50175 research outputs found
Sort by
Femtosecond coherent nuclear dynamics of excited tetraphenylethylene: Ultrafast transient absorption and ultrafast Raman loss spectroscopic studies
No full textUltrafast torsional dynamics plays an important role in the photoinduced excited state dynamics. Tetraphenylethylene (TPE), a model system for the molecular motor, executes interesting torsional dynamics upon photoexcitation. The photoreaction of TPE involves ultrafast internal conversion via a nearly planar intermediate state (relaxed state) that further leads to a twisted zwitterionic state. Here, we report the photoinduced structural dynamics of excited TPE during the course of photoisomerization in the condensed phase by ultrafast Raman loss (URLS) and femtosecond transient absorption (TA) spectroscopy. TAmeasurements on the S1 state reveal step-wise population relaxation from the FranckCondon (FC) state -> relaxed state -> twisted state, while the URLS study provides insights on the vibrational dynamics during the course of the reaction. The TA spectral dynamics and vibrational Raman amplitudes within 1 ps reveal vibrational wave packet propagating from the FC state to the relaxed state. Fourier transformation of this oscillation leads to a similar to 130 cm(-1) low-frequency phenyl torsional mode. Two vibrational marker bands, C-et=C-et stretching (similar to 1512cm(-1)) and C-ph=C-ph stretching (similar to 1584 cm(-1)) modes, appear immediately after photoexcitation in the URLS spectra. The initial red-shift of the C-ph=C-ph stretching mode with a time constant of similar to 400 fs (in butyronitrile) is assigned to the rate of planarization of excited TPE. In addition, the C-et=C-et stretching mode shows initial blue-shift within 1 ps followed by frequency red-shift, suggesting that on the subpicosecond time scale, structural relaxation is dominated by phenyl torsion rather than the central C-et=C-et twist. Furthermore, the effect of the solvent on the structural dynamics is discussed in the context of ultrafast nuclear dynamics and solute-solvent coupling. Published by AIP Publishing
Microwave irradiation-assisted deposition of Ga2O3 on III-nitrides for deep-UV opto-electronics
No full textWe report on the deposition of Ga2O3 on III-nitride epi-layers using the microwave irradiation technique. We also report on the demonstration of a Ga2O3 device: a visible-blind, deep-UV detector, with a GaN-based heterostructure as the substrate. The film deposited in the solution medium, at <200 degrees C, using a metalorganic precursor, was nanocrystalline. XRD confirms that the as-deposited film, when annealed at high temperature, turns to polycrystalline beta-Ga2O3. SEM shows the as-deposited film to be uniform, with a surface roughness of 4-5 nm, as revealed by AFM. Interdigitated metal-semiconductor-metal devices with Ni/Au contact exhibited a peak spectral response at 230 nm and a good visible rejection ratio. This demonstration of a deep-UV detector on the beta-Ga2O3/III-nitride stack is expected to open up possibilities of functional and physical integration of beta-Ga2O3 and GaN material families towards enabling next-generation high-performance devices by exciting band and heterostructure engineering. Published by AIP Publishing
Resonant Column Tests and Nonlinear Elasticity in Simulated Rocks
No full textRocks are generally regarded as linearly elastic even though the manifestations of nonlinearity are prominent. The variations of elastic constants with varying strain levels and stress conditions, disagreement between static and dynamic moduli, etc., are some of the examples of nonlinear elasticity in rocks. The grain-to-grain contact, presence of pores and joints along with other compliant features induce the nonlinear behavior in rocks. The nonlinear elastic behavior of rocks is demonstrated through resonant column tests and numerical simulations in this paper. Resonant column tests on intact and jointed gypsum samples across varying strain levels have been performed in laboratory and using numerical simulations. The paper shows the application of resonant column apparatus to obtain the wave velocities of stiff samples at various strain levels under long wavelength condition, after performing checks and incorporating corrections to the obtained resonant frequencies. The numerical simulation and validation of the resonant column tests using distinct element method are presented. The stiffness reductions of testing samples under torsional and flexural vibrations with increasing strain levels have been analyzed. The nonlinear elastic behavior of rocks is reflected in the results, which is enhanced by the presence of joints. The significance of joint orientation and influence of joint spacing during wave propagation have also been assessed and presented using the numerical simulations. It has been found that rock joints also exhibit nonlinear behavior within the elastic limit
Matrix product solution of a left-permeable two-species asymmetric exclusion process
No full textWe study a two-species partially asymmetric exclusion process where the left boundary is permeable for the ``slower'' species but the right boundary is not. We find a matrix product solution for the stationary state and the exact stationary phase diagram for the densities and currents. By calculating the density of each species at the boundaries, we find further structure in the stationary phases. In particular, we find that the slower species can reach and accumulate at the far boundary, even in phases where the bulk density of these particles approaches zero
A routinely used protein staining dye acts as an inhibitor of wild type and mutant alpha-synuclein aggregation and modulator of neurotoxicity
No full textInhibition of amyloid formation along with modulation of toxicity employing small molecules is emerging as a potential therapeutic approach for protein misfolding disorders which includes Parkinson's disease, Alzheimer's disease and Multiple System Atrophy etc. Countless current interventional strategies for treating alpha-synucleinopathies consider using peptidic and non-peptidic inhibitors for arresting fibrillisation, disrupting existing fibrils and reducing associated toxicity. One group of molecules less exploited in this regard are triphenylmethane dyes. Herein we tested the inhibitory effect of two routinely used protein staining dyes viz Coomassie Brilliant blue G (CBBG) and Coomassie Brilliant blue R (CBBR) employing several biophysical and cell based methods. Our results showed that both the dyes not only efficiently inhibit fibrillisation but also disrupt existing fibrils. Nonetheless, only CBBR prevented the appearance of A11 epitopes which are marker of toxicity. Moreover, CBBR was also able to stall fibrillisation of A53T mutant alpha-synuclein and reduce associated neurotoxicity. This study thus reports the potential of CBBR as a therapeutic molecule. (C) 2017 Elsevier Masson SAS. All rights reserved
Search for low mass vector resonances decaying into quark-antiquark pairs in proton-proton collisions at root s=13 TeV
No full textA search for narrow vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in proton-proton collisions at root s = 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). The hypothetical resonance is produced with sufficiently high transverse momentum that its decay products are merged into a single jet with two-prong substructure. A signal would be identified as a peak over a smoothly falling background in the distribution of the invariant mass of the jet, using novel jet substructure techniques. No evidence for such a resonance is observed within the mass range of 50-300 GeV. Upper limits at 95% confidence level are set on the production cross section, and presented in a mass-coupling parameter space. The limits further constrain simplified models of dark matter production involving a mediator interacting between quarks and dark matter particles through a vector or axial-vector current. In the framework of these models, the results are the most sensitive to date, extending for the first time the search region to masses below 100 GeV
Fluorescence Investigations on Interactions between 7,8-benzo-4-azidomethyl Coumarin and Ortho- and Para-phenylenediamines in Binary Solvent Mixtures of THF and Water
No full textFluorescence investigations on interactions between 7,8-benzo-4-azidomethyl coumarin (7BAMC) and quenchers ortho-phenylenediamine (OPD) and para-phenylenediamines (PPD) in binary solvent mixtures (THF + water) have been reported. UV-absorption study indicated a weak hydrophobic interaction between 7BAMC and the para isomer. NMR spectral studies indicated the presence of an interaction between 7BAMC and PPD. Magnitudes of the parameters associated with FRET, showed the presence of interactions between 7BAMC and PPD quencher is more predominant than OPD. Fluorescence quenching studies reveal the role of static and dynamic quenching pathways, depending upon Stern-Volmer constant, dielectric constant and dominant non-radiative processes. Binding equilibria analysis indicates a strong interaction between 7BAMC and PPD than OPD and formation of H-bonding. Based on the magnitudes of free energy, enthalpy change and entropy, bimolecular interaction process may be considered as spontaneous and hydrophobic
Variational formulation for dissipative continua and an incremental J-integral
No full textOur aim is to rationally formulate a proper variational principle for dissipative (viscoplastic) solids in the presence of inertia forces. As a first step, a consistent linearization of the governing nonlinear partial differential equations (PDEs) is carried out. An additional set of complementary (adjoint) equations is then formed to recover an underlying variational structure for the augmented system of linearized balance laws. This makes it possible to introduce an incremental Lagrangian such that the linearized PDEs, including the complementary equations, become the Euler-Lagrange equations. Continuous groups of symmetries of the linearized PDEs are computed and an analysis is undertaken to identify the variational groups of symmetries of the linearized dissipative system. Application of Noether's theorem leads to the conservation laws (conserved currents) of motion corresponding to the variational symmetries. As a specific outcome, we exploit translational symmetries of the functional in the material space and recover, via Noether's theorem, an incremental J-integral for viscoplastic solids in the presence of inertia forces. Numerical demonstrations are provided through a two-dimensional plane strain numerical simulation of a compact tension specimen of annealed mild steel under dynamic loading
Gradient-Based Adaptive Stochastic Search for Simulation Optimization Over Continuous Space
No full textWe extend the idea of model-based algorithms for deterministic optimization to simulation optimization over continuous space. Model-based algorithms iteratively generate a population of candidate solutions from a sampling distribution and use the performance of the candidate solutions to update the sampling distribution. By viewing the original simulation optimization problem as another optimization problem over the parameter space of the sampling distribution, we propose to use a direct gradient search on the parameter space to update the sampling distribution. To improve the computational efficiency, we further develop a two-timescale updating scheme that updates the parameter on a slow timescale and estimates the quantities involved in the parameter updating on the fast timescale. We analyze the convergence properties of our algorithms through techniques from stochastic approximation, and demonstrate the good empirical performance by comparing with two state-of-the-art model-based simulation optimization methods
THE FRS NOMINATION OF SIR PRAFULLA C. RAY AND THE CORRESPONDENCE OF N. R. DHAR
No full textSir Prafulla Chandra Ray (1861-1944) was the first Indian chemist to achieve high international reputation. Originally trained at the University of Edinburgh, he worked for many years at Presidency College in Calcutta and then at Calcutta University. He built up a remarkable school of chemical research by attracting many outstanding students to work with him and published about 150 papers-many of them in leading British and German journals. Ray was highly respected by his British peers and was the first Indian of that era to be nominated for FRS, in 1913. At the time when his nomination was being considered by the Royal Society, Ray's favourite student, Nil Ratan Dhar (1892-1986), who was to become the second Indian chemist to achieve high international reputation, worked in London and Paris for a few years. Even when Dhar was merely a 24-year-old student, he lobbied with several leading British chemists for the election of Ray and kept Ray informed in a series of fascinating letters-giving us a rare glimpse of what election to the Royal Society meant for Indian scientists of that era. During this time, Ray received a knighthood for his contributions to chemistry, and Nature published a front-page article on Ray's `life-work'. Many British chemists felt strongly that Ray should be elected FRS and were willing to discuss Ray's case with the young Dhar quite openly. But, rather mysteriously, Ray never got elected