Estimation of electron transfer rate constants by static (optical and electrochemical) measurements

A kinetic study of the reduction of Co(NH₃)₅(DMSO)³⁺ (DMSO=dimethylsulfoxide) by Fe(CN)₆⁴⁻ has been carried out in several water–cosolvent mixtures at 298.2 K. The cosolvents used were ethylene glycol, acetonitrile, methanol and glucose. The free energies of activation for this thermal electron-transfer reaction have been calculated from a combination of spectroscopic and electrochemical data and compared with those obtained from the kinetic study. Quantitative agreement is found between both series of data. This shows the possibility of estimating activation free energies for electron transfer reactions from these (static) measurements.     

CaO-MgO-MnO-Al_2O_3-SiO_2系夹杂物组成的最小自由能变化模型

利用规划理论和共存理论,以夹杂物与钢水之间氧化还原反应的自由能变化最小化为目标,以夹杂物中分子离子之间的化学反应达到平衡条件下的质量平衡方程为约束条件,建立了夹杂物组成与钢水成分、温度之间关系的数学模型.经生产试验检验,模型计算与实测值基本上能够很好地吻合.     

CSRe减速模拟

对兰州重离子加速器冷却储存环实验环中束流的减速过程进行了模拟研究,采用变换谐波的方式将粒子减速到较低能量,以适应高精度原子物理实验的需要.根据模拟结果得到了减速过程各个时刻粒子在纵向相空间分布,并给出了高频参数在减速过程中的变化曲线.     

Simple square pulses for implementing spike‐timing‐dependent plasticity in phase‐change memory

Phase‐change memory (PCM) is a promising candidate as an artificial synapse. A compact operation method to implement synaptic functions with low power consumption is critical for constructing large‐scale neuromorphic system. Here we propose a square spike strategy for implementing spike‐timing‐dependent plasticity (STDP) in PCM. Based on the heat accumulation effect in PCM, modulating the time intervals of pre‐ and post‐spikes results in different heat generation and dissipation conditions, which lead to various crystalline/ amorphous ratios in the phase change material layer in devices with diverse synaptic weights. Four forms of STDP learning rule are experimentally demonstrated. This study will further promote the development of PCM technology involved in neuromorphic systems. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Bonding Nature of Local Structural Motifs in Amorphous GeTe

Despite its simple chemical constitution and unparalleled technological importance, the phase‐change material germanium telluride (GeTe) still poses fundamental questions. In particular, the bonding mechanisms in amorphous GeTe have remained elusive to date, owing to the lack of suitable bond‐analysis tools. Herein, we introduce a bonding indicator for amorphous structures, dubbed “bond‐weighted distribution function” (BWDF), and we apply this method to amorphous GeTe. The results underline a peculiar role of homopolar Ge? Ge bonds, which locally stabilize tetrahedral fragments but not the global network. This atom‐resolved (i.e., chemical) perspective has implications for the stability of amorphous “zero bits” and thus for the technologically relevant resistance‐drift phenomenon.     

Multivariate asset‐pricing model based on subordinated stable processes

In this paper, we consider a multidimensional time‐changed stochastic process in the context of asset‐pricing modeling. The proposed model is constructed from stable processes, and its construction is based on two popular concepts: multivariate subordination and Lévy copulas. From a theoretical point of view, our main result is Theorem 1, which yields a simulation method from the considered class of processes. Our empirical study shows that the model represents the correlation between asset returns quite well. Moreover, we provide some evidence that this model is more appropriate for describing stock prices than classical time‐changed Brownian motion, at least if the cumulative amount of transactions is used for a stochastic time change.     

Laser-driven switching dynamics in phase change materials investigated by time-resolved X-ray absorption spectroscopy

Time-dependent X-ray absorption spectroscopy at the Ge L₃ edge is used to study the optical switching dynamics of epitaxial phase change materials grown on Si(111) membranes. Small differences between the static absorption spectra of the crystalline and laser-amorphized phase of GeTe are observed. Furthermore, a new approach for pump-probe studies on phase change materials is presented. However, no time-dependent change in the X-ray absorption > 0.1% has been detected so far. This is mainly attributed to sample deterioration at 3 kHz pump-probe rates.     

Dynamics and structural changes of small water clusters on ionization

Despite utmost importance in understanding water ionization process, reliable theoretical results of structural changes and molecular dynamics (MD) of water clusters on ionization have hardly been reported yet. Here, we investigate the water cations [(H₂O)_{n = 2–6}⁺] with density functional theory (DFT), Möller–Plesset second‐order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The complete basis set limits of interaction energies at the CCSD(T) level are reported, and the geometrical structures, electronic properties, and infrared spectra are investigated. The characteristics of structures and spectra of the water cluster cations reflect the formation of the hydronium cation moiety (H₃O⁺) and the hydroxyl radical. Although most density functionals fail to predict reasonable energetics of the water cations, some functionals are found to be reliable, in reasonable agreement with high‐level ab initio results. To understand the ionization process of water clusters, DFT‐ and MP2‐based Born‐Oppenheimer MD (BOMD) simulations are performed on ionization. On ionization, the water clusters tend to have an Eigen‐like form with the hydronium cation instead of a Zundel‐like form, based on reliable BOMD simulations. For the vertically ionized water hexamer, the relatively stable (H₂O)₅⁺ (5sL4A) cluster tends to form with a detached water molecule (H₂O). © 2013 Wiley Periodicals, Inc.     

Free energy simulation of helical transitions

An umbrella sampling method for the calculation of free energies for helical transitions is presented. The method biases structures toward helices of a desired radius and pitch. Although computationally complex, the method has negligible overhead in actual applications. To illustrate the method, calculations of the helical free energy landscape of several peptides are presented for both the CHARMM and the AMBER force fields. © 2012 Wiley Periodicals, Inc.     

Native Biomolecules in the Gas Phase? The Case of Green Fluorescent Protein

Green fluorescent protein (GFP) was ionized by native electrospray ionization and trapped for many seconds in high vacuum, allowing fluorescence emission to be measured as a probe of its biological function, to answer the question whether GFP exists in the native form in the gas phase or not. Although a narrow charge‐state distribution, a collision cross‐section very close to that expected for correctly folded GFP, and a large stability against dissociation all support a near‐native gas‐phase structure, no fluorescence emission was observed. The loss of the native form is attributed to the absence of residual water in the gas phase, which normally stabilizes the para‐hydroxybenzylidene imidazolone chromophore of GFP.