14,878 research outputs found
Possible evidence that pulsars are quark stars
It is a pity that the real state of matter in pulsar-like stars is still not
determined confidently because of the uncertainty about cold matter at
supranuclear density, even 40 years after the discovery of pulsar. Nuclear
matter (related to neutron stars) is one of the speculations for the inner
constitution of pulsars even from the Landau's time more than 70 years ago, but
quark matter (related to quark stars) is an alternative due to the fact of
asymptotic freedom of interaction between quarks as the standard model of
particle physics develops since 1960s. Therefore, one has to focus on
astrophysical observations in order to answer what the nature of pulsars is. In
this presentation, I would like to summarize possible observational
evidence/hints that pulsar-like stars could be quark stars, and to address
achievable clear evidence for quark stars in the future experiments.Comment: 6 pages, 2 figures; a talk at the international conference
"Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China);
http://vega.bac.pku.edu.cn/rxxu/publications/index_C.htm. A mistake in Fig.1
is corrected; Correction of typo
Forward Private Searchable Symmetric Encryption with Optimized I/O Efficiency
Recently, several practical attacks raised serious concerns over the security
of searchable encryption. The attacks have brought emphasis on forward privacy,
which is the key concept behind solutions to the adaptive leakage-exploiting
attacks, and will very likely to become mandatory in the design of new
searchable encryption schemes. For a long time, forward privacy implies
inefficiency and thus most existing searchable encryption schemes do not
support it. Very recently, Bost (CCS 2016) showed that forward privacy can be
obtained without inducing a large communication overhead. However, Bost's
scheme is constructed with a relatively inefficient public key cryptographic
primitive, and has a poor I/O performance. Both of the deficiencies
significantly hinder the practical efficiency of the scheme, and prevent it
from scaling to large data settings. To address the problems, we first present
FAST, which achieves forward privacy and the same communication efficiency as
Bost's scheme, but uses only symmetric cryptographic primitives. We then
present FASTIO, which retains all good properties of FAST, and further improves
I/O efficiency. We implemented the two schemes and compared their performance
with Bost's scheme. The experiment results show that both our schemes are
highly efficient, and FASTIO achieves a much better scalability due to its
optimized I/O
Vertices of degree k in a minimally k-edge-connected digraph
AbstractLet k be a positive integer and D=(V,E) be a minimally k-edge-connected simple digraph. For a vertex x∈V(D), its outdegree δ+(x) (indegree δ−(x)) is the number of edges leaving (entering) x. Let u+(D) (resp. u±(D) and u−(D)) denote the number of vertices x in D such that δ+(x)=k<δ−(x) (resp. δ+(x)=δ−(x)=k and δ+(x)>k=δ−(x)). In this paper we prove thatu+(D)+2u±(D)+u−(D)⩾2k+2,which was conjectured by Mader (Combinatorics 2 (1996) 423–449). We also present a lower bound on u+(D)+u±(D)+u−(D) when |D|⩾4k−1
Revisiting B_s\to\mu^+\mu^- and B\to K^{(*)}\mu^+\mu^- decays in the MSSM with and without R-parity
The rare decays B_s -> \mu^+\mu^- and B -> K^{(*)}\mu^+\mu^- are sensitive to
new particles and couplings via their interferences with the standard model
contributions. Recently, the upper bound on B(B_s -> \mu^+\mu^-) has been
improved significantly by the CMS, LHCb, CDF, and D{\O} experiments. Combining
with the measurements of B(B-> K^{(*)}\mu^+\mu^-), we derive constraints on the
relevant parameters of minimal supersymmetic standard model with and without
R-parity, and examine their contributions to the dimuon forward-backward
asymmetry in B-> K^{*}\mu^+\mu^- decay. We find that (i) the contribution of
R-parity violating coupling products
\lambda^{\prime}_{2i2}\lambda^{\prime*}_{2i3} due to squark exchange is
comparable with the theoretical uncertainties in B-> K \mu^+\mu^- decay, but
still could be significant in B-> K^{*}\mu^+\mu^- decay and could account for
the forward-backward asymmetry in all dimuon invariant mass regions; (ii) the
constrained mass insertion (\delta^{u}_{LL})_{23} could have significant
contribution to dA_{FB}(B-> K^{*}\mu^+\mu^-)/ds, and such effects are favored
by thr recent results of the Belle, CDF, and LHCb experiments.Comment: 20 pages, 9 figures, published versio
Scalable hierarchical parallel algorithm for the solution of super large-scale sparse linear equations
The parallel linear equations solver capable of effectively using 1000+
processors becomes the bottleneck of large-scale implicit engineering
simulations. In this paper, we present a new hierarchical parallel
master-slave-structural iterative algorithm for the solution of super
large-scale sparse linear equations in distributed memory computer cluster.
Through alternatively performing global equilibrium computation and local
relaxation, our proposed algorithm will reach the specific accuracy requirement
in a few of iterative steps. Moreover, each set/slave-processor majorly
communicate with its nearest neighbors, and the transferring data between
sets/slave-processors and master is always far below the set-neighbor
communication. The corresponding algorithm for implicit finite element analysis
has been implemented based on MPI library, and a super large 2-dimension square
system of triangle-lattice truss structure under random static loads is
simulated with over one billion degrees of freedom and up to 2001 processors on
"Exploration 100" cluster in Tsinghua University. The numerical experiments
demonstrate that this algorithm has excellent parallel efficiency and high
scalability, and it may have broad application in other implicit simulations.Comment: 23 page, 9 figures 1 tabl
Efficient infrared upconversion via a ladder-type atomic configuration
We have demonstrated experimentally that infrared light at 1529.4nm can be
converted into the visible at 780nm with 54% efficiency through a ladder-type
atomic configuration in 85Rb. Specifically we theoretically analyze that high
efficiency is due to the large nonlinear dispersion of the index of refraction
from the off-resonant enhancement in a four-wave mixing (FWM) process. By using
two perpendicular polarized pump fields, the coherence of two FWM processes in
this configuration is verified.Comment: The new version is published in Journal of Modern Optic
DACH1 suppresses breast cancer as a negative regulator of CD44.
Dachshund homolog 1 (DACH1), a key cell fate determination factor, contributes to tumorigenesis, invasion, metastasis of human breast neoplasm. However, the exact molecular mechanisms for the anti-tumor roles of DACH1 in breast carcinoma are still lack of extensive understanding. Herein, we utilized immunohistochemistry (IHC) staining and public microarray data analysis showing that DACH1 was higher in normal breast, low-grade and luminal-type cancer in comparison with breast carcinoma, high-grade and basal-like tumors respectively. Additionally, both correlation analysis of public databases of human breast carcinoma and IHC analysis of mice xenograft tumors demonstrated that DACH1 inversely related to cancer stem cells (CSCs) markers, epithelial-mesenchymal transition (EMT) inducers and basal-enriched molecules, while cluster of differentiation 44 (CD44) behaved in an opposite manner. Furthermore, mice transplanted tumor model indicated that breast cancer cells Met-1 with up-regulation of DACH1 were endowed with remarkably reduced potential of tumorigenesis. Importantly, meta-analysis of 19 Gene Expression Omnibus (GEO) databases of breast cancer implicated that patients with higher DACH1 expression had prolonged time to death, recurrence and metastasis, while CD44 was a promising biomarker predicting worse overall survival (OS) and metastasis-free survival (MFS). Collectively, our study indicated that CD44 might be a novel target of DACH1 in breast carcinoma
Half Metallic Bilayer Graphene
Charge neutral bilayer graphene has a gapped ground state as transport
experiments demonstrate. One of the plausible such ground states is layered
antiferromagnetic spin density wave (LAF) state, where the spins in top and
bottom layers have same magnitude with opposite directions. We propose that
lightly charged bilayer graphene in an electric field perpendicular to the
graphene plane may be a half metal as a consequence of the inversion and
particle-hole symmetry broken in the LAF state. We show this explicitly by
using a mean field theory on a 2-layer Hubbard model for the bilayer graphene.Comment: 4+ pages, 4 figure
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