The sublimation and condensation of ices play a very important role in the formation of planetary systems, in the evolution of some solar system bodies as well as in the equilibrium and matter ...exchanges between surface and atmosphere of most planets and satellites. The precise knowledge of vapour pressure of molecular solids at all relevant temperatures is mandatory, but the published sublimation relations are not always accurate enough. All published experimental measurements, and empirical and thermodynamical relations for the vapour pressure of 53 different species in their pure solid phases are reviewed. For several species, we also calculate the vapour pressure with accurate thermodynamic formulae from the triple point down to low temperatures. For 27 species (H
2O, O
2, O
3, CO, CO
2, CH
3OH, HCOOH, CH
4, C
2H
2, C
2H
4, C
2H
6, C
6H
6, HCN, HC
3N, C
2N
2, C
4N
2, N
2, NH
3, NO, N
2O, H
2S, SO
2, AsH
3, Ne, Ar, Kr, and Xe) we are able to propose vapour pressure relations, either empirical or theoretical, valid over a large range of temperatures, representative of astrophysical environments. All these relations are more accurate than those currently used in the astrophysical literature. In particular, most of the relations commonly used in the astrophysical literature are based on the data reported by
Lide (2006) in the CRC Handbook of Chemistry and Physics, which are inaccurate for several compounds. The most problematic case is CO ice, for which a sublimation relation extrapolated from the liquid–gas equilibrium (
Fanale and Salvail, 1990) is used in most of the models simulating the activity of comet nuclei.
Here we report a comparison between reflectance spectroscopy of meteorites under asteroidal environment (high vacuum and temperature) and Main Belt and Near Earth Asteroids spectra. Focusing on the ...–OH absorption feature around 3 μm, we show that the asteroidal environment induces a reduction of depth and width of the band, as well as a shift of the reflectance minimum. We then decompose the –OH feature into several components with a new model using Exponentially Modified Gaussians. Unlike previous studies, we confirme the link between these components, the aqueous alteration history and the amount of water molecules inside of the sample, using the shape of this spectral feature only. We then apply this deconvolution model to asteroids spectra which were obtained with a space-borne telescope and two space probes, and find a strong similarity with the components detected on meteorites, and among asteroids from a same type. Based on the conclusions drawn from our meteorites experiment, we suggest to use the 3-μm band as a tracer of the alteration history of the small bodies. Using the 3-μm band only, we show that Ryugu has been heavily altered by water, which is consistent with its parent body being covered with water ice, then went through a high temperature sequence, over 400 °C. We also point out that the 3-μm band of Bennu shows signs of its newly discovered surface activity.
•Exponentially Modified Gaussians are used to model the shape of the 3-μm band.•The components of the band depend on the aqueous alteration and relative humidity.•Similar components are detected on the asteroids spectra.•The components are used to retrieve the alteration history of the asteroids.•Signs of activity on Bennu and two Cgh-types are detected through the –OH band.
Generally, the reflectance of a particulate surface depends on the phase angle at which it is observed. This is true for laboratory measurements on powders of natural materials as well as remote ...observations of Solar System surfaces. Here, we measured the dependences of reflectance spectra with phase angles, of a suite of 72 meteorites in the 400–2600 nm range. The 10–30° phase angle range is investigated in order to study the contribution of Shadow Hiding Opposition Effect (SHOE) to the phase behavior. The behavior is then extrapolated to phase angle of 0° using a polynomial fit, in order to provide grounds for comparison across meteorite groups (enabling to remove the contribution of shadows to reflectance) as well as to provide “equivalent albedo” values that should be comparable to geometric albedo values derived for small bodies. We find a general behavior of increasing strength of the SHOE with lower reflectance values (whether between samples or for a given samples with absorption features). This trend provides a first order way to correct any reflectance spectra of meteorite powders measured under standard conditions (g = 30°) from the contribution of shadows. The g = 0° calculated reflectance and equivalent albedos are then compared to typical values of albedos for main-belt asteroids. This reveals that among carbonaceous chondrites only Tagish Lake group, CI, and CM chondrites have equivalent albedo compatible with C- and D-type asteroids. On the other hand equivalent albedo derived with CO, CR and CK chondrites are compatible with L- and K-type asteroids. The equivalent albedo derived for ordinary chondrites is related to petrographic types, with low-grade petrographic type (type 3.6 and less) being generally darker that higher petrographic types. This works provides a framework for further understanding of the asteroids meteorite linkage in particular when combining with colors and spectroscopy.
•Reflectance spectra of 72 different meteorite are obtained low phase angle (10–30°).•Zero-phase spectra reflectance and an equivalent to geometric albedo are calculated.•A general law is derived to convert standard geometry measurement to zero-phase.•The albedo of asteroids is compared to meteorite groups.
As the Internet provides massive amounts of heterogeneous information, people may perceive this medium as challenging. The difficulty to evaluate and select relevant information increases as more and ...more diverse sources and content are available. Information overload (IO) may be the consequence. The research presented here gives a first comprehensive overview of possible indicators for IO in the context of online news exposure. Based on an online survey (N=419), we found that younger people with less information-seeking self-efficacy were more susceptible to experience IO. Additionally, we identified motivations for media consumption and information retrieval strategies in the Internet that imply IO. With our results, we contribute to a further understanding of IO and provide an important basis for future research needed to face the challenges resulting from the rising media diversity.
Reactive jammers have been shown to be a serious threat for wireless communication. Despite this, it is difficult to detect their presence reliably. We propose a novel method to detect such ...sophisticated jammers in direct sequence spread spectrum (DSSS) wireless communication systems. The key idea is to extract statistics from the jamming-free symbols of the DSSS synchronizer to discern jammed packets from those lost due to bad channel conditions. Our contribution is twofold. First, we experimentally evaluate new empirical models utilizing the preamble symbols of IEEE 802.15.4 packets, thus enabling the accurate prediction of the packet delivery ratio (PDR). We show that the chip error rate-based metric is superior to metrics used in the literature, offering an accurate and reactive indicator of the true PDR. Our second contribution is the design and evaluation of a detection technique relying on this metric to detect reactive jammers. We build a software-defined radio testbed and show that our technique enables the error-free detection of reactive jammers that jam all packets on links with a PDR above 0.3. To the best of our knowledge, our detector is the first to detect reactive jamming attacks targeting the physical layer header of DSSS packets, and does not require any modifications of the wireless communication system.
Industry represents a very promising application area for solar thermal technology, since it accounts for 27% of the total final energy consumption in Germany and uses 74% of its energy consumption ...as thermal energy. In order to develop this application area, it is necessary to know which industrial sectors have the highest potential and which processes within these sectors are most suitable for the integration of solar heat. For this paper the industrial heat consumption in Germany was analyzed, which leads to the selection of the most promising sectors within industry. Furthermore, the quantitative potential for Germany in total and for 11 selected sectors, that were identified to be most promising for the use of solar heat, was calculated. These are Chemicals, Food and beverages, Motor vehicles, Paper, Fabricated metal, Machinery and equipment, Rubber and plastic, Electrical equipment, Textiles, Printing and Wood. These sectors are analyzed to identify suitable processes for the integration of solar heat. In total the theoretical potential of solar heat for industrial processes below 300°C in Germany accounts for 134TWh per year, the technical potential being 16TWh per year or 3.4% of the overall industrial heat demand. This is the highest share of the European potential of 72TWh per year. The results of this study facilitate the prioritized application of solar thermal energy in industrial sectors and processes for Germany and other countries.
The composition of Solar System surfaces can be inferred through reflectance and emission spectroscopy, by comparing these observations to laboratory measurements and radiative transfer models. While ...several populations of objects appear to be covered by sub-micrometre sized particles (D < 1 μm) (referred to as hyperfine), there are limited studies on reflectance and emission of particulate surfaces composed of particles smaller than the visible and infrared wavelengths. We have undertaken an effort to determine the reflectance of hyperfine particulate surfaces in conjunction with high-porosity, in order to simulate the physical state of cometary surfaces and their related asteroids (P- and D-types). In this work, we present a technique developed to produce hyperfine particles of astrophysical relevant materials (silicates, sulphides, macromolecular organics). This technique is used to prepare hyperfine powders that were measured in reflectance in the 0.4–2.6 μm range. These powders were then included in water ice particles, sublimated under vacuum, in order to produce a hyperporous sample of hyperfine material (refers as to sublimation residue). When grinded below one micrometre, the four materials studied (olivine, smectite, pyroxene and amorphous silica), show strong decrease of their absorption features together with a blueing of the spectra. This “small grain degeneracy” implies that surfaces covered by hyperfine grains should show only shallow absorption features if any (in the case of moderately absorbing particles as studied here). These two effects, decrease of band depth and spectral blueing, appear magnified when the grains are incorporated in the hyperporous residue. We interpret the distinct behaviour between hyperporous and more compact surfaces by the distancing of individual grains and a decrease in the size of the elemental scatterers. This work implies that hyperfine grains are unabundant at the surfaces of S- or V-type asteroids, and that the blue nature of B-type may be related to a physical effect rather than a compositional effect.
•A protocol for production of sub-μm grains in hyperporous surfaces was developed•Reflectance of sub-μm grains shows attenuated absorptions and blue spectral slope•Increasing porosity of a surface of sub-μm grains increases these spectral effects•Consequently, spectra of primitive bodies need to be interpreted with caution
Carbonaceous chondrites record processes of aqueous alteration in the presence of hydrated and hydroxylated minerals, which could have provided a source of water in the inner solar system (Alexander ...et al., 2012, 2013). In this study, thermogravimetric analysis (TGA) was performed on 26 CM chondrites, which cover a range of degree of aqueous alteration from 2.0, such as Meteorite Hills (MET) 01070, to 2.6, such as Queen Alexandra Range (QUE) 97990, in order to quantify their water content. In addition, by measuring the release of volatile elements as a function of temperature, we obtained information on the mineralogy of water-bearing phases and provide indicators of aqueous alteration based on water released by phyllosilicates. These analyses are combined with infrared spectroscopy (IR) made on meteorite pellets heated up to 300°C. The infrared features (–OH band at 3-μm and SiO4 around 10-μm) revealed a correlation with TGA. The two techniques are in agreement with the scheme of aqueous alteration proposed by Rubin et al. (2007) and Alexander et al. (2013) based on phyllosilicate abundance.
The low temperature (200–400°C) mass loss observed in TGA is attributed to Fe-oxy-hydroxydes (ferrihydrite, goethite). However, the proportion of these minerals formed by terrestrial alteration remains unknown. TGA also revealed two anomalous CM chondrites, Pecora Escarpment (PCA) 02012 and PCA 02010. Their TGA curves are significantly different from those of “regular” CMs with little mass loss, which can be related to the dehydration history of these meteorites in response to a heating event (Raman measurements also point toward a thermal event, Quirico et al., 2013). In the case of more mildly heated chondrites, such as with Wisconsin Range (WIS) 91600, the TGA curve presents similar mass loss to the other CMs.
Seven bulk measurements of CR chondrites and 3 measurements of matrix-enriched parts of CR meteorites were also studied by TGA, and confirm the low hydration level of chondrules and a significant alteration of the matrix. The water content of the matrix of the CM 2.6 QUE 97990 was estimated and compared to TGA of the matrix enriched portion of the CR2 EET 92159 and that of Orgueil.
Results suggest a similar aqueous alteration degree between Orgueil and the matrix of CMs (around 25wt.%) and a lower alteration of the CR2 matrix (11wt.% of H2O).
We present here several laboratory analyses performed on the freshly fallen Mukundpura CM chondrite. Results of infrared transmission spectroscopy, thermogravimetry analysis, and reflectance ...spectroscopy show that Mukundpura is mainly composed of phyllosilicates. The rare earth trace elements composition and ultrahigh‐resolution mass spectrometry of the soluble organic matter give results consistent with CM chondrites. Finally, Raman spectroscopy shows no signs of thermal alteration of the meteorite. All the results agree that Mukundpura has been strongly altered by water on its parent body. Comparison of the results obtained on the meteorite with those of other chondrites of known petrologic types leads to the conclusion that Mukundpura is similar to CM1 chondrites, which differ from its original classification as a CM2.
The hope of reaching diverse and large target groups has motivated civic education practitioners to offer their content on social media. The question has therefore long ceased to be whether civic ...education should take place on the internet, but rather how civic education goals can be implemented digitally to foster civic literacy. At first glance, the possibility of reaching a broad audience in a short time seems tempting. At a second glance, social media reveals several challenges that can impair educational processes. The present paper discusses the following questions: What are the opportunities and pitfalls of civic education in social media? How can we ensure successful civic education in a digitalized world? In our article, we want to provide an interdisciplinary perspective on the topic by drawing among others from the literature in the fields of media psychology, communication studies, and education science. By integrating insights from various disciplines, our paper seeks to enrich the academic dialogue and to promote a nuanced understanding of the evolving dynamics of civic education in the digital realm. With its practical focus, our paper further aims to underscore the applicability of scientific research.
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