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1.
The geometrical cell structure of the chemically reacting system is discussed. The boundary of the cell uniquely defines the dividing surface between the initial reactant side and the final product side. Introducing the concept of the intrinsic reaction time (IRT) and the accumulation time (AT) of reaction along the meta-IRC (intrinsic reaction coordinate), the intrinsic dynamism in the cell is discussed. Then, the stable limit theorems with respect to the intrinsic nature of the normal vibrations are derived. The theory is elucidated by using a model potential surface. 相似文献
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Minimum principles of chemical reaction coordinates are established. IRC (intrinsic reaction coordinate) draws the path of minimum distance from reactant to product. The distance is measured in the rigged configuration Riemannian space whose metric is determined by the distribution of the adiabatic potential energy. Moreover, minimum property of the intrinsic principle of least action is established for the intrinsic dynamism of chemical reaction. Minimum principle of the path connecting intercell boundary with cell is also discussed. 相似文献
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Recently, the intrinsic sampling method has been developed in order to obtain, from molecular simulations, the intrinsic structure of the liquid-vapor interface that is presupposed in the classical capillary wave theory. Our purpose here is to study dynamical processes at the liquid-vapor interface, since this method allows tracking down and analyzing the movement of surface molecules, thus providing, with great accuracy, dynamical information on molecules that are "at" the interface. We present results for the coefficients for diffusion parallel and perpendicular to the liquid-vapor interface of the Lennard-Jones fluid, as well as other time and length parameters that characterize the diffusion process in this system. We also obtain statistics of permanence and residence time. The generality of our results is tested by varying the system size and the temperature; for the latter case, an existing model for alkali metals is also considered. Our main conclusion is that, even if diffusion coefficients can still be computed, the turnover processes, by which molecules enter and leave the intrinsic surface, are as important as diffusion. For example, the typical time required for a molecule to traverse a molecular diameter is very similar to its residence time at the surface. 相似文献
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高分子动力学的单链模型 总被引:1,自引:0,他引:1
高分子单链模型是高分子稀溶液理论研究的基本模型.对其进行深入地分析,不仅有助于解决高分子稀溶液体系中溶液黏度和分子链扩散等基本问题,而且能够增进人们对高分子链结构与溶液性质间关联性的理解.虽然基于经典连续性介质力学的流体动力学理论可以定性,甚至半定量地获得稀溶液的一些重要性质,但是,随着科学技术的发展,人们从分子水平上建立了许多描述高分子稀溶液性质的模型和理论,期望能够定量地描述高分子稀溶液的性质.本文以高分子稀溶液中3个典型的单链模型为例(包括:不含流体力学相互作用的Rouse模型、含二体流体力学相互作用的Zimm模型和含多体流体力学相互作用的部分穿透球模型),综述高分子稀溶液的重要性质,并详细地给出其动力学方程的推导过程及其重要的研究进展.特别是,对于Rouse模型,本文还将其预言结果拓展到了短链高分子流体体系;此外,还介绍了这一领域的关键科学问题、发展前景和研究方向. 相似文献
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How useful it is to think about the potential energy landscape of a complex many-body system depends in large measure on how direct the connection is to the system's dynamics. In this paper we show that, within what we call the potential-energy-landscape ensemble, it is possible to make direct connections between the geometry of the landscape and the long-time dynamical behaviors of systems such as supercooled liquids. We show, in particular, that the onset of slow dynamics in such systems is governed directly by the lengths of their geodesics--the shortest paths through their landscapes within the special ensemble. The more convoluted and labyrinthine these geodesics are, the slower that dynamics is. Geodesics in the landscape ensemble have sufficiently well-defined characteristics that it is straightforward to search for them numerically, a point we illustrate by computing the geodesic lengths for an ordinary atomic liquid and a binary glass-forming atomic mixture. We find that the temperature dependence of the diffusion constants of these systems, including the precipitous drop as the glass-forming system approaches its empirical mode-coupling transition, is predicted quantitatively by the growth of the geodesic path lengths. 相似文献
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Chen Zhixing 《Theoretical chemistry accounts》1989,75(6):481-484
A procedure for calculating the distance between two points on an intrinsic reaction coordinate (IRC) obtained from two separate runs is proposed. The procedure mainly involves the rotation of the geometrical configuration of one point in order to obtain a configuration not rotated relative to the other point. 相似文献
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Effects of the polyanion synthesis conditions and composition on the viscometric behavior of poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPS) and two random copolymers, poly(sodium 2-acrylamido-2-methylpropanesulfonate-co-methylmethacrylate) (PAMPSMM) and poly(sodium 2-acrylamido-2-methylpropanesulfonate-co-tert-butylacrylamide) (PAMPSTBA), in a wide range of concentrations were reported in this paper. The experimental data obtained in salt-free aqueous solution were plotted in terms of the Fuoss and the Rao equations in order to obtain the intrinsic viscosity values. The C∗ values obtained as the reciprocal of the intrinsic viscosity were compared with the experimentally determined values and with those calculated according to the Odijk theory. An acceptable agreement between C∗ values obtained by different approaches was found for the PAMPS samples with high molar masses (0.83 × 106-1.4 × 106 g/mol). For the same charge density and the same concentration the reduced viscosity values were higher for PAMPSMM comparative with PAMPSTBA indicating a higher chain extension of the former copolymer. 相似文献
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In this paper, we build on our previous research on probabilistic foundations of dynamical systems and introduce a theory of linear representation for ordinary differential equations. The theory is developed for explicit ODEs and can be further extended to cover implicit cases. In this report, we investigate the case of a canonical single unknown autonomous system. First we construct a linear representation to get an infinite linear ODE set with a constant coefficient matrix which can be transformed into an upper triangular form. Then we find its approximate truncated solutions. We describe a number of properties of the theory using this framework. The companion of this paper expands this canonical approach to cover multidimensional cases using the theory of folded arrays which is another line of research established by our research group. 相似文献
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Fundamental properties of polymethyl acrylate solutions were examined: the reasonable Houwink-Mark-Sakurada relations and the theta temperature (θ) were determined to be 5 °C in toluene. Further, the measurements of intrinsic viscosity for polymethyl acrylate solutions as a function of temperature yielded a thermal transition due to a conformation change at 56 ± 1 °C, irrespective of molecular weight and solvent. An application of the two-parameter theory to such a transition gave a stepwise change of the short-range interaction: K×102=9.5 below 50 °C and 10.3 above 60 °C. This conformation transition is explained on the basis of the steric hindrance of the planar substituent to the main chain above 60 °C. 相似文献
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用数值方案,在RHF/3-21G分子轨道从头算法的水平上,得到了氟化异氰FNC到氟化氰FCN重排反应的反应途径(内禀反应坐标IRC).沿着IRC;讨论了反应过程中体系几何构型的变化,计算了沿IRC运动与垂直于IRC简正振动之间的耦合常数(BK,F),各振动模式对应的频率(ωK),使用统一的半经典徽扰和无限级突然(SCP-IOS)近似理论计算了在一定能量下产物的振动分配.结果表明,在过渡态后,耦合常数(BK,F)的大小强烈地影响产物的振动态分布,另外用传统过渡态、变分过渡态理论及相关的隧道效应校正计算了该反应的速率常数. 相似文献
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Bilayers and monolayers are excellent models of biological membranes. The constituents of the biological membranes such as lipids, cholesterols and proteins are chiral. Chiral molecules are abundant in nature (protein, nucleic acid and lipid). It is obvious that relationship between chirality and morphology (as well as function) of biological membrane is of interest for its fundamental importance and has technological implication regarding various membrane functions. The recent years have witnessed that a number of experimental studies in biomimetic systems have shown fascinating morphologies where chirality of the constituent molecule has decisive influence. Significant progress is made towards the understanding of these systems from the theoretical and computational studies. Helfrich's concept of intrinsic force arising from chirality is a milestone in understanding the biomimetic system such as bilayer and the related concepts, further progresses in molecular understanding made in recent years and experimental studies revealing the influence of chirality on morphology are the focus of the present review. Helfrich's concept of intrinsic force arising due to chirality is useful in understanding two-dimensional bilayers and one-dimensional monolayers and related mimetic systems. Various experimental techniques are used, which can probe the molecular architecture of these mimetic systems at different length scales and both macroscopic (thermodynamic) as well as microscopic (molecular) theories are developed. These studies are aimed to understand the role of chirality in the molecular interaction when the corresponding molecule is present in an aggregate. When one looks into the variety of morphologies exhibited by three-dimensional bilayer and two-dimensional monolayer, the later types of systems are more exotic in the sense that they show more diversity and interesting chiral discrimination. Helfrich's concept of intrinsic force may be considered useful in both cases. The intrinsic force due to chirality is the decisive factor in determining morphology which is explained by molecular approaches. Finally, biological and technological implications of such morphological variations are briefly mentioned. 相似文献
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Eberle AP Castañeda-Priego R Kim JM Wagner NJ 《Langmuir : the ACS journal of surfaces and colloids》2012,28(3):1866-1878
We report an experimental study of the dynamical arrest transition for a model system consisting of octadecyl coated silica suspended in n-tetradecane from dilute to concentrated conditions spanning the state diagram. The dispersion's interparticle potential is tuned by temperature affecting the brush conformation leading to a thermoreversible model system. The critical temperature for dynamical arrest, T*, is determined as a function of dispersion volume fraction by small-amplitude dynamic oscillatory shear rheology. We corroborate this transition temperature by measuring a power-law decay of the autocorrelation function and a loss of ergodicity via fiber-optic quasi-elastic light scattering. The structure at T* is measured using small-angle neutron scattering. The scattering intensity is fit to extract the interparticle pair-potential using the Ornstein-Zernike equation with the Percus-Yevick closure approximation, assuming a square-well interaction potential with a short-range interaction (1% of particle diameter). (1) The strength of attraction is characterized using the Baxter temperature (2) and mapped onto the adhesive hard sphere state diagram. The experiments show a continuous dynamical arrest transition line that follows the predicted dynamical percolation line until ? ≈ 0.41 where it subtends the predictions toward the mode coupling theory attractive-driven glass line. An alternative analysis of the phase transition through the reduced second virial coefficient B(2)* shows a change in the functional dependence of B(2)* on particle concentration around ? ≈ 0.36. We propose this signifies the location of a gel-to-glass transition. The results presented herein differ from those observed for depletion flocculated dispersion of micrometer-sized particles in polymer solutions, where dynamical arrest is a consequence of multicomponent phase separation, suggesting dynamical arrest is sensitive to the physical mechanism of attraction. 相似文献
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Ab initio molecular dynamics simulations at the Hartree-Fock/6-31G level of theory are performed on methyl chloride hydrolysis
with explicit consideration of one solute and two solvent water molecules at a temperature of 298 K. The reaction involves
the formation of a reactant complex and the energy surface to the transition state is found to be simple. Two types of trajectories
toward the product are observed. In the first type, the system reaches an intermediate complex (complex-P1) region after two
nearly concerted proton transfers involving the attacking water molecule and the solvent water molecules. These trajectories
resemble the intrinsic reaction coordinate trajectory. The thermal motion of the atoms leads the system to another intermediate
complex (complex-P2) region. A second type of trajectory is found in which the system reaches the complex-P2 region directly
after the proton transfers. In both of these forward trajectories, back proton transfers lead the system to a final complex-F
region which resembles protonated methanol.
Received: 3 July 1998 / Accepted: 2 September 1998 / Published online: 15 February 1999 相似文献
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Acid hydrolysis of some industrial pulps: effect of hydrolysis conditions and raw material 总被引:2,自引:0,他引:2
Dilute acid hydrolysis of pulps was studied by following the decrease in intrinsic viscosity of preparations of microcrystalline cellulose. The decrease in intrinsic viscosity and the loss of weight during hydrolysis at reaction temperatures of 60 and 80 °C was investigated, using acid concentrations from 0.5 to 4 M and two different acids (HCl and H2SO4). The same levelling-off degree of polymerisation (LODP) was reached under all hydrolysis conditions, but a longer time was needed under milder conditions. An appropriate method of determining the intrinsic viscosity at LODP was established and used in this investigation. The greatest difference in LODP was found between a birch prehydrolysed kraft pulp and a mixed hardwood prehydrolysed kraft pulp; the intrinsic viscosities at LODP being 178 and 72 dm3/kg, respectively. The effect of the intrinsic viscosity of a given starting material was also investigated, but only a small difference (10%) in the LODP was found for pulp samples with very different initial intrinsic viscosities. 相似文献