3,363 research outputs found
Viscous spreading of an inertial wave beam in a rotating fluid
We report experimental measurements of inertial waves generated by an
oscillating cylinder in a rotating fluid. The two-dimensional wave takes place
in a stationary cross-shaped wavepacket. Velocity and vorticity fields in a
vertical plane normal to the wavemaker are measured by a corotating Particule
Image Velocimetry system. The viscous spreading of the wave beam and the
associated decay of the velocity and vorticity envelopes are characterized.
They are found in good agreement with the similarity solution of a linear
viscous theory, derived under a quasi-parallel assumption similar to the
classical analysis of Thomas and Stevenson [J. Fluid Mech. 54 (3), 495-506
(1972)] for internal waves
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
Improving the Segmentation of Anatomical Structures in Chest Radiographs using U-Net with an ImageNet Pre-trained Encoder
Accurate segmentation of anatomical structures in chest radiographs is
essential for many computer-aided diagnosis tasks. In this paper we investigate
the latest fully-convolutional architectures for the task of multi-class
segmentation of the lungs field, heart and clavicles in a chest radiograph. In
addition, we explore the influence of using different loss functions in the
training process of a neural network for semantic segmentation. We evaluate all
models on a common benchmark of 247 X-ray images from the JSRT database and
ground-truth segmentation masks from the SCR dataset. Our best performing
architecture, is a modified U-Net that benefits from pre-trained encoder
weights. This model outperformed the current state-of-the-art methods tested on
the same benchmark, with Jaccard overlap scores of 96.1% for lung fields, 90.6%
for heart and 85.5% for clavicles.Comment: Presented at the First International Workshop on Thoracic Image
Analysis (TIA), MICCAI 201
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
Processing and Transmission of Information
Contains reports on four research projects.National Aeronautics and Space Administration (Grant NsG-334)Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E
Coriolis force in Geophysics: an elementary introduction and examples
We show how Geophysics may illustrate and thus improve classical Mechanics
lectures concerning the study of Coriolis force effects. We are then interested
in atmospheric as well as oceanic phenomena we are familiar with, and are for
that reason of pedagogical and practical interest. Our aim is to model them in
a very simple way to bring out the physical phenomena that are involved.Comment: Accepted for publication in European Journal of Physic
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
The decay of turbulence in rotating flows
We present a parametric space study of the decay of turbulence in rotating
flows combining direct numerical simulations, large eddy simulations, and
phenomenological theory. Several cases are considered: (1) the effect of
varying the characteristic scale of the initial conditions when compared with
the size of the box, to mimic "bounded" and "unbounded" flows; (2) the effect
of helicity (correlation between the velocity and vorticity); (3) the effect of
Rossby and Reynolds numbers; and (4) the effect of anisotropy in the initial
conditions. Initial conditions include the Taylor-Green vortex, the
Arn'old-Beltrami-Childress flow, and random flows with large-scale energy
spectrum proportional to . The decay laws obtained in the simulations for
the energy, helicity, and enstrophy in each case can be explained with
phenomenological arguments that separate the decay of two-dimensional from
three-dimensional modes, and that take into account the role of helicity and
rotation in slowing down the energy decay. The time evolution of the energy
spectrum and development of anisotropies in the simulations are also discussed.
Finally, the effect of rotation and helicity in the skewness and kurtosis of
the flow is considered.Comment: Sections reordered to address comments by referee
Enhanced immunogenicity of pneumococcal surface adhesin A (PsaA) in mice via fusion to recombinant human B lymphocyte stimulator (BLyS)
A stealth health approach to dietary fibre
Average dietary fibre intakes have increased little in the past twenty years in many countries, including the USA1. Multi-million-dollar campaigns promoting fruits, vegetables, whole grains and other foods high in fibre have delivered only small changes in diets2, and consumers have not changed from traditional staples to whole-grain options3. UK millers report that consumption of whole-wheat bread has actually declined over the past decade (P. Shewry, personal communication). In the US, white flour, which is lower in fibre than whole-wheat flour, accounts for nearly 40% of the fibre intake4. We believe that as motivating consumers to change food choices has proven difficult, changing food itself — a so-called stealth health approach — could be a useful strategy to increase fibre in the foods people choose to eat
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