检索结果-南通市图书馆

Approximate solutions of the Alekseevskii–Tate model of long-rod penetration

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 Mechanica Sinica 2018年第2期34卷 334-348页

作者： w.J.Jiao X.w.Chen Department of Modern Mechanics University of Science and Technology of China Institute of Systems Engineering China Academy of Engineering Physics Advanced Research Institute for Multidisciplinary Science Beijing Institute of Technology The State Key Lab of Explosion Science and Technology Beijing Institute of Technology

The Alekseevskii–Tate model is the most successful semi-hydrodynamic model applied to long-rod penetration into semi-infinite targets. However, due to the nonlinear nature of the equations, the rod(tail) velocity, penetration velocity, rod length, and penetration depth were obtained implicitly as a function of time and solved numerically By employing a linear approximation to the logarithmic relative rod length, we obtain two sets of explicit approximate algebraic solutions based on the implicit theoretica solution deduced from primitive equations. It is very convenient in the theoretical prediction of the Alekseevskii–Tate model to apply these simple algebraic solutions. In particular, approximate solution 1 shows good agreement with the theoretical(exact) solution, and the first-order perturbation solution obtained by walters et al.(Int. J. Impac Eng. 33:837–846, 2006) can be deemed as a special form of approximate solution 1 in high-speed penetration. Meanwhile, with constant tail velocity and penetration velocity approximate solution 2 has very simple expressions, which is applicable for the qualitative analysis of long-rod penetration. Differences among these two approximate solutions and the theoretical(exact) solution and their respective scopes of application have been discussed, and the inferences with clear physical basis have been drawn. In addition, these two solutions and the first-order perturbation solution are applied to two cases with different initial impact velocity and different penetrator/target combinations to compare with the theoretical(exact) solution. Approximate solution 1 is much closer to the theoretical solution of the Alekseevskii–Tate model than the first-order perturbation solution in both cases, whilst approximate solution 2 brings us a more intuitive understanding of quasi-steady-state penetration.

关键词： Long-rod penetration Alekseevskii–Tate model Theoretical solution Approximate solution Perturbation solution

Inducible competitors and adaptive diversification

在线全文

学校读者我要写书评

暂无评论

Current Zoology 2013年第4期59卷 537-552页

作者： Beren w. ROBINSON David w. PFENNIG Department of Integrative Biology University of Guelph Guelph Ontario N 1G 2W 1 Canada Department of Biology University of North Carolina Chapel Hill NC 27599 USA

Identifying the causes of diversification is central to evolutionary biology. The ecological theory of adaptive diversi- fication holds that the evolution of phenotypic differences between populations and species--and the formation of new spe- cies-stems from divergent natural selection, often arising from competitive interactions. Although increasing evidence suggests that phenotypic plasticity can facilitate this process, it is not generally appreciated that competitively mediated selection often also provides ideal conditions for phenotypic plasticity to evolve in the first place. Here, we discuss how competition plays at least two key roles in adaptive diversification depending on its pattern. First, heterogenous competition initially generates heterogeneity in resource use that favors adaptive plasticity in the form of ＂inducible competitors＂. Second, once such competitively induced plas- ticity evolves, its capacity to rapidly generate phenotypic variation and expose phenotypes to alternate selective regimes allows populations to respond readily to selection favoring diversification, as may occur when competition generates steady diversifying selection that permanently drives the evolutionary divergence of populations that use different resources. Thus, competition plays two important roles in adaptive diversification---one well-known and the other only now emerging--mediated through its effect on the evolution ofphenotypic plasticity

关键词： Phenotypic plasticity Competition Adaptive radiation Character displacement Genetic assimilation Resourcepolymorphism

How tribology has been helping us to advance and to survive

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Friction 2017年第3期5卷 233-247页

作者： Gwidon w.STACHOwIAK Tribology Laboratory School of Mechanical and Civil Engineering Curtin University Bentley Western Australia 6102 Australia

Movement between contacting surfaces ranges from macro to micro scales,from the movement of continental plates and glaciers to the locomotion of animals and *** topographies,lubricant layers,contaminants,operating conditions,and others control it,i.e.,this movement depends on the tribological characteristics of a *** the industrial revolution,friction and wear were controlled by the application of animal fat or *** the industrial revolution,with the introduction of trains and other machinery,the operating conditions at the contacting surfaces changed *** bearings were designed and built and simple lubrication measures were no longer *** became critical to understand the lubrication mechanisms *** that period,solid theoretical foundations,leading to the development of new technologies,were *** field of tribology had gained a significant prominence,i.e.,it became clear that without advancements in tribology the technological progress would be *** was no longer necessary to build oversized ship bearings hoping that they would *** ship or automobile bearings could now be optimized and their behavior *** the middle of the 20th century,lubrication mechanisms in non-conformal contacts,i.e.,in gears,rolling contact bearings,cams and tappets,etc.,were also finally ***,we face new challenges such as sustainability,climate change and gradual degradation of the *** of providing enough food,clean water and sufficient energy to the human population to pursue a civilized life still remain largely *** challenges require new solutions and innovative *** the humanity progresses,tribology continue to make vital contributions in addressing the demands for advanced technological developments,resulting in,for example,reducing the fuel consumption and greenhouse gases emission,increasing machine durability and improving the quality of life through

关键词： tribology friction lubrication and wear

Finding vibrations of inclined cable structures by approximately solving governing equations for exterior matrix

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2015年第11期36卷 1383-1402页

作者： w.PAULSEN M.MANNING Department of Mathematics and Statistics Arkansas State University

In this paper, how to compute the eigenfrequencies of the structures composed of a series of inclined cables is shown. The physics of an inclined cable can be complicated, so solving the differential equations even approximately is difficult. However, rather than solving the system of 4 first-order equations governing the dynamics of each cable, the governing equations are instead converted to a set of equations that the exterior matrix satisfies. Therefore, the exterior matrix method （EMM） is used without solving the original governing equations. Even though this produces a system of 6 first-order equations, the simple asymptotic techniques to find the first three terms of the perturbative solution can be used. The solutions can then be assembled to produce a 6 x 6 exterior matrix for a cable section. The matrices for each cable in the structure are multiplied together, along with the exterior matrices for each joint. The roots of the product give us the eigenfrequencies of the system.

关键词： exterior matrix method (EMM) eigenfrequency inclined cable

Nucleon transition form factors at JLab:status and outlook

在线全文

学校读者我要写书评

暂无评论

Chinese Physics C 2009年第12期33卷 1216-1221页

作者： R. w. Gothe University of South Carolina Columbia SC 29208 USA

The measurements of exclusive single-meson and double-pion electro-production cross sections off the proton to study nucleon resonances will be extended to higher momentum transfers with the CLAS12 detector and the energy upgraded CEBAF beam. Based on new theoretical developments to extract and interpret the electromagnetic transition form factors and on the experience gained from the most recent results, the newly formed collaboration of experimentalists and theorists shall enable us to provide unprecedented high- precision data, high-quality analyses, and state-of-the-art model and QCD based calculations in a Q2 domain up to 10 GeV2. For the first time nucleon resonance structures will be studied at still unexplored distance scales, where the dressed quark contributions are the dominating degrees of freedom and their strong interaction is responsible for the ground and excited nucleon state formation. These studies also open up a promising opportunity to understand the origin of more than 98% of the nucleon mass that is created by strong fields predominantly at these distance scales by dressing the current quarks.

关键词： baryon structure strong degrees of freedom

Assessment of Seedling Establishment and Growth Performance of Leucaena leucocephala(Lam.) De wit., Senna siamea(Lam.) and Eucalyptus grandisw. Hill ex Maid. in Amended and Untreated Pyrite and Copper Tailings

在线全文

学校读者我要写书评

暂无评论

Journal of Biosciences and Medicines 2014年第1期2卷 33-50页

作者： Jamilu Edirisa Ssenku Mohammad Ntale Ingvar Backéus Hannington Oryem-Origa Department of Biological Sciences College of Natural Sciences Makerere University Kampala Uganda Department of Chemistry College of Natural Sciences Makerere University Kampala Uganda School of Natural Sciences Technology and Environmental Studies S&ouml dertö rn University Huddinge Sweden

Growth and survival performance of Leucaena leucocephala (Lam.) De wit., Senna siamea Lam. and Eucalyptus grandis w. Hill ex Maid. in amended and untreated pyrite and copper tailings were evaluated under field conditions. The physico-chemical characteristics of the pyrite soil and tailings were determined. Growth in height, basal diameter and later dbh, relative growth rate due to height (RGRh) and basal diameter (RGRd) and survival were determined every after six months. A split block experimental design was used and the data collected were analyzed using a statistical package R, with an additional package lme4. Tailings and pyrite soils had extremely low pH, poor nutritional status, low organic matter content and elevated concentrations of available heavy metals as compared to the unpolluted soils and treated pyrite soil and copper tailings. Growth performance was extremely poor on the untreated pyrite soil and copper tailings for all the species but significantly enhanced by the application of compost and limestone. Treatment had a significant effect on all parameters at all sites. Eucalyptus grandis displayed a higher potential of phytomass accumulation than Leucaena leucocephala and Senna siamea. Even though Leucaena leucocephala grew fastest reaching reproductive maturity in 7 months after planting, relative growth rates of the three species were not significantly different at all sites. The three species can be used for phytostabilisation of the tailings at Kilembe tailings dam sites (KTDS) after treatment while at Low polluted pyrite trail site (LPPTS) and Highly polluted pyrite trail sites (HPPTS) Senna siamea is more suitable as Eucalyptus grandis and Leucaena leucocephala are susceptible to attacks by Syncerus caffer (Buffalos) and Kobus kob thomasi (Uganda Kob).

关键词： Seedling Establishment Growth Performance Pyrite Phytostabilization Tailings QECA

Calibration of the Albian/Cenomanian Boundary by Ammonite Biostratigraphy:*** Interior

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 Geologica Sinica(English Edition) 2007年第6期81卷 940-948页

作者： Robert w.SCOTT University of Tulsa and Precision Stratigraphy Associates

Calibration of numerical ages to the geological time scale is a long scientific pursuit that requires the integration of multiple data sets. A case study of the Albian/Cenomanian stage boundary, also the Lower/Upper Cretaceous series boundary, illustrates the calibration process. The numerical age of this boundary has shifted from 96 Ma to 99 Ma over a time span of nearly fifty years. Recalibration resulted first from improvements in radiometric dating, and later from inferences about ammonite phylogeny, and most recently from radiometric dates of newly discovered volcanic beds interbedded with diagnostic guide fossils. However, the calibration process continues with study of cosmopolitan dinoflagellates.

关键词： Albian/Cenomanian ammonite biostratigraphy age calibration

Regulating regulatory T cells to achieve transplant tolerance

在线全文

学校读者我要写书评

暂无评论

Hepatobiliary & Pancreatic Diseases International 2007年第4期6卷 348-357页

作者： wayne w. Hancock Division of Transplantation Immunology Department of Pathology and Laboratory MedicineJoseph StokesJr.Research Institute and Biesecker Pediatric Liver Center Children's Hospital of Philadelphia and University of Pennsylvania Philadelphia PA 19104 USA

BACKGROUND:Regulatory T cells(Tregs) play crucial roles in both induction and maintenance of tolerance. This active immune regulation may contribute not only to the control of immune responses to self-antigens and thereby prevent autoimmune diseases,but also the control of responses to non-self molecules in adaptive immunity. Numerous experimental and clinical studies indicate that manipulating the balance between regulatory and responder T cells is an effective strategy to control immune responsiveness after transplantation. DATA SOURCES:Literature search was conducted using PubMed on the related subjects. Part of the material was based on the most recent work in the authors’ laboratory. RESULTS:we propose some new strategies to achieve transplant tolerance in rodent animals via manipulating Treg function,including using histone deacetylase(HDAC) inhibitor to regulate Foxp3 transcription and enhance Treg suppression,induction of Treg-sparing apoptosis via Nur77,and identification of the co-inhibitory molecule herpes virus entry mediator(HVEM) as an effector molecule for Treg function. CONCLusION:Regulation of Treg function will definitely provide us very promising tools to achieve clinical tolerance in the future.

关键词： regulatory T cells transplant tolerance HDAC inhibitor apoptosis Nur77 co-stimulation

Interactive Effect of Potassium and Phosphorus on Grain Quality and Profitability of Sunflower in Northwest Pakistan

在线全文

学校读者我要写书评

暂无评论

Pedosphere 2011年第4期21卷 532-538页

作者： AM ANULLAH M.w.KHAN Department of Agronomy Khyber Pakhtunkhwa Agricultural University

A field experiment was conducted using a split plot randomized complete block design with three replications to study the effects of potassium (K) and phosphorus (P) application on sunflower (Helianthus annuus L.) growth at the New Developmental Research Farm of Khyber Pakhtunkhwa Agricultural University in Peshawar,*** levels of K (0,25,50,75,100 and 125 kg K ha-1) were main plots while four levels of P (0,45,90 and 135 kg P ha-1) were *** in both K and P levels enhanced grain oil concentration of *** in P level increased grain protein concentration,while increase in K level decreased grain protein *** oil and protein yields increased significantly with increase in K and P *** increase in oil and protein yields of sunflower was mainly attributed to the improvement in yield components (grains per head,grain weight and head size) and the significant increase in grain *** highest net returns of 297 and 368 us$ ha-1 based on grain and oil yields,respectively,were obtained from a combination of 100 kg K ha-1 + 45 kg P ha-1.

关键词： economic analysis grain yield oil content protein content