Indian Journal of Physics最新文献

Many a scientific study was carried out on the in vivo bioluminescence emission of the firefly. In those studies, the wavelength peaks of different species of firefly were documented at fixed positions—showing no variation. Here we record steady state emission spectra of the Indian species of firefly Asymmetricata circumdata at its normal flashing temperature. An observation of the spectra of different specimens of this summer species recorded over three years reveals that positions of the peaks are not the same; these differ by 9 nm. This non-negligible difference points towards slight changes in the structure of, or in the localised microenvironment around, the enzyme catalyst luciferase in this species itself.

This study investigates the dielectric properties of an Au/SnO₂/p-InP (MOS) capacitor through admittance measurements over a broad frequency and temperature range. The experimental results demonstrate the dependence of capacitance and conductance on temperature, frequency, and applied bias voltage. Key findings reveal a temperature-dependent capacitance behavior where capacitance decreases under reverse bias due to carrier freezing and increases under forward bias due to carrier activation. In the forward bias region, the capacitance also exhibits a decreasing trend with increasing frequency, which is attributed to the limited response of interface states at higher frequencies. The dielectric constant and loss increase with temperature but decrease at higher frequencies as a result of the reduced ability of dipoles to follow the alternating field. The ac conductivity behavior is consistent with a short-range hopping mechanism, where both temperature and frequency contribute to enhanced conductivity. The results align with the correlated barrier hopping (CBH) conduction model. This work provides a comprehensive analysis of the frequency- and temperature-dependent electrical characteristics of MOS capacitors, thereby addressing existing gaps in the literature. The findings are important for the design and optimization of semiconductor devices and sensor technologies, improving electronic performance in various applications.

High-entropy alloys (HEAs) are designed by combining chemical elements in equal or nearly equal amounts to create strong, ductile materials. Some attributes of HEAs can be modified by doping elements that are chosen based on the working environments. This study examines the impact of (Al) addition on the mechanical properties of ({Al}_{x}{(CoCrFeNi)}_{1-x}) high-entropy alloys (HEAs) through molecular dynamics (MD) simulations. We examined a variety of mechanical properties, including yield strength, lattice distortion, elastic constants, elastic moduli, anisotropy, and melting point. Increasing the (Al) content in ({Al}_{x}{(CoCrFeNi)}_{1-x}) HEAs there was noticeable influences on strength and ductility which directly alters the mechanical properties of this alloys. The calculations of melting points indicate that incorporating (Al) contents significantly influence thermal properties, leading to increased melting points. Our findings emphasize the importance of understanding these effects, as they can provide useful insights for the design and progress of HEAs with superior mechanical properties appropriate for a variety of technological applications.

We investigated the magnetic properties of an Ising diluted nanotube with a mixed-spin (1/2,3/2) hexagonal core-shell structure, using a combination of effective field theory (EFT) and probability distribution techniques. The study uniquely explored the effects of disorder in both the core and shell in relation to the uniaxial anisotropy (D_z) and core-shell exchange interactions (R_{cs}). Additionnaly, the research highlighted a diverse range of compensation behaviors (Q-, R-, S-, N-, L-, and P-types) based on Néel’s classification. To invoke the enegetic aspect, we studied also the internal energy, the magnetic susceptibiliy and the free energy. The discovery of triple hysteresis loops under specific parameter conditions, added a significant new dimension to the understanding of such systems.

This paper presents the design of a highly birefringent and highly nonlinear photonic crystal fiber based on sulfur-based glass (As₂Se₃). The structure incorporates two elliptical air holes and four circular air holes of different sizes at the fiber core. Using the full vector finite element method (FEM) with anisotropic perfectly matched layers, the birefringence characteristics, nonlinear properties, dispersion, and beat length in the wavelength range of 1.2–1.8 μm are investigated by tuning the structural parameters of the fiber. The results show that the birefringence of the photonic crystal fiber reaches 0.172 at 1.55 μm wavelength, while the nonlinear coefficients in the X-polarization direction are 149.31 m⁻¹ W⁻¹, and the nonlinear coefficients in the Y-polarization direction are 215.41 m⁻¹ W⁻¹. In addition, the PCF dispersion is normal in this band range and shows positive dispersion in the X-polarization direction and negative dispersion in the Y-polarization direction. Photonic crystal optical fibers based on the sulfur-based glass As₂Se₃ have a simple structure and show significant potential for applications in various fields, such as optical coherence tomography (OCT) and super-resolution imaging technology in the medical field, optical sensors, and optical communications.

In the present paper, the FeAlBSn nano-composite was synthesized using powder metallurgy technique in order to investigate the effect of milling time on its structural and magnetic properties. Comprehensive characterization was conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS), and vibrating sample magnetometry (VSM). XRD analysis of the initial powder (0 h) revealed distinct peaks that correspond to the elements Fe, Al, B, and Sn. Upon 20 h of milling, progressive solid-state reactions and structural transformations led to the formation of multiple intermetallic phases, including FeB, Fe₂B, FeAl, AlB₂, AlB₁₂, FeSn, Fe₂Sn₂, Fe₂Sn, and Fe₂AlB₂. The average crystallite size decreased from 54 to 13 nm, accompanied by an increase in lattice strain from 0.08% to 0.6%. SEM–EDS analysis confirmed significant morphological refinement and uniform elemental distribution, with the mean particle size reducing from ~ 40 µm to ~ 10 µm after milling. In addition, Magnetic measurements revealed a significant dependence on milling time, with coercivity (Hc), remanent magnetization (Mr), and squareness ratio (Mr/Ms) reached 220.74 Oe, 1.66 emu/g, and 0.15, respectively, after 20 h. However, saturation magnetization (Ms) decreased considerably from 103.28 emu/g (0 h) to 11.16 emu/g (20 h), indicating the formation of weakly magnetic or non-magnetic intermetallic phases. These findings highlight the impact of mechanical milling on tailoring the structural and magnetic properties of FeAlBSn nanocomposite for advanced applications.

The PbO–SiO₂ system has a wide range of industrial applications, including optical glasses, optoelectronics, and radiation shielding. In this study, the structure of lead-silicate glasses was investigated using molecular dynamics (MD) simulations with Buckingham-type rigid ion potentials combined with Coulomb interactions. Three glass compositions, xPbO–(100 − x)SiO₂ with x = 50, 60, and 65 mol%, were examined. In the simulated structures, Si⁴⁺ ions are tetrahedrally coordinated with oxygen atoms, with an average coordination number of four. The PbO₄ units serve as the fundamental structural motifs in lead-silicate glasses. The number of Pb–Pb nearest neighbors follows a statistical model in which modifier cations (Pb²⁺) bond to non-bridging oxygens (Onb), and M(Onb)_n polyhedra are primarily connected via corner-sharing. The Pb–Pb partial pair distribution function, T_PbPb(r), exhibits a peak height that increases with PbO concentration, as expected. The distribution of Qⁿ species varies systematically with silica content, reflecting the depolymerization of the silicate network upon the addition of lead oxide. All structural models demonstrate good agreement with experimental data and Reverse Monte Carlo (RMC) modeling results, including parameters such as short-range order, average bond lengths, bond angle distributions, and Qⁿ species distributions.

Solid-state energy storage devices hold significant potential owing to their superior safety features, increased energy density, and minimized packaging needs, positioning them as ideal candidates for extensive energy storage systems. The sustainable development of contemporary infrastructure significantly depends on clean and efficient transportation solutions, with lithium-ion batteries (LIBs) leading this transformative shift. This study investigates the structural, mechanical, electronic, and optical properties of Li₁₀GeP₂Se₁₂ through first-principles density functional theory (DFT) to assess its potential as a solid electrolyte in Li-metal batteries and supercapacitors. The evaluation of mechanical stability was conducted utilizing the IR-Elast code, resulting in a bulk modulus (B) of 110.5 GPa, a shear modulus (G) of 80.2 GPa, a Young’s modulus (E) of 229.3 GPa, and a Poisson’s ratio (v) of 0.25. The computed Pugh’s ratio (B/G) of 1.09 suggests a moderate level of ductility accompanied by significant mechanical strength. The electronic structure analysis indicates that Li₁₀GeP₂Se₁₂ functions as a semiconductor, exhibiting a direct band gap of around 2.1 eV. This characteristic positions it well for use in optoelectronic and energy storage applications. Calculations of optical properties indicate a significant dielectric constant of ε₁ (0) ≈ 5.1 and a peak refractive index of around 2.2 in the low-energy region. The material demonstrates significant absorption peaks in the ultraviolet range at approximately 9.8 eV and marked optical anisotropy across various polarization directions. These properties underscores the promise of Li₁₀GeP₂Se₁₂ as a versatile material for solid-state lithium batteries and integrated optoelectronic energy devices.

This research work presents a complete classification of Friedmann–Robertson–Walker (FLRW) spacetimes based on Noether symmetries. Various classes are analyzed for flat, open, and closed universe models. According to this classification we have various forms of cosmic scale factor b(t). Different sets of Noether symmetries are reported for different classes of FLRW universe. We obtained different classes of the said spacetime along with their Noether symmetries and the corresponding conservation laws. The main objective of this research is to find all possible forms of the scale factor b(t) and discuss their physical significance.