Hoang Vinh

CREAD EA 3875, Sciences Education, Post-Doc

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Papers by Hoang Vinh

Effect of the acid properties on the diffusion of C 7 hydrocarbons in UL-ZSM-5 materials

Microporous and Mesoporous Materials, 2006

In this study, a series of UL-MFI materials with different Si/Al ratios has been synthesized foll... more In this study, a series of UL-MFI materials with different Si/Al ratios has been synthesized following a solid-state crystallization starting from amorphous wormhole-like mesostructured aluminosilicates. The acid properties of UL-MFI materials are varied by changing the content of aluminum as observed by FTIR spectra of adsorbed pyridine. The effect of the acid properties on the diffusion of C 7 hydrocarbons n-heptane and toluene in UL-MFI materials was further studied using the ZLC technique. As expected, the interaction with the acid sites causes a decrease in the diffusivities of both sorbates. The values of the activation energy of diffusion for both C 7 hydrocarbons in H-form UL-MFI materials are higher than those in Na-forms. The effect of the acid properties on the decrease of these values is more pronounced at high Si/Al ratio.

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Flood risk management for the RUA of Hanoi : Importance of community perception of catastrophic flood risk in disaster risk planning

Disaster Prevention and Management, 2007

Purpose -This paper aims to investigate reasons for unusual overdevelopment of floodplain areas o... more Purpose -This paper aims to investigate reasons for unusual overdevelopment of floodplain areas outside river dyke, provide an insight into the importance of community perception of catastrophic flood risk in the riverside urban areas (RUA) of Hanoi and establishes the need for participatory disaster management planning and disaster management education in the study location. Design/methodology/approach -Structured survey was conducted in five wards in the RUA to understand how residents perceived flood risk. Findings -The low perception of catastrophic flood risk among communities was found to be an important factor in the continued development of the RUA and led to the trust in their houses as a prominent protective solution. Moreover, the flood vulnerability of the areas has been increasing due to the missing link between local authorities and community. Research limitations/implications -This paper examines community perception of flood risk as one of main factors. Other factors such as availability of options for housing, public participation and relevant policy interventions are beyond the scope of the paper and need to be studied in the same location. Practical implications -To regulate the development of the RUA, community perception of catastrophic flood risk should be changed and community leaders should be motivated, with involvement of local authority at ward offices, to conduct comprehensive hands-on community education programs. Originality/value -Few researches have been done on the overdevelopment and community perception in the flood-prone areas. This paper not only reaffirms the few studies made in the past but also suggests broad interventions for enhancing the flood risk perception among the community members.

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Preparation of chitosan/magnetite composite beads and their application for removal of Pb(II) and Ni(II) from aqueous solution

Materials Science and Engineering: C, 2010

Fe 3 O 4 nanoparticles Chitosan/magnetite composite beads Adsorption isotherm Pb and Ni(II) A sim... more Fe 3 O 4 nanoparticles Chitosan/magnetite composite beads Adsorption isotherm Pb and Ni(II) A simple and effective process has been proposed to prepare chitosan/magnetite nanocomposite beads with saturation magnetization value as high as uncoated Fe 3 O 4 nanoparticles (ca. 54 emu/g). The reason was that the coating chitosan layer was so thin that it did not affect magnetic properties of these composite beads. Especially, chitosan on the surface of the magnetic Fe 3 O 4 nanoparticles is available for coordinating with heavy metal ions, making those ions removed with the assistance of external magnets. Maximum adsorption capacities for Pb(II) and Ni(II), occurred at pH 6 and under room temperature were as high as 63.33 and 52.55 mg/g respectively, according to Langmuir isotherm model. These results permitted to conclude that chitosan/magnetite nanocomposite beads could serve as a promising adsorbent not only for Pb(II) and Ni(II) (pH = 4-6) but also for other heavy metal ions in wastewater treatment technology.

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Ar–Ar ages in phlogopites from marble-hosted ruby deposits in northern Vietnam: evidence for Cenozoic ruby formation

Chemical Geology, 2002

Ruby growth in phlogopite-bearing marbles has been indirectly dated using the 40 Ar/ 39 Ar laser ... more Ruby growth in phlogopite-bearing marbles has been indirectly dated using the 40 Ar/ 39 Ar laser stepwise heating technique on purified syngenetic phlogopite and other micas from ruby deposits in Yen Bai, Luc Yen and Quy Chau mining districts, in northern Vietnam. The principal results indicate the following. (1) Across the Red River shear zone, the phlogopites from the Yen Bai deposits yielded Miocene cooling ages between 23.2 and 24.4 Ma identical to those previously published using the same dating method on magmatic and metamorphic rocks from the Day Nui Con Voi range. (2) Luc Yen ruby deposits in the Lo Gam zone, on the eastern flank of the Red River shear zone, yielded Oligocene cooling 40 Ar/ 39 Ar mica ages between 30.8 and 34.0 Ma. Regarding the age of ruby crystallisation itself, the most plausible hypothesis is that all rubies in both zones formed during the period 40 to 35 Ma. Diachronism of cooling in adjacent zones leads to the conclusion that around 35 Ma, the ductile deformation in the Lo Gam zone ended and the ruby-bearing marbles cooled rapidly while the high-temperature deformation remained in the Red River shear zone, resulting in cooling through blocking temperature, some 15 Ma later. (3) The Quy Chau ruby deposit is restricted to the Quy Chau shear zone that bounds the eastern part of the Oligocene -Miocene Bu Khang dome. Phlogopite and biotite samples reveal Miocene cooling ages between 21 and 22.5 Ma which are minimum ages for ruby formation. These ages could be linked with the end of the extension of the Bu Khang dome. Vietnamese ruby formation is 0009-2541/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 -2 5 4 1 ( 0 2 ) 0 0 0 6 3 -3 linked to Cenozoic tectonics resulting from continental collision between the Asian and Eurasian plates as for other marblehosted ruby deposits in Central and Southeast Asia. D

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Evaluation of the Main Diffusion Path in Novel Micro-Mesoporous Zeolitic Materials with the Zero Length Column Method

Industrial & Engineering Chemistry Research, 2007

The past several years have seen a dramatic increase in research interest regarding ordered and d... more

CO 2–H 2S–COS–S 8–AlO(OH)-bearing fluid inclusions in ruby from marble-hosted deposits in Luc Yen area, North Vietnam

Chemical Geology, 2003

Fluid inclusions have been studied in rubies from marble-hosted deposits in the Luc Yen mining di... more Fluid inclusions have been studied in rubies from marble-hosted deposits in the Luc Yen mining district, North Vietnam. Raman and Infrared spectroscopy combined with microthermometry investigations on primary and secondary fluid inclusions provided evidence of CO 2 -H 2 S -COS -S 8 -AlO(OH)-bearing fluids with native sulphur and diaspore daughter minerals, without visible water. Diaspore appeared as a nonvisible film of 2 -3 Am coating the wall of the fluid inclusion cavity and native sulphur was generally nucleated during Raman irradiation. The presence of diaspore and COS in the fluid inclusions indicates that water was present in the paleofluid. The mole fractions of H 2 O and CO 2 are around 10 À 2 and the expected concentration of water in the fluid inclusions is in the 1 -10 mol.% range. Crush-leach identified sulphates and chlorides that are assigned to the presence of anhydrite and Na -Ca -Cl salts found by SEM in the ruby crystals. The CO 2 -rich inclusions which do not coexist with an aqueous phase by immiscibility process demonstrate that ruby grew from this CO 2 -rich and water-poor fluid at equilibrium with Na -Ca -Cl salts. Thermal reduction of evaporitic sulphates based on an initial assemblage of anhydrite, calcite and graphite, originating from the metamorphism of organic matter is proposed to explain the original fluid chemistry of these marble-hosted 0009-2541/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 -2 5 4 1 ( 0 2 ) 0 0 2 7 6 -0 Chemical Geology 194 rubies. The marbles acted as a closed system and the carbonic composition of the parent fluids in ruby indicates that aluminium can be transported in CO 2 -rich fluids at high P -T. D

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Facile surface modification of nanoprecipitated calcium carbonate by adsorption of sodium stearate in aqueous solution

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2010

A simple and solvent free two-step process for nanosized and surface-modified precipitated calciu... more A simple and solvent free two-step process for nanosized and surface-modified precipitated calcium carbonate (ns-PCC) synthesis has been proposed. Synthesized ns-PCC was thoroughly characterized by infra-red (IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Langmuir adsorption study. Dynamic laser scattering (DLS) results on particle size showed a good correlation with those obtained by the proposed empirical model. Two aspects of nucleation and surface modification and the relationship of particle size on impact experimental parameters were also discussed.

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Dissolution of ionisable groups and lignocellulosic components during low-temperature kraft pulping of pinus radiata

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2006

A wide range of kraft pulps from radiata pine produced by low-temperature kraft pulping in flow-t... more A wide range of kraft pulps from radiata pine produced by low-temperature kraft pulping in flow-through reactors was assessed for carboxyl and hexenuronic acid (HexA) contents using the conductometric titrations and UV spectrophotometer, respectively. The Kappa number of pulps varied from 20.8 to 84.7 when using a cooking liquor of 1 M effective alkali as Na 2 O, 25% sulfidity, and cooking time of 100-250 min. The experimental results showed that the carboxyl groups (including HexA) and HexA groups dissolved and their residual values in the pulp samples correlate linearly with Kappa number and pulp yield. The dissolving rate of all carboxyl groups is much faster than the loss of HexA. The HexA/lignin ratio decreased non-linearly with Kappa number.

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A Performance Comparison of Routing Protocols for Maritime Wireless Mesh Networks

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Visible-light-driven TiO2 photocatalyst synthesis and photocatalytic properties

Nano TiO2 was synthesized by hydrothermal method. The sample was modified by doping transition me... more Nano TiO2 was synthesized by hydrothermal method. The sample was modified by doping transition metal ion (V, Cr and Fe) and non metal (N). Doped TiO2 samples were characterized by XRD (X-ray diffraction), FE-SEM (Fieldemission scanning electron microscopy) and UV-Vis (UV-Vis diffuse reflectance spectroscopy). Photocatalytic activity in mineralization of xylene (vapor phase), methylene blue and active dyer PR (liquid phase) were tested. In comparison to non-doped TiO2, V-,Cr-,Fe-doped TiO2 and N-doped TiO2 samples exhibited much higher photocatalytic activity using visible light instead of UV.

Airfoil shaping for reduced radar cross section

Journal of Aircraft, 1994

ABSTRACT Field methods based on finite difference approximations of the time-domain Maxwell&#... more ABSTRACT Field methods based on finite difference approximations of the time-domain Maxwell&#39;s equations and the potential-flow equation have been developed to evaluate the electromagnetic scattering and aerodynamic characteristics of airfoils. Strong similarities in the two analysis methods facilitate a synergistic approach to solve the multidisciplinary problem of airfoil shaping for aerodynamic efficiency and low radar cross section (RCS). Results for standard test cases demonstrate that both methods are quite accurate. A parametric study shows that for frontal radar illumination, the RCS of an airfoil is independent of the chordwise location of maximum thickness, but depends strongly on the maximum thickness, leading-edge radius, and leading-edge shape. In addition, the study shows that the RCS of an airfoil can be reduced without significant effects on its transonic aerodynamic efficiency by reducing the leading-edge radius and/or modifying the shape of the leading edge.

Finite-difference methods for computational electromagnetics (CEM

The authors examine the characteristics of the Lax-Wendroff and Crank-Nicolson schemes as applied... more The authors examine the characteristics of the Lax-Wendroff and Crank-Nicolson schemes as applied to the time-domain Maxwell's equations. The numerical results, in terms of the surface current and radar cross section (RCS), are compared for two-dimensional scattering problems. The Lax-Wendroff and Crank-Nicolson schemes were applied to the first- and second-order Maxwell's equations, respectively. The explicit Lax-Wendroff scheme eliminates the need for staggered meshes associated with the popular Yee (1966) algorithm while the implicit Crank-Nicolson scheme eliminates both the need for staggered meshes and the time-step restriction of the explicit schemes. The accuracy of the results obtained for the two-dimensional test problem is very encouraging, indicating that both schemes are good candidates for solving electromagnetic scattering problems in the time domain.>

Finite-difference algorithms for the time-domain Maxwell's equations - A numerical approach to RCS analysis

The applications of two CFD-based finite-difference methods to computational electromagnetics are... more The applications of two CFD-based finite-difference methods to computational electromagnetics are investigated. In the first method, the time-domain Maxwell's equations are solved using the explicit Lax-Wendroff scheme and in the second method, the second-order wave equations satisfying the Maxwell's equations are solved using the implicit Crank-Nicolson scheme. The governing equations are transformed to a generalized curvilinear coordinate system and solved on a body-conforming mesh using the scattered-field formulation. The induced surface current and the bistatic radar cross section are computed and the results are validated for several two-dimensional test cases involving perfectly-conducting scatterers submerged in transverse-magnetic plane waves.

Finite Difference Maxwell Solver to Study Geometric Shape Effects on Radar Signature

Journal of Aircraft, 1997

Service quality models: a review

Purpose -The main objective of this paper is to critically appraise various service quality model... more Purpose -The main objective of this paper is to critically appraise various service quality models and identify issues for future research based on the critical analysis of literature. Design/methodology/approach -The paper critically examines 19 different service quality models reported in the literature. The critical review of the different service quality models is intended to derive linkage between them, and highlight the area for further research. Findings -The review of various service quality model revealed that the service quality outcome and measurement is dependent on type of service setting, situation, time, need etc factors. In addition to this even the customer's expectations towards particular services are also changing with respect to factors like time, increase in the number of encounters with a particular service, competitive environment, etc. This paper provides a rich agenda for future research in the subject.

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