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Professor John Edwin Field passed away on October 21st, 2020 at the age of 84. Professor Field was widely regarded as a leader in high-strain rate physics and explosives. During his career in the Physics and Chemistry of Solids (PCS) Group of the Cavendish Laboratory at Cambridge University, John made major contributions into our understanding of friction and erosion, brittle fracture, explosives, impact and high strain-rate effects in solids, impact in liquids, and shock physics. The contributions made by the PCS group are recognized globally and the impact of John’s work is a lasting addition to our knowledge of the dynamic effects in materials. John graduated 84 Ph.D. students and collaborated broadly in the field. Many who knew him attribute their success to the excellent grounding in research and teaching they received from John Field.

Saturn's magnetospheric magnetic field, planetary radio emissions, plasma populations, and magnetospheric structure are all known to be modulated at periods close to the assumed rotation period of the planetary interior. These oscillations are readily apparent despite the high degree of axisymmetry in the internally produced magnetic field of the planet and have different rotation periods in the northern and southern hemispheres. In this paper we study the spatial structure of (near‐)planetary period magnetic field oscillations in Saturn's equatorial magnetosphere. Extending previous analyses of these phenomena, we include all suitable data from the entire Cassini mission during its orbital tour of the planet so as to be able to quantify both the amplitude and phase of these field oscillations throughout Saturn's equatorial plane, to distances of 30 planetary radii. We study the structure of these field oscillations in view of both independently rotating northern and southern systems, finding spatial variations in both magnetic fields and inferred currents flowing north‐south that are common to both systems. With the greatly expanded coverage of the equatorial plane achieved during the latter years of the mission, we are able to present a complete survey of dawn‐dusk and day‐night asymmetries in the structure of the oscillating fields and currents. We show that the general structure of the rotating currents is simpler than previously reported and that the relatively enhanced nightside equatorial fields and currents are due in part to related periodic vertical motion of Saturn's magnetotail current sheet. Saturn's magnetic field, produced in its interior by dynamo processes, is apparently perfectly symmetric with respect to the spin axis of the planet. Despite this, measurements of magnetic fields in Saturn's magnetosphere, radio emissions, and plasma populations all show oscillations with periods close to the (inferred) rotation rate of the interior of the planet. The origin of these oscillations is yet to be fully explained, but electrodynamic coupling between the upper atmosphere/ionosphere and magnetosphere plays a central role. In this study, we use magnetic field measurements from NASA's Cassini spacecraft to statistically study the spatial structure of the magnetic field oscillations and the electrical currents producing them. Expanding on previous studies, we find good overall agreement with existing theoretical models but with discrepancies suggestive of the influence of solar wind magnetosphere coupling on the system. We conduct a complete analysis of the structure of Saturn's equatorial magnetic field oscillationsSeasonal and beat‐phase variations are accounted for in an analysis of dual period oscillationsElectrical currents flow vertically through the equatorial plane in two linked spirals

Results obtained in the Martian ionosphere by the Langmuir Probe and Waves instrument aboard the Mars Atmosphere and Volatile EvolutioN Mission spacecraft are presented. The results include ionospheric electron densities determined from the frequency of Langmuir waves. Since the amplitude of thermal Langmuir waves is often below the instrument's detection level, Langmuir Probe and Waves excites these waves by injecting into the plasma a 3.3‐V white noise signal. Electric field spectral measurements obtained shortly after the excitation show a resonance line at frequencies slightly below the local plasma frequency. The observed resonance line is interpreted to originate from plasma waves excited in the wake behind the spacecraft. These results reveal an important phenomenon in electron density estimation from stimulated Langmuir waves. The observed phenomenon, not previously reported by earlier missions, may be a common process in active sounding that can affect in situ electron density measurements. Electric field spectra in active sounding show an anomalous resonance line at frequencies below the local electron plasma frequencyThe observed resonance line is interpreted as the signature of the plasma waves excited within the spacecraft wakeThe observed phenomenon may have affected results in similar active missions that were incapable of identifying this process

We present the electron density (ne) altitude profiles of Saturn's ionosphere at near‐equatorial latitudes from all 23 orbits of Cassini's Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The neprofiles are shown to be more variable and connected to the D‐ring below 5,000 km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the D‐ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini's final plunge, where the main ionospheric peak is crossed at ∼1,550‐km altitude. The Cassini Langmuir probe measured directly the uppermost layer of Saturn's atmosphere, the ionosphere, during its Grand Finale. The observations revealed a layered electron density altitude profile with evidence in the southern hemisphere of an electrodynamic type of interaction with the planet innermost D‐ring. Moreover, the main peak of the ionosphere is observed for the first time in the final plungearound 1,550 km. Cassini RPWS observations during the Grand Finale show an electrodynamic type of interaction between the topside ionosphere and the D‐ring in the southern hemisphereA layered electron density profile is observed, characterized by at least a diffusive and a chemical equilibrium regionThe main ionospheric peak is observed around 1,550 km in the final plunge

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar sounder on board the Mars Express spacecraft revealed oblique reflections coming systematically from apparently stable density structures in the Martian ionosphere. Although these were typically interpreted by assuming a straight line propagation of the sounding signal at the speed of light, the ionospheric plasma is clearly a dispersive medium. Consequently, the ray propagation paths may be significantly bent, and, moreover, the observed time delays need to be interpreted in terms of realistic group velocities of the signal propagation. We select a single particularly well‐pronounced event with oblique reflections observable over a large range of signal frequencies, and we employ raytracing calculations to perform its detailed analysis. An isolated density structure responsible for the reflection of the sounding signal back to the spacecraft is assumed, and the relevant ionospheric signal propagation is properly evaluated. We show that initially oblique sounding signals get progressively more oblique during their propagation, imposing an upper threshold on the angular propagation distance between the spacecraft and the reflecting density structure, in line with the observations. Considering realistic propagation paths further allows us to explain the frequency dependence of the observed time delays and to accurately model the entire event. The obtained results are consistent with the spacecraft passing very close to a spatially limited density structure. We also show that the results obtained using realistic raytracing calculations are significantly different from the results obtained using additional simplifying assumptions. Raytracing analysis is carried out to obtain realistic trajectories of oblique echoes through the ionosphere and appropriate time delaysInitially oblique sounding signals are significantly bent, resulting in an upper limit on the propagation distance and related time delaysThe results are used to perform a detailed case study of oblique reflections observed in the Mars Express MARSIS data

Measurements of electrons and ions in Saturn's ionosphere down to 1,500‐km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spacecraft are presented. Five nearly identical deep ionosphere flybys during the Grand Finale orbits and the Final plunge orbit revealed a rapid increase in the plasma densities and discrepancies between the electrons and ions densities (Neand Ni) near the closest approach. The small Ne/Niratio indicates the presence of a dusty plasma, a plasma which charge carrier is dominated by negatively charged heavy particles. Comparison of the Langmuir probe obtained density with the light ion density obtained by the Ion and Neutral Mass Spectrometer confirmed the presence of heavy ions. An unexpected positive floating potential of the probe was also observed when Ne/Ni≪ 1. This suggests that Saturn's ionosphere near the density peak is in a dusty plasma state consisting of negatively and positively charged heavy cluster ions. The electron temperature (Te) characteristics in the ionosphere are also investigated and unexpectedly high electron temperature value, up to 5000 K, has been observed below 2,500‐km altitude in a region where electron‐neutral collisions should be prominent. A well‐defined relationship between Teand Ne/Niratio was found, implying that the electron heating at low altitudes is related to the dusty plasma state of the ionosphere. Cassini Langmuir probe measurements revealed ion densities in excess of the electron densities, indicative of a dusty plasma, in Saturn's ionosphere below 2,500‐km altitude. Comparison of the Langmuir probe measurements with those of the Ion and Neutral Mass Spectrometer, sensitive to only lighter ions during this period, showed that heavy ions dominate in this region. Positive spacecraft potentials were also found, suggesting that Saturn's ionosphere contains dusty plasma of negatively and positively charged heavy ions. In situ measurements of Saturn's ionospheric plasma densities down to 1,500 km and the ring above the ionosphere is presentedCharge imbalance in the ions and electrons, evidence of the negatively charged heavy particles, has been observed below 2,500 kmObservations suggest that Saturn's ionosphere consists of a significant amount of negatively and positively charged heavy ions

Third-harmonic scattering is a nonlinear optical process that involves the molecular second-hyperpolarizability, γ. This work presents a rigorous quantum electrodynamical analysis of the scattering process, involving a partially index-symmetric construction of the fourth-rank γ tensordispensing with the Kleinman symmetry condition. To account for stochastic molecular rotation in fluids, methods of isotropic averaging must be employed to relate the molecular properties to accessible experimental quantities such as depolarization ratio. A complete eighth-rank tensor rotational average yields results for observable third-harmonic scattering rates, cast as a function of the natural-invariant γ components, and the polarization geometry of the experiment. Decomposing the tensor γ into irreducible weights allows specific predictions to be made for each molecular point group, allowing greater discrimination between the results for different molecular symmetries.

We use more than 10 years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to derive an empirical model of electron densities from the peak altitude up to 325 km. Altogether, 16,044 electron density profiles obtained at spacecraft altitudes lower than 425 km and at solar zenith angles lower than 80° are included in the analysis. Each of the measured electron density profiles is accurately characterized by the peak electron density, peak altitude, and three additional parameters describing the profile shape above the peak: (i) steepness at high altitudes, (ii) main layer thickness, and (iii) transition altitude. The dependence of these parameters on relevant controlling factors (solar zenith angle, solar irradiance, crustal magnetic field magnitude, and Sun‐Mars distance) is evaluated, allowing for a formulation of a simple empirical model. Mars Atmosphere and Volatile EvolutioN Extreme Ultraviolet monitor data are used to show that the solar ionizing flux can be accurately approximated by the F10.7 index when taking into account the solar rotation. Electron densities predicted by the resulting empirical model are compared with electron densities locally evaluated based on the Mars Advanced Radar for Subsurface and Ionosphere Sounding measurements, with the Langmuir Probe and Waves electron density measurements on board the Mars Atmosphere and Volatile EvolutioN spacecraft, and with electron densities obtained by radio occultation measurements. Although the electron densities measured by the Langmuir Probe and Waves instrument are systematically somewhat lower than the model electron densities, consistent with former findings, the model performs reasonably well. The ionosphere of Mars is the ionized part of its atmosphere, on the dayside ultimately controlled by the solar irradiation. Information about the electron density in there can be, among others, obtained by the radar sounding from a spacecraft orbiting the planet. Such measurements have been performed since 2005 by the Mars Advanced Radar for Subsurface and Ionosphere Sounding on board the Mars Express spacecraft, and they provide us with electron density profiles from the spacecraft altitude down to the altitude of the peak electron density. We use more than 10 years of such measurements to develop an empirical model of typical ionospheric electron densities. The obtained results are compared with electron densities measured in situ by the Langmuir Probe and Waves instrument on board the MAVEN spacecraft available since 2014. A reasonable agreement between the model predictions and these independent observations is found. Finally, the analysis of solar radiation measured by Extreme Ultraviolet monitor on board the MAVEN spacecraft is used to show that, when the solar rotation is properly accounted for, the solar ionizing flux at Mars can be surprisingly well approximated by the solar radio flux measured at Earth. Each electron density profile is described by five parameters, allowing for a simple empirical modelSolar ionizing flux is well expressed by F10.7 index when taking into account the solar rotationModel densities agree with radio occultation and Mars Express MARSIS and MAVEN LPW local electron density measurements

The ion sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA‐3) experiment detects accelerated ions during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express. Accelerated ions (O 2+, O+, and lighter ions) are observed in an energy range up to 800 eV when MARSIS transmits at a frequency close to the plasma frequency. Individual observations consist of almost monoenergetic ion beams aligned with the MARSIS antenna or lying in the plane perpendicular to the antenna. The observed ion beams are often accompanied by a small decrease in the electron flux observed by the electron sensor of Analyzer of Space Plasmas and Energetic Atoms 3. Observations indicate that the voltage applied to the antenna causes charging of the spacecraft to several hundreds of volts by the electrons of the ambient plasma. Positively charged ions are accelerated when the spacecraft discharges. Accelerated ions are detected by IMA of ASPERA‐3 during sounding phase of MARSIS radarThe energy of accelerated ions is found to be in a range of 20 to 800 eVObservations coincide in time with periods when MARSIS transmits close to the plasma frequency

We report on unusual dynamics in Titan's ionosphere as a significant difference in ionospheric electron density is observed between the T118 and T119 Cassini nightside flybys. Two distinct nightside electron density peaks were present during T118, at 1,150 and 1,200 km, and the lowest density ever observed in Titan's ionosphere at altitudes 1,000–1,350 km was during T118. These flybys were quite similar in geometry, Saturn local time, neutral density, extreme ultraviolet flux, and ambient magnetic field conditions. Despite this, the Radio and Plasma Waves/Langmuir Probe measured a density difference up to a factor of 6 between the passes. The overall difference was present and similar during both inbound and outbound legs. By ruling out other factors, we suggest that an exceptionally low rate of particle impact ionization in combination with dynamics in the ionosphere is the explanation for the observations. Using the Cassini satellite in orbit around Saturn, we make measurements during two close passes of the moon Titan. We observe how the electron density in the uppermost part of the moon's atmosphere—the ionosphere—changes drastically from one pass to the next. We also observe unexpectedly high peaks of electron density in a specific altitude range during the first pass. The findings are attributed to low influx of charged particles from Saturn's magnetosphere as well as to increased dynamics of the plasma in the ionosphere. The study emphasizes the complexity of the physical process at play at the moon and aims at gaining further understanding of this environment. Large difference in ionospheric electron density is seen between T118 and T119 despite similar geometryThe lowest density ever observed in the altitude range 1,000‐1,350 km in Titan's nightside ionosphere was during T118Low fluxes of impact ionizing particles and ionospheric dynamics is suggested as the most probable explanation

Knowledge of Mars's ionosphere has been significantly advanced in recent years by observations from Mars Express and lately Mars Atmosphere and Volatile EvolutioN. A topic of particular interest are the interactions between the planet's ionospheric plasma and its highly structured crustal magnetic fields and how these lead to the redistribution of plasma and affect the propagation of radio waves in the system. In this paper, we elucidate a possible relationship between two anomalous radar signatures previously reported in observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on Mars Express. Relatively uncommon observations of localized, extreme increases in the ionospheric peak density in regions of radial (cusp‐like) magnetic fields and spread echo radar signatures are shown to be coincident with ducting of the same radar pulses at higher altitudes on the same field lines. We suggest that these two observations are both caused by a high electric field (perpendicular to B) having distinctly different effects in two altitude regimes. At lower altitudes, where ions are demagnetized and electrons magnetized, and recombination dominantes, a high electric field causes irregularities, plasma turbulence, electron heating, slower recombination, and ultimately enhanced plasma densities. However, at higher altitudes, where both ions and electrons are magnetized and atomic oxygen ions cannot recombine directly, the high electric field instead causes frictional heating, a faster production of molecular ions by charge exchange, and so a density decrease. The latter enables ducting of radar pulses on closed field lines, in an analogous fashion to interhemispheric ducting in the Earth's ionosphere. MARSIS on MEX observed both echoes from distant ionospheric irregularities as well as locally ducted echoes in close successionBoth effects are consistent with the presence of extended, small‐scale field‐aligned density irregularitiesWe suggest that these may be the direct result of strong electric fields present at ionospheric altitudes

We report on the electron, ion, and dust number densities and the electron temperatures obtained by the Radio and Plasma Wave Science instruments onboard Cassini during the Ring‐Grazing orbits. The numerous ring passage observations show a consistent picture as follows: (1) Beyond 0.1 RSabove and below the equator the electron and ion densities are quasi‐neutral with a distribution similar to the one obtained in the plasma disk. (2) A sharp ion density enhancement occurs at |Z| < 0.1 RS, to more than 200 cm−3at the equator, while the electron density remains low only to values of 50 cm−3. The electron/ion density ratio is ≦0.1 at the equator. (3) Micrometer‐sized dust has also been observed at the equator. However, the region of intense dust signals is significantly narrower (|Z| < 0.02 RS) than the enhanced ion density regions. (4) The electron temperature (Te) generally decreases with decreasing Zwith small Teenhancements near the equator. We show that the dust size characteristics are different depending on the distance from the equator, and the large micrometer‐sized grains are more perceptible in a narrow region near the equator where the power law slope of the dust size distribution becomes less steep. As a result, different scale heights are obtained for nanometer and micrometer grains. Throughout the ring, the dominant part of the negative charges is carried by the small nanometer‐sized grains. The electron/ion density ratio is variable from orbit to orbit, suggesting changes in the dust charging over time scales of weeks. The Radio and Plasma Wave Science instrument onboard Cassini observed a dusty plasma during the Ring‐Grazing orbits. Dusty plasma is composed of, in addition to the electrons and ions, charged dust grains, and those grains play an important role in the plasma dynamics. The observed electron, ion, and dust number densities and the electron temperatures showed the layered structure of the faint Janus/Epimetheus rings. The core of the dusty ring composed of micron‐sized dust is surrounded by a dusty plasma consisting of the ions and the negatively charged nanometer grains and further surrounded by the pristine plasma. The electron/ion density ratio of the dusty plasma varies from orbit to orbit, implying that the dust charging characteristics of the dusty ring change over time scales of weeks. Cassini RPWS observations during dust‐grazing orbits show a consistent picture of the dusty plasma composed of nanometer grains near the Janus/Epimetheus ringThree different height scales were found for the plasma disk plasma, nanometer‐sized dust, and the micron‐sized dustThe electron‐to‐ion density ratio varies from orbit to orbit, suggesting the dust charging variation

For the first time at Mars the statistical distribution of (1‐D) electric field wave power in the magnetosphere is presented, along with the distribution of magnetic field wave power, as observed by the Mars Atmosphere and Volatile EvolutioN spacecraft from the first 14.5 months of the mission. Wave power in several different frequency bands was investigated, and the strongest wave powers were observed at the lowest frequencies. The presented statistical studies suggest that the full thermalization of ions within the magnetosheath does not appear to occur, as has been predicted by previous studies. Manual inspection of 140 periapsis passes on the dayside shows that Poynting fluxes (at 2–16 Hz) between ∼10−11and 10−8Wm−2reach the upper ionosphere for all 140 cases. Wave power is not observed in the ionosphere for integrated electron densities greater than 1010.8cm−2, corresponding to typical depths of 100–200 km. The observations presented support previous suggestions that energy from the Mars‐solar wind interaction can propagate into the upper ionosphere and may provide an ionospheric heating source. Upstream of the shock, the orientation of the solar wind interplanetary magnetic field was shown to significantly affect the statistical distribution of wave power, based on whether the spacecraft was likely magnetically connected to the shock or not—something that is predicted but has not been quantitatively shown at Mars before. In flight performance and caveats of the Langmuir Probe and Waves electric field power spectra are also discussed. First statistical study of the distribution of electric field wave power in the Martian magnetosphereWave power from magnetosheath is observed to reach the upper ionosphere in all of 140 cases in a smaller statistical studySolar wind IMF orientation shown to significantly affect the statistical distribution of wave power in the Martian magnetosphere

We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding‐Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov‐Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO‐A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110–111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn. Study of the propagation of an ICME up to 111 AU; comparison of Forbush decreases triggered by the same ICME at 1.4, 3.1, and 9.9 AUModel‐predicted ICME arrival times are in agreement with the observationsAn ICME disturbed the Solar wind during the Siding Spring comet flyby at Mars on 19 October 2014

This paper is a phenomenological description of the ionospheric plasma and induced magnetospheric boundary (IMB) response to two different types of upstream solar wind events impacting Mars in March 2008, at the solar minimum. A total of 16 Mars Express orbits corresponding to five consecutive days is evaluated. Solar TErrestrial RElations Observatory‐B (STEREO‐B) at 1 AU and Mars Express and Mars Odyssey at 1.644 AU detected the arrival of a small transient interplanetary coronal mass ejection (ICME‐like) on the 6 and 7 of March, respectively. This is the first time that this kind of small solar structure is reported at Mars's distance. In both cases, it was followed by a large increase in solar wind velocity that lasted for ~10 days. This scenario is simulated with the Wang‐Sheeley‐Arge (WSA) ‐ ENLIL + Cone solar solar wind model. At Mars, the ICME‐like event caused a strong compression of the magnetosheath and ionosphere, and the recovery lasted for ~3 orbits (~20 h). After that, the fast stream affected the upper ionosphere and the IMB, which radial and tangential motions in regions close to the subsolar point are analyzed. Moreover, a compression in the Martian plasma system is also observed, although weaker than after the ICME‐like impact, and several magnetosheath plasma blobs in the upper ionosphere are detected by Mars Express. We conclude that, during solar minimum and at aphelion, small solar wind structures can create larger perturbations than previously expected in the Martian system. Martian plasma system response to space weather disturbances during low solar activityPropagation of an ICME‐like transient and a fast solar wind stream from STEREO‐B to MarsLongitudinal and radial inner boundary movements at Mars

Since Mars lacks a global intrinsic magnetic field, the solar wind interacts directly with the Martian upper atmosphere and ionosphere. The presence of localized intense remnant crustal magnetic fields adds to this interaction, making the Martian plasma system a unique environment within the solar system. Rapid reductions in the electron flux, referred to as “electron holes,” occur within the Martian induced magnetosphere (IM). We present a statistical analysis of this phenomenon identified from proxy measurements of the electron flux derived from measurements by the Analyser of Space Plasmas and Energetic Neutral Atoms Electron Spectrometer experiment on board the Mars Express (MEX) spacecraft. The study is completed for the period of 9 February 2004 to 9 May 2014. Electron holes are observed within the IM in more than 56% of MEX orbits during this study period, occurring predominantly at altitudes less than 1300 km, with the majority in the negative X Mars‐Centric Solar Orbital direction. The spatial distribution above the surface of Mars is observed to bear close resemblance to that of the crustal magnetic fields as predicted by the Cain et al. [[Cain, J. C., 2003]] magnetic field model, suggesting that they play an important role in the formation of these phenomena. Extreme reductions in proxy measurements of electron flux observed by MEX within illuminated induced magnetosphereElectron holes distributed near or over regions of significant crustal magnetic field magnitudeAt higher altitudes more events occur over regions of larger model crustal magnetic field magnitude

Recent results from the MAVEN Langmuir Probe and Waves instrument suggest higher than predicted electron temperatures (Te) in Mars' dayside ionosphere above ~180 km in altitude. Correspondingly, measurements from Neutral Gas and Ion Mass Spectrometer indicate significant abundances of O2+up to ~500 km in altitude, suggesting that O2+may be a principal ion loss mechanism of oxygen. In this article, we investigate the effects of the higher Te(which results from electron heating) and ion heating on ion outflow and loss. Numerical solutions show that plasma processes including ion heating and higher Temay greatly increase O2+loss at Mars. In particular, enhanced Tein Mars' ionosphere just above the exobase creates a substantial ambipolar electric field with a potential (eΦ) of several kBTe, which draws ions out of the region allowing for enhanced escape. With active solar wind, electron, and ion heating, direct O2+loss could match or exceed loss via dissociative recombination of O2+. These results suggest that direct loss of O2+may have played a significant role in the loss of oxygen at Mars over time. O2+outflow at Mars is greatly enhanced by ambipolar electric fieldEnhanced electron temperatures result in a strong ambipolar electric fieldIn the past, direct loss of O2+could have exceeded that of associative recombination

We present initial analyses and conclusions from plasma observations made during the reported “Mars plume event” of March–April 2012. During this period, multiple independent amateur observers detected a localized, high‐altitude “plume” over the Martian dawn terminator, the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that the only similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars. Data from ASPERA‐3 and MARSIS were obtained during the unusual atmospheric plume eventPlume observations likely follow the impact of large interplanetary coronal mass ejectionsIonospheric plasma structures associated with the plume are not conclusively observed

The first in situ nightside electron density and temperature profiles at Mars are presented as functions of altitude and local time (LT) from the Langmuir Probe and Waves (LPW) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft. LPW is able to measure densities as low as ∼100  cm−3, a factor of up to 10 or greater improvement over previous measurements. Above 200 km, near‐vertical density profiles of a few hundred cubic centimeters were observed for almost all nightside LT, with the lowest densities and highest temperatures observed postmidnight. Density peaks of a few thousand cubic centimeters were observed below 200 km at all nightside LT. The lowest temperatures were observed below 180 km and approach the neutral atmospheric temperature. One‐dimensional modeling demonstrates that precipitating electrons were able to sustain the observed nightside ionospheric densities below 200 km. First in situ nightside electron density and temperature profiles on the nightside of MarsElectron temperatures approach neutral atmospheric temperatures below  200 kmElectron densities below 200 km require additional ionization source

We present Mars' electron temperature (Te) and density (ne) altitude profiles derived from the MAVEN (Mars Atmosphere and Volatile EvolutioN) mission deep dip orbits in April 2015, as measured by the Langmuir probe instrument. These orbits had periapsides below 130 km in altitude at low solar zenith angles. The periapsides were above the peak in neduring this period. Using a Chapman function fit, we find that scale height and projected altitude of the nepeak are consistent with models and previous measurements. The peak electron density is slightly higher than earlier works. For the first time, we present in situ measurements of Tealtitude profiles in Mars' dayside in the altitude range from ~130 km to 500 km and provide a functional fit. Importantly, Terises rapidly with altitude from ~180 km to ~300 km. These results and functional fit are important for modeling Mars' ionosphere and understanding atmospheric escape. First in situ measurements of the electron temperature at MarsElectron density and temperature profiles at Mars

We report on initial observations made by the Langmuir Probe and Waves relaxation soundingexperiment on board the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. These measurements yield the ionospheric thermal plasma density, and we use these data here for an initial survey of its variability. Studying orbit‐to‐orbit variations, we show that the relative variability of the ionospheric plasma density is lowest at low altitudes near the photochemical peak, steadily increases toward higher altitudes and sharply increases as the spacecraft crosses the terminator and moves into the nightside. Finally, despite the small volume of data currently available, we show that a clear signature of the influence of crustal magnetic fields on the thermal plasma density fluctuations is visible. Such results are consistent with previously reported remote measurements made at higher altitudes, but crucially, here we sample a new span of altitudes between ∼130 and ∼300 km using in situ techniques. Data from the Langmuir Probe and Waves instrument reveal density structures in the Mars ionosphereMAVEN samples an altitude range which previously has only been sparsely explored in situMAVEN/LPW data also reveal the stabilizing influence of intense crustal fields

We present observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument onboard Mars Express of the thermal electron plasma density of the Martian ionosphere and investigate the extent to which it is influenced by the presence of Mars's remnant crustal magnetic fields. We use locally measured electron densities, derived when MARSIS is operating in active ionospheric sounding (AIS) mode, covering an altitude range from ∼300 km to ∼1200 km. We compare these measured densities to an empirical model of the dayside ionospheric plasma density in this diffusive transport‐dominated regime. We show that small spatial‐scale departures from the averaged values are strongly correlated with the pattern of the crustal fields. Persistently elevated densities are seen in regions of relatively stronger crustal fields across the whole altitude range. Comparing these results with measurements of the (scalar) magnetic field also obtained by MARSIS/AIS, we characterize the dayside strength of the draped magnetic fields in the same regions. Finally, we provide a revised empirical model of the plasma density in the Martian ionosphere, including parameterizations for both the crustal field‐dominated and draping‐dominated regimes. Local plasma densities and magnetic fields are measured by MARSIS onboard MEXCrustal magnetic fields influence the configuration of the ionosphereDensities are elevated over regions where the crustal field dominates

The Martian ionosphere directly interacts with the solar wind due to lack of a significant intrinsic magnetic field, and an interface is formed in between. The interface is usually recognized by two kinds of indicators: the ionopause identified from ionospheric density profiles and the photoelectron boundary (PEB) determined from the electron energy spectrum at higher energies. However, the difference between them remains unclear. We have determined the locations of crossings of the ionopause and PEB from Mars Express observations during 2005–2013 and found that the average position of the PEB appears to be ~200 km higher than that of the ionopause, which corresponds to 103cm–3in the electron density profile. The discrepancy can be explained by cross‐field transport of photoelectrons. The average altitude of the PEB is ~200 km higher than that of the ionopauseThe discrepancy can be explained by cross-field transport of photoelectronsBoth the Martian ionopause and PEB heights depend slightly on the SZA

AN AMERICAN PILGRIM T he autumn magazine was meaningful to me because I visited Plymouth Rock this summer. WRITE-OF-WAY WRITE-OF-WAY WRITE-OF-WAY Letters from Our Readers SPRING 2021 10 Post correspondence to AMERICAN ROAD • PO Box 46519 • Mt. Clemens, Michigan 48046 • letters@americanroadmagazine.com • Letters may be edited for clarity and space. Robert Robert Robert Robert Robert Robert Robert Robert Hegyes Hegyes Hegyes Hegyes Hegyes Hegyes Hegyes (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) (1951-2012) was was was was an an an American American American American American American American American American American American actor actor actor actor actor actor actor best best best best best known known known known known known known for for for for for his his his his his portrayal portrayal portrayal portrayal portrayal portrayal portrayal portrayal portrayal portrayal portrayal of of of of of high high high high high high school school school school school school school school school student student student student student student student student and and and and "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" "Sweathog" Juan Juan Juan Juan Juan Epstein Epstein Epstein Epstein Epstein Epstein Epstein Epstein Epstein on on on on the the the the 1970s 1970s 1970s 1970s 1970s 1970s 1970s TV TV TV TV comedy comedy comedy comedy comedy comedy comedy comedy comedy series series series series series series series series Welcome Welcome Welcome Welcome Welcome Welcome Welcome Welcome Welcome Back, Back, Back, Back, Back, Back, Kotter Kotter Kotter Kotter Kotter Kotter Kotter Kotter.. CONGRATULATIONS TO JOHN GRABAK OF BELLEVILLE, ILLINOIS!. [Extracted from the article]

We examine the “planetary period” magnetic field oscillations observed in the “core” region of Saturn's magnetosphere (dipole L≤ 12), on 56 near‐equatorial Cassini periapsis passes that took place between vernal equinox in August 2009 and November 2012. Previous studies have shown that these consist of the sum of two oscillations related to the northern and southern polar regions having differing amplitudes and periods that had reached near‐equal amplitudes and near‐converged periods ~10.68 h in the interval to ~1 year after equinox. The present analysis shows that an interval of strongly differing behavior then began ~1.5 years after equinox, in which abrupt changes in properties took place at ~6‐ to 8‐month intervals, with three clear transitions occurring in February 2011, August 2011, and April 2012, respectively. These are characterized by large simultaneous changes in the amplitudes of the two systems, together with small changes in period about otherwise near‐constant values of ~10.63 h for the northern system and ~10.69 h for the southern (thus, not reversed postequinox) and on occasion jumps in phase. The first transition produced a resumption of strong southern system dominance unexpected under northern spring conditions, while the second introduced comparably strong northern system dominance for the first time in these data. The third resulted in suppression of all core oscillations followed by re‐emergence of both systems on a time scale of ~85 days, with the northern system remaining dominant but not as strongly as before. This behavior poses interesting questions for presently proposed theoretical scenarios. New rotation period phenomena at Saturn are studied using magnetic field dataSeveral abrupt changes in amplitudes and periods of both N and S oscillationsUnexpected interval of S system dominance, followed by interval of N dominance.

L-arginine cardioplegia decreases biochemical markers of myocardial damage and oxidative stress in patients with normal left ventricular function. We investigated the effects of L-arginine supplemented cardioplegic arrest in patients with reduced ejection fraction. Fifty-three adult patients with left ventricular ejection fraction <35% undergoing elective coronary artery bypass surgery were randomised to receive blood cardioplegia with or without L-arginine. Following cardiopulmonary bypass, measured endpoints were cardiac troponin-I concentration at 12 and 24 hours, coronary sinus concentrations of malondialdehyde and superoxide dismutase activity at five and 15 minutes, lactic acid flux at one, five and 15 minutes and left ventricular systolic and diastolic function after protamine administration. There were no differences in cardiac troponin-I between groups. Malondialdehyde was lower in L-arginine group, 0.28±0.12 vs 0.48±0.32 (5 minutes) and 0.31±0.14 vs 0.38±0.15 nmol.ml−1(15 minutes) (P=0.0004). Superoxide dismutase activity was higher in L-arginine group, 229±87 vs 191.3±68 (5 minutes), 229±54 vs 198±15 nmol.minute−1.ml (15 minutes) (P=0.005). Lactic acid flux was lower in the L-arginine group, 0.15±0.23 vs 0.48±0.32 (1 minute), 0.08±0.19 vs 0.38±0.31 (5 minutes) and −0.15±0.13 vs 0.26±0.30 mmol.l−1(15 minutes), (P=0.0003). There was no difference in left ventricular systolic function. The mitral annular tissue Doppler inflow (eʹ) velocity during early diastole improved in the L-arginine group following cardiopulmonary bypass (control 4.2±1.9 cm.s−1to 3.6±1.2 cm.s−1vs L-arginine 3.8±1.2 cm.s−1to 4.6±1.4 cm.s−1) (P=0.018). In patients with reduced ejection fraction, L-arginine supplemented cardioplegic arrest did not affect postoperative cardiac troponin-I levels, but attenuated cardiac cellular peroxidation and improved early left ventricular diastolic function.

This review summarises the most recent data in support of the role of the mitochondrial permeability transition pore (mPTP) in ischaemia-reperfusion injury, how anaesthetic agents interact with this molecular channel, and the relevance this holds for current anaesthetic practice. Ischaemia results in damage to the electron transport chain of enzymes and sets into play the assembly of a non-specific mega-channel (the mPTP) that transgresses the inner mitochondrial membrane. During reperfusion, uncontrolled opening of the mPTP causes widespread depolarisation of the inner mitochondrial membrane, hydrolysis of ATP, mitochondrial rupture and eventual necrotic cell death. Similarly, transient opening of the mPTP during less substantial ischaemia leads to differential swelling of the intermembrane space compared to the mitochondrial matrix, rupture of the outer mitochondrial membrane and release of pro-apoptotic factors into the cytosol. Recent data suggests that cellular protection from volatile anaesthetic agents follows specific downstream interactions with this molecular channel that are initiated early during anaesthesia. Intravenous anaesthetic agents also prevent the opening of the mPTP during reperfusion. Although by dissimilar mechanisms, both volatiles and propofol promote cell survival by preventing uncontrolled opening of the mPTP after ischaemia. It is now considered that anaesthetic-induced closure of the mPTP is the underlying effector mechanism that is responsible for the cytoprotection previously demonstrated in clinical studies investigating anaesthetic-mediated cardiac and neuroprotection. Manipulation of mPTP function offers a novel means of preventing ischaemic cell injury. Anaesthetic agents occupy a unique niche in the pharmacological armamentarium available for use in preventing cell death following ischaemia-reperfusion injury.

We tested the hypothesis that the Cobra Perilaryngeal Airway (PLA) with its high volume low-pressure cuff would provide superior airway leakage pressure compared with the Classic Laryngeal Mask Airway (LMA) in spontaneously breathing adult patients. Ninety consecutive adult patients were randomly allocated to receive one of these two supralaryngeal devices. The airway leakage pressure was higher for the PLA compared with the LMA (22±9 cmH2O vs. 18±6 cmH2O; P <0.05). The mean airway device intracuff pressure was lower for the PLA compared to the LMA (36.1±15.2 mmHg vs. 86.3±25.3 mmHg P <0.0001). The time required to achieve successful insertion was greater for the PLA compared with the LMA (39±21 seconds vs. 27±10 seconds; P <0.005). The number of attempts required to achieve successful insertion and the incidence of postoperative complications were similar in both groups. The findings suggest that the PLA provides a superior airway seal at a lower intracuff pressure compared to the LMA. However, the time for successful insertion may be increased.

The interaction of twisted light beams with nematic liquid crystals is described in terms of Landau's free energy formalism and the uniaxial dielectric model for the liquid crystal. This leads us to a partial differential equation, which is characterized by one position-dependent coefficient, governing the changes in the spatial distribution of the director orientation in the liquid crystal. Numerical solutions are determined for a typical arrangement involving a twisted nematic liquid crystal illuminated by a linearly polarized twisted light beam, predicting significant director re-orientations due to the twisted light.

The article clarifies the facts associated with the term joint fires observer (JFO) and the plans of the United States Army and Air Force to train JFO. It explains the JFO based on the Joint Pub 3-0 Doctrine for Joint Operations. It cites the facts associated with providing the close air support portion of joint fire support.

Discusses techniques for deploying the joint close air support (JCAS) of the United States Armed Forces in defending valleys and riverbeds in the Middle East. Details of initial positions; Illustration of hypothetical combat scenarios; Techniques proposed to ensure the maximum defense.

A new and practical method for the synthesis of 1- and 1,3-substituted xanthines is reported. Direct base-promoted condensation of the imidazole precursor 1 with carbamates 2 gives 1-substituted 7-PMB xanthines 7 in good yields. Alkylation of these derivatives or their potassium salts proceeds under mild conditions to give functionalized 1,3-substituted 7-PMB xanthines 9 in good to excellent yields. The obtained 7-PMB-protected derivatives can be readily deprotected to give the parent 1- and 1,3-substituted xanthines.

Lectins have been widely used in glycan structure analysis. The studies described here exploit this fact to select glycopeptides carrying disease-associated modifications in their oligosaccharides. Coupling lectin affinity selection with recent advances in stable isotope coding for quantitative proteomics allowed a comparative proteomics method to be developed for examining aberrant glycosylation in cancer. Control and experimental samples were individually tryptic digested and differentially coded with stable isotope coding agents before they were mixed and affinity selected with a lectin affinity chromatography column. Glycopeptides carrying an α-l-fucose residue were selected with Lotus tetragonolobus agglutinin (LTA) immobilized on a chromatography matrix. Because the oligosaccharides of glycoproteins are generally heterogeneous and often of unknown structure, it was necessary to deglycosylate the selected peptides with PNGase F before they could be compared to sequences in DNA and protein databases. After deglycosylated peptides were transferred to a reversed phase chromatography (RPC) column and fractionated by gradient elution with increasing amounts of acetonitrile. The RPC fractions were then analyzed by both matrix-assisted laser desorption ionization mass spectrometry (MALDI−MS) and electrospray ionization mass spectrometry (ESI−MS). When this method was applied to a study of lymphosarcoma in canines, it was found that during chemotherapy, a series of fucosylated proteins in the blood of patients decreased in concentration more than 2-fold. Two of the proteins identified, CD44 and E-selectin, are known to be involved in cell adhesion and cancer cell migration. The observed aberrant fucosylation of these proteins is consistent with the hypothesis that CD44 and E-selectin play a key role in metastasis and the spread of cancer cells to remote sites. Keywords: proteomics • cancer • glycoproteins • quantification • comparative proteomics • post-translational modification • glycosylation • GIST

In this, the second of two Letters, the optimization of the pyrrolidine-5,5-trans-lactam template (exemplified by 1a) as a mechanism-based inhibitor of hepatitis C NS3/4A protease is described. “Right Box” analysis of cassette dosing screening pharmacokinetic data was used to rapidly categorize the compounds. GW0014 (compound 4d) emerged as the compound displaying an optimal balance of biochemical and replicon potency, along with low i.v. clearance in the dog.