VNU Journal of Science: Mathematics - Physics

Abstract: This paper presents the results of simulation study of hollow caves in the body of dikes, dams through theoretical modeling and calculation based on the knowledge of Mathematics, Informatics, Physics in general and Geophysics in particular and also the information processed by the software of EarthImage 2D and Reflex 2D on the methods of multi-electrode electrical sounding and ground penetrating radar. From there, it is possible to draw conclusions on the applicability of both methods for finding, identifying hollow cave, and also looking at ways to conduct field work appropriate to improve the efficiency of the methods mentioned above. These results will be applied as the basis for the discovery of the hollow cave of dikes and dams inVietnam.Keywords: Simulation, hazard, hollow cave, dike, dam.

Abstract: The analytic expressions of the free energy, the mean nearest neighbor distance between two atoms, the elastic moduli such as the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C11, C12, C44 for interstitial alloy AB with BCC structure under pressure are derived from the statistical moment method. The elastic deformations of main metal A is special case of elastic deformation for interstitial alloy AB. The theoretical results are applied to alloy FeC under pressure. The numerical results for this alloy are compared with the numerical results for main metal Fe and experiments. Keywords: interstitial alloy, elastic deformation, Young modulus, bulk modulus, rigidity modulus, elastic constant, Poisson ratio.

In this work, Morse potential parameters of bcc crystals have been calculated based on the calculation of volume per atom and atomic number in each elementary cell, as well as the energy of sublimation, the compressibility and the lattice constant. They are used for studying the anharmonic interatomic effective potential, local force constant in XAFS (X-ray Absorption Fine Structure) theory. Numerical results for Fe, W and Mo are found to be in good agreement with experiment and with those of other theories.Keywords: Morse potential parameter, effective potential, local force constant, bcc crystals.

Abstract: Simple geometry model structures can be useful in quantitative evaluation of self-potential data. In this paper, we solve local wavenumber equation to estimate the horizontal position, the depth and the type of the causative source geometry by using a linear least-squares approximation. The advantages of the algorithm in determining the horizontal position and depth measure are its independence to shape factor of the sources and also its simple computations. The algorithm is built in Matlab environment. The validity of the algorithm is illustrated on variable noise-free and random noise included synthetic data from two-dimensional (2-D) models where the achieved parametric quantities coincide well with the actual ones. The algorithm is also utilized to real self-potential data from Ergani Copper district, Turkey. The results from the actual data application are in good agreement with the published literature for the study area. The source code of the algorithm is available from the authors on request. Keywords: Local wavenumber, Self-potential, a linear least-squares approximation, Ergani copper field.

Abstract: Well-aligned CuO nanorods were successfully prepared  by thermal oxidation method. The effect of annealing time and annealing temperature on the morphology of the nanorods were studied by scanning electron microscopy. The results show that annealing temperature plays a more critical role in affecting the diameter and density of nanorods. Besides SEM images, the effect of annealing time and temperatures on the structure of the product were also studied by X-ray diffraction and Raman spectroscopy. The diameter of CuO nanorods varies from 30 nm to above 100 nm when annealing temperature changes from 400 °C to 600 °C, while the length of the rods is up to several tens of  micrometers. The most uniform nanorods with highest crystal quality of CuO were obtained when annealing temperature is 500 °C and annealing time was 2 h as suggested by SEM images together with Raman results. Keywords: Cupric, Nanorods, Raman, Thermal oxidation.

Abstract: The capture and storage of gases for the applications of energy, environment, and biomedicine are closely related to the major concerns of the modern world about energy crisis, air pollution and global warming, and human’s health. Many materials and techniques have been developed to tackle these widespread issues, in which metal-organic frameworks (MOFs) – a new class of porous materials with exceptionally high surface areas – have emerged as the most promising candidate for the capture and storage of gases based on the adsorption of gases on the surface of MOFs. This article provides a short overview of the current status in the capture and storage of gases within the structure of MOFs.Keywords: Metal – organic frameworks, gas storage, hydrogen, carbon dioxide, methane, nitric oxide.

Abstract: In this paper, substitution of Fe3+ for Al3+ in the structure of aluminosilicate and aluminogermanate nanotubes was investigated at various mole ratios of Fe/Al from the mixed Al2O3-Fe2O3-SiO2 (GeO2)-H2O solution in experimental conditions of 2 mM initial concentration and 2 day aging time at 980C. The synthesized products were confirmed and characterized by using FT-IR spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetometer. The results indicated that Fe-substituted aluminosilicate and aluminogermanate nanotubes were successfully synthesized with the Fe/Al ratio of the initial solutions up to 2. For both Fe-substituted nanotubes, the paramagnetic property exhibits at room temperature (300 K) and a ferromagnetic property at low temperature (5 K). The materials with new properties appear to have promising practical application in other fields in the future.Key words: Imogolite, nanotube, substitution, aluminosilicate, aluminogermanate

The year 2019 marks 45 years in the development of Deep Level Transient Spectroscopy (DLTS) - the signal processing method for determination of overalpping deep levels in semiconductors. From its introduction in 1974 by David Lang (D.V. Lang, J. Appl. Phys. 45, 1974, p.3023) to this date the DLTS method has undergone many changes and modifications: some were purely theoretical speculations, some were to also include new experimental arrangement and technique. This paper provides almost complete review on DLTS, focusing on the main three approaches widely used today. We also summarize the development of this method in the Faculty of Physics, VNU-Hanoi University of Sciences.

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