物理最新文献

A combined analytical and numerical study of oscillating elastic waves propagating in a 1D hyperelastic material modeled by the Lennard–Jones hyperelastic potential reveals that, due to different velocities of oscillating waves, the faster parts of the initially harmonic wave overtake the slower moving parts with formation and propagation of multiple shock wave fronts. These shock fronts cause the mechanical energy to decay with the release of heat. Thus, it is shown that in the considered purely mechanical system without viscous or dry friction, the mechanical energy can dissipate. The observed phenomenon opens up the possibility for creating a new type of vibration isolators without viscous or dry friction dampers. The use of the Lennard–Jones hyperelastic potential together with the Yeoh polynomial potential has recently been proposed for modeling different rubber-based cross-linked polymers.

The paper discusses the optimization of gas sensor performance using heterojunctions and nanostructure morphology modulation. It specifically focuses on TiO₂/Fe₂O₃ heterojunction combinations based on sawtooth shaped nanostructures prepared using an electron beam evaporation method. The study explores an optimization scheme for enhancing NH₃ sensing performance of TiO₂ at room temperature. Various sawtooth shaped TiO₂/Fe₂O₃ nanorod arrays with different material ratios and deposition orders were prepared and characterized using scanning electron microscopy and X-ray diffraction. Gas sensing tests including NH₃ concentration gradient, repeatability, and selectivity were conducted at room temperature. The results show that the gas sensing performance varies with different material ratios in the heterojunction combinations. The combination where TiO₂ is deposited in the lower layer at three times the height of Fe₂O₃ outperformed other combinations in NH₃ room temperature sensing, showing significant improvement compared to pure TiO₂ materials. The study also explores the impact of humidity on the sensor’s performance at room temperature.

Water molecules with their hydrogen bonding capability, exhibit exceptional properties in the bulk as well as in cluster form. In the present work, we study the size-dependent trends in the structure, energetics, bonding, ionisation potential, fragmentation pattern, and optical properties of water clusters in the size range of n = 2–20, and an interplay between them. We have extensively searched for the lowest energy structures of the water clusters using the artificial bee colony algorithm, optimised them first with the classical force field TIP4P and then relaxed at least 10 lowest energy structures using density functional theory. We have found new lowest energy structures for all the sizes as against the ones reported earlier. The structures and stability of water clusters are primarily dictated by the H-bond network. However, we found the weak van der Waals interactions also play a crucial role in stabilising the clusters giving them unique characteristics. Some of the clusters such as those with (n=4, 8, 10, 12) and 15 molecules were structurally symmetric, yet a close analysis of various properties reveals that the clusters with (n=4, 8, 12, 14) and 19 molecules are more stable than others. Spherical or nearly spherical clusters were found to be the most stable, corroborated by the shape deformation parameters and the fragmentation pattern, which indicated a higher likelihood of forming fragments of sizes (n=4, 8, 12, 14), and 16. A blueshift of the H-O-H vibrational modes and a redshift of the O–H stretching modes is seen for most clusters. Such characteristics in the vibrational spectra is associated with an increase in the H-bond strength which is seen to increase with size of the cluster. Large optical band gaps for (n=4, 8, 12) and 16 along with blueshifts in optical spectra implies these clusters to be chemically more stable than others.

Considering the quantum memory channel, we investigate the connection between quantum correlation and coherence for correlated channels. Initially, various results were obtained by considering the action of noise channels on the initial state. The quantum correlation behavior does not increase by the quantum operation or by the action of noise channel. Similarly, coherence remains slow for various initial states under correlated channels. In this work, we observed the decrement of quantum correlation and coherence, which can be improved by choosing the initial state and by adjusting the parameters. Our results provide valuable insight into defining the robustness of the pure state in comparison with the mixed state under correlated channels, which offers practical solutions for quantum information processing task.

Thermoelectric materials, such as SiGe alloys, have gained significant attention for their application in electricity generation at high temperatures. However, improving the thermal and electrical transport properties of n-type SiGe remains a challenge. In this work, n-type Silicon-Germanium alloys (SiGe) with dispersed nano-TiO₂ particles (Si₈₀Ge₂₀P₃-x wt% nano-TiO₂, x = 0, 3, 4, 5, 6) were synthesized by ball milling followed by spark plasma sintering. The effects of nano-TiO₂ particles on the electrical and thermal transport properties were investigated. The power factor of n-type SiGe alloys dispersed nano-TiO₂ particles was slightly decreased. However, the thermal conductivity had a significant reduction because of enhanced phonon scattering resulted from the multi-dimensional defect features. Coherent interfaces formed between SiGe alloys and nano-TiO₂ particles can generate phonon scattering in the range of medium to long wavelength. A dimensionless figure-of-merit (zT) of 1.64 at 1073 K was obtained in the sample of Si₈₀Ge₂₀P₃-4 wt% nano-TiO₂, which is 40% higher than the Si₈₀Ge₂₀P₃ alloy. This work provides a new approach to optimizing the thermoelectric performance and promoting the potential applications.

This work deals with the presence of the cuscuton term in the otherwise standard dark energy evolution under the usual FLRW background. We disclose a first-order framework similar to the Hamilton-Jacobi formalism, which helps us to solve the equations of motion and find analytical solutions. We explore several possibilities, concentrating mainly on how the cuscuton-like contribution works to modify cosmic evolution. Some results are of current interest since they describe scenarios capable of changing the evolution, adding or excluding possible distinct phases during the Universe’s expansion history. Additionally, we present interesting constraints on the cuscuton-like contribution for the dark energy evolution using a set of homogeneous geometrical observational probes. Finally, based on the Akaike Information Criterion (AIC), we perform a statistical comparison of the cuscuton-like model with (Lambda )CDM, and find strong support for our model.

Fabrication of thin films of WSe₂ is challenging and various methods are being explored. This study investigates the thermoelectric properties of tungsten diselenide thin films. The thin films are fabricated on Si substrates by using two-step processes. Here, the selenization of DC sputtered W thin films was carried out at different temperatures in the range of 400 to 500^oC in the steps of 50^oC. The crystal structure is found to be hexagonal and crystallite sizes increase with the selenization temperature. The morphology of the thin films selenized at 400^oC shows no separated particles while raising the selenization temperature from 450^oC to 500 °C uniform distribution of particles is observed. The shape of the particles was found spherical and rod-like. The Raman spectra show four modes: E_1g,(:{text{E}}_{2text{g}}^{1})_, A_1g, and (:{text{B}}_{2text{g}}^{1}). Here, (:{text{B}}_{2text{g}}^{1}) is associated with the interlayer interaction. The electrical resistivities of these thin films exhibit the conduction mechanism of the band conduction model. The highest Seebeck coefficient was reported for S500 (-9.15µV/K). Also, the power factor of S500 is the highest i.e. 13.4 Χ 10^− 5µW/mK² This study shows the potential use of the selenization process to fabricate the WSe₂ thin films and optimize temperature for better thermoelectric properties.

Silicon carbide (SiC), as a key material in the third-generation semiconductor industry, holds critical importance due to its superior thermal conductivity, high breakdown voltage, and wide bandgap. However, the conventional chemical mechanical polishing (CMP) process used in SiC wafer manufacturing is time-consuming and resource-intensive, involving significant material consumption and prolonged processing times. In this study, we explored the application of laser-assisted dry ablation as a pre-treatment for CMP. The experimental results showed that the single laser ablation depth of SiC is about 2 μm, and demonstrated that a laser spot overlap rate between 30% and 60% can generate a relatively lower surface roughness of SiC. This optimal range of overlap ensures a smoother ablation process, minimizing the irregularities on the SiC wafer surface. After a single pass of laser dry ablation, SiC hardness can be reduced to less than 3% of its original value, while material removal depth can be precisely controlled by adjusting the number of laser passes. With 50 repetitions, a material removal depth of nearly 30 μm was achieved. This reduction in hardness and enhanced material removal directly contribute to improve the efficiency of subsequent CMP processes by reducing polishing time and wear on grinding heads. In addition, after more than 5 times of laser treatment and then wet grinding, the thickness achievement rate can be increased from 73 to 93%. These results provide the important academic reference value. The integration of laser-assisted ablation into SiC wafer processing presents significant advantages in terms of increasing production throughput and reducing overall manufacturing costs. By simplifying the polishing steps and minimizing consumable usage, this approach offers a promising avenue for industrial applications, particularly in enhancing SiC wafer yield and optimizing semiconductor production workflows.

Photon sphere has attracted significant attention since the capture of black hole shadow images by Event Horizon Telescope. Recently, a number of studies have highlighted that the number of photon spheres and their distributions near black holes are strongly constrained by black hole properties. Specifically, for black holes with event horizons and proper asymptotic behaviors, the number of stable and unstable photon spheres satisfies the relation (n_{text {stable}} - n_{text {unstable}} = -1.) In this study, we provide a new proof on this relation using a geometric analysis, which is carried out using intrinsic curvatures in the optical geometry of black hole spacetimes. Firstly, we demonstrate the existence of photon spheres near black holes assuming most general asymptotic behaviors (asymptotically flat black holes, asymptotically de-Sitter and anti-de-Sitter black holes). Subsequently, we prove that the stable and unstable photon spheres near black holes must be one-to-one alternatively separated from each other, such that each unstable photon sphere is sandwiched between two stable photon spheres (and each stable photon sphere is sandwiched between two unstable photon spheres). Our analysis in this study is applicable to any spherically symmetric black hole spacetimes.

In this work, we will explore the precession of particle spins in spherical spacetimes. We first argue that the geometrical optics (WKB) approximation is insufficient, due to the absence of a glory spot in the backward scattering of massless particles, making an analysis of spin precession necessary. We then derive the precession equation assuming the spin is parallel transported, which is supported by the sub-leading order of the WKB approximation. The precession equation applies to both massless and massive particles. For particles moving at the speed of light, we show that spin is always reversed after backward scattering in any spherically symmetric spacetime, confirming the absence of a glory spot for massless particles. Finally, we solve the precession equation for Schwarzschild and Reissner–Nordström spacetimes and discuss the spin precession of massive particles, particularly in the non-relativistic limit. We find that, in Schwarzschild spacetime, the spin precession for particles moving with very small velocities compared to the speed of light depends only on the deflection angle, while in Reissner–Nordström spacetime, it also depends on the black hole charge, as revealed by the expansion derived from the strong lensing approximation.