4,463 research outputs found
Multichannel pulse height analyzer is inexpensive, features low power requirements
Consumption multichannel pulse height analyzer performs balloon and rocket investigations of solar neutrons with energies greater than 10 MeV. The lightweight unit can operate in a temperature range of minus 30 degrees to plus 70 degrees C and withstand storage temperatures from minus 50 degrees to plus 90 degrees C
The exact solution of the Riemann problem with non-zero tangential velocities in relativistic hydrodynamics
We have generalised the exact solution of the Riemann problem in special
relativistic hydrodynamics for arbitrary tangential flow velocities. The
solution is obtained by solving the jump conditions across shocks plus an
ordinary differential equation arising from the self-similarity condition along
rarefaction waves, in a similar way as in purely normal flow. The dependence of
the solution on the tangential velocities is analysed, and the impact of this
result on the development of multidimensional relativistic hydrodynamic codes
(of Godunov type) is discussed.Comment: 26 pages, 4 figures. Accepted for publication in Journal of Fluid
Mechanic
Wavefront sensing of atmospheric phase distortions at the Palomar 200-in. telescope and implications for adaptive optics
Major efforts in astronomical instrumentation are now being made to apply the techniques of adaptive optics to the correction of phase distortions induced by the turbulent atmosphere and by quasi-static aberrations in telescopes themselves. Despite decades of study, the problem of atmospheric turbulence is still only partially understood. We have obtained video-rate (30 Hz) imaging of stellar clusters and of single-star phase distortions over the pupil of the 200" Hale telescope on Palomar Mountain. These data show complex temporal and spatial behavior, with multiple components arising at a number of scale heights in the atmosphere; we hope to quantify this behavior to ensure the feasibility of adaptive optics at the Observatory. We have implemented different wavefront sensing techniques to measure aperture phase in wavefronts from single stars, including the classical Foucault test, which measures the local gradient of phase, and the recently-devised curvature sensing technique, which measures the second derivative of pupil phase and has formed the real-time wavefront sensor for some very productive astronomical adaptive optics. Our data, though not fast enough to capture all details of atmospheric phase fluctuations, provide important information regarding the capabilities that must be met by the adaptive optics system now being built for the 200" telescope by a team at the Jet Propulsion Lab. We describe our data acquisition techniques, initial results from efforts to characterize the properties of the turbulent atmosphere at Palomar Mountain, and future plans to extract additional quantitative parameters of use for adaptive optics performance predictions
Dynamic system classifier
Stochastic differential equations describe well many physical, biological and
sociological systems, despite the simplification often made in their
derivation. Here the usage of simple stochastic differential equations to
characterize and classify complex dynamical systems is proposed within a
Bayesian framework. To this end, we develop a dynamic system classifier (DSC).
The DSC first abstracts training data of a system in terms of time dependent
coefficients of the descriptive stochastic differential equation. Thereby the
DSC identifies unique correlation structures within the training data. For
definiteness we restrict the presentation of DSC to oscillation processes with
a time dependent frequency {\omega}(t) and damping factor {\gamma}(t). Although
real systems might be more complex, this simple oscillator captures many
characteristic features. The {\omega} and {\gamma} timelines represent the
abstract system characterization and permit the construction of efficient
signal classifiers. Numerical experiments show that such classifiers perform
well even in the low signal-to-noise regime.Comment: 11 pages, 8 figure
Classical light dispersion theory in a regular lattice
We study the dynamics of an infinite regular lattice of classical charged
oscillators. Each individual oscillator is described as a point particle
subject to a harmonic restoring potential, to the retarded electromagnetic
field generated by all the other particles, and to the radiation reaction
expressed according to the Lorentz--Dirac equation. Exact normal mode
solutions, describing the propagation of plane electromagnetic waves through
the lattice, are obtained for the complete linearized system of infinitely many
oscillators. At variance with all the available results, our method is valid
for any values of the frequency, or of the ratio between wavelength and lattice
parameter. A remarkable feature is that the proper inclusion of radiation
reaction in the dynamics of the individual oscillators does not give rise to
any extinction coefficient for the global normal modes of the lattice. The
dispersion relations resulting from our solution are numerically studied for
the case of a simple cubic lattice. New predictions are obtained in this way
about the behavior of the crystal at frequencies near the proper oscillation
frequency of the dipoles.Comment: 15 pages, 1 figure; typos correcte
Saturn's aurora observed by the Cassini camera at visible wavelengths
The first observations of Saturn's visible-wavelength aurora were made by the
Cassini camera. The aurora was observed between 2006 and 2013 in the northern
and southern hemispheres. The color of the aurora changes from pink at a few
hundred km above the horizon to purple at 1000-1500 km above the horizon. The
spectrum observed in 9 filters spanning wavelengths from 250 nm to 1000 nm has
a prominent H-alpha line and roughly agrees with laboratory simulated auroras.
Auroras in both hemispheres vary dramatically with longitude. Auroras form
bright arcs between 70 and 80 degree latitude north and between 65 and 80
degree latitude south, which sometimes spiral around the pole, and sometimes
form double arcs. A large 10,000-km-scale longitudinal brightness structure
persists for more than 100 hours. This structure rotates approximately together
with Saturn. On top of the large steady structure, the auroras brighten
suddenly on the timescales of a few minutes. These brightenings repeat with a
period of about 1 hour. Smaller, 1000-km-scale structures may move faster or
lag behind Saturn's rotation on timescales of tens of minutes. The persistence
of nearly-corotating large bright longitudinal structure in the auroral oval
seen in two movies spanning 8 and 11 rotations gives an estimate on the period
of 10.65 0.15 h for 2009 in the northern oval and 10.8 0.1 h for 2012
in the southern oval. The 2009 north aurora period is close to the north branch
of Saturn Kilometric Radiation (SKR) detected at that time.Comment: 39 pages, 8 figures, 1 table, 6 supplementary movies, accepted to
Icaru
Entwicklung und MachbarkeitsĂŒberprĂŒfung eines Kern-Sets von QualitĂ€tsindikatoren fĂŒr die pĂ€diatrische PrimĂ€rversorgung in Europa - Core Set of Indicators for Paediatric Primary Care in Europe, COSI-PPC-EU
EinfĂŒhrung und Hintergrund
Die medizinische QualitĂ€t in den einzelnen europĂ€ischen LĂ€ndern zeigt erhebliche Unterschiede und Defizite [20, 86, 87]. Die FreizĂŒgigkeit im Schengen Raum fĂŒhrt durch Cross-Border Medizin zu weiteren Verschiebungen und Ungleichgewichten [6, 61, 70]. Die EU gesteht jedem EU-BĂŒrger zu, in einem anderen europĂ€ischen Land mindestens die gleiche medizinische QualitĂ€t wie in seinem Heimatland zu bekommen [34]. Studien legen nahe, dass die qualitativen Defizite in der pĂ€diatrischen PrimĂ€rversorgung (Paediatric Primary Care, PPC) besonders hoch sind, insbesondere weil verschiedene Fachgruppen an der Behandlung von Kindern und Jugendlichen in Europa beteiligt, unterschiedlich ausgebildet und trainiert sind [32, 50].
Benchmarking-Instrumente, wie QualitĂ€tsindikatoren (QI), können ein Lernen an der âbest-practiceâ fördern und QualitĂ€t und Patientensicherheit verbessern [45, 54]. QI speziell fĂŒr pĂ€diatrische PrimĂ€rversorgungs-Einrichtungen in Europa existieren nicht â werden jedoch von der EU gefordert [33]. Um diese LĂŒcke zu schlieĂen, wurde das âCore Set of Indicators for Paediatric Primary Care in Europeâ (COSI-PPC-EU) entwickelt [36] und hinsichtlich seiner Machbarkeit getestet [37].
Methode
Die Studie besteht aus drei Teilprojekten. In den ersten beiden Teilprojekten wurde untersucht, ob ein valides und machbares QI-Sets fĂŒr europĂ€ische PPC-Einrichtungen zu entwickeln und von einem Experten-Gremium zu konsentieren ist. Mittels einer modifizierten RAND/UCLA Appropriateness Method [9] wurde eine Literaturrecherche, eine nachfolgende Bearbeitung der gefundenen QI und ein mehrstufiger Konsensus-Prozess durch ein internationales Experten-Panel durchgefĂŒhrt.
Mit dem dritten Teilprojekt wurde die Machbarkeit dieses QI-Sets untersucht. Dazu wurden europĂ€ische Kinder- und JugendĂ€rzte befragt, ob die zusammengestellten QI in den europĂ€ischen Praxen machbar sind. Sie eruierten anhand ihrer Krankenakten, ob die Daten fĂŒr die QI in den europĂ€ischen Praxen vorhanden sind, mit welchem Aufwand sie zu erheben sind, ob die QI fĂŒr ihre Praxen zutreffen, relevant und reliabel sind und von ihnen akzeptiert werden können. Die Praxen wurden gezielt von LĂ€nderkoordinatoren ausgewĂ€hlt und sollten möglichst viele unterschiedliche Praxis-Typen reprĂ€sentieren. Die Studie war qualitativ explorativ angelegt mit dem Ziel, aus 10 LĂ€ndern je 10 Teilnehmer zu rekrutieren.
â
Ergebnisse
Die erste Teilstudie ergab nach der Literaturrecherche einen QI-Satz von 1516 QI, der durch das Experten-Panel in der Folge teilweise zusammengefasst und umformuliert oder mangels Evidenz oder Machbarkeit auf 50 reduziert wurde. Von diesen 50 QI wurden schlieĂlich im zweiten Studienteil 42 konsentiert.
Die QI können inhaltlich in 5 Kategorien eingeteilt werden: (A) Gesundheitsförderung, PrÀvention und Screening (13 QI), (B) akute Krankheitsbilder (9 QI), (C) chronische Krankheiten (8 QI), (D) Praxisorganisation (3 QI), (E) Patientensicherheit (9 QI).
79 KinderĂ€rzte aus 8 europĂ€ischen LĂ€ndern nahmen an der dritten Teilstudie teil. Nachgewiesen werden konnte, dass in der Stichprobe die Daten fĂŒr die Berechnung der QI vorhanden sind, der technische Aufwand fĂŒr ihr Auslesen zeitaufwendig und die praktische Machbarkeit eingeschrĂ€nkt ist. Die Kriterien Akzeptanz, Relevanz und ReliabilitĂ€t sowie ein Zutreffen der QI fĂŒr die Praxis wurden besser bewertet, wenn auch sehr unterschiedlich innerhalb der einzelnen QI-Kategorien. Die Kategorie (A) zeigte in nahezu allen Kriterien die höchsten Zustimmungsraten. Die geringfĂŒgig vorhandenen lĂ€nderspezifischen Trends können aufgrund der gezielt ausgewĂ€hlten Studien-Teilnehmer und der statistisch zu kleinen Stichprobe nicht sicher interpretiert werden.
Diskussion und Ausblick
Ein valides und machbares QI-Set fĂŒr europĂ€ische PPC-Ărzte mit einer groĂen inhaltlichen Bandbreite konnte in Form des COSI-PPC-EU zusammengestellt werden. Das Set unterscheidet sich von anderen QI-Sets durch seine gezielte Ausrichtung auf PPC-Einrichtungen und umfasst neben rein medizinischen Indikatoren auch solche fĂŒr das Praxismanagement und die Patientensicherheit. Konsens der PPC-Experten und Evidenz sind vergleichbar zu anderen QI-Sets fĂŒr PPC, die jedoch lĂ€nderspezifisch und nicht international ausgerichtet sind. Dies bestĂ€tigte sich in der Machbarkeitsstudie anhand der Zustimmungswerte durch die PPC-Ărzte. Technische HĂŒrden scheinen noch die VerfĂŒgbarkeit der vorhandenen Daten zur Berechnung der QI zu behindern und die Machbarkeit zum jetzigen Zeitpunkt zu mindern.
Sollten die Akteure in den Gesundheitssystemen Europas und vor allem die europĂ€ischen Gesundheitspolitiker ein wahres Interesse an einem Benchmarking-Prozess in der PPC haben, kommen sie nicht umhin, die politischen, finanziellen und juristischen Voraussetzungen fĂŒr die technische Datenerhebung zu schaffen. COSI-PPC-EU kann dann ein Voneinander-Lernen der Gesundheitsdienstleister ermöglichen und nicht nur die Cross-Border Medizin fĂŒr Kinder- und Jugendliche-Patienten in Europa sicherer und qualitativ hochwertiger gestalten helfen
Magneto-elastic oscillations of neutron stars with dipolar magnetic fields
By means of two dimensional, general-relativistic, magneto-hydrodynamical
simulations we investigate the oscillations of magnetized neutron star models
(magnetars) including the description of an extended solid crust. The aim of
this study is to understand the origin of the QPOs observed in the giant flares
of SGRs. We confirm the existence of three different regimes: (a) a weak
magnetic field regime B<5 x 10^13 G, where crustal shear modes dominate the
evolution; (b) a regime of intermediate magnetic fields 5 x 10^13 G<B< 10^15 G,
where Alfv\'en QPOs are mainly confined to the core of the neutron star and the
crustal shear modes are damped very efficiently; and (c) a strong field regime
B>10^15 G, where magneto-elastic oscillations reach the surface and approach
the behavior of purely Alfv\'en QPOs. When the Alfv\'en QPOs are confined to
the core of the neutron star, we find qualitatively similar QPOs as in the
absence of a crust. The lower QPOs associated with the closed field lines of
the dipolar magnetic field configuration are reproduced as in our previous
simulations without crust, while the upper QPOs connected to the open field
lines are displaced from the polar axis. Additionally, we observe a family of
edge QPOs. Our results do not leave much room for a crustal-mode interpretation
of observed QPOs in SGR giant flares, but can accommodate an interpretation of
these observations as originating from Alfv\'en-like, global, turning-point
QPOs in models with dipolar magnetic field strengths in the narrow range of 5 x
10^15 G < B < 1.4 x 10^16 G. This range is somewhat larger than estimates for
magnetic field strengths in known magnetars. The discrepancy may be resolved in
models including a more complicated magnetic field structure or with models
taking superfluidity of the neutrons and superconductivity of the protons in
the core into account.Comment: 25 pages, 17 figures, 7 tables, minor corrections to match published
version in MNRA
Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations
We discuss torsional oscillations of highly magnetised neutron stars
(magnetars) using two-dimensional, magneto-elastic-hydrodynamical simulations.
Our model is able to explain both the low- and high-frequency quasi-periodic
oscillations (QPOs) observed in magnetars. The analysis of these oscillations
provides constraints on the breakout magnetic-field strength, on the
fundamental QPO frequency, and on the frequency of a particularly excited
overtone. More importantly, we show how to use this information to generically
constraint properties of high-density matter in neutron stars, employing
Bayesian analysis. In spite of current uncertainties and computational
approximations, our model-dependent Bayesian posterior estimates for SGR
1806-20 yield a magnetic-field strength G and a crust thickness of km, which are both in remarkable agreement with
observational and theoretical expectations, respectively (1- error bars
are indicated). Our posteriors also favour the presence of a superfluid phase
in the core, a relatively low stellar compactness, , indicating a
relatively stiff equation of state and/or low mass neutron star, and high shear
speeds at the base of the crust, cm/s. Although the
procedure laid out here still has large uncertainties, these constraints could
become tighter when additional observations become available.Comment: 14 pages, 8 figures, 6 tables, submitted to MNRA
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