26,305 research outputs found
Binding of Vav to Grb2 through dimerization of Src homology 3 domains
The protooncogenic protein Vav has the structure of an intracellular signal transducer. It is exclusively expressed in cells of hematopoietic lineage and plays a crucial role in hematopoietic cell differentiation. Here we report that both in cell extracts and within intact mammalian cells Vav binds to Grb2 (Sem-5/ASH/Drk), an adaptor molecule which plays a key role in Ras activation. The interaction became evident from a yeast two-hybrid screen and its specificity was demonstrated by in vitro binding assays. It is mediated by an unusual protein-protein binding reaction: dimerization of specific intact Src homology 3 domains of each of the partners. Signaling during hematopoietic lineage differentiation may therefore involve the tissue-specific signal transducer Vav linking into the ubiquitous pathway involving Grb2 and ultimately Ras
Vortex-line condensation in three dimensions: A physical mechanism for bosonic topological insulators
Bosonic topological insulators (BTI) in three dimensions are
symmetry-protected topological phases (SPT) protected by time-reversal and
boson number conservation {symmetries}. BTI in three dimensions were first
proposed and classified by the group cohomology theory which suggests two
distinct root states, each carrying a index. Soon after, surface
anomalous topological orders were proposed to identify different root states of
BTI, which even leads to a new BTI root state beyond the group cohomology
classification. In this paper, we propose a universal physical mechanism via
\textit{vortex-line condensation} {from} a 3d superfluid to achieve all {three}
root states. It naturally produces bulk topological quantum field theory (TQFT)
description for each root state. Topologically ordered states on the surface
are \textit{rigorously} derived by placing TQFT on an open manifold, which
allows us to explicitly demonstrate the bulk-boundary correspondence. Finally,
we generalize the mechanism to symmetries and discuss potential SPT
phases beyond the group cohomology classification.Comment: ReVTeX 4.1 (published version
Properties and Origin of Galaxy Velocity Bias in the Illustris Simulation
We use the hydrodynamical galaxy formation simulations from the Illustris
suite to study the origin and properties of galaxy velocity bias, i.e., the
difference between the velocity distributions of galaxies and dark matter
inside halos. We find that galaxy velocity bias is a decreasing function of the
ratio of galaxy stellar mass to host halo mass. In general, central galaxies
are not at rest with respect to dark matter halos or the core of halos, with a
velocity dispersion above 0.04 times that of the dark matter. The central
galaxy velocity bias is found to be mostly caused by the close interactions
between the central and satellite galaxies. For satellite galaxies, the
velocity bias is related to their dynamical and tidal evolution history after
being accreted onto the host halos. It depends on the time after the accretion
and their distances from the halo centers, with massive satellites generally
moving more slowly than the dark matter. The results are in broad agreements
with those inferred from modeling small-scale redshift-space galaxy clustering
data, and the study can help improve models of redshift-space galaxy
clustering.Comment: 15 pages, 11 figures. Accepted for publication in Ap
Content Distribution by Multiple Multicast Trees and Intersession Cooperation: Optimal Algorithms and Approximations
In traditional massive content distribution with multiple sessions, the
sessions form separate overlay networks and operate independently, where some
sessions may suffer from insufficient resources even though other sessions have
excessive resources. To cope with this problem, we consider the universal
swarming approach, which allows multiple sessions to cooperate with each other.
We formulate the problem of finding the optimal resource allocation to maximize
the sum of the session utilities and present a subgradient algorithm which
converges to the optimal solution in the time-average sense. The solution
involves an NP-hard subproblem of finding a minimum-cost Steiner tree. We cope
with this difficulty by using a column generation method, which reduces the
number of Steiner-tree computations. Furthermore, we allow the use of
approximate solutions to the Steiner-tree subproblem. We show that the
approximation ratio to the overall problem turns out to be no less than the
reciprocal of the approximation ratio to the Steiner-tree subproblem.
Simulation results demonstrate that universal swarming improves the performance
of resource-poor sessions with negligible impact to resource-rich sessions. The
proposed approach and algorithm are expected to be useful for
infrastructure-based content distribution networks with long-lasting sessions
and relatively stable network environment
Safe Screening With Variational Inequalities and Its Application to LASSO
Sparse learning techniques have been routinely used for feature selection as
the resulting model usually has a small number of non-zero entries. Safe
screening, which eliminates the features that are guaranteed to have zero
coefficients for a certain value of the regularization parameter, is a
technique for improving the computational efficiency. Safe screening is gaining
increasing attention since 1) solving sparse learning formulations usually has
a high computational cost especially when the number of features is large and
2) one needs to try several regularization parameters to select a suitable
model. In this paper, we propose an approach called "Sasvi" (Safe screening
with variational inequalities). Sasvi makes use of the variational inequality
that provides the sufficient and necessary optimality condition for the dual
problem. Several existing approaches for Lasso screening can be casted as
relaxed versions of the proposed Sasvi, thus Sasvi provides a stronger safe
screening rule. We further study the monotone properties of Sasvi for Lasso,
based on which a sure removal regularization parameter can be identified for
each feature. Experimental results on both synthetic and real data sets are
reported to demonstrate the effectiveness of the proposed Sasvi for Lasso
screening.Comment: Accepted by International Conference on Machine Learning 201
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