14,451 research outputs found
The intrinsic value of HFO features as a biomarker of epileptic activity
High frequency oscillations (HFOs) are a promising biomarker of epileptic
brain tissue and activity. HFOs additionally serve as a prototypical example of
challenges in the analysis of discrete events in high-temporal resolution,
intracranial EEG data. Two primary challenges are 1) dimensionality reduction,
and 2) assessing feasibility of classification. Dimensionality reduction
assumes that the data lie on a manifold with dimension less than that of the
feature space. However, previous HFO analyses have assumed a linear manifold,
global across time, space (i.e. recording electrode/channel), and individual
patients. Instead, we assess both a) whether linear methods are appropriate and
b) the consistency of the manifold across time, space, and patients. We also
estimate bounds on the Bayes classification error to quantify the distinction
between two classes of HFOs (those occurring during seizures and those
occurring due to other processes). This analysis provides the foundation for
future clinical use of HFO features and buides the analysis for other discrete
events, such as individual action potentials or multi-unit activity.Comment: 5 pages, 5 figure
Loneliness, Depression, and Inflammation: Evidence from the Multi-Ethnic Study of Atherosclerosis
Objective
Both objective and subjective aspects of social isolation have been associated with alterations in immune markers relevant to multiple chronic diseases among older adults. However, these associations may be confounded by health status, and it is unclear whether these social factors are associated with immune functioning among relatively healthy adults. The goal of this study was to examine the associations between perceived loneliness and circulating levels of inflammatory markers among a diverse sample of adults.
Methods
Data come from a subset of the Multi-Ethnic Study of Atherosclerosis (n = 441). Loneliness was measured by three items derived from the UCLA Loneliness Scale. The association between loneliness and C-reactive protein (CRP) and fibrinogen was assessed using multivariable linear regression analyses. Models were adjusted for demographic and health characteristics.
Results
Approximately 50% of participants reported that they hardly ever felt lonely and 17.2% felt highly lonely. Individuals who were unmarried/unpartnered or with higher depressive symptoms were more likely to report being highly lonely. There was no relationship between perceived loneliness and ln(CRP) (β = -0.051, p = 0.239) adjusting for demographic and health characteristics. Loneliness was inversely associated with ln(fibrinogen) (β = -0.091, p = 0.040), although the absolute magnitude of this relationship was small.
Conclusion
These results indicate that loneliness is not positively associated with fibrinogen or CRP among relatively healthy middle-aged adults
Adjacency labeling schemes and induced-universal graphs
We describe a way of assigning labels to the vertices of any undirected graph
on up to vertices, each composed of bits, such that given the
labels of two vertices, and no other information regarding the graph, it is
possible to decide whether or not the vertices are adjacent in the graph. This
is optimal, up to an additive constant, and constitutes the first improvement
in almost 50 years of an bound of Moon. As a consequence, we
obtain an induced-universal graph for -vertex graphs containing only
vertices, which is optimal up to a multiplicative constant,
solving an open problem of Vizing from 1968. We obtain similar tight results
for directed graphs, tournaments and bipartite graphs
Thermodynamic Phase Diagram of the Quantum Hall Skyrmion System
We numerically study the interacting quantum Hall skyrmion system based on
the Chern-Simons action. By noticing that the action is invariant under global
spin rotations in the spin space with respect to the magnetic field direction,
we obtain the low-energy effective action for a many skyrmion system.
Performing extensive molecular dynamics simulations, we establish the
thermodynamic phase diagram for a many skyrmion system.Comment: 4 pages, RevTex, 2 postscript figure
Bag Formation in Quantum Hall Ferromagnets
Charged skyrmions or spin-textures in the quantum Hall ferromagnet at filling
factor nu=1 are reinvestigated using the Hartree-Fock method in the lowest
Landau level approximation. It is shown that the single Slater determinant with
the minimum energy in the unit charge sector is always of the hedgehog form. It
is observed that the magnetization vector's length deviates locally from unity,
i.e. a bag is formed which accommodates the excess charge. In terms of a
gradient expansion for extended spin-textures a novel O(3) type of effective
action is presented, which takes bag formation into account.Comment: 13 pages, 3 figure
Quantum fluctuations of classical skyrmions in quantum Hall Ferromagnets
In this article, we discuss the effect of the zero point quantum fluctuations
to improve the results of the minimal field theory which has been applied to
study %SMG the skyrmions in the quantum Hall systems. Our calculation which is
based on the semiclassical treatment of the quantum fluctuations, shows that
the one-loop quantum correction provides more accurate results for the minimal
field theory.Comment: A few errors are corrected. Accepted for publication in Rapid
Communication, Phys. Rev.
Massive skyrmions in quantum Hall ferromagnets
We apply the theory of elasticity to study the effects of skyrmion mass on
lattice dynamics in quantum Hall systems. We find that massive Skyrme lattices
behave like a Wigner crystal in the presence of a uniform perpendicular
magnetic field. We make a comparison with the microscopic Hartree-Fock results
to characterize the mass of quantum Hall skyrmions at and investigate
how the low temperature phase of Skyrme lattices may be affected by the
skyrmion mass.Comment: 6 pages and 2 figure
Maximum Coronal Mass Ejection Speed as an Indicator of Solar and Geomagnetic Activities
We investigate the relationship between the monthly averaged maximal speeds
of coronal mass ejections (CMEs), international sunspot number (ISSN), and the
geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar
cycle 23). Our new findings are as follows. (1) There is a noteworthy
relationship between monthly averaged maximum CME speeds and sunspot numbers,
Ap and Dst indices. Various peculiarities in the monthly Dst index are
correlated better with the fine structures in the CME speed profile than that
in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not
exhibit a double peak maximum. Instead, the CME speed profile peaks during the
declining phase of solar cycle 23. Similar to the Ap index, both CME speed and
the Dst indices lag behind the sunspot numbers by several months. (3) The CME
number shows a double peak similar to that seen in the sunspot numbers. The CME
occurrence rate remained very high even near the minimum of the solar cycle 23,
when both the sunspot number and the CME average maximum speed were reaching
their minimum values. (4) A well-defined peak of the Ap index between 2002 May
and 2004 August was co-temporal with the excess of the mid-latitude coronal
holes during solar cycle 23. The above findings suggest that the CME speed
index may be a useful indicator of both solar and geomagnetic activities. It
may have advantages over the sunspot numbers, because it better reflects the
intensity of Earth-directed solar eruptions
Non-commutative field theory approach to two-dimensional vortex liquid system
We investigate the non-commutative (NC) field theory approach to the vortex
liquid system restricted to the lowest Landau level (LLL) approximation. NC
field theory effectively takes care of the phase space reduction of the LLL
physics in a -product form and introduces a new gauge invariant form of
a quartic potential of the order parameter in the Ginzburg-Landau (GL) free
energy. This new quartic interaction coupling term has a non-trivial
equivalence relation with that obtained by Br\'ezin, Nelson and Thiaville in
the usual GL framework. The consequence of the equivalence is discussed.Comment: Add vortex lattice formation, more references, and one autho
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