Magnetic refrigeration (MR) is a key technique for hydrogen liquefaction. Although the MR has ideally higher performance than the conventional gas compression technique around the hydrogen ...liquefaction temperature, the lack of MR materials with high magnetic entropy change in a wide temperature range required for the hydrogen liquefaction is a bottle-neck for practical applications of MR cooling systems. Here, we show a series of materials with a giant magnetocaloric effect (MCE) in magnetic entropy change (-∆S
> 0.2 J cm
K
) in the Er(Ho)Co
-based compounds, suitable for operation in the full temperature range required for hydrogen liquefaction (20-77 K). We also demonstrate that the giant MCE becomes reversible, enabling sustainable use of the MR materials, by eliminating the magneto-structural phase transition that leads to deterioration of the MCE. This discovery can lead to the application of Er(Ho)Co
-based alloys for the hydrogen liquefaction using MR cooling technology for the future green fuel society.
Gravity waves have a significant impact on both the dynamics and energy budget of the Martian thermosphere. Strong density variations of spatial scales indicative of gravity waves have previously ...been identified in this region by using in situ observations. Here we use observations from the Neutral Gas and Ion Mass Spectrometer (NGIMS) mass spectrometer on Mars Atmosphere and Volatile EvolutioN Mission to identify such waves in the observations of different atmospheric species. The wave signatures seen in CO2 and Ar are almost identical, whereas the wave signature seen in N2, which is lighter and has a larger scale height, is generally smaller in amplitude and slightly out of phase with those seen in CO2 and Ar. Examination of the observed wave properties in these three species suggests that relatively long vertical wavelength atmospheric gravity waves are the likely source of the waves seen by NGIMS in the upper thermosphere. A two‐fluid linear model of the wave perturbations in CO2 and N2 has been used to find the best fit intrinsic wave parameters that match the observed features in these two species. We report the first observationally based estimate of the heating and cooling rates of the Martian thermosphere created by the waves observed in this region. The observed wave density amplitudes are anticorrelated with the background atmospheric temperature. The estimated heating rates show a weak positive correlation with the wave amplitude, whereas the cooling rates show a clearer negative correlation with the wave amplitude. Our estimates support previous model‐based findings that atmospheric gravity waves are a significant source of both heating and cooling.
Key Points
This study presents an analysis of the observations of atmospheric wave perturbations in multiple species in the Martian thermosphere
The observed properties of the waves in different species show that gravity waves are the most likely atmospheric waves seen
From an estimation of the wave parameters, we show that the net heating or cooling produced by these waves is significant
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Ion loss to space has played an important role in atmospheric escape and climate change on Mars because of intense solar activity during a younger, more active phase of the Sun. Although the ...existence of an intrinsic magnetic field on ancient Mars is also a key factor in ion loss, its effect remains unclear. Based on multispecies magnetohydrodynamics (MHD) simulations, we investigated processes and rates of ion loss from Mars under extreme solar conditions and the existence of a dipole field with different strengths. The effects of a dipole field on ion loss depend on whether the dipolar magnetic pressure is strong enough to sustain the solar wind dynamic pressure. When the dipole field is existent but weak, it facilitates the cusp outflow and increases the loss rates of molecular ions (O2+ and CO2+) by a factor of 6 through the high‐latitude magnetotail. When the dipole field is strong enough, the loss rates of molecular ions are decreased by 2 orders of magnitude, and peaks of the escape flux are located near the equatorial plane due to the magnetic reconnection in the northern‐dusk or southern‐dawn lobe regions. The pickup process on the extended oxygen corona created by the strong EUV flux contributes to the total O+ loss. Therefore, the effects of the dipole field are less pronounced for O+. Under more moderate solar EUV conditions, the effects on O+ loss can be stronger and thus contribute to climate change.
Plain Language Summary
It has been suggested that ancient Mars had an atmosphere thick enough to sustain liquid water on its surface, while present Mars only has a thin atmosphere. Ion loss to space is one of the important processes for the removal of the atmosphere because a younger Mars would have been exposed to much stronger solar activity. Over 4 Ga, Mars had an intrinsic magnetic field like that of the Earth. The existence of an intrinsic magnetic field changes the electromagnetic environment around the planet and affects the ion loss. We investigate the ion loss from Mars at approximately 4.5 Ga, assuming both the strong solar conditions and the existence of an intrinsic magnetic field using numerical simulations. The results show that the existence of the weak dipole field increases the loss of molecular ions such as O2+ and CO2+. Contrary to the weak intrinsic magnetic field, however, a strong intrinsic magnetic field substantially decreases the loss of molecular ions. The ion loss processes are also affected by the intrinsic magnetic field. These effects of the intrinsic magnetic field are less pronounced for O+ loss because of the extended O+ corona.
Key Points
A weak intrinsic magnetic field increases ion loss rates when the solar wind dynamic pressure exceeds the magnetic pressure (overpressure)
The existence of intrinsic magnetic field facilitates cusp outflows enabling more escape of molecular ions (O2+ and CO2+) by a factor of 6
In nonoverpressure cases, the ion loss rates decrease by 2 orders for molecular ions, but the effect is mild for O+ with extended corona
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Ion escape has played a key role in atmospheric loss on ancient Mars due to intense solar activity. Under the existence of a strong global intrinsic magnetic field, as expected on ancient Mars, ...differential flows between different ion species can be important for ion escape. To assess effects of differential flows, we here developed a new global multifluid magnetohydrodynamics model with a cubed sphere grid named Multifluid Atmospheric Escape Simulations Toward Real elucidatiOn (MAESTRO). A test simulation under present‐day Mars conditions showed solar wind‐Mars interactions, for example, plasma boundaries, ionospheric profiles, and tailward outflows, consistent with observations and simulation studies. We then conducted multifluid and multispecies simulations with six different dipole field strengths under ancient Mars conditions. The multifluid cases show asymmetric outflow distributions with respect to the solar wind convection electric field, as pointed out by previous studies on present‐day Mars. Compared with multispecies cases, the multifluid representation increases the escape rates of O2+ and CO2+ by more than two orders of magnitude in the strong dipole field cases where the cusp outflow is dominant. The O+ escape rate is slightly lower in the multifluid cases with no or weak dipole field due to suppression of ion pickup in the −E hemisphere, while it is reduced by one order of magnitude in the strongest dipole field case. The existence of a dipole field can reduce the total escape rate by a factor of six. The impact on atmospheric evolution is diminished but still significant.
Plain Language Summary
Mars lost a significant part of the atmosphere during its early period and experienced a drastic climate change. The escape of charged atmospheric particles to space, called ion escape, is a significant removal process of the atmosphere because the activity of the young Sun was much stronger and stripped out the upper atmosphere of early Mars more powerfully. However, it is thought that Mars once had an intrinsic magnetic field like Earth, which can affect the escape of charged particles via electromagnetic forces. To reproduce the realistic processes and morphology of ion escape under the presence of a planetary intrinsic magnetic field, we developed a new simulation model that treats each ion species as a separate fluid. The simulation results of the new model show much stronger molecular ion outflow from the ionosphere at relatively low altitudes compared to our previous studies. The outflow enhancement is more remarkable when a stronger intrinsic magnetic field is assumed. On the other hand, atomic ion escape from high altitudes is not affected largely. The new model indicates that the effects of a planetary intrinsic magnetic field on ion escape are reduced, though still of significance.
Key Points
A new global multifluid magnetohydrodynamics (MHD) model of solar wind‐Mars interactions with a cubed sphere grid system named Multifluid Atmospheric Escape Simulations Toward Real elucidatiOn is developed
The multispecies MHD cases underestimate outflows of ionospheric ions in strong dipole field cases where cusp outflow is important
The effects of the multifluid representation on the O+ escape rate are small in no and weak dipole field cases where ion pickup is dominant
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•MAVEN has observed the Martian upper atmosphere for a full Martian year, and has determined the rate of loss of gas to space and the driving processes; 1–2 kg/s of gas are being lost.•The loss rate ...extrapolated back in time gives an estimate of the total loss of gas to space and its impact on Martian climate history; an estimated 0.8 bars or more of CO2 likely has been lost.•Loss to space has been the major process driving climate change on Mars.
Observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 – 3 Oct 2016). Loss rates for H and O are sufficient to remove ∼2–3 kg/s to space. By itself, this loss would be significant over the history of the planet. In addition, loss rates would have been greater early in history due to the enhanced solar EUV and more-active Sun. Integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar CO2 or 23 m global equivalent layer of H2O; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. Combined with the lack of surface or subsurface reservoirs for CO2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of Mars from an early, warmer environment to the cold, dry one that we see today.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This paper introduces a new Earth's atmosphere‐ionosphere coupled model that treats seamlessly the neutral atmospheric region from the troposphere to the thermosphere as well as the ...thermosphere‐ionosphere interaction including the electrodynamics self‐consistently. The model is especially useful for the study of vertical connection between the meteorological phenomena and the upper atmospheric behaviors. As an initial simulation using the coupled model, we have carried out a 30 day consecutive run in September. The result reveals that the longitudinal structure of the F‐region ionosphere varies on a day‐to‐day basis in a highly complex way and that a four‐peak structure of the daytime equatorial ionization anomaly (EIA) similar to the recent observations appears as an averaged feature. The simulation reproduces and thus confirms the vertical coupling processes proposed so far with respect to the formation of the averaged EIA longitudinal structure; the excitation of solar nonmigrating tides in the troposphere, their propagation through the middle atmosphere, and the modulation of ionospheric dynamo, which in turn affects EIA generation. The simulation result indicates that not only the ionospheric averaged longitudinal structure but also the day‐to‐day variation can be modulated significantly by the lower atmospheric effect.
Ion escape is one of the key processes responsible for drastic climate change on ancient Mars. Ion escape is affected by the solar X‐ray and EUV (X‐ray and extreme ultraviolet (XUV)) flux, the solar ...wind, and the presence of a planetary intrinsic magnetic field, all of which was much different at ancient Mars. We investigated how the presence and strength of a dipole field affects the ion escape under 50 or 10 times higher solar XUV flux and strong solar wind with multispecies magnetohydrodynamics model. The results showed two opposite effects on the escape rates, which is associated with the pressure ratio of the dipolar magnetic pressure at the equatorial surface to the solar wind dynamic pressure. The escape rates increase by up to a factor of 6 for O2+ and CO2+ but change little for O+ if the pressure ratio is below 0.1. On the other hand, the escape rates decrease by more than one order of magnitude for the three ions if the pressure ratio is above 0.1. The threshold can be described by the pressure balance between the solar wind flow and the dipole field at high latitudes, where the ionospheric outflow emerges in the unmagnetized cases. The effects on the escape rates are stronger under lower solar XUV cases. The total escape rate reaches 1027 s−1 in the unmagnetized case, which may lead to a large contribution to atmospheric loss at ancient Mars, but it can be reduced by an order of magnitude in the presence of a dipole field.
Plain Language Summary
Escape of the ionized atmosphere is thought to be one of the important processes on ancient Mars because it has experienced drastic climate change. Mars was exposed to strong solar X‐ray and EUV (X‐ray and extreme ultraviolet (XUV)) flux and strong solar wind plasma flow, while it had a global intrinsic magnetic field. As these factors change the plasma and electromagnetic environment, ion escape at ancient Mars was much different from the current one. We studied how ion escape on ancient Mars are affected by the presence and the strength of an intrinsic magnetic field using numerical simulations. The escape rates increase for O2+ and CO2+ but does not increase for O+ when the dipole field is weak, while the escape rates of these three ions are strongly decreased when the dipole field is strong. Whether the dipole field is weak or strong is determined by the pressure ratio between the magnetic pressure of dipole field at the equatorial surface and the solar wind dynamic pressure. The effects of the dipole field on the ion escape rates are stronger under lower solar XUV cases.
Key Points
Escape rates of molecular ions change by more than two orders of magnitude with the dipole field strength, while that of O+ changes less
Dipole field's effects on the escape rates depend on the pressure ratio of the dipole field to the solar wind at high latitudes
The lower solar X‐ray and extreme ultraviolet flux enhances the dipole field's effects on escape rates and slightly changes O+ contribution to the total escape rate
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Interleukin (IL)-23 is an essential cytokine involved in expansion of the Th17 lineage, which is associated with many immune-related destructive tissue diseases. We hypothesized that the ...IL-23-induced Th17 pathway plays a role in periodontal pathology and examined the expression of cytokines, and related molecules, in periodontal lesions and control sites. IL-23 and IL-12 were expressed at significantly higher levels in periodontal lesions than in control sites. However, the relative expression of the IL-23 receptor compared with the IL-12 receptor β2 was significantly higher in periodontal lesions. Moreover, IL-17 expression was significantly higher in periodontal lesions, especially in the tissue adjacent to bone destruction, than in control sites. There was no significant difference in the expression levels of IFN-γ, an important cytokine inhibiting differentiation toward the Th17 pathway, between periodontal lesions and control sites. Together, these results suggest that the IL-23-induced Th17 pathway is stimulated in inflammatory periodontal lesions.
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CMK, NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Fe2P-type compounds exhibit a giant magnetocaloric effect (MCE) and are extensively studied for room temperature applications. The reduction of their transition temperature below 77 K can pave the ...way for the potential application of these materials for hydrogen liquefaction using cryogenic magnetic refrigeration. Most of the known magnetocaloric materials with a giant MCE below 77 K are rare-earth-based compounds. In order to explore the possibility of developing rare-earth-free compounds with cryogenic MCE, we collected a dataset by conducting data mining on published experimental results on Fe2P-type magnetocaloric compounds and used machine learning for composition optimization aiming at lowering the transition temperature below 77 K. Guided by the predictions of an artificial neural network, we found a promising composition of Mn1.70Fe0.30P0.63Si0.37 with a transition temperature of 97 K at 1 T magnetic field which was lowered to 73 K by the minor substitution of Fe with Co. The developed rare-earth-free compounds exhibit a large magnetocaloric performance in isothermal magnetic entropy change (∆SM) of 7.5–11.5 J/kgK at the temperatures below 100 K. This study demonstrates that data-driven development of magnetocaloric materials can efficiently boost the optimization of their properties, thus aiding the practical applicability of magnetic refrigeration technology.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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