5,522 research outputs found
Numerical simulations for the precession dynamo experiment in the framework of the DRESDYN project
How often are clinicians performing genital exams in children with disorders of sex development?
Background:
We sought to determine the frequency with which genital exams (GEs) are performed in children with disorders of sex development (DSD) and ambiguous genitalia (AG) during routine visits to the pediatric endocrine clinic.
Methods:
Medical records of children with DSD and AG seen at one large academic center since 2007 were reviewed. Data analyzed included diagnosis, sex of rearing, age, initial or follow up visit, number of individuals present and sex of the pediatric endocrinologist. Repeated measures analysis was performed to evaluate associations between GEs and patient/physician factors.
Results:
Eighty-two children with DSD and AG who had a total of 632 visits were identified. Sex of rearing was female in 78% and the most common diagnosis was congenital adrenal hyperplasia (CAH) (68%). GEs were performed in 35.6% of visits. GEs were more likely in patients with male sex of rearing (odds ratio [OR] 17.81, p=0.006), during initial vs. follow-up visits (OR 5.99, p=0.012), and when the examining endocrinologist was female (OR 3.71, p=0.014). As patients aged, GEs were less likely (OR 0.76, p<0.0001).
Conclusions:
GEs were performed in approximately one-third of clinic visits in children with DSD and AG. Male sex of rearing, initial visits and female pediatric endocrinologist were associated with more frequent GEs
Modulated rotating waves in the magnetized spherical Couette system
We present a study devoted to a detailed description of modulated rotating
waves (MRW) in the magnetized spherical Couette system. The set-up consists of
a liquid metal confined between two differentially rotating spheres and
subjected to an axially applied magnetic field. When the magnetic field
strength is varied, several branches of MRW are obtained by means of three
dimensional direct numerical simulations (DNS). The MRW originate from parent
branches of rotating waves (RW) and are classified according to Rand's (Arch.
Ration. Mech. Anal 79:1-37, 182) and Coughling & Marcus (J. Fluid Mech.
234:1-18,1992) theoretical description. We have found relatively large
intervals of multistability of MRW at low magnetic field, corresponding to the
radial jet instability known from previous studies. However, at larger magnetic
field, corresponding to the return flow regime, the stability intervals of MRW
are very narrow and thus they are unlikely to be found without detailed
knowledge of their bifurcation point. A careful analysis of the spatio-temporal
symmetries of the most energetic modes involved in the different classes of MRW
will allow in the future a comparison with the HEDGEHOG experiment, a
magnetized spherical Couette device hosted at the Helmholtz-Zentrum
Dresden-Rossendorf.Comment: Contains 3 tables and 8 figures. Published in the Journal of
Nonlinear Scienc
Magnetic Field Saturation in the Riga Dynamo Experiment
After the dynamo experiment in November 1999 had shown magnetic field
self-excitation in a spiraling liquid metal flow, in a second series of
experiments emphasis was placed on the magnetic field saturation regime as the
next principal step in the dynamo process. The dependence of the strength of
the magnetic field on the rotation rate is studied. Various features of the
saturated magnetic field are outlined and possible saturation mechanisms are
discussed.Comment: 4 pages, 8 figure
The effect of television on the leisure time activities of sixth grade children in Medford, Massachusetts.
Thesis (Ed.M.)--Boston Universit
Contactless inductive flow tomography
The three-dimensional velocity field of a propeller driven liquid metal flow
is reconstructed by a contactless inductive flow tomography (CIFT). The
underlying theory is presented within the framework of an integral equation
system that governs the magnetic field distribution in a moving electrically
conducting fluid. For small magnetic Reynolds numbers this integral equation
system can be cast into a linear inverse problem for the determination of the
velocity field from externally measured magnetic fields. A robust
reconstruction of the large scale velocity field is already achieved by
applying the external magnetic field alternately in two orthogonal directions
and measuring the corresponding sets of induced magnetic fields. Kelvin's
theorem is exploited to regularize the resulting velocity field by using the
kinetic energy of the flow as a regularizing functional. The results of the new
technique are shown to be in satisfactory agreement with ultrasonic
measurements.Comment: 9 Figures; to appear in Phys. Rev
Triadic resonances in non-linear simulations of a fluid flow in a precessing cylinder
We present results from three-dimensional non-linear hydrodynamic simulations
of a precession driven flow in cylindrical geometry. The simulations are
motivated by a dynamo experiment currently under development at
Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which the possibility of
generating a magnetohydrodynamic dynamo will be investigated in a cylinder
filled with liquid sodium and simultaneously rotating around two axes. In this
study, we focus on the emergence of non-axisymmetric time-dependent flow
structures in terms of inertial waves which - in cylindrical geometry - form
so-called Kelvin modes. For a precession ratio
the amplitude of the forced Kelvin mode
reaches up to one fourth of the rotation velocity of the cylindrical container
confirming that precession provides a rather efficient flow driving mechanism
even at moderate values of . More relevant for dynamo action might
be free Kelvin modes with higher azimuthal wave number. These free Kelvin modes
are triggered by non-linear interactions and may constitute a triadic resonance
with the fundamental forced mode when the height of the container matches their
axial wave lengths. Our simulations reveal triadic resonances at aspect ratios
close to those predicted by the linear theory except around the primary
resonance of the forced mode. In that regime we still identify various free
Kelvin modes, however, all of them exhibit a retrograde drift around the
symmetry axis of the cylinder and none of them can be assigned to a triadic
resonance. The amplitudes of the free Kelvin modes always remain below the
forced mode but may reach up to 6% of the of the container's angular velocity.
The properties of the free Kelvin modes will be used in future simulations of
the magnetic induction equation to investigate their ability to provide for
dynamo action.Comment: 26 pages, 14 figures, submitted to New J. Phy
Role of soft-iron impellers on the mode selection in the VKS dynamo experiment
A crucial point for the understanding of the von-K\'arm\'an-Sodium (VKS)
dynamo experiment is the influence of soft-iron impellers. We present numerical
simulations of a VKS-like dynamo with a localized permeability distribution
that resembles the shape of the flow driving impellers. It is shown that the
presence of soft-iron material essentially determines the dynamo process in the
VKS experiment. % An axisymmetric magnetic field mode can be explained by the
combined action of the soft-iron disk and a rather small -effect
parametrizing the induction effects of unresolved small scale flow
fluctuations
- …