397 research outputs found
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Assimilation of TES data from the Mars Global Surveyor scientifc mapping phase
The Thermal Emission Spectrometer (TES)aboard Mars Global Surveyor has produced data which cover almost two Martian years so far (during its scientific mapping phase). Thermal profiles for the atmosphere below 40 km and total dust opacities can be retrieved from TES nadir spectra and assimilated into a Mars general circulation model (MGCM), by using the assimilation techniques described in detail by Lewis et al. (2002). This paper describes some preliminary results from assimilations of temperature data from the period Ls=141°- 270° corresponding to late northern summer until winter solstice on Mars. Work in progress is devoted to assimilate both temperature and total dust opacity data for the full period for which they are already available
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Data assimilation for the Martian atmosphere using MGS Thermal Emission Spectrometer observations
From the introduction: Given the quantity of data expected from current and forthcoming spacecraft missions to Mars, it is now possible to use data assimilation as a means of atmospheric analysis for the first time for a planet other than the Earth. Several groups have described plans to develop assimilation schemes for Mars [Banfield et al., 1995; Houben, 1999; Lewis and Read, 1995; Lewis et al., 1996, 1997; Zhang et al., 2001]. Data assimilation is a technique for the analysis of atmospheric observations which combines currently valid information with prior knowledge from previous observations and dynamical and physical constraints, via the use of a numerical model. Despite the number of new missions, observations of the atmosphere of Mars in the near future are still likely to be sparse when compared to those of the Earth, perhaps
comprising one orbiter and a few surface stations at best
at any one time. Data assimilation is useful as a means
to extract the maximum information from such observations,
both by a form of interpolation in space and time
using model constraints and by the combination of information from different observations, e.g. temperature
profiles and surface pressure measurements which may
be irregularly distributed. The procedure can produce a
dynamically consistent set of meteorological fields and
can be used directly to test and to refine an atmospheric
model against observations
Equilibration through local information exchange in networks
We study the equilibrium states of energy functions involving a large set of
real variables, defined on the links of sparsely connected networks, and
interacting at the network nodes, using the cavity and replica methods. When
applied to the representative problem of network resource allocation, an
efficient distributed algorithm is devised, with simulations showing full
agreement with theory. Scaling properties with the network connectivity and the
resource availability are found.Comment: v1: 7 pages, 1 figure, v2: 4 pages, 2 figures, simplified analysis
and more organized results, v3: minor change
Promising Findings that the Cultivating Healthy Intentional Mindful Educators’ Program (CHIME) Strengthens Early Childhood Teachers’ Emotional Resources: An Iterative Study
Findings suggest that an eight-week mindfulness compassion-based program, Cultivating Healthy Intentional Mindful Educators (CHIME), is a feasible professional development intervention for early childhood (EC) teachers to support their emotion regulation and psychological and workplace well-being. We offer preliminary evidence that learning about mindfulness, self-compassion, and social-emotional learning supports EC teachers in strengthening their knowledge and application of practices to be more mindful and less emotionally reactive and emotionally exhausted at work. In analyzing both EC teacher feedback and survey data from two pilot studies, there was promising evidence that participating in CHIME enhanced awareness of emotions and the development of strategies to manage emotions. As CHIME is further developed and refined it will be integral to have collaborative engagement and participation from EC teachers and programs to ensure that learning these practices are relevant, helpful, meaningful, and sustainable
Optimal Location of Sources in Transportation Networks
We consider the problem of optimizing the locations of source nodes in
transportation networks. A reduction of the fraction of surplus nodes induces a
glassy transition. In contrast to most constraint satisfaction problems
involving discrete variables, our problem involves continuous variables which
lead to cavity fields in the form of functions. The one-step replica symmetry
breaking (1RSB) solution involves solving a stable distribution of functionals,
which is in general infeasible. In this paper, we obtain small closed sets of
functional cavity fields and demonstrate how functional recursions are
converted to simple recursions of probabilities, which make the 1RSB solution
feasible. The physical results in the replica symmetric (RS) and the 1RSB
frameworks are thus derived and the stability of the RS and 1RSB solutions are
examined.Comment: 38 pages, 18 figure
Fermions and Loops on Graphs. I. Loop Calculus for Determinant
This paper is the first in the series devoted to evaluation of the partition
function in statistical models on graphs with loops in terms of the
Berezin/fermion integrals. The paper focuses on a representation of the
determinant of a square matrix in terms of a finite series, where each term
corresponds to a loop on the graph. The representation is based on a fermion
version of the Loop Calculus, previously introduced by the authors for
graphical models with finite alphabets. Our construction contains two levels.
First, we represent the determinant in terms of an integral over anti-commuting
Grassman variables, with some reparametrization/gauge freedom hidden in the
formulation. Second, we show that a special choice of the gauge, called BP
(Bethe-Peierls or Belief Propagation) gauge, yields the desired loop
representation. The set of gauge-fixing BP conditions is equivalent to the
Gaussian BP equations, discussed in the past as efficient (linear scaling)
heuristics for estimating the covariance of a sparse positive matrix.Comment: 11 pages, 1 figure; misprints correcte
Loop series for discrete statistical models on graphs
In this paper we present derivation details, logic, and motivation for the
loop calculus introduced in \cite{06CCa}. Generating functions for three
inter-related discrete statistical models are each expressed in terms of a
finite series. The first term in the series corresponds to the Bethe-Peierls
(Belief Propagation)-BP contribution, the other terms are labeled by loops on
the factor graph. All loop contributions are simple rational functions of spin
correlation functions calculated within the BP approach. We discuss two
alternative derivations of the loop series. One approach implements a set of
local auxiliary integrations over continuous fields with the BP contribution
corresponding to an integrand saddle-point value. The integrals are replaced by
sums in the complimentary approach, briefly explained in \cite{06CCa}. A local
gauge symmetry transformation that clarifies an important invariant feature of
the BP solution, is revealed in both approaches. The partition function remains
invariant while individual terms change under the gauge transformation. The
requirement for all individual terms to be non-zero only for closed loops in
the factor graph (as opposed to paths with loose ends) is equivalent to fixing
the first term in the series to be exactly equal to the BP contribution.
Further applications of the loop calculus to problems in statistical physics,
computer and information sciences are discussed.Comment: 20 pages, 3 figure
Nucleation and Growth of the Superconducting Phase in the Presence of a Current
We study the localized stationary solutions of the one-dimensional
time-dependent Ginzburg-Landau equations in the presence of a current. These
threshold perturbations separate undercritical perturbations which return to
the normal phase from overcritical perturbations which lead to the
superconducting phase. Careful numerical work in the small-current limit shows
that the amplitude of these solutions is exponentially small in the current; we
provide an approximate analysis which captures this behavior. As the current is
increased toward the stall current J*, the width of these solutions diverges
resulting in widely separated normal-superconducting interfaces. We map out
numerically the dependence of J* on u (a parameter characterizing the material)
and use asymptotic analysis to derive the behaviors for large u (J* ~ u^-1/4)
and small u (J -> J_c, the critical deparing current), which agree with the
numerical work in these regimes. For currents other than J* the interface
moves, and in this case we study the interface velocity as a function of u and
J. We find that the velocities are bounded both as J -> 0 and as J -> J_c,
contrary to previous claims.Comment: 13 pages, 10 figures, Revte
Message Passing for Optimization and Control of Power Grid: Model of Distribution System with Redundancy
We use a power grid model with generators and consumption units to
optimize the grid and its control. Each consumer demand is drawn from a
predefined finite-size-support distribution, thus simulating the instantaneous
load fluctuations. Each generator has a maximum power capability. A generator
is not overloaded if the sum of the loads of consumers connected to a generator
does not exceed its maximum production. In the standard grid each consumer is
connected only to its designated generator, while we consider a more general
organization of the grid allowing each consumer to select one generator
depending on the load from a pre-defined consumer-dependent and sufficiently
small set of generators which can all serve the load. The model grid is
interconnected in a graph with loops, drawn from an ensemble of random
bipartite graphs, while each allowed configuration of loaded links represent a
set of graph covering trees. Losses, the reactive character of the grid and the
transmission-level connections between generators (and many other details
relevant to realistic power grid) are ignored in this proof-of-principles
study. We focus on the asymptotic limit and we show that the interconnects
allow significant expansion of the parameter domains for which the probability
of a generator overload is asymptotically zero. Our construction explores the
formal relation between the problem of grid optimization and the modern theory
of sparse graphical models. We also design heuristic algorithms that achieve
the asymptotically optimal selection of loaded links. We conclude discussing
the ability of this approach to include other effects, such as a more realistic
modeling of the power grid and related optimization and control algorithms.Comment: 10 page
Surgical-pathological findings in type 1 and 2 endometrial cancer: An NRG Oncology/Gynecologic Oncology Group study on GOG-210 protocol
To report clinical and pathologic relationships with disease spread in endometrial cancer patients
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