1,324 research outputs found
Semi-Supervised Single- and Multi-Domain Regression with Multi-Domain Training
We address the problems of multi-domain and single-domain regression based on
distinct and unpaired labeled training sets for each of the domains and a large
unlabeled training set from all domains. We formulate these problems as a
Bayesian estimation with partial knowledge of statistical relations. We propose
a worst-case design strategy and study the resulting estimators. Our analysis
explicitly accounts for the cardinality of the labeled sets and includes the
special cases in which one of the labeled sets is very large or, in the other
extreme, completely missing. We demonstrate our estimators in the context of
removing expressions from facial images and in the context of audio-visual word
recognition, and provide comparisons to several recently proposed multi-modal
learning algorithms.Comment: 24 pages, 6 figures, 2 table
Partially Linear Estimation with Application to Sparse Signal Recovery From Measurement Pairs
We address the problem of estimating a random vector X from two sets of
measurements Y and Z, such that the estimator is linear in Y. We show that the
partially linear minimum mean squared error (PLMMSE) estimator does not require
knowing the joint distribution of X and Y in full, but rather only its
second-order moments. This renders it of potential interest in various
applications. We further show that the PLMMSE method is minimax-optimal among
all estimators that solely depend on the second-order statistics of X and Y. We
demonstrate our approach in the context of recovering a signal, which is sparse
in a unitary dictionary, from noisy observations of it and of a filtered
version of it. We show that in this setting PLMMSE estimation has a clear
computational advantage, while its performance is comparable to
state-of-the-art algorithms. We apply our approach both in static and dynamic
estimation applications. In the former category, we treat the problem of image
enhancement from blurred/noisy image pairs, where we show that PLMMSE
estimation performs only slightly worse than state-of-the art algorithms, while
running an order of magnitude faster. In the dynamic setting, we provide a
recursive implementation of the estimator and demonstrate its utility in the
context of tracking maneuvering targets from position and acceleration
measurements.Comment: 13 pages, 5 figure
Constitutive Association of Tie1 and Tie2 with Endothelial Integrins is Functionally Modulated by Angiopoietin-1 and Fibronectin
Functional cross-talk between Tie2 and Integrin signaling pathways is essential to coordinate endothelial cell adhesion and migration in response to the extracellular matrix, yet the mechanisms behind this phenomenon are unclear. Here, we examine the possibility that receptor cross-talk is driven through uncharacterized Tie-integrin interactions on the endothelial surface. Using a live cell FRET-based proximity assay, we monitor Tie-integrin receptor recognition and demonstrate that both Tie1 and Tie2 readily associate with integrins α5ß1 and αVß3 through their respective ectodomains. Although not required, Tie2-integrin association is significantly enhanced in the presence of the extracellular component and integrin ligand fibronectin. In vitro binding assays with purified components reveal that Tie-integrin recognition is direct, and further demonstrate that the receptor binding domain of the Tie2 ligand Ang-1, but not the receptor binding domain of Ang-2, can independently associate with α5ß1 or αVß3. Finally, we reveal that cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang-1 and fibronectin, suggesting a molecular mechanism to sensitize Tie2 to extracellular matrix. We provide a mechanistic model highlighting the role of receptor localization and association in regulating distinct signaling cascades and in turn, the angiogenic switch
Ionic profiles close to dielectric discontinuities: Specific ion-surface interactions
We study, by incorporating short-range ion-surface interactions, ionic
profiles of electrolyte solutions close to a non-charged interface between two
dielectric media. In order to account for important correlation effects close
to the interface, the ionic profiles are calculated beyond mean-field theory,
using the loop expansion of the free energy. We show how it is possible to
overcome the well-known deficiency of the regular loop expansion close to the
dielectric jump, and treat the non-linear boundary conditions within the
framework of field theory. The ionic profiles are obtained analytically to
one-loop order in the free energy, and their dependence on different
ion-surface interactions is investigated. The Gibbs adsorption isotherm, as
well as the ionic profiles are used to calculate the surface tension, in
agreement with the reverse Hofmeister series. Consequently, from the
experimentally-measured surface tension, one can extract a single adhesivity
parameter, which can be used within our model to quantitatively predict hard to
measure ionic profiles.Comment: 14 pages, 6 figure
Field theory for mechanical criticality in disordered fiber networks
Strain-controlled criticality governs the elasticity of jamming and fiber
networks. While the upper critical dimension of jamming is believed to be
=2, non mean-field exponents are observed in numerical studies of 2D and
3D fiber networks. The origins of this remains unclear. In this study we
propose a minimal mean-field model for strain-controlled criticality of fiber
networks. We then extend this to a phenomenological field theory, in which non
mean-field behavior emerges as a result of the disorder in the network
structure. We predict that the upper critical dimension for such systems is
=4 using a Gaussian approximation. Moreover, we identify an order
parameter for the phase transition, which has been lacking for fiber networks
to date
Effective Medium Theory for Mechanical Phase Transitions of Fiber Networks
Networks of stiff fibers govern the elasticity of biological structures such
as the extracellular matrix of collagen. These networks are known to stiffen
nonlinearly under shear or extensional strain. Recently, it has been shown that
such stiffening is governed by a strain-controlled athermal but critical phase
transition, from a floppy phase below the critical strain to a rigid phase
above the critical strain. While this phase transition has been extensively
studied numerically and experimentally, a complete analytical theory for this
transition remains elusive. Here, we present an effective medium theory (EMT)
for this mechanical phase transition of fiber networks. We extend a previous
EMT appropriate for linear elasticity to incorporate nonlinear effects via an
anharmonic Hamiltonian. The mean-field predictions of this theory, including
the critical exponents, scaling relations and non-affine fluctuations
qualitatively agree with previous experimental and numerical results
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