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31.
Helmut Alt Esther M. Arkin Alon Efrat George Hart Ferran Hurtado Irina Kostitsyna Alexander Kröller Joseph S. B. Mitchell Valentin Polishchuk 《Theory of Computing Systems》2014,54(4):689-714
We show how to compute the smallest rectangle that can enclose any polygon, from a given set of polygons, in nearly linear time; we also present a PTAS for the problem, as well as a linear-time algorithm for the case when the polygons are rectangles themselves. We prove that finding a smallest convex polygon that encloses any of the given polygons is NP-hard, and give a PTAS for minimizing the perimeter of the convex enclosure. We also give efficient algorithms to find the smallest rectangle simultaneously enclosing a given pair of convex polygons. 相似文献
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采用固相反应法用不同的烧结速率在1850℃烧结合成过烧钇铝石榴石(YAG)陶瓷,YAG陶瓷晶界形貌随烧结速率的变化而不同。高纯的毋Al2O3和Y2O3原料粉体经高能球磨在1400℃空气中煅烧,生成主相为YAG相的多相粉体化合物。真空烧结YAG陶瓷时烧结速率800℃/h并在1850℃真空烧结4h会使陶瓷中晶粒长大不充分,晶粒与晶粒之间仍保留明显的面接触,陶瓷内部残存大量直径约1μm的气孔,尺寸与可见光波长接近,对透过率的影响大,陶瓷成半透明;在以100~C/h升至1850℃真空烧结4h的YAG多晶陶瓷半透明化,陶瓷晶粒粗大,晶界宽化且保留熔融态凝固,用TEM及EDS确认晶界处存在毋α-Al2O3和钙钛型YAP共晶相。 相似文献
34.
J. Kratt M. Spicker A. Guayaquil M. Fiser S. Pirk O. Deussen J. C. Hart B. Benes 《Computer Graphics Forum》2015,34(2):361-372
We present a botanical simulation of secondary (cambial) tree growth coupled to a physical cracking simulation of its bark. Whereas level set growth would use a fixed resolution voxel grid, our system extends the deformable simplicial complex (DSC), supporting new biological growth functions robustly on any surface polygonal mesh with adaptive subdivision, collision detection and topological control. We extend the DSC with temporally coherent texturing, and surface cracking with a user‐controllable biological model coupled to the stresses introduced by the cambial growth model. 相似文献
35.
Current methods underpinning environmental flow (eFlow) decisions often lack transparency, do not adequately consider uncertainties and rarely include adaptive management principles. We report the development and application of an eFlow Bayesian Network (BN) model that links four flow components with an ecological model to predict the spawning and recruitment of two important native fish species, the Australian Grayling and River Blackfish, in the highly regulated and flow‐stressed lower Latrobe River in Victoria, Australia. Autumn high flows, in conjunction with low stream temperature, are critical for Grayling spawning. The BN model was used to predict the probability of spawning and recruitment of these two native fish species for four flow scenarios. Quantitative data, flow simulation models and expert judgement were used to parameterize the BN model. The model results showed clearly that currently, and into the future, there is a very low likelihood of spawning and recruitment of Australian Grayling in the lower Latrobe. River Blackfish are minimally affected by the predicted reductions in flow and increased stream temperatures. Management scenarios aimed at modifying flows and stream temperatures to increase the likelihood of successful spawning and recruitment of Australian Grayling were assessed. Self‐sustaining populations of Australian Grayling could conceivably be achieved in the upper reaches of this river if fish passage was provided through an on‐stream reservoir. A major benefit in building and applying an eFlow BN model is that it can facilitate meaningful analysis and discussion of the ecological effects of particular eFlow regimes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
36.
A. Loui F.T. Goericke T.V. Ratto J. Lee B.R. Hart W.P. King 《Sensors and actuators. A, Physical》2008,147(2):516-521
We have designed, fabricated, and tested five piezoresistive cantilever configurations to investigate the effect of shape and piezoresistor placement on the sensitivity of microcantilevers under both point loading and surface stress loading. The experimental study reveals that: (1) high aspect ratio cantilevers that are much longer than they are wide are optimal for point-loading applications such as microscopy and force measurements; (2) low aspect ratio cantilevers that are short and wide are optimal for surface stress-loading scenarios such as those that occur in biological and chemical sensor applications. The sensitivity data for both point loads and surface stress are consistent with previously developed finite-element models. 相似文献
37.
Practical Interdomain Routing Security 总被引:1,自引:0,他引:1
This article reviews risks and vulnerabilities in interdomain routing and best practices that can have near-term benefits for routing security. It includes examples of routing failures and common attacks on routers, and countermeasures to reduce router vulnerabilities. 相似文献
38.
Shi JF Wang CJ Berryman F Hart W 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2008,222(5):657-667
In this paper fixed- and mobile-bearing implants were simulated using a multibody dynamic model and a finite element model to investigate the contact pressure distribution in the ultra high molecular weight polyethylene tibial bearing component. The thickness of polyethylene varied from 6.8 to 12.3 mm and the polyethylene was modelled as a non-linear material. It was found that the contact pressure on the polyethylene decreased in the fixed-bearing implant when the thickness of polyethylene increased from 6.8 to 8 and 9.6 mm, but there was little further decrease in pressure with the increase of polyethylene thickness from 9.6 to 11.0 and 12.3 mm. In the mobile-bearing implant, no increase in contact pressure on the superior surface was found with the increase in the thickness of the polyethylene; however, the contact pressures on the inferior contact surface of the thicker designs were higher than those in the 6.8 mm design. The numerical results obtained in this paper are in good agreement with published experimental test results. Moreover, the paper presents a detailed pressure distribution on the tibial bearing component during a full gait cycle. 相似文献
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40.
BT Teh S Kyt?l? F Farnebo L Bergman FK Wong G Weber N Hayward C Larsson B Skogseid A Beckers C Phelan M Edwards M Epstein F Alford D Hurley S Grimmond G Silins M Walters C Stewart J Cardinal S Khodaei F Parente L Tranebjaerg R Jorde P Salmela 《Canadian Metallurgical Quarterly》1998,83(8):2621-2626
Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal dominant disease characterized by neoplasia of the parathyroid glands, the endocrine pancreas, and the anterior pituitary gland. In addition, families with isolated endocrine neoplasia, notably familial isolated hyperparathyroidism (FIHP) and familial acromegaly, have also been reported. However, whether these families constitute MEN 1 variants or separate entities remains speculative as the genetic bases for these diseases are unclear. The gene for MEN 1 has recently been cloned and characterized. Using single strand conformation analysis (SSCA) and sequencing, we performed mutation analysis in: a) a total of 55 MEN 1 families from 7 countries, b) 13 isolated MEN 1 cases without family history of the disease, c) 8 acromegaly families, and d) 4 FIHP families. Mutations were identified in 27 MEN 1 families and 9 isolated cases. The 22 different mutations spread across most of the 9 translated exons and included frameshift (11), nonsense (6), splice (2), missense mutations (2), and in-frame deletions (1). Among the 19 Finnish MEN 1 probands, a 1466del12 mutation was identified in 6 families with identical 11q13 haplotypes and in 2 isolated cases indicating a common founder. One frameshift mutation caused by 359del4 (GTCT) was found in 1 isolated case and 4 kindreds of different origin and haplotypes; this mutation therefore represents a common "warm" spot in the MEN1 gene. By analyzing the DNA of the parents of an isolated case one mutation was confirmed to be de novo. No mutation was found in any of the acromegaly and small FIHP families, suggesting that genetic defects other than the MEN1 gene might be involved and that additional such families need to be analyzed. 相似文献