Analysis of Mesoscopic Structured 2-Propanol/Water Mixtures Using Pressure Perturbation Calorimetry and Molecular Dynamic Simulation

In this paper we demonstrate the application of pressure perturbation calorimetry (PPC) to the characterization of 2-propanol/water mixtures. PPC of different 2-propanol/water mixtures provides two useful measurements: (i) the change in heat (ΔQ); and (ii) the [δC¯p/δp]T[δC¯p/δp]T value. The results demonstrate that the ΔQ values of the mixtures deviate from that expected for a random mixture, with a maximum at ~20–25 mol% 2-propanol. This coincides with the concentration at which molecular dynamics (MD) simulations show a maximum deviation from random distribution, and also the point at which alcohol–alcohol hydrogen bonds become dominant over alcohol–water hydrogen bonds. Furthermore, the [δC¯p/δp]T[δC¯p/δp]T value showed transitions at 2.5 mol% 2-propanol and at approximately 14 mol% 2-propanol. Below 2.5 mol% 2-propanol the values of [δC¯p/δp]T[δC¯p/δp]T are negative; this is indicative of the presence of isolated 2-propanol molecules surrounded by water molecules. Above 2.5 mol% 2-propanol [δC¯p/δp]T[δC¯p/δp]T rises, reaching a maximum at ~14 mol% corresponding to a point where mixed alcohol–water networks are thought to dominate. The values and trends identified by PPC show excellent agreement not only with those obtained from MD simulations but also with results in the literature derived using viscometry, THz spectroscopy, NMR and neutron diffraction

An empirical orthogonal function reanalysis of the northern polar external and induced magnetic field during solar cycle 23

We apply the method of data-interpolating Empirical Orthogonal Functions (EOFs) to ground-based magnetic vector data from the SuperMAG archive to produce a series of month-length reanalyses of the surface external and induced magnetic field (SEIMF) in 110,000 km2 equal-area bins over the entire northern polar region at 5-minute cadence over solar cycle 23, from 1997.0 to 2009.0. Each EOF re-analysis also decomposes the measured SEIMF variation into a hierarchy of spatio-temporal patterns which are ordered by their contribution to the monthly magnetic field variance. We find that the leading EOF patterns can each be (subjectively) interpreted as well-known SEIMF systems or their equivalent current systems. The relationship of the equivalent currents to the true current flow is not investigated. We track the leading SEIMF or equivalent current systems of similar type by inter-monthly spatial correlation, and apply graph theory to (objectively) group their appearance and relative importance throughout a solar cycle, revealing seasonal and solar cycle variation. In this way, we identify the spatiotemporal patterns which maximally contribute to SEIMF variability over a solar cycle. We propose this combination of EOF and graph theory as a powerful method for objectively defining and investigating the structure and variability of the SEIMF or their equivalent ionospheric currents for use in both geomagnetism and space weather applications. It is demonstrated here on solar cycle 23, but is extendable to any epoch with sufficient data coverage

Direct experimental verification of applicability of single-site model for angle integrated photoemission of small TKT_{K} concentrated Ce compounds

Bulk-sensitive high-resolution Ce 4f spectra have been obtained from 3d $\to$ 4f resonance photoemission measurements on La$_{1-x}$Ce$_x$Al$_2$ and La$_{1-x}$Ce$_x$Ru$_2$ for $x = 0.0, 0.04, 1.0$. The 4f spectra of low-Kondo-temperature ($T_{K}$) (La,Ce)Al$_2$ are essentially identical except for a slight increase of the Kondo peak with $x$, which is consistent with a known increase of $T_{K}$ with $x$. In contrast, the 4f spectra of high-$T_{K}$ (La,Ce)Ru$_2$ show a Kondo-like peak and also a 0.5 eV structure which increases strongly with $x$. The resonance photon-energy dependences of the two contributions are different and the origin of the 0.5 eV structure is still uncertain.Comment: submitted to SCES 2001, two-columnn format, modified tex

A solution for galactic disks with Yukawian gravitational potential

We present a new solution for the rotation curves of galactic disks with gravitational potential of the Yukawa type. We follow the technique employed by Toomre in 1963 in the study of galactic disks in the Newtonian theory. This new solution allows an easy comparison between the Newtonian solution and the Yukawian one. Therefore, constraints on the parameters of theories of gravitation can be imposed, which in the weak field limit reduce to Yukawian potentials. We then apply our formulae to the study of rotation curves for a zero-thickness exponential disk and compare it with the Newtonian case studied by Freeman in 1970. As an application of the mathematical tool developed here, we show that in any theory of gravity with a massive graviton (this means a gravitational potential of the Yukawa type), a strong limit can be imposed on the mass (m_g) of this particle. For example, in order to obtain a galactic disk with a scale length of b ~ 10 kpc, we should have a massive graviton of m_g << 10^{-59} g. This result is much more restrictive than those inferred from solar system observations.Comment: 7 pages; 1 eps figure; to appear in General Relativity and Gravitatio

Magnetic and electronic structures of superconducting RuSr2_2GdCu2_2O8_8

The coexistence of ferromagnetism and superconductivity in RuSr$_2$GdCu$_2$O$_8$ was reported both from experiments (by Tallon et. al.) and first-principles calculations (by Pickett et. al.). Here we report that our first-principles full-potential linearized augmented plane wave (FLAPW) calculations, employing the precise crystal structure with structural distortions (i.e., RuO$_6$ rotations) determined by neutron diffraction, demonstrate that antiferromagnetic ordering of the Ru moments is energetically favored over the previously proposed ferromagnetic ordering. Our results are consistent with recently performed magnetic neutron diffraction experiments (Lynn et. al). Ru $t_{2g}$ states, which are responsible for the magnetism, have only a very small interaction with Cu $e_g$ states, which results in a small exchange splitting of these states. The Fermi surface, characterized by strongly hybridized $dp\sigma$ orbitals, has nesting features similar to those in the two-dimensional high $T_c$ cuprate superconductors.Comment: 6 pages,6 figures, accepted for publication in Phys. Rev.

Spatial variation in the responses of the surface external and induced magnetic field to the solar wind

We analyse the spatial variation in the response of the surface geomagnetic field (or the equivalent ionospheric current) to variations in the solar wind. Specifically, we regress a reanalysis of surface external and induced magnetic field (SEIMF) variations onto measurements of the solar wind. The regression is performed in monthly sets, independently for 559 regularly‐spaced locations covering the entire northern polar region above 50° magnetic latitude. At each location, we find the lag applied to the solar wind data that maximises the correlation with the SEIMF. The resulting spatial maps of these independent lags and regression coefficients provide a model of the localised SEIMF response to variations in the solar wind, which we call ‘Spatial Information from Distributed Exogenous Regression’ (SPIDER). We find that the lag and regression coefficients vary systematically with ionospheric region, season, and solar wind driver. In the polar cap region the SEIMF is best described by the By component of the interplanetary magnetic field (50–75% of total variance explained) at a lag ∼20–25 min. Conversely, in the auroral zone the SEIMF is best described by the solar wind ϵ function (60–80% of total variance explained), with a lag that varies with season and magnetic local time (MLT), from ∼15–20 min for dayside and afternoon MLT (except in Oct‐Dec) to typically 30–40 min for nightside and morning MLT, and even longer (60–65 min) around midnight MLT

Thermodynamic properties of thin films of superfluid 3He-A

The pairing correlations in superfluid He-3 are strongly modified by quasiparticle scattering off a surface or an interface. We present theoretical results and predictions for the order parameter, the quasiparticle excitation spectrum and the free energy for thin films of superfluid He-3. Both specular and diffuse scattering by a substrate are considered, while the free surface is assumed to be a perfectly reflecting specular boundary. The results are based on self-consistent calculations of the order parameter and quasiparticle excitation spectrum at zero pressure. We obtain new results for the phase diagram, free energy, entropy and specific heat of thin films of superfluid He-3.Comment: Replaced with an updated versio

A New Composite Restorative Based on a Hydrophobic Matrix

A hydrophobic restorative composite based on a fluorocarbon analog of an alkyl methacrylate and a bisphenol adduct was formulated into a one-paste system, which polymerized in the presence of blue light. Physical, mechanical, and water-related properties were determined. High contact angles and low water sorption were shown by the experimental composite. Capillary penetration of oral fluids around restorations, therefore, could be prevented in the presence of this highly hydrophobic surface. The physical and mechanical properties of the experimental composite were either comparable to or somewhat less favorable than commercial Bis-GMA composites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67042/2/10.1177_00220345790580100401.pd

Attentive Learning of Sequential Handwriting Movements: A Neural Network Model

Defense Advanced research Projects Agency and the Office of Naval Research (N00014-95-1-0409, N00014-92-J-1309); National Science Foundation (IRI-97-20333); National Institutes of Health (I-R29-DC02952-01)