http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/109 Sun, 17 May 2026 14:15:26 GMT 2026-05-17T14:15:26Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12037 The dependence of the parametric transformation coefficient of acoustic and optical phonons in doped superlattices on concentration of impurities Hoang, Dinh Trien; et al. The parametric transformation of acoustic and optical phonons in doped superlattices is theoretically studied by using a set of quantum kinetic equations for the phonons. The analytic expression of parametric transformation coefficient of acoustic and optical phonons in doped superlattices is obtained, that depends non-linear on the concentration of impurities. Numerical computations of theoretical results and graph are performed for GaAs:Si/GaAs:Be doped superlattices. Thu, 01 Jan 2009 00:00:00 GMT http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12037 2009-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12030 Hazard removal solution by synchronization Nguyen, Quy Thuong There are many methods to design digital circuits without hazard, such as the use of Boolean algebra, algebra hazard, karnaugh map, matrix method, VHDL, etc. However, these methods are not very suitable for the design of circuit system such as design of GALS circuits. In this case, synchronization is the most optimal method. Thu, 01 Jan 2009 00:00:00 GMT http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12030 2009-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12024 The establishment of the Vietnam atomic time scale Le, Van Ninh; et al. The national metrology institutes always establish their time scale UTC(k) (UTC of k laboratory) based on the atomic clocks. Atomic clocks and a time scale algorithm provides an ensemble time which is better than any component clock in the system. This paper introduces establishing of Vietnam time scale UTC(VMI) (UTC of Vietnam Metrology Institute) using the comparison data of commercial ceasium atomic clocks. We applied the time scale algorithm named AT1 and an own our method and present instrument at the time and frequency laboratory – VMI. UTC(VMI) data has appeared on the BIPM website since 2008. Thu, 01 Jan 2009 00:00:00 GMT http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12024 2009-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12008 Design of phase-coded transmitter and high sensitive receiver of radar system Do, Trung Kien; et al. This paper reports experimental results of a radar system design. In the radar transmitter, a 13-bit Barker code with bit duration 3.24 µs and various other codes are generated by the microcontroller PIC16F877A. This code is then used to modulate IF 10.3 MHz to become BPSK signal. A stable local oscillator is also designed by PLL, VCO, and PIC16F877A. The operation frequency range of the oscillator is from 800 MHz to 900 MHz with an error only about ±10 Hz. A microwave power amplifier is fabricated with structure of two stages of 45 W and 90 W in case of input 300 mW. In this amplifier microstrip technique is implemented for input/output matching network. In the receiver, subsystem can receive and decode very small signal with amplitude from -30 dBm to -108 dBm and frequency range from 800 MHz to 900 MHz. Thu, 01 Jan 2009 00:00:00 GMT http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/12008 2009-01-01T00:00:00Z