Vietnam Academy of Science and Technology: Journals Online
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MODAL ANALYSIS OF CRACKED TOWER CRANE WITH AN EXPERIMENTAL VALIDATION
No full textIn this paper, dynamic stiffness model of a cracked frame structure that represents a planar tower crane is established in an explicit form based on general solution of cracked 2D-beam element vibration. The crack is modeled by a pair of equivalent springs of stiffness calculated from the crack depth. An explicit form of frequency equation is first established and then solved for numerical sensitivity analysis of natural frequencies of the structure to cracks. An experimental study is accomplished to validate the theoretical developmen
Distribution features of meteorological parameters in Truong Sa archipelago area
No full textThis paper presents the distribution features of observed meteorological parameters in Truong Sa archipelago area including wind, tropical cyclone, and average values of solar radiation, air temperature, air humidity, rainfall. Observed data were collected from Truong Sa island hydro-meteorological station. In particular, data of tropical cyclones affecting Truong Sa archipelago area were collected from the websites http://www.jma.go.jp/jma/jma-eng/jma-center/(Japan). Study results show that the main meteorological parameters in Truong Sa archipelago area are affected by solar radiation and monsoonal wind regimes in East Asia region which are Northeast monsoon occurring from November to April and Southwest monsoon occurring from June to September. Transition periods are May and October. Tropical cyclones occur mainly in November–December, maximum wind speed was 64 m/s in typhoon HAIYAN (November 2013). The highest average solar radiation occurs in April (277 hours), the lowest in January (181 hours). The highest average air temperature occurs in April (29.5oC), the lowest in January (26.6oC). The highest average rainfall occurs in November (341 mm), the lowest in March (62 mm). The highest average air humidity occurs in November–December (85%), the lowest in April–May (79%). The highest average water evaporation occurs in March (129 mm), the lowest in December (87 mm)
GLOBAL DYNAMICS OF A COMPUTER VIRUS PROPAGATION MODEL WITH FEEDBACK CONTROLS
No full textA computer virus propagation model with feedback controls is first proposed and investigated. We show that the control variables do not influence on the global stability of the original differential model, they only alter the position of the unique viral equilibrium. The mathematical analyses and numerical simulations show that this equilibrium can be completely eliminated, namely, moved to the origin of coordinates if suitable values of the control variables are chosen. In the other words, the control variables are effective in the prevention of viruses in computer systems. Some numerical simulations are presented to demonstrate the validity of the obtained theoretical results.
DEGRADATION OF DEPROTEINIZED NATURAL RUBBER BY GORDONIA SP. ISOLATED FROM ENRICHMENT CONSORTIA
Get PDFBiodegradation is a potential way of decomposing deproteinized natural rubber (DPNR). The enrichment consortia were demonstrated from a rubber processing factor waste. Nine DPNR-degrading bacteria were isolated from those consortia. The highest DPNR film weight loss in a mineral salt medium (MSM) was 43.92 ± 2.30 % after 30 days incubation using strain 5A1. The formation of aldehyde group during rubber degradation of 5A1 was determined using Schiff staining and Fourier Transform Infrared spectroscopy (FTIR) analysis. The 16S rRNA gene sequence, of 5A1 showed the highest identity with that of Gordonia soli CC-AB07. This is the first report to demonstrate a strong ability to degrade DPNR by Gordonia sp
Chemical compositions of amphiboles and their references to formation conditions of granitoids from Nam Rom and Song Ma massifs, Northwest Vietnam
No full textIn this paper, the mineralogical and geochemical characteristics of amphiboles and plagioclases of granitoids from the Nam Rom and Song Ma massifs have been investigated to understand their formation conditions. The Nam Rom amphibole and plagioclase are subhedral to euhedral fine- to medium-grained crystals. Whereas, the Song Ma amphibole and plagioclase are anhedral to subhedral fine-grained crystals. Geochemical compositions of amphiboles suggest that Nam Rom and Song Ma amphiboles are edenite and ferro-edenite, respectively. Nam Rom edenite has higher contents of basic constituents (Mg and Ca) and lower contents of felsic constituents (Na and K) compared with the Song Ma ferro-edenite. On the other hand, Si-(Na+K) and Si-Ca apfu ratios of the Nam Rom edenite and the Song Ma ferro-edenite and Al/(Na+K)-Al/(Ca+Na+K) atom per formula unit (apfu) ratios of the Nam Rom edenite and andesine and the Song Ma ferro-edenite, andesine and oligoclase are similar. Formation conditions of the Nam Rom and Song Ma granitoids were calculated using amphibole-plagioclase geobarometer. The Nam Rom granitoid was formed at 3.07-5.32 kbar (10.1-17.6 km under paleo-surface) and 750-785°C. The Song Ma granitoid was formed at 1.04-3.08 kbar (3.4-10.2 km under paleo-surface) and 715-745°C. Therefore, Nam Rom and Song Ma granitoids are thought to be crystallized from the same magma. The former was formed from the immature and more basic stage of magma; the latter was formed from the mature and more felsic stage of magma
FAR-RED EMISSION OF CAYALO4:MN4+ SYNTHESIZED BY CO-PRECIPITATION METHOD
No full textLight absorption of the most plants is in range of blue (440 nm), deep-red (660 nm) and far-red around 700-740 nm. The deep-red and far-red light plays important roles in reactions of photomorphogenesis of plants. Although red emission phosphors have been researched extensively for white light-emitting diodes, deep-red and far-red emission phosphors for plant growth have been reported inadequately. Thus, in this work, far-red emitting CaYAlO4:Mn4+ phosphor was synthesized by co-precipitation method coupled with various annealing temperature from 800oC to 1300oC for 5 h. The crystal structure, morphology, and photoluminescence properties of CaYAlO4:Mn4+ phosphors were investigated in detail. The crystallinity of the phosphor belongs to tetragonal system with space group I4/mmm. Y3+ and Ca2+ ions are coordinated by nine oxygen atoms to form [YO9] and [CaO9] polyhedrons, and the Al3+ ions are coordinated by six oxygen atoms forming [AlO6] octahedrons that provided suitable sites for Mn4+ ions. The obtained sample showed an irregular surface morphology with micro size particles. Under the excitation of 320 nm, CaYAlO4:Mn4+ phosphors gave bright far-red emission around 710 nm due to the 2Eg→4A2g transition of Mn4+ ions. The critical concentration of Mn4+ doped in CaYAlO4 host lattice is 0.5 mol.%. The results show that the CaYAlO4:Mn4+ phosphors may be applied to indoor plant growth illumination
FINITE ELEMENT MODELLING FOR ELECTRIC FIELD DISTRIBUTION AROUND POSITIVE STREAMERS IN OIL
Get PDFElectric field distribution of positive streamers during propagation was determined with the finite element method by using COMSOL multiphysics. Modelling was performed at 210 kV and 270 kV. The geometrical shape of streamers was modelled with cylinder and sphere for the case of 210 kV while a growing cylinder was used for streamer propagation at 270 kV. In addition, a spherical model was used for determining the correlation between streamer branching and the electric field. It is obtained from the simulation results that the 2nd mode streamers has the electric field at channel tips of about 0.1 MV/cm while 8.3 MV/cm was received for the 4th mode streamers. The simulation results also reveal that the shielding effect resulting from streamer branching significantly reduces the electric field at the channel tips, and the shielding effect disappears with the angle a between channels is about 30o-60o depending on the size of streamer envelope. The hypothesis on correlation among velocity, streamer branching and electric field is suggested
Assessing status and habitat of siamese fireback (Lophura diardi) by using camera trap in Lo Go-Xa Mat National Park, Vietnam
Get PDFSiamese fireback, Lophura diardi, belonging to Galliformes is at risk due to habitat loss and hunting, which are main challenges to conservation of the species. In order to provide scientific information to conserve the L. diardi, we implemented a camera-trap survey in Lo Go-Xa Mat National Park from 2017 to 2018. Occupancy and Poisson regression models were used to investigate presence of the species and potential factors influencing the occurrence of the species in the study area. Our results showed that the probability of occurrence of the species at locations within the park was high at 0.84 (0.69–0.92) and detection probability was relative low at 0.19 (0.16–0.23). The best models consistently suggested that the abundance of the species was high in closed canopy forest cover (β = 0.41), but appeared to be notably lower in areas far away from the ranger stations (β = -0.25) and in places with high frequency of human (β = -0.22). This research provided the first quantitative information of status and potential factors influencing occurrence of the L. diardi in the park, which is an essential data for developing practical actions to protect the species and monitoring program in the future for the park.
FINITE ELEMENT MODELLING FOR FREE VIBRATION RESPONSE OF CRACKED STIFFENED FGM PLATES
No full textThis paper presents the new numerical results of vibration response analysis of cracked FGM plate based on phase-field theory and finite element method. Effects of geometrical and material properties on the vibration behaviors of the plate are investigated in this work. The computed results show that the crack and stiffener have a strong influence on both the vibration responses and vibration mode shapes of the structure. The computed results can be used as a good reference to study some related mechanical problems
SYNTHESIS AND BLEND OF BIO-BASED BENZOXAZINES FROM CARDANOL AND DIPHENOLIC ACID
No full textIn this study, two benzoxazine monomers, m-alkylphenyl-3,4-dihydro-2H-benzoxazine (CA-Bz) and 4,40-Bis-[6-(3-phenyl-3,4-dihydro-2H-1, 3-benzoxazine)] pentanoic acid (DPA-Bz) were successfully synthesized from fully bio-based phenols (cardanol and diphenolic acid). Their structures were confirmed by FTIR and NMR spectroscopy. CA-Bz/DPA-Bz blend with weight ratio of 3:1 was prepared and polymerization of the monomers were characterized by DSC. The ring-opening polymerization of CA-Bz was found to decrease significantly by incorporation of carboxyl groups in DPA-Bz showing thereby the catalytic effect of acid functionality. The modified polybenzoxazine also showed an enhancement of the thermal properties