http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/102 2026-05-17T02:11:36Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/865 Implementation of the digital phase-sensitive system for low signal measurement Pham, Quoc Trieu; Nguyen, Anh Duc In this paper we present the implementation of a digital lock-in amplifier (LIA) completely based on Labview with a general-purpose data acquisition board (or a high quality sound card) and a high-gain low-noise amplifier. The signal analysis is processed by the software. We describe some characteristics of the LIA including output voltage vs. frequency and output phase vs. noise. The LIA can be used to measure the small signals, even in presence of broadband noise which is several times greater than the signal itself. Since the signal processing takes place on the computer, the ones can display the waveform – as a time series or power spectrum – as it progresses through the instrument, which makes it an excellent tool for the senior-level physics lab. VNU Journal of Science, Mathematics - Physics. Vol. 24 (2008), No 4 (M.P), P. 239-244 2008-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/860 Photo-catalytic transparent heat mirror film TiO2/TiN/TiO2 Le, Tran; Nguyen, Huu Chi; Tran, Tuan Transparent heat mirror thin films have high transmittance in the visible range of wavelength and high reflectance in the infrared range of wavelength. TiO2/TiN/TiO2 films prepared via a D.C reactive magnetron sputtering method on Corning glass and Alkali glass substrates, serve as transparent heat mirrors. The outer TiO2 layer has both the photo-catalytic and anti-reflective properties. The experiment data showed that the film thickness required for photocatalytic properties exceeds 350nm. In this report, we found the relationship between the thicknesses of the films via calculation and experiment. Prepared films have both catalytic and transparent heat mirror properties with an inner TiO2 layer thickness of 40 - 300nm, a sandwich TiN layer thickness of 22 - 35nm and an outer TiO2 layer thickness exceeding 350nm. VNU Journal of Science, Mathematics - Physics. Vol. 24 (2008), No 4 (M.P), P. 231-237 2008-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/857 Calculation of dispersion relation and real atomic vibration of fcc crystals containing dopant atom using effective potential Nguyen, Van Hung; Nguyen, Thi Nu; Nguyen, Bao Trung A new procedure for calculation and analysis of dispersion relation and real atomic vibration of fcc crystals containing dopant atom has been developed using anharmonic effective potential. Analytical expressions for dispersion relation separated by acoustic and optical branches; forbidden zone; effective force constant; Debye frequency and temperature; amplitude and phase of real vibration of atomic chain containing dopant atom have been derived. They contain Morse potential parameters characterizing vibration of each pair of atoms. Numerical calculations have been carried out for Cu doped by Ni or by Al. The results agree well with fundamental properties of these quantities and with experimental values extracted from measured Morse parameters. VNU Journal of Science, Mathematics - Physics. Vol. 24 (2008), No 4 (M.P), P. 223-230 2008-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/856 Analysis and identification of multi-variate random pressure fields using covariance and spectral proper transformations Le, Thai Hoa; Tamura, Yukio This paper will present applications of the Proper Transformations based on both cross spectral matrix and covariance matrix branches to analysis and identification of multi-variate random pressure fields. The random pressure fields are determined due to the physical measurements on some typical rectangular models in the wind tunnel tests. The significant roles of the first covariance mode associated with the first principal coordinates as well as of the first spectral eigenvalue and associated spectral mode are clarified in reconstructing the random pressure fields and identifying the hidden physical phenomena inside this pressure fields. VNU Journal of Science, Mathematics - Physics. Vol. 24 (2008), No 4 (M.P), P. 209-222 2008-01-01T00:00:00Z