Modelling solar low-lying cool loops with optically thick radiative losses

We investigate the increase of the DEM (differential emission measure) towards the chromosphere due to small and cool magnetic loops (height $\lesssim8$~Mm, $T\lesssim10^5$~K). In a previous paper we analysed the conditions of existence and stability of these loops through hydrodynamic simulations, focusing on their dependence on the details of the optically thin radiative loss function used. In this paper, we extend those hydrodynamic simulations to verify if this class of loops exists and it is stable when using an optically thick radiative loss function. We study two cases: constant background heating and a heating depending on the density. The contribution to the transition region EUV output of these loops is also calculated and presented. We find that stable, quasi-static cool loops can be obtained by using an optically thick radiative loss function and a background heating depending on the density. The DEMs of these loops, however, fail to reproduce the observed DEM for temperatures between $4.6<\log T<4.8$. We also show the transient phase of a dynamic loop obtained by considering constant heating rate and find that its average DEM, interpreted as a set of evolving dynamic loops, reproduces quite well the observed DEM.Comment: Accepted for publication in A&A on Aug 21st 2015. arXiv admin note: text overlap with arXiv:1112.030

Surface-enhanced Raman spectroscopy in 3D electrospun nanofiber mats coated with gold nanorods

Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments.Comment: 29 pages, 9 figures, 1 Tabl

Insights in disease management - Editorial

Editorial on the Research Topic Insights in disease management The Research Topic “Insights in Disease Management” brings together innovative Research Topics from the disease management sector. This is a key time to reduce losses to diseases so that we can produce more food that we need for the growing global population but also to control diseases in a way that minimises the environmental footprint of crop production. The issue covers insights using examples in both protected and field crops, covering most pathogen groups – bacteria (Reglinski et al.), viruses (Codod et al.), fungi (Dutta et al.; Sangiorgio et al.), and oomycetes (Sharma et al.). Underpinning many current approaches to disease management is the idea of integrated pest management, which is often portrayed as a triangle representing different tiers of approaches. The foundations of the IPM triangle are practices such as crop rotation to separate crops and pathogens in space and time, use of resistant varieties, and various effects of management practices such as under-sowing or inter-cropping to alter the microclimate, release biofumigants, maintain beneficial microbes or to act as a physical barrier. Papers in this issue connected with this layer of the IPM triangle cover aspects such as improved host resistance with marker-assisted selection, genome sequencing, and improved understanding of resistance genes (Sharma et al.). Also connected to host resistance is the paper by Reglinski et al. except that this concerns host resistance induced by application of a chemical elicitor. This human intervention is preferable to applications of chemical pesticides (usually depicted at the top of the IPM triangle to represent a measure used only as a last resort), which despite often providing efficient disease control and associated benefits of enhanced yield, is acknowledged to have potential non-target effects in the environment. One such non-target effect is the impact of fungicides and other pesticides on microbial endophytes and more broadly, the phytobiome, which Sangiorgio et al. argue, has potential to confer a degree of natural biological control, protecting against pathogens both on the plant surface and within host tissues. They review how genetic sequencing techniques are providing new insights into the degree of protection conferred by the phytobiome towards pathogens in addition to other roles affecting resistance to abiotic stress and nutrient uptake, ultimately affecting plant phenotype, growth, yield and quality. They conclude that future research on plant disease control should also consider impacts to microbe-mediated plant fitness. Indeed, even applications of biological control agents have potential to affect the phytobiome, but this approach is nevertheless regarded as less damaging to the environment compared to chemical control. One of the main biocontrol agents that has been used successfully for over 50 years is Trichoderma. This fungal genus is reviewed by Dutta et al., covering its use as a bio-fungicide, long-term biocontrol agent, defence activator and plant growth stimulator. The use of available biologicals or chemical control options are greatly enhanced by monitoring and forecasting schemes to indicate exactly when the target pathogen will occur. This is increasingly being seen as a form of precision agriculture, directing not only where but also when to make an intervention to protect crops from imminent disease. Various processes have been investigated, ranging from optical sensing from platforms such as satellites, drones or tractor and hand-held devices, to weather-based forecasts, or taking environmental samples (irrigation water, soil or the air) and performing various diagnostic tests, some of which are compatible with being automated and linked to wireless reporting. One key step in determining an efficient sampling or monitoring regime is to understand the spatial distribution of the pest or pathogen in question. The paper by Codod et al. is an example of this – explaining how the whitefly-transmitted virus complex affecting yellow squash (Cucurbita pepo) occurs initially in a sparse, random pattern, mainly around edges of fields but becomes aggregated, with spread mainly along rows, which will inform future developments to improve scouting, monitoring, and management strategies. This issue therefore brings together the core components of IPM, including traditional epidemiological studies, bio-control and cutting-edge ‘omics’, which are currently reshaping IPM, particularly through studies of functional genomics and the microbiome. These approaches are increasingly necessary to deliver sustainable crop production that will feed the world, while having a low environmental impact

Signatures of impulsive localized heating in the temperature distribution of multi-stranded coronal loops

We study the signatures of different coronal heating regimes on the differential emission measure (DEM) of multi-stranded coronal loops by means of hydrodynamic simulations. We consider heating either uniformly distributed along the loops or localized close to the chromospheric footpoints, in both steady and impulsive conditions. Our simulations show that condensation at the top of the loop forms when the localized heating is impulsive with a pulse cadence time shorter than the plasma cooling time, and the pulse energy is below a certain threshold. A condensation does not produce observable signatures in the global DEM structure. Conversely, the DEM coronal peak is found sensitive to the pulse cadence time. Our simulations can also give an explanation of the warm overdense and hot underdense loops observed by TRACE, SOHO and Yohkoh. However, they are unable to reproduce both the transition region and the coronal DEM structure with a unique set of parameters, which outlines the need for a more realistic description of the transition region.Comment: 31 pages, 7 figure

Comparing weak versions of separability

Our aim is to investigate spaces with sigma-discrete and meager dense sets, as well as selective versions of these properties. We construct numerous examples to point out the differences between these classes while answering questions of Tkachuk [30], Hutchinson [17] and the authors of [8]