1,367 research outputs found
The Hawking temperature in the context of dark energy for four-dimensional asymptotically AdS black holes with scalar hair
In this paper, we considered new solutions for four-dimensional
asymptotically AdS black holes with scalar hair and discuss about Hawking
temperature in the context of dark energy by using the tunneling method. We
obtain modification of the Hawking temperature due to presence of the dark
energy
Self-diffusion of polymers in cartilage as studied by pulsed field gradient NMR
Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) was used to investigate the self-diffusion behaviour of polymers in cartilage. Polyethylene glycol and dextran with different molecular weights and in different concentrations were used as model compounds to mimic the diffusion behaviour of metabolites of cartilage. The polymer self-diffusion depends extremely on the observation time: The short-time self-diffusion coefficients (diffusion time Delta approximately 15 ms) are subjected to a rather non-specific obstruction effect that depends mainly on the molecular weights of the applied polymers as well as on the water content of the cartilage. The observed self-diffusion coefficients decrease with increasing molecular weights of the polymers and with a decreasing water content of the cartilage. In contrast, the long-time self-diffusion coefficients of the polymers in cartilage (diffusion time Delta approximately 600 ms) reflect the structural properties of the tissue. Measurements at different water contents, different molecular weights of the polymers and varying observation times suggest that primarily the collagenous network of cartilage but also the entanglements of the polymer chains themselves are responsible for the observed restricted diffusion. Additionally, anomalous restricted diffusion was shown to occur already in concentrated polymer solutions
Vitamin D Deficiency
Previously, known actions of vitamin D were confined to skeletal health, but accumulating evidence has consistently suggested that vitamin D has pleomorphic roles in overall human physiology. Hence, no other micronutrient deficiency in the modern times has gained as much global attention as vitamin D deficiency. In this chapter, the author reinforces what is already known in vitamin D and highlights several important findings in vitamin D research, with a special focus on one of the most vitamin D-deficient regions in the world, the Middle East, and Saudi Arabia, in particular
Attraction between Neutral Dielectrics Mediated by Multivalent Ions in an Asymmetric Ionic Fluid
We study the interaction between two neutral plane-parallel dielectric bodies
in the presence of a highly asymmetric ionic fluid, containing multivalent as
well as monovalent (salt) ions. Image charge interactions, due to dielectric
discontinuities at the boundaries, as well as effects from ion confinement in
the slit region between the surfaces are taken fully into account, leading to
image-generated depletion attraction, ion correlation attraction and
steric-like repulsive interactions. We investigate these effects by employing a
combination of methods including explicit-ion and implicit-ion Monte-Carlo
simulations, as well as an effective interaction potential analytical theory.
The latter incorporates strong ion-image charge correlations, which develop in
the presence of high valency ions in the mixture. We show that the implicit-ion
simulations and the proposed analytical theory can describe the explicit
simulation results on a qualitative level, while excellent quantitative
agreement can be obtained for sufficiently large monovalent salt
concentrations. The resultant attractive interaction between the neutral
surfaces is shown to be significant, as compared with the usual van der Waals
interactions between semi-infinite dielectrics, and can thus play a significant
role at the nano scale.Comment: 9 pages, 4 figure
Quenched Charge Disorder and Coulomb Interactions
We develop a general formalism to investigate the effect of quenched fixed
charge disorder on effective electrostatic interactions between charged
surfaces in a one-component (counterion-only) Coulomb fluid. Analytical results
are explicitly derived for two asymptotic and complementary cases: i)
mean-field or Poisson-Boltzmann limit (including Gaussian-fluctuations
correction), which is valid for small electrostatic coupling, and ii)
strong-coupling limit, where electrostatic correlations mediated by counterions
become significantly large as, for instance, realized in systems with
high-valency counterions. In the particular case of two apposed and ideally
polarizable planar surfaces with equal mean surface charge, we find that the
effect of the disorder is nil on the mean-field level and thus the plates
repel. In the strong-coupling limit, however, the effect of charge disorder
turns out to be additive in the free energy and leads to an enhanced long-range
attraction between the two surfaces. We show that the equilibrium inter-plate
distance between the surfaces decreases for elevated disorder strength (i.e.
for increasing mean-square deviation around the mean surface charge), and
eventually tends to zero, suggesting a disorder-driven collapse transition.Comment: 13 pages, 2 figure
Counterion-mediated Electrostatic Interactions between Helical Molecules
We study the interaction of two cylinders with helical charge distribution
mediated by neutralizing counterions, by analyzing the separation as well as
the azimuthal angle dependence of the interaction force in the weak and strong
coupling limit. While the azimuthal dependence of the interaction in the weak
coupling limit is overall small and mostly negligible, the strong coupling
limit leads to qualitatively new features of the interaction, among others also
to an orientationally dependent optimal configuration that is driven by angular
dependence of the correlation attraction. We investigate the properties of this
azimuthal ordering in detail and compare it to existing results.Comment: 11 pages, 12 figure
Electrostatic Disorder-Induced Interactions in Inhomogeneous Dielectrics
We investigate the effect of quenched surface charge disorder on
electrostatic interactions between two charged surfaces in the presence of
dielectric inhomogeneities and added salt. We show that in the linear
weak-coupling regime (i.e., by including mean-field and Gaussian-fluctuations
contributions), the image-charge effects lead to a non-zero disorder-induced
interaction free energy between two surfaces of equal mean charge that can be
repulsive or attractive depending on the dielectric mismatch across the
bounding surfaces and the exact location of the disordered charge distribution.Comment: 7 pages, 2 figure
Electromagnetic fluctuation-induced interactions in randomly charged slabs
Randomly charged net-neutral dielectric slabs are shown to interact across a
featureless dielectric continuum with long-range electrostatic forces that
scale with the statistical variance of their quenched random charge
distribution and inversely with the distance between their bounding surfaces.
By accounting for the whole spectrum of electromagnetic field fluctuations, we
show that this long-range disorder-generated interaction extends well into the
retarded regime where higher-order Matsubara frequencies contribute
significantly. This occurs even for highly clean samples with only a trace
amount of charge disorder and shows that disorder effects can be important down
to the nano scale. As a result, the previously predicted non-monotonic behavior
for the total force between dissimilar slabs as a function of their separation
distance is substantially modified by higher-order contributions, and in almost
all cases of interest, we find that the equilibrium inter-surface separation is
shifted to substantially larger values compared to predictions based solely on
the zero-frequency component. This suggests that the ensuing non-monotonic
interaction is more easily amenable to experimental detection. The presence of
charge disorder in the intervening dielectric medium between the two slabs is
shown to lead to an additional force that can be repulsive or attractive
depending on the system parameters and can, for instance, wash out the
non-monotonic behavior of the total force when the intervening slab contains a
sufficiently large amount of disorder charges.Comment: 9 pages, 5 figure
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