Influence of water temperature and salinity on pH during dry season in lower Dong Nai river system, Vietnam

This paper uses the gvSIG 2.2.0 software, IDW interpolation method, river and stream network data, and 36 sampling sites to build the maps of three monitored parameters such as pH, water temperature, and salinity in the Lower Dong Nai River system (2009–2010) in dry season. Based on an analysis of these maps and statistical assessment by using the R software, the correlations between pH, temperature, and salinity are clarified. The results show that the pH and temperature values have a tendency to decrease, whereas the salinity tends to increase annually. The pH value has good and significant correlations with the water temperature and salinity in both simple and multiple linear regression models. The results aim to provide a scientific reference for further research on the water environment in this area

Building forecast maps of water quaůity for main rivers and canals in Tien Giang province, Vietnam

This study aims to enhance the mapping of forecast for water quality assessment in Mekong Delta provinces. The data from 32 sites from main rivers and canals in an area of around 2,482 km2 in Tien Giang Province, Vietnam, were used for calculation and mapping. The ArcGIS 9.3 software, Inverse Distance Weighting (IDW) interpolation method, hydrologic data, and water quality parameters in March (2010-2014) were applied to build the maps showing 2020 water quality predictions for main rivers and canals in Tien Giang Province. The estimation was based on the Water Quality Index (WQI) with 6 parameters such as pH, total suspended solid (TSS), dissolved oxygen (DO), biochemical oxygen demand (BOD), total nitrogen (T_N), and coliform. The results showed that water quality in the studied area in dry season will not be improved by the year 2020. The finding could be a scientific reference for the selection of effective approaches to improve water quality in main rivers and canals in Tien Giang Province

Boundary identification for an elastic solid partly immersed in a liquid

The authors consider a long elastic cylinder of constant section Ω partly immersed in a liquid of constant density. It is assumed that the body is in the state of plane strain and that Ω has a boundary consisting of two piecewise smooth arcs assumed to meet each other at two, and only two, points on a horizontal line. The upper arc Γ, which is exposed to air, is assumed known, while the lower arc ϒ, assumed to be totally immersed in a liquid of constant density, is unknown and is to be determined. Under the conditions that the displacements and surface stresses on a subarc of Γ are known and that the lower arc ϒ is subjected to a known constant hydrostatic pressure, the authors prove a uniqueness theorem and in the case of existence of a solution, show the existence of a sequence of regularized solutions converging to the exact solution

Water Quality Assessment Using Benthic Macroinvertebrates In Saigon River and Its Tributaries, Vietnam

This study to enhance the discussion about the usefulness of benthic macroinvertebrates for water quality assessment in Saigon River and its tributaries. Data from 16 sites were used as a representative example for Saigon River and its tributaries in the area of basin over 4,500 km2, the length through provinces of Tay Ninh, Binh Phuoc, Binh Duong, and Ho Chi Minh City of about 280 km. The data covered the period of dry and rainy seasons in 2015, the survey sampled 16 sites (32 events) of the Saigon River and its tributaries selected. To implement this evaluation, the analyses were based on MRC methods and classifications these improved by the scientific group. The analysis of general characteristics of benthic macroinvertebrates and bio-indices were used to examine the spatial patterns of water quality and biological groups. The value of good water quality was recorded in the sites far from industrial parks, crowded citizen areas, big cities (SG1 and SG2) while the sites in near urban Ho Chi Minh City and Thu Dau Mot Town or industrial areas (the section of Saigon River from SG6 to SG13) where had the value of worse water quality because of the more human activities. Especially, there was not any animal that was collected in the site SG7 because of too heavy pollution. The results demonstrated that these organisms could be applied to describe the ecological health in the Saigon River and its tributaries

A RESEARCH ON MULTI-OBJECTIVE OPTIMIZATION OF THE GRINDING PROCESS USING SEGMENTED GRINDING WHEEL BY TAGUCHI-DEAR METHOD

In this study, the mutil-objective optimization was applied for the surface grinding process of SAE420 steel. The aluminum oxide grinding wheels that were grooved by 15 grooves, 18 grooves, and 20 grooves were used in the experimental process. The Taguchi method was applied to design the experimental matrix. Four input parameters that were chosen for each experiment were the number of grooves in cylinder surface of grinding wheel, workpiece velocity, feed rate, and cutting depth. Four output parameters that were measured for each experimental were the machining surface roughness, the system vibrations in the three directions (X, Y, Z). The DEAR technique was applied to determine the values of the input parameters to obtaine the minimum values of machining surface roughness and vibrations in three directions. By using this technique, the optimum values of grinding wheel groove number, workpiece velocity, feed-rate, cutting depth were 18 grooves, 15 m/min, 2 mm/stroke, and 0.005 mm, respectively. The verified experimental was performed by using the optimum values of input parameters. The validation results of surface roughness and vibrations in X, Y, Z directions were 0.826 (µm), 0.531 (µm), 0.549 (µm), and 0. 646 (µm), respectively. These results were great improved in comparing to the normal experimental results. Taguchi method and DEAR technique can be applied to improve the quality of grinding surface and reduce the vibrations of the technology system to restrain the increasing of the cutting forces in the grinding process. Finally, the research direction was also proposed in this stud

Comparison of two hydrological model simulations using NAM and XINANJIANG for Nong Son catchment

The study presents the hydrological simulations for the Nong Son catchment, a drainage area of the Vu Gia-Thu Bon basin in the Central Vietnam, by using the NAM and XINANJIANG models. Simulation results for both models show good agreement between calculated and observed discharges at the stream gauge. The overall water balance error is less than ±10%, Nash-Sut cliffe efficiency $R^2$  above 0.85, and Pearson correlation coefficient $r$ above 0.92 in both model calibration and verification period. Although NAM's performance shows a slightly better correspondence between the discharges at the stream gauge, the XINANJIANG model shows a relatively better reproduction of the runoff components (i.e. overland flow, interflow and baseflow)

Potential evapotranspiration estimation and its effect on hydrological model response

Potential evapotranspiration can be directly calculated by the Penman-Monteith equation, known as the one-step method. The approach requires data on the land cover and related-vegetation parameters based on AVHRR and LDAS information, which are available in recent years. The Nong Son basin, a sub-catchment of the Vu Gia-Thu Bon basin in the Central Vietnam, is selected for this study. To this end, NAM model was used; the results obtained show that the NAM model has the potential to reproduce the effects of potential evapotranspiration on hydrological response. This is seemingly manifested in the good agreement between model simulation of discharge and the observed at the stream gauge

Numerical model for simulation of waves in surfzone and nearshore areas based on Boussinesq equations: results for plane beaches

A numerical model based on the 2D Boussinesq equations has been developed using the Finite Volume Method. The model was verified against experimental data for the case of wave breaking on a sloping beach. Simulated results by the model showed that the model has good capability of simulation of waves in the nearshore area. Numerical simulation was also carried out for the problem of waves on a plane beach with a breakwater and submerged dunes. Simulated results were compared with those computed by MIKE 21. The comparison showed that good agreements were obtained and confirmed the applicability of the Boussinesq model to the simulation of physical phenomena of waves in the nearshore areas, especially, suitable for the simulation of wave-induced current including rip currents

OPTIMIZATION OF GINGER OLEORESIN EXTRACTION FROM FRESH GINGER BY USING MICROWAVE - ASSISTED ENERGY

Nowadays, the active compounds from natural products are interested in not only research fields but also industrial area. Steam distillation is widely employed for the isolation of bioactive substances from natural sources. However, the process is usually long time consuming, high energy consumption and unwanted chemicals can be entrained with the main products. Microwave-assisted extraction is now recognized as an efficient extraction technique that dramatically reduces extraction time, increases yields and higher quality of the extracts can be obtained. The aim of this study is evaluation of the major factors affected by operating parameters such as concentration of solvent, radiation time, ratio of microwave power to material, volume of solvent on yield of products by microwave-assisted extraction. In addition, comparison between traditional extraction methods and microwave-assisted extraction is also carried out. The results show that application of microwave energy for the extraction of active substances from fresh ginger have faster heating, reduce thermal gradients and extraction time

Influence Of Fabrication Condition on the Microstructural and Optical Properties of Lead-Free Ferroelectric Bi0.5_{0.5}Na0.5_{0.5}TiO3_{3} Materials

Lead-free ferroelectric materials have attracted considerable attention due to the increasing potential application in environmental benign materials. Among lead-free ferroelectric materials, the Bi0.5Na0.5TiO3 (BNT) materials were more studied because it exhibited the good ferroelectric and piezoelectric properties which could be promising candidate materials replacing Pb(Zr,Ti)O3. In this work, the lead-free ferroelectric BNT materials were synthesized by sol-gel method. The effects of fabrication process to microstructural and optical properties were studied which includes Na precursor concentration and calcining temperature. The result indicated that the Na precursor concentration were higher 40 mol.% and the calcining temperature