141 research outputs found
Toward more realistic analytic models of the heliotail: Incorporating magnetic flattening via distortion flows
Both physical arguments and simulations of the global heliosphere indicate
that the tailward heliopause is flattened considerably in the direction
perpendicular to both the incoming flow and the large-scale interstellar
magnetic field. Despite this fact, all of the existing global analytical models
of the outer heliosheath's magnetic field assume a circular cross section of
the heliotail. To eliminate this inconsistency, we introduce a mathematical
procedure by which any analytically or numerically given magnetic field can be
deformed in such a way that the cross sections along the heliotail axis attain
freely prescribed, spatially dependent values for their total area and aspect
ratio. The distorting transformation of this method honors both the
solenoidality condition and the stationary induction equation with respect to
an accompanying flow field, provided that both constraints were already
satisfied for the original magnetic and flow fields prior to the
transformation. In order to obtain realistic values for the above parameters,
we present the first quantitative analysis of the heliotail's overall
distortion as seen in state-of-the-art three-dimensional hybrid MHD-kinetic
simulations.Comment: 15 pages, 8 figures. Published in The Astrophysical Journa
The interaction of multiple stellar winds in stellar clusters: potential flow
While several studies have investigated large-scale cluster winds resulting
from an intra-cluster interaction of multiple stellar winds, as yet they have
not provided details of the bordering flows inside a given cluster. The present
work explores the principal structure of the combined flow resulting from the
interaction of multiple stellar winds inside stellar clusters. The theory of
complex potentials is applied to analytically investigate stagnation points,
boundaries between individual outflows, and the hydrodynamic structure of the
asymptotic large-scale cluster wind. In a second part, these planar
considerations are extended to fully three-dimensional, asymmetric
configurations of wind-driving stars.
We find (i) that one can distinguish regions in the large-scale cluster wind
that are determined by the individual stellar winds, (ii) that there are
comparatively narrow outflow channels, and (iii) that the large-scale cluster
wind asymptotically approaches spherical symmetry at large distances. The
combined flow inside a stellar cluster resulting from the interaction of
multiple stellar winds is highly structured.Comment: 8 pages, 8 Figure
Efficacy of silver-bearing external ventricular drain catheters in comparison to standard non-impregnated external ventricular drain catheters
In der Neurochirurgie sind temporäre externe Ableitungen von Liquor cerebrospinalis häufige Eingriffe zur Behandlung von Liquorabflußstörungen. Besonders bei externen Ableitungen besteht eine unmittelbare Kommunikation zwischen Liquorraum und Hautoberfläche. Infektionen durch den Katheterweg sind häufige Komplikationen. Ziel der vorliegenden Arbeit war es, die Wirksamkeit silberhaltiger EVD Katheter in vivo zu objektivieren. Dazu wurde die Infektionshäufigkeit konventioneller unbeschichteter EVD Katheter mit dem seit 2004 eingeführten antimikrobiellen silberhaltigen EVD Katheter verglichen. Mit einer statistischen Erfassung der Infektionsparameter aller Patienten die im Studienzeitraum eine externe Ventrikel-Drainage erhielten, wurde überprüft ob eine signifikante bzw. klinisch relevante Senkung der Infektionshäufigkeit vorlag. Hierzu wurden 231 Patienten in der Klinik für Neurochirurgie der Johann Wolfgang Goethe-Universitätsklinik retrospektiv untersucht. Von 231 Patienten wurden nach Anwendung der Ausschlußkriterien 164 in die statistische Analyse aufgenommen. In der Studiengruppe mit silberhaltigen EVD Kathetern befanden sich 74 Patienten, 90 in der Kontrollgruppe. In beiden Patientenkollektiven bestanden keine statistisch relevanten Unterschiede bezüglich der klinischen Charakteristika. Besonders die Verteilung von Antibiotika und Glukokortikoiden war annähernd gleich in beiden Gruppen. In unserer Studie ist der Einsatz silberhaltiger EVD Katheter zur Behandlung chronischer oder akuter Liquorabflußstörungen hinsichtlich des primären Endpunktes positive Liquorkulturen, Katheterkolonisierungen oder erhöhten Zellzahlen im Liquor, mit einer statistisch signifikanten Abnahme der Häufigkeit von positiven Infektionsparametern gegenüber herkömmlichen EVD Kathetern assoziiert (18,9 verglichen mit 33,7%; p=0,04 Chi-Quadrat-Test). Da externe Ventrikeldrainagen die Eintrittspforte für fakultativ pathogene Keime sein können, ist die Anwendung silberhaltiger EVD Katheter im Sinne einer lokalen Infektionsbarriere sinnvoll. Das Risiko katheterassoziierter Infektionen bei neurochirurgischen Patienten kann so gesenkt werden.In neurosurgery temporary external drains for cerebrospinal fluid are frequently used for the treatment of acute hydrocephalus. When using external ventricular drains, contact between the ventricular system and skin surface is present. Infection because of colonization along the catheter track is possible and a major complication. The aim of this study was to objectify the usefulness in vivo. We compared the infection incidence of standard non-impregnated EVD catheters with silver-bearing external ventricular drains, first used in 2004. For assessing the primary outcome, we reviewed the patient charts of all patients who received an EVD catheter in the study period and analyzed if there was a statistically significant reduce of positive infection parameters. Two hundred and thirty-one patients were retrospectively reviewed at the Department of Neurosurgery at the Johann Wolfgang Goethe-University Medical Center. Of 231 patients 164 were included in the final analysis. Of these 164 patients, 90 were assigned to the control group and 74 to the study group with silver-bearing external ventricular drains. With respect to all clinical characteristics, there were no statistically significant differences in both patient collectives. Administration of antibiotics and glucocorticoids was almost equal in both groups. In our study, the use of silver-bearing external ventricular drain catheters for the treatment of chronic or acute hydrocephalus, was associated with a statistically significant reduce of positive infection parameters in comparison to the control group. In the primary outcome, the occurrence of either positive cerebrospinal fluid culture, colonization of catheter tip or raised liquor cell counts was two times less in the study group (18.9 compared with 33.7%, p=0.04 chi-square test). External ventricular drain catheters can be a path for microorganisms. The use of silverbearing external ventricular drain catheters as a local infection barrier is effective. With the results of this study, it is possible to reduce the risk of catheter associated infections in neurosurgical patients
An Exact, Time-dependent Analytical Solution for the Magnetic Field in the Inner Heliosheath
We derive an exact, time-dependent analytical magnetic field solution for the
inner heliosheath, which satisfies both the induction equation of ideal
magnetohydrodynamics in the limit of infinite electric conductivity and the
magnetic divergence constraint. To this end, we assume that the magnetic field
is frozen into a plasma flow resembling the characteristic interaction of the
solar wind with the local interstellar medium. Furthermore, we make use of the
ideal Ohm's law for the magnetic vector potential and the electric scalar
potential. By employing a suitable gauge condition that relates the potentials
and working with a characteristic coordinate representation, we thus obtain an
inhomogeneous first-order system of ordinary differential equations for the
magnetic vector potential. Then, using the general solution of this system, we
compute the magnetic field via the magnetic curl relation. Finally, we analyze
the well-posedness of the corresponding Dirichlet boundary value problem,
specify compatibility conditions for the boundary values, and outline the
implementation of boundary conditions.Comment: 14 page
Cosmic-ray propagation around the Sun: investigating the influence of the solar magnetic field on the cosmic-ray Sun shadow
The cosmic-ray Sun shadow, which is caused by high-energy charged cosmic rays
being blocked and deflected by the Sun and its magnetic field, has been
observed by various experiments, such as Argo-YBJ, HAWC, Tibet, and IceCube.
Most notably, the shadow's size and depth was recently shown to correlate with
the 11-year solar cycle. The interpretation of such measurements, which help to
bridge the gap between solar physics and high-energy particle astrophysics,
requires a solid theoretical understanding of cosmic-ray propagation in the
coronal magnetic field. It is the aim of this paper to establish theoretical
predictions for the cosmic-ray Sun shadow in order to identify observables that
can be used to study this link in more detail. To determine the cosmic-ray Sun
shadow, we numerically compute trajectories of charged cosmic rays in the
energy range of 5-316 TeV for five different mass numbers. We present and
analyze the resulting shadow images for protons and iron, as well as for
typically measured cosmic-ray compositions. We confirm the observationally
established correlation between the magnitude of the shadowing effect and both
the mean sunspot number and the polarity of the magnetic field during the solar
cycle. We also show that during low solar activity, the Sun's shadow behaves
similarly to that of a dipole, for which we find a non-monotonous dependence on
energy. In particular, the shadow can become significantly more pronounced than
the geometrical disk expected for a totally unmagnetized Sun. For times of high
solar activity, we instead predict the shadow to depend monotonously on energy,
and to be generally weaker than the geometrical shadow for all tested energies.
These effects should become visible in energy-resolved measurements of the Sun
shadow, and may in the future become an independent measure for the level of
disorder in the solar magnetic field.Comment: 18 pages, 88 figure
Lack of Increase in Intracranial Pressure After Epidural Blood Patch in Spinal Cerebrospinal Fluid Leak
Background and Importance: Epidural blood patch (EBP) is one therapeutic measure for patients suffering from spontaneous intracranial hypotension (SIH) or post-lumbar puncture headaches. It has been proposed that an EBP may directly seal a spinal cerebrospinal fluid (CSF) fistula or result in an increase in intracranial pressure (ICP) by a shift of CSF from the spinal to the intracranial compartment. To the best of our knowledge this is the first case of a patient with SIH and neurological deterioration in whom ICP was measured before, during, and after spinal EBP. Clinical Presentation: This 52-year old previously healthy man presented with holocephal headaches. MRI showed a left hemispheric subdural fluid collection causing a significant mass effect. Myelography revealed a CSF leak with epidural contrast at the left side of the L-2 level. To seal the CSF leak, we performed an EBP procedure targeted at left L-2 level and recorded ICP. After applying the epidural blood patch (15 cc) the patient improved rapidly, ICP however remained unchanged before, during, and after the procedure. One day post-treatment, he had a GCS score increase from 12 to 15 and no headache or neurological deficits. Conclusion: A shift of CSF from the spinal to the cranial compartment with a subsequent rise in ICP might not be a beneficial therapeutic mechanism of spinal epidural blood patchin
Cosmic rays in astrospheres
Cosmic rays passing through large astrospheres can be efficiently cooled
inside these "cavities" in the interstellar medium. Moreover, the energy
spectra of these energetic particles are already modulated in front of the
astrospherical bow shocks. We study the cosmic ray flux in and around lambda
Cephei as an example for an astrosphere. The large-scale plasma flow is modeled
hydrodynamically with radiative cooling. We studied the cosmic ray flux in a
stellar wind cavity using a transport model based on stochastic differential
equations. The required parameters, most importantly, the elements of the
diffusion tensor, are based on the heliospheric parameters. The magnetic field
required for the diffusion coefficients is calculated kinematically. We discuss
the transport in an astrospheric scenario with varying parameters for the
transport coefficients. We show that large stellar wind cavities can act as
sinks for the galactic cosmic ray flux and thus can give rise to small-scale
anisotropies in the direction to the observer. Small-scale cosmic ray
anisotropies can naturally be explained by the modulation of cosmic ray spectra
in huge stellar wind cavities
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