An ASCA Study of the Heavy Element Distribution in Clusters of Galaxies

We perform a spatially resolved X-ray spectroscopic study of a set of 11 relaxed clusters of galaxies observed by the ROSAT/PSPC and ASCA/SIS. Using a method which corrects for the energy dependent effects of the ASCA PSF based on ROSAT images, we constrain the spatial distribution of Ne, Si, S and Fe in each cluster. Theoretical prescriptions for the chemical yields of Type Ia and II supernovae, then allow determination of the Fe enrichment from both types of supernovae as a function of radius within each cluster. Using optical measurements from the literature, we also determine the iron mass-to-light ratio (IMLR) separately for Fe synthesized in both types of supernovae. For clusters with the best photon statistics, we find that the total Fe abundance decreases significantly with radius, while the Si abundance is either flat or decreases less rapidly, resulting in an increasing Si/Fe ratio with radius. This result indicates a greater predominance of Type II SNe enrichment at large radii in clusters. We suggest that the high Si/Fe ratios in the outskirts of rich clusters may arise from enrichment by Type II SNe released to ICM via galactic star burst driven winds. Abridged.Comment: 17 pages, ApJ in press (Nov. 2000), a study of systematics is adde

Drawing Trees with Perfect Angular Resolution and Polynomial Area

We study methods for drawing trees with perfect angular resolution, i.e., with angles at each node v equal to 2{\pi}/d(v). We show: 1. Any unordered tree has a crossing-free straight-line drawing with perfect angular resolution and polynomial area. 2. There are ordered trees that require exponential area for any crossing-free straight-line drawing having perfect angular resolution. 3. Any ordered tree has a crossing-free Lombardi-style drawing (where each edge is represented by a circular arc) with perfect angular resolution and polynomial area. Thus, our results explore what is achievable with straight-line drawings and what more is achievable with Lombardi-style drawings, with respect to drawings of trees with perfect angular resolution.Comment: 30 pages, 17 figure

An international longitudinal registry of patients with atrial fibrillation at risk of stroke (GARFIELD) : the UK protocol

Background Atrial fibrillation (AF) is an independent risk factor for stroke and a significant predictor of mortality. Evidence-based guidelines for stroke prevention in AF recommend antithrombotic therapy corresponding to the risk of stroke. In practice, many patients with AF do not receive the appropriate antithrombotic therapy and are left either unprotected or inadequately protected against stroke. The purpose of the Global Anticoagulant Registry in the FIELD (GARFIELD) is to determine the real-life management and outcomes of patients newly diagnosed with non-valvular AF. Methods/design GARFIELD is an observational, international registry of newly diagnosed AF patients with at least one additional investigator-defined risk factor for stroke. The aim is to enrol 55,000 patients at more than 1000 centres in 50 countries worldwide. Enrolment will take place in five independent, sequential, prospective cohorts; the first cohort includes a retrospective validation cohort. Each cohort will be followed up for 2 years. The UK stands to be a significant contributor to GARFIELD, aiming to enrol 4,582 patients, and reflecting the care environment in which patients with AF are managed. The UK protocol will also focus on better understanding the validity of the two main stroke risk scores (CHADS2 and CHA2DS2VASC) and the HAS-BLED bleeding risk score, in the context of a diverse patient population. Discussion The GARFIELD registry will describe how therapeutic strategies, patient care, and clinical outcomes evolve over time. This study will provide UK-specific comprehensive data that will allow a range of evaluations both at a national level and in relation to global data and contribute to a better understanding of AF management in the UK

Development of Improved Sorbents for Radiochemical Separations at the SRS

High-level nuclear waste produced from fuel reprocessing operations at the Savannah River Site (SRS) requires pretreatment to remove {sup 137}Cs, {sup 90}Sr and alpha-emitting radionuclides (i.e., actinides) prior to disposal. Separation processes planned at SRS include caustic side solvent extraction, for {sup 137}Cs removal, and ion exchange/sorption of {sup 90}Sr and alpha-emitting radionuclides with monosodium titanate (MST). The predominant alpha-emitting radionuclides in the highly alkaline waste solutions include plutonium isotopes {sup 238}Pu, {sup 239}Pu and {sup 240}Pu. This paper describes results from a project to produce sorbents that exhibit increased removal kinetics and capacity for {sup 90}Sr and alpha-emitting radionuclides versus that of the baseline MST material. Testing indicated that MST samples prepared in the presence of organic-based templating agents showed limited improvements in performance compared to the baseline MST. We observed significantly improved plutonium and neptunium removal performance with MST samples prepared upon the addition of a proprietary reagent. The modified MST offers the possibility of increased throughput and reduced solids handling in waste processing facilities at the SRS

Boron in Very Metal-Poor Stars

We have observed the B I 2497 A line to derive the boron abundances of two very metal-poor stars selected to help in tracing the origin and evolution of this element in the early Galaxy: BD +23 3130 and HD 84937. The observations were conducted using the Goddard High Resolution Spectrograph on board the Hubble Space Telescope. A very detailed abundance analysis via spectral synthesis has been carried out for these two stars, as well as for two other metal-poor objects with published spectra, using both Kurucz and OSMARCS model photospheres, and taking into account consistently the NLTE effects on the line formation. We have also re-assessed all published boron abundances of old disk and halo unevolved stars. Our analysis shows that the combination of high effective temperature (Teff > 6000 K, for which boron is mainly ionized) and low metallicity ([Fe/H]<-1) makes it difficult to obtain accurate estimates of boron abundances from the B I 2497 A line. This is the case of HD 84937 and three other published objects (including two stars with [Fe/H] ~ -3), for which only upper limits can be established. BD +23 3130, with [Fe/H] ~ -2.9 and logN(B)_NLTE=0.05+/-0.30, appears then as the most metal-poor star for which a firm measurement of the boron abundance presently exists. The evolution of the boron abundance with metallicity that emerges from the seven remaining stars with Teff < 6000 K and [Fe/H]<-1, for which beryllium abundances were derived using the same stellar parameters, shows a linear increase with a slope ~ 1. Furthermore, the B/Be ratio found is constant at a value ~ 20 for stars in the range -3<[Fe/H]<-1. These results point to spallation reactions of ambient protons and alpha particles with energetic particles enriched in CNO as the origin of boron and beryllium in halo stars.Comment: 38 pages, 11 Encapsulated Postscript figures (included), uses aaspp4.sty. Accepted for publication in The Astrophysical Journal. The preprint is also available at: http://www.iac.es/publicaciones/preprints.htm

An Ultra-High-Resolution Survey of the Interstellar ^7Li-to-^6Li Isotope Ratio in the Solar Neighborhood

In an effort to probe the extent of variations in the interstellar ^7Li/^6Li ratio seen previously, ultra-high-resolution (R ~ 360,000), high signal-to-noise spectra of stars in the Perseus OB2 and Scorpius OB2 Associations were obtained. These measurements confirm our earlier findings of an interstellar ^7Li/^6Li ratio of about 2 toward o Per, the value predicted from models of Galactic cosmic ray spallation reactions. Observations of other nearby stars yield limits consistent with the isotopic ratio ~ 12 seen in carbonaceous chondrite meteorites. If this ratio originally represented the gas toward o Per, then to decrease the original isotope ratio to its current value an order of magnitude increase in the Li abundance is expected, but is not seen. The elemental K/Li ratio is not unusual, although Li and K are formed via different nucleosynthetic pathways. Several proposals to account for the low ^7Li/^6Li ratio were considered, but none seems satisfactory. Analysis of the Li and K abundances from our survey highlighted two sight lines where depletion effects are prevalent. There is evidence for enhanced depletion toward X Per, since both abundances are lower by a factor of 4 when compared to other sight lines. Moreover, a smaller Li/H abundance is observed toward 20 Aql, but the K/H abundance is normal, suggesting enhanced Li depletion (relative to K) in this direction. Our results suggest that the ^7Li/^6Li ratio has not changed significantly during the last 4.5 billion years and that a ratio ~ 12 represents most gas in the solar neighborhood. In addition, there appears to be a constant stellar contribution of ^7Li, indicating that one or two processes dominate its production in the Galaxy.Comment: 54 pages, accepted for publication in the Astrophysical Journa

Precipitation and Deposition of Aluminum-Containing Species in Tank Wastes

Aluminum-containing phases represent the most prevalent solids that can appear or disappear during the processing of radioactive tank wastes. Processes such as sludge washing and leaching are designed to dissolve Al-containing phases and thereby minimize the volume of high-level waste glass required to encapsulate radioactive sludges. Unfortunately, waste-processing steps that include evaporation can involve solutions that are supersaturated with respect to cementitious aluminosilicates that result in unwanted precipitation and scale formation. Of all the constituents of tank waste, limited solubility cementitious aluminosilicates have the greatest potential for clogging pipes and transfer lines, fouling highly radioactive components such as ion exchangers, and completely shutting down processing operations. For instance, deposit buildup and clogged drain lines experienced during the tank waste volume-reduction process at the Savannah River Site (SRS) required an evaporator to be shut down in October 1999. The Waste Processing Technology Section of Westinghouse Savannah River Company at SRS now is collaborating with team members from Pacific Northwest National Laboratory (PNNL) to verify the thermodynamic stability of aluminosilicate compounds under waste tank conditions in an attempt to solve the deposition and clogging problems. The primary objectives of this study are (1) to understand the major factors controlling precipitation, heterogeneous nucleation, and growth phenomena of relatively insoluble aluminosilicates; (2) to determine the role of organics for inhibiting aluminosilicate formation, and (3) to develop a predictive tool to control precipitation, scale formation, and cementation under tank waste processing conditions. The results of this work will provide crucial information for (1) avoiding problematical sludge processing steps and (2) identifying and developing effective technologies to process retrieved sludges and supernatants before ultimate vitrification of wastes

A lower to middle Eocene astrochronology for the Mentelle Basin (Australia) and its implications for the geologic time scale

The geologic time scale for the Cenozoic Era has been notably improved over the last decades by virtue of integrated stratigraphy, combining high-resolution astrochronologies, biostratigraphy and magnetostratigraphy with high-precision radioisotopic dates. However, the middle Eocene remains a weak link. The so-called “Eocene time scale gap” reflects the scarcity of suitable study sections with clear astronomically-forced variations in carbonate content, primarily because large parts of the oceans were starved of carbonate during the Eocene greenhouse. International Ocean Discovery Program (IODP) Expedition 369 cored a carbonate-rich sedimentary sequence of Eocene age in the Mentelle Basin (Site U1514, offshore southwest Australia). The sequence consists of nannofossil chalk and exhibits rhythmic clay content variability. Here, we show that IODP Site U1514 allows for the extraction of an astronomical signal and the construction of an Eocene astrochronology, using 3-cm resolution X-Ray fluorescence (XRF) core scans. The XRF-derived ratio between calcium and iron content (Ca/Fe) tracks the lithologic variability and serves as the basis for our U1514 astrochronology. We present a 16 million-year-long (40-56 Ma) nearly continuous history of Eocene sedimentation with variations paced by eccentricity and obliquity. We supplement the high-resolution XRF data with low-resolution bulk carbon and oxygen isotopes, recording the long-term cooling trend from the Paleocene-Eocene Thermal Maximum (PETM – ca. 56 Ma) into the middle Eocene (ca. 40 Ma). Our early Eocene astrochronology corroborates existing chronologies based on deep-sea sites and Italian land sections. For the middle Eocene, the sedimentological record at U1514 provides a single-site geochemical backbone and thus offers a further step towards a fully integrated Cenozoic geologic time scale at orbital resolution