Vietnam Academy of Science and Technology: Journals Online
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Diversity of phytoplankton in lower Thu Bon river and Cu Lao Cham
No full textData on characteristics of phytoplankton communities is important scientific information in marine ecosystem, especially in assessment of environmental impacts on biodiversity in a specific waters. In the present study, two-year phytoplankton data was analyzed for species diversity, community structure changes and variation in 4 adjacent waters: Lower Thu Bon river (TB), transition waters (CT), Cu Lao Cham island (CLC) and offshore site (BM) to provide basic scientific data of phytoplankton communities, compare and assess seasonal changes and possible linkage of these adjacent waters. A total of 364 phytoplankton taxa of 12 classes were identified, showing high diversity and with seasonal variation of the investigated waters. There was strong difference of phytoplankton communities among the adjacent waters with low similarity index and the change of dominant species seasonally in each area. The species richness and diversity in the lower Thu Bon river were lower than in other areas. Variation of phytoplankton abundance and diversity along the river transect showed changes in species composition between the dry and rainy seasons but with similar trend in abundance. The low community similarity between the adjacent waters and the transition waters may indicate low impacts of river flow on phytoplankton communities in the coastal waters
Picosecond Pulse Generation by Second-Order Distributed Feedback Dye Laser
No full textA Configuration of a second-order distributed feedback dye laser pumped by a nanosecond Nd:YAG laser is setup. The tuning range is narrower than that in the case of the first-order DFDL but lower noise and more stable is obtained. Single picoseconds pulse tunable in range of 543 to 596 nm can be observed by using different laser dyes. The tuning range is extended to the shorter wavelengths, which is closed to pumping wavelength
Statistical Analsysis to Evaluate Heavy Metal Pollution in the Air Obatained by Moss Technique in Hanoi and its Surrounding Region
Get PDFThe aim of this paper was the application of statistical analysis including principal component analysis to evaluate heavy metal pollution obtained by moss technique in the air of Ha Noi and its surrounding areas and to evaluate potential pollution sources. The concentrations of 33 heavy metal elements in 27 samples of Barbula Indica moss in the investigated region collected in December of 2016 in the investigated area have been examined using multivariate statistical analysis. Five factors explaining 80% of the total variance were identified and their potential sources have been discussed
Dynamic responses of an inclined FGSW beam traveled by a moving mass based on a moving mass element theory
No full textDynamic analysis of an inclined functionally graded sandwich (FGSW) beam traveled by a moving mass is studied. The beam is composed of a fully ceramic core and two skin layers of functionally graded material (FGM). The material properties of the FGM layers are assumed to vary in the thickness direction by a power-law function, and they are estimated by Mori-Tanaka scheme. Based on the first-order shear deformation theory, a moving mass element, taking into account the effect of inertial, Coriolis and centrifugal forces, is derived and used in combination with Newmark method to compute dynamic responses of the beam. The element using hierarchical functions to interpolate the displacements and rotation is efficient, and it is capable to give accurate dynamic responses by small number of the elements. The effects of the moving mass parameters, material distribution, layer thickness ratio and inclined angle on the dynamic behavior of the FGSW beam are examined and highlighted
CHARACTERIZATION OF CARBONATED STEELMAKING SLAG AND ITS POTENTIAL APPLICATION IN CONSTRUCTION
Get PDFIn the current context of Vietnam, the solid waste of steel slag occupy ground for dumping and lead to severe environmental issue due to their high content of heavy metal and fine dust. For the purpose of large-scale recycling steel slag, up to now one of the most relevant solutions is to use as aggregate for asphaltic and/or cement concrete. In this paper, we aim to analyze the influence of the accelerated carbonation condition in the laboratory on the physio-chemical properties of carbonated steel slag. Materials composition were characterized by using different analysis techniques of XRD, SEM, TG and others measurement of the physio-properties (density, L.O.I..) were also realized with regards to the requirement of the national standard for concrete aggregate. In conclusion, we will discuss the effect of reaction condition and on the feasibility of implementing this specific treatment method on a larger scale.Keywords: steelmaking slag, solid waste, CO2 sequestration, accelerated carbonation, concrete aggregate
SYNTHESIS OF MoS2/GRAPHENE NANOCOMPOSITE BY FACILE ULTRASONIC-ASSISTED HYDROTHERMALMETHOD
Get PDFIn this report, thin layers of MoS2 were in-situ incorporated into graphene oxide (GO) to form MoS2/graphene nanocomposite by a facile ultrasonic-assisted hydrothermal method. X-ray Diffraction (XRD) and Raman analysis revealed that the as-synthesized MoS2 nanosheets crystalized in hexagonal phase 2H-MoS2 while High Resolution Transmission Electron Microscopy (HRTEM) images confirmed that MoS2 layers with average thickness of ~5–6 nm (6–8 layers) attached on the edges and surfaces of graphene sheets with high density and uniform shape restacking in three-dimensional (3D) architectures. The Scanning Transmission Electron Microscopy – Energy Dispersive X-ray spectrum (STEM-EDX) investigation further confirmed the low impurity of MoS2/graphene composite, and the well repairing of defects in GO surfaces during the hydrothermal process. Our approach is promising for a scalable, inexpensive, and accurate strategy to fabricate state-of-the-art materials with a certain structure for various practical applications such as electrode material for Lithium battery or supercapacitor
Purification and bioactivity of fucoidan from kappaphycus alvarezii alga
Get PDFKappaphycus alvarezii is a type of seaweed containing numerous carbohydrate with biological activities, especially fucoidan. About chemical aspect, fucoidan is fucose polysaccharides (FCSPs) with diverse biological activities including antioxidant, anticoagulant, anti-inflammatory, antiviral, antitumor... Fucoidan is found not only in brown algae but also in K. alvarezii alga from the central coast of Vietnam. In this study, fucoidan purification, fucoidan structure and biological activities of K. alvarezii alga (collected at Dam Mon area, Khanh Hoa province) were investigated. The yield recovery of two-stage precipitation by ethanol 99% was 84.4%. The protocol of fucoidan purification by ion-exchange chromatography was applied with tris-HCl buffer, elution solvent NaCl 1M; The yield was 60.99%. The structure of fucoidan from K. alvarezii was determined by 1H-NMN spectrum with the specific characteristic properties of fucoidan. The antioxidant activity of the purified fucoidan via IC50 was 303.51±0.12 μg/mL (DPPH assay), 299.97±3.12 μg/mL (ABTS essay). The purified fucoidan was shown better ability in cases of anti-coagulant, antibacterial activities than that of the crude extract. The anti-coagulation time of the purified fucoidan was 22.52 minutes. The minimum inhibitory concentrations (MICs) of the antibacterial activity (Bacillus cereus, Escherichia coli) were 400μg/mL. MICs was 500 μg/mL (Aspergillus flavus) and 600 μg/mL (Aspergillus niger)
Neural Machine Translation between Vietnamese and English: an Empirical Study
Get PDFMachine translation is shifting to an end-to-end approach based on deep neural networks. The state of the art achieves impressive results for popular language pairs such as English - French or English - Chinese. However for English - Vietnamese the shortage of parallel corpora and expensive hyper-parameter search present practical challenges to neural-based approaches. This paper highlights our efforts on improving English-Vietnamese translations in two directions: (1) Building the largest open Vietnamese - English corpus to date, and (2) Extensive experiments with the latest neural models to achieve the highest BLEU scores. Our experiments provide practical examples of effectively employing different neural machine translation models with low-resource language pairs
Recent geodynamic characteristics of the Southern Central coast and the relations with geological hazards
Get PDFRecent geodynamic characteristics of the Southern Central coast are analyzed on the basis of vertical and horizontal displacement velocities along active fault zones. The horizontal displacement velocity varies in magnitude from this fault system to another fault system, from 0.11–0.3 mm/year on the strike-slip - normal faults to 0–0.058 mm/year on the strike-slip faults and normal faults. The subsidence velocity changes complicatedly, different from one fault to another fault, depending on the mechanism of faults. On the continental shelf, most of the values of high subsidence’s velocity are related to the normal and strike-slip faults. Subsidence activities make the sea level increase highly, the subsidence activity makes the sea level rise at structures that fall close to the shore, reach about 0.2–0.48 mm/year in late Pleistocene - Holocene. The increase of sea level directly affects the intensity of erosion, flood, salinity and land loss events in coastal lowlands. Slippage of the seabed, earthquakes, volcanoes are geological hazards directly related to the geodynamic regime of the Southern Central coast
Comparative stable walking gait optimization for small-sized biped robot using meta-heuristic optimization algorithms
No full textThis paper proposes a new way to optimize the biped walking gait design for biped robots that permits stable and robust stepping with pre-set foot lifting magnitude. The new meta-heuristic CFO-Central Force Optimization algorithm is initiatively applied to optimize the biped gait parameters as to ensure to keep biped robot walking robustly and steadily. The efficiency of the proposed method is compared with the GA-Genetic Algorithm, PSO-Particle Swarm Optimization and Modified Differential Evolution algorithm (MDE). The simulated and experimental results carried on the prototype small-sized humanoid robot demonstrate that the novel meta-heuristic CFO algorithm offers an efficient and stable walking gait for biped robots with respect to a pre-set of foot-lift height value