http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/97 2026-05-17T13:00:34Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/1094 Some problem on the shadow of segments infinite boolean rings Tran, Huyen; Le, Cao Tu In this paper , we consider finite Boolean rings in which were defined two orders: natural order and antilexicographic order. The main result is concerned to the notion of shadow of a segment. We shall prove some necessary and sufficient conditions for the shadow of a segment to be a segment. VNU Journal of Science, Mathematics - Physics. Vol. 23 (2007), No 4, P. 221-224 2007-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/1090 Land-vehicle mems INS/GPS positioning during GPS signal blockage periods T., D. Tan; L., M.Ha; N., T. Long; N., D. Duc; N., P. Thuy The demand of vehicle navigation and guidance has been urgent for many years. The idea of integrating multisensor navigation systems was implemented. The most efficient multisensor configuration is the system integrating an inertial navigation system (INS) consisting of MEMS based micro sensors and a global positioning system (GPS). In such system, the GPS is used for providing position and velocity whereas the INS for providing orientation. The estimation of the system errors is performed by a Kalman filter (KF). A serious problem occurs in the INS/GPS system application that is caused by the accidental GPS signal blockages. In this paper, the main objective is to improve the accuracy of the obtained navigation parameters during periods of GPS signal outages using different methods. The overall performance of the system have been analyzed by experimentation data; and results show that these methods indeed improve the quality of the navigation and guidance systems. VNU Journal of Science, Mathematics - Physics. Vol. 23 (2007), No 4, P. 243-251 2007-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/1086 Investigation of the embedded fiber bragg grating temperature sensor Tran, Thi Tam; Dang, Quoc Trung; Tran, Anh Vu; Le, Huu Minh; Do, Ngoc Chung An embedded fiber Bragg grating (FBG) sensor, which fabricated in IMS, for temperature sensing was proposed. The temperature responses of the in-fiber Bragg gratings (FBGs) have been investigated. It was found that these responses ranged from 10.6 pm/°C to 12.0 pm/°C. The temperature sensitivity of the FBGs was 0.2°C. The strain responses remained temperature independent over a temperature range of 20 – 180 C. The results obtained are in agreement, within the experimental error, with predictions based on material parameters. Although the temperature response is nonlinear over the temperature range 20 °C to 180 °C, in practical systems the temperature response of the sensor may be assumed to be linear within the temperature range 20 °C to 80 °C. VNU Journal of Science, Mathematics - Physics. Vol. 23 (2007), No 4, P. 237-242 2007-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/1067 Preparation and characteristics of LiF:Mg,Cu,Na,Si thermoluminescent material Vu, Thi Thai Ha; Nguyen, Thi Quy Hai; Nguyen, Ngoc Long; Le, Van Vu Lithium fluoride (LiF) thermoluminescent powder doped with Mg, Cu, Na, and Si as activators was prepared. X-ray diffraction analysis indicated that doping LiF with different activators makes crystal lattice somewhat expand. The dosimetric properties of the powder were studied. The main dosimetric peak of LiF:Mg,Cu,Na,Si appeared in the range of 227−247oC and the ratio of the height of the main peak to that of the other small peaks in the LiF:Mg,Cu,Na,Si is much greater than that in the LiF:Mg,Ti and LiF:Mg,Cu,P. The preparation conditions such as annealing temperature and duration, annealing atmosphere, doping with different activators etc. were investigated. VNU Journal of Science, Mathematics - Physics. Vol. 23 (2007), No 4, P. 225-231 2007-01-01T00:00:00Z