مجله فیزیک کاربردی
سال پانزدهم شماره 1 (پیاپی 40، بهار 1404)

The geometrical configuration of the electrode significantly affects the physical and chemical properties of the discharge. This article presents the influence of cold atmospheric pressure Surface Dielectric Barrier Discharge (SDBD) plasma structures with square, hexagonal, and circular configurations, developed at the Plasma Research Institute of Kharazmi University, and their profound effects on the device's power consumption, the uniformity of micro-discharges (MD), and the plasma production temperature. Increasing the number of corner points in the electrode design led to an increase in discharge power. Experiments showed that the uniformity of the Surface Dielectric Barrier Atmospheric Micro-Discharge (SDBAMD) was strongly influenced by the electrode structure, with the most uniform discharge observed when the electrode configuration was circular. Additionally, our analysis demonstrates that different electrode configurations can alter the plasma temperature, ultimately affecting the application of this atmospheric cold plasma generation source. Finally, the results indicate that surface dielectric barrier discharge devices with circular electrode configurations exhibit the highest power consumption, the most uniform micro-discharge, and the lowest production temperature.

Zinc oxide (ZnO) nanosheets, recognized as one of the semiconductor materials with unique characteristics, have garnered significant attention in various scientific and industrial fields in recent years. Due to their relatively high band gap (approximately 3.3 electron volts) and ability to absorb light in the ultraviolet region, this material is widely used in light-emitting diodes, sensors, and solar cells. This study examines a comprehensive range of structural, electronic, and optical properties of this material within the framework of density functional theory (DFT). The results indicate that the presence of cadmium impurities in zinc oxide nanosheets significantly affects the structural, electronic, and optical properties of these materials. Incorporating cadmium into the zinc oxide structure can lead to notable changes in the crystal lattice and enhance structural stability. These changes may result in a reduction of crystal defects and an increase in the surface-to-volume ratio, which in turn positively impacts the optical and electronic properties of the nanosheets. Furthermore, cadmium impurities can lead to a reduction in the band gap and an increase in the overall magnetic moment of the material. These modifications may create new electronic states within the nanosheet structure, contributing to the enhancement of optical properties, including light absorption and emission, and improving optical characteristics for applications in photovoltaic devices.

The challenge in developing a theory of quantum gravity stems from the fundamentally different ways the two theories describe physical systems. Quantum mechanics operates on discrete, probabilistic principles, while general relativity is a continuous, deterministic theory. The generalized uncertainty principle is a modified version of Heisenberg's uncertainty principle that applies quantum gravitational corrections to systems with strong gravity. As a clear example of these systems, white dwarfs can be mentioned. In white dwarfs, the gravitational pressure provides the necessary support against gravitational collapse, however, the generalized uncertainty principle has been shown to negate the Chandrasekhar limit in the presence of a minimum length, allowing white dwarfs to grow to any size, even infinitely large, which is in contradiction with physical astrophysical observations. This paper modifies the relationship between degeneracy pressure and density in white dwarfs using an alternative form of the uncertainty principle that incorporates a maximum length. We demonstrate that this new formalism recovers the Chandrasekhar limit and resolves the discrepancy between theory and observation.

In this study, we explore the localization and transport behaviors of a one-dimensional system using a hybrid model that combines the Power-Law Random Banded Matrix (PRBM) model and the Random Dimer (RD) model. The primary objective of this research is to examine phase transitions and the influence of system parameters on quantum states. To achieve a precise analysis of these transitions, we utilize quantities such as the participation ratio and the energy level spacing ratio, each providing valuable insights into the system's dynamics. The results indicate that by varying parameters α and , the transition from extended to localized states can be effectively controlled. Specifically, α emerges as a critical factor in determining phase transitions, playing a key role in inducing phase shifts. This hybrid model, with its capacity for accurate simulation, enables a comprehensive examination of quantum behaviors in complex systems and paves the way for future studies on the effects of disorder and random variations in quantum phase transitions. This research establishes a robust foundation for deeper understanding of phase transition mechanisms in disordered systems.

Transient absorption spectroscopy allows the observation of excited state dynamics following optical excitation across a wide range of time scales, from femtoseconds to milliseconds. This article presents an ultrafast transient absorption spectroscopy setup based on the pump-probe method, utilizing femtosecond pulses from a Ti:sapphire laser at both fundamental and second harmonic wavelengths. We investigated the transient absorption spectrum of deionized water, the most common solvent, with femtosecond time resolution in two modes: one with a fixed delay time for probe wavelengths ranging from 740 to 820 nm, and the other with a fixed probe wavelength for various time delays up to 1.1 picoseconds. The transient absorption spectra reveal a negative signal peaking at 788 nm, attributed to ground state bleaching caused by the depopulation of the ground state induced by the pump. Additionally, a negative signal at 798 nm, resulting from stimulated emission, overlaps with a 10 nm Stokes shift of the ground state bleaching band. The temporal evolution of the transient absorbance spectra shows an absorption peak at a 70 femtosecond delay between the pump and probe pulses, indicating an unstable intermediate level resulting from a two-photon absorption process—one photon from the pump pulse at 392 nm and another from the probe pulse at 784 nm. Fitting a biexponential function to the relaxation data yields a lifetime of approximately 150 femtoseconds for this intermediate leve.

This research investigates one of the stimulated Brillouin scattering applications related to distributed-temperature sensors that utilize common single-mode optical fibers. The aim is to find a relation between the Brillouin frequency shift (BFS) and temperature up to 15000C in these distributed-temperature sensors. At first, a linear approximation of the acoustic wave velocity and a reported polynomial of the refractive index with temperature are employed to calculate BFS. A comparison of the obtained BFS with two independent sets of recent experimental data shows that the linear relation between acoustic wave velocity and temperature, which is generally considered valid, is not valid, especially at high temperatures. Then, using a curve-fitting method based on another reported experimental data set, different-order polynomials of degrees up to six are considered for the acoustic wave velocity with temperature. The results show that the proposed second and third-order polynomials of the acoustic wave velocity can be used to calculate BFSs that align more closely with experimental data, even at elevated temperatures.

This paper investigates how the synthesis of aluminum hydroxide, silver nanoparticles, and nanostructures, as coatings on wood surfaces, can enhance their antifungal and fire-retardant properties. The microwave method is employed for synthesis to investigate properties of the resulting coatings, including antibacterial and fire-retardant properties. They have been  examined using SEM, XRD, TGA analyses, fire tests such as UL-94 , and Limiting Oxygen Index (LOI). The results show that bilayer coatings with silver and aluminum hydroxide, respectively, have better antifungal and fire-retardant properties compared to single-layer coatings ones. Furthermore, in the another sample, where both aluminum nitrate and silver nitrate salts are used simultaneously, a good correlation between antifungal and fire-retardant properties has been observed. Overall, these findings contribute to a deeper understanding of the functional properties and potential applications of silver and aluminum hydroxide-coated wood surfaces in various fields such as antimicrobial coatings and environmental remediation.

This article presents the fabrication and characterization of a titanium target deposited on a copper substrate, designed for generating neutron particles in the ES-150 electrostatic accelerator. The selection of copper as the substrate and titanium as the target material was based on their respective properties: copper's exceptional thermal conductivity and titanium's high hydrogen absorption coefficient. A titanium thin film was deposited onto the copper substrate using ion beam sputtering. The resulting crystal structure, surface morphology, and elemental composition of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray spectrophotometry (EDX), respectively. X-ray diffraction (XRD) analysis revealed distinct titanium peaks, primarily oriented along the Ti (002) plane at an angle of 38.42o. The scanning electron microscopy (SEM) results indicate a uniform film with a regular grain distribution and no visible defects. Energy Dispersive X-ray analysis (EDX) further confirmed the presence of titanium and copper elements in the target. Ion beam analysis-based elemental characterization revealed a thick copper substrate and a titanium layer, which was 1.90 ± 0.19 µm thick. The neutron flux produced by the targets in the 150 KeV electrostatic accelerator was investigated, and the neutron yield was measured along the beam axis. A maximum neutron yield of 107 n/s was achieved.

The use of heat-reflective glass has recently gained attention for its potential to reduce the electrical energy consumption required to cool buildings and mitigate electricity shortages. In this research, theoretical and experimental investigations of multi-layered coatings on glass, which is called spectrally selective glass, have been conducted. The aim was to prevent the entry of infrared thermal radiation and control radiation in the visible range. Using the theoretical method of multilayer thin film structures, the structure of three layers of zirconium dioxide/gold/zirconium dioxide has been simulated on glass and then made by the electron beam method. The simulations showed that this three-layer structure with a thickness of about 160 nm for ZrO2 and a gold coating thickness of about 20 nm is a proper choice. The sample made in the laboratory for this structure with a thickness of 160/20/160 nm matches well with the spectrum of the simulated samples and there is a slight deviation due to experimental error sources. The simulated and fabricated sample has more than 50% transmittance in the visible spectral range from 500 to 700 nm. There is a transmittance peak of more than 70% in the center of the visible range. The transmittance is less than 20% in the near-infrared spectrum range for the wavelength of 750 nm to 1100 nm. Therefore, this structure is very suitable for use as a reflector of infrared thermal radiation. This structure is a spectrally selective glass that can be used as a smart glass for radiant cooling purposes.