Hanoi University of Science

hus.vnu.edu.vn
Hanoi, Vietnam

Hanoi University of Science is a member of Vietnam National University, Hanoi. Founded in 1904 as Indochina University, the university has changed its name three times: School of Basic Science , University of Hanoi , Hanoi University of Science . Since the last name change, Hanoi University of Science is a member of Vietnam National University, Hanoi. Wikipedia.

SEARCH FILTERS
Time filter
Source Type

Thac Dung N.,Hanoi University of Science
Differential Geometry and its Application | Year: 2017

In this note, we show an Hamilton type gradient estimate for the solution of time-dependent of nonlinear diffusion equation on smooth metric measure space (M,g,e−fdv). As the application, we show a dimension-free Harnack inequality and prove a Liouville property for f-harmonic functions. © 2017 Elsevier B.V.


Hung N.V.,Hanoi University of Science
Journal of the Physical Society of Japan | Year: 2014

A pressure-dependent anharmonic correlated Einstein model is derived for extended X-ray absorption fine structure (EXAFS) Debye-Waller factors (DWFs), which are presented in terms of cumulant expansion up to the third order. The model is based on quantum thermodynamic perturbation theory and includes anharmonic effects based on empirical potentials. Explicit analytical expressions of the pressure-dependent changes in the interatomic distance, anharmonic effective potential, thermodynamic parameters, first, second, and third EXAFS cumulants, and thermal expansion coefficient have been derived. This model avoids the use of extensive full lattice dynamical calculations, yet provides good and reasonable agreement of numerical results for Cu with experimental results of X-ray diffraction (XRD) analysis and pressure-dependent EXAFS. Significant pressure effects are shown by the decrease in the pressure-induced changes in the interatomic distance, EXAFS cumulants and thermal expansion coefficient, as well as by the increase in the pressure-induced changes in the interatomic effective potential, effective spring constant, correlated Einstein frequency, and temperature. © 2014 The Physical Society of Japan.


Vinh P.C.,Hanoi University of Science
Wave Motion | Year: 2013

In this paper, formulae for the velocity of Scholte waves propagating along the interface between a fluid half-space and an isotropic elastic half-space are derived using the complex function method. From these formulae it is shown that if a Scholte wave exists, then it is unique, and for any given parameters of the solid and the fluid, a Scholte wave is always possible. © 2012 Elsevier B.V.


Vinh P.C.,Hanoi University of Science | Linh N.T.K.,Water Resources University
Wave Motion | Year: 2012

The present paper is concerned with the propagation of Rayleigh waves in an orthotropic elastic half-space coated with a thin orthotropic elastic layer and the main purpose of the paper is to establish an approximate secular equation of the wave. By using the effective boundary condition method an approximate secular equation of third-order in terms of the dimensionless thickness of the layer has been derived. From this equation two different third-order approximate secular equations are obtained for the case when the half-space and the layer are both isotropic, one of which recovers the secular equation of second-order derived by Bovik [P.Bovik, A comparison between the Tiersten model and O(H) boundary conditions for elastic surface waves guided by thin layers, J. Appl. Mech. 63 (1996) 162-167]. An explicit second-order approximate formula for the Rayleigh wave velocity has been created based on the obtained approximate secular equation. Since explicit dispersion relations are employed as theoretical bases for extracting the mechanical properties of the thin films from experimental data, the obtained secular equation and formula for the velocity may be useful in practical applications. © 2012 Elsevier B.V.


Vinh P.C.,Hanoi University of Science | Ngoc Anh V.T.,Hanoi University of Science
International Journal of Engineering Science | Year: 2014

In the present paper, we are interested in the propagation of Rayleigh waves in an orthotropic elastic half-space coated with a thin orthotropic elastic layer. The contact between the layer and the half space is assumed to be smooth. The main aim of the paper is to establish an approximate secular equation of the wave. By using the effective boundary condition method, an approximate secular equations of third-order in terms of the dimensionless thickness of the layer is derived. It is shown that this approximate secular equation has high accuracy. From the secular equation obtained, an approximate formula of third-order for the Rayleigh wave velocity is derived and it is a good approximation. © 2013 Elsevier Ltd. All rights reserved.


Vinh P.C.,Hanoi University of Science
Wave Motion | Year: 2011

In this paper, formulas for the velocity of Rayleigh waves in compressible isotropic solids subject to uniform initial deformations are derived using the theory of cubic equation. They are explicit, have simple algebraic forms, and hold for a general strain energy function. Unlike the previous investigations where the derived formulas for Rayleigh wave velocity are approximate and valid for only small enough values of pre-strains, this paper establishes exact formulas for Rayleigh wave velocity being valid for any range of pre-strains. When the prestresses are absent, the obtained formulas recover the Rayleigh wave velocity formula for compressible elastic solids. Since obtained formulas are explicit, exact and hold for any range of pre-strains, they are good tools for evaluating nondestructively prestresses of structures. © 2011 Elsevier B.V.


Chi Vinh P.,Hanoi University of Science | Thi Khanh Linh N.,Water Resources University
International Journal of Non-Linear Mechanics | Year: 2013

The present paper is concerned with the propagation of Rayleigh waves in a pre-stressed elastic half-space coated with a thin pre-stressed elastic layer. The half-space and the layer are assumed to be compressible and in welded contact with each other. By using the effective boundary condition method, an explicit third-order approximate secular equation of the wave has been derived that is valid for any pre-strains and for a general strain-energy function. When the pre-strains are absent, the secular equation obtained coincides with the one for the isotropic case. Numerical investigation shows that the approximate secular equation obtained is a good approximation. Since explicit dispersion relations are employed as theoretical bases for extracting pre-stresses from experimental data, the secular equation obtained will be useful in practical applications. © 2012 Elsevier Ltd. All rights reserved.


Tuan T.T.,Hanoi University of Science | Scherbaum F.,University of Potsdam | Malischewsky P.G.,Friedrich - Schiller University of Jena
Geophysical Journal International | Year: 2011

One of the key challenges in the context of local site effect studies is the determination of frequencies where the shakeability of the ground is enhanced. In this context, the H/V technique has become increasingly popular and peak frequencies of H/V spectral ratio are sometimes interpreted as resonance frequencies of the transmission response. In the present study, assuming that Rayleigh surface wave is dominant in H/V spectral ratio, we analyse theoretically under which conditions this may be justified and when not. We focus on 'layer over half-space' models which, although seemingly simple, capture many aspects of local site effects in real sedimentary structures. Our starting point is the ellipticity of Rayleigh waves. We use the exact formula of the H/V-ratio presented by Malischewsky & Scherbaum (2004) to investigate the main characteristics of peak and trough frequencies. We present a simple formula illustrating if and where H/V-ratio curves have sharp peaks in dependence of model parameters. In addition, we have constructed a map, which demonstrates the relation between the H/V-peak frequency and the peak frequency of the transmission response in the domain of the layer's Poisson ratio and the impedance contrast. Finally, we have derived maps showing the relationship between the H/V-peak and trough frequency and key parameters of the model such as impedance contrast. These maps are seen as diagnostic tools, which can help to guide the interpretation of H/V spectral ratio diagrams in the context of site effect studies. © 2010 The Authors Geophysical Journal International © 2010 RAS.


Vinh P.C.,Hanoi University of Science
Journal of Applied Mechanics, Transactions ASME | Year: 2010

In the present paper, formulas for the velocity of Rayleigh waves in incompressible isotropic solids subject to a general pure homogeneous prestrain are derived using the theory of cubic equation. They have simple algebraic form and hold for a general strainenergy function. The formulas are concretized for some specific forms of strain-energy function. They then become totally explicit in terms of parameters characterizing the material and the prestrains. These formulas recover the (exact) value of the dimensionless speed of Rayleigh wave in incompressible isotropic elastic materials (without prestrain). Interestingly that, for the case of hydrostatic stress, the formula for the Rayleigh wave velocity does not depend on the type of strain-energy function. © 2010 by ASME.


Landslides are one of the most dangerous hazards in Vietnam. Most landslides occur at excavated slopes, and natural slope failures are rare in the country. However, the volume of natural slope failures can be very significant and can badly affect large areas. After a long period of heavy rainfall in the fourth quarter of 2005 in Van Canh district, a series of landslides with volumes of 20,000-195,000 m3 occurred on 15 December 2005. The travel distances for the landslides reached over 300-400 m, and the landslides caused some remarkable loud booming noises. The failures took place on natural slopes with unfavorable geological settings and slope angles of 28-31°. The rainfall in the fourth quarter of 2005 is estimated to have a return period of 100 years and was the main triggering factor. Because of the large affected area and low population density, resettling people from the dangerous landslide-prone residential areas to safer sites was the most appropriate solution. In order to do so, a map of landslide susceptibility was produced that took into account slope angle, distance to faults, and slope aspect. The map includes four levels from low to very high susceptibility to landslides. © 2012 The Author(s).

Loading Hanoi University of Science collaborators
Loading Hanoi University of Science collaborators