Clusters in the inner spiral arms of M51: the cluster IMF and the formation history

We study the cluster population in a region of 3.2x3.2 kpc^2 in the inner spiral arms of the intergacting galaxy M51, at a distance of about 1 to 3 kpc from the nucleus, based on HST--WFPC2 images taken through five broadband and two narrowband filters. We found 877 cluster candidates and we derived their ages, initial masses and extinctions by comparing their energy distribution with the Starburst99 cluster models. We describe the 3 and 2-dimensional least-square energy fitting method that was used (3DEF, 2DEF). The lack of [OIII] emission in even the youngest clusters with strong H-alpha emission, indicates the absence of the most massive stars and suggests a mass upper limit of about 25 to 30 solar masses. The mass versus age distribution of the clusters shows a drastic decrease in the number of clusters with age, which indicates that cluster disruption is occurring on a timescale of about 10 Myr for low mass clusters. The cluster initial mass function for clusters younger than 10 Myr has an exponent of alpha = 2.0 (+- 0.05) We derived the cluster formation history from clusters with an initial mass larger than 10^4 solar masses. There is no evidence for a peak in the cluster formation rate within a factor two at about 200 to 400 Myr ago, i.e. at the time of the interaction with the companion galaxy NGC 5194.Comment: 15 pages, 15 figures. Accepted for publication by Astronomy and Astrophysic

Altered TMPRSS2 usage by SARS-CoV-2 Omicron impacts infectivity and fusogenicity

The SARS-CoV-2 Omicron BA.1 variant emerged in 20211 and has multiple mutations in its spike protein2. Here we show that the spike protein of Omicron has a higher affinity for ACE2 compared with Delta, and a marked change in its antigenicity increases Omicron’s evasion of therapeutic monoclonal and vaccine-elicited polyclonal neutralizing antibodies after two doses. mRNA vaccination as a third vaccine dose rescues and broadens neutralization. Importantly, the antiviral drugs remdesivir and molnupiravir retain efficacy against Omicron BA.1. Replication was similar for Omicron and Delta virus isolates in human nasal epithelial cultures. However, in lung cells and gut cells, Omicron demonstrated lower replication. Omicron spike protein was less efficiently cleaved compared with Delta. The differences in replication were mapped to the entry efficiency of the virus on the basis of spike-pseudotyped virus assays. The defect in entry of Omicron pseudotyped virus to specific cell types effectively correlated with higher cellular RNA expression of TMPRSS2, and deletion of TMPRSS2 affected Delta entry to a greater extent than Omicron. Furthermore, drug inhibitors targeting specific entry pathways3 demonstrated that the Omicron spike inefficiently uses the cellular protease TMPRSS2, which promotes cell entry through plasma membrane fusion, with greater dependency on cell entry through the endocytic pathway. Consistent with suboptimal S1/S2 cleavage and inability to use TMPRSS2, syncytium formation by the Omicron spike was substantially impaired compared with the Delta spike. The less efficient spike cleavage of Omicron at S1/S2 is associated with a shift in cellular tropism away from TMPRSS2-expressing cells, with implications for altered pathogenesis

Observations in eastern England of elevated methyl iodide concentrations in air of Atlantic origin

Atmospheric methyl iodide (CHI) has been measured at a ground-based site in eastern England for two consecutive summers. Maximum values of 43.1 pptv and 28.9 pptv were recorded in 1989 and 1990, respectively. CHI was not detectable in the autumn and winter months. Episodes of elevated concentrations persisted for periods ranging from a few hours to several days. The origin of much of the observed CHI would appear to be the Atlantic Ocean, indicating the presence of large source areas, possibly phytoplankton blooms, in ocean waters. Estimates are made of the dry deposition velocity of CHI, and the potential impact of elevated tropospheric levels on the human uptake of iodine

An estimate of the anthropogenic contribution to atmospheric methyl bromide

A global, 2-D, atmospheric chemistry model of latitude versus altitude, employing a prescribed hydroxyl field, is used to estimate the anthropogenic contribution to atmospheric CHBr. An even spatial distribution is applied to natural emissions, whilst an anthropogenic source is assumed for the northern hemispheric mid-latitudes. Model calculations, constrained by observed concentrations of CHBr and its interhemispheric ratio, lead to the conclusion that the total emission source of CHBr has a strength of 75-105 ktonnes yr with a 33-74% anthropogenic contribution of 25-80 ktonnes yr. The best estimate is a total strength of 91 ktonnes yr, with a 54% anthropogenic contribution of 49 ktonnes yr. The sensitivity of these results are discussed with respect to OH concentration, transport, seasonality, altitude, and the representative nature of the latitudinal spread of data and spatial distribution of emissions. -Author

Production of isoprene by marine phytoplankton cultures

While release of isoprene from the terrestrial biosphere is well established and known to influence the tropospheric concentrations of a number of reactive species including ozone, very little is known of its production in the ocean and possible release to the marine boundary layer. Measurements reported here of low molecular weight trace gases produced by a series of laboratory phytoplankton have shown that isoprene is a major component. -from Author

An interhemispheric comparison of the concentrations of bromine compounds in the atmosphere

At least seven organic bromine compounds have been positively identified in the atmosphere1,2 (CH3Br, CH2Br2, CHBr3, CH2BrCl, CF3Br, CF2BrCl and C2H4Br2) and others have been observed in coastal seawater samples (C2H5Br, C3H7Br and CHBr2Cl) (S. A. P. and R. A. Rasmussen, unpublished data). The atmospheric chemistry of bromine compounds has considerable consequence in the stratosphere, where bromine acts as a more efficient catalyst than chlorine in removing ozone3,4. Several bromine compounds also fulfil an important role in the geochemical cycling of the element through the troposphere5. Here we present measurements of four bromine compounds (CF3Br, CH3Br, CH2Br2 and CHBr3) over a large latitudinal range (40° N to 75° S). These data suggest that the major source of bromine in the atmosphere could be bromoform (CHBr3), probably emitted from the ocean and with a short lifetime due to photolysis. Our data also suggest that the major emission of methyl bromide (CH3Br), and hence most bromine entering the stratosphere, will be anthropogenic

Measurements of HCFC-142b and HCFC-141b in the Cape Grim air archive:1978-1993

Stored air samples collected at Cape Grim, Tasmania since 1978, have been analyzed by GC-MS to investigate the change in the tropospheric concentration of HCFC-142b and HCFC-141b over the past 15 years. Between April 1978 and September 1993 the concentration of HCFC-142b rose, with the majority of this increase occurring from 1989 onwards. From 1989 to 1991 the average concentration of HCFC-141b was 0.08 ± 0.01 pptv. A very sharp increase in concentration began in 1992 however. Using a 2-D model of atmospheric chemistry, constrained by these observations, global emissions of these two compounds have been calculated and found to differ from other estimates. -from Author

Nuclear magnetic resonance studies of erythrocyte membranes

The use of nuclear magnetic resonance spectroscopy for studying molecular interactions in biological membranes has been investigated using erythrocyte membrane fragments. Sonic dispersion of these fragments produces a sharp and well-defined high-resolution nuclear magnetic resonance spectrum. The spectrum shows peaks which can be assigned to various groups of the lipid, sugar and protein. The choline N+ (CH3)3 signal of the membrane lipid is prominent but the signal due to (CH2)n protons of the hydrocarbon chains is broadened as a result of interaction. This signal narrows at higher temperatures or when exposed to increasing concentrations of sodium deoxycholate. Signals due to amino acids of the membrane protein are unresolved in the spectrum but appear as well-defined peaks after treatment with urea or trifluoroacetic acid. Co-dispersion of the membrane fragments with lysolecithin gives a spectrum which indicates the formation of an additive comple