371 research outputs found
Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?
Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted
by their own melt at the triple point. We present extensive simulations for
NaCl, followed by calculations of the solid-vapor, solid-liquid, and
liquid-vapor free energies showing that solid NaCl(100) is a nonmelting
surface, and that its full behavior can quantitatively be accounted for within
a simple Born-Meyer-Huggins-Fumi-Tosi model potential. The incomplete wetting
is traced to the conspiracy of three factors: surface anharmonicities
stabilizing the solid surface; a large density jump causing bad liquid-solid
adhesion; incipient NaCl molecular correlations destabilizing the liquid
surface. The latter is pursued in detail, and it is shown that surface
short-range charge order acts to raise the surface tension because incipient
NaCl molecular formation anomalously reduces the surface entropy of liquid NaCl
much below that of solid NaCl(100).Comment: 4 pages, 3 figure
Terahertz response of dipolar impurities in polar liquids: On anomalous dielectric absorption of protein solutions
A theory of radiation absorption by dielectric mixtures is presented. The
coarse-grained formulation is based on the wavevector-dependent correlation
functions of molecular dipoles of the host polar liquid and a density-density
structure factor of the positions of the solutes. A nonlinear dependence of the
absorption coefficient on the solute concentration is predicted and originates
from the mutual polarization of the liquid surrounding the solutes by the
collective field of the solute dipoles aligned along the radiation field. The
theory is applied to terahertz absorption of hydrated saccharides and proteins.
While the theory gives an excellent account of the observations for saccharides
without additional assumptions and fitting parameters, experimental absorption
coefficient of protein solutions significantly exceeds theoretical calculations
within standard dielectric models and shows a peak against the protein
concentration. A substantial polarization of protein's hydration shell is
required to explain the differences between standard theories and experiment.
When the correlation function of the total dipole moment of the protein with
its hydration shell from numerical simulations is used in the present
analytical model an absorption peak similar to that seen is experiment is
obtained. The result is sensitive to the specifics of protein-protein
interactions in solution. Numerical testing of the theory requires the
combination of terahertz dielectric and small-angle scattering measurements.Comment: 11 p
IL-10-conditioned dendritic cells, decommissioned for recruitment of adaptive immunity, elicit innate inflammatory gene products in response to danger signals
Dendritic cells (DCs) are the professional APCs of the immune system, enabling T cells to perceive and respond appropriately to potentially dangerous microbes, while also being able to maintain T cell tolerance toward self. In part, such tolerance can be determined by IL-10 released from certain types of regulatory T cells. IL-10 has previously been shown to render DCs unable to activate T cells and it has been assumed that this process represents a general block in maturation. Using serial analysis of gene expression, we show that IL-10 pretreatment of murine bone marrow-derived DCs alone causes significant changes in gene expression. Furthermore, these cells retain the ability to respond to Toll-like receptor agonists, but in a manner skewed toward the selective induction of mediators known to enhance local inflammation and innate immunity, among which we highlight a novel CXCR2 ligand, DC inflammatory protein-1. These data suggest that, while the presence of a protolerogenic and purportedly anti-inflammatory agent such as IL-10 precludes DCs from acquiring their potential as initiators of adaptive immunity, their ability to act as initiators of innate immunity in response to Toll-like receptor signaling is enhanced
Anomalous temperature dependence of surface tension and capillary waves at liquid gallium
The temperature dependence of surface tension \gamma(T) at liquid gallium is
studied theoretically and experimentally using light scattering from capillary
waves. The theoretical model based on the Gibbs thermodynamics relates the
temperature derivative of \gamma to the surface excess entropy -\Delta S.
Although capillary waves contribute to the surface entropy with a positive sign
the effect of dipole layer on \Delta S is negative. Experimental data collected
at a free Ga surface in the temperature range from 30 to 160 C show that the
temperature derivative of the tension changes sign near 100 C.Comment: 11 pages, 1 Postscript figure, submitted to J. Phys.
Does Young's equation hold on the nanoscale? A Monte Carlo test for the binary Lennard-Jones fluid
When a phase-separated binary () mixture is exposed to a wall, that
preferentially attracts one of the components, interfaces between A-rich and
B-rich domains in general meet the wall making a contact angle .
Young's equation describes this angle in terms of a balance between the
interfacial tension and the surface tensions ,
between, respectively, the - and -rich phases and the wall,
. By Monte Carlo simulations
of bridges, formed by one of the components in a binary Lennard-Jones liquid,
connecting the two walls of a nanoscopic slit pore, is estimated from
the inclination of the interfaces, as a function of the wall-fluid interaction
strength. The information on the surface tensions ,
are obtained independently from a new thermodynamic integration method, while
is found from the finite-size scaling analysis of the
concentration distribution function. We show that Young's equation describes
the contact angles of the actual nanoscale interfaces for this model rather
accurately and location of the (first order) wetting transition is estimated.Comment: 6 pages, 6 figure
Corrections to scaling in 2--dimensional polymer statistics
Writing for the mean
square end--to--end length of a self--avoiding polymer chain of
links, we have calculated for the two--dimensional {\em continuum}
case from a new {\em finite} perturbation method based on the ground state of
Edwards self consistent solution which predicts the (exact) exponent.
This calculation yields . A finite size scaling analysis of data
generated for the continuum using a biased sampling Monte Carlo algorithm
supports this value, as does a re--analysis of exact data for two--dimensional
lattices.Comment: 10 pages of RevTex, 5 Postscript figures. Accepted for publication in
Phys. Rev. B. Brief Reports. Also submitted to J. Phys.
Melting of Hard Cubes
The melting transition of a system of hard cubes is studied numerically both
in the case of freely rotating cubes and when there is a fixed orientation of
the particles (parallel cubes). It is shown that freelly rotating cubes melt
through a first-order transition, whereas parallel cubes have a continuous
transition in which positional order is lost but bond-orientational order
remains finite. This is interpreted in terms of a defect-mediated theory of
meltingComment: 5 pages, 3 figures included. To appear in Phys. Rev.
An investigation of Digoxin by Cyclic Voltammetry using Gold and Silver Solid Electrodes and Chemometric Analysis
Digoxin, one of the main cardiac glycosides medication, has shown to have a strong analytical response under investigation by voltammetric analysis using mercury electrodes, achieving nanomole sensitivity. In this study we investigated the suitability of solid electrodes as gold and silver electrodes in voltammetric analysis of this active pharmaceutical ingredient. The scope of the investigation was to evaluate if the use of these solid electrodes, more practical and especially less dangerous, under an operative and environmental aspects could represent a valid further possibility to add to the use of the mercury ones. Both of the solid electrodes have been tested at different pH of 5, 7.4, 10, and 11. PCA analysis has been performed and specific responses achieved. Micromole sensitivity has been achieved for both of the electrodes, showing that the use of these sensors could represent a preliminary analytical approach when the more accurate alternative choice is not necessary, being more practical and less environmental impacting than using mercury
Dynamics of viscous amphiphilic films supported by elastic solid substrates
The dynamics of amphiphilic films deposited on a solid surface is analyzed
for the case when shear oscillations of the solid surface are excited. The two
cases of surface- and bulk shear waves are studied with film exposed to gas or
to a liquid. By solving the corresponding dispersion equation and the wave
equation while maintaining the energy balance we are able to connect the
surface density and the shear viscocity of a fluid amphiphilic overlayer with
experimentally accessible damping coefficients, phase velocity, dissipation
factor and resonant frequency shifts of shear waves.Comment: 19 pages, latex, 3 figures in eps-forma
Associations involving delays (particularly long delays) between certain weather parameters and geomagnetic activity
Four sunspot-minimum periods (1963-1966, 1971-1977, 1983-1987 and 1992-1997) have been examined for the results which are presented. Using several different weather parameters, tropospheric gravity waves, enhanced cold fronts and two rainfall data sets in Eastern Australia, associations at reasonably high levels of significance have been found with enhanced geomagnetic activity (EGA). Statistically this EGA involved either short delays of several days or long delays of about 20 days. The geomagnetic parameters used were (a) the AE index (b) the hourly H component for a number of stations and (c) the daily K-P-sum value. The K-P-sum analyses have shown that the EGA associated with the delays form part of four or five cycles of recurrent geomagnetic activity for 27-day periodicities. Furthermore statistically two recurrent cycles are found to exist concurrently, one apparently related to the short delays and the other to the long delays. Periodicities of 13.5 days are created because the two sets are displaced from each other by approximately this interval. A brief reference is made to the 13.5 periodicity known to exist for geomagnetic activity and the evidence in the literature for active regions on the sun to be displaced by 180 degrees of solar longitude
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