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971.
David J.Mladenoff 《中国科学E辑(英文版)》2006,49(Z1)
In this study forests were visualized at various scales by placing individual trees into a forest with realistic sizes and densities. Tree images were used from two sources: high quality field photos and images created using graphic design software. The terrain, species composition, and tree sizes and density from forest inventory were all represented in GIS data format. In addition, non-tree objects and features that are essential for close-to-reality visualization were combined with the tree images in a 3-D visualization software package. We further portrayed stand level effects by animating a simulated fly-through of a forest. To visualize temporal change, a case study of four different forest patches was animated. The advantages of this approach comparing to other visualization approaches are: (1) it represents the forests with realistic individual tree images; and (2) it maintains both visual and informational realism in a forest viewable from within-stand to landscape scales. Thus, this approach is realistic in two aspects. First, it is almost as realistic as a photograph, and secondly, its information content is actual forest composition, density, and height. 相似文献
972.
973.
David E. Wilkins 《Artificial Intelligence》1982,18(1):1-51
PARADISE (PAttern Recognition Applied to DIrecting SEarch) uses a knowledge-based analysis and little searching to find the correct move in chess middle game positions. PARADISE's search does not have a depth limit or any other artificial effort limit. This paper describes the methods used to constrain the search. The ideas of using different strategies to show that one move is best and using ranges to express the values of moves (first developed in Berliner's B1 search), are extended and clarified. PARADISE combines these ideas with the use of plans, a threshold, and various measures of possibility. Examples are presented, including one in which PARADISE uses an indirect strategy to prove that one move is best without finding the winning line (a first for a chess program). 相似文献
974.
975.
Photocatalysts: Enhanced Solar‐to‐Hydrogen Generation with Broadband Epsilon‐Near‐Zero Nanostructured Photocatalysts (Adv. Mater. 27/2017) 下载免费PDF全文
976.
Zekun Liu Gang Li Zhaozhu Zheng Yuling Li Yifan Han David L. Kaplan Xiaoqin Wang 《Journal of materials science. Materials in medicine》2018,29(4):46
A novel seamless silk fibroin-based endovascular prosthesis (SFEPs) with bifurcated woven structure and anticoagulant function for the improvement of patency is described. The SFEPs were prepared from silk fibroin (SF) and polyester filaments using an installed weaving machine. The production processing parameters were optimized using orthogonal design methods. The inner surface of SFEPs was modified with polyethylenimine (PEI) and EDC/NHS-activated low-molecular-weight heparin (LMWH) to enhance anticoagulant function. The surface morphology and mechanical properties of the SFEPs were evaluated according to standard protocols. The thickness of modified SFEPs was lower than 0.085?±?0.004?mm and water permeability was lower than 5.19?±?0.30?mL/(cm2?×?min). The results of mechanical properties showed that the diametral tensile strength and burst strength reached 61.6?±?1.8 and 23.7?±?2.2?MPa, respectively. Automatic coagulometer and energy-dispersive X-ray (EDX) confirmed LMWH immobilization on the surface of the SFEPs and the blood compatibility was improved with the heparin modification with PEI polymerization. In conclusion, the new prosthesis has potential applications in the blood vessel repairs where minimal thickness but superior mechanical strength and biocompatibility are important. 相似文献
977.
David Riley 《Accident; analysis and prevention》1987,19(6):449-462
The impact of drinking and driving is one focus of the mounting concern in the West over the widespread incidence of alcohol-related problems. Conventional wisdom, in the United Kingdom as well as in other countries, suggests that reducing average consumption levels will diminish the impact of the negative effects of alcohol including drinking and driving. But whether policies designed to achieve changes in per capita consumption by increasing alcohol taxes across the board constitute the most effective strategy to reduce drinking and driving is called into question. A number of competing interventions directed at the alcohol beverage industry are analysed and new directions for producers and policymakers are proposed. 相似文献
978.
Gerhard Randers-Pehrson Gary W. Johnson Stephen A. Marino Yanping Xu Alexander D. Dymnikov David J. Brenner 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2009,609(2-3):294-299
A lens system consisting of two electrostatic quadrupole triplets has been designed and constructed at the Radiological Research Accelerator Facility (RARAF) of Columbia University. The lens system has been used to focus 6 MeV 4He ions to a beam spot in air with a diameter of 0.8 μm. The quadrupole electrodes can withstand voltages high enough to focus 4He ions up to 10 MeV and protons up to 5 MeV. The quadrupole triplet design is novel in that alignment is made through precise construction and the relative strengths of the quadrupoles are accomplished by the lengths of the elements, so that the magnitudes of the voltages required for focusing are nearly identical. The insulating sections between electrodes have had ion implantation to improve the voltage stability of the lens. The lens design employs Russian symmetry for the quadrupole elements. 相似文献
979.
980.
Xiao Yan Chunsen Liu Chao Li Wenzhong Bao Shijin Ding David Wei Zhang Peng Zhou 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(34)
The burgeoning 2D semiconductors can maintain excellent device electrostatics with an ultranarrow channel length and can realize tunneling by electrostatic gating to avoid deprivation of band‐edge sharpness resulting from chemical doping, which make them perfect candidates for tunneling field effect transistors. Here this study presents SnSe2/WSe2 van der Waals heterostructures with SnSe2 as the p‐layer and WSe2 as the n‐layer. The energy band alignment changes from a staggered gap band offset (type‐II) to a broken gap (type‐III) when changing the negative back‐gate voltage to positive, resulting in the device operating as a rectifier diode (rectification ratio ~104) or an n‐type tunneling field effect transistor, respectively. A steep average subthreshold swing of 80 mV dec?1 for exceeding two decades of drain current with a minimum of 37 mV dec?1 at room temperature is observed, and an evident trend toward negative differential resistance is also accomplished for the tunneling field effect transistor due to the high gate efficiency of 0.36 for single gate devices. The I ON/I OFF ratio of the transfer characteristics is >106, accompanying a high ON current >10?5 A. This work presents original phenomena of multilayer 2D van der Waals heterostructures which can be applied to low‐power consumption devices. 相似文献