Kinetics of the Titanium Alloy Structure at High-Speed Penetration of a Striker

Physics of the Solid State - Behavior of a titanium alloy is studied under conditions of a high-speed penetration at a speed of ~2.0 km/s. Three penetration zones with different mechanisms of...     

Structure and Freezing of a Disordered Flux Line System

Recent progress in the understanding of the phase behaviour of disordered type-II superconductors is discussed in the context of three studies. The first describes a physically appealing picture of correlations in the "vortex glass" or "pinned liquid" phase in BSCCO; calculations based on this picture agree well with experimental data from muon-spin-rotation experiments. The second details a new proposal for the phase behaviour of disordered low-T c materials. In the third, a universal phase diagram for all disordered type-II superconductors is proposed. The attributes of this phase diagram are discussed briefly and the experimental, theoretical and simulational evidence in its favour summarized.     

团簇连接对Cu10Ag90快速凝固中晶体结构的影响

快速凝固得到的晶体通常都会形成多种孪晶结构,但其成因一直是一个谜。本文采用分子动力学模拟Cu10Ag90合金在0、20和40 GPa压强下的快速凝固过程,分别形成了五重孪晶、层片状孪晶和复杂晶体,通过最大标准团簇方法(LaSCA)分析了短程有序结构的演变和晶体团簇之间的连接形式。结果发现,结晶转变温度Tc随着压强的增大而升高,平均原子势能也随之增加。非晶共有近邻子团簇(CNS)会在温度降至Tc时转变为晶体CNS,同时晶体团簇数量急剧增加,结构有序度提升。此外,通过分析晶体团簇之间的连接方式发现,五重孪晶中心团簇截边十面体(tDh)只能与具有相同S422的HCP相连形成五重孪晶轴;FCC与HCP有相同的S421,但只能以彼此的顶层或者底层原子作为彼此的中心原子连接形成层片状结构;BCC与FCC、HCP虽然没有共同的CNS,但是可以通过D-S6结构及其变形体连接,其连接方式的多样性是形成复杂晶体的主要原因。这些结果为研究晶体结构不同排列方式提供了新的理解。     

Structure Model of a One-Dimensional Disordered System with Short-Range Order

An ensemble of disordered linear chains is described by a probability density distribution without making use of the laws of thermodynamical equilibrium statistics. Short-range order is present in the system, because the position of an arbitrary particle depends on the location of the nearest neighbours. The nearest neighbour distance statistics is assumed to be of the Gaussian type. All correlation functions are calculated for finite and infinite systems. The superposition approximation is found to hold rigorously. The pair correlation is of fundamental importance for the system. The radial pair distribution function is investigated thoroughly. The configurational entropy of the system is calculated and discussed.     

RDX晶体结构与固相生成焓的理论研究

采用分子模拟的方法计算含能化合物的晶体结构和固相生成焓,有助于进一步从理论上计算其主要爆轰参数.本文通过密度泛函理论(DFT)与开放力场(OFF)相结合的方法计算了黑索金(RDX)的晶体结构和固相生成焓.首先采用分子力学(MM)和分子动力学(MD)方法对RDX分子进行驰豫和模拟;然后采用GGA-BLYP泛函,DNP基组对RDX分子进行几何结构优化;最后对优化后的分子进行Mont Carlo模拟退火、簇分析、晶体结构优化等步骤的计算得到能量最低的结构作为最终的晶体结构:空间群为PBCA,密度为1.8208,晶胞参数为a=13.6561,b=11.3015,c=10.500,α=90,β=90,γ=90,与实验值相符.在此基础上,利用DFT GGA-BLYP计算求得RDX的固相生焓为171.86 kJ/mol,与实验测定值168.9J/mol相比的误差为1. 8%.     

Gyrotropic Features of a Nonideal Optically Active 1D Photonic Orientationally Disordered Crystal

Journal of Applied Spectroscopy - The gyrotropic characteristics of a nonideal unidimensional photonic crystal with an arbitrary number of sublattices (one of which, potassium dithionate K2S2O6, is...     

On the Structure of KMS States of Disordered Systems

We study the set of KMS states of spin systems with random interactions. This is done in the framework of operator algebras by investigating Connes and Borchers –invariants of W*–dynamical systems. In the case of KMS states exhibiting a property of invariance with respect to the spatial translations, some interesting properties emerge naturally. Such a situation covers KMS states obtained by infinite–volume limits of finite–volume Gibbs states, that is the quenched disorder. This analysis can be considered as a step towards fully understanding the very complicated structure of the set of temperature states of quantum spin glasses, and its connection with the breakdown of the symmetry for replicas.     

Acousto-Optically Q-Switched Operation of Yb:CNGG Disordered Crystal Laser

We report the repetitively Q-switched laser operation of the Yb-doped calcium niobium gallium garnet disordered garnet crystal, achieved with an acousto-optic modulator in a compact plano-concave resonator that is endpumped by a 935-nm diode laser. An average output power of 1.96 W is produced at pulse repetition rate of50 k Hz at emission wavelengths around 1035 nm, with a slope efficiency of 16%. The highest pulse energy of 269 μJ is generated at pulse repetition rate of 1 k Hz, with pulse width 12.1 ns and peak power 20.53 kW.     

Grain Boundary Kinetics in Oxide Ceramics with the Cubic Fluorite Crystal Structure and its Derivatives

Kinetics of grain boundaries in oxides with the cubic fluorite structure and its derivatives has been investigated using fine grain ceramics that are fully dense. Grain growth measurements in these materials have provided information on grain boundary diffusivity over a diffusion distance of the order of the initial grain size. With the addition of solute cations, grain boundary mobility can be varied over many orders of magnitude, often with very different activation energies. This is caused by the variation of defect population and the defect-solute association. Definitive evidence for solute drag has also been observed in some cases, but solute drag can not be confirmed as a general mechanism in solid solutions. Lastly, while grain boundary at low temperature may continue to serve as a fast diffusion path, it may not be able to migrate because of additional pinning mechanisms such as those exerted by grain boundary nodal points or lines. This means that sintering without grain growth is possible, opening up an avenue for obtaining ultrafine ceramics by pressureless sintering.     

一种发光二极管模型中无序光子晶体对光输出影响的研究

摘要利用Order-N算法及超晶格技术讨论了位置无序及尺寸无序对石墨点阵柱状光子晶体光子带隙的影响.计算结果表明,对于电场偏振模,光子带隙对尺寸无序更加敏感.在此基础上,利用三维时域有限差分方法进一步讨论了无序光子晶体对石墨点阵柱状中心柱光子晶体GaN发光二极管模型光输出效率的影响.计算结果表明,无序对这种光子晶体发光二极管模型光输出效率的影响较小,且这种影响也是随机的.     

Multiparametric Analysis of Vocal Fold Vibrations in Healthy and Disordered Voices in High-Speed Imaging

Objectives

The aim of this study was to look for visual subjective and objective parameters of vocal fold dynamics being capable of differentiating healthy from pathologic voices in daily clinical practice applying endoscopic high-speed digital imaging (HSI).

Study Design and Methods

Four hundred ninety-six datasets containing 80 healthy and 416 pathologic subjects (232 functional dysphonia (FD), 13 bilateral, and 171 unilateral vocal fold nerve paralysis) were analyzed retrospectively. Videos at 4000 Hz (256 × 256 pixel) were recorded during sustained phonation. Subjective parameters were visually evaluated and complemented by an analysis of objective parameters. Visual subjective parameters were mucosal wave, glottal closure type, glottal closure insufficiency (GI), asymmetries of the vocal folds, and phonovibrogram (PVG) symmetry. After image segmentation, objective parameters were computed: closed quotient, perturbation measures (PMs) of glottal area, and left-right asymmetry values.

Results

HSI evaluation enabled to distinguish healthy from pathologic voices. For visual subjective parameters, GI, symmetrical behavior, and PVG symmetry exhibited statistical significant differences. For 95% of the data, objective parameters could be computed. Among objective parameters, closed quotient, jitter, shimmer, harmonic-to-noise ratio, and signal-to-noise ratio for the glottal area function differentiated statistically significant normal from pathologic voices. Applying linear discriminant analysis by combining visual subjective and objective parameters, accurate classifications were made for 63.2% of the female and 87.5% of the male group for the three-class problem (healthy, FD, and unilateral vocal fold nerve paralysis).

Conclusion

Actual acoustically applied PMs can be transferred to clinical beneficial HSI analysis. Combining visual subjective and objective basic parameters succeeds in differentiating pathologic from healthy voices. The presented evaluation can easily be included into everyday clinical practice. However, further research is needed to broaden our understanding of the variability within and across healthy and pathologic vocal fold vibrations for diagnosing voice disorders and therapy control.     

Correlation Between Solidification Behavior and Melt Crystallization Kinetics of Isotactic Polypropylene (iPP) during Injection Molding

The relationship between solidification behavior and crystallization kinetics, during the injection molding process of isotactic polypropylene (iPP) was investigated. It was found that the crystallization rate was in proportion to the cooling rate. The existence of a turning point (TP) in the dimensionless temperature (θ) vs. ln t curve, which is potentially applicable for the estimation of cooling time, was experimentally verified for iPP. The present study is expected to be useful for the optimization of the processing conditions during injection molding of crystalline polymers, and also supplies a good insight into further study of the “processing-structure-property” relationship of polymeric materials.     

Structure Formation of Blend and Sheath/Core Conjugated Fibers in High-Speed Spinning of PET,Including a Small Amount of PMMA

The blend of poly(ethylene terephthalate) (PET) and a small amount of polymer that has higher T _g than PET, such as polymethylmethacrylate (PMMA)—and is dispersed finely as immiscible particles in PET—exhibits lower molecular orientation than pure PET under high-speed fiber spinning. To obtain insight into the mechanism of the lower molecular orientation of the blend fiber, the sheath/core structure of PET (sheath)/PMMA (core) conjugated fiber (the same PET/PMMA weight ratio as in the blend fiber), was produced as a model. The thinning profile of the fiber diameter along the spinning line and the birefringence distribution of the cross-section were examined and compared among pure PET fiber, the conjugated fiber, and the blend fiber. The conjugated fiber had the lowest molecular orientation of PET in the sheath part, and its thinning process was accelerated similar to the blend fiber. As a result of the distribution of molecular orientation across the diameter of the conjugated fiber, it is considered that PMMA, having the high T _g , tends to solidify at a higher temperature (upstream) than PET in the thinning process, making the flow of PET accelerate as if it was pushed by PMMA. This causes the maximum dv/dx just before the solidification point to be smaller; therefore, the lower spinning stress, resulting in smaller birefringence of PET, can be considerable. This acceleration was generated at the interface of PET and PMMA, and spread toward the fiber surface as both polymers were thinning in elongational flow (in melt). On the other hand, close to the interface, molecules of PET were stretched by PMMA, resulting in an increase of birefringence. Such discussion is also considered to apply to the blend fiber. However, because the blend fiber had a significantly larger interface area compared with the conjugated fiber, it is considered that the increase of birefringence of PET by the interface drag force cannot be neglected. The larger particles of PMMA dispersed in PET results in the lower birefringence of PET that is supported by the elongation effect (i.e., the interface drag force).     

The Interface Kinetics of Crystal Growth Processes

A brief review of the present state of our understanding of the kinetic processes which take place on the atomic scale at the interface during crystal growth is presented in this paper. Computer simulations have played a central role in the development of this understanding. Three aspects will be discussed:(1) There are two classes of materials based on their different modes of crystallization. Molecular dynamics modeling has demonstrated that the growth rate for many simple materials is not thermally activated, but instead depends on the thermal velocity of the atoms.(2) The cooperative processes which give rise to the surface roughening transition. Kinetic Monte Carlo studies played a central role in the development of our understanding of how interface roughness dominates growth morphologies.(3) Solute trapping in alloys. Kinetic Monte Carlo simulations of alloys have led to an understanding of these kinetic effects during alloy crystallization.     

Kinetics of Spherical Interface in Crystal Growth

The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations.The growth rates of crystals are found to increase with the grain radius. The simulations show that the interface thickness and the Jackson α-factor increase as the growth proceeds, indicating that the interface becomes increasingly rough during growth. Due to the increasing interface roughening, the fraction of repeatable growth sites at interface f is proposed to actually increase in growth. An attachment rate, which is defined as the fraction of atoms that join the crystal interface without leaving, is used to approximate f, displaying a linear increase. With this approximation, we predict the growth rates as a function of the crystal radius, and the results qualitatively agree with those from the direct simulations.     

Kinetics of the Ordered Phase Growth across the Isotropic-Nematic Phase Transition in Liquid Crystal Azomethine Polymers during Cooling

Main-chain azomethine liquid crystal (LC) polymers varying in spacer length were studied using differential scanning calorimetry and polarizing optical microscopy. The nematic droplets appearing across the isotropic-nematic phase transition during cooling the polymer melt were treated statistically and their size distributions were described with equation based on the principles of irreversible thermodynamics. Kinetics of the ordered phase growth was described analytically with the universal law for cluster growth. Analysis of the mean LC droplet diameter as a function of time allowed recognition of two regimes of the ordered phase growth: i) nucleation and fast LC droplet growth and ii) consequent cluster coarsening. The length of the spacer in the polymer chain was shown to have an influence on the duration of the LC droplet growth regimes.     

Kinetics of the surface charging of a semiconductor during adsorption

The kinetic characteristics of the surface charging of a semiconductor during adsorption are analyzed, due allowance being made for the recharging of the biographic surface states during the adsorption process. It is shown that the form of the kinetic curves depends very substantially on the relationship between the characteristic relaxation times of the adsorption and biographic surface states.