Vietnam Journal of Science and Technology

The dynamic vibration absorber (DVA) has been widely applied in various technical fields. This paper presents a  procedure for designing the optimal parameters of  a dynamic vibration absorber attached to a damped primary system. The values of the optimal parameters of the DVA obtained by the Taguchi’s method are compared by the results obtained by other methods. The comparison results show the advantages of the procedure presented in this study

A novel ZnBi2O4/rGO hybrid catalysts had been synthesized by a simple precipitation method. The crystallinity, structural, and morphological features were studied by XRD, FE-SEM and UV-Vis diffused reflectance  techniques. The photocatalytic activity of ZnBi2O4/rGO catalysts were evaluated by degradation of Indigo Carmine dye under visible-light irradiation. The enhancement of photocatalytic properties of ZnBi2O4/rGO attributed to the synergistic effect between ZnBi2O4 and rGO, which effectively separation of the photogenerated electron-hole pairs in ZnBi2O4. Moreover, the obtained ZnBi2O4/rGO displayed high chemical stability after four consecutive experiments under visible light.

In the paper, the program motion of an unloading manipulator which is treated as a first integral of the considered system, is investigated. Currently, the popular way to solve such problem is the method of Lagrange multipliers. In the paper, the authors use another approach, the Priciple of Compatibility, in which the required program is treated as one of motion equations of the system. In the particular case, the program is considered as one of first integrals of the system. For illustrating the proposed method, the motion of an unloading manipulator of three degrees of freedom is considered.

The application of raw-starch hydrolysis enzymes to ethanol production by no-cook technology at very high gravity (VHG) (311.5 g/L) from rice would reduce the energy consumption compared to traditional process. In this study, the Taguchi design and the desirability function were used to identify the optimized production process for economic and technological targets. Three factors: dosage of alpha- and gluco-amylase enzyme (Stargen 002 – A), dosage of protease enzyme (Fermgen – B) and dosage of yeast (C) were investigated. With the expected Desirability = 0.74, the no-cook process from rice would be optimized with following dosage: Stargen 002, Fermgen and yeast at 700 µL/L (1140 GAU/kg raw material), 151 µL/L (431 SAPU/kg raw material) and 0.25 g/L (6.25 x 106 cells/mL), respectively. After 120h of fermentation, ethanol concentration reached 17.45 ± 0.07 %v/v, corresponding to ethanol yield of 86.08 ± 0.2 %, and the cost of raw material was at 3225.5 VND/L of rice slurry.

In this work, nano silver catalyst loaded on vanadium phosphorus oxide (Ag/VPO) for oxidation of styrene to benzaldehyde was synthesized by impregnating method including impregnating of VPO substrate with colloid solution of nano silvers. VPO substrate was prepared by microwave-assisted reaction of vanadium and phosphorus precursors. Meanwhile, nano Ag/PVP was prepared in solution using NaBH4 as reducing agent and polyvinylpyrrolidone (PVP) as protecting agent and spherical-shaped nano particles with mean diameter of about 7.5 nm determined by transmission electron microscopy (TEM) was obtained. 

Amine-SiO2 material was synthesized and applied as a novel adsorbent for nitrate and phosphate removal from aqueous solution. The characterization of Amine-SiO2 were done by using TGA, FTIR, BET, and SEM analyses. Results showed that Amine-SiO2 had higher nitrate and phosphate adsorption capacity of 1.14 and 4.16 times, respectively, than commercial anion exchange resin (Akualite A420). In addition, Amine-SiO2 also had good durability with stable performance after at least 10 regeneration times, indicating that this material is very promising for commercialization in the future as an adsorbent for water treatment.

Two Nguyenibacter vanlangensis strains TN01LGIT and VTH-AC01 isolated by an enrichment approach using nitrogen free LGI medium from Asian rice isolation sources are expected as an additional PGPB within the Acetobacteraceae family. In this study, nitrogen fixing capability of the two N. vanlangensis strains was confirmed through nitrogenase activity’s detection by acetylene reduction analysis...

Purple nonsulfur bacteria are a group that has so much biotechnological applications, particularly in producing of functional food rich with unsaturated fatty acids. A purple nonsulfur bacterium (named HPB.6) was chosen based on its strong growth, high lipid and synthesis of unsaturated fatty acid (omega 6,7,9). Studying on basic biological characteristics showed that the cells of HPB.6 were observed as ovoid-rod shape, none motility, Gram negative staining. The diameter of single bacterium was about 0.8-1.0 µm. The cells divide by binary fission and had bacteriochlorophyll a (Bchl a). This bacterium grew well on medium with carbon and nitrogen sources such as acetate, succinate, pyruvate, butyrate, glutamate, arginine, leucine, tyrosine, alanine, methionine, threonine, glutamine, yeast extract and NH4Cl. This selected strain grew well on medium with salt concentrations from 1.5 - 6.0% (optimum 3%), pH from 5.0 to 8.0 (optimum at pH 6.5) and could withstand Na2S at 4.0 - 5.2 mM. Based on morphological, physiological properties and 16S rRNA analysis received demonstrated that HPB.6 strain belongs to the species Rhodovulum sulfidophilum.

Trong bài báo này, bài toán tối ưu tần số dao động tự do của trục chịu xoắn sử dụng nguyên lý cực đại Pontryagin, một nguyên lý điều khiển tối ưu, được trình bày. Trong đó, biến điều khiển là đường kính của các đoạn trục, hàm mục tiêu chứa các tần số dao động tự do của trục. Các biến đổi trong bài báo cho phép xác định dấu của hệ số tỉ lệ trong điều kiện cần tối ưu của bài toán. Cấu hình tối ưu và tần số tối ưu của trục được khảo sát với các trường hợp tối ưu tần số thứ nhất và thứ hai.

In recently, large capacity steam turbines have come into wider use and have been designed to ever higher performance specifications. As we all know, it’s hard to maintain the concentricity of a rotor-bearing system during operating, especially for multi-rotors within specified level of vibration. Rotor vibration could be caused by many reason, mass unbalance and bent shaft are amongst almost frequently occurring. Mass unbalance and bent shaft both give to force excitation at a frequency corresponding to once per revolution. Taking a LP B rotor of a 1000MW USC steam turbine as an example, this paper studies the lateral vibration of the LP B rotor based on finite element. Responses of mass unbalance and bent shaft are analyzed and compared.