Hydrological consequences of landscape fragmentation in mountainous northern Vietnam: Buffering of Hortonian overland flow

Title:

	Hydrological consequences of landscape fragmentation in mountainous northern Vietnam: Buffering of Hortonian overland flow
Authors:	Ziegler, Alan D Tran T. Liem Tran Duc Vien
Keywords:	land-cover conversion deforestation KINEROS2 swidden agriculture tropical watershed hydrology SE Asia runoff generation filter strips
Issue Date:	2007
Publisher:	ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS
Citation:	ISIKNOWLEDGE
Abstract:	We use a hydrology-based fragmentation index to explore the influence of land-cover distribution on the generation and buffering of Hortonian overland flow (HOF) in two disturbed upland basins in northern Vietnam (Tan Minh). Both the current degree of fragmentation in Tan Minh and the current spatial arrangement of buffers (relative to HOF source areas) provide only limited opportunities for infiltrating surface runoff from upslope source areas, in part because of the high connectivity of swidden fields on long hillslopes. The intentional placement of buffers below HOF sources and the reduction of the down-slope lengths of swidden fields could reduce the occurrence of HOF on individual hillslopes. Reduction of the total watershed total depth of HOF would require maintaining a sufficient area of buffering land covers; and this may necessitate the use of longer fallow periods. These measures are, however, counter to the land-practice trends witnessed in the last several decades (i.e., no buffers, cultivation of long slopes, and increasingly shorter fallow periods). The two most likely scenarios of future land-cover change in Tan Minh-one representing increased fragmentation, the other decreased-both lead to an increase in HOF because of reduced buffering potential. The unlikely scenario of abandonment of agriculture and subsequent regeneration of forest, leads to both less fragmentation and less HOF. The study highlights the hydrological impacts associated with fragmentation at Tan Minh, which is the product of decades of local and regional forcing factors that have dictated the degree and timing of timber removal and swiddening at the site. (c) 2007 Elsevier B.V. All rights reserved.
Description:	JOURNAL OF HYDROLOGY Volume: 337 Issue: 1-2 Pages: 52-67 Published: APR 15 2007 ; TNS07629
URI:	http://www.sciencedirect.com/science/article/pii/S0022169407000236 http://repository.vnu.edu.vn/handle/VNU_123/31368
ISSN:	0022-1694
Appears in Collections:	Bài báo của ĐHQGHN trong Web of Science

Distribution of persistent organic pollutants and polycyclic aromatic hydrocarbons in sediment samples from Vietnam

 Title:

	Distribution of persistent organic pollutants and polycyclic aromatic hydrocarbons in sediment samples from Vietnam
Authors:	Nguyen Thi Phuong Thao Pham Hung Viet Tran Thi Ngoc Lan
Keywords:	persistent organic pollutant polycyclic aromatic hydrocarbon Vietnam sediment sample high resolution gas chromatography/high resolution mass spectrometry
Issue Date:	2007
Publisher:	PHARMACEUTICAL SOC JAPAN, 2-12-15 SHIBUYA, SHIBUYA-KU, TOKYO, 150-0002, JAPAN
Citation:	ISIKNOWLEDGE
Abstract:	The presence of eight kinds of persistent organic pollutants (POPs) such as DDT and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), chlordane compounds (CHLs), drin compounds (Drins), heptachlor, hexachlorobenzene (HCB), heptachlor-epoxide, polychlorinated biphenyls (PCBs) and sixty-four polycyclic aromatic hydrocarbon compounds (PAHs) was identified using high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) to investigate their distribution in surface sediment from Hanoi, Hue, and Ho Chi Minh in Vietnam. A survey of sediment samples from Osaka was conducted for comparison. The concentrations of Sigma DDTs, Sigma CHLs, Sigma PCBs and Sigma PAHs in Vietnam were 0.19-140, N.D.-9.0, 0.11-110, and 30-5500 ng/g-dry, respectively. Concentrations of these compounds in urban areas were higher than those in other areas. In addition, the Sigma DDT concentrations in Vietnamese urban areas were higher than those in Osaka. These results suggest that most DDTs would be used as insecticides for the purpose of health services rather than as agricultural chemicals. PAH pollution in urban areas and suburbs is caused mainly by runoff of petrol, whereas in rural areas, the combustion of fossil fuels and biomass is the major pollutant source.
Description:	TNS07623 ; JOURNAL OF HEALTH SCIENCE Volume: 53 Issue: 3 Pages: 291-301 Published: JUN 2007
URI:	http://repository.vnu.edu.vn/handle/VNU_123/31214
ISSN:	1344-9702 1347-5207
Appears in Collections:	Bài báo của ĐHQGHN trong Web of Science

Managing Vietnam's maritime boundary disputes

Title:

	Managing Vietnam's maritime boundary disputes
Authors:	Thao, Nguyen Hong Amer, Ramses
Keywords:	boundary Gulf of Thailand Gulf of tonkin maritime disputes spratly archipelago Vietnam
Issue Date:	2007
Publisher:	TAYLOR & FRANCIS INC, 325 CHESTNUT ST, SUITE 800, PHILADELPHIA, PA 19106 USA
Citation:	ISIKNOWLEDGE
Abstract:	This article examines the progress made in managing Vietnam's maritime boundary disputes and analyzes the challenges that lie ahead relating to unsettled disputes. The continuity and change in Vietnam's approach to dispute a settlement and the difficulties in managing the unresolved maritime disputes are assessed. Vietnam has made considerable progress in managing its maritime disputes; however, continued efforts are needed to address the unresolved disputes.
Description:	TNS07622 ; OCEAN DEVELOPMENT AND INTERNATIONAL LAW Volume: 38 Issue: 3 Pages: 305-324 Published: JUL-SEP 2007
URI:	http://repository.vnu.edu.vn/handle/VNU_123/31210
ISSN:	0090-8320
Appears in Collections:	Bài báo của ĐHQGHN trong Web of Science

On the exponential stability of dynamic equations on time scales

 Title:

	On the exponential stability of dynamic equations on time scales
Authors:	Nguyen Huu Du Le Huy Tien
Keywords:	exponential stability uniformly exponential stability time scales perron theorem linear dynamic equation
Issue Date:	2007
Publisher:	ACADEMIC PRESS INC ELSEVIER SCIENCE, 525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA
Citation:	ISIKNOWLEDGE
Abstract:	In this paper, we deal with some theorems on the exponential stability of trivial solution of time-varying non-regressive dynamic equation on time scales with bounded graininess. In particular, well-known Perron's theorem is generalized on time scales. Under rather restrictive condition, that is, integral boundedness of coefficient operators, we obtain a characterization of the uniformly exponential stability. (c) 2006 Elsevier Inc. All rights reserved.
Description:	TNS07619 ; JOURNAL OF MATHEMATICAL ANALYSIS AND APPLICATIONS Volume: 331 Issue: 2 Pages: 1159-1174 Published: JUL 15 2007
URI:	http://repository.vnu.edu.vn/handle/VNU_123/31172
ISSN:	0022-247X
Appears in Collections:	Bài báo của ĐHQGHN trong Web of Science

An approach for obtaining approximate formulas for the Rayleigh wave velocity

 Authors:

	Pham Chi Vinh Peter G. Malischewsky
Keywords:	rayleigh waves rayleigh wave velocity rayleigh wave speed approach of least squares the best approximation approximate formula approximate expression
Issue Date:	2007
Publisher:	ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS
Citation:	ISIKNOWLEDGE
Abstract:	In this paper, we introduce an approach for finding analytical approximate formulas for the Rayleigh wave velocity for isotropic elastic solids and anisotropic elastic media as well. The approach is based on the least-square principle. To demonstrate its application, we applied it in order to obtain an explanation for Bergmann's approximation, the earliest known approximation of the Rayleigh wave velocity for isotropic elastic solids, and used it to establish a new approximation. By employing this approach, the best approximate polynomials of the second order of the cubic power and the quartic power in the interval [0, 1] were found. By using the best approximate polynomial of the second order of the cubic power, we derived an approximate formula for the Rayleigh wave speed in isotropic elastic solids which is slightly better than the one given recently by Rahman and Michelitsch by employing Lanczos's approximation. Also by using this second order polynomial, analytical approximate expressions for orthotropic, incompressible and compressible elastic solids were found. For incompressible case, it is shown that the approximation is comparable with Rahman and Michelitsch's approximation, while for the compressible case, it is shown that our approximate formulas are more accurate than Mozhaev's ones. Remarkably, by using the best approximate polynomials of the second order of the cubic power and the quartic power in the interval [0, 1], we derived an approximate formula of the Rayleigh wave velocity in incompressible monoclinic materials, where the explicit exact formulas of the Rayleigh wave velocity so far are not available. (c) 2007 Elsevier B.V. All rights reserved.
Description:	TNS07618 ; WAVE MOTION Volume: 44 Issue: 7-8 Pages: 549-562 Published: AUG 2007
URI:	http://repository.vnu.edu.vn/handle/VNU_123/31160
ISSN:	0165-2125
Appears in Collections:	Bài báo của ĐHQGHN trong Web of Science

Anharmonic effective potential, correlation effects, and EXAFS cumulants calculated from a morse interaction potential for fcc metals

 Anharmonic effective pair potentials and effective local force constants have been studied for fee metals, assuming an interaction Morse potential and taking into account the influence of nearest neighbours of absorber and backscatterer atoms. Analytical expressions for the first three extended X-ray absorption fine structure (EXAFS) cumulants, as well as for the atomic mean square displacements, have been derived as a function of the Morse parameters. Numerical results for copper and nickel are compared with experimental data. A good agreement is found for the second cumulant. Non-negligible discrepancies are instead found for the first and third cumulants, which are tentatively attributed to the central nature of the Morse potential, which neglects many-body effects. URI: http://repository.vnu.edu.vn/handle/VNU_123/31148

Mitochondrial control region and population genetic patterns of Nycticebus bengalensis and N-Pygmaeus

Abstract:

	Bengal slow lorises (Nycticebus bengalensis) and pygmy slow lorises (Nycticebus pygmaeus) are nocturnal which creates difficulties to study them in the field. There is a scarcity of data on them and their population genetics are poorly understood. We sequenced and analyzed a partial fragment in the first hypervariable region of the mitochondrial control region or D-loop HVRI of 21 Nycticebus bengalensis and 119 N. pygmaeus from the boundary between China and Vietnam where they are sympatric. Though the sample size for Nycticebus pygmaeus is much larger, the polymorphism level is much lower than that of N. bengalensis, possibly because of (1) external gene flow from other habitats of N. bengalensis, (2) gene ingression from Sunda slow lorises (N. coucang coucang) to N. bengalensis, (3) a skewed birth sex ratio in N. pygmaeus, and (4) a possible low survival rate of infant N. pygmaeus. Based on genetic comparisons to Nycticebus bengalensis, we propose that N. pygmaeus in southern China and northern Vietnam might have migrated from middle or southern Vietnam recently.
Description:	TNS07616 ; INTERNATIONAL JOURNAL OF PRIMATOLOGY Volume: 28 Issue: 4 Pages: 791-799 Published: AUG 2007
URI:	http://repository.vnu.edu.vn/handle/VNU_123/31136

Giant exchange bias in MnPd/Co bilayers

 A systematic study of exchange bias in MnPd/Co bilayers has been carried out, where the dependences of exchange bias, unidirectional anisotropy constant and coercivity on the thicknesses of MnPd and Co layers were investigated. A huge unidirectional anisotropy constant, J(K) = 2.5 erg/cm(2) was observed, which is in reasonable agreement with the theoretical prediction based on the model by Meiklejohn and Bean. The angular dependences of exchange bias field and coercivity have also been examined showing that both exchange bias and coercivity follow 1/ cos alpha rule. (c) 2007 Elsevier B.V. All rights reserved. http://repository.vnu.edu.vn/handle/VNU_123/31126

Manganese perovskites for room temperature magnetic refrigeration applications

 We found the large magnetocaloric effect (MCE) in La0.6Ca0.3Pb0.1MnO3 (sample No. 1), La0.7Ca0.2Pb0.1MnO3 (sample No. 2), and La0.7Ca0.1Pb0.2MnO3 (sample No. 3) perovskites, which were prepared by a conventional ceramic method. For a magnetic field change of 13.5 kOe, the magnetic entropy change (Delta S-M) reached values of 2.55, 2.53 and 3.72 J/kg K for samples Nos. 1, 2 and 3, respectively. Interestingly, the large Delta S-M was found to occur around 300 K for all samples investigated, which allows magnetic refrigeration at room temperature. These perovskites have the large magnetic entropy changes induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. (C) 2007 Elsevier B.V. All rights reserved. http://repository.vnu.edu.vn/handle/VNU_123/31120

Longitudinal Hall effect in Terfecohan thin films with perpendicular magnetic anisotropy

 Longitudinal extraordinary Hall Effect (LEHE) of magnetic Tb( Fe0.55Co0.45)(1.5) (known as Terfecohan) thin films with perpendicular magnetic anisotropy has been investigated as a function of both the intensity of applied magnetic fields and the angle alpha between the applied field and film normal directions. The Hall voltage loops exhibit a parallelogram shape, which is almost similar to those of the perpendicular magnetization. The high-field Hall voltage susceptibility is positive at alpha = 0. Its value decreases with increasing alpha and changes in sign at alpha(m) 20 degrees, which is considered as the easy magnetizable direction of the film. This finding is comparable with those obtained from the magnetization, magnetic force microscopy (MFM) and conversion electron Mossbauer spectra (CEMS) measurements. The obtained LEHE behaviors are rather promising for applications such as magnetic recording heads and magnetic field detectors, where a large output signal is required at low magnetic fields. (c) 2007 Elsevier B.V. All rights reserved.. Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31096

Magnetization and magnetostriction process in spring-magnet TbFeCo/Fe multilayers with variable TbFeCo thickness

 Different natures of the magnetization reversal are studied by means of magnetization and magnetostriction measurements for magnetostrictive "spring-magnet'' multilayers of TbFeCo/Fe with a. fixed Fe layer thickness of 10 nm and variable TbFeCo layer thickness of 12, 16 and 20 nm. In such multilayered systems, magnetization reversal occurs at different coercive fields for each layer related to formation of the domain wall at interfaces. The results show that at low temperatures, transition from the ferromagnetic saturation state (with domain walls) to the ferrimagnetic transient saturation state (without domain walls) takes place by the reversal of the magnetic moments in the high-magnetization Fe layers. This process is governed by large magnetic anisotropy of the TbFeCo layer. Increasing temperature, this anisotropy decreases and transition results from the reversal of magnetic moments in the small magnetization TbFeCo layers. Formation of the domain wall at interfaces is clearly evidenced by the negative contribution to the parallel magnetostriction. (c) 2007 Elsevier B.V. All rights reserved. Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31064

Study of the determination of inorganic arsenic species by CE with capacitively coupled contactless conductivity detection

 The determination of arsenic(III) and arsenic(V), as inorganic arsenite and arsenate, was, investigated by CE with capacitively coupled contactless conductivity detection (CE-C-4 D). It was found necessary to determine the two inorganic arsenic species separately employing two different electrolyte systems. Electrolyte solutions consisting of 50 mM CAPS/2 MM L-arginine (Arg) (pH 9.0) and of 45 mM acetic acid (pH 3.2) were used for arsenic(III) and arsenic(V) determinations, respectively. Detection limits of 0.29 and 0.15 mu M were achieved for As(III) and As(V), respectively by using large-volume injection to maximize the sensitivity. The analysis of contaminated well water samples from Vietnam is demonstrated.
Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31059

New fully portable instrument for the versatile determination of cations and anions by capillary electrophoresis with contactless conductivity detection

 A new portable capillary electrophoresis instrument with capacitively coupled contactless conductivity detection was developed and optimized for the sensitive field measurements of ionic compounds in environmental samples. It is powered by batteries and the high voltage modules are capable of delivering up to 15 kV at either polarity for more than one working day. Inorganic cations and anions, including ions of heavy metals and arsenate, could be determined with detection limits in the range from about 0.2 to 1 mu M. The instrument was field tested in a remote region of Tasmania and nitrite and ammonium could be determined on-site at concentrations as low as 10 ppb in presence of other common inorganic ions at concentrations which were 2 to 3 orders of magnitude higher.
Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31052

Continuous parallel-iterated RKN-type PC methods for nonstiff IVPs

 This paper investigates parallel predictor-corrector (PC) iteration schemes based on direct collocation Runge-Kutta-Nystrom (RKN) corrector methods with continuous output formulas for solving nonstiff initial-value problems (IVPs) for systems of special T second-order differential equations y ''(t) = f(t, y(t)). Consequently, the resulting parallel-iterated RKN-type PC methods are provided with continuous output formulas. The continuous numerical approximations are also used for predicting the stage values in the PC iteration processes. In this way, we obtain parallel PC methods with continuous output formulas and high-order predictors. Applications of the resulting parallel PC methods to a few widely-used test problems reveal that these new parallel PC methods are much more efficient when compared with the parallel-iterated RKN (PIRKN) methods and the sequential ODEX2 and DOPRIN codes from the literature. (c) 2006 IMACS. Published by Elsevier B.V. All rights reserved.
 Mời bạn đọc xem tại đây:  http://repository.vnu.edu.vn/handle/VNU_123/31026

A novel efficient two-phase algorithm for training interpolation radial basis function networks

 nterpolation radial basis function (RBF) networks have been widely used in various applications. The output layer weights are usually determined by minimizing the sum-of-squares error or by directly solving interpolation equations. When the number of interpolation nodes is large, these methods are time consuming, difficult to control the balance between the convergence rate and the generality, and difficult to reach a high accuracy. In this paper, we propose a two-phase algorithm for training interpolation RBF networks with bell-shaped basis functions. In the first phase, the width parameters of basis functions are determined by taking into account the tradeoff between the error and the convergence rate. Then, the output layer weights are determined by finding the fixed point of a given contraction transformation. The running time of this new algorithm is relatively short and the balance between the convergence rate and the generality is easily controlled by adjusting the involved parameters, while the error is made as small as desired. Also, its running time can be further enhanced thanks to the possibility to parallelize the proposed algorithm. Finally, its efficiency is illustrated by simulations. (c) 2007 Elsevier B.V. All rights reserved. Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31018

Chemical composition of the flower essential oil of Artabotrys hexapetalus (L. f.) bhandare of Vietnam

 The pleasant smelling flower essential oil of Artabotrys hexapetalus (L. f.) Bhandare (Annonaceae) was analyzed by GC and GC/MS. Twenty-six components of the oil including sesquiterpene hydrocarbons (33.3% of the oil) and oxygenated sesquiterpenoids (47.7%) were identified. P-caryophyllene (11.4%) and caryophyllene oxide (31.5%) were identified as the major components of the oil.
Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31011

Chemical composition of the essential oil from the rhizomes of Alpinia henryi K. Schum. of Vietnam

 The essential oil from the fresh rhizomes of Alpinia henryi K. Schum. (Zingiberaceae) collected in Vietnam was analyzed by GC and GC/MS. Twenty-five compounds, representing 86.4% of the oil, were identified. The oil was characterized by a high content of 1,8-cineole (45.1%).

 Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/31005

Arsenic in groundwater of the Red River floodplain, Vietnam: Controlling geochemical processes and reactive transport modeling

 The mobilization of arsenic (As) to the groundwater was studied in a shallow Holocene aquifer on the Red River flood plain near Hanoi, Vietnam. The groundwater chemistry was investigated in a transect of 100 piezometers. Results show an anoxic aquifer featuring organic carbon decomposition with redox zonation dominated by the reduction of Fe-oxides and methanogenesis. Enhanced PCO2 pressure causes carbonate dissolution to take place but mainly in the soil and unsaturated zone. The concentration of As increases over depth to a concentration of up to 550 mu g/L. Most As is present as As(III) but some As(V) is always found. Arsenic correlates well with NH4, relating its release to organic matter decomposition and the source of As appears to be the Fe-oxides being reduced. Part of the produced Fe(II) is apparently reprecipitated as siderite containing less As. Results from sediment extraction indicate most As to be related to the Fe-oxide fractions. The measured amount of sorbed As is low. In agreement, speciation calculations for a Fe-oxide surface suggest As(III) to constitute only 3% of the surface sites while the remainder is occupied by carbonate and silica species. The evolution in water chemistry over depth is homogeneous and a reactive transport model was constructed to quantify the geochemical processes along the vertical groundwater flow component. A redox zonation model was constructed using the partial equilibrium approach with organic carbon degradation in the sediment as the only rate controlling parameter. Apart from the upper meter a constant degradation rate of 0.15 C mmol/L/yr could explain the redox zonation throughout the aquifer. Modeling also indicates that the Fe-oxide being reduced is of a stable type like goethite or hematite. Arsenic is contained in the Fe-oxides and is first released during their dissolution. Our model further suggests that part of the released As is adsorbed on the surface of the remaining Fe-oxides and in this way may be retarded. (c) 2007 Elsevier Ltd. All rights reserved.
 Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/30997

Systematic testing of an integrated systems model for coastal zone management using sensitivity and uncertainty analyses

 Systematic testing of integrated systems models is extremely important but its difficulty is widely underestimated. The inherent complexity of the integrated systems models, the philosophical debate about the model validity and validation, the uncertainty in model inputs, parameters and future context and the scarcity of field data complicate model validation. This calls for a validation framework and procedures which can identify the strengths and weaknesses of the model with the available data from observations, the literature and experts' opinions. This paper presents such a framework and the respective procedure. Three tests, namely, Parameter-Verification, Behaviour-Anomaly and Policy-Sensitivity are selected to test a Rapid assessment Model for Coastal-zone Management (RaMCo). The Morris sensitivity analysis, a simple expert elicitation technique and Monte Carlo uncertainty analysis are used to facilitate these three tests. The usefulness of the procedure is demonstrated for two examples. (C) 2006 Published by Elsevier Ltd.
Mời bạn xem đọc tại đây: http://repository.vnu.edu.vn/handle/VNU_123/30984

A new approach to testing an integrated water systems model using qualitative scenarios

 Integrated systems models have been developed over decades, aiming to support the decision-makers in the planning and managing of natural resources. The inherent model complexity, lack of knowledge about the linkages among model components, scarcity of field data, and uncertainty involved with internal and external factors of the real system call their practical usefulness into doubt. Validation tests designed for such models are just immature, and are argued to have some characteristics that differ from the ones used for validating other types of models. A new approach for testing integrated water systems models is proposed, and applied to test the RaMCo model. Expert knowledge is elicited in the form of qualitative scenarios and translated into quantitative projections using fuzzy set theory. Trend line comparison of the projections made by the RaMCO model and the qualitative projections based on expert knowledge revealed an insufficient number of land-use types adopted by the RaMCo model. This insufficiency makes the model inadequate to describe the consequences of the changes in socio-economic factors and policy options on the erosion from the catchment and the sediment yields at the inlet of a storage lake. (C) 2007 Elsevier Ltd. All rights reserved.
Mời bạn đọc xem tại đây: http://repository.vnu.edu.vn/handle/VNU_123/30973