3,174 research outputs found
A Proximity-Aware Hierarchical Clustering of Faces
In this paper, we propose an unsupervised face clustering algorithm called
"Proximity-Aware Hierarchical Clustering" (PAHC) that exploits the local
structure of deep representations. In the proposed method, a similarity measure
between deep features is computed by evaluating linear SVM margins. SVMs are
trained using nearest neighbors of sample data, and thus do not require any
external training data. Clusters are then formed by thresholding the similarity
scores. We evaluate the clustering performance using three challenging
unconstrained face datasets, including Celebrity in Frontal-Profile (CFP),
IARPA JANUS Benchmark A (IJB-A), and JANUS Challenge Set 3 (JANUS CS3)
datasets. Experimental results demonstrate that the proposed approach can
achieve significant improvements over state-of-the-art methods. Moreover, we
also show that the proposed clustering algorithm can be applied to curate a set
of large-scale and noisy training dataset while maintaining sufficient amount
of images and their variations due to nuisance factors. The face verification
performance on JANUS CS3 improves significantly by finetuning a DCNN model with
the curated MS-Celeb-1M dataset which contains over three million face images
Effects of Neutron-Proton Short-Range Correlation on the Equation of State of Dense Neutron-Rich Nucleonic Matter
The strongly isospin-dependent tensor force leads to short-range correlations
(SRC) between neutron-proton (deuteron-like) pairs much stronger than those
between proton-proton and neutron-neutron pairs. As a result of the short-range
correlations, the single-nucleon momentum distribution develops a high-momentum
tail above the Fermi surface. Because of the strongly isospin-dependent
short-range correlations, in neutron-rich matter a higher fraction of protons
will be depleted from its Fermi sea and populate above the Fermi surface
compared to neutrons. This isospin-dependent nucleon momentum distribution may
have effects on: (1) nucleon spectroscopic factors of rare isotopes, (2) the
equation of state especially the density dependence of nuclear symmetry energy,
(3) the coexistence of a proton-skin in momentum space and a neutron-skin in
coordinate space (i.e., protons move much faster than neutrons near the surface
of heavy nuclei). In this talk, we discuss these features and their possible
experimental manifestations. As an example, SRC effects on the nuclear symmetry
energy are discussed in detail using a modified Gogny-Hartree-Fock (GHF) energy
density functional (EDF) encapsulating the SRC-induced high momentum tail (HMT)
in the single-nucleon momentum distribution
Density slope of the nuclear symmetry energy from the neutron skin thickness of heavy nuclei
Expressing explicitly the parameters of the standard Skyrme interaction in
terms of the macroscopic properties of asymmetric nuclear matter, we show in
the Skyrme-Hartree-Fock approach that unambiguous correlations exist between
observables of finite nuclei and nuclear matter properties. We find that
existing data on neutron skin thickness of Sn isotopes give an
important constraint on the symmetry energy and its
density slope at saturation density . Combining these
constraints with those from recent analyses of isospin diffusion and double
neutron/proton ratio in heavy-ion collisions at intermediate energies leads to
a more stringent limit on approximately independent of . The implication of these new constraints on the of
Pb as well as the core-crust transition density and pressure in neutron
stars is discussed.Comment: 18 pages, 9 figures, 1 table. Significantly expanded to include a
number of details and discussions. Title shortened. Accepted version to
appear in PR
Temperature effects on the nuclear symmetry energy and symmetry free energy with an isospin and momentum dependent interaction
Within a self-consistent thermal model using an isospin and momentum
dependent interaction (MDI) constrained by the isospin diffusion data in
heavy-ion collisions, we investigate the temperature dependence of the symmetry
energy and symmetry free energy for hot,
isospin asymmetric nuclear matter. It is shown that the symmetry energy
generally decreases with increasing temperature while the
symmetry free energy exhibits opposite temperature
dependence. The decrement of the symmetry energy with temperature is
essentially due to the decrement of the potential energy part of the symmetry
energy with temperature. The difference between the symmetry energy and
symmetry free energy is found to be quite small around the saturation density
of nuclear matter. While at very low densities, they differ significantly from
each other. In comparison with the experimental data of temperature dependent
symmetry energy extracted from the isotopic scaling analysis of intermediate
mass fragments (IMF's) in heavy-ion collisions, the resulting density and
temperature dependent symmetry energy is then used to
estimate the average freeze-out density of the IMF's.used to estimate the
average freeze-out density of the IMF's.Comment: 9 pages, 7 figures, 1 figure added to show the temperature dependence
of the potential and kinetic parts of the symmetry energy. Revised version to
appear in PR
Transition density and pressure in hot neutron stars
Using the momentum-dependent MDI effective interaction for nucleons, we have
studied the transition density and pressure at the boundary between the inner
crust and liquid core of hot neutron stars. We find that their values are
larger in neutrino-trapped neutron stars than in neutrino-free neutron stars.
Furthermore, both are found to decrease with increasing temperature of a
neutron star as well as increasing slope parameter of the nuclear symmetry
energy, except that the transition pressure in neutrino-trapped neutron stars
for the case of small symmetry energy slope parameter first increases and then
decreases with increasing temperature. We have also studied the effect of the
nuclear symmetry energy on the critical temperature above which the inner crust
in a hot neutron star disappears and found that with increasing value of the
symmetry energy slope parameter, the critical temperature decreases slightly in
neutrino-trapped neutron stars but first decreases and then increases in
neutrino-free neutron stars.Comment: 7 pages, 6 figures, version to appear in Phys. Rev.
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