25,959 research outputs found
High Rayleigh number convection with double diffusive fingers
An electrodeposition cell is used to sustain a destabilizing concentration
difference of copper ions in aqueous solution between the top and bottom
boundaries of the cell. The resulting convecting motion is analogous to
Rayleigh-B\'enard convection at high Prandtl numbers. In addition, a
stabilizing temperature gradient is imposed across the cell. Even for thermal
buoyancy two orders of magnitude smaller than chemical buoyancy, the presence
of the weak stabilizing gradient has a profound effect on the convection
pattern. Double diffusive fingers appear in all cases. The size of these
fingers and the flow velocities are independent of the height of the cell, but
they depend on the ion concentration difference between top and bottom
boundaries as well as on the imposed temperature gradient. The scaling of the
mass transport is compatible with previous results on double diffusive
convection
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A Statistical Treatment of Angular Momentum Fractionation in Heavy Ion Reactions
TPCI: The PLUTO-CLOUDY Interface
We present an interface between the (magneto-) hydrodynamics code PLUTO and
the plasma simulation and spectral synthesis code CLOUDY. By combining these
codes, we constructed a new photoionization hydrodynamics solver: The
PLUTO-CLOUDY Interface (TPCI), which is well suited to simulate
photoevaporative flows under strong irradiation. The code includes the
electromagnetic spectrum from X-rays to the radio range and solves the
photoionization and chemical network of the 30 lightest elements. TPCI follows
an iterative numerical scheme: First, the equilibrium state of the medium is
solved for a given radiation field by CLOUDY, resulting in a net radiative
heating or cooling. In the second step, the latter influences the (magneto-)
hydrodynamic evolution calculated by PLUTO. Here, we validated the
one-dimensional version of the code on the basis of four test problems:
Photoevaporation of a cool hydrogen cloud, cooling of coronal plasma, formation
of a Stroemgren sphere, and the evaporating atmosphere of a hot Jupiter. This
combination of an equilibrium photoionization solver with a general MHD code
provides an advanced simulation tool applicable to a variety of astrophysical
problems.Comment: 13 pages, 10 figures, accepted for publication in A&
On the nature of the near-UV extended light in Seyfert galaxies
We study the nature of the extended near-UV emission in the inner kiloparsec
of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow
band [OIII] high resolution Hubble images. For the majority of the objects we
find a very similar morphology in both bands. From the [OIII] images we
construct synthetic images of the nebular continuum plus the emission line
contribution expected through the F330W filter, which can be subtracted from
the F330W images. We find that the emission of the ionised gas dominates the
near-UV extended emission in half of the objects. A further broad band
photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that
the remaining emission is dominated by the underlying galactic bulge
contribution. We also find a blue component whose nature is not clear in 4 out
of 15 objects. This component may be attributed to scattered light from the
AGN, to a young stellar population in unresolved star clusters, or to
early-disrupted clusters. Star forming regions and/or bright off-nuclear star
clusters are observed in 4/15 galaxies of the sample.Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRA
Correlated and zonal errors of global astrometric missions: a spherical harmonic solution
We propose a computer-efficient and accurate method of estimation of
spatially correlated errors in astrometric positions, parallaxes and proper
motions obtained by space and ground-based astrometry missions. In our method,
the simulated observational equations are set up and solved for the
coefficients of scalar and vector spherical harmonics representing the output
errors, rather than for individual objects in the output catalog. Both
accidental and systematic correlated errors of astrometric parameters can be
accurately estimated. The method is demonstrated on the example of the JMAPS
mission, but can be used for other projects of space astrometry, such as SIM or
JASMINE.Comment: Accepted by AJ, to be published in 201
Characterization of a two-transmon processor with individual single-shot qubit readout
We report the characterization of a two-qubit processor implemented with two
capacitively coupled tunable superconducting qubits of the transmon type, each
qubit having its own non-destructive single-shot readout. The fixed capacitive
coupling yields the \sqrt{iSWAP} two-qubit gate for a suitable interaction
time. We reconstruct by state tomography the coherent dynamics of the two-bit
register as a function of the interaction time, observe a violation of the Bell
inequality by 22 standard deviations after correcting readout errors, and
measure by quantum process tomography a gate fidelity of 90%
Experimental study of super-rotation in a magnetostrophic spherical Couette flow
We report measurements of electric potentials at the surface of a spherical
container of liquid sodium in which a magnetized inner core is differentially
rotating. The azimuthal angular velocities inferred from these potentials
reveal a strong super-rotation of the liquid sodium in the equatorial region,
for small differential rotation. Super-rotation was observed in numerical
simulations by Dormy et al. [1]. We find that the latitudinal variation of the
electric potentials in our experiments differs markedly from the predictions of
a similar numerical model, suggesting that some of the assumptions used in the
model - steadiness, equatorial symmetry, and linear treatment for the evolution
of both the magnetic and velocity fields - are violated in the experiments. In
addition, radial velocity measurements, using ultrasonic Doppler velocimetry,
provide evidence of oscillatory motion near the outer sphere at low latitude:
it is viewed as the signature of an instability of the super-rotating region
Liquorproteine bei der Neuromyelitis optica
Es werden zwei Fälle von Neuromyelitis optica beschrieben, die jeweils eine hochgradige Erhöhung der Proteine im Liquor aufwiesen. Während ein Patient nach 6monatigem Krankheitsverlauf starb und pathologisch-anatomisch untersucht werden konnte, überlebte der andere Patient mit erheblichen Residuen. Dieser Fall zeichnete sich dadurch aus, daß deutlich erhöhte IgA- und IgM-Werte sowohl im Liquor als auch im Serum vorlagen. Es wird diskutiert, ob die gefundenen Liquorveränderungen möglicherweise eine Abgrenzung entsprechender Fälle gegenüber der multiplen Sklerose zulassen
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