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Effect of Solvent on Average Size and Size Distribution of Platinum Nanoparticles
No full textSynthesis process engineering to alter size of nanoparticles has been a subject of constant exploration. Effect of reaction solvent on nanoparticle size evolution in wet chemistry based techniques has however been scarcely explored. This report illustrates interesting dependence of average size and size distribution of Pt nanoparticles on synergistic variations in reaction solvent type, precursor-to-surfactant molar ratio and reaction mixture heating rate. It is illustrated that using a suitable combination of above reaction variables Pt nanoparticles with average sizes from 3 to 21 nm and with a variety of size distribution characteristics can be synthesized
Vision-based Control for Aerial Obstacle Avoidance in Forest Environments
No full textThe increasing application of unmanned aerial vehicles (UAVs) in unstructured, natural environments raises the demand for robust obstacle avoidance systems that work in realtime. In view of this problem, we present a control algorithm for quadrotors based on monocular vision that is specifically designed for obstacle avoidance in forest environments. The algorithm presented is an enhancement of an existing algorithm, originally proposed and tested for usage with rovers, that uses a weighted combination of texture features to compute distances to nearest obstacle in various longitudinal strips of the image frame. The weights are pre-computed by means of supervised learning of correspondences of the features to ground-truth distances processed on frames derived from a simulated forest environment. The modifications proposed on the original algorithm show significant improvement in its obstacle-distance estimation accuracy and computational efficiency as observed from actual autonomous flying experiments carried out on an off-the-shelf quadrotor. The modified algorithm works at 15 frames/sec for a frame size of 160 x 120 pixels as profiled on an Odroid XU4 mini-computer. Results from both simulated images and real videos have been presented. (C) 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved
A new variant of Arnoldi method for approximation of eigenpairs
No full textArnoldi method approximates exterior eigenvalues of a large sparse matrix, but may fail to approximate corresponding eigenvectors. The refined Arnoldi method approximates an eigenpair by solving a related singular value problem. In this paper, we propose a new procedure to extract an approximate eigenpair from a Krylov subspace in Arnoldi method, using a minimization problem. Unlike the refined Arnoldi method, the suggested procedure requires solving a linear system. (C) 2018 Elsevier B.V. All rights reserved
Critical Evaluation of Relative Importance of Stress and Stress Gradient in Whisker Growth in Sn Coatings
No full textThe role of stress state and stress gradient in whisker growth in Sn coatings electrodeposited on brass is examined. The bulk stress in Sn coatings was measured using a laser-optics-based curvature setup, whereas glancing angle x-ray diffraction was employed to quantify the stress near the surface; this also allowed studying the role of the out-of-plane stress gradient in whisker growth. Both bulk stress and near-surface stress in the Sn coating evolved with time, wherein both were compressive immediately after the deposition, and thereafter while the bulk stress monotonically became more compressive and subsequently saturated with aging at room temperature, the stress near the surface of the Sn coating continually became more tensile with aging. These opposing evolutionary behaviors of bulk and near-surface stresses readily reveals establishment of a negative out-of-plane stress gradient, which is required for the spontaneous growth of whiskers. The importance of the out-of-plane stress gradient was also validated by externally imposing widely different stress states and stress gradients in Sn coatings using a 3-point bending apparatus. Additional whisker growth occurred in the coatings subjected to external tensile stress; however, this was accompanied by a higher negative out-of-plane stress gradient. The results conclusively demonstrate the important role of the negative out-of-plane stress gradient on whisker growth, as compared to only sign and magnitude of stress
Cuspidality and the growth of Fourier coefficients of modular forms
No full textWe characterize Siegel cusp forms in the space of Siegel modular forms of large weight k > 2n on any Siegel congruence subgroup Gamma of any degree n and any level N, by a suitable growth of their Fourier coefficients (e.g., by the well-known Hecke bound) at any one of the cusps. For this, we use a `local' approach as compared to our previous results on this topic. We also touch upon the question in the context of vector-valued modular forms
The Evolution of GX 339-4 in the Low-hard State as Seen by NuSTAR and Swift
No full textWe analyze 11 Nuclear Spectroscopic Telescope Array and Swift observations of the black hole X-ray binary GX. 339-4. in the hard state, 6 of which were taken during the end of the 2015 outburst and 5 during a failed outburst in 2013. These observations cover luminosities from 0.5% to 5% of the Eddington luminosity. Implementing the most recent version of the reflection model relxillCp, we perform simultaneous spectral fits on both data sets to track the evolution of the properties in the accretion disk, including the inner edge radius, the ionization, and the temperature of the thermal emission. We also constrain the photon index and electron temperature of the primary source (the ``corona''). We observe a maximum truncation radius of 37 R-g in the preferred fit for the 2013 data set, and a marginal correlation between the level of truncation and luminosity. We also explore a self-consistent model under the framework of coronal Comptonization, and find consistent results regarding the disk truncation in the 2015 data, providing a more physical preferred fit for the 2013 observations
Molecular dynamics studies on the domain swapped Salmonella typhimurium survival protein SurE: insights on the possible reasons for catalytic cooperativity
No full textStationary phase survival protein SurE from Salmonella typhimurium is a dimeric protein formed by the swapping of a tetramerization loop involved in the formation of a loose tetramer and a C-terminal helix. It functions as a phosphatase. The two-fold symmetry of the dimeric protein was lost in the mutants H234A and D230A/H234A in which a crucial hydrogen bond in the hinge involved in C-terminal helix swapping was eliminated. The catalytic activity of both mutants was drastically reduced. In contrast to the native protein, H234A exhibited positive cooperativity in its catalytic activity. In order to relate these observations to the dynamics of the native and distorted mutants, molecular dynamics (MD) simulations were carried out using GROMACS v4.0.7. In all the simulations, the swapped segments and a segment near the active site were found to be highly flexible. These segments exhibited distinct dynamic features in the two protomers (A and B) of the dimeric protein. The dimeric organization was more significantly affected in the mutants when compared to the native structure, suggesting that the mutations enhance the intrinsic flexibility of the protein. The larger flexibility of the mutants affects the relative movement between the loops near the two active sites. The positive cooperativity observed in H234A mutant is most likely due to this increased flexibility and loop movement
Engineering Defects in Graphene Oxide for Selective Ammonia and Enzyme-Free Glucose Sensing and Excellent Catalytic Performance for para-Nitrophenol Reduction
No full textRecently, extensive attention has been given to developing an active and durable metal-free economical sensor and catalyst. Graphene oxide (GO)-based sensors and catalysts have been considered as a promising candidate in current material science research. However, the sensing and catalytic properties of GO also need to be further improved to satisfy the specific applications, such as gas detection in harsh environments, medical diagnosis based on human breath, blood glucose detection, catalytic activity, and so forth. Therefore, the effect of nitrogen in GO on the performance of glucose and ammonia sensing, and catalytic activity has been investigated. Herein, we propose a practical, high-sensitive sensor and catalyst based on high-quality defect N-enriched GO. One-step, low-cost solvothermal synthesis of N-enriched GO has been exploited for the development of high-performance sensors and excellent catalyst at room temperature. The resultant N-enriched GO (N8GO) has been studied as a promising sensing material for ammonia, glucose, and para-nitrophenol (PNP) reduction. The prevalent outstanding sensing and catalytic performance may be due to the synergistic effect of nitrogen. A probable mechanism for sensing and catalytic reduction of PNP using N8GO has been proposed
Wafer-scale epitaxial germanium (100), (111), (110) films on silicon using liquid phase crystallization
No full textA wafer-scale method to obtain epitaxial germanium (Ge) on crystalline silicon (Si) using liquid-phase-crystallization (LPC) is presented. The technique provides a simple yet versatile method to grow epitaxial germanium on silicon with any crystallographic orientation: (100), (110) or (111). The process starts with amorphous Ge, which is melted and cooled in a controlled manner to form epitaxial germanium. LPC Ge films are continuous with an average grain-size of 2-5 mu m. Rocking scan confirms that the LPC Ge is oriented with a threading dislocation density of similar to 109 cm(-2). The phi-scan confirms that LPC germanium is epitaxial with Ge (100), Ge (110) and Ge (111) showing four-fold, two-fold, and three-fold symmetry, respectively. The epitaxial quality of the Ge is influenced by the cleanliness of the Ge/Si interface; rate of cooling and ambient gas during LPC; and Ge layer thickness. Best films are obtained for 1 mu m thick LPC Ge(100), cooled at similar to 3-4 C/min in hydrogen ambient. Electron Hall mobility in these LPC Ge films is 736cm(2)/Vs, a high value that confirms the electronic quality of LPC Ge film. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license
Potential of fly ash to suppress the susceptible behavior of lime-treated gypseous soil
No full textThe use of lime and fly ash to improve the properties of certain types of soil is well established. However, the potential of fly ash to control the adverse effects of lime-treated gypseous/sulphatic soil has not been well investigated. In the present work, an attempt is made to quantify the fly ash content used to suppress the susceptible behavior of lime-treated gypseous soil. Series of one-dimensional swell and compressibility analyses are performed on various combinations of expansive soil with a predominance of montmorillonite mineral containing lime, gypsum (0-6%), and fly ash (0-30%). It is observed that the volume change behavior of the lime-treated gypseous soil is not controlled completely by addition of fly ash. However, the maximum improvement in the volume change behavior of the lime-treated gypseous soil is observed with a 20% fly ash content, and hence, can be taken as the Optimum Fly ash Content (OFC). Microanalyses revealed that the relative dominance of the change in gradation and the formation of cementitious compounds of different compositions and ettringite crystals are the key factors in controlling the volume change behavior of lime-treated gypseous soil with fly ash. However, several factors, such as the types of minerals present in the soil, the types of fly ash and lime, and other physico-chemical environmental conditions (temperature, method of curing, and so on), are seen in the present study to affect the value of the obtained OFC. (C) 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society