On the reliability of initial conditions for dissipationless cosmological simulations

We present the study of ten random realizations of a density field characterized by a cosmological power spectrum P(k) at redshift z=50. The reliability of such initial conditions for n-body simulations are tested with respect to their correlation properties. The power spectrum P(k), and the mass variance sigmaM(r) do not show detectable deviations from the desired behavior in the intermediate range of scales between the mean interparticle distance and the simulation volume. The estimator for xi(r) is too noisy to detect any reliable signal at the initial redshift z=50. The particle distributions are then evolved forward until z=0. This allows us to explore the cosmic variance stemming from the random nature of the initial conditions. With cosmic variance we mean the fact that a simulation represents a single realization of the stochastic initial conditions whereas the real Universe contains many realizations of regions of the size of the box; this problem affects most importantly the scales at about the fundamental mode. We study morphological descriptors of the matter distribution such as the genus, as well as the internal properties of the largest object(s) forming in the box. We find that the scatter is at least comparable to the scatter in the fundamental mode.Comment: 22 pages, 12 figures, replaced with major revision to previous submission, PASA in pres

Theory of Sorption Hysteresis in Nanoporous Solids: II. Molecular condensation

Motivated by the puzzle of sorption hysteresis in Portland cement concrete or cement paste, we develop in Part II of this study a general theory of vapor sorption and desorption from nanoporous solids, which attributes hysteresis to hindered molecular condensation with attractive lateral interactions. The classical mean-field theory of van der Waals is applied to predict the dependence of hysteresis on temperature and pore size, using the regular solution model and gradient energy of Cahn and Hilliard. A simple "hierarchical wetting" model for thin nanopores is developed to describe the case of strong wetting by the first monolayer, followed by condensation of nanodroplets and nanobubbles in the bulk. The model predicts a larger hysteresis critical temperature and enhanced hysteresis for molecular condensation across nanopores at high vapor pressure than within monolayers at low vapor pressure. For heterogeneous pores, the theory predicts sorption/desorption sequences similar to those seen in molecular dynamics simulations, where the interfacial energy (or gradient penalty) at nanopore junctions acts as a free energy barrier for snap-through instabilities. The model helps to quantitatively understand recent experimental data for concrete or cement paste wetting and drying cycles and suggests new experiments at different temperatures and humidity sweep rates.Comment: 26 pages, 10 fig

Surface plasmon resonance in gold nanoparticle infiltrated dielectric opals

Light reflectance in three-dimensional metallo-dielectric photonic crystals of polyelectrolyte-coated latex spheres infiltrated with gold nanoparticles has been studied. Broad directional reflectance bands associated with the surface plasmon resonance in the lattice of the gold nanoparticle shells are observed in a wavelength range well separated from the diffraction resonance of the opal lattice. Dependence of surface plasmon resonance spectra on the Au nanoparticle distribution has been demonstrated

A systematic study of transport, magnetic and thermal properties of layered iridates

A unique feature of the 5d-iridates is that the spin-orbit interaction (SOI) and Coulomb interactions U are of comparable strength and therefore compete vigorously. The relative strength of these interactions stabilizes new exotic ground states that provide a fertile ground for studying new physics. SOI is proportional to Z^4 (Z is the atomic number), and it is now recognized that strong SOI can drive novel narrow-gap insulating states in heavy transition metal oxides such as iridates. Indeed, strong SOI necessarily introduces strong lattice degrees of freedom that become critical to new physics in the iridates. This dissertation thoroughly examines a wide array of newly observed novel phenomena induced by adjusting the relative strengths of U and SOI interactions via slight chemical doping and application of hydrostatic pressure in the layered iridates, particularly, BaIrO3 and Sr2IrO4