3,548 research outputs found
Turbulent Vortex Flow Responses at the AB Interface in Rotating Superfluid 3He-B
In a rotating two-phase sample of 3He-B and magnetic-field stabilized 3He-A
the large difference in mutual friction dissipation at 0.20 Tc gives rise to
unusual vortex flow responses. We use noninvasive NMR techniques to monitor
spin down and spin up of the B-phase superfluid component to a sudden change in
the rotation velocity. Compared to measurements at low field with no A-phase,
where these responses are laminar in cylindrically symmetric flow, spin down
with vortices extending across the AB interface is found to be faster,
indicating enhanced dissipation from turbulence. Spin up in turn is slower,
owing to rapid annihilation of remanent vortices before the rotation increase.
As confirmed by both our NMR signal analysis and vortex filament calculations,
these observations are explained by the additional force acting on the B-phase
vortex ends at the AB interface.Comment: 6 pages, 6 figure
The spin-up of a linearly stratified fluid in a sliced, circular cylinder
A linearly stratified fluid contained in a circular cylinder with a linearly-sloped base, whose axis is aligned with the rotation axis, is spun up from a rotation rate Î to Î + ÎÎ (with ÎÎ << Î ) by Rossby waves propagating across the container. Experimental results presented here, however, show that if the Burger number S is not small, then that spinup looks quite different from that reported by Pedlosky & Greenspan [J. Fluid Mech., vol. 27, 1967, pp. 291â304] for S = 0. That is particularly so if the Burger number is large, since the Rossby waves are then confined to a region of height Sâ1/2 above the sloped base. Axial vortices, ubiquitous features even at tiny Rossby numbers of spin-up in containers with vertical corners (see van Heijst et al. [Phys. Fluids A, vol. 2, 1990, pp. 150â159] and Munro & Foster [Phys. Fluids, vol. 26, 2014, article no. 026603], for example), are less prominent here, forming at locations that are not obvious a priori, but in the âwestern halfâ of the container only, and confined to the bottom Sâ1/2 region. Both decay rates from friction at top and bottom walls and the propagation speed of the waves are found to increase with S as well. An asymptotic theory for Rossby numbers that are not too large shows good agreement with many features seen in the experiments. The full frequency spectrum and decay rates for these waves are discussed, again for large S, and vertical vortices are found to occur only for Rossby numbers comparable to E1/2, where E is the Ekman number. Symmetry anomalies in the observations are determined by analysis to be due to second-order corrections to the lower-wall boundary condition
Personalized Pancreatic Tumor Growth Prediction via Group Learning
Tumor growth prediction, a highly challenging task, has long been viewed as a
mathematical modeling problem, where the tumor growth pattern is personalized
based on imaging and clinical data of a target patient. Though mathematical
models yield promising results, their prediction accuracy may be limited by the
absence of population trend data and personalized clinical characteristics. In
this paper, we propose a statistical group learning approach to predict the
tumor growth pattern that incorporates both the population trend and
personalized data, in order to discover high-level features from multimodal
imaging data. A deep convolutional neural network approach is developed to
model the voxel-wise spatio-temporal tumor progression. The deep features are
combined with the time intervals and the clinical factors to feed a process of
feature selection. Our predictive model is pretrained on a group data set and
personalized on the target patient data to estimate the future spatio-temporal
progression of the patient's tumor. Multimodal imaging data at multiple time
points are used in the learning, personalization and inference stages. Our
method achieves a Dice coefficient of 86.8% +- 3.6% and RVD of 7.9% +- 5.4% on
a pancreatic tumor data set, outperforming the DSC of 84.4% +- 4.0% and RVD
13.9% +- 9.8% obtained by a previous state-of-the-art model-based method
A review of recent determinations of the composition and surface pressure of the atmos- phere of mars
Recent determinations of composition and surface pressure of Mars atmospher
Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment
The first observation of fast and slow magnetocoriolis (MC) waves in a
laboratory experiment is reported. Rotating nonaxisymmetric modes arising from
a magnetized turbulent Taylor-Couette flow of liquid metal are identified as
the fast and slow MC waves by the dependence of the rotation frequency on the
applied field strength. The observed slow MC wave is damped but the observation
provides a means for predicting the onset of the Magnetorotational Instability
An evaluation of the Goddard Space Flight Center Library
The character and degree of coincidence between the current and future missions, programs, and projects of the Goddard Space Flight Center and the current and future collection, services, and facilities of its library were determined from structured interviews and discussions with various classes of facility personnel. In addition to the tabulation and interpretation of the data from the structured interview survey, five types of statistical analyses were performed to corroborate (or contradict) the survey results and to produce useful information not readily attainable through survey material. Conclusions reached regarding compatability between needs and holdings, services and buildings, library hours of operation, methods of early detection and anticipation of changing holdings requirements, and the impact of near future programs are presented along with a list of statistics needing collection, organization, and interpretation on a continuing or longitudinal basis
Super Stability of Laminar Vortex Flow in Superfluid 3He-B
Vortex flow remains laminar up to large Reynolds numbers (Re~1000) in a
cylinder filled with 3He-B. This is inferred from NMR measurements and
numerical vortex filament calculations where we study the spin up and spin down
responses of the superfluid component, after a sudden change in rotation
velocity. In normal fluids and in superfluid 4He these responses are turbulent.
In 3He-B the vortex core radius is much larger which reduces both surface
pinning and vortex reconnections, the phenomena, which enhance vortex bending
and the creation of turbulent tangles. Thus the origin for the greater
stability of vortex flow in 3He-B is a quantum phenomenon. Only large flow
perturbations are found to make the responses turbulent, such as the walls of a
cubic container or the presence of invasive measuring probes inside the
container.Comment: 4 pages, 6 figure
Asymptotic theory for a moving droplet driven by a wettability gradient
An asymptotic theory is developed for a moving drop driven by a wettability
gradient. We distinguish the mesoscale where an exact solution is known for the
properly simplified problem. This solution is matched at both -- the advancing
and the receding side -- to respective solutions of the problem on the
microscale. On the microscale the velocity of movement is used as the small
parameter of an asymptotic expansion. Matching gives the droplet shape,
velocity of movement as a function of the imposed wettability gradient and
droplet volume.Comment: 8 fig
Connections between Non-Rotating, Slowly Rotating, and Rapidly Rotating Turbulent Convection Transport Scalings
Buoyancy-driven convection is likely the dominant driver of turbulent motions
in the universe, and thus, is widely studied by physicists, engineers,
geophysicists and astrophysicists. Maybe unsurprisingly, these different
communities discuss the gross convective behaviors in different ways, often
without significant cross-talk existing between them. Here, we seek to draw
connections between these communities. We do so by carrying out a set of basic
scale estimations for how heat and fluid momentum transport should behave in
non-rotating, slowly rotating and rapidly rotating buoyancy-driven convective
environments. We find that slowly and rapidly rotating scalings can be
inter-related via one parameter, the so-called convective Rossby number \RoC,
a dissipation-free parameter measuring the importance of buoyancy driving
relative to rotation. Further, we map between non-flux-based and the
flux-based, buoyancy-driven scalings used by different groups. In doing so,
these scalings show that there are clean connections between the different
communities' approaches and that a number of the seemingly different scalings
are actually synonymous with one another.Comment: 15 pages, 3 figures, 2 Table
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