Catastrophe Bonds: An Interview with Oliver Ressler

An Interview with Brandon Bauer and Oliver Ressler on the occasion of his exhibition at St. Norbert College and the University of Wisconsin - Green Bay: Catastrophe Bonds , the first survey of Oliver Ressler‘s work in the United States. The exhibition focuses on forms of grassroots democracy as well as economic and political alternatives to the existing state of global affairs. This interview was published in the book that accompanied the exhibition.https://digitalcommons.snc.edu/faculty_staff_works/1010/thumbnail.jp

Structure-function relationship of Strong Metal-Support Interaction studied on supported Pd reference catalysts

Transition metal oxide supported, nano-scaled noble metal catalysts are known to show a variety of surface modifications when they are being reduced at increasing temperatures. Such processes involve for example (surface) alloying and the formation of partially reduced oxidic support overlayers that are both induced by the so-called strong metal-support interaction (SMSI). The present work investigated a series of oxide supported Palladium powder catalysts with a loading variation between 1-5 wt.-% on their structure-function relationship after reduction in different media and at different temperatures to create a reference system and explore the nature of SMSI. Hereby surface and bulk sensitive techniques like XPS, chemisorption, TEM, DRIFTS or XRD were applied to study the influence of electronic and structural modifications on the activity in catalytic oxidation of carbon monoxide which served as the main test reaction and was conducted at ambient pressure. The catalysts were synthesized reproducibly by a controlled co-precipitation approach and by impregnation. The investigated Pd/iron oxide system shows palladium surface decoration at comparably low reduction temperatures. The surface cover was found to be volatile in oxygen containing atmosphere and formed reversibly. Dependent on the Pd particle size it increases the CO oxidation activity. Alloy formation occurs at higher reduction temperatures. In case of the Pd/zinc oxide system reversible surface alloying takes place during reduction that is also beneficial for CO oxidation, but again deactivates fast. When being reduced at even higher temperatures the additional formation of an oxidic overlayer could be observed that does not further activate the system but leads to an overall reduction of active sites. Due to alloy formation, the zinc oxide system at higher conversions shows a different selectivity behavior in acetylene hydrogenation, compared to the iron oxide system. Also in case of the Pd/titania system, reversible surface decoration by partially reduced support happens during reduction. Different to the other investigated systems the surface-cover reversibly decreases CO oxidation activity however. The Pd/alumina system was studied as a less reducible reference. As expected, it does not show SMSI-induced modifications. In the end the work clearly shows that CO oxidation is a convenient method to study activity and stability of SMSI and decouple it from other involved processes. The effects of surface modification on the catalytic activity in this test reaction however strongly depend on the specific system and pre-conditioning and can either be of activating or deactivating nature. The basic principles involved in case of SMSI seem to apply both in UHV model systems and at powder systems at ambient pressure as found by the catalytic measurements.Übergangsmetalloxid geträgerte, nano-skalige Edelmetall-Katalysatoren sind bekannt dafür, eine Reihe von Oberflächen-Veränderungen zu erfahren, wenn sie bei erhöhter Temperatur reduziert werden. Diese Prozesse beinhalten beispielsweise (Oberflächen-) Legierungsbildung und die Ausblidung von teilweise reduzierten, oxidischen Träger- Schichten, in beiden Fällen hervorgerufen durch Starke Metall-Träger Wechselwirkung (Strong Metal-Support Interaction, SMSI). Die vorliegende Arbeit untersuchte eine Reihe von oxid-geträgerten Palladium Pulverkatalysatoren mit einer Variation der Beladung von 1- 5 Gewichts-% auf ihre Struktur-Eigenschafts Beziehungen nach Reduktion in verschiedenen Medien und bei veschiedenen Temperaturen, um ein Referenzsystem zu entwickeln und der Natur von SMSI auf den Grund zu gehen. Dabei kamen oberflächen- und volumensensitive Methoden wie XPS, Chemisorption, TEM, DRIFTS oder XRD zum Einsatz, um den Einfluss von elektronischen und strukturellen Veränderungen auf die Aktivität bei katalytischer Oxidation von Kohlenmonoxid zu untersuchen, welche als wichtigste Testreaktion bei Normaldruck durchgeführt wurde. Die Katalysatoren wurden auf reproduzierbare Weise durch kontrollierte Ko-Fällung und durch Imprägnierung hergestellt. Das untersuchte Pd/Eisenoxid System zeigt Bedeckung der Pd Oberfläche nach Reduktion bei vergleichsweise niedrigen Temperaturen. Diese Bedeckung war instabil in sauerstoffhaltiger Umgebung und bildete sich reversibel aus. Abhängig von der Pd Partikelgröße erhöht sie die Aktivität bei der CO-Oxidation. Legierungsbildung findet bei höheren Reduktionstemperaturen statt. Im Falle von Pd/Zinkoxid findet reversible Legierungsbildung an der Oberfläche statt, die ebenfalls die CO-Oxidation begünstigt, aber ebenfalls schnell deaktiviert. Nach Reduktion bei noch höheren Temperaturen konnte die zusätzliche Ausbildung einer oxidischen Überschicht beobachtet werden, die das System nicht weiter aktivierte, sondern insgesamt die Zahl der aktiven Plätze reduzierte. Wegen Legierungsbildung zeigt das Zinkoxid-System bei höheren Umsätzen in der Acetylenhydrierung ein anderes Selektivitätsverhalten als das Eisenoxid-System. Im Fall von Pd/Titanoxid kommt es während der Reduktion ebenfalls zu reversibler Oberflächen- Bedeckung durch teilweise reduzierten Träger. Anders als in den beiden anderen Fällen verringert diese Schicht hier jedoch die Aktivität in der CO-Oxidation. Pd/Aluminiumoxid wurde als schwer reduzierbares Referenz-System untersucht. Wie erwartet zeigt es keine durch SMSI hervorgerufenen Veränderungen. Schlussendlich konnte in dieser Arbeit gezeigt werden, dass CO-Oxidation eine einfache und geeignete Methode ist, SMSI zu untersuchen und ihren Einfluss auf Aktivität und Stabilität von dem anderer Prozesse zu trennen. Die Effekte von Oberflächenveränderungen auf die katalytische Aktivität dieser Test-Reaktion hängen jedoch stark vom entsprechenden System und der Vorbehandlung ab und können sowohl aktivierender als auch deaktivierender Natur sein. Die Grundlegenden Prinzipien, die bei SMSI eine Rolle spielen, scheinen sowohl im Fall von Modell-Systemen unter UHV-Bedingungen als auch bei Pulver-Systemen bei Normaldruck zu gelten, wie durch die katalytischen Messungen gezeigt wurde

Magnetic-Field Amplification in the Thin X-ray Rims of SN1006

Several young supernova remnants (SNRs), including SN1006, emit synchrotron X-rays in narrow filaments, hereafter thin rims, along their periphery. The widths of these rims imply 50 to 100 $\mu$G fields in the region immediately behind the shock, far larger than expected for the interstellar medium compressed by unmodified shocks, assuming electron radiative losses limit rim widths. However, magnetic-field damping could also produce thin rims. Here we review the literature on rim width calculations, summarizing the case for magnetic-field amplification. We extend these calculations to include an arbitrary power-law dependence of the diffusion coefficient on energy, $D \propto E^{\mu}$. Loss-limited rim widths should shrink with increasing photon energy, while magnetic-damping models predict widths almost independent of photon energy. We use these results to analyze Chandra observations of SN 1006, in particular the southwest limb. We parameterize the full widths at half maximum (FWHM) in terms of energy as FWHM $\propto E^{m_E}_{\gamma}$. Filament widths in SN1006 decrease with energy; $m_E \sim -0.3$ to $-0.8$, implying magnetic field amplification by factors of 10 to 50, above the factor of 4 expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules out magnetic damping models. It also favors short mean free paths (small diffusion coefficients) and strong dependence of $D$ on energy ($\mu \ge 1$).Comment: Accepted by ApJ, 49 pages, 10 figure

Thermal Model Calibration for Minor Planets Observed with Wide-Field Infrared Survey Explorer/Neowise

With the Wide-field Infrared Survey Explorer (WISE), we have observed over 157,000 minor planets. Included in these are a number of near-Earth objects, main-belt asteroids, and irregular satellites which have well measured physical properties (via radar studies and in situ imaging) such as diameters. We have used these objects to validate models of thermal emission and reflected sunlight using the WISE measurements, as well as the color corrections derived in Wright et al. for the four WISE bandpasses as a function of effective temperature. We have used 50 objects with diameters measured by radar or in situ imaging to characterize the systematic errors implicit in using the WISE data with a faceted spherical near-Earth asteroid thermal model (NEATM) to compute diameters and albedos. By using the previously measured diameters and H magnitudes with a spherical NEATM model, we compute the predicted fluxes (after applying the color corrections given in Wright et al.) in each of the four WISE bands and compare them to the measured magnitudes. We find minimum systematic flux errors of 5%-10%, and hence minimum relative diameter and albedo errors of ~10% and ~20%, respectively. Additionally, visible albedos for the objects are computed and compared to the albedos at 3.4 μm and 4.6 μm, which contain a combination of reflected sunlight and thermal emission for most minor planets observed by WISE. Finally, we derive a linear relationship between subsolar temperature and effective temperature, which allows the color corrections given in Wright et al. to be used for minor planets by computing only subsolar temperature instead of a faceted thermophysical model. The thermal models derived in this paper are not intended to supplant previous measurements made using radar or spacecraft imaging; rather, we have used them to characterize the errors that should be expected when computing diameters and albedos of minor planets observed by WISE using a spherical NEATM model

Mid-infrared Imaging of a Circumstellar Disk Around HR 4796: Mapping the Debris of Planetary Formation

We report the discovery of a circumstellar disk around the young A0 star, HR 4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By fitting a model of the emission from a flat dusty disk to an image at lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face on, with the long axis of emission at PA 28 +/-6 deg. The intensity of emission does not decrease with radius as expected for circumstellar disks but increases outward from the star, peaking near both ends of the elongated structure. We simulate this appearance by varying the inner radius in our model and find an inner hole in the disk with radius R_in = 55+/-15 AU. This value corresponds to the radial distance of our own Kuiper belt and may suggest a source of dust in the collision of cometesimals. By contrast with the appearance at 20.8 microns, excess emission at lambda = 12.5 microns is faint and concentrated at the stellar position. Similar emission is also detected at 20.8 microns in residual subtraction of the best-fit model from the image. The intensity and ratio of flux densities at the two wavelengths could be accounted for by a tenuous dust component that is confined within a few AU of the star with mean temperature of a few hundred degrees K, similar to that of zodiacal dust in our own solar system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that its disk is in a transitional planet-forming stage, between that of massive gaseous proto-stellar disks and more tenuous debris disks such as the one detected around Vega.Comment: 9 pages, 4 figures as LaTex manuscript and postscript files in gzipped tar file. Accepted for publication in Astrophysical Journal Letters. http://upenn5.hep.upenn.edu/~davidk/hr4796.htm