13,178 research outputs found
Ceramides: a new player in the inflammation-insulin resistance paradigm?
No abstract available
Electron-Spin Excitation Coupling in an Electron Doped Copper Oxide Superconductor
High-temperature (high-Tc) superconductivity in the copper oxides arises from
electron or hole doping of their antiferromagnetic (AF) insulating parent
compounds. The evolution of the AF phase with doping and its spatial
coexistence with superconductivity are governed by the nature of charge and
spin correlations and provide clues to the mechanism of high-Tc
superconductivity. Here we use a combined neutron scattering and scanning
tunneling spectroscopy (STS) to study the Tc evolution of electron-doped
superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing
process. We find that spin excitations detected by neutron scattering have two
distinct modes that evolve with Tc in a remarkably similar fashion to the
electron tunneling modes in STS. These results demonstrate that
antiferromagnetism and superconductivity compete locally and coexist spatially
on nanometer length scales, and the dominant electron-boson coupling at low
energies originates from the electron-spin excitations.Comment: 30 pages, 12 figures, supplementary information include
Growth dynamics and the evolution of cooperation in microbial populations
Microbes providing public goods are widespread in nature despite running the
risk of being exploited by free-riders. However, the precise ecological factors
supporting cooperation are still puzzling. Following recent experiments, we
consider the role of population growth and the repetitive fragmentation of
populations into new colonies mimicking simple microbial life-cycles.
Individual-based modeling reveals that demographic fluctuations, which lead to
a large variance in the composition of colonies, promote cooperation. Biased by
population dynamics these fluctuations result in two qualitatively distinct
regimes of robust cooperation under repetitive fragmentation into groups.
First, if the level of cooperation exceeds a threshold, cooperators will take
over the whole population. Second, cooperators can also emerge from a single
mutant leading to a robust coexistence between cooperators and free-riders. We
find frequency and size of population bottlenecks, and growth dynamics to be
the major ecological factors determining the regimes and thereby the
evolutionary pathway towards cooperation.Comment: 26 pages, 6 figure
Correlation functions quantify super-resolution images and estimate apparent clustering due to over-counting
We present an analytical method to quantify clustering in super-resolution
localization images of static surfaces in two dimensions. The method also
describes how over-counting of labeled molecules contributes to apparent
self-clustering and how the effective lateral resolution of an image can be
determined. This treatment applies to clustering of proteins and lipids in
membranes, where there is significant interest in using super-resolution
localization techniques to probe membrane heterogeneity. When images are
quantified using pair correlation functions, the magnitude of apparent
clustering due to over-counting will vary inversely with the surface density of
labeled molecules and does not depend on the number of times an average
molecule is counted. Over-counting does not yield apparent co-clustering in
double label experiments when pair cross-correlation functions are measured. We
apply our analytical method to quantify the distribution of the IgE receptor
(Fc{\epsilon}RI) on the plasma membranes of chemically fixed RBL-2H3 mast cells
from images acquired using stochastic optical reconstruction microscopy (STORM)
and scanning electron microscopy (SEM). We find that apparent clustering of
labeled IgE bound to Fc{\epsilon}RI detected with both methods arises from
over-counting of individual complexes. Thus our results indicate that these
receptors are randomly distributed within the resolution and sensitivity limits
of these experiments.Comment: 22 pages, 5 figure
Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory
Inspired by recent lattice measurements, we determine the short-distance (a
> omega >> pi T) asymptotics
of scalar (trace anomaly) and pseudoscalar (topological charge density)
correlators at 2-loop order in hot Yang-Mills theory. The results are expressed
in the form of an Operator Product Expansion. We confirm and refine the
determination of a number of Wilson coefficients; however some discrepancies
with recent literature are detected as well, and employing the correct values
might help, on the qualitative level, to understand some of the features
observed in the lattice measurements. On the other hand, the Wilson
coefficients show slow convergence and it appears uncertain whether this
approach can lead to quantitative comparisons with lattice data. Nevertheless,
as we outline, our general results might serve as theoretical starting points
for a number of perhaps phenomenologically more successful lines of
investigation.Comment: 27 pages. v2: minor improvements, published versio
Observation of the Dynamical Casimir Effect in a Superconducting Circuit
One of the most surprising predictions of modern quantum theory is that the
vacuum of space is not empty. In fact, quantum theory predicts that it teems
with virtual particles flitting in and out of existence. While initially a
curiosity, it was quickly realized that these vacuum fluctuations had
measurable consequences, for instance producing the Lamb shift of atomic
spectra and modifying the magnetic moment for the electron. This type of
renormalization due to vacuum fluctuations is now central to our understanding
of nature. However, these effects provide indirect evidence for the existence
of vacuum fluctuations. From early on, it was discussed if it might instead be
possible to more directly observe the virtual particles that compose the
quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing
relativistic motion could convert virtual photons into directly observable real
photons. This effect was later named the dynamical Casimir effect (DCE). Using
a superconducting circuit, we have observed the DCE for the first time. The
circuit consists of a coplanar transmission line with an electrical length that
can be changed at a few percent of the speed of light. The length is changed by
modulating the inductance of a superconducting quantum interference device
(SQUID) at high frequencies (~11 GHz). In addition to observing the creation of
real photons, we observe two-mode squeezing of the emitted radiation, which is
a signature of the quantum character of the generation process.Comment: 12 pages, 3 figure
Connecting the Holographic and Wilsonian Renormalization Groups
Inspired by the AdS/CFT correspondence, we develop an explicit formal duality
between the planar limit of a d-dimensional gauge theory and a classical field
theory in a (d+1)-dimensional anti-de Sitter space. The key ingredient is the
identification of fields in AdS with generalized Hubbard-Stratonovich
transforms of single-trace couplings of the QFT. We show that the Wilsonian
renormalization group flow of these transformed couplings matches the
holographic (Hamilton-Jacobi) flow of bulk fields along the radial direction in
AdS. This result allows one to outline an AdS/CFT dictionary that does not rely
on string theory.Comment: 11 pages, 1 figure; metadata modified in v2; added references and
minor changes in v3; v4 as published in JHE
Mixed RG Flows and Hydrodynamics at Finite Holographic Screen
We consider quark-gluon plasma with chemical potential and study
renormalization group flows of transport coefficients in the framework of
gauge/gravity duality. We first study them using the flow equations and compare
the results with hydrodynamic results by calculating the Green functions on the
arbitrary slice. Two results match exactly. Transport coefficients at arbitrary
scale is ontained by calculating hydrodynamics Green functions. When either
momentum or charge vanishes, transport coefficients decouple from each other.Comment: 22 pages, 6 figure
Maximizing the impact of malaria funding through allocative efficiency: using the right interventions in the right locations.
BACKGROUND: The high burden of malaria and limited funding means there is a necessity to maximize the allocative efficiency of malaria control programmes. Quantitative tools are urgently needed to guide budget allocation decisions. METHODS: A geospatial epidemic model was coupled with costing data and an optimization algorithm to estimate the optimal allocation of budgeted and projected funds across all malaria intervention approaches. Interventions included long-lasting insecticide-treated nets (LLINs), indoor residual spraying (IRS), intermittent presumptive treatment during pregnancy (IPTp), seasonal mass chemoprevention in children (SMC), larval source management (LSM), mass drug administration (MDA), and behavioural change communication (BCC). The model was applied to six geopolitical regions of Nigeria in isolation and also the nation as a whole to minimize incidence and malaria-attributable mortality. RESULTS: Allocative efficiency gains could avert approximately 84,000 deaths or 15.7 million cases of malaria in Nigeria over 5 years. With an additional US$300 million available, approximately 134,000 deaths or 37.3 million cases of malaria could be prevented over 5 years. Priority funding should go to LLINs, IPTp and BCC programmes, and SMC should be expanded in seasonal areas. To minimize mortality, treatment expansion is critical and prioritized over some LLIN funding, while to minimize incidence, LLIN funding remained a priority. For areas with lower rainfall, LSM is prioritized over IRS but MDA is not recommended unless all other programmes are established. CONCLUSIONS: Substantial reductions in malaria morbidity and mortality can be made by optimal targeting of investments to the right malaria interventions in the right areas
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