1,318 research outputs found
Abelian subgroups of Garside groups
In this paper, we show that for every abelian subgroup of a Garside
group, some conjugate consists of ultra summit elements and the
centralizer of is a finite index subgroup of the normalizer of .
Combining with the results on translation numbers in Garside groups, we obtain
an easy proof of the algebraic flat torus theorem for Garside groups and solve
several algorithmic problems concerning abelian subgroups of Garside groups.Comment: This article replaces our earlier preprint "Stable super summit sets
in Garside groups", arXiv:math.GT/060258
On the Plants Leaves Boundary, "Jupe \`a Godets" and Conformal Embeddings
The stable profile of the boundary of a plant's leaf fluctuating in the
direction transversal to the leaf's surface is described in the framework of a
model called a "surface \`a godets". It is shown that the information on the
profile is encoded in the Jacobian of a conformal mapping (the coefficient of
deformation) corresponding to an isometric embedding of a uniform Cayley tree
into the 3D Euclidean space. The geometric characteristics of the leaf's
boundary (like the perimeter and the height) are calculated. In addition a
symbolic language allowing to investigate statistical properties of a "surface
\`a godets" with annealed random defects of curvature of density is
developed. It is found that at the surface exhibits a phase transition
with critical exponent from the exponentially growing to the flat
structure.Comment: 17 pages (revtex), 8 eps-figures, to appear in Journal of Physics
Generation and Structure of Solitary Rossby Vortices in Rotating Fluids
The formation of zonal flows and vortices in the generalized
Charney-Hasegawa-Mima equation is studied. We focus on the regime when the size
of structures is comparable to or larger than the deformation (Rossby) radius.
Numerical simulations show the formation of anticyclonic vortices in unstable
shear flows and ring-like vortices with quiescent cores and vorticity
concentrated in a ring. Physical mechanisms that lead to these phenomena and
their relevance to turbulence in planetary atmospheres are discussed.Comment: 3 pages in REVTeX, 5 postscript figures separately, submitted to
Phys. Rev.
Measurement of the electron electric dipole moment using GdIG
A new method for the detection of the electron edm using a solid is
described. The method involves the measurement of a voltage induced across the
solid by the alignment of the samples magnetic dipoles in an applied magnetic
field, H. A first application of the method to GdIG has resulted in a limit on
the electron edm of 5E-24 e-cm, which is a factor of 40 below the limit
obtained from the only previous solid-state edm experiment. The result is
limited by the imperfect discrimination of an unexpectedly large voltage that
is even upon the reversal of the sample magnetization.Comment: 10 pages, 5 figures, v2:references corrected, submitted to PRL,
v3:added labels to figure
Power-law persistence and trends in the atmosphere: A detailed study of long temperature records
We use several variants of the detrended fluctuation analysis to study the
appearance of long-term persistence in temperature records, obtained at 95
stations all over the globe. Our results basically confirm earlier studies. We
find that the persistence, characterized by the correlation C(s) of temperature
variations separated by s days, decays for large s as a power law, C(s) ~
s^(-gamma). For continental stations, including stations along the coastlines,
we find that gamma is always close to 0.7. For stations on islands, we find
that gamma ranges between 0.3 and 0.7, with a maximum at gamma = 0.4. This is
consistent with earlier studies of the persistence in sea surface temperature
records where gamma is close to 0.4. In all cases, the exponent gamma does not
depend on the distance of the stations to the continental coastlines. By
varying the degree of detrending in the fluctuation analysis we obtain also
information about trends in the temperature records.Comment: 5 pages, 4 including eps figure
Symmetry Analysis of Barotropic Potential Vorticity Equation
Recently F. Huang [Commun. Theor. Phys. V.42 (2004) 903] and X. Tang and P.K.
Shukla [Commun. Theor. Phys. V.49 (2008) 229] investigated symmetry properties
of the barotropic potential vorticity equation without forcing and dissipation
on the beta-plane. This equation is governed by two dimensionless parameters,
and , representing the ratio of the characteristic length scale to
the Rossby radius of deformation and the variation of earth' angular rotation,
respectively. In the present paper it is shown that in the case there
exists a well-defined point transformation to set . The
classification of one- and two-dimensional Lie subalgebras of the Lie symmetry
algebra of the potential vorticity equation is given for the parameter
combination and . Based upon this classification, distinct
classes of group-invariant solutions is obtained and extended to the case
.Comment: 6 pages, release version, added reference for section
On the state dependency of fast feedback processes in (palaeo) climate sensitivity
Palaeo data have been frequently used to determine the equilibrium (Charney)
climate sensitivity , and - if slow feedback processes (e.g. land
ice-albedo) are adequately taken into account - they indicate a similar range
as estimates based on instrumental data and climate model results. Most studies
implicitly assume the (fast) feedback processes to be independent of the
background climate state, e.g., equally strong during warm and cold periods.
Here we assess the dependency of the fast feedback processes on the background
climate state using data of the last 800 kyr and a conceptual climate model for
interpretation. Applying a new method to account for background state
dependency, we find K(Wm) using the latest LGM
temperature reconstruction and significantly lower climate sensitivity during
glacial climates. Due to uncertainties in reconstructing the LGM temperature
anomaly, is estimated in the range K(Wm).Comment: submitted to Geophysical Research Letter
Quasi-Two-Dimensional Dynamics of Plasmas and Fluids
In the lowest order of approximation quasi-twa-dimensional dynamics of planetary atmospheres and of plasmas in a magnetic field can be described by a common convective vortex equation, the Charney and Hasegawa-Mirna (CHM) equation. In contrast to the two-dimensional Navier-Stokes equation, the CHM equation admits "shielded vortex solutions" in a homogeneous limit and linear waves ("Rossby waves" in the planetary atmosphere and "drift waves" in plasmas) in the presence of inhomogeneity. Because of these properties, the nonlinear dynamics described by the CHM equation provide rich solutions which involve turbulent, coherent and wave behaviors. Bringing in non ideal effects such as resistivity makes the plasma equation significantly different from the atmospheric equation with such new effects as instability of the drift wave driven by the resistivity and density gradient. The model equation deviates from the CHM equation and becomes coupled with Maxwell equations. This article reviews the linear and nonlinear dynamics of the quasi-two-dimensional aspect of plasmas and planetary atmosphere starting from the introduction of the ideal model equation (CHM equation) and extending into the most recent progress in plasma turbulence.U. S. Department of Energy DE-FG05-80ET-53088Ministry of Education, Science and Culture of JapanFusion Research Cente
The Genetic Interacting Landscape of 63 Candidate Genes in Major Depressive Disorder: An Explorative Study
Background:
Genetic contributions to major depressive disorder (MDD) are thought to result from multiple genes interacting with each other. Different procedures have been proposed to detect such interactions. Which approach is best for explaining the risk of developing disease is unclear.
This study sought to elucidate the genetic interaction landscape in candidate genes for MDD by conducting a SNP-SNP interaction analysis using an exhaustive search through 3,704 SNP-markers in 1,732 cases and 1,783 controls provided from the GAIN MDD study. We used three different methods to detect interactions, two logistic regressions models (multiplicative and additive) and one data mining and machine learning (MDR) approach. Results:
Although none of the interaction survived correction for multiple comparisons, the results provide important information for future genetic interaction studies in complex disorders. Among the 0.5% most significant observations, none had been reported previously for risk to MDD. Within this group of interactions, less than 0.03% would have been detectable based on main effect approach or an a priori algorithm. We evaluated correlations among the three different models and conclude that all three algorithms detected the same interactions to a low degree. Although the top interactions had a surprisingly large effect size for MDD (e.g. additive dominant model Puncorrected = 9.10E-9 with attributable proportion (AP) value = 0.58 and multiplicative recessive model with Puncorrected = 6.95E-5 with odds ratio (OR estimated from β3) value = 4.99) the area under the curve (AUC) estimates were low (\u3c 0.54). Moreover, the population attributable fraction (PAF) estimates were also low (\u3c 0.15). Conclusions:
We conclude that the top interactions on their own did not explain much of the genetic variance of MDD. The different statistical interaction methods we used in the present study did not identify the same pairs of interacting markers. Genetic interaction studies may uncover previously unsuspected effects that could provide novel insights into MDD risk, but much larger sample sizes are needed before this strategy can be powerfully applied
Turbulent spectrum of the Earth's ozone field
The Total Ozone Mapping Spectrometer (TOMS) database is subjected to an
analysis in terms of the Karhunen-Loeve (KL) empirical eigenfunctions. The
concentration variance spectrum is transformed into a wavenumber spectrum, . In terms of wavenumber is shown to be in the
inverse cascade regime, in the enstrophy cascade regime with the
spectral {\it knee} at the wavenumber of barotropic instability.The spectrum is
related to known geophysical phenomena and shown to be consistent with physical
dimensional reasoning for the problem. The appropriate Reynolds number for the
phenomena is .Comment: RevTeX file, 4 pages, 4 postscript figures available upon request
from Richard Everson <[email protected]
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