Technical review: Improvement of mechanical properties and suitability towards armor applications – Alumina composites

Ceramic Matrix Composites (CMCs) have many interesting properties, mainly light weight, cost efficiency, low density, high compressive strength, high hardness and durability. Hence, they emerged as a boon to the development of personnel armors in the past. The current work aims to review various new methodologies adapted for the reinforcement of Alumina (Al₂O₃) CMCs in recent times, including some of the interesting results obtained with respect to mechanical properties, suitability of the synthesized composites for armor applications, and the upcoming reinforcement trends. Finally, studies related to reinforcement in Al₂O₃ CMCs, specifically towards armor applications have been consolidated to arrive at some of the important inferences for concluding reasonably.     

Structural modification of aminoclay for catalytic applications

Abstract

An eco-friendly catalyst system was synthesized using three step reaction. The Cu nanoparticles bridged aminoclay catalyst was analyzed using various analytical techniques. The structure of the catalyst was confirmed by FTIR and XRD. The synthesized catalyst system was used for the reduction of p-nitrophenol (NP), Cr(VI), and fluorescein (Flur) dye individually, as well as in their mixture forms. The k_app value was computed to access the efficiency of the catalyst. The results indicated that the k_app value of the individual system is higher than that of the mixture systems due to the absence of the complex formation reaction. The catalytic performance of the catalyst was also tested for the Schiff base (SB) formation between poly(ethyleneglycol) (PEG) and aniline (ANI) in an oxygen atmosphere. The ¹H-NMR spectroscopy result indicates that the present catalyst system produced 86% yield.     

CFD Modeling of Active Volume Creation in a Non‐Newtonian Fluid Agitated by Submerged Recirculating Jets

Computational fluid dynamics (CFD) models were employed to investigate flow conditions inside a model reactor in which yield stress non‐Newtonian liquid is mobilized using submerged recirculating jets. The simulation results agree well with the experimental results of active volume in the reactor obtained using flow visualization by the authors in a previous study. The models developed are capable of predicting a critical jet velocity (v_c) that determines the extent of active volume obtained due to jet mixing. The v_c values are influenced both by the rheological properties of the liquid and the nozzle orientation. The liquid with higher effective viscosity leads to higher v_c for a downward facing injection nozzle. However, an upward facing injection nozzle along with a downward facing suction nozzle generates enhanced complementary flow fields which overcome the rheological constraints of the liquid and lead to lower v_c.     

Electrocatalytic Reduction of CO2 to Ethylene by Molecular Cu‐Complex Immobilized on Graphitized Mesoporous Carbon

The electrochemical reduction of carbon dioxide (CO₂) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO₂ to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO₂ to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO₂ in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.     

Study of impurity induced modifications in amorphous N-type (GeSe3·5)100−x Bi x using high pressure technique

The technique of high pressure is utilized to study the carrier transport behaviour in doped and undoped bulk amorphous (GeSe_3·5)_100−x Bi _x (x=0, 2, 4, 10) down to liquid nitrogen temperature to observe impurity induced modifications in amorphous semiconductors. It is observed that pressure induced effects in lightly doped (2 at % Bi) and heavily doped (x=4, 10) semiconductors are markedly different. Results are discussed in view of the incorporation behaviour of the bismuth impurity.     

Parallelization of WHILE loops on pipelined architectures

Modulo scheduling theory can be applied successfully to overlap Fortran DO loops on pipelined computers issuing multiple operations per cycle both with and without special loop architectural support. This paper shows that a broader class of loops—REPEAT-UNTIL, WHILE, and loops with more than one exit, in which the trip count is not known beforehand—can also be overlapped efficiently on multiple-issue pipelined machines. The approach is described with respect to a specific machine model, but it can be extended to other models. Special features in the architecture, as well as compiler representations for accelerating these loop constructs, are discussed. Performance results are presented for a few select examples.An earlier version of this paper was presented at Supercomputing '90.     

On the improvement of detection characteristics of trans-stilbene crystals by improving crystal perfection

Organic molecular scintillating crystals are noted for their good timing and particle discrimination process. Trans-stilbene is one such candidate noted for its good particle detection characteristics for the past five decades. Progressive strengthening of detection characteristics of trans-stilbene has been attempted by improving crystal perfection. A series of timing resolution studies have been carried out for the Bridgman grown trans-stilbene crystals under different experimental conditions. The results were compared with the previously reported values. Pulse shape discrimination process has been carried out for ²⁴¹Am and ²⁵²Cf sources and good discrimination has been obtained for gamma-alpha and gamma-neutron sources from the grown organic phosphor crystal. Electronic Publication     

Theoretical Analysis of the Fiber Pullout and Pushout Tests

The fiber pullout and pushout tests have been analyzed to predict the load-displacement behavior in terms of fiber/matrix interface parameters. The effects of residual axial strain in the fiber and fiber surface topography were included. The residual axial strain was found to be a significant parameter. It is shown that the interface failure can be progressive or catastrophic. In the case of a progressive failure of the interface, the load-displacement curve is nonlinear. The portion of the curve from above the first nonlinearity to near the peak load can be predicted in terms of parameters of the interface, viz., the friction coefficient, the radial stress at the interface, the fracture toughness of the interface, and the residual axial strain in the fiber. Values for these parameters can be obtained from a single loaddeflection curve. The peak load and load drop, which are usually reported, are found not to be directly relatable to any interface property, since the length of the last portion of the fiber to debond is influenced by end effects and hence not easily predicted. However, for data which describe the peak load as a function of initial embedded length, that factor can be eliminated and the data reduced to yield the relevant interface parameters. In pullout, the peak and friction loads saturate with large specimen thickness. Catastrophic failure is favored when the debond initiation load is high or when residual stress is low. Finally, a methodology to extract interface parameters from experimental data is suggested.     

Structural health monitoring of railway tracks using IoT-based multi-robot system

Neural Computing and Applications - A multi-robot-based fault detection system for railway tracks is proposed to eliminate manual human visual inspection. A hardware prototype is designed to...     

An expressive framework and efficient algorithms for the analysis of collaborative tagging

The rise of Web 2.0 is signaled by sites such as Flickr, del.icio.us, and YouTube, and social tagging is essential to their success. A typical tagging action involves three components, user, item (e.g., photos in Flickr), and tags (i.e., words or phrases). Analyzing how tags are assigned by certain users to certain items has important implications in helping users search for desired information. In this paper, we develop a dual mining framework to explore tagging behavior. This framework is centered around two opposing measures, similarity and diversity, applied to one or more tagging components, and therefore enables a wide range of analysis scenarios such as characterizing similar users tagging diverse items with similar tags or diverse users tagging similar items with diverse tags. By adopting different concrete measures for similarity and diversity in the framework, we show that a wide range of concrete analysis problems can be defined and they are NP-Complete in general. We design four sets of efficient algorithms for solving many of those problems and demonstrate, through comprehensive experiments over real data, that our algorithms significantly out-perform the exact brute-force approach without compromising analysis result quality.