429 research outputs found
A preliminary characterization of applied-field MPD thruster plumes
Electric probes, quantitative imaging, and emission spectroscopy were used to study the plume characteristics of applied field magnetohydrodynamic thrusters. The measurements showed that the applied magnetic field plays the dominant role in establishing the plume structure, followed in importance by the cathode geometry and propellant. The anode radius had no measurable impact on the plume characteristics. For all cases studied the plume was highly ionized, though spectral lines of neutral species were always present. Centerline electron densities and temperatures ranged from 2 times 10 (exp 18) to 8 times 10 (exp 18) m(exp -3) and from 7500 to 20,000 K, respectively. The plume was strongly confined by the magnetic field, with radial density gradients increasing monotonically with applied field strength. Plasma potential measurements show a strong effect of the magnetic field on the electrical conductivity and indicate the presence of radial current conduction in the plume
A Multi-wavelength Study of the Sunyaev-Zel'dovich Effect in the Triple-Merger Cluster MACS J0717.5+3745 with MUSTANG and Bolocam
We present 90, 140, and 268GHz sub-arcminute resolution imaging of the
Sunyaev-Zel'dovich effect (SZE) in MACSJ0717.5+3745. Our 90GHz SZE data result
in a sensitive, 34uJy/bm map at 13" resolution using MUSTANG. Our 140 and
268GHz SZE imaging, with resolutions of 58" and 31" and sensitivities of 1.8
and 3.3mJy/beam respectively, was obtained using Bolocam. We compare these maps
to a 2-dimensional pressure map derived from Chandra X-ray observations. Our
MUSTANG data confirm previous indications from Chandra of a pressure
enhancement due to shock-heated, >20keV gas immediately adjacent to extended
radio emission seen in low-frequency radio maps. The MUSTANG data also detect
pressure substructure that is not well-constrained by the X-ray data in the
remnant core of a merging subcluster. We find that the small-scale pressure
enhancements in the MUSTANG data amount to ~2% of the total pressure measured
in the 140GHz Bolocam observations. The X-ray template also fails on larger
scales to accurately describe the Bolocam data, particularly at the location of
a subcluster known to have a high line of sight optical velocity (~3200km/s).
Our Bolocam data are adequately described when we add an additional component -
not described by a thermal SZE spectrum - coincident with this subcluster.
Using flux densities extracted from our model fits, and marginalizing over the
temperature constraints for the region, we fit a thermal+kinetic SZE spectrum
to our data and find the subcluster has a best-fit line of sight proper
velocity of 3600+3440/-2160km/s. This agrees with the optical velocity
estimates for the subcluster. The probability of velocity<0 given our
measurements is 2.1%. Repeating this analysis using flux densities measured
non-parametrically results in a 3.4% probability of a velocity<=0. We note that
this tantalizing result for the kinetic SZE is on resolved, subcluster scales.Comment: 10 Figures, 18 pages. this version corrects issues with the previous
arXiv versio
Fabrication and Assessment of 3D Printed Anatomical Models of the Lower Limb for Anatomical Teaching and Femoral Vessel Access Training in Medicine
For centuries, cadaveric dissection has been the touchstone of anatomy education. It offers a medical student intimate access to his or her first patient. In contrast to idealized artisan anatomical models, it presents the natural variation of anatomy in fine detail. However, a new teaching construct has appeared recently in which artificial cadavers are manufactured through three-dimensional (3D) printing of patient specific radiological data sets. In this article, a simple powder based printer is made more versatile to manufacture hard bones, silicone muscles and perfusable blood vessels. The approach involves blending modern approaches (3D printing) with more ancient ones (casting and lost-wax techniques). These anatomically accurate models can augment the approach to anatomy teaching from dissection to synthesis of 3D-printed parts held together with embedded rare earth magnets. Vascular simulation is possible through application of pumps and artificial blood. The resulting arteries and veins can be cannulated and imaged with Doppler ultrasound. In some respects, 3D-printed anatomy is superior to older teaching methods because the parts are cheap, scalable, they can cover the entire age span, they can be both dissected and reassembled and the data files can be printed anywhere in the world and mass produced. Anatomical diversity can be collated as a digital repository and reprinted rather than waiting for the rare variant to appear in the dissection room. It is predicted that 3D printing will revolutionize anatomy when poly-material printing is perfected in the early 21st century. (C) 2015 American Association of Anatomists
Fabrication and Assessment of 3D Printed Anatomical Models of the Lower Limb for Anatomical Teaching and Femoral Vessel Access Training in Medicine
For centuries, cadaveric dissection has been the touchstone of anatomy education. It offers a medical student intimate access to his or her first patient. In contrast to idealized artisan anatomical models, it presents the natural variation of anatomy in fine detail. However, a new teaching construct has appeared recently in which artificial cadavers are manufactured through three-dimensional (3D) printing of patient specific radiological data sets. In this article, a simple powder based printer is made more versatile to manufacture hard bones, silicone muscles and perfusable blood vessels. The approach involves blending modern approaches (3D printing) with more ancient ones (casting and lost-wax techniques). These anatomically accurate models can augment the approach to anatomy teaching from dissection to synthesis of 3D-printed parts held together with embedded rare earth magnets. Vascular simulation is possible through application of pumps and artificial blood. The resulting arteries and veins can be cannulated and imaged with Doppler ultrasound. In some respects, 3D-printed anatomy is superior to older teaching methods because the parts are cheap, scalable, they can cover the entire age span, they can be both dissected and reassembled and the data files can be printed anywhere in the world and mass produced. Anatomical diversity can be collated as a digital repository and reprinted rather than waiting for the rare variant to appear in the dissection room. It is predicted that 3D printing will revolutionize anatomy when poly-material printing is perfected in the early 21st century. (C) 2015 American Association of Anatomists
Micro-mechanical testing of transition metal (oxy)nitride coatings
Transition metal (oxy)nitride coatings are used in polymer forming operations for a combination of outstanding wear resistance and chemical compatibility with the polymer materials. Varying the chemical composition and deposition parameters for the coatings will optimise mechanical properties by a combination of chemistry and microstructural optimisation. By developing a representative model for these materials, these materials can be rapidly and efficiently prototyped and improved. However, as both chemistry and microstructure play a role in the material properties, both of these variables must be taken account of in this model. This work demonstrates the first steps in linking quantum-mechanics, micro-mechanics, and meso-scale finite element models together in order to fully understand the behaviour of these coatings.
Please click Additional Files below to see the full abstract
CARMA Measurements of the Sunyaev-Zel'dovich Effect in RXJ1347.5-1145
We demonstrate the Sunyaev-Zel'dovich (SZ) effect imaging capabilities of the
Combined Array for Research in Millimeter-wave Astronomy (CARMA) by presenting
an SZ map of the galaxy cluster RXJ1347.5-1145. By combining data from multiple
CARMA bands and configurations, we are able to capture the structure of this
cluster over a wide range of angular scales, from its bulk properties to its
core morphology. We find that roughly 9% of this cluster's thermal energy is
associated with sub-arcminute-scale structure imparted by a merger,
illustrating the value of high-resolution SZ measurements for pursuing cluster
astrophysics and for understanding the scatter in SZ scaling relations. We also
find that the cluster's SZ signal is lower in amplitude than suggested by a
spherically-symmetric model derived from X-ray data, consistent with
compression along the line of sight relative to the plane of the sky. Finally,
we discuss the impact of upgrades currently in progress that will further
enhance CARMA's power as an SZ imaging instrument.Comment: 8 pages, 6 figure
On the frequency, intensity and duration of starburst episodes triggered by galaxy interactions and mergers
We investigate the intensity enhancement and the duration of starburst
episodes, triggered by major galaxy interactions and mergers. To this aim, we
analyze two large statistical datasets of numerical simulations. These have
been obtained using two independent and different numerical techniques to model
baryonic and dark matter evolution, that are extensively compared for the first
time. One is a Tree-SPH code, the other one is a grid-based N-body
sticky-particles code. We show that, at low redshift, galaxy interactions and
mergers in general trigger only moderate star formation enhancements. Strong
starbursts where the star formation rate is increased by a factor larger than 5
are rare and found only in about 15% of major galaxy interactions and mergers.
Merger-driven starbursts are also rather short-lived, with a typical duration
of the activity of a few 10^8 yr. These conclusions are found to be robust,
independent from the numerical techniques and star formation models. At higher
redshifts where galaxies contain more gas, gas inflow-induced starbursts are
neither stronger neither longer than their local counterparts. In turn, the
formation of massive gas clumps, results of local Jeans instability that can
occur spontaneously in gas-rich disks or be indirectly favored by galaxy
interactions, could play a more important role in determining the duration and
intensity of star formation episodes.Comment: 22 pages, 28 figures, A&A accepted. High resolution version available
at http://aramis.obspm.fr/~paola/SFR_frequency
Reconfigurable quantum metamaterials
By coupling controllable quantum systems into larger structures we introduce
the concept of a quantum metamaterial. Conventional meta-materials represent
one of the most important frontiers in optical design, with applications in
diverse fields ranging from medicine to aerospace. Up until now however,
metamaterials have themselves been classical structures and interact only with
the classical properties of light. Here we describe a class of dynamic
metamaterials, based on the quantum properties of coupled atom-cavity arrays,
which are intrinsically lossless, reconfigurable, and operate fundamentally at
the quantum level. We show how this new class of metamaterial could be used to
create a reconfigurable quantum superlens possessing a negative index gradient
for single photon imaging. With the inherent features of quantum superposition
and entanglement of metamaterial properties, this new class of dynamic quantum
metamaterial, opens a new vista for quantum science and technology.Comment: 16 pages, 8 figure
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