50175 research outputs found
Sort by
Generation of large-scale magnetic fields due to fluctuating alpha in shearing systems
No full textWe explore the growth of large-scale magnetic fields in a shear flow, due to helicity fluctuations with a finite correlation time, through a study of the Kraichnan-Moffatt model of zero-mean stochastic fluctuations of the alpha parameter of dynamo theory. We derive a linear integro-differential equation for the evolution of the large-scale magnetic field, using the first-order smoothing approximation and the Galilean invariance of the alpha-statistics. This enables construction of a model that is non-perturbative in the shearing rate S and the alpha-correlation time tau(alpha). After a brief review of the salient features of the exactly solvable white-noise limit, we consider the case of small but non-zero tau(alpha). When the large-scale magnetic field varies slowly, the evolution is governed by a partial differential equation. We present modal solutions and conditions for the exponential growth rate of the large-scale magnetic field, whose drivers are the Kraichnan diffusivity, Moffatt drift, shear and a non-zero correlation time. Of particular interest is dynamo action when the alpha-fluctuations are weak; i.e. when the Kraichnan diffusivity is positive. We show that in the absence of Moffatt drift, shear does not give rise to growing solutions. But shear and Moffatt drift acting together can drive large-scale dynamo action with growth rate gamma proportional to vertical bar S vertical bar
Patterning Cr Film by Passing Electric Current through a Traversing Pointy Stylus: Introduction to Electrolithography and Its Prospects
No full textHere, we introduce electrolithography, which is a recently developed lithography technique. Upon passage of electric current through a pointy cathode electrode placed on Cr film leads to formation and liquefaction of a Cr compound, which then flows away from the cathode in a radially symmetric fashion, thereby removing the Cr layer. If the pointy electrode, akin to a stylus, is traversed along a path, a trench will be patterned in the Cr film, which can then be transferred to other materials. Firstly, we describe the process of electrolithography and then we discuss the effects of the force applied on the stylus and the polymer layer placed in between substrate and Cr film on this lithography process. Finally, we discuss future prospects of electrolithography
Temporal evolution of radiative rate reveals the localization of holes in CuInS2-based quantum dots
No full textThe collapse of carriers into polarons strongly impacts properties such as charge transport, separation and recombination that are of fundamental relevance to opto-electronic devices such as photovoltaics. Here we observe the real-time process of the collapse of a wavefunction using ultrafast spectroscopy. We develop a method to extract changes in spontaneous lifetimes of an emitter over the course of its emission lifetime. This method enables us to detect the wavefunction collapse of photogenerated holes in CuInS2/CdS quantum dots (QDs). In particular, we observe that the spontaneous emission lifetime of these QDs is similar to 46 ns immediately after excitonic cooling but changes drastically to similar to 294 ns over the first 15 ps. The evolution in emission lifetimes and the corresponding variation in emission energetics imply changes in the hole wavefunction even after usual excitonic cooling is complete, and is consistent in its migration into a phonon coupled state located within the semiconductor band gap
Genetic analysis of the glucocerebrosidase gene in South Indian patients with Parkinson's disease
No full textBackground: Mutations in the glucocerebrosidase ( GBA) gene have been associated with Parkinson's disease ( PD). Several variants in the gene have been identified as risk factors for the development of PD, but there is difference in the prevalence of this mutation in various ethnic groups and countries. There is no published study related to this field on the Indian population. Aims and Objectives: The aim of the study was to investigate the frequency of mutations in the GBA gene in Indian patients with PD. Materials and Methods: To perform the mutation analysis of the GBA gene, we amplified its entire coding region, spanning 11 exons and intron/ exon junctions in three fragments, with a set of three primer pairs using the long polymerase chain reaction enzyme mix from Fermentas, Canada. Results: We screened a total of 100 PD patients for mutations in the GBA gene. The sequence analysis identified the following five variants in this gene: IVS1 + 191G > C, IVS4 + 47G > A ( rs. 2075569), IVS6 - 86A > G ( rs. 114099990), IVS9 + 141A > G ( rs. 28373017), and IVS10 + 3G > A. Of these, two variants IVS1 + 191G > C and IVS10 + 3G > A are novel, and the remaining three are known variants reported in the Single Nucleotide Polymorphism database ( dbSNP). All the known variants were detected in homozygous as well as in heterozygous states. Both novel variants were identified in only one patient in a heterozygous state. Conclusion: GBA mutation may not be so common in Indian patients with PD as compared to the other ethnic populations. These findings need to be confirmed in larger studies
Polarization inversion applied to proton MAS-NMR spectroscopy - Methylene and methine free proton NMR spectra
No full textPolarization-inversion (PI) has been applied to proton magic angle spinning (MAS) NMR spectra recorded under fast MAS conditions. The combination of cross-polarization (CP) from carbon to proton and subsequent polarization-inversion produces strong oscillatory behavior in the proton signal intensities at high MAS speeds of 60 kHz. It is observed that by a suitable choice of the polarization-inversion time, a proton spectrum free of methylene and methine protons can be obtained. Such a spectrum, on the one hand, increases the resolution of the crowded proton spectrum and on the other hand provides exclusively chemical shifts of protons such as NH, OH and SH which might otherwise overlap with carbon attached protons. The oscillations observed during PI can also be used to estimate the dipolar coupling between proton and carbon by Fourier transformation of data acquired at equally incremented time periods. The utility of the above ideas has been demonstrated on a set of molecules with both C-13 labeled and C-13 in natural abundance. (C) 2018 Elsevier Inc. All rights reserved
Active dendrites regulate the spatiotemporal spread of signaling microdomains
No full textMicrodomains that emerge from spatially constricted spread of biochemical signaling components play a central role in several neuronal computations. Although dendrites, endowed with several voltage-gated ion channels, form a prominent structural substrate for microdomain physiology, it is not known if these channels regulate the spatiotemporal spread of signaling microdomains. Here, we employed a multiscale, morphologically realistic, conductance-based model of the hippocampal pyramidal neuron that accounted for experimental details of electrical and calcium-dependent biochemical signaling. We activated synaptic N-Methyl-D-Aspartate receptors through theta-burst stimulation (TBS) or pairing (TBP) and assessed microdomain propagation along a signaling pathway that included calmodulin, calcium/calmodulin-dependent protein kinase II (CaMKII) and protein phosphatase 1. We found that the spatiotemporal spread of the TBS-evoked microdomain in phosphorylated CaMKII (pCaMKII) was amplified in comparison to that of the corresponding calcium microdomain. Next, we assessed the role of two dendritically expressed inactivating channels, one restorative (A-type potassium) and another regenerative (T-type calcium), by systematically varying their conductances. Whereas A-type potassium channels suppressed the spread of pCaMKII microdomains by altering the voltage response to TBS, T-type calcium channels enhanced this spread by modulating TBS-induced calcium influx without changing the voltage. Finally, we explored cross-dependencies of these channels with other model components, and demonstrated the heavy mutual interdependence of several biophysical and biochemical properties in regulating microdomains and their spread. Our conclusions unveil a pivotal role for dendritic voltage-gated ion channels in actively amplifying or suppressing biochemical signals and their spatiotemporal spread, with critical implications for clustered synaptic plasticity, robust information transfer and efficient neural coding
Evidence for Bingham plastic boundary layers in shear banding of metals
No full textWe study material flow in the vicinity of single shear bands in high strain-rate (10(4) -10(5) per second) deformation of metals. Shear band plastic flow, in three different materials, is shown to resemble unsteady planar Couette flow (Stokes first problem) of a Bingham fluid. Equivalent shear band viscosities and yield stresses are obtained, with the former similar to liquid metal viscosities and the latter being similar to 0.5 times the band nucleation stress. Reynolds and Bingham numbers, computed based on the shear band displacement measurements, are suggestive of boundary layer formation, consistent with the severe localization of deformation within shear bands. (C) 2018 Elsevier Ltd. All rights reserved
Search for black holes and sphalerons in high-multiplicity final states in proton-proton collisions a root s=13 TeVt
No full textA search in energetic, high-multiplicity final states for evidence of physics beyond the standard model, such as black holes, string balls, and electroweak sphalerons, is presented. The data sample corresponds to an integrated luminosity of 35.9 fb(-1) collected with the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV in 2016. Standard model backgrounds, dominated by multijet production, are determined from control regions in data without any reliance on simulation. No evidence for excesses above the predicted background is observed. Model-independent 95% confidence level upper limits on the cross section of beyond the standard model signals in these final states are set and further interpreted in terms of limits on semiclassical black hole, string ball, and sphaleron production. In the context of models with large extra dimensions, semiclassical black holes with minimum masses as high as 10.1 TeV and string balls with masses as high as 9.5 TeV are excluded by this search. Results of the first dedicated search for electroweak sphalerons are presented. An upper limit of 0.021 is set at 95% confidence level on the fraction of all quark-quark interactions above the nominal threshold energy of 9 TeV resulting in the sphaleron transition
Cooperative effect between BaTiO3 and CaFe2O4 in a cocatalyst-free heterojunction composite for improved photochemical H-2 generation
No full textA series of novel BaTiO3/CaFe2O4 heterojunction composites with different weight ratios of CaFe2O4 vs BaTiO3 was successfully fabricated by sonication-calcination method using the pre-prepared BaTiO3 and CaFe2O4 powders synthesized in hydrothermal and sol-gel methods, respectively. The composites were well characterized using XRD, UV-vis DRS, SEM, TEM, EDS and XPS to substantiate that BaTiO3 and CaFe2O4 coexist in the heterojunction composite. The highest photocatalytic hydrogen generation rate was obtained for BaTiO3/CaFe2O4 (40 wt%) compared to either of its individual counterparts and this improvement indicated the existence of a cooperative effect between BaTiO3 and CaFe2O4 in the heterojunction. Based on UV-vis-DRS, photoluminescence and time-resolved fluorescence lifetime measurements, the cooperative effect between BaTiO3 and CaFe2O4 originated from the improved photoresponse in the visible light region and efficient separation of the photogenerated electron-hole pairs augmenting their availability for the photocatalytic reaction. A plausible photocatalytic mechanism was also deduced using electrochemical impedance spectroscopy measurements, describing the migration direction of the separated charge carriers. Moreover, the best composite BaTiO3/CaFe2O4 (40 wt %) exhibited fairly stable photoactivity for H-2 production using the sacrificial agent (Na2S and Na2SO3) without the assistance of any noble metals as cocatalysts. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
Composition of MoO2 Nanoparticles with RGO Sheets as Improved Lithium Ion Battery Anode
No full textThough molybdenum dioxide (MoO2) has attractive properties, conductivity is still threat to its implementation as it is very low compared to graphite. Herein, we have come up with MoO2-rGO nanocomposite to mitigate this drawback, where nano sized MoO2 particles have been synthesised and supported with graphene sheets. Several physicochemical characterization techniques have been used to confirm the desired state of the obtained material. In this report, rGO supported MoO2 nanoparticles have been investigated as an anode for lithium ion battery and its electrochemical properties have been extensively studied. The new architecture exhibits excellent electrochemical performance by delivering a high discharge capacity of 1205 mA h g(-1) even after 100 cycles. It also exhibits good rate capability by delivering discharge capacities of 809, 753, 675 mA h g(-1) at current rates of 1 C, 3 C and 5 C, respectively