29,046 research outputs found
On the Application of Gluon to Heavy Quarkonium Fragmentation Functions
We analyze the uncertainties induced by different definitions of the momentum
fraction in the application of gluon to heavy quarkonium fragmentation
function. We numerically calculate the initial fragmentation
functions by using the non-covariant definitions of with finite gluon
momentum and find that these fragmentation functions have strong dependence on
the gluon momentum . As , these fragmentation
functions approach to the fragmentation function in the light-cone definition.
Our numerical results show that large uncertainties remains while the
non-covariant definitions of are employed in the application of the
fragmentation functions. We present for the first time the polarized gluon to
fragmentation functions, which are fitted by the scheme exploited in
this work.Comment: 11 pages, 7 figures;added reference for sec.
Experimental demonstration of phase-remapping attack in a practical quantum key distribution system
Unconditional security proofs of various quantum key distribution (QKD)
protocols are built on idealized assumptions. One key assumption is: the sender
(Alice) can prepare the required quantum states without errors. However, such
an assumption may be violated in a practical QKD system. In this paper, we
experimentally demonstrate a technically feasible "intercept-and-resend" attack
that exploits such a security loophole in a commercial "plug & play" QKD
system. The resulting quantum bit error rate is 19.7%, which is below the
proven secure bound of 20.0% for the BB84 protocol. The attack we utilize is
the phase-remapping attack (C.-H. F. Fung, et al., Phys. Rev. A, 75, 32314,
2007) proposed by our group.Comment: 16 pages, 6 figure
Real-time motion data annotation via action string
Even though there is an explosive growth of motion capture data, there is still a lack of efficient and reliable methods to automatically annotate all the motions in a database. Moreover, because of the popularity of mocap devices in home entertainment systems, real-time human motion annotation or recognition becomes more and more imperative. This paper presents a new motion annotation method that achieves both the aforementioned two targets at the same time. It uses a probabilistic pose feature based on the Gaussian Mixture Model to represent each pose. After training a clustered pose feature model, a motion clip could be represented as an action string. Then, a dynamic programming-based string matching method is introduced to compare the differences between action strings. Finally, in order to achieve the real-time target, we construct a hierarchical action string structure to quickly label each given action string. The experimental results demonstrate the efficacy and efficiency of our method
Interdimensional degeneracies for a quantum -body system in dimensions
Complete spectrum of exact interdimensional degeneracies for a quantum
-body system in -dimensions is presented by the method of generalized
spherical harmonic polynomials. In an -body system all the states with
angular momentum in dimensions are degenerate where
and are given and is an arbitrary integer if the representation
exists for the SO() group and . There is an
exceptional interdimensional degeneracy for an -body system between the
state with zero angular momentum in dimensions and the state with zero
angular momentum in dimensions.Comment: 8 pages, no figure, RevTex, Accepted by EuroPhys.Let
Coexistence of hexatic and isotropic phases in two-dimensional Yukawa systems
We have performed Brownian dynamics simulations on melting of two-dimensional
colloidal crystal in which particles interact with Yukawa potential. The pair
correlation function and bond-orientational correlation function was calculated
in the Yukawa system. An algebraic decay of the bond orientational correlation
function was observed. By ruling out the coexistence region, only a unstable
hexatic phase was found in the Yukawa systems. But our work shows that the
melting of the Yukawa systems is a two-stage melting not consist with the KTHNY
theory and the isotropic liquid and the hexatic phase coexistence region was
found. Also we have studied point defects in two-dimensional Yukawa systems.Comment: 9 pages, 8 figures. any comments are welcom
Decoherence and the retrieval of lost information
We found that in contrast with the common premise, a measurement on the
environment of an open quantum system can {\em reduce} its decoherence rate. We
demonstrate it by studying an example of indirect qubit's measurement, where
the information on its state is hidden in the environment. This information is
extracted by a distant device, coupled with the environment. We also show that
the reduction of decoherence generated by this device, is accompanied with
diminution of the environmental noise in a vicinity of the qubit. An
interpretation of these results in terms of quantum interference on large
scales is presented.Comment: 9 pages, 8 figures, additional explanations added, Phys. Rev. B, in
pres
Transport properties and anisotropy in rare earth doped CaFe2As2 single crystals with Tc above 40 K
In this paper we report the superconductivity above 40 K in the electron
doping single crystal Ca1-xRexFe2As2 (Re = La, Ce, Pr). The x-ray diffraction
patterns indicate high crystalline quality and c-axis orientation. the
resistivity anomaly in the parent compound CaFe2As2 is completely suppressed by
partial replacement of Ca by rare earth and a superconducting transition
reaches as high as 43 K, which is higher than the value in electron doping
FeAs-122 compounds by substituting Fe ions with transition metal, even
surpasses the highest values observed in hole doping systems with a transition
temperature up to 38 K. The upper critical field has been determined with the
magnetic field along ab-plane and c-axis, yielding the anisotropy of 2~3.
Hall-effect measurements indicate that the conduction in this material is
dominated by electron like charge carriers. Our results explicitly demonstrate
the feasibility of inducing superconductivity in Ca122 compounds via electron
doping using aliovalent rare earth substitution into the alkaline earth site,
which should add more ingredients to the underlying physics of the iron-based
superconductors.Comment: 21 pages, 7 figure
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