Herein, we describe the design of a laboratory setup operating as a high-precision tribometer. The whole design procedure is presented, starting with a concept, followed by the creation of an exact ...3D model and final assembly of all functional parts. The functional idea of the setup is based on a previously designed device that was used to perform more simple tasks. A series of experiments revealed certain disadvantages of the initial setup, for which pertinent solutions were found and implemented. Processing and correction of the data obtained from the device are demonstrated with an example involving backlash and signal drift errors. Correction of both linear and non-linear signal drift errors is considered. We also show that, depending on the research interests, the developed equipment can be further modified by alternating its peripheral parts without changing the main frame of the device.
Thermal stability is an important feature of the materials used as components and parts of sensors and other devices of nanoelectronics. Here we report the results of the computational study of the ...thermal stability of the triple layered Au@Pt@Au core-shell nanoparticles, which are promising materials for H
O
bi-directional sensing. A distinct feature of the considered sample is the raspberry-like shape, due to the presence of Au nanoprotuberances on its surface. The thermal stability and melting of the samples were studied within classical molecular dynamics simulations. Interatomic forces were computed within the embedded atom method. To investigate the thermal properties of Au@Pt@Au nanoparticles, structural parameters such as Lindemann indexes, radial distribution functions, linear distributions of concentration, and atomistic configurations were calculated. As the performed simulations showed, the raspberry-like structure of the nanoparticle was preserved up to approximately 600 K, while the general core-shell structure was maintained up to approximately 900 K. At higher temperatures, the destruction of the initial fcc crystal structure and core-shell composition was observed for both considered samples. As Au@Pt@Au nanoparticles demonstrated high sensing performance due to their unique structure, the obtained results may be useful for the further design and fabrication of the nanoelectronic devices that are required to work within a certain range of temperatures.
The phenomenon of rate-dependent adhesion has long been recognized as an intricate problem, and the so-far-developed physics and mechanics-based approaches resulted in analytical relations between ...the implicit form between the work of adhesion and the contact front velocity which are difficult to implement in practice. To address this issue in the framework of spherical indentation, the adhesion relaxation test in a nominal point contact is introduced to estimate the rate-dependent adhesion. Based on a stretched exponent approximation for the contact radius evolution with time, a relatively simple four-parameter model is proposed for the functional relation between the work of adhesion and the contact front velocity, and its fitting performance is compared to that of the known Greenwood–Johnson and Persson–Brener models.
The adhesive contact between a spherical steel indenter and a fragment of a transparent soft rubber sheet fixed on a glass substrate has been studied experimentally. Comparison of experimental data ...with the results of analytic theory and numerical simulation has revealed quantitative agreement of the results of these three approaches. We have also studied the effect of the duration of the contact between the indenter and the indentation depth on its adhesion strength. The peculiarities of experiments performed with a controllable displacement and a controllable force are considered.
The results of application in monopulse lasers based on yttrium aluminum garnet resonators with Nd
3+
ions based on the optical scheme of a four-pass amplifier with one-sided lateral pumping of the ...active element by monospectral laser diode arrays are presented. The proposed resonator schemes make it possible to increase the output energy of single pulses of laser radiation. Monospectral gratings with efficient heat removal from laser diodes are capable of ensuring the operability of lasers with an increase in the repetition rate of monopulses and an expansion of the ambient temperature range.
We consider analytical, numerical, and experimental approaches developed to describe the mechanical contact between a rigid indenter and an elastic half-space coated with an elastic layer. Numerical ...simulations of the indentation process were performed using the recently generalized boundary element method (BEM). Analytical approximation of the dependence of contact stiffness on the indenter diameter was used to verify the results of BEM simulations. Adhesive contacts of hard indenters of different shapes with soft rubber layers have been experimentally studied using specially designed laboratory equipment. The comparison of the results from all three implemented methods shows good agreement of the obtained data, thus supporting the generalized BEM simulation technique developed for the JKR limit of very small range of action of adhesive forces. It was shown that the half-space approximation is asymptotical at high ratios of layer thickness h to cylindrical indenter diameter D; however, it is very slowly. Thus, at the ratio h/D = 3.22, the half-space approximation leads to 20% lower contact stiffness compared with that obtained for finite thickness using both an experiment and simulation.
•A newly developed W-N potential based on Tersoff-Brenner formalism was used.•N accumulation reduces W sputtering yield by almost an order of magnitude.•Approximately half of sputtered W atoms leave ...the surface as a WN molecule.•Nitrogen saturation occurs by the growth of the N sputtering yield with the fluence.•Nitrogen reflection coefficient remains constant during the accumulation.
Gaseous nitrogen is planned to be used as a seeding species to control the power flux in future fusion reactors with ITER-like divertors. Nitrogen interacts with the first wall materials, particularly with tungsten, leading to sputtering and changes of chemical composition of the material. We use the molecular dynamics methods with a recently developed WN potential to analyze the mechanisms leading to these modifications. We performed the simulations of cumulative nitrogen irradiation runs of tungsten surface. The sputtering yields obtained in our cumulative runs are in good agreement with experimental data. We observe the decrease of the tungsten sputtering yield with nitrogen accumulation and determine the reasons for the observed trend. The cluster analysis reveals the composition of the sputtered particles, suggesting the swift chemical sputtering process that occurs under the prolonged nitrogen irradiation of tungsten. We also observe and analyze the nitrogen saturation in the temperature range below the thermal stability limit.
The problem of a collision of a spherical homogeneous particle with a half-space is solved numerically. The coefficient of the normal velocity restitution is calculated as a function of the initial ...velocity in the presence of the mechanical energy dissipation due to plastic deformations and adhesion interaction between the surfaces of contacting bodies. The strain hardening effect is taken into account using the criterion of nonlocal plasticity introduced before. The study is carried out in dimensionless parameters, which makes it universal. The analytical expression is found for the critical initial velocity above which a plastic deformation starts. The simulation results agree well with the available experimental data.
The magnetic response related to the paramagnetic Meissner effect (PME) is studied in a high quality single crystal ZrB12 with non-monotonic vortex-vortex interactions. We observe the expulsion and ...penetration of magnetic flux in the form of vortex clusters with increasing temperature. A vortex phase diagram is constructed, and shows that the PME can be explained by considering the interplay among the flux compression, the different temperature dependencies of the vortex-vortex and the vortex-pin interactions, and thermal fluctuations. Such a scenario is in good agreement with the results of magnetic relaxation measurements.
The results of determination of the peak power of monopulses of YAG:Nd
3+
laser emission by two methods are presented. It is shown that the most reliable data can be obtained by the procedure from ...GOST and by the often used method when recording the time form of the monopulse of radiation using an FK-15 coaxial photocell. An often used technique using the measured value of the monopulse duration by the level of 0.5 of the amplitude value, when recording the time shape using an LFD-2 avalanche photodiode overestimates the value of the peak power of the monopulse compared to a reliable one by 12%.
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