through analysis of linewidths measured by photoemission and related techniques, which give an estimate of the upper limit for electron and hole relaxation; however, many factors can contribute to spectral broadening, thus it is difficult to extract specific information on electronic relaxation processes. With femtosecond lasers it is possible to probe directly in a time-resolved fashion the charge carrier dynamics in metals by a variety of linear and nonlinear optical techniques. Femtosecond time-resolved two-photon photoemission has attracted particularly strong interest because it incorporates many of the surface analytical capabilities of photoemission and inverse photoemission — the traditional probes for surface and bulk band structures of solid state materials — with time-resolution that is approaching the fundamental response of electrons to optical excitation. Advances in the direct measurements of electron-hole excitation, charge carrier relaxation, and dynamics of intrinsic and adsorbate induced surface states are reviewed. With femtosecond lasers it also is possible to probe a variety of coherent phenomena, and even to control the charge carrier dynamics in metals through the optical phase of the excitation light. Pioneering experiments in this new field also are discussed.     

On Elevator polling with globally gated regime

We consider a polling system consisting ofN queues and a single server where polling is performed according to anElevator (scan) scheme. The server first serves queues in the up direction, i.e. in the order 1, 2,...,N – 1,N, and then serves these queues in the opposite (down) direction, i.e. visiting them in the orderN,N–1,...,2,1. The server then changes direction again, and so on. A globally gating regime is used each time the server changes direction. We show that, for this Elevator scheme,the expected waiting times in all channels are equal. This is the only known non-symmetric polling system that exhibits such afairness phenomenon. We then discuss the problem of optimally ordering the queues so as to minimize some measure of variability of the waiting times.Supported by a grant from the France-Israel Scientific Cooperation (in Computer Science and Engineering) between the French Ministry of Research and Technology and the Israeli Ministry of Science and Technology, Grant No. 3321190.     

Molecular level model for the agonist/antagonist selectivity of the 1,4-dihydropyridine calcium channel receptor

Summary Crystal structures of the 1,4-dihydropyridine (1,4-DHP) calcium channel activators Bay K 8643 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3-nitrophenyl)-pyridine-5-carboxylate], Bay O 8495 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3-trifluoromethylphenyl)-pyridine-5-carboxylate], and Bay O 9507 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(4-nitrophenyl)-pyridine-5-carboxylate] were determined. The conformations of the 1,4-DHP rings of these activator analogues of Bay K 8644 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5- carboxylate] do not suggest that their activator properties are as strongly correlated with the degree of 1,4-DHP ring flattening as was indicated for members of the corresponding antagonist series. The solid state hydrogen bonding of the N(1)-H groups of the activators is not, unlike that of their antagonist counterparts, to acceptors that are directly in line with the donor. Rather, acceptor groups are positioned within ± 60 degrees of the N(1)-H bond in the vertical plane of the 1,4-DHP ring. Previously determined structure-activity relationships have indicated the importance of this N(1)-H group to the activity of the 1,4-DHP antagonists. Based on these observations, a model is advanced to describe the 1,4-DHP binding site of the voltage-gated Ca²⁺ channel and its ability to accommodate both antagonist and activator ligands.     

Molecular electronics at electrode–electrolyte interfaces

Four contemporary examples, all published in recent years, of studies of molecular electronics at electrode–electrolyte interfaces are reviewed in this opinion article. The first illustrative example involves the switching of the redox active molecular wire between redox states, with concomitant changes in molecular conductance. This example illustrates how molecular electronics at electrode–electrolyte interfaces can be used to analyse mechanisms of electron transfer, to distinguish electrolyte effects and to provide details not readily available from ensemble measurements. The second example shows that the fluctuations of molecular conductance of a redox active molecular wire can be followed as a function of electrode potential. This shows how the stochastic kinetics of individual reaction events at electrode–electrolyte interfaces can be followed. The third example demonstrates how electrochemistry can be used to control quantum interference in single molecular wires. The fourth example shows a single-molecule electrochemical transistor concept for well-defined metal cluster containing molecular wires.     

Characterization of electrokinetic gating valve in microfluidic channels

Electrokinetic gating, functioning as a micro-valve, has been widely employed in microfluidic chips for sample injection and flow switch. Investigating its valving performance is fundamentally vital for microfluidics and microfluidics-based chemical analysis. In this paper, electrokinetic gating valve in microchannels was evaluated using optical imaging technique. Microflow profiles at channels junction were examined, revealing that molecular diffusion played a significant role in the valving disable; which could cause analyte leakage in sample injection. Due to diffusion, the analyte crossed the interface of the analyte flow and gating flow, and then formed a cometic tail-like diffusion area at channels junction. From theoretical calculation and some experimental evidences, the size of the area was related to the diffusion coefficient and the velocity of analytes. Additionally, molecular diffusion was also believed to be another reason of sampling bias in gated injection.     

Biocatalytic Stimuli‐Responsive Asymmetric Triblock Terpolymer Membranes for Localized Permeability Gating

The functionalization with phosphotriesterase of poly(isoprene‐b‐styrene‐b‐4‐vinylpyridine)‐based nanoporous membranes fabricated by self‐assembly and nonsolvent induced phase separation (SNIPS) is shown to enable dynamically responsive membranes capable of substrate‐specific and localized gating response. Integration of the SNIPS process with macroporous nylon support layers yields mechanically robust textile‐type films with high moisture vapor transport rates that display rapid and local order‐of‐magnitude modulation of permeability. The simplicity of the fabrication process that is compatible with large‐area fabrication along with the versatility and efficacy of enzyme reactivity offers intriguing opportunities for engineered biomimetic materials that are tailored to respond to a complex range of external parameters, providing sensing, protection, and remediation capabilities.     

多尺度分子模拟研究来自于无类囊体蓝藻的五聚体门控离子通道门控机理

五聚体门控离子通道是一个重要膜蛋白家族, 在生理学过程中起到重要作用. 我们以来自无类囊体蓝藻(Gloebacter violaceus: GLIC)的五聚体门控离子通道X-ray结构为模型, 进行总共1.05 μs的粗粒化分子模拟, 并结合原子级分子模拟方法, 观察到其离子通道的闭合和相应的四级结构扭转. 我们发现其位于跨膜区组成通道的M2螺旋通过倾斜-旋转(指向通道中心)的协调运动来完成通道闭合. 进一步分析并结合前人的实验结果, 我们提出了该离子通道门控过程的可能的“连锁反应”机理: 由单独亚基的M2螺旋前部构象变化引发, 使该亚基发生整体的构象变化, 并且将这种变化传递到了邻近的亚基, 进而带动整个通道的构象变化, 最终完成通道的闭合.