Aluminum equation-of-state data in the warm dense matter regime

Isochore measurements were performed in the warm dense matter regime. Pressure and internal energy variation of aluminum plasma (density 0.1 g/cm(3) and 0.3 g/cm(3)) are measured using a homogeneous and thermally equilibrated media produced inside an isochoric plasma closed vessel in the internal energy range 20-50 MJ/kg. These data are compared to detailed calculations obtained from ab initio quantum molecular dynamics, average atom model within the framework of the density functional theory, and standard theories. A dispersion between theoretical isochore equation of state is found in the studied experimental thermodynamic regime.     

Comparison of Fe and Ni opacity calculations for a better understanding of pulsating stellar envelopes

Opacity is an important ingredient of the evolution of stars. The calculation of opacity coefficients is complicated by the fact that the plasma contains partially ionized heavy ions that contribute to opacity dominated by H and He. Up to now, the astrophysical community has greatly benefited from the work of the contributions of Los Alamos [1], Livermore [2], [2a] and [2b] and the Opacity Project (OP) [3]. However unexplained differences of up to 50% in the radiative forces and Rosseland mean values for Fe have been noticed for conditions corresponding to stellar envelopes. Such uncertainty has a real impact on the understanding of pulsating stellar envelopes, on the excitation of modes, and on the identification of the mode frequencies. Temperature and density conditions equivalent to those found in stars can now be produced in laboratory experiments for various atomic species. Recently the photo-absorption spectra of nickel and iron plasmas have been measured during the LULI 2010 campaign, for temperatures between 15 and 40 eV and densities of ∼3 mg/cm³. A large theoretical collaboration, the “OPAC”, has been formed to prepare these experiments. We present here the set of opacity calculations performed by eight different groups for conditions relevant to the LULI 2010 experiment and to astrophysical stellar envelope conditions.     

Finite-temperature exchange-correlation functional in an ab initio molecular dynamics code

We study the role of finite-temperature exchange-correlation functional in an ab initio molecular dynamics code using a variational approach to describe the electronic and ionic structures. We use the method proposed by Perrot and Dharma-wardana [Phys. Rev. B 62, 16536, 2000] to take into account the finite-temperature effect in the exchange-correlation functional. We find small influence of finite-temperature exchange-correlation functional compared to zero-temperature exchange-correlation functional for aluminum in the warm dense matter regime.     

Electron-ion temperature relaxation in hydrogen plasmas

We present an ad hoc method to correct the Coulomb logarithm of known models in order to match electron and ion temperature relaxation based on molecular dynamic simulations. A thermodynamic analysis is done. Numerical results are presented and discussed.     

Angle-resolved photoelectron spectrometry studies of the autoionization of the 2s(2)2p 2P triply excited state of atomic lithium: experimental results and R-matrix calculations

We have measured the angle-resolved energy dependence of the electrons emitted over the energy range of the triply excited 2s(2)2p 2P lithium resonance using synchrotron radiation. We have also calculated the behavior of the angular distribution parameter beta using the R-matrix approximation. Experimental and theoretical results are in good agreement and show deep minima in the 1s2p (1, 3)P ionic channels. The energy at which the minima occur does not coincide with the resonance energy, but is shifted towards higher energy.     

Stopping power modeling in warm and hot dense matter

A model is presented to calculate the stopping power of ions propagating in dense matter. Comparisons with experiment in the cold dense regime are presented and discussed. Further, we present results from the warm dense matter regime and the field of high energy density physics.     

Study of the molecular interaction between lysozyme and heparin and application in affinity chromatography

Lysozyme interacts with heparin by giving a stable and insoluble complex that dissociates at increased ionic strength. The formation of the complex and its stability towards pH and sodium chloride concentration were studied in solution and in a heterogeneous phase by means of heparin immobilized on agarose beads. The two sets of results are in agreement and show that the interaction between heparin and lysozyme is essentially ionic. The practical consequence is the possibility of developing a one-step method of purification of egg-white lysozyme by affinity chromatography with a particularly high yield of biochemical activity.     

Probing matrix isolated SiO molecular clusters by X-ray absorption spectroscopy

TheK absorption edge of Si in matrix isolated SiO molecular clusters was studied for various dilutionsR(Ar/SiO). The spectra from the clusters at different dilutions show a dramatic evolution in their relative intensity. Two types of spectral features from Si atoms present in the clusters could be detected in the spectra. The first is due to the Si atoms which are tetrahedrally coordinated to Si and O atoms responsible for the presence of different Si oxidation states. The Si⁺, Si³⁺ and Si⁴⁺ oxidation states in SiO clusters and in bulk were readily identified. The Si²⁺ oxidation state whose abundance in SiO clusters is predicted by structural considerations is not clearly observed. The second type of feature, whose intensity decreases with the dilution R, can be attributed to the presence of Si atoms possessing unsaturated bonds. In order to explain this the clustering of 4–6 SiO molecules is simulated to yield different tetrahedral bonding microstructures in which the well coordinated as well as under coordinated Si atoms are present. The behaviour of the spectral features resulting from these microstructures is discussed.     

Pressure and Electrical Resistivity Measurements on Hot Expanded Metals: Comparisons with Quantum Molecular Dynamics Simulations and Average‐Atom Approaches

We present experimental results on pressures and resistivities of expanded nickel and titanium at respective densities of 0.1 g/cm³ and 0.2 g/cm³, and in a range of temperature of 1‐3 eV that corresponds to the warm dense matter (WDM) regime. These data are used to benchmark different theoretical approaches. A comparison is presented between fully 3‐dimensional quantum molecular dynamics (QMD) methods, based on density functional theory, with average‐atom (AA) methods, that are essentially one dimensional. AA methods are used to identify interband transitions and photoionization thresholds. In this regime the evaluation of the thermodynamic properties as well as electrical properties is difficult due to the concurrence of density and thermal effects which directly drive the metal‐non‐metal transition. QMD simulations are also helpful to give a precise estimation of the temperature of experiments which is not directly accessible [1] (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)