Vietnam Academy of Science and Technology: Journals Online
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STRUCTURAL HEALTH MONITORING ON SPANS USING THE RESONANCE REGIONS OF THE POWER SPECTRUM DENSITY (RR-PSD)
No full textThis article proposes a new method which can be used to evaluate the mechanical responses of damage detection in spans. This method can monitor the stiffness degradation of spans over time. This monitoring processes will be conducted at different measuring points on spans, on different spans at the same or different measuring periods. The obtained results show that the change of acreage in the resonance regions of the power spectrum density has brought many positive preliminary outcomes in evaluating the quality of projects during their operational period. The study also shows that the change of acreage in the resonance regions allows us to identify the dangerous points on different spans of a bridge
Pore water pressure accumulation and settlement of clays with a wide range of Atterberg’s limits subjected to multi-directional cyclic shear
No full textIn this study, normally consolidated specimens on four clays with a wide range of Atterberg’s limits were tested by applying several series of undrained multi-directional cyclic shear followed by drainage. The cyclic shear tests were carried out under the shear strain amplitudes (γ = 0.05%-2.00%), number of cycles n = 200 and the phase difference θ = 90o. Then the accumulation of cyclic shear-induced pore water pressure and the post-cyclic settlement in strain (εv, %) were observed and discussed. In conclusion, it is clarified that the pore water pressure ratio (Udyn/σ’vo) increases with g and the soils with higher Atterberg’s limits show lower Udyn/σ’vo, and under the multi-directional cyclic shear strain at γ 0.4%, Hue clay and Kaolinite clay with relatively low plasticity suffer from cyclic failure. In addition, the post-cyclic settlement has a tendency of decreasing with the Atterberg’s limits in the range of plasticity index from Ip = 25.5 to 63.8, meanwhile when Ip 25.5, different tendencies were observed e.g., Hue clay (with lower Ip) shows a smaller settlement compared with those on Kaolin (with higher Ip). Furthermore, the threshold number of cycles (ntp) and cumulative shear strain (G*tp) for pore water pressure buildup were then clarified
Free vibration of FG sandwich plates partially supported by elastic foundation using a quasi-3D finite element formulation
No full textFree vibration of functionally graded (FG) sandwich plates partially supported by a Pasternak elastic foundation is studied. The plates consist of three layers, namely a pure ceramic hardcore and two functionally graded skin layers. The effective material properties of the skin layers are considered to vary in the plate thickness by a power gradation law, and they are estimated by Mori--Tanaka scheme. The quasi-3D shear deformation theory, which takes the thickness stretching effect into account, is adopted to formulate a finite element formulation for computing vibration characteristics. The accuracy of the derived formulation is confirmed through a comparison study. The numerical result reveals that the foundation supporting area plays an important role on the vibration behavior of the plates, and the effect of the layer thickness ratio on the frequencies is governed by the supporting area. A parametric study is carried out to highlight the effects of material distribution, layer thickness ratio, foundation stiffness and area of the foundation support on the frequencies and mode shapes of the plates. The influence of the side-to-thickness ratio on the frequencies of the plates is also examined and discussed
On a Standard Model Extension with Vector-like Fermions and Abelian Symmetry
Get PDFWe investigate an extension of the standard model with vector-like fermions and an extra Abelian gauge symmetry. The particle mass spectrum is calculated explicitly. The Lagrangian terms for all the gauge interactions of leptons and quarks in the model are derived. We observe that while there is no new mixing in the lepton sector, the quark mixing plays an important role in the magnitudes of gauge interactions for quarks, particularly the interactions with massive , and bosons. We calculate the contributions of the new vector-like leptons and quarks to the Peskin-Takeuchi parameters as well as the parameter of the electroweak precision tests, and show that the model is realistic
Size and Layer Dependence of Hybrid Graphene/h-BN Models Upon Heating
Get PDFDifferent models contained graphene layer are studied via molecular dynamics simulation. Models are heated up from 50K to 8000K via Tersoff and Lennard-Jones potentials to have an entire picture about the evolution of graphene layer in the models upon heating. Various thermodynamic quantities, structural characteristics, and the occurrence of liquidlike atoms are studied, such as, the total energy per atom, the heat capacity per atom, the radial distribution functions, and the appearance of liquid atoms upon heating. The phase transition exhibits the first order. The melting point of graphene layer depends on the number of layers in the models while it does not depend on the size in the range of this study. The melting process of hybrid graphene and hexagonal boron nitride (h-BN) satisfies the first step towards Devil's staircase type phase transition. The melting point of hybrid graphene/h-BN is close to the one of experiment of graphite
Simulation Study of Mid-infrared Supercontinuum Generation at Normal Dispersion Regime in Chalcogenide Suspended-core Fiber Infiltrated with Water
Get PDFWe report simulation results of supercontinuum generation in the suspended-core optical fibers made of chalcogenide (As2S3) infiltrated with water at mid-infrared wavelength range. Applying water-hole instead of the air-hole in fibers allows improving the dispersion characteristics, hence, contributing to supercontinuum generations. As a result, the broadband supercontinuum generation ranging from 1177 nm to 2629 nm was achieved in a 10 cm fiber by utilizing very low input pulse energy of 0.01 nJ and pulse duration of 100 fs at 1920 nm wavelength
Transport Properties of a GaAs/InGaAs/GaAs Quantum Well: Temperature, Magnetic Field and Many-body Effects
Get PDFWe investigate the zero and finite temperature transport properties of a quasi-two-dimensional electron gas in a GaAs/InGaAs/GaAs quantum well under a magnetic field, taking into account many-body effects via a local-field correction. We consider the surface roughness, roughness-induced piezoelectric, remote charged impurity and homogenous background charged impurity scattering. The effects of the quantum well width, carrier density, temperature and local-field correction on resistance ratio are investigated. We also consider the dependence of the total mobility on the multiple scattering effect
Molecular characterization of submergence tolerance genes and locus in the deep-water rice cultivars
Get PDFMost of the rice cultivars exhibit suspension of growth when submerged to overcome the reduced availability of oxygen. When the situation continues, majority of the cultivars unable to recover after the flood recedes. However, there are fortunately some rice genotypes that can withstand such submerged condition for up to two weeks by adapting two totally opposite mechanisms. One type of cultivars elongates enormously at a very short span of time and the leaves come above the water level. In the second type, they remain under water without any growth. Cultivars of both types tolerate the submergence but the first category easily lodges when flood water recede. In those lines, yields are reduced drastically. In this study, we focus on characterize the genetic variation at the Sub1 locus and to associate its relevance, if any, to submergence tolerance among the deep water landraces. As a first step, seeds of some rice cultivars collected from North-east Indian regions were initially selected for the characterization of genetic variation. The PCR based analysis involving several genes known to be associated with submergence tolerance did not reveal much difference. However, Southern hybridization revealed certain differences between submergence tolerant and susceptible cultivars. Although we did not notice major difference with regard to Sub1 genes when tried with EcoRI and BamHI, differences were noticed with adh1 and RAmy3C genes. Representative, Southern analysis showed the genetic variation among the deep-water cultivars as compared to Swarna and Sub1-Swarna. It is possible that deep-water rice cultivars may not differ in their genome at Sub1 locus but they respond through SNORKEL genes under submergence
Degradation of 2,3,7,8-TCDD by a consortium of bacterial strains isolated from heavil herbicide/dioxin contaminated soil in Bienhoa airbase
Get PDFFrom two different soil sources in Bienhoa airbase (heavy herbicide/dioxin contaminated West-South region and bioremediated cell), five microbial strains were isolated and their 2,3,7,8-TCDD biodegrability in consortium was investigated. Based on the colony and cell morphological characteristics as well as 16S rRNA gene sequences, these strains were classified into 5 genera, including Methylobacterium (strain BHBi1), Hydrocarboniphaga (strain BHBi4), Agrobacterium (strain BHBi5), Bosea (strain BHBi7) and Microbacterium (strain BH09). Two strains BHBi7 and BHBi4 were the first representatives of the genera Bosea and Hydrocarboniphaga that were isolated from heavyly herbicide/dioxin contaminated soil. All five strains were able to grow well in mineral salt medium (MSM) supplemented with soil extract (SE) containing 2,3,7,8-TCDD (this congener is the main soil total compound toxicity) and other congeners, including PCDDs, PCDFs, 2,4,5-T, 2,4-D, PAHs and their intermediates. This microbial consortium degraded 2,537.34 ngTEQ/kg of 2,3,7,8-TCDD congener in soil, equivalent to 59.1% lost of total toxicity in comparison to the control without bacterial seeding (4,294.12 ng TEQ/kg). Such a high ratio of dioxin degradation by a bacterial consortium was reported here for the first time, contributing more evidences for convincing the successful dioxin bioremediation of “Active Landfill” technology at large scale in Z1 area at Bienhoa airbase, Dongnai, Vietnam
PURIFICATION OF PHOSPHOGYPSUM FOR USE AS CEMENT RETARDER BY SULPHURIC ACID TREATMENT
Get PDFPhosphogypsum is a by-product of the wet phosphoric acid production. In this study, chemical compositions of phosphogypsum waste (PG) in Hai Phong diammonium phosphate plant (DAP1) and Lao Cai diammonium phosphate plant (DAP2) in Vietnam were surveyed for the purpose of gypsum recovery by P2O5, F removal to meet TCVN11833 for use treated gypsum as cement retarder. Studies of impurities P2O5, F, TOC removal by sulfuric acid 10 % at 28 0C was presented. The results found that the combination of a low concentration of sulfuric acid treatment, washing, lime neutralizing, and thermal treatment was successful in Phoshogypsum treatment for use as cement retarder. The cement test proved that treated PG could partially replace natural gypsum as a retarder.Keywords: phosphogypsum treatment, phosphorus pentoxide removal, calcium sulfate transition phase, cement retarder.