Atomic force microscopy study of silica nanopowder compacts

Nanometer silica powders compacted at different pressures have been studied by atomic force microscopy (AFM). Local elastic moduli measurements made on the powder compacts yield values smaller than that of bulk silica. Loading force-distance curves measured show break points at some critical pressures. AFM images obtained at constant contact forces above and below the critical force at which a break point occured show the break point was a result of AFM tip plowing into the nanometer powder compacts. The applied force required for break points to occur increases with sample density. Such a behavior has been qualitatively explained in terms of adhesion force between nanoparticle and sample surface morphology.     

High-strain hysteresis of rubber vulcanizates over a range of compositions,rates, and temperatures

Hysteresis loss of natural rubber (NR) and styrene–butadiene rubber (SBR) vulcanizates having variations of loading of carbon black, silica, clay, resin, and curatives has been measured over a wide range of strain rates and temperatures as well as under swollen conditions. Hysteresis loss increases with an increase in strain rate, filler loading, resin loading (at high rates), crosslink density, and strain level. Hysteresis decreases with an increase in temperature, particle diameter of filler, and resin loading at high testing temperature. All the data of hysteresis loss of filled NR and SBR compounds have been found to be superimposable on single master curves with the help of the WLF shift factor. The master curves can be divided into three regions. The slope of the intermediate region, Δlog(hysteresis)/Δlog(Ra_T) has been found to be 0.1 for almost all the vulcanizates. Similar master plots have been obtained when the hysteresis loss has been measured at higher cycles and higher extensions and also by using the data of the hysteresis loss ratio. The hysteresis loss ratio of all the vulcanizates follows a similar trend, except for the highly crosslinked system, which shows a lower value. Carbon black contributes significantly to the hysteresis loss even when the energy dissipation is minimized by swelling. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1429–1439, 1997     

Characterization of Phytagel® modified soy protein isolate resin and unidirectional flax yarn reinforced “green” composites

The mechanical properties and moisture resistance of the soy protein isolate (SPI) resin and flax yarn reinforced composites were improved significantly by incorporation of a poly‐carboxylic acid based modifier, Phytagel®. SPI and Phytagel® were blended to form an interpenetrating network‐like cross‐linked complex. This complex showed significantly improved tensile and moisture properties as well as higher thermal stability as compared to the unmodified SPI resin. The incorporation of Phytagel® (40% w/w of SPI powder) in SPI resin and subsequent lowering of the amount of glycerol (from 30% to 12.5%) led to an overall 10‐fold increase in the tensile fracture stress and a nine‐fold increase in the Young's moduli of the SPI resin along with a seven‐fold decrease in fracture strain. The dynamic mechanical properties such as storage and loss modulus of the modified resin increased and the glass transition temperature also increased by about 56°C. The unidirectional flax yarn reinforced composites were made using two modified resins with 20% and 40% Phytagel® contents. Both resins contained 12.5% glycerol. The composites fabricated using resin containing 20% Phytagel® showed significantly higher tensile and flexural moduli as well as fracture stress in the axial direction than the composites with resin containing 40% Phytagel®, which was higher than the SPI resin based composites. POLYM. COMPOS., 26:647–659, 2005. © 2005 Society of Plastics Engineers     

Numerical Design of Megawatt Gyrotron with 120 GHz Frequency and 50% Efficiency for Plasma Fusion Application

The design of 120 GHz, 1 MW gyrotron for plasma fusion application is presented in this paper. The mode selection is carried out considering the aim of minimum mode competition, minimum cavity wall heating, etc. On the basis of the selected operating mode, the interaction cavity design and beam-wave interaction computation are carried out by using the PIC code. The design of triode type Magnetron Injection Gun (MIG) is also presented. Trajectory code EGUN, synthesis code MIGSYN and data analysis code MIGANS are used in the MIG designing. Further, the design of MIG is also validated by using the another trajectory code TRAK. The design results of beam dumping system (collector) and RF window are also presented. Depressed collector is designed to enhance the overall tube efficiency. The design study confirms >1 MW output power with tube efficiency around 50% (with collector efficiency).     

Bimetallic (Ni–Fe) anode-supported solid oxide fuel cells with gadolinia-doped ceria electrolyte

Anode-supported solid oxide fuel cells (SOFC) comprising nickel + iron anode support and gadolinia-doped ceria (GDC) of composition Gd_0.1Ce_0.9O_2−δ thin film electrolyte were fabricated, and their performance was evaluated. The ratio of Fe₂O₃ to NiO in the anode support was 3 to 7 on a molar basis. Fe₂O₃ and NiO powders were mixed in the desired proportions and discs were die-pressed. All other layers were sequentially applied on the anode support. The cell structure consisted of five distinct layers: anode support – Ni + Fe; anode functional layer – Ni + GDC; electrolyte – GDC; cathode functional layer – LSC (La_0.6Sr_0.4CoO_3−δ) + GDC; and cathode current collector – LSC. Cells with three different variations of the electrolyte were made: (1) thin GDC electrolyte (∼15 μm); (2) thick GDC electrolyte (∼25 μm); and (3) tri-layer GDC/thin yttria-stabilized zirconia (YSZ)/GDC electrolyte (∼25 μm). Cells were tested with hydrogen as fuel and air as oxidant up to 650 °C. The maximum open circuit voltage measured at 650 °C was ∼0.83 V and maximum power density measured was ∼0.68 W cm⁻². The present work shows that cells with Fe + Ni containing anode support can be successfully made.     

A semi-analytical method for the elastic-plastic large deflection analysis of welded steel or aluminum plating under combined in-plane and lateral pressure loads

The aim of the present paper is to develop a semi-analytical method which can quickly and accurately compute the elastic–plastic large deflection response of welded steel or aluminum plating under a combination of biaxial compression/tension, biaxial in-plane bending, edge shear and lateral pressure loads, until the ultimate limit state is reached. The post-weld initial imperfections (i.e. initial deflection and residual stresses) are included in the method as parameters of influence. It is assumed that the plating is simply supported at all (four) edges which are kept straight. A unique feature of the developed method is that geometric nonlinearity associated with large deflection response of plating under combined loads is treated by analytically solving the nonlinear governing differential equations of the elastic large deflection plate theory, while material nonlinearity due to plasticity is dealt with implicitly by a numerical procedure. This approach reduces the magnitude of numerical computations, resulting in a saving of modeling effort and computing time. As another contribution, this paper investigates and discusses the ultimate strength characteristics of plating, by varying the plate properties and load combinations, based on elastic–plastic large deflection analysis using the developed method.     

Densification and mechanical properties of mullite-SiC nanocomposites synthesized through sol-gel coated precursors

Mullite-SiC nanocomposites are synthesized by introducing surface modified sol-gel mullite coated SiC particles in the matrix and densification and associated microstructural features of such precursor are reported. Nanosize SiC (average size 180 nm) surface was first provided with a mullite precursor coating which was characterized by the X-ray analysis and TEM. An average coating thickness of 120 nm was obtained on the SiC particles. The green compacts obtained by cold isostatic pressing were sintered in the range 1500–1700°C under pressureless sintering in the N₂ atmosphere. The percentage of the theoretical sintered density decreases with increase in SiC content. A maximum sintered density of 97% was achieved for mullite-5 vol.% SiC. The fractograph of the sintered composite showed a highly dense, fine grained microstructure with the SiC particles uniformly distributed along the grains as well as at the grain boundaries inside the mullite. The Vicker’s microhardness of mullite-5 vol.% SiC composite was measured as 1320 kg/mm² under an applied indentation load of 500 g. This value gradually decreased with an increase in SiC content.     

Capacity of wireless networks under SINR interference constraints

A fundamental problem in wireless networks is to estimate their throughput capacity—given a set of wireless nodes and a set of connections, what is the maximum rate at which data can be sent on these connections. Most of the research in this direction has focused either on random distributions of points, or has assumed simple graph-based models for wireless interference. In this paper, we study the capacity estimation problem using a realistic Signal to Interference Plus Noise Ratio (SINR) model for interference, on arbitrary wireless networks without any assumptions on node distributions. The problem becomes much more challenging for this setting, because of the non-locality of the SINR model. Recent work by Moscibroda et al. (IEEE INFOCOM 2006, ACM MobiHoc 2006) has shown that the throughput achieved by using SINR models can differ significantly from that obtained by using graph-based models. In this work, we develop polynomial time algorithms to provably approximate the throughput capacity of wireless network under the SINR model.     

Fuzzy Logic Based Group Maturity Rating for Software Performance Prediction

Driven by market requirements,software services organizations have adopted various software engineering process models (such as capability maturity model (CMM),capability maturity model integration (CMMI),ISO 9001:2000,etc.) and practice of the project management concepts defined in the project management body of knowledge.While this has definitely helped organizations to bring some methods into the software development madness,there always exists a demand for comparing various groups within the organization in terms of the practice of these defined process models.Even though there exist many metrics for comparison,considering the variety of projects in terms of technology,life cycle,etc.,finding a single metric that caters to this is a difficult task.This paper proposes a model for arriving at a rating on group maturity within the organization.Considering the linguistic or imprecise and uncertain nature of software measurements,fuzzy logic approach is used for the proposed model.Without the barriers like technology or life cycle difference,the proposed model helps the organization to compare different groups within it with reasonable precision.     

Titanium for Automotive Applications: Challenges and Opportunities in Materials and Processing

Titanium offers performance as well as mass saving benefits in automotive components subjected to reciprocating and suspension loads and in components subjected to extreme temperatures and gradients. However, the extensive use of titanium is hampered by the high cost of the raw material and the special handling that is needed. This article outlines the technological and economic challenges faced and highlights some example materials and process developments that attempt to address these hurdles.