Time filter

Source Type

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.

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. Source

Tuan N.A.,Hanoi University of Science
Journal of Applied Physics | Year: 2012

We present a density functional study on the geometric structure, electronic structure, and spin transition of a series of Fe II spin-crossover (SCO) molecules, i.e., [Fe(abpt) 2(NCS) 2] (1), [Fe(abpt) 2(NCSe) 2] (2), and [Fe(dpbo)(HIm) 2] (3) with dpbo {diethyl(E,E)-2,2′-[1,2- phenylbis(iminomethylidyne)]bis[3-oxobutanoate](2-)-N,N',O 3,O 3'}, and abpt {4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole} in order to explore more about the way to control SCO behavior of transition metal complexes. Our calculated results show that the spin transition of these Fe II molecules is accompanied with charge transfer between the Fe atom and ligands. This causes change in the electrostatic energy (δU) as well as the total electronic energy of SCO molecules. Moreover, our calculated results demonstrate an important contribution of the interionic interactions to δU, and there is the relation between U and the thermal hysteresis behavior of SCO molecules. These results should be helpful for developing new SCO molecules. © 2012 American Institute of Physics. Source

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. Source

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. Source

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. Source

Discover hidden collaborations