Anisotropic Radiation in Heterostructured “Emitter in a Cavity” Nanowire

Tailorable synthesis of axially heterostructured epitaxial nanowires (NWs) with a proper choice of materials allows for the fabrication of novel photonic devices, such as a nanoemitter in the resonant cavity. An example of the structure is a GaP nanowire with ternary GaPAs insertions in the form of nano-sized discs studied in this work. With the use of the micro-photoluminescence technique and numerical calculations, we experimentally and theoretically study photoluminescence emission in individual heterostructured NWs. Due to the high refractive index and near-zero absorption through the emission band, the photoluminescence signal tends to couple into the nanowire cavity acting as a Fabry–Perot resonator, while weak radiation propagating perpendicular to the nanowire axis is registered in the vicinity of each nano-sized disc. Thus, within the heterostructured nanowire, both amplitude and spectrally anisotropic photoluminescent signals can be achieved. Numerical modeling of the nanowire with insertions emitting in infrared demonstrates a decay in the emission directivity and simultaneous rise of the emitters coupling with an increase in the wavelength. The emergence of modulated and non-modulated radiation is discussed, and possible nanophotonic applications are considered.

Experimental Study and CFD Modeling of Fluid Flow and Heat Transfer Characteristics in a Mini-Channel Heat Sink Using Simcenter STAR-CCM+ Software

The present work describes an experimental study and CFD modeling of fluid flow and heat transfer characteristics in a heat sink with several asymmetrical heated mini-channels. The data from the experimental research were the basis for numerical calculations. During experiments, the temperature measurement of the outer heater surface was performed by infrared thermography to verify the results of numerical calculations performed in Simcenter STAR-CCM+ software. The main objective was to determine the values of the parameters tested to evaluate the intensity of the heat transfer processes. In the numerical simulations, important variables, mainly the working fluid, heater material, the spatial orientation of the test section, and the number of mini-channels, were assumed. The results of the numerical computations were discussed. Due to simulations, it was possible to indicate which parameters tested in terms of heat transfer turned out to be the most effective. Furthermore, a mesh dependency analysis based on the grid convergence index (GCI) was performed. The residuals, as good indicators of convergence, achieved low values. Generally, the data presented showed satisfactory convergence of the results achieved as a result of the computational procedure.

Light Absorption Enhancement and Laser-Induced Damage Ability Improvement of AA 6061 with Non-porous Alumina /CdSe@Al2O3/SiO2 Functional Gradient Films

Numerical calculations of ultraviolet to near-infrared absorption spectra by cadmium selenide quantum dots (CdSe QDs) doped in anodic aluminum oxide pores were performed using a finite-difference time-domain model. The height, diameter, and periodic spacing of the pores were optimized. Light absorption by the dots was enhanced by increasing the height and decreasing the diameter of the pores. When the height was less than 1 μm, visible light absorption was enhanced as the spacing was reduced from 400 nm to 100 nm. No enhancement was observed for heights greater than 6 μm. Finally, the optical mode coupling of the aluminum oxide and the quantum dots was enhanced by decreasing the pore diameter and periodic spacing, and increasing the height. Laser ablation verified light absorption enhancement by the CdSe QDs. The experiment verified the improvement of the laser-induced damage ability with wavelength of 355-nm after aluminum alloy 6061 coated with functional films, which was fabricated based on numerical calculations.

Large Deformation Characteristics of Surrounding Rock and Support Technology of Shallow-Buried Soft Rock Roadway: A Case Study

The coal resources in the coal-rich area of western China are mostly located in the late diagenetic Cretaceous and Jurassic strata. In this paper, a study on the support of soft rock roadways was carried out in the background of the soft rock track roadway in the Jiebangou coal mine. The field investigation showed that the surrounding rocks of the roadway were weak, soft, and broken, and the surrounding rocks were cemented, with the roadway local deformation exceeding 1 m. The borehole television results showed that the surrounding rocks were mainly weak sandy mudstone and yellow mudstone. The average uniaxial compressive strength of the surrounding rock was 15.49 MPa. The roadway is a shallow buried soft rock roadway; site investigation revealed that the original U-shaped steel shed had an extremely low resistance to slip, the filling body behind the U-shaped steel shed fell off, the interaction between the U-shaped steel shed and the surrounding rock was poor, the U-shaped steel shed could not provide sufficient timely support resistance, and the bearing capacity of the U-shaped steel shed was far from consideration. The floor was not effectively supported. The floor had different degrees of the bottom drum, and frequent undercover caused new stress disturbances, which loosened the bottom corners of both rock types and made the shed legs move continuously inward, reducing the bearing capacity and actual support resistance of the bracket. Numerical calculations were performed to study the deformation characteristics of the surrounding rock of the tunnel and the yielding damage characteristics of the brace. The results showed that the current U-shack support strength was insufficient, the two sides were deformed by 950 mm, the bottom of the roadway bulged by 540 mm, and the surrounding rock was mainly shear damaged. The fall of the filler behind the shed caused damage to the U-shaped steel shed spire. Through site investigation results and numerical calculations, the deformation and damage characteristics of the soft rock roadway and its damage causes were analyzed, and the support technology system of ‘strengthening support for weak structural parts’ was proposed. This improved the mechanical properties of the weak structural support body, the stress state of the local surrounding rock, and the bearing capacity of the support structure, and effectively controlled the deformation, damage, and instability of the surrounding rock of the roadway, and deformation, damage, and destabilization of the roadway, thereby achieving overall stability for the surrounding rock of the roadway.

Experimental and numerical investigation of metal-polymer riveted joints

This paper presents the modeling and analysis of the joints of metal inserts with polyamide 6 using the injection technique. Based on the conducted experiments, modeling and numerical calculations of joints were carried out for various joint configurations. Metal parts, made of steel grade DC 04, are mechanically locked with polyamide 6 (PA6) with rivets. The mechanical connection with rivets of both elements was achieved by filling the holes in the metal parts in the injection process. As part of the work, mechanical-clamp connections made of steel / PA6 were mechanically tested in a single-axis joint tensile test using appropriate tabs. The main goal was to study and numerically analyze the number of rivets and their location on the metal plate for the strength of the connector. An important element of the work was the modeling process of both the PA6 material behavior and the joint itself. As part of the experimental research, the rivet deformation was also observed using computer thermography with the use of an IR camera. The tests and simulation showed that for the sample, the polymer-metal connected with less than three rivets was destroyed by shear. On the other hand, when the polymer-metal junction was made of three rivets, the jamming mechanism was mainly related to damage to the polymer part. For these joints, the maximum values of the breaking force of the joint were obtained in uniaxial tensile and shear tests where three rivets were used. Similar values were obtained during the numerical calculations performed with the use of Abaqus software.

Vector-Field Visualization of the Total Reflection of the EM Wave by an SRR Structure at the Magnetic Resonance

Metamaterials are artificially structured composite media with a unique electromagnetic (EM) response that is absent from naturally occurring materials, which appears counterintuitive and aggravates traditional difficulties in perceiving the behavior of EM waves. The aim of this study was to better understand the interaction of EM waves with metamaterials by virtual visualizing the accompanying physical phenomena. Over the years, virtual visualization of EM wave interactions with metamaterials has proven to be a powerful tool for explaining many phenomena that occur in metamaterials. In this study, we performed virtual visualization of the interaction of an EM plane wave with a split-ring resonator (SRR) metamaterial structure, employing CST Studio software for modeling and comprehensive simulations of high-frequency EM fields of 3D objects. The SRR structure was designed to have its magnetic resonance at the frequency f = 23.69 GHz, which is of interest for antennas supporting wireless microwave point-to-point communication systems (e.g., in satellite systems). Our numerical calculations of the coefficients of absorption, reflection, and transmission of the EM plane wave incident on the SRR structure showed that the SRR structure totally reflected the plane EM wave at the magnetic resonance frequency. Therefore, we focused our research on checking whether the results of numerical calculations could be confirmed by visualizing the total reflection phenomenon on the SRR structure. The performed vector-field visualization resulted in 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period, which demonstrated the existence of characteristic features of the total reflection phenomenon when the EM plane interacted with the studied SRR, i.e., no EM field behind the SRR structure and the standing electric and magnetic waves before the SRR structure, thus, confirming the numerical calculations visually. For deeper understanding the interaction of the EM plane wave with the SRR structure of reflection characteristics at the magnetic resonance frequency f = 23.69 GH, we also visualized the SRR structure response at the frequency f = 21 GHz, i.e., at the so-called detuned frequency. As expected, at the detuned frequency, the SRR structure lost its metamaterial properties and the obtained 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period showed the transmitted EM wave behind the SRR structure and no EM (fully) standing waves before the SRR structure. The visualizations presented in this study are both unique educational presentations to help understand the interaction of EM plane waves with the SRR structure of reflection characteristics at the magnetic resonance and detuned frequencies.

Interpretation of the generalized parameter of the probability of failure through the plastic stress intensity factor

The main purpose of this work is to statistically analyze the fracture toughness of compact specimens made of S55C steel in terms of elastic and plastic stress intensity factors. The fracture toughness tests results at three-point bending were used for a comparative statistical analysis of the fracture parameters. Five type of specimen configuration with various thicknesses were tested at a constant ratio between crack length and specimen width. The critical loads were obtained as a tests result for various combinations of crack length and specimen thickness. In addition, uniaxial tensile tests were carried out to determine the main mechanical properties of the material. Obtained material properties were used in numerical calculations. Numerical calculations were carried out to determine the elastic and plastic stress intensity factors. Three-dimensional finite element analysis was performed on the basis of the experimental data on curvilinear crack front positions in tested specimens. The crack tip stress-strain fields were obtained for each of the tested samples as a result of numerical calculations. These fields were used to calculate the values of the plastic intensity factors along the curvilinear crack fronts. A statistical analysis of the fracture toughness of compact specimens made of S55C steel was carried out based on the obtained critical values of elastic and plastic stress intensity factors. The advantages of using the plastic stress intensity factor as a generalized parameter for the fracture probability are demonstrated. In addition, the sensitivity of the plastic stress intensity factor to constraint effects avoids the introduction of additional parameters into the statistical models.

Design and development of combustion chambers for gas turbine engines based on calculations of various levels of complexity

The article proposes a method for designing combustion chambers for gas turbine engines based on a combination of the use of calculations in a one-dimensional and three-dimensional formulation of the problem. This technique allows you to quickly design at the initial stage of creating and development of the existing combustion chambers using simplified calculation algorithms. At the final stage, detailed calculations are carried out using three-dimensional numerical calculations. The method includes hydraulic calculations, on the basis of which the distribution of the air flow passing through the main elements of the combustion chamber is determined. Then, the mixing of the gas flow downstream of the flame tube head and the air passing through the holes in the flame tube is determined. The mixing quality determines the distribution of local mixture compositions along the length of the flame tube. The calculation of the combustion process is carried out with the determination of the combustion efficiency, temperature, concentrations of harmful substances and other parameters. The proposed method is tested drawing on the example of a combustion chamber of the cannular type. The results of numerical calculations, experimental data and values obtained using the proposed method for various operating modes of the engine are compared.

Opening the reheating box in multifield inflation

The robustness of multi-field inflation to the physics of reheating is investigated. In order to carry out this study, reheating is described in detail by means of a formalism which tracks the evolution of scalar fields and perfect fluids in interaction (the inflatons and their decay products). This framework is then used to establish the general equations of motion of the background and perturbative quantities controlling the evolution of the system during reheating. Next, these equations are solved exactly by means of a new numerical code. Moreover, new analytical techniques, allowing us to interpret and approximate these solutions, are developed. As an illustration of a physical prediction that could be affected by the micro-physics of reheating, the amplitude of non-adiabatic perturbations in double inflation is considered. It is found that ignoring the fine-structure of reheating, as usually done in the standard approach, can lead to differences as big as ∼ 50%, while our semi-analytic estimates can reduce this error to ∼ 10%. We conclude that, in multi-field inflation, tracking the perturbations through the details of the reheating process is important and, to achieve good precision, requires the use of numerical calculations.