Fundamental Aspects of the ISM Fractality

The ubiquitous clumpy state of the ISM raises a fundamental and open problem of physics, which is the correct statistical treatment of systems dominated by long range interactions. A simple solvable hierarchical model is presented which explains why systems dominated by gravity prefer to adopt a fractal dimension around 2 or less, like the cold ISM and large scale structures. This has direct relation with the general transparency, or blackness, of the Universe.Comment: 6 pages, LaTeX2e, crckapb macro, no figure, uuencoded compressed tar file. To be published in the proceeedings of the "Dust-Morphology" conference, Johannesburg, 22-26 January, 1996, D. Block (ed.), (Kluwer Dordrecht

Passive water control at the surface of a superhydrophobic lichen

Some lichens have a super-hydrophobic upper surface, which repels water drops, keeping the surface dry but probably preventing water uptake. Spore ejection requires water and is most efficient just after rainfall. This study was carried out to investigate how super-hydrophobic lichens manage water uptake and repellence at their fruiting bodies, or podetia. Drops of water were placed onto separate podetia of Cladonia chlorophaea and observed using optical microscopy and cryo-scanning-electron microscopy (cryo-SEM) techniques to determine the structure of podetia and to visualise their interaction with water droplets. SEM and optical microscopy studies revealed that the surface of the podetia was constructed in a three-level structural hierarchy. By cryo-SEM of water-glycerol droplets placed on the upper part of the podetium, pinning of the droplet to specific, hydrophilic spots (pycnidia/apothecia) was observed. The results suggest a mechanism for water uptake, which is highly sophisticated, using surface wettability to generate a passive response to different types of precipitation in a manner similar to the Namib Desert beetle. This mechanism is likely to be found in other organisms as it offers passive but selective water control

The Formation of the First Low-Mass Stars From Gas With Low Carbon and Oxygen Abundances

The first stars in the Universe are predicted to have been much more massive than the Sun. Gravitational condensation accompanied by cooling of the primordial gas due to molecular hydrogen, yields a minimum fragmentation scale of a few hundred solar masses. Numerical simulations indicate that once a gas clump acquires this mass, it undergoes a slow, quasi-hydrostatic contraction without further fragmentation. Here we show that as soon as the primordial gas - left over from the Big Bang - is enriched by supernovae to a carbon or oxygen abundance as small as ~0.01-0.1% of that found in the Sun, cooling by singly-ionized carbon or neutral oxygen can lead to the formation of low-mass stars. This mechanism naturally accommodates the discovery of solar mass stars with unusually low (10^{-5.3} of the solar value) iron abundance but with a high (10^{-1.3} solar) carbon abundance. The minimum stellar mass at early epochs is partially regulated by the temperature of the cosmic microwave background. The derived critical abundances can be used to identify those metal-poor stars in our Milky Way galaxy with elemental patterns imprinted by the first supernovae.Comment: 14 pages, 2 figures (appeared today in Nature

A Minimum Column Density of 1 g cm^-2 for Massive Star Formation

Massive stars are very rare, but their extreme luminosities make them both the only type of young star we can observe in distant galaxies and the dominant energy sources in the universe today. They form rarely because efficient radiative cooling keeps most star-forming gas clouds close to isothermal as they collapse, and this favors fragmentation into stars <~1 Msun. Heating of a cloud by accreting low-mass stars within it can prevent fragmentation and allow formation of massive stars, but what properties a cloud must have to form massive stars, and thus where massive stars form in a galaxy, has not yet been determined. Here we show that only clouds with column densities >~ 1 g cm^-2 can avoid fragmentation and form massive stars. This threshold, and the environmental variation of the stellar initial mass function (IMF) that it implies, naturally explain the characteristic column densities of massive star clusters and the difference between the radial profiles of Halpha and UV emission in galactic disks. The existence of a threshold also implies that there should be detectable variations in the IMF with environment within the Galaxy and in the characteristic column densities of massive star clusters between galaxies, and that star formation rates in some galactic environments may have been systematically underestimated.Comment: Accepted for publication in Nature; Nature manuscript style; main text: 14 pages, 3 figures; supplementary text: 8 pages, 1 figur

The Dynamical Structure and Evolution of Giant Molecular Clouds

Giant molecular clouds (GMCs) are the sites of star formation in the Galaxy. Many of their properties can be understood in terms of a model in which the GMCs and the star-forming clumps within them are in approximate pressure equilibrium, with turbulent motions treated as a separate pressure component

The importance of plasma apolipoprotein E concentration in addition to its common polymorphism on inter-individual variation in lipid levels: results from Apo Europe

The ApoEurope group, collaborating centres, and their associated investigators: Portugal: Unidade de Química Clínica, Instituto Nacional de Saúde, Lisboa: Maria do Carmo Martins, Maria Odete Rodrigues, Maria Isabel Albergaria, Maria Liseta AlpendreInterindividual variation in the concentration of plasma lipids which are associated with coronary artery disease (CAD) risk is determined by a combination of genetic and environmental factors. This study investigates the effects of apoE genotype and plasma concentration on cholesterol and triglycerides (TG) levels in subjects from five countries: Finland, France, Northern Ireland, Portugal, and Spain. Age and sex significantly influenced serum cholesterol, TG and apoE concentrations. The age effect differs in males and females. The allele frequencies of the apoE gene, one of the most widely studied CAD susceptibility genes, were determined: the epsilon2 allele frequency and the apoE concentration showed a north-south increasing gradient while the epsilon4 allele frequency showed the reverse. ApoE plays an important role in lipid metabolism. Total cholesterol and TG concentrations were significantly dependent on apoE genotype in both sexes. These differences in lipids between genotypes were more pronounced when plasma apoE concentrations were taken into account

The influence of Mechanical bowel preparation in elective colorectal surgery for diverticulitis

Background: Mechanical bowel preparation (MBP) has been shown to have no influence on the incidenc

Factors associated with pre-ART loss-to-follow up in adults in rural KwaZulu-Natal, South Africa:a prospective cohort study

Background: Timely initiation of antiretroviral treatment (ART) requires sustained engagement in HIV care before treatment eligibility. We assessed loss to follow-up (LTFU) correlates in HIV-positive adults accessing HIV treatment and care, not yet ART-eligible (CD4 &gt;500 cells/mm3).Methods: This was a sub-study of a prospective cohort study (focusing on sexual behaviour) in an area of high HIV prevalence and widespread ART availability in rural KwaZulu-Natal, South Africa. Psychosocial, clinical and demographic data were collected at recruitment from individuals with CD4 &gt;500 cells/mm3. LTFU was defined as not attending clinic within 13 months of last visit or before death. Individuals starting ART were censored at ART initiation. Data were collected between January 2009 and January 2013. Analysis used Competing Risks regression.Results: Two hundred forty-seven individuals (212 females) were recruited (median follow-up 2.13 years, total follow-up 520.15 person-years). 86 remained in pre-ART care (34.8 %), 94 were LTFU (38.1 %), 58 initiated ART (23.5 %), 7 died (2.8 %), 2 transferred out (0.8 %). The LTFU rate was 18.07 per 100 person-years (95 % CI 14.76–21.12). LTFU before a competing event was 13.5 % at one and 34.4 % at three years. Lower LTFU rates were significantly associated with age (&gt;37 versus ?37 years: adjusted sub-Hazard ratio (aSHR) 0.51, 95 % CI 0.30–0.87), openness with family/friends (a little versus not at all, aSHR 0.81, 95 % CI 0.45–1.43; a lot versus not at all, aSHR 1.57, 95 % CI 0.94–2.62), children (0 versus 4+, aSHR 0.68, 95 % CI 0.24–1.87; 1 versus 4+, aSHR 2.05 95 % CI 1.14–3.69, 2 versus 4+; aSHR 1.71, 95 % CI 0.94–3.09; 3 versus 4a, aSHR 1.14, 95 % CI 0.57–2.30), previous CD4 counts (1 versus 0, aSHR 0.81, 95 % CI 0.45–1.43; 2+ versus 0, aSHR 0.43, 95 % CI 0.25–0.73), and most recent partner HIV status (not known versus HIV-positive, aSHR 0.77, 95 % CI 0.50–1.19; HIV-negative versus HIV-positive, aSHR 2.40, 95 % CI 1.18–4.88). The interaction between openness with family/friends and HIV partner disclosure was close to significance (p?=?0.06). Those who had neither disclosed to partners nor were open with family/friends had lowest LTFU rates.Conclusions: Strategies to retain younger people in pre-ART care are required. How openness with others, partner HIV status and disclosure, and children relate to LTFU needs further exploration.<br/

Sharing brain mapping statistical results with the neuroimaging data model

Only a tiny fraction of the data and metadata produced by an fMRI study is finally conveyed to the community. This lack of transparency not only hinders the reproducibility of neuroimaging results but also impairs future meta-analyses. In this work we introduce NIDM-Results, a format specification providing a machine-readable description of neuroimaging statistical results along with key image data summarising the experiment. NIDM-Results provides a unified representation of mass univariate analyses including a level of detail consistent with available best practices. This standardized representation allows authors to relay methods and results in a platform-independent regularized format that is not tied to a particular neuroimaging software package. Tools are available to export NIDM-Result graphs and associated files from the widely used SPM and FSL software packages, and the NeuroVault repository can import NIDM-Results archives. The specification is publically available at: http://nidm.nidash.org/specs/nidm-results.html

High-Throughput Sequencing of Three Lemnoideae (Duckweeds) Chloroplast Genomes from Total DNA

BACKGROUND: Chloroplast genomes provide a wealth of information for evolutionary and population genetic studies. Chloroplasts play a particularly important role in the adaption for aquatic plants because they float on water and their major surface is exposed continuously to sunlight. The subfamily of Lemnoideae represents such a collection of aquatic species that because of photosynthesis represents one of the fastest growing plant species on earth. METHODS: We sequenced the chloroplast genomes from three different genera of Lemnoideae, Spirodela polyrhiza, Wolffiella lingulata and Wolffia australiana by high-throughput DNA sequencing of genomic DNA using the SOLiD platform. Unfractionated total DNA contains high copies of plastid DNA so that sequences from the nucleus and mitochondria can easily be filtered computationally. Remaining sequence reads were assembled into contiguous sequences (contigs) using SOLiD software tools. Contigs were mapped to a reference genome of Lemna minor and gaps, selected by PCR, were sequenced on the ABI3730xl platform. CONCLUSIONS: This combinatorial approach yielded whole genomic contiguous sequences in a cost-effective manner. Over 1,000-time coverage of chloroplast from total DNA were reached by the SOLiD platform in a single spot on a quadrant slide without purification. Comparative analysis indicated that the chloroplast genome was conserved in gene number and organization with respect to the reference genome of L. minor. However, higher nucleotide substitution, abundant deletions and insertions occurred in non-coding regions of these genomes, indicating a greater genomic dynamics than expected from the comparison of other related species in the Pooideae. Noticeably, there was no transition bias over transversion in Lemnoideae. The data should have immediate applications in evolutionary biology and plant taxonomy with increased resolution and statistical power