检索结果-南通市图书馆

The use of spermatogonial stem cells to correct a mutation causing meiotic arrest

在线全文

学校读者我要写书评

暂无评论

Asian Journal of Andrology 2021年第6期23卷 600-601页

作者： Qijing Lei Geert Hamer Center for Reproductive Medicine Reproductive Biology LaboratoryAmsterdam Reproduction and Development Research InstituteAmsterdam UMCLocation AMCUniversity of AmsterdamMeibergdreef 9Amsterdam 1105 AZThe Netherlands

The basis of life-long spermatogenesis is spermatogonial stem cells (SSCs) located at the basal membrane of the seminiferous tubules in the testis. After several rounds of proliferation and spermatogonial differentiation, the male germ cells will eventually undergo meiosis to form haploid spermatids. Disturbance of the molecular regulation of spermatogenesis can lead to spermatogenic arrest, in humans often during meiosis,1,2 and subsequent azoospermia. Unfortunately, no treatment option enabling conception of a genetically own child is currently available for men suffering from spermatogenic arrest before spermatids are formed.

关键词： eventually arrest sperma

Note on the Stability of a Slowly Rotating Timoshenko Beam with Damping

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Advances in Applied Mathematics and Mechanics 2015年第6期7卷 736-753页

作者： J.Wo´zniak M.Firkowski Institute of Mathematics University of SzczecinWielkopolska 1570-451 SzczecinPoland Department of Mathematics and Physics University of SzczecinWielkopolska 1570-451 SzczecinPoland

This paper continues the senior author’s previous investigation of the slowly rotating Timoshenko beam in a horizontal plane whose movement is controlled by the angular acceleration of the disk of the driving motor into which the beam is rigidly *** was shown before that this system preserves the total *** consider the problem of stability of the system after introducing a particular type of *** show that the energy of only part of the system *** illustrate obtained solution with the critical case of the infinite value of the damping coefficient.

关键词： Timoshenko beam stability transfer function

MICROSTRUCTURE AND MECHANICAL BEHAVIOR OF Nb-(10, 15)A1-20V ALLOYS

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2004年第4期17卷 575-583页

作者： H.S.Jiao F.Barradas T.S.Rong I.P.Jones M.Aindow Department of Metallurgy and Materials University of Birmingham B15 2TT UKDepartment of Metallurgy and Materials University of Birmingham B15 2TT UKDepartment of Metallurgy and Materials University of Birmingham B15 2TT UKDepartment of Metallurgy and Materials University of Birmingham B15 2TT UKDepartment of Metallurgy and Materials Engineering Institute of Materials Science University of Connecticut CT 06269-3136 USA

Compression tests at room and high temperature and creep tests at high temperature have been performed on B2 Nb15A120V and Nb10Al20V alloys. At room temperature, in the as-cast state, both alloys exhibited significant ductility in compression. The Burgers vectors of the dislocations were found to be 1/2lipping on {112}. The dislocations showed good mobility. Dislocation clusters also triggered the formation of pseudotwins, which resulted in serrated yielding. In steady state creep, deformation occurred by a combination of dislocation glide and climb, giving a homogeneous mi-crostructure. The dislocations in NblOAl20V were determined to be 1/2(111) slipping on {110} with some egments. After creep at 1100℃, Nb 15A120V showed a two phase structure with a few dislocations in the A15 phase but no dislocations in the A2 phase.

关键词： dislocation pseudotwin NbAlV alloy creep

Aerodynamic Cost of Flapping

在线全文

学校读者我要写书评

暂无评论

Journal of Bionic Engineering 2015年第1期12卷 61-69页

作者： Gottfried Sachs Institute of Flight System Dynamics Technische Universitat München Boltzmannstr. 15 85748 Garching Germany

A new modeling approach is presented for mathematically describing the drag due to wing flapping. It is shown that there is an aerodynamic cost of flapping in terms of an increase in the drag when compared with non-flapping. The drag increase con- cerns the induced drag which results from lift generation. There are two effects that yield the induced drag increase caused by flapping. The first effect is due to changes in the direction of the lift vectors at the left and right wings during the flapping cycle by tilting them according to the flapping angle of the wings. Because of tilting the lift vectors, more lift has to be generated than is required for the vertical force balance in flapping flight. This lift enlargement causes an increase of the induced drag. The second effect that increases the induced drag is due to changes in the magnitude of the lift vector in the course of the flapping cycle. Changes in the magnitude of the lift vector are necessary for generating thrust which is required for the longitudinal force balance. As a result, both effects of lift vector changes cause a drag increase when compared with non-flapping. Solutions on an analytical basis and as well as results using a computational fluid dynamics method are presented.

关键词： wing flapping induced drag lift vector tilting lift vector magnitude change

DEM simulations of die filling during pharmaceutical tabletting

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2008年第6期6卷 412-418页

作者： Chuan-Yu Wu School of Chemical Engineering University of Birmingham Edgbaston Birmingham B15 2TT UK

The flow behaviour of powders from a stationary shoe into a moving die, which mimics the die filling process in a rotary tablet press, was analysed using a discrete element method （DEM）, in which 2D irregular shaped particles were considered. The influence of the particle shape, size and size distribution, the number of particles used in the simulation, the initial height of powder bed in the shoe, and the filling speed on the average mass flow rate and the critical filling speed （the highest speed at which the die can be completely filled） were explored. It has been found that a maximum flow rate is obtained at the critical filling speed for all systems investigated and poly-disperse systems have higher mass flow rates and higher critical filling speeds than mono-disperse systems. In addition, the powder with particles which can tessellate generally has a lower filling rate and a lower critical titling speed.

关键词： DEM Die filling Tabletting Powder compaction Mass flow rate Critical filling speed

“一带一路”倡议沿线国家健康状况时空特征及影响因素

在线全文

学校读者我要写书评

暂无评论

地理研究 2024年第10期43卷 2541-2557页

作者：李颉许泽嘉朱竑广州大学地理科学与遥感学院广州510006 广东省城市与移民研究中心广州510006 广东省哲学社会科学重点实验室(广州大学海上丝绸之路重点实验室GD22TWCXGC15) 广州510006

卫生健康合作是“一带一路”倡议的重要组成部分,合作的前提是深入了解沿线国家人民健康状况及其影响因素。现有关于“一带一路”倡议的研究主要以政策、贸易、经济为主,对沿线国家的健康状况、健康状况的时空分布特征及其自然和社会经... 详细信息

卫生健康合作是“一带一路”倡议的重要组成部分,合作的前提是深入了解沿线国家人民健康状况及其影响因素。现有关于“一带一路”倡议的研究主要以政策、贸易、经济为主,对沿线国家的健康状况、健康状况的时空分布特征及其自然和社会经济影响因素的研究较少。本文首先构建健康指标体系,客观、全面地对沿线国家2013—2019年间的健康状况进行量化;然后,采用探索性空间分析、莫兰指数等空间分析方法对沿线国家健康状况的时空分异特征进行分析;最后,基于自然环境、社会发展水平、经济水平和个人生活习惯等健康影响因素,综合运用地理探测器、空间杜宾模型等空间分析方法,对沿线国家健康状况的影响因素进行分析。结果表明:①总体而言,“一带一路”沿线国家的健康状况好于世界平均水平,但国家之间的差异显著且具有空间相关性。欧洲及其周边区域预期寿命较高,死亡率较低,而非洲以及拉丁美洲部分区域预期寿命较低、死亡率较高。中国健康状况处于中等偏高水平。②2013—2019年沿线国家健康状况持续改善,体现在预期寿命持续上升,生育率与死亡率持续下降,并且改善的幅度显著大于非沿线国家。③多种因素在国家尺度上影响沿线国家健康状况,其中反映健康服务水平的政府健康支出、反映卫生服务可达性的全民健康覆盖程度、以及反映个人健康习惯的酒精消费和吸烟率等指标的影响最为显著。“一带一路”倡议提出以来,沿线国家的健康状况有了显著的提高,但区域发展不平衡的问题依然存在。未来,有必要继续深化与沿线国家在卫生健康方面的合作,继续提高人民健康水平,促进经济社会发展。

关键词：健康状况空间格局空间分析社会经济因素可持续发展目标 “一带一路”倡议

Microstructure and Strength of Brazed Joints of Ti_(3)Al Base Alloy with Cu-P Filler Metal

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2005年第4期21卷 493-498页

作者： Peng HE Jicai FENG Heng ZHOU National Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin 15{}001 China

Brazing of Ti3Al alloys with the filler metal Cu-P was carried out at 1173-1273 K for 60-1800 s. When products are brazed, the optimum brazing parameters are as follows： brazing temperature is 1215-1225 K; brazing time is 250-300 s. Four kinds of reaction products were observed during the brazing of Ti3Al alloys with the filler metal Cu-P, i.e., Ti3Al phase with a small quantity of Cu （Ti3Al（Cu）） formed close to the Ti3Al alloy; the TiCu intermetallic compounds layer and the Cu3P intermetallic compounds layer formed between Ti3Al（Cu） and the filler metal, and a Cu-base solid solution formed with the dispersed Cu3P in the middle of the joint. The interracial structure of brazed Ti3Al alloys joints with the filler metal Cu-P is Ti3Al/Ti3Al（Cu）/TiCu/Cu3P/Cu solid solution （Cu3P）/Cu3P/TiCu/Ti3Al（Cu）/Ti3Al, and this structure will not change with brazing time once it forms. The thickness of TiCu＋Cu3P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity/to of reaction layer TiCu＋Cu3P in the brazed joints of Ti3Al alloys with the filler metal Cu-P are 286 kJ/mol and 0.0821 m2/s, respectively, and growth formula was y2=O.O821exp（-34421.59/T）*** control of the growth for the reaction layer TiCu＋Cu3P can influence the final joint strength. The formation of the intermetallic compounds TiCu＋Cu3P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti3Al brazed.

关键词： Brazed joints Microstructure Ti3Al base alloy

Positron emission particle tracking——Application and labelling techniques

在线全文

学校读者我要写书评

暂无评论

Particuology 2008年第1期6卷 16-23页

作者： David J. Parker School of Physics and Astronomy the University of Birmingham Edgbaston Birmingham B15 2TT UK

The positron emission particle tracking （PEPT） technique has been widely used in science and engineering to obtain detailed information on the motion and flow fields of fluids or granular materials in multiphase systems, for example, fluids in rock cracks, chemical reactors and food processors; dynamic behaviour of granular materials in chemical reactors, granulators, mixers, dryers, rotating kilns and ball mills. The information obtained by the PEPT technique can be used to optimise the design, operational conditions for a wide range of industrial process systems, and to evaluate modelling work. The technique is based on tracking radioactively labelled particles （up to three particles） by detecting the pairs of backto-back 511 keV γ-rays arising from annihilation of emitted positrons. It therefore involves a positron camera, location algorithms for calculating the tracer location and speed, and tracer labelling techniques. This paper will review the particle tracking technique from tracking algorithm, tracer labelling to their application.

关键词： PEPT Tracer Algorithm Tracking

Validation of fluid-particle interaction force relationships in binary-solid suspensions

在线全文

学校读者我要写书评

暂无评论

Particuology 2015年第6期13卷 40-48页

作者： Marco Rotondi Renzo Di Felice Paolo Pagliai Department of Civil Chemical and Environmental Engneering University of Genova Via Opera Pia 15 16145 Genova Italy

In this work several relationships governing solid-fluid dynamic interaction forces were validated against experimental data for a single particle settling in a suspension of other smaller particles. It was observed that force relationships based on Lattice-Boltzmann simulations did not perform as well as other inter- action types tested. Nonetheless, it is apparent that, in the case of a suspension of different particle types, it is important that the correct choice is made as to how the contribution to the overall fluid-particle interaction force is split between buoyancy and drag. Experimental evidence clearly suggests that the ＂generalized＂ Archimedes＇ principle （where the foreign particle is considered to displace the whole suspension and not just the fluid） provides the best result.

关键词： Solid-fluid suspensionsSolid-fluid interaction forcesDrag forceBuoyancy force