Vietnam Academy of Science and Technology: Journals Online
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Determining of the laser heat flux for three-dimensional conduction model by the sequential method
Get PDFWhen performing a laser processing, one of the parameters to consider is the laser heat flux. This is a very important parameter of the processing. It is difficult to directly and correctly measure this parameter during the processing. Therefore, to estimate this parameter, a solution has been implemented. In this study, the Newton–Raphson method has been calibrated as an operational algorithm to evaluate the laser heat flux value accurately in the 3-D conduction model. The outstanding features in this algorithm: the unaware absorption coefficient's functional form is no preset, and the nonlinear least-squares are no necessary. To confirm the effectiveness of the presented method, the paper has given two specific applications. Indeed, in this research, based on the results that have been achieved in two illustrations, the sequential method to determine the inversely laser heat flux in the three-dimensional conduction model is a reasonable, correct, and powerful method
Osteogenesis activity of fractions extracted from Clinacanthus nutans (Burm. F.) Lindau
Get PDFOsteogenesis activity of fractions extracted from Clinacanthus nutans was evaluated on an in vitro model using osteoblast MC3T3-E1 cells. The results showed that all fractions, including ethanol (EtOH), n-hexane, ethyl acetate (EtOAc) and butanol (BuOH) were not significantly toxic to the osteoblast cells at the test concentrations of 5, 10, 25, and 50 µg/mL. The EtOH and EtOAc fractions exhibited the highest osteogenesis activity in terms of enhancement of alkaline phosphatase (ALP) and mineralization activity of MC3T3-E1 cells, especially the EtOAc fraction which increased ALP activity up to 30% and mineralization activity up to 100%. Thus, the EtOAc fraction shows osteogenesis activity through stimulating activites of the two markers for bone generation including ALP and mineralization in osteoblast cells. The fraction is now under extensive investigation to isolate and fully understand the modes of action of the active compounds.
Investigating the diversity of arbuscular mycorrhizal fungi from Gymnema sylvestre and Curcuma longa in Vietnam
Get PDFArbuscular mycorrhizal (AM) fungi are soil eukaryotes that belong to phylum Glomeromycota and have symbiosis with the vast majority of higher plants’ roots. AM fungi are believed to be coevolved with terrestrial plants, the abundance and diversity of AM fungal communities as a result are host plant dependent. A survey of AM fungi from the rhizospheres of medicinal plants in Northern Vietnam including gurma Gymnema sylvestre and turmeric Curcuma longa was carried out. From the extracted total DNAs of the medicinal plants’ rhizosphere soil samples, 35 mycorrhizal fungal species were identified by analyzing small subunit rRNA gene sequences. Result revealed that genus Glomus is the most abundant in the AM communities of G. sylvestre and C. longa, followed by Gigaspora and Acaulospora. Besides, AM species belonging to genera Scutellospora, Diversispora and Rhizophagus were observed in almost all rhizosphere soil samples. The spore counting by wet sieving and decanting method uncovered a variation in AM spore density of gurma and turmeric rhizosphere. In general, AM species were found more abundantly and more diverse in collected rhizome soil samples of C. longa (27 species belonging to 10 genera) than of G. sylvestre (17 species found belonging to 7 genera). The observed difference in AM communities of G. sylvestre and C. longa supports evidence for the dependence of AM fungal species on host plants, and indicates that AM fungi may have relation to the host plants’ secondary metabolite production
Bacterial community analysis in the rice straw sample before and after composting by PCR-DGGE and cloning method
No full textApplicability of PCR-DGGE (Polymerase Chain Reaction-Denaturing Gel Gradient Eletrophoresis) technique to analyze microbial community is based on the V3 gene fragments in the rice straw sample (R) and after composting rice straw samples (Rn). Besides clonning method combined with analyzing Rn samples and comparing the results of microbial community analysis with PCR-DGGE method had the same reuslts is the main goal in this study. Results obtained from PCR-DGGE technique of R sample had 5 the V3 gene fragments (R1, R2, R3, R4 and R5) and Rn had 4 the V3 genes fragments (Rn1, Rn2, Rn3 and Rn4). Comparison of bacterial groups in R and Rn samples showed that bacteria in R samples including Agrobacterium, Clostridium, Bacteroidetes, Thermopolysporasa and Bacillus species, but in the Rn sample after incubation, the remaining bacterial results of 2 main species are Agrobacterium and Clostridium. Using Clonning method of Rn sample also gave 4 positions and gene fragment sizes corresponding to the positions of Rn1, Rn2, Rn3 and Rn4 from representatives of about 30 samples collected from the Clonning products. Based on the comparison of the similarity among the sequence of V3 gene fragments in PCR-DGGE and Clonning with reference to the data base in NCBI gene bank the results that Rn1 and Rn4 genes are similar to Agrobacterium species, about 96%, Rn2 and Rn3 are similar to Clostridium about 99%. In summary the results of microbial community analysis in the R sample show that the diversity of bacteria in the R sample is larger than in the Rn sample. Summarize the results of microbial community analysis in the R sample show the diversity of bacteria but less stable than the Rn sample. In addition, cloning and PCR-DGGE produced similar results on the sample Rn
AMMONIA GAS SENSING PROPERTIES AT LOW TEMPERATURES OF NANOCOMPOSITES OF GRAPHENE OXIDE AND TUNGSTEN OXIDE NANOBRICKS
No full textNanocomposites of graphene oxide (GO) and tungsten oxide (WO3) nanobricks are synthesized by co-dispersing graphene oxide and tungsten oxide nanobricks in bi-distilled water with different weight ratios (0.1, 0.3 and 0.5 wt.% of graphene oxide). The ammonia gas sensing properties of nanocomposites are studied at low temperatures range (50, 100 and 150 oC) with the static gas-testing system. The co-appearance and the strong interaction between graphene oxide and tungsten oxide in the nanocomposite are confirmed by Raman scattering analysis. The content of GO in nanocomposite strongly affects the resistance of nanocomposite-based sensors. When the working temperature increase from 50 oC to 150 oC, the response of sensors switches from the p-type (at 50 oC) to n-type (at 150 oC) behavior. At 150 oC, the nanocomposite-based sensors show the most stable ammonia gas sensing characteristics. The working resistance of the pristine WO3 sensor reduced from 1.35 MΩ to 90, 72 and 27 kΩ when compositing with 0.1, 0.3 and 0.5 wt.% GO at 150 oC, respectively. The 0.5 wt.% GO/WO3 -based sensor shows low response but with low working resistance, shorter response and recovery times (20 s and 280 s, respectively) which is promising for low power-consumption gas sensors.
Creating Fatigue Curve for Steel Machine Elements Using Fatigue Test Method with Gradually Increasing Stress Amplitude
Get PDFIn order to create a fatigue curve, the traditional fatigue test method is applied to specimens using a cyclic stress with constant amplitude. However, this method has disadvantages such as the experimental results could not be used because of specimens broken before reaching the expected stress amplitude, or the tests may be stopped before specimen broken because of limitation of time. To overcome this hurdle of the traditional method, a new experimental method using cyclic stress with gradually increasing amplitude was proposed to build the fatigue curve for steel machine elements
EVAPORATION MEASUREMENT FROM FREE WATER SURFACE
Get PDFThis paper aims to quantify the amount of water surface evaporation with special regard to the EWM evaporation pan and to relate the direct measurements to the Penman and other empirical equations. Based on the available 10-minute interval data on the EWM pan evaporation and the data on precipitation for the same intervals, the net water surface evaporation was estimated for the period from July 2010 to October 2012 (excluding the time EWM pan did not function in winter). From the processing data, raingauge appeared to underestimate the actual precipitation on average 5:3 times, and malfunction when heavy rains occurred. Thus, the net evaporation was estimated only from the fluctuation of water level in EWM pan. Other available weather data, including the dry/wet bulb temperature, water surface temperature, air humidity, wind speed and short-wave solar radiation were also summarized and corrected. These data were then used as input for the Penman equations to obtain semi-empirical daily values of evaporation from water surface. A comparison between the evaporation rates directly measured and those calculated by different methods shows that different values of albedo would improve the performance of the Penman equations. The result of this study contributed to optimization of the EWM data processing methods and to the analysis of variation of water surface evaporation within the diurnal cycle, as well as over longer periods
DOLABRANE-TYPE DITERPENOID AND LIGNAN CONSTITUENTS FROM THE STEM BARKS OF CERIOPS DECANDRA (GRIFF.) W. THEOB.
Get PDFThree dolabrane-type diterpenoids (1‒3) and a lignan derivative (4) were isolated from a methanolic extract of C. decandra stem barks using various chromatographic separations. Their structures were elucidated to be tagalsine X (1), tagalsin P (2), ent-5α,2-oxodolabr-3-ene-3,15,16-triol (3), and (+)-pinoresinol (4) by detailed analysis via spectroscopic techniques (1D, 2D NMR, and ESI-MS data) as well as comparison with those reported. This is the first report of compound 4 from the Ceriops genus
Impacts of pollution discharges from Dinh Vu industrial zone on water quality in the Hai Phong coastal area
Get PDFThe hydrodynamic and water quality models (the Delft3D model) were established based on the measured data and the estimated pollution discharges from Dinh Vu industrial zones to Nam Trieu estuary. With seven separate simulation scenarios, the results show that in case of increased wastewater with the control of pollution discharge (water and concentration), the impact of pollution is only limited to a small area around the discharge point. Their influences on water quality in other areas in Nam Trieu estuary are quite small. Meanwhile, in case of environmental risk, a strongly increasing pollution load would cause the significantly increasing pollutant concentration in this area, they have almost exceeded the value in the National Technical Regulation on surface water quality (QCVN 10-MT:2015/BTNMT), such as NH4, COD, and BOD. Dissolved oxygen in the water would also decrease significantly. The spatial influence extends from the discharge point to Nam Trieu estuary, inside Cam, Bach Dang rivers, and Cat Hai coastal area
Research on the stability of the 3D frame on coral foundation subjected to impact load
Get PDFThis article presents an application of the finite element method (FEM) for the stability analysis of 3D frame (space bar system) on the coral foundation impacted by collision impulse. One-way joints between the rod and the coral foundation are described by the contact element. Numerical analysis shows the effect of some factors on the stability of the bar system on coral foundation. The results of this study can be used for stability analysis of the bar system on coral foundation subjected to sea wave load