Vietnam Academy of Science and Technology: Journals Online
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Species composition and distribution of seaweeds in Phu Yen province
No full textResults of four field surveys, conducted from June 2017 to June 2018 found that in the Phu Yen coastal water, a total of 103 seaweed species have been recorded, increasing the total number of seaweed species in Phu Yen province to 133 species, with 81 newly recorded species for Phu Yen geographic area. Among 103 seaweed species, 4 species belong to Cyanobacteria, 38 species belong to Rhdophytes, 24 species belong to Phaeophytes, and 37 species belong to Chlorophytes. The number of species at surveyed sites V1 to V9 varies from 3 species/site (V3) to 83 species/site (V7) and on average 27 species/site. Sørensen’s similarity coefficient varies from 0.05 (between V3 and V7) to 0.86 (V3 and V4) and on average 0.25. 74/103 species were collected in the littoral zone, 67 species in sublittoral zone and most of them are distributed at 0-4 m water depth of subtidal zone. The marine algal flora is represented by mixing of subtropical and tropical characteristics as Cheney index was 3
ON THE CONTRIBUTION FACTORS OF ENHANCED PHOTOCATALYTIC ACTIVITY OF DOPED SEMICONDUCTORS: STRUCTURAL AND OPTICAL INTVESTIGATION OF CU2+ DOPED ZnO NANOPARTICLE
No full textAs a traditional direct bandgap oxide semiconductor, ZnO, showed as a promising photocatalytic candidate. Researchers worldwide reported many possibilities to improve its photocatalytic activity such as doped with metal, non-metal ions. As a result of heterojunction formation between ZnO and its intentional impurity, previous reports showed beneficial characteristics for enhancing photocatalytic activity in these ZnO-based materials, i.e. bandgap narrowing, recombination rate of photoelectron-hole prolonging, visible light absorption improving. This work will present the photocatalytic acitivity improvement of ZnO when doping with ion Cu2+ and try to illustrate the crucial photocatalytic enhancement factors
On models with wobbling disk for brake squeal
No full textAmong many mathematical models of disk brakes for the explanation of brake squeal, models with wobbling disk have their own advantage over planar models. Applying a recently developed matrix form of Euler equations in rigid body dynamics, the equations establishment process can now be performed with almost all popular computing software. Furthermore, the presented models are more generalized in terms of damping, in-plane vibration, and unsymmetrical mounting
BIOACTIVE SAPONINS FROM PANAX BIPINNATIFIDUS SEEM. GROWING IN VIETNAM
No full textPanax bipinnatifidus Seem. belonging to the family Araliaceae has been used as a folk medicine in Viet Nam. Our ongoing study on bioactive compounds from Panax bipinnatifidus Seem. collected in Sapa, Lao Cai resulted in the isolation of two saponins together with the well-known saponin Stipuleanoside R2. Their structures were identified as 3-O-β-D-glucopyranosyl-(1→3)-β-D-glucuronopyranosyloleanolic acid (1) and Stipuleanoside R1 (2) based on NMR spectroscopic data as well as comparison with the literature data. For the first time, 3-O-β-D-glucopyranosyl-(1→3)-β-D-glucuronopyranosyloleanolic acid (1) was found in genus Panax. On biological screening, the crude extract and the principal saponin, stipuleanoside R2 showed weak inhibitory effect on markedly nitric oxide production in lipopolysaccharide-treated RAW 264.7 cells
CHEMICAL COMPOSITION OF ESSENTIAL OILS FROM LEAVES OF VITEX NEGUNDO L. GROWING IN VIETNAM AND LARVICIDAL ACTIVITY AGAINST AEDES AEGYPTI L.
No full textAbstract – HCTN7. The leaves of Vitex negundo L. (Verbenaceae) were collected from Dan Nang City and the Pu Hoat Nature Reserve, Nghe An province, and were hydrodistilled to give the essential oils. The leaf oils (six separate samples) were analyzed by gas chromatographic – mass spectrometric methods, and showed very different chemical compositions. The major components in the four essential oils from Da Nang were sabinene (6.0-19.9%), 1,8-cineole (1.6-13.7%), α-terpinyl acetate (1.9-7.8%), (E)-caryophyllene (5.7-18.3%), eremophilene (13.1-33.6%), caryophyllene oxide (4.9-18.1%), and an unidentified diterpenoid (5.2-8.3%); while the major components in the two Pu Hoat samples were sabinene (14.7% and trace), trans-β-elemene (0.2% and 11.1%), (E)-caryophyllene (57.0% and 48.2%), and caryophyllene oxide (5.4% and 3.2%). One sample of V. negundo leaf essential oil from Da Nang and one from Pu Hoat were screened for larvicidal activity against Aedes aegypti, a vector of dengue fever, chikungunya, Zika fever, Mayaro and yellow fever viruses. The Da Nang essential oil showed only marginal larvicidal activity (24-h LC50 = 82.9 μg/mL; 48-h LC50 = 72.2 μg/mL), but the Pu Hoat sample was significantly more active (24-h LC50 = 16.8 μg/mL; 48-h LC50 = 14.2 μg/mL). As a test for pesticidal selectivity, V. negundo leaf oil from Pu Hoat was also screened against the water bug, Diplonychus rusticus, an insect predator of mosquito larvae. The essential oil was significantly less toxic to D. rusticus (24-h LC50 = 136 μg/mL; 48-h LC50 = 134 μg/mL)
Unfolding Band and Absorption Energy Shift of Nano Crystals from First-principles Calculations
No full textPhysical properties of the SiGe alloys ( being the composition of Ge) can be understood and predicted from their electronic band structures. In this paper, electronic band structures of the SiGe alloys are calculated using the first-principles density functional theory. The supper cell approach employed in our calculations leads to folding of electronic bands into the smaller Brillouin zone of the supercell, especially at the point. This often leads to the misinterpretation that the materials have direct band gap. The problem can be resolved by an unfolding band technique which allows us to recover the primitive cell picture of band structure of SiGe. As a result, unfolded electronic bands correctly show an indirect band gap with the valence band maximum (VBM) at the point and the conduction band minimum (CBM) shifted away from . CBM is gradually shifted from a point along symmetry line (associated with Si) to the L point (associated with Ge) with the increased Ge composition and the switching occurs at in the range of 0.60.8 which is in accordance with the calculation using \textbf{\textit{kp}} method. Moreover, the additional electron pockets appear and develop at and . This provides more comprehensive understanding for our recent experimental observations on the shift of the absorption energy assigned to direct transitions within and points in the Brillouin zone of SiGe alloy nanocrystals
Anisotropic Magnetoresistance Effect of Nickel Nanowires
No full textIn this work, we study the magnetic properties of nickel nanowires by measuring their anisotropic magnetoresistance at room temperature. The single nickel nanowire is grown by electrodeposition in a polymer membrane (Polycarbonate). We measure the anisotropic magnetoresistance effect of nickel nanowires for the various values of the magnitudes and orientations of an external magnetic field. The results clearly show the existence the anisotropic magnetoresistance effect in the nickel nanowires. Besides, the experimental data are best fit to the analytical calculations using the Stoner-Wohlfarth model for the magnetization of the wires
SCENARIO ANALYSIS ON ROAD TRANSPORT SERVICE: ENERGY CONSUMPTION AND GHG EMISSIONS
No full textThe aim of this study is to evaluate energy consumption and greenhouse gas (GHG) emissions from Vietnam’s road transport service through establishing scenarios in 2015-2050. Four scenarios are firstly developed toward improving energy efficiency, floating automotive industry strategy and then energy demands, GHG emissions for road transport in these scenarios are estimated. Transport demand, technology penetrative rate, fuel type, fuel economy, emission standard and influence of other factors on emissions are bases of the selected input data. Calculator 2050 is used as a support tool of interface and calculation. The results are shown as following: Energy consumption and GHG emissions of road transport service will reach 11.28 Mtoe and 32.07 MtCO2e in 2030 as well as 36.95 Mtoe and 105.04 MtCO2e in 2050 in basic scenario, respectively, with annual average growth rate reach 6.4%. The contribution to increasing the energy consumption and GHG emissions of freight transport service is higher than that of passenger transport service. In the best case, energy consumption and GHG emissions are reduced by 27.4%, 30.3% in 2030 and 37.8%, 50.7% in 2050 compared to the basic scenario. This reduction is mainly due to the use of alternative fuels/vehicles in these activities
Evaluation of the effect of the concentration of seeding particles on spike-excitation doppler UVP measurement
No full textIn the study of fluid flows, one of the important parameters is the spatial-temporal velocity distribution. Experimental measurement of the parameter is required for the development and validation of various models in this field. Techniques for the measurement of flow velocity at single points have been in operation with great success for many years. However, there are situations where the measured data at one point is obviously not enough to understand structures in, e.g., turbulent/transient flows. One of the well-established and powerful methods for measuring velocity distribution is the UVP - Ultrasonic Velocity Profile method that enables measurements of the instantaneous velocity profile along a measurement line, i.e. the sound path. The new application of spike excitation along with the Doppler signal processing to the UVP method has recently been successfully tested. Regarding this new method, factors influencing the measurement result require further careful investigations. This study addresses, to some extent, the effect of the seeding-particle concentration on the results of spike-excitation UVP measurements. For the investigation, experimental measurements of water pipe flow have been carefully executed for a wide range of the particle concentration. The dependence of the measured data on the particle concentration is evaluated and reported. The result of this study suggests an appropriate range of the seeding-particle concentration in setting up spike-excitation UVP measurements
RESPONSE SURFACE OPTIMIZED EXTRACTION OF TRITERPENOIDS FROM RED VIETNAMESE GANODERMA LUCIDUM AND ANTICANCER EVALUATION OF THE EXTRACT
No full textTriterpenoids are considered to be the major pharmaceutical active compounds found in the macrofungus Ganoderma lucidum (G. lucidum). Extraction conditions of triterpenoids from the Vietnamese red G. lucidum were optimized by response surface methodology using ultrasound –assisted extraction (UAE) method. A Box – Behnken experimental design was used to determine the simultaneous influences of three independent variables, namely solvent-to-material ratio, extraction time, and ultrasonic power on the yield of triterpenoids. The highest yield of triterpenoids obtained under optimum conditions including extraction time of 55 min, ultrasonic power of 480 W, solvent-to-material ratio of 27:1 mL/g was 9.5768 ± 0.228 mg/g according to ultraviolet-visible spectroscopy (UV-Vis) analysis. Besides, the hot water extraction method was carried out in order to compare with UAE in terms of the yield of triterpenoids. The results of anticancer evaluation of the extract obtained indicated that with the half-maximal inhibitory concentration value of 67.25 ± 0.82 µg/mL on the human Hep-G2 liver cancer cell lines, triterpenoids extracted from G. lucidum could be regarded as a potential agent for medicinal treatment