Subsurface damage during dry sliding wear of Al-Al3Ni eutectic alloy

Cylindrical Al-Al₃Ni eutectic alloy wear pins (10 mm in diameter) were slid against a polished steel surface in a pin-on-disc rotating machine under unlubricated conditions with bearing pressures of 6–60 kPa and a constant sliding speed of 70 m min^?1. Metallographic changes in the subsurface region of contact were examined by optical microscopy and microhardness measurements. In the bearing pressure range investigated the alloy exhibited “mild” wear in two linear regions identified as pure “oxidative” wear at low bearing pressures and oxidative with superimposed “metallic” wear at higher bearing pressures. Plastic deformation and fragmentation of the Al₃Ni phase occurred under all bearing pressures. However, in composites prepared by unidirectional solidification containing large Al₃Ni particles fragmentation was insignificant. In all other specimens the size of the fragmented particles in the subsurface region of contact was about 5 μm irrespective of the bearing pressure.     

Simultaneous determination of thickness and refractive index based on time-of-flight measurements of terahertz pulse

We present a simple technique for simultaneous determination of thickness and refractive index of plane-parallel samples in the terahertz radiation domain. The technique uses time-of-flight measurements of the terahertz pulse. It has been employed on nine different polymers and semiconductor materials, which are transparent for terahertz frequencies. Our results of thickness measurement are in good agreement with micrometer reading. The accuracy in the determination of refractive index is on the order of two decimal points.     

Estimation of Clark’s Instantaneous Unit Hydrograph Parameters and Development of Direct Surface Runoff Hydrograph

We present a method to estimate Time of Concentration (T _c) and Storage Coefficient (R) to develop Clark’s Instantaneous Unit Hydrograph (CIUH). T _c is estimated from Time Area Diagram of the catchment and R is determined using optimization approach based on Downhill Simplex technique (code written in FORTRAN). Four different objective functions are used in optimization to determine R. The sum of least squares objective function is used in a novel way by relating it to slope of a linear regression best fit line drawn between observed and simulated peak discharge values to find R. Physical parameters (delineation, land slope, stream lengths and associated drainage areas) of the catchment are derived from SPOT satellite imageries of the basin using ERDAS: Arc GIS is used for geographic data processing. Ten randomly selected rainfall–runoff events are used for calibration and five for validation. Using CIUH, a Direct surface runoff hydrograph (DSRH) is developed. Kaha catchment (5,598 km²), part of Indus river system, located in semi-arid region of Pakistan and dominated by hill torrent flows is used to demonstrate the applicability of proposed approach. Model results during validation are very good with model efficiency of more than 95% and root mean square error of less than 6%. Impact of variation in model parameters T _c and R on DSRH is investigated. It is identified that DSRH is more sensitive to R compared to T _c. Relatively equal values of R and T _c reveal that shape of DSRH for a large catchment depends on both runoff diffusion and translation flow effects. The runoff diffusion effect is found to be dominant.     

Non-linear stress analysis of composite layered plates and shells using a mesh reduction method

This paper represents an attempt for reducing the dimensionality of the finite element method, based on applying a new concept to the finite strip method. Mindlin's plate-bending theory has been employed for the derivation of an efficient element for buckling and stress analysis of folded and stiffened plates made of composite layered materials. The plate midplane is to be discretized in one direction in terms of this new element, leading to a simple mesh reduced by one dimension as compared with standard finite element meshes. The interpolation in the other direction is achieved by employing independently a smooth polynomial over the plate width. An efficient modular programming package based on the new element has been designed, and a number of case studies have been employed for its validation. The package has proved to be an efficient tool for numerical modelling of trapezoidal and stiffened plates, and cylindrical shells, made of isotropic or composite layered materials.     

Microstructure and mechanical properties of Al-Al2O3-MgO cast particulate composites

Al-Al₂O₃-MgO cast particle composites prepared by an MgO coating technique were investigated for their microstructural and mechanical property features. In all, sixteen compositions of the composite were subjected to this study. Generally, a uniform distribution of Al₂O₃ particles was observed in the composites. But in the upper half portion of the cylindrical castings, Al₂O₃ particles were found to segregate along the grain boundaries and also within the grain-forming chain-like structures. The microhardness of the base matrix revealed that the retention of submicrometre MgO particles causes dispersion strengthening. In the case of maximum strengthening, the microhardness of the base matrix rises to 35 kg mm^–2 from 19 kg mm^–2 for as-cast pure aluminium. The composites also displayed excellent high-temperature tensile properties up to 250°C (523 K). At the level of 21%V _f retention of Al₂O₃, the composite displayed a UTS value of 110 MN m^–2 with corresponding 0.2% offset yield strength of 65 MN m^–2 and 12% elongation at ambient temperature. At 150° C (423 K) and 250° C (523 K), the composite retains 69% and 53%, respectively, of its room-temperature UTS value. This was the optimum retention of Al₂O₃ and the best composite obtained in the present work. The excellent high-temperature characteristics of the composite are thought to be due to the sum total effect of both the submicrometre MgO particles and the coarser Al₂O₃ particles retained in the aluminium base matrix.     

Improving sentiment analysis efficacy through feature synchronization

Multimedia Tools and Applications - Social media platforms are becoming a rich source of valuable information through sharing and publishing user generated reviews and comments. The identification...     

Acidic ionic liquid polymers: <Emphasis Type="Italic">poly</Emphasis>(<Emphasis Type="Italic">bis</Emphasis>-imidazolium-<Emphasis Type="Italic">p</Emphasis>-phenylenesulfonic acid) and applications as catalysts in the preparation of 1-amidoalkyl-2-naphthols

A new class of polymeric acidic ionic liquids with imidazolium hydrogen sulfate and p-phenylene sulfonic acid units built into the main polymer chain were prepared by a simple two step method in 87–89% yield. These new polymers were characterized by elemental analysis, ¹H, ¹³C NMR, FT-IR, TGA and GPC. The catalytic activity of sulfonic acid group functionalized ionic liquid polymers was demonstrated through the synthesis of 1-amidoalkyl-2-naphthols in 78–90% yield by condensation of 2-naphthol, benzaldehyde and amides without a solvent at 100 °C.     

Self‐Phosphorization of MOF‐Armored Microbes for Advanced Energy Storage

Utilization of microbes as the carbon source and structural template to fabricate porous carbon has incentivized great interests owing to their diverse micromorphology and intricate intracellular structure, apart from the obvious benefit of “turning waste into wealth.” Challenges remain to preserve the biological structure through the harsh and laborious post‐synthetic treatments, and tailor the functionality as desired. Herein, Escherichia coli is directly coated with metal–organic frameworks (MOFs) through in situ assembly to fabricate N, P co‐doped porous carbon capsules expressing self‐phosphorized metal phosphides. While the MOF coating serves as an armoring layer for facilitating the morphology inheritance from the bio‐templates and provides metal sources for generating extra porosity and electrochemically active sites, the P‐rich phospholipids and N‐rich proteins from the plasma membrane enable carbon matrix doping and further yield metal phosphides. These unique structural and compositional features endow the carbon capsules with great capabilities in suppressing polysulfide shuttling and catalyzing reversible oxygen conversion, ultimately leading to the superb performance of lithium–sulfur batteries and zinc–air batteries. Combining the bio‐templating strategy with hierarchical MOF assembly, this work opens a new avenue for the fabrication of highly porous and functional carbon for advanced energy applications.     

Concurrent processing in nonlinear column stability

A concurrent processing algorithm is developed for materially nonlinear stability analysis of imperfect columns with biaxial partial rotational end restraints. The algorithm for solving the governing nonlinear ordinary differential equations is implemented on a multiprocessor computer called the finite element machine, developed at the NASA Langley Research Center. Numerical results are obtained on up to nine concurrent processors. A substantial computational gain is achieved in using the parallel processing approach.