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

Hydrological long-term dry and wet periods in the Xijiang River basin, South China

In this study, hydrological long-term dry and wet periods are analyzed for the Xijiang River basin in South China. Daily precipitation data of 118 stations and data on daily discharge at Gaoyao hydrological station at the mouth of the Xijiang River for the period 1961–2007 are used. At a 24-month timescale, the standardized precipitation index (SPI-24) for the six sub-basins of the Xijiang River and the standardized discharge index (SDI-24) for Gaoyao station are applied. The monthly values of the SPI-24 averaged for the Xijiang River basin correlate highly with the monthly values of the SDI-24. Distinct long-term dry and wet sequences can be detected. <br><br> The principal component analysis is applied and shows spatial disparities in dry and wet periods for the six sub-basins. The correlation between the SPI-24 of the six sub-basins and the first principal component score shows that 67% of the variability within the sub-basins can be explained by dry and wet periods in the east of the Xijiang River basin. The spatial dipole conditions (second and third principal component) explain spatiotemporal disparities in the variability of dry and wet periods. All sub-basins contribute to hydrological dry periods, while mainly the northeastern sub-basins cause wet periods in the Xijiang River. We can also conclude that long-term dry events are larger in spatial extent and cover all sub-basins while long-term wet events are regional phenomena. <br><br> A spectral analysis is applied for the SPI-24 and the SDI-24. The results show significant peaks in periodicities of 11–14.7 yr, 2.8 yr, 3.4–3.7 yr, and 6.3–7.3 yr. The same periodic cycles can be found in the SPI-24 of the six sub-basins but with some variability in the mean magnitude. A wavelet analysis shows that significant periodicities have been stable over time since the 1980s. Extrapolations of the reconstructed SPI-24 and SDI-24 represent the continuation of observed significant periodicities at given magnitudes until 2030. The projected hydrological long-term dry and wet periods can be used for planning purposes in water resources management. The applied methodologies prove to be able to identify spatial disparities, and to detect significant periodicities in hydrological long-term dry and wet periods in the Xijiang River basin

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

Land use dynamics in favorable and unfavorable areas of southwest Germany

Since the “Neolithic Revolution” and the beginning of agriculture in central Europe about 7.500 a ago human influence on the environment is increasing. Human activities led to quasi-natural relief formation and created in many places a cultural landscape. Colluvial deposits are the correlate sediments of human induced soil erosion on slopes and depict an excellent archive for land use and landscape history. The present study combines pedological, archaeological and palynological analyses and knowledge with AMS 14C and luminescence datings to build up a stratigraphy of colluvial deposits, thereby allowing the reconstruction of past land use dynamics southwest Germany. Compared with Black Forest and the Swabian Jura, the Baar is a favorable area for agricultural land use, where seven main phases of colluvial deposition could be detected. Increased colluviation, and thus land use intensity, took place during the younger Neolithic, the early to middle Bronze Age, the Iron Age, the Roman Empire, and in three phases from the High Middle Ages onwards. The southeastern Black Forest low mountain range is an unfavorable area characterized by low temperatures, high precipitation and steep slopes. Nevertheless, human influence dates back to the Neolithic. Minor colluvial deposition phases were detected before the Middle Ages and increased formation of colluvial deposits during the High Middle Ages and the Modern Times. The colluvial stratigraphy shows an intense land use of the Black Forest area from the Middle Ages onwards. In the western Swabian Jura the pattern of colluvial deposition indicates land use from the Bronze Age onwards and for one site even since the Neolithic. The different land use dynamics in the Baar area compared to the Black Forest and Swabian Jura will be discussed against the paleoenvironmental conditions reconstructed from different archives. It is to analyze whether climate was the main determining factor for the settlement pattern in time and space or if there were other factors responsible, such as: different human motivations to settle the land depending on natural or cultural resources, conflicts in neighboring areas or trading relations. Feedback mechanisms of the anthropogenically modified landscape might also interact and determine settlement and land use dynamics

Electromagnetic Couplings of Nucleon Resonances

An effective Lagrangian calculation of pion photoproduction including all nucleon resonances up to $\sqrt s = 1.7$ GeV is presented. We compare our results to recent calculations and show the influence of different width parametrizations and offshell cutoffs on the photoproduction multipoles. We determine the electromagnetic couplings of the resonances from a new fit to the multipole data.Comment: 20 pages, latex, 6 figures. Misprints corrected, text & 3 figures adde

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