eta-meson photoproduction off protons and deuterons

We present a unitary and gauge-invariant model with coupled channels, which provides a consistent description of pion photoproduction off nucleons in the E$_{0+}$ channel and eta-meson photoproduction off protons and deuterons. An effective field theory with hadrons and photons is constructed, which includes non-resonant Born terms as well as the S$_{11}$(1535) and S$_{11}$(1650) baryon resonances. Due to the coupling between the channels, the production of eta-mesons is strongly affected by the S$_{11}$(1650) although its direct coupling to the $\eta$N channel is negligible. The rho- and omega-meson exchange terms are important for achieving a consistent description of both pion- and photon-induced reactions.Comment: 11 pages Latex, 4 Postscript Figure

Minimal Model for Sand Dunes

We propose a minimal model for aeolian sand dunes. It combines an analytical description of the turbulent wind velocity field above the dune with a continuum saltation model that allows for saturation transients in the sand flux. The model provides a qualitative understanding of important features of real dunes, such as their longitudinal shape and aspect ratio, the formation of a slip face, the breaking of scale invariance, and the existence of a minimum dune size.Comment: 4 pages, 4 figures, replaced with publishd versio

Extraction of the Ratio of the N^*(1535) Electromagnetic Helicity Amplitudes from Eta Photoproduction off Neutrons and Protons

Using the recent precise measurements of eta photopro- duction in proton and deuteron targets, we extract the ratio of the helicity amplitudes A^n_1/2 / A^p_1/2, for the excitation of N^*(1535), in the effective Lagrangian approach, It is fairly model-independent, free from the final-state interaction effects, and negative as predicted by the quark models. We stress the importance of polarization observables in further elucidation of the N^*(1520) photoexcitation amplitudes.Comment: 4 figures. It will be published in Phys. Lett.

Analysis of resonance multipoles from polarization observables in eta photoproduction

A combined analysis of new eta photoproduction data for total and differential cross sections, target asymmetry and photon asymmetry is presented. Using a few reasonable assumptions we perform the first model-independent analysis of the E0+, E2- and M2- eta photoproduction multipoles. Making use of the well-known A3/2 helicity amplitude of the D13(1520) state we extract its branching ratio to the eta-N channel, Gamma(eta,N)/Gamma = (0.08 +- 0.01)%. At higher energies, we show that the photon asymmetry is extremely sensitive to small multipoles that are excited by photons in the helicity 3/2 state. The new GRAAL photon asymmetry data at higher energy show a clear signal of the F15(1680) excitation which permits extracting an F15(1680)->eta,N branching ratio of (0.15 +0.35 -0.10)%.Comment: 14 pages of LATEX including 7 postscript figure

Wer bremst verliert - Antimon in Straßenrandböden

Seit dem weitreichenden Verbot von Asbest in den 1980er Jahren wurde verstärkt das Halbmetall Antimon (Sb) in Bremsbelägen von PKW und LKW verwendet. Im Zuge des Bremsvorganges wird dieses in Form von Feinstaub freigesetzt und straßennah in die Böden eingetragen. Grundsätzlich sind Antimoneinträge in Böden negativ zu bewerten, da das Halbmetall toxische Wirkungen hervorrufen kann. Um die räumliche Verteilung von Antimon und seinen Bindungsformen in Straßenrandböden zu untersuchen, wurden 5 parallele Transekte mit jeweils 7 Entfernungen und 4 Probentiefen entlang einer Kölner Kreisstraße (Verkehrsaufkommen ca. 9.600 Fahrzeuge pro Tag) beprobt. Neben einer allgemeinen physikochemischen Charakterisierung der Bodenproben wurden ihre königswasser-löslichen Antimongehalte bestimmt. Zusätzlich wurde an einem Transekt eine sequentielle Extraktion nach Wenzel et al. 2001 durchgeführt, um die Bindungsformen von Antimon zu ermitteln. Die Antimongehalte nahmen von bis zu 6,18 g kg–1 unmittelbar am Straßenrand bis auf 0,513 g kg–1 in 10 m Entfernung ab. Ebenfalls konnte eine deutliche Abnahme mit der Bodentiefe (0 bis 30 cm) festgestellt werden. Dieses Verteilungsmuster deutet auf den Verkehr als Antimoneintragsquelle hin. Als Hinweis auf einen durch den Bremsabrieb metallener Bremsscheiben dominierten Eintrag wurde die magnetische Suszeptibilität gemessen. Allerdings lieferte der Korrelationskoeffizient (Spearman) von Antimon gegenüber der magnetischen Suszeptibilität 0,423 (p = 0,023) nur einen eher schwachen Beleg. Die ursprünglich für Arsen entwickelte sequentielle Extraktion ließ sich reproduzierbar ebenfalls für Antimon anwenden. Anhand dieser konnten im Wesentlichen drei Trends der Bindungsformen erfasst werden: i) spezifisch gebundenes Antimon (Fraktion 2: 0,05 mol l–1 (NH4)H2P2O4) konnte lediglich innerhalb 1 m Entfernung zur Straße und mit der Bodentiefen abnehmenden Gehalten nachgewiesen werden, ii) der Anteil an schwachkristallinen Eisenoxiden gebundenem Antimon (Fraktion 3: 0,2 mol l–1 (NH4)2-Oxalatpuffer; pH 3,25) nahm signifikant mit steigender Entfernung zur Straße ab, während iii) die prozentualen Gehalte in den starkkristallinen Eisenoxiden (Fraktion 4: 0,2 mol l–1 (NH4)2-Oxalatpuffer + 0,1 mol l–1 Ascorbinsäure; pH 3,25) und in der Residualphase (Fraktion 5: Königswasser) zunahmen

Preservation of individuals’ privacy in shared COVID-19 related data

Preprint VersionThis paper provides insight into how restricted data can be incorporated in an open-be-default-by-design digital infrastructure for scientific data. We focus, in particular, on the ethical component of FAIRER (Findable, Accessible, Interoperable, Ethical, and Reproducible) data, and the pseudo-anonymization and anonymization of COVID-19 datasets to protect personally identifiable information (PII). First we consider the need for the customisation of the existing privacy preservation techniques in the context of rapid production, integration, sharing and analysis of COVID-19 data. Second, the methods for the pseudo-anonymization of direct identification variables are discussed. We also discuss different pseudo-IDs of the same person for multi-domain and multi-organization. Essentially, pseudo-anonymization and its encrypted domain specific IDs are used to successfully match data later, if required and permitted, as well as to restore the true ID (and authenticity) in individual cases of a patient's clarification.Third, we discuss application of statistical disclosure control (SDC) techniques to COVID-19 disease data. To assess and limit the risk of re-identification of individual persons in COVID-19 datasets (that are often enriched with other covariates like age, gender, nationality, etc.) to acceptable levels, the risk of successful re-identification by a combination of attribute values must be assessed and controlled. This is done using statistical disclosure control for anonymization of data. Lastly, we discuss the limitations of the proposed techniques and provide general guidelines on using disclosure risks to decide on appropriate modes for data sharing to preserve the privacy of the individuals in the datasets

Science PhD Career Preferences: Levels, Changes, and Advisor Encouragement

Even though academic research is often viewed as the preferred career path for PhD trained scientists, most U.S. graduates enter careers in industry, government, or “alternative careers.” There has been a growing concern that these career patterns reflect fundamental imbalances between the supply of scientists seeking academic positions and the availability of such positions. However, while government statistics provide insights into realized career transitions, there is little systematic data on scientists' career preferences and thus on the degree to which there is a mismatch between observed career paths and scientists' preferences. Moreover, we lack systematic evidence whether career preferences adjust over the course of the PhD training and to what extent advisors exacerbate imbalances by encouraging their students to pursue academic positions. Based on a national survey of PhD students at tier-one U.S. institutions, we provide insights into the career preferences of junior scientists across the life sciences, physics, and chemistry. We also show that the attractiveness of academic careers decreases significantly over the course of the PhD program, despite the fact that advisors strongly encourage academic careers over non-academic careers. Our data provide an empirical basis for common concerns regarding labor market imbalances. Our results also suggest the need for mechanisms that provide PhD applicants with information that allows them to carefully weigh the costs and benefits of pursuing a PhD, as well as for mechanisms that complement the job market advice advisors give to their current students

Corridors of barchan dunes: stability and size selection

Barchans are crescentic dunes propagating on a solid ground. They form dune fields in the shape of elongated corridors in which the size and spacing between dunes are rather well selected. We show that even very realistic models for solitary dunes do not reproduce these corridors. Instead, two instabilities take place. First, barchans receive a sand flux at their back proportional to their width while the sand escapes only from their horns. Large dunes proportionally capture more than they loose sand, while the situation is reversed for small ones: therefore, solitary dunes cannot remain in a steady state. Second, the propagation speed of dunes decreases with the size of the dune: this leads -- through the collision process -- to a coarsening of barchan fields. We show that these phenomena are not specific to the model, but result from general and robust mechanisms. The length scales needed for these instabilities to develop are derived and discussed. They turn out to be much smaller than the dune field length. As a conclusion, there should exist further - yet unknown - mechanisms regulating and selecting the size of dunes.Comment: 13 pages, 13 figures. New version resubmitted to Phys. Rev. E. Pictures of better quality available on reques

Pure Stationary States of Open Quantum Systems

Using Liouville space and superoperator formalism we consider pure stationary states of open and dissipative quantum systems. We discuss stationary states of open quantum systems, which coincide with stationary states of closed quantum systems. Open quantum systems with pure stationary states of linear oscillator are suggested. We consider stationary states for the Lindblad equation. We discuss bifurcations of pure stationary states for open quantum systems which are quantum analogs of classical dynamical bifurcations.Comment: 7p., REVTeX