656 research outputs found
Distribution-free specification tests of conditional models
This article proposes a class of asymptotically distribution-free specification tests for parametric conditional distributions. These tests are based on a martingale transform of a proper sequential empirical process of conditionally transformed data. Standard continuous functionals of this martingale provide omnibus tests while linear combinations of the orthogonal components in its spectral representation form a basis for directional tests. Finally, Neyman-type smooth tests, a compromise between directional and omnibus tests, are discussed. As a special example we study in detail the construction of directional tests for the null hypothesis of conditional normality versus heteroskedastic contiguous alternatives. A small Monte Carlo study shows that our tests attain the nominal level already for small sample sizes.Publicad
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Generation of Micro Mechanical Devices Using Stereo Lithography
A high resolution machining setup for creating three-dimensional precision components from a
UV-curable photo-resin has been developed. By using frequency-converted diode-pumped solid
state lasers, functional micro-mechanical devices are directly fabricated in a successive layer-bylayer fashion. Within this paper, the direct generation of micro assemblies having
moving components without further assembly of parts will be presented. The micro system
design is based on user-defined 3D-CAD data and will completively be built up within the
fabrication cycle. By using specially developed ÎĽSL materials with suitable properties for micromechanical parts, the development from Rapid Prototyping towards Rapid Production of small
series is intended.Mechanical Engineerin
X-ray emission from Planetary Nebulae. I. Spherically symmetric numerical simulations
(abridged) The interaction of a fast wind with a spherical Asymptotic Giant
Branch (AGB) wind is thought to be the basic mechanism for shaping
Pre-Planetary Nebulae (PPN) and later Planetary Nebulae (PN). Due to the large
speed of the fast wind, one expects extended X-ray emission from these objects,
but X-ray emission has only been detected in a small fraction of PNs and only
in one PPN. Using numerical simulations we investigate the constraints that can
be set on the physical properties of the fast wind (speed, mass-flux, opening
angle) in order to produce the observed X-ray emission properties of PPNs and
PNs. We combine numerical hydrodynamical simulations including radiative
cooling using the code FLASH with calculations of the X-ray properties of the
resulting expanding hot bubble using the atomic database ATOMDB. In this first
study, we compute X-ray fluxes and spectra using one-dimensional models.
Comparing our results with analytical solutions, we find some agreements and
many disagreements. In particular, we test the effect of different time
histories of the fast wind on the X-ray emission and find that it is determined
by the final stage of the time history during which the fast wind velocity has
its largest value. The disagreements which are both qualitative and
quantitative in nature argue for the necessity of using numerical simulations
for understanding the X-ray properties of PNs.Comment: 17 pages, accepted for publication in ApJ (July 27, 2006), uses
emulateap
Hydrodynamical simulations of the jet in the symbiotic star MWC 560 III. Application to X-ray jets in symbiotic stars
In papers I and II in this series, we presented hydrodynamical simulations of
jet models with parameters representative of the symbiotic system MWC 560.
These were simulations of a pulsed, initially underdense jet in a high density
ambient medium. Since the pulsed emission of the jet creates internal shocks
and since the jet velocity is very high, the jet bow shock and the internal
shocks are heated to high temperatures and should therefore emit X-ray
radiation. In this paper, we investigate in detail the X-ray properties of the
jets in our models. We have focused our study on the total X-ray luminosity and
its temporal variability, the resulting spectra and the spatial distribution of
the emission. Temperature and density maps from our hydrodynamical simulations
with radiative cooling presented in the second paper are used together with
emissivities calculated with the atomic database ATOMDB. The jets in our models
show extended and variable X-ray emission which can be characterized as a sum
of hot and warm components with temperatures that are consistent with
observations of CH Cyg and R Aqr. The X-ray spectra of our model jets show
emission line features which correspond to observed features in the spectra of
CH Cyg. The innermost parts of our pulsed jets show iron line emission in the
6.4 - 6.7 keV range which may explain such emission from the central source in
R Aqr. We conclude that MWC 560 should be detectable with Chandra or
XMM-Newton, and such X-ray observations will provide crucial for understanding
jets in symbiotic stars.Comment: 10 pages, 12 figures, accepted for publication in ApJ, uses
emulateap
Ovartorsion nach In-vitro-Fertilisation
Zusammenfassung: Das Risiko für das Auftreten einer Adnextorsion nach einer IVF-Behandlung wird auf ca. 0,1% geschätzt. Aufgrund der Seltenheit und des initial oft unauffälligen sonographischen Befundes wird eine Adnextorsion oft fehldiagnostiziert und die Behandlung verzögert. Die einzige effektive Therapie ist eine sofortige Laparoskopie, Retorsion und Verkleinerung des Ovar
A conservative orbital advection scheme for simulations of magnetized shear flows with the PLUTO code
Explicit numerical computations of super-fast differentially rotating disks
are subject to the time-step constraint imposed by the Courant condition. When
the bulk orbital velocity largely exceeds any other wave speed the time step is
considerably reduced and a large number of steps may be necessary to complete
the computation.
We present a robust numerical scheme to overcome the Courant limitation by
extending the algorithm previously known as FARGO (Fast Advection in Rotating
Gaseous Objects) to the equations of magnetohydrodynamics (MHD). The proposed
scheme conserves total angular momentum and energy to machine precision and
works in Cartesian, cylindrical, or spherical coordinates. The algorithm is
implemented in the PLUTO code for astrophysical gasdynamics and is suitable for
local or global simulations of accretion or proto-planetary disk models.
By decomposing the total velocity into an average azimuthal contribution and
a residual term, the algorithm solves the MHD equations through a linear
transport step in the orbital direction and a standard nonlinear solver applied
to the MHD equations written in terms of the residual velocity. Since the
former step is not subject to any stability restriction, the Courant condition
is computed only in terms of the residual velocity, leading to substantially
larger time steps. The magnetic field is advanced in time using the constrained
transport method in order to preserve the divergence-free condition.
Conservation of total energy and angular momentum is enforced at the discrete
level by properly expressing the source terms in terms of upwind fluxes
available during the standard solver.
Our results show that applications of the proposed orbital-advection scheme
to problems of astrophysical relevance provides, at reduced numerical cost,
equally accurate and less dissipative results than standard time-marching
schemes.Comment: 16 pages, 13 figures. Accepted for publication in A&
Assessing the Effects of a Paired TBL Session and Patient Simulation on Pharmacy Student HIV Treatment Knowledge
Description of the Problem: Pharmacists can play a crucial role in monitoring, counseling, and providing adherence checks across practice pharmacy settings; but they may not gain experience in this area until after graduating from pharmacy school.
Statement of Innovation: Students participated in an intentionally aligned team-based learning session followed by completion of an HIV patient treatment worksheet and an HIV patient care simulation. This sequence was assessed using the HIV Treatment Knowledge Scale.
Description of the Innovation: Second-year pharmacy students (N=48, 98% response rate) participated in a baseline knowledge assessment before a four-hour HIV team-based learning (TBL) session, which included the use of an online HIV Patient Management Simulator. Students were administered the scale again post-session. Three days before the simulation, students had access to an HIV patient treatment worksheet that was required to be completed before the simulation. Ten days after the initial assessment, students participated in an HIV patient simulation where they proposed a new antiretroviral plan while also addressing monitoring, barriers, and maximizing adherence for the patient. Post-simulation, students were again administered the scale. Data were analyzed using descriptive statistics, Wilcoxon and paired t-tests, as appropriate.
Critical Analysis: A total of 48 second-year pharmacy students participated. HIV knowledge increased significantly post-TBL (p \u3c 0.001). Post-simulation, scores improved, but not significantly (p = 0.291). Knowledge on 15 of the 21 items on the HIV Treatment Knowledge Scale significantly improved from pre-TBL to post-simulation (p ≤ 0.025).
Next Steps: Future investigation should focus on the impact that HIV simulation training has on skills, abilities, confidence, and empathy
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