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Atomization modes for levitating emulsified droplets undergoing phase change
No full textAbstract: We delineate and examine the distinct breakup modes of evaporating water-in-oil emulsion droplets under acoustic levitation. The emulsion droplets consist of decane/dodecane/tetradecane as oil, while the water concentration is varied from 10 to 30 (v/v). The droplets were heated under different laser irradiation intensities and were observed to exhibit three broad breakup mechanisms, viz., breakup through bubble growth, sheet breakup, and catastrophic breakup. The occurrence of these modes of the breakup is found to be primarily dependent on the volatility differential among the components. Early nucleation in water/decane emulsions results in the growth of vapor bubble, which is characterized by intricate patterns of wave propagation on the droplet surface. The formation of these patterns suggests that the short time scale and length scale of wave patterns is the manifestation of Faraday instability, triggered on the droplet surface by the acoustic field induced resonance. A sheet-like breakup, on the contrary, occurs predominantly in emulsions comprising of components with relatively high volatility difference (water/dodecane emulsions) due to the breakup of an indiscernible small sized bubble. Intense catastrophic breakup occurs for emulsions with significantly vast volatility difference (water/tetradecane emulsions) where the droplet undergoes prompt fragmentation into fine secondary droplets
Electrical and Chemical Tuning of Exciton Lifetime in Monolayer MoS2 for Field-Effect Transistors
No full textWe report the room temperature tuning of excitonic lifetime in pristine and hole-doped monolayer MoS2 based field effect transistor (FET) devices by systematically controlling the free carrier density. We observed that in pristine MoS2 devices, with intrinsic electron doping, an exciton dominant regime with an exciton lifetime of 3 ns exists, when doped electrostatically with holes. Interestingly we observe a sharp decrease in exciton lifetime and population with an increase of the electron density by electrostatic doping, with a corresponding increase in negative trion population. With increased hole doping by a chemical method, the exciton lifetime decreases, but it remains almost constant with electrostatic carrier density tuning. This decrease in lifetime, compared to that of the pristine case, might be due to the exciton-exciton annihilation mechanism which is proposed to be existent in a high exciton density regime. Further hole doping by a chemical method leads to a transition to a positive trion dominated regime, in which the exciton lifetime decreases further due to nonradiative energy transfer to the positive trions. We observe a slight increase in exciton lifetime due to partial neutralization of positive trions at high electrostatic electron doping and a corresponding increase in the probability of excitons. We suggest that when calculating the lifetime of excitons, the exciton-to-trions formation and exciton-exciton annihilation mechanisms should be considered. These fine-tunings of excitons in monolayer MoS2 can provide a platform for probing the excitonic physics and photonic applications. © 2019 American Chemical Society
Quantum channels over graph states using generalized measurement-based quantum computation framework
No full textMeasurement-based quantum computation (MBQC) is an alternative way of quantum information processing that describes the unitary evolution of a quantum state using the cluster state and well-defined sequential measurements. We give a closed form expression for the unitary evolution that a state goes through in terms of the network parameters and measurement outcomes on various qubits of the network. We extend the framework of MBQC to describe quantum channels. Using the new framework, we define a valid quantum unital channel between any two nodes of a graph consisting of nodes connected by edges. We describe the channel in terms of the network parameters and initial state. Our generalization consists of modifying the unitary operation, measurement operators, initial arbitrary state of the qubits at all the nodes of the network. We also study the inverse problem of devising an appropriate approximate unitary in the generalized MBQC to create any given quantum channel
Ion pair correlations due to interference between solvent polarizations induced in water
No full textMotions of two distinct ions can get correlated because the polarization induced by the ions can propagate through intervening water and can interfere with each other. This important aspect, which is not included in the continuum model based theories, has not been studied adequately. We calculate the effective force between two oppositely charged and similarly charged ions fixed in water as a function of separation distance R. At short separations, R less than 1.5 nm, the effective force vastly differs from the 1/ϵsR2 dependence advocated by the screened Coulomb's force law (SCFL), where ϵs is the static dielectric constant of the medium. This breakdown of the SCFL is shown to be due to the persistent interference between the polarizations created by the two charges in a manner similar to the vortex-antivortex pair formation in the XY model Hamiltonian. The distance dependence of dielectric constants, ϵs(R), extracted from our simulation exhibits interesting features and can be used in future modeling. In addition, we show that the force-force time autocorrelation between two neighboring ions decays differently at short separation and analyze the friction on the ion pair at different separation distances
Investigation of Swift Heavy Ion Irradiated Reduced Graphene Oxide (rGO)/Molybdenum Disulfide (MoS2) Nanocomposite Using Raman Spectroscopy
No full textIn this work, a few layer molybdenum disulfide (MoS2) and reduced graphene oxide (rGO) nanocomposite have been synthesized by liquid exfoliation method. The morphological and structural properties are analyzed using scanning electron microscopy and X-ray diffraction technique. The optical properties are also investigated using absorption and Raman spectroscopy. This report presents quantification of swift heavy ion irradiation induced defects using Raman spectroscopy. We found both Raman mode E-2g(1) and A(1g) corresponding to MoS2 and Raman modes of rGO are strongly affected by increasing ions doses. The defect induced lattice strain in the rGO/MoS2 nanocomposite is also estimated from Raman spectroscopy. MoS2 layers are found to be much more sensitive than rGO in the rGO/MoS2 nanocomposite. These types of study further used in device based application of rGO/MoS2 nanocomposite system
Robust emergence of sharply tuned place-cell responses in hippocampal neurons with structural and biophysical heterogeneities
No full textHippocampal pyramidal neurons sustain propagation of fast electrical signals and are electrotonically non-compact structures exhibiting cell-to-cell variability in their complex dendritic arborization. In this study, we demonstrate that sharp place-field tuning and several somatodendritic functional maps concomitantly emerge despite the presence of geometrical heterogeneities in these neurons. We establish this employing an unbiased stochastic search strategy involving thousands of models that spanned several morphologies and distinct profiles of dispersed synaptic localization and channel expression. Mechanistically, employing virtual knockout models (VKMs), we explored the impact of bidirectional modulation in dendritic spike prevalence on place-field tuning sharpness. Consistent with the prior literature, we found that across all morphologies, virtual knockout of either dendritic fast sodium channels or N-methyl-d-aspartate receptors led to a reduction in dendritic spike prevalence, whereas A-type potassium channel knockouts resulted in a non-specific increase in dendritic spike prevalence. However, place-field tuning sharpness was critically impaired in all three sets of VKMs, demonstrating that sharpness in feature tuning is maintained by an intricate balance between mechanisms that promote and those that prevent dendritic spike initiation. From the functional standpoint of the emergence of sharp feature tuning and intrinsic functional maps, within this framework, geometric variability was compensated by a combination of synaptic democracy, the ability of randomly dispersed synapses to yield sharp tuning through dendritic spike initiation, and ion-channel degeneracy. Our results suggest electrotonically non-compact neurons to be endowed with several degrees of freedom, encompassing channel expression, synaptic localization and morphological microstructure, in achieving sharp feature encoding and excitability homeostasis
A Tight Rate Bound and Matching Construction for Locally Recoverable Codes with Sequential Recovery from Any Number of Multiple Erasures
No full textThis paper considers the natural extension of locally recoverable codes (LRC) to the case of t > 1 erased symbols. While several approaches have been proposed for the handling of multiple erasures, in the approach considered here, the t erased symbols are recovered in succession, each time contacting at most r other symbols for assistance. Under the local-recovery constraint, this sequential approach is the most general and hence offers the maximum possible code rate. We characterize the rate of an LRC with sequential recovery for any r \geq 3 and any t, by first deriving an upper bound on the code rate and then constructing a binary code achieving this optimal rate. The upper bound derived here proves an earlier conjecture. Our approach permits us to deduce the structure of the parity-check matrix of a rate-optimal LRC with sequential recovery. The derived structure of parity-check matrix leads to a graphical description of the code used in code construction. A subclass of binary codes that are both rate and block-length optimal, are shown to correspond to certain regular graphs known as Moore graphs, that have the smallest number of vertices for a given girth. A connection with Tornado codes is also made
Investigating photoresponsivity of graphene-silver hybrid nanomaterials in the ultraviolet
No full textThere have been several reports of plasmonically enhanced graphene photodetectors in the visible and the near infrared regime but rarely in the ultraviolet. In a previous work, we have reported that a graphene-silver hybrid structure shows a high photoresponsivity of 13 A/W at 270 nm. Here, we consider the likely mechanisms that underlie this strong photoresponse. We investigate the role of the plasmonic layer and examine the response using silver and gold nanoparticles of similar dimensions and spatial arrangement. The effect on local doping, strain, and absorption properties of the hybrid is also probed by photocurrent measurements and Raman and UV-visible spectroscopy. We find that the local doping from the silver nanoparticles is stronger than that from gold and correlates with a measured photosensitivity that is larger in devices with a higher contact area between the plasmonic nanomaterials and the graphene layer
A New Analysis on Reduction of Undesired Beam Bending in Electrostatic Comb Drive MEMS Actuator
No full textIn electrostatic comb drive-based sensors and actuators, often there is a possibility of nonparallel motion or bending in individual comb which considerably affects the device performance including pull-in characteristic. In this paper, we have presented a theoretical and experimental investigation to reduce such undesired beam bending in gap closing-type comb drive actuator. It has been envisaged that three key parameters, responsible for beam bending, are spring stiffness, beam stiffness, and number of actuation beams. Subsequently, a design guideline has been proposed to reduce the undesired bending by appropriate selection of these parameters. A specific comb drive actuator having multiple actuation regions with varying number of beams is designed, simulated, and analyzed using a semianalytical approach and FEM tool. Further, the structure is fabricated by establishing a silicon-on-insulator (SOI)-based single mask fabrication process and tested with an in-house experimental setup. The theoretical predictions are validated with the experimental results to demonstrate how the undesired beam bending can be reduced significantly by suitable selection of number of actuation combs for a given ratio of spring and beam stiffness. The proposed guidelines enable the micro-electromechanical system (MEMS) designers to cautiously choose the key parameters while designing in order to avoid the undesired comb bending and operate the device safely
Effect of lanio3 on the impedance and dielectric properties of CoFe2O4: A high temperature study
No full textIn this article, we report the impedance and dielectric properties of the nanocomposites comprising of CoFe2O4 (CFO) and LaNiO3 (LNO) with varying LNO content (0, 5, 10 and 15) in the temperature range from 35 °C-400 °C. The impedance and modulus spectroscopy show the non-Debye type dielectric relaxation behaviour of the grain and grain boundary separately in pure CFO with an additional relaxation in the composite with 15 LNO, arising from the electrode polarization. Mostly the grain boundary of the composites is affected by the presence of LNO as its activation energy in the composite with 15 LNO is reduced by �0.2 eV compared to pure CFO, whereas that of the grain remains similar. The dielectric constant increases consistently with increasing LNO content in the composites owing to the Maxwell-Wagner-Sillar type polarization effect between the interfaces of LNO and CFO. The dielectric constant manifests a negative value in both pure CFO and the composite with 15 LNO at all temperatures in the frequency of hundreds of MHz which is explained by the interband transition. The ac conductivity of pure CFO reveals short range and orientational hopping inside the grains and across the grain boundary, respectively. However, in the composite with 15 LNO, the reduced activation energy assists the charge carriers for short range hopping across the grain boundary while the conductivity inside the grain remains unaffected