The Vietnam Academy of Science and Technology is a large national university in Vietnam. It was founded in 1975 as the Vietnam Academy of Science, and renamed the Vietnam Academy of Science and Technology in 2008. Its infrastructure spans Hanoi, Ho Chi Minh City, Hai Phong, Nha Trang, Da Lat, and Huế.In March 2010, the Vietnam Academy of Science and Technology launched a peer reviewed open access journal Advances in Natural science: Nanoscience and Nanotechnology . The journal is jointly published with IOP Publishing. Wikipedia.
Van Tri N.,Vietnam Academy of Science and Technology
Zootaxa | Year: 2013
A new species of Bent-toed Gecko, Cyrtodactylus dati sp. nov. is described from the secondary evergreen forests of Bu Dop District, Binh Phuoc Province, Vietnam. It differs from all other species of Indochinese and Thai-Malay Cyrtodactylus by having a maximum SVL of 70.1 mm (n=6); no distinct dark blotches on the head in adults; no continuous nuchal loop; a blotched dorsal pattern; 17-19 interorbital scales across the frontal bone; 23-26 scales in a straight line between eye and nostril; 42-48 rows of ventral scales between ventrolateral folds; 20-22 irregular, longitudinal rows of keeled tubercles at midbody between the ventrolateral folds; a series of five or six precloacal pores medially interrupted by one poreless scale in males; three or four femoral pores on each thigh in males; 4-7 enlarged scales beneath thighs; 12-13 subdigital lamellae on first toe; 18-19 subdigital lamellae on fourth toe; and small subcaudal scales. Copyright © 2013 Magnolia Press.
Nguyen K.,Vietnam Academy of Science and Technology
Advances in Structural Engineering | Year: 2015
This paper presents the influence of a crack on the dynamic behavior of a beam-type bridge subjected to separately or simultaneously a moving vehicle and earthquake excitation. In this study, the bridge is modelled as a 3D beam by the finite element method. The stiffness matrix of a cracked beam element with rectangular section adopted from fracture mechanics is presented. The influences of crack appearance time, crack location, crack depth, and vehicle speed on the dynamic response of the bridge are investigated. When a crack is induced during external excitation the stiffness of the structure is changed leading to a change in natural frequencies during vibration. This change in the frequency is analysed by wavelet spectrum, a time-frequency analysis which can examine locally a signal in both time and frequency domains. The relationship between the crack depth and the instantaneous frequency (IF) of the structure is established which may prove useful for assessment of the crack depth. Numerical simulation results are presented to investigate the efficiency of the method.
Nguyen K.V.,Vietnam Academy of Science and Technology
Engineering Structures | Year: 2013
In this paper, based on the comparison between open and breathing crack detections of a vehicle-bridge system subjected to a moving vehicle, a wavelet spectrum technique for detection of breathing crack phenomenon is presented. The stiffness of element with an open crack is calculated from fracture mechanics and the stiffness of element with a breathing crack is modeled as a time dependent stiffness matrix using the stiffness of the element with an open crack. When there is a breathing crack, the stiffness matrix of the structure at each moment depends on the curvature of the structure at the crack position. The simulation results show that when the crack "breaths" the amplitude of the vibration of the beam is smaller than in the case of an open crack. This is a warning for crack detection by using the amplitude of the dynamic response when there is a breathing crack in the structure. The open and breathing cracks can be distinguished by monitoring the instantaneous frequency (IF) of the system using the wavelet spectrum. While the IF in the case of open cracks remains unchanged during vibration, it is varying when there is a presence of breathing cracks. It is interesting that peaks in the wavelet transform of the response used to determine crack positions in case of breathing crack(s) are much larger in comparison with the case of open crack(s). The cracks can be detected with a noise level up to 10% for the case of breathing cracks while it is only 5% for the case of open cracks . These imply that the wavelet-based method for crack detection is much more efficient when breathing crack(s) are present in comparison with the case of open crack(s). © 2013 Elsevier Ltd.
Chinh P.D.,Vietnam Academy of Science and Technology
Philosophical Magazine | Year: 2011
A randomly inhomogeneous material may have macroscopic properties (elasticity, conductivity) scattered over some uncertainty intervals, despite the idealistic uniqueness assumption of homogenization theory. Based on minimum energy principles and certain statistical isotropy-symmetry hypotheses, our partly third-order bounds on the effective properties of random polycrystals are expected to estimate those scatter ranges. Explicit expressions are given and calculated for the elastic moduli of the random aggregates of some known monoclinic and triclinic crystals, which yield results in agreement with those calculated for higher-symmetry crystals: the moduli are determinable within an accuracy of two or three significant digits in most cases. It is shown, however, that with some real-world exotic crystals the bounds may fall far apart, and further theoretical and experimental studies on them deserve attention. © 2011 Taylor & Francis.
Dong P.V.,Vietnam Academy of Science and Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
We argue that the gauge symmetry which includes SU(3)L as a higher weak-isospin symmetry is manifestly given by SU(3)C - SU(3)L - U(1)X - U(1)N, where the last two factors determine the electric charge and B-L, respectively. This theory not only provides a consistent unification of the electroweak and B-L interactions, but also gives insights in dark matter, neutrino masses, and inflation. The dark matter belongs to a class of new particles that have wrong B-L numbers, and is stabilized due to a newly realized W-parity as residual gauge symmetry. The B-L breaking field is important to define the W-parity, seesaw scales, and the inflaton. Furthermore, the number of fermion generations and the electric charge quantization are explained naturally. We also show that the previous 3-3-1 models are only an effective theory, as the B-L charge and the unitarity argument are violated. This work substantially generalizes our recently proposed 3-3-1-1 model. © 2015 American Physical Society. © 2015 American Physical Society.