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.     

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.     

Boron diffusion into 6H-SiC through graphite mask

Experimental results are reported of selective diffusion of boron in 6H−SiC. Photoluminescence spectroscopy scanning electron microscopy cathodoluminescence imaging, secondary-ion mass spectroscopy optical microscopy, and stain-groove technique were used to characterize the selectively doped regions fabricated by diffusion from the vapor phase through a graphite mask. Local p-doped regions of dimensions down to ∼20 μm in diameter were formed on an n-type substrate using the graphite mask. Maximum concentration of boron atoms at the surface, obtained by SIMS, varied from 3×10¹⁹ cm⁻³ to 6×10¹⁹ cm⁻³, depending upon the temperature of diffusion, while the p-n junction depth measured by the stain-groove technique varied from 0.5 μm to 1.2 μm. Planar p-n junction diodes fabricated on the diffused regions exhibited good rectification characteristics with a breakdown voltage of about 1000 V.     

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.     

Characteristics of Dislocation Half-Loop Arrays in 4H-SiC Homo-Epilayer

Dislocation “half-loop arrays” (HLAs) in 4H-SiC homo-epilayers are studied by molten KOH etching and atomic force microscopy (AFM). It is found that the dislocation half-loops in an array exist at different depths in the epilayer, and they are aligned roughly but not exactly perpendicular to the off-cut direction. These results indicate that the dislocation half-loops in an array are not formed simultaneously, but the array extends by generation of new half-loops during growth. It is also demonstrated that the HLAs can be artificially induced by creating strain in the material, followed by annealing.     

Interaction of lanthanide and actinide with BaHfO3 perovskite: A case study with cerium and uranium

Speciation of actinide (An) and lanthanide (Ln) in technologically important ceramics is very important from both fundamental as well as technological aspects. The intrinsic structural flexibility of perovskite containing AO₆ and BO₁₂ polyhedra makes them suitable and rich hosts for An and Ln. In this work, emphasis was given to deciphering information such as oxidation state, local dopant site, charge compensating defects, excited state kinetics, and so forth in BaHfO₃ (BHO) related to dopant uranium (BHO-U) and cerium (BHO-Ce). Several spectroscopic techniques namely, time-resolved photoluminescence (TRPL), positron annihilation lifetime spectra (PALS), and thermoluminescence (TL) spectroscopy coupled with density functional theory (DFT) were employed to probe the same. Ce and U though are distributed at both Ba and Hf sites, Ce prefers the former, while U prefers the latter site. Uranium on the other hand stabilizes as U⁶⁺ in the form of octahedral uranate ion giving green emission. PALS suggested the formation of defects in BHO-Ce and BHO-U with oxygen vacancies predominating in the former whereas BHO-U perovskites are loaded with cation vacancies and vacancy clusters. These cation vacancies are responsible for lower TL output in BHO-U. TL measurements also suggested cerium doping leads to a higher density of deeper traps in BHO-Ce compared to uranium doping in BHO-U which is in concurrence with DFT results and may have implications in designing afterglow phosphors based on perovskite. We believe this work would have a long-term impact on exploring the potential of perovskite for nuclear waste host and afterglow phosphors applications.     

Understanding the swelling of poly (N-isopropyl acrylamide) gels through the study of free volume hole size distributions using positron annihilation spectroscopy

Poly (N-isopropyl acrylamide) gels were prepared by UV polymerization with different degree of cross-linking in different solvents. Ethylene glycol dimethacrylate and penta-erythritol tetra-acrylate were used as cross-linkers, and methanol and dimethyl formamide (DMF) were used as solvents for gel preparation. The free volume fraction and hole size distribution in the dry gels were measured using positron annihilation lifetime spectroscopy. The equilibrium swelling of the samples in water was measured at room temperature. Both swelling properties of gels and the free volume distributions were seen to be sensitive to the amount, type, and functionality of cross-linkers as well as solvent medium used for synthesis. The gels prepared in DMF showed poor swelling properties than those prepared in methanol. The mean free volume hole size was higher while the variance of hole size distribution was smaller in the gels prepared in DMF medium compared to those prepared in methanol. The free volume fractions in the gels were found to be inversely correlated to the extent of equilibrium swelling for similar chemical compositions. The possible reasons are discussed.     

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.     

Metal hydride material requirements for automotive hydrogen storage systems

The United States Department of Energy (DOE) has published a progression of technical targets to be satisfied by on-board rechargeable hydrogen storage systems in light-duty vehicles. By combining simplified storage system and vehicle models with interpolated data from metal hydride databases, we obtain material-level requirements for metal hydrides that can be assembled into systems that satisfy the DOE targets for 2017. We assume minimal balance-of-plant components for systems with and without a hydrogen combustion loop for supplemental heating. Tank weight and volume are driven by the stringent requirements for refueling time. The resulting requirements suggest that, at least for this specific application, no current on-board rechargeable metal hydride satisfies these requirements.