195 research outputs found
On the energy dependence of hadronic production
An estimate is presented of the production cross section of mesons
between threshold and LHC energies using lowest-order perturbation theory and
non-relativistic bound state approximation. It is shown that the ratio of the
production cross sections for mesons and for quarks varies strongly
with energy.Comment: 5 pages, 1 figure, Latex; Contribution to the 5th International
Workshop on -Physics at Hadron Machines, 1997, Los Angeles, California,
US
Production of Bc mesons in photon-photon and hadron-hadron collisions
We discuss two-photon and hadronic production of Bc mesons in nonrelativistic
bound state approximation and to lowest order in the coupling
constants a and a s . It is shown that in photon-photon collisions, heavy
quark fragmentation is dominated by recombination of b and c quarks up
to the highest accessible transverse momenta. In contrast, in hadroproduction,
which at high energies mainly involves gluon-gluon collisions, the
fragmentation mechanism dominates at transverse momenta py > mRc,
providing a simple and satisfactory approximation of the complete 0(a ) )
results in the high-px regime. Contradictions in previous publications
on hadroproduction of Bc mesons are clarified. We also present predictions
for cross sections and differential distributions at present and future
accelerators
A characterization of quasi-rational polygons
The aim of this paper is to study quasi-rational polygons related to the
outer billiard. We compare different notions introduced, and make a synthesis
of those.Comment: 15 pages, 9 figure
Fibre-optic delivery of time and frequency to VLBI station
The quality of Very Long Baseline Interferometry (VLBI) radio observations
predominantly relies on precise and ultra-stable time and frequency (T&F)
standards, usually hydrogen masers (HM), maintained locally at each VLBI
station. Here, we present an operational solution in which the VLBI
observations are routinely carried out without use of a local HM, but using
remote synchronization via a stabilized, long-distance fibre-optic link. The
T&F reference signals, traceable to international atomic timescale (TAI), are
delivered to the VLBI station from a dedicated timekeeping laboratory.
Moreover, we describe a proof-of-concept experiment where the VLBI station is
synchronized to a remote strontium optical lattice clock during the
observation.Comment: 8 pages, 8 figures, matches the version published in A&A, section
Astronomical instrumentatio
Search for New Physics in e-e- Scattering
Considering the physics potential of an e-e- collider in the TeV energy
range, we indicate a few interesting examples for exotic processes and discuss
the standard model backgrounds. Focussing on pair production of weak gauge
bosons, we report some illustrative predictions.Comment: 11 LaTeX pages; axodraw.sty and 6 figures included as an uuencoded
file; MPI-PhT/94-33 and LMU-09/9
Damage analysis and fracture toughness evaluation in a thin woven composite laminate under static tension using infrared thermography
This work deals with the issue of damage growth in thin woven composite laminates subjected to tensile loading. The conducted tensile tests were monitored on-line with an infrared camera, and tested specimens were analysed using Scanning Electron Microscopy (SEM). Combined with SEM micrographs, observation of heat source fields enabled us to assess the damage sequence. Transverse weft cracking was confirmed to be the main damage mode and fiber breakage was the final damage leading to failure. For cracks which induce little variation of specimen stiffness, the classic “Compliance method” could not be used to compute energy release rate. Hence, we present here a new procedure based on the estimation of heat source fields to calculate the energy release rate associated with transverse weft cracking. The results are then compared to those computed with a simple 3D inverse model of the heat diffusion problem and those presented in the literature
A comparison between monolithic and wire gauze structured catalytic reactors for CH<sub>4</sub> and CO removal from biogas-fuelled engine exhaust
The application of the wire gauzes as the catalytic supports can provide a number of advantages in
biogas exhaust abatement. In this paper, a model of wire
gauze structured reactor for biogas exhaust removal is
proposed and model based calculations are performed to
compare the wire gauze catalytic reactor with the classic
monolith. The modelling bases on kinetic data experimentally obtained in a small-scale tubular reactor for cobalt
and palladium (as reference) oxide catalysts doped with
promoters (Ce, Pd). The heat and mass transfer characteristics of the wire gauze reactor are taken from the former
studies by the authors. The simulations show that for
assumed reactor parameters, a combination of the promoted cobalt oxide catalyst and the wire gauze support can
give high conversion of methane and carbon monoxide
Conductance spectra of (Nb, Pb, In)/NbP -- superconductor/Weyl semimetal junctions
The possibility of inducing superconductivity in type-I Weyl semimetal
through coupling its surface to a superconductor was investigated. A single
crystal of NbP, grown by chemical vapor transport method, was carefully
characterized by XRD, EDX, SEM, ARPES techniques and by electron transport
measurements. The mobility spectrum of the carriers was determined. For the
studies of interface transmission, the (001) surface of the crystal was covered
by several hundred nm thick metallic layers of either Pb, or Nb, or In. DC
current-voltage characteristics and AC differential conductance through the
interfaces as a function of the DC bias were investigated. When the metals
become superconducting, all three types of junctions show conductance increase,
pointing out the Andreev reflection as a prevalent contribution to the subgap
conductance. In the case of Pb-NbP and Nb-NbP junctions, the effect is
satisfactorily described by modified Blonder-Tinkham-Klapwijk model. The
absolute value of the conductance is much smaller than that for the bulk
crystal, indicating that the transmission occurs through only a small part of
the contact area. An opposite situation occurs in In-NbP junction, where the
conductance at the peak reaches the bulk value indicating that almost whole
contact area is transmitting and, additionally, a superconducting proximity
phase is formed in the material. We interpret this as a result of indium
diffusion into NbP, where the metal atoms penetrate the surface barrier and
form very transparent superconductor-Weyl semimetal contact inside. However,
further diffusion occurring already at room temperature leads to degradation of
the effect, so it is observed only in the pristine structures. Despite of this,
our observation directly demonstrates possibility of inducing superconductivity
in a type-I Weyl semimetal.Comment: Accepted for Phys. Rev. B. 13 pages, 12 figures. Second version with
major revisions. The title was changed. One author R. Jakiela added. New
inset to Fig. 8(A). New fits in Fig. 8 (B) and Fig. 10 (B). Added figures 12
(C)-(E). Added Fig. 12 (F) with SIMS data. Rewritten chapters III-C-2 and
III-C-3. Reference no. 38 removed, 11 new references: 9, 21, 22, 40-44, 46-49
were adde
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