Relationships between carbon isotopic composition and mode of binding of natural organic matter in selected marine sediments

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Organic Geochemistry 38 (2007):1824-1837, doi:10.1016/j.orggeochem.2007.07.008.We have investigated the relationships between radiocarbon (14C) and stable carbon (13C) isotopic composition and the different modes of binding of organic matter (OM) present in surficial sediments from near-shore and continental margin sites that vary in terms of input and depositional conditions. To improve our understanding of the entire OM pool, isotopic analysis of sedimentary sub-fractions, as opposed to individual compounds, was performed. This was achieved by sequentially treating sediments by solvent extraction to examine unbound compounds, followed by saponification to cleave ester linked moieties. Isotopic analysis was then performed on the bulk sediment and resulting residues. The molecular composition of the extracts was examined using gas chromatography/mass spectrometry (GC/MS), and the relative contributions of terrestrial and marine biomarkers were assessed. Radiocarbon abundances (Δ14C) of the bulk sediment reflect a mixture of modern, pre-aged and fossil carbon. Offsets in Δ14C between the bulk sediment and sediment residues demonstrate varying associations of these carbon pools. For the majority of sites, a negative offset between extracted (EX2 RES) and saponified (SA-RES) sediment 1 residues results from the removal of relatively 4C-rich material during saponification. Saponification extracts (SAEs) are mainly composed of short chain (n-C12 to n-C24) alkanoic acids with an even/odd dominance indicating a predominantly marine algal or microbial source. This provides evidence for the protection of labile marine carbon by chemical binding. This study aims to bridge the gap between molecular level and bulk OM analyses in marine sediments.The work was supported by funds from the National Science Foundation (CHE-0089172; OCE-0526268)

Microlensing of the Lensed Quasar SDSS0924+0219

We analyze V, I and H band HST images and two seasons of R-band monitoring data for the gravitationally lensed quasar SDSS0924+0219. We clearly see that image D is a point-source image of the quasar at the center of its host galaxy. We can easily track the host galaxy of the quasar close to image D because microlensing has provided a natural coronograph that suppresses the flux of the quasar image by roughly an order of magnitude. We observe low amplitude, uncorrelated variability between the four quasar images due to microlensing, but no correlated variations that could be used to measure a time delay. Monte Carlo models of the microlensing variability provide estimates of the mean stellar mass in the lens galaxy (0.02 Msun < M < 1.0 Msun), the accretion disk size (the disk temperature is 5 x 10^4 K at 3.0 x 10^14 cm < rs < 1.4 x 10^15 cm), and the black hole mass (2.0 x 10^7 Msun < MBH \eta_{0.1}^{-1/2} (L/LE)^{1/2} < 3.3 x 10^8 Msun), all at 68% confidence. The black hole mass estimate based on microlensing is consistent with an estimate of MBH = 7.3 +- 2.4 x 10^7 Msun from the MgII emission line width. If we extrapolate the best-fitting light curve models into the future, we expect the the flux of images A and B to remain relatively stable and images C and D to brighten. In particular, we estimate that image D has a roughly 12% probability of brightening by a factor of two during the next year and a 45% probability of brightening by an order of magnitude over the next decade.Comment: v.2 incorporates referee's comments and corrects two errors in the original manuscript. 28 pages, 10 figures, published in Ap

Estimating the number of UK stroke patients eligible for endovascular thrombectomy

Introduction: Endovascular thrombectomy (EVT) is a highly effective treatment for acute ischemic stroke due to large arterial occlusion. Routine provision will require major changes in service configuration and workforce. An important first step is to quantify the population of stroke patients that could benefit. We estimated the annual UK population suitable for EVT using standard or advanced imaging (AI) for patient selection. Patients and Methods: Evidence from randomised control trials and national registries was combined to estimate UK stroke incidence and define a decision-tree describing the EVT eligible population. Results: Between 9,620 and 10,920 UK stroke patients (approximately 10% of stroke admissions) would be eligible for EVT annually. The majority (9,140 to 9,620) would present within 4 hours of onset and be suitable for intravenous thrombolysis. Advanced Imaging would exclude 500 patients presenting within 4 hours, but identify an additional 1,310 patients as eligible who present later. Discussion: Information from randomised control trials and large registry data provided the evidence criterion for 9 of the 12 decision points. The best available evidence was used for 2 decision-points with sensitivity analyses to determine how key branches of the tree affected estimates. Using the mid-point estimate for eligibility (9.6% of admissions) and assuming national EVT coverage, 4,280 patients would have reduced disability. Conclusion: A model combining published trials and register data suggests approximately 10% of all stroke admissions in the UK are eligible for EVT. The use of AI based on current published evidence did not have a major impact on overall numbers, but could alter eligibility status for 16% of cases

Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves

Aims. Radio emission observations from the Learmonth and Bruny Island radio spectrographs are analysed to determine the nature of a train of discrete, periodic radio “sparks” (finite-bandwidth, short-duration isolated radio features) which precede a type II burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA at multiple wavelengths and identify a series of quasi-periodic rapidly-propagating enhancements, which we interpret as a fast wave train, and link these to the detected radio features. Methods. The speeds and positions of the periodic rapidly propagating fast waves and the coronal mass ejection (CME) were recorded using running-difference images and time-distance analysis. From the frequency of the radio sparks the local electron density at the emission location was estimated for each. Using an empirical model for the scaling of density in the corona, the calculated electron density was used to obtain the height above the surface at which the emission occurs, and the propagation velocity of the emission location. Results. The period of the radio sparks, δtr = 1.78 ± 0.04 min, matches the period of the fast wave train observed at 171 Å, δtEUV = 1.7 ± 0.2 min. The inferred speed of the emission location of the radio sparks, 630 km s-1, is comparable to the measured speed of the CME leading edge, 500 km s-1, and the speeds derived from the drifting of the type II lanes. The calculated height of the radio emission (obtained from the density) matches the observed location of the CME leading edge. From the above evidence we propose that the radio sparks are caused by the quasi-periodic fast waves, and the emission is generated as they catch up and interact with the leading edge of the CME

Starspot-induced optical and infrared radial velocity variability in T Tauri star Hubble 4

We report optical (6150 Ang) and K-band (2.3 micron) radial velocities obtained over two years for the pre-main sequence weak-lined T Tauri star Hubble I 4. We detect periodic and near-sinusoidal radial velocity variations at both wavelengths, with a semi-amplitude of 1395\pm94 m/s in the optical and 365\pm80 m/s in the infrared. The lower velocity amplitude at the longer wavelength, combined with bisector analysis and spot modeling, indicates that there are large, cool spots on the stellar surface that are causing the radial velocity modulation. The radial velocities maintain phase coherence over hundreds of days suggesting that the starspots are long-lived. This is one of the first active stars where the spot-induced velocity modulation has been resolved in the infrared.Comment: Accepted for publication in The Astrophysical Journa

The Globular Cluster Systems in the Coma Ellipticals. II: Metallicity Distribution and Radial Structure in NGC 4874, and Implications for Galaxy Formation

Deep HST/WFPC2 (V,I) photometry is used to investigate the globular cluster system (GCS) in NGC 4874, the central cD galaxy of the Coma cluster. The luminosity function of the clusters displays its normal Gaussian-like shape and turnover level. Other features of the system are surprising: the GCS is (a) spatially extended, with core radius r_c = 22 kpc, (b) entirely metal-poor (a narrow, unimodal metallicity distribution with mean [Fe/H] = -1.5), and (c) modestly populated, with specific frequency S_N = 3.7 +- 0.5. We suggest on the basis of some simple models that as much as half of this galaxy might have accreted from low-mass satellites, but no single one of the three classic modes of galaxy formation (accretion, disk mergers, in situ formation) can supply a fully satisfactory formation picture. Even when they are used in combination, strong challenges to these models remain. The principal anomaly in this GCS is essentially the complete lack of metal-rich clusters. If these were present in normal (M87-like) numbers in addition to the metal-poor ones that are already there, then the GCS in total would more closely resemble what we see in many other giant E galaxies.Comment: 27 pp. with 9 Figures. Astrophys.J. 533, in press (April 10, 2000

A new modelling approach of evaluating preventive and reactive strategies for mitigating supply chain risks

Supply chains are becoming more complex and vulnerable due to globalization and interdependency between different risks. Existing studies have focused on identifying different preventive and reactive strategies for mitigating supply chain risks and advocating the need for adopting specific strategy under a particular situation. However, current research has not addressed the issue of evaluating an optimal mix of preventive and reactive strategies taking into account their relative costs and benefits within the supply network setting of interconnected firms and organizations. We propose a new modelling approach of evaluating different combinations of such strategies using Bayesian belief networks. This technique helps in determining an optimal solution on the basis of maximum improvement in the network expected loss. We have demonstrated our approach through a simulation study and discussed practical and managerial implications

Advances in the subseasonal prediction of extreme events: relevant case studies across the globe

Extreme weather events have devastating impacts on human health, economic activities, ecosystems, and infrastructure. It is therefore crucial to anticipate extremes and their impacts to allow for preparedness and emergency measures. There is indeed potential for probabilistic subseasonal prediction on time scales of several weeks for many extreme events. Here we provide an overview of subseasonal predictability for case studies of some of the most prominent extreme events across the globe using the ECMWF S2S prediction system: heatwaves, cold spells, heavy precipitation events, and tropical and extratropical cyclones. The considered heatwaves exhibit predictability on time scales of 3–4 weeks, while this time scale is 2–3 weeks for cold spells. Precipitation extremes are the least predictable among the considered case studies. ­Tropical cyclones, on the other hand, can exhibit probabilistic predictability on time scales of up to 3 weeks, which in the presented cases was aided by remote precursors such as the Madden–Julian oscillation. For extratropical cyclones, lead times are found to be shorter. These case studies clearly illustrate the potential for event-dependent advance warnings for a wide range of extreme events. The subseasonal predictability of extreme events demonstrated here allows for an extension of warning horizons, provides advance information to impact modelers, and informs communities and stakeholders affected by the impacts of extreme weather events.Peer Reviewed"Article signat per 40 autors/es: Daniela I. V. Domeisen, Christopher J. White, Hilla Afargan-Gerstman, Ángel G. Muñoz, Matthew A. Janiga, Frédéric Vitart, C. Ole Wulff, Salomé Antoine, Constantin Ardilouze, Lauriane Batté, Hannah C. Bloomfield, David J. Brayshaw, Suzana J. Camargo, Andrew Charlton-Pérez, Dan Collins, Tim Cowan, Maria del Mar Chaves, Laura Ferranti, Rosario Gómez, Paula L. M. González, Carmen González Romero, Johnna M. Infanti, Stelios Karozis, Hera Kim, Erik W. Kolstad, Emerson LaJoie, Llorenç Lledó, Linus Magnusson, Piero Malguzzi, Andrea Manrique-Suñén, Daniele Mastrangelo, Stefano Materia, Hanoi Medina, Lluís Palma, Luis E. Pineda, Athanasios Sfetsos, Seok-Woo Son, Albert Soret, Sarah Strazzo, and Di Tian"Postprint (published version