2,005 research outputs found
A relativistic parton cascade with radiation
We consider the evolution of a parton system which is formed at the central
rapidity region just after an ultrarelativistic heavy ion collision. The
evolution of the system, which is composed of gluons, quarks and antiquarks, is
described by a relativistic Boltzmann equations with collision terms including
radiation and retardation effects. The equations are solved by the test
particle method using Monte-Carlo sampling. Our simulations do not show any
evidence of kinetic equilibration, unless the cross sections are artificially
increased to unrealistically large values.Comment: 14 pages, 4 figure
Effectiveness of Bicycle Safety Helmets in Preventing Facial Injuries in Road Accidents
Background: The effectiveness of bicycle safety helmets in preventing head injuries is well- documented. Recent studies differ regarding the effectiveness of bicycle helmets in preventing facial injuries, especially those of the mid-face and the mandible.
Objectives: The present study was conducted to determine the protective effect of a bicycle helmet in preventing mid-face and mandibular fractures.
Patients and Methods: Data from an accident research unit were analyzed to collect technical collision details (relative collision speed, type of collision, collision partner, and use of a helmet) and clinical data (type of fracture).
Results: Between 1999 and 2011, 5,350 bicycle crashes were included in the study. Of these, 175 (3.3%) had fractures of the mid-face or mandible. In total, 228 mid-face or mandibular fractures were identified. A significant correlation was found between age and relative collision speed, and the incidence of a fracture. While no significant correlation was found between the use of a helmet and the incidence of mid-facial fractures, the use of a helmet was correlated with a significantly increased incidence of mandibular fractures.
Conclusions: Higher age of cyclists and increasing speed of the accident opponent significantly increase the likelihood of sustaining facial fractures. The use of bicycle helmets does not significantly reduce the incidence of mid-facial fractures, while being correlated with an even increased incidence of mandibular fractures
Sex chromosome positions in human interphase nuclei as studied by in situ hybridization with chromosome specific DNA probes
Two cloned repetitive DNA probes, pXBR and CY1, which bind preferentially to specific regions of the human X and Y chromosome, respectively, were used to study the distribution of the sex chromosomes in human lymphocyte nuclei by in situ hybridization experiments. Our data indicate a large variability of the distances between the sex chromosomes in male and female interphase nuclei. However, the mean distance observed between the X and Y chromosome was significantly smaller than the mean distance observed between the two X-chromosomes. The distribution of distances determined experimentally is compared with three model distributions of distances, and the question of a non-random distribution of sex chromosomes is discussed. Mathematical details of these model distributions are provided in an Appendix to this paper. In the case of a human translocation chromosome (XqterXp22.2::Yq11Y qter) contained in the Chinese hamster x human hybrid cell line 445 x 393, the binding sites of pXBR and CY1 were found close to each other in most interphase nuclei. These data demonstrate the potential use of chromosome-specific repetitive DNA probes to study the problem of interphase chromosome topography
Chromosome assignment of two cloned DNA probes hybridizing predominantly to human sex chromosomes
In situ hybridization experiments were carried out with two clones, YACG 35 and 2.8, which had been selected from two genomic libraries strongly enriched for the human Y chromosome. Besides the human Y chromosome, both sequences strongly hybridized to the human X chromosome, with few minor binding sites on autosomes. In particular, on the X chromosome DNA from clone YACG 35 hybridized to the centromeric region and the distal part of the short arm (Xp2.2). On the Y chromosome, the sequence was assigned to one site situated in the border region between Yq1.1 and Yq1.2. DNA from clone 2.8 also hybridized to the centromeric region of the X and the distal part of the short arm (Xq2.2). On the Y, however, two binding sites were observed (Yp1.1 and Yq1.2). The findings indicate that sex chromosomal sequences may be localized in homologous regions (as suggested from meiotic pairing) but also at ectopic sites
Finite-size behaviour of the microcanonical specific heat
For models which exhibit a continuous phase transition in the thermodynamic
limit a numerical study of small systems reveals a non-monotonic behaviour of
the microcanonical specific heat as a function of the system size. This is in
contrast to a treatment in the canonical ensemble where the maximum of the
specific heat increases monotonically with the size of the system. A
phenomenological theory is developed which permits to describe this peculiar
behaviour of the microcanonical specific heat and allows in principle the
determination of microcanonical critical exponents.Comment: 15 pages, 7 figures, submitted to J. Phys.
Organization of Multinational Activities and Ownership Structure
We develop a model in which multinational investors decide about the modes of organization, the locations of production, and the markets to be served. Foreign investments are driven by market-seeking and cost-reducing motives. We further assume that investors face costs of control that vary among sectors and increase in distance. The results show that (i) production intensive sectors are more likely to operate a foreign business independent of the investment motive, (ii) that distance may have a non-monotonous effect on the likelihood of horizontal investments, and (iii) that globalization, if understood as reducing distance, leads to more integration
Follow-up study of sensory-motor polyneuropathy in Type 1 (insulin-dependent) diabetic subjects after simultaneous pancreas and kidney transplantation and after graft rejection
The influence of successful simultaneous pancreas and kidney transplantation on peripheral polyneuropathy was investigated in 53 patients for a mean observation period of 40.3 months. Seventeen patients were followed-up for more than 3 years. Symptoms and signs were assessed every 6 months using a standard questionnaire, neurological examination and measurement of sensory and motor nerve conduction velocities. While symptoms of polyneuropathy improved (pain, paraesthesia, cramps, restless-legs) and nerve conduction velocity increased, there was no change of clinical signs (sensation, muscle-force, tendon-reflexes). Following kidney-graft-rejection there was a slight decrease of nerve conduction verlocity during the first year, which was not statistically significant. Following pancreas-graft rejection there was no change of nerve conduction velocity during the first year. Comparing the maximum nerve conduction velocity of the patients with pancreas-graft-rejection to the nerve conduction velocities of these patients at the end of the study, there was a statistically significant decrease of 6.5 m/s.
In conclusion, we believe that strict normalization of glucose metabolism alters the progressive course of diabetic polyneuropathy. It may be stabilized or partly reversed after successful grafting even in long-term diabetic patients
Pulsed quantum optomechanics
Studying mechanical resonators via radiation pressure offers a rich avenue
for the exploration of quantum mechanical behavior in a macroscopic regime.
However, quantum state preparation and especially quantum state reconstruction
of mechanical oscillators remains a significant challenge. Here we propose a
scheme to realize quantum state tomography, squeezing and state purification of
a mechanical resonator using short optical pulses. The scheme presented allows
observation of mechanical quantum features despite preparation from a thermal
state and is shown to be experimentally feasible using optical microcavities.
Our framework thus provides a promising means to explore the quantum nature of
massive mechanical oscillators and can be applied to other systems such as
trapped ions.Comment: 9 pages, 4 figure
Review of the k-Body Embedded Ensembles of Gaussian Random Matrices
The embedded ensembles were introduced by Mon and French as physically more
plausible stochastic models of many--body systems governed by one--and
two--body interactions than provided by standard random--matrix theory. We
review several approaches aimed at determining the spectral density, the
spectral fluctuation properties, and the ergodic properties of these ensembles:
moments methods, numerical simulations, the replica trick, the eigenvector
decomposition of the matrix of second moments and supersymmetry, the binary
correlation approximation, and the study of correlations between matrix
elements.Comment: Final version. 29 pages, 4 ps figures, uses iopart.st
Ferromagnetic Kondo-Lattice Model
We present a many-body approach to the electronic and magnetic properties of
the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The
coupling between itinerant conduction electrons and localized magnetic moments
leads, on the one hand, to a distinct temperature-dependence of the electronic
quasiparticle spectrum and, on the other hand, to magnetic properties, as
e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly
influenced by the band electron selfenergy and therewith in particular by the
carrier density. We present results for the single-band Kondo-lattice model in
terms of quasiparticle densities of states and quasiparticle band structures
and demonstrate the density-dependence of the self-consistently derived Curie
temperature. The transition from weak-coupling (RKKY) to strong-coupling
(double exchange) behaviour is worked out.
The multiband model is combined with a tight-binding-LMTO bandstructure
calculation to describe real magnetic materials. As an example we present
results for the archetypal ferromagnetic local-moment systems EuO and EuS. The
proposed method avoids the double counting of relevant interactions and takes
into account the correct symmetry of atomic orbitals.Comment: 15 pages, 10 figure
- …