Structure of dislocations in Al and Fe as studied by positron-annihilation spectroscopy

Positron-lifetime-spectra measurements have been performed on single crystals of Al and polycrystals of Fe deformed under the tensile mode at room temperature and 77 K, respectively. It is shown that the positron-trapping component in Al depends on the number of slip systems activated: The positron lifetime is 215, 220, and 240 ps when single-, double-, and multiple-slip planes are activated, respectively. This dependence is well understood if positrons annihilate at dislocation-associated defects (jogs) with different positron-annihilation characteristics revealing different jog structures. In iron, the positron-lifetime spectra associated with dislocations were found to be independent of the annealing temperature between 110 and 360 K. In this temperature range, screw dislocations should transform into nonscrew dislocations, suggesting that the positrons are not sensitive to the different types of dislocations. These results are interpreted on the basis that positrons annihilate at defects associated with the dislocations rather than at the dislocation lines. © 1992 The American Physical Society.Peer Reviewe

Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).

Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362

Technical Note: The single particle soot photometer failsto reliably detect PALAS soot nanoparticles

The single particle soot photometer (SP2) useslaser-induced incandescence (LII) for the measurement of at-mospheric black carbon (BC) particles. The BC mass con-centration is obtained by combining quantitative detectionof BC mass in single particles with a counting efficiency of100 % above its lower detection limit. It is commonly ac-cepted that a particle must contain at least several tenths ofa femtogram BC in order to be detected by the SP2.Here we show the result that most BC particles froma PALAS spark discharge soot generator remain undetectedby the SP2, even if their BC mass, as independently de-termined with an aerosol particle mass analyser (APM),is clearly above the typical lower detection limit of theSP2. Comparison of counting efficiency and effective densitydata of PALAS soot with flame generated soot (combustionaerosol standard burner, CAST), fullerene soot and carbonblack particles (Cabot Regal 400R) reveals that particle mor-phology can affect the SP2’s lower detection limit. PALASsoot particles are fractal-like agglomerates of very small pri-mary particles with a low fractal dimension, resulting in avery low effective density. Such loosely packed particles be-have like “the sum of individual primary particles” in theSP2’s laser. Accordingly, most PALAS soot particles remainundetected as the SP2’s laser intensity is insufficient to heatthe primary particles to their vaporisation temperature be-cause of their small size (Dpp≈5–10 nm). Previous knowl-edge from pulsed laser-induced incandescence indicated thatparticle morphology might have an effect on the SP2’s lowerdetection limit, however, an increase of the lower detection limit by a factor of∼5–10, as reported here for PALAS soot,was not expected.In conclusion, the SP2’s lower detection limit at a cer-tain laser power depends primarily on the total BC massper particle for compact particles with sufficiently high ef-fective density. By contrast, the BC mass per primary par-ticle mainly determines whether fractal-like particles withlow fractal dimension and very small primary particles aredetectable, while their total BC mass has only a minor in-fluence. This effect shifts the lower detection limit to muchhigher BC mass, or makes them completely undetectable.Consequently, care has to be taken when using the SP2 inapplications dealing with loosely packed particles that havevery small primary particles as building blocks.ISSN:1867-1381ISSN:1867-854

An Arctic CCN-limited cloud-aerosol regime

On average, airborne aerosol particles cool the Earth's surface directly by absorbing and scattering sunlight and indirectly by influencing cloud reflectivity, life time, thickness or extent. Here we show that over the central Arctic Ocean, where there is frequently a lack of aerosol particles upon which clouds may form, a small increase in aerosol loading may enhance cloudiness thereby likely causing a climatologically significant warming at the ice-covered Arctic surface. Under these low concentration conditions cloud droplets grow to drizzle sizes and fall, even in the absence of collisions and coalescence, thereby diminishing cloud water. Evidence from a case study suggests that interactions between aerosol, clouds and precipitation could be responsible for attaining the observed low aerosol concentrations.ISSN:1680-7375ISSN:1680-736

Mass spectrometry of refractory black carbon particles from six sources: carbon-cluster and oxygenated ions

We discuss the major mass spectral features of different types of refractory carbona-ceous particles, ionized after laser vapourization with an Aerodyne High-ResolutionSoot-Particle Aerosol Mass Spectrometer (SP-AMS). The SP-AMS was operated witha switchable 1064 nm laser and a 600◦C thermal vapourizer, yielding respective measurements of the refractory and non-refractory particle components. Six samples wereinvestigated, all of which were composed primarily of refractory material: fuel-rich andfuel-lean propane/air diffusion-flame combustion particles; graphite-spark-generatedparticles; a commercial Fullerene-enriched Soot; Regal Black, a commercial carbonblack; and nascent aircraft-turbine combustion particles.All samples exhibited a spectrum of carbon-cluster ions Cn+xin their refractory massspectrum. Smaller clusters (x1). In all six cases, the ions C+1and C+3contributed over 60% to the total15C+15 were present. When such signalswere present, C+1/C+3was close to 1. When absent, C+1/C+3was<0.8. This ratio maytherefore serve as a proxy to distinguish between the two types of spectra in atmo-spheric SP-AMS measurements. Significant refractory oxygenated ions such as CO+and CO+2were also observedfor all samples. We discuss these signals in detail for Regal Black, and describe theirformation via decomposition of oxygenated moieties incorporated into the refractorycarbon structure. These species may be of importance in atmospheric processes suchas water uptake, aging and heterogeneous chemistryISSN:1680-7375ISSN:1680-736

Mass spectrometry of refractory black carbon particles from six sources: carbon-cluster and oxygenated ions

We discuss the major mass spectral features of different types of refractory carbonaceous particles, ionized after laser vaporization with an Aerodyne high-resolution soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS was operated with a switchable 1064 nm laser and a 600 °C thermal vaporizer, yielding respective measurements of the refractory and non-refractory particle components. Six samples were investigated, all of which were composed primarily of refractory material: fuel-rich and fuel-lean propane/air diffusion-flame combustion particles; graphite-spark-generated particles; a commercial fullerene-enriched soot; Regal Black, a commercial carbon black; and nascent aircraft-turbine combustion particles. All samples exhibited a spectrum of carbon-cluster ions Cxn+ in their refractory mass spectrum. Smaller clusters (x 1). In all six cases, the ions C1+ and C3+ contributed over 60% to the total C1+ intensity. Furthermore, the ratio of these major ions C1+ / C3+ could be used to predict whether significant Cxn+ signals with x > 5 were present. When such signals were present, C1+ / C3+ was close to 1. When absent, C1+ / C3+ was < 0.8. This ratio may therefore serve as a proxy to distinguish between the two types of spectra in atmospheric SP-AMS measurements. Significant refractory oxygenated ions such as CO+ and CO2+ were also observed for all samples. We discuss these signals in detail for Regal Black, and describe their formation via decomposition of oxygenated moieties incorporated into the refractory carbon structure. These species may be of importance in atmospheric processes such as water uptake and heterogeneous chemistry. If atmospherically stable, these oxidized species may be useful for distinguishing between different combustion sources. If unstable, they may provide a means to estimate the atmospheric age of an rBC sample. Future studies should attempt to establish which of these scenarios is more realistic.ISSN:1680-7375ISSN:1680-736

The Arctic Summer Cloud-Ocean Study (ASCOS): Overview and experimental design

The climate in the Arctic is changing faster than anywhere else on Earth. Poorly un-derstood feedback processes relating to Arctic clouds and aerosol-cloud interactionscontribute to a poor understanding of the present changes in the Arctic climate system,and also to a large spread in projections of future climate in the Arctic. The problem is exacerbated by the paucity of research-quality observations in the central Arctic. Im-proved formulations in climate models require such observations, which can only comefrom measurements in-situ in this difficult to reach region with logistically demandingenvironmental conditions.The Arctic Summer Cloud-Ocean Study (ASCOS) was the most extensive central Arctic Ocean expedition with an atmospheric focus during the International Polar Year(IPY) 2007–2008. ASCOS focused on the study of the formation and life cycle of low-level Arctic clouds. ASCOS departed from Longyearbyen on Svalbard on 2 August andreturned on 9 September 2008. In transit into and out of the pack ice, four short re-search stations were undertaken in the Fram Strait; two in open water and two in the marginal ice zone. After traversing the pack-ice northward an ice camp was set up on12 August at 87◦21′N 01◦29′W and remained in operation through 1 September, drift-ing with the ice. During this time extensive measurements were taken of atmosphericgas and particle chemistry and physics, mesoscale and boundary-layer meteorology,marine biology and chemistry, and upper ocean physics. ASCOS provides a unique interdisciplinary data set for development and testing ofnew hypotheses on cloud processes, their interactions with the sea ice and ocean andassociated physical, chemical, and biological processes and interactions. For exam-ple, the first ever quantitative observation of bubbles in Arctic leads, combined withthe unique discovery of marine organic material, polymer gels with an origin in the ocean, inside cloud droplets suggest the possibility of primary marine organically de-rived cloud condensation nuclei in Arctic stratocumulus clouds. Direct observations ofsurface fluxes of aerosols could, however, not explain observed variability in aerosol concentrations and the balance between local and remote aerosols sources remainsopen. Lack of CCN was at times a controlling factor in low-level cloud formation, andhence for the impact of clouds on the surface energy budget. ASCOS provided de-tailed measurements of the surface energy balance from late summer melt into theinitial autumn freeze-up, and documented the effects of clouds and storms on the surface energy balance during this transition. In addition to such process-level studies, theunique, independent ASCOS data set can and is being used for validation of satelliteretrievals, operational models, and reanalysis data sets.ISSN:1680-7375ISSN:1680-736