Vietnam Academy of Science and Technology: Journals Online
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Buckling and postbuckling of axially-loaded CNT-reinforced composite cylindrical shell surrounded by an elastic medium in thermal environment
Get PDFBuckling and postbuckling behaviors of nanocomposite cylindrical shells reinforced by single walled carbon nanotubes (SWCNTs), surrounded by an elastic medium, exposed to a thermal environment and subjected to uniform axial compression are investigated in this paper. Material properties of carbon nanotubes (CNTs) and isotropic matrix are assumed to be temperature dependent, and effective properties of nanocomposite are estimated by extended rule of mixture. The CNTs are embedded into matrix via uniform distribution (UD) or functionally graded (FG) distribution along the thickness direction. Governing equations are based on Donnell’s classical shell theory taking into account von Karman-Donnell nonlinear terms and interaction between the shell and surrounding elastic medium. Three-term form of deflection and stress function are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to obtain load-deflection relation from which buckling and postbuckling behaviors are analyzed. Numerical examples are carried out to analyze the effects of CNT volume fraction and distribution types, geometrical ratios, environment temperature and surrounding elastic foundation on the buckling loads and postbuckling strength of CNTRC cylindrical shells
Performance analysis of global local mean square error criterion of stochastic linearization for nonlinear oscillator
Get PDFThe paper presents a performance analysis of global-local mean square error criterion of stochastic linearization for some nonlinear oscillators. This criterion of stochastic linearization for nonlinear oscillators bases on dual conception to the local mean square error criterion (LOMSEC). The algorithm is generally built to multi-degree of freedom (MDOF) nonlinear oscillators. Then, the performance analysis is carried out for two applications which comprise a rolling ship oscillation and two-degree of freedom one. The improvement on accuracy of the proposed criterion has been shown in comparison with the conventional Gaussian equivalent linearization (GEL)
Crack identification in multiple cracked beams made of functionally graded material by using stationary wavelet transform of mode shapes
Get PDFThis paper presents crack identification in multiple cracked beams made of functionally graded material (FGM) by using stationary wavelet transform (SWT) of mode shapes and taking into account influence of Gaussian noise. Mode shapes are obtained from multiple cracked FGM beam element and spring model of cracks. The theoretical development was illustrated and validated by numerical examples. The investigated results show that crack identification method by using SWT of mode shapes is efficient and realizable
Vibroacoustic analysis of a clamped finite orthotropic laminated double-composite plate with an air cavity
Get PDFThe vibroacoustic analysis of a clamped finite orthotropic laminated double-composite plate with a closed air cavity is investigated analytically presented within classical laminated plate theory for laminated composite plate. Using the method of modal decomposition, a double Fourier series solution is obtained to characterize the vibroacoustic performance of the structure. The sound transmission loss (STL) is calculated from the ratio of incident to transmitted acoustic powers. The accuracy of the solution is shown with comparing the STL values obtained from this presented model with the experimental and theoretical results available in literature. The soundproof ability of finite double-composite plate with a clamed boundary is shown. The effects of thickness of faceplates, thickness of air cavity and the angles of the incident sound are systematically examined
Diet of Odorrana chapaensis (Bourret, 1937) from Son La Province, Vietnam
Get PDFSince there is currently a lack of data on the natural history and feeding ecology of Odorrana chapaensis, which was listed in the IUCN Red List (2019), we herein provided the feeding ecology of this amphibian species is virtually lacking. We herein provide data about the diet of O. chapaensis based on the results of our field work in Ngoc Chien Commune, Muong La District and Xim Vang Commune, Bac Yen District, Son La Province, Vietnam. We used the stomach-flushing method to obtain the stomach contents of 85 individuals at two survey sites. A total of 20 prey categories with 334 items, comprising 299 items of invertebrates and 35 unidentified items, were found in the stomachs of O. chapaensis. The dominant prey items of O. chapaensis were Araneae, Polydesmida, insect larvae, Blattodea, Coleoptera, Dermaptera, Lepidoptera, Hymenoptera, and Orthoptera. The importance index for these categories ranged from 3.5% to 32.5%. Coleoptera was the category with the highest frequency of prey items; its representatives were found in 45 stomaches.
Floristic composition of different habitats of indochinese silvered langur (Trachypithecus germaini) in the Chua Hang karst in Kien Luong district, Kien Giang province, Vietnam
Get PDFThe Indochinese silvered langur (Trachypithecus germaini) is a leaf monkey species that occurs on four karst hills in the Kien Luong District, Kien Giang Province, Vietnam. In this study, the floristic composition of four habitats where the silvered langur were observed feeding was analyzed. These habitats include cliffs, slopes, the peak of the Chua Hang karst and the adjacent mangroves. We identified 185 plant species belonging to 61 families distributing across the habitats, and the silvered langurs fed on 60 plant species of 37 families. Among food plants selected by the silvered langur, 41 plant species were distributed on the cliff, followed by the slope (31 species), the peak (24 species), and the mangroves (4 species). The silvered langurs fed on about 67% of plant species on the cliff. Plant species richness of the slope areas was highest (at D=0.45, D: Simpson index, and d=20.0, d: Margalef index) compared with the other habitats. The floristic composition of the cliff, slope and peak was quite similar to each other, with the similarity index (SI) ranging from 0.47 to 0.56. The results showed that four plant species, Phyllathus reticulatus Poir, Ficus rumphii Blume, Streblus ilicifolia (Kurz.) Corn. and Cayratia trifolia L. were consumed throughout of the year. In summary, present results add important information for conservation of the Indochinese silvered langur in Vietnam.
SCHEDULING FOR MASSIVE MIMO USING CHANNEL AIGING UNDER QOS CONSTRAINTS
Get PDFMassive multiple-input multiple-output (MIMO) networks support QoS (Quality of Service) by adding a new sublayer Service Data Adaption Protocol on the top of Packet Data Convergence Protocol layer to map between QoS flows and data radio bearers. In downlink for Guaranteed Bit Rate (GBR) flows, the gNB guarantees the Guaranteed Flow Bit Rate (GFBR) that defines the minimum bit rate the QoS flow can provide. So, one of the most important requirements is the minimum rate. The channel aiging helps to improve the sum-rate of Massive MIMO systems by serving more users to increase the spatial multiplexing gain without incurring additional pilot overhead. In this paper, a novel scheduler, termed QoS-Aware scheduling, is designed and proposed for Massive MIMO to use the channel aiging to increase the sum-rate but guarantee the minimum bit rate per user to support QoS. We investigate how many users are enough to serve to maximize the sum-rate while keeping the data rate per user meeting a given threshold. Through the numerical analysis we confirmed that QoS-Aware scheduling can guarantee a minimum rate per user and get a higher useful through-put (goodput) than conventional channel aiging schedulers
COPPER TRIFLATE CATALYZED BAEYER- VILLIGER OXIDATION OF KETONES
Get PDFA simple, efficient and eco-friendly method for Baeyer-Villiger oxidation reaction has been developed. The reaction employed m-CPBA as the oxidant with Cu(OTf)2 catalyst and was carried out in CH2Cl2 at room temperature. Nine lactones and ester were obtained in excellent yield (85-94%). Furthermore, the catalyst could be reused twice without considerable loss in activity
ELECTROCHEMICAL PREPARATION OF NANO SILVER BY HIGH DC VOLTAGE COMBINED WITH ANODIC PLASMA
No full textSilver nanoparticles (AgPNs) were prepared by high-voltage electrochemical methods using silver anode to produce silver ions and hydrogen gas at the cathode from electrolysis of distilled water as solvents. The electrolyte solution resulting from the AgPNs product obtained does not contain ions of the electrolyte solution such as conventional chemical or electrochemical methods. Silver anode dissolution process will provide Ag+ and disperse it into distilled water. The process of generating H2 from the electrolysis of H2O disperses into distilled water and escapes upward towards the anode due to the arrangement of the electrolytic vaporizer vertically above the anode and the cathode below. Ag+ and H2's encounter in the aqueous solution will take the oxidation-reduction reaction to form AgPNs. Due to the high-voltage DC electrolytic processes that generate gas on the electrodes, both high-voltage and high magnetic fields, as well as high water-distillation resistance, will increase the solution temperature as favorable conditions to form an electrochemical plasma on the electrodes. The plasma electrode process that separates water into H2 and O2 can occur simultaneously by electrochemical reactions that contribute to the supply of large amounts of gas to participate in oxidative reactions - reducing the formation of AgPNs. The properties of the AgPNs solution prepared by high-voltage DC lines were determined by UV-Vis, electrical conductivity, TEM, zeta potential, particle size distribution as well as content determined by weight lost method, Faraday's law and AAS analysis. Anodic plasma can be generated by stable high voltage mode to decompose water that supports electrochemical reactions that form AgPNs with structural, physicochemical and structural properties as well as comparable constituents be with the current methods
PRELIMINARY STUDY ON CHEMICAL MECHANISM OF DECREASE OF TETRODOTOXIN CONTENT IN OVARIES OF A PUFFER FISH Lagocephalus inermis (Temminck and Schlegel, 1850) FERMENTED WITH RICE BRAN
Get PDFTetrodotoxins in salted and fermented ovaries with rice bran of a puffer fish Lagocephalus inermis (Temminck Schlegel, 1850) during five months were determined by high-performance liquid chromatography with fluorometric detector (HPLC- FLD). The analysed results showed that the original ovaries contained only tetrodotoxin with content of 7.59 µg/g fresh weight. 4,9-Anhydrotetrodotoxin - an isomer which is less toxic than tetrodotoxin has been found in all ovary samples since the second month. Tetrodotoxin in the ovaries disappeared in the 4th month of the experiment. In addition, 4,9-anhydrotetrodotoxin level in ovaries increased during fermentation. The present study contributes to clarifying the chemical mechanism of decreasing tetrodotoxin content in fermented ovary of puffer fish.Tetrodotoxins in salted and fermented ovaries with rice bran of a puffer fish Lagocephalus inermis (Temminck and Schlegel, 1850) during five months were determined by high-performance liquid chromatography with fluorometric detector (HPLC- FLD). The analysed results showed that the original ovaries contained only Tetrodotoxin with content of 7.59 µg/g fresh weight. 4,9-Anhydrotetrodotoxin- an isomer which is less toxic than Tetrodotoxin has been found in all ovary samples since the second month. Tetrodotoxin in the ovaries disappeared in the 4th month of the experiment. In addition, 4,9-Anhydrotetrodotoxin level in ovaries increased during fermentation. The present study contributes to clarify the chemical mechanism of decreasing Tetrodotoxin content in fermented ovary of puffer fish