检索结果-南通市图书馆

Consistent constitutive modeling of metallic target penetration using empirical, analytical, and numerical penetration models

在线全文

学校读者我要写书评

暂无评论

Defence Technology（防务技术） 2016年第2期12卷 201-213页

作者： John(Jack) p.RIEGEL III david DAVISON R3 Technology Inc. 7324 Fountain Spring Ct. Shock Transients Inc.

Historically, there has been little correlation between the material properties used in(1) empirical formulae,(2) analytical formulations, and(3) numerical models. The various regressions and models may each provide excellent agreement for the depth of penetration into semi-infinite targets. But the input parameters for the empirically based procedures may have little in common with either the analytical model or the numerical model. This paper builds on previous work by Riegel and Anderson(2014) to show how the Effective Flow Stress(EFS) strength model, based on empirical data, can be used as the average flow stress in the analytical Walker–Anderson penetration model(WApEN)(Anderson and Walker,1991) and how the same value may be utilized as an effective von Mises yield strength in numerical hydrocode simulations to predict the depth of penetration for eroding projectiles at impact velocities in the mechanical response regime of the materials. The method has the benefit of allowing the three techniques(empirical, analytical, and numerical) to work in tandem. The empirical method can be used for many shot line calculations, but more advanced analytical or numerical models can be employed when necessary to address specific geometries such as edge effects or layering that are not treated by the simpler methods. Developing complete constitutive relationships for a material can be costly. If the only concern is depth of penetration, such a level of detail may not be required. The effective flow stress can be determined from a small set of depth of penetration experiments in many cases, especially for long penetrators such as the L/D = 10 ones considered here, making it a very practical approach. In the process of performing this effort, the authors considered numerical simulations by other researchers based on the same set of experimental data that the authors used for their empirical and analytical assessment. The goals were to establish a baseline with a full constitut

关键词：本构模型渗透模型数值模型金属靶材料性质流动应力程序模拟数值计算

Oxygation Enhances Growth,Gas Exchange and Salt Tolerance of Vegetable Soybean and Cotton in a Saline Vertisol

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative plant Biology 2009年第7期51卷 675-688页

作者： Surya p. Bhattarai david J. Midmore Centre for plant and Water Science Department of Molecular and Life SciencesCentral Queensland University

Impacts of salinity become severe when the soil is deficient in oxygen. OxygaUon （using aerated water for subsurface drip irrigation of crop） could minimize the impact of salinity on plants under oxygen-limiting soil environments. pot experiments were conducted to evaluate the effects of oxygation （12% air volume/volume of water） on vegetable soybean （moderately salt tolerant） and cotton （salt tolerant） in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency （WUE） by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na^＋ and CI^- concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na^＋ or CI^- concentration. Oxygation invariably increased, whereas salinity reduced the K^＋： Na^＋ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.

关键词： cotton irrigation light interception oxygation saline soil salt exclusion stem diameter vegetable soybean

Negative consequences of positive feedbacks in US wild-fire management

在线全文

学校读者我要写书评

暂无评论

Forest Ecosystems 2015年第2期2卷 57-66页

作者： david E Calkin Matthew p Thompson Mark A Finney Forestry Sciences Laboratory US Forest Service Rocky Mountain Research Station Fire Sciences Laboratory US Forest Service Rocky Mountain Research Station

Over the last two decades wildfire activity, damage, and management cost within the US have increased substantially. These increases have been associated with a number of factors including climate change and fuel accumulation due to a century of active fire suppression. The increased fire activity has occurred during a time of significant ex-urban development of the Wildland Urban Interface （WUI） along with increased demand on water resources originating on forested landscapes. These increased demands have put substantial pressure on federal agencies charged with wildfire management to continue and expand the century old policy of aggressive wildfire suppression. However, aggressive wildfire suppression is one of the major factors that drive the increased extent, intensity, and damage associated with the small number of large wildfires that are unable to be suppressed. In this paper we discuss the positive feedback loops that lead to demands for increasing suppression response while simultaneously increasing wildfire risk in the future. Despite a wealth of scientific research that demonstrates the limitations of the current management paradigm pressure to maintain the existing system are well entrenched and driven by the existing social systems that have evolved under our current management practice. Interestingly, US federal wildland fire policy provides considerable discretion for managers to pursue a range of management objectives however, societal expectations and existing management incentive structures result in policy implementation that is straining the resilience of fire adapted ecosystems and the communities that reside in and adjacent to them.

关键词： Wildfire suppression Wildfire paradox Wildland urban interface Resilience

Oxygen Reduction Reaction Catalyzed by Carbon-Supported platinum Few-Atom Clusters:Significant Enhancement by Doping of Atomic Cobalt

在线全文

学校读者我要写书评

暂无评论

Research 2020年第1期2020卷 1756-1767页

作者： Bingzhang Lu Qiming Liu Forrest Nichols Rene Mercado david morris Ning Li peng Zhang peng Gao Yuan ping Shaowei Chen Department of Chemistry and Biochemistry University of California1156 High StreetSanta CruzCalifornia 950564USA Department of Chemistry Dalhousie University6274 Coburg RoadHalifaxNova ScotiaCanada B3H 4R2 International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Electron Microscopy Laboratory School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Centre of Quantum Matter Beijing 100871China

Oxygen reduction reaction(ORR)plays an important role in dictating the performance of various electrochemical energy *** platinum nanoparticles have served as the catalysts of choice towards ORR,minimizing the cost of the catalysts by diminishing the platinum nanoparticle size has become a critical route to advancing the technological ***,first-principle calculations show that carbon-supported pt9 clusters represent the threshold domain size,and the ORR activity can be significantly improved by doping of adjacent cobalt *** is confirmed experimentally,where platinum and cobalt are dispersed in nitrogen-doped carbon nanowires in varied forms,single atoms,few-atom clusters,and nanoparticles,depending on the initial *** sample consisting primarily of pt_(2~7)clusters doped with atomic Co species exhibits the best mass activity among the series,with a current density of 4:16Amg^(-1)_(pt)at+0.85V *** that is almost 50 times higher than that of commercial pt/C.

关键词： platinum Oxygen cobalt

Numerical Simulation of a Weakly Nonlinear Model for Internal Waves

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Communications in Computational physics 2012年第10期12卷 1461-1481页

作者： Robyn Canning Gregory david p.Nicholls Department of Mathematics Statistics and Computer ScienceUniversity of Illinois at ChicagoChicagoIL 60607USA

Internal waves arise in a wide array of oceanographic problems of both theoretical and engineering *** this contribution we present a newmodel,valid in the weakly nonlinear regime,for the propagation of disturbances along the interface between two ideal fluid layers of infinite extent and different ***,we present a novel high-order/spectral algorithm for its accurate and stable *** validation results and simulations of wave-packet evolution are provided.

关键词： Internal waves weakly nonlinear waves high-order spectral methods Dirichlet Neumann operators surface formulation

Zwitterion-doped liquid crystal speckle reducers for immersive displays and vectorial imaging

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Light(Science & Applications) 2023年第11期12卷 2363-2377页

作者： Yihan Jin Nathan p.Spiller Chao He Grahame Faulkner Martin J.Booth Steve J.Elston Stephen M.morris Department of Engineering Science University of OxfordParks RoadOxford OX13PJUK

Lasers possess many attractive features(e.g.,high brightness,narrow linewidth,well-defined polarization)that make them the ideal illumination source for many different scientific and technological endeavors relating to imaging and the display of high-resolution ***,their high-level of coherence can result in the formation of noise,referred to as speckle,that can corrupt and degrade ***,we demonstrate a new electro-optic technology for combatting laser speckle using a chiral nematic liquid crystal(LC)dispersed with zwitterionic *** are presented that demonstrate when driven at the optimum electric field conditions,the speckle noise can be reduced by>90%resulting in speckle contrast(C)values of C=0.07,which is approaching that required to be imperceptible to the human *** LC technology is then showcased in an array of different display and imaging applications,including a demonstration of speckle reduction in modern vectorial laser-based imaging.

关键词： polarization speckle crystal

Machine Learning Techniques for predicting Crop photosynthetic Capacity from Leaf Reflectance Spectra

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Molecular plant 2017年第6期10卷 878-890页

作者： david Heckmann Urte Schluter Andreas p.M. Weber Heinrich-Heine-Universitat Institute for Computer Science Heinrich-Heine-Universitat Institute of Plant Biochemistry Cluster of Excellence on plant Sciences (CEpLAS) 'From Complex Traits towards Synthetic Modules' 40225 Dusseldorf Germany

Harnessing natural variation in photosynthetic capacity is a promising route toward yield increases, but physiological phenotyping is still too laborious for large-scale genetic screens. Here, we evaluate the potential of leaf reflectance spectroscopy to predict parameters of photosynthetic capacity in Brassica oleracea and Zea mays, a C3 and a C4 crop, respectively. To this end, we systematically evaluated properties of reflectance spectra and found that they are surprisingly similar over a wide range of species. We assessed the performance of a wide range of machine learning methods and selected recursive feature elimination on untransformed spectra followed by partial least squares regression as the preferred algorithm that yielded the highest predictive power. Learning curves of this algorithm suggest optimal species-specific sample sizes. Using the Brassica relative Moricandia, we evaluated the model transferability between spe- cies and found that cross-species performance cannot be predicted from phylogenetic proximity. The final intra-species models predict crop photosynthetic capacity with high accuracy. Based on the estimated model accuracy, we simulated the use of the models in selective breeding experiments, and showed that high-throughput photosynthetic phenotyping using our method has the potential to greatly improve breeding success. Our results indicate that leaf reflectance phenotyping is an efficient method for improving crop photosynthetic capacity.

关键词： leaf spectrometry photosynthesis machine learning crops C4 phenotyping

Simplified seismic performance assessment and implications for seismic design

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Earthquake Engineering and Engineering Vibration 2014年第S1期13卷 95-122页

作者： Timothy J.Sullivan david p.Welch Gian Michele Calvi University of pavia Department of Civil Engineering & ArchitecturePavia 27100Italy European Centre for Training and Research in Earthquake Engineering Pavia 27100Italy UME School ROSE ProgrammeIUSS Pavia phD candidate IUSS pavia professor

The last decade or so has seen the development of refined performance-based earthquake engineering(pBEE) approaches that now provide a framework for estimation of a range of important decision variables,such as repair costs,repair time and number of casualties. This paper reviews current tools for pBEE,including the pACT software,and examines the possibility of extending the innovative displacement-based assessment approach as a simplified structural analysis option for performance assessment. Details of the displacement-based s+eismic assessment method are reviewed and a simple means of quickly assessing multiple hazard levels is proposed. Furthermore,proposals for a simple definition of collapse fragility and relations between equivalent single-degree-of-freedom characteristics and multi-degree-of-freedom story drift and floor acceleration demands are discussed,highlighting needs for future research. To illustrate the potential of the methodology,performance measures obtained from the simplified method are compared with those computed using the results of incremental dynamic analyses within the pEER performance-based earthquake engineering framework,applied to a benchmark building. The comparison illustrates that the simplified method could be a very effective conceptual seismic design tool. The advantages and disadvantages of the simplified approach are discussed and potential implications of advanced seismic performance assessments for conceptual seismic design are highlighted through examination of different case study scenarios including different structural configurations.

关键词： performance-based earthquake engineering displacement-based assessment seismic assessment

Localized CO2 laser bonding process for MEMS packaging

在线全文

学校读者我要写书评

暂无评论

Transactions of Nonferrous Metals Society of China 2006年第S2期 577-581页

作者： A．p.MALSHE S．CUNNINGHAM A．morris Department of Mechanical EngineeringUniversity of Arkansas Fayetteville AR 72701USA wiSpry Inc.Irvine CA 92618USA wiSpry Inc.Cary NC 27513 USA

The packaging poses a critical challenge for commercialization of MEMS products. Major problems with the packaging process include degraded reliability caused by the excess stress due to thermal mismatch and altered performance of the MEMS device after packaging caused by thermal exposure. The localized laser bonding technique for ceramic MEMS packaging to address above-mentioned challenges was investigated. A continuous wave CO2 laser was used to locally heat sealing material for ceramic MEMS package lid to substrate bonding. To determine the laser power density and scanning speed, finite element analysis thermal models were constructed to simulate the localized laser bonding process. Further, the effect of external pressure at sealing ring on the bonding formation was studied. pull testing results show that the scanning speed and external pressure have significant influence on the pull strength at the bonding interface. Cross-sectional microscopy of the bonding interface indicates that the packages bonded with relatively low scanning speed and external pressure conditions have higher bonding quality. This research demonstrates the potential of localized laser bonding process for ceramic MEMS packaging.

关键词： localized laser bonding MEMS packaging FEA mechanical pull tests cross-sectional microscopy