Electro magnetic interference shielding characteristic of silver coated copper powder

The present investigation deals with the synthesis of silver coated copper powder for potential application as filler material in conductive polymers for electro magnetic interference (EMI) shielding. Copper powders were obtained by the reaction of cuprous oxide and, hydrazine in a mixed solvent (H₂O:ethanol) at various reaction conditions. The cuprous oxide powder was produced by the reaction of CuSO₄, NaOH and D-glucose. The synthesized copper powder was silver coated by its reaction with (NH₄)₂SO₄, C₄H₄O₆KNa and AgNO₃. The prepared powders were characterized by XRD, SEM, TGA and XPS. The coaxial transmission line method was used to measure the EMI shielding effectiveness of the powders. The silver coated copper powders exhibited an improved oxidation resistance and higher EMI shielding effectiveness as compared to the uncoated copper powders.     

Volume Expansion of Compacted Graphite Iron Induced by Pearlite Decomposition and the Effect of Oxidation at Elevated Temperature

Engine cylinder blocks and heads, made of compacted graphite iron, are subjected to prolonged periods of cyclic heating and cooling. These conditions may give rise to the decomposition of the pearlite matrix accompanied by the formation of lower-density graphite and oxides, which will lead to an increase of material volume. The microstructural instability deteriorates the physical and mechanical properties of CGI and accordingly the thermal fatigue properties. In the present work it was shown that the extent and mechanism of volume change are drastically affected by the presence of an oxide atmosphere. It was found that after annealing under atmospheric conditions internal oxidation largely inhibited the progress of pearlite decomposition and therefore much smaller growth rates were obtained as compared to those observed under vacuum conditions in the dilatometer. After 16 h of annealing time at 700 °C in vacuum, the CGI samples exhibited 6 times faster growth kinetics as compared to annealing in open atmosphere.     

Influence of material microstructure on grindability of bearing steel

Innovative new materials and microstructures are being continually developed to meet increasingly challenging applications. These newly developed microstructures pose significant challenges in terms of grindability and component distortion. This fundamental study sheds light on the grindability of microstructure variations of through hardened A485–1 grade steel. Results indicate that the phase composition and carbide distribution significantly influence grindability which is characterized in terms of specific grinding energy, G-ratio and part distortion. The study also demonstrates that the numerically quantified carbide distribution exhibits a strong correlation to grindability when phase compositions are similar.     

Early Stages of Composite Formation by Oxidation ofLiquid Aluminum Alloys

Microstructure evolution during the early stages in the directed oxidation of molten Al-Mg and Al-Mg-Si alloys was investigated to provide needed insight into the origins of the incubation period and its practical elimination by SiO₂ additions. Oxidation experiments were performed primarily in thermogravimetric balances and microstructures were analyzed by optical and scanning electron microscopy. Continuous heating above the alloy liquidus produces first a thin MgO layer and then a brief rapid growth of a spinel + metal mixture within a temperature range which depends on the alloy Mg content and the heating rate. The initial rapid oxidation terminates abruptly with the formation of a dense spinel layer at the surface, leading to a long incubation period of negligible weight gain. The surface MgO regenerates in this regime, while the metal channels slowly advance upward by dissolution of the dense spinel, eventually reaching the MgO and inducing the formation of composite nodules. These consist initially of spinel + metal upon which the conventional A1₂O₃+ metal growth starts after the Mg in the near-surface alloy is depleted to a critical level. SiO₂ surface additions promote composite nucleation by locally hindering surface passivation, acting as an O source for continued spinel growth, and modifying the local chemistry to facilitate the formation of A1₂O₃.     

Synergistic Antiproliferative Effects of γ-Tocotrienol and Statin Treatment on Mammary Tumor Cells

Statins are potent inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCoA) reductase and display anticancer activity, but their clinical use is limited by their high-dose toxicity. Similarly, γ-tocotrienol, an isoform of vitamin E, also reduces HMGCoA reductase activity and displays potent anticancer activity. Studies were conducted to determine if combined low dose treatment of γ-tocotrienol with individual statins resulted in a synergistic antiproliferative effect on neoplastic mouse +SA mammary epithelial cells. Treatment with 3–4 μM γ-tocotrienol or 2–8 μM simvastatin, lovastatin or mevastatin alone resulted in a significant decrease, whereas treatment with 10–100 μM pravastatin had no effect on +SA cell growth. However, combined treatment of subeffective doses (0.25 or 10 μM) of individual statins with 0.25–2.0 μM γ-tocotrienol resulted in a dose-responsive synergistic inhibition in +SA cell proliferation. Additional studies showed that treatment with subeffective doses of individual statins or γ-tocotrienol alone had no effect, whereas combined treatment of these compounds resulted in a relatively large decrease in intracellular levels of phosphorylated (activated) MAPK, JNK, p38, and Akt. These findings strongly suggest that combined low dose treatment of γ-tocotrienol with individual statins may have potential value in the treatment of breast cancer without causing myotoxicity that is associated with high dose statin treatment.     

Connected sensor cover for area information coverage in wireless sensor networks

Coverage is an important issue in wireless sensor networks (WSNs) and is often used to measure how well a sensor field is monitored by the deployed sensors. If the area covered by a sensor can also be covered by some other sensors, this sensor can go into an energy‐saving sleep state without sacrificing the coverage requirement. In this paper, we study the problem of how to select active sensors with the constraints that the selected active sensors can provide complete field coverage and are completely connected. We propose to use the notion of information coverage, which is based on estimation theory to exploit the collaborative nature of WSNs, instead of using the conventional definition of coverage. Owing to the use of information coverage, a point that is not within the sensing disk of any sensor can still be considered to be covered without loss of estimation reliability. We propose a heuristic to approximately solve our problem. The basic idea is to grow a connected sensor tree to maximize the profit from the covered points of the selected sensors in each step. Simulations are used to validate the effectiveness of the proposed algorithm and the results illustrate that the number of active sensors to provide area coverage can be greatly reduced by using the notion of information coverage compared with that by using the conventional definition of coverage. Copyright © 2008 John Wiley & Sons, Ltd.     

Diversity sustains an evolving network

We study an evolutionary model of a complex system that evolves under catalytic dynamics and Darwinian selection and exhibits spontaneous growth, stasis and then a collapse of its structure. We find that the typical lifetime of the system increases sharply with the diversity of its components or species. We also find that the prime reason for crashes is a naturally occurring internal fragility of the system. This fragility is captured in the network organizational character and is related to a reduced multiplicity of pathways or feedback loops between its components. These results apply to several generalizations of the model as well. This work suggests new parameters for understanding the robustness of evolving molecular networks, ecosystems, societies and markets.     

The simulation of stress fibre and focal adhesion development in cells on patterned substrates.

The remodelling of the cytoskeleton and focal adhesion (FA) distributions for cells on substrates with micro-patterned ligand patches is investigated using a bio-chemo-mechanical model. We investigate the effect of ligand pattern shape on the cytoskeletal arrangements and FA distributions for cells having approximately the same area. The cytoskeleton model accounts for the dynamic rearrangement of the actin/myosin stress fibres. It entails the highly nonlinear interactions between signalling, the kinetics of tension-dependent stress-fibre formation/dissolution and stress-dependent contractility. This model is coupled with another model that governs FA formation and accounts for the mechano-sensitivity of the adhesions from thermodynamic considerations. This coupled modelling scheme is shown to capture a variety of key experimental observations including: (i) the formation of high concentrations of stress fibres and FAs at the periphery of circular and triangular, convex-shaped ligand patterns; (ii) the development of high FA concentrations along the edges of the V-, T-, Y- and U-shaped concave ligand patterns; and (iii) the formation of highly aligned stress fibres along the non-adhered edges of cells on the concave ligand patterns. When appropriately calibrated, the model also accurately predicts the radii of curvature of the non-adhered edges of cells on the concave-shaped ligand patterns.     

Microstructure and texture evolution during cold rolling and annealing of a high Mn TWIP steel

The microstructure during cold rolling and annealing of a low-stacking fault energy austenitic Fe–Mn–C alloy was studied by means of electron microscopy. The contribution of both slip and microtwinning to the development of a brass-type cold-rolling texture was illustrated. During subsequent recrystallization annealing, a retained rolling texture was observed. It was shown that the mechanism behind this phenomenon was based on the nucleation and growth of the recrystallized state without preferred orientation in an energetically relatively homogeneous microstructure.     

Parallel state-space search for a first solution with consistent linear speedups

Consider the problem of exploring a large state-space for a goal state where although many such states may exist in the state-space, finding any one state satisfying the requirements is sufficient. All the methods known until now for conducting such search in parallel using multiprocessors fail to provide consistent linear speedups over sequential execution. The speedups vary between sublinear to superlinear and from one execution to another. Further, adding more processors may sometimes lead to a slow-down rather than speedup, giving rise to speedup anomalies reported in literature. We present a prioritizing strategy which yields consistent speedups that are close toP withP processors, and that monotonically increase with the additon of processors. This is achieved by keeping the total number of nodes expanded during parallel search very close to that of a sequential search. In addition, the strategy requires substantially smaller memory relative to other methods. The performance of this strategy is demonstrated on a multiprocessor with several state-space search problems.This research has been supported in part by the National Science Foundation under Contract No. CCR-89-02496.