Vietnam Academy of Science and Technology: Journals Online
Vietnam Academy of Science and Technology: Journals OnlineNot a member yet
7064 research outputs found
Sort by
EVALUATING FUTURE WATER QUALITY OF URBAN RIVERS IN HANOI UNDER EFFECT OF URBANIZATION AND CLIMATE CHANGE - THE APPLICATION OF WEAP MODEL FOR CAU BAY RIVER
Get PDFEvery day, up to 750,000 cubic meters of wastewater in Hanoi metropolitan areas is discharged directly into rivers and lake, of which only 10% is treated to the Vietnamese standards. According to the water drainage development master plan for the capital city of Hanoi until 2030, the government aim at dealing with flooding and improve environmental sanitation for local residents. With respect to the baseline and Master plan implementation scenarios, this study evaluates the future water quality of urban rivers in Hanoi under the effect of urbanization and climate change using Water Evaluation And Planning tool (WEAP) and take the Cau Bay catchment as the case study. The result shows that, without implementation of wastewater treatment plant, the water quality of Cau Bay River will be worse with the DO in dry season is 0.2-1.2 mg/l and BOD is 52.0-55.0 mg/l. With the implementation of Master plan, the level of DO and BOD would be 7.1-7.3 mg/l and 7.0-13.8 mg/l respectively in the dry season whereas the values are 3.7 mgO/l and 36.1-41.8 mg/l in the wet season. The degradation of wastewater during the wet season is results from the combine- overflow sewage system as designed in the master plan
LIGNANS FROM LEAVES OF AMESIODENDRON CHINENSE AND THEIR CYTOTOXIC ACTIVITY
Get PDFABSTRACTFrom leaves of Amesiodendron chinense (Mer.) Hu four lignans (+)-aptosimon (1), (+)-isolariciresinol (2), (-)-cleomiscosin A (3), and (-)-cleomiscosin C (3) were isolated. Their structures were determined by spectroscopic analysis including MS, 1D and 2D NMR as well as by comparison with reported data in literature. All compounds were evaluated for cytotoxic activities against five human cancer cell lines, KB, SK-LU-1, MCF-7, HepG-2, and SW-480. They showed weak cytotoxic activity on five tested human cancer cell lines with IC50 values ranging from 32.61 to 95.18 µg/ml
A numerical model for simulation of near-shore waves and wave induced currents using the depth-averaged non-hydrostatic shallow water equations with an improvement of wave energy dissipation
Get PDFThis study proposes a numerical model based on the depth-integrated non-hydrostatic shallow water equations with an improvement of wave breaking dissipation. Firstly, studies of parameter sensitivity were carried out using the proposed numerical model for simulation of wave breaking to understand the effects of the parameters of the breaking model on wave height distribution. The simulated results of wave height near the breaking point were very sensitive to the time duration parameter of wave breaking. The best value of the onset breaking parameter is around 0.3 for the non-hydrostatic shallow water model in the simulation of wave breaking. The numerical results agreed well with the published experimental data, which confirmed the applicability of the present model to the simulation of waves in near-shore areas
Study of CYP3A5 genetic polymorphism in Vietnamese Kinh ethnic group
Get PDFCytochrome P450 3A5 (CYP) belongs to the CYP3A cluster, which encode for several enzymes involved in metabolism of various drugs, endogenous substrates as well as exogenous compounds. Among the four genes of CY3A cluster, CYP3A5 plays an important role in pharmacogenetics since this enzyme metabolizes over 30% of the clinically prescribed drugs. The inter-individual variability in clearance of CYP3A substrates mainly depends on the genetic factors. In the present study, after collecting peripheral bloods samples from 100 unrelated healthy Kinh ethnic group in Vietnam, Sanger sequencing was used in order to determine the CYP3A5 variants responsible for enzyme activity alteration (*3, *6, *8 and *9). It was shown that CYP3A5*3 is the most prevalent variant with 67.5%, in which a haft of individuals carrying *3 were homozygous for this allele. In contrast, the variants *6, *8 and *9 were not found the study subjects. The data observed in current study would support dosing of drugs that metabolized by CYP3A5 and thereby increase treatment outcome.
SOI PHOTONIC CRYSTAL WAVEGUIDES OPERATING IN TELECOMMUNICATION RANGE FOR INTEGRATED CIRCUITS
Get PDFSilicon photonics has been of great interest and plays an significant role in optical communications. Various devices acting as the key components of integrated circuits can be generated based on silicon-on-insulator (SOI) platform. Among those, SOI photonic crystal waveguide (SOI PCW) have been considered as one of the most fundamental and essential elements. In this report, we present the design and the numerical property of SOI PCWs operating in telecommunication range, i.e., O-band (1260 – 1360 nm)with TE and/or TM polarizations. The SOI PCWsincluding conventional W1 and slot SOI PCWs have been designed in order to exploit two kinds of mode: W1-like and true-slot.For that purpose, the geometric parameters of the SOI PCW withthe triangular PhC structure are chosen as follows. The thickness of the silicon slab was fixed at 300 nm to match with the fabrication in industrial scale, the size of the hole was around 210 nm and the lattice constant was tuned in the range of 300 nm to 400 nm. The width of waveguide was modified fromW1 to W1.50 and the width of the slot was of about 100 nm. In addition,the covering materials were selected with refractive index of 1.0 corresponding to air as well as refractive indices of from 1.45 to 1.50 corresponding to the active materials. The demonstrated SOI PCWs in this work might find applications in optical integrated circuits and our investigation on the dependence of the dispersion on the width of waveguide and refractive index of the covering material will provide a general guide line for guiding signal and for monitoring or sensing purposes
The scale of the central beach change processes in the west coast of Nha Trang bay
Get PDFThe central beach in west coast of Nha Trang bay has experienced erosion in recent years. The determination of hydrodynamic regime and causes of this beach fluctuation is still an open problem and is concerned by scientists and managers. This study shows the causes and scales of the shoreline change processes based on the results of shoreline change model and the analysis of remote sensing images of shoreline location
Evaluation of the changes of the shoreline in Cua Tung in Quang Tri province before and after the construction of groin on the south riverbank of Ben Hai river
Get PDFThe process of erosion-sedimentation of Cua Tung, Quang Tri province has been mentioned in previous studies, but there have been no studies that apply satellite images to evaluate the changes of shoreline before and after the construction of groin along the south of Ben Hai river. This paper aims to evaluate the changes and rate of erosion - sedimentation of Cua Tung shoreline before and after the construction, using Landsat satellite images from 1990 to 2017. We used Envi 5.0 to analyse and interpret multiple-spectral Landsat satellite images in combination with analysis algorithm to identify the shoreline change over the years by adopting the ratio image method by Gathot Winasor to separate water zone and shoreline zone automatically. We then calculated the rate of shoreline changes by the function DSAS (Digital Shoreline Analysis System) proposed by Thieler et al., in Avenue programming language in ArcView software. The results showed that the process of erosion-sedimentation in Cua Tung-Quang Tri from 1990 to 2017 was divided into 6 stages in which the stage of 2000–2005 had the clearest indication in the process of erosion-sedimentation. This research has demonstrated that GIS and remote sensing technologies have been good tools to assist policy maker in their decision-making to properly evaluate erosion-sedimentation in Cua Tung- Quang Tri, so that appropriate solutions will be delivered to guarantee the local socio-economic sustainable development
Characteristics of top coal fall in front of face support in longwall: A case study
No full textTop coal fall in front of face support severely affects the safety and productivity in mechanized longwall mining. This paper presents a discontinuous numerical analysis on the important characteristics of the fall such as abutment stress, material failure, and fall mode. A top coal fall model is validated against site observation and past numerical and empirical studies. The numerical results provide further evidence confirming that horizontal stress relaxation, vertical stress concentration, and strength and structure of coal seam control the failure of top coal ahead of support. Top coal fall in longwall mining with large caving height is found in “stress caving” mode or, in other words, “horizontal stress-driven guttering” mechanism. A pre-existing fault running into a mined-out area can facilitate the occurrence of face spall but may not lead to top coal fall. The results of this study are particularly helpful to engineers in developing proper remedy or prevention solutions to top coal/roof fall incidents
Exact Mode Shapes of T-shaped and Overhang-shaped Microcantilevers
Get PDFResonance frequencies and mode shapes of microcantilevers are of important interest in micro-mechanical systems for enhancing the functionality and applicable range of the cantilevers in vibration transducing, energy harvesting, and highly sensitive measurement. In this study, using the Euler-Bernoulli theory for beam, we figured out the exact mode shapes of cantilevers of varying widths such as the overhang- or T-shaped cantilevers. The obtained mode shapes have been shown to significantly deviate from the approximate forms of a rectangular cantilever that are commonly used in mechanics and physics. They were then used to figure out the resonance frequencies of the cantilever. The analytical solutions have been confirmed by using the finite element method simulations with very low deviation. This study suggested a method for correctly obtaining the resonance frequency of microcantilevers with complicated dimensions, such as the doubly clamped cantilever with the undercut, with the overhangs at the clamped positions, or with an attached mass in the middle
Food selection of maize weevil Sitophilus Zeamais (motschulsky)
Get PDFThe instintive behaviour exhibited by insects in the selecting food is always a matter of interests to entomologists, and it is one of the fundamental principles underlining the application of entomology to agriculture, horticulture and forestry. Food seclection is an important characteristic of insects that help them survive in periods with insufficient foods.Three grain types of food, maize grain, long-grain rice and soybean grain, were used in this sudy for detecting food selection behaviours of maize weevil, Sitophilus zeamais. Grains were kept in box traps put in the different stores in Son La during 90 days. The result showed that maize weevil, Sitophilus zeamais, prefered traps with maize grains (71.4%) considerably more than ones with long-grain rice (14.3%) and soybean grain (14.3%). Meanwhile, the cornsap beetle, Carpophilus dimidiatus, was mostly observed in maize grain (98.5%) and to a lesser degree, in soybean grain (1.5%); and the dried-fruit beetle, Carpophilus hemipterus, was abundantly observed in maize grain (93.1%) and less in soybean grain (6.9%). The red flour, Tribolium castaneum, also tended to select all the three food grain, i.e. maize grain: 53.5%, long-rice grain: 35.2%, and soybean grain: 11.3%.Comparing f beetle individuals captured on three types of food grains showed that the maize weevil, Sitophilus zeamais, is the most abundant species. The percentage this store beetle among all beetles observed in maize, soybean grains and long-rice grains were 57.0%, 84.9% and 27.6%, respectively. Interestingly, Ahasverus advena, foreign grain beetle, occurred abundantly on long-rice gain (61.7%), i.e. this grain is a suitable food for the development of this beetle.