102,879 research outputs found
Distances of qubit density matrices on Bloch sphere
We recall the Einstein velocity addition on the open unit ball \B of
and its algebraic structure, called the Einstein gyrogroup. We
establish an isomorphism between the Einstein gyrogroup on \B and the set of
all qubit density matrices representing mixed states endowed with an
appropriate addition. Our main result establishes a relation between the trace
metric for the qubit density matrices and the rapidity metric on the Einstein
gyrogroup \B.Comment: I thank to my supervisor, Jimmie Lawson. This was accepted in Journal
of Mathematical Physics at September 26, 201
Generation of tunable Terahertz out-of-plane radiation using Josephson vortices in modulated layered superconductors
We show that a moving Josephson vortex in spatially modulated layered
superconductors generates out-of-plane THz radiation. Remarkably, the magnetic
and in-plane electric fields radiated are of the same order, which is very
unusual for any good-conducting medium. Therefore, the out-of-plane radiation
can be emitted to the vacuum without the standard impedance mismatch problem.
Thus, the proposed design can be more efficient for tunable THz emitters than
previous proposals, for radiation only propagating along the ab-plane.Comment: 7 pages, 1 figure. Phys. Rev. B (2005), in pres
Description of Charged Particle Pseudorapidity Distributions in Pb+Pb Collisions with Tsallis Thermodynamics
The centrality dependence of pseudorapidity distributions for charged
particles produced in Au+Au collisions at GeV and 200 GeV
at RHIC, and in Pb+Pb collisions at TeV at LHC are
investigated in the fireball model, assuming that the rapidity axis is
populated with fireballs following one distribution function. We assume that
the particles in the fireball fulfill the Tsallis distribution. The theoretical
results are compared with the experimental measurements and a good agreement is
found. Using these results, the pseudorapidity distributions of charged
particles produced in Pb+Pb central collisions at TeV and
10 TeV are predicted.Comment: 9 pages, 8 figure
Testing Cluster Structure of Graphs
We study the problem of recognizing the cluster structure of a graph in the
framework of property testing in the bounded degree model. Given a parameter
, a -bounded degree graph is defined to be -clusterable, if it can be partitioned into no more than parts, such
that the (inner) conductance of the induced subgraph on each part is at least
and the (outer) conductance of each part is at most
, where depends only on . Our main
result is a sublinear algorithm with the running time
that takes as
input a graph with maximum degree bounded by , parameters , ,
, and with probability at least , accepts the graph if it
is -clusterable and rejects the graph if it is -far from
-clusterable for , where depends only on . By the lower
bound of on the number of queries needed for testing graph
expansion, which corresponds to in our problem, our algorithm is
asymptotically optimal up to polylogarithmic factors.Comment: Full version of STOC 201
Superconducting properties of Gd-Ba-Cu-O single grains processed from a new, Ba-rich precursor compound
Gd-Ba-Cu-O (GdBCO) single grains have been previously melt-processed successfully in air using a generic Mg-Nd-Ba-Cu-O (Mg-NdBCO) seed crystal. Previous research has revealed that the addition of a small amount of BaO2 to the precursor powders prior to melt processing can suppress the formation of Gd/Ba solid solution, and lead to a significant improvement in superconducting properties of the single grains. Research into the effects of a higher Ba content on single grain growth, however, has been limited by the relatively small grain size in the earlier studies. This has been addressed by developing Ba-rich precursor compounds Gd-163 and Gd-143, fabricated specifically to enable the presence of greater concentrations of Ba during the melt process. In this study, we propose a new processing route for the fabrication of high performance GdBCO single grain bulk superconductors in air by enriching the precursor powder with these new Ba rich compounds. The influence of the addition of the new compounds on the microstructures and superconducting properties of GdBCO single grains is reported
Radiation hardness qualification of PbWO_4 scintillation crystals for the CMS Electromagnetic Calorimeter
Ensuring the radiation hardness of PbWO_4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered
Neutron scattering study of commensurate magnetic ordering in single crystal CeSb
Temperature and field-dependent magnetization measurements and
neutron scattering study of a single crystal CeSb are presented. Several
anomalies in the magnetization curves have been confirmed at low magnetic
field, i.e., 15.6 K, 12 K, and 9.8 K. These three transitions are all
metamagnetic transitions (MMT), which shift to lower temperatures as the
magnetic field increases. The anomaly at 15.6 K has been suggested as
paramagnetic (PM) to ferromagnetic (FM) phase transition. The anomaly located
at around 12 K is antiferromagnetic-like transition, and this turning point
will clearly split into two when the magnetic field T. Neutron
scattering study reveals that the low temperature ground state of CeSb
orders antiferromagnetically with commensurate propagation wave vectors
and , with N\'eel
temperature K. This transition is of first-order, as shown in the
hysteresis loop observed by the field cooled cooling (FCC) and field cooled
warming (FCW) processes.Comment: 7 pages,9 figure
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