Vietnam Academy of Science and Technology: Journals Online
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Species diversity, taxon structure and distribution of the Chlorophytes on Truong Sa archipelago
No full textThe results of research on characteristic of distribution and taxa structure of Chlorophytes (Chlorophyta) at nine islands of Truong Sa archipelago (Truong Sa, Da Tay, Thuyen Chai, Toc Tan, Sinh Ton, Nam Yet, Song Tu Tay, Da Nam and Son Ca) indicate that there are 67 species of Chlorophytes, they belong to 4 orders, 14 families and 22 genera. The number of species at the sampling islands ranged from 13 species/island (Toc Tan isd.) to 43 species/island (Nam Yet isd.) with the average of 25.5 species/island. Sorensen similarity coefficient at the sampling sections ranged from 0.24 (between Song Tu Tay and Thuyen Chai) to 0.74 (between Nam Yet and Song Tu Tay) with the average of 0.45. Among 67 species in nine islands, there are 10 species distributed only in the intertidal zone (they are occupying 14.9% of total species), 14 species (31.4%) in subtidal zone only and 43 species (64.2%) in both intertidal zone and subtidal zone. The number of species concentrates on some genera (Halimeda: 10 species; Caulerpa: 10 species; Codium: 6 species,...), they belong to Codiacea, Siphonales. There are some genera with only 1 species (Tydemania, Anadyomene, Microdictyon,...)
Limit analysis of microstructures based on homogenization theory and the element-free Galerkin method
No full textThis paper presents a novel numerical formulation of computational homogenization analysis of materials at limit state. The fluctuating displacement field are approximated using the Element-Free Galerkin (EFG) meshless method. The estimated yield surface of materials can be determined by handling the multiscale (macro-micro) transition. Taking advantage of high-order EFG shape function and the second-order cone programming, the resulting optimization problem can be solved rapidly with the great accuracy. Several benchmark examples will be investigated to demonstrate the computational efficiency of proposed method
A comprehensive review on dual approach to the vibration analysis: Some dual techniques and application
Full text linkThis paper reviews key ideas of the researches on the dual approach to the vibration analysis. Three types of dual techniques, namely, forward - return dual technique, global-local dual technique, weighted averaging dual technique for the problem of equivalent replacement are summarized. Different implements and realizations of dual techniques to nonlinear vibration analysis and design of dynamic absorbers are reviewed. Finally, the challenging issues based on the dual techniques are discussed. A number of possibilities for developing analytical techniques related to dual techniques are proposed. The review shows that the dual approach is an appropriate one and the dual techniques are effective tools for studying random and deterministic nonlinear vibrational systems
Stress Contours in The Connecting-rod under The Dynamic Load and The Oil Film’s Pressure of The Connecting-rod Big End
Full text linkUnder load apply to the connecting-rod and the pressure in the lubricant oil film change the stress in the connecting-rod during the operating cycle. This problem is the one of the characteristics we need to consider when studying the connecting-rod big end bearing. A specific experimental device and the connecting-rod model of photoelastic material are used to determine the load diagram, measure the oil film pressure, and visualize the state of stress. The connecting-rod is subjected to simulation load as in the engine. The lubricated oil film pressure is measured by the pressure sensor and also calculated by numerical modelization method with the same load diagram. The method chosen to visualize the stress state in the dynamically loaded connecting rod is the transmission photoelasticimetry. This method allows the visualization of the isochrones fringes, which are lines of equal difference regarding main stresses in the connecting-rod. The stress contour’s images of the connecting-rod at different angles of the crankshaft are realized by a CCD camera. The measured stress contours are compared to the calculated stress contours by the Algor software. The results show globally a correspondence between the experimental isochrones fields and the calculated isochrones fields
High-temperature oxidation-resistant NiCr/Al DUPLEX coating on CT3 STEEL SUBSTRATE
No full textThe oxidation resistance property of NiCr/Al duplex coating system has been evaluated at 800oC during retention times of 1.5; 3; 4.5 and 6 hours. After the oxidation test, SEM-EDS data indicated the diffusion of aluminum into the NiCr coating, whereas XRD patterns revealed the appearance of new phases (Al3Ni2, Al2O3). In addition, an increase in micro-hardness (up to 518 - 842 Hv) was obtained after oxidation test. These obtained findings indicated that NiCr/Al coating had higher oxidation resistance than NiCr coating
Gene expressions involved in immune system control and serum CA125 content in polycythemia vera. Tap
Full text linkPolycythemia Vera (PV) is a slowly progressing blood cancer associated with myeloproliferative neoplasms. The disease is characterized by an abnormal proliferation of three cell types including red blood cells, white blood cells and platelets and a symptom of pruritus caused by release of itching agents of activated mast cells. The enhanced expression of several genes involved in immune system control including CTLA-4, PD-1 and LAG3 are linked to activation immune tolerance. Klotho gene has anti-aging, anti-inflammation and anti-cancer functions. The SHP gene group belongs to the tyrosine phosphatase protein signaling family that regulates cancer cell proliferation through maturation, migration and apoptosis and includes two main genes, SHP-1 and SHP-2. The increased serum content of cancer antigen CA125 is considered as a cancer marker of several blood and hematopoietic disorders. In this study, we conducted experiments to determine mRNA expression of above genes in PV patients by realtime-PCR and CA125 concentration by ELISA. Results showed that expression of klotho, LAG3, CTLA-4 and PD-1 genes was decreased in PV patients, indicating that the immune tolerance was inactivated in PV patients. CA125 concentration was significantly increased in PV patients compared to healthy individuals and interestingly, there was a positive association among three patients, who having increased CA125 concentration and biochemical indicators including LDH, AST and ALT. The results in this study provide an important reference document for further studies that serve for the early detection of PV disease.
CONTROLLER DESIGN BASED ON A KINEMATIC ESTIMATOR FOR A 3RRR PLANAR PARALLEL ROBOT DRIVEN BY ELECTRIC MOTORS
Full text linkThe control of parallel robotic manipulator requires feedbacks of all the redundant coordinates and their derivatives. In practice, to have all feedback variables for the controller, a robot needs more sensors than its degree of freedom. These sensors measure not only the actuated joint variables, but also the auxiliary variables, position and velocity of the moving platform. In this paper, a novel method is introduced to estimate dependently generalized coordinates and motion of the moving platform. A kinematic error feedback technique is exploited to ensure the estimated motion converge to the actual motion of the robot
FREE VIBRATION OF TAPERED FUNCTIONALLY GRADED CARBON NANOTUBE-REINFORCED COMPOSITE BEAMS USING A HIERARCHICAL BEAM ELEMENT
Full text linkFree vibration of tapered functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams is investigated. The beams with four types of carbon nanotube distribution in the thickness, namely the uniform (UD-CNT), X-type (FGX-CNT), A-type (FGA-CNT) and O-type (FGO-CNT), are assumed to be linearly tapered in longitudinal direction by three different taper cases. Based on the first-order shear deformation theory, equations of motion with variable coefficients are derived from Hamilton’s principle. Using hierarchical functions to interpolate the displacement field, a two-node beam element with nine degrees of freedom is formulated and employed to compute frequencies of the beams. The accuracy of the derived formulation is confirmed by comparing frequencies obtained in the present work with the published data. The effects of the total CNT volume fraction, CNT distribution type, taper cases, taper ratio, aspect ratio, boundary conditions, etc., on the vibration characteristics of the beams are examined and discussed
Novel Approach of Robust Hinf Tracking Control for Uncertain Fuzzy Descriptor Systems Using Parametric Lyapunov Function
No full textThis paper proposes a novel uncertain fuzzy descriptor system which is an extension from standard T-S fuzzy system. A fixed Lyapunov function-based approach is considered and controller design for this rich class of fuzzy descriptor systems is formulated as a problem of solving a set of LMIs. The design conditions for the descriptor fuzzy system are more complicated than the standard state-space-based systems. However, the descriptor fuzzy system-based approach has the advantage of possessing fewer number of matrix inequality conditions for certain special cases. Hence, it is suitable for complex systems represented in descriptor form which is often observed in nonlinear mechanical systems
Numerical investigation of force transmission in granular media using discrete element method
Full text linkIn this paper, a numerical Discrete Element Method (DEM) model was calibrated to investigate the transmission of force in granular media. To this aim, DEM simulation was performed for reproducing the behavior of a given granular material under uniform compression. The DEM model was validated by comparing the obtained shear stress/normal stress ratio with results published in the available literature. The network of contact forces was then computed, showing the arrangement of the material microstructure under applied loading. The number and distribution of the contacts force were also examined statistically, showing that the macroscopic behavior of the granular medium highly depended on the force chain network. The DEM model could be useful in exploring the mechanical response of granular materials under different loadings and boundary conditions