Design of metallic nanoparticles gratings for filtering properties in the visible spectrum

Plasmonic resonances in metallic nanoparticles are exploited to create efficient optical filtering functions. A Finite Element Method is used to model metallic nanoparticles gratings. The accuracy of this method is shown by comparing numerical results with measurements on a two-dimensional grating of gold nanocylinders with elliptic cross section. Then a parametric analysis is performed in order to design efficient filters with polarization dependent properties together with high transparency over the visible range. The behavior of nanoparticle gratings is also modelled using the Maxwell-Garnett homogenization theory and analyzed by comparison with the diffraction by a single nanoparticle. The proposed structures are intended to be included in optical systems which could find innovative applications.Comment: submitted to Applied Optic

The static and dynamic conductivity of warm dense Aluminum and Gold calculated within a density functional approach

The static resistivity of dense Al and Au plsmas are calculated where all the needed inputs are obtained from density functional theory (DFT). This is used as input for a study of the dynamic conductivity. These calculations involve a self-consistent determination of (i) the equation of state (EOS) and the ionization balance, (ii) evaluation of the ion-ion, and ion-electron pair-distribution functions, (iii) Determination of the scattering amplitudes, and finally the conductivity. We present data for the static resistivity of Al for compressions 0.1-2.0, and in the temperature range T= 0.1 - 10 eV. Results for Au in the same temperature range and for compressions 0.1-1.0 is also given. In determining the dynamic conductivity for a range of frequencies consistent with standard laser probes, a knowledge of the electronic eigenstates and occupancies of Al- or Au plasma becomes necessary. They are calculated using a neutral-pseudoatom model. We examine a number of first-principles approaches to the optical conductivity, including many-body perturbation theory, molecular-dynamics evaluations, and simplified time-dependent DFT. The modification to the Drude conductivity that arises from the presence of shallow bound states in typical Al-plasmas is examined and numerical results are given at the level of the Fermi Golden rule and an approximate form of time-dependent DFT.Comment: 5 figures, Latex original. Cross-referencced to PLASMA PHYSIC

Implications of the B20 Crystal Structure for the Magneto-electronic Structure of MnSi

Due to increased interest in the unusual magnetic and transport behavior of MnSi and its possible relation to its crystal structure (B20) which has unusual coordination and lacks inversion symmetry, we provide a detailed analysis of the electronic and magnetic structure of MnSi. The non-symmorphic P2_13 spacegroup leads to unusual fourfold degenerate states at the zone corner R point, as well as ``sticking'' of pairs of bands throughout the entire Brillouin zone surface. The resulting Fermi surface acquires unusual features as a result of the band sticking. For the ferromagnetic system (neglecting the long wavelength spin spiral) with the observed moment of 0.4 \mu_B/Mn, one of the fourfold levels at R in the minority bands falls at the Fermi energy (E_F), and a threefold majority level at k=0 also falls at E_F. The band sticking and presence of bands with vanishing velocity at E_F imply an unusually large phase space for long wavelength, low energy interband transitions that will be important for understanding the unusual resistivity and far infrared optical behavior.Comment: Nine two-column pages with eight figures include

Thomas-Fermi Calculation of the Interlayer Force in Graphite

A model of a graphite crystal is proposed in which planar layers of positive charge are considered instead of the point charges of nuclei. The interlayer electronic density is calculated integrating both the Thomas-Fermi and the Thomas-Fermi-Dirac equations. From these densities, the total energy of the electrons is calculated including corrections for inhomogeneity in the form of Weizsäcker and Kirzhnits. The influence of the different corrections is studied with the result that the best method is to calculate the density from the Thomas-Fermi-Dirac equation and to take into account the inhomogeneity corrections in the form of Kirzhnits

Ten months of temporal variation in the clinical journey of hospitalised patients with COVID-19: an observational cohort

Background: There is potentially considerable variation in the nature and duration of the care provided to hospitalised patients during an infectious disease epidemic or pandemic. Improvements in care and clinician confidence may shorten the time spent as an inpatient, or the need for admission to an intensive care unit (ICU) or high density unit (HDU). On the other hand, limited resources at times of high demand may lead to rationing. Nevertheless, these variables may be used as static proxies for disease severity, as outcome measures for trials, and to inform planning and logistics. Methods: We investigate these time trends in an extremely large international cohort of 142,540 patients hospitalised with COVID-19. Investigated are: time from symptom onset to hospital admission, probability of ICU/HDU admission, time from hospital admission to ICU/HDU admission, hospital case fatality ratio (hCFR) and total length of hospital stay. Results: Time from onset to admission showed a rapid decline during the first months of the pandemic followed by peaks during August/September and December 2020. ICU/HDU admission was more frequent from June to August. The hCFR was lowest from June to August. Raw numbers for overall hospital stay showed little variation, but there is clear decline in time to discharge for ICU/HDU survivors. Conclusions: Our results establish that variables of these kinds have limitations when used as outcome measures in a rapidly-evolving situation. Funding: This work was supported by the UK Foreign, Commonwealth and Development Office and Wellcome [215091/Z/18/Z] and the Bill and Melinda Gates Foundation [OPP1209135]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript