Vietnam Academy of Science and Technology: Journals Online
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Nonlinear vibration of nonlocal strain gradient nanotubes under longitudinal magnetic field
No full textThe nonlinear free vibration of embedded nanotubes under longitudinal magnetic field is studied in this paper. The governing equation for the nanotube is formulated by employing Euler – Bernoulli beam model and the nonlocal strain gradient theory. The analytical expression of the nonlinear frequency of the nanotube is obtained by using Galerkin method and the equivalent linearization method with the weighted averaging value. The accuracy of the obtained solution has been verified by comparison with the published solutions and the exact solution. The influences of the nonlocal parameter, material length scale parameter, aspect ratio, diameter ratio, Winkler parameter and longitudinal magnetic field on the nonlinear vibration responses of the nanotubes with pinned-pinned and clamped-clamped boundary conditions are investigated and discussed
FUZZY DISTANCE-BASED FILTER-WRAPPER INCREMENTAL ALGORITHMS FOR ATTRIBUTE REDUCTION WHEN ADDING OR DELETING ATTRIBUTE SET
No full textAttribute reduction is a critical problem in the data preprocessing step with the aim of minimizing redundant attributes to improve the efficiency of data mining models. The fuzzy rough set theory is considered an effective tool to solve the attribute reduction problem directly on the original decision system, without data preprocessing. With the current digital transformation trend, decision systems are larger in size and updated. To solve the attribute reduction problem directly on change decision systems, a number of recent studies have proposed incremental algorithms to find reducts according to fuzzy rough set approach to reduce execution time. However, the proposed algorithms follow the traditional filter approach. Therefore, the obtained reduct is not optimal in both criteria: the number of attribute of the reducts and the accuracy of classification model. In this paper, we propose incremental algorithms that find reducts following filter-wrapper approach using fuzzy distance measure in the case of adding and deleting attribute set. The experimental results on the sample datasets show that the proposed algorithms significantly reduce the number of attributes in reduct and improve the classification accuracy compared to other algorithms using filter approac
EXTRACTION AND PHYSICO-CHEMICAL CHARACTERIZATION OF WATER-SOLUBLE POLYSACCHARIDES FROM OPUNTIA DILLENII (KER GAWL.) HAW. CLADODES
No full textOpuntia dillenii (Ker Gawl.) Haw., a well-known member of the Cactaceae family, played an important role in agriculture and medicine. In this study, the extraction conditions and the physico-chemical properties of water-soluble polysaccharides (OMP) from Opuntia dillenii mucilage were investigated. The cactus cladodes used in the study were collected from Binh Thuan province, Vietnam. The optimum extraction conditions of water extraction with conventional heating included at temperature 70oC in 120 min. The crude and deproteinized polysaccharides yield were 17.7 % and 7.9 %. By analysis of gel permeation chromatography (GPC), the study showed that the polysaccharides possessed a low average molecular weight (129,681 Da). In addition, the characterization of polysaccharide was determined by Fourier-Transform Infrared Spectroscopy (FTIR), and High-Performance Liquid Chromatography (HPLC). The results indicated that the types of sugars in the water-soluble polysaccharides extracted
INVESTIGATION OF ANTI-HELICOBACTER PYLORI ACTIVITY AND CHEMICAL CONSTITUENTS OF LUDWIGIA HYSSOPIFOLIA
No full textHelicobacter pylori (H. pylori) is considered as the main cause of peptic ulcer and gastric carcinoma. Due to the growing trend of antimicrobial resistance, the control of H. pylori infections need to be recommended. Recently, screening for natural sources with potential antimicrobial activity is a strong demand. Ludwigia hyssopifolia was traditionally used so far for treatment of H. pylori infection in Mekong Delta region of Vietnam. In this study, the five extracts of Ludwigia hyssopifolia including n-hexane, chloroform, ethyl acetate, methanol and ethanol ones were screened for anti H. pylori activity by disk diffusion method. The preliminary results showed that all these five extracts displayed a moderate activity in which the methanol one exhibited a stronger activity with the inhibition zone (d = 17 mm) at the concentration of 0.5 mg/disk. Phytochemical study on the bioactive methanol extract led to the isolation of four known compounds as β-sitosterol (1), oleanolic acid (2), 3-O-β-D-glucopyranosyl-β-sitosterol (3), and ellagic acid (4). Their structures were elucidated by spectroscopic methods including 1D and 2D-NMR and in comparison with literature data
DIFFERENTIATION OF VIETNAMESE COFFEE ORIGIN AND CULTIVARS BY AMINO AND FATTY ACID PROFILE ANALYSIS PRELIMINARY STUDY
No full textCompositions of fatty acids and amino acids compound were investigated in coffee beans included Arabica and Robusta cultivars grown in three region of Vietnam. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were performed on the complete data set to reveal chemical differences among all samples and identify markers characteristic of a particular botanical geographical origin of the coffee. The major fatty acids in the coffee oil analyzed in this study were linoleic acid (C18:2), stearic acid (C18:0), oleic acid (C18:1) palmitic acid (C16:0) and myristic acid (C14:0), followed by small amounts of arachic acid (C20:0), docosanoic acid (C22:0) and eicosenoic acid (C20:1). Glutamic acid and aspartic acid were found at high amount in robusta coffee, from 271 mg/100gDW to 786 mg/100g DW and 373mg/100g DW to 486 mg/100g DW, respectively, whereas alanine and glutamic acid in arabica coffee were in high amount at 268 mg/100g DW to 351 mg/100g DW and 209 mg/100g DW to 285 mg/100g DW, respectively. Leucine (301 to 416 mg/100 g DW), phenylalanine (226 to 305 mg/100 g DW), and lysine (199 to 269 mg/100 g DW). PCA of the complete data matrix demonstrated that there were significant differences among all coffee cultivars and geographical origin, HCA supported the results of PCA and achieved a satisfactory classification performance
STRUCTURE AND BIOLOGICAL ACTIVITY OF FIVE FLAVO-NOIDS FROM AMPELOPSIS CANTONIENSIS
No full textIn this paper, phytochemical studied on ethanol extract of Ampelopsi cantoniensis led to obtain five flavonoid compounds: myricitrin, myricetin, quercetin, dihydromyricetin, and phloretin. Their structure was confirmed by NMR and ESI-MS methods. Antioxidant and anti-diabetic activities of the compounds were evaluated. The results showed that all five flavonoids have strong DPPH radical scavenging activity with SC50 values ranging from 9.42–35.37 μM. Four of them (myricetin, phloretin, myricitrin and quercetin) are strong α-glucosidase and α-amylase inhibitors with IC50 values ranging from 8.92–18.74 µM for α-glucosidase inhibition and from 9.64 – 136.58 µM for α-amylase inhibition
Estimation of the spawning ground of some fish species in the Nha Trang bay
No full textThe paper presents the results of determining the spawning grounds of some fish species in Nha Trang bay MPA, which were sampled in 9/2018, 11/2018, 5/2019 and 7/2019. The analysis results are based on the distribution of the general density and the developmental stages, analysis of decision trees from egg density, location of stations and months by CHAID (Chi-square Automatic Interaction Detector), allowing a relatively accurate estimate of the spawning ground of the red anchovy (Encrasicholina punctifer Fowler, 1938) and the species of the genus Scarus. As a result, the main spawning grounds for red anchovy were the east of Hon Rua and the northeast of Hon Tam and that of Scarus is the southwest of Hon Mun island
Genome mining of a marine-derived Streptomyces sp. PDH23 isolated from sponge in Da Nang sea for secondary metabolite gene clusters
No full textThe streptomyces is one of the best characterized ubiquitous filamentous bacteria from the actinobacteriaclass. They are known to produce thousands of specialized metabolite biosynthesis gene clusters (SMBG). Their SMBG clusters have multiple activities ranging from antimicrobial, antitumor, antiviral and probiotic. Streptomyces strain and their isolates with interesting biological activities against gram-positive and gram-negative indicator strains was recently characterised. Currently, they are employed in more than half of all antibiotics used in human and veterinary medicine. With the increase in drug resistance bacteria, it is important to mine for new natural chemicals.In this study, screening via disk-diffusion agar method revealed that Streptomyces sp. PDH23 isolated from the Rhabdastrellaglobostellata marine sponge sample from Da Nang, Vietnam produce antimicrobial agents with a wide spectrum of activities. This species can produce highly active enzymes, which breakdown celluloses, amyloses and proteins. On top of that they are shown to restrict the grow of the gram positive Bacillus cereus ATCC14579 (BC), Staphylococcus aureus ATCC25923 (SA), the gram-negativeVibrio parahaemolyticus ATCC17802 (VP) and the Candida albicans ATCC10231 fungus (CA). They are antimethicillin-resistant S. aureus(MRSA) ATCC33591 andmethicillin-resistantS. epidermidis (MRSE) ATCC35984. The taxonomy of PDH23 was characterized using 16S rRNA analysis. Whole genome sequencing of PDH23 showed 8594820 base pairs with GC content of 72.03%. Mining of secondary metabolites reveals gene clusters responsible for the biosynthesis of known and/or novel secondary metabolites, including different types of terpene, NRPS-like , PKS, PKS-like, hglE-KS, betalactone, melanin, t1pks, t2pks, t3pks, nrps, indole, siderophore, bacteriocin, ectoine, butyrolactone, phenazine
Seasonal change in growth rate, carrageenan yield and quality from the red alga (Kappaphycus striatus) cultivated in Cam Ranh bay
No full textThe red alga Kappaphycus striatus was cultivated at Camranh Bay, KhanhHoa, Vietnam. For a 30 day cultivation period, the alga showed the higher growth rate (4.1 - 5.8 % day-1) from October 2014 to April 2015 and in September 2015, while the lower growth rate (2.5 - 3.1 % day-1) was found from May to August 2015. The carrageenan quality was done for a 60-day cultivation period, the carrageenan yield and gel strength showed little variation with the higher values (28.1 - 28.7 % and 855 - 935 g cm-2, respectively) obtained from November 2014 to March 2015 and lower ones (25.1 - 26.7 % and 555 - 758 g cm-2, respectively) from April to September 2015. The data on moisture content of alga (33.5 - 36.8 %), clean anhydrous algal/salt ratio (0.92 - 1.07), and carrageenan yield obtained in this study fulfilled those of standards for carrageenophytes. This study shows that the red alga K. striatus can be grown in the tropical waters of the Camranh Bay during the northeast monsoon and a part of the southwest monsoon as a source of materials for carrageenan production
DEVELOPING AND VALIDATING A GT-SUITE BASED MODEL FOR A SECOND GENERATION COMMONRAIL SOLENOID INJECTOR
No full textCấu hình phun, chứa các thông số quan trọng như tốc độ phun, ảnh hưởng trực tiếp đến cấu trúc phun, chất lượng hỗn hợp nhiên liệu-không khí, cũng như các quá trình vật lý và hóa học xảy ra trong buồng đốt của động cơ vi mạch. Do đó, cấu hình phun là một trong những chìa khóa để cải thiện công suất, hiệu suất nhiệt và giảm thiểu phát thải cho động cơ vi mạch. Trong bài báo này, một mô hình mô phỏng dựa trên GT-SUITE cho một kim phun điện từ chung thế hệ thứ hai thường được sử dụng trong động cơ diesel Hyundai 2.5 TCI-A, đã được phát triển và xác nhận thành công. Việc xác nhận được thực hiện bằng cách sử dụng dữ liệu thử nghiệm do Máy phân tích tiêm dựa trên phương pháp của Zeuch (UniPg STS) ở Đại học Perugia, Ý. Dữ liệu hiệu chuẩn được đo trên một phạm vi rộng của áp suất đường ray và thời gian cấp điện tương ứng với điều kiện hoạt động của động cơ. Kết quả cho thấy mô hình kim phun được phát triển ở đây là đáng tin cậy và phù hợp để kiểm tra các đặc tính thủy lực của kim phun. Sự khác biệt về giá trị bắt đầu phun thu được thông qua thí nghiệm và mô phỏng chỉ khoảng 15 µs. Tổng khối lượng phun thu được thông qua thí nghiệm và mô phỏng trong ET = 0,6 ms là ít hơn 10% trong khi sự khác biệt là khá cao khi ET 0,6 ms và áp suất đường sắt cao (lên đến 34,5%)