49,899 research outputs found
Josephson effect in ballistic graphene
We solve the Dirac-Bogoliubov-De-Gennes equation in an impurity-free
superconductor-normal-superconductor (SNS) junction, to determine the maximal
supercurrent that can flow through an undoped strip of graphene with heavily
doped superconducting electrodes. The result is determined by the
superconducting gap and by the aspect ratio of the junction (length L, small
relative to the width W and to the superconducting coherence length). Moving
away from the Dirac point of zero doping, we recover the usual ballistic result
in which the Fermi wave length takes over from L. The product of critical
current and normal-state resistance retains its universal value (up to a
numerical prefactor) on approaching the Dirac point.Comment: 4 pages, 2 figure
Investigation of the role of selenium in the nutrition and physiology of neural tissues of chickens and turkeys
Endogenous selenium concentrations in selected tissue of chickens, turkeys, and coturni
The Noncommutative Doplicher-Fredenhagen-Roberts-Amorim Space
This work is an effort in order to compose a pedestrian review of the
recently elaborated Doplicher, Fredenhagen, Roberts and Amorim (DFRA)
noncommutative (NC) space which is a minimal extension of the DFR space. In
this DRFA space, the object of noncommutativity () is a
variable of the NC system and has a canonical conjugate momentum. The DFRA
formalism is constructed in an extended space-time with independent degrees of
freedom associated with the object of noncommutativity . A
consistent algebra involving the enlarged set of canonical operators is
described, which permits one to construct theories that are dynamically
invariant under the action of the rotation group. A consistent classical
mechanics formulation is analyzed in such a way that, under quantization, it
furnishes a NC quantum theory with interesting results. The Dirac formalism for
constrained Hamiltonian systems is considered and the object of
noncommutativity plays a fundamental role as an independent
quantity. It is also explained about the generalized Dirac equation issue, that
the fermionic field depends not only on the ordinary coordinates but on
as well. The dynamical symmetry content of such fermionic
theory is discussed, and we show that its action is invariant under . In the last part of this work we analyze the complex scalar fields using
this new framework. As said above, in a first quantized formalism,
and its canonical momentum are seen as
operators living in some Hilbert space. In a second quantized formalism
perspective, we show an explicit form for the extended Poincar\'e generators
and the same algebra is generated via generalized Heisenberg relations. We also
consider a source term and construct the general solution for the complex
scalar fields using the Green function technique
Pushing the precision limit of ground-based eclipse photometry
Until recently, it was considered by many that ground-based photometry could
not reach the high cadence sub-mmag regime because of the presence of the
atmosphere. Indeed, high frequency atmospheric noises (mainly scintillation)
limit the precision that high SNR photometry can reach within small time bins.
If one is ready to damage the sampling of his photometric time-series, binning
the data (or using longer exposures) allows to get better errors, but the
obtained precision will be finally limited by low frequency noises. To observe
several times the same planetary eclipse and to fold the photometry with the
orbital period is thus generally considered as the only option to get very well
sampled and precise eclipse light curve from the ground. Nevertheless, we show
here that reaching the sub-mmag sub-min regime for one eclipse is possible with
a ground-based instrument. This has important implications for transiting
planets characterization, secondary eclipses measurement and small planets
detection from the ground.Comment: Transiting Planets Proceeding IAU Symposium No.253, 2008. 7 pages, 4
figure
Congestion-Aware Routing (CAR):Vehicular Traffic Routing Based on Real-Time Road Occupancy Estimates
This work addresses the problem of routing vehicular traffic on road networks. Fair routing is effected using real-time data acquired from a sensor network superimposed on road networks. Routing information is in the form of which route provides the fastest set of interlinked road segments between any departure-destination pair of nodes. The work adopts Dijkstra’s Shortest Path First (SPF) routing algorithm and derives a suitable routing metric from road occupancy data as a major contribution of this work that makes the SPF algorithm applicable to vehicular traffic routing on road networks. Also, a hypothetical road network and a corresponding Mobile App is used to illustrate our novel vehicular traffic routing algorithm. It is shown in this work that the method is more practical and easier to realize than a method in literature — Spatial and Traffic Aware Vehicular Routing (STAR)
Expression of connexins in human preimplantation embryos in vitro
Intercellular communication via gap junctions is required to coordinate developmental processes in the mammalian embryo. We have investigated if the connexin (Cx) isoforms known to form gap junctions in rodent preimplantation embryos are also expressed in human embryos, with the aim of identifying species differences in communication patterns in early development. Using a combination of polyA PCR and immunocytochemistry we have assessed the expression of Cx26, Cx31, Cx32, Cx40, Cx43 and Cx45 which are thought to be important in early rodent embryos. The results demonstrate that Cx31 and Cx43 are the main connexin isoforms expressed in human preimplantation embryos and that these isoforms are co-expressed in the blastocyst. Cx45 protein is expressed in the blastocyst but the protein may be translated from a generally low level of transcripts: which could only be detected in the PN to 4-cell embryos. Interestingly, Cx40, which is expressed by the extravillous trophoblast in the early human placenta, was not found to be expressed in the blastocyst trophectoderm from which this tissue develops. All of the connexin isoforms in human preimplantation embryos are also found in rodents pointing to a common regulation of these connexins in development of rodent and human early embryos and perhaps other species
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