Microwave synthesis of magnetoresistive La0.7Ba0.3MnO3 using inorganic precursors

We report here the use of inorganic precursors as good microwave absorbers, by virtue of its polarity and high dielectric constant, to synthesize high temperature stable rare earth manganite, La_0.7Ba_0.3MnO₃. Compared to other wet chemical methods, the oxides prepared by microwave assisted route give fine particle oxides (<30 nm) with effective BET surface area of 25 m²/g. Two factors contribute to the rapid synthesis of these high temperature phases. Firstly, the dielectric constant of the precursors employed increases the microwave power loss in the material and this leads to a local heating effect. Secondly decomposition of these precursors, lead to formation of finely divided oxides often accompanied by an exothermic reaction which provides the needed energy to effect the formation of the product. This method offers a new approach to employ inorganic precursors as starting materials to realize fast and effective reaction in microwave assisted material synthesis.     

Synthesis and Surface Properties of a Novel Sodium 3‐(3‐Alkyloxy‐3‐oxopropoxy)‐3‐oxopropane‐1‐sulfonate at the Air–Water Interface

The present paper describes the synthesis and evaluation of surface properties of a novel series of anionic surfactant, namely sodium 3‐(3‐alkyloxy‐3‐oxopropoxy)‐3‐oxopropane‐1‐sulfonate with varying alkyl chain length (C8–C16). Synthesis involves initial formation of the 3‐alkyloxy‐3‐oxopropyl acrylate along with fatty acrylate during the direct esterification of fatty alcohol with acrylic acid in the presence of 0.5 % NaHSO₄ at 110 °C followed by sulfonation of the terminal double bond of the 3‐alkyloxy‐3‐oxopropyl acrylate. Synthesized compounds were evaluated for surface and thermodynamic properties such as critical micelle concentration (CMC), surface tension at CMC (γ_cmc), efficiency of surface adsorption (pC₂₀), surface excess (Γ_max), minimum area per molecule at the air–water interface (A_min), free energy of adsorption (?G°_ads), free energy of micellization (?G°_mic), wetting time, emulsifying properties, foaming power and calcium tolerance. Effect of chain length on CMC follows the classic trend, i.e. decrease in CMC with the increase in alkyl chain length. High pC₂₀ (>3) value indicates higher hydrophobic character of the surfactant. These surfactants showed very poor wetting time and calcium tolerance, but exhibited good emulsion stability and excellent foamability. Foaming power and foam stability of C14‐sulfonate were found to be the best among the studied compounds. Foam stability of C14‐sulfonate was also studied at different concentrations over time and excellent foam stability was obtained at a concentration of 0.075 %. Thus this novel class of surfactant may find applications as foam boosters in combination with other suitable surfactants.     

Joining of ZrB2-Based Ultra-High-Temperature Ceramic Composites to Cu–Clad–Molybdenum for Advanced Aerospace Applications

Three hot-pressed ZrB₂-based ultra-high-temperature ceramic composites (UHTCC), ZrB₂–SiC_p (ZS), ZrB₂–SiC_p–C (ZSC), and ZrB₂–SCS9A (SiC fiber)–SiC_p (ZSS), were joined to Cu–clad–Mo using AgCuTi brazes ( T _L∼1073–1173K) and Pd-base brazes ( T _L∼1493–1513K). More extensive chemical interactions occurred in Pd-base joints than in AgCuTi-base joints. The Pd-braze region displayed higher hardness in joints made using ZS than ZSS and ZSC. Residual stress calculations point toward negative strain energy up to ∼23% clad layer thickness because α_{Cu–clad–Mo}<α_ZS (α=coefficients of thermal expansion). Above this thickness, α_{Cu–clad–Mo}>α_ZS, strain energy is positive, and it increases with increasing thickness. Projected reductions in the thermal resistance highlight the benefits of joining the UHTCC to Cu–clad–Mo.     

CloudSim: a toolkit for modeling and simulation of cloud computing environments and evaluation of resource provisioning algorithms

Cloud computing is a recent advancement wherein IT infrastructure and applications are provided as ‘services’ to end‐users under a usage‐based payment model. It can leverage virtualized services even on the fly based on requirements (workload patterns and QoS) varying with time. The application services hosted under Cloud computing model have complex provisioning, composition, configuration, and deployment requirements. Evaluating the performance of Cloud provisioning policies, application workload models, and resources performance models in a repeatable manner under varying system and user configurations and requirements is difficult to achieve. To overcome this challenge, we propose CloudSim: an extensible simulation toolkit that enables modeling and simulation of Cloud computing systems and application provisioning environments. The CloudSim toolkit supports both system and behavior modeling of Cloud system components such as data centers, virtual machines (VMs) and resource provisioning policies. It implements generic application provisioning techniques that can be extended with ease and limited effort. Currently, it supports modeling and simulation of Cloud computing environments consisting of both single and inter‐networked clouds (federation of clouds). Moreover, it exposes custom interfaces for implementing policies and provisioning techniques for allocation of VMs under inter‐networked Cloud computing scenarios. Several researchers from organizations, such as HP Labs in U.S.A., are using CloudSim in their investigation on Cloud resource provisioning and energy‐efficient management of data center resources. The usefulness of CloudSim is demonstrated by a case study involving dynamic provisioning of application services in the hybrid federated clouds environment. The result of this case study proves that the federated Cloud computing model significantly improves the application QoS requirements under fluctuating resource and service demand patterns. Copyright © 2010 John Wiley & Sons, Ltd.