4,410 research outputs found
Too massive neutron stars: The role of dark matter?
The maximum mass of a neutron star is generally determined by the equation of
state of the star material. In this study, we take into account dark matter
particles, assumed to behave like fermions with a free parameter to account for
the interaction strength among the particles, as a possible constituent of
neutron stars. We find dark matter inside the star would soften the equation of
state more strongly than that of hyperons, and reduce largely the maximum mass
of the star. However, the neutron star maximum mass is sensitive to the
particle mass of dark matter, and a very high neutron star mass larger than 2
times solar mass could be achieved when the particle mass is small enough. Such
kind of dark-matter- admixed neutron stars could explain the recent measurement
of the Shapiro delay in the radio pulsar PSR J1614-2230, which yielded a
neutron star mass of 2 times solar mass that may be hardly reached when
hyperons are considered only, as in the case of the microscopic Brueckner
theory. Furthermore, in this particular case, we point out that the dark matter
around a neutron star should also contribute to the mass measurement due to its
pure gravitational effect. However, our numerically calculation illustrates
that such contribution could be safely ignored because of the usual diluted
dark matter environment assumed. We conclude that a very high mass measurement
of about 2 times solar mass requires a really stiff equation of state in
neutron stars, and find a strong upper limit (<= 0.64 GeV) for the particle
mass of non-self- annihilating dark matter based on the present model.Comment: Astroparticle Physics (2012) in Pres
Inhomogeneous graph trend filtering via a l2,0 cardinality penalty
We study estimation of piecewise smooth signals over a graph. We propose a
-norm penalized Graph Trend Filtering (GTF) model to estimate
piecewise smooth graph signals that exhibits inhomogeneous levels of smoothness
across the nodes. We prove that the proposed GTF model is simultaneously a
k-means clustering on the signal over the nodes and a minimum graph cut on the
edges of the graph, where the clustering and the cut share the same assignment
matrix. We propose two methods to solve the proposed GTF model: a spectral
decomposition method and a method based on simulated annealing. In the
experiment on synthetic and real-world datasets, we show that the proposed GTF
model has a better performances compared with existing approaches on the tasks
of denoising, support recovery and semi-supervised classification. We also show
that the proposed GTF model can be solved more efficiently than existing models
for the dataset with a large edge set.Comment: 21 pages, 3 figures, 4 table
A quantitative study of the relationship between the oxide charge trapping over the drain extension and the off-state drain leakage current
In this letter, we report an approach to quantitative study of the relationship between the oxide charge trapping over the drain extension due to electrical stress and the off-state drain leakage current. It is found that positive charge trapping over the drain extension leads to a significant increase in the off-state drain current if the edge direct tunneling (EDT) is dominant in the drain current but in contrast, it leads to a reduction in the drain current if the band-to-band tunneling in the Si surface is dominant. A quantitative relationship between the charge trapping and the off-state drain leakage current in the EDT regime is established. From the measurement of the off-state current in the EDT regime, the charge trapping can be determined by using the approach developed in this study. © 2004 American Institute of Physics.published_or_final_versio
Influence of interfacial nitrogen on edge charge trapping at the interface of gate oxide/drain extension in metal-oxide-semiconductor transistors
The influence of interfacial nitrogen on edge charge trapping at the interface of gate oxide/drain extension in metal-oxide-semiconductor transistors was investigated. Positive edge charge trapping was observed for both pure and nitrided oxides with an oxide thickness of 6.5 nm. Results showed that nitrogen at the interface enhance the edge charge trapping.published_or_final_versio
Progressive Learning without Forgetting
Learning from changing tasks and sequential experience without forgetting the
obtained knowledge is a challenging problem for artificial neural networks. In
this work, we focus on two challenging problems in the paradigm of Continual
Learning (CL) without involving any old data: (i) the accumulation of
catastrophic forgetting caused by the gradually fading knowledge space from
which the model learns the previous knowledge; (ii) the uncontrolled tug-of-war
dynamics to balance the stability and plasticity during the learning of new
tasks. In order to tackle these problems, we present Progressive Learning
without Forgetting (PLwF) and a credit assignment regime in the optimizer. PLwF
densely introduces model functions from previous tasks to construct a knowledge
space such that it contains the most reliable knowledge on each task and the
distribution information of different tasks, while credit assignment controls
the tug-of-war dynamics by removing gradient conflict through projection.
Extensive ablative experiments demonstrate the effectiveness of PLwF and credit
assignment. In comparison with other CL methods, we report notably better
results even without relying on any raw data
- …