Limited contributions of plant pathogens to density‐dependent seedling mortality of mast fruiting Bornean trees

Fungal pathogens are implicated in driving tropical plant diversity by facilitating strong, negative density‐dependent mortality of conspecific seedlings (C‐NDD). Assessment of the role of fungal pathogens in mediating coexistence derives from relatively few tree species and predominantly the Neotropics, limiting our understanding of their role in maintaining hyper‐diversity in many tropical forests. A key question is whether fungal pathogen‐mediated C‐NDD seedling mortality is ubiquitous across diverse plant communities. Using a manipulative shadehouse experiment, we tested the role of fungal pathogens in mediating C‐NDD seedling mortality of eight mast fruiting Bornean trees, typical of the species‐rich forests of South East Asia. We demonstrate species‐specific responses of seedlings to fungicide and density treatments, generating weak negative density‐dependent mortality. Overall seedling mortality was low and likely insufficient to promote overall community diversity. Although conducted in the same way as previous studies, we find little evidence that fungal pathogens play a substantial role in determining patterns of seedling mortality in a SE Asian mast fruiting forest, questioning our understanding of how Janzen‐Connell mechanisms structure the plant communities of this globally important forest type

Effect of core cross-linking on the physical properties of poly(dimethylsiloxane)-based diblock copolymer worms prepared in silicone oil

A trithiocarbonate-capped poly(dimethylsiloxane) (PDMS) precursor is chain-extended via reversible addition–fragmentation chain transfer dispersion polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) in decamethylcyclopentasiloxane (D5) silicone oil at 90 °C. For a fixed mean degree of polymerization (DP) of 66 for the PDMS steric stabilizer block, targeting core-forming PDMA block DPs of between 105 and 190 enables the preparation of either well-defined worms or vesicles at a copolymer concentration of 25% w/w. The as-synthesized linear PDMS66–PDMA100 worms exhibit thermoresponsive behavior in D5, undergoing a worm-to-sphere transition on heating to 100 °C. Variable temperature 1H NMR spectroscopy indicates that this thermal transition is driven by reversible solvent plasticization of the PDMA cores. This change in copolymer morphology is characterized by transmission electron microscopy (TEM) studies, variable temperature dynamic light scattering and small-angle X-ray scattering experiments. Oscillatory rheology studies indicate that degelation occurs at 32 °C, but shear-induced polarized light imaging measurements suggest that full conversion of worms into spheres requires significantly higher temperatures (∼110 °C). 1,2-Bis(2-iodoethoxy)ethane (BIEE) is evaluated as a cross-linker for PDMS66–PDMAx diblock copolymer nano-objects in D5. This bifunctional reagent quaternizes the tertiary amine groups on the DMA residues within the worm cores, introducing cross-links via the Menshutkin reaction. TEM studies confirm that such covalently-stabilized worms no longer undergo a worm-to-sphere transition when heated to 100 °C. Kinetic studies performed on PDMS66–PDMA176 vesicles suggest that cross-linking requires approximately 13 h at 20 °C to ensure that these nano-objects remain intact when dispersed in chloroform, which is a good solvent for both blocks. Oscillatory rheology studies of a PDMS66–PDMA100 worm gel indicated that covalent stabilization using a BIEE/DMA molar ratio of 0.15 increased its dynamic elastic modulus (G′) by almost two orders of magnitude. Furthermore, such cross-linked worms exhibit a much lower critical gelation concentration (∼2% w/w) compared to that of the linear precursor worms (∼12% w/w)

RAFT dispersion polymerization of benzyl methacrylate in silicone oil using a silicone-based methacrylic stabilizer provides convenient access to spheres, worms, and vesicles

Reversible addition–fragmentation chain transfer (RAFT) solution polymerization of 3-[tris(trimethylsiloxy)silyl] propyl methacrylate (SiMA) was conducted in toluene to prepare three PSiMA precursors with mean degrees of polymerization (DP) of 12, 13, or 15. Each precursor was then chain-extended in turn via RAFT dispersion polymerization of benzyl methacrylate (BzMA) in a low-viscosity silicone oil (decamethylcyclopentasiloxane, D5). 1H NMR studies confirmed that such polymerizations were relatively fast, with more than 99% BzMA conversion being achieved within 100 min at 90 °C. Moreover, gel permeation chromatography analysis indicated that these polymerizations were well controlled, with dispersities remaining below 1.25 when targeting PBzMA DPs up to 200. A phase diagram was constructed at a constant copolymer concentration of 20% w/w. Only spherical micelles were accessible when the PSiMA15 stabilizer was utilized, as determined by transmission electron microscopy and small-angle X-ray scattering (SAXS) studies. Nevertheless, these spheres exhibited narrow size distributions and tunable z-average diameters ranging between 19 and 49 nm, as determined by dynamic light scattering. In contrast, spheres, worms, or vesicles could be prepared depending on the target PBzMA DP when utilizing the relatively short PSiMA12 precursor. Moreover, each of these nano-objects could be obtained at copolymer concentrations as low as 5% w/w. To obtain more detailed structural information, these spheres, worms and vesicles were further characterized by SAXS. PSiMA12-PBzMA55 worms formed reasonably transparent free-standing gels when prepared at copolymer concentrations as low as 5% w/w and exhibited an elastic modulus (G′) of 90 Pa at 25 °C, as judged by oscillatory rheology studies. Finally, broadening of the molecular weight distribution was observed during the long-term storage of PSiMA-PBzMA dispersions at ambient temperature. We tentatively suggest that this instability is related to hydroxyl impurities in the SiMA, which leads to cross-linking side reactions. This problem also causes incipient flocculation of the spheres and worms during the long-term storage of such dispersions at 20 °C

Active Galaxies in the UV

In this article we present different aspects of AGN studies demonstrating the importance of the UV spectral range. Most important diagnostic lines for studying the general physical conditions as well as the metalicities in the central broad line region in AGN are emitted in the UV. The UV/FUV continuum in AGN excites not only the emission lines in the immediate surrounding but it is responsible for the ionization of the intergalactic medium in the early stages of the universe. Variability studies of the emission line profiles of AGN in the UV give us information on the structure and kinematics of the immediate surrounding of the central supermassive black hole as well as on its mass itself.Comment: 29 pages, 13 figures, Ap&SS in pres

Aspects of String-Gas Cosmology at Finite Temperature

We study string-gas cosmology in dilaton gravity, inspired by the fact that it naturally arises in a string theory context. Our main interest is the thermodynamical treatment of the string-gas and the resulting implications for the cosmology. Within an adiabatic approximation, thermodynamical equilibrium and a small, toroidal universe as initial conditions, we numerically solve the corresponding equations of motions in two different regimes describing the string-gas thermodynamics: (i) the Hagedorn regime, with a single scale factor, and (ii) an almost-radiation dominated regime, which includes the leading corrections due to the lightest Kaluza Klein and winding modes, with two scale factors. The scale factor in the Hagedorn regime exhibits very slow time evolution with nearly constant energy and negligible pressure. By contrast, in case (ii) we find interesting cosmological solutions where the large dimensions continue to expand and the small ones are kept undetectably small.Comment: 21 pages, 5 eps figure

Debris disk size distributions: steady state collisional evolution with P-R drag and other loss processes

We present a new scheme for determining the shape of the size distribution, and its evolution, for collisional cascades of planetesimals undergoing destructive collisions and loss processes like Poynting-Robertson drag. The scheme treats the steady state portion of the cascade by equating mass loss and gain in each size bin; the smallest particles are expected to reach steady state on their collision timescale, while larger particles retain their primordial distribution. For collision-dominated disks, steady state means that mass loss rates in logarithmic size bins are independent of size. This prescription reproduces the expected two phase size distribution, with ripples above the blow-out size, and above the transition to gravity-dominated planetesimal strength. The scheme also reproduces the expected evolution of disk mass, and of dust mass, but is computationally much faster than evolving distributions forward in time. For low-mass disks, P-R drag causes a turnover at small sizes to a size distribution that is set by the redistribution function (the mass distribution of fragments produced in collisions). Thus information about the redistribution function may be recovered by measuring the size distribution of particles undergoing loss by P-R drag, such as that traced by particles accreted onto Earth. Although cross-sectional area drops with 1/age^2 in the PR-dominated regime, dust mass falls as 1/age^2.8, underlining the importance of understanding which particle sizes contribute to an observation when considering how disk detectability evolves. Other loss processes are readily incorporated; we also discuss generalised power law loss rates, dynamical depletion, realistic radiation forces and stellar wind drag.Comment: Accepted for publication by Celestial Mechanics and Dynamical Astronomy (special issue on EXOPLANETS

Gamma-ray Observations Under Bright Moonlight with VERITAS

Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727+502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations

In utero exposure to benzo[a]pyrene increases mutation burden in the soma and sperm of adult mice

Background: Mosaicism, the presence of genetically distinct cell populations within an organism, has emerged as an important contributor to disease. Mutational events occurring during embryonic development can cause mosaicism in any tissue, but the influence of environmental factors on levels of mosaicism is unclear. Objectives: We investigated whether in utero exposure to the widespread environmental mutagen benzo[a]pyrene (BaP) has an impact on the burden and distribution of mutations in adult mice. Methods: We used the Muta™Mouse transgenic rodent model to quantify and characterize mutations in the offspring of pregnant mice exposed to BaP during postconception days 7 through 16, covering the major period of organogenesis in mice. Next-generation DNA sequencing was then used to determine the spectrum of mutations induced in adult mice that were exposed to BaP during fetal development. Results: Mutation frequency was significantly increased in the bone marrow, liver, brain, and sperm of first filial generation (F1) males. Developing embryos accumulated more mutations and exhibited higher proportions of mosaicism than exposed adults, particularly in the brain. Decreased sperm count and motility revealed additional negative impacts on the reproductive function of F1 males. Conclusion: In utero exposure to environmental mutagens contributes to somatic and germline mosaicism, permanently affecting both the genetic health of the F1 and the population gene pool. Citation: Meier MJ, O’Brien JM, Beal MA, Allan B, Yauk CL, Marchetti F. 2017. In utero exposure to benzo[a]pyrene increases mutation burden in the soma and sperm of adult mice

Anthropogenic Space Weather

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure

Social-ecological, motivational and volitional factors for initiating and maintaining physical activity in the context of HIV

Sport and exercise can have several health benefits for people living with HIV. These benefits can be achieved through different types of physical activity, adapting to disease progression, motivation and social-ecological options. However, physical activity levels and adherence to exercise are generally low in people living with HIV. At the same time, high drop-out rates in intervention studies are prevalent; even though they often entail more favourable conditions than interventions in the natural settings. Thus, in the framework of an intervention study, the present study aims to explore social-ecological, motivational and volitional correlates of South African women living with HIV with regard to physical activity and participation in a sport and exercise health promotion programme. The qualitative data was produced in the framework of a non-randomised pre-post intervention study that evaluated structure, processes and outcomes of a 10-week sport and exercise programme. All 25 participants of the programme were included in this analysis, independent of compliance. Data was produced through questionnaires, participatory group discussions, body image pictures, research diaries and individual semi-structured interviews. All participants lived in a low socioeconomic, disadvantaged setting. Hence, the psychological correlates are contextualised and social-ecological influences on perception and behaviour are discussed. The results show the importance of considering social-cultural and environmental influences on individual motives, perceptions and expectancies, the fear of disclosure and stigmatisation, sport and exercise-specific group dynamics and self-supporting processes. Opportunities and strategies to augment physical activity and participation in sport and exercise programmes in the context of HIV are discussed.Scopu