Topological dislocation-type defects and mechanisms of plasticity and failure of nanostructured and amorphous materials

Possible mechanisms of plastic deformation and failure of nanostructured and cluster amorphous materials have been considered. It is shown that the most probable carriers of plastic deformation in these materials are macrodislocations—linear topological defects of the regular nanocrystallite packing in the nanostructure or cluster packing in amorphous materials. Continuum models are proposed to describe the processes of plastic deformation and failure of nanostructured and cluster amorphous materials. Original Russian Text ? L.S. Vasil’ev, S.F. Lomaeva, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 128–131.     

Polarity of the Medium and Quenching of Fluorescence of Caratenoids and Phthalimides

The relation for the dependence of the rate of radiationless energy conversion of the S ₁ state k _q on the polarity of the medium, obtained previously by the author, has been used to interpret the known literature data on the lifetime of the S ₁ state of solutions of some caratenoids and phthalimides. It has been shown that in alcohols and water (normal and deuterated ones) the fluorescence quenching of 4-amino-, 4-methylamino-, and 4-dimethylamino-N-methylphthalimides (4AMP, 4MAMP, and 4DMAMP) as well as of peridinine in alcohols is due to H-bond formation. It has been established that a twofold increase in the number of amine atoms of hydrogen on passing from 4MAMP to 4AMP, as well as deuteration of solvents in the case of 4DMAMP, is followed by a decrease in k _q by a factor of 1.6 and 1.75, respectively. The mechanism of quenching in complexes formed with solvent molecules by means of the H-bond is discussed. It has been concluded that the quenching of fluorescence of phthalimides in such complexes is mainly due to the intersystem crossing initiated by the oscillations of the protons or deuterons of the H-bonds.     

Geometry and scaling laws of excursion and iso-sets of enstrophy and dissipation in isotropic turbulence

Motivated by interest in the geometry of high intensity events of turbulent flows, we examine the spatial correlation functions of sets where turbulent events are particularly intense. These sets are defined using indicator functions on excursion and iso-value sets. Their geometric scaling properties are analysed by examining possible power-law decay of their radial correlation function. We apply the analysis to enstrophy, dissipation and velocity gradient invariants Q and R and their joint spatial distributions, using data from a direct numerical simulation of isotropic turbulence at Re_λ ≈ 430. While no fractal scaling is found in the inertial range using box-counting in the finite Reynolds number flow considered here, power-law scaling in the inertial range is found in the radial correlation functions. Thus, a geometric characterisation in terms of these sets’ correlation dimension is possible. Strong dependence on the enstrophy and dissipation threshold is found, consistent with multifractal behaviour. Nevertheless, the lack of scaling of the box-counting analysis precludes direct quantitative comparisons with earlier work based on multifractal formalism. Surprising trends, such as a lower correlation dimension for strong dissipation events compared to strong enstrophy events, are observed and interpreted in terms of spatial coherence of vortices in the flow.     

NOx formation and flame velocity profiles of iso- and n-isomers of butane and butanol

NO formation and flame propagation are studied in premixed flames of iso- and n-isomers of butane and butanol through experimental measurements and direct simulation of experimental profiles. The stabilized flame is realized through the impingement of a premixed combustible jet from a contraction nozzle against a temperature-controlled plate. The velocity field is obtained by means of Particle Image Velocimetry (PIV) and nitric oxide concentration profiles are measured using Planar Laser Induced Fluorescence (PLIF), calibrated using known NO seeding levels. It is found that NO formation in n- and iso-isomers is comparable under the conditions considered, except for rich butanol mixtures, whereby NO formation is higher for iso-butanol. Generally, less NO is formed in butanol flames than in the butane flames. The experiment is simulated by a 1D chemically reacting stagnation flow model, using literature models of C1–C4 hydrocarbons [Wang et al., 2010] and butanol combustion chemistry [Sarathy et al., 2009, 2012]. NO prediction is tested using two of these mechanisms with a previously-published NO_x submechanism added into the butane and butanol models. While a good level of agreement is observed in the velocity field prediction under lean and stoichiometric conditions, discrepancies exist under rich conditions. Greater discrepancies are observed in NO prediction, except for the C1–C4 mechanism which shows good agreement with the experiment under lean and stoichiometric conditions. The current study provides data for further development of mechanisms with NO_x prediction capabilities for the fuels considered here.     

Experimental and Theoretical Study of the Electronic States and Spectra of TeH and TeLi

Gas-phase emission spectra of the hitherto unknown free radical TeLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which tellurium vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands were measured at high spectral resolution in the ranges 8000-9000 and 5700-6700 cm(-1) and vibrational and rotational analyses were performed. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of TeLi and the isovalent TeH and also electric dipole transition moments connecting them. As in the TeH system, the ground state of TeLi is found to be X(2)Pi(i), but with a remarkably smaller spin-orbit splitting. The TeLi calculations indicate a strongly bound A(2)Sigma(+) state, while in TeH the analogous state is computed to lie significantly higher at approximately 32 000 cm(-1), and it is strongly predissociated. Based on the theoretical analysis, the observed TeLi band systems are assigned to the transitions A(2)Sigma(+)(A1/2)-->X(1)(2)Pi(3/2)(X(1)3/2) and A(2)Sigma(+)(A1/2)-->X(2)(2)Pi(1/2)(X(2)1/2). Analysis of the spectra has yielded the molecular constants (in cm(-1)) X(1)(2)Pi(3/2):omega(e)=457.49(3), omega(e)x(e)=2.482(9), B(0)=0.408908(8); X(2)(2)Pi(1/2): T(e)=2353.44(3), omega(e)=456.28(4), omega(e)x(e)=2.635(8), B(0)=0.414954(8), p(0)=1.00637(4); A(2)Sigma(+): T(e)=8574.64(2), omega(e)=437.81(3), omega(e)x(e)=2.581(8), B(0)=0.423903(8), p(0)=-0.19915(2), where the numbers in parentheses are the standard deviations of the parameters. Comparison of the isovalent TeLi and TeH systems emphasizes that the difference in bonding character (ionic in TeLi vs covalent in TeH) is responsible for qualitative differences in the electronic spectra of these two molecules. Copyright 2001 Academic Press.     

Coherent Raman and hyper-Raman spectroscopy of excited and autoionizing states of atoms and ions in laser-produced and electric-discharge plasma

Summary The experimental results on four-wave Raman and hyper-Raman scattering in a laser-produced and electric-discharge plasma are presented. It has been shown that in spectra of four-wave mixing processes resonances appear due to the Raman and hyper-Raman scattering on atomic and ionic excited states. The temporal behaviour of the scattered-signal intensity has been found to be connected with the population relaxation of atomic and ionic excited states. We have observed for the first time the resonance in the spectrum of coherent hyper-Raman scattering in electric-discharge plasma associated with the electron transition between the excited and autoionizing state of a copper atom. Paper presented at the ?XI European CARS Workshop?, Florence, Italy, 23–25 March, 1992.     

高光谱成像技术在果蔬品质与安全无损检测中的原理及应用

水果和蔬菜的品质与安全是消费者最为关心的问题。传统的化学检测方法是一种费时费力的破坏性检测技术。随着成像和光谱技术的快速发展,高光谱成像技术已经广泛应用于农产品品质与安全的快速无损检测中。高光谱成像技术融合了传统的成像和光谱技术的优点,可以同时获取被检测物体的空间信息和光谱信息,因此该技术既可以像检测物体的外部品质,又可以像光谱技术一样检测物体的内部品质和品质安全。目前,已经有大量的基于高光谱成像技术检测水果和蔬菜品质与安全的研究性论文发表,为了深入了解高光谱成像技术的检测原理并跟踪国内外最新的研究进展,综述了高光谱成像技术在水果和蔬菜外部品质、内部品质和品质安全检测中的原理、发展和应用。另外,还简要介绍和讨论了高光谱成像系统的构成、常用的数据分析方法、发展趋势及面临的挑战。     

Instability and disruption of precision cumulation of cavities and mass flows in the field of gravitational and inertial forces and other dipole perturbations

The effect of gravitational and inertial forces on the precision cumulation of cavities, fast mass flows, and detonation and shock waves is studied in stages. The possible effects of these forces on the motion of masses and waves (the velocity, direction and structure of the waves can change) and on the properties of the medium in front of the waves that influence the change in the parameters and refraction of the waves are noted. It is shown that it is advantageous to perform precision cumulation experiments in zero-gravity. Zh. éksp. Teor. Fiz. 111, 2001–2015 (June 1997)     

Plasticity and strength of micro- and nanocrystalline materials

This review is devoted to the effect of grain boundaries on the deformational and strength properties of poly-, micro-, and nanocrystalline materials (predominantly metals). The main experimental facts and mechanisms concerning the dislocation structure and mechanical behavior of these materials over wide ranges of temperatures and grain sizes are presented. The experimentally established regularities are analyzed theoretically in terms of equations of dislocation kinetics taking into account the properties of grain boundaries as barriers, sources, and sinks for dislocations and as places where dislocations annihilate. The origin of the Hall-Petch relations for the yield stress and the flow stress as functions of the grain size, as well as the deviations from these relations observed in nano- and microcrystalline materials, is discussed in detail in terms of the dislocation-kinetics approach. Embrittlement of micro- and nanocrystalline materials at low temperatures and superplasticity of these materials at elevated temperatures are also analyzed in terms of the dislocation-kinetics approach.     

Solubility and charge inversion of complexes of DNA and basic proteins

The basic proteins, protamines and histones H1, are known to condense DNA in vivo. We examine here their ability to condense and solubilize in vitro linear DNA [and a synthetic polyanion, Poly(Styrene-Sulfonate) or PSS] at low ionic concentrations by varying the charge concentration ratio. Phase separation is observed in a very narrow range of ratios for short DNA and PSS; on both sides of this range, polydisperse and charged complexes are formed. A charge inversion is detected. For long DNA chains however, a different behavior is observed: the complexes are not soluble in excess of proteins.     

Magnetic properties and structures of PrPt and NdPt

The magnetic properties of the CrB-type orthorhombic phase of PrPt and NdPt are presented. Below their ordering temperature which is 15 and 23 K respectively, these compounds exhibit a ferromagnetic behaviour. The magnetic structures determined by neutron diffraction are collinear. While in PrPt, the magnetic moments are parallel to c, in NdPt, the moments lie in the (a, c) plane and make an angle of 22° with a. These properties and especially the peculiar moment direction in NdPt are discussed in terms of crystalline electric field effects on the rare earth ion.     

Kinetics and dynamics of muon localisation and trapping

The physics of muons in solids involved three basic questions: Where do muons go? Through which states do they pass during their lifetime? How can we establish mechanisms for these solid state processes? This paper discusses the underlying factors of quantum diffusion, the dynamics of trapping, and the importance of metastable states. A further central factor is the random strain present in even the best crystals, and its character and influence are outlined. I shall summarise the growing evidence for the importance of transient states in semiconductors, metal hydrides and in metals like Al and Cu, and indicate some of the consequences of the non-equilibrium behaviour.     

电动力学课程思政建设的思考与实践

开展专业课程的思政建设是当今教育领域的一个重要的研究问题,本文结合物理学专业的电动力学课程进行课程思政建设的研究和实践,有机结合课程内容和特点,挖掘课程思政元素和切入点,通过教学实践初步取得教学效果,对理科专业课程思政建设起到积极的借鉴和推动作用,真正做到课程育人,发挥课程应有的作用,并提出总结和展望.     

Quantum and surface properties of free films and nanoshells of molecular and atomic thicknesses

An original technology and the properties of new thin film nanoobjects, free films and shells of molecular and atomic thicknesses, are presented. Special attention is paid to shells of monoatomic or monomoleculer thickness with unique surface properties that have not been found in bulk materials.     

金刚石中氦、氢含量的变化及在金刚石生长中的意义

天然金刚石自中心至边缘的显微傅里叶变换红外光谱研究表明:氮和氢在金刚石中的分布是不均匀的,这说明金刚石在整个生长过程中的物质环境是有差异的;中心至边缘的含氮总量、C-H键含量的总体降低趋势表明金刚石的生长过程是一个氮、氢的消耗过程,而中部的升高变化说明金刚石生长环境中存在氮、氢的补充,但氮补充得比氢更早一些.据此,可以将金刚石的生长过程划分为早期成核与长大、中期长大及末期长大三个阶段,其中早期和末期是氮和氢的消耗阶段,中期需要进行氮和氢的补充,且氮应该更早补充.氢对金刚石的生长是有利的,氢和氮不是以氮氢化合物的形式存在于金刚石生长的物质环境中,这暗示着在高温高压合成金刚石中欲引入氢,应当避免氮氢化合物的形成.     

番茄红素可见吸收光谱和荧光光谱的测量与分析

采用ICCD光谱探测系统对不同浓度番茄红素的二硫化碳溶液吸收谱的相对吸收强度进行了测量,结果显示在一定浓度范围内,番茄红素稀溶液的吸收规律满足朗伯-比尔定律;分别用丙酮、正己烷、石油醚、苯、乙酸乙酯和二硫化碳作为溶剂对番茄红素可见吸收光谱进行了测量,对结果进行分析后发现苯、乙酸乙酯和二硫化碳的番茄红素溶液的特征吸收峰的波长位置与以丙酮作为溶剂相比有不同程度的红移效应;番茄红素-丙酮溶液中加入水后溶液颜色随着加水量的增加逐渐变浅,溶液吸光度降低,当丙酮与水的体积比为4∶1时吸收光谱在紫外出现一新的吸收峰。产生这些现象的原因是番茄红素溶于不同溶剂时,溶剂分子对番茄红素分子作用不同。用荧光光度计采集不同浓度的番茄红素丙酮溶液的荧光光谱,结果表明番茄红素溶液的荧光光谱主要集中在500～680 nm波段,浓度低于50 μg·mL^-1时,番茄红素的荧光强度随着浓度的增加而呈线性增加。当浓度高于60 μg·mL^-1时,荧光强度因为番茄红素分子间的相互作用而下降。     

Investigation of radiation damage and hardness of H- and He-implanted SiC

In this study, an investigation was conducted in order to determine the effects of high-dose H and He ion implantation on the structure of 3C-SiC and 6H-SiC as well as the effects on material hardness in order to understand the role of H and He produced in SiC by neutron-induced transmutations as described by Heinisch et al. [J. Nucl. Mater. 2004, 327, 175–181.]. H and He ions were implanted into polycrystalline 3C-SiC on a Si substrate and single-crystal bulk 6H-SiC, respectively, at an ion energy of 100 keV, and the total dose that was used for both species was 10¹⁷ ions/cm² in the temperature range of 473–573 K. The specimens were annealed at 1000°C for 20 min in an inert Ar atmosphere. The damaged region in the He-implanted 6H-SiC had a high density of small bubbles, but no cracks were observed. Severe cracking was observed along the damaged region in the H-implanted 3C-SiC specimens as well as a high density of hydrogen platelets. Neither specimen displayed any amorphization. Nanoindentation hardness measurements showed a marked increase in the hardness of the annealed He-implanted 6H-SiC, which was ascribed to the creation of point defects inhibiting interplanar slip. There was also a large decrease in hardness corresponding to the depth of the ion damage.     

Growth mechanism and modification of electronic and magnetic properties of silicene

Silicene, a monolayer of silicon atoms arranged in a honeycomb lattice, has been undergoing rapid development in recent years due to its superior electronic properties and its compatibility with mature silicon-based semiconductor technology. The successful synthesis of silicene on several substrates provides a solid foundation for the use of silicene in future microelectronic devices. In this review, we discuss the growth mechanism of silicene on an Ag(111) surface, which is crucial for achieving high quality silicene. Several critical issues related to the electronic properties of silicene are also summarized, including the point defect effect, substrate effect, intercalation of alkali metal, and alloying with transition metals.     

Geometry and Elasticity of Strips and Flowers

We solve several problems that involve imposing metrics on surfaces. The problem of a strip with a linear metric gradient is formulated in terms of a Lagrangian similar to those used for spin systems. We are able to show that the low energy state of long strips is a twisted helical state like a telephone cord. We then extend the techniques used in this solution to two–dimensional sheets with more general metrics. We find evolution equations and show that when they are not singular, a surface is determined by knowledge of its metric, and the shape of the surface along one line. Finally, we provide numerical evidence by minimizing a suitable energy functional that once these evolution equations become singular, either the surface is not differentiable, or else the metric deviates from the target metric.     

ORSAT and modifications of SEFT and APT

Up to now, three subspectra are usually needed for the complete assignment of all signals in 13C spectrum: two DEPT spectra (phi = 90 degrees and phi = 135 degrees) and a proton decoupled spectrum. In this paper, we present a method in which a complete assignment becomes possible with merely two spectra. For this purpose, a new pulse sequence (ORSAT) has been elaborated by using off-resonance irradiation. The method described here is a further development of SEFT and APT. The second required spectrum is a DEPT (phi = 135 degrees). Signal assignment of cholesteryl acetate is demonstrated as an example. 13C routine spectroscopy can be significantly accelerated by applying this method.