Absorption of short laser pulses on solid targets in the ultrarelativistic regime

We report the first direct measurements of total absorption of short laser pulses on solid targets in the ultrarelativistic regime. The data show an enhanced absorption at intensities above 10(20) W/cm(2), reaching 60% for near-normal incidence and 80%-90% for 45 degrees incidence. Two-dimensional particle-in-cell simulations demonstrate that such high absorption is consistent with both interaction with preplasma and hole boring by the intense laser pulse. A large redshift in the second harmonic indicates a surface recession velocity of 0.035c.     

Hot-electron energy coupling in ultraintense laser-matter interaction

We investigate the hydrodynamic response of plasma gradients during the interaction with ultraintense energetic laser pulses, using kinetic particle simulations. Energetic laser pulses are capable of compressing preformed plasma gradients over short times while accelerating low-density plasma backwards. As light is absorbed on a steepened interface, hot-electron temperature and coupling efficiency drop below the ponderomotive scaling, and we are left with a new absorption mechanism that strongly relies on the electrostatic potential caused by low-density preformed plasma. We describe this process, explain electron spectra, and identify the parameter regime where strong compression occurs. Finally, we discuss the implications for fast ignition and other applications.     

Interaction of giant extracellular Glossoscolex paulistus hemoglobin (HbGp) with zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS): effects of oligomeric dissociation

The present work focuses on the interaction between the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp). Electronic optical absorption, fluorescence emission and circular dichroism spectroscopy techniques, together with Gel-filtration chromatography, were used in order to evaluate the oligomeric dissociation as well as the autoxidation of HbGp as a function of the interaction with HPS. A peculiar behavior was observed for the HPS–HbGp interaction: a complex ferric species formation equilibrium was promoted, as a consequence of the autoxidation and oligomeric dissociation processes. At pH 7.0, HPS is more effective up to 1 mM while at pH 9.0 the surfactant effect is more intense above 1 mM. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to two factors: (i) the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants, and (ii) the low cmc of HPS, which probably reduces the interaction of the surfactant in the monomeric form with the protein. The present work emphasizes the importance of the electrostatic contribution in the interaction between ionic surfactants and HbGp. Furthermore, in the whole HPS concentration range used in this study, no folding and autoxidation decrease induced by this surfactant were observed. This is quite different from the literature data on the interaction between surfactants and tetrameric hemoglobins, that supports the occurrence of this behavior for the intracellular hemoglobins at low surfactant concentration range. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin–surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on their structure–activity relationship.     

Data‐Driven Optimal Transport

The problem of optimal transport between two distributions ρ(x) and μ(y) is extended to situations where the distributions are only known through a finite number of samples {x_i} and {y_j}. A weak formulation is proposed, based on the dual of the Kantorovich formulation, with two main modifications: replacing the expected values in the objective function by their empirical means over the {x_i} and {y_j}, and restricting the dual variables u(x) and v(y) to a suitable set of test functions adapted to the local availability of sample points. A procedure is proposed and tested for the numerical solution of this problem, based on a fluidlike flow in phase space, where the sample points play the role of active Lagrangian markers. © 2016 Wiley Periodicals, Inc.     

Interaction of meso-tetrakis (4-sulfonatophenyl) porphyrin with cationic CTAC micelles investigated by small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR)

Small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been used to investigate the interaction of the water-soluble meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS(4)) with cationic cethyltrimethylammonium chloride (CTAC) micelles. To evaluate if the porphyrin protonation state affects its interaction with the micelle, both SAXS and EPR measurements were performed at pH 4.0 and 9.0. The best-fit SAXS curves were obtained assuming for CTAC micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS(4). SAXS results show that the presence of porphyrin impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. Lineshapes of EPR spectra of 5- and 16-doxyl stearic acids (5- and 16-DSA, respectively) bound to 100 mM CTAC micelles exhibited slight changes as a function of porphyrin concentration. Spectral simulations revealed an increase of mobility restriction for both spin probes, especially at higher porphyrin concentration, where a small reduction of environment polarity was also observed for 16-DSA. The spin labels monitored only slight differences between pH 4.0 and 9.0, in agreement with the SAXS results.     

Quantifying price fluctuations in the Brazilian stock market

This paper investigates price fluctuations in the Brazilian stock market. We employ a recently developed methodology to test whether the Brazilian stock price returns present a power law distribution and find that we cannot reject such behavior. Empirical results for sub-partitions of the time series suggests that for most of the time the power law is not rejected, but that in some cases the data set does not conform with a power law distribution.     

Mixing in simple models for turbulent diffusion

Simple turbulent diffusive models are proposed as conceptual tools for exploring scenarios involving mixing of stratified flows. Applications include the dynamics of the ocean's top mixed layer, shear instability, breaking internal waves, and turbulent stirring of sharp interfaces. A novel measure of mixing is developed, based on arguments from statistical physics. It is shown that, under turbulent diffusion, this measure grows, and that there are strong indications that, under stirring, flows tend to settle down at a maximum of this measure, subject to global dynamical constraints. © 2004 Wiley Periodicals, Inc.