检索结果-南通市图书馆

Optimum Determination of Partial Transmission Ratios of Mechanical Driven Systems Using a V-belt and a Three-Step Helical Gearbox

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

Journal of Environmental Science and Engineering(B) 2017年第6期6卷 328-331页

作者： Dang anh Tuan Nguyen Khac Tuan vu Ngoc Pi Mechanical Engineering Faculty Thai Nguyen University of Technology Thai Nguyen 23000 Vietnam Automotive and Power Machinery Faculty Thai Nguyen University of Technology Thai Nguyen 23000 Vietnam

This paper introduces a new study on the optimum calculation of partial transmission ratios of a mechanical drive system using a V-belt and a three-step helical gearbox in order to get the minimum size of the system. The chosen objective function was the cross section dimension of the system. In solving the optimization problem, the design equation for pitting resistance of a gear set was investigated and equations on moment equilibrium condition of a mechanic system including a V-belt and three helical gear units and their regular resistance condition were analysed. From the results of the study, effective formulas for determination of the partial ratios of the V-belt and three-step helical gearboxes were introduced. As using explicit models, the partial ratios can be determined accurately and simply.

关键词： Transmission ratio gearbox design optimum design V-belt drive helical gearbox.

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

人民币升值对越中贸易影响研究

人民币升值对越中贸易影响研究

作者： BUI hai anh 北京交通大学

学位级别：硕士

越中两国是山水相连的友好邻邦,传统友谊源远流长。越中边境贸易历史悠久,特别是1991年越中关系正常化后,两国经贸合作关系恢复和迅速发展,双边贸易发展势头强劲。越中双边贸易额1991年为3200万美元,2012年已突破410亿美元,增长1000多... 详细信息

越中两国是山水相连的友好邻邦,传统友谊源远流长。越中边境贸易历史悠久,特别是1991年越中关系正常化后,两国经贸合作关系恢复和迅速发展,双边贸易发展势头强劲。越中双边贸易额1991年为3200万美元,2012年已突破410亿美元,增长1000多倍。但越中贸易极不平衡,中国既是越南最大的贸易伙伴,也是越南最大的贸易逆差国。中国出口越南的商品中85%为机械制造设备,而越南出口到中国的主要是农产品和资源性产品。未来随着人民币的升值,是否会改变这种格局?本文运用实证分析和规范分析相结合的方法,着重研究人民币升值对越中贸易的影响,这些影响对两国的对外贸易政策提出建议。研究结果表明,人民币升值并未改变越中贸易基本格局。越中两国贸易经过近几十年发展,形成了越方出口初级农产品到中国,换取工业制成品的基本格局,由于越方对中方贸易依赖度高,对中国贸易产品需求弹性小,因此越方贸易逆差,并且逆差额越来越大。但是人民币升值将强化越中垂直分工体系。由于货币贬值,越南对中国出口的初级农产品、资源产品竞争力加大,因此多年来规模不断扩大,相应的产业部门不断扩大;当越南从出口初级农产品、资源产品中换取越来越多的外汇时,可以进一步增加对中国工业制造品的进口需求,因此使两国垂直分工体系得到强化。最后,论文总结了人民币升值背景下越中贸易存在的问题,并针对问题对两国提出了相应的政策建议。

关键词：人民币升值国际贸易越中贸易

Evaluation of Interaction between Surface Water and Groundwater in the South of Hanoi City by Stable Isotope Technique

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

Journal of Environmental Protection 2022年第11期13卷 870-880页

作者： Vo Thi anh Tran Khanh Minh Ha Lan anh Mai Dinh Kien vu Hoai Dang Duc Nhan Institute for Nuclear Science and Technology Hanoi Vietnam

The δ18O and δ2H stable isotope techniques for studying properties of groundwater and surface help us to understand more clearly about the distribution and movement of groundwater in the South of Hanoi area. There were 68 water samples from the studying area and analyzed by a Liquid Water Isotope Analyzer (LWIA-24D). The stable isotope values of the groundwater from Pleistocene aquifers were range from -3.21‰ to -9.55‰ δ18O and -35.32‰ to -67.44‰ δ2H;rainwater from -8.18‰ to -4.13‰ δ18O and -61.19‰ to -17.93‰ δ2H;Red river water from -7.51‰ to -5.29‰ δ18O and -51.60‰ to -38.99‰ δ2H. Based on stable isotope characteristics, the results show that there was a relationship between surface water and groundwater in the South of Hanoi city. It is that groundwater recharges for river water in the dry season with 74%, and in the rainfall season groundwater is recharged from river with 87%.

关键词： Stable Isotopes Groundwater Surface Water River Water Precipitation Recharge

Xanthine oxidase inhibitors from Archidendron clypearia(Jack.) I.C. Nielsen: Results from systematic screening of Vietnamese medicinal plants

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Asian Pacific Journal of Tropical Medicine 2017年第6期10卷 619-626页

作者： Nguyen Thuy Duong Pham Duc Vinh Phuong Thien Thuong Nguyen Thi Hoai Le Nguyen Thanh Tran The Bach Nguyen hai Nam Nguyen Hoang anh Department of Pharmacology Hanoi University of Pharmacy Department of Pharmaceutical Analysis and Standardization National Institute of Medicinal Materials Department of Pharmacognosy Hue University of Medicine and Pharmacy Institute of Marine Biochemistry Vietnam Academy of Science and Technology Institute of Ecology and Biological Resources Vietnam Academy of Science and Technology Department of Medicinal Chemistry Hanoi University of Pharmacy

Objective: To screen Vietnamese medicinal plants for xanthine oxidase(XO) inhibitory activity and to isolate XO inhibitor(s) from the most active plant. Methods: The plants materials were extracted by methanol. The active plant materials were fractionated using different organic solvents, including n-hexane, ethyl acetate, and n-butanol. Bioassay-guided fractionation and column chromatography were used to isolate compounds. The compounds structures were elucidated by analysis of spectroscopic data, including IR, MS, and NMR. Results: Three hundreds and eleven methanol extracts(CME) belonging to 301 Vietnamese herbs were screened for XO inhibitory activity. Among these plants, 57 extracts displayed XO inhibitory activity at 100 μg/m L with inhibition rates of over 50%. The extracts of Archidendron clypearia, Smilax poilanei, Linociera ramiflora and Passiflora foetida exhibited the greatest potency with IC_(50) values below 30 μg/m L. Chemical study performed on the extract of Archidendron clypearia resulted in the isolation of six compounds, including 1-octacosanol, docosenoic acid, daucosterol, methyl gallate, quercitrin and(-)-7-O-galloyltricetiflavan. The compound(-)-7-O-galloyltricetiflavan showed the most potent XO inhibitory activity with an IC_(50) value of 25.5 μmol/L. Conclusions: From this investigation, four Vietnamese medicinal plants were identified to have XO inhibitory effects with IC_(50) values of the methanol extracts below 30 μg/m L. Compound(-)-7-O-galloyltricetiflavan was identified as an XO inhibitor from Archidendron clypearia with IC_(50) value of 25.5 μmol/L.

关键词： Xanthine oxidase Inhibitor Medicinal plants Vietnam

Improved flood susceptibility mapping using a best first decision tree integrated with ensemble learning techniques

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Geoscience Frontiers 2021年第3期12卷 333-342页

作者： Binh Thai Pham Abolfazl Jaafari Tran Van Phong Hoang Phan hai Yen Tran Thi Tuyen vu Van Luong Huu Duy Nguyen Hiep Van Le Loke Kok Foong University of Transport Technology Ha Noi 100000Viet Nam Research Institute of Forests and Rangelands Agricultural ResearchEducation and Extension Organization(AREEO)TehranIran Institute of Geological Sciences Vietnam Academy of Sciences and Technology84 Chua Lang StreetDong daHa NoiViet Nam Department of Geography School of Social EducationVinh UniversityViet Nam Department of Resource and Environment Management School of Agriculture and ResourcesVinh UniversityViet Nam Faculty of Geography VNU University of Science334 Nguyen TraiHa NoiViet Nam Institute of Research and Development Duy Tan UniversityDa Nang 550000Viet Nam Department for Management of Science and Technology Development Ton Duc Thang UniversityHo Chi Minh CityViet Nam Faculty of Civil Engineering Ton Duc Thang UniversityHo Chi Minh CityViet Nam

Improving the accuracy of flood prediction and mapping is crucial for reducing damage resulting from flood *** this study,we proposed and validated three ensemble models based on the Best First Decision Tree(BFT)and the Bagging(Bagging-BFT),Decorate(Bagging-BFT),and Random Subspace(RSS-BFT)ensemble learning techniques for an improved prediction of flood susceptibility in a spatially-explicit manner.A total number of 126 historical flood events from the Nghe An Province(Vietnam)were connected to a set of 10 flood influencing factors(slope,elevation,aspect,curvature,river density,distance from rivers,flow direction,geology,soil,and land use)for generating the training and validation *** models were validated via several performance metrics that demonstrated the capability of all three ensemble models in elucidating the underlying pattern of flood occurrences within the research area and predicting the probability of future flood *** on the Area Under the receiver operating characteristic Curve(AUC),the ensemble Decorate-BFT model that achieved an AUC value of 0.989 was identified as the superior model over the RSS-BFT(AUC=0.982)and Bagging-BFT(AUC=0.967)models.A comparison between the performance of the models and the models previously reported in the literature confirmed that our ensemble models provided a reliable estimate of flood susceptibilities and their resulting susceptibility maps are trustful for flood early warning systems as well as development of mitigation plans.

关键词： Machine learning Ensemble learners Hybrid modeling

Optimum Determination of Partial Transmission Ratios of Mechanical Driven Systems Using a Chain Drive and a Two-step Helical Gearbox

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Journal of Environmental Science and Engineering(B) 2017年第2期6卷 80-83页

作者： vu Ngoc Pi Tran Thi Phuong Thao Dang anh Tuan Mechanical Engineering Faculty Thai Nguyen University of Technology Thai Nguyen 250000 Vietnam

This paper presents a study on optimum determination of partial ratios of mechanical drive systems using a chain drive and two-step helical gearbox for getting minimum size of the system. The chosen objective function was the cross section dimension of the system. In solving the optimization problem, the design equation for pitting resistance of a gear set was investigated and equations on moment equilibrium condition of a mechanic system including a chain drive and two helical gear units and their regular resistance condition were analyses. From the results of the study, effective formulas for determination of the partial ratios of the chain drive and two-step helical gearboxes were introduced. As the formulas are explicit, the partial ratios can be calculated accurately and simply.

关键词： Gearbox design optimum design helical gearbox chain drive transmission ratio.

Investigation of Polymorphisms in Coding Region of OsHKT1in Relation to Salinity in Rice

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Rice science 2016年第6期23卷 334-338页

作者： pham quynh-hoa tran xuan-an nguyen thi-nha-trang tran thi-thuy-anh hoang hai-yen nguyen thi-hong-van tang thi-hanh do thi-phuc Faculty of Biology VNU University of ScienceHanoi334 Nguyen TraiThanh XuanHanoiVietnam Faculty of Agronomy Vietnam National University of AgricultureNgo Xuan Quang StreetTrau QuyGia LamHanoiVietnam

Rice （Oryza sativa） is sensitive to salinity, but the salt tolerance level differs among cultivars,which might result from natural variations in the genes that are responsible for salt tolerance. High-affinitypotassium transporter （HKTs） has been proven to be involved in salt tolerance in plants. Therefore, wescreened for natural nucleotide polymorphism in the coding sequence of OsHKT1, which encodes the HKTprotein in eight Vietnamese rice cultivars differing in salt tolerance level. In total, seven nucleotidesubstitutions in coding sequence of OsHKT1 were found, including two non-synonymous and five synonymoussubstitutions. Further analysis revealed that these two non-synonymous nucleotide substitutions （G50Tand T1209A） caused changes in amino acids （Gly17Val and Asp403Glu） at signal peptide and the loop ofthe sixth transmembrane domain, respectively. To assess the potential effect of these substitutions on theprotein function, the 3D structure of HKT protein variants was modelled by using PHYRE2 webserver. Theresults showed that no difference was observed when compared those predicted 3D structure of HKTprotein variants with each other. In addition, the codon bias of synonymous substitutions cannot clearlyshow correlation with salt tolerance level. It might be interesting to further investigate the functional roles ofdetected non-synonymous substitutions as it might correlate to salt tolerance in rice.

关键词： polymorphism salt stress OsHKT1 gene rice

Characteristics of Suspended Particulate Matter and the Coastal Turbidity Maximum Areas of the Mekong River

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Journal of Environmental Science and Engineering(A) 2015年第2期4卷 67-78页

作者： vu Duy Vinh Tran anh Tu Tran Dinh Lan Nguyen Ngoc Tien Institute of Marine Environment and Resources Vietnam Academy of Science and Technology Haiphong 35999 Vietnam Institute of Marine Geology and Geophysics Vietnam Academy of Science and Technology Hanoi 10999 Vietnam

This paper presents the results of application of a 3D （three-dimensional） numerical model to study on MTZ （maximum turbidity zone） in the coastal zone of Mekong River Delta. In this study, a 3D system model with combination of hydrodynamics--wave and suspended sediment transport was set up and validated with measured data in the study area. Based on calculated scenarios for the flood and the dry season, the results have shown appearance of MTZs in the coastal zone of Mekong River with suspended sediment concentration prevalent of 0.04-0.07 kg·m^3 （the dry season） and 0.05-0.1kg·m^3 （the flood season）. The position and MTZs scale change with the interaction between fresh water and tidal oscillations. The MTZ occur more in the dry seasons compared to the wet season. The MTZs are prevalent located far away from estuaries about in 12-22 km （in the dry season）, and 5-15 km in the flood season.

关键词： Modelling maximum turbidity zone suspended sediment transport Me Kong river coastal area.

Research on Subcontractor Risk of EPC Hydropower Project in Vietnam

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

World Journal of Engineering and Technology 2019年第1期7卷 54-67页

作者： Dinh Bui Sy Hung Mai Huu hai vu Department of Construction Management Can Loc Committee Ha Tinh Vietnam Department of Hydraulic Engineering and Construction National University of Civil Engineering Hanoi Vietnam

Engineering, procurement and construction (EPC) contracts are becoming the most popular form to undertake construction works on large-scale hydropower projects.?The EPC general contractors in Vietnam have been coped with lots of difficulties during the construction phase of hydropower projects, resulting in significant schedule delays and cost overrun. One of the reasons is poor Subcontractors capacity.?In order to overcome above, the current study attempts?to research on identification and control Subcontractors risks of delay process of EPC hydropower project in Vietnam.?Through summarizing international research achievements of previous researches relating on EPC hydropower projects combining with analysis characteristics of developing construction of EPC hydropower projects in Vietnam, the current study pointed out all kinds of subcontractor risk of delay process of EPC hydropower project in Vietnam;?a questionnaire with 18 risk elements was designed and then delivered to experts in EPC hydropower project management area. Based on the risk model, 11 main risk elements were identified which can be categorized into 3 groups.?Lastly, the current study proposed suggestions to reduce or avoid risks as well as approach to control risks.?Furthermore, the findings of this study can be a good managerial reference for project management teams who are working in other countries that have similar economic and investment environment to Vietnam to get their EPC construction project completed on schedule, thus ensuring the benefits to the government, the investor, the contractor, and the parties involved.

关键词： EPC Hydropower Project Risk Analysis and Evaluation Risk Control Prevent Risks