Future Prospects: Deep Imaging of Galaxy Outskirts using Telescopes Large and Small

The Universe is almost totally unexplored at low surface brightness levels. In spite of great progress in the construction of large telescopes and improvements in the sensitivity of detectors, the limiting surface brightness of imaging observations has remained static for about forty years. Recent technical advances have at last begun to erode the barriers preventing progress. In this Chapter we describe the technical challenges to low surface brightness imaging, describe some solutions, and highlight some relevant observations that have been undertaken recently with both large and small telescopes. Our main focus will be on discoveries made with the Dragonfly Telephoto Array (Dragonfly), which is a new telescope concept designed to probe the Universe down to hitherto unprecedented low surface brightness levels. We conclude by arguing that these discoveries are probably only scratching the surface of interesting phenomena that are observable when the Universe is explored at low surface brightness levels.Comment: 27 pages, 10 figures, Invited review, Book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres

Estimation of Radiation Doses in the Marshall Islands Based on Whole Body Counting of Cesium-137 (137Cs) and Plutonium Urinalysis

Under the auspices of the U.S. Department of Energy (USDOE), researchers from the Lawrence Livermore National Laboratory (LLNL) have recently implemented a series of initiatives to address long-term radiological surveillance needs at former nuclear test sites in the Republic of the Marshall Islands (RMI). The aim of this radiological surveillance monitoring program (RSMP) is to provide timely radiation protection for individuals in the Marshall Islands with respect to two of the most important internally deposited fallout radionuclides-cesium-137 ({sup 137}Cs) and long-lived isotopes 239 and 240 of plutonium ({sup 239+240}Pu) (Robison et al., 1997 and references therein). Therefore, whole-body counting for {sup 137}Cs and a sensitive bioassay for the presence of {sup 239+240}Pu excreted in urine were adopted as the two most applicable in vivo analytical methods to assess radiation doses for individuals in the RMI from internally deposited fallout radionuclides (see Hamilton et al., 2006a-c; Bell et al., 2002). Through 2005, the USDOE has established three permanent whole-body counting facilities in the Marshall Islands: the Enewetak Radiological Laboratory on Enewetak Atoll, the Utrok Whole-Body Counting Facility on Majuro Atoll, and the Rongelap Whole-Body Counting Facility on Rongelap Atoll. These whole-body counting facilities are operated and maintained by trained Marshallese technicians. Scientists from LLNL provide the technical support and training necessary for maintaining quality assurance for data acquisition and dose reporting. This technical basis document summarizes the methodologies used to calculate the annual total effective dose equivalent (TEDE; or dose for the calendar year of measurement) based on whole-body counting of internally deposited {sup 137}Cs and the measurement of {sup 239+240}Pu excreted in urine. Whole-body counting provides a direct measure of the total amount (or burden) of {sup 137}Cs present in the human body at the time of measurement. The amount of {sup 137}Cs detected is often reported in activity units of kilo-Becquerel (kBq), where 1 kBq equals 1000 Bq and 1 Bq = 1 nuclear transformation per second (t s{sup -1}). [However, in the United States the Curie (Ci) continues to be used as the unit of radioactivity; where 1 Ci = 3.7 x 10{sup 10} Bq.] The detection of {sup 239}Pu and {sup 240}Pu in bioassay (urine) samples indicates the presence of internally deposited (systemic) plutonium in the body. Urine samples that are collected in the Marshall Islands from volunteers participating in the RSMP are transported to LLNL, where measurements for {sup 239+240}Pu are performed using a state-of-the-art technology based on Accelerator Mass Spectrometry (AMS) (Hamilton et al., 2004, 2007; Brown et al., 2004). The urinary excretion of plutonium by RSMP volunteers is usually described in activity units, expressed as micro-Becquerel ({micro}Bq) of {sup 239+240}Pu (i.e., representing the sum of the {sup 239}Pu and {sup 240}Pu activity) excreted (lost) per day (d{sup -1}), where 1 {micro}Bq d{sup -1} = 10{sup -6} Bq d{sup -1} and 1 Bq = 1 t s{sup -1}. The systemic burden of plutonium is then estimated from biokinetic relationships as described by the International Commission on Radiological Protection (e.g., see ICRP, 1990). In general, nuclear transformations are accompanied by the emission of energy and/or particles in the form of gamma rays ({gamma}), beta particles ({beta}), and/or alpha particles ({alpha}). Tissues in the human body may adsorb these emissions, where there is a potential for any deposited energy to cause biological damage. The general term used to quantify the extent of any radiation exposure is referred to as the dose. The equivalent dose is defined by the average absorbed dose in an organ or tissue weighted by the average quality factor for the type and energy of the emission causing the dose. The effective dose equivalent (EDE; as applied to the whole body), is the sum of the average dose equivalent for each tissue weighted by each applicable tissue-specific weighing factor (which equates to the sensitivity of that tissue to damage by the equivalent radiation dose it receives). The SI unit of effective dose equivalent is the joule per kilogram (J kg{sup -1}), named the Sievert (Sv). The unit often used by federal and state agencies in the United States to describe EDE continues to be the more historical radiation equivalent man (rem); where 1 rem = 0.01 Sv

Galileo dust data from the jovian system: 2000 to 2003

The Galileo spacecraft was orbiting Jupiter between Dec 1995 and Sep 2003. The Galileo dust detector monitored the jovian dust environment between about 2 and 370 R_J (jovian radius R_J = 71492 km). We present data from the Galileo dust instrument for the period January 2000 to September 2003. We report on the data of 5389 particles measured between 2000 and the end of the mission in 2003. The majority of the 21250 particles for which the full set of measured impact parameters (impact time, impact direction, charge rise times, charge amplitudes, etc.) was transmitted to Earth were tiny grains (about 10 nm in radius), most of them originating from Jupiter's innermost Galilean moon Io. Their impact rates frequently exceeded 10 min^-1. Surprisingly large impact rates up to 100 min^-1 occurred in Aug/Sep 2000 when Galileo was at about 280 R_J from Jupiter. This peak in dust emission appears to coincide with strong changes in the release of neutral gas from the Io torus. Strong variability in the Io dust flux was measured on timescales of days to weeks, indicating large variations in the dust release from Io or the Io torus or both on such short timescales. Galileo has detected a large number of bigger micron-sized particles mostly in the region between the Galilean moons. A surprisingly large number of such bigger grains was measured in March 2003 within a 4-day interval when Galileo was outside Jupiter's magnetosphere at approximately 350 R_J jovicentric distance. Two passages of Jupiter's gossamer rings in 2002 and 2003 provided the first actual comparison of in-situ dust data from a planetary ring with the results inferred from inverting optical images.Comment: 59 pages, 13 figures, 6 tables, submitted to Planetary and Space Scienc

Cryogenic Characterization of Commercial SiC Power MOSFETs

The cryogenic performance of two commercially available SiC power MOSFETs are presented in this work. The devices are characterised in static and dynamic tests at 10 K intervals from 20-320 K. Static current-voltage characterisation indicates that at low temperatures threshold voltage, turn-on voltage, on-state resistance, transconductance, and the body diode turn-on voltage all increase while saturation current decreases. Dynamic, 60 V, 3A switching tests within the cryogenic chamber are also reported and the trends of switching speed, losses, and total power losses, which rise at low temperature, are presented. Overall, both MOSFETs are fully operable down to 20 K with both positive and negative changes in behaviour.</p

Perspective: Advancing the research agenda for improving understanding of cyanobacteria in a future of global change

Harmful cyanobacterial blooms (=cyanoHABs) are an increasing feature of many waterbodies throughout the world. Many bloom-forming species produce toxins, making them of particular concern for drinking water supplies, recreation and fisheries in waterbodies along the freshwater to marine continuum. Global changes resulting from human impacts, such as climate change, over-enrichment and hydrological alterations of waterways, are major drivers of cyanoHAB proliferation and persistence. This review advocates that to better predict and manage cyanoHABs in a changing world, researchers need to leverage studies undertaken to date, but adopt a more complex and definitive suite of experiments, observations, and models which can effectively capture the temporal scales of processes driven by eutrophication and a changing climate. Better integration of laboratory culture and field experiments, as well as whole system and multiple-system studies are needed to improve confidence in models predicting impacts of climate change and anthropogenic over-enrichment and hydrological modifications. Recent studies examining adaptation of species and strains to long-term perturbations, e.g. temperature and carbon dioxide (CO2) levels, as well as incorporating multi-species and multi-stressor approaches emphasize the limitations of approaches focused on single stressors and individual species. There are also emerging species of concern, such as toxic benthic cyanobacteria, for which the effects of global change are less well understood, and require more detailed study. This review provides approaches and examples of studies tackling the challenging issue of understanding how global changes will affect cyanoHABs, and identifies critical information needs for effective prediction and management

Predicting the resilience and recovery of aquatic systems: A framework for model evolution within environmental observatories

Maintaining the health of aquatic systems is an essential component of sustainable catchment management, however, degradation of water quality and aquatic habitat continues to challenge scientists and policy-makers. To support management and restoration efforts aquatic system models are required that are able to capture the often complex trajectories that these systems display in response to multiple stressors. This paper explores the abilities and limitations of current model approaches in meeting this challenge, and outlines a strategy based on integration of flexible model libraries and data from observation networks, within a learning framework, as a means to improve the accuracy and scope of model predictions. The framework is comprised of a data assimilation component that utilizes diverse data streams from sensor networks, and a second component whereby model structural evolution can occur once the model is assessed against theoretically relevant metrics of system function. Given the scale and transdisciplinary nature of the prediction challenge, network science initiatives are identified as a means to develop and integrate diverse model libraries and workflows, and to obtain consensus on diagnostic approaches to model assessment that can guide model adaptation. We outline how such a framework can help us explore the theory of how aquatic systems respond to change by bridging bottom-up and top-down lines of enquiry, and, in doing so, also advance the role of prediction in aquatic ecosystem management

Simplifying superstring and D-brane actions in AdS(4) x CP(3) superbackground

By making an appropriate choice for gauge fixing kappa-symmetry we obtain a relatively simple form of the actions for a D=11 superparticle in AdS(4) x S(7)/Z_k, and for a D0-brane, fundamental string and D2-branes in the AdS(4) x CP(3) superbackground. They can be used to study various problems of string theory and the AdS4/CFT3 correspondence, especially in regions of the theory which are not reachable by the OSp(6|4)/U(3) x SO(1,3) supercoset sigma-model. In particular, we present a simple form of the gauge-fixed superstring action in AdS(4) x CP(3) and briefly discuss issues of its T-dualization.Comment: 1+36 pages, v2,v3 clarifications and references adde