8,781 research outputs found
The Entanglement in Anisotropic Heisenberg XYZ Chain with inhomogeneous magnetic field
The thermal entanglement of a two-qubit anisotropic Heisenberg chain
under an inhomogeneous magnetic field b is studied. It is shown that when
inhomogeneity is increased to certain value, the entanglement can exhibit a
larger revival than that of less values of b. The property is both true for
zero temperature and a finite temperature. The results also show that the
entanglement and critical temperature can be increased by increasing
inhomogeneous exteral magnetic field
DropMAE: Masked Autoencoders with Spatial-Attention Dropout for Tracking Tasks
In this paper, we study masked autoencoder (MAE) pretraining on videos for matching-based downstream tasks, including visual object tracking (VOT) and video object segmentation (VOS). A simple extension of MAE is to randomly mask out frame patches in videos and reconstruct the frame pixels. However, we find that this simple baseline heavily relies on spatial cues while ignoring temporal relations for frame reconstruction, thus leading to sub-optimal temporal matching representations for VOT and VOS. To alleviate this problem, we propose DropMAE, which adaptively performs spatial-attention dropout in the frame reconstruction to facilitate temporal correspondence learning in videos. We show that our DropMAE is a strong and efficient temporal matching learner, which achieves better finetuning results on matching-based tasks than the ImageNet-based MAE with 2× faster pre-training speed. Moreover, we also find that motion diversity in pre-training videos is more important than scene diversity for improving the performance on VOT and VOS. Our pre-trained DropMAE model can be directly loaded in existing ViT-based trackers for fine-tuning without further modifications. Notably, DropMAE sets new state-of-the-art performance on 8 out of 9 highly competitive video tracking and segmentation datasets. Our code and pre-trained models are available at https://github.com/jimmy-dq/DropMAE.git
Weak-lensing calibration of a stellar mass-based mass proxy for redMaPPer and Voronoi Tessellation clusters in SDSS Stripe 82
We present the first weak lensing calibration of , a new galaxy
cluster mass proxy corresponding to the total stellar mass of red and blue
members, in two cluster samples selected from the SDSS Stripe 82 data: 230
redMaPPer clusters at redshift and 136 Voronoi Tessellation
(VT) clusters at . We use the CS82 shear catalog and stack
the clusters in bins to measure a mass-observable power law
relation. For redMaPPer clusters we obtain , . For VT clusters, we find
, and , for a low and a high redshift bin, respectively. Our results are
consistent, internally and with the literature, indicating that our method can
be applied to any cluster finding algorithm. In particular, we recommend that
be used as the mass proxy for VT clusters. Catalogs including
measurements will enable its use in studies of galaxy evolution
in clusters and cluster cosmology.Comment: Updated to be consistent with the published versio
A conjecture on the origin of dark energy
The physical origin of holographic dark energy (HDE) is investigated. The
main existing explanations, namely the UV/IR connection argument of Cohen et
al, Thomas' bulk holography argument, and Ng's spacetime foam argument, are
shown to be not satisfactory. A new explanation of the HDE model is then
proposed based on the ideas of Thomas and Ng. It is suggested that the dark
energy might originate from the quantum fluctuations of spacetime limited by
the event horizon of the universe. Several potential problems of the
explanation are also discussed.Comment: 11 pages, no figure
Genomic landscape of a relict fir-associated fungus reveals rapid convergent adaptation towards endophytism
Comparative and pan-genomic analyses of the endophytic fungus Pezicula neosporulosa (Helotiales, Ascomycota) from needles of the relict fir, Abies beshanzuensis, showed expansions of carbohydrate metabolism and secondary metabolite biosynthetic genes characteristic for unrelated plant-beneficial helotialean, such as dark septate endophytes and ericoid mycorrhizal fungi. The current species within the relatively young Pliocene genus Pezicula are predominantly saprotrophic, while P. neosporulosa lacks such features. To understand the genomic background of this putatively convergent evolution, we performed population analyses of 77 P. neosporulosa isolates. This revealed a mosaic structure of a dozen non-recombining and highly genetically polymorphic subpopulations with a unique mating system structure. We found that one idiomorph of a probably duplicated mat1-2 gene was found in putatively heterothallic isolates, while the other co-occurred with mat1-1 locus suggesting homothallic reproduction for these strains. Moreover, 24 and 81 genes implicated in plant cell-wall degradation and secondary metabolite biosynthesis, respectively, showed signatures of the balancing selection. These findings highlight the evolutionary pattern of the two gene families for allowing the fungus a rapid adaptation towards endophytism and facilitating diverse symbiotic interactions
Lattice-Boltzmann and finite-difference simulations for the permeability for three-dimensional porous media
Numerical micropermeametry is performed on three dimensional porous samples
having a linear size of approximately 3 mm and a resolution of 7.5 m. One
of the samples is a microtomographic image of Fontainebleau sandstone. Two of
the samples are stochastic reconstructions with the same porosity, specific
surface area, and two-point correlation function as the Fontainebleau sample.
The fourth sample is a physical model which mimics the processes of
sedimentation, compaction and diagenesis of Fontainebleau sandstone. The
permeabilities of these samples are determined by numerically solving at low
Reynolds numbers the appropriate Stokes equations in the pore spaces of the
samples. The physical diagenesis model appears to reproduce the permeability of
the real sandstone sample quite accurately, while the permeabilities of the
stochastic reconstructions deviate from the latter by at least an order of
magnitude. This finding confirms earlier qualitative predictions based on local
porosity theory. Two numerical algorithms were used in these simulations. One
is based on the lattice-Boltzmann method, and the other on conventional
finite-difference techniques. The accuracy of these two methods is discussed
and compared, also with experiment.Comment: to appear in: Phys.Rev.E (2002), 32 pages, Latex, 1 Figur
Impurity-induced in-gap state and Tc in sign-reversing s-wave superconductors: analysis of iron oxypnictide superconductors
The sign-reversing fully gapped superconducting state, which is expected to
be realized in oxypnictide superconductors, can be prominently affected by
nonmagnetic impurities due to the interband scattering of Cooper pairs. We
study this problem based on the isotropic two-band BCS model: In oxypnictide
superconductors, the interband impurity scattering is not equal to the
intraband one . In the Born scattering regime, the reduction in Tc is
sizable and the impurity-induced density of states (DOS) is prominent if , due to the interband scattering. Although impurity-induced DOS can yield a
power-law temperature dependence in , a sizable suppression in Tc is
inevitably accompanied. In the unitary scattering regime, in contrast, impurity
effect is very small for both Tc and DOS except at . By comparing theory
and experiments, we expect that the degree of anisotropy in the -wave
gap function strongly depends on compounds.Comment: 16 pages, 5 figures, to be published in New. J. Phy
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