361,243 research outputs found
Newly Discovered Global Temperature Structures in the Quiet Sun at Solar Minimum
Magnetic loops are building blocks of the closed-field corona. While active
region loops are readily seen in images taken at EUV and X-ray wavelengths,
quiet Sun loops are seldom identifiable and therefore difficult to study on an
individual basis. The first analysis of solar minimum (Carrington Rotation
2077) quiet Sun (QS) coronal loops utilizing a novel technique called the
Michigan Loop Diagnostic Technique (MLDT) is presented. This technique combines
Differential Emission Measure Tomography (DEMT) and a potential field source
surface (PFSS) model, and consists of tracing PFSS field lines through the
tomographic grid on which the Local Differential Emission Measure (LDEM) is
determined. As a result, the electron temperature Te and density Ne at each
point along each individual field line can be obtained. Using data from
STEREO/EUVI and SOHO/MDI, the MLDT identifies two types of QS loops in the
corona: so-called "up" loops in which the temperature increases with height,
and so-called "down" loops in which the temperature decreases with height. Up
loops are expected, however, down loops are a surprise, and furthermore, they
are ubiquitous in the low-latitude corona. Up loops dominate the QS at higher
latitudes. The MLDT allows independent determination of the empirical pressure
and density scale heights, and the differences between the two remain to be
explained. The down loops appear to be a newly discovered property of the solar
minimum corona that may shed light on the physics of coronal heating. The
results are shown to be robust to the calibration uncertainties of the EUVI
instrument.Comment: Accepted for publication in The Astrophysical Journal, waiting for
the full biblio inf
High-accuracy two-loop computation of the critical mass for Wilson fermions
We test an algebraic algorithm based on the coordinate-space method,
evaluating with high accuracy the critical mass for Wilson fermions in lattice
QCD at two loops. We test the results by using different types of infrared
regularization.Comment: Lattice2001(improvement): 3 page
A Pair of Smarandachely Isotopic Quasigroups and Loops of the Same Variety
The isotopic invariance or universality of types and varieties of quasigroups
and loops described by one or more equivalent identities has been of interest
to researchers in loop theory in the recent past. A variety of
quasigroups(loops) that are not universal have been found to be isotopic
invariant relative to a special type of isotopism or the other. Presently,
there are two outstanding open problems on universality of loops: semi
automorphic inverse property loops(1999) and Osborn loops(2005). Smarandache
isotopism(S-isotopism) was originally introduced by Vasantha Kandasamy in 2002.
But in this work, the concept is re-restructured in order to make it more
explorable. As a result of this, the theory of Smarandache isotopy inherits the
open problems as highlighted above for isotopy. In this short note, the
question 'Under what type of S-isotopism will a pair of S-quasigroups(S-loops)
form any variety?' is answered by presenting a pair of specially S-isotopic
S-quasigroups(loops) that both belong to the same variety of
S-quasigroups(S-loops). This is important because pairs of specially S-isotopic
S-quasigroups(e.g Smarandache cross inverse property quasigroups) that are of
the same variety are useful for applications(e.g cryptography).Comment: 10 page
d dimensional SO(d)-Higgs Models with Instanton and Sphaleron: d=2,3
The Abelian Higgs model and the Georgi-Glashow model in 2 and 3 Euclidean
dimensions respectively, support both finite size instantons and sphalerons.
The instantons are the familiar Nielsen-Oleson vortices and the 't
Hooft-Polyakov monopole solutions respectively. We have constructed the
sphaleron solutions and calculated the Chern-Simons charges N_cs for sphalerons
of both models and have constructed two types of noncontractible loops between
topologically distinct vacuua. In the 3 dimensional model, the sphaleron and
the vacuua have zero magnetic and electric flux while the configurations on the
loops have non vanishing magnetic flux.Comment: 24 pages, 3 figures, LaTe
Exact conjectured expressions for correlations in the dense O loop model on cylinders
We present conjectured exact expressions for two types of correlations in the
dense O loop model on square lattices with periodic
boundary conditions. These are the probability that a point is surrounded by
loops and the probability that consecutive points on a row are on the
same or on different loops. The dense O loop model is equivalent to the
bond percolation model at the critical point. The former probability can be
interpreted in terms of the bond percolation problem as giving the probability
that a vertex is on a cluster that is surrounded by \floor{m/2} clusters and
\floor{(m+1)/2} dual clusters. The conjectured expression for this
probability involves a binomial determinant that is known to give weighted
enumerations of cyclically symmetric plane partitions and also of certain types
of families of nonintersecting lattice paths. By applying Coulomb gas methods
to the dense O loop model, we obtain new conjectures for the asymptotics
of this binomial determinant.Comment: 17 pages, replaced by version accepted by JSTA
Phase transitions in diluted negative-weight percolation models
We investigate the geometric properties of loops on two-dimensional lattice
graphs, where edge weights are drawn from a distribution that allows for
positive and negative weights. We are interested in the appearance of spanning
loops of total negative weight. The resulting percolation problem is
fundamentally different from conventional percolation, as we have seen in a
previous study of this model for the undiluted case.
Here, we investigate how the percolation transition is affected by additional
dilution. We consider two types of dilution: either a certain fraction of edges
exhibit zero weight, or a fraction of edges is even absent. We study these
systems numerically using exact combinatorial optimization techniques based on
suitable transformations of the graphs and applying matching algorithms. We
perform a finite-size scaling analysis to obtain the phase diagram and
determine the critical properties of the phase boundary.
We find that the first type of dilution does not change the universality
class compared to the undiluted case whereas the second type of dilution leads
to a change of the universality class.Comment: 8 pages, 7 figure
Enhanced entrainability of genetic oscillators by period mismatch
Biological oscillators coordinate individual cellular components so that they
function coherently and collectively. They are typically composed of multiple
feedback loops, and period mismatch is unavoidable in biological
implementations. We investigated the advantageous effect of this period
mismatch in terms of a synchronization response to external stimuli.
Specifically, we considered two fundamental models of genetic circuits: smooth-
and relaxation oscillators. Using phase reduction and Floquet multipliers, we
numerically analyzed their entrainability under different coupling strengths
and period ratios. We found that a period mismatch induces better entrainment
in both types of oscillator; the enhancement occurs in the vicinity of the
bifurcation on their limit cycles. In the smooth oscillator, the optimal period
ratio for the enhancement coincides with the experimentally observed ratio,
which suggests biological exploitation of the period mismatch. Although the
origin of multiple feedback loops is often explained as a passive mechanism to
ensure robustness against perturbation, we study the active benefits of the
period mismatch, which include increasing the efficiency of the genetic
oscillators. Our findings show a qualitatively different perspective for both
the inherent advantages of multiple loops and their essentiality.Comment: 28 pages, 13 figure
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