A method to experimentally clamp leaf water content to defined values to assess its effects on apoplastic pH

Background Leaf hydration is controlled by feedback mechanisms, e.g. stomatal responses, adjustments of osmotic potential and hydraulic conductivity. Leaf water content thus is an input into related feedback-loops controlling the balance of water uptake and loss. Apoplastic alkalisation upon leaf dehydration is hypothesized to be involved in water stress related signaling on tissue level. When studying these mechanisms and their intermediate signaling steps, an experimenter has only poor means to actually control the central experimental variable, leaf water content (LWC), because it is not only dependent on external variables (e.g. air humidity), which are under experimental control, but is also governed by the biological influences controlling transpiration and water uptake. Those are often unknown in their magnitude, unpredictable and fluctuating throughout an experiment and will prevent true repetitions of an experiment. The goal of the method presented here is to experimentally control and manipulate leaf water content (LWC) of attached intact leaves enclosed in a cuvette. Results An experimental setup was developed where LWC is measured by a sensor based on IR-transmission and its signal processed to control a pump which circulates air from the cuvette through a cold trap. Hereby a feedback-loop is formed, which by adjusting vapour pressure deficit (VPD) and consequently leaf transpiration can precisely control LWC. This technique is demonstrated here in a combination with microscopic fluorescence imaging of apoplastic pH (pH apo ) as indicated by the excitation ratio of the pH sensitive dye OregonGreen. Initial results indicate that pH apo of the adaxial epidermis of Vicia faba is linearly related to reductions in LWC. Conclusions Using this setup, constant LWC levels, step changes or ramps can be experimentally applied while simultaneously measuring physiological responses. The example experiments demonstrate that bringing LWC under experimental control in this way allows better controlled and more repeatable experiments to probe quantitative relationships between LWC and signaling and regulatory processes.

Interpreting exoplanet biosignatures with a coupled atmosphere-interior-geochemical evolution model

<p>The atmospheric evolution of rocky planets is shaped by a range of astrophysical, geophysical, and geochemical processes. Interpreting observations of potentially habitable exoplanets will require an improved understanding of how these competing influences interact on long timescales. In particular, the interpretation of biosignature gases, such as oxygen, is contingent upon understanding the probable redox evolution of lifeless worlds. Here, we develop a generalized model of terrestrial planet atmospheric evolution to anticipate and interpret future observations of habitable worlds. The model connects early magma ocean evolution to subsequent, temperate geochemical cycling. The thermal evolution of the interior, cycling of carbon-hydrogen-oxygen bearing volatiles, surface climate, crustal production, and atmospheric escape are explicitly coupled throughout this evolution. The redox evolution of the atmosphere is controlled by net planetary oxidation via the escape of hydrogen to space, the loss of atmospheric oxygen to the magma ocean, and oxygen consumption via crustal sinks such as outgassing of reduced species, serpentinization reactions, and direct “dry” oxidation of fresh crust.</p><p>The model can successfully reproduce the atmospheric evolution of a lifeless Earth: it consistently predicts an anoxic atmosphere and temperate surface conditions after 4.5 Gyrs of evolution. This result is insensitive to model uncertainties such as the details of atmospheric escape, mantle convection parameterizations, initial radiogenic inventories, mantle redox, the efficiency of crustal oxygen sinks, and unknown carbon cycle and deep-water cycle parameters. This suggests abundant oxygen is a reliable biosignature for literal Earth twins, defined as Earth-sized planets at 1 AU around sunlike stars with 1-10 Earth oceans and less initial carbon dioxide than water.</p><p>However, if initial volatile inventories are permitted to vary outside these “Earth-like” ranges, then dramatically different redox evolution trajectories are permitted. We identify three scenarios whereby Earth-sized planets in the habitable zones of sunlike stars could accumulate oxygen rich atmospheres (0.01 - 10 bar) in the absence of life. Specifically, (i) high initial CO<sub>2</sub>:H<sub>2</sub>O endowments, (ii), >50 Earth ocean water inventories, or (iii) extremely volatile poor initial inventories, could all result in oxygen-rich atmospheres after 4.5 Gyrs of evolution. These false positives arise despite the assumption that there is always sufficient non-condensible atmospheric gases, N<sub>2</sub>, to maintain an effective cold trap. Fortunately, all three oxygen false positive scenarios could potentially be identified by thorough characterization of the planetary context, such as from using time resolved photometry to constrain surface water inventories.</p><p>The model also sheds light on the atmospheric evolution of Venus and Venus-like exoplanets. We can successfully recover the modern state of Venus’ atmosphere, including a dense CO<sub>2</sub>-dominated atmosphere with negligible water vapor and molecular oxygen. Moreover, there is a clear dichotomy in the evolutionary scenarios that recover modern Venus conditions, one in which Venus was never habitable and perpetually in runaway greenhouse since formation, and another whereby Venus experienced ~1-2 Gyr of surface habitability with a ~100 m deep ocean. We explore the likelihood of each scenario and suggest future in situ observations that could help discriminate between these two alternative histories.</p>

Science and Exploration of the Moon: Overview

Earth’s moon, hereafter referred to as “the Moon,” has been an object of intense study since before the time of the Apollo and Luna missions to the lunar surface and associated sample returns. As a differentiated rocky body and as Earth’s companion in the solar system, much study has been given to aspects such as the Moon’s surface characteristics, composition, interior, geologic history, origin, and what it records about the early history of the Earth-Moon system and the evolution of differentiated rocky bodies in the solar system. Much of the Apollo and post-Apollo knowledge came from surface geologic exploration, remote sensing, and extensive studies of the lunar samples. After a hiatus of nearly two decades following the end of Apollo and Luna missions, a new era of lunar exploration began with a series of orbital missions, including missions designed to prepare the way for longer duration human use and further exploration of the Moon. Participation in these missions has become international. The more recent missions have provided global context and have investigated composition, mineralogy, topography, gravity, tectonics, thermal evolution of the interior, thermal and radiation environments at the surface, exosphere composition and phenomena, and characteristics of the poles with their permanently shaded cold-trap environments. New samples were recognized as a class of achondrite meteorites, shown through geochemical and mineralogical similarities to have originated on the Moon. New sample-based studies with ever-improving analytical techniques and approaches have also led to significant discoveries such as the determination of volatile contents, including intrinsic H contents of lunar minerals and glasses. The Moon preserves a record of the impact history of the solar system, and new developments in timing of events, sample based and model based, are leading to a new reckoning of planetary chronology and the events that occurred in the early solar system. The new data provide the grist to test models of formation of the Moon and its early differentiation, and its thermal and volcanic evolution. Thought to have been born of a giant impact into early Earth, new data are providing key constraints on timing and process. The new data are also being used to test hypotheses and work out details such as for the magma ocean concept, the possible existence of an early magnetic field generated by a core dynamo, the effects of intense asteroidal and cometary bombardment during the first 500 million–600 million years, sequestration of volatile compounds at the poles, volcanism through time, including new information about the youngest volcanism on the Moon, and the formation and degradation processes of impact craters, so well preserved on the Moon. The Moon is a natural laboratory and cornerstone for understanding many processes operating in the space environment of the Earth and Moon, now and in the past, and of the geologic processes that have affected the planets through time. The Moon is a destination for further human exploration and activity, including use of valuable resources in space. It behooves humanity to learn as much about Earth’s nearest neighbor in space as possible.

Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)

Context. WASP-121 b is a hot Jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere. Aims. We survey the transmission spectrum of WASP-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the Hubble Space Telescope (HST). Methods. We applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, TiO, VO, and SH in high-resolution transit spectra obtained with the HARPS spectrograph. We injected models assuming chemical and hydrostatic equilibrium with a varying temperature and composition to enable model comparison, and employed two bootstrap methods to test the robustness of our detections. Results. We detect neutral Mg, Na, Ca, Cr, Fe, Ni, and V, which we predict exists in equilibrium with a significant quantity of VO, supporting earlier observations by HST/WFC3. Non-detections of Ti and TiO support the hypothesis that Ti is depleted via a cold-trap mechanism, as has been proposed in the literature. Atomic line depths are under-predicted by hydrostatic models by a factor of 1.5 to 8, confirming recent findings that the atmosphere is extended. We predict the existence of significant concentrations of gas-phase TiO2, VO2, and TiS, which could be important absorbers at optical and near-IR wavelengths in hot Jupiter atmospheres. However, accurate line-list data are not currently available for them. We find no evidence for absorption by SH and find that inflated atomic lines can plausibly explain the slope of the transmission spectrum observed in the near-ultraviolet with HST. The Na I D lines are significantly broadened (FWHM ~50 to 70 km s−1) and show a difference in their respective depths of ~15 scale heights, which is not expected from isothermal hydrostatic theory. If this asymmetry is of astrophysical origin, it may indicate that Na I forms an optically thin envelope, reminiscent of the Na I cloud surrounding Jupiter, or that it is hydrodynamically outflowing.

Measurement of Thermal Decomposition Temperature and Rate of Sodium Hydride

In decommissioning sodium-cooled fast reactors, the operators can be exposed to radiation during dismantling of cold trap equipment (C/T). The C/T is higher dose equipment because the C/T trapped tritium of fission products during the operation to purify the sodium coolant. In this study, thermal decomposition temperature and rate of sodium hydride (NaH) were measured as a fundamental research for development of “thermolysis” process prior to the dismantling. We measured the thermal decomposition temperature and rate using NaH powder (95.3%, Sigma-Aldrich) in alumina pan with ThermoGravimetry-Differential Thermal Analysis (TG-DTA) instrument (STA2500 Regulus, NETZSCH Japan). The heating rates of TG-DTA were set to β = 2.0, 5.0, 10.0 and 20.0 K/min. The DTA showed endothermic reaction and the TG showed two-steps mass-loss over 580K. This first-step mass-loss was consistent with change of chemical composition of the NaH with heating (NaH → Na+1/2H2). The thermal decomposition temperature and rate were obtained from the onset temperature of the mass-loss and the simplified Kissinger plots, respectively. Furthermore, we set to the thermal decomposition temperature of around 590K, and the mass-loss rates were measured. As a result, over 590K, the thermal decomposition occurred actively, and showed good agreement with the estimation curves obtained by the simplified Kissinger plots. The thermal decomposition rate strongly depended on the heating temperature.

Performance of Mesoporous Organo Silica Membrane for Desalination

Clean water is essential source for household purpose. However, many surface water contain high salt concentration was found. In this work, membrane was made using tetraethyl orthosilicate (TEOS) as silica precursors and citric acid as single organo catalyst. Membranes were calcined at 200 and 250 °C using Rapid thermal processing (RTP). All membranes were tested via pervaporation. Pervaporation processes allow membrane to separate salt from water as vapour phase with vacuum condition required. Permeate was collected in the cold trap after condenses. This study focus to the performance of organo silica membrane in variance of refluxed 0 and 50 °C and feed concentrations (0.3, 3.5 and 5wt% NaCl) at room temperature (~25 °C). Optimum condition was obtained at reflux 50 °C with high siloxane and Si-C bonds. Carbon content from citric acid promote silica network more strength. The good performances in variance feed concentration were also showed at reflux 50°C with 0.3324 kg.m-2.h-1 (0.3 wt%), 0,2290 kg.m-2.h-1 (3.5 wt%) and 0.2168 kg.m-2.h-1 (5 wt%). These membranes are categorized as mesoporous and achieve excellent salt rejection >95%.

Searching for thermal inversion agents in the transmission spectrum of KELT-20b/MASCARA-2b: detection of neutral iron and ionised calcium H&K lines

ABSTRACT We analyse the transmission spectra of KELT-20b/MASCARA-2b to search for possible thermal inversion agents. The data consist of three transits obtained using HARPSN and one using CARMENES. We removed stellar and telluric lines before cross-correlating the residuals with spectroscopic templates produced using a 1D plane-parallel model, assuming an isothermal atmosphere and chemical equilibrium at solar metallicity. Using a likelihood-mapping method, we detect Fe i at > 13σ, Ca ii H$\&$K at > 6σ and confirm the previous detections of Fe ii, Ca ii IR Triplet, and Na i D. The detected signal of Fe i is shifted by −3.4 ± 0.4 km s−1 from the planetary rest frame, which indicates a strong day–night wind. Our likelihood-mapping technique also reveals that the absorption features of the detected species extend to different altitudes in the planet’s atmosphere. Assuming that the line lists are accurate, we do not detect other potential thermal inversion agents (NaH, MgH, AlO, SH, CaO, VO, FeH, and TiO) suggesting that non-chemical equilibrium mechanisms (e.g. a cold-trap) might have removed Ti- and V-bearing species from the upper atmosphere. Our results, therefore, show that KELT-20b/MASCARA-2b cannot possess an inversion layer caused by a TiO/VO-related mechanism. The presence of an inversion layer would therefore likely be caused by metal atoms such as Fe i and Fe ii. Finally, we report a double-peak structure in the Fe i signal in all of our data sets that could be a signature of atmospheric dynamics. However, further investigation is needed to robustly determine the origin of the signal.