The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

7th Drug hypersensitivity meeting: part two

No abstract availabl

Does the law of diminishing returns in leaf scaling apply to vines? - Evidence from 12 species of climbing plants

Shapes, sizes and biomass investment per unit area (LMA) of vine leaves are characterized by high diversity that results in variation in leaf arrangement, light harvesting efficiency and photosynthetic activity. There exists a scaling relationship between leaf dry mass and surface area for many broad-leaved plants, and most estimates of the scaling exponent are greater than unity, implying that they follow the "law of diminishing returns", i.e. that larger leaves require progressively greater investments of dry mass and accordingly have a greater LMA. Previous studies have primarily focused on trees and crops and there are few data available for vines. Yet, as vines have lower support investments in stems than self-supporting plants, they can have larger biomass investments in support within the leaves and stronger rise of biomass costs with increasing leaf area. In this study, we chose twelve species of vines (five woody vines and seven herbaceous vines) to investigate the following scientific questions: (i) whether there are significant differences in LMA between woody and herbaceous vines, (ii) whether leaf dry mass and surface area scaling relationships show evidence of diminishing returns in vines. We observed that LMA values of woody vines were significantly higher than those of the herbaceous vines. Leaf dry mass vs. surface area scaling relationship followed the law of diminishing returns in all 12 studied vine species. The existence of diminishing returns indicates that there is a trade-off between leaf surface area expansion and the energy investment for vines to support leaf physical structures. (C) 2019 The Authors. Published by Elsevier B.V

Search for the semi-leptonic decays Λc+→Λπ+π−e+νe and Λc+→pKS0π−e+νe

We search for the semi-leptonic decays Λc+→Λπ+π−e+νe and Λc+→pKS0π−e+νe in a sample of 4.5fb−1 of e+e− annihilation data collected in the center-of-mass energy region between 4.600GeV and 4.699GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Λc+→Λπ+π−e+νe)<3.9×10−4 and B(Λc+→pKS0π−e+νe)<3.3×10−4 at the 90% confidence level, respectively