Ultrafast electron diffraction: dynamical structures on complex energy landscapes.

In this contribution, we report studies in ultrafast electron diffraction (UED), with the aim of exploring new directions. The main focus is on the determination of complex structures and their dynamics with spatial and temporal resolutions sufficient to give an atomic-scale picture for the evolution in chemical or biological change. We also provide the theoretical framework for UED, and compare the experimental findings of UED to those predicted by density functional and charge density calculations. Selected applications are given in order to highlight phenomena related to concepts such as bifurcation of trajectories in dynamics, far-from-equilibrium coherent structures, and conformational robustness in biological structures. For the former two cases, we consider chemical systems, and, for the latter, we examine proteins of 200 atoms (angiotensin I) or more.     

Nonmonotonic Transient Potential Signals with an 18‐Crown‐6 based Ion‐Selective Electrode in a Flow‐Injection System

The dynamic potential response of an 18‐crown‐6 based ion‐selective electrode towards Li⁺, Na⁺, K⁺ and Ca²⁺, in a flow‐injection system is studied. Different double nonmonotonic transient signals are obtained for the different ions. The influence of the flow‐injection variables and of ion concentration on the signals is studied. Two signal parameters, the relative return rates, are found to be characteristic for each ion and are constant for a concentration range of 1–3 decades. The nonmomotonic transient signals obtained are explained by reference to the theoretical models reported.     

全细胞膜片钳法研究铜对急性分离大鼠海马细胞钾电流的影响

Using the whole cell patch clamp technique, the effect of Cu^2＋on transient outward K^＋current （/to） and delayed rectifier K^＋ current （Idr） was studied in acutely isolated rat hippocampal neurons.Ito and Idr were increased when the concentration of Cu^2＋ was lower than 2 × 10^-5 and 10^-5 tool/L, respectively, and increased ratio was decreased with increasing Cu^2＋concentration in the bath solutions. When the concentration continued to increase to 5× 10^-5 and 2 × 10^- 5 mol/L, the currents were hardly changed, while the concentration was more than 10^-4 and 5 × 10^-5 mol/L, the currents were inhibited remarkably. Cu^2＋ （10^-5 mol/L） did not affect the activation and inactivation process of Ito. The activation curve of Idr was shifted toward positive potential, but 10^-5 mol/L Cu^2＋did not affect slope factor. According to these results, it was considered that Cu^2＋at low concentration in the bath solution could promote Ito and Idr while at high concentration could inhibit them, and change of amplitude was different with different membrane voltage. Conclusion was drawn： Cu^2＋may be involved in the pathophysiologic mechanism of diseases with neuropathological components.     

Time behaviour of the modifier involved in the general mechanism of Botts and Morales assuming rapid equilibrium in the modifier bindings

To date, the classification as activator or inhibitor of a modifier involved in an enzyme catalysed reaction is established according to its kinetic behaviour at the steady state. Inhibitors and activators are defined as modifiers which decrease or increase, respectively, the steady state rate of an enzyme-catalysed reaction. At this state, in some cases, a modifier always acts as an activator or as an inhibitor for all its possible concentration values. In other cases the action of a modifier as activator or inhibitor depends on its concentration. In this paper we extend the analysis of the kinetic behaviour of a modifier as inhibitor or nonessential activator to the transient phase of the reaction, i.e. to the whole course of the reaction, including both the transient phase and the steady state. Moreover, concerning to the behaviour of a modifier at the transient phase, we suggest its classification as activator or inhibitor based on the concentration and activator or inhibitor based on the rate. We have studied the behaviour of the modifier involved in the general modifier mechanisms of Botts and Morales in which the reversible bindings of the modifier to the enzyme forms are assumed in rapid equilibrium. The result is that depending on the values of the rate constants, equilibrium constants and the initial concentrations of both the involved substrate and modifier, the latter can act during the whole reaction course only as an activator, only as an inhibitor, first as an activator and then, from a determined reaction time, as inhibitor, or vice versa. Therefore, it is possible that a modifier showing an activating behaviour at the steady state behaves as an inhibitor in the transient phase, or vice versa. Novel indices pointing to the conditions under which the modifier can show any of the behaviours indicated above are suggested. The goodness of the analytical results is tested by comparison with the simulated curves obtained by numerical integration. From these results, those corresponding to several reaction mechanisms involving a modifier, and which can be regarded as particular cases of the general case analysed here, can be directly and easily obtained.     

含三苯胺类富勒烯吡咯烷衍生物的合成、表征及理论计算

N-Methyl-2-（4-N,N-diphenylaminophenyl）fulleropyrrolidine and N-methyl-2-（4-di-p-tolylaminophenyl）fulleropyrrolidine were synthesized via the 1,3-dipolar cycloaddition reactions under microwave irradiation. The molecular structures were identified and characterized by MS, UV-Vis, FT-IR, ^1H NMR and fluorescence spectra. Photoinduced intramolecular electron transfer process from C60 moiety to triphenylamine moiety have been studied by nanosecond laser flash photolysis. The optimized structure and the distribution of the frontier molecular orbitals for C60-TPA were obtained by using DFT method at B3LYP/6-31G（d） level. The results indicated that the intramolecular photoinduced electron transfer could occur in these compounds, which were in excellent agreement with the nanosecond transient absorption spectra observed experimentally in polar solvent. The electronic spectrum of the compound C60-TPA was studied by ZINDO method on the basis of the optimized geometrics, which was essentially consistent with experimental values.     

Structural differences in wave propagation in discrete and continuous systems

Summary The harmonic and transient behaviours of one-dimensional discrete semi-infinite cascades of masses and springs have been derived from analytical pulse response solutions [1]. The investigation shows structural differences between the dynamic behaviour of models with distributions of mass over the finite elements as compared to continuous models. Two generally accepted ideas are scrutinized. Firstly, that the dynamic behaviour of a discrete model after a refinement of the mesh converges to the response of the underlying continuous model. Secondly, that a symmetric mass distribution over the element results in a better convergence. Both ideas need some adjustment.This paper has been presented at the 2nd ESMC, Genua, Italy, 1994.     

Transient analysis of queues with heterogeneous arrivals

In this paper we consider a discrete time queueing model where the time axis is divided into time slots of unit length. The model satisfies the following assumptions: (i) an event is either an arrival of typei of batch sizeb _i, i=1,...,r with probability _i or is a depature of a single customer with probability or zero depending on whether the queue is busy or empty; (ii) no more than one event can occur in a slot, therefore the probability that neither an arrival nor a departure occurs in a slot is 1––_{i i} or 1–_{i i} according as the queue is busy or empty; (iii) events in different slots are independent. Using a lattice path representation in higher dimensional space we will derive the time dependent joint distribution of the number of arrivals of various types and the number of completed services. The distribution for the corresponding continuous time model is found by using weak convergence.     

Development of a thermal conductivity cell with nanolayer coating for thermal conductivity measurement of fluids

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.     

Unraveling the Photophysical Characteristics,Aromaticity, and Stability of π–Extended Acene-Quinodimethyl Thioamides†

Poly-aromatic systems that contain quinodimethyl (QDM) units are appealing for several photonic and spintronic applications owing to the unique electronic structure, aromaticity, and spin state(s) of the QDM ring. Herein, we report the synthesis and characterization of novel QDM-based chromophores 1 – 3 , which exhibit unique photo-excited behavior and aromaticity. Extending the aromatic core with a biphenyl/phenanthryl- and a pyrrolo-fragment led to reducing the optoelectronic bandgap and modulating the photophysics QDM 1 – 3 . Yet, QDM 2 and 3 suffer from “aromaticity imbalance” and become relatively unstable compared to the parent compound QDM 1 . Further assessment of local aromaticity using computational tools revealed that the pseudo-quinoidal ring B is the main driving force allowing to easily populate the excited triplet state of these chromophores. The present study provides complementary guidelines for designing novel non-classical poly-aromatic systems.     

Self-similar solution for deep-penetrating hydraulic fracture propagation

The propagation of a vertical hydraulic fracture of a constant height driven by a viscous fluid injected into a crack under constant pressure, is considered. The fracture is assumed to be rectangular, symmetric with respect to the well, and highly elongated in the horizontal direction (the Perkins and Kern model). The fracturing fluid viscosity is assumed to be different from the stratum saturating fluid viscosity, and the stratum fluid displacement by a fracturing fluid in a porous medium is assumed to be piston-like. The compressibility of the fracturing fluid is neglected. The stratum fluid motion is governed by the equation of transient seepage flow through a porous medium.A self-similar solution to the problem is constructed under the assumption of the quasi-steady character of the fracturing fluid flow in a crack and in a stratum and of a locally one-dimensional character of fluid-loss through the crack surfaces. Crack propagation under a constant injection pressure is characterized by a variation of the crack sizel in timet according to the lawl(t)=l _o (1+At)^1/4, where the constantA is the eigenvalue of the problem. In this case, the crack volume isVl, the seepage volume of fracturing fluidV _f l ³, and the flow rate of a fluid injected into a crack isQ ₀l ^–1.