1,680 research outputs found
Testing the relevance of effective interaction potentials between highly charged colloids in suspension
Combining cell and Jellium model mean-field approaches, Monte Carlo together
with integral equation techniques, and finally more demanding many-colloid
mean-field computations, we investigate the thermodynamic behavior, pressure
and compressibility of highly charged colloidal dispersions, and at a more
microscopic level, the force distribution acting on the colloids. The
Kirkwood-Buff identity provides a useful probe to challenge the
self-consistency of an approximate effective screened Coulomb (Yukawa)
potential between colloids. Two effective parameter models are put to the test:
cell against renormalized Jellium models
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
Pneumococcal surface protein A of invasive Streptococcus pneumoniae isolates from Colombian children.
Pneumococcal surface protein A (PspA) elicits protection in mice against fatal bacteremia and sepsis caused by genetically diverse pneumococci and protects against carriage and lung infection. We determined the PspA families of invasive isolates of Streptococcus pneumoniae recovered from Colombian children <5 years of age. That 97.5% of Colombian isolates belong to PspA families 1 and 2 supports the hypothesis that a human PspA vaccine covering a few PspA families could be broadly effective
Boundary Term in Metric f(R) Gravity: Field Equations in the Metric Formalism
The main goal of this paper is to get in a straightforward form the field
equations in metric f(R) gravity, using elementary variational principles and
adding a boundary term in the action, instead of the usual treatment in an
equivalent scalar-tensor approach. We start with a brief review of the
Einstein-Hilbert action, together with the Gibbons-York-Hawking boundary term,
which is mentioned in some literature, but is generally missing. Next we
present in detail the field equations in metric f(R) gravity, including the
discussion about boundaries, and we compare with the Gibbons-York-Hawking term
in General Relativity. We notice that this boundary term is necessary in order
to have a well defined extremal action principle under metric variation.Comment: 12 pages, title changes by referee recommendation. Accepted for
publication in General Relativity and Gravitation. Matches with the accepted
versio
Será Deseada: A graphic novel about experiences of abortion in Mexico
This is the final version. Available on open access from the link in this recordEconomic and Social Research Council (ESRC
Generally covariant state-dependent diffusion
Statistical invariance of Wiener increments under SO(n) rotations provides a
notion of gauge transformation of state-dependent Brownian motion. We show that
the stochastic dynamics of non gauge-invariant systems is not unambiguously
defined. They typically do not relax to equilibrium steady states even in the
absence of extenal forces. Assuming both coordinate covariance and gauge
invariance, we derive a second-order Langevin equation with state-dependent
diffusion matrix and vanishing environmental forces. It differs from previous
proposals but nevertheless entails the Einstein relation, a Maxwellian
conditional steady state for the velocities, and the equipartition theorem. The
over-damping limit leads to a stochastic differential equation in state space
that cannot be interpreted as a pure differential (Ito, Stratonovich or else).
At odds with the latter interpretations, the corresponding Fokker-Planck
equation admits an equilibrium steady state; a detailed comparison with other
theories of state-dependent diffusion is carried out. We propose this as a
theory of diffusion in a heat bath with varying temperature. Besides
equilibrium, a crucial experimental signature is the non-uniform steady spatial
distribution.Comment: 24 page
Electrophysiological and morphological heterogeneity of slow firing neurons in medial septal/diagonal band complex as revealed by cluster analysis
Slow firing septal neurons modulate hippocampal and neocortical functions. Electrophysiologically, it is unclear whether slow firing neurons belong to a homogeneous neuronal population. To address this issue, whole-cell patch recordings and neuronal reconstructions were performed on rat brain slices containing the medial septum/diagonal band complex (MS/DB). Slow firing neurons were identified by their low firing rate at threshold (\u3c 5Hz) and lack of time-dependent inward rectification (Ih). Unsupervised cluster analysis was used to investigate whether slow firing neurons could be further classified into different subtypes. The parameters used for the cluster analysis included latency for first spike, slow afterhyperpolarizing potential, maximal frequency and action potential (AP) decay slope. Neurons were grouped into three major subtypes. The majority of neurons (55%) were grouped as cluster I. Cluster II (17% of neurons) exhibited longer latency for generation of the first action potential (246.5±20.1 ms). Cluster III (28% of neurons) exhibited higher maximal firing frequency (25.3±1.7 Hz) when compared to cluster I (12.3±0.9 Hz) and cluster II (11.8±1.1 Hz) neurons. Additionally, cluster III neurons exhibited faster action potentials at suprathreshold. Interestingly, cluster II neurons were frequently located in the medial septum whereas neurons in cluster I and III appeared scattered throughout all MS/DB regions. Sholl’s analysis revealed a more complex dendritic arborization in cluster III neurons. Cluster I and II neurons exhibited characteristics of “true” slow firing neurons whereas cluster III neurons exhibited higher frequency firing patterns. Several neurons were labeled with a cholinergic marker, Cy3-conjugated 192 IgG (p75NTR), and cholinergic neurons were found to be distributed among the three clusters. Our findings indicate that slow firing medial septal neurons are heterogeneous and that soma location is an important determinant of their electrophysiological properties. Thus, slow firing neurons from different septal regions have distinct functional properties, most likely related to their diverse connectivity
Myotonia in a patient with a mutation in an S4 arginine residue associated with hypokalaemic periodic paralysis and a concomitant synonymous CLCN1 mutation
The sarcolemmal voltage gated sodium channel NaV1.4 conducts the key depolarizing current that drives the upstroke of the skeletal muscle action potential. It contains four voltage-sensing domains (VSDs) that regulate the opening of the pore domain and ensuing permeation of sodium ions. Mutations that lead to increased NaV1.4 currents are found in patients with myotonia or hyperkalaemic periodic paralysis (HyperPP). Myotonia is also caused by mutations in the CLCN1gene that result in loss-of-function of the skeletal muscle chloride channel ClC-1. Mutations affecting arginine residues in the fourth transmembrane helix (S4) of the NaV1.4 VSDs can result in a leak current through the VSD and hypokalemic periodic paralysis (HypoPP), but these have hitherto not been associated with myotonia. We report a patient with an Nav1.4 S4 arginine mutation, R222Q, presenting with severe myotonia without fulminant paralytic episodes. Other mutations affecting the same residue, R222W and R222G, have been found in patients with HypoPP. We show that R222Q channels have enhanced activation, consistent with myotonia, but also conduct a leak current. The patient carries a concomitant synonymous CLCN1 variant that likely worsens the myotonia and potentially contributes to the amelioration of muscle paralysis. Our data show phenotypic variability for different mutations affecting the same S4 arginine that have implications for clinical therapy
Nonadiabatic pumping in classical and quantum chaotic scatterers
We study directed transport in periodically forced scattering systems in the
regime of fast and strong driving where the dynamics is mixed to chaotic and
adiabatic approximations do not apply. The model employed is a square potential
well undergoing lateral oscillations, alternatively as two- or single-parameter
driving. Mechanisms of directed transport are analyzed in terms of asymmetric
irregular scattering processes. Quantizing the system in the framework of
Floquet scattering theory, we calculate directed currents on basis of
transmission and reflection probabilities obtained by numerical wavepacket
scattering. We observe classical as well as quantum transport beyond linear
response, manifest in particular in a non-zero current for single-parameter
driving where according to adiabatic theory, it should vanish identically.Comment: 13 pages, 8 figure
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