364 research outputs found
Proximity to Fermi-surface topological change in superconducting LaO0.54F0.46BiS2
The electronic structure of nearly optimally-doped novel superconductor
LaOFBiS ( = 0.46) was investigated using
angle-resolved photoemission spectroscopy (ARPES). We clearly observed band
dispersions from 2 to 6 eV binding energy and near the Fermi level (), which are well reproduced by first principles calculations when
the spin-orbit coupling is taken into account. The ARPES intensity map near
shows a square-like distribution around the (Z) point
in addition to electronlike Fermi surface (FS) sheets around the X(R) point,
indicating that FS of LaOFBiS is in close proximity to
the theoretically-predicted topological change.Comment: 6 pages, 3 figures, + supplemental materia
Population Dynamics and Non-Hermitian Localization
We review localization with non-Hermitian time evolution as applied to simple
models of population biology with spatially varying growth profiles and
convection. Convection leads to a constant imaginary vector potential in the
Schroedinger-like operator which appears in linearized growth models. We
illustrate the basic ideas by reviewing how convection affects the evolution of
a population influenced by a simple square well growth profile. Results from
discrete lattice growth models in both one and two dimensions are presented. A
set of similarity transformations which lead to exact results for the spectrum
and winding numbers of eigenfunctions for random growth rates in one dimension
is described in detail. We discuss the influence of boundary conditions, and
argue that periodic boundary conditions lead to results which are in fact
typical of a broad class of growth problems with convection.Comment: 19 pages, 11 figure
Morphological Instabilities in a growing Yeast Colony: Experiment and Theory
We study the growth of colonies of the yeast Pichia membranaefaciens on
agarose film. The growth conditions are controlled in a setup where nutrients
are supplied through an agarose film suspended over a solution of nutrients. As
the thickness of the agarose film is varied, the morphology of the front of the
colony changes. The growth of the front is modeled by coupling it to a
diffusive field of inhibitory metabolites. Qualitative agreement with
experiments suggests that such a coupling is responsible for the observed
instability of the front.Comment: RevTex, 4 pages and 3 figure
Non-Hermitian Localization and Population Biology
The time evolution of spatial fluctuations in inhomogeneous d-dimensional
biological systems is analyzed. A single species continuous growth model, in
which the population disperses via diffusion and convection is considered.
Time-independent environmental heterogeneities, such as a random distribution
of nutrients or sunlight are modeled by quenched disorder in the growth rate.
Linearization of this model of population dynamics shows that the fastest
growing localized state dominates in a time proportional to a power of the
logarithm of the system size. Using an analogy with a Schrodinger equation
subject to a constant imaginary vector potential, we propose a delocalization
transition for the steady state of the nonlinear problem at a critical
convection threshold separating localized and extended states. In the limit of
high convection velocity, the linearized growth problem in dimensions
exhibits singular scaling behavior described by a (d-1)-dimensional
generalization of the noisy Burgers' equation, with universal singularities in
the density of states associated with disorder averaged eigenvalues near the
band edge in the complex plane. The Burgers mapping leads to unusual transverse
spreading of convecting delocalized populations.Comment: 22 pages, 11 figure
Deletion of the gabra2 gene results in hypersensitivity to the acute effects of ethanol but does not alter ethanol self administration
Human genetic studies have suggested that polymorphisms of the GABRA2 gene encoding the GABA(A) α2-subunit are associated with ethanol dependence. Variations in this gene also convey sensitivity to the subjective effects of ethanol, indicating a role in mediating ethanol-related behaviours. We therefore investigated the consequences of deleting the α2-subunit on the ataxic and rewarding properties of ethanol in mice. Ataxic and sedative effects of ethanol were explored in GABA(A) α2-subunit wildtype (WT) and knockout (KO) mice using a Rotarod apparatus, wire hang and the duration of loss of righting reflex. Following training, KO mice showed shorter latencies to fall than WT littermates under ethanol (2 g/kg i.p.) in both Rotarod and wire hang tests. After administration of ethanol (3.5 g/kg i.p.), KO mice took longer to regain the righting reflex than WT mice. To ensure the acute effects are not due to the gabra2 deletion affecting pharmacokinetics, blood ethanol concentrations were measured at 20 minute intervals after acute administration (2 g/kg i.p.), and did not differ between genotypes. To investigate ethanol's rewarding properties, WT and KO mice were trained to lever press to receive increasing concentrations of ethanol on an FR4 schedule of reinforcement. Both WT and KO mice self-administered ethanol at similar rates, with no differences in the numbers of reinforcers earned. These data indicate a protective role for α2-subunits, against the acute sedative and ataxic effects of ethanol. However, no change was observed in ethanol self administration, suggesting the rewarding effects of ethanol remain unchange
Universality in Bacterial Colonies
The emergent spatial patterns generated by growing bacterial colonies have
been the focus of intense study in physics during the last twenty years. Both
experimental and theoretical investigations have made possible a clear
qualitative picture of the different structures that such colonies can exhibit,
depending on the medium on which they are growing. However, there are
relatively few quantitative descriptions of these patterns. In this paper, we
use a mechanistically detailed simulation framework to measure the scaling
exponents associated with the advancing fronts of bacterial colonies on hard
agar substrata, aiming to discern the universality class to which the system
belongs. We show that the universal behavior exhibited by the colonies can be
much richer than previously reported, and we propose the possibility of up to
four different sub-phases within the medium-to-high nutrient concentration
regime. We hypothesize that the quenched disorder that characterizes one of
these sub-phases is an emergent property of the growth and division of bacteria
competing for limited space and nutrients.Comment: 12 pages, 5 figure
Evidence for geometry-dependent universal fluctuations of the Kardar-Parisi-Zhang interfaces in liquid-crystal turbulence
We provide a comprehensive report on scale-invariant fluctuations of growing
interfaces in liquid-crystal turbulence, for which we recently found evidence
that they belong to the Kardar-Parisi-Zhang (KPZ) universality class for 1+1
dimensions [Phys. Rev. Lett. 104, 230601 (2010); Sci. Rep. 1, 34 (2011)]. Here
we investigate both circular and flat interfaces and report their statistics in
detail. First we demonstrate that their fluctuations show not only the KPZ
scaling exponents but beyond: they asymptotically share even the precise forms
of the distribution function and the spatial correlation function in common
with solvable models of the KPZ class, demonstrating also an intimate relation
to random matrix theory. We then determine other statistical properties for
which no exact theoretical predictions were made, in particular the temporal
correlation function and the persistence probabilities. Experimental results on
finite-time effects and extreme-value statistics are also presented. Throughout
the paper, emphasis is put on how the universal statistical properties depend
on the global geometry of the interfaces, i.e., whether the interfaces are
circular or flat. We thereby corroborate the powerful yet geometry-dependent
universality of the KPZ class, which governs growing interfaces driven out of
equilibrium.Comment: 31 pages, 21 figures, 1 table; references updated (v2,v3); Fig.19
updated & minor changes in text (v3); final version (v4); J. Stat. Phys.
Online First (2012
Hepatitis C virus cell-cell transmission and resistance to direct-acting antiviral agents
Hepatitis C virus (HCV) is transmitted between hepatocytes via classical cell entry but also uses direct cell-cell transfer to infect neighboring hepatocytes. Viral cell-cell transmission has been shown to play an important role in viral persistence allowing evasion from neutralizing antibodies. In contrast, the role of HCV cell-cell transmission for antiviral resistance is unknown. Aiming to address this question we investigated the phenotype of HCV strains exhibiting resistance to direct-acting antivirals (DAAs) in state-of-the-art model systems for cell-cell transmission and spread. Using HCV genotype 2 as a model virus, we show that cell-cell transmission is the main route of viral spread of DAA-resistant HCV. Cell-cell transmission of DAA-resistant viruses results in viral persistence and thus hampers viral eradication. We also show that blocking cell-cell transmission using host-targeting entry inhibitors (HTEIs) was highly effective in inhibiting viral dissemination of resistant genotype 2 viruses. Combining HTEIs with DAAs prevented antiviral resistance and led to rapid elimination of the virus in cell culture model. In conclusion, our work provides evidence that cell-cell transmission plays an important role in dissemination and maintenance of resistant variants in cell culture models. Blocking virus cell-cell transmission prevents emergence of drug resistance in persistent viral infection including resistance to HCV DAAs
Increased susceptibility of Huh7 cells to HCV replication does not require mutations in RIG-I
<p>Abstract</p> <p>Background</p> <p>The cytosolic retinoic acid-inducible gene I (RIG-I) is a pattern recognition receptor that senses HCV double-stranded RNA and triggers type I interferon pathways. The clone Huh7.5 of human hepatoma Huh7 cells contains a mutation in RIG-I that is believed to be responsible for the improved replication of HCV in these cells relative to the parental strain. We hypothesized that, in addition to RIG-I, other determinant(s) outside the RIG-I coding sequence are involved in limiting HCV replication in cell culture. To test our hypothesis, we analyzed Huh7 cell clones that support the efficient replication of HCV and analyzed the RIG-I gene.</p> <p>Results</p> <p>One clone, termed Huh7D, was more permissive for HCV replication and more efficient for HCV-neomycin and HCV-hygromycin based replicon colony formation than parental Huh7 cells. Nucleotide sequence analysis of the RIG-I mRNA coding region from Huh7D cells showed no mutations relative to Huh7 parental cells.</p> <p>Conclusions</p> <p>We derived a new Huh7 cell line, Huh7D, which is more permissive for HCV replication than parental Huh7 cells. The higher permissiveness of Huh7D cells is not due to mutations in the RIG-I protein, indicating that cellular determinants other than the RIG-I amino-acid sequence are responsible for controlling HCV replication. In addition, we have selected Huh7 cells resistant to hygromycin via newly generated HCV-replicons carrying the hygromycin resistant gene. Further studies on Huh7D cells will allow the identification of cellular factors that increased the susceptibility to HCV infection, which could be targeted for anti-HCV therapies.</p
Seismic tomography of the uppermost mantle beneath southwestern Japan: Seismological constraints on modelling subduction and magmatism for the Philippine Sea slab
- …