463 research outputs found
Classical and quantum dynamics of a spin-1/2
We reply to a comment on `Semiclassical dynamics of a spin-1/2 in an
arbitrary magnetic field'.Comment: 4 pages, submitted to Journal of Physics
Infectious Complications in Peritoneal Dialysis: The Spectrum of Causative Organisms and Recommended Treatment Options
Peritoneal dialysis (PD) has become a real alternative to hemodialysis (HD) in recent decades, with comparable survival rates, lower costs, and improved patient quality of life. Nevertheless, PDârelated infections, including peritonitis, exitâsite infections (ESI), and tunnel infections, are important complications, resulting in significant morbidity and a 3.5â10.0% risk of death. Patients with peritonitis usually present with cloudy PDâfluid and abdominal pain; however, PDâassociated peritonitis should always be included in differential diagnosis of PD patients with abdominal pain. The most common causative organisms for PDâassociated peritonitis are gramâpositive bacteria; however, gramânegative species are clinically important, due to the antibiotic resistance. The selection of empiric antibiotics depends on the centerâspecific distribution of microorganisms and antimicrobial susceptibility profiles. Typically, a firstâgeneration cephalosporin is used in combination with broad gramânegative coverage (e.g., aminoglycoside, ceftazidime, or cefepime). High levels of methicillinâresistant Staphylococcus epidermidis or Enterococcus spp. strains require the use of vancomycin in many centers. Furthermore, for patients without clinical improvement after 5 days, or with fungal peritonitis, catheter removal is indicated
Semiclassical theory of spin-orbit interactions using spin coherent states
We formulate a semiclassical theory for systems with spin-orbit interactions.
Using spin coherent states, we start from the path integral in an extended
phase space, formulate the classical dynamics of the coupled orbital and spin
degrees of freedom, and calculate the ingredients of Gutzwiller's trace formula
for the density of states. For a two-dimensional quantum dot with a spin-orbit
interaction of Rashba type, we obtain satisfactory agreement with fully
quantum-mechanical calculations. The mode-conversion problem, which arose in an
earlier semiclassical approach, has hereby been overcome.Comment: LaTeX (RevTeX), 4 pages, 2 figures, accepted for Physical Review
Letters; final version (v2) for publication with minor editorial change
Multiple electromagnetic electron positron pair production in relativistic heavy ion collisions
We calculate the cross sections for the production of one and more
electron-positron pairs due to the strong electromagnetic fields in
relativistic heavy ion collisions. Using the generating functional of fermions
in an external field we derive the N-pair amplitude. Neglecting the
antisymmetrisation in the final state we find that the total probability to
produce N pairs is a Poisson distribution. We calculate total cross sections
for the production of one pair in lowest order and also include higher-order
corrections from the Poisson distribution up to third order. Furthermore we
calculate cross sections for the production of up to five pairs including
corrections from the Poisson distribution.Comment: 13 pages REVTeX, 4 Postscript figures, This and related papers may
also be obtained from http://www.phys.washington.edu/~hencken
Osteoarthritis of the knee â clinical assessments and inflammatory markers11Supported by a grant from the Robert Bosch Stiftung, Stuttgart, Germany.
AbstractObjective: The present cross sectional study was performed to test the hypothesis that in osteoarthritis (OA) of the knee severity of this disease is related to local levels of inflammatory metabolites and their corresponding enzymes.Methods: From 41 patients with OA of the knee (age range 45â79 years) undergoing arthroscopy blood, synovial fluid (SF) and synovial membrane (SM) were collected. Clinical conditions were primarily assessed by the WOMAC-index and radiographic grading (K&L-grade). Concentrations of PGE2, TxB2and NO2/3and that of IL-6, IL-1α, IL-1ÎČ, TNFα, COX-2 and iNOS were determined in SF and SM, respectively.Results: With advancing age K&L-grade and COX-2 in SM increased significantly (P=0.005 and P=0.01, respectively). TNFα and IL-1α were not detectable in SM samples. Apart from a correlation between PGE2and WOMAC-index (r=0.36, P=0.035) no significant relationships could be found between the various inflammatory parameters and any of the assessed clinical signs.Conclusions: Apparently no direct relationships exist between the measured markers of inflammation (e.g. PGE2, NO2/3) or the involved enzymes (e.g. COX-2, iNOS) and the severity of OA of the knee. The degenerative condition of this disease might be due to the more local, mainly mechanical injury with little systemic upset. However, further longitudinal studies are needed to clarify whether the assessed biochemical markers could serve as predictors for the progression of OA
Semiclassical dynamics of a spin-1/2 in an arbitrary magnetic field
The spin coherent state path integral describing the dynamics of a
spin-1/2-system in a magnetic field of arbitrary time-dependence is considered.
Defining the path integral as the limit of a Wiener regularized expression, the
semiclassical approximation leads to a continuous minimal action path with
jumps at the endpoints. The resulting semiclassical propagator is shown to
coincide with the exact quantum mechanical propagator. A non-linear
transformation of the angle variables allows for a determination of the
semiclassical path and the jumps without solving a boundary-value problem. The
semiclassical spin dynamics is thus readily amenable to numerical methods.Comment: 16 pages, submitted to Journal of Physics
Semiclassical theory of spin-orbit interaction in the extended phase space
We consider the semiclassical theory in a joint phase space of spin and
orbital degrees of freedom. The method is developed from the path integrals
using the spin-coherent-state representation, and yields the trace formula for
the density of states. We discuss special cases, such as weak and strong
spin-orbit coupling, and relate the present theory to the earlier approaches.Comment: 36 pages, 8 figures. Version 2: revised Sec. 4.4 and Appendix B;
minor corrections elsewher
Podoplanin-positive cells are a hallmark of encapsulating peritoneal sclerosis
Background. Encapsulating peritoneal sclerosis (EPS) and simple peritoneal sclerosis are important complications of long-term peritoneal dialysis (PD). Podoplanin is expressed by mesothelial cells and lymphatic vessels, which are involved in inflammatory reactions in the peritoneal cavity. Methods. We studied 69 peritoneal biopsies from patients on PD (n = 16), patients with EPS (n = 18) and control biopsies taken at the time of hernia repair (n = 15) or appendectomy (n = 20). Immunohistochemistry was performed to localize podoplanin. Additionally, markers of endothelial cells, mesothelial cells, myofibroblasts (smooth muscle actin), proliferating cells, and double labelling for smooth muscle actin/podoplanin were used on selected biopsies. Results. Podoplanin was present on the endothelium of lymphatic vessels in the submesothelial fibrous tissue and on mesothelial cells. In patients on PD and in biopsies with appendicitis, the mesothelial cells demonstrated a cuboidal appearance and circumferential podoplanin staining, with gaps between the cells. The number of lymphatic vessels was variable, but prominent at sites of fibrosis. In patients with EPS, a diffuse infiltration of podoplanin-positive cells with a fibroblastic appearance was present in 15 out of 18 biopsies. This pattern was focally present in 3 out of 16 on PD and none in the 35 controls. The podoplanin-positive cells did not express the endothelial marker or the mesothelial marker (calretinin). Conclusions. EPS is characterized by a population of podoplanin and smooth muscle actin double-positive cells. Podoplanin might be a suitable morphological marker supporting the diagnosis and might be involved in the pathogenesis of EP
A light-fronts approach to electron-positron pair production in ultrarelativistic heavy-ion collisions
We perform a gauge-transformation on the time-dependent Dirac equation
describing the evolution of an electron in a heavy-ion collision to remove the
explicit dependence on the long-range part of the interaction. We solve, in an
ultra-relativistic limit, the gauged-transformed Dirac equation using
light-front variables and a light-fronts representation, obtaining
non-perturbative results for the free pair-creation amplitudes in the collider
frame. Our result reproduces the result of second-order perturbation theory in
the small charge limit while non-perturbative effects arise for realistic
charges of the ions.Comment: 39 pages, Revtex, 7 figures, submitted to PR
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