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Role of aging induced alpha precipitation on the mechanical and tribocorrosive performance of a beta Ti-Nb-Ta-O orthopedic alloy
No full textA low modulus beta Ti-Nb-Ta-O alloy was subjected to heat treatment to investigate its phase stability upon aging. The resultant effect on the mechanical and functional properties was systematically evaluated. The aging of the beta-only microstructure, obtained by solutionizing and quenching, resulted in the formation of ultrafine alpha-precipitates with increasing order of size as the aging temperature increased from 400 degrees C to 600 degrees C. The variation in the size of alpha-precipitates effected the mechanical properties at the three different aging temperature. The highest hardening observed at 400 degrees C was associated with macroscopic embrittlement, whereas age softening was observed in samples aged at 600 degrees C due to coarsening of precipitates and softening of the beta-matrix. In contrast, aging at 500 degrees C resulted in about 32% increase in tensile strength from the beta-solutionized condition. As the samples aged at 500 degrees C showed optimum combination of mechanical properties among the aged samples, these were further characterized for their electrochemical, tribological and biological responses. The fretting wear studies showed that the wear rate of the solution-treated samples increased after aging due to the higher corrosion rate leading to a higher rate of tribocorrosive dissolution and formation of a transfer layer harder than that of solution treated sample. The Ti-Nb-Ta-O alloy supported the attachment and proliferation of osteoblasts similar to that on commercially pure Ti. Taken together, this work provides new insights into the preparation of next-generation Ti alloys for biomedical applications with high strength and low modulus through microstructural control induced by heat treatment
Sharing from the Same Bowl: Resource Partitioning between Sympatric Macaque Species in the Western Himalaya, India
No full textComparative studies of closely related species with similar ecological requirements are essential to understand the behavioral adaptations that allow them to live in sympatry. We investigated the mechanisms that enable the coexistence of two congeneric macaques-the Assamese macaque (Macaca assamensis) and rhesus macaque (M. mulatta)-in the Western Himalaya along the India-Nepal border in the State of Uttarakhand, India. For five months from December 2016, we collected scan samples of the behavior of one Assamese macaque group (N = 9975 samples) and two rhesus macaque groups (N = 14,402). Activity budget comparisons revealed that the former spent more time on feeding and the latter on resting and moving. Although the two species had 29 (37%) of 78 food items in common, only Mallotus philippensis and agricultural crops formed a major part of their shared diet (contributing to >1% of feeding scans). The Assamese macaque fed predominantly on leaves and had a broader niche than did the rhesus macaque, which fed mostly on fruits. We also observed differences in feeding schedules and feeding heights of the two species. The two species showed variation in home range, daily movement patterns, habitat use, and sleeping sites that need further investigation. The two species exhibited a lower dietary and spatial niche overlap in winter, a period of relatively low resource abundance than in spring. The observed differences in diet and space use suggest that the niches of the two macaques are separated in several dimensions, which may have promoted their coexistence in this region. Similar long-term studies across different habitats and seasons can improve our understanding of resource use by primates in sympatry
Concentration dependent energy levels shifts in donor-acceptor mixtures due to intermolecular electrostatic interaction
No full textRecent progress in the improvement of organic solar cells lead to a power conversion efficiency to over 16%. One of the key factors for this improvement is a more favorable energy level alignment between donor and acceptor materials, which demonstrates that the properties of interfaces between donor and acceptor regions are of paramount importance. Recent investigations showed a significant dependence of the energy levels of organic semiconductors upon admixture of different materials, but its origin is presently not well understood. Here, we use multiscale simulation protocols to investigate the molecular origin of the mixing induced energy level shifts and show that electrostatic properties, in particular higher-order multipole moments and polarizability determine the strength of the effect. The findings of this study may guide future material-design efforts in order to improve device performance by systematic modification of molecular properties
Cross-modal retrieval in challenging scenarios using attributes
No full textCross-modal retrieval is an important field of research today because of the abundance of multi-media data. In this work, we attempt to address two challenging scenarios that we may encounter in real-life cross-modal retrieval, but which are relatively unexplored in literature. First, due to the ever-increasing number of new categories of data, cross-modal algorithms should be able to generalize to categories which it has not seen during training. Second, the data that is available during testing may be degraded (for example, it has low resolution or noise) as compared to those available during training. Here, we evaluate how these adverse conditions affect the performance of the state-of-the-art cross-modal approaches. We also propose a unified framework that can handle all these diverse and challenging scenarios without any modification. In the proposed approach, the data from different modalities are projected into a common semantic preserving latent space in which semantic relations as given by the classname embeddings (attributes) are preserved. Extensive experiments on diverse cross-modal data including image-text, RGB-depth and comparison with the state-of-the-art approaches show the usefulness of the proposed approach for these challenging scenarios
Recent advances in thermodynamics and nucleation of gas hydrates using molecular modeling
No full textMolecular modeling and simulations have provided valuable insights into our understanding of science of gas hydrates. In this article, we review the role played by molecular modeling towards advancing our knowledge of gas hydrate systems, with specific focus on thermodynamics and nucleation. We highlight the key recent advances achieved through computational research that have led to (i) substantial improvement in the accuracy of the thermodynamic theory and (ii) elucidation of molecular mechanisms involved in the nucleation of gas hydrates
Reliability analysis of near-surface disposal facility using subset simulation
No full textNear-surface disposal facility is intended for the disposal of low-level nuclear wastes. The reliability analysis of this facility is carried out to estimate the efficiency of the system in containing the nuclear wastes. Subset simulation, an advanced simulation technique, is used for the reliability analysis of the system, and the bootstrap method of resampling is used to quantify uncertainties in sampling. Further, Sobol indices are used for sensitivity analysis. In the present analysis, radionuclide diffusion model is used assuming diffusion of radionuclides through the multibarrier system to reach the aquifer, and in the aquifer, the contaminant transport model is used for determining the radionuclide concentration at different distances from the source
Polarization-Graded AlGaN Solar-Blind p-i-n Detector With 92% Zero-Bias External Quantum Efficiency
No full textWe report on record high zero-bias external quantum efficiency (EQE) of 92% for back-illuminated Al0.40Ga0.60N p-i-n ultra-violet (UV) photodetectors on sapphire. The zero-bias responsivity measured 211 mA/W at 289 nm, which is the highest value reported for solar-blind, p-i-n detectors realized over any epitaxial wide band-gap semiconductor. This is also the first report for a p-i-n detector, where a polarization-graded Mg-doped AlGaN layer is utilized as the p-contact layer. The devices exhibited a ten-orders of magnitude rectification, a low reverse leakage current density of 1 nA/cm(2) at 10 V, a high R(0)A product of 1.3 x 1011 Omega.cm(2) and supported fields exceeding 5 MV/cm. The light-to-dark current ratio and the UV-to-visible rejection ratio for the detectors exceeded six-orders of magnitude and the thermal noise limited detectivity (D*) measured 6.1 x 1014 cmHz(1/2)W(-1). The state-of-the-art performance parameters can be attributed to a high crystalline quality absorbing AlGaN epi-layer resulting from the use of an AlN/AlGaN superlattice buffer and an improved p-contact via polarization grading
Study and tailoring of screen-printed resistive films for disposable strain gauges
No full textThe present work aims at fabrication and characterization of the novel dispersion based piezoresistive strain gauges. The novelty of present work is in the material-set and technique used to synthesize the low-cost, graphite powder based composites of various proportions without the need for additional pretreatment or functionalization. When filler and resins are properly formulated, they can be printed in variety of shapes over different substrates such as glass, acrylic, plastics (such as PVC, PDMS, PMMA, PET, PI), metal foils, paper etc. They may be of great interest to integrate mechanical, chemical or temperature sensing functions in many electronic circuits and devices. In the current work, the resistive composite dispersions are screen-printed on glass substrate to fabricate the strain gauges and to study their piezoresistive strain performance. Graphite particles in the powder are found to have irregular shape and size. Thickness of screen-printed films varies in the range 13-27 mu m. Gauge factors ranging from 17 up to 70 is achieved for the strain gauges having satisfactory stability, linearity and repeatability. The variation in GF is found to be less than 2%. Maximum hysteresis and nonlinearity were observed to be less than 2% FSO (Full Scale Output). Repeatability is found to be minimum 98%. The dispersion composition is tuned to obtain a better sensitivity. Regarding temperature effects, all the strain gauge samples exhibited a negative value of TCR, lowest being -2 x 10(-4)/degrees C. Graphite powder and printing ink are inexpensive and commercially-available. Also, technique used to fabricate strain gauges avoids high-end equipment and expensive clean room facilities. These devices are robust, easy to scale & pattern, safely disposable strain gauges with are fairly good performance fabricated at low cost. These features make them a good candidate for pressure sensors, weigh bridges, displacement sensors, crack sensors, strain sensors etc. The real time potential applications are in different sectors such as automotive, aerospace, biomedical, oceanography and industrial purposes
Generalized Zero-Shot Cross-Modal Retrieval
No full textCross-modal retrieval is an important research area due to its wide range of applications, and several algorithms have been proposed to address this task. We feel that it is the right time to take a step hack and analyze the current status of research in this area. As new object classes are continuously being discovered over time, it is necessary to design algorithms that can generalize to data from previously unseen classes. Towards that goal, our first contribution is to establish protocols for generalized zero-shot cross-modal retrieval and analyze the generalization ability of the standard cross-modal algorithms. Second, we propose a semantic-aware ranking algorithm that can be used as an add-on to any existing cross-modal approach to improve its performance on both seen and unseen classes. Finally, we propose a modification of the standard evaluation metric (MAP for single-label data and NUCG for multi-label data), which we feel is a more intuitive measure of the cross-modal retrieval performance. Extensive experiments on two single-label and three multi-label crass-modal datasets show the effectiveness of the proposed approach
High-range noise immune supersensitive graphene-electrolyte capacitive strain sensor for biomedical applications
No full textThis paper presents development and performance assessment of an innovative and a highly potent graphene-electrolyte capacitive sensor (GECS) based on the supercapacitor model. Although graphene has been widely researched and adapted in supercapacitors as electrode material, this combination has not been applied in sensor technology. A low base capacitance, generally the impeding factor in capacitive sensors, is addressed by incorporating electric double layer capacitance in GECS, and a million-fold increase in base capacitance is achieved. The high base capacitance (similar to 22.0 mu F) promises to solve many inherent issues pertaining to capacitive sensors. GECS is fabricated by using thermally reduced microwave exfoliated graphene oxide material to form interdigitated electrodes coated with solid-state electrolyte which forms the double layer capacitance. The capacitance response of GECS on subjecting to strain is examined and an enormous operating range (similar to 300 nF) is seen, which is the salient feature of this sensor. The GECS showed an impressive device sensitivity of 11.24 nF kPa-1 and good immunity towards noise i.e. lead capacitance and stray capacitance. Two regimes of operation are identified based on the procedure of device fabrication. The device can be applied to varied applications and one such biomedical application of breath pattern monitoring is demonstrated