1,784 research outputs found
Scattering Theory of Kondo Mirages and Observation of Single Kondo Atom Phase Shift
We explain the origin of the Kondo mirage seen in recent quantum corral
Scanning Tunneling Microscope (STM) experiments with a scattering theory of
electrons on the surfaces of metals. Our theory combined with experimental data
provides the first direct observation of a single Kondo atom phase shift. The
Kondo mirage at the empty focus of an elliptical quantum corral is shown to
arise from multiple electron bounces off the walls of the corral in a manner
analagous to the formation of a real image in optics. We demonstrate our theory
with direct quantitive comparision to experimental data.Comment: 13 pages; significant clarifications of metho
Histone Posttranslational Modifications Predict Specific Alternative Exon Subtypes in Mammalian Brain
A compelling body of literature, based on next generation chromatin immunoprecipitation and RNA sequencing of reward brain regions indicates that the regulation of the epigenetic landscape likely underlies chronic drug abuse and addiction. It is now critical to develop highly innovative computational strategies to reveal the relevant regulatory transcriptional mechanisms that may underlie neuropsychiatric disease. We have analyzed chromatin regulation of alternative splicing, which is implicated in cocain exposure in mice. Recent literature has described chromatin-regulated alternative splicing, suggesting a novel function for drug-induced neuroepigenetic remodeling. However, the extent of the genome-wide association between particular histone modifications and alternative splicing remains unexplored. To address this, we have developed novel computational approaches to model the association between alternative splicing and histone posttranslational modifications in the nucleus accumbens (NAc), a brain reward region. Using classical statistical methods and machine learning to combine ChIP-Seq and RNA-Seq data, we gound that specific histone modifications are strongly associated with various aspects of differential splicing. H3K36me3 and H3K4me1 have the strongest association with splicing indicating they play a significant role in alternative splicing in brain reward tissue
The scaling dimension of low lying Dirac eigenmodes and of the topological charge density
As a quantitative measure of localization, the inverse participation ratio of
low lying Dirac eigenmodes and topological charge density is calculated on
quenched lattices over a wide range of lattice spacings and volumes. Since
different topological objects (instantons, vortices, monopoles, and artifacts)
have different co-dimension, scaling analysis provides information on the
amount of each present and their correlation with the localization of low lying
eigenmodes.Comment: Lattice2004(topology), Fermilab, June 21 - 26, 2004; 3 pages, 3
figure
The Phase Diagram of High Temperature QCD with Three Flavors of Improved Staggered Quarks
We report on progress in our study of high temperature QCD with three flavors
of improved staggered quarks. Simulations are being carried out with three
degenerate quarks with masses less than or equal to the strange quark mass,
, and with degenerate up and down quarks with masses in the range , and the strange quark mass fixed near its physical
value. For the quark masses studied to date we find rapid crossovers, which
sharpen as the quark mass is reduced, rather than bona fide phase transitions.Comment: Lattice 2003 (Nonzero temperature and density
Three Flavor QCD at High Temperatures
We have continued our study of the phase diagram of high temperature QCD with
three flavors of improved staggered quarks. We are performing simulations with
three degenerate quarks with masses less than or equal to the strange quark
mass m_s and with degenerate up and down quarks with masses m_{u,d} less than
the strange quark mass. For the quark masses studied to date, we find a
crossover that strengthens as m_{u,d} decreases, rather than a bona fide phase
transition. We present new results for the crossover temperature extrapolated
to the physical value of m_{u,d}, and for quark number susceptibilities.Comment: Poster presented at Lattice 2004 (non-zero), Fermilab, June 21-26,
2004, 3 pages, 3 figure
Light hadron properties with improved staggered quarks
Preliminary results from simulations with 2+1 dynamical quark flavors at a
lattice spacing of 0.09 fm are combined with earlier results at a=0.13 fm. We
examine the approach to the continuum limit and investigate the dependence of
the pseudoscalar masses and decay constants as the sea and valence quark masses
are separately varied.Comment: Lattice2002(spectrum
Light pseudoscalar decay constants, quark masses, and low energy constants from three-flavor lattice QCD
As part of our program of lattice simulations of three flavor QCD with
improved staggered quarks, we have calculated pseudoscalar meson masses and
decay constants for a range of valence quark masses and sea quark masses on
lattices with lattice spacings of about 0.125 fm and 0.09 fm. We fit the
lattice data to forms computed with staggered chiral perturbation theory. Our
results provide a sensitive test of the lattice simulations, and especially of
the chiral behavior, including the effects of chiral logarithms. We find:
f_\pi=129.5(0.9)(3.5)MeV, f_K=156.6(1.0)(3.6)MeV, and f_K/f_\pi=1.210(4)(13),
where the errors are statistical and systematic. Following a recent paper by
Marciano, our value of f_K/f_\pi implies |V_{us}|=0.2219(26). Further, we
obtain m_u/m_d= 0.43(0)(1)(8), where the errors are from statistics, simulation
systematics, and electromagnetic effects, respectively. The data can also be
used to determine several of the constants of the low energy effective
Lagrangian: in particular we find 2L_8-L_5=-0.2(1)(2) 10^{-3} at chiral scale
m_\eta. This provides an alternative (though not independent) way of estimating
m_u; 2L_8-L_5 is far outside the range that would allow m_u=0. Results for
m_s^\msbar, \hat m^\msbar, and m_s/\hat m can be obtained from the same lattice
data and chiral fits, and have been presented previously in joint work with the
HPQCD and UKQCD collaborations. Using the perturbative mass renormalization
reported in that work, we obtain m_u^\msbar=1.7(0)(1)(2)(2)MeV and
m_d^\msbar=3.9(0)(1)(4)(2)MeV at scale 2 GeV, with errors from statistics,
simulation, perturbation theory, and electromagnetic effects, respectively.Comment: 86 pages, 22 figures. v3: Remarks about m_u=0 and the strong CP
problem modified; reference added. Figs 5--8 modified for clarity. Version to
be published in Phys. Rev. D. v2: Expanded discussion of finite volume
effects, normalization in Table I fixed, typos and minor errors correcte
First determination of the strange and light quark masses from full lattice QCD
We compute the strange quark mass and the average of the and
quark masses using full lattice QCD with three dynamical quarks
combined with experimental values for the pion and kaon masses. The simulations
have degenerate and quarks with masses as low as
, and two different values of the lattice spacing. The bare lattice
quark masses obtained are converted to the \msbar scheme using perturbation
theory at . Our results are: m_s^\msbar(2 GeV) = 76(0)(3)(7)(0)
MeV, \hat m^\msbar(2 GeV) = 2.8(0)(1)(3)(0) MeV and =
27.4(1)(4)(0)(1), where the errors are from statistics, simulation,
perturbation theory, and electromagnetic effects, respectively.Comment: 5 pages, revtex, 2 figures. v2: New ms/hat(m) discussion and
reference, v3: slight change in discussion of referenc
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Relationships between changes in sustained fronto-striatal connectivity and positive affect with antidepressant treatment in major depression
Objective: Deficits in positive affect and their neural bases have been associated with major depression. However, whether reductions in positive affect result solely from an overall reduction in nucleus accumbens activity and fronto-striatal connectivity or the additional inability to sustain engagement of this network over time is unknown. The authors sought to determine whether treatment-induced changes in the ability to sustain nucleus accumbens activity and fronto-striatal connectivity during the regulation of positive affect are associated with gains in positive affect.
Method: Using fMRI, the authors assessed the ability to sustain activity in reward-related networks when attempting to increase positive emotion during per- formance of an emotion regulation para- digm in 21 depressed patients before and after 2 months of antidepressant treat- ment. Over the same interval, 14 healthy comparison subjects underwent scanning as well.
Results: After 2 months of treatment, self-reported positive affect increased. The patients who demonstrated the largest increases in sustained nucleus accumbens activity over the 2 months were those who demonstrated the largest increases in positive affect. In addition, the patients who demonstrated the largest increases in sustained fronto-striatal connectivity were also those who demonstrated the largest increases in positive affect when control- ling for negative affect. None of these associations were observed in healthy comparison subjects.
Conclusions: Treatment-induced change in the sustained engagement of fronto- striatal circuitry tracks the experience of positive emotion in daily life. Studies examining reduced positive affect in a va- riety of psychiatric disorders might benefit from examining the temporal dynamics of brain activity when attempting to under- stand changes in daily positive affect
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