3,747 research outputs found
Geometric Poisson brackets on Grassmannians and conformal spheres
In this paper we relate the geometric Poisson brackets on the Grassmannian of
2-planes in R^4 and on the (2,2) Moebius sphere. We show that, when written in
terms of local moving frames, the geometric Poisson bracket on the Moebius
sphere does not restrict to the space of differential invariants of Schwarzian
type. But when the concept of conformal natural frame is transported from the
conformal sphere into the Grassmannian, and the Poisson bracket is written in
terms of the Grassmannian natural frame, it restricts and results into either a
decoupled system or a complexly coupled system of KdV equations, depending on
the character of the invariants. We also show that the biHamiltonian
Grassmannian geometric brackets are equivalent to the non-commutative KdV
biHamiltonian structure. Both integrable systems and Hamiltonian structure can
be brought back to the conformal sphere.Comment: 33 page
Droplets and the configurational entropy crisis for random first order transitions
We consider the effect of droplet excitations in the random first order
transition theory of glasses on the configurational entropy. The contribution
of these excitations is estimated both at and above the ideal glass transition
temperature. The temperature range where such excitations could conceivably
modify or `round-out' an underlying glass transition temperature is estimated,
and found to depend strongly on the surface tension between locally metastable
phases in the supercooled liquid. For real structural glasses this temperature
range is found to be very narrow, consistent with the quantitative success of
the theory. For certain finite-range spin-glass models, however, the surface
tension is estimated to be significantly lower leading to much stronger entropy
renormalizations, thus providing an explanation for the lack of a strict
thermodynamic glass transition in simulations of these models.Comment: 5 page
Changes in precipitation and river flow in northeast Turkey: associations with the North Atlantic Oscillation
This paper explores the relationships between the North Atlantic Oscillation (NAO) index and precipitation and river flow over northeast Turkey. Precipitation totals and maximum, mean and minimum river flow are analysed at the seasonal scale for 12 and 10 stations, respectively. Pearson’s and Mann-Kendall correlation tests are applied to assess relationships between the NAO index and precipitation and river flow metrics, and to detect trends in time-series. Autumn precipitation totals display significant increasing trends, especially for coastal stations, while inland stations show significant increasing trends for spring precipitation. Minimum and maximum river flow decreases significantly for spring and summer. This tendency implies varying conditions towards a drier regime. Seasonal precipitation patterns show a negative association with the NAO for December–January–February (DJF), March–April–May (MAM) and September–October–November (SON) for some stations. Positive associations between the NAO and winter-extended winter (December–March) river flows are detected for some stations in northeast Turkey
Bowen-York Tensors
There is derived, for a conformally flat three-space, a family of linear
second-order partial differential operators which send vectors into tracefree,
symmetric two-tensors. These maps, which are parametrized by conformal Killing
vectors on the three-space, are such that the divergence of the resulting
tensor field depends only on the divergence of the original vector field. In
particular these maps send source-free electric fields into TT-tensors.
Moreover, if the original vector field is the Coulomb field on
, the resulting tensor fields on
are nothing but the family of
TT-tensors originally written down by Bowen and York.Comment: 12 pages, Contribution to CQG Special Issue "A Spacetime Safari:
Essays in Honour of Vincent Moncrief
INCORPORATING SUBSISTENCE INTO A PROBIT ANALYSIS OF HOUSEHOLD NUTRITION LEVELS
Previous nutrient demand and consumption analyses show that several economic and sociodemographic variables are often associated with intakes. However, most of the literature does not account for differences among individuals within households. This study reviewed possible definitions of nutrient differences with respect to nutritional needs. Nutrient levels defined by the Thrifty Food Plan were used as subsistence levels for households in the 1977-78 Nationwide Food Consumption Survey. Probit analysis showed that the usual variables found related to nutrient intakes did not differentiate among subsistence groups. Household life cycle and working female heads influenced whether the household was under its requirement level.Food Consumption/Nutrition/Food Safety,
Oxygen therapy management for patients at risk of respiratory dysfunction
Oxygen therapy is a major intervention used to manage respiratory dysfunction. Research findings revealed a need for health care professionals to review oxygen device selection in specific clinical settings, the importance of involving patients in their care decisions and to document appropriately care that is provided associated with oxygen therapy
A combinatorial formula for homogeneous moments
We establish a combinatorial formula for homogeneous moments and give some
examples where it can be put to use. An application to the statistical
mechanics of interacting gauged vortices is discussed.Comment: 8 pages, LaTe
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