820 research outputs found
Could the Hercules satellite be a stellar stream in the Milky Way halo?
We investigate the possibility that Hercules, a recently discovered Milky Way
(MW) satellite, is a stellar stream in the process of formation. This
hypothesis is motivated by Hercules' highly elongated shape as well as the
measurement of a tentative radial velocity gradient along its body. The
application of simple analytical techniques on radial velocity data of its
member stars provides tight constraints on the tangential velocity of the
system (v_t = -16^{+6}_{-22} km/s, relative to the Galactic Standard of Rest).
Combining this with its large receding velocity (145 km/s) and distance (138
kpc) yields an orbit that would have taken Hercules to within 6^{+9}_{-2} kpc
of the Galactic centre approximately 0.6 Gyr ago. This very small
perigalacticon can naturally explain the violent tidal destruction of the dwarf
galaxy in the MW's gravitational potential, inducing its transformation into a
stellar stream.Comment: Conference proceedings of "A Universe of dwarf galaxies:
Observations, Theories, Simulations" held in Lyon, France (June 14-18, 2010
Transhumanism: at the Rim of Science: Report from the Conference "The Posthuman: Differences, Embodiments, Performativity", the 5th Beyond Humanism Conference. Rome, italy, September 11-14, 2013
Are the Ultra-Faint Dwarf Galaxies Just Cusps?
We develop a technique to investigate the possibility that some of the
recently discovered ultra-faint dwarf satellites of the Milky Way might be cusp
caustics rather than gravitationally self-bound systems. Such cusps can form
when a stream of stars folds, creating a region where the projected 2-D surface
density is enhanced. In this work, we construct a Poisson maximum likelihood
test to compare the cusp and exponential models of any substructure on an equal
footing. We apply the test to the Hercules dwarf (d ~ 113 kpc, M_V ~ -6.2, e ~
0.67). The flattened exponential model is strongly favored over the cusp model
in the case of Hercules, ruling out at high confidence that Hercules is a cusp
catastrophe. This test can be applied to any of the Milky Way dwarfs, and more
generally to the entire stellar halo population, to search for the cusp
catastrophes that might be expected in an accreted stellar halo.Comment: Accepted for publication in ApJ Letters. Minor revisions from version
Prometheus' Legacy: Responsibility and Technology
A prominent view in contemporary philosophy of technology suggests that more technology implies more possibilities and, therefore, more responsibilities. Consequently, the question ‘What technology?’ is discussed primarily on the backdrop of assessing, assigning, and avoiding technology-borne culpability. The view is reminiscent of the Olympian gods’ vengeful and harsh reaction to Prometheus’ play with fire. However, the Olympian view leaves unexplained how technologies increase possibilities. Also, if Olympians are right, endorsing their view will at some point demand putting a halt to technological development, which is absurd. Hence, we defend an alternative perspective on the relationship between responsibility and technology: Our Promethean view recognises technology as the result of collective, forward-looking responsibility and not only as a cause thereof. Several examples illustrate that technologies are not always the right means to tackle human vulnerabilities. Together, these arguments prompt a change in focus from the question ‘What technology?’ to ‘Why technology?
Kondo physics in tunable semiconductor nanowire quantum dots
We have observed the Kondo effect in strongly coupled semiconducting nanowire
quantum dots. The devices are made from indium arsenide nanowires, grown by
molecular beam epitaxy, and contacted by titanium leads. The device
transparency can be tuned by changing the potential on a gate electrode, and
for increasing transparencies the effects dominating the transport changes from
Coulomb Blockade to Universal Conductance Fluctuations with Kondo physics
appearing in the intermediate region.Comment: 4 pages, 4 figure
Shadow epitaxy for in-situ growth of generic semiconductor/superconductor devices
Uniform, defect-free crystal interfaces and surfaces are crucial ingredients
for realizing high-performance nanoscale devices. A pertinent example is that
advances in gate-tunable and topological superconductivity using
semiconductor/superconductor electronic devices are currently built on the hard
proximity-induced superconducting gap obtained from epitaxial indium
arsenide/aluminium heterostructures. Fabrication of devices requires selective
etch processes; these exist only for InAs/Al hybrids, precluding the use of
other, potentially superior material combinations. We present a crystal growth
platform -- based on three-dimensional structuring of growth substrates --
which enables synthesis of semiconductor nanowire hybrids with in-situ
patterned superconductor shells. This platform eliminates the need for etching,
thereby enabling full freedom in choice of hybrid constituents. We realise and
characterise all the most frequently used architectures in superconducting
hybrid devices, finding increased yield and electrostatic stability compared to
etched devices, along with evidence of ballistic superconductivity. In addition
to aluminium, we present hybrid devices based on tantalum, niobium and
vanadium.
This is the submitted version of the manuscript. The accepted, peer reviewed
version is available from Advanced Materials:
http://doi.org/10.1002/adma.201908411
Previous title: Shadow lithography for in-situ growth of generic
semiconductor/superconductor device
Fornærmelsens retorikk En studie av Gregor av Nazianz taler mot keiser Julian den frafalne
Dette en er bearbeidet utgave av oppgaven. Rettelser gjelder skrivefeil (august 2007
Bioethik – Normenbegründung zwischen Naturwissenschaft und Menschenbild: Bericht von der Abschlusstagung des Graduiertenkollegs „Bioethik“ am Internationalen Zentrum für Ethik in den Wissenschaften der Universität Tübingen. Tübingen, 7.–8. Februar 2013
Partizipation in Politik und Wissenschaft und ihre Schwierigkeiten: Bericht zur Tagung „Partizipationsforschung und Partizipationsverfahren in der sozialwissenschaftlichen Klimaforschung“. Müncheberg, 25.–26. April 2012
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