Mars's Dayside Upper Ionospheric Composition Is Affected by Magnetic Field Conditions

Previous observations have shown that electron density and temperature in the dayside ionosphere of Mars vary between strongly and weakly magnetized regions of the planet. Here we use data from the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft to examine whether dayside ion densities and ionospheric composition also vary. We find that O+,O 2 + , andCO 2 + densities above ~200 km are greater in strongly magnetized regions than in weakly magnetized regions. Fractional abundances of ion species are also affected. TheO + / O 2 + ratio at 300-km altitude increases from ~0.5 in strongly magnetized regions to ~0.8 in weakly magnetized regions. Consequently, the plasma reservoir available for escape is fundamentally different between strongly magnetized and weakly magnetized regions.

Ion Densities in the Nightside Ionosphere of Mars: Effects of Electron Impact Ionization

We use observations from the Mars Atmosphere and Volatile EvolutioN(MAVEN) mission to show how superthermal electron fluxes and crustal magnetic fields affect ion densities in the nightside ionosphere of Mars. We find that, due to electron impact ionization, high electron fluxes significantly increase the CO2+ , O⁺, and O2+ densities below 200 km, but only modestly increase the NO⁺ density. High electron fluxes also produce distinct peaks in the CO2+ , O⁺, and O2+ altitude profiles. We also find that superthermal electron fluxes are smaller near strong crustal magnetic fields. Consequently, nightside ion densities are also smaller near strong crustal fields because they decay without being replenished by electron impact ionization. Furthermore, the NO+/O2+ ratio is enhanced near strong crustal fields because, in the absence of electron impact ionization, O2+ is converted into NO⁺ and not replenished. Our results show that electron impact ionization is a significant source of CO2+ , O⁺, and O2+ in the nightside ionosphere of Mars.

Mars' atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar

The history of Mars' atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of ³⁸Ar/³⁶Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars' atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today's cold, dry atmosphere.

MAVEN observations of the response of Mars to an interplanetary coronal mass ejection

Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.

Early MAVEN Deep Dip campaign reveals thermosphere and ionosphere variability

The Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above the well-mixed atmosphere, the layer of peak extreme ultraviolet heating and primary reservoir for atmospheric escape. In situ measurements of the upper atmosphere reveal previously unmeasured populations of neutral and charged particles, the homopause altitude at approximately 130 kilometers, and an unexpected level of variability both on an orbit-to-orbit basis and within individual orbits. These observations help constrain volatile escape processes controlled by thermosphere and ionosphere structure and variability.

Structure and composition of the neutral upper atmosphere of Mars from the MAVEN NGIMS investigation

The Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) provides sensitive detections of neutral gas and ambient ion composition. NGIMS measurements of nine atomic and molecular neutral species, and their variation with altitude, latitude, and solar zenith angle are reported over several months of operation of the MAVEN mission. Sampling NGIMS signals from multiple neutral species every several seconds reveals persistent and unexpectedly large amplitude density structures. The scale height temperatures are mapped over the course of the first few months of the mission from high down to midlatitudes. NGIMS measurements near the homopause of ⁴⁰Ar/N₂ ratios agree with those reported by the Sample Analysis at Mars investigation and allow the altitude of the homopause for the most abundant gases to be established.

Structure and composition of the neutral upper atmosphere of Mars from the MAVEN NGIMS investigation

The Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) provides sensitive detections of neutral gas and ambient ion composition. NGIMS measurements of nine atomic and molecular neutral species, and their variation with altitude, latitude, and solar zenith angle are reported over several months of operation of the MAVEN mission. Sampling NGIMS signals from multiple neutral species every several seconds reveals persistent and unexpectedly large amplitude density structures. The scale height temperatures are mapped over the course of the first few months of the mission from high down to midlatitudes. NGIMS measurements near the homopause of ⁴⁰Ar/N₂ ratios agree with those reported by the Sample Analysis at Mars investigation and allow the altitude of the homopause for the most abundant gases to be established.

Cardiometabolic risk clustering in spinal cord injury: results of exploratory factor analysis

BACKGROUND

Evidence suggests an elevated prevalence of cardiometabolic risks among persons with spinal cord injury (SCI); however, the unique clustering of risk factors in this population has not been fully explored.

OBJECTIVE

The purpose of this study was to describe unique clustering of cardiometabolic risk factors differentiated by level of injury.

METHODS

One hundred twenty-one subjects (mean 37 ± 12 years; range, 18-73) with chronic C5 to T12 motor complete SCI were studied. Assessments included medical histories, anthropometrics and blood pressure, and fasting serum lipids, glucose, insulin, and hemoglobin A1c (HbA1c).

RESULTS

The most common cardiometabolic risk factors were overweight/obesity, high levels of low-density lipoprotein (LDL-C), and low levels of high-density lipoprotein (HDL-C). Risk clustering was found in 76.9% of the population. Exploratory principal component factor analysis using varimax rotation revealed a 3-factor model in persons with paraplegia (65.4% variance) and a 4-factor solution in persons with tetraplegia (73.3% variance). The differences between groups were emphasized by the varied composition of the extracted factors: Lipid Profile A (total cholesterol [TC] and LDL-C), Body Mass-Hypertension Profile (body mass index [BMI], systolic blood pressure [SBP], and fasting insulin [FI]); Glycemic Profile (fasting glucose and HbA1c), and Lipid Profile B (TG and HDL-C). BMI and SBP formed a separate factor only in persons with tetraplegia.

CONCLUSIONS

Although the majority of the population with SCI has risk clustering, the composition of the risk clusters may be dependent on level of injury, based on a factor analysis group comparison. This is clinically plausible and relevant as tetraplegics tend to be hypo- to normotensive and more sedentary, resulting in lower HDL-C and a greater propensity toward impaired carbohydrate metabolism.

Teleassessment compared with live assessment of pressure ulcers in a wound clinic: a pilot study

OBJECTIVE

To compare teleassessment of pressure ulcers in individuals with spinal cord injury in a simulated remote setting with in-person assessments in a wound clinic.

DESIGN

Pressure ulcers were assessed using a 3-megapixel digital camera; images of each ulcer were forwarded to a laptop in a separate room. Nurses completed a medical history and wound database form. A plastic surgeon reviewed the images and database and completed a questionnaire concerning the "remote" teleassessment or teleconsultation. When needed, the plastic surgeon obtained additional information using live audio-video interaction with the participant or nurse. After the teleassessment was completed, the plastic surgeon then assessed the individual and wound live and completed the same questionnaire used for the teleassessment.

SETTING

Wound clinic of a rehabilitation hospital.

PARTICIPANTS

Individuals with a spinal cord injury and 1 or more pressure ulcers who were seen for initial or follow-up evaluations.

MAIN OUTCOME MEASURES

Percentage of agreement for teleassessment versus live responses to 4 yes/no questions regarding the need to change wound management, satisfaction with teleassessment, need for referral, and need for additional information.

MAIN RESULTS

Seventeen individuals with 20 wounds were evaluated. The total percentage of agreement for teleassessment versus live decisions was 89% (80% to 95%). The highest percentages of agreement were for the need to change wound management and the need for referral (both 95%); the lowest percentages of agreement were for satisfaction with teleassessment for making treatment decisions (85%) and the need to obtain additional information (80%).

CONCLUSIONS

Teleassessment of pressure ulcers in individuals with a spinal cord injury using digital images and a standard database compared well with in-person assessment, which is similar to results reported for other pathologic conditions.

Characterization of a putative calcium-binding site in tobacco mosaic virus

Lead has been used as a substitute for calcium binding to tobacco mosaic virus (TMV). The high atomic number of lead has allowed us to use difference maps from X-ray fiber diffraction data to characterize a calcium-binding site in the virus. The metal ligands are slightly different from those previously believed to bind calcium to TMV, although the binding site is very close to one previously described. Two acetate groups are also bound to the lead atom. There is no significant backbone conformational change in the protein as a result of metal binding; the binding is accomplished by means of relatively small movements in amino acid side chains.