The habitability of the surface of any planet is determined by a complex evolution of its interior, surface, and atmosphere. The electromagnetic and particle radiation of stars drive thermal, ...chemical, and physical alteration of planetary atmospheres, including escape. Many known extrasolar planets experience vastly different stellar environments than those in our solar system: It is crucial to understand the broad range of processes that lead to atmospheric escape and evolution under a wide range of conditions if we are to assess the habitability of worlds around other stars. One problem encountered between the planetary and the astrophysics communities is a lack of common language for describing escape processes. Each community has customary approximations that may be questioned by the other, such as the hypothesis of H‐dominated thermosphere for astrophysicists or the Sun‐like nature of the stars for planetary scientists. Since exoplanets are becoming one of the main targets for the detection of life, a common set of definitions and hypotheses are required. We review the different escape mechanisms proposed for the evolution of planetary and exoplanetary atmospheres. We propose a common definition for the different escape mechanisms, and we show the important parameters to take into account when evaluating the escape at a planet in time. We show that the paradigm of the magnetic field as an atmospheric shield should be changed and that recent work on the history of Xenon in Earth's atmosphere gives an elegant explanation to its enrichment in heavier isotopes: the so‐called Xenon paradox.
Plain Language Summary
In addition to having the right surface temperature, a planet needs an atmosphere to keep surface liquid water stable. Although many planets have been found that may lie in the right temperature range, the existence of an atmosphere is not guaranteed. In particular, for planets that are kept warm by being close to dim stars, there are a number of ways that the star may remove a planetary atmosphere. These atmospheric escape processes depend on the behavior of the star as well as the nature of the planet, including the presence of a planetary magnetic field. Under certain conditions, a magnetic field can protect a planet's atmosphere from the loss due to the direct impact of the stellar wind, but it may actually enhance total atmospheric loss by connecting to the highly variable magnetic field of the stellar wind. These enhancements happen especially for planets close to dim stars. We review the complete range of atmospheric loss processes driven by interaction between a planet and a star to aid in the identification of planets that are both the correct temperature for liquid water and that have a chance of maintaining an atmosphere over long periods of time.
Key Points
The different escape processes at planets and exoplanets are reviewed along with their mathematical formulation
The major parameters for each escape processes are described; some escape processes negligible in the solar system may be major source at exoplanets, or for the early solar system
A magnetic field should not be a priori considered as a protection for the atmosphere
Standard laboratory coagulation tests (SLTs) such as prothrombin time/international normalized ratio or partial thromboplastin time are frequently used to assess coagulopathy and to guide haemostatic ...interventions. However, this has been challenged by numerous reports, including the current European guidelines for perioperative bleeding management, which question the utility and reliability of SLTs in this setting. Furthermore, the arbitrary definition of coagulopathy (i.e. SLTs are prolonged by more than 1.5-fold) has been questioned. The present study aims to review the evidence for the usefulness of SLTs to assess coagulopathy and to guide bleeding management in the perioperative and massive bleeding setting. Medline was searched for investigations using results of SLTs as a means to determine coagulopathy or to guide bleeding management, and the outcomes (i.e. blood loss, transfusion requirements, mortality) were reported. A total of 11 guidelines for management of massive bleeding or perioperative bleeding and 64 studies investigating the usefulness of SLTs in this setting were identified and were included for final data synthesis. Referenced evidence for the usefulness of SLTs was found in only three prospective trials, investigating a total of 108 patients (whereby microvascular bleeding was a rare finding). Furthermore, no data from randomized controlled trials support the use of SLTs. In contrast, numerous investigations have challenged the reliability of SLTs to assess coagulopathy or guide bleeding management. There is actually no sound evidence from well-designed studies that confirm the usefulness of SLTs for diagnosis of coagulopathy or to guide haemostatic therapy.
We present observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission of a substantial plume‐like distribution of escaping ions from the Martian atmosphere, organized by the upstream ...solar wind convection electric field. From a case study of MAVEN particle‐and‐field data during one spacecraft orbit, we identified three escaping planetary ion populations: plume fluxes mainly along the upstream electric field over the north pole region of the Mars‐Sun‐Electric field (MSE) coordinate system, antisunward ion fluxes in the tail region, and much weaker upstream pickup ion fluxes. A statistical study of O+ fluxes using 3 month MAVEN data shows that the plume is a constant structure with strong fluxes widely distributed in the MSE northern hemisphere, which constitutes an important planetary ion escape channel. The escape rate through the plume is estimated to be ~30% of the tailward escape and ~23% of the total escape for > 25 eV O+ ions.
Key Points
Three escaping planetary ion populations near Mars are identified in MAVEN observations
MAVEN observed a substantial plume with strong escaping ion fluxes over the MSE north pole region
The plume contributes ~23% to the total >25 eV O+ escape of ~2 × 1024 s−1
We present the results of an initial effort to statistically map the fluxes of planetary ions on a closed surface around Mars. Choosing a spherical shell ~1000 km above the planet, we map both ...outgoing and incoming ion fluxes (with energies >25 eV) over a 4 month period. The results show net escape of planetary ions behind Mars and strong fluxes of escaping ions from the northern hemisphere with respect to the solar wind convection electric field. Planetary ions also travel toward the planet, and return fluxes are particularly strong in the southern electric field hemisphere. We obtain a lower bound estimate for planetary ion escape of ~3 × 1024 s−1, accounting for the ~10% of ions that return toward the planet and assuming that the ~70% of the surface covered so far is representative of the regions not yet visited by Mars Atmosphere and Volatile EvolutioN (MAVEN).
Key Points
MAVEN ion measurements are mapped to a spherical surface around Mars
Planetary ion fluxes are organized in four spatial regions on the shell
Heavy ion escape rates exceed 2 × 1024 s−1 for energies >25 eV
The occurrence of Venusian lighting has been debated for decades. Terrestrial lightning generates whistler waves, and many whistlers have been observed in Venus's ionosphere and induced ...magnetosphere. Venusian lightning occurrence rates derived from these whistler observations are relatively high. However, optical flashes on Venus are exceedingly rare and Venus encounters by multiple spacecrafts have not detected lightning. These non‐detections and rare optical observations are consistent with low Venusian lightning occurrence rates, which is incompatible with the high whistler‐derived rates. We present observations of whistlers during a Parker Solar Probe Venus gravity assist and eliminate lightning as a possible source. These waves are observed at an altitude of 0.39 Venus radii on Venus' nightside with planetward propagation and are simultaneous with Langmuir waves. This provides a mechanism for whistler generation near Venus that does not require lightning, and suggests that whistler‐based lightning occurrence rates may be overestimated.
Plain Language Summary
Whistler waves are a type of plasma wave. These waves can be generated in several ways, including by lightning. Every lightning strike on Earth generates a whistler wave, but only some of the whistler waves in near‐Earth space are generated by lightning. Many whistler waves have been detected near Venus and have been used to argue that lightning likely occurs on Venus at a relatively high rate. However, other signatures of lightning (including flashes of light in the sky) on Venus are very rare, which indicates that Venusian lightning must occur at a very low rate. The discrepancy between these different signatures of lightning on Venus means that we do not know how often Venus actually experiences lightning. We use data from Parker Solar Probe during a Venus gravity assist to study whistler waves that occurred on the nightside of Venus, very close to the planet. We observe that these waves are traveling toward Venus, which means they could not have been generated by lightning. This shows that whistler waves can occur near Venus without being generated by lightning and indicates that the occurrence rates of Venusian lightning based on whistler wave observations might be overestimated.
Key Points
Whistler waves were observed at an altitude of 0.39 Venus radii on Venus's nightside with planetward Poynting vector
Langmuir waves occurred simultaneously with the whistlers, suggesting electron beam driving with magnetotail origins
Lightning is eliminated as a possible generation mechanism for these whistler waves
Measurement of the dense cold thermal plasma in planetary ionospheres via orbiting spacecraft is challenging because ion energies are small (0–4 eV), densities can vary by four orders of magnitude, ...composition varies with altitude, spacecraft charging varies in time and must be measured very accurately, and instrumental effects (e.g., detector dead‐time and background) can be significant. The SupraThermal And Thermal Ion Composition instrument team has recently released a new set of data products that contain density moments of the primary ion species at Mars, including those derived at periapsis, subject to the full suite of calibration factors required. This article discusses the challenges associated with deriving these densities and provides examples of the key caveats that users of the data should be aware of. A preliminary statistical study of this new data set focuses on the structure and variability of Mars' ionosphere, demonstrating that solar zenith angle effects, the crustal magnetic fields, and electron precipitation on the nightside, drive the strongest structural features, consistent with photochemical theory and previous studies. Dayside ionospheric density profiles are highly repeatable below altitudes of 200 km, marking the region where photochemistry and collisions dominate. In the upper dayside ionosphere (altitudes >300–400 km) changes in the solar wind dynamic pressure on timescales of Mars Atmosphere and Volatile EvolutioN's orbit (hr) drive the largest (factors of 1–3) variability in ionospheric density. In contrast variability in ionospheric density peaks between 150 and 250 km altitude on the nightside (factors of 1–2), consistent with electron precipitation driving ionization in this region.
Plain Language Summary
Making accurate measurements of the ions present in planetary atmospheres via orbiting spacecraft is difficult due to the large changes in conditions encountered throughout spacecraft orbits. This paper describes the techniques implemented to address the full array of difficulties associated with measuring planetary ions at Mars using measurements made by the SupraThermal And Thermal Ion Composition instrument. These techniques are used to calculate ion densities in Mars' atmosphere and we perform a preliminary investigation of this new data set, revealing several important characteristics of how ions behave in Mars' atmosphere. In particular, we find that on the dayside of the planet, there is a transition region between the upper and lower atmosphere where planetary ions behave differently. Above this transition region planetary ions are influenced by forces that arise in the space environment about Mars, while below this transition region, planetary ions are well shielded from these effects. Our results provide insight into the processes that shape Mars' atmosphere and tell us how energy is transported through the Mars system.
Key Points
The calibration challenges and caveats of ion densities derived from SupraThermal And Thermal Ion Composition observations are discussed
Solar zenith angle effects and the crustal magnetic fields drive the strongest structural features in ionospheric density
A variety of processes drive ionospheric variability throughout different regions of the Martian ionosphere
The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been continuously observing the variability of solar soft X‐rays and EUV irradiance, monitoring the upstream solar wind and ...interplanetary magnetic field conditions and measuring the fluxes of solar energetic ions and electrons since its arrival to Mars. In this paper, we provide a comprehensive overview of the space weather events observed during the first ∼1.9 years of the science mission, which includes the description of the solar and heliospheric sources of the space weather activity. To illustrate the variety of upstream conditions observed, we characterize a subset of the event periods by describing the Sun‐to‐Mars details using observations from the MAVEN solar Extreme Ultraviolet Monitor, solar energetic particle (SEP) instrument, Solar Wind Ion Analyzer, and Magnetometer together with solar observations using near‐Earth assets and numerical solar wind simulation results from the Wang‐Sheeley‐Arge‐Enlil model for some global context of the event periods. The subset of events includes an extensive period of intense SEP electron particle fluxes triggered by a series of solar flares and coronal mass ejection (CME) activity in December 2014, the impact by a succession of interplanetary CMEs and their associated SEPs in March 2015, and the passage of a strong corotating interaction region (CIR) and arrival of the CIR shock‐accelerated energetic particles in June 2015. However, in the context of the weaker heliospheric conditions observed throughout solar cycle 24, these events were moderate in comparison to the stronger storms observed previously at Mars.
Key Points
We present a comprehensive overview of the first 1.9 years of MAVEN space weather conditions measured upstream at Mars
We characterize a subset of Mars‐impacting events due to an extensive period of SEP electrons, a succession of ICMEs, and a strong CIR
We discuss the space weather implications of the weaker solar cycle 24 heliospheric conditions on the events observed by MAVEN
•Nursery pigs infected with PEDV can recover digestive function within 7 days.•Sialomucin to sulfomucins ratio change over time in nursery pig jejunum.•Abundance of claudin 2 and 4 are reduced in ...nursery pig jejunum during PEDV infection.
The pig intestinal epithelium can be compromised by pathogens leading to reduced integrity and function. Porcine epidemic diarrhea virus (PEDV), recently detected in North America, exemplifies intestinal epithelial insult. Although several studies have investigated the molecular aspects and host immune response to PEDV, there are little data on the impact of PEDV on pig intestinal physiology. The objective of this study was to investigate the longitudinal impact of PEDV on nursery pig intestinal function and integrity. Fifty recently-weaned, 5-week-old barrows and gilts (BW=9.92±0.49kg) were sorted based on body weight (BW) and sex into two treatments: 1) Control or 2) PEDV inoculated. At 2, 5, 7, and 14days post inoculation (dpi), 4 pigs per treatment were euthanized and jejunum sections collected. PEDV antigen was detected in inoculated pigs by immunohistochemistry in 50% (2/4) at dpi 2, 100% (4/4) at dpi 5, and none at later time points. PEDV-infected pigs had reduced (P<0.05) villus height and decreased transepithelial resistance compared with controls. Total acidic mucins, particularly sialomucin, were reduced in PEDV pigs at dpi 2 and then increased compared with controls at dpi 7 and 14. In addition, PEDV pigs had increased stem cell proliferation (P<0.05) and a numerical increase in DNA fragmentation compared with controls through dpi 7 which coincided with an observed return of digestive function to that of controls. Collectively, these data reveal that PEDV infection results in time-dependent changes not only in intestinal morphology but also barrier integrity and function.
The identification, documentation, and discussion of the main threats affecting the golden-flowered Camellia species endemic to Hon Giao Pass are discussed. Observations, published literature, and ...collations of data accumulated from field trips throughout Vietnam since 1999 are analyzed and researched for the preparation of the article. The major anthropogenic risk factors affecting the golden-flowered Camellia species and their habitats on the Dalat Plateau and along the Hon Giao Pass are named and reviewed. These risk factors include habitat loss due to population growth, logging, habitat fragmentation and degradation, poaching, collection of wild plant species, fire, and the construction of dams and their associated water impoundments.
In vitro and in vivo experiments were conducted to study the effects of synbiotic supplementation on Salmonella enterica ser. Enteritidis (SE) proliferation, cecal content load, and broiler carcass ...contamination. Lactobacillus reuteri, Enterococcus faecium, Bifidobacterium animalis, and Pediococcus acidilactici culture supernatants decreased (P < 0.05) the in vitro proliferation of SE at 1:1 supernatant: pathogen dilution. A total of 240 Cobb-500 broiler chicks were randomly allotted to three treatment groups (8 replicates/group with 10 birds/replicate): control (basal diet), antibiotic (Virginiamycin at 20 mg/kg feed), synbiotic (PoultryStar® ME at 0.5 g/kg feed containing L. reuteri, E. faecium, B. animalis, P. acidilactici and a Fructooligosaccharide) from day of hatch. At 21 d of age, all birds in experimental groups were orally inoculated with 250 μl of 1 X 109 CFU SE. Antibiotic supplementation increased (P < 0.05) body weight and feed consumption, compared to the control group. Birds in the synbiotic supplementation had intermediate body weight and feed consumption that were not significantly different from both the control and antibiotic group at 42 d of age in SE infected birds. No significant effects were observed in feed efficiency at 42 d of age among the groups. Antibiotic and synbiotic supplementation decreased (P < 0.05) SE load in cecal contents by 0.90 and 0.85 log units/ g and carcass SE load by 1.4 and 1.5 log units/mL of rinsate compared to the control group at 42 d of age (21 dpi). The relative abundance of IL-10, IL-1, TLR-4, and IFNγ mRNA was decreased (P < 0.05) in the antibiotic and synbiotic supplementation groups compared to the control birds at 42 d of age (21 dpi). It can be concluded that synbiotic supplementation decreased SE proliferation in vitro and decreased SE load in the cecal contents and broiler carcass.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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