Action Of Pulses Research Articles

Strain-Induced Luminescence of a Composite Material Based on Polymethyl Methacrylate and a Fine Powder of a Phosphor

A mechanoluminescent layer of a composite material based on a polymer of polymethyl methacrylate and a fine powder of phosphor SrAl2O4:(Eu2+,Dy3+) on the surface of polymethyl methacrylate is obtained. The mechanoluminescence of the composite layer under the action of short acoustic pulses and a mechanical impactor is studied. It is shown the composite layer has high efficiency of the mechanical-to-optical conversion.

Influence of Oxygen Pressure on Switching in Memoristors Based on Electromoformed Open Sandwich Structures

Samples of nonvolatile electrically reprogrammable memory elements (memristors) based on electroformed TiN–TiO2–SiO2–W open sandwich structures, made using thin-film technology, are studied. A technique is developed and experimental studies are performed of the effect of oxygen pressure over the surface of the insulating gap of structures and the current limiting mode during the action of a switching pulse from a low to a highly conductive state on the characteristics of memory elements. The existence of a threshold value of oxygen pressure at which switching stops and its dependence on the value of the limiting current are shown. An interpretation of the experimental results based on the ideas developed on the mechanisms of the processes of the formation and disappearance of particles of the conducting phase in the insulating gap of an electroformed structure is presented.

Increasing the Efficiency of Coagulation of Submicron Particles under Ultrasonic Action

The results of studies into the coagulation process of submicron particles (smaller than 1–2.5 μm) under various conditions of ultrasonic exposure are presented to identify the possibility of increasing the efficiency of coagulation. An analysis of the peculiarities of the coagulation process both with a sinusoidal effect and with shock-wave (pulsed) action has made it possible to establish that the shock-wave action provides a coagulation rate of submicron particles that is up to 20 times higher when compared with the sinusoidal effect at the same total energy of exposure. It is shown that the cause of the acceleration of the process is nonlinear effects arising from shock-wave action and affecting the coagulation rate of particles (a change in the cross-sectional area of collision, local medium compaction, and mutual diffusion of the gas surrounding the particle during the transitional flow regime between the free and continuous molecules).

Functional materials based on the effect of mechanoluminescence for monitoring the state of load-bearing structures

Researches of light-generating converters based on zinc sulfide allowed us to describe the physical nature of the light signal. The description of the physical nature of light generation by semiconductors is based on the band theory of conductivity. This allowed us to determine the conditions for the possibility of registering mechanical impacts using mechanoluminescent pulse pressure sensors. One of the important conditions, as it turned out, is the presence of manganese impurities in the material, which become centers of light emission. Also a necessary condition for the appearance of luminescence is the hardness of the sensor element, it facilitates the transfer of mechanical stress to the crystal lattice of mechanoluminescent material and the changes in it with the release of energy as light. This property of these materials allows them to operate in generator mode and convert mechanical action into an optical signal without additional energy sources. As a result, theoretical and experimental data on the possibility of detecting pulsed mechanical action using distributed mechanoluminescent converters were obtained. As one of the directions of application of such converters, it is proposed to create composite materials with the insertion of light-conducting fibers with longitudinal light transmission, covered with mecanoluminophore particles. This will allow to create composite materials with a self-diagnosis function and the ability to connect to optical data channels for continuous monitoring of the technical condition of load-bearing structures of buildings. Such materials are devoid of such disadvantages as: the need for power supply or a reference light stream, sensitivity to electromagnetic interference, and a low degree of embeddability in the structure, inherent in the devices currently used.

Resonance-enhanced two-photon ionization of hydrogen atom in intense laser field investigated by Bohmian-mechanics**Project supported by Jilin Province Science and Technology Development Plan Project–Excellent Youth Talents Fund Project, China (Grant No. 20180520174JH) and the National Natural Science Foundation of China (Grant Nos. 11704145 11904050, 11774129, 11747007, and 11534004).

Resonance enhanced two-photon ionization process of hydrogen atom via the resonant laser pulse is studied by Bohmian mechanics (BM) method. By analyzing the trajectories and energies of Bohmian particles (BPs), we find that under the action of high frequency and low intensity multi-circle resonant laser pulses, the ionized BPs first absorb one photon completing the excitation, and then absorb another photon, completing the ionization after staying in the first excited state for a period of time. The analysis of work done by the forces shows that the electric field force and quantum force play a major role in the whole ionization process. At the excitation moment and in the excitation-ionization process, the effect of the quantum force is greater than that of the electric field force. Finally, we discuss the principle of work and energy for BPs, and find that the electric field force and quantum force are non-conservative forces whose work is equal to the increment of mechanical energy of the system. In addition, it is proved that the quantum potential energy actually comes from the kinetic energy of the system and the increment of kinetic energy is equal to that of the kinetic energy of the system.

Dynamic stress control of bi-material structure subjected to sawtooth shock pulse based on interface characteristics

This paper focuses on dynamic stress control of bi-material structure under the action of sawtooth shock pulse. The factors that are likely to influence the dynamic stress are studied based on the analytical method. Then two bi-material models and a homogenous material model are investigated through the finite element method. The supplement of tungsten carbide layer could reduce the stress of aluminum alloy significantly are proposed here, while the supplement of polyamides layer, to some extent, enlarge the stress of aluminum alloy. It also suggests that the stress control is related to several key factors - the acoustic impedance, the Poisson's ratio, the ratio of thickness to width of material, the deformation and the wave frequency.

Laser Formation of Periodic Micro- and Nanostructures on the Surface of Monocrystalline Silicon

Experimental studies of the features of the formation of laser-induced periodic nanostructures on the surface of silicon wafers in the zones of action of second, millisecond and nanosecond laser pulses are conducted in the work. The results of microscopic investigations by optical and electron microscopes of periodic structures formed on surfaces with crystallographic orientation (111), (100) are presented. The obtained results can be used to optimize the laser pulse mode for controlled micro- nanostructuring of the semiconductor surface.

Излучение электромагнитной волны из магнитной пленки при воздействии фемтосекундного импульса света

Излучение электромагнитной волны из магнитной пленки при воздействии фемтосекундного импульса света

Numerical modeling of plasmonic properties of gold nanostars to prove the threshold nature of their modification under laser pulse

A mathematical model for the calculation of the optical and thermal properties of an ensemble of gold nanostars with different tip lengths L = 10 to 20 nm in an aqueous environment is proposed. The heating of a nanoparticle ensemble under irradiation by a laser pulse of a nanosecond duration: resonant λ = 808 nm and nonresonant λ = 1064 nm is studied. A significant blue shift of surface plasmon resonance during the formation of a vapor bubble around the nanoparticle was detected and described. Based on the analysis of the kinetics of nanoparticle heating under the action of a laser pulse before and after the formation of a vapor bubble, a theoretical description of the experimentally observed threshold nature of particle photomodification is given. It was found that the laser intensity Im necessary to achieve the melting temperature Tm (photomodification threshold) tends to increase with decreasing nanostar tip length and for an individual nanostar differs by an order of magnitude. However, up to 45% of the nanoparticles are heated to the melting temperature Tm by a single pulse with an intensity only 2.5 times higher than the minimum value of Im. At a wavelength of 1064 nm, Im is ∼6 times higher than at a wavelength of 808 nm.

Nonlocal Problem for a System of Partial Differential Equations of Higher Order with Pulsed Actions

We consider a nonlocal problem for a system of partial differential equations of higher order with pulsed actions. By introducing new unknown functions, the analyzed problem is reduced to an equivalent problem including a nonlocal problem for the impulsive system of the second-order hyperbolic equations and integral relations. We propose an algorithm for finding the solutions of the equivalent problem based on the solution of the nonlocal problem for the system of hyperbolic equations of the second order with pulsed action for fixed values of the introduced additional functions, which are then determined from the integral relations in terms of the obtained solution. Sufficient conditions for the existence of unique solution of the nonlocal problem for an impulsive system of hyperbolic equations of the second order are obtained by method of introduction of functional parameters. The algorithms for finding its solutions are constructed. Conditions for the unique solvability of the nonlocal problem for a system of partial differential equations of higher order with pulsed actions are established in terms of the coefficients of the system and boundary matrices.

Mathematical and Physical Modeling of Nonstationary Electromagnetic Processes in Elements with Reactive Power Self-Compensation

A mathematical model is proposed for analyzing nonstationary electromagnetic processes in a coil capacitor (a katkon, an electromagnetic element with reactive power self-compensation). Transients in the katkon are modeled physically. Qualitative features of unsteady electromagnetic processes at the katkon’s input and output are generalized and systematized for different types of loads under pulsed action.

Many-electron effects in secondary radiation generation during the interaction of atoms with intense laser pulses

A parallel program has been developed for numerically simulating the interaction of intense laser pulses with many-electron atoms based on non-stationary Kohn–Sham equations. With the use of this program, we calculate the nonlinear electron currents excited during ionization of argon atoms by intense two-color laser pulses. Based on the comparison with the solution of the time-dependent Schrödinger calculations for hydrogen atoms, the importance of taking into account many-electron effects in simulating the generation of secondary radiation in atomic gases under the action of ultrashort laser pulses is shown.

The study of the liquid metal drops fragmentation

The main models of the fragmentation of liquid metal droplets in a steam explosion based on thermal stress, shock-acoustic effects and explosive boiling water inside the melt were analyzed. Experimental installations are described and research results are presented. The experiments were carried out with samples of various metals (tin, nickel, zinc, stainless steel), which were heated in levitation mode using an inductor. The maximum temperature for heating a sample of ball-bearing steel did not exceeded 1600 °C. Then, in the molten state, the samples (droplets) fell into a cell filled with distilled water at room temperature. In the experiments, the temperature of the melting sample was monitored and the crushing process was recorded. An experimental material indicating the diversity of the forms of the fragments being formed was obtained. The latter circumstance confirms the assumption of the existence of various fragmentation mechanisms, including the method of breaking drops under the action of intense sound waves caused by the collapse of vapor formations. The results of numerical estimates are given, which indicate that the rate of cooling of particles formed in the process of fragmentation can reach values from 109 to 1010 K/s. These values are quite sufficient for obtaining various alloys with an amorphous structure. The possibility of destruction of vapor shells around hot drops under the action of pressure pulses caused by the collapse of adjacent vapor-gas formations has been experimentally confirmed.

Simulation of amplitude-frequency characteristics of friction strengthening process of flat machine parts’ surfaces

Friction treatment refers to surface strengthening (hardening) methods using highly concentrated energy sources, in the process of which a surface hardened layer with a nanocrystalline structure is formed. A highly concentrated energy source is formed in the contact area of the tool-part due to the high-speed friction (60-90 m/s) of the tool on the treatment surface. Friction treatment according to the kinematics of the process is similar to grinding. Transverse grooves are formed on the working surface of the tool to intensify the process of forming a reinforced layer with a nanocrystalline structure. The width of the groove provided a complete escaping of the tool from contact with the treated surface. Additional shock loads occur in the tool-contact area. The friction treatment process is discontinuous. The contact zone on the treated surface receives the pulsed action of thermal energy, shear deformation and additional shock load. The frequency of shock loads depends on the number of grooves on the working part of the tool.The calculation scheme of the elastic system of the machine is developed. A mathematical model to study the dynamic processes that take place during the friction treatment of flat surfaces is built. The amplitude-frequency characteristic of the processing is obtained. The developed model of the machining process based on the analysis of the dynamic characteristics of the process gives the possibility to select the required number of grooves on the working part of the tool, the rotation speed of the tool. The parameters of the elastic system of the machine and the processing parameters at which resonance is possible are determined.

Electrohydraulic adaptive hydropulse system


 
 
 The results of researches of functioning of electrohydraulic adaptive hydropulse system with definition of optimum range of energy of charging of the hydropneumatic accumulator are resulted. Based on the Taylor series, differential-difference transformations were synthesized and an iterative cycle was calculated and implemented on a computer to calculate the motion of a hydraulic hammer, which is characterized by dependences that reflect dynamic processes in accordance with the hydrohammer operation cycle. The range of regulation of energy of charging depending on the course of the conjugated boi-ka and the valve within 1,7 ... 3,05 kJ is established; and the volume of the pneumatic accumulator chamber is 2.6 ... 3.05 kJ. Maximum values of control ranges, respectively: 1.35 kJ and 0.45 kJ. To determine the control parameters of the adaptation process experimentally, within the industrial tests of the variant of the hydropulse system of impact on the oil well collector, it was found that the stabilization of oscillations from the pulse action, depending on the working environment, is achieved in 10-15 s. The developed electrohydraulic adaptive hydropulse system is recommended for introduction into production.
 
 

BEHAVIOR OF THE Ti-Zr-Ni THIN FILM CONTAINING QUASICRYSTALLINE AND APPROXIMANT PHASES UNDER RADIATIVE-THERMAL ACTION IN TRANSITION MODES

X-ray diffraction and SEM microscopy were used to study the structural and phase changes in a thin film obtained by magnetron sputtering of a Ti52Zr30Ni18 target (at.%) on a steel substrate under the radiation-thermal influence of pulsed hydrogen plasma on an QSPA Kh-50 accelerator. A technique has been worked out for the formation of the quasicrystalline and crystal-approximant phases as a result of high-speed quenching using pulsed action with a heat load of 0.6 MJ/m2. The changes in the contents of these phases as well as in their structure and substructure parameters were studied during isothermal vacuum annealing at a temperature of 550 °C and also as a result of irradiation with 5 plasma pulses in the range of heat load from 0.1 to 0.4 MJ/m2. The quasicrystalline phase was found to be resistant to irradiation with hydrogen plasma.

Increasing the Efficiency of Underground Short-Hole Drilling by Combined Action of Axial and Moment Pulses

The article substantiates the possibility of improving the efficiency of short-hole drilling by combining axial and moment pulses with a rotating drill cutter. The control of regime parameters of drilling, including parameters of axial and moment pulses, in order to establish rational ratios of parameters can be carried out by boring machines of the mechatronic class directly in the process of short-hole drilling. A methodology has been developed for conducting experimental studies in accordance with which experiments have been carried out and dependencies obtained that reflect the effect of the combined effect of axial and moment pulses on the penetration rate. The stress-strain state of the rock in the undercutter zone of the short-hole with the combined effect of axial and momentum pulses on the drilling tool is investigated using the method of finite element analysis.

The use of an adaptive mesh based on a quadtree for modeling the final state of a quantum field system under pulsed external action

The success of using mathematical models that determine the behavior of quantum field systems in parametric spaces critically depends on the level of optimization of the procedure of finding the solution. The paper considers the problem of calculating the density of carriers arising in graphene as a result of the action of a pulsed electric field. The basis of the model is a system of kinetic equations that provide the calculation of the residual distribution function. Its integration over momentum space gives the desired carrier density. The problem lies in the high computational complexity of covering the momentum space with a uniform mesh, which provides an accurate calculation of the density for various parameters of the field momentum. Moreover, the model does not contain criteria for determining satisfactory mesh parameters. The article proposes and implements a procedure for constructing an adaptive mesh in the form of a quadtree having a variable size of covering squares. The procedure is iterative and combined with the process of calculating the values of the distribution function.

DEGRADATION PROCESSES IN THE AI-TI-SI SYSTEM UNDER THERMAL SHOCK

In recent years, much attention of developers of integrated microcircuits is given to designing novel types of microprocessors, development, and mastery of technologies of both multilayer 3D integrated circuits and making devices based on complex semiconductors. The aim of the present work is to study thermal processes in the Al-Ti-Si multilayer system up to the development of degradation processes. The degradation issues in aluminum metallization with titanium sublayer deposited onto silicon surface are considered. The evolution of processes of irreversible destruction of film conductor under passage through it of single square-wave current pulses with energy up to 300 mJ and duration of 50…1000 μs was analyzed. It was found that, under the action of a single square-wave current pulse with a duration of no more than 80 μs and energy of 85 mJ, the priority process of structural damage is the melting of the metal film. Increasing pulse duration (τ > 80 μs) changes the priority of thermal degradation, and contact melting becomes the main mechanism of structure damage. It was also found that isothermal annealing leads to improving system heat-conducting properties and increasing critical current densities. This is related to the improvement of adhesion properties of the structure as well as with phase transformations in the Al-Ti-Si system in the course of annealing. The results of the article can be used in further studies of the properties of the AI-TI-SI system, as well as in the creation of semiconductor structures taking into account properties such as high electrical conductivity, good processability, the absence of chemical components in the Al-Si system, chemical stability, and a tendency to electromigration, the possibility of short circuit, high diffusion mobility, low melting point, the inability to attach the wire by soldering.

Laser-induced spin dynamics in the iron-yttrium garnet film doped with Si ions

A continuous increase in the volume of stored and processed data leads to stricter requirements for storage media. The most common information storage technology is currently based on magnetic materials, where information in the form of 0 and 1 is associated with the local direction of magnetization, determined by the external magnetic field created by the recording device. It is known that this approach has fundamental limitations on the recording speed which is almost achieved. The requirements for energy efficiency of storage media are also being made stricter. These circumstances lead to the development of alternative approaches to recording information. One of these approaches has been demonstrated in the field of ultrafast opto-magnetism, which has been booming over the past 20 years. It consists in recording information with short optical pulses without the application of an external magnetic field. However, it requires fundamental studies of physical processes, as well as materials, in which magnetization can be controlled by short optical pulses. In this paper, we consider the spin dynamics in a magnetic dielectric: a film of iron - yttrium garnet doped with silicon. The studies were carried out using the pump – probe technique over a time range of up to 800 ns. The spot size was 30 μm, the optical pulse duration was 35 fs, and the pump fluence was about 50 mJ/cm 2 . It is shown that a change in the magnetocrystalline anisotropy constants due to the action of a pump pulse on the structure causes a long-decaying magnetization precession with a period of about 200 ps. The dependences of the amplitude, phase, and decay of the precession on the magnitude of the external magnetic field in the range up to 1.84 kOe were obtained and analyzed. The studied processes can be considered on the basis of the Landau-Lifshitz-Gilbert model, and be of interest for the optical switching of magnetization, as well as the creation of various spintronic devices. It is shown that films of iron-yttrium garnet doped with silicon are a promising material for magnetic information carriers based on ultrafast opto-magnetism.