Vietnam Academy of Science and Technology: Journals Online
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Threadfin bream (Nemipteridae) resources in the sea of Vietnam based on the bottom trawl surveys
Get PDFThe threadfin bream (Nemipteridae) resources in the sea of Vietnam were analysed using the results of bottom trawl surveys conducted by the assessment of living marine resources project in Vietnam (ALMRV) in period 2000–2005 and comprehensive investigation of marine fisheries resources project in Vietnam sea during 2012–2013. Results showed that a total of 23 species belonging to 4 genera of Nemipterus, Parascolopsis, Pentapodus and Scolopsis were recorded. The Southeast region has the highest number of species encountered with 26 species, and the lowest number in Central waters with 16 species. The highest number of species was encountered at 50–100 m depth range with 25 species and the lowest number at the depth of less than 20 m with 9 species. Catch of threadfin bream comprised more than 1% of total catch of surveys. In threadfin bream family, genus Nemipterus was the most abundant, the catch of this genus contributed from 75.1% to 88.4% of the family catch. The catch per unit effort decreased from Northern region to Southern region, while the catch in the Northeast monsoon was higher than in the Southwest monsoon. The biomass of threadfin bream in Vietnamese water was estimated to be 7,534 to 12,229 tons depending on the monsoon patterns
DYNAMIC MODEL WITH A NEW FORMULATION OF CORIOLIS/CENTRIFUGAL MATRIX FOR ROBOT MANIPULATORS
Get PDFThe paper presents a complete generalized procedure based on the Euler-Lagrange equations to build the matrix form of dynamic equations, called dynamic model, for robot manipulators. In addition, a new formulation of the Coriolis/centrifugal matrix is proposed. The link linear and angular velocities are formulated explicitly. Therefore, the translational and rotational Jacobian matrices can be derived straightforward from definition, which makes the calculation of the generalized inertia matrix more convenient. By using Kronecker product, a new Coriolis/centrifugal matrix formulation is set up directly in matrix-based manner and guarantees the skew symmetry property of robot dynamic equations. This important property is usually exploited for developing many control methodologies. The validation of the proposal formulation is confirmed through the symbolic solution and simulation of a typical robot manipulator
Design and analysis of a displacement sensor-integrated compliant microgripper based on parallel structure
Get PDFThis study evaluates the displacement sensitivity of a new compliant microgripper. The microgripper is designed based on a four-bar mechanism and the concept of a compliant mechanism. The effects of the width of the right circular hinge, the thickness of microgripper, and the material properties on the dis-placement sensitivity are considered via using the finite element method. In the beginning, the stress and deformation of the compliant microgripper are evaluated. Subsequently, the displacement of the microgripper is then analyzed. The results showed that the design parameter and the displacement sensitivity have a close relationship. To increase the grasping reliability and measure the displacement or force, a micro-displacement sensor is integrated with the proposed microgripper. Finally, the modeling and analysis of the proposed sensor are conducted
Insights into the magnetic origin of CunCr (n= 9÷11) clusters: A superposition of magnetic and electronic shells
Get PDFInterests in Cu-Cr sub-nanometer systems have been increasing due to the recently-found icosahedral Cu12Cr cluster as a superatomic molecule, where the 3d-Cr and 4s-Cu electrons can phenomenologically form the 18-e molecular shell (1S21P61D10) of Cu12Cr. In this report, we set out to investigate the energetically-preferred geometries and stabilities of CunCr (n = 9÷11) clusters using the density-functional-theory calculations. It is found that not all of 3d-Cr electrons involve in the formation of the cluster shell and the remaining localized ones cause the magnetic moment of the clusters, which is different from what was believed
Effect of pre-alloy composition on the content of ferromagnetic phase of MnBi Melt spun ribbons
No full textThe rare-earth-free hard magnetic material MnBi is potential for permanent magnet high-temperature applications. The ferromagnetic phase (noted as a Low Temperature Phase – LTP) MnBi has the moderate spontaneous magnetization Ms ~ 74 emu/g, the high magneto-crystalline energy Ka of ~ 0.9 MJ/m3, and the elevated Curie temperature Tc ~ 360 oC and especially, the positive thermal coefficient of coercivity d(iHc)/dT 0. Up to now, the MnBi powders with high LTP content and coercivity have usually been prepared using the melt-spinning technique. However, the large difference in the melting temperature Tm of the two constituents, Mn and Bi, and the strong reactivity of Bi with the copper-based wheel make the preparation of high-performance MnBi ribbons difficult. Using a novel approach, we overcame these difficulties and prepared the MnBi ribbons on the conventional commercial melt-spinning furnace ZGK-1. The influences of pre-alloy compositions on the magnetic properties of MnBi melt – spun ribbons will be discussed in detail
Initial evaluation of nitrogen uptake of Thalassia hemprichii in Nha Trang, Khanh Hoa
Get PDFThe uptake rate of nitrate by leaves and roots was simultaneously investigated in the seagrass T. hemprichii collected from Lo river, Nha Trang. The principle of nutrient uptake of seagrass was based on the approaches of the Michaelis-Menten model. The laboratory experiments of nitrate uptake were done the ranges of ambient nitrate concentrations in the separate water column of leaves and roots. The calculated results indicated that the nitrate uptake rate through the leaves was higher than that of the roots. The maximum uptake rate (Vmax) through the leaves and the roots was 1,777.0 mgN/g DW/h and 131.6 mgN/g DW/h, respectively. From these results, the nitrate uptake rate by the seagrass in Lo river was estimated at 52.2 mgNm-2h-1. The value plays an important role in developing and implementing plans for the protection and rehabilitation of seagrass beds in coastal areas
Water resources potential in Co To island and exploitation orientation to use
Get PDFCo To is an island of the Co To district in Quang Ninh province with an area of about 18 km2. Average rainfall on the island is 1,738.8 mm/yr, evaporation is 925 mm/yr. On the island, there are some small streams but they are temporary flow in the rainy season, there is not any natural lakes. There are 2 aquifers. The Quaternary aquifer (q) is distributed in a low terrain with area of about 9 km2, thin thickness and saline water is in about half of the area, so it does not make sense for water supply. The fissured aquifer of the ocdovic-silua (o-s) formation is distributed in the high terrain with an area of about 9 km2, this is low potential water layer. The flow rate in the boreholes in the fractured zone due to tectonic activity can be 1–1.5 l/s, it can satisfy small-scale water supply. Potential groundwater reserve of Co To island is 6,472 m3/day, exploitable reserve is 1941 m3/day, exploited reserve level at C1 range is 1,144 m3/day. This can satisfy the water demand for the living of people on the island today. Small-scale groundwater exploitation in the island has just been beginning, but it has the prospect of replication and at the same time there must be reasonable measures to protect and develop water resources to ensure sustainable development and meet the larger water requirements in the future
ƯƠNG GIỐNG CUA BIỂN (Scylla paramamosain) VỚI CÁC LOẠI THỨC ĂN VÀ MẬT ĐỘ KHÁC NHAU
Get PDFThis study aims to determine the appropriate feed type and stocking density to improve the survival rate and growth performance of mud crab crablet during the nursery stage. The study consisted of 2 experiments as follows: (1) Rearing crablets with different feed types (including commercial feed, artemia biomass and acetes biomass) and (2) rearing crablets at different stocking densities (including 100; 200; 300 and 400 inds/m2). All treatments were randomly set up in triplicate. The initial sizes of crablet were 3.24 ± 0.54 mm in length, 4.54 ± 0.79 mm in width and 0.018 ± 0.004 g in weight. The result showed that using acetes biomass gave the best results compared to other treatments. The survival rate was 58.8% and biomass was 118 inds/m2. The second experiment showed that rearing crablets at 100 inds/m2 reached the highest survival rate (90.7%) and biomass (91 inds/m2).Nghiên cứu nhằm xác định loại thức ăn và mật độ ương thích hợp để nâng cao tỷ lệ sống và tăng trưởng trong ương giống cua biển. Nghiên cứu gồm 2 thí nghiệm: (1) ương cua giống với các loại thức ăn khác nhau (thức ăn công nghiệp, artemia sinh khối và con ruốc sinh khối) và (2) ương cua giống với các mật độ khác nhau (100; 200; 300 và 400 con/m2). Các nghiệm thức được bố trí hoàn toàn ngẫu nhiên và được lặp lại 3 lần. Cua giống có chiều dài ban đầu là 3,24 mm, chiều rộng 4,54 mm và khối lượng 0,018 g. Kết quả thí nghiệm 1 cho thấy, khi sử dụng thức ăn con ruốc sinh khối cho kết quả tốt nhất về tỷ lệ sống (58,8%) và sinh khối đạt 118 con/m2. Thí nghiệm 2 cho thấy, khi ương cua ở mật độ 100 con/m2 cho kết tốt nhất về tỷ lệ sống (90,7%) và sinh khối đạt 91 con/m2
Biodiversity and characteristic of octocoral communities (Octocorallia: Alcyonacea and Gorgonacea) in Cu Lao Cham Marine Protected Area, Quang Nam province
Get PDFThe article showed the biodiversity and characteristic of Octocoral communities in Cu Lao Cham Marine Protected Area (MPA). A total of 165 samples were collected and identified as material of the Octocorals from 9 survey sites of Cu Lao Cham Marine Protected Area. The material represents 45 taxa belonging to 12 genera and seven families. Among them, Sinularia genus has the highest diversity with 19 species, Sarcophyton with 8 species and Lobophytum with 6 species. The other genera have one or two species. The diversity of Octocorals species in Cu Lao Cham Marine Protected Area is quite high after Nha Trang and Ly Son MPAs. Soft coral cover in Cu Lao Cham Marine Protected Area is the highest with average coverage 21.2% (±7.0 SE) compared with other MPAs of Vietnam. Distribution of Octocorals in Cu Lao Cham Marine Protected Area is mainly at 4–6 m (average coverage obtained 30%) and the cover decreases to the end of reef distribution. Our results showed that there are two distinguishing assemblages of Octocoral communities whose differences are the distribution characteristics, dominance of genera and species diversity
AN EFFICIENT ALGORITHM FORMINING HIGH UTILITY ASSOCIATION RULES FROM LATTICE
Get PDFIn business, most of companies focus on growing their profits. Besides considering profit from each product, they also focus on the relationship among products in order to support effective decision making, gain more profits and attract their customers, e.g. shelf arrangement, product displays, or product marketing, etc. Some high utility association rules have been proposed, however, they consume much memory and require long time processing. This paper proposes LHAR (Lattice-based for mining High utility Association Rules) algorithm to mine high utility association rules based on a lattice of high utility itemsets. The LHAR algorithm aims to generates high utility association rules during the process of building lattice of high utility itemsets, and thus it needs less memory and runtim