Derivation of a Non-Local Interfacial Hamiltonian for Short-Ranged Wetting II: General Diagrammatic Structure

In our first paper, we showed how a non-local effective Hamiltionian for short-ranged wetting may be derived from an underlying Landau-Ginzburg-Wilson model. Here, we combine the Green's function method with standard perturbation theory to determine the general diagrammatic form of the binding potential functional beyond the double-parabola approximation for the Landau-Ginzburg-Wilson bulk potential. The main influence of cubic and quartic interactions is simply to alter the coefficients of the double parabola-like zig-zag diagrams and also to introduce curvature and tube-interaction corrections (also represented diagrammatically), which are of minor importance. Non-locality generates effective long-ranged many-body interfacial interactions due to the reflection of tube-like fluctuations from the wall. Alternative wall boundary conditions (with a surface field and enhancement) and the diagrammatic description of tricritical wetting are also discussed.Comment: (14 pages, 2 figures) Submitted J. Phys. Condens. Matte

Correlation function algebra for inhomogeneous fluids

We consider variational (density functional) models of fluids confined in parallel-plate geometries (with walls situated in the planes z=0 and z=L respectively) and focus on the structure of the pair correlation function G(r_1,r_2). We show that for local variational models there exist two non-trivial identities relating both the transverse Fourier transform G(z_\mu, z_\nu;q) and the zeroth moment G_0(z_\mu,z_\nu) at different positions z_1, z_2 and z_3. These relations form an algebra which severely restricts the possible form of the function G_0(z_\mu,z_\nu). For the common situations in which the equilibrium one-body (magnetization/number density) profile m_0(z) exhibits an odd or even reflection symmetry in the z=L/2 plane the algebra simplifies considerably and is used to relate the correlation function to the finite-size excess free-energy \gamma(L). We rederive non-trivial scaling expressions for the finite-size contribution to the free-energy at bulk criticality and for systems where large scale interfacial fluctuations are present. Extensions to non-planar geometries are also considered.Comment: 15 pages, RevTex, 4 eps figures. To appear in J.Phys.Condens.Matte

Spatially Confined Redox Chemistry in Periodic Mesoporous Hydridosilica-Nanosilver Grown in Reducing Nanopores

Cataloged from PDF version of article.Periodic mesoporous hydridosilica, PMHS, is shown for the first time to function as both a host and a mild reducing agent toward noble metal ions. In this archetypical study, PMHS microspheres react with aqueous Ag(I) solutions to form Ag(0) nanopartides housed in different pore locations of the mesostructure. The dominant reductive nucleation and growth process involves groups located within the pore walls and yields molecular scale Ag(0) nanoclusters trapped and stabilized in the pore walls of the PMHS microspheres that emit orange-red photoluminescence. Lesser processes initiated with pore surface SiH groups produce some larger spherical and worm-shaped Ag(0) nanoparticles within the pore voids and on the outer surfaces of the PMHS microspheres. The intrinsic reducing power demonstrated in this work for the pore walls of PMHS speaks well for a new genre of chemistry that benefits from the mesoscopic confinement of Si-H groups

Van Allen Probes observations of direct wave-particle interactions

Abstract Quasiperiodic increases, or bursts, of 17-26 keV electron fluxes in conjunction with chorus wave bursts were observed following a plasma injection on 13 January 2013. The pitch angle distributions changed during the burst events, evolving from sinN(α) to distributions that formed maxima at α = 75-80°, while fluxes at 90° and \u3c60° remained nearly unchanged. The observations occurred outside of the plasmasphere in the postmidnight region and were observed by both Van Allen Probes. Density, cyclotron frequency, and pitch angle of the peak flux were used to estimate resonant electron energy. The result of ∼15-35 keV is consistent with the energies of the electrons showing the flux enhancements and corresponds to electrons in and above the steep flux gradient that signals the presence of an Alfvén boundary in the plasma. The cause of the quasiperiodic nature (on the order of a few minutes) of the bursts is not understood at this time

Plasticity and memory effects in the vortex solid phase of twinned YBa2Cu3O7 single crystals

We report on marked memory effects in the vortex system of twinned YBa2Cu3O7 single crystals observed in ac susceptibility measurements. We show that the vortex system can be trapped in different metastable states with variable degree of order arising in response to different system histories. The pressure exerted by the oscillating ac field assists the vortex system in ordering, locally reducing the critical current density in the penetrated outer zone of the sample. The robustness of the ordered and disordered states together with the spatial profile of the critical current density lead to the observed memory effects

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance

Steric Effects in Electrolytes: A Modified Poisson-Boltzmann Equation

The adsorption of large ions from solution to a charged surface is investigated theoretically. A generalized Poisson--Boltzmann equation, which takes into account the finite size of the ions is presented. We obtain analytical expressions for the electrostatic potential and ion concentrations at the surface, leading to a modified Grahame equation. At high surface charge densities the ionic concentration saturates to its maximum value. Our results are in agreement with recent experiments.Comment: 4 pages, 2 figure