Porosity of detonation-deposited chromium carbide-base coatings

Conclusions The variation of the open porosity of a coating as a function of detonation-deposition process conditions matches that of the quality of the coating as assessed by other parameters. The open porosity of a coating is strongly affected by its surface roughness, and consequently estimates of _op may be high. The size of a specimen for open porosity testing should not be greater than 1.2 times the barrel bore. Under optimum conditions the visible porosity of coatings does not exceed 1%.Translated from Poroshkovaya Metallurgiya, No. 7(259), pp. 17–20, July, 1984.     

Repeated Price Search

Consumers check few sites in online purchases. Previous research and experiments we perform demonstrate that consumers can not calculate the optimal strategy for price search. They use heuristics whose performance is better than random and less than optimal. To investigate online price search performance we survey student online textbook purchases. Students achieve good performance because they start with a good strategy and online market organization of marketplace and meta-search sites. An important factor is that algorithms at sites searched perform calculations that reduce the computational complexity of the search.     

Controlled microtribology of a metal oxide surface

The rational control of the friction and wear (damage) of engineering, as opposed to model, surfaces under practical conditions such as high contact pressures has long been a technological challenge with much fundamental interest. Lubricant fluids and physisorbed surfactant monolayers (boundary lubricants) are effective friction modifiers but often fail at high loads. We show that the chemisorption of a suitably designed single-chained phosphonate surfactant onto crystalline α-alumina surfaces produces robust protective monolayers that significantly reduce the friction forces and wear even at high loads. The mechanisms are explained, which point to some general principles that offer a basis for scale-up in many different engineering systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Design Considerations Pertaining to a Battery Powered Regenerative System

The requirement for transforming dc power from one voltage level to another, and processing this power for compatibility with the load exists in many industrial and vehicular applications.     

Field D* path-finding on weighted triangulated and tetrahedral meshes

Classic shortest path algorithms operate on graphs, which are suitable for problems that can be represented by weighted nodes or edges. Finding a shortest path through a set of weighted regions is more difficult and only approximate solutions tend to scale well. The Field D* algorithm efficiently calculates an approximate, interpolated shortest path through a set of weighted regions and was designed for navigating robots through terrains with varying characteristics. Field D* operates on unit grid or quad-tree data structures, which require high resolutions to accurately model the boundaries of irregular world structures. In this paper, we extend the Field D* cost functions to 2D triangulations and 3D tetrahedral meshes: structures which model polygonal world structures more accurately. Since robots typically have limited resources available for computation and storage, we pay particular attention to computation and storage overheads when detailing our extensions. We begin by providing analytic solutions to the minimum of each cost function for 2D triangles and 3D tetrahedra. Our triangle implementation provides a 50 % improvement in performance over an existing triangle implementation. While our 3D extension to tetrahedra is the first full analytic extension of Field D* to 3D, previous work only provided an approximate minimization for a single cost function on a 3D cube with unit lengths. Each cost function is expressed in terms of a general function whose characteristics can be exploited to reduce the calculations required to find a minimum. These characteristics can also be exploited to cache the majority of cost functions, producing a speedup of up to 28 % in the 3D tetrahedral case. We demonstrate that, in environments composed of non-grid aligned data, Multi-resolution quad-tree Field D* requires an order of magnitude more faces and between 15 and 20 times more node expansions, to produce a path of similar cost to one produced by a triangle implementation of Field D* on a lower resolution triangulation. We provide examples of 3D pathing through models of complex topology, including pathing through anatomical structures extracted from a medical data set. To summarise, this paper details a robust and efficient extension of Field D* pathing to data sets represented by weighted triangles and tetrahedra, and also provides empirical data which demonstrates the reduction in storage and computation costs that accrue when one chooses such a representation over the more commonly used quad-tree and grid-based alternatives.     

依据规范设计的钢板剪力墙的抗震性能

目前美国钢结构协会(AISC)抗震设计规范纳入了钢板剪力墙(SPSWs)的设计要求。钢板剪力墙由薄钢板中夹着被称为水平边界单元(HBEs)的钢梁和被称为竖直边界单元(VBEs)的钢柱组成。无加劲薄钢板在较低剪力作用下屈曲并发展变形,通过屈服变形达到延性和耗能的目的。HBEs的作用是加劲和提高整体强度,并将屈服局限于薄钢板内。VBEs的作用是促进梁端塑性铰的形成。研究依据规范设计的钢板剪力墙的性能,设计了一系列钢板剪力墙试件,采用不同震级的地面震动反应谱的非线性时程分析对其进行性能研究。研究发现,依据现行规范设计的试件能满足各种地震烈度下最大层间位移的要求,并且在最高地震烈度下最大层间位移比小于5%。由于高阶振型对反应的影响,低层钢板剪力墙的延性要求比高层钢板剪力墙要高。由钢板承担的楼层剪力与由边界框架承担的楼层剪力之比为60%～80%,此比值与板的长宽比和地震烈度无关,而与板的厚度有关。9层或以上钢板剪力墙在低烈度地震下对VBEs的需求比规范计算方法要小很多。     

Thermal, productive, and reproductive responses of high yielding cows exposed to short-term cooling in summer

Effect of cooling on body temperature, milk production, estrous behavior, and reproductive performance was examined in 66 estrous-synchronized, Israeli-Holstein dairy cows. Cooling was by an automated system, which actuated sprinkling (30 s) followed by forced ventilation (4.5 min) for 30-min periods. Cows were cooled 9 times/d between 0500 and 2100 h over 10 d, starting 1 d before expected estrus until d 8 post estrus. Cooling reduced typical diurnal rise of body temperature in summer heat-stressed cows by .5 to .9 degrees C, and body temperature was maintained close to normothermic temperature (38.6 degrees C). Milk production of cooled cows was 2.6 kg/d (+8%) above control at end of the cooling period. More cooled cows than noncooled exhibited standing estrous behavior; in noncooled cows, silent ovulations or anestrus were more frequent. Conception rate of cooled cows did not differ from control, suggesting need for a longer than a 10-d cooling period for improvement of fertility. The cooling system has potential to alleviate heat stress in dairy cows and to improve their thermal balance, productive, and reproductive performances.