30,826 research outputs found
Phases of the infinite U Hubbard model
We apply the density matrix renormalization group (DMRG) to study the phase
diagram of the infinite U Hubbard model on 2-, 4-, and 6-leg ladders. Where the
results are largely insensitive to the ladder width, we consider the results
representative of the 2D square lattice model. We find a fully polarized
ferromagnetic Fermi liquid phase when n, the density of electrons per site, is
in the range 1>n>n_F ~ 4/5. For n=3/4 we find an unexpected commensurate
insulating "checkerboard" phase with coexisting bond density order with 4 sites
per unit cell and block spin antiferromagnetic order with 8 sites per unit
cell. For 3/4 > n, the wider ladders have unpolarized groundstates, which is
suggestive that the same is true in 2D
IN-SYNC. VIII. Primordial Disk Frequencies in NGC 1333, IC 348, and the Orion A Molecular Cloud
In this paper, we address two issues related to primordial disk evolution in
three clusters (NGC 1333, IC 348, and Orion A) observed by the INfrared Spectra
of Young Nebulous Clusters (IN-SYNC) project. First, in each cluster, averaged
over the spread of age, we investigate how disk lifetime is dependent on
stellar mass. The general relation in IC 348 and Orion A is that primordial
disks around intermediate mass stars (2--5) evolve faster than those
around loss mass stars (0.1--1), which is consistent with previous
results. However, considering only low mass stars, we do not find a significant
dependence of disk frequency on stellar mass. These results can help to better
constrain theories on gas giant planet formation timescales. Secondly, in the
Orion A molecular cloud, in the mass range of 0.35--0.7, we provide
the most robust evidence to date for disk evolution within a single cluster
exhibiting modest age spread. By using surface gravity as an age indicator and
employing 4.5 excess as a primordial disk diagnostic, we observe a
trend of decreasing disk frequency for older stars. The detection of
intra-cluster disk evolution in NGC 1333 and IC 348 is tentative, since the
slight decrease of disk frequency for older stars is a less than 1-
effect.Comment: 25 pages, 26 figures; submitted for publication (ApJ
Running mass of the b-quark in QCD and SUSY QCD
The running mass of the b-quark defined in DRbar-scheme is one of the
important parameters of SUSY QCD. To find its value it should be related to
some known experimental input. In this paper the b-quark running mass defined
in nonsupersymmetric QCD is chosen for determination of corresponding parameter
in SUSY QCD. The relation between these two quantities is found by considering
five-flavor QCD as an effective theory obtained from its supersymmetric
extension. A numerical analysis of the calculated two-loop relation and its
impact on the MSSM spectrum is discussed. Since for nonsupersymmetric models
MSbar-scheme is more natural than DRbar, we also propose a new procedure that
allows one to calculate relations between MSbar- and DRbar-parameters.
Unphysical epsilon-scalars that give rise to the difference between mentioned
schemes are assumed to be heavy and decoupled in the same way as physical
degrees of freedom. By means of this method it is possible to ``catch two
rabbits'', i.e., decouple heavy particles and turn from DRbar to MSbar, at the
same time. Explicit two-loop example of DRbar -> MSbar transition is given in
the context of QCD. The advantages and disadvantages of the method are briefly
discussed.Comment: 33 pages, 6 figures, 1 table, typos corrected, added references
Loss Guided Activation for Action Recognition in Still Images
One significant problem of deep-learning based human action recognition is
that it can be easily misled by the presence of irrelevant objects or
backgrounds. Existing methods commonly address this problem by employing
bounding boxes on the target humans as part of the input, in both training and
testing stages. This requirement of bounding boxes as part of the input is
needed to enable the methods to ignore irrelevant contexts and extract only
human features. However, we consider this solution is inefficient, since the
bounding boxes might not be available. Hence, instead of using a person
bounding box as an input, we introduce a human-mask loss to automatically guide
the activations of the feature maps to the target human who is performing the
action, and hence suppress the activations of misleading contexts. We propose a
multi-task deep learning method that jointly predicts the human action class
and human location heatmap. Extensive experiments demonstrate our approach is
more robust compared to the baseline methods under the presence of irrelevant
misleading contexts. Our method achieves 94.06\% and 40.65\% (in terms of mAP)
on Stanford40 and MPII dataset respectively, which are 3.14\% and 12.6\%
relative improvements over the best results reported in the literature, and
thus set new state-of-the-art results. Additionally, unlike some existing
methods, we eliminate the requirement of using a person bounding box as an
input during testing.Comment: Accepted to appear in ACCV 201
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