Network rigidity and properties of SiO2 and GeO2 glasses under pressure

We report in situ studies of SiO2 glass under pressure and find that temperature-induced densification takes place in a pressure window. To explain this effect, we study how rigidity of glasses changes under pressure, with rigidity percolation affecting the dynamics of local relaxation events. We link rigidity percolation in glasses to other effects, including a large increase of crystallization temperature and logarithmic relaxation under pressure.     

Recent Advances on Nitrogen-Doped Porous Carbons Towards Electrochemical Supercapacitor Applications

Due to ever-increasing global energy demands and dwindling resources, there is a growing need to develop materials that can fulfil the World's pressing energy requirements. Electrochemical energy storage devices have gained significant interest due to their exceptional storage properties, where the electrode material is a crucial determinant of device performance. Hence, it is essential to develop 3-D hierarchical materials at low cost with precisely controlled porosity and composition to achieve high energy storage capabilities. After presenting the brief updates on porous carbons (PCs), then this review will focus on the nitrogen (N) doped porous carbon materials (NPC) for electrochemical supercapacitors as the NPCs play a vital role in supercapacitor applications in the field of energy storage. Therefore, this review highlights recent advances in NPCs, including developments in the synthesis of NPCs that have created new methods for controlling their morphology, composition, and pore structure, which can significantly enhance their electrochemical performance. The investigated N-doped materials a wide range of specific surface areas, ranging from 181.5 to 3709 m² g⁻¹, signifies a substantial increase in the available electrochemically active surface area, which is crucial for efficient energy storage. Moreover, these materials display notable specific capacitance values, ranging from 58.7 to 754.4 F g⁻¹, highlighting their remarkable capability to effectively store electrical energy. The outstanding electrochemical performance of these materials is attributed to the synergy between heteroatoms, particularly N, and the carbon framework in N-doped porous carbons. This synergy brings about several beneficial effects including, enhanced pseudo-capacitance, improved electrical conductivity, and increased electrochemically active surface area. As a result, these materials emerge as promising candidates for high-performance supercapacitor electrodes. The challenges and outlook in NPCs for supercapacitor applications are also presented. Overall, this review will provide valuable insights for researchers in electrochemical energy storage and offers a basis for fabricating highly effective and feasible supercapacitor electrodes.     

Effect of carbon ion bombardment and surface oxidation on the twinning rate of single-crystal bismuth

A study is made of the change in the dependences of the normal velocity of twinning boundaries on the magnitude of shear stresses in the twinning plane v _n =v _n (τ) in bismuth crystals owing to ion-cluster doping and oxidation of the irradiated surface. Irradiation was by 25 keV carbonions at a dose of 10¹⁷ ion/cm². Twinning of the crystals took place under pulsed loading conditions with pulse durations of 10⁻⁵−10⁻⁴ s and stress amplitudes of (0.2–2.0)×10³ g/mm³. Carbon ion bombardment of single-crystal bismuth causes a shift in the v _n =v _n (τ) curve toward lower stresses. An oxide film slows down the motion of twinning dislocations. Zh. Tekh. Fiz. 69, 130–131 (May 1999)     

Study of the Possibility Of Replacing an Integrated Airframe with a Flat Polygonal Screen to Estimate The Efficiency of Noise Screening of Engines Using Geometric Diffraction Theory

Acoustical Physics - Using the example of an integrated airframe, we performed a computational and experimental study of the possibility of using geometric diffraction theory (GDT) to calculate the...     

Experimental Confirmation of an Analytical Model of the Sound Propagation in a Rectangular Duct in the Presence of Impedance Transitions and Development of an Impedance Eduction Method Based on it

Acoustical Physics - The authors have carried out a systematic study of the accuracy in the impedance eduction of liners in “interferometer with flow” rigs in the absence of grazing...     

Application of corona discharge acoustic characteristics to determine its properties

The operation of a unipolar pulse-periodic corona discharge is considered. A new method is proposed for analyzing its properties by considering the structure of discharge-emitted sound. Decomposition of the acoustic field into azimuthal components makes it possible to relate them to the force or thermal influence of a corona discharge on a medium and evaluate their relative contribution in this case.     

On determining the acoustic properties of main helicopter rotor models on an open test bench

The paper presents the results of experimental studies on developing a technique to determine the acoustic properties of models of main helicopter rotors on an open test bench. The method of maximum length sequences is used to choose the optimum arrangement of microphones for an open test bench that would minimize the influence of parasitic echo. The results of processing the data of an acoustic experiment with a model rotor are detailed.     

Studying the effect of flap angle on the noise of interaction of a high-bypass jet with a swept wing in a co-flow

Jet–flap interaction noise for a small-scale swept wing model of a trendsetter plane has been studied experimentally, with a double-stream nozzle installed nearby. The effect of the flap angle on the noise of jet–wing interaction has been analyzed. It has been discovered that the flap angle considerably affects the interaction noise in a wide frequency range in such a way that the noise intensity in each frequency band grows exponentially as the flap edge approaches the shear-layer boundary (on a logarithmic scale, this corresponds to linear scaling of the spectrum depending on the flap angle). The exponential noise reduction as the flap angle decreases agrees with the known theoretical simplified-configuration models that are based on the effect of interaction of the near field of instability wave with the edge. Not only does this agreement show that noise increase/reduction mechanism may be associated with similar processes, it also provides an effective tool for controlling the interaction noise.     

Twinning in bismuth single crystals induced by thermal cycling

The role of twinning in bismuth single crystal plastic deformation under thermal cycling (cooling to 77 K and heating to 373 K) is studied. It is found that, under these conditions, the twinning of the crystals proceeds in several stages.     

Space charge effects on radiative ultrashort laser-plasma interactions: Relativistic fluid model

Ultrashort laser-gas interaction is a promising candidate for the intense broad band far-infrared radiation in which the gas ionization and the resultant plasma formation occur consequently. The electron current produced in the process is the most important influential parameter which affects the far-infrared radiation generation. Although the interacting forces of the process are the space charge electric and the laser electromagnetic forces, the effect of the former one, has not been investigated on the gas-plasma THz generation. It is noteworthy that the space charge electric force, due to its effect on the electron distribution, has potential influence on the produced electron current and its consequent emission. Here, a 2D relativistic fluid model is presented in which the ions and the resultant space charge field are incorporated. The model investigates the air ionization, electron-ion plasma formation, and the system's evolution, spatiotemporally. Moreover, as the model is based on the transient electron current, as the source for the electromagnetic pulse radiation, it gives the temporal profile of the radiated field in which the space charge effects are observable. Our results show that the space charge field affects the electron velocity and its resultant current. Therefore, the temporal profiles and amplitudes of the radiated field components are affected and their resemblance to the experimental data is enhanced. The results indicate that the amplitude of the radiated field increases in the presence of the space charge field. In addition, it is shown that the space charge effects become more pronounced with the laser intensity.