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

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

Fluctuations of sensorimotor processing in migraine: A controlled longitudinal study of beta event related desynchronization

Background: The migraine brain seems to undergo cyclic fluctuations of sensory processing. For instance, during the preictal phase, migraineurs experience symptoms and signs of altered pain perception as well as other well-known premonitory CNS-symptoms. In the present study we measured EEG-activation to non-painful motor and sensorimotor tasks in the different phases of the migraine cycle by longitudinal measurements of beta event related desynchronization (beta-ERD). Methods: We recorded electroencephalography (EEG) of 41 migraine patients and 31 healthy controls. Each subject underwent three EEG recordings on three different days with classification of each EEG recording according to the actual migraine phase. During each recording, subjects performed one motor and one sensorimotor task with the flexion-extension movement of the right wrist. Results: Migraine patients had significantly increased beta-ERD and higher baseline beta power at the contralateral C3 electrode overlying the primary sensorimotor cortex in the preictal phase compared to the interictal phase. We found no significant differences in beta-ERD or baseline beta power between interictal migraineurs and controls. Conclusion: Increased preictal baseline beta activity may reflect a decrease in pre-activation in the sensorimotor cortex. Altered pre-activation may lead to changes in thresholds for inhibitory responses and increased beta-ERD response, possibly reflecting a generally increased preictal cortical responsivity in migraine. Cyclic fluctuations in the activity of second- and third-order afferent somatosensory neurons, and their associated cortical and/or thalamic interneurons, may accordingly also be a central part of the migraine pathophysiology.publishedVersio

The enigmatic pair of dwarf galaxies Leo IV and Leo V: coincidence or common origin?

We have obtained deep photometry in two 1x1 degree fields covering the close pair of dwarf spheroidal galaxies (dSph) Leo IV and Leo V and part of the area in between. We find that both systems are significantly larger than indicated by previous measurements based on shallower data and also significantly elongated. With half-light radii of r_h=4'.6 +- 0'.8 (206 +- 36 pc) and r_h=2'.6 +- 0'.6 (133 +- 31 pc), respectively, they are now well within the physical size bracket of typical Milky Way dSph satellites. Their ellipticities of epsilon ~0.5 are shared by many faint (M_V>-8) Milky Way dSphs. The large spatial extent of our survey allows us to search for extra-tidal features with unprecedented sensitivity. The spatial distribution of candidate red giant branch and horizontal branch stars is found to be non-uniform at the ~3 sigma level. This substructure is aligned along the direction connecting the two systems, indicative of a possible `bridge' of extra-tidal material. Fitting the stellar distribution with a linear Gaussian model yields a significance of 4 sigma for this overdensity, a most likely FWHM of ~16 arcmin and a central surface brightness of ~32 mag arcsec^{-2}. We investigate different scenarios to explain the close proximity of Leo IV and Leo V and the possible tidal bridge between them. Orbit calculations demonstrate that they are unlikely to be remnants of a single disrupted progenitor, while a comparison with cosmological simulations shows that a chance collision between unrelated subhalos is negligibly small. Leo IV and Leo V could, however, be a bound `tumbling pair' if their combined mass exceeds 8 +- 4 x 10^9 M_sun. The scenario of an internally interacting pair appears to be the most viable explanation for this close celestial companionship. (abridged)Comment: 9 pages, 8 figures, small number of minor textual changes, accepted for publication in Astrophysical Journa