Detailed Specifications for Global Heat Treatment Sourcing and Materials

The very nature of global sourcing means that components must carry clear and detailed specifications for material, heat treatment, and test methods. Qualified global heat treat facilities can achieve good control of not only the common features such as surface and gradient hardness, but also of microstructure, core hardness, residual stress, and other critical metallurgical parameters. This paper will discuss a new concept for material specifications and more detailed heat treatment specifications for the global marketplace.     

The effect of solidification direction with respect to gravity on ice-templated TiO2 microstructures

Unidirectional ice-templating produces materials with aligned, elongated pores via: (i) directional solidification of particle suspensions wherein suspended particles are rejected and incorporated between aligned dendrites, (ii) sublimation of the solidified fluid, and (iii) sintering of the particles into elongated walls which are templated by the ice dendrites. Most ice-templating studies utilize upward solidification techniques, where solid ice is located at the bottom of the solidification mold (closest to the cold source), the liquid suspension is above the ice, and the solidification front advances upward, against gravity. Liquid water reaches its maximum density at 4 °C; thus, liquid nearest the solid/liquid interface, at 0ºC, is less dense than warmer liquid above (up to 4 °C, above which, a density inversion occurs, and liquid density decreases with increasing temperature). The lower density liquid nearest the solidification front is thus expected to rise due to buoyancy, promoting convective fluid motion in the liquid during solidification. Here, we investigate the effect of solidification direction with respect to the direction of gravity on ice-templated microstructures to study the role of buoyancy-driven fluid motion during solidification. We hypothesize that, for upward solidification, the convective fluid motion that results from the liquid density gradient occurs near the solidification front. For downward solidification, we expect that this fluid motion occurs farther away from the solidification front. Aqueous suspensions of TiO₂ nanoparticles (10–30 nm in size, 10, 15, and 21 vol.%) are solidified upward (against gravity, with ice on bottom and water on top), downward (water on bottom, ice on top), and horizontally (perpendicular to gravity). Microstructural investigation of sintered samples shows evidence of buoyancy-driven, convective fluid flow during solidification for samples solidified upwards (against gravity), including (i) tilting of the wall (and pore) orientation with respect to the induced temperature gradient, (ii) ice lens defects (cracks oriented perpendicular to the freezing direction), and (iii) radial macrosegregation. These features are not observed for downward nor horizontal solidification configurations, consistent with the hypothesis that convective fluid motion does not interact directly with the solidification front for downward solidification.     

Static fatigue and compressive stress generation in an aged crack

In classic experiments by Michalske and others, it was found that cracks aged statically below the fatigue limit acquired a temporary strength increase compared to the non‐aged crack. In our previous publication we observed that cracks growing near the fatigue limit exhibited a time dependent slowing down of crack growth. Both of these phenomena are related to a toughening of the crack tip that we attribute to a water‐assisted surface stress relaxation mechanism. To test this hypothesis, the K‐v crack growth curves have been measured using the double cantilever beam (DCB) experimental technique for two commercial glasses, a sodium aluminosilicate, and a potassium aluminosilicate, both of which exhibit clear fatigue limits in air. Using polarimetry, it is shown that the stress state near an unloaded but previously aged crack tip is opposite in sign to the stress state near the tip of a crack held in Mode I loading. These results clearly indicate that a stress relaxation mechanism is occurring at the crack tip.     

Cryptographic Versus Trust-based Methods for MANET Routing Security

Mobile Ad-hoc Networks (MANETs) allow wireless nodes to form a network without requiring a fixed infrastructure. Early routing protocols for MANETs failed to take security issues into account. Subsequent proposals used strong cryptographic methods to secure the routing information. In the process, however, these protocols created new avenues for denial of service (DoS). Consequently, the trade-off between security strength and DoS vulnerability has emerged as an area requiring further investigation. It is believed that different trust methods can be used to develop protocols at various levels in this trade-off. To gain a handle on this exchange, real world testing that evaluates the cost of existing proposals is necessary. Without this, future protocol design is mere speculation. In this paper, we give the first comparison of SAODV and TAODV, two MANET routing protocols, which address routing security through cryptographic and trust-based means respectively. We provide performance comparisons on actual resource-limited hardware. Finally, we discuss design decisions for future routing protocols.     

如何让钱成为生财工具

当问到这样一个问题：如果所有工作任你选,你会选择做什么？人们会梦想自己能在充满异国风情的地方工作,或是位居要职,或是有份喝酒赚钱两不误的美差。     

Analytical simulation models for solar heating system design

Presented here is a method of simulating the performance of solar heating systems which can be incorporated into a microcomputer-based system design and sizing procedure. A general analytical solution to the storage energy balance is presented, and a scheme for varying the parameters of the general solution to represent changes in the operating mode and the driving forces is detailed. Three different simulation methods which employ the general solution are described. Two of these methods use hourly data and the third uses daily data. Measured results from an actual system are compared with simulated results to validate the models. Also, simulated results and computing speeds are compared with the general simulation model TRNSYS. Finally, an example of a microcomputer application is discussed.