A finite range failure model

In the present article the characterstics of a finite range failure time distribution, that includes the rectangular distribution as a particular case, are studied. When shape parameter surpass unity then the distribution is IFR otherwise it always remains IFRA. A graphic shape of the distribution is also formed for certain admissible values of the constants.     

Thermal stability in bulk cryomilled ultrafine-grained 5083 Al alloy

Thermal stability in bulk ultrafine-grained (UFG) 5083 Al that was processed by gas atomization followed by cryomilling, consolidation, and extrusion, and that exhibited an average grain size of 305 nm, was investigated in the temperature range of 473 to 673 K (0.55 to 0.79 T _m , where T _m is the melting temperature of the material) for different annealing times. Appreciable grain growth was observed at temperatures > 573 K, whereas there was limited grain growth at temperatures < 573 K even after long annealing times. The values of the grain growth exponent, n, deduced from the grain growth data were higher than the value of 2 predicted from elementary grain growth theories. The discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination of the microstructure of the alloy suggests that the origin of the pinning forces is most likely related to the presence of dispersion particles, which are mostly introduced during cryomilling. Two-grain growth regimes were identified: the low-temperature region (<573 K) and the high-temperature region (>573 K). For temperatures lower than 573 K, the activation energy of 25 ± 5 kJ/mol was determined. It is suggested that this low activation energy represents the energy for the reordering of grain boundaries in the UFG material. For temperatures higher than 573 K, an activation energy of 124 ± 5 kJ/mol was measured. This value of activation energy, 124 ± 5 kJ/mol, lies between that for grain boundary diffusion and lattice diffusion in analogous aluminum polycrystalline systems. The results show that the strength and ductility of bulk UFG 5083 Al, as obtained from tensile tests, correlate well with substructural changes introduced in the alloy by the annealing treatment.     

Energy-Efficient Thermal-Aware Autonomic Management of Virtualized HPC Cloud Infrastructure

Virtualized datacenters and clouds are being increasingly considered for traditional High-Performance Computing (HPC) workloads that have typically targeted Grids and conventional HPC platforms. However, maximizing energy efficiency and utilization of datacenter resources, and minimizing undesired thermal behavior while ensuring application performance and other Quality of Service (QoS) guarantees for HPC applications requires careful consideration of important and extremely challenging tradeoffs. Virtual Machine (VM) migration is one of the most common techniques used to alleviate thermal anomalies (i.e., hotspots) in cloud datacenter servers as it reduces load and, hence, the server utilization. In this article, the benefits of using other techniques such as voltage scaling and pinning (traditionally used for reducing energy consumption) for thermal management over VM migrations are studied in detail. As no single technique is the most efficient to meet temperature/performance optimization goals in all situations, an autonomic approach that performs energy-efficient thermal management while ensuring the QoS delivered to the users is proposed. To address the problem of VM allocation that arises during VM migrations, an innovative application-centric energy-aware strategy for Virtual Machine (VM) allocation is proposed. The proposed strategy ensures high resource utilization and energy efficiency through VM consolidation while satisfying application QoS by exploiting knowledge obtained through application profiling along multiple dimensions (CPU, memory, and network bandwidth utilization). To support our arguments, we present the results obtained from an experimental evaluation on real hardware using HPC workloads under different scenarios.     

Modelling Gas Holdup in Flotation Column Froths

A one‐dimensional steady‐state model is developed for the prediction of axial variation of the gas holdup in flotation column froths. Froth is considered as an inverse fluidized bed of bubbles and hence the frictional pressure gradient is obtained based on the energy balance. Pressure gradient can also be obtained from the Ergun equation with adjustable constants. The model correctly captures the effect of superficial gas velocity, superficial liquid velocity and bubble diameter on the variation of the gas holdup along the froth height. The predictions of the model are in agreement with the experimental data from the literature.     

Confinement, composition, and spin-coating effects on the glass transition and stress relaxation of thin films of polystyrene and styrene-containing random copolymers: Sensing by intrinsic fluorescence

The glass transition temperatures (T_gs) of polystyrene (PS) and styrene/methyl methacrylate (S/MMA) random copolymer films are characterized by intrinsic fluorescence, i.e., monomer fluorescence from an excited-state phenyl ring and excimer fluorescence from an excited-state dimer of two phenyl rings. The T_g is determined from the intersection of the rubbery- and glassy-state temperature dependences of the integrated fluorescence intensity measured upon cooling from an equilibrated state. With PS, the effects of nanoconfinement on T_g and the transition strength agree with results from studies using probe fluorescence and ellipsometry. The T_g-nanoconfinement effect is “tuned” by copolymer composition. As S-content is reduced from 100 mol% to 22 mol%, the confinement effect changes from a reduction to an enhancement of T_g relative to bulk T_g. Intrinsic fluorescence is also a powerful tool for characterizing relaxation of residual stresses. Stresses induced by spin coating affect local conformations, which in turn affect excimer and monomer fluorescence and thereby integrated intensity. The heating protocol needed to achieve apparently equilibrated local conformations is determined by equivalence in the integrated intensities obtained upon heating and subsequent cooling. While partial stress relaxation occurs upon heating in the glassy state, full relaxation of local conformations requires that a film be heated above T_g for times that are long relative to the average cooperative segmental relaxation time. For example, in thin and ultrathin films, equilibration is achieved by heating slowly (∼1 K/min) to 15-20 K above T_g. Dilute solution fluorescence of PS and S/MMA copolymers is also characterized and compared to reports in the literature.     

Dynamic hardness of detonation sprayed WC-Co coatings

The objective of the present work was to determine the dynamic hardness of WC-Co coatings from the dynamic hardness of the coating substrate system. It was also the purpose of this work to evaluate the influence of coating composition, coating thickness, and substrate materials on the dynamic hardness of the coating. To achieve the above-mentioned objectives, WC-12%Co and WC-17%Co coatings were deposited by detonation spraying on three different substrate materials: mild steel, commercially pure (CP) aluminum, and CP titanium. The dynamic hardness of the coating/substrate composite was evaluated by a drop weight system. The dynamic hardness of the coating independent of the substrate was determined from the dynamic hardness of the coating/substrate composite.     

Linguistic Discriminative Aggregation in Multicriteria Decision Making

Several new aggregation operators are proposed in the context of multicriteria decision making (MCDM) in the linguistic domain. The proposed operators first infer the discrimination index, based on the extent of variability in the various linguistic evaluations against a criterion. This value is then utilized in the actual aggregation step to discriminate among the alternatives. Besides, the proposed operators also take into account the a priori weights associated with the criteria. The proposed concepts are illustrated through an example in group MCDM.     

Proactive thermal management in green datacenters

The increasing demand for faster computing and high storage capacity has resulted in an increase in energy consumption and heat generation in datacenters. Because of the increase in heat generation, cooling requirements have become a critical concern, both in terms of growing operating costs as well as their environmental and societal impacts. Presently, thermal management techniques make an effort to thermally profile and control datacenters’ cooling equipment to increase their efficiency. In conventional thermal management techniques, cooling systems are triggered by the temperature crossing predefined thresholds. Such reactive approaches result in delayed response as the temperature may already be too high, which can result in performance degradation of hardware.