A comparison of multiple Rosetta data sets and 3D model calculations of 67P/Churyumov-Gerasimenko coma around equinox (May 2015)

We have used the latest available shape model for gas and dust simulations of the inner coma of comet 67P/Churyumov-Gerasimenko for the period around May 2015 (equinox). We compare results from a purely insolation-driven model with a complementary set of observations made by ROSINA, VIRTIS, MIRO, and OSIRIS within the same period. The observations include - for the first time - inverted MIRO measurements of gas density, temperature and bulk velocity to constrain the model. The comparisons show that, as in November 2014 (Marschall et al., 2016), insolation-driven activity does not provide an adequate fit to the data. Both VIRTIS and MIRO observations indicate that emissions from the Hatmehit and Imhotep regions of the nucleus are strongly depleted in total gas, H2O, and dust emissions in this case. The MIRO inversion provides a challenging constraint to the models as a consequence of the terminator orbit and nucleus pointing of the spacecraft. Nonetheless a consistent picture with a dominance of outgassing from the Hapi region, even at equinox, is clearly evident. An inhomogeneous model consistent with models proposed for the November 2014 time-frame was constructed and provides a better fit to the data. As far as we are aware this is the first time comae data from four Rosetta instruments have been used to constrain within one self-contained model the emission distribution at the nucleus surface and study the dynamics of the gas and dust outflow

Contaminant biotransport by Pacific Salmon in Lake Michigan: analysis of salmon and stream-resident fish in Great Lakes tributaries

Pacific salmon (Oncorhynchus spp.) can deliver a significant pulse of biomass, including its bioaccumulated contaminants, to tributaries during spawning runs. Thus, salmon transport contaminants accumulated in the Great Lakes (e.g., persistent organic pollutants [POPs], total mercury [THg]) to tributaries that otherwise lack point source pollution. We used a combination of observational surveys, experimental manipulations, and modeling, to (1) assess the extent of salmon-mediated biotransport across the upper Great Lakes; (2) determine pathways by which stream fish become contaminated by salmon; and (3) forecast areas at significant risk from salmon biotransport. Resident stream fish (e.g., brook trout Salvelinus fontinalis) in salmon spawning reaches had higher POP concentrations than fish in upstream reaches lacking salmon, but the extent of contamination varied among lake basins and streams. In contrast, THg concentrations in the same fish did not differ between reaches with and without salmon spawners but exhibited considerable among-site variability. In general, resident fish in Lake Michigan tributaries were the most contaminated by POPs, suggesting a direct relationship between salmon-derived contaminant inputs and resident fish contaminant levels. Experimental exposure to salmon carcasses and eggs for 50 days increased brook trout POP concentrations by 50 times. Eggs are elevated in POPs but depleted in THg compared to whole salmon, suggesting that resident fish contaminant levels reflect direct consumption of eggs rather than indirect food web pathways. Our model suggests that salmon-mediated bioaccumulation is primarily influenced by the size and duration of salmon runs, and secondarily by factors including individual consumption rates, temperature regime, and background pollutant levels. Overall, our research provides increased understanding on the physical, chemical, and biological controls of salmon contaminant biotransport in the Great Lakes region. This research will help inform management decisions in this region with respect to legacy pollution, dam removal, stream connectivity, fish stocking, and non-native species in stream ecosystems

On deviations from free-radial outflow in the inner coma of comet 67P/Churyumov–Gerasimenko

The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) onboard the European Space Agency's Rosetta spacecraft acquired images of comet 67P/Churyumov–Gerasimenko (67P) and its surrounding dust coma starting from May 2014 until September 2016. In this paper we present methods and results from analysis of OSIRIS images regarding the dust outflow in the innermost coma of 67P. The aim is to determine the global dust outflow behaviour and place constraints on physical processes affecting particles in the inner coma. We study the coma region right above the nucleus surface, spanning from the nucleus centre out to a distance of about 50 km comet centric distance (approximately 25 average comet radii). We primarily adopt an approach used by Thomas and Keller (1990) to study the dust outflow. We present the effects on azimuthally-averaged values of the dust reflectance of non-radial flow and non-point-source geometry, acceleration of dust particles, sublimation of icy dust particles after ejection from the surface, dust particle fragmentation, optical depth effects and the influence of gravitationally bound particles. All of these physical processes could modify the observed distribution of light scattered by the dust coma. In the image analysis, profiles of azimuthally averaged dust brightness as a function of impact parameter b (azimuthal average, “Ā-curve”) were fitted with a simple function that best fits the shape of our profile curves (f(b;u,v,w,z)=u/bv+wb+z). The analytical fit parameters (u, v, w, z), which hold the key information about the dust outflow behaviour, were saved in a comprehensive database. Through statistical analysis of these information, we show that the spatial distribution of dust follows free-radial outflow behaviour (i.e. force-free radial outflow with constant velocity) beyond distances larger than ∼11.9 km from the comet centre, which corresponds to a relative distance of about 6 average comet radii from the comet centre. Hence, we conclude that beyond this distance, and on average, fragmentation and gravitationally bound particles are negligible processes in determining the optically scattered light distribution in the innermost coma. Closer to the nucleus we observe dust outflow behaviour that deviates from free-radial outflow. A comparison of our result profiles with numerical models using a Direct Simulation Monte Carlo (DSMC) approach with dust particle distributions calculated using a test particle approach has been used to demonstrate the influence of a complex shape and particle acceleration on the azimuthal average profiles. We demonstrate that, while other effects such as fragmentation or sublimation of dust particles cannot be ruled out, acceleration of the dust particles and effects arising from the shape of the irregular nucleus (non-point source geometry) are sufficient to explain the observed dust outflow behaviour from image data analysis. As a by-product of this work, we have calculated “Afρ” values for the 1/r regime. We found a peak in the coma activity in terms of Afρ (normalised to a phase angle of 90°) of ∼210 cm 20 days after perihelion. Furthermore, based on simplified models of particle motion within bound orbits, it is shown that limits on the total cross-sectional area of bound particles might be derived through further analysis. An example is given

Regional Gray Matter Growth, Sexual Dimorphism, and Cerebral Asymmetry in the Neonatal Brain

Although there has been recent interest in the study of childhood and adolescent brain development, very little is known about normal brain development in the first few months of life. In older children, there are regional differences in cortical gray matter development, whereas cortical gray and white matter growth after birth has not been studied to a great extent. The adult human brain is also characterized by cerebral asymmetries and sexual dimorphisms, although very little is known about how these asymmetries and dimorphisms develop. We used magnetic resonance imaging and an automatic segmentation methodology to study brain structure in 74 neonates in the first few weeks after birth. We found robust cortical gray matter growth compared with white matter growth, with occipital regions growing much faster than prefrontal regions. Sexual dimorphism is present at birth, with males having larger total brain cortical gray and white matter volumes than females. In contrast to adults and older children, the left hemisphere is larger than the right hemisphere, and the normal pattern of fronto-occipital asymmetry described in older children and adults is not present. Regional differences in cortical gray matter growth are likely related to differential maturation of sensory and motor systems compared with prefrontal executive function after birth. These findings also indicate that whereas some adult patterns of sexual dimorphism and cerebral asymmetries are present at birth, others develop after birth

Statistical Computing on Non-Linear Spaces for Computational Anatomy

International audienceComputational anatomy is an emerging discipline that aims at analyzing and modeling the individual anatomy of organs and their biological variability across a population. However, understanding and modeling the shape of organs is made difficult by the absence of physical models for comparing different subjects, the complexity of shapes, and the high number of degrees of freedom implied. Moreover, the geometric nature of the anatomical features usually extracted raises the need for statistics on objects like curves, surfaces and deformations that do not belong to standard Euclidean spaces. We explain in this chapter how the Riemannian structure can provide a powerful framework to build generic statistical computing tools. We show that few computational tools derive for each Riemannian metric can be used in practice as the basic atoms to build more complex generic algorithms such as interpolation, filtering and anisotropic diffusion on fields of geometric features. This computational framework is illustrated with the analysis of the shape of the scoliotic spine and the modeling of the brain variability from sulcal lines where the results suggest new anatomical findings

Teasing apart the heterogeneity of autism: Same behavior, different brains in toddlers with fragile X syndrome and autism

To examine brain volumes in substructures associated with the behavioral features of children with FXS compared to children with idiopathic autism and controls. A cross-sectional study of brain substructures was conducted at the first time-point as part of an ongoing longitudinal MRI study of brain development in FXS. The study included 52 boys between 18–42 months of age with FXS and 118 comparison children (boys with autism-non FXS, developmental-delay, and typical development). Children with FXS and autistic disorder had substantially enlarged caudate volume and smaller amygdala volume; whereas those children with autistic disorder without FXS (i.e., idiopathic autism) had only modest enlargement in their caudate nucleus volumes but more robust enlargement of their amygdala volumes. Although we observed this double dissociation among selected brain volumes, no significant differences in severity of autistic behavior between these groups were observed. This study offers a unique examination of early brain development in two disorders, FXS and idiopathic autism, with overlapping behavioral features, but two distinct patterns of brain morphology. We observed that despite almost a third of our FXS sample meeting criteria for autism, the profile of brain volume differences for children with FXS and autism differed from those with idiopathic autism. These findings underscore the importance of addressing heterogeneity in studies of autistic behavior

White Matter Development in Early Puberty: A Longitudinal Volumetric and Diffusion Tensor Imaging Twin Study

White matter microstructure and volume show synchronous developmental patterns in children. White matter volume increases considerably during development. Fractional anisotropy, a measure for white matter microstructural directionality, also increases with age. Development of white matter volume and development of white matter microstructure seem to go hand in hand. The extent to which the same or different genetic and/or environmental factors drive these two aspects of white matter maturation is currently unknown. We mapped changes in white matter volume, surface area and diffusion parameters in mono- and dizygotic twins who were scanned at age 9 (203 individuals) and again at age 12 (126 individuals). Over the three-year interval, white matter volume (+6.0%) and surface area (+1.7%) increased, fiber bundles expanded (most pronounced in the left arcuate fasciculus and splenium), and fractional anisotropy increased (+3.0%). Genes influenced white matter volume (heritability ∼85%), surface area (∼85%), and fractional anisotropy (locally 7% to 50%) at both ages. Finally, volumetric white matter growth was negatively correlated with fractional anisotropy increase (r = –0.62) and this relationship was driven by environmental factors. In children who showed the most pronounced white matter growth, fractional anisotropy increased the least and vice-versa. Thus, white matter development in childhood may reflect a process of both expansion and fiber optimization

A Prototype Representation to Approximate White Matter Bundles with Weighted Currents

International audienceQuantitative and qualitative analysis of white matter fibers resulting from tractography algorithms is made difficult by their huge number. To this end, we propose an \textit{approximation scheme} which gives as result a more concise but at the same time exhaustive representation of a fiber bundle. It is based on a novel computational model for fibers, called \textit{weighted currents}, characterised by a metric that considers both the pathway and the anatomical locations of the endpoints of the fibers. Similarity has therefore a twofold connotation: geometrical and related to the connectivity. The core idea is to use this metric for approximating a fiber bundle with a set of weighted prototypes, chosen among the fibers, which represent ensembles of similar fibers. The weights are related to the number of fibers represented by the prototypes. The algorithm is divided into two steps. First, the main modes of the fiber bundle are detected using a \textit{modularity based clustering} algorithm. Second, a \textit{prototype fiber selection} process is carried on in each cluster separately. This permits to explain the main patterns of the fiber bundle in a fast and accurate way

Dayside-to-nightside dust coma brightness asymmetry and its implications for nightside activity at Comet 67P/Churyumov–Gerasimenko

We have determined the dust coma brightness ratio between the dayside and the nightside (DS:NS) in OSIRISimages of comet 67P/Churyumov–Gerasimenko and compared them to results from numerical dust comasimulations to learn more about the dynamic processes that are involved in coma formation. The primaryfocus of this paper lies in the analysis of a subset of OSIRIS images acquired during one comet rotation on11. April 2015 when the spacecraft was at a phase angle of 90◦and therefore directly above the terminator.The DS:NS ratio was found to be 2.49±0.18 on average - a very low value if insolation-driven sublimation ofwater dominates dust emission. We investigated two possible hypotheses: First, the influence of direct activityfrom non-illuminated (nightside) areas of the comet and second, the brightness contribution of large gravity-dominated particles in the innermost coma. For our numerical simulations, we used a combination of DSMCgas dynamics simulation and particle propagation by an equation of motion to simulate the dust coma. Oursimulations show that direct activity from the nightside is preferred, contributing≈10% of the total emission.We show that intensity profiles, used to quantify dust outflow behaviour, fit the observations better whennightside activity is present and we suggest that nightside gas emission by CO2or CO is responsible for theobserved dust flux. With the help of a simplified Keplerian modelling approach we exclude large particles ongravitationally bound or ballistic orbits from being the major contributor to the observed dust coma brightness.Additionally, we show the DS:NS ratio as a function of days to perihelion and observe that it is on a similarlevel as in the April OSIRIS time series from February to mid-June 2015, but increases towards a maximum of≥4.07±0.49 shortly after perihelion passage. We suggest that this is correlated to the increasing importanceof H2O production when approaching perihelio

The effect of thermal conductivity on the outgassing and local gas dynamics from cometary nuclei

Aims. The aim of this work is to investigate the parameters influencing the generation of the inner comae of a comet with a spherical nucleus and to model the gas activity distribution around its nuclei. Here, we investigate the influence of thermal conductivity combined with sub-surface H2O and CO2-ice sources on insolation-driven sublimation and the resulting gas flow field. In the process, we adopted some of the rotational and surface properties of the target of the Rosetta mission, comet 67P/Churyumov-Gerasimenko (67P/CG). Methods. We used a simplified model of heat transport through the surface layer to establish sublimation rates from a H2O- and CO2-ice sub-surface into a vacuum. We then applied the 3D Direct Simulation Monte Carlo method to model the coma as a sublimation-driven flow. The free parameters of the model were used to test the range of effects arising from thermal inertia and the depth of the source on the gas outflow. Results. Thermal inertia and the depth of the sublimation front can have a strong effect on the emission distribution of the flow at the surface. In models with a thermal inertia up to 80 TIU (thermal inertia units: J m−2 K−1 s−1∕2), the H2O distribution can be rotated about the rotation axis by about 20° relative to models with no thermal lag. For CO2, the maximum activity can be shifted towards the sunset terminator with activity going far into the nightside for cases with low thermal diffusivity. The presence of a small amount of CO2 can reduce the presence of H2O by at least an order of magnitude on the nightside by blocking H2O flow. In addition, CO2 can also decrease the speed of the mixed flow in the same region up to 200 m s−1, compared to cases with no CO2 activity. Conclusions. Even low values of the thermal inertia can substantially modify the gas flow field. Including CO2 leads to strong variations in the local CO2/H2O density ratio between the dayside and nightside. CO2 can dominate the gas composition above the nightside and can also act to modify the H2O flow field close to the terminator