Radio detection of cosmic rays in the Pierre Auger Observatory

In small-scale experiments such as CODALEMA and LOPES, radio detection of cosmic rays has demonstrated its potential as a technique for cosmic ray measurements up to the highest energies. Radio detection promises measurements with high duty-cycle, allows a direction reconstruction with very good angular resolution, and provides complementary information on energy and nature of the cosmic ray primaries with respect to particle detectors at ground and fluorescence telescopes. Within the Pierre Auger Observatory, we tackle the technological and scientific challenges for an application of the radio detection technique on large scales. Here, we report on the results obtained so far using the Southern Auger site and the plans for an engineering array of radio detectors covering an area of ~20 km^2.Comment: 4 pages, Proceedings of the 11th Pisa Meeting on Advanced Detector

REAS3: Monte Carlo simulations of radio emission from cosmic ray air showers using an "end-point" formalism

In recent years, the freely available Monte Carlo code REAS for modelling radio emission from cosmic ray air showers has evolved to include the full complexity of air shower physics. However, it turned out that in REAS2 and all other time-domain models which calculate the radio emission by superposing the radiation of the single air shower electrons and positrons, the calculation of the emission contributions was not fully consistent. In this article, we present a revised implementation in REAS3, which incorporates the missing radio emission due to the variation of the number of charged particles during the air shower evolution using an "end-point formalism". With the inclusion of these emission contributions, the structure of the simulated radio pulses changes from unipolar to bipolar, and the azimuthal emission pattern becomes nearly symmetric. Remaining asymmetries can be explained by radio emission due to the variation of the net charge excess in air showers, which is automatically taken into account in the new implementation. REAS3 constitutes the first self-consistent time-domain implementation based on single particle emission taking the full complexity of air shower physics into account, and is freely available for all interested users.Comment: 18 pages, 13 figures accepted by Astroparticle Physics (2010

Deconstructing Instructions in the Art Academy

Drawing as a manual discipline was long taught in the West according to specific ‘academic’ principles, culminating institutionally in the art academies of the 19th century. This educational process was mediated by visual images and three-dimensional objects, and relied on copying as a means to acquire manual skill along with a ‘vocabulary’ of idealized forms. During the twentieth century the roles, values and practices of art changed profoundly, and consequently methods of artistic education changed as well. As symbols of a tradition overcome, many (modernizing) art academies, many instruction books, plaster casts of sculptures, and écorchés were either discarded or consigned to storage rooms and libraries. In one such art school, Minerva Art Academy in Groningen (the Netherlands), a didactic experiment was undertaken in the spring semester of 2019. Art historian Vanessa van ‘t Hoogt and artist Henrike Scholten designed and taught an elective course that investigates and reflects critically on the art academy’s history. Using a historically informed, experimental and practice-based pedagogic approach, the 16-week course challenged 23 undergraduate art students to engage with the material and didactic heritage of the art academy. Not in a nostalgic or neo-academic fashion, but on their own terms as contemporary art students. This project report describes some aspects of the authors’ didactic approach during the course. As an investigative and sometimes performative project, it toes the line between educational action research and object-based teaching. The aim of the course was to provide art students with new tools to engage with the history of their discipline and its processes of skill acquisition in a reflective and generative way

Single-Shot Electron Diffraction using a Cold Atom Electron Source

Cold atom electron sources are a promising alternative to traditional photocathode sources for use in ultrafast electron diffraction due to greatly reduced electron temperature at creation, and the potential for a corresponding increase in brightness. Here we demonstrate single-shot, nanosecond electron diffraction from monocrystalline gold using cold electron bunches generated in a cold atom electron source. The diffraction patterns have sufficient signal to allow registration of multiple single-shot images, generating an averaged image with significantly higher signal-to-noise ratio than obtained with unregistered averaging. Reflection high-energy electron diffraction (RHEED) was also demonstrated, showing that cold atom electron sources may be useful in resolving nanosecond dynamics of nanometre scale near-surface structures.Comment: This is an author-created, un-copyedited version of an article published in Journal of Physics B: Atomic, Molecular and Optical Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/0953-4075/48/21/21400

Comparing phenomenological recipes with a microscopic model for the electric amplitude in strangeness photoproduction

Corrections to the Born approximation in photo-induced strangeness production off a proton are calculated in a semi-realistic microscopic model. The vertex corrections and internal contributions to the amplitude of the $\gamma p \to K^+ \Lambda$ reaction are included on the one-loop level. Different gauge-invariant phenomenological prescriptions for the modification of the Born contribution via the introduction of form factors and contact terms are discussed. In particular, it is shown that the popular minimal-substitution method of Ohta corresponds to a special limit of the more realistic approach.Comment: 10 pages, 6 figures in the tex

Microfabricated optofluidic ring resonator structures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98683/1/ApplPhysLett_99_141108.pd