Silicon abundance from RESIK solar flare observations

The RESIK instrument on the CORONAS-F spacecraft obtained solar flare and active region X-ray spectra in four channels covering the wavelength range 3.8 -- 6.1 \AA in its operational period between 2001 and 2003. Several highly ionized silicon lines were observed within the range of the long-wavelength channel (5.00 -- 6.05 \AA). The fluxes of the \sixiv Ly-$\beta$ line (5.217 \AA) and the \sixiii $1s^2 - 1s3p$ line (5.688 \AA) during 21 flares with optimized pulse-height analyzer settings on RESIK have been analyzed to obtain the silicon abundance relative to hydrogen in flare plasmas. As in previous work, the emitting plasma for each spectrum is assumed to be characterized by a single temperature and emission measure given by the ratio of emission in the two channels of GOES. The silicon abundance is determined to be $A({\rm Si}) = 7.93 \pm .21$ (\sixiv) and $7.89 \pm .13$ (\sixiii) on a logarithmic scale with H = 12. These values, which vary by only very small amounts from flare to flare and times within flares, are $2.6 \pm 1.3$ and $2.4 \pm 0.7$ times the photospheric abundance, and are about a factor of three higher than RESIK measurements during a period of very low activity. There is a suggestion that the Si/S abundance ratio increases from active regions to flares.Comment: To be published, Solar Physic

Varying Calcium Abundances in Solar Flares seen by Solar Maximum Mission

We report on calcium abundance $A({\rm Ca})$ estimates during the decay phases of 194 solar X-ray flares using archived data from the Bent Crystal Spectrometer (BCS) on Solar Maximum Mission (operational 1980~--~1989). The abundances are derived from the ratio of the total calcium X-ray line emission in BCS channel~1 to that in neighboring continuum, with temperature from a satellite-to-resonance line ratio. Generally the calcium abundance is found to be about three times the photospheric abundance, as previously found, indicating a ``FIP'' (first ionization potential) effect for calcium which has a relatively low FIP value. The precision of the abundance estimates (referred to hydrogen on a logarithmic scale with $A({\rm H}) = 12$), is typically $\sim \pm 0.01$, enabling any time variations of $A({\rm Ca})$ during the flare decay to be examined. For a total of 270 short time segments with $A({\rm Ca})$ determined to better than 2.3\% accuracy, many (106; 39\%) showed variations in $A({\rm Ca})$ at the $3\sigma$ level. For the majority, 74 (70\%) of these 106 segments $A({\rm Ca})$ decreased with time, and for 32 (30\%) $A({\rm Ca})$ increased with time. For 79 out of 270 (29\%) we observed constant or nearly constant $A({\rm Ca})$, and the remaining 85 (31\%) with irregular time behavior. A common feature was the presence of discontinuities in the time behavior of $A({\rm Ca})$. Relating these results to the ponderomotive force theory of Laming, we attribute the nature of varying $A({\rm Ca})$ to the emergence of loop structures in addition to the initial main loop, each with its characteristic calcium abundance.Comment: Astrophysical Journal (to be published). 14 pages with 8 figure

Running Large-Scale Simulations on the Neurorobotics Platform to Understand Vision – The Case of Visual Crowding

Traditionally, human vision research has focused on specific paradigms and proposed models to explain very specific properties of visual perception. However, the complexity and scope of modern psychophysical paradigms undermine the success of this approach. For example, perception of an element strongly deteriorates when neighboring elements are presented in addition (visual crowding). As it was shown recently, the magnitude of deterioration depends not only on the directly neighboring elements but on almost all elements and their specific configuration. Hence, to fully explain human visual perception, one needs to take large parts of the visual field into account and combine all the aspects of vision that become relevant at such scale. These efforts require sophisticated and collaborative modeling. The Neurorobotics Platform (NRP) of the Human Brain Project offers a unique opportunity to connect models of all sorts of visual functions, even those developed by different research groups, into a coherently functioning system. Here, we describe how we used the NRP to connect and simulate a segmentation model, a retina model, and a saliency model to explain complex results about visual perception. The combination of models highlights the versatility of the NRP and provides novel explanations for inward-outward anisotropy in visual crowding

An integrated approach for evaluating climate change risks: a case study in Suriname

This paper combines long-term state-of-the-art climate projections and indices to provide detailed insights into the future climate of Suriname to facilitate comprehensive information of areas and sectors at high climate risk for political decision-making. The study analyses Suriname's historical climate (1990-2014) and provides climate projections for three time horizons (2020-2044, 2045-2069, 2070-2094) and two emissions scenarios (intermediate/SSP2-4.5 and severe/SSP5-8.5). Coupled Model Intercomparison Project (CMIP6) modeling is used to analyze changes in sea level, temperature, precipitation, relative humidity, and winds. In addition, risk impact chains were produced for the country's four most important socio-economic sectors: agriculture and fisheries, forestry, water, and infrastructure. Results show the temperature is expected to increase for all regions and timeframes, reaching warming up to 6 degrees C in the southern region in the long-term future (2070-2094). Projections point towards a reduction in precipitation in the southwest and coastal regions and a rise in mean sea level. Regarding risk, Paramaribo and Wanica face the highest climate risk. Coronie and Nickerie face the least climate risk. These regions remain the most and least vulnerable in both the SSP2-4.5 and SSP5-8.5 scenarios, but overall values of their risk indices increase substantially over time

The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks

Aims. Photodissociation by UV light is an important destruction mechanism for CO in many astrophysical environments, ranging from interstellar clouds to protoplanetary disks. The aim of this work is to gain a better understanding of the depth dependence and isotope-selective nature of this process. Methods. We present a photodissociation model based on recent spectroscopic data from the literature, which allows us to compute depth-dependent and isotope-selective photodissociation rates at higher accuracy than in previous work. The model includes self-shielding, mutual shielding and shielding by atomic and molecular hydrogen, and it is the first such model to include the rare isotopologues C17O and 13C17O. We couple it to a simple chemical network to analyse CO abundances in diffuse and translucent clouds, photon-dominated regions, and circumstellar disks. Results. The photodissociation rate in the unattenuated interstellar radiation field is 2.6e-10 s^-1, 30% higher than currently adopted values. Increasing the excitation temperature or the Doppler width can reduce the photodissociation rates and the isotopic selectivity by as much as a factor of three for temperatures above 100 K. The model reproduces column densities observed towards diffuse clouds and PDRs, and it offers an explanation for both the enhanced and the reduced N(12CO)/N(13CO) ratios seen in diffuse clouds. The photodissociation of C17O and 13C17O shows almost exactly the same depth dependence as that of C18O and 13C18O, respectively, so 17O and 18O are equally fractionated with respect to 16O. This supports the recent hypothesis that CO photodissociation in the solar nebula is responsible for the anomalous 17O and 18O abundances in meteorites.Comment: Accepted by A&

Electronic and optical spectra in a diluted magnetic semiconductor multilayer

The effects of random distribution of magnetic impurities with concentration $x$ in a semiconductor alloy multilayer at a paramagnetic temperature are investigated by means of coherent potential approximation and tight-binding model. The change in the electronic states and the optical absorption spectrum with $x$ is calculated for weak and strong exchange interactions between carrier spins and localized spin moments on magnetic ions. We find that the density of states and optical absorption are strongly layer-dependent due to the quantum size effects. The electronic and optical spectra are broadened due to the spin fluctuations of magnetic ions and in the case of strong exchange interaction, an energy gap appears in both spectra. Furthermore, the interior layers show higher contribution in the optical absorption of the system. The results can be helpful for magneto-optical devices at a paramagnetic temperature.Comment: 7 pages, 5 figure