Heterogeneous Creep Deformations and Correlation to Microstructures in Fe-30Cr-3Al Alloys Strengthened by an Fe<Subscript>2</Subscript>Nb Laves Phase

A new Fe-Cr-Al (FCA) alloy system has been developed with good oxidation resistance and creep strength at high temperature. The alloy system is a candidate for use in future fossil-fueled power plants. The creep strength of these alloys at 973 K (700 °C) was found to be comparable with traditional 9 pct Cr ferritic–martensitic steels. A few FCA alloys with general composition of Fe-30Cr-3Al-.2Si-xNb (x = 0, 1, or 2) with a ferrite matrix and Fe₂Nb-type Laves precipitates were prepared. The detailed microstructural characterization of samples, before and after creep rupture testing, indicated precipitation of the Laves phase within the matrix, Laves phase at the grain boundaries, and a 0.5 to 1.5 μm wide precipitate-free zone (PFZ) parallel to all the grain boundaries. In these alloys, the areal fraction of grain boundary Laves phase and the width of the PFZ controlled the cavitation nucleation and eventual grain boundary ductile failure. A phenomenological model was used to compare the creep strain rates controlled by the effects of the particles on the dislocations within the grain and at grain boundaries. (The research sponsored by US-DOE, Office of Fossil Energy, the Crosscutting Research Program).     

Synthesis,Characterization, and Spectroscopic Analysis of NdxY1−xTiNbO6 Microwave Ceramics

Solid solutions of Nd_xY_1−xTiNbO₆ ceramics were prepared through the solid-state ceramic route. The materials were calcined at 1250°C and sintered in the range 1400–1550°C. The structure of the system was analyzed using the X-ray diffraction and vibrational spectroscopic analysis. The morphology and the sintering behavior of the samples were analyzed using scanning electron microscopy. The dielectric constant (ɛ_r), temperature coefficient of resonant frequency (τ_f), and the unloaded quality factor (Q_u) were measured in the microwave frequency region using the cavity resonator method. The ɛ_r and τ_f increased with an increase in the concentration of Nd in the solid solutions. Nearly zero temperature coefficient of resonant frequency was obtained for the Nd_0.6Y_0.4TiNbO₆ ceramic. Samples are of high quality factor and are useful for microwave applications.     

Multi-level image thresholding using Otsu and chaotic bat algorithm

Multi-level thresholding is a helpful tool for several image segmentation applications. Evaluating the optimal thresholds can be applied using a widely adopted extensive scheme called Otsu’s thresholding. In the current work, bi-level and multi-level threshold procedures are proposed based on their histogram using Otsu’s between-class variance and a novel chaotic bat algorithm (CBA). Maximization of between-class variance function in Otsu technique is used as the objective function to obtain the optimum thresholds for the considered grayscale images. The proposed procedure is applied on a standard test images set of sizes (512 × 512) and (481 × 321). Further, the proposed approach performance is compared with heuristic procedures, such as particle swarm optimization, bacterial foraging optimization, firefly algorithm and bat algorithm. The evaluation assessment between the proposed and existing algorithms is conceded using evaluation metrics, namely root-mean-square error, peak signal to noise ratio, structural similarity index, objective function, and CPU time/iteration number of the optimization-based search. The results established that the proposed CBA provided better outcome for maximum number cases compared to its alternatives. Therefore, it can be applied in complex image processing such as automatic target recognition.

     

Densification and alloying of ball milled Silicon-Germanium powder mixture during spark plasma sintering

In this research, the influence of process parameters such as sintering temperature and current during alloying and densification of silicon-germanium (Si₈₀-Ge₂₀) powder mixture using spark plasma sintering (SPS) was reported. Si₈₀-Ge₂₀ powder mixture was consolidated at the temperature range 900–1200 °C with 40 MPa pressure for 5 min. soaking. X-ray diffraction (XRD) study was made on sintered compacts to confirm the Si(Ge) alloy formation. Scanning electron microscope (SEM) was used to understand the morphology, particle size and distribution of un-milled and milled Si₈₀-Ge₂₀ powder mixture. Transmission electron microscope (TEM) study was made on milled Si₈₀-Ge₂₀ powder mixture and bulk SiGe alloy to confirm the nano-crystallinity and alloy formation. Fracture toughness of sintered bulk SiGe alloy was determined from Palmqvist cracks geometry model using Vickers hardness testing. It is understood that, during spark plasma sintering nano-structured Si₈₀-Ge₂₀ powder simultaneously increases the densification and reaction kinetics. It helps to achieve homogenous nanostructured SiGe alloy of near theoretical density. The superior hardness and benchmarked fracture toughness (K_IC) values of 630 VHN and 2.19 MPa√m was achieved for SiGe alloy sintered at 1200 °C, respectively.     

False alarm detection using dynamic threshold in medical wireless sensor networks

Sensor networks suffer from various sensor faults and false measurements in healthcare application and this vulnerability of the delay should handle efficiently and timely response in various application of WSN. For instance, in healthcare application, the false measurements generate false alarms which require to take unnecessary action from the healthcare department. The quality of the health care service can improve in remote healthcare monitoring system by introducing a new approach to identify the true medical condition and differentiate true and false alarms. In this paper, we proposed a novel approach to analysis past historical data collected from various medical sensors to identify the sensor anomaly. The main goal of this approach is to differentiate between true and false alarms effectively. The proposed system analysis the historical data to predicts the sensor value which compares with real sensed values at a time incident. The dynamically adjust the threshold value by comparing the difference between predicted value and historic value to determine the anomaly of sensor value. This system has been worked on huge real-time healthcare dataset and result shows that the new approach has been applied on real healthcare datasets and result of this system shows the detection rate is high and false positive rate is low which conclude that this approach is very useful in WSN application such as health monitoring system and it will be competitive with others.

     

Wavelength Conversion Placement in WDM Mesh Optical Networks*

Wavelength conversion helps improve the performance of wavelength division multiplexed (WDM) optical networks that employ wavelength routing. In this paper, we address the problem of optimally placing a limited number of wavelength converters in mesh topologies. Two objective functions, namely, minimizing the average blocking probability and minimizing the maximum blocking probability over all routes, are considered. In the first part of the paper, we extend an earlier analytical model to compute the blocking probability on an arbitrary route in a mesh topology, given the traffic and locations of converters. We then propose heuristic algorithms to place wavelength converters, and evaluate the performance of the proposed heuristics using the analytical model. Results suggest that simple heuristics are sufficient to give near-optimal performance.     

Crack initiation in cyclic compression and its applications

The characteristics and applications of crack initiation under far-field cyclic compressive loads are examined in notched specimens of a lower strength steel. The fatigue cracks, initiated at the notch root due to residual tensile stresses, grow at a progressively decreasing velocity before arresting completely. Simple correlations are explored between the total fatigue crack growth distance and the size of an effective damage zone estimated from the initial crack growth rate. Some important applications of crack initiation in cyclic compression in both long and short fatigue crack problems are demonstrated. Experimental results are presented to show that crack initiation in cyclic compression offers some interesting possibilities for obtaining accelerated estimates of slow fatigue crack growth rates, while minimizing some of the inherent uncertainties arising from the artifacts of conventional test techniques. Possible applications of this method are also discussed with respect to the study of physically-short flaws and of the evaluation of the progressive development closure during fatigue.     

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH₄) and ammonia borane (NH₃BH₃) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH₄ as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm⁻² at a load current density of 83 mA cm⁻² is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm⁻² at 105 mA cm⁻² is obtained in the case of AB-based fuel cell at 353 K.