High resistivity measurement of SiC wafers using different techniques

To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique, and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer was also obtained and reported in this work.     

Meshfree method for fluctuating hydrodynamics

In the current study a meshfree Lagrangian particle method for the Landau–Lifshitz Navier–Stokes (LLNS) equations is developed. The LLNS equations incorporate thermal fluctuation into macroscopic hydrodynamics by the addition of white noise fluxes whose magnitudes are set by a fluctuation–dissipation theorem. The study focuses on capturing the correct variance and correlations computed at equilibrium flows, which are compared with available theoretical values. Moreover, a numerical test for the random walk of standing shock wave has been considered for capturing the shock location.     

Operational Fault Detection in cellular wireless base-stations

The goal of this work is to improve availability of operational base-stations in a wireless mobile network through non-intrusive fault detection methods. Since revenue is generated only when actual customer calls are processed, we develop a scheme to minimize revenue loss by monitoring real-time mobile user call processing activity. The mobile user call load profile experienced by a base-station displays a highly non-stationary temporal behavior with time-of-day, day-of-the-week and time-of-year variations. In addition, the geographic location also impacts the traffic profile, making each base-station have its own unique traffic patterns. A hierarchical base-station fault monitoring and detection scheme has been implemented in an IS-95 CDMA Cellular network that can detect faults at - base station level, sector level, carrier level, and channel level. A statistical hypothesis test framework, based on a combination of parametric, semi-parametric and non-parametric test statistics are defined for determining faults. The fault or alarm thresholds are determined by learning expected deviations during a training phase. Additionally, fault thresholds have to adapt to spatial and temporal mobile traffic patterns that slowly changes with seasonal traffic drifts over time and increasing penetration of mobile user density. Feedback mechanisms are provided for threshold adaptation and self-management, which includes automatic recovery actions and software reconfiguration. We call this method, Operational Fault Detection (OFD). We describe the operation of a few select features from a large family of OFD features in Base Stations; summarize the algorithms, their performance and comment on future work.     

Distributed Multi-Level Recovery in Main-Memory Databases

In this paper we present recovery techniques for distributed main-memory databases, specifically for client-server and shared-disk architectures. We present a recovery scheme for client-server architectures which is based on shipping log records to the server, and two recovery schemes for shared-disk architectures—one based on page shipping, and the other based on broadcasting of the log of updates. The schemes offer different tradeoffs, based on factors such as update rates.Our techniques are extensions to a distributed-memory setting of a centralized recovery scheme for main-memory databases, which has been implemented in the Dalì main-memory database system. Our centralized as well as distributed-memory recovery schemes have several attractive features—they support an explicit multi-level recovery abstraction for high concurrency, reduce disk I/O by writing only redo log records to disk during normal processing, and use per-transaction redo and undo logs to reduce contention on the system log. Further, the techniques use a fuzzy checkpointing scheme that writes only dirty pages to disk, yet minimally interferes with normal processing—all but one of our recovery schemes do not require updaters to even acquire a latch before updating a page. Our log shipping/broadcasting schemes also support concurrent updates to the same page at different sites.     

Dielectric surface flashover in vacuum. Experimental design issues

In order to determine the influence of intrinsic material properties of dielectric materials on high field surface flashover characteristics in vacuum, it is important that we minimize or eliminate the influence of the experimental test structure on the high field processes. In this paper we shall examine the flashover characteristics of polycrystalline alumina insulators, using a lateral test structure similar to the one used in semiconductor devices. A significant improvement in surface flashover strengths (~200%) was found using a metalized contact electrode system compared with a classical solid electrode system. The results indicate that, using a metalized film cathode, the scatter in the flashover data is significantly reduced compared with the solid electrode system, implying that the electron-dielectric interaction processes that lead to flashover occur in a more predictable fashion. The new metal contact electrode system reveals the dependence of flashover strength on the surface preparation and the grain size of the dielectric material. The average flashover strength increases and the scatter in the flashover data decrease with a decrease in the average grain size of the particles composing the alumina ceramic. Thus the surface flashover processes in vacuum are related to the dielectric surface microstructure, specifically the surface and sub-surface microdamage and grain-boundary defects     

A multilevel hybrid anomaly detection scheme for industrial wireless sensor networks

Real-time sensing plays an important role in ensuring the reliability of industrial wireless sensor networks (IWSNs). Sensor nodes in IWSNs have inherent limitations that give rise to different anomalies in the network. These anomalies can lead to disastrous and harmful situations or even serious system failures. This article presents a formulation to the design of an anomaly detection scheme for detecting the anomalous node along with the type of anomaly. The proposed scheme is divided into two major parts. First, spatiotemporal correlation within a cluster is obtained for the normal and anomalous behavior of sensor nodes. Second, the multilevel hybrid classifier is used by combining the sequential minimal optimization support vector machine (SMO-SVM) as a binary classifier with optimally pruned extreme learning machine (OP-ELM) as a multiclass classifier for detection of an anomalous node and type of anomalies, respectively. Mahalanobis distance-based lightweight K-Medoid clustering is used to build a new set of training datasets that represents the original training dataset, by significantly reducing the training time of a multilevel hybrid classifier. Results are analyzed using standard WSN datasets. The proposed model shows high accuracy, i.e., 94.79% and detection rate, i.e., 94.6% with a reduced false positive rate as compared to existing hybrid methods.     

Tensile and Fracture Properties of Aluminium Alloy AA2219-T87 Friction Stir Weld Joints for Aerospace Applications

Metallurgical and Materials Transactions A - The purpose of the present work is to study the mechanical behaviour of AA2219-T87 friction stir weld (FSW) joints at different temperatures (Room...     

Analysis of blood and tissue in gallbladder cancer

Particle induced X-ray emission, particle induced γ-ray emission studies has been carried out to analyse normal and carcinoma tissues and blood samples of gallbladder of both sexes and seventeen trace elements namely Na, Mg, Al, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br and Pb were estimated in the tissue and blood samples. In the present study, concentration of Zn in the carcinoma gallbladder tissue is less than that of the normal gallbladder tissue. Tobacco habit could be one of the important factors to decrease the elemental concentrations in blood and tissue samples.     

Dynamic Embrittlement in Cu-Cr-Zr-Ti Alloy: Evidence of Intergranular Segregation of Sulphur

In the present investigation, Cu-0.6Cr-0.005Zr-0.0045Ti alloy was subjected to different heat treatment and thermomechanical treatment (TMT) to simulate the conditions experienced during brazing and forming, respectively. Grain coarsening was observed in the samples subjected to heat treatment, and grain refinement was observed in the samples subjected to TMT. Tensile tests conducted with these samples at room temperature and 600 °C have shown that Cu-Cr-Zr-Ti alloy was susceptible to dynamic embrittlement (DE). However, the observation was limited to coarse-grained samples (280-350 μm) at 600 °C. On the other hand, the fine-grained samples (20-40 μm) showed good ductility. Electron microscopy studies conducted on the tensile-tested specimens prone to DE indicated the presence of sulfur on the fractured surface and intergranular segregation of sulfur. Therefore, it can be inferred from the results that DE due to sulfur can occur in Cu-Cr-Zr-Ti alloy at elevated temperature for coarse-grained samples.