Dust in Supernovae and Supernova Remnants I : Formation Scenarios

Supernovae are considered as prime sources of dust in space. Observations of local supernovae over the past couple of decades have detected the presence of dust in supernova ejecta. The reddening of the high redshift quasars also indicate the presence of large masses of dust in early galaxies. Considering the top heavy IMF in the early galaxies, supernovae are assumed to be the major contributor to these large amounts of dust. However, the composition and morphology of dust grains formed in a supernova ejecta is yet to be understood with clarity. Moreover, the dust masses inferred from observations in mid-infrared and submillimeter wavelength regimes differ by two orders of magnitude or more. Therefore, the mechanism responsible for the synthesis of molecules and dust in such environments plays a crucial role in studying the evolution of cosmic dust in galaxies. This review summarises our current knowledge of dust formation in supernova ejecta and tries to quantify the role of supernovae as dust producers in a galaxy.Peer reviewe

Prospective observational cohort study of the association between antiplatelet therapy, bleeding and thrombosis in patients with coronary stents undergoing noncardiac surgery

Background: The perioperative management of antiplatelet therapy in noncardiac surgery patients who have undergone previous percutaneous coronary intervention (PCI) remains a dilemma. Continuing dual antiplatelet therapy (DAPT) may carry a risk of bleeding, while stopping antiplatelet therapy may increase the risk of perioperative major adverse cardiovascular events (MACE). Methods: Occurrence of Bleeding and Thrombosis during Antiplatelet Therapy In Non-Cardiac Surgery (OBTAIN) was an international prospective multicentre cohort study of perioperative antiplatelet treatment, MACE, and serious bleeding in noncardiac surgery. The incidences of MACE and bleeding were compared in patients receiving DAPT, monotherapy, and no antiplatelet therapy before surgery. Unadjusted risk ratios were calculated taking monotherapy as the baseline. The adjusted risks of bleeding and MACE were compared in patients receiving monotherapy and DAPT using propensity score matching. Results: A total of 917 patients were recruited and 847 were eligible for inclusion. Ninety-six patients received no antiplatelet therapy, 526 received monotherapy with aspirin, and 225 received DAPT. Thirty-two patients suffered MACE and 22 had bleeding. The unadjusted risk ratio for MACE in patients receiving DAPT compared with monotherapy was 1.9 (0.93–3.88), P=0.08. There was no difference in MACE between no antiplatelet treatment and monotherapy 1.03 (0.31–3.46), P=0.96. Bleeding was more frequent with DAPT 6.55 (2.3–17.96) P=0.0002. In a propensity matched analysis of 177 patients who received DAPT and 177 monotherapy patients, the risk ratio for MACE with DAPT was 1.83 (0.69–4.85), P=0.32. The risk of bleeding was significantly greater in the DAPT group 4.00 (1.15–13.93), P=0.031. Conclusions: OBTAIN showed an increased risk of bleeding with DAPT and found no evidence for protective effects of DAPT from perioperative MACE in patients who have undergone previous PCI

The impact of oxic alteration on plume-derived transition metals in ridge flank sediments from the East Pacific Rise

We describe transition metal behaviour during early diagenesis in sediments collected along a transect across the eastern flank of the East Pacific Rise (EPR) at 14°S overlying crust with magnetic ages of 0.36 Ma to 4.6 Ma.The sediments are lithologically simple and consist of biogenic carbonate, hydrothermal plume precipitates and minor basaltic debris. Sedimentation rates range from 1 cm/ka in the near-axis region (0.36 Ma) to 0.1–0.2 cm/ka across the young ridge flank (by 1.9 Ma, or within 142 km from axis). Redox indicators (porewater Mn(II)aq and solid phase Mo/Mn ratios) indicate fully oxic conditions in near-axis sediments, changing to mildly suboxic conditions across the ridge flank.Sequential extraction analysis of sediments from the 0.36 Ma site indicates that oxic alteration of Fe oxyhydroxides is dominated by transformation of ferrihydrite to goethite, implying that alteration occurs via dissolution followed by nucleation and precipitation. The extent of alteration (amorphous Fe/total plume-derived Fe) ranges from 0.3 to 0.8, and the time to half conversion is on the order of 100 ka. V associated with plume-derived ferrihydrite is strongly discriminated against during alteration to goethite and the distribution coefficient (DV = (V/Fe)goethite/(V/Fe)dissolved) is in the range 0.45–0.59. Cu, Zn and Ni are delivered to the sediment in association with both Fe oxyhydroxides and Mn oxides, where 70% of Cu and Zn and 10% of Ni are associated with Fe oxyhydroxides. The Fe-adsorbed Cu and Zn are incorporated quantitatively into the lattice structure of goethite during alteration. The Fe-associated Ni most likely represents Ni co-precipitated as Ni–Fe ferrihydrite and incorporated into goethite during alteration. Co is associated only with Mn oxides. The oxic alteration of hydrothermal Fe oxyhydroxides therefore represents a relatively permanent sink (where goethite dissolution is a prerequisite for metal release) for a maximum of 70% of plume-derived Cu and Zn, 50% of V, 10% of Ni and 0% of Co. In oxic sediments, the remaining plume-derived metals are retained in association with amorphous Fe oxyhydroxides and Mn oxides, although this fraction is highly susceptible to diagenetic remobilization under suboxic conditions

CAN HYDRATE DISSOLUTION EXPERIMENTS PREDICT THE FATE OF A NATURAL HYDRATE SYSTEM?

Here, we present a dissolution study of exposed hydrate from outcrops at Barkley Canyon. Previously, a field experiment on synthetic methane hydrate samples showed that mass transfer controlled dissolution in under-saturated seawater. However, seafloor hydrate outcrops have been shown to have significant longevity compared to expected dissolution rates based upon convective boundary layer diffusion calculations. To help resolve this apparent disconnect between the dissolution rates of synthetic and natural hydrate, an in situ dissolution experiment was performed on two distinct natural hydrate fabrics. A hydrate mound at Barkley Canyon was observed to contain a “yellow” hydrate fabric overlying a “white” hydrate fabric. The yellow hydrate fabric was associated with a light condensate phase and was hard to core. The white hydrate fabric was more porous and relatively easier to core. Cores from both fabrics were inserted to a mesh chamber within a few meters of the hydrate mound. Time-lapse photography monitored the dissolution of the hydrate cores over a two day period. The diameter shrinkage rate for the yellow hydrate was 45.5 nm/s corresponding to a retreat rate of 0.7 m/yr for an exposed surface. The white hydrate dissolved faster at 67.7 nm/s yielding a retreat rate of 1.1 m/yr. It is possible these hydrate mounds were exposed due to the fishing trawler incident in 2001. If these dissolution experiments give a correct simulation, then the exposed faces should have retreated ~ 3.5 m and 5.5 m, respectively, from 2001 to this expedition in August 2006. While the appearance of the hydrate mounds appeared quite similar to photographs taken in 2002, these dissolution experiments show natural hydrate dissolves rapidly in ambient seawater. The natural hydrate dissolution rate is on the same order as the synthetic dissolution experiment strongly implying another control for the dissolution rates of natural hydrate outcrops. Several factors could contribute to the apparent longevity of these exposed mounds from upward flux of methane-rich fluid to protective bacterial coatings.Non UBCUnreviewe

Coastal measurements of short-lived reactive iodocarbons and bromocarbons at Roscoff, Brittany during the RHaMBLe campaign

Atmospheric concentrations of the volatile reactive iodocarbons C[subscript 2]H[subscript 5]I, 1-C[subscript 3]H[subscript 7]I, 2-C[subscript 3]H[subscript 7]I, CH[subscript 2]ICl, CH[subscript 2]IBr, CH[subscript 2]I[subscript 2] and bromocarbons CH[subscript 2]Br[subscript 2] and CHBr[subscript 3] were determined by GC/MS analysis of marine boundary layer air at Roscoff, Brittany on the northwest coast of France during September 2006. Comparison with other coastal studies suggests that emissions of these trace gases are strongly influenced by site topography, seaweed populations and distribution, as well as wind speed and direction and tide height. Concentrations of the very short-lived dihalomethanes CH[subscript 2]IBr and CH[subscript 2]I[subscript 2] in particular showed evidence of tidal dependence, with higher concentrations observed at low tide during maximum exposure of seaweed beds. We also present a limited number of halocarbon measurements in surface seawater and estimate sea-air fluxes based on these and simultaneous air measurements. CH[subscript 2]Br[subscript 2] and CHBr[subscript 3] were strongly correlated both in air and in seawater, with CH[subscript 2]Br[subscript 2]/CHBr[subscript 3] ratios of 0.19 in air and 0.06 in water. The combined midday I atom flux from the photolabile diahlomethanes CH[subscript 2]I[subscript 2], CH[subscript 2]IBr and CH[subscript 2]ICl of ~5×10[superscript 3] molecules cm[superscript −3] s[superscript −1] is several orders of magnitude lower than the estimated I atom flux from I[subscript 2] based on coinciding measurements at the same site, which indicates that at Roscoff the major I atom precursor was I[subscript 2] rather than reactive iodocarbons

Veiligheid in het luchtruim

ARTIKELEN: 1. P.A.M. Verrest en J.A.C. Bevers - Rechtshandhaving in het luchtruim 2. R.P. Bron en D. de Hoog - Civiele luchtvaart en terroristische incidenten, historische ontwikkelingen en toekomstige trends 3. W.C.J.M. van Dijk - Toegang tot een veilig luchtruim; 'security' op luchthavens 4. P.M.J. Mendes de Leon, m.m.v. M. Gurvits - De ontwikkeling van een trans-Atlantische luchtvaartrelatie in de periode 1992-2007 5. R.M. Schnitker - Het melden van voorvallen in de luchtvaart binnen een 'just culture' 6. B. Baksteen - Dilemma's van een gezagvoerder 7. F.G. von der Dunk - Ruimtepuin en ruimterecht 8. Internetsites. SAMENVATTING: Gezien de internationale context roept het streven naar veiligheid in het luchtruim tal van interessante vragen op op het terrein van wet- en regelgeving, internationale verdragen, rechtsmacht, rechtshandhaving en -vervolging. Er bestaat een grote variëteit aan overtredingen en misdrijven die kunnen worden begaan, zowel delicten aan boord van vliegtuigen als tegen en met het gebruik van vliegtuigen. Vanuit het perspectief van de reguliere rechtshandhaving zijn de omstandigheden waaronder luchttransport plaatsvindt uniek: in een vrijwel geïsoleerd en kwetsbaar voertuig worden internationale grenzen met grote snelheden gepasseerd

Folga organizacional no processo de gestão do orçamento: um estudo no SENAC de Santa Catarina

A folga organizacional no processo orçamentário tem recebido atenção de pesquisadores e gestores em vista de possíveis conflitos de interesses entre principal e agente. Neste sentido, o estudo objetiva identificar a propensão de criar folga organizacional no processo de gestão do orçamento pelos Gestores das Unidades de Negócios do SENAC de Santa Catarina. Pesquisa descritiva, com abordagem quantitativa, foi realizada por meio de uma survey. A população da pesquisa compreende os 21 Gestores das Unidades Operativas do SENAC de Santa Catarina. Um questionário foi encaminhado no mês de julho de 2010, sendo que a amostra constitui-se dos 15 respondentes da pesquisa. O instrumento de coleta de dados consistiu de um questionário traduzido da pesquisa de Onsi (1973), composto por 42 questões fechadas, envolvendo escala Likert, com fatores de oito dimensões da prática da gestão do orçamento, focalizando a folga orçamentária. Os dados foram importados para o software estatístico SPSS versão 13, para fins de análise dos elementos de folga por meio de estatística descritiva, do Alfa de Cronbach e da técnica de análise fatorial. Os resultados do estudo indicam que os gestores têm propensão para criar folga em seus orçamentos, apesar do SENAC não remunerar seus gestores com base nos resultados, o que por si só deveria ser um fator que não motiva a criação de folga orçamentária. Diferente da pesquisa realizada por Onsi (1973), no SENAC os motivos para a criação de folga orçamentária decorrem do interesse dos gestores em apresentar desempenho superior em relação ao previsto no orçamento