7,678 research outputs found
New Results for Light Gravitinos at Hadron Colliders - Tevatron Limits and LHC Perspectives
We derive Feynman rules for the interactions of a single gravitino with
(s)quarks and gluons/gluinos from an effective supergravity Lagrangian in
non-derivative form and use them to calculate the hadroproduction cross
sections and decay widths of single gravitinos. We confirm the results obtained
previously with a derivative Lagrangian as well as those obtained with the
non-derivative Lagrangian in the high-energy limit and elaborate on the
connection between gauge independence and the presence of quartic vertices. We
perform extensive numerical studies of branching ratios, total cross sections,
and transverse-momentum spectra at the Tevatron and the LHC. From the latest
CDF monojet cross section limit, we derive a new and robust exclusion contour
in the gravitino-squark/gluino mass plane, implying that gravitinos with masses
below to eV are excluded for
squark/gluino-masses below 200 and 500 GeV, respectively. These limits are
complementary to the one obtained by the CDF collaboration,
eV, under the assumption of infinitely heavy squarks and gluinos. For the LHC,
we conclude that SUSY scenarios with light gravitinos will lead to a striking
monojet signal very quickly after its startup.Comment: 30 pages, 12 figures. Tevatron limit improved and unitarity limit
included. Version to be published in Phys. Rev.
Energy Conversion Using New Thermoelectric Generator
During recent years, microelectronics helped to develop complex and varied
technologies. It appears that many of these technologies can be applied
successfully to realize Seebeck micro generators: photolithography and
deposition methods allow to elaborate thin thermoelectric structures at the
micro-scale level. Our goal is to scavenge energy by developing a miniature
power source for operating electronic components. First Bi and Sb micro-devices
on silicon glass substrate have been manufactured with an area of 1cm2
including more than one hundred junctions. Each step of process fabrication has
been optimized: photolithography, deposition process, anneals conditions and
metallic connections. Different device structures have been realized with
different micro-line dimensions. Each devices performance will be reviewed and
discussed in function of their design structure.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
3D printing of gas jet nozzles for laser-plasma accelerators
Recent results on laser wakefield acceleration in tailored plasma channels
have underlined the importance of controlling the density profile of the gas
target. In particular it was reported that appropriate density tailoring can
result in improved injection, acceleration and collimation of laser-accelerated
electron beams. To achieve such profiles innovative target designs are
required. For this purpose we have reviewed the usage of additive layer
manufacturing, commonly known as 3D printing, in order to produce gas jet
nozzles. Notably we have compared the performance of two industry standard
techniques, namely selective laser sintering (SLS) and stereolithography (SLA).
Furthermore we have used the common fused deposition modeling (FDM) to
reproduce basic gas jet designs and used SLA and SLS for more sophisticated
nozzle designs. The nozzles are characterized interferometrically and used for
electron acceleration experiments with the Salle Jaune terawatt laser at
Laboratoire d'Optique Appliqu\'ee
Entangled photons from a strongly coupled quantum dot-cavity system
A quantum dot strongly coupled to a photonic crystal has been recently
proposed as a source of entangled photon pairs [R. Johne et al., Phys. Rev.
Lett. 100, 240404 (2008)]. The biexction decay via intermediate polariton
states can be used to overcome the natural splitting between the exciton states
coupled to the horizontally and vertically polarized light modes, so that high
degrees of entanglement can be expected. We investigate theoretically the
features of realistic dot-cavity systems, including the effect of the different
oscillator strength of excitons resonances coupled to the different
polarizations of light. We show that in this case, an independent adjustment of
the cavity resonances is needed in order to keep a high entanglement degree. We
also consider the case when the biexciton-exciton transition is also strongly
coupled to a cavity mode. We show that a very fast emission rate can be
achieved allowing the repetition rates in the THz range. Such fast emission
should however be paid for by a very complex tuning of the many strongly
coupled resonances involved and by a loss of quantum efficiency. Altogether a
strongly coupled dot-cavity system seems to be very promising as a source of
entangled photon pairs.Comment: 7 pages, 5 figure
Yield stress and shear-banding in granular suspensions
We study the emergence of a yield stress in dense suspensions of non-Brownian
particles, by combining local velocity and concentration measurements using
Magnetic Resonance Imaging with macroscopic rheometric experiments. We show
that the competition between gravity and viscous stresses is at the origin of
the development of a yield stress in these systems at relatively low volume
fractions. Moreover, it is accompanied by a shear banding phenomenon that is
the signature of this competition. However, if the system is carefully density
matched, no yield stress is encountered until a volume fraction of 62.7 0.3%
Genomic plasticity and rapid host switching can promote the evolution of generalism : a case study in the zoonotic pathogen Campylobacter
This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/I02464X/1, the Medical Research Council (MRC) grants MR/M501608/1 and MR/L015080/1, and the Wellcome Trust grant 088786/C/09/Z. GM was supported by a NISCHR Health Research Fellowship (HF-14â13).Peer reviewedPublisher PD
Francis F. Maury, M.D. (1840 to 1879): an often forgotten pioneer in early American surgery.
Francis F. Maury (Fig. 1) was born on August 9, 1840, in Danville, Kentucky, where he was raised on a farm by his mother and father. His father was an Episcopal clergyman of Huguenot descent, whose forefathers had fled from France to escape religious persecution. After receiving a Bachelor of Arts degree from Center College in the summer of 1860, he entered medical school at the University of Virginia. After one full term, he matriculated to Philadelphiaâs Jefferson Medical College and completed his medical education as a private student under the direction of Dr. Samuel D. Gross.1, 2 He obtained his Doctorate of Medicine in March of 1862 at the age of only 21 years. Such were his talents as a medical student that he was appointed resident physician at the Philadelphia Hospital one month before his graduation. Although he spent only one year there, he developed a reputation as a tireless, devoted, and charming surgeon. In April 1863, Maury was assigned to duty at the South Street General Hospital to serve as acting assistant surgeon in the U.S. Army for two years. In October 1863, he was appointed assistant professor to Dr. Gross and six months later became chief of Dr. Grossâ surgical clinic at Jefferson Medical College. In November 1865, at the age of only 25 years, he returned to the Philadelphia Hospital, where he was appointed one of the chief surgeons on the retirement of Dr. Gross from that institution. In April of 1866, Maury founded the Summer Course on Venereal and Cutaneous Diseases in the Jefferson Medical College, where he taught until his death.1 Although Maury did not consider himself a dermatologist, his expertise in this emerging field was widely recognized
Pairing dynamics in particle transport
We analyze the effect of pairing on particle transport in time-dependent
theories based on the Hartree-Fock-Bogoliubov (HFB) or BCS approximations. The
equations of motion for the HFB density matrices are unique and the theory
respects the usual conservation laws defined by commutators of the conserved
quantity with the Hamiltonian. In contrast, the theories based on the BCS
approximation are more problematic. In the usual formulation of TDHF+BCS, the
equation of continuity is violated and one sees unphysical oscillations in
particle densities. This can be ameliorated by freezing the occupation numbers
during the evolution in TDHF+BCS, but there are other problems with the BCS
that make it doubtful for reaction dynamics. We also compare different
numerical implementations of the time-dependent HFB equations. The equations of
motion for the and Bogoliubov transformations are not unique, but it
appears that the usual formulation is also the most efficient. Finally, we
compare the time-dependent HFB solutions with numerically exact solutions of
the two-particle Schrodinger equation. Depending on the treatment of the
initial state, the HFB dynamics produces a particle emission rate at short
times similar to that of the Schrodinger equation. At long times, the total
particle emission can be quite different, due to inherent mean-field
approximation of the HFB theory.Comment: 11 pages, 9 figure
- âŠ