A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site

This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be ≥3--5 m thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poisson’s ratio, P- and S-wave velocities, Young’s modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission.Additional co-authors: Nick Teanby and Sharon Keda

Chronic Stroke Sensorimotor Impairment Is Related to Smaller Hippocampal Volumes: An ENIGMA Analysis

BACKGROUND: Persistent sensorimotor impairments after stroke can negatively impact quality of life. The hippocampus is vulnerable to poststroke secondary degeneration and is involved in sensorimotor behavior but has not been widely studied within the context of poststroke upper-limb sensorimotor impairment. We investigated associations between non-lesioned hippocampal volume and upper limb sensorimotor impairment in people with chronic stroke, hypothesizing that smaller ipsilesional hippocampal volumes would be associated with greater sensorimotor impairment. METHODS AND RESULTS: Cross-sectional T1-weighted magnetic resonance images of the brain were pooled from 357 participants with chronic stroke from 18 research cohorts of the ENIGMA (Enhancing NeuoImaging Genetics through Meta-Analysis) Stroke Recovery Working Group. Sensorimotor impairment was estimated from the FMA-UE (Fugl-Meyer Assessment of Upper Extremity). Robust mixed-effects linear models were used to test associations between poststroke sensorimotor impairment and hippocampal volumes (ipsilesional and contralesional separately; Bonferroni-corrected, P<0.025), controlling for age, sex, lesion volume, and lesioned hemisphere. In exploratory analyses, we tested for a sensorimotor impairment and sex interaction and relationships between lesion volume, sensorimotor damage, and hippocampal volume. Greater sensorimotor impairment was significantly associated with ipsilesional (P=0.005; β=0.16) but not contralesional (P=0.96; β=0.003) hippocampal volume, independent of lesion volume and other covariates (P=0.001; β=0.26). Women showed progressively worsening sensorimotor impairment with smaller ipsilesional (P=0.008; β=−0.26) and contralesional (P=0.006; β=−0.27) hippocampal volumes compared with men. Hippocampal volume was associated with lesion size (P<0.001; β=−0.21) and extent of sensorimotor damage (P=0.003; β=−0.15). CONCLUSIONS: The present study identifies novel associations between chronic poststroke sensorimotor impairment and ipsilesional hippocampal volume that are not caused by lesion size and may be stronger in women.Artemis Zavaliangos-Petropulu, PhD, Bethany Lo, BSc, Miranda R. Donnelly, MS, Nicolas Schweighofer, PhD, Keith Lohse, PhD, PStat, Neda Jahanshad, PhD, Giuseppe Barisano, MD, Nerisa Banaj, PhD, Michael R. Borich, PhD, Lara A. Boyd, PhD, Cathrin M. Buetefisch, MD, PhD, Winston D. Byblow, PhD, Jessica M. Cassidy, PhD, Charalambos C. Charalambous, PhD, Adriana B. Conforto, PhD, Julie A. DiCarlo, MSc, Adrienne N. Dula, PhD, Natalia Egorova-Brumley, PhD, Mark R. Etherton, MD, PhD, Wuwei Feng, MD, Kelene A. Fercho, PhD, Fatemeh Geranmayeh, PhD, Colleen A. Hanlon, PhD, Kathryn S. Hayward, PhD, Brenton Hordacre, PhD, Steven A. Kautz, PhD, Mohamed Salah Khlif, PhD, Hosung Kim, PhD, Amy Kuceyeski, PhD, David J. Lin, MD, Jingchun Liu, MD, Martin Lotze, MD, Bradley J. MacIntosh, PhD, John L. Margetis, OTD, Feroze B. Mohamed, PhD, Fabrizio Piras, PhD, Ander Ramos-Murguialday, PhD, Kate P. Revill, PhD, Pamela S. Roberts, PhD, Andrew D. Robertson, PhD, Heidi M. Schambra, MD, Na Jin Seo, PhD, Mark S. Shiroishi, MD, Cathy M. Stinear, PhD, Surjo R. Soekadar, MD, Gianfranco Spalletta, MD, PhD, Myriam Taga, PhD, Wai Kwong Tang, MD, Gregory T. Thielman, EdD, Daniela Vecchio, PhD, Nick S. Ward, MD, Lars T. Westlye, PhD, Emilio Werden, PhD, Carolee Winstein, PhD, PT, George F. Wittenberg, MD, PhD, Steven L. Wolf, PhD, Kristin A. Wong, MD, Chunshui Yu, MD, Amy Brodtmann, MD, PhD, Steven C. Cramer, MD, Paul M. Thompson, PhD, Sook-Lei Liew, PhD, OTR,

Quantum turbulence in 4He, oscillating grids, and where do we go next?

Experimental approaches to the study of quantum turbulence (QT) in superfluid 4He in the low temperature limit, where the normal fluid density is effectively zero, are considered. A succinct general introduction covers liquid 4He, superfluidity, critical velocities for the onset of dissipation, quantized vortex lines and QT. The QT can be created mechanically by the oscillation of wires or grids above characteristic critical velocities. The interesting dynamics of the oscillating grid are discussed. It exhibits an enhanced effective mass due to backflow, as expected from classical hydrodynamics. It is found that the critical velocity attributable to the onset of QT production rises with increasing temperature. Oscillating objects like grids or wires create QT that is not well-characterized in terms of length scale, and the QT is not spatially homogeneous. The QT can be detected by the trapping of negative ions on vortex cores. Although the corresponding capture cross-section has not yet been measured, it is evidently very small, so that the technique cannot be expected to be a very sensitive one. In the future it is hoped to create well-characterized, homogeneous QT by means of a drawn grid. Improved sensitivity in the detection of QT is being sought through calorimetric techniques that monitor the temperature rise of the liquid caused by the decay of the vortex lines