2,180 research outputs found
Equivalent of a Thouless energy in lattice QCD Dirac spectra
Random matrix theory (RMT) is a powerful statistical tool to model spectral
fluctuations. In addition, RMT provides efficient means to separate different
scales in spectra. Recently RMT has found application in quantum chromodynamics
(QCD). In mesoscopic physics, the Thouless energy sets the universal scale for
which RMT applies. We try to identify the equivalent of a Thouless energy in
complete spectra of the QCD Dirac operator with staggered fermions and
lattice gauge fields. Comparing lattice data with RMT predictions we
find deviations which allow us to give an estimate for this scale.Comment: LATTICE99 (theor. devel.), 3 pages, 4 figure
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Precise Control of Molecular Self-Diffusion in Isoreticular and Multivariate Metal-Organic Frameworks.
Understanding the factors that affect self-diffusion in isoreticular and multivariate (MTV) MOFs is key to their application in drug delivery, separations, and heterogeneous catalysis. Here, we measure the apparent self-diffusion of solvents saturated within the pores of large single crystals of MOF-5, IRMOF-3 (amino-functionalized MOF-5), and 17 MTV-MOF-5/IRMOF-3 materials at various mole fractions. We find that the apparent self-diffusion coefficient of N,N-dimethylformamide (DMF) may be tuned linearly between the diffusion coefficients of MOF-5 and IRMOF-3 as a function of the linker mole fraction. We compare a series of solvents at saturation in MOF-5 and IRMOF-3 to elucidate the mechanism by which the linker amino groups tune molecular diffusion. The ratio of the self-diffusion coefficients for solvents in MOF-5 to those in IRMOF-3 is similar across all solvents tested, regardless of solvent polarity. We conclude that average pore aperture, not solvent-linker chemical interactions, is the primary factor responsible for the different diffusion dynamics upon introduction of an amino group to the linker
On quantum equivalence of dual sigma models: examples
The equivalence of several sigma models and their special Abelian
duals is investigated in the two loop order of perturbation theory. The
investigation is based on extracting and comparing various functions of
the original and dual models. The role of the discrete global symmetries is
emphasized.Comment: Plain TEX, 24 page
Perturbative Quantum (In)equivalence of Dual Models in dimensions
Various examples of target space duality transformations are investigated up
to two loop order in perturbation theory. Our results show that when using the
tree level (`naive') transformation rules the dual theories are in general {\it
inequivalent} at two loops to the original ones, (both for the Abelian and the
non Abelian duality).Comment: 11 pages, Latex, uses espcrc2.st
Decoupling a Cooper-pair box to enhance the lifetime to 0.2 ms
We present a circuit QED experiment in which a separate transmission line is
used to address a quasi-lumped element superconducting microwave resonator
which is in turn coupled to an Al/AlO/Al Cooper-pair box (CPB) charge
qubit. In our measurements we find a strong correlation between the measured
lifetime of the CPB and the coupling between the qubit and the transmission
line. By monitoring perturbations of the resonator's 5.44 GHz resonant
frequency, we have measured the spectrum, lifetime (), Rabi, and Ramsey
oscillations of the CPB at the charge degeneracy point while the CPB was
detuned by up to 2.5 GHz . We find a maximum lifetime of the CPB was s for to 4.5 GHz. Our measured 's are consistent with
loss due to coupling to the transmission line, spurious microwave circuit
resonances, and a background decay rate on the order of
s of unknown origin, implying that the loss tangent in the AlO
junction barrier must be less than about at 4.5 GHz, about 4
orders of magnitude less than reported in larger area Al/AlO/Al tunnel
junctions
Modeling the functional genomics of autism using human neurons.
Human neural progenitors from a variety of sources present new opportunities to model aspects of human neuropsychiatric disease in vitro. Such in vitro models provide the advantages of a human genetic background combined with rapid and easy manipulation, making them highly useful adjuncts to animal models. Here, we examined whether a human neuronal culture system could be utilized to assess the transcriptional program involved in human neural differentiation and to model some of the molecular features of a neurodevelopmental disorder, such as autism. Primary normal human neuronal progenitors (NHNPs) were differentiated into a post-mitotic neuronal state through addition of specific growth factors and whole-genome gene expression was examined throughout a time course of neuronal differentiation. After 4 weeks of differentiation, a significant number of genes associated with autism spectrum disorders (ASDs) are either induced or repressed. This includes the ASD susceptibility gene neurexin 1, which showed a distinct pattern from neurexin 3 in vitro, and which we validated in vivo in fetal human brain. Using weighted gene co-expression network analysis, we visualized the network structure of transcriptional regulation, demonstrating via this unbiased analysis that a significant number of ASD candidate genes are coordinately regulated during the differentiation process. As NHNPs are genetically tractable and manipulable, they can be used to study both the effects of mutations in multiple ASD candidate genes on neuronal differentiation and gene expression in combination with the effects of potential therapeutic molecules. These data also provide a step towards better understanding of the signaling pathways disrupted in ASD
Simple algebras of Weyl type
Over a field of any characteristic, for a commutative associative algebra
with an identity element and for the polynomial algebra of a
commutative derivation subalgebra of , the associative and the Lie
algebras of Weyl type on the same vector space are
defined. It is proved that , as a Lie algebra (modular its center) or as
an associative algebra, is simple if and only if is -simple and
acts faithfully on . Thus a lot of simple algebras are obtained.Comment: 9 pages, Late
The QCD sign problem and dynamical simulations of random matrices
At nonzero quark chemical potential dynamical lattice simulations of QCD are
hindered by the sign problem caused by the complex fermion determinant. The
severity of the sign problem can be assessed by the average phase of the
fermion determinant. In an earlier paper we derived a formula for the
microscopic limit of the average phase for general topology using chiral random
matrix theory. In the current paper we present an alternative derivation of the
same quantity, leading to a simpler expression which is also calculable for
finite-sized matrices, away from the microscopic limit. We explicitly prove the
equivalence of the old and new results in the microscopic limit. The results
for finite-sized matrices illustrate the convergence towards the microscopic
limit. We compare the analytical results with dynamical random matrix
simulations, where various reweighting methods are used to circumvent the sign
problem. We discuss the pros and cons of these reweighting methods.Comment: 34 pages, 3 figures, references added, as published in JHE
The role of the North Atlantic Oscillation in controlling U.K. butterfly population size and phenology
Copyright @ 2012 The Authors. This article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.1. The North Atlantic Oscillation (NAO) exerts considerable control on U.K. weather. This study investigates the impact of the NAO on butterfly abundance and phenology using 34 years of data from the U.K. Butterfly Monitoring Scheme (UKBMS). 2. The study uses a multi-species indicator to show that the NAO does not affect overall U.K. butterfly population size. However, the abundance of bivoltine butterfly species, which have longer flight seasons, were found to be more likely to respond positively to the NAO compared with univoltine species, which show little or a negative response. 3. A positive winter NAO index is associated with warmer weather and earlier flight dates for Anthocharis cardamines (Lepidoptera: Pieridae), Melanargia galathea (Lepidoptera: Nymphalidae), Aphantopus hyperantus (Lepidoptera: Nymphalidae), Pyronia tithonus (Lepidoptera: Nymphalidae), Lasiommata megera (Lepidoptera: Nymphalidae) and Polyommatus icarus (Lepidoptera: Lycaenidae). In bivoltine species, the NAO affects the phenology of the first generation, the timing of which indirectly controls the timing of the second generation. 4. The NAO influences the timing of U.K. butterfly flight seasons more strongly than it influences population size.This study was supported by a multi-agency consortium led by the U.K. Department for Environment, Food and Rural Affairs (Defra), including the Countryside Council for Wales, the Joint Nature Conservation Committee, the Forestry Commission, Natural England, the Natural Environment Research Council, the Northern Ireland Environment Agency and Scottish Natural Heritage. This article is made available through the Brunel Open Access Publishing Fund
The -theorem and the Asymptotics of 4D Quantum Field Theory
We study the possible IR and UV asymptotics of 4D Lorentz invariant unitary
quantum field theory. Our main tool is a generalization of the
Komargodski-Schwimmer proof for the -theorem. We use this to rule out a
large class of renormalization group flows that do not asymptote to conformal
field theories in the UV and IR. We show that if the IR (UV) asymptotics is
described by perturbation theory, all beta functions must vanish faster than
as (). This implies that the
only possible asymptotics within perturbation theory is conformal field theory.
In particular, it rules out perturbative theories with scale but not conformal
invariance, which are equivalent to theories with renormalization group
pseudocycles. Our arguments hold even for theories with gravitational
anomalies. We also give a non-perturbative argument that excludes theories with
scale but not conformal invariance. This argument holds for theories in which
the stress-energy tensor is sufficiently nontrivial in a technical sense that
we make precise.Comment: 41 pages, 2 figures. v2: Arguments clarified, some side comments
corrected, connection to previous work by Jack and Osborn described,
conclusions unaffecte
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