Single-domain magnetic nanoparticles in an alternating magnetic field as mediators of local deformation of the surrounding macromolecules

The forces, deformations, and stresses generated in macromolecules attached to single-domain magnetic nanoparticles under the influence of a low-frequency (nonheating) magnetic field have been analyzed analytically and numerically. It has been shown that, in bioactive macromolecules, an alternating magnetic field with an induction of 0.1–1.0 T and a circular frequency of ?10⁴ s^?1 can induce forces up to several hundred piconewtons, absolute deformations up to a few tens of nanometers, as well as compressive and shear stresses exceeding 10⁷ Pa. These mechanical stimuli are sufficient for a significant change of interatomic distances in active centers, conformation of macromolecules, and even a breaking of some bonds, which makes it possible to develop a new technological platform for targeted delivery of drugs, remote control of their activity, and cancer-cell destruction.     

Hardening and softening during fatigue fracture

Summary The comparison of the change of hardness and plastic deformation amplitude at a constant stress loading or stress amplitude at a constant deformation loading during the fatigue process shows some singularity of the hardening and softening effects. These effects were investigated on mean carbon and low-alloyed steel and on globular cast iron.The fatigue fractures at cycle numbers 10⁴÷10⁶ under stresses below the yield strength predominate in the softening process, which arises after an inconsiderable hardness increase extends in the region to 0·2 from the fracturing cycle number. Under the stresses above the yield strength, which in some cases for annealed and coarse-grained states are below the fatigue limit, the hardening process predominates, followed by a hardness increase in the field up to 0·25 and above the fracturing cycle number.At low cycle fatigue fractures with cycle numbers < 10⁴ depending on the cyclic plastic properties of steels the fatigue process can be followed by a continuous hardening or softening till fracture. This process is characterized by the change of the deformation amplitude and a one-sided accumulation of plastic deformations at a constant amplitude of active stresses. The one-sided accumulation of deformations commonly ends in a quasistatic failure. Under loading with a constant deformation amplitude during softening a fatigue fracture takes place as a result of damage accumulation under the alternating stresses with amplitudes decreasing with cycle number.     

The effects of substructure on fatigue crack propagation

The correlation between the initiation and propagation of fatigue cracks and the substructure formation was examined using aluminium specimens. The effects of substructures introduced by static and alternating stresses and those of the recovery of the substructure on the propagation rates of fatigue cracks were also studied. Observations of the substructures were made by means of the X-ray micro-beam technique. The principal results obtained are as follows:

1. At the time of fatigue crack initiation a definite substructure develops at the root of a notch made on the specimen edge.
2. The rate of fatigue crack propagation has a relation to the characteristics of the substructures at the tip of the fatigue cracks.
3. While the rates of propagation are retarded by static pre-strains, they increase in proportion to the degree of substructure formation due to alternating stresses.
4. The rates are usually reduced by the recovery after alternating deformation.

On the basis of the above results, the significance of substructures for fatigue fracture is discussed.     

On the application of X-ray diffraction in studying heat-transfer surfaces of steam generators

The effect of thermal cycling on the appearance of alternating stresses in the walls of tubes of perlite low-alloyed and austenitic chromium–nickel steels is studied by X-ray diffraction to develop the criteria of their compatibility. Optimal operating temperatures are estimated for the basic metals and the weld seam realized on their basis. Coincidence between experimental estimates and optimal temperatures established under long-term operation is noted. This may be considered as confirmation of the possibility of applying the stated approaches in predicting the development of hot cracks in the zone of a weld seam and the selection of operating temperatures, at which fields of internal stresses of certain value and sign are formed.     

Role of stability of the structural state in the change in microcontact spectra of zinc single crystals

This study is devoted to the problem of obtaining microcontacts with a controllable structure and geometry. Laws are established which govern the change in features of microcontact spectra (MCS) in the presence of stable and metastable small-angle twist boundaries in material subjected simultaneously to mechanical loading and a high-density electric field. It is shown that the effect of basis dislocations on the MCS can be discerned thanks to the fact that the field of internal stresses from dislocations pinned in a hexagonal network is considerably greater than the diameter of the microcontact. A quantitative study is made of the parameters characterizing the MCS with a specified structural state in the micro-contraction region. The effect of instability of the structural state resulting from alternating torsion on the MCS is also examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 65–68, December, 1989.In conclusion, we would like to thank I. K. Yanson for discussing our findings with us.     

埋置量子点应力分布的有限元分析

通过衬底材料和外延材料的交替生长方式制备出多层排列的自组装量子点超晶格结构.这些埋置量子点的应力/应变场影响着它们的光电性能、压电性能以及力学稳定性.基于各向异性弹性理论的有限元方法,研究了埋置金字塔形应变自组织Ge/Si半导体量子点的应力/应变分布以及流体静应变和双轴应变分布,并与非埋置量子点的应力/应变分布做了比较,指出了它们之间的异同以及覆盖层对量子点应力/应变分布的影响. 关键词： 量子点 应力分布 应变分布     

Oscillations of the charge in oxide at silicon surface as an origin of the process leading to the long-range effect

A model of the excitation of the periodical stress pulses in the silicon-oxide system leading to generation of moving discrete breathers (local nonlinear wave disturbances of the atomic system) has been suggested. The latter can provide transportation of energy through the bulk of a sample at the external effect on its surface (the long-range effect). Several scenarios of evolving alternating electrical fields in oxide resulting (due to its local piezoelectricity) in corresponding changes of stresses have been considered.     

Laser generation of acoustic waves at a periodic domain structure in lithium niobate

Generation of coherent acoustic oscillations due to the interaction of laser pulses with the periodic domain structure formed in a lithium niobate single crystal is observed. It is found that the excitation of acoustic waves is most efficient when the generated wavelength is equal to the period of the domain structure. The proposed mechanism of the optical generation of acoustic oscillations consists of the photogeneration of free carriers, which compensate the polarization fields within the domains, and the occurrence of alternating elastic stresses caused by the piezoelectric effect.     

交叉缩放椭圆管CaCO3污垢特性的实验研究

采用对比实验的方法对交叉缩放椭圆管与铜光管的传热和CaCO3污垢特性进行了研究,并用数值方法模拟了交叉缩放椭圆管的内部流场和壁面剪切力。实验结果表明：交叉缩放椭圆管的换热和抗垢性能均优于在对应状态下的铜光管,这主要是由于交叉缩放椭圆管的内部流场和壁面剪切力的周期性变化所引起的。交叉缩放椭圆管在低流速时污垢热阻渐近值较大...     

Elastic deformation of Ti films during alternating bending

The effect of the state of stress at a film-substrate interface on the elastic deformation of Ti films is studied during alternating bending. The Al substrate compliance is shown to cause coherent deformation of the film-substrate system, resulting in the corrugation of a Ti film and the appearance of a wavelike film-substrate interface. Fatigue tests lead to the formation of a periodic distribution of normal and tangential stresses along the interface, and this distribution favors periodic film corrugation. The corrugation of a Ti film on a Ti substrate occurs randomly in local film separation areas and is caused by defects accumulated at the interface.     

交叉缩放椭圆管换热与流阻实验研究及分析

对交叉缩放椭圆管进行了实验和数值研究,给出了换热和沿程阻力系数实验拟合关联式。交叉缩放椭圆管管内 截面交叉变化诱导产生强烈的二次流和纵向涡流,改善了速度场与温度场之间的协同关系。实验和数值模拟结果表明,交 叉缩放椭圆管管内的流动在Re≥500即表现为湍流,换热强化效果显著。     

X-Ray determination of residual stresses after machining

Two-sided repeated inclined patterns ate used. The principal directions of the state of stress may not coincide with directions related to the shape, which is due to the way in which residual stresses arise. The residual change in lattice constant in the surface layers is due to macroscopic stresses, not to oriented microscopic stresses.     

Dynamic analysis of flexible linkage mechanisms under uniform temperature change

Deformation and stresses are produced not by mechanical forces alone, but by temperature variation as well. The additional stresses of a flexible mechanism caused by the temperature change should not be ignored. The generalized equations of motion for flexible linkage mechanisms, in which the thermal effects are taken into account, are developed by utilizing the virtual work method and the finite element theory in this paper. Since the determination of thermal stresses plays an important role in the design of mechanisms operating at elevated temperatures, the stress–strain relationship should include the effects of temperature. Based on the closed-form numerical algorithm, the equations are solved and the recursive scheme is proved to be efficient and converged in a few iterations for the cases examined. The Runge–Kutta method is also applied to study the transient response of the temperature change. Numerical solution results show that a small change of temperature will cause a significant change of the stresses of a flexible mechanism. The effects of temperature change should not be ignored when analyzing the dynamic performance of flexible mechanisms.     

Effect of Mechanical Stresses and Annealing on the Magnetic Structure and the Magnetic Impedance of Amorphous CoFeSiBCr Microwires

The structural and magnetic properties of amorphous ferromagnetic microwires can undergo significant measurements under the action of external mechanical stresses and heat treatment. The study of transformations occurring in this case is important for designing various sensors of mechanical stresses, loading, and temperature and also for inducing in the wires a certain type of magnetic anisotropy that plays a significant role in the realization of various effects in them. In this work, the influence of external stresses and annealing on the processes of the magnetization and the magnetic impedance of Co₇₁Fe₅B₁₁Si₁₀Cr₃ microwires having a low positive magnetostriction (~10^-8) in amorphous state has been studied. The influence of external stresses leads to a sharp change in the character of the magnetization reversal curve, which was due to the change in the sign of the magnetostriction and the type of magnetic anisotropy. The amplitude of higher harmonics and the value of the magnetic impedance, respectively, are sensitive to mechanical stresses. Elastic stresses in the wires with a partial crystallization do not lead to a marked change in the magnetic properties; however, annealing can lead to a substantial increase in the axial magnetic anisotropy of the wires existing in the stressed state. The experimental results are analyzed in the framework of a magnetostriction model of induced magnetic anisotropy.     

Change of surface properties of high-chromium cast iron under conditions of laser treatment and wear in a pellet stream

We investigate the influence of laser treatment on the formation of residual stresses relative to the changing structure-phase composition in the surface layers of high-chromium cast iron with 16% chromium. We show that appreciable tensile stresses are produced in the region of the laser action and that their distribution depends on whether the laser treatment was or was not accompanied by surface melting. The produced residual stresses are responsible for the formation of a large number of cracks. Preheating to 400°C lowers the level of the tensile residual stresses and prevents crack formation. A pellet stream acting on the surface produces cold-work hardening layers in which the tensile stresses change into compressive ones. The depth, hardness, and magnitude of the compressive residual stresses depend on the method used to work harden the cast iron and on the angle of attack of the pellet as it acts on the surface.Translation of Preprint No. 195, Lebedev Institute of Physics, Academy of Sciences of the USSR.     

Influence of the stress field of a tilt boundary on a Frank-Read source generating dislocations under the action of ultrasound

The influence of a nonuniform field of internal stresses and the generation of a dislocation loop by a Frank-Read source operating under the action of an alternating load is investigated by computer simulation. It is shown that the field of a tilt boundary affects every stage of development of a dislocation loop until its closure. The influence of the boundary field is determined by the ratio between the length of the source and the space scale of the field nonuniformities. It is established that not only the value of the dynamic yield point but also the form of its dependence on the ultrasonic frequency can vary in an internal stress field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 35–39, February, 1985.     

Electroviscous effect in an alternating electric field

Experimental dependence of the relative dynamic viscosities of liquid dielectrics on the applied alternating voltage amplitude and frequency is presented. The voltage frequency was varied from 20 Hz to 2 kHz. The variation of viscosity can be attributed to a change in the liquid structure, with ion-molecule complexes centered at the ions produced as a result of charge injection from an electrode. A change in the injection regime leads to a change in viscosity.     

Microplastic deformation of polycrystalline iron and molybdenum subjected to high-current electron-beam irradiation

A technique for determination of residual stresses at various distances from the irradiated surface is proposed. It is established for iron and molybdenum that compressive stresses are set up under irradiation by low-energy high-current electron beams and that their values decrease sharply with increasing distance from the surface. The residual stresses are much smaller in absolute magnitude than those operating during irradiation. It is shown that the change in resistance to microplastic deformation on irradiation with low-energy high-current electron beams is governed not only by formation of a gradient dislocation substructure in the surface layer, but also by the residual stresses and the appearance of the Bauschinger effect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 126–132, March, 1996.     

New Phase Transitions of the Ising Model on Cayley Trees

We show that the nearest neighbor Ising model on the Cayley tree exhibits new temperature–driven phase transitions. These transitions occur at various inverse temperatures different from the critical one. They are characterised by a change in the number of Gibbs states as well as by a drastic change of the behavior of free energies at these new transition points. We also consider the model in the presence of an external field and compute the free energies of translation invariant and some alternating boundary conditions.     

Acoustical wave propagator for time-domain dynamic stress concentration in a plate with a sharp change of section

The acoustical wave propagator technique is applied to study the time-domain dynamic stress concentration in a two-dimensional flexible plate with a sharp change of section. As a wave packet approaches the plate discontinuity where the sharp change of thickness is introduced, the spatial interference patterns in the displacement of the plate and internal stresses vary with time. The constructive interference of stresses is referred to as time-domain stress concentration. The superposition of wave fronts of incident and reflected wave packets is used to explain the spatial distribution of the interference patterns. The increase of dynamic stress near the vicinity of the discontinuity boundary of the plate is studied as a function of time and the thickness ratio of the plates.