2,828 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
Hierarchical Models for Independence Structures of Networks
We introduce a new family of network models, called hierarchical network
models, that allow us to represent in an explicit manner the stochastic
dependence among the dyads (random ties) of the network. In particular, each
member of this family can be associated with a graphical model defining
conditional independence clauses among the dyads of the network, called the
dependency graph. Every network model with dyadic independence assumption can
be generalized to construct members of this new family. Using this new
framework, we generalize the Erd\"os-R\'enyi and beta-models to create
hierarchical Erd\"os-R\'enyi and beta-models. We describe various methods for
parameter estimation as well as simulation studies for models with sparse
dependency graphs.Comment: 19 pages, 7 figure
Structural change of vortex patterns in anisotropic Bose-Einstein condensates
We study the changes in the spatial distribution of vortices in a rotating
Bose-Einstein condensate due to an increasing anisotropy of the trapping
potential. Once the rotational symmetry is broken, we find that the vortex
system undergoes a rich variety of structural changes, including the formation
of zig-zag and linear configurations. These spatial re-arrangements are well
signaled by the change in the behavior of the vortex-pattern eigenmodes against
the anisotropy parameter. The existence of such structural changes opens up
possibilities for the coherent exploitation of effective many-body systems
based on vortex patterns.Comment: 5 pages, 4 figure
Large Area Crop Inventory Experiment (LACIE). Intensive test site assessment report
There are no author-identified significant results in this report
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
Children's Counterfactual Reasoning About Causally Overdetermined Events
In two experiments, one hundred and sixty-two 6- to 8-year-olds were asked to reason counterfactually about events with different causal structures. All events involved overdetermined outcomes in which two different causal events led to the same outcome. In Experiment 1, children heard stories with either an ambiguous causal relation between events or causally unrelated events. Children in the causally unrelated version performed better than chance and better than those in the ambiguous condition. In Experiment 2, children heard stories in which antecedent events were causally connected or causally disconnected. Eight-year-olds performed above chance in both conditions, whereas 6-year-olds performed above chance only in the connected condition. This work provides the first evidence that children can reason counterfactually in causally overdetermined contexts by age 8. © 2017 The Authors. Child Development © 2017 Society for Research in Child Development, Inc
Replicated Bethe Free Energy: A Variational Principle behind Survey Propagation
A scheme to provide various mean-field-type approximation algorithms is
presented by employing the Bethe free energy formalism to a family of
replicated systems in conjunction with analytical continuation with respect to
the number of replicas. In the scheme, survey propagation (SP), which is an
efficient algorithm developed recently for analyzing the microscopic properties
of glassy states for a fixed sample of disordered systems, can be reproduced by
assuming the simplest replica symmetry on stationary points of the replicated
Bethe free energy. Belief propagation and generalized SP can also be offered in
the identical framework under assumptions of the highest and broken replica
symmetries, respectively.Comment: appeared in Journal of the Physical Society of Japan 74, 2133-2136
(2005
Statistical physics-based reconstruction in compressed sensing
Compressed sensing is triggering a major evolution in signal acquisition. It
consists in sampling a sparse signal at low rate and later using computational
power for its exact reconstruction, so that only the necessary information is
measured. Currently used reconstruction techniques are, however, limited to
acquisition rates larger than the true density of the signal. We design a new
procedure which is able to reconstruct exactly the signal with a number of
measurements that approaches the theoretical limit in the limit of large
systems. It is based on the joint use of three essential ingredients: a
probabilistic approach to signal reconstruction, a message-passing algorithm
adapted from belief propagation, and a careful design of the measurement matrix
inspired from the theory of crystal nucleation. The performance of this new
algorithm is analyzed by statistical physics methods. The obtained improvement
is confirmed by numerical studies of several cases.Comment: 20 pages, 8 figures, 3 tables. Related codes and data are available
at http://aspics.krzakala.or
Contextual Object Detection with a Few Relevant Neighbors
A natural way to improve the detection of objects is to consider the
contextual constraints imposed by the detection of additional objects in a
given scene. In this work, we exploit the spatial relations between objects in
order to improve detection capacity, as well as analyze various properties of
the contextual object detection problem. To precisely calculate context-based
probabilities of objects, we developed a model that examines the interactions
between objects in an exact probabilistic setting, in contrast to previous
methods that typically utilize approximations based on pairwise interactions.
Such a scheme is facilitated by the realistic assumption that the existence of
an object in any given location is influenced by only few informative locations
in space. Based on this assumption, we suggest a method for identifying these
relevant locations and integrating them into a mostly exact calculation of
probability based on their raw detector responses. This scheme is shown to
improve detection results and provides unique insights about the process of
contextual inference for object detection. We show that it is generally
difficult to learn that a particular object reduces the probability of another,
and that in cases when the context and detector strongly disagree this learning
becomes virtually impossible for the purposes of improving the results of an
object detector. Finally, we demonstrate improved detection results through use
of our approach as applied to the PASCAL VOC and COCO datasets
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