Search

We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope from sublimated H2O and radiolytically produced H2 using the Direct Simulation Monte Carlo (DSMC) method. The spatial morphology of this corona produced via photo- and magnetospheric electron impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O2 component. Our results presented indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark non-ice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H2 component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument, providing the first evidence of H2 in Callisto's atmosphere. Finally, we discuss the implications of these results, in particular how they compare to Europa and Ganymede.

DNA mismatch repair (MMR) in eukaryotes is believed to occur post-replicatively, wherein nicks or gaps in the nascent DNA strand are suggested to serve as strand discrimination signals. However, how such signals are generated in the nascent leading strand has remained unclear. Here we examine the alternative possibility that MMR occurs in conjunction with the replication fork. To this end, we utilize mutations in the PCNA interacting peptide (PIP) domain of the Pol3 or Pol32 subunit of DNA polymerase δ (Polδ) and show that these pip mutations suppress the greatly elevated mutagenesis in yeast strains harboring the pol3-01 mutation defective in Polδ proofreading activity. And strikingly, they suppress the synthetic lethality of pol3-01 pol2-4 double mutant strains, which arises from the vastly enhanced mutability due to defects in the proofreading functions of both Polδ and Polε. Our finding that suppression of elevated mutagenesis in pol3-01 by the Polδ pip mutations requires intact MMR supports the conclusion that MMR operates at the replication fork in direct competition with other mismatch removal processes and with extension of synthesis from the mispair by Polδ. Furthermore, the evidence that Polδ pip mutations eliminate almost all the mutability of pol2-4 msh2Δ or pol3-01 pol2-4 adds strong support for a major role of Polδ in replication of both the leading and lagging DNA strands.

Electron impact ionization is critical in producing the ionospheres on many planetary bodies and, as discussed here, is critical for interpreting spacecraft and telescopic observations of the tenuous atmospheres of the icy Galilean satellites of Jupiter (Europa, Ganymede, and Callisto), which form an interesting planetary system. Fortunately, laboratory measurements, extrapolated by theoretical models, were developed and published over a number of years by K. Becker and colleagues (see Deutsch et al. 2009) to provide accurate electron impact ionization cross sections for atoms and molecules, which are crucial to correctly interpret these measurements. Because of their relevance for the Jovian icy satellites we provide useful fits to the complex, semi-empirical Deutsch-Mark formula for energy-dependent electron impact ionization cross-sections of gas-phase water products (i.e., H2O, H2, O2, H, O). These are then used with measurements of the thermal plasma in the Jovian magnetosphere to produce ionization rates for comparison with solar photo-ionization rates at the icy Galilean satellites.

We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope (Roth et al. 2017a) from sublimated H2O and radiolytically produced H2 using the Direct Simulation Monte Carlo (DSMC) method. The spatial morphology of this corona produced via photo- and magnetospheric electron impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O2 component. Our results indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark non-ice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H2 component can reproduced the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument (Gurnett et al., 1997, 2000), providing the first evidence of H2 in Callisto's atmosphere. The range of H2 surface densities explored, under a variety of conditions, that are consistent with these observations is ~(0.4-1)x10^8 cm^-3. The simulated H2 escape rates and estimated lifetimes suggest that Callisto has a neutral H2 torus. We also place a rough upper limit on the peak H2O number density (

DNA polymerase ζ (Polζ) belongs to the same B-family as high-fidelity replicative polymerases, yet is specialized for the extension reaction in translesion DNA synthesis (TLS). Despite its importance in TLS, the structure of Polζ is unknown. We present cryo-EM structures of the Saccharomyces cerevisiae Polζ holoenzyme in the act of DNA synthesis (3.1 A) and without DNA (4.1 A). Polζ displays a pentameric ring-like architecture, with catalytic Rev3, accessory Pol31‚ Pol32 and two Rev7 subunits forming an uninterrupted daisy chain of protein–protein interactions. We also uncover the features that impose high fidelity during the nucleotide-incorporation step and those that accommodate mismatches and lesions during the extension reaction. Collectively, we decrypt the molecular underpinnings of Polζ’s role in TLS and provide a framework for new cancer therapeutics. Cryo-EM structures of free and DNA-bound pol ζ holoenzyme from budding yeast reveal how this DNA polymerase ensures fidelity and facilitates lesion bypass during translesion DNA synthesis.

The action mechanisms revealed by the biochemical and structural analyses of replicative and translesion synthesis (TLS) DNA polymerases (Pols) are retained in their cellular roles. In this regard, DNA polymerase θ differs from other Pols in that whereas purified Polθ misincorporates an A opposite 1,N(6)-ethenodeoxyadenosine (ϵdA) using an abasic-like mode, Polθ performs predominantly error-free TLS in human cells. To test the hypothesis that Polθ adopts a different mechanism for replicating through ϵdA in human cells than in the purified Pol, here we analyze the effects of mutations in the two highly conserved tyrosine residues, Tyr-2387 and Tyr-2391, in the Polθ active site. Our findings that these residues are indispensable for TLS by the purified Pol but are not required in human cells, as well as other findings, provide strong evidence that the Polθ active site is reconfigured in human cells to stabilize ϵdA in the syn conformation for Hoogsteen base pairing with the correct nucleotide. The evidence that a DNA polymerase can configure its active site entirely differently in human cells than in the purified Pol establishes a new paradigm for DNA polymerase function.

Cytarabine (AraC) is the mainstay chemotherapy for acute myeloid leukemia (AML). Whereas initial treatment with AraC is usually successful, most AML patients tend to relapse, and AraC treatment-induced mutagenesis may contribute to the development of chemo-resistant leukemic clones. We show here that whereas the high-fidelity replicative polymerase Polδ is blocked in the replication of AraC, the lower-fidelity translesion DNA synthesis (TLS) polymerase Polη is proficient, inserting both correct and incorrect nucleotides opposite a template AraC base. Furthermore, we present high-resolution crystal structures of human Polη with a template AraC residue positioned opposite correct (G) and incorrect (A) incoming deoxynucleotides. We show that Polη can accommodate local perturbation caused by the AraC via specific hydrogen bonding and maintain a reaction-ready active site alignment for insertion of both correct and incorrect incoming nucleotides. Taken together, the structures provide a novel basis for the ability of Polη to promote AraC induced mutagenesis in relapsed AML patients.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections were rising during early summer 2021 in many countries as a result of the Delta variant. We assessed reverse transcription polymerase chain reaction swab positivity in the Real-time Assessment of Community Transmission–1 (REACT-1) study in England. During June and July 2021, we observed sustained exponential growth with an average doubling time of 25 days, driven by complete replacement of the Alpha variant by Delta and by high prevalence at younger, less-vaccinated ages. Prevalence among unvaccinated people [1.21% (95% credible interval 1.03%, 1.41%)] was three times that among double-vaccinated people [0.40% (95% credible interval 0.34%, 0.48%)]. However, after adjusting for age and other variables, vaccine effectiveness for double-vaccinated people was estimated at between ~50% and ~60% during this period in England. Increased social mixing in the presence of Delta had the potential to generate sustained growth in infections, even at high levels of vaccination.

A simulation tool which utilizes parallel processing is developed to describe molecular kinetics in 2D, single- and multi-component atmospheres on Callisto. This expands on our previous study on the role of collisions in 1D atmospheres on Callisto composed of radiolytic products (Carberry Mogan et al., 2020) by implementing a temperature gradient from noon to midnight across Callisto’s surface and introducing sublimated water vapor. We compare single-species, ballistic and collisional O 2 , H 2 and H 2 O atmospheres, as well as an O 2 +H 2 O atmosphere to 3-species atmospheres which contain H 2 in varying amounts. Because the H 2 O vapor pressure is extremely sensitive to the surface temperatures, the density drops several orders of magnitude with increasing distance from the subsolar point, and the flow transitions from collisional to ballistic accordingly. In an O 2 +H 2 O atmosphere the local temperatures are determined by H 2 O near the subsolar point and transition with increasing distance from the subsolar point to being determined by O 2 . When radiolytically produced H 2 is not negligible in O 2 +H 2 O+H 2 atmospheres, this much lighter molecule, with a scale height roughly an order of magnitude larger than that for the heavier species, can cool the local temperatures via collisions. In addition, if the H 2 component is dense enough, particles originating on the day-side and precipitating into the night-side atmosphere deposit energy via collisions, which in turn heats the local atmosphere relative to the surface temperature. Moreover, the difference between H 2 atmospheric escape rates in single-species and multi-species atmospheres is small: the H 2 only has to diffuse through a few hundred km of the heavier gases before it is the lone species in the atmosphere out to the Hill sphere. Finally, we discuss the potential implications of this study on the presence of H 2 in Callisto’s atmosphere and how the simulated densities correlate with expected detection thresholds at flyby altitudes of the proposed JUpiter ICy moons Explorer (JUICE) spacecraft.

The parameter space for the very uncertain composition of sublimated H2O and its photochemical products H and H2 in Callisto's atmosphere is examined using the Direct Simulaton Monte Carlo (DSMC) method. We focus on two significantly different versions of H2O production in which: (1) the ice and dark, non-ice/ice-poor material are intimately mixed and H2O sublimates at Callisto's warm day-side temperatures (e.g., as in most atmospheric modeling efforts at Callisto to date [1-4]); and (2) the ice and dark, non-ice/ice-poor material are segregated (e.g., consistent with interpretations of images of Callisto's surface taken by Voyager [5, 6] and Galileo [7]) and H2O sublimates at "ice" temperatures [8]. Our 2D molecular kinetic models track the motion H2O, whose sublimation yield varies several orders of magnitude depending on the description of Callisto's surface, its photochemical products H and H2, and a relatively dense O2 component. Whereas H is assumed to react in the regolith on return to the surface, H2 is assumed to thermalize and re-enter the atmosphere. We compare the simulated LOS column densities of H to the detected H corona at Callisto [9], which was suggested to be produced primarily by photodissociation of sublimated H2O. Our goal is to use the corona observations to help constrain the source rate for H2O from Callisto’s complex surface. References [1] Liang et al., 2005. Atmosphere of Callisto. Journal of Geophysical Research: Planets. [2] Vorburger et al., 2015. Monte-Carlo simulation of Callisto’s exosphere. Icarus. [3] Hartkorn et al., 2017. Structure and density of Callisto’s atmosphere from a fluid-kinetic model of its ionosphere: Comparison with Hubble Space Telescope and Galileo observations. Icarus. [4] Carberry Mogan et al., 2021 (under review). A tenuous, collisional atmosphere on Callisto. Icarus. [5] Spencer and Maloney, 1984. Mobility of water ice on Callisto: Evidence and implications. Geophysical Research Letters. [6] Spencer, 1987. Thermal segregation of water ice on the Galilean satellites. Icarus. [7] Moore et al., 1999. Mass movement and landform degradation on the icy Galilean satellites: Results of the Galileo nominal mission. Icarus. [8] Grundy et al., 1999. Near-infrared spectra of icy outer solar system surfaces: Remote determination of H2O ice temperatures. Icarus. [9] Roth et al., 2017. Detection of a hydrogen corona at Callisto. Journal of Geophysical Research: Planets.

The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on board JUICE is designed to measure neutrals, ions, electrons, and energetic particles over an energy range from eV to MeV. In the vicinity of Callisto, PEP will characterize the Jovian plasma environment and the outer parts of Callisto’s atmosphere and ionosphere. Roughly twenty Callisto flybys with closest approaches between 200 km and 5000 km altitude are planned over the course of the JUICE mission. This study aims at optimizing the scientific insight gained from the foreseen flybys by combining the input from the PEP science team and operation planning with recent model efforts for Callisto’s atmosphere, the plasma environment and the production of Energetic Neutral Atoms. The results of this study will inform both science operation planning of PEP and JUICE and they will guide future model development for Callisto’s atmosphere, ionosphere, and their interaction with the plasma environment.

PrimPol is a human DNA polymerase-primase that localizes to mitochondria and nucleus and bypasses the major oxidative lesion 7,8-dihydro-8-oxoguanine (oxoG) via translesion synthesis, in mostly error-free manner. We present structures of PrimPol insertion complexes with a DNA template-primer and correct dCTP or erroneous dATP opposite the lesion, as well as extension complexes with C or A as a 3′−terminal primer base. We show that during the insertion of C and extension from it, the active site is unperturbed, reflecting the readiness of PrimPol to accommodate oxoG(anti). The misinsertion of A opposite oxoG(syn) also does not alter the active site, and is likely less favorable due to lower thermodynamic stability of the oxoG(syn)•A base-pair. During the extension step, oxoG(syn) induces an opening of its base-pair with A or misalignment of the 3′-A primer terminus. Together, the structures show how PrimPol accurately synthesizes DNA opposite oxidatively damaged DNA in human cells., The human DNA primase and DNA polymerase PrimPol replicates through the major oxidative DNA damage lesion 7,8-dihydro-8-oxoguanine (oxoG) via translesion synthesis in a mostly error-free manner thus suppressing oxoG-induced mutagenesis in mitochondria and the nucleus. Here, the authors present crystal structures of PrimPol in complex with an oxoG lesion in different contexts that provide mechanistic insights into how PrimPol performs predominantly accurate synthesis on oxidative-damaged DNAs in human cells.

Chemotherapy with cisplatin becomes limiting due to toxicity and secondary malignancies. In principle, therapeutics could be improved by targeting translesion synthesis (TLS) polymerases (Pols) that promote replication through intrastrand cross-links, the major cisplatin-induced DNA adduct. However, to specifically target malignancies with minimal adverse effects on normal cells, a good understanding of TLS mechanisms in normal versus cancer cells is paramount. We show that in normal cells, TLS through cisplatin intrastrand cross-links is promoted by Polη- or Polι-dependent pathways, both of which require Rev1 as a scaffolding component. In contrast, cancer cells require Rev1-Polζ. Our findings that a recently identified Rev1 inhibitor, JH-RE-06, purported to specifically disrupt Rev1 interaction with Polζ to block TLS through cisplatin adducts in cancer cells, abrogates Rev1's ability to function with Y family Pols as well, implying that by inactivating Rev1-dependent TLS in normal cells, this inhibitor will exacerbate the toxicity and tumorigenicity of chemotherapeutics with cisplatin.

Here we show that translesion synthesis (TLS) opposite 1,N6-ethenodeoxyadenosine (εdA), which disrupts Watson–Crick base pairing, occurs via Polι/Polζ-, Rev1-, and Polθ-dependent pathways. The requirement of Polι/Polζ is consistent with the ability of Polι to incorporate nucleotide opposite εdA by Hoogsteen base pairing and of Polζ to extend synthesis. Rev1 polymerase and Polθ conduct TLS opposite εdA via alternative error-prone pathways. Strikingly, in contrast to extremely error-prone TLS opposite εdA by purified Polθ, it performs predominantly error-free TLS in human cells. Reconfiguration of the active site opposite εdA would provide Polθ the proficiency for error-free TLS in human cells.

The innovative Saturn Ring Skimmer mission concept enables a wide range of investigations that address fundamental questions about Saturn and its rings, as well as giant planets and astrophysical disk systems in general. This mission would provide new insights into the dynamical processes that operate in astrophysical disk systems by observing individual particles in Saturn's rings for the first time. The Ring Skimmer would also constrain the origin, history, and fate of Saturn's rings by determining their compositional evolution and material transport rates. In addition, the Ring Skimmer would reveal how the rings, magnetosphere, and planet operate as an inter-connected system by making direct measurements of the ring's atmosphere, Saturn's inner magnetosphere and the material owing from the rings into the planet. At the same time, this mission would clarify the dynamical processes operating in the planet's visible atmosphere and deep interior by making extensive high-resolution observations of cloud features and repeated measurements of the planet's extremely dynamic gravitational field. Given the scientific potential of this basic mission concept, we advocate that it be studied in depth as a potential option for the New Frontiers program., Comment: White paper submitted to the Planetary Science and Astrobiology Decadal Survey (submission #420)

International audience

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase.

Purpose The purpose of this study was to document the effect of coronavirus disease 2019 (COVID-19) on patients presenting to the University of Washington Oral and Maxillofacial Surgery (UW OMS) with an odontogenic infection. Materials and Methods The investigators designed a retrospective cohort study and enrolled a sample of 889 subjects who presented for an odontogenic infection from March 19 to June 18 in the years 2017, 2018, 2019, and 2020. The primary predictor variable was OMS consultation for an odontogenic infection during a non-COVID-19 (2017, 2018, and 2019) year (control) or during the COVID-19 pandemic in 2020 (experimental). The primary outcome variable was treatment rendered. Appropriate univariate and bivariate statistics were computed, and the level of significance was set at .05 for all tests. Results There was no significant difference in the incidence of OMS consults in the 2 cohorts (P > .05). The number of patients presenting to the UW emergency department (ED) for an odontogenic infection decreased from an average of 246 in non-COVID years to 151 in 2020. Patients in the experimental cohort were more likely (55 vs 30.0%; P = .04) to present primarily to UW than a dentist and were less likely to undergo an incision and drainage (70.0 vs 88.8%; P = .04), aerosol-generating procedure (70.0 vs 88.8%; P = .04), and incision and drainage in the ED (15.0 vs 41.3%; P = .03). Conclusions The investigators did not find evidence of increased hospital or ED burden by odontogenic infections during the COVID-19 pandemic.

We examine high altitude gravity waves in the upper atmosphere of Mars using the data from the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, orbiting Mars since late 2014. Since the Martian atmosphere is very thin it is also highly perturbed and the effects of these perturbations are debated. Therefore, on 252 trajectories through the Martian atmosphere large amplitude, high altitude perturbations seen in the NGIMS database are examined. When the perturbations are organized by column density rather than altitude, the perturbations both peak and dissipate at similar column densities. These perturbations also increase the O/CO2 ratio above that measured for orbits without a significant perturbation. To understand this effect, the perturbations are subsequently categorized by location and found to be roughly consistent with wave activity seen lower in the atmosphere. Because the NGIMS data for each perturbation cannot measure the temperature or long term behavior, we simulate wave propagation using a Direct Simulation Monte Carlo (DSMC) model. The results from such simulations suggest that these perturbations are most likely large amplitude acoustic gravity waves, whose high frequency and fast phase speed allow them to propagate into the Martian exosphere, affecting the diffusive separation of species and depositing heat.

At 30-50 K, the temperatures typical for surfaces in the Kuiper Belt (e.g. Stern & Trafton 2008), only seven species have sublimation pressures higher than 1 nbar (Fray & Schmitt 2009): Ne, N$_2$, CO, Ar, O$_2$, CH$_4$, and Kr. Of these, N$_2$, CO, and CH$_4$ have been detected or inferred on the surfaces of Trans-Neptunian Objects (TNOs). The presence of tenuous atmospheres above these volatile ices depends on the sublimation pressures, which are very sensitive to the composition, temperatures, and mixing states of the volatile ices. Therefore, the retention of volatiles on a TNO is related to its formation environment and thermal history. The surface volatiles may be transported via seasonally varying atmospheres and their condensation might be responsible for the high surface albedos of some of these bodies. The most sensitive searches for tenuous atmospheres are made by the method of stellar occultation, which have been vital for the study of the atmospheres of Triton and Pluto, and has to-date placed upper limits on the atmospheres of 11 other bodies. The recent release of the Gaia astrometric catalog has led to a "golden age" in the ability to predict TNO occultations in order to increase the observational data base.

Early in the Moon's history volcanic outgassing may have produced a periodic millibar level atmosphere (Needham and Kring, 2017). We examined the relevant atmospheric escape processes and lifetime of such an atmosphere. Thermal escape rates were calculated as a function of atmospheric mass for a range of temperatures including the effect of the presence of a light constituent such as H2. Photochemical escape and atmospheric sputtering were calculated using estimates of the higher EUV and plasma fluxes consistent with the early Sun. The often used surface Jeans calculation carried out in Vondrak (1974) is not applicable for the scale and composition of the atmosphere considered. We show that solar driven non-thermal escape can remove an early CO millibar level atmosphere on the order of 1 Myr if the average exobase temperature is below 350 - 400 K. However, if solar UV/EUV absorption heats the upper atmosphere to temperatures > 400 K thermal escape increasingly dominates the loss rate, and we estimated a minimum lifetime of 100's of years considering energy limited escape., Submitted to Icarus

Extrasolar satellites are generally too small to be detected by nominal searches. By analogy to the most active body in the Solar System, Io, we describe how sodium (Na I) and potassium (K I) $\textit{gas}$ could be a signature of the geological activity venting from an otherwise hidden exo-Io. Analyzing $\sim$ a dozen close-in gas giants hosting robust alkaline detections, we show that an Io-sized satellite can be stable against orbital decay below a planetary tidal $\mathcal{Q}_p \lesssim 10^{11}$. This tidal energy is focused into the satellite driving a $\sim 10^{5 \pm 2}$ higher mass loss rate than Io's supply to Jupiter's Na exosphere, based on simple atmospheric loss estimates. The remarkable consequence is that several exo-Io column densities are on average $\textit{more than sufficient}$ to provide the $\sim$ 10$^{10 \pm 1}$ Na cm$^{-2}$ required by the equivalent width of exoplanet transmission spectra. Furthermore, the benchmark observations of both Jupiter's extended ($\sim 1000$ R$_J$) Na exosphere and Jupiter's atmosphere in transmission spectroscopy yield similar Na column densities that are purely exogenic in nature. As a proof of concept, we fit the "high-altitude" Na at WASP 49-b with an ionization-limited cloud similar to the observed Na profile about Io. Moving forward, we strongly encourage time-dependent ingress and egress monitoring along with spectroscopic searches for other volcanic volatiles., Comment: 23 pages, 5 figures, accepted to ApJ

Mass spectroscopy of bio-molecules by heavy ion induced sputtering, which became a practical laboratory procedure, was also suggested as a potential tool for spacecraft studies of targets of interest in astrobiology. With the planning of new missions to Europa, there is renewed interest in the possibility of detecting organic molecules that might have originated in its subsurface ocean and can be sputtered from its surface often intact by impacting energetic heavy ions trapped in Jupiter's magnetosphere. Here we review the laboratory data and modeling bearing on this issue. We then give estimates of the ejection into the gas-phase of trace organic species embedded in an ice matrix on Europa's surface and their possible detection during a flyby mission.

Purpose The objective of this study was to determine attitudes toward and the prevalence of using a surgical safety checklist in ambulatory oral and maxillofacial surgery (OMS) practice. Materials and Methods The authors designed and implemented a cross-sectional study and enrolled a random sample of oral and maxillofacial surgeons. The predictor variable was years removed from residency. The primary outcome was the prevalence of surgical safety checklist usage in ambulatory OMS practice. The secondary outcome was to determine whether surgeons who do not currently use a checklist would be willing to do so if provided with one. Other demographic variables included age, gender, location of practice, type of practice, and number of ambulatory procedures performed per week. Appropriate uni- and bivariate statistics were computed and the level of significance set at .05; 95% confidence intervals also were calculated. Results The study sample was composed of 120 clinicians. Forty-two percent of respondents reported that they were not using a surgical safety checklist for ambulatory surgery. Ninety-three percent of those respondents not currently using a checklist reported they would consider implementing a surgical safety checklist in their practice if provided with one. In addition, 45.3% of surgeons performing more than 30 procedures a week reported not using a surgical safety checklist. Most respondents (67.9%) who had completed OMS training more than 20 years previously reported not using a checklist in their practice. Conclusion According to this survey, most practicing oral and maxillofacial surgeons do not currently use surgical safety checklists. Although the response rate was only 12%, the survey does reflect a clear lack of use of checklists among practicing oral and maxillofacial surgeons despite its widespread acceptance in the medical community.

Molecular kinetic simulations are typically used to accurately describe the tenuous regions of the upper atmospheres on planetary bodies. These simulations track the motion of particles representing real atmospheric atoms and/or molecules subject to collisions, the object's gravity, and external influences. Because particles can end up in very large ballistic orbits, upper boundary conditions (UBC) are typically used to limit the domain size thereby reducing the time for the atmosphere to reach steady-state. In the absence of a clear altitude at which all molecules are removed, such as a Hill sphere, an often used condition is to choose an altitude at which collisions become infrequent so that particles on escape trajectories are removed. The remainder are then either specularly reflected back into the simulation domain or their ballistic trajectories are calculated analytically or explicitly tracked so they eventually re-enter the domain. Here we examine the effect of the choice of the UBC on the escape rate and the structure of the atmosphere near the nominal exobase in the convenient and frequently used 1D spherically symmetric approximation. Using Callisto as the example body, we show that the commonly used specular reflection UBC can lead to significant uncertainties when simulating a species with a lifetime comparable to or longer than a dynamical time scale, such as an overestimation of escape rates and an inflated exosphere. Therefore, although specular reflection is convenient, the molecular lifetimes and body's dynamical time scales need to be considered even when implementing the convenient 1D spherically symmetric simulations in order to accurately estimate the escape rate and the density and temperature structure in the transition regime.

The first measurements of the emission brightness of the oxygen atomic exosphere by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission have clearly shown that it is composed of a thermal component produced by the extension of the upper atmosphere and of a non-thermal component. Modeling these measurements allows us to constrain the origins of the exospheric O and, as a consequence, to estimate Mars' present oxygen escape rate. We here propose an analysis of three periods of MAVEN observations based on a set of three coupled models: a hybrid magnetospheric model (LatHyS), an Exospheric General Model (EGM) and the Global Martian Circulation model of the Laboratoire de Meteorologie Dynamique (LMD-GCM), which provide a description of Mars' environment from the surface up to the solar wind. The simulated magnetosphere by LatHyS is in good agreement with MAVEN Plasma and Field Package instruments data. The LMD-GCM modeled upper atmospheric profiles for the main neutral and ion species are compared to NGIMS/MAVEN data showing that the LMD-GCM can provide a satisfactory global view of Mars' upper atmosphere. Finally, we were able to reconstruct the expected emission brightness intensity from the oxygen exosphere using EGM. The good agreement with the averaged measured profiles by IUVS during these three periods suggests that Mars' exospheric non-thermal component can be fully explained by the reactions of dissociative recombination of the O2+ ion in Mars' ionosphere, limiting significantly our ability to extract information from MAVEN observations of the O exosphere on other non-thermal processes, such as sputtering.

Vision in dim light depends on synapses between rods and rod bipolar cells (RBCs). Here, we find that these synapses exist in multiple configurations, in which single release sites of rods are apposed by one to three postsynaptic densities (PSDs). Single RBCs often form multiple PSDs with one rod; and neighboring RBCs share ~13% of their inputs. Rod-RBC synapses develop while ~7% of RBCs undergo programmed cell death (PCD). Although PCD is common throughout the nervous system, its influences on circuit development and function are not well understood. We generate mice in which ~53 and ~93% of RBCs, respectively, are removed during development. In these mice, dendrites of the remaining RBCs expand in graded fashion independent of light-evoked input. As RBC dendrites expand, they form fewer multi-PSD contacts with rods. Electrophysiological recordings indicate that this homeostatic co-regulation of neurite and synapse development preserves retinal function in dim light., Retinal rod bipolar cells (RBCs) partially undergo programmed cell death triggering cell density-dependent plasticity. This study shows that increased removal of RBCs using genetic approaches causes dendrites of the remaining RBCs to expand and contact more rod photoreceptors while reducing connectivity with each.

The so-called ‘PacMan’ features on the leading hemispheres of the icy Saturnian moons of Mimas, Tethys and Dione were initially identified as anomalous optical discolorations and subsequently shown to have greater thermal inertia than the surrounding regions. The shape of these regions matches calculated deposition contours of high energy plasma electrons moving opposite to the moon’s orbital direction, thus suggesting that electron interactions with the grains produce the observed anomalies. Here, descriptions of radiation-induced diffusion processes are given, and various sintering models are considered to calculate the rate of increase in the contact volume between grains in an icy regolith. Estimates of the characteristic sintering timescale, i.e. the time necessary for the thermal inertia to increase from that measured outside the anomalous regions to that within, are given for each of the moons. Since interplanetary dust particle (IDP) impact gardening and E-ring grain infall would be expected to mix the regolith and obscure the effects of high energy electrons, sintering rates are compared to rough estimates of the impact-induced resurfacing rates. Estimates of the sintering timescale determined by extrapolating laboratory measurements are below ∼0.03 Myr, while the regolith renewal timescales are larger than ∼0.1 Myr, thus indicating that irradiation by the high energy electrons should be sufficient to form stable thermal anomalies. More detailed models developed for sintering of spherical grains are able to account for the radiation-induced anomalies on Mimas and Tethys only if the regoliths on those bodies are relatively compact and composed of small (≲ 5 µm) grains or grain aggregates, and/or the grains are highly non-spherical with surface defect densities in the inter-grain contact regions that are much higher than expected for crystalline water ice grains at thermal equilibrium. These results are consistent with regolith thermal conductivity models which can only be reconciled with spacecraft observations if the contacts between grains are assumed to have much lower thermal conductance than predicted for idealized grains. The strength of the anomalies on Tethys and Dione appear to be limited by E-ring grain infall, while on Mimas IDP gardening limits the strength of the anomaly. The smaller flux of more deeply penetrating high energy (>1 MeV) electrons on Dione can account for the small thermal inertia differences measured there. Determining regolith sintering rates and the corresponding effect on thermal conductivity can, in principle, provide an independent constraint on the regolith grain geometries and exposure timescales for icy bodies.

Observations by the MESSENGER spacecraft during its flyby and orbital observations of Mercury in 2008–2015 indicated the presence of cold icy materials hiding in permanently-shadowed craters in Mercury's north polar region. These icy condensed volatiles are thought to be composed of water ice and frozen organics that can persist over long geologic timescales and evolve under the influence of the Mercury space environment. Polar ices never see solar photons because at such high latitudes, sunlight cannot reach over the crater rims. The craters maintain a permanently cold environment for the ices to persist. However, the magnetosphere will supply a beam of ions and electrons that can reach the frozen volatiles and induce ice chemistry. Mercury's magnetic field contains magnetic cusps , areas of focused field lines containing trapped magnetospheric charged particles that will be funneled onto the Mercury surface at very high latitudes. This magnetic highway will act to direct energetic protons, ions and electrons directly onto the polar ices. The radiation processing of the ices could convert them into higher-order organics and dark refractory materials whose spectral characteristics are consistent with low-albedo materials observed by MESSENGER Laser Altimeter (MLA) and RADAR instruments. Galactic cosmic rays (GCR), scattered UV light and solar energetic particles (SEP) also supply energy for ice processing. Cometary impacts will deposit H 2 O , CH 4 , CO 2 and NH 3 raw materials onto Mercury's surface which will migrate to the poles and be converted to more complex C H N O S-containing molecules such as aldehydes, amines, alcohols, cyanates, ketones, hydroxides, carbon oxides and suboxides, organic acids and others. Based on lab experiments in the literature, possible specific compounds produced may be: H 2 CO, HCOOH, CH 3 OH, HCO, H 2 CO 3 , CH 3 C(O)CH 3 , C 2 O, C x O, C 3 O 2 , C x O y , CH 3 CHO, CH 3 OCH 2 CH 2 OCH 3 , C 2 H 6 , C x H y, NO 2, HNO 2 , HNO 3 , NH 2 OH, HNO, N 2 H 2 , N 3 , HCN, Na 2 O, NaOH, CH 3 NH 2, SO, SO 2 , SO 3 , OCS, H 2 S, CH 3 SH, even B x H y . Three types of radiation processing mechanisms may be at work in the ices: (1) Impact/dissociation, (2) Ion implantation and (3) Nuclear recoil (hot atom chemistry). Magnetospheric energy sources dominate the radiation effects. Total energy fluxes of photons, SEPs and GCRs are all around two or more orders of magnitude less than the fluxes from magnetospheric energy sources (in the focused cusp particles). However, SEPs and GCRs cause chemical processing at greater depths than other particles leading to thicker organic layers. Processing of polar volatiles on Mercury would be somewhat different from that on the Moon because Mercury has a magnetic field while the Moon does not. The channeled flux of charged particles through these magnetospheric cusps is a chemical processing mechanism unique to Mercury as compared to other airless bodies.

Purpose The purpose of this study was to determine if American Association of Oral and Maxillofacial Surgeons members have integrated the current American Society of Anesthesiologists (ASA) nil per os (NPO) guidelines into their preoperative instructions. Materials and Methods We designed and implemented a cross-sectional study and enrolled a random sample of private-practice American Association of Oral and Maxillofacial Surgeons members who practice in the United States. The predictor variables were year of graduation from residency, dual degree (MD and DDS or DMD) or single degree, and region. The primary outcome variable was adoption of the ASA NPO guidelines, defined as recommending fasting times of 2 hours for clear liquids and 6 hours for solid foods. To collect data, a systematic online search was implemented. Appropriate univariate and bivariate statistics were computed, and the level of significance was set at .05; in addition, 95% confidence intervals were calculated. Results The study sample was composed of 431 oral and maxillofacial surgeons (OMSs). Almost all of the study sample (99.1%) did not adopt the ASA guidelines. The fasting recommendations were different from 2 hours for clear liquids and 6 hours for solid foods. However, recommendations of 2 hours or greater for clear liquids were made by 99.8% of OMSs, and recommendations of 6 hours or greater for solid foods were made by 99.3%. Only 4.4% of OMSs made different recommendations for clear liquids and solid foods. No substantial association was found between whether OMSs adopted the most current ASA guidelines and the year they graduated from residency or the obtainment of dual degrees. Conclusions OMSs in private practice are overwhelmingly recommending longer fasting times for clear liquids and solid foods on their Web sites when compared with the current ASA guidelines before ambulatory anesthesia. The ASA guidelines are based on meta-analysis; therefore, deviations in practice, although not incorrect, may call for discussion.

DNA polymerase δ (Polδ) plays pivotal roles in eukaryotic DNA replication and repair. Polδ is conserved from yeast to humans, and mutations in human Polδ have been implicated in various cancers. Saccharomyces cerevisiae Polδ consists of catalytic Pol3 and the regulatory Pol31 and Pol32 subunits. Here, we present the near atomic resolution (3.2 A) cryo-EM structure of yeast Polδ holoenzyme in the act of DNA synthesis. The structure reveals an unexpected arrangement in which the regulatory subunits (Pol31 and Pol32) lie next to the exonuclease domain of Pol3 but do not engage the DNA. The Pol3 C-terminal domain contains a 4Fe−4S cluster and emerges as the keystone of Polδ assembly. We also show that the catalytic and regulatory subunits rotate relative to each other and that this is an intrinsic feature of the Polδ architecture. Collectively, the structure provides a framework for understanding DNA transactions at the replication fork. A unique arrangement of catalytic and regulatory subunits revealed by cryo-EM analysis of DNA polymerase δ holoenzyme in a template–primer complex suggests how interactions between the functional modules promote DNA synthesis and proofreading activities.