29,740 research outputs found
The interstellar cloud surrounding the Sun: a new perspective
Aims: We offer a new, simpler picture of the local interstellar medium, made
of a single continuous cloud enveloping the Sun. This new outlook enables the
description of a diffuse cloud from within and brings to light some unexpected
properties. Methods: We re-examine the kinematics and abundances of the local
interstellar gas, as revealed by the published results for the ultraviolet
absorption lines of MgII, FeII, and HI. Results: In contrast to previous
representations, our new picture of the local interstellar medium consists of a
single, monolithic cloud that surrounds the Sun in all directions and accounts
for most of the matter present in the first 50 parsecs around the Sun. The
cloud fills the space around us out to about 9 pc in most directions, although
its boundary is very irregular with possibly a few extensions up to 20 pc. The
cloud does not behave like a rigid body: gas within the cloud is being
differentially decelerated in the direction of motion, and the cloud is
expanding in directions perpendicular to this flow, much like a squashed
balloon. Average HI volume densities inside the cloud vary between 0.03 and 0.1
cm-3 over different directions. Metals appear to be significantly depleted onto
grains, and there is a steady increase in depletion from the rear of the cloud
to the apex of motion. There is no evidence that changes in the ionizing
radiation influence the apparent abundances. Secondary absorption components
are detected in 60% of the sight lines. Almost all of them appear to be
interior to the volume occupied by the main cloud. Half of the sight lines
exhibit a secondary component moving at about -7.2 km/s with respect to the
main component, which may be the signature of a shock propagating toward the
cloud's interior.Comment: Accepted for publication in Astronomy & Astrophysic
Analytical solution of the tooling/workpiece contact interface shape during a flow forming operation
Flow forming involves complicated tooling/workpiece interactions. Purely
analytical models of the tool contact area are difficult to formulate,
resulting in numerical approaches that are case-specific. Provided are the
details of an analytical model that describes the steady-state
tooling/workpiece contact area allowing for easy modification of the dominant
geometric variables. The assumptions made in formulating this analytical model
are validated with experimental results attained from physical modelling. The
analysis procedure can be extended to other rotary forming operations such as
metal spinning, shear forming, thread rolling and crankshaft fillet rolling.Comment: 28 pages, 11 figure
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Selective Laser Sintering of Passive Dynamic Ankle-Foot Orthoses
Passive dynamic ankle-foot orthoses (AFO’s) are used to improve gait performance in
those with various neuromuscular disorders. An important design characteristic of passive
dynamic AFOs is the storage and release of elastic energy within its structure to help satisfy the
energetic demands of walking. Thus, minimizing energy dissipation through internal friction is a
fundamental criterion for selecting the appropriate AFO material. This study compared the
mechanical damping of a carbon-fiber AFO to three geometrically identical AFO’s fabricated
using selective laser sintering with different materials. Mechanical damping characteristics
ranked the materials as Nylon 11 (best), followed by DuraformTM PA and DuraformTM GF
(worst).Mechanical Engineerin
Nonrigid reconstruction of 3D breast surfaces with a low-cost RGBD camera for surgical planning and aesthetic evaluation
Accounting for 26% of all new cancer cases worldwide, breast cancer remains
the most common form of cancer in women. Although early breast cancer has a
favourable long-term prognosis, roughly a third of patients suffer from a
suboptimal aesthetic outcome despite breast conserving cancer treatment.
Clinical-quality 3D modelling of the breast surface therefore assumes an
increasingly important role in advancing treatment planning, prediction and
evaluation of breast cosmesis. Yet, existing 3D torso scanners are expensive
and either infrastructure-heavy or subject to motion artefacts. In this paper
we employ a single consumer-grade RGBD camera with an ICP-based registration
approach to jointly align all points from a sequence of depth images
non-rigidly. Subtle body deformation due to postural sway and respiration is
successfully mitigated leading to a higher geometric accuracy through
regularised locally affine transformations. We present results from 6 clinical
cases where our method compares well with the gold standard and outperforms a
previous approach. We show that our method produces better reconstructions
qualitatively by visual assessment and quantitatively by consistently obtaining
lower landmark error scores and yielding more accurate breast volume estimates
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