Nucleon spectra in heavy ion collision prior to equilibrium

Energy spectra and angular distribution of nucleons emitted in intermediate energy heavy ion collisions prior to equilibrium are calculated. The spectra have two components: (a) promptly emitted particles (PEPS) or Fermi jets; (b) emission from a localized excited region at the interface of the two colliding ions. The results obtained with this model have been compared with experiment and the agreement is good.     

Mechanisms for the convergence of time-parallelized,parareal turbulent plasma simulations

Parareal is a recent algorithm able to parallelize the time dimension in spite of its sequential nature. It has been applied to several linear and nonlinear problems and, very recently, to a simulation of fully-developed, two-dimensional drift wave turbulence. The mere fact that parareal works in such a turbulent regime is in itself somewhat unexpected, due to the characteristic sensitivity of turbulence to any change in initial conditions. This fundamental property of any turbulent system should render the iterative correction procedure characteristic of the parareal method inoperative, but this seems not to be the case. In addition, the choices that must be made to implement parareal (division of the temporal domain, election of the coarse solver and so on) are currently made using trial-and-error approaches. Here, we identify the mechanisms responsible for the convergence of parareal of these simulations of drift wave turbulence. We also investigate which conditions these mechanisms impose on any successful parareal implementation. The results reported here should be useful to guide future implementations of parareal within the much wider context of fully-developed fluid and plasma turbulent simulations.     

Solvation dynamics of a protein in the pre molten globule state

The nature of solvent molecules around proteins in native and different non-native states is crucial for understanding the protein folding problem. We have characterized two compact denatured states of glutaminyl-tRNA synthetase (GlnRS) under equilibrium conditions in the presence of a naturally occurring osmolyte, l-glutamate. The solvation dynamics of the compact denatured states and the fully unfolded state has been studied using a covalently attached probe, acrylodan, near the active site. The solvation dynamics progressively becomes faster as the protein goes from the native to the molten globule to the pre molten globule to the fully unfolded state. Anisotropy decay measurements suggest that the pre-molten-globule intermediate is more flexible than the molten globule although the secondary structure is largely similar. Dynamic light scattering studies reveal that both the compact denatured states are aggregated under the measurement conditions. The implications of solvation dynamics in aggregated compact denatured states have been discussed.     

Reductivity of methanol and ethanol towards permanganate in absence and presence of Tween-20 in perchloric acid medium. Mechanism of the oxidation processes

The reducing behaviour of methanol and ethanol towards permanganate in perchloric acid medium have been investigated in the absence and presence of the surfactant Tween-20. In the absence of surfactant the reaction is of first order with respect to both oxidant and H⁺ but of complex order in substrate. The alcohol molecule reacts with HMnO4 to form an intermediate complex which decomposes in the rate-determining step to give the product and Mn^v. Effects of urea and acetonitrile on the reaction rate have also been studied. In the presence of Tween-20, the reaction appears to follow Berezin’s model where both the oxidant and the substrate are partitioned between the aqueous and the micellar phase and then react. Different thermodynamic and kinetic parameters have been evaluated. The reaction in the presence of the surfactant is entropy-controlled rather than enthalpy-controlled.     

Harnessing Quantumness of States using Discrete Wigner Functions under (non)-Markovian Quantum Channels

The negativity of the discrete Wigner functions (DWFs) is a measure of non-classicality and is often used to quantify the degree of quantum coherence in a system. The study of Wigner negativity and its evolution under different quantum channels can provide insight into the stability and robustness of quantum states under their interaction with the environment, which is essential for developing practical quantum computing systems. The variation of DWF negativity of qubit, qutrit, and two-qubit systems under the action of (non)-Markovian random telegraph noise (RTN) and amplitude damping (AD) quantum channels is investigated. Different negative quantum states that can be used as a resource for quantum computation and quantum teleportation are constructed. The success of quantum computation and teleportation is estimated for these states under (non)-Markovian evolutions.     

Dynamics of entanglement in two-qubit open system interacting with a squeezed thermal bath via dissipative interaction

We study the dynamics of entanglement in a two-qubit system interacting with a squeezed thermal bath via a dissipative system-reservoir interaction with the system and reservoir assumed to be in a separable initial state. The resulting entanglement is studied by making use of concurrence as well as a recently introduced measure of mixed state entanglement via a probability density function which gives a statistical and geometrical characterization of entanglement by exploring the entanglement content in the various subspaces spanning the two-qubit Hilbert space. We also make an application of the two-qubit dissipative dynamics to a simplified model of quantum repeaters.     

Parallelization in time of numerical simulations of fully-developed plasma turbulence using the parareal algorithm

It is shown that numerical simulations of fully-developed plasma turbulence can be successfully parallelized in time using the parareal algorithm. The result is far from trivial, and even unexpected, since the exponential divergence of Lagrangian trajectories as well as the extreme sensitivity to initial conditions characteristic of turbulence set these type of simulations apart from the much simpler systems to which the parareal algorithm has been applied to this day. It is also shown that the parallel gain obtainable with this method is very promising (close to an order of magnitude for the cases and implementations described), even when it scales with the number of processors quite differently to what is typical for spatial parallelization.     

Beam localization in HIFU temperature measurements using thermocouples, with application to cooling by large blood vessels

Experimental studies of thermal effects in high-intensity focused ultrasound (HIFU) procedures are often performed with the aid of fine wire thermocouples positioned within tissue phantoms. Thermocouple measurements are subject to several types of error which must be accounted for before reliable inferences can be made on the basis of the measurements. Thermocouple artifact due to viscous heating is one source of error. A second is the uncertainty regarding the position of the beam relative to the target location or the thermocouple junction, due to the error in positioning the beam at the junction. This paper presents a method for determining the location of the beam relative to a fixed pair of thermocouples. The localization technique reduces the uncertainty introduced by positioning errors associated with very narrow HIFU beams. The technique is presented in the context of an investigation into the effect of blood flow through large vessels on the efficacy of HIFU procedures targeted near the vessel. Application of the beam localization method allowed conclusions regarding the effects of blood flow to be drawn from previously inconclusive (because of localization uncertainties) data. Comparison of the position-adjusted transient temperature profiles for flow rates of 0 and 400 ml/min showed that blood flow can reduce temperature elevations by more than 10%, when the HIFU focus is within a 2 mm distance from the vessel wall. At acoustic power levels of 17.3 and 24.8 W there is a 20- to 70-fold decrease in thermal dose due to the convective cooling effect of blood flow, implying a shrinkage in lesion size. The beam-localization technique also revealed the level of thermocouple artifact as a function of sonication time, providing investigators with an indication of the quality of thermocouple data for a given exposure time. The maximum artifact was found to be double the measured temperature rise, during initial few seconds of sonication.