Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

Aims. We investigated the response of the solar atmosphere to non-thermal electron beam heating using the radiative transfer and hydrodynamics modelling code RADYN. The temporal evolution of the parameters that describe the non-thermal electron energy distribution were derived from hard X-ray observations of a particular flare, and we compared the modelled and observed parameters.

Methods. The evolution of the non-thermal electron beam parameters during the X1.5 solar flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The RADYN flare model was allowed to evolve for 110 s, after which the electron beam heating was ended, and was then allowed to continue evolving for a further 300 s. The modelled flare parameters were compared to the observed parameters determined from extreme-ultraviolet spectroscopy.

Results. The model produced a hotter and denser flare loop than that observed and also cooled more rapidly, suggesting that additional energy input in the decay phase of the flare is required. In the explosive evaporation phase a region of high-density cool material propagated upward through the corona. This material underwent a rapid increase in temperature as it was unable to radiate away all of the energy deposited across it by the non-thermal electron beam and via thermal conduction. A narrow and high-density (ne ≤ 1015 cm-3) region at the base of the flare transition region was the source of optical line emission in the model atmosphere. The collision-stopping depth of electrons was calculated throughout the evolution of the flare, and it was found that the compression of the lower atmosphere may permit electrons to penetrate farther into a flaring atmosphere compared to a quiet Sun atmosphere.

Microstructural evolution and mechanical properties of short-term thermally exposed 9/12Cr heat-resistant steels

The microstructural evolution during short-term (up to 3000 hours) thermal exposure of three 9/12Cr heat-resistant steels was studied, as well as the mechanical properties after exposure. The tempered martensitic lath structure, as well as the precipitation of carbide and MX type carbonitrides in the steel matrix, was stable after 3000 hours of exposure at 873 K (600 °C). A microstructure observation showed that during the short-term thermal exposure process, the change of mechanical properties was caused mainly by the formation and growth of Laves-phase precipitates in the steels. On thermal exposure, with an increase of cobalt and tungsten contents, cobalt could promote the segregation of tungsten along the martensite lath to form Laves phase, and a large size and high density of Laves-phase precipitates along the grain boundaries could lead to the brittle intergranular fracture of the steels.

Late-Glacial and early Holocene marine 14C reservoir ages off North Iceland (16-9 cal kyr BP)

Tephrochronological age models and 48 14C age determinations on molluscs and foraminifera (planktonic and benthic) are applied for the calculation of marine 14C reservoir age variability during a time period covering the Heinrich event H1 to early Holocene (16–9 cal kyr BP). Our data source consists of four high-resolution marine sediment cores (HM107-04, HM107-05, MD99-2271, MD99-2275) from the North Icelandic shelf. The marine reservoir age (ΔR) is found to be extremely variable, ranging from 385 to 1065 14C years. Extreme ΔR values occur at the end of H1, with values around 1000 14C years (~15 cal kyr BP), probably due to reduced northward flow of well-ventilated subtropical surface waters and a southward expansion of polar waters, as well as an expansion of sea ice limiting air-sea gas exchange. With the onset of the Bølling-Allerød interstadial, the ΔR values decrease towards 0 14C years suggesting a more vigorous North Atlantic Current and an active meridional overturning circulation system. During the Younger Dryas stadial, ΔR values are consistently around 700 14C years suggesting e renewed expansion of polar waters and a weakened meridional overtuning circulation. Interestingly, ΔR values remain high (~200 14C years) at the onset of the Holocene suggesting continued high influence of polar waters. Subsequently, ΔR values rapidly decrease to ~¬ 250 14C years around 11 cal kyr BP, indicating increased air-sea CO2 exchange with the coeval atmosphere. The ΔR values average around 0 14C years from around 10.5 to 9.0 cal kyr BP.

Still Unequal at Birth: Birth Weight, Socioeconomic Status and Outcomes at Age 9

The prevalence of low birth weight is an important aspect of public health which has been linked to increased risk of infant death, increased cost of care, and a range of later life outcomes. Using data from a new Irish cohort study, I document the relationship between birth weight and socio-economic status. The association of maternal education with birth weight does not appear to be due to the timing of birth or complications during pregnancy, even controlling for a wide range of background characteristics. However, results do suggest intergenerational persistence in the transmission of poor early life conditions. Birth weight predicts a number of outcomes at age 9, including test scores, hospital stays and health. An advantage of the data is that I am able to control for a number of typically unmeasured variables. I determine whether parental investments (as measured by the quality of interaction with the child, parenting style, or school quality) mediate the association between birth weight and later indicators. For test scores, there is evidence of non-linearity, and boys are more adversely affected than girls. I also consider whether there are heterogeneous effects by ability using quantile regression. These results are consistent with a literature which finds that there is a causal relationship between early life conditions and later outcomes.

5.9-keV Mn K-shell X-ray luminosity from the decay of 55Fe in Type Ia supernova models

We show that the X-ray line flux of the Mn Kα line at 5.9 keV from the decay of 55Fe is a promising diagnostic to distinguish between Type Ia supernova (SN Ia) explosion models. Using radiation transport calculations, we compute the line flux for two three-dimensional explosion models: a near-Chandrasekhar mass delayed detonation and a violent merger of two (1.1 and 0.9 M⊙) white dwarfs. Both models are based on solar metallicity zero-age main-sequence progenitors. Due to explosive nuclear burning at higher density, the delayed-detonation model synthesizes ˜3.5 times more radioactive 55Fe than the merger model. As a result, we find that the peak Mn Kα line flux of the delayed-detonation model exceeds that of the merger model by a factor of ˜4.5. Since in both models the 5.9-keV X-ray flux peaks five to six years after the explosion, a single measurement of the X-ray line emission at this time can place a constraint on the explosion physics that is complementary to those derived from earlier phase optical spectra or light curves. We perform detector simulations of current and future X-ray telescopes to investigate the possibilities of detecting the X-ray line at 5.9 keV. Of the currently existing telescopes, XMM-Newton/pn is the best instrument for close (≲1-2 Mpc), non-background limited SNe Ia because of its large effective area. Due to its low instrumental background, Chandra/ACIS is currently the best choice for SNe Ia at distances above ˜2 Mpc. For the delayed-detonation scenario, a line detection is feasible with Chandra up to ˜3 Mpc for an exposure time of 106 s. We find that it should be possible with currently existing X-ray instruments (with exposure times ≲5 × 105 s) to detect both of our models at sufficiently high S/N to distinguish between them for hypothetical events within the Local Group. The prospects for detection will be better with future missions. For example, the proposed Athena/X-IFU instrument could detect our delayed-detonation model out to a distance of ˜5 Mpc. This would make it possible to study future events occurring during its operational life at distances comparable to those of the recent supernovae SN 2011fe (˜6.4 Mpc) and SN 2014J (˜3.5 Mpc).

The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 au heliocentric distance range inbound

Context. The ESA Rosetta spacecraft, currently orbiting around comet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments,particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution.
Aims. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014.
Methods. A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately.
Results. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is α = −3, instead of α = −2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.