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Influence of the mode of deformation on recrystallisation behaviour of titanium through experiments, mean field theory and phase field model
No full textThe influence of the mode of deformation on recrystallisation behaviour of Ti was studied by experiments and modelling. Ti samples were deformed through torsion and rolling to the same equivalent strain of 0.5. The deformed samples were annealed at different temperatures for different time durations and the recrystallisation kinetics were compared. Recrystallisation is found to be faster in the rolled samples compared to the torsion deformed samples. This is attributed to the differences in stored energy and number of nuclei per unit area in the two modes of deformation. Considering decay in stored energy during recrystallisation, the grain boundary mobility was estimated through a mean field model. The activation energy for recrystallisation obtained from experiments matched with the activation energy for grain boundary migration obtained from mobility calculation. A multi-phase field model (with mobility estimated from the mean field model as a constitutive input) was used to simulate the kinetics, microstructure and texture evolution. The recrystallisation kinetics and grain size distributions obtained from experiments matched reasonably well with the phase field simulations. The recrystallisation texture predicted through phase field simulations compares well with experiments though few additional texture components are present in simulations. This is attributed to the anisotropy in grain boundary mobility, which is not accounted for in the present study
Electrical switching in Si20Te80 - Bi-x(x) (0 <= x <= 3) chalcogenide glassy alloys
No full textChalcogenide glasses have attained enormous research interest due to their importance in finding electronic memories. Here we report electrical switching and thermal crystallization behavior of Si20Te80 (-) (x)Bix (0 <= x <= 3) glasses. We observe a significant decrease in the threshold voltage (V-T) and the thermal stability (Delta T), indicating that in Si20Te80 (-) Bi-X(X) glasses, the resistivity of the additive element Bi plays a dominant role over network connectivity/rigidity. The variation of V-T with respect to thickness and temperature of the sample indicates that the memory switching observed in Si20Te80 -XBiX glasses is influenced by the thermally induced transitions (thermal mechanism). Scanning electron microscopy (SEM) studies on pre-switched and post switched samples reveal the morphological changes on the surface of the sample, and serve as an experimental evidence for the formation of the crystalline filament between two electrodes during switching. Furthermore, the decrease in Delta T values indicates that the Si-Te glasses become de-vitrifiable more easily with the addition of Bi, influencing the decrease of V-T. Structural evaluation like thermal devitrification studies and morphological changes elucidate the restricted glass formability of the studied glass system
Nanoscale Heterogeneities Drive Enhanced Binding and Anomalous Diffusion of Nanoparticles in Model Biomembranes
No full textInteraction of functional nanoparticles with cells and model biomembranes has been widely studied to evaluate the effectiveness of the particles as potential drug delivery vehicles and bioimaging labels as well as in understanding nanoparticle cytotoxicity effects. Charged nanoparticles, in particular, with tunable surface charge have been found to be effective in targeting cellular membranes as well as the subcellular matrix. However, a microscopic understanding of the underlying physical principles that govern nanoparticle binding, uptake, or diffusion on cells is lacking. Here, we report the first experimental studies of nanoparticle diffusion on model biomembranes and correlate this to the existence of nanoscale dynamics and structural heterogeneities using super-resolution stimulated emission depletion (STED) microscopy. Using confocal and STED microscopy coupled with fluorescence correlation spectroscopy (FCS), we provide novel insight on why these nanoparticles show enhanced binding on two-component lipid bilayers as compared to single-component membranes and how binding and diffusion is correlated to subdiffraction nanoscale dynamics and structure. The enhanced binding is also dictated, in part, by the presence of structural and dynamic heterogeneity, as revealed by STED-FCS studies, which could potentially be used to understand enhanced nanoparticle binding in raft-like domains in cell membranes. In addition, we also observe a clear correlation between the enhanced nanoparticle diffusion on membranes and the extent of membrane penetration by the nanoparticles. Our results not only have a significant impact on our understanding of nanoparticle binding and uptake as well as diffusion in cell and biomembranes, but have very strong implications for uptake mechanisms and diffusion of other biomolecules, like proteins on cell membranes and their connections to functional membrane nanoscale platform
Solution processed Li5AlO4 dielectric for low voltage transistor fabrication and its application in metal oxide/quantum dot heterojunction phototransistors
No full textLi5AlO4, a well-known material for solid state electrolyte application, has never been considered hitherto as a gate dielectric of metal oxide thin film transistors (TFTs). Here we demonstrate the salient features of Li5AlO4 as a gate dielectric outperforming the conventional inorganic dielectrics used in TFTs. The high dielectric constant (k) of this insulator has been achieved by utilizing the improved capacitance contributed by mobile lithium ions (Li+) within the dielectric film. We have synthesized this dielectric via a cost-effective sol-gel method followed by a low-temperature annealing process yielding three phases such as amorphous-Li5AlO4 (a-Li5AlO4), a-Li5AlO4, and b-Li5AlO4 under different annealing conditions. Optimized TFTs fabricated with all of these three phases of Li5AlO4 on top of a highly doped silicon (p(++)-Si) wafer and a solution processed semiconducting layer of indium zinc oxide (IZO) exhibit an excellent TFT performance at different operating voltages. Among these three different types of TFTs, the device with an alpha-Li5AlO4 gate dielectric annealed at 500 degrees C shows the best device performance with an on/off ratio of 5 x 10(4) and an electron mobility of 21.4 +/- 2.16 cm(2) V-1 s(-1). In addition, this device requires the least drain voltage (<2 V) to reach the saturation drain current due to the higher Li+ mobility of the alpha-Li5AlO4( gate dielectric. This TFT performance on the p(++)-Si substrate is superior to that of a previously reported device with a sodium beta-alumina (SBA) gate dielectric, where the percentage of mobile ions within the dielectric material was comparatively much lower. Moreover, this dielectric requires B300 degrees C lower annealing temperature compared to the SBA dielectric. A metal oxide/quantum dot heterojunction phototransistor was fabricated by coating an IZO TFT with colloidal lead sulphide (PbS) quantum dots that shows a responsivity and a response time of 4.5 x 10(-4)A W-1 and 2.2 s respectively
Shell Thickness-Dependent Tunable Threshold Voltage Single Quantum Dot Rectification Diode
No full textAmbient atmosphere single colloidal quantum dot (QD) rectifying diode with tunable threshold voltage has been fabricated by using a type-II heterojunction core/shell structure with a device geometry ITO/ZnO/QDs. Specifically, in our work we have used ZnTe/CdS core/shell QDs in which hole wave function strongly confined to the core, whereas the lowest-lying conduction band state resides in the shell. Current voltage (I-V) characterization of this device has been done using an ambient atmosphere scanning tunneling microscope. The scanning tunneling spectra (STS) shows high rectification with a ratio of 10(3). The rectification is found to arise because of the bias-dependent band alignment of ZnO/QDs heterojunction and the effect of shell of each QD that presents a barrier for hole tunneling into the substrate. This barrier is overcome by the externally applied bias. This mechanism is distinct from the rectification observed in conventional p-n junction diodes. In particular, we find that even for QDs with optical band gaps of eV, the threshold voltage may be tuned from similar to 1 to 3 V by regulating shell thickness
Industrial waste fly ash cenosphere composites based broad band microwave absorber
No full textThe utilization of industrial waste fly ash cenosphere (FAC) for microwave absorption is explored in this study. FAC, the industrial waste, was pre-treated with conventional acid-base wash. As soft magnetic metal oxides are viewed with interest for microwave applications owing to their possessing many advantageous properties, in this work, NiO and CoOx was coated over FAC by chemical precipitation and thermal reduction method for studying the microwave absorption property. The polyvinylbutyral (PVB)FAC, PVB-CoOx-FAC and PVB-NiO-FAC composites were prepared by solution processing and dielectric property study was carried out in X-band (8.2-12.4 GHz) and Ku-band (12.4-18 GHz) microwave frequencies. The minimum reflection loss (RL) was observed for PVB-NiO-FAC composite in a large band width as compared to PVB-CoOx-FAC and PVB-FAC composites. In the X-band, the lowest RL value of PVBNiO-FAC composite was observed to be similar to-32 dB (similar to 12.3 GHz) and it decreased to similar to-49.7 dB in the Ku-band (15.8 GHz). Additionally, the thickness dependent RL was also studied for all the composites. The enhancement of EM attenuation constant and loss factor (LF) was found to be intrinsically high for PVBNiO-FAC composite along with dielectric dissipation as compared to other composites (i.e., PVB-FAC and PVB-CoOx-FAC) pointing to its excellent microwave absorption property. Therefore, the prepared composites are suitable for microwave absorption based applications such as radar, robotic engineering, military applications, electromagnetic gasket, aircraft and unmanned vehicles. (C) 2017 Elsevier Ltd. All rights reserved
Rate Adaptation, Scheduling, and Mode Selection in D2D Systems With Partial Channel Knowledge
No full textDevice-to-device (D2D) communication enables simultaneous data transmissions by cellular users (CU) and D2D user pairs, but at the expense of additional interference between them. The literature on resource allocation in D2D systems often assumes that the base station (BS) has complete channel state information (CSI) about all the links between all the users in a cell. However, acquiring the CSI of cross links between the CUs and the D2D receivers is a critical bottleneck because the number of cross links is the product of the number of CUs and D2D pairs. We study a novel partial CSI model in which the overhead of feeding back the CSI of the cross links is much lower. For a cell with one D2D pair and multiple CUs, we propose a novel throughput-optimal joint mode selection, user scheduling, and rate adaptation policy that exploits information about the statistics of the cross links and incorporates inter-cell interference. We derive closed-form expressions for the feedback-conditioned goodput for the underlay mode, which drives this optimal policy. We also present extensions that incorporate user fairness, quantized CSI, and multiple D2D pairs and multiple subchannels
Laboratory scale investigation of stress wave propagation and vibrational characteristics in sand when subjected to air-blast loading
No full textThe main objective of this study is to develop a new approach for evaluating the effects of air-blast on protective barrier made of sand. The air-blast loading is simulated experimentally laboratory using the shock tube test facility. The stress wave propagation in medium dense and dense sand medium are investigated under simulated air-blast loading. Synchronised pressure and accelerometer measurement system is used to capture peak stress wave pressure and peak particle velocity (PPV). The blast wave impact generates a stress wave in the medium leading to the compaction of the soil skeleton, which has led to stress enhancement (4-5 times of peak over-pressure) in top most sand layer, following which the high-pressure gas behind the shock front permeates through the sample. The intensity of stress waves and gas permeation rate gradually decrease with depth. Further, from the result of the simulated air-blast experiments, an empirical equation has been developed with a power law index of 1.88 and 1.36 for medium dense and dense sand respectively, to predict PPV against scaled blast distance. Visualisation of the sand deformation was possible with the help of a high-speed camera; displacement trajectories and strain contours are obtained through digital image correlation (DIC) analyses
Groundwater Level Dynamics in Bengaluru City, India
No full textGroundwater accounts for half of Indian urban water use. However, little is known about its sustainability, because of inadequate monitoring and evaluation. We deployed a dense monitoring network in 154 locations in Bengaluru, India between 2015 and 2017. Groundwater levels collected at these locations were analyzed to understand the behavior of the city's groundwater system. At a local scale, groundwater behavior is non-classical, with valleys showing deeper groundwater than ridge-tops. We hypothesize that this is due to relatively less pumping compared to artificial recharge from leaking pipes and wastewater in the higher, city core areas, than in the rapidly growing, lower peripheral areas, where the converse is true. In the drought year of 2016, groundwater depletion was estimated at 27 mm, or 19 Mm(3) over the study area. The data show that rainfall has the potential to replenish the aquifer. High rainfall during August-September 2017 led to a mean recharge of 67 mm, or 47 Mm(3) for the study area. A rainfall recharge factor of 13.5% was estimated from the data for 2016. Sustainable groundwater management in Bengaluru must account for substantial spatial socio-hydrological heterogeneity. Continuous monitoring at high spatial density will be needed to inform evidence-based policy
Investigation of Disorder in Mixed Phase, sp(2)-sp(3) Bonded Graphene-Like Nanocarbon
No full textDisorder in a mixed phase, sp(2)-sp(3) bonded graphene-like nanocarbon (GNC) lattice has been extensively studied for its electronic and field emission properties. Morphological investigations are performed using scanning electron microscopy (SEM) which depicts microstructures comprising of atomically flat terraces (c-planes) with an abundance of edges (ab planes which are orthogonal to c-planes). Scanning tunneling microscopy (STM) is used to observe the atomic structure of basal planes whereas field emission microscopy (FEM) is found to be suitable for resolving nanotopography of edges. STM images revealed the hexagonal and non-hexagonal atomic arrangements in addition to a variety of defect structures. Scanning tunneling spectroscopy is carried out to study the effect of this short-range disorder on the local density of states. Current versus voltage (I-V) characteristics have been recorded at different defect sites and are compared with respect to the extent of the defect. As sharp edges of GNC are expected to be excellent field emitters, because of low work function and high electric field, enhancement in current is observed particularly when applied electric field is along basal planes. Therefore, it is worthwhile to investigate field emission from these samples. The FEM images show a cluster of bright spots at low voltages which later transformed into an array resembling ledges of ab-planes with increasing voltage. Reproducible I-V curves yield linear Fowler-Nordheim plots supporting field emission as the dominant mechanism of electron emission. Turn on field for 10 mu A current is estimated to be similar to 3 V/mu m