Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2, Laube et al., 2010a), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (εapp) for mid- and high-latitude stratospheric samples are (-2.4±0.5) ‰ and (-2.3±0.4) ‰ for CFC-11, (-12.2±1.6) ‰ and (-6.8±0.8) ‰ for CFC-12 and (-3.5±1.5) ‰ and (-3.3±1.2) ‰ for CFC-113, respectively. Assuming a constant isotope composition of emissions, we calculate the expected trends in the tropospheric isotope signature of these gases based on their stratospheric 37Cl enrichment and stratosphere-troposphere exchange. We compare these projections to the long-term δ(37Cl) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978 – 2010) and tropospheric firn air samples from Greenland (NEEM site) and Antarctica (Fletcher Promontory site). From 1970 to the present-day, projected trends agree with tropospheric measurements, suggesting that within analytical uncertainties a constant average emission isotope delta is a compatible scenario. The measurement uncertainty is too high to determine whether the average emission isotope delta has been affected by changes in CFC manufacturing processes, or not. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes (approximately 200 ml), using a single-detector gas chromatography-mass spectrometry system

UBVRI photopolarimetry of the long period eclipsing AM Herculis binary V1309

We report simultaneous UBVRI photo-polarimetric observations of the long period (7.98 h) AM Her binary V1309 Ori. The length and shape of the eclipse ingress and egress varies from night to night. We suggest this is due to the variation in the brightness of the accretion stream. By comparing the phases of circular polarization zero-crossovers with previous observations, we confirm that V1309 Ori is well synchronized, and find an upper limit of 0.002 percent for the difference between the spin and orbital periods. We model the polarimetry data using a model consisting of two cyclotron emission regions at almost diametrically opposite locations, and centered at colatitude 35 (deg) and 145 (deg) on the surface of the white dwarf. We also present archive X-ray observations which show that the negatively polarised accretion region is X-ray bright.Comment: 11 pages, 12 figures (2 colour), Fig1 and Fig 4 are in lower resolution than in original paper, accepted for publication in Monthly Notices of the Royal Astronomical Societ

A Population of Faint Non-Transient Low Mass Black Hole Binaries

We study the thermal and viscous stability of accretion flows in Low Mass Black Hole Binaries (LMBHBs). We consider a model in which an inner advection-dominated accretion flow (ADAF) is surrounded by a geometrically thin accretion disk, the transition between the two zones occurring at a radius R_tr. In all the known LMBHBs, R_tr appears to be such that the outer disks could suffer from a global thermal-viscous instability. This instability is likely to cause the transient behavior of these systems. However, in most cases, if R_tr were slightly larger than the estimated values, the systems would be globally stable. This suggests that a population of faint persistent LMBHBs with globally stable outer disks could be present in the Galaxy. Such LMBHBs would be hard to detect because they would lack large amplitude outbursts, and because their ADAF zones would have very low radiative efficiencies, making the systems very dim. We present model spectra of such systems covering the optical and X-ray bands.Comment: LateX, 37 pages, 11 figures; Accepted for publication in The Astrophysical Journa

Infrared and Optical Spectroscopy of Type Ia Supernovae in the Nebular Phase

We present near-infrared (NIR) spectra for Type Ia supernovae at epochs of 13 to 338 days after maximum blue light. Some contemporary optical spectra are also shown. All the NIR spectra exhibit considerable structure throughout the J-, H- and K-bands. In particular they exhibit a flux `deficit' in the J-band which persists as late as 175 days. This is responsible for the well-known red J-H colour. To identify the emission features and test the $^{56}$Ni hypothesis for the explosion and subsequent light curve, we compare the NIR and optical nebular-phase data with a simple non-LTE nebular spectral model. We find that many of the spectral features are due to iron-group elements and that the J-band deficit is due to a lack of emission lines from species which dominate the rest of the IR/optical spectrum. Nevertheless, some emission is unaccounted for, possibly due to inaccuracies in the cobalt atomic data. For some supernovae, blueshifts of 1000--3000 km/s are seen in infrared and optical features at 3 months. We suggest this is due to clumping in the ejecta. The evolution of the cobalt/iron mass ratio indicates that $^{56}$Co-decay dominates the abundances of these elements. The absolute masses of iron-group elements which we derive support the basic thermonuclear explosion scenario for Type Ia supernovae. A core-collapse origin is less consistent with our data.Comment: 33 Latex pages, 12 Postscript figures: accepted by Monthly Notices of the Royal Astronomical Societ

Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal

Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained. New AMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazards models indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon. Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reaching the Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fill the canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffected by long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very different statistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controlling the frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transport during the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that a temporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events

Defining and evaluating novel procedures for involving patients in Core Outcome Set research: creating a meaningful long list of candidate outcome domains

Background Tinnitus is a complex audiological condition affecting many different domains of everyday life. Clinical trials of tinnitus interventions measure and report those outcome domains inconsistently and this hinders direct comparison between study findings. To address this problem, an ongoing project is developing a Core Outcome Set; an agreed list of outcome domains to be measured and reported in all future trials. Part of this project uses a consensus methodology (‘Delphi’ survey), whereby all relevant stakeholders identify important and critical outcome domains from a long list of candidates. This article addresses a gap in the patient involvement literature by describing and reflecting on our involvement of patients to create a meaningful long list of candidate outcome domains. Methods Two Public Research Partners with lived experience of tinnitus reviewed an initial list of 124 outcome domains over two face-to-face workshops. With the Study Management Team, they interpreted each candidate outcome domain and generated a plain language description. Following this, the domain names and descriptions underwent an additional lay review by 14 patients and 5 clinical experts, via an online survey platform. Results Insights gained from the workshops and survey feedback prompted substantial, unforeseen modifications to the long list. These included the reduction of the number of outcome domains (from 124 to 66) via the exclusion of broad concepts and consolidation of equivalent domains or domains outside the scope of the study. Reviewers also applied their lived experience of tinnitus to bring clarity and relevance to domain names and plain language descriptions. Four impacts on the Delphi survey were observed: recruitment exceeded the target by 171%, there were equivalent numbers of patient and professional participants (n=358 and n=312, respectively), feedback was mostly positive, and retention was high (87%). Conclusions Patient involvement was an integral and transformative step of the study design process. Patient involvement was impactful because the online Delphi survey was successful in recruiting and retaining participants, and there were many comments about a positive participatory experience. Seven general methodological features are highlighted which fit with general principles of good patient involvement. These can benefit other Core Outcome Set developers

Oxygen uptake estimation in humans during exercise using a Hammerstein model

This paper aims to establish a block-structured model to predict oxygen uptake in humans during moderate treadmill exercises. To model the steady state relationship between oxygen uptake (oxygen consumption) and walking speed, six healthy male subjects walked on a motor driven treadmill with constant speed from 2 to 7 km/h. The averaged oxygen uptake at steady state (VO 2) was measured by a mixing chamber based gas analysis and ventilation measurement system (AEI Moxus Metabolic Cart). Based on these reliable date, a nonlinear steady state relationship was successfully established using Support Vector Regression methods. In order to capture the dynamics of oxygen uptake, the treadmill velocity was modulated using a Pseudo Random Binary Signal (PRBS) input. Breath by breath analysis of all subjects was performed. An ARX model was developed to accurately reproduce the measured oxygen uptake dynamics within the aerobic range. Finally, a Hammerstein model was developed, which may be useful for implementing a control system for the regulation of oxygen uptake during treadmill exercises. © 2007 Biomedical Engineering Society