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

RESIK and RHESSI observations of the 20 September 2002 flare

Soft X-ray spectra 3.33 A - 6.15 A from the RESIK instrument on CORONAS-F constitute a unique database for the study of the physical conditions of solar flare plasmas, enabling the calculation of differential emission measures. The two RESIK channels for the shortest wavelengths overlap with the lower end of RHESSI spectral energy range, which is located around 3 keV, making it possible to compare both data sets. We aim to compare observations from RESIK and RHESSI spectrometers and cross-correlate these instruments. Observations are compared with synthetic spectra calculated based on the results of one-dimensional hydrodynamical (1D-HD) modelling. The analysis was performed for the flare on 20 September 2002. We estimated the geometry of the flaring loop, necessary for 1D-HD modelling, based on images from RHESSI and SOHO/EIT. The distribution of non-thermal electrons (NTEs) was determined from RHESSI spectra. The 1D-HD model assumes that non-thermal electrons with a power-law spectrum were injected at the apex of the flaring loop. The NTEs then heat and evaporate the chromosphere, filling the loop with hot and dense plasma radiating in soft X-rays. The total energy of electrons was constrained by comparing observed and calculated fluxes from GOES 1 - 8 A data. We determined the temperature and density at every point of the flaring loop throughout the evolution of the flare, calculating the resulting X-ray spectra. The synthetic spectra calculated based on the results of hydrodynamic modelling for the 20 September 2002 flare are consistent within a factor of two with the observed RESIK spectra during most of the duration of the flare. This discrepancy factor is probably related to the uncertainty on the cross-calibration between RESIK and RHESSI instruments

A Unique Resource for Solar Flare Diagnostic Studies: the SMM Bent Crystal Spectrometer

The {\em Bent Crystal Spectrometer}\/ (BCS) on the NASA {\em Solar Maximum Mission}\/ spacecraft observed the X-ray spectra of numerous solar flares during the periods 1980 February to November and 1984~--~1989. The instrument, the first of its kind to use curved crystal technology, observed the resonance lines of He-like Ca (\caxix) and Fe (\fexxv) and neighboring satellite lines, allowing the study of the rapid evolution of flare plasma temperature, turbulence, mass motions etc. To date there has not been a solar X-ray spectrometer with comparable spectral and time resolution, while subsequent solar cycles have delivered far fewer and less intense flares. The BCS data archive thus offers an unparalleled resource for flare studies. A recent re-assessment of the BCS calibration and its operations is extended here by using data during a spacecraft scan in the course of a flare on 1980 November~6 that highlights small deformations in the crystal curvature of the important channel~1 (viewing lines of \caxix\ and satellites). The results explain long-standing anomalies in spectral line ratios which have been widely discussed in the past. We also provide an in-flight estimation of the BCS collimator field of view which improves the absolute intensity calibration of the BCS. The BCS channel~1 background is shown to be entirely due to solar continuum radiation, confirming earlier analyses implying a time-variable flare abundance of Ca. We suggest that BCS high-resolution \caxix\ and \fexxv\ line spectra be used as templates for the analysis of X-ray spectra of non-solar sources.Comment: To be published, Astrophysical Journa

Desarrollo y validación Rasch del "Inventario de Ojo Seco de Medellín" (ME-Dry), un instrumento para medir el compromiso multidimensional de la calidad de vida en pacientes con enfermedad de ojo seco.

Propósito: La enfermedad de ojo seco (DED) es una condición común que afecta la calidad de vida. Existe una gran necesidad de escalas mejor desarrolladas que cumplan los requisitos del modelo de Rasch. Métodos: Estudio prospectivo que incluye pacientes con DED. Se realizaron una serie de grupos focales para determinar los mejores ítems a incluir. Se utilizó una metodología de modelos de Rasch para validar el Inventario de Ojo Seco de Medellín (ME-Dry). Tras un análisis iterativo y la modificación de la escala, se alcanzó una versión final de la escala que cumplía con las expectativas del análisis de Rasch. Se evaluó la correlación entre las diferentes subescalas del ME-Dry y el Ocular Surface Disease Index (OSDI) mediante correlación de Spearman. Resultados: Se incluyeron un total de 166 pacientes con DED. El modelado Rasch demostró un comportamiento excelente para el ME-Dry, incluyendo cuatro subescalas: Síntomas, Desencadenantes, Limitación de la Actividad y Compromiso Emocional. Los parámetros Infit y Outfit estaban todos entre 0,50 y 1,50, con una excelente utilización de las categorías. La separación entre personas e ítems y la fiabilidad fueron excelentes en todas las subescalas. Hubo necesidad de un colapso de categoría para la subescala de Compromiso Emocional. Hubo una fuerte correlación entre las diferentes subescalas del ME-Dry excepto para la subescala de Compromiso Emocional, que parece ser independiente. Conclusiones: La ME-Dry es una escala fiable, que cumple con las expectativas del modelo de Rasch, y que permite medir de forma fiable el compromiso de la calidad de vida en pacientes con DED. El compromiso emocional secundario a la DED no parece correlacionarse con la gravedad de la enfermedad evaluada por las otras subescalas de calidad de vida.Purpose: Dry eye disease (DED) is a common condition that affects the quality of life. There is a great need for better‑developed scales that comply with Rasch model requirements. Methods: Prospective study including patients with DED. A series of focus groups were performed to determine the best items to be included. A Rasch modeling methodology was used to validate the Medellín Dry Eye Inventory (ME·Dry). After iterative analysis and scale modification, a final version of the scale was attained which complied with the Rasch analysis expectations. Correlation between the different subscales of the ME·Dry and the Ocular Surface Disease Index (OSDI) was evaluated through Spearman correlation. Results: A total of 166 patients with DED were included. Rasch modeling demonstrated an excellent behavior for the ME·Dry, including four subscales: Symptoms, Triggers, Activity Limitation, and Emotional Compromise. Infit and Outfit parameters were all between 0.50 and 1.50, with excellent category utilization. Person and item separation and reliability were excellent for all subscales. There was a need for a category collapsing for the Emotional Compromise subscale. There was a strong correlation between the different subscales of the ME·Dry except for the Emotional Compromise subscale, which seems to be independent. Conclusion: The ME·Dry is a reliable scale, complying with the Rasch model expectations, that allows for a reliable measurement of quality of life compromise in patients with DED. Emotional compromise secondary to DED does not seem to correlate with disease severity as assessed by the other quality‑of‑life subscales

Half-BPS cosmic string in N=2 supergravity in the presence of a dilaton

We construct new half-BPS cosmic string solutions in D=4 N=2 supergravity compatible with a consistent truncation to N=1 supergravity where they describe D-term cosmic strings. The constant Fayet-Iliopoulos term in the N=1 D-term is not put in by hand but is geometrically engineered by a gauging in the mother N=2 supergravity theory. The coupling of the N=2 vector multiplets is characterized by a cubic prepotential admitting an axion-dilaton field, a common property of many compactifications of string theory. The axion-dilaton field survives the truncation to N=1 supergravity. On the string configuration the BPS equations constrain the dilaton to be an arbitrary constant. All the cosmic string solutions with different values of the dilaton have the same energy per unit length but different lenght scales.Comment: 52 pages; typos correcte