Sensitivity to Hand Path Curvature during Reaching

People optimize reaching to make straight and smooth movements. We performed experiments characterizing human sensitivity to hand path deviations from a straight reach. Vision of the arm was blocked. Subjects either moved the hand along paths of constrained curvature, or a robot moved the relaxed limb along similar trajectories (active and passive conditions, respectively). Subjects responded after each trial whether or not they thought the movement curved convex right. In a series of three experiments, we tested the effects of modifying visual feedback of hand position to suppress curvature, isotonic muscle activation, and a distracter task on subjects ability to detect curvature during reaching. We found that both active reaching and artificial minimization of visual hand path deviations significantly decreased proprioceptive curvature sensitivity. Specifically, isotonic contraction of muscles antagonistic to the movement decreased sensitivity to curvature while agonistic contraction had no effect. The distracter task did not significantly affect proprioceptive sensitivity, though it did interfere with the detrimental effect of minimizing visual error feedback. These findings demonstrate that: 1) antagonist muscle activation decreases efficacy of proprioceptive feedback during hand path curvature estimation, and 2) vision\u27s dominance over proprioception can be manipulated by altering the attentional demands of the task

Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields and electron pitch angle distributions on electron impact ionization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95654/1/jgre2678.pd

Measurements of Forbush decreases at Mars: both by MSL on ground and by MAVEN in orbit

The Radiation Assessment Detector (RAD), on board Mars Science Laboratory's (MSL) Curiosity rover, has been measuring ground level particle fluxes along with the radiation dose rate at the surface of Mars since August 2012. Similar to neutron monitors at Earth, RAD sees many Forbush decreases (FDs) in the galactic cosmic ray (GCR) induced surface fluxes and dose rates. These FDs are associated with coronal mass ejections (CMEs) and/or stream/corotating interaction regions (SIRs/CIRs). Orbiting above the Martian atmosphere, the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has also been monitoring space weather conditions at Mars since September 2014. The penetrating particle flux channels in the Solar Energetic Particle (SEP) instrument onboard MAVEN can also be employed to detect FDs. For the first time, we study the statistics and properties of a list of FDs observed in-situ at Mars, seen both on the surface by MSL/RAD and in orbit detected by the MAVEN/SEP instrument. Such a list of FDs can be used for studying interplanetary CME (ICME) propagation and SIR evolution through the inner heliosphere. The magnitudes of different FDs can be well-fitted by a power-law distribution. The systematic difference between the magnitudes of the FDs within and outside the Martian atmosphere may be mostly attributed to the energy-dependent modulation of the GCR particles by both the pass-by ICMEs/SIRs and the Martian atmosphere

Impact demagnetization of the Martian crust: Current knowledge and future directions

The paleomagnetism of the Martian crust has important implications for the history of the dynamo, the intensity of the ancient magnetic field, and the composition of the crust. Modification of crustal magnetization by impact cratering is evident from the observed lack of a measurable crustal field (at spacecraft altitude) within the youngest large impact basins (e.g., Hellas, Argyre and Isidis). It is hoped that comparisons of the magnetic intensity over impact structures, forward modeling of subsurface magnetization, and experimental results of pressure-induced demagnetization of rocks and minerals will provide constraints on the primary magnetic mineralogy in the Martian crust. Such an effort requires: (i) accurate knowledge of the spatial distribution of the shock pressures around impact basins, (ii) crustal magnetic intensity maps of adequate resolution over impact structures, and (iii) determination of demagnetization properties for individual rocks and minerals under compression. In this work, we evaluate the current understanding of these three conditions and compile the available experimental pressure demagnetization data on samples bearing (titano-) magnetite, (titano-) hematite, and pyrrhotite. We find that all samples demagnetize substantially at pressures of a few GPa and that the available data support significant modification of the crustal magnetic field from both large and small impact events. However, the amount of demagnetization with applied pressure does not vary significantly among the possible carrier phases. Therefore, the presence of individual mineral phases on Mars cannot be determined from azimuthally averaged demagnetization profiles over impact basins at present. The identification of magnetic mineralogy on Mars will require more data on pressure demagnetization of thermoremanent magnetization and forward modeling of the crustal field subject to a range of plausible initial field and demagnetization patterns.United States. National Aeronautics and Space Administration (NNG04GD17G)United States. National Aeronautics and Space Administration (NNX07AQ69G)United States. National Aeronautics and Space Administration (NNX06AD14G

Four Martian years of nightside upper thermospheric mass densities derived from electron reflectometry: Method extension and comparison with GCM simulations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95498/1/jgre2766.pd

Study of Acute Liver Failure in Children Using Next Generation Sequencing Technology

OBJECTIVE: To use next generation sequencing (NGS) technology to identify undiagnosed, monogenic diseases in a cohort of children who suffered from acute liver failure (ALF) without an identifiable etiology. STUDY DESIGN: We identified 148 under 10 years of age admitted to King's College Hospital, London, with ALF of indeterminate etiology between 2000 and 2018. A custom NGS panel of 64 candidate genes known to cause ALF and/or metabolic liver disease was constructed. Targeted sequencing was carried out on 41 children in whom DNA samples were available. Trio exome sequencing was performed on 4 children admitted during 2019. A comparison of the clinical characteristics of those identified with biallelic variants against those without biallelic variants was then made. RESULTS: Homozygous and compound heterozygous variants were identified in 8 out of 41 children (20%) and 4 out of 4 children (100%) in whom targeted and exome sequencing were carried out, respectively. The genes involved were NBAS (3 children); DLD (2 children); and CPT1A, FAH, LARS1, MPV17, NPC1, POLG, SUCLG1, and TWINK (1 each). The 12 children who were identified with biallelic variants were younger at presentation and more likely to die in comparison with those who did not: median age at presentation of 3 months and 30 months and survival rate 75% and 97%, respectively. CONCLUSIONS: NGS was successful in identifying several specific etiologies of ALF. Variants in NBAS and mitochondrial DNA maintenance genes were the most common findings. In the future, a rapid sequencing NGS workflow could help in reaching a timely diagnosis and facilitate clinical decision making in children with ALF

Hot oxygen escape from Mars: Simple scaling with solar EUV irradiance

The evolution of the atmosphere of Mars and the loss of volatiles over the lifetime of the solar system is a key topic in planetary science. An important loss process for atomic species, such as oxygen, is ionospheric photochemical escape. Dissociative recombination of O2+ ions (the major ion species) produces fast oxygen atoms, some of which can escape from the planet. Many theoretical hot O models have been constructed over the years, although a number of uncertainties are present in these models, particularly concerning the elastic cross sections of O atoms with CO2. Recently, the Mars Atmosphere and Volatile Evolution mission has been rapidly improving our understanding of the upper atmosphere and ionosphere of Mars and its interaction with the external environment (e.g., solar wind), allowing a new assessment of this important loss process. The purpose of the current paper is to take a simple analytical approach to the oxygen escape problem in order to (1) study the role that variations in solar radiation or solar wind fluxes could have on escape in a transparent fashion and (2) isolate the effects of uncertainties in oxygen cross sections on the derived oxygen escape rates. In agreement with several more elaborate numerical models, we find that the escape flux is directly proportional to the incident solar extreme ultraviolet irradiance and is inversely proportional to the backscatter elastic cross section. The amount of O lost due to ion transport in the topside ionosphere is found to be about 5–10% of the total

Mercury's Surface Magnetic Field Determined from Proton-Reflection Magnetometry

Solar wind protons observed by the MESSENGER spacecraft in orbit about Mercury exhibit signatures of precipitation loss to Mercury's surface. We apply proton-reflection magnetometry to sense Mercury's surface magnetic field intensity in the planet's northern and southern hemispheres. The results are consistent with a dipole field offset to the north and show that the technique may be used to resolve regional-scale fields at the surface. The proton loss cones indicate persistent ion precipitation to the surface in the northern magnetospheric cusp region and in the southern hemisphere at low nightside latitudes. The latter observation implies that most of the surface in Mercury's southern hemisphere is continuously bombarded by plasma, in contrast with the premise that the global magnetic field largely protects the planetary surface from the solar wind

Mars Aurora: A Comparison of MAVEN/IUVS and EMM/EMUS Observations

peer reviewedMars' lack of a global magnetic field led to initial expectations of minimal auroral activity. Mars Express's SPICAM instrument nonetheless discovered an unusual form of aurora in 2005. The ultraviolet emissions were confined near Mars' strong crustal field region, showing that even weak magnetic fields can be responsible for aurora. These discrete aurora emissions were identified in 19 observations over SPICAM's decade of observations.  The MAVEN spacecraft arrived at Mars in 2014 carrying the Imaging UltraViolet Spectrograph (IUVS). Thanks to its high sensitivity and observing cadence, IUVS increased detections of discrete aurora twenty-fold. IUVS also discovered two new widespread forms of aurora. Diffuse aurora is a planet-engulfing phenomenon, caused by solar energetic protons and electrons directly impacting the entire unshielded planet. Proton aurora is caused by solar wind protons charge-exchanging into the atmosphere and causing Lyman alpha emission across the dayside. IUVS studies the aurora at mid- and far-UV wavelengths in both limb scans and nadir imaging. The Emirates Mars Mission (EMM) arrived in 2021 carrying the Emirates Mission UltraViolet Spectrometer (EMUS). EMUS quickly added to the menagerie of auroral phenomena thanks to its high far-UV sensitivity. Discrete aurora emissions were seen in a substantial fraction of nightside observations, and appear to take on new forms not seen by IUVS (sinuous, "non-crustal field", among others). Furthermore, EMUS detected a spatially-variable form of proton aurora called patchy proton aurora. EMUS studies the aurora through nadir imaging at far- and extreme-UV wavelengths. The net result of the tremendous influx of new observations is a lag in cataloguing and cross-comparing the types of observations made with different instruments at different wavelength ranges in different observing modes. We now have the perspective to identify the causes of these auroral phenomena, which gives a more physics-based nomenclature: suprathermal electron aurora: hot electrons from the Mars environment appear to be responsible for most forms of discrete aurora solar energetic particle aurora: SEP electrons and protons from the Sun cause the planet-wide diffuse aurora  solar wind aurora: solar wind protons charged-exchange into the atmosphere to cause dayside aurora This presentation seeks to give that broader context, highlighting what phenomena IUVS and EMUS observe, depending on their distinct instrumental capabilities whether they’re actually seeing the same phenomena or different ones,  how can one type of observation can complement the other,  where one’s capabilities are unique, and  what are the best directions for collaboration; how in situ measurements of particles and fields can contribute to the next stage of understanding of the conditions for particle precipitation A more coherent observational perspective, as outlined above, may grant a framework for developing a deeper physical understanding of Mars unexpected diverse auroral processes