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.

Weak magnetism of Martian impact basins may reflect cooling in a reversing dynamo.

Understanding the longevity of Mars's dynamo is key to interpreting the planet's atmospheric loss history and the properties of its deep interior. Satellite data showing magnetic lows above many large impact basins formed 4.1-3.7 billion years ago (Ga) have been interpreted as evidence that Mars's dynamo terminated before 4.1 Ga-at least 0.4 Gy before intense late Noachian/early Hesperian hydrological activity. However, evidence for a longer-lived, reversing dynamo from young volcanics and the Martian meteorite ALH 84001 supports an alternative interpretation of Mars's apparently demagnetized basins. To understand how a reversing dynamo would affect basin fields, here we model the cooling and magnetization of 200-2200 km diameter impact basins under a range of Earth-like reversal frequencies. We find that magnetic reversals efficiently reduce field strengths above large basins. In particular, if the magnetic properties of the Martian mantle are similar to most Martian meteorites and late remagnetization of the near surface is widespread, >90% of large ( > 800 km diameter) basins would appear demagnetized at spacecraft altitudes. This ultimately implies that Mars's apparently demagnetized basins do not require an early dynamo cessation. A long-lived and reversing dynamo, unlike alternative scenarios, satisfies all available constraints on Mars's magnetic history.

The Emirates Mars Mission.

The Emirates Mars Mission (EMM) was launched to Mars in the summer of 2020, and is the first interplanetary spacecraft mission undertaken by the United Arab Emirates (UAE). The mission has multiple programmatic and scientific objectives, including the return of scientifically useful information about Mars. Three science instruments on the mission's Hope Probe will make global remote sensing measurements of the Martian atmosphere from a large low-inclination orbit that will advance our understanding of atmospheric variability on daily and seasonal timescales, as well as vertical atmospheric transport and escape. The mission was conceived and developed rapidly starting in 2014, and had aggressive schedule and cost constraints that drove the design and implementation of a new spacecraft bus. A team of Emirati and American engineers worked across two continents to complete a fully functional and tested spacecraft and bring it to the launchpad in the middle of a global pandemic. EMM is being operated from the UAE and the United States (U.S.), and will make its data freely available.

Discovery of diffuse aurora on Mars.

Planetary auroras reveal the complex interplay between an atmosphere and the surrounding plasma environment. We report the discovery of low-altitude, diffuse auroras spanning much of Mars' northern hemisphere, coincident with a solar energetic particle outburst. The Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, detected auroral emission in virtually all nightside observations for ~5 days, spanning nearly all geographic longitudes. Emission extended down to ~60 kilometer (km) altitude (1 microbar), deeper than confirmed at any other planet. Solar energetic particles were observed up to 200 kilo--electron volts; these particles are capable of penetrating down to the 60 km altitude. Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth.

Changes in alcohol consumption by 18-year-olds following an increase in New York State's purchase age to 19.

A household-based telephone survey of 1800 16- to 20-year-old New Yorkers was conducted during November 1982, approximately one month before New York's minimum legal purchase age for alcoholic beverages was raised from 18 to 19. A second sample was surveyed during December 1983, approximately one year following the change. Comparisons between 1982 and 1983 of prevalence measures for various drinking levels for each age group were made. The prevalence of all drinking levels decreased significantly for 18-year-olds as well as 17-year-olds. Decreases for 19- and 20-year-olds were significant for less than half the measures and were less in magnitude than decreases for 18-year-olds. Prior to the purchase age change, prevalence measures for 18-year-olds were similar to those for 19- and 20-year-olds. Following the increase, measures for 18-year-olds were significantly lower than those for 19- and 20-year-olds. Analysis by sex showed that prevalence measures for 18-year-old men and women generally declined significantly. The public health implications of these findings as well as the highway safety aspects are discussed.

Neck pain and head restraint position relative to the driver's head in rear-end collisions.

This two-year investigation was designed to estimate the incidence of driver neck pain in rear-struck vehicles involved in two-vehicle collisions and to determine the relationship between neck pain and specific vehicle, human, and environmental factors. Neck pain percentages were significantly higher for female (45%) than for male (28%) drivers. For female and male drivers, neck pain likelihood increased as head restraint height decreased below the head's center of gravity, although this effect was significant only for females. Head restraint backset, the horizontal distance measured from the back of the driver's head to the front of the head restraint, was not found to be related to neck pain for female drivers. Backset trends for male drivers could not be evaluated because few male drivers had head restraints that were high enough for backset to be relevant. Reported neck pain decreased for older drivers (females only), drivers in less severe crashes, and drivers in heavier cars (females only); all head restraint analyses were adjusted for these characteristics. Women, and most likely men, in the United States would benefit greatly from international harmonization to European head restraint standards. Until then, both women and men should be encouraged to adjust their adjustable head restraints, if possible, behind their heads' centers of gravity and to sit with the backs of their heads as close as possible to their head restraints.

Trophic regulation of nodose ganglion cell development: evidence for an expanded role of nerve growth factor during embryogenesis in the rat.

Peripheral sensory neurons are derived from two distinct embryonic tissues, the neural crest and epibranchial placodes. Studies in the chick suggest that embryonic lineage and trophic dependence are interrelated, such that many crest-derived cells depend on NGF for survival during development, whereas placodal derivates, including nodose ganglion neurons, do not (30). It remains controversial, however, whether or not a similar dichotomy exists in mammalian species, in which trophic requirements during early development of placodal ganglia have not been defined. To approach this issue, the present study examined the effects of nerve growth factor (NGF) on neuronal survival in embryonic rat nodose ganglion cultures. Treatment of E13.5-14.5 nodose explants with 20 ng/ml NGF resulted in a four-fold increase in neuronal survival that was blocked by anti-NGF antiserum. Increased neuronal survival and neurite outgrowth were also observed in neuron-enriched dissociated cell cultures; these effects were seen within 12 h of plating, indicating that NGF-responsive neurons or neuroblasts were already present in the ganglion at the time of explantation. This was further supported by immunocytochemical staining of nodose cell bodies in situ with the monoclonal antibody 192-IgG against the NGF receptor (12). These findings indicate that NGF may be important in regulating nodose development during early gangliogenesis in mammals and suggest that NGF plays a more widespread role in peripheral nervous system ontogeny than previously recognized.

Interactions of Escherichia coli endonuclease IV and exonuclease III with abasic sites in DNA.

Duplex oligodeoxynucleotides with synthetic analogs of abasic sites were used to study the specificity of the abasic endonucleases of Escherichia coli. The apparent Km values of exonuclease III for the tetrahydrofuranyl, propanyl, and deoxyribosyl substrates varied only somewhat (20-140 nM) in either Mg2+ or Ca2+ and were similar to those for endonuclease IV. In Mg2+, exonuclease III had a turnover number 4-13-fold higher than measured for endonuclease IV (ranging 5.6-18 min-1), but was lowered in Ca2+ to values similar to those for endonuclease IV. The rate of cleavage of tetrahydrofuranyl (F) substrate by both enzymes was unaffected by the base in the opposite strand or its replacement by a tetrahydrofuranyl moiety. A C:C mismatch on the 5' but not the 3' side of F strongly inhibited cleavage by exonuclease III in Ca2+, while mismatches on both sides were required to diminish endonuclease IV cleavage significantly. A phosphorothioate ester linked 5' to the tetrahydrofuranyl moiety inhibited both enzymes, with the Rp stereoisomer most effective. Endonuclease IV bound stably to duplex substrates containing the Rp phosphorothioate in the presence of poly(dI-dC). Although the apurinic/apyrimidinic-cleaving activities of endonuclease IV and exonuclease III have some common features they also differ in their specific interactions with DNA containing abasic sites.

Intracellular localization of the Apn1 DNA repair enzyme of Saccharomyces cerevisiae. Nuclear transport signals and biological role.

The Apn1 DNA repair enzyme of Saccharomyces cerevisiae acts on abasic sites and oxygen radical damages. Apn1 is homologous to the repair endonuclease IV of Escherichia coli, but the yeast protein is approximately 80 residues longer at the C terminus. The Apn1 C terminus is rich in basic amino acids and includes two lysine/arginine clusters related to the nuclear transport signals of some other proteins. We show here by indirect immunofluorescence that Apn1 is localized to the yeast nucleus. Mutant Apn1 proteins were engineered with progressive deletions inward from the C terminus. Elimination of just the last 12 residues from Apn1 (to yield Apn355) did not alter the stability in yeast cells or the in vitro activity of the enzyme. Greater truncation of Apn1 produced proteins of apparently lower (Apn334) or much lower (Apn315 and Apn293) in vivo stability. Both Apn355 and Apn334 failed to concentrate in the yeast nucleus and remained in the cytoplasm. These delocalized derivatives also failed to restore wild-type resistance to oxidative or alkylating agents in a delta apn1 strain. Apn355 and Apn334 complemented repair-deficient E. coli as effectively as did wild-type Apn1. Resistance to these DNA-damaging agents in yeast was restored if Apn355 and Apn334 (but not Apn315 or Apn293) were overproduced approximately 20-fold, which suggests either weak active transport or passive diffusion of these derivatives into the nucleus. Replacement of the C-terminal 12 residues of Apn1 with the nuclear targeting sequence of SV40 T-antigen did not restore effective function or nuclear localization in yeast.

Deaths from motor vehicle crashes: patterns of injury in restrained and unrestrained victims.

A time comparison study of motor vehicle crashes in Monroe County, New York, from 1983 to 1986 was completed. Using a database of police accident reports, hospital logs, and autopsy reports from the county coroner, the hospital and autopsy reports of 91 unrestrained and 27 restrained fatally injured victims were reviewed. The hypothesis was that safety belts do not change patterns of injury in fatally injured victims. Patient data, seating position, and direction of impact were the same for both groups, while ejections occurred only in the unrestrained group (19.8%). Injury Severity Score (ISS), major injuries in AIS-85 categories for the Head, Thorax, Abdomen, and in AIS-85 Code 5 or 6 categories for the Head, Thorax, Abdomen were the same in unrestrained and restrained victims, except for the greater incidence of cerebral contusions in the unrestrained group (71% vs. 37%, p = 0.002). Cranial injuries were the most likely cause of death in nearly two thirds of the victims in both groups. The incidence of major head (other than cerebral contusion), thoracic, and abdominal injuries in unrestrained and restrained fatally injured victims was the same. This suggests that severe collisions with crushing, intrusion, or significant deceleration exceed the ability of restraints to prevent many fatal injuries.