Closed-form expressions for correlated density matrices: application to dispersive interactions and example of (He)2

Empirically correlated density matrices of N-electron systems are investigated. Exact closed-form expressions are derived for the one- and two-electron reduced density matrices from a general pairwise correlated wave function. Approximate expressions are proposed which reflect dispersive interactions between closed-shell centro-symmetric subsystems. Said expressions clearly illustrate the consequences of second-order correlation effects on the reduced density matrices. Application is made to a simple example: the (He)2 system. Reduced density matrices are explicitly calculated, correct to second order in correlation, and compared with approximations of independent electrons and independent electron pairs. The models proposed allow for variational calculations of interaction energies and equilibrium distance as well as a clear interpretation of dispersive effects on electron distributions. Both exchange and second order correlation effects are shown to play a critical role on the quality of the results.Comment: 22 page

Non-resonant pitch-angle scattering, and parallel mean-free-path

Abstract A new, non-resonant pitch-angle scattering process has been found, which very efficiently scatters the cosmic ray particles through the zero pitch-angle cosine. Combined with the effects of gyroresonance and transit-time damping, it can solve the "flatness problem" for the parallel mean-free-path as a function of the particles rigidity. The main lines of its derivation, and the implications on the mean-free-path at low rigidities ( ¢ ¡ ¤ £ ¦ ¥ MV), are summarized here

Fourier-Legendre expansion of the one-electron density-matrix of ground-state two-electron atoms

The density-matrix rho(r, r') of a spherically symmetric system can be expanded as a Fourier-Legendre series of Legendre polynomials Pl(cos(theta) = r.r'/rr'). Application is here made to harmonically trapped electron pairs (i.e. Moshinsky's and Hooke's atoms), for which exact wavefunctions are known, and to the helium atom, using a near-exact wavefunction. In the present approach, generic closed form expressions are derived for the series coefficients of rho(r, r'). The series expansions are shown to converge rapidly in each case, with respect to both the electron number and the kinetic energy. In practice, a two-term expansion accounts for most of the correlation effects, so that the correlated density-matrices of the atoms at issue are essentially a linear functions of P1(cos(theta)) = cos(theta). For example, in the case of the Hooke's atom: a two-term expansion takes in 99.9 % of the electrons and 99.6 % of the kinetic energy. The correlated density-matrices obtained are finally compared to their determinantal counterparts, using a simplified representation of the density-matrix rho(r, r'), suggested by the Legendre expansion. Interestingly, two-particle correlation is shown to impact the angular delocalization of each electron, in the one-particle space spanned by the r and r' variables.Comment: 31 pages, 7 figure

Exact Kohn-Sham versus Hartree-Fock in momentum-space: examples of two-fermion systems

The question of how density functional theory (DFT) compares with Hartree-Fock (HF) for the computation of momentum-space properties is addressed in relation to systems for which (near) exact Kohn-Sham (KS) and HF one-electron matrices are known. This makes it possible to objectively compare HF and exact KS and hence to assess the potential of DFT for momentum space studies. The systems considered are the Moshinsky atom, the Hooke's atom and light two-electron ions, for which expressions for correlated density-matrices or momentum densities have been derived in closed-form. The results obtained show that it is necessary to make a distinction between true and approximate DFT.Comment: 30 pages, accepted for publication in J. Chem. Phys. (2006

Cyclooxygenase-2-Derived Prostacyclin Protective Role on Endotoxin-Induced Mouse Cardiomyocyte Mortality

Cardiovascular dysfunction characterizes septic shock, inducing multiple organ failure and a high mortality rate. In the heart, it has been shown an up-regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expressions with subsequent overproduction of nitric oxide (NO) and eicosanoids. This study is focused on the links between these products of inflammation and cell loss of mouse cardiomyocytes during treatment by the Salmonella typhimurium lipopolysaccharide (LPS) in presence or in absence of NOS or COX inhibitors. LPS induced RelA/NF-κB p65 activation, iNOS and COX-2 up-regulations, resulting in NO and prostacyclin releases. These effects were reversed by the NO-synthase inhibitor and increased by the specific COX-2 inhibitor. Immunostainings with FITC-conjugated anti-Annexin-V and propidium iodide and caspase 3/7 activity assay showed that cardiomyocyte necrosis was inhibited by L-NA during LPS treatment challenge, while apoptosis was induced in presence of both LPS and NS-398. No effect on LPS cellular injury was observed using the specific cyclooxygenase-1 (COX-1) inhibitor, SC-560. These findings strongly support the hypothesis of a link between iNOS-dependent NO overproduction and LPS-induced cell loss with a selective protective role allotted to COX-2 and deriving prostacyclins

Novel robotic assistive technologies: choosing appropriate training for healthcare professionals

One of the key challenges for the training of healthcare professionals (HCPs) is to maintain a good understanding and knowledge of new assistive technologies (ATs) that are currently on the market [1]. Indeed, at present, available training on ATs is limited and does not meet the practice-related needs of HCPs. It is in this context that the ADAPT European project aims to develop a new AT training programme for healthcare professionals, which will also introduce them to the project’s new AT developments - a smart powered wheelchair and a virtual reality wheelchair-driving simulator. The program consists of six multimodal units; five delivered via e-learning and one through a blended method of e-learning and face-to-face sessions. The development of the content is guided by findings from an earlier literature review and an online survey of AT training needs for HCP’s, both undertaken by the ADAPT cross-national research team, comprised of UK and French experts. The level of technical difficulty increases with successive units in order to train all HCPs to use innovative ATs more widely in their practice. A Learning Management System enables the dissemination of the e-learning AT program. Preliminary results from participant unit-specific evaluations available at this stage are overall positive and encouraging

Angular versus radial correlation effects on momentum distributions of light two-electron ions

We investigate different correlation mechanisms for two-electron systems and compare their respective effects on various electron distributions. The simplicity of the wave functions used allows for the derivation of closed-form analytical expressions for all electron distributions. Among other features, it is shown that angular and radial correlation mechanisms have opposite effects on Compton profiles at small momenta.Comment: 22 pages, 5 figures, 3 tabl

The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event

We investigate multi-spacecraft observations of the January 17, 2010 solar energetic particle event. Energetic electrons and protons have been observed over a remarkable large longitudinal range at the two STEREO spacecraft and SOHO suggesting a longitudinal spread of nearly 360 degrees at 1AU. The flaring active region, which was on the backside of the Sun as seen from Earth, was separated by more than 100 degrees in longitude from the magnetic footpoints of each of the three spacecraft. The event is characterized by strongly delayed energetic particle onsets with respect to the flare and only small or no anisotropies in the intensity measurements at all three locations. The presence of a coronal shock is evidenced by the observation of a type II radio burst from the Earth and STEREO B. In order to describe the observations in terms of particle transport in the interplanetary medium, including perpendicular diffusion, a 1D model describing the propagation along a magnetic field line (model 1) (Dr\"oge, 2003) and the 3D propagation model (model 2) by (Dr\"oge et al., 2010) including perpendicular diffusion in the interplanetary medium have been applied, respectively. While both models are capable of reproducing the observations, model 1 requires injection functions at the Sun of several hours. Model 2, which includes lateral transport in the solar wind, reveals high values for the ratio of perpendicular to parallel diffusion. Because we do not find evidence for unusual long injection functions at the Sun we favor a scenario with strong perpendicular transport in the interplanetary medium as explanation for the observations.Comment: The final publication is available at http://www.springerlink.co