871 research outputs found
Zum Handlungsfeld Polizierende PrĂ€senz:Forschungsprojekt "Kooperative Sicherheitspolitik in der Stadt" an der Hessischen Hochschule fĂŒr Polizei und Verwaltung
Criticality and Bifurcation in the Gravitational Collapse of a Self-Coupled Scalar Field
We examine the gravitational collapse of a non-linear sigma model in
spherical symmetry. There exists a family of continuously self-similar
solutions parameterized by the coupling constant of the theory. These solutions
are calculated together with the critical exponents for black hole formation of
these collapse models. We also find that the sequence of solutions exhibits a
Hopf-type bifurcation as the continuously self-similar solutions become
unstable to perturbations away from self-similarity.Comment: 18 pages; one figure, uuencoded postscript; figure is also available
at http://www.physics.ucsb.edu/people/eric_hirschman
QualitÀtssicherung interdisziplinÀrer Polytraumaversorgung: Möglichkeiten und Grenzen retrospektiver Standarderfassung
Zusammenfassung: Hintergrund: Inwieweit kann die Auswertung standardmĂ€Ăig erhobener Patienten- und Krankenhausdaten einen Behandlungsvergleich mit anderen Erhebungen gestatten? Material und Methoden: Es wurde eine retrospektive Analyse epidemiologischer und klinisch-technischer Parameter aller Mehrfachverletzten [Injury Severity Score (ISS)>15] einer Zentrumsklinik (n=172; Zeitraum: 01.01.1997-31.12.1999) bezĂŒglich der Ablauforganisation und des Outcome (p74Jahre, Hypotension, initial verminderte HĂ€moglobin- und Quick-Werte, verminderte Glasgow Coma Scale (GCS) sowie Anzahl erhaltener Blutkonzentrate. Eine GegenĂŒberstellung der erhobenen Daten mit der zeitgleichen prospektiven Multizenterstudie der Deutschen Gesellschaft fĂŒr Unfallchirurgie (DGU) bestĂ€tigte die Ergebnisse bezĂŒglich des Ablaufs und des Outcome. Schlussfolgerung: Die interdisziplinĂ€re retrospektive Datenauswertung ist unter Fokussierung auf prognoserelevante und routinemĂ€Ăig erhobene Parameter eine praktikable sowie aussagefĂ€hige Alternative zu prospektiven Erfassungen und ermöglicht eine erste qualitative Standortbestimmun
Constraining AGN triggering mechanisms through the clustering analysis of active black holes
The triggering mechanisms for active galactic nuclei (AGN) are still debated. Some of the most popular ones include galaxy interactions (IT) and disc instabilities (DIs). Using an advanced semi-analytic model (SAM) of galaxy formation, coupled to accurate halo occupation distribution modelling, we investigate the imprint left by each separate triggering process on the clustering strength of AGN at small and large scales. Our main results are as follows: (i) DIs, irrespective of their exact implementation in the SAM, tend to fall short in triggering AGN activity in galaxies at the centre of haloes wit
Black hole formation from massive scalar fields
It is shown that there exists a range of parameters in which gravitational
collapse with a spherically symmetric massive scalar field can be treated as if
it were collapsing dust. This implies a criterion for the formation of black
holes depending on the size and mass of the initial field configuration and the
mass of the scalar field.Comment: 11 pages, RevTeX, 3 eps figures. Submitted to Class. Quantum Gra
Relativistic MHD with Adaptive Mesh Refinement
This paper presents a new computer code to solve the general relativistic
magnetohydrodynamics (GRMHD) equations using distributed parallel adaptive mesh
refinement (AMR). The fluid equations are solved using a finite difference
Convex ENO method (CENO) in 3+1 dimensions, and the AMR is Berger-Oliger.
Hyperbolic divergence cleaning is used to control the
constraint. We present results from three flat space tests, and examine the
accretion of a fluid onto a Schwarzschild black hole, reproducing the Michel
solution. The AMR simulations substantially improve performance while
reproducing the resolution equivalent unigrid simulation results. Finally, we
discuss strong scaling results for parallel unigrid and AMR runs.Comment: 24 pages, 14 figures, 3 table
Painful knee joint after ACL reconstruction using biodegradable interference screws- SPECT/CT a valuable diagnostic tool? A case report
With the presented case we strive to introduce combined single photon emission computerized tomography and conventional computer tomography (SPECT/CT) as new diagnostic imaging modality and illustrate the possible clinical value in patients after ACL reconstruction. We report the case of a painful knee due to a foreign body reaction and delayed degradation of the biodegradable interference screws after ACL reconstruction. The MRI showed an intact ACL graft, a possible tibial cyclops lesion and a patella infera. There was no increased fluid collection within the bone tunnels. The 99mTc-HDP-SPECT/CT clearly identified a highly increased tracer uptake around and within the tibial and femoral tunnels and the patellofemoral joint. On 3D-CT out of the SPECT/CT data the femoral graft attachment was shallow (50% along the Blumensaat's line) and high in the notch. At revision arthroscopy a diffuse hypertrophy of the synovium, scarring of the Hoffa fat pad and a cyclops lesion of the former ACL graft was found. The interference screws were partially degraded and under palpation and pressure a grey fluid-like substance drained into the joint. The interference screws and the ACL graft were removed and an arthrolysis performed
Reionization with galaxies and active galactic nuclei
In this work we investigate the properties of the sources that reionized the intergalactic medium (IGM) in the high-redshift Universe. Using a semi-Analytical model aimed at reproducing galaxies and black holes in the first âŒ1.5 Gyr of the Universe, we revisit the relative role of star formation and black hole accretion in producing ionizing photons that can escape into the IGM. Both star formation and black hole accretion are regulated by supernova feedback, resulting in black hole accretion being stunted in low-mass haloes. We explore a wide range of combinations for the escape fraction of ionizing photons (redshift-dependent, constant, and scaling with stellar mass) from both star formation () and AGN () to find: (i) the ionizing budget is dominated by stellar radiation from low stellar mass () galaxies at z > 6 with the AGN contribution (driven by black holes in galaxies) dominating at lower redshifts; (ii) AGN only contribute to the cumulative ionizing emissivity by z = 4 for the models that match the observed reionization constraints; (iii) if the stellar mass dependence of is shallower than , at z < 7 a transition stellar mass exists above which AGN dominate the escaping ionizing photon production rate; (iv) the transition stellar mass decreases with decreasing redshift. While AGN dominate the escaping emissivity above the knee of the stellar mass function at z âŒ6.8, they take-over at stellar masses that are a tenth of the knee mass by z = 4
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