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Ho Chi Minh City, Vietnam

Ho Chi Minh City University of Science was re-founded in March 1996 following a split from Đại học Tổng hợp . The school has since been a member university of Vietnam National University, Ho Chi Minh City. It is entrusted with providing education at undergraduate and postgraduate levels and undertaking scientific research as well as technological transfer. Wikipedia.

Cuong T.V.,University of Ulsan | Pham V.H.,University of Ulsan | Tran Q.T.,Ho Chi Minh City University of Natural Sciences | Hahn S.H.,University of Ulsan | And 3 more authors.
Materials Letters

Photoluminescence (PL) and Raman studies have been performed to investigate the optical properties of graphene thin films prepared by chemical and thermal reductions of graphene oxide (GO). The G peak in Raman spectra red-shifted after reduction of GO. Thermal reduction resulted in a more red-shift of the G peak than chemical reduction. A strong intensity of the D peak indicated that the prepared graphene films have significant structural disorders. A blue-shifted emission in PL spectra suggested that sp2 clusters are embedded in a sp3 matrix that acts as a tunnel barrier, causing a strong fluctuation in the local band gap. © 2009 Elsevier B.V. All rights reserved. Source

Le T.H.,Ho Chi Minh City University of Natural Sciences | Van H.T.,Ho Chi Minh City University of Technology
Pattern Recognition

Reference point plays an important role in fingerprint identification systems. The reference point is widely used for the fingerprint retrieval in large-scale databases. This paper proposes a novel algorithm for detecting a convex core point as a unique reference point consistently and accurately for all types of fingerprints. In order to detect robust core point candidates, a modified complex filter, called semi-radial symmetry filter, is proposed to detect correctly rotational symmetries of core points. Moreover, a vertical orientation variation feature, called VORIV feature, is proposed to remove spurious core points and concave core points. Therefore, the proposed technique computes the Variation and Symmetry Combined Energy (VSCOME). Then, the reference point is located by searching the global VSCOME maximum. The experimental results on the public database (FVC2004 DB1 set A) show that the proposed technique exhibits a very high robustness and gets the best performance in comparing with other approaches in literature. © 2012 Elsevier Ltd. All rights reserved. Source

Noh S.,Gwangju Institute of Science and Technology | Choi M.,Gwangju Institute of Science and Technology | Kim E.,Gwangju Institute of Science and Technology | Dan N.P.,Ho Chi Minh City University of Technology | And 4 more authors.
Geochimica et Cosmochimica Acta

The lower Mekong and Saigon River Basins are dominated by distinctive monsoon seasons, dry and rainy seasons. Most of the Mekong River is a freshwater region during the rainy season, whereas during the dry season, salt water intrudes approximately 70km inland. To understand the role of salinity intrusion controlling Hg behavior in the Mekong and Saigon River Basins, Hg and monomethylmercury (MMHg) in surface water and sediment of the Mekong River and in sediment of the Saigon River were investigated in the dry season. Sediment Hg distribution, ranging from 0.12 to 0.76nmolg-1, was mainly controlled by organic carbon distribution in the Mekong River; however, the location of point sources was more important in the Saigon River (0.21-0.65nmolg-1). The MMHg concentrations in Mekong (0.16-6.1pmolg-1) and Saigon (0.70-8.7pmolg-1) sediment typically showed significant increases in the estuarine head, with sharp increases of acid volatile sulfide. Unfiltered Hg (4.6-222pM) and filtered Hg (1.2-14pM) in the Mekong River increased in the estuarine zone due to enhanced particle loads. Conversely, unfiltered MMHg (0.056-0.39pM) and filtered MMHg (0.020-0.17pM) was similar between freshwater and estuarine zones, which was associated with mixing dilution of particulate MMHg by organic- and MMHg-depleted resuspended sediment. Partitioning of Hg between water and suspended particle showed tight correlation with the partitioning of organic carbon across study sites, while that of MMHg implied influences of chloride: enhanced chloride in addition to organic matter depletion decreased particulate MMHg in the estuarine zone. Primary production was an important determinant of inter-annual variation of particulate Hg and sediment MMHg. The bloom year showed relatively low particulate Hg with low C/N ratio, indicating biodilution of Hg. In contrast, the percentage of MMHg in sediment increased significantly in the bloom year, likely due to greater availability of metabolizable fresh organic matter. The overall results emphasize that Hg behavior in the lower Mekong River Basin is strongly connected to the local monsoon climate, via alterations in particle loads, biological productivity, and availability of sulfate, chloride and organic matter. © 2012 Elsevier Ltd. Source

Nguyen L.-T.T.,Ho Chi Minh City University of Natural Sciences | Nguyen D.M.,The University of Medicine & Pharmacy at Ho Chi Minh City | Nguyen L.-H.D.,Ho Chi Minh City University of Natural Sciences
Natural Product Research

A new xanthone, calothorexanthone, together with five known compounds, garbogiol, 1,4,8-trihydroxyxanthone, δ-tocotrienol, 1,7-dihydroxyxanthone and globuxanthone, was isolated from a petroleum ether extract of the bark of Calophyllum thorelii. Their structures were established on the basis of spectroscopic methods, mainly one- and two-dimensional NMR. Antioxidant activity of the isolated compounds was tested using DPPH free radical scavenging assay and some exhibited remarkable effects with IC50 of 13.63-17.46 μg mL-1. © 2013 Copyright Taylor and Francis Group, LLC. Source

Phuong N.L.,Ho Chi Minh City University of Natural Sciences | Ito K.,Kyushu University
Building and Environment

Breathing is one of the most essential processes in the human body. The basic functions of breathing are to exchange gases (supplying oxygen from ambient air and removing carbon dioxide from the blood) and also to exchange heat and moisture through mucous surfaces of the airway. During an average lifetime, human beings experience significant exposure to indoor air and countless of contaminants/particles via inhalation. In this study, experimental and numerical results of flow fields in a realistic respiratory model were obtained. Flow patterns in a realistic replica model of the human respiratory tract were investigated with particle image velocimetry (PIV) under three constant breathing conditions; 7.5, 15 and 30 L/min. Computational fluid dynamics (CFD) analyses were conducted on turbulent models with boundary conditions corresponding to the experimental models. We used four RANS turbulence models to predict airflow in a realistic human airway model: two low Reynolds (Re) number-type k-ε turbulence models, RNG k-ε model, and the SST k-ω model. The CFD results were compared with PIV data and showed relatively good agreement in trachea region in all cases. © 2015. Source

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