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introductionthe selected landing site of the exomars mission (oxia planum) [1] shows mineralogical and morphological evidence that it was characterized by a hydrothermal history and by a long duration of aqueous superficial activity [2; 3]. these factors are consistent with conditions favourable to life development. in this framework, we planned a field campaign in the rio tinto [4] area (europlanet ta1 facility 2) where to perform a set of vis-nir measurements using our portable spectrometer. in addition, for each analyzed mineral/rock on-field, we collect a representative sample to be measured with the ma_miss instrument laboratory model. fig.1: ta1.2 rio tinto, south-west spain a very acidic 100 km river with intense red dark colour (credits f. gomez).the ma_miss instrumentma_miss is the visible and near-infrared miniaturized spectrometer hosted in the drill system of the exomars rover that will characterize the mineralogy and stratigraphy of the excavated borehole wall at different depths (<2 m) [5]. ma_miss with a spectral range of 0.5-2.3 μm, a spectral resolution of about 20 nm in the ir, a snr~100, and a spatial resolution of 120 μm will accomplish the following scientific objectives: (1) determine the composition of the subsurface materials; (2) map the distribution of the subsurface h2o and hydrated phases; (3) characterize important optical and physical properties of the materials (e.g., grain size); (4) produce a stratigraphic column that will provide information on the subsurface geology. ma_miss will operate periodically during pauses in drilling activity and will produce hyperspectral images of the drill's borehole.field activityduring the field campaign, we perform a set of vis-nir (0.35 - 2.5 μm) measurements using our asd fieldspec4 portable spectrometer on biosignatures-bearing rocks and acidic alteration products. for each selected lithotype we collect several reflectance spectra using solar light as the light source and a 99% spectralon target as a reference in the vis-nir range, with particular attention to those that hypothetically host organic matter in the form of bacterial communities. in addition, for each measured mineral/rock we collect a representative sample to be used for the laboratory measurements with the ma_miss laboratory model. with this setup, it is possible to perform measurements with samples in different configurations (powders, slabs, or holed rock blocks); hence, we collect samples with different specific dimensions. in the case of incoherent sediments/salts, we sample a minimum amount of 20-30 g. on the contrary, in the case of coherent samples, we collect blocks with a maximum size of 10x10x10 cm, which are the optimal dimensions useful for performing the drilling operations and in-hole measurements with the davis setup [6,7]. for each collected sample, we record the following data at the time of collection: imagery of the context and the sampling site with a reference scale, the three-dimensional orientation of the sample, and the geographic coordinates at the collection point using a gnss dual-frequency gps. every sample is sealed in a specific container to avoid any contamination [8]. the samples' metadata are registered in the system for earth samples registration (sesar) for long-term archival of the physical samples which can be retrieved from a unique isgn code (isgn.org) for referencing in this and future projects.laboratory activitythe collected samples were measured with the davis (drill for analogues and visible-infrared spectrometer) setup at the inaf-iaps laboratories. this laboratory facility is constituted by a drilling tool that reproduces the exomars drill functionality (laboratory drill, ld [6]) and by a measurement tool, reproducing ma_miss optical characteristics (ma_miss optical tool, mot [7]). consisting of spare elements of the flight instrument, the davis setup can be considered an instrument completely comparable to the one that will investigate the martian subsurface. for this reason, the measurements on the collected samples become very important for instrument characterization and future data interpretation. the collected sample blocks are drilled to obtain a hole with the same characteristics as those that the exomars drill will do on mars. finally, we perform a series of in-hole spectral scans to characterize the chemical-physical properties of the collected samples. the data collected on-field and in the laboratory are analyzed and compared to reconstruct the composition of the analyzed samples. we will focus our efforts on any spectral signature related to the presence of biomarkers in the collected data since we know that the ma_miss tool can aid in detecting organics [9] in the martian subsoil, which is one of the main scientific objectives of the exomars mission.conclusionsin this work, we describe the procedures followed during our geological field analysis campaign in the rio tinto area. this geologically/biologically well-documented site with its rock/water/biology interaction represents an ideal open-air laboratory where to collect spectral data and samples useful for testing the exomars/ma_miss spectrometer. the scientific results obtained by this and previous works made with other drilling equipment [10] and with other scientific instruments [11] confirm that this type of activity in the rio tinto area site is important for enriching the scientific community's grasp on the martian environment and for obtaining key information on the mineralogical and geochemical evolution of the martian surface/subsurface. in addition, this work provides crucial preparation for the exploitation and interpretation of the scientific data that the ma_miss instrument will supply during the active phase of the mission. this activity is also useful for defining the priorities of the astrobiological objectives on the ground.acknowledgementsthis work is supported by the italian space agency grant asi-inaf n. 2017-412-h.0. ma_miss is funded by asi and inaf. europlanet 2024 ri has received funding from the european union's horizon 2020 research and innovation programme under grant agreement no 871149.references[1]vago, j.l. et al. (2017) astrobiology; [2]mandon, l. et al. (2021) astrobiology; [3]quantin-nataf, c. et al. (2021) astrobiology; [4]amils, r. et al. (2014) life; [5]de sanctis, m.c. et al. (2017) astrobiology; [6]rossi, l. et al. (2022) 53rd lpsc #1353; [7]de angelis, s. et al. 53rd lpsc (2022) #1796; [8]cockell, c.s., et al. (2019) space sci rev. [9]ferrari, m. et al. (2020), epsc2020-348; [10]bonaccorsi, r. et al (2008) astrobiology; [11]gomez, f. et al., (2011) int. j. astrobiology. | in-situ measurement and sampling of martian analogues in the rio tinto area in support of the ma_miss scientific activity |
observations of the solar photosphere show many spatially compact doppler velocity events with short life spans and extreme values. in the imax spectropolarimetric inversion data of the first flight of the sunrise balloon in 2009 these striking flashes in the intergranule lanes and complementary outstanding values in the centers of granules have line of sight doppler velocity values in excess of 4 sigma from the mean. we conclude that values outside 4 sigma are a result from the superposition of the granulation flows and the p-modes.to determine how granulation and p-modes contribute to these outstanding doppler events, i separate the two components using the fast fourier transform. i produce the power spectrum of the spatial wave frequencies and their corresponding frequency in time for each image, and create a k-omega filter to separate the two components. using the filtered data, test the hypothesis that extreme events occur because of strict superposition between the p-mode doppler velocities and the granular velocities. i compare event counts from the observational data to those produced by random superposition of the two flow components and find that the observational event counts are consistent with the model event counts in the limit of small number statistics. poisson count probabilities of event numbers observed are consistent with expected model count probability distributions. | the coincident coherence of extreme doppler velocity events with p-mode patches in the solar photosphere. |
the minority carrier lifetime is a crucial material parameter in silicon (si) wafers for use in solar cell applications, and precise measurements of carrier lifetime as a function of the excess carrier concentration (injection level) is of high importance. in this paper we present a method for extracting injection-dependent lifetime data with high spatial resolution, without the need for advanced time-resolved camera detection systems. this enables investigations of single grains, grain boundaries and structural defects in wafers with spatially non-uniform lifetime, such as high performance multicrystalline si wafers. the local injection dependent lifetime curves are constructed from a series of photoluminescence images acquired using different steady state generation rates, carefully calibrated by a secondary quasi-steady state photoconductance measurement at a fixed light intensity. the local lifetime has been analyzed by linear parameterization of the shockley-read-hall recombination model and solved for all combinations of defect parameters describing the observed recombination behavior. the recombination parameters found to dominate at high injection corresponds well with published recombination parameters due to cri. | identifying recombination parameters by injection-dependent lifetime spectroscopy on mc-silicon based on photoluminescence imaging |
not available 1. a general overview on the development directions of different egas and typical emission reduction examples for various diesel engine and vehicle applications; 2. the interaction between legislative emission test cycles, combustion system development and the kind of egas used. based on current development work and test results, ranking considerations with regard to the application and development probability of egas are given. the addition of a proprietary zeolite as a hydrocarbon trap and a small amount of pt to the platform ceo 2 catalyst enables european emission standards for co, hc and particulates to be met. commercialization of this technology in europe began in the first part of 1996. the light-off temperatures for carbon monoxide (co) and hydrocarbons (hc) were significantly lower for catalysts with a high platinum loading, as compared to catalysts with palladium and low platinum loadings. the particulate (pm) emission at light load operation was reduced by 75% to 85% with all catalysts due to the high conversion rate of the pm soluble organic fraction (sof). the pm efficiency still increased by 5% at medium load operation, and then started to decrease at a temperature around 550 k due to increased sulfate formation. the sulfate formation could be minimized by a higher space velocity, an optimized washcoat, and a lower platinum or palladium loading, respectively. on the us transient cycle, pm was reduced by 20% to 35% with all catalysts tested. among the two catalysts with 35% efficiency, the low pt catalyst d which produced less sulfate at high temperatures was selected as first choice. deterioration of catalyst d over 2200 h was 8% for pm, 13% for co and 21% for hc. on the european 13-mode cycle, pm was reduced by 9% only with the optimized low pt catalyst g, but increased dramatically with all other catalysts (including those selected for us) due to a considerable sulfate formation. since the sof fraction is lower on this cycle compared to the us transient cycle, the pm removal potential of an oxidation catalyst is generally lower under european certification conditions, and different catalyst technologies will have to be selected for us and european applications. only if rape seed methyl ester (rsme) is used as an alternative to diesel fuel, an oxidation catalyst is an effective means not only for decreasing hc and co, but also pm. a system which is currently being proposed for the simultaneous control of diesel particulate matter and no x emissions involves the use of a cerium fuel-borne catalyst/filter/egr system. this paper describes the principles of operation of rhoˆne-poulenc's cerium fuel-borne catalyst and the factors that govern its use. effects of sulfur dioxide (so 2) and space velocity (sv) have been investigated as part of a strategy to optimize no x removal with lean no x catalysts. elimination of feedgas so 2 can lower no x light off temperature for both pt and cu zeolite. some pt catalysts do not show this behavior. additional evaluation of a cu zeolite catalyst demonstrates that poisoning by feedgas so 2 is reversible during evaluation or aging. this result suggests that if sulfur could be removed from diesel fuel, aged cu zeolite catalysts could be practical. decreasing space velocity will help no x removal over pt by (i) lowering no x light off temperature, (ii) lowering the temperature at which peak no x conversion occurs, (iii) increasing the level of peak no x conversion, and (iv) widening the temperature window for no x reduction. for cu zeolite, decreasing space velocity can help mainly by lowering no x light off temperature and temperature where maximum no x conversion starts. both increased catalyst volume and sulfur removal provide pt catalysts with a no x temperature window that coincides better with low temperatures where most no x mass is emitted. sv effects on lean no x reduction are explained by discussion of possible mechanistic features. all the la 2cu 1 - x pd xo 4 catalysts are activated under reacting conditions. this activation corresponds to the destruction of the mixed-oxide structure, with formation of reduced pd 0 ions atomically dispersed, surrounded by cu + and cu 2+ species on a lanthanum oxycarbonate matrix. this high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial la 2cu 1 - xpd xo 4 structure. after a reductive pretreatment, the pt/coo x/sio 2 catalyst shows a better selectivity to n 2 than ptrh/al 2o 3, while the latter catalyst is more selective to n 2 after an oxidative pretreatment. pt/mno x/sio 2 produces a considerable amount of n 2o, even at a reducing gas mixture. in general, the addition of co 3o 4 or mno 2 to pt/sio 2 leads to more n 2o production at stoichiometric gas mixtures. analysis of the lightoff converter as taken from the vehicle showed a dramatic axial gradient in the lean and stoichiometric lightoff and warmed-up (600°c) performance for hc, co and no x, with most of the deterioration having taken place in the forward-most 1″ section of the converter, which was consistent with the gradient in the deposition of phosphorus (p) and zinc (zn) in this converter. comparison of these data sets with those obtained after removal of the p and zn poisons indicates that most of the total deterioration of lean hc and co activity can be attributed to p and zn poisoning of the forwardmost 1″ section. when tested under stoichiometric conditions, most of the deterioration of hc activity is attributable to p and zn poisoning, while most of the deterioration of co and no x activity is attributable to thermal deterioration. a similar activity and poison deposition gradient was detected in the underfloor converter, but to a smaller extent. the impact of sulfur on the oxygen storage of both warmup and underfloor converter sections was dramatic. sections in the forward part of the warmup converter and in the front brick of the underfloor converter had relatively modest oxygen storage capacity which was almost completely blocked as the sulfur concentration reached 75-150 ppm (equivalent in gasoline). other sections such as the rear of the warmup converter and the rear monolith of the underfloor converter had more oxygen storage capacity, which was significantly decreased as the sulfur concentration reached 150 ppm equivalent in fuel, and was approached complete loss near 500 ppm sulfur equivalent in fuel. a cu/k/mo-catalyst as a coating on small segments of a wall flow monolith downstream of a diesel engine showed a relatively low activity. besides, the catalyst was found to deactivate rather fast, which corroborated the outcome of the above mentioned model study. as a result, the feasibility of this cu/k/mo-catalyst for use in practical applications is low due to a progressive loss of catalytic material by high vapour pressures of active components formed by solid-solid reactions of less volatile compounds present in the catalyst. the composition of these catalysts, suitable for greatly accelerating the combustion of carbonaceous materials, was investigated by x-ray diffraction (xrd), fourier transformed infrared spectroscopy (ftir) and scanning electron microscopy (sem). their activity in the combustion of amorphous carbon was assessed by differential scanning calorimetry (dsc). the latter showed that the combustion peak temperature can be decreased from 617°c (uncatalysed oxidation) down to 382°c for the best prepared cu sbnd k sbnd v catalyst (atomic ratio: cu:k:v = 2:2:1). the results of activity tests and the identification of the compounds present in the catalyst samples suggested that the catalyst activity is mainly due to the synergic action of some vanadates (cu 3(vo 4) 2, kvo 3, k 0.7cu 0.3vo 3, cuvo 3) and chlorides (kcl, cu 2(oh) 3cl). other catalysts based on each of these vanadates + kcl were prepared, characterised and tested, getting slightly lower activities than that of the best cu sbnd k sbnd v catalyst. on the basis of the obtained results the presence of liquid eutectic phases (whose formation was detected via dsc runs performed in the absence of carbon) is found to be a key factor in determining the catalytic activity of all tested catalysts since it dramatically improves the catalyst-carbon contact. once liquid phases are formed at suitable temperatures (ranging from 330 to 480°c depending on the catalyst nature), the catalytic combustion likely proceeds according to redox mechanisms. a delaminated pillared clay was subjected to cu 2+ ion-exchange and studied for scr by c 2h 4 in this work. the cu 2+ ion-exchanged delaminated al 2o 3-pillared clay yielded substantially higher scr rates than both cu 2+-exchanged tio 2-pillared clay and cu 2+-zsm-5 at temperatures above 400°c. the peak no conversion was 90% at 550°c and at a space velocity of 15,000 h -1 (with o 2 = 2%). the peak temperature decreased as the concentration of o 2 was increased. the macroporosity in the delaminated pillared clay was partially responsible for its higher peak temperatures (than that for laminated pillared clays). at 1000 ppm each for no and c 2h 4, the no conversion peaked at 2% o 2 for all temperatures. h 2o and so 2 caused only mild deactivation, likely due to competitive adsorption (of so 2 on cu 2+ sites and h 2o on acid sites). the high activity of cu 2+-exchanged al 2o 3-pillared clay was due to a unique combination of the redox property of the cu 2+ sites and the strong lewis acidity of the pillared clay. the suggested mechanism involved no chemisorption (in the presence of o 2) on cu 2+ sbnd o sbnd al 3+-on the pillars, and c 2h 4 activation on the lewis acid sites to form an oxygenated species. it was further observed that not all cu cations exchanged into mfi catalysts have equivalent catalytic activity for no scr, which made the existence of different copper environments on cumfi catalysts evident, isolated cu 2+ ions being the most active species for no scr by propene. moreover, the results showed an improvement of the cumfi catalytic activity at low temperatures by increasing the catalyst copper exchange level and, consequently, decreasing the number of brönsted acid sites, which can be performed either by increasing the zeolite si/al ratio or copper loading. it was found that the isolated cu 2+ ions are the most effective species for no adsorption and the most active species for no scr. the performance of the catalyst peaked for t s around 400°c. for t s<300°c, the presence of catalyst material on the substrate could be deduced with tem only from the grainy appearance of the support, but for higher t s, mos 2 was seen arranged with its basal planes normal to the support. xps revealed increased concentrations of mo 4+, as mos 2, with rising t s. the co 2 p 3/2-s 2 p binding energy splitting increased from 616.0±0.2 ev at t s=200°c to 617.3±0.1 ev at t s=350°c, indicating that the co increasingly decorated the edges of the mos 2. using the selected catalyst, trichloroethylene photocatalytic oxidation tests showed complete mineralization at operating temperatures between 80°c and 110°c, and residence times lower than 0.03 s without any thermocatalytic contribution. although toluene did not reach appreciable photoactivity between 130°c and 200°c and a residence time of 0.06 s, this compound can be completely oxidized between 250°c and 300°c with the help of infrared radiation without significant production of by-products. consequently, the operating conditions needed to achieve the complete mineralization of the voc by photocatalytic oxidation are strongly dependent on the type of compound to be removed. realistic industrial claus conditions imply, in addition to cs 2 and h 2o, the presence of h 2s, so 2 and o 2 traces in the feed. it appears that the presence of o 2 traces in the cs 2-h 2o mixture brings about a decrease in activity of the alumina and titania. this is due to sulfate formation as shown by the ir analysis of the catalysts after the reaction. moreover, ir studies evidence that sulfate species are reduced by h 2s at 320°c on tio 2, contrary to results obtained on al 2o 3, explaining why tio 2 is much more effective than al 2o 3 when the cs 2+h 2o feed also contains h 2s and o 2 traces. the decomposition of mtbe into methanol and i-butene (2-methyl-1-propene) was kinetically significant at these conditions. both methanol and i-butene were present in the effluent from the catalyst at all operating conditions. carbon dioxide and water had no significant effect on the kinetics of mtbe disappearance. the rate of mtbe destruction was faster than the oxidation of i-octane. the main contributions to the previous knowledge are the following: it is possible to distinguish co bound to isolated and non-isolated cu + ions; the isolated cu 2+ ions are reducible under vacuum without participation of organic impurities; the more active solids for the no reduction into n 2 are characterized by the presence of isolated cu n+ ions beside the additional influence of the zeolitic framework; after the formation of cu + ions the redox cycles are reversible but, after the formation of cu 0, the reversibility or irreversibility of the redox cycles and the restoration of the scr activity are function of the copper content; the activity decreases after agglomeration into bulk oxides; there is no formation of bulk cuo during the reaction and, with reducing and moderate oxidizing mixtures, part of the copper remains as cuprous ions. the catalysts have shown high activity towards both co-o 2 and no-co reactions. the same order of activity of catalysts sb800<sb1000<sb1050<sb1150 has been established for both reactions. the activity of catalysts has been correlated with the amount of (cu+co) engaged as a cu-co spinel phase which increases in the same order. in the case of co-no reaction, the `onset' temperatures for the co-o surf reaction is lower than that for the co-no reaction itself. at temperatures above 240°c, the co-no reaction is affected by the competition of co-o surf reaction. it has been suggested that the low-temperature (below 200°c) mechanism of no-co reaction includes formation of (no·co) * complexes which is the rate-limiting step. a comparison with a wo 3/tio 2 catalyst having similar molar composition indicates that the wo 3- and moo 3-containing samples exhibit similar structural and morphological characteristics, but different reactivity: the wo 3/tio 2 sample is less active but more selective in the scr reaction. on the basis of epr data, the different catalytic behavior has been tentatively ascribed to the different redox characteristics of the samples. a high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high sio 2:al 2o 3 ratio, enhances the conversion of no. a vibrational band at 1631 cm -1 is observed below the light-off temperature and interpreted as a bridged nitrato group bound to cu 2+-o-cu 2+ dimers. this band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. we interpret that these bridge bound nitrato groups act as siteblockers on the active sites for no conversion and that a tentative reaction intermediate, n 2o 3, also binds in a bridge configuration to the same cu 2+-o-cu 2+ dimers. a second nitrato group with unidentate coordination and vibrational bands at 1598/1575 cm -1 probes isolated copper ions. a third infrared band at 2130 cm -1 confirms previous observations of no + 2-ions bound to the zeolite. we conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for no + 2 adsorption are blocked by cu 2+ ion-exchange. the 2130 cm -1 species appear to have no role in direct no decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice. prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers. a high sio 2:al 2o 3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. excessive amounts of copper escalates the deactivation of the cu-zsm5 catalyst through the migration and sintering of cupric oxide crystallites. for inlet feed streams between 50 and 1600 ppm of tce in humid air, overall destruction levels were typically above 99%. also, since the falling furnace system required heating only during the desorption/reaction portion of the process (5-10% of the cycle time), energy comparison with conventional catalytic reactors is extremely favorable. the selectivity for no abatement, reaction orders in o 2, no or ch 4, and apparent activation energy were independent of the manganese content, suggesting that the same surface complexes were formed on all mn-zsm5 catalysts. on mn-zsm5, turnover frequencies (molecules s -1 mn-atom -1) for both no abatement and ch 4 reaction were nearly independent of the manganese content and close to the relevant values on co-zsm5 (previously investigated in our laboratory), but substantially higher than those on cu-zsm5 (cu percent exchange 98%, studied for a comparison). on mn-zsm5, co-zsm5 and cu-zsm5, the adsorption at rt of no+o 2 or no 2 caused the formation of nitrates. the normalised intensity (per atom) of monodentate nitrate bands (∼1520 and ∼1320 cm -1) was (i) independent of the metal content, (ii) the same in mn-zsm5 and co-zsm5, and (iii) much higher in mn-zsm5 and co-zsm5 than in cu-zsm5. on all these catalysts, no abatement rates were proportional to the concentration of these monodentate nitrates. on ftir evidence, these species reacted with methane at the same temperature at which the various catalysts were active. these findings suggest a role of monodentate nitrates in the scr reaction. on the basis of the obtained results the csvo 3+kcl catalyst was found to allow the best compromise between satisfactory catalyst activity and stability. at lower temperatures, no is adsorbed as nitrates and the nh 3 adsorption as coordinated nh 3 species is enhanced. these two factors drive the activity decrease. the turnover frequency for sulfur dioxide oxidation was very low, 10 -4 to 10 -6 s -1 at 400°c, and was independent of vanadia coverage suggesting that only one vanadia site is required for the oxidation reaction. as the support was varied, sulfur dioxide oxidation activity of the supported vanadia catalysts varied by one order of magnitude (ce>zr, ti>al>si). the basicity of the bridging v-o-m oxygen appears to be responsible for influencing the adsorption and subsequent oxidation of the acidic sulfur dioxide molecule. over the range of conditions studied, the rate of sulfur dioxide oxidation is zero-order in oxygen, first-order in sulfur dioxide and inhibited by sulfur trioxide. the turnover frequency for sulfur dioxide oxidation over wo 3/tio 2 was an order of magnitude lower than that found for v 2o 5/tio 2, and no redox synergism between the surface vanadia and tungsten oxide species was evident for a ternary v 2o 5/wo 3/tio 2 catalyst. this suggests that wo 3 promoted catalysts may be suitable for low-temperature scr where minimal sulfur dioxide oxidation activity is required. by using relatively large amounts of catalyst in the large semi-pilot reactor, it was possible to maintain high conversions for up to 50 h without appreciable carbon deposition in the bed. however, the activity of the catalyst for the water gas shift reaction declined progressively with process time. this deactivation effect was reversed by treatment with steam over prolonged periods, leading to the speculation that shift activity is poisoned by exposure to hcl in the product. this process offers an attractive alternative to conventional technologies (thermal incineration and catalytic combustion) for the destruction of chlorocarbons used as industrial solvents or found in waste streams, and applicable process conditions are given. we found that using copper acetate solutions with concentrations in the range 0.008 m≤[cu 2+]≤0.1 m, both at room temperature and at 323 k, it is very easy to prepare over-exchanged cu-zsm-5, cu-s-1 and cu-msa catalysts. xrd and vis-uv drs techniques show that after thermal treatments of the fresh samples in air at 823 k for 4 h no segregation of cuo phase occurs, suggesting the presence of low nuclearity [cu no x(oh) y] q+ species (q=2(n- x)- y≥0). these results were confirmed by tpr studies. at 773 k only over-exchanged cu-zsm-5 catalysts showed no decomposition activity (no 1% in he, w/ f=0.1 gs/cm 3) with a turnover frequency essentially determined by the si/al ratio, in agreement with previous literature data. instead, the activity of cu-s-1 and cu-msa catalysts was not measurable under our experimental conditions. the present results confirm that the framework topology and the presence of framework alo - 4 species are fundamental to develop active copper species for no decomposition. it is demonstrated that the active sites in cu-zsm-5 consist of copper species strongly anchored to framework alo - 4 species. the most active sites, as they occur only on zsm-5 support with the lower si/al atomic ratios, might consist of dimeric cu species (cu +⋯cu 2+⋯o -) strongly anchored to next-nearest-neighbour framework alo 4 - species. it has been found that the activity of these solids is directly related to the reducibility of cobalt, thus indicating that the reaction is carried out by a redox mechanism. potassium plays different roles in these catalysts: (i) it increases the catalyst-soot contact by increasing surface mobility, (ii) it preserves the reducibility and dispersion of cobalt by improving stability against thermal treatments, and (iii) it favors the oxidation of soot by consuming the carbon to form carbonate species during soot combustion. it was also found that soot with a higher content of sulfur (1050 ppm) is more efficiently burned than that containing low amounts of sulfur (70 ppm). however, the severe sulfation of the catalyst leads to a noticeable loss of activity. in experiments of carbon monoxide oxidation, it was found that conversion is practically total between 400°c and 500°c under the conditions used in this work. the direct impregnation of the soot with either co or co and k, showed lower combustion temperatures if compared with the mechanical mixtures of soot and co/mgo or co,k/mgo, suggesting that the soot-catalyst contact poses a physical limitation on the oxidation activity. this important result suggests that the soot-catalyst contacting problem is the main difficulty to be overcome in order to obtain useful catalysts. all research effort towards developing catalyst formulations will be unable to reduce the temperature for combustion until this problem is solved. the non-chlorinated polyaromatic compounds (including non-chlorinated dibenzodioxin and dibenzofuran) are destroyed at temperatures as low as 150°c with an efficiency of more than 95%. pcdd and pcdf were also removed from the gas phase with an efficiency of >98%. however, at 150°c they remained mainly unchanged (up to 75%) adsorbed on the catalyst. a decrease in the oxidation rate with increasing chlorine substitution was found for the pcdd/pcdf. this could be explained by an increasing "redox potential" with increasing chlorine substitution due to the electron withdrawing effect of the chlorine. for the more volatile monoaromatic pcbz, however, the effect of lowering the volatility with increasing chlorine substitution (resulting in longer residence time on the catalyst) over-compensates the effect of the increasing "redox potential" with higher degree of chlorination. the results of this study strengthen the possible benefit of the lack of a gaseous reducing agent (such as ammonia or hydrocarbons) since the reduction of no x is performed by the carbon support itself. from experimental results, under the condition of 7.5 g/l tio 2, ph 3, and light intensity of 2.25 mw/cm 2, 0.1 mm of substituted phenol could be completely decomposed in 2 h. the reaction was found to be apparent first-order following langmuir-hinshelwood model. in the presence of chloride ions, a significant inhibition of reaction was found at ph 3, but not at higher ph levels. at ph 3, a slight inhibition was found for nitrate ions, but uncertain for sulfate ions. for the experiment with co-existing 2-chloro and 2-nitrophenol, the result differed from that of the individual specie. in the mineralization experiments, substitution in the phenol ring had no applicable influence on the reaction rate, however, complete mineralization to carbon dioxide could not be completed within 9 h. bromomethanes degrade through combined reductive and oxidative processes. the importance of reductive pathways decreases from cbr 4 to chbr 3 and ch 2br 2. brominated and oxygenated intermediates have been quantified until complete degradation or debromination was achieved. reactions accounting for the observed results are presented based on presumed transient species and identified intermediates. the effect of hole and electron scavengers was evaluated on chbr 3 and ch 2br 2 to elucidate the importance of reductive and oxidative pathways. electron scavengers as periodate, enhance the rate of disappearance for ch 2br 2. the hole scavengers as alcohols, have limited effect on the degradation rate of chbr 3 but interestingly, have different effects on the degradation rate of ch 2br 2. tert-butanol does not significantly affect the degradation rate whilst methanol increases it. methanol generates radicals that efficiently react with ch 2br 2, notably if the system is oxygen-free. hydrolysis of these titanium 1,2-diolates in water was a simple way to produce high surface porous titania with bet surface area up to 300 m 2 g -1. these as-synthesised titania contain anatase crystallites and show photocatalytic activity versus formaldehyde degradation prior to calcination. nevertheless, the decomposition rate of formaldehyde increased notably when titania samples were annealed at 773 k. this thermal treatment increases their crystallinity at the expense of a bet surface area decrease down to 75 m 2 g -1 or less. the photocatalytic performance of the annealed samples is superior than that of commercial tio 2 (degussa p-25, hombikat uv-100). conversion of ch 3cl over pt follow first-order kinetics, with a rate constant that follows the arrhenius equation over a wide temperature range. product compositions support a reaction network in which a consecutive steam reforming-water gas shift sequence occurs in parallel hydrogenolysis. the qualitative dependence of these reactions on process conditions were studied and it was found that shift and hydrogenolysis activities decreased as the temperature increased but increased with high concentrations of ch 3cl. platinum was equally effective for the conversion of ch 3ccl 3, chclccl 2, and ccl 2ccl 2, except that no hydrogenolysis was detected. extremely high levels of destruction (>0.99999) were maintained for periods over 20 h without carbon formation or catalyst deactivation other than a progressive loss of shift activity. isotopically labeled oxygen was used to discriminate between possible reaction schemes. the isotope distribution indicates that initially, co mainly reacts with oxygen from the catalyst, even on the pre-reduced sample. however, it was difficult to draw unambiguous conclusions from the isotope distribution, since there is likely also isotope exchange. the presence of water in the feed had no large influence on the total activity for co 2 formation at low temperatures, but it altered the isotope composition of the co 2 formed, since some co is oxidized by water instead of by oxygen. at temperatures above 140°c, water did increase the total co oxidation activity by the wgs reaction. pt and pd catalysts had the highest no decomposition activity (n 2 production > 80%) among the tested metal catalysts. kinetic analysis was realized in a suitable temperature range for each catalyst, and activation energies of 91, 55, 18, and 14 kj mol -1 were found for pd, pt, ru, and rh, respectively. all the catalysts showed good activity in no reduction by ethylene in a non-oxidizing atmosphere (no-c 2h 4), giving around 70-90% n 2 production. the following activity scale: pt < rh < pd < ru was individualized. catalytic activity decreased with increasing o 2concentration for all the catalysts. a kinetic interpretation of the collected data permitted evaluating the ratio between the rate constants of the o 2-c 2h 4 to no-c 2h 4 reactions. on this basis, a scale of catalyst activity reflecting the ability of reducing no in high oxidizing atmosphere was individualized: ru ⪡ pd <pt < rh. a new porous glass material (vycor) has been found to be a promising carrier for platinum in the selective hydrogenation of ccl 4 to chcl 3 ensuring high selectivity and durability. palladium on alumina showed the best performance in the deep dehalogenation of chcl 3 and ch 2cl 2 to ch 4 and hcl. chlorobenzene dehalogenation is a fast reaction with many catalytic systems. however, palladium catalysts produce mostly c 6h 6, whereas platinum ones induce overhydrogenation to cyclohexane. a comparison of reductive and oxidative processes for chloromethane disposal is presented. the activity of the pt/fe/al 2o 3 catalyst was greater than that of the pt/al 2o 3 catalyst after the o 2-h 2-o 2 treatment for the stoichiometric mixture. also, the activity of the pt/fe/al 2o 3 catalyst after the o 2-h 2 treatment was greater than that after the o 2 and o 2-h 2-o 2 treatments. pt particles were found to react with fe additives to form homogeneous pt/fe alloy particles on al 2o 3 under reducing conditions. also, the pt/fe alloy particles on al 2o 3 were found to segregate into pt and fe 2o 3 and to form a fe 2o 3 coverage layer on pt particles so that pt particles were prevented from sintering when heated at 800°c for a lean mixture. on the other hand, the activity of the pt/al 2o 3 catalyst was greater than that of the pt/fe/al 2o 3 catalyst after the o 2-h 2-o 2 treatment for lean mixture. the layer of fe 2o 3 on pt is responsible for the low activity. scr activities were found to depend mainly on the vanadia loading and the support material. high loadings of dispersed vanadia (6-10 μmol m -2) were favourable on all aerogel supports. vanadia grafted on titania aerogel was superior in activity compared to vanadia deposited on the other aerogels. v 2o 5-sio 2 as well as v 2o 5-tio 2-sio 2 catalysts showed significant deactivation at temperatures ca. >500 k. deactivation of vanadia deposited on tio 2-sio 2 could be avoided at loadings ca. >6 μmol m -2. deactivated catalysts showed a decrease in both brönsted as well as lewis sites, as revealed by desorption studies after exposure to scr conditions. for 2,4,6-trichlorophenol (tcp), an increase in the molar influent concentration resulted in a decrease in removal efficiency but in an increase in removal rate. the degradation rate of 2,4,6-tcp followed a saturation type dependancy with the effluent concentration, suggesting a langmuir-hinshelwood (l-h) reaction rate equation. a l-h equation was employed to determine the reaction rate constant and the adsorption coefficient for 2,4,6-tcp. the photonic efficiency increased from 0.68% at an influent concentration of 0.13 mmol/l to 2.06% at an influent concentration of 1.0 mmol/l. thermal ageing and water vapour in the feed caused a modest decrease in activity and did not affect the cuo x-ceo 2/al 2o 3 and cumn 2o 4/al 2o 3 catalysts differently. in addition, no difference in intermediates formed over the two catalysts was observed. characterisation with xrd, ft-raman and tpr indicates that the copper oxide is present as a copper aluminate surface phase on alumina at low loading. at high loading, bulk cuo crystallites are present as well. modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk cuo crystallites associated to the ceria, in addition to the two copper oxide species on the bare alumina. the distribution of copper species depends on the ceria and copper oxide loading. the alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of crystalline cumn 2o 4 and mn 2o 3, respectively, on al 2o 3. specific surface areas of perovskites were in the range 13-20 m 2 g -1. xrd analysis showed that lamno 3, ndmno 3, smmno 3 and sm 1- xsr xmno 3 (x = 0.1) are single phase perovskite type oxides. traces of sm 2o 3 besides the perovskite phase were detected in the sm 1- xsr xmno 3 catalysts for x = 0.3, 0.5. chemical analysis gave evidence of the presence of a significant fraction of mn(iv) in amno 3. the fraction of mn(iv) in the sm 1- xsr xmno 3 samples increased with x. tpr measurements on amno 3 showed that the perovskites were reduced in two steps at low and high temperature, related to mn(iv) → mn(iii) and mn(iii) → mn(ii) reductions, respectively. the onset temperatures were in the order lamno 3 > ndmno 3 > smmno 3. in sm 1- xsr xmno 3 the sr substitution for sm caused the formation of mn(iv) easily reducible to mn(ii) even at low temperature. catalytic activity tests showed that all samples gave methane complete conversion with 100% selectivity to co 2 below 1023 k. the activation energies of the amno 3 perovskites varied in the same order as the onset temperatures in tpr experiments suggesting that the catalytic activity is affected by the reducibility of manganese. sr substitution for sm in smmno 3 perovskites resulted in a reduction of activity with respect to the unsubstituted perovskite. this behaviour was related to the reduction of mn(iv) to mn(ii), occurring under reaction conditions, hindering the redox mechanism. such a reaction demonstrated that complex aromatic water pollutants, originating either from industry or from biomass, could be totally mineralized and that they could produce clean water. hydrodechlorination experiments were carried out in discontinuous micro-reactors at 50 bar of hydrogen and at 300°c, and during reaction times of 30, 60 and 90 min, using 4 vol% solutions of the organochlorinated compounds in heptane. pt catalysts were found to yield the highest conversions for the reactions studied. the co-feeding of hydrocarbons invariably reduced the output of polychlorinated benzenes, which are formed as byproducts in the combustion of chlorobenzene on pt/γ-al 2o 3. again, especially toluene, ethene, and 2-butene were very efficient. benzene - as well as cyclohexane, cyclohexene, and 1,4-cyclohexadiene, which were converted in situ into benzene - was much less effective, due to chlorination of the aromatic nucleus. in chlorobenzene-co mixtures the levels of polychlorinated benzenes were almost as high as with chlorobenzene per se. removal of cl from the surface (mainly in the form of hcl) by (non-aromatic) hydrocarbons is responsible for reducing the formation of byproducts. catalytic wet air oxidation (cwao) of phenol and of acrylic acid (160°c and 20 bar of o 2) was investigated over these catalysts and their performance (activity, selectivity to intermediate compounds) compared with that of a reference ru/ceo 2 catalyst. carbon-supported catalysts were very active for the cwao of phenol but not for acrylic acid. although high conversions were obtained, phenol was not totally mineralized after 3 h. it was shown that acrylic acid was more strongly adsorbed than phenol. moreover, the number of contact points between ru particles and ceo 2 crystallites constitutes a key parameter in these reactions. a high surface area of ceria is required to insure o 2 activation when the organic molecule is strongly adsorbed. product distributions indicated two parallel catalytic reactions: steam reforming, leading to complete destruction of the aromatic ring and production of h 2, co, co 2, and hcl; and hydrogenolysis, giving less chlorinated aromatic intermediates, c 6h 6 and hcl. the aromatic intermediates further react by steam reforming. platinum was found more selective towards c 6h 6 formation than ni, with selectivity increasing at lower temperatures. comparisons between c 6h 11cl and c 6h 5cl revealed that saturation of the ring increases the rate of overall dechlorination. above 596°c for ni and 650°c for pt, reactivities increase for higher chlorine levels of the aromatic ring. the catalysts have been tested for the selective reduction of no x with iso-c 4h 10 under o 2-rich conditions and in the absence of o 2, both with dry and wet feeds. a bifunctional mechanism appears to operate at low temperature: oxo-ions or co 3o 4 clusters first oxidize no to no 2, which is chemisorbed as no y (y≥2) and reduced. in this modus operandi catalyst sub shows the highest n 2 yield ∼90% near 390°c for dry and wet feeds. it is found to be quite stable in a 52 h run with a wet feed. in contrast, the wie catalyst, which mainly contains isolated co 2+ ions and has poor activity below 400°c, excels at t>430°c. this and the observation that, at high temperature, no is reduced in o 2-free feeds over co/mfi catalysts, suggest that no can be reduced over co 2+ ions without intermediate formation of no 2. the bifunctional mechanism at low temperature is supported by the fact that a strongly enhanced performance is obtained by mixing wie with fe/fer, a catalyst known to promote no 2 formation. the reaction rate seems to be first-order with respect to no and zero-order with respect to nh 3. a langmuir-type dependence between no conversion and oxygen concentration was observed. correlation between chemical composition, textural, structural and redox properties of the oxides is reported. while for pure ceria almost no reducibility occurs below 773 k, mixed oxides, independently of their composition, exhibit an oxygen storage and buffering capacity at low temperature, which remains stable even after several oxidation/reduction cycles. this improvement with respect to ceo 2 is remarkably high in the oxides with high zirconia content and is not affected by worsening of textural properties induced by redox-aging. phase transformation and/or structural modification are detected as a consequence of the redox treatments, which could be at the origin of such effects. the catalytic properties of pd-gf cloths were evaluated as a function of pd loading as well of chemical composition of the glass, specific surface area and weaving mode of the fibrous support. investigated catalysts showed the same level of specific activity (per g pd) as conventional powdered catalysts for liquid-phase hydrogenation of nitrites but their activity for nitrates was about one order of magnitude lower. the nitrite and nitrate removal activities were independent of the catalyst structure; the formation of ammonium ions was highly sensitive to reactant concentration. the stability of pd-gf cloths is discussed. a novel technique based on photocatalysis to eliminate cr(vi) ions, a toxic pollutant in the environment, was applied. the photoreduction of cr(vi) to cr(iii) ion in aqueous suspensions using new-mixed oxides as photocatalysts (cr 2o 3·moo 2.5, co 2o 3·moo 2.5, nio·moo 3, and cuo·moo 3) under air-equilibration and irradiation by a medium pressure mercury lamp (uv-vis) was investigated. tdpac characterization indicates the presence of two in species both in the monometallic and in the bimetallic catalysts: in 2o 3 and (ino) +z - (in at exchange positions), the latter being the active in species for the reaction under study. tpr results also suggest the presence of highly dispersed non-crystalline in oxide species not bonded to the zeolite matrix. neither exafs results nor tdpac characterization show the presence of intermetallic pt-in species. the results of this work prove that exafs and tdpac techniques, combined with tpr and activity measurements, are powerful tools for the characterization of bimetallic catalysts. characterization by xrd, h 2-tpr, and ftir reveals that wie contains isolated co 2+ and (co-oh) + ions that are only reducible at 700°c. sub catalysts show additional tpr peaks at low temperature, including a feature at 220-250°c, ascribed to multinuclear co oxo-ions. the formation of an no y chemisorption complex is most rapid on these catalysts. no oxidation states between co 0 and co 2+ are detectable; the one-step reduction of co 2+ to co 0 clusters could be a cause for the unique propensity of co/mfi to reduce no x with ch 4. the effect of the temperature and h 2/cfc ratio were also studied. the main conclusion is that the cl coverage decreases with the concentration of h 2 and, associated herewith, the selectivity for cl-containing products, in particular chcl 2f, decreases; selectivity for methane and alkanes is not very much affected by the conditions studied. the results show that the dehalogenation reactions do not occur according to serial kinetics and that the alkane formation takes place according to a parallel pathway. apparently, the same reaction network applied in the hydrogenolysis of dichlorodifluoromethane [e.j.a.x. van de sandt, a. wiersma, m. makkee, h. van bekkum, j.a. moulijn, recl. trav. chim. pays-bas 115 (1996) 505] can explain the product spectra of the hydrogenolysis of ccl 3f, considering that the key carbene intermediate (cclf 2 rad) is not so stable as difluorocarbene, key intermediate in ccl 2f 2 hydrogenolysis. methanol, acting as a hole scavenger, strongly increases the rate of disappearance for ccl 3br and cbr 3f. in this study, the deactivation of sulfided red mud as a catalyst for the hydrodechlorination of tetrachloroethylene at 100 bar and 350°c was studied. the variation of conversion with reaction time was determined in the presence and absence of carbon sulfide in the feed, a notorious increase in the catalyst life being observed in the presence of carbon sulfide. fresh and used catalysts were characterised by nitrogen adsorption, x-ray diffraction, scanning electron microscopy and x-ray dispersion spectrometry. an increase in the specific surface and chlorine surface concentration of the catalyst and a decrease in sulphur surface concentration were observed, as well as crystallographic changes in iron species. transmission electronic microscopy analyses indicated that before ozonation of sa, ruthenium was distributed within the whole volume of the grain of ceo 2 for the ae catalyst, and included only in an external layer for the i catalyst. the size of the particles determined by x-ray diffraction (xrd) was around 3.5 nm for ru and in the range 10-75 nm for ceo 2. in most cases, the catalytic ozonation induced ru sintering with the formation of clusters. after four successive ozonation experiments the ae catalyst efficiency was significantly decreased and the structure totally disorganized. pt(iv) nitrate solution is prone to hydrolysis upon dilution forming an amorphous reddish-brown precipitate pto 2· xh 2o. pt nitrate has more complete adsorption on alumina than h 2ptcl 6 with no significant change of pt coordination and oxidation state observed upon adsorption. upon calcination to 500°c, pt complexes undergo structural changes but remain as pt(iv). h 2 tpr of pt nitrate on alumina is consistent with pt(iv) to pt metal reduction. the rapid and strong adsorption of pt nitrate results in pt depositing only at the outer surface of catalyst washcoats, in sharp contrast to uniform distribution from h 2ptcl 6. pt/rh three-way catalysts made from pt nitrate/rh nitrate have equivalent light-off but better hydrocarbon, co and no x conversions than those made from h 2ptcl 6/rhcl 3 solutions. co chemisorption reflected a 'palladium site blocking' by tin species in both kinds of catalysts and indirectly indicated the generation of palladium-tin ensembles. in case of the csr preparation the palladium is alloyed by metallic tin. the palladium surface is diluted by tin atoms, i.e. bimetallic pdsn x ensembles are generated which are able to adsorb and activate nitrate ions. there is an optimum of tin loading, i.e. the activity decreases and the undesired ammonium production in a site reaction increases when the surface becomes too tin rich. sn(ii) species, being preferentially present in catalysts obtained by sncl 2 impregnation also strongly modify the chemisorption properties of the palladium surface, but obviously these species inhibit the nitrate reduction on the bimetallic pdsn ensembles, which are also present in these catalysts. after reaction, the pd/sio 2 and pd-au/sio 2 catalysts contain dissolved carbon. hydrogen treatment of carbonized pd-au/sio 2 catalysts removes this carbon. xrd study of the regenerated samples shows no change in the structure and composition of pd-au phase, compared to freshly prereduced bimetallic catalysts. in this context, the resulting ann model is used as a "black-box" to approximate the complex non-linear conversion rate of the wet oxidation coke. the conversion rate is thus, expressed in terms of the tpo ramp temperature, running oxygen concentration, wet oxidation temperature, and phenol oxidation time. the proposed ann-based modeling approach proved to be an accurate, reliable and effective tool for the quantification of the coke burn-off kinetics. the method has then great potential as a means to compensate for the lack of efficient phenomenological kinetic modeling techniques. it can also be used in the design of regenerative units downstream of catalytic wastewater treatment reactors based on wet oxidation. the addition of water to the feed stream did not alter the activity order of the zeolites observed in dry conditions. better conversions were anticipated over h-mor and h-zsm-5 at low temperatures and excess of water concluding that both oxygen and water accounted for the tce destruction. in contrast, h-y showed a low activity in humid air due to its strong hydrophilic character. it was found that water promoted the formation of co 2 and limited the generation of undesired chlorinated by-products (cl 2 and c 2cl 4). xrd analysis indicated that h-zsm-5 was the most resistant zeolite to dealumination by chlorination. the co scrambling was found to be most rapid over pt, while the adsorption and dissociation of no was most extensive over rh; in the no reduction by co the weak co activation over rh was overwhelmed by the strong no dissociation. on the other hand, the extensive no adsorption and dissociation over rh hindered the dissociation of hydrogen, which resulted in the lowest activity in the no reduction by h 2 accompanied by an intermediate formation of n 2o. this was not the case with pt, over which easily dissociated hydrogen reacted with probably molecularly adsorbed no. the reduction of n 2o by hydrogen proceeded readily over all metallic clusters at room temperature, being thus, either of the same activity as that of no+h 2 reaction, or even of higher activity over pd and especially over rh. the easy reduction of n 2o by hydrogen does not agree with the reduction by co, which was found to proceed worse than that of no. in some cases, also bimetallic species (ptrh/nax, ptpd/nax, pdrh/nax) were employed, as well as oxidized m clusters. the fe-compound on the aged pt/ba/fe/al 2o 3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the pt/ba/al 2o 3 catalyst without the fe-compound. xrd and edx show that the fe-compound inhibits the growth in the size of baso 4 particles formed on the pt/ba/fe/al 2o 3 catalyst under oxidizing conditions in the presence of so 2 and promotes the decomposition of baso 4 and desorption of the sulfur compound under reducing conditions. in order to study the causes of deactivation, fresh and used catalysts were characterised by nitrogen porosimetry, x-ray diffraction, transmission electronic microscopy, thermogravimetry, x-ray photoelectron spectroscopy, temperature-programmed oxidation and temperature-programmed reduction. characterisation results indicate that the deactivation is caused mainly by the formation of carbonaceous deposits. these studies indicated that the major source of permanent deactivation is loss of platinum surface area due to crystallite sintering and encapsulation caused by phase transition in the support. chlorine poisoning decreases the water gas shift activity but not the main reaction. however, chlorine saturation of the surface deters steam from removing carbon and maintaining a clean catalyst. coke formation only becomes significant as these other factors enlarge the reaction zone and provide the opportunity for pyrolysis and hydrogenolysis reactions to occur within the pores. no was decomposed into n 2o and n 2 accompanied with the formation of so 2; this serious oxidation of lattice sulfur resulted in the deactivation of the catalysts. the addition of co to the no stream suppressed so 2 formation and yielded cos instead. a stoichiometric conversion of no and co to n 2 and co 2 was observed above 350°c on the como and the femo catalysts. although the co addition lengthened catalyst life, it was not enough to maintain activity. after the noco reaction, an xps analysis showed the growth of mo 6+ and so 4 2- peaks, especially for the sulfided femo/al 2o 3; the femo catalyst underwent strong oxidation in the noco reaction. the no and the noco reactions proceeded non-catalytically, consuming catalyst lattice sulfur to yield so 2 or cos. the addition of so 2 in the noco system enabled in situ regeneration of the catalysts; the catalysts oxidized through abstraction of lattice sulfur experienced anew reduction and sulfurization through the so 2co reaction at higher temperature. no and so 2 were completely and catalytically converted at 400°c on the sulfided como/al 2o 3. by contrast, the sulfided femo/al 2o 3 was easily oxidized by no and hardly re-sulfided under the test conditions. oxidation states of the metals before and after the reactions were determined. silica and titania-supported como catalysts were also evaluated to study support effects. the non-poisoned catalytic filter showed destruction and removal efficiencies for pcdd/pcdf and the "toxic equivalents" (teq) of more than 99%. the laboratory comparison confirmed this activity did not decrease after 2 years of operation in a municipal waste incinerator. the laboratory test provides a deep insight into the dependence of both the removal and destruction of semivolatile compounds in relation to their physical and chemical properties because it excludes any interfering adsorption effect of dust particles from the flue gas stream. the catalytic decomposition of pcdd/pcdf strongly depends on their volatility and oxidative behavior, both related to the degree of chlorination. in addition, four different non-chlorine containing polyaromatic hydrocarbons (pahs) varying in their number of rings and boiling points were tested. for these, the destruction was dependent only on the volatility of the respective molecule and was in the similar order of magnitude as the pcdd/f. for propene and propane, the extent of photo-conversion depended on the gas-phase hydrocarbon concentration, and had maxima at 500 and 1000 ppm, respectively. the observed decrease at higher concentrations was attributed to hydrocarbon blocking oxygen adsorption sites, and thereby inhibiting the production of the photo-generated reactive oxygen species responsible for hydrocarbon oxidation. durability of the photo-oxidation reaction without catalyst deactivation was demonstrated for propene, propane, ethene and ethane. in contrast with n-butane and to a greater extent n-hexane, the deposition of stable carbonaceous species on the tio 2 surface led to catalyst deactivation. in this paper, the photocatalytic degradation of a monoalkyl dithiocarbamate (vapam ®) by tio 2 illuminated suspensions has been investigated at bench scale. the determination of the effects of various kinetic factors on the photocatalytic degradation and the determination of the nature of the principal intermediates form part of the focus of this study. this research also involves the characterisation of the titanium dioxide surface by x-ray photoelectron spectroscopy to obtain information about the composition and chemical state of the catalyst surface. preliminary field tests have shown that this pesticide can not be completely mineralized when treating diluted industrial wastes from manufacturing industries. the experimental results presented suggest that inactivation of titanium dioxide by sulphur occurs. these results have significant implications to commercialise solar photocatalytic detoxification technology since the catalyst cost has a major impact on the wastewater cost. when the magnesium content increases in the catalysts, both the activity and selectivity to benzene greatly increases and the deactivation of the catalysts becomes slower. the highest tof and selectivity to benzene values at 523 k (100%) are achieved by the catalyst which has the most content of mg without any significant change in activity even at reaction times higher than 500 min. this catalytic behaviour can be explained because the mgo modifies the electronic properties of the nickel particle causing the hydrogen desorption at lower temperatures and also adsorbs the hcl produced during the hydrodechlorination reaction. environmental samples of pcdds and pcdfs were extracted from the fly ashes of a municipal solid waste incinerator (mswi), and had a relatively high toxicity equivalent concentration (572 and 735 pgteq/ml, respectively). the samples were successfully hydrodechlorinated using the described detoxification methodology, and yielded mixtures where the concentration of contaminants determined by gc-hrms, was lower than the experimentally detectable limit. the procedure has the potential to become a practical method for the detoxification of pcdds and pcdfs. both pulse and steady-state pco of tce showed that although p-25 was more active than so 4 2-/tio 2, the co 2 production rate decreased with time on p-25 but not on so 4 2-/tio 2. furthermore, co 2 selectivity increased with time as pco of tce approached steady-state on so 4 2-/tio 2, whereas it decreased on p-25. selectivity to phosgene formation on p-25 was twice that on so 4 2-/tio 2. sulfated tio 2 was more active and deactivated more slowly than p-25 during pco of acetaldehyde above 373 k. since acetaldehyde is an intermediate for pco of several organics, so 4 2-/tio 2 may be preferable to degussa p-25 for pco at elevated temperatures. activity experiments carried out close to the real operation conditions (ghsv, concentration, etc.) with a pt/ceo 2/al 2o 3 catalyst supplied data on the co and hc oxidation and no reduction reactions in environments formed by different reactant combinations (from binary mixtures to the whole mixture simulating the real conditions at the automobile converter). the obtained results have shown notable variations in the oxidation/reduction mechanisms depending on the presence (or absence) of components in the environment. the presence of water always promoted the three-way activity of the catalyst. the compensation effect applied to the co, no and hc conversions confirmed that kinetic expressions obtained with partial mixtures (not very close to the real converter environment) have only limited application for determining the whole kinetic scheme occurring in the automobile converters. it is uncertain whether the adsorbed diatomic oxygen is present as a superoxide ion, as previously detected by esr on fe/mfi, co/mfi and v/mfi at 77 k, or as a peroxo groups bridging over two iron ions, as identified in dft analysis. formation of nitrate ions is visualized by interaction of nitrogen oxide with a superoxide ion, possibly via a peroxynitrite ion. temperature-programmed -desorption and -reaction, coupled with mass spectrometric analysis, allowed to better understand some aspects of the catalytic behaviour shown by the present samples for the cited reaction. in particular, an interesting correlation between the availability of oxygen at various temperatures, as revealed by the so-called α and β oxygen desorption peaks, and reaction mechanism was found for the different b metals. this final fabrication procedure yielded catalysts that in conditions of high spatial velocities (11 000-25 000 h -1) and negligible pressure drop, showed a high catalytic activity at 150°c, with no x reduction percentages close to 85%, selectivities above 95% and low gasification rates of the carbonaceous support. with the proper synthesis and deposition route, such systems were tailor-made with a meso-porous structure similar to that of commercial catalysts and with significant resistance to pore collapse and surface area loss upon thermal aging. all the prepared nanophase systems exhibited low light-off temperatures (in the range 500-550 k) achieved with half the amount of washcoat and half the amount of noble metals compared to currently available commercial catalysts. the performance of these systems was found to depend strongly on the deposition method (directly from the sol or from suspensions of sol-gel derived powders), on the type of precursor used for preparing the starting sols (metallo-organic or inorganic) and on the method used to insert the noble metal(s) in/on the washcoat. the performance and thermal stability of some of these systems makes them excellent candidates for three-way automotive catalysis, with a very low quantity of noble metals. in this study, pcb were destroyed on a v 2o 5/wo 3 supported titanium catalyst at low temperature in the range of 150-300°c. at a space velocity of 5000 h -1 more than 98% could be removed. below 250°c, the higher chlorinated pcb remained partly unchanged on the catalyst for several minutes. in contrast, the oxidation process lasted up to hours at a temperature of 150°c. at around 200°c and below a significant part of the pcb were oxidised to the more toxic polychlorinated dibenzofurans (pcdf). the pcdf remained mainly adsorbed on the catalyst. at 250°c, no significant amount of pcdf were detected and at 300°c no byproducts were found. the oxidation of selected individual pcb isomers and the isomer specific analysis of pcdf formed give an insight into the initial step of degradation of chlorinated aromatics on v 2o 5/wo 3-tio 2 catalysts. the results indicated that hydrogen abstraction is the preferred step and an initial abstraction of chlorine is only a minor pathway. this suggests an electrophilic oxygen transfer during the destruction of pcb. during the destruction experiments, a slight chlorination of the non-degraded pcb occurred. on the other hand, no measurable dechlorination/hydrogenation was observed. fresh and used samples of the catalysts tested were characterised by nitrogen adsorption, x-ray diffraction, scanning electron microscopy, x-ray dispersion spectroscopy, temperature programmed oxidation, nh 3 temperature programmed desorption and thermogravimetric analysis. results lead to think than in the case of modified red mud, deactivation is related with fouling phenomena, whereas in the case of unmodified red mud, the poisoning by hcl is the main deactivation cause. finally, the kinetic of the hydrodechlorination of tetrachlorethylene over the two modified red mud was studied, both with and without addition of cs 2 in the reaction feed. in all the cases a kinetic model based on the langmuir-hinselwood postulates, considering chemisorption of both ttce and h 2 (associatively adsorption) in analogous active sites, provided a good fit to the experimental data. catalytic properties of fe-zsm-5 were studied in the oxidation of phenol. the reaction was performed in a static system, at the atmospheric pressure, 343 k, and with h 2o 2 concentration, which exceeds stoichiometric concentration for complete oxidation of phenol to carbon dioxide and water. from the catalytic results, it can be concluded that framework fe can catalyze more completely phenol oxidation than the extra-framework fe does. 4-chlorophenol (4-cp), a model pollutant for waste waters, was then chosen for the study of the influence of the surface areas and of the concentration of millennium-pc photocatalysts. the initial apparent rate constants of 4-cp degradation in presence of all millennium-pc catalysts were all higher than that obtained with degussa p-25. when choosing the total organic carbon (toc) disappearance rate as an overall kinetic parameter, millennium-pc/10 and pc/25 appeared as less active than degussa p-25, with longer solar exposures (by about 10%) necessary to obtain a total mineralisation. however, millennium-pc/50 resulted as the best catalyst in all cases. the optimal slurry concentration (g l -1) has been determined for each millennium tio 2 sample. while the optimum of degussa p-25 had previously been found equal to 0.2 g l -1, higher amounts of millennium-pc samples were required. a twice higher concentration (0.4 g l -1) increased the activities by factors equal to 1.2 and 1.5 for millennium-pc/50 and pc/10, respectively. the rate constants of disappearance of intermediates and of toc were quantitatively affected by factors in agreement with a multiple consecutive reactions model. in any case, titania millennium-pc/50 appeared as the best catalyst among all those tested, including degussa p-25. the combination of scr and cold plasma enhances the overall reaction and allows an effective removal of no x at relatively low temperatures. certain modifications of al 2o 3 and zro 2 have been found to be effective as catalysts in this reaction. with an energy effort of ca. 30 ev per no-molecule, a temperature of 300 °c and a space velocity of 20,000 h -1 at the catalyst, it is possible to reduce 500 ppm no in excess oxygen by more than half. the synergistic combination of ntp and hc-scr has been verified under real conditions with exhaust gas from a diesel engine. characterisation and catalysis results indicated that impregnation with cuso 4 or sulphation via gas-phase yielded nearly identical catalysts. covalent sulphates of various nuclearity formed on both sulphated zro 2 and copper-containing sulphated zro 2. sulphated zro 2 catalysts were only slightly more active than unsulphated zro 2. as the cuso 4-content in the cuso 4/zro 2 catalysts increased, (i) the (polynuclear)/(mononuclear) sulphate ratio, (ii) the concentration and strength of lewis acid sites, (iii) the concentration of brönsted acid sites, and (iv) the scr activity increased in parallel. in the temperature region 473-600 k, a range at which cuso 4/zro 2 yielded nearly 100% scr selectivity, no molecules converted to n 2 per second per cu-site were nearly independent of the cu-content, up to 2.3 nm -2 of cuso 4 molecules. cuso 4/zro 2 were much more selective than the relevant unsulphated cuo x/zro 2. the higher selectivity of cuso 4/zro 2 depended on their lower activity in the nh 3 oxidation reaction. rh supported on an oxygen storage component could catalyze no reduction in the periodic lean and rich excursions much more effectively than rh supported on other supports. reaction mechanisms of the no reduction on rh/oxygen storage component were deliberated. results indicate that an osc function would play an important role in the no reduction on rh/ceria. furthermore, two kinds of reaction mechanisms have been proposed for the no reduction on rh/osc material. results for single compounds show that temperature at which 50% conversion is attained (t 50) increases as concentration increases for benzene and toluene, while the opposite behaviour is observed for n-hexane. results for mixtures show that, while the presence of n-hexane does not affect the conversion of benzene and toluene, the presence of benzene or toluene inhibits the combustion of hexane, and the aromatic compounds inhibits each other when are reacted together. results obtained in absence of mass transfer limitations were fit to kinetic expressions: simple mars-van krevelen kinetic expressions for single compounds, and a modified mars-van krevelen mechanism, considering competitive adsorption of the hydrocarbons, for binary mixtures. the influence of co 2 and h 2o on kinetic behavior can be described by assuming they compete with reactants for adsorption on surface sites, including them in the site balance equation, and using the rate expression proposed previously for no reduction by ch 4 in excess o 2. with o 2 in the feed, integral conversions of ch 4 and o 2 frequently occurred due to the direct combustion of ch 4 by o 2, although no conversions remained differential; thus, an integral reactor model was chosen to analyze the data which utilized a recently determined rate equation for ch 4 combustion on la 2o 3 in conjunction with a previously proposed model for no reduction by ch 4. the following rate expression described the rate of n 2 formation: r n 2 t= k' no p no p ch 4 p o 2 0.5/(1+ k no p no+ k ch 4 p ch 4+ k o 2 0.5 p o 2 0.5+ k co 2 p co 2+ k h 2o p h 2o) 2. it gave a good fit to the experimental rate data for no reduction, as well as providing enthalpies and entropies of adsorption obtained from the fitting parameters that demonstrated thermodynamic consistency and were similar to previous values. the heats of adsorption were altered somewhat when either co 2 or h 2o was added to the feed, and the following ranges of values (kcal/mol) were obtained for the different components: no (31-43), ch 4 (16-32), o 2 (35-54), and h 2o (37). apparent activation energies were typically near 30 kcal/mol. irrespective of the preparation method (i) catalysts with the same sulphate content had the same covalent sulphates, and (ii) catalysts with the same copper content and with the same sulphate content were equally active and selective. sulphated samples were far more selective than the correspondent unsulphated cuo x/zro 2, particularly sulphated samples with higher copper content. the presence of sulphates (i) made cu(ii) less reducible than in cuo x/zro 2 and (ii) prevented cuo segregation. the catalytic activity and selectivity of copper-sulphated catalysts depends on a cooperative effect of copper and sulphate. the role of copper is to determine the activity for the no reduction, and that of sulphate to maintain high the selectivity. in order to propose a phenol oxidation pathway, several runs were carried out where the main intermediates detected in the phenol oxidation were fed to the fbr under different temperatures and catalyst loadings. it was found that catechol oxidation does not yield either benzoquinone or maleic acid but oxalic acid which finally mineralized to co 2. however, benzoquinone and maleic acid are products clearly detected in the hydroquinone oxidation. oxidation reactions of phenol and those intermediates studied take place not only on the solid surface but also in the liquid phase. when bimetallic co-pt/hy catalysts were applied, pt was present in metallic form in the working catalysts. over these catalysts, conversion of no increased with increase in the amount of pt loading, however, selectivity to n 2 decreased. the maximum yield of n 2 was achieved over 0.1 wt.% pt-1.0 wt.% co-hy catalyst. it is concluded that metallic form of pt and ion-exchanged co are essential to obtain high yield of n 2, and that the role of pt is to catalyze the oxidation of no to no 2, which is successfully reduced by propylene over co sites to nitrogen. it is concluded, after the investigation of hundreds of catalyst formulations, that many of the fundamental questions relating to lean deno x reactions have been addressed and the main boundary conditions have been established. it seems clear that catalysts with sufficient activity, selectivity or stability to satisfy the demanding conditions that appertain in automotive applications are still far away. the rapidly growing interest in no x storage systems reflects this situation, and it now seems to be the case that acceptable direct no x reduction catalysts may be very difficult to find for lean-burn applications. besides atrazine, photodegradation of its intermediates 2-chloro-4-ethylamino-6-amino-1,3,5-triazine (ceat), 2-chloro-4-isopropylamino-6-amino-1,3,5-triazine (ciat) and 2-chloro-4,6-diamino-1,3,5-triazine (caat) was also investigated separately. while the degradation rates for ceat and ciat were found similar as for atrazine in all investigated systems, the degradation of caat proceeded comparably fast only in the q-tio 2 colloidal suspension but was markedly slower in the other systems. surface metal fluorides produced on binary metal oxide catalysts by the reaction with hf were hydrolyzed under temperature programmed mode and the products were analyzed by a mass spectrometer. it was clearly demonstrated from the experiments that the amount of released hf was well correlated with the corresponding catalytic activity. further the amounts of l-acid sites measured by in situ ft-ir studies of adsorbed pyridine on the various binary metal oxides also followed the same order as the catalytic activity. these results suggest that breaking of cf bond in cf 4 molecule by l-acid sites is a rate-limiting step in the hydrolysis reaction of cf 4 and resulting surface fluoride is easily hydrolyzed with water. other physical techniques such as xrd, weight and surface area of samples before and after the cf 4 hydrolysis reaction were demonstrated that some of binary oxide catalysts were stable under the reaction conditions, especially ga-al and ni-al binary oxide catalysts. the effect of temperature and space time in ttce conversion at the period of constant catalytic activity can be modelled by a kinetic model assuming first order for ttce and zero-order for h 2. finally, the performance of the pd alumina-supported catalyst is compared with that of a pd carbon-supported catalyst with the same metal load, used in previous works. although the carbon-supported catalyst yields higher initial conversion, the alumina-supported catalyst is more resistant to deactivation. catalyst α-alf 3 is more active than catalyst γ-alf 3 for both reactions. this is due to both its higher amount of lewis acid sites, as deduced from ammonia-tpd and pyridine ft-ir studies, and its higher tof values, which favours the cl/f exchange in cfc and hcfc compounds. the main products obtained are those which result from the exchange of one chlorine by one fluorine, cclf 3 and chf 3 for the exchange reaction of ccl 2f 2 and chclf 2, respectively. it is also shown that isolated pd atoms located at the surface of ni rich bimetallic particles are more active than those lying in larger ensembles. finally bimetallic pd-ni catalysts containing only between 20 and 50 pd atom%, although less active than pure pd, lead to 75% of useful compounds, i.e. benzene, mono and dichlorobenzene. drs and xps results showed that the presence of sulphates prevented the formation of co 3o 4. xps indicated the presence of co(ii) alone. irrespective of the preparation method, ftir showed that catalysts with the same sulphate content had the same covalent sulphates. as the sulphate content in the sample increased, ftir with co or no showed that the lewis acid strength of co(ii) increased, whereas the reducibility and heterogeneity of co(ii) decreased. sulphated samples with a cobalt content higher than 2 atoms/nm 2 were far more active and selective than the corresponding unsulphated coo x/zro 2. the presence of sulphates had a weaker effect on the catalytic behaviour of samples with lower co content (<2 atoms/nm 2). we conclude that cobalt and sulphate cooperate in determining the catalytic activity and selectivity of cobalt sulphated-zro 2 catalysts. in these conditions, the activation of the catalyst does not depend on the so 2/so 3 feed ratio; however high temperatures and activation times over 50 h are required. the activation of the catalyst carried out at low so x concentrations slightly improve the final activity as compared with those obtained by the conventional activation step where higher so x and o 2 concentrations are used. two types of titanium dioxide electrode have been used. 'thermal' electrodes were made by oxidation of titanium metal mesh; 'sol-gel' electrodes were made by depositing and then heating a layer of titania gel on titanium mesh. cyclic voltammetry was used to carry out an initial characterisation and optimisation of both electrode types. the best 'thermal electrodes'-i.e. those with the highest photocurrents-were prepared by heating titanium mesh at ∼700 °c in air. for sol-gel derived electrodes, optimum performance was obtained by heating at ∼600 °c. these electrodes were then used, in a gas sparged reactor, to disinfect e. coli suspensions with an initial concentration of 10 7 colony forming units (cfu) ml -1. films prepared by the oxidation of titanium metal were shown to be superior to sol-gel derived films. direct experimental comparison demonstrates that the photoelectrochemical system is more efficient than photocatalytic disinfection effected by slurries of degussa p25 titanium dioxide. since in practical systems the tio 2 would be exposed to a variety of species additional to those that are targeted, we also examined the effects of h 2po 4 - and hco 3 - ions on the measured disinfection rates. phosphate addition poisons both the electrode and particulate-slurry systems and is only partially reversible. by contrast, although bicarbonate addition affects all three systems, the effects are reversible. the influence of poisons as water and so 2 was investigated. while water does not affect the soot combustion activity, so 2 slightly shift the tpo peak to higher temperature. surface basicity, which is a key factor, was analysed by measuring the interactions of the catalytic surface with co 2 using the high frequency co 2 pulses technique, which proved to be very sensitive, detecting minor changes by modifications in the dynamics of the co 2 adsorption-desorption process. water diminishes the interaction with co 2, probably as a consequence of an adsorption competition. the so 2 treated catalyst is equilibrated with the co 2 atmosphere more rapidly if compared with the untreated one, also showing a lower interaction. the lower the interaction with the co 2, the lower the activity. differential scanning calorimetric (dsc) results indicate that the soot combustion reaction coexists with the thermal decomposition of hydroxide and carbonate species, occurring in the same temperature range (350-460 °c). the presence of potassium increases surface basicity shifting the endothermic decomposition signal to higher temperatures. we also found that no 2 strongly interacts with both la 2o 3 and k/la 2o 3 solids, probably through the formation of monodentate nitrate species which are stable under he atmosphere until 490 °c. these nitrate species further react with the solid to form bulk nitrate compounds. the addition of cobalt decreases the nitrates stability and catalyses the no x to n 2 reduction under a reducing atmosphere, which is a necessary step for a working no x catalytic trap. preliminary studies performed in this work demonstrated the feasibility of using these catalysts to simultaneously remove no x and soot particles from diesel exhausts. the nitrate formation is still observed during the catalytic combustion of soot in the presence of no x, making our k/la 2o 3 a very interesting system for practical applications in simultaneous soot combustion and no x storage in diesel exhausts. in part i, the unusual properties of these new materials were illustrated for lacoo 3 and laco (1- x)fe xo 3 perovskites [1]. it was shown that controlling the calcination conditions allows to tailor the surface properties of these materials. in part ii, a preliminary account of the catalytic behaviour of such catalysts in n-hexane oxidation was reported [2]. in the present contribution, the fine control of the nature and the concentration of the various sites active in redox catalysis is demonstrated through a kinetic study of the total oxidation of n-hexane by oxygen. the roles of two oxygen species o 2 - and o -, respectively, associated with α and β oxygens are discussed. catalysts doped with cs were the most active and stable also after several combustion cycles and in the presence of sulfur in the stream. the activity measurements and microstructural results suggest that the combustion of soot is favored on catalysts where amorphous phases and/or mixed fevo phases, ensuring an intimate contact between iron and vanadium, are present. a reaction mechanism involving the participation of the redox couple fe(ii)-fe(iii) in the activation of the vanadium combustion sites, is proposed. the sba-15 film supported on mff provided the highest dispersion of the deposited noble metals (pd, pt) with an average particle size ∼2.0 nm. the metal nanoparticles formed within the mesopore channels were stable against sintering during calcination and the particle diameter was observed not to exceed the diameter of the silica pores. these catalysts did not undergo deactivation under reaction conditions at temperatures up to 500 °c. on the contrary, the pd supported on mff coated by the microporous sio 2 and al 2o 3 films, prepared by sol-gel technique, suffered from metal sintering during the calcination step and also during reaction, demonstrating strong catalyst deactivation. the catalytic filters are suitable materials for assembling different multiple layers to obtain structured catalytic beds with the composition/concentration gradients of active component in the axial direction. the enhanced overall catalytic performance was observed in adiabatic catalytic reactor during propane combustion due to a synergy of the 0.5% pd/sba-15/mff and the 0.5% pt/sba-15/mff catalytic layers assembled in the appropriate order forming gradient catalytic bed. a detailed kinetic study was carried out on this last perovskite by ft-ir analysis as well as by temperature-programmed and isothermal oxidation tests, by assessing the effect of the prevalent affecting parameters. some of the reaction intermediates were singled out and several different and rather complex reaction schemes were finally hypothesized, involving reaction intermediates either present on the catalyst surface or on that of the carbon particulate itself. the role of the various elements on the perovskite composition was also defined. the effect of vanadium in particular seemed to be dominant in assuring a peculiar activity towards no x reduction. results indicate that the fastest initial degradation rate for substituted phenols occurs for p-methoxyphenol and the slowest for the p-nitrophenol. quantum chemically derived properties and experimental data for each phenol derivative were used to establish structure-photoreactivity relationships (spr) for these compounds using regression techniques. according to the statistical calculations, the most critical electronic properties responsible for the photoreactivity of p-substituted phenols were the zero-point energy, the total energy divided by the molecular weight, and the quadrupolar moment for the xy plane. these molecular descriptors encode information related to the molecular vibration frequencies, intra-molecular interactions, and total electron distribution around the molecule, respectively. this spr approach offer a better explanation of the para-phenols photoreactivity properties than the use of hammett constant because it considers properties derived from whole molecules whose atoms interact with the light based on the electron density and electronic molecular shape. the reverse reaction of the no 2 disproportionation has also been observed. if no is added to the feed, nitrates previously formed on the sorbent will decompose into no 2. therefore, the above chemical equation should be considered as an equilibrium reaction. applying this finding to the no x storage and reduction catalyst means that no probably reacts with the previously formed nitrates yielding no 2 as an intermediate product. this no 2 is subsequently reduced by the reducing agents (hydrocarbons and co) present during the regeneration period. ftir studies have shown that while phenol interacts with tio 2 yielding a phenoxide, in the catalyst low ac containing catalysts mixtures the surfacial hydroxylic groups are inserted in the aromatic ring in the symmetric position to the -oh group. additionally, the 4-aminophenol study shows that the molecule interacts with the tio 2 surface by means of the amino group, while in the catalyst containing ac the interaction takes place through the hydroxylic group. these results have confirmed the catalyst acid-base properties changes determined by the characterisation studies already performed. also, it has been observed that catalysts with the lowest ac content show better catalytic behaviour than the untreated tio 2 and those with higher ac load. another interesting result is the efficiency of these catalysts under solar irradiation. the present study shows that the ac not only exerts a synergistic effect when is combined with tio 2 as some authors suggest, but it also modifies the catalyst characteristics. water turbidity negatively affects the photocatalytic inactivation of bacteria. tio 2 immobilized on nafion ® membranes inactivates e. coli with efficiencies close to those observed for bacterial suspension containing the same concentration of suspended tio 2. for fixed tio 2 on glass, the dose (w min/m 2) necessary for the total inactivation decreases by increasing the fixed tio 2 amount. fixed tio 2 p-25 was more active to photocatalytic inactivation when compared with immobilized rutile and anatase. however fixed rutile enhances e. coli inactivation as anatase. the effect of temperature and turbidity were made using wastewater sample. the destruction of chlorinated mixtures induced an inhibition of the reactivity of each compound leading to a significant increase in the ignition temperature, which varied form one compound to other. on the other hand, a moderate decrease in chlorinated intermediates/by-products formation was noted. likewise, the presence of hydrogen, either as a part of the additional chlorinated molecule or as a part of water generated as a reaction product, was determined to be important for efficient combustion of the chlororganics to hcl. soluble reaction products-the ammonium nitrate and the formamide-undergo further a gradual degradation under the conditions of a catalytic denitration reaction that starts when the urea decomposition is completed. it was shown that a platinum catalyzed decomposition of urea in 2-8 m hno 3 proceeds in the presence of 0.2-1.5 m formic acid as a result of the reaction with nitrous acid generated in the process of catalytic denitration. the decomposition proceeds according to a "zero"-order with respect to the urea concentration and exhibits an induction period for [hno 3]<2.5 m. the order of the process with respect to [hcooh] is 1. the rate of reaction decreases when the concentration of nitric acid is increased that is explained by the hydrogen ions competitive adsorption on the catalyst's surface. the rate-determining step of the urea catalytic decomposition is a reaction of heterogeneous catalytic formation of nitrous acid. it was found that an activity of the pt/sio 2 catalyst decreases reversibly with the increase of the drying temperature during its regeneration. propene and toluene, used as probe molecules for vehicle emissions, were found to absorb under ambient conditions on all forms of bea. there appear to be two adsorption mechanisms at play, one involving charge gradients in the zeolite framework and characterised by lower desorption temperatures (molecular adsorption) and the other related to zeolite acidity (oligomeric adsorption). both the presence of water and simulated ageing reduced the adsorption capacity of the zeolites. hydrothermal ageing was found to result in dealumination of the zeolite framework, a process that can be reduced by incorporation of lanthanum into the lattice. water in the gas stream was found to block pores and reduce adsorption. a combination of a more hydrophilic zeolite with bea zeolite is suggested to overcome the loss in capacity by the presence of water in car exhaust. from the experiments, it was concluded that a combination of platinum and rhodium is required to achieve good no x storage and reduction performance. the no x storage capacity was, however, found higher for catalysts containing only platinum compared to catalysts including rhodium. when exposed to so 2 the no x storage capacity also seemed to deactivate faster for the samples containing rhodium than for samples with platinum as the sole noble metal. additionally, it was observed that platinum gives high no oxidation activity during the lean periods both with and without so 2 present in the gas feed. during the rich periods, rhodium showed high activity for no reduction in sulphur free gas feed as well as in the presence of so 2. finally, the results implied that to provide good sulphur regeneration ability of the no x storage catalyst, a combination of platinum and rhodium is necessary. with reference to the soluble counterpart immobilized urease was found to exhibit (i) a shift of the optimum ph towards more acidic values; (ii) a shift of the optimum temperature towards higher temperatures; (iii) higher values of k m. the latter result indicated an apparent loss of affinity of immobilized urease towards urea. to recovery this affinity loss, the catalytic membranes were employed in a bioreactor operating under non-isothermal conditions. under these conditions the catalytic membranes exhibited reaction rates higher and apparent k m smaller than those measured under comparable isothermal conditions. as a consequence, percentage increases of enzyme activity and reduction of the production times, proportional to the magnitude of the applied temperature difference were observed. results have been discussed in the frame of reference of the process of thermodialysis. the technology of the non-isothermal bioreactors confirmed its usefulness also in the reduction of urea concentration in aqueous solutions. a catalyst with 1.6 g/in. 3 (0.098 g/cm 3) of an alumina washcoat containing 5 wt.% pt/al 2o 3 promoted with 0.5 wt.% fe was selected for detailed investigation. the effects of both space velocity and linear velocity were studied. external transport was a significant resistance with this catalyst, at the above experimental conditions. the external resistances to heat and mass transfer, coupled with the effect of the r-wgs reaction, reduced the observed co conversion and selectivity. brønsted acid sites in mordenites were active for the selective catalytic reduction of no with ch 4. co-mor samples were far more active than na-mor and h-mor samples, showing that acid protons play a negligible role when co is present. co-mor catalysts showing the highest activity had the largest amount of co ii-carbonyls in the main channels. this result strongly suggests that co ii in the main channels of mor are the active sites for the ch 4+no+o 2 reaction. | nutrition guidelines of complementary feeding for infants and toddlers (ws/t 678-2020) |
the presence of dust on the lunar surface has been identified as one of the key challenges for landed mission sand for establishing long-term human habitats. the risk of dust accumulation on photovoltaic and other mechanical or optical surfaces goes beyond mere coverage as the electrostatic charge buildup can affect the operations and lifetime of electrical components. the dayside lunar regolith is exposed to solar uv radiation and the flow of solar wind plasma resulting in electrostatic charging of the surface. small dust particles can collect sufficiently large charges, that combined with intense localized electric fields, are capable of overcoming adhesion and mobilizing or transporting the dust particles. in addition to plasma charging processes, grains can also become charged due to mechanical processes that generate triboelectric processes. for example, walking astronauts or turning wheels can generate unexpectedly large electric fields due to tribocharging, the efficient separation of positive and negative charges in the extremely dry lunar environment. this process is expected to be most efficient in unlit regions where the contributions of uv and plasma exposure are inefficient to provide discharging currents to limit the buildup of intense electric fields. hence, missions visiting the resource rich permanently shadowed lunar regions will have to be prepared to mitigate the effects of tribocharging. in this presentation we report on the initial experimental investigation of the interaction between a rover wheel and two different lunar regolith simulants. we used the nasa ames dust bed facility, a small remote-controlled rover with rubber wheels, and a calibrated faraday cup (fc) on the surface to measure the charge distribution of dust particles landing in our fc. we find that the dust particles forming the so-called "rooster tails", the cloud of particles forming behind the spinning wheels of a rover, are positively charged. we will report on the measure charge distribution and suggest ways to mitigate the triboelectric effects for rovers designed to explore lunar permanently shadowed regions to gauge their availability for in-situ resource utilization. | triboelectric charging of lunar dust by rover wheels |
interest in searching for life in the outer solar system has intensified recently with the new start of the europa multiple flyby mission and the insertion through a nasa community announcement of an ocean worlds (titan and enceladus) theme in the list of admissible new frontiers missions. as part of a discovery proposal called "enceladus life finder", or elf, a multidisciplinary team of scientists led by the authors developed a set of measurements for determining the habitability of enceladus' internal ocean and the presence of biological activity therein, obtained by flying two mass spectrometers through enceladus' plume - one optimized for gas, the other for grains. the measurements and information derived therefrom cut to the heart of what biological activity does that distinguishes it from abiotic processes. they also tightly constrain the essential parameters of ocean habitability including ph, redox state, available free energy, and temperature of any active hydrothermal systems on the floor of the enceladus ocean. in addition to enceladus, such a protocol is applicable to europa should deep-seated plumes be present there, but the much higher gravity requires that the grain mass spectrometer be flown at a very low altitude. on the europa flyby mission, this would require a small spacecraft that would detach from the main spacecraft and fly within a few kilometers of the surface. proposed to nasa as sylph, this simple plume probe would provide a low-cost way to equip the europa multiple flyby mission to prepare for potential plumes, and use them to determine the habitability and biopotential of the europan ocean. | looking for life in the plumes of ocean worlds |
the device based on a mn-doped niox htl retained 70% of its initial efficiency after 35 days' storage under a continuous halogen lamp matrix exposure. organic/inorganic hybrid perovskite solar cells (pscs) have represented a promising field of renewable energy in recent years due to the compelling advantages of high efficiency, facile fabrication process and low cost. the development of inorganic p-type metal oxide materials plays an important role in the performance and stability of pscs for commercial purposes. herein a facile and effective way to improve hole extraction and conductivity of niox films by manganese (mn) doping is demonstrated in this study. a mn-doped niox layer was prepared by the sol–gel process and served as the hole transport layer (htl) in inverted pscs. the results suggest that mn-doped niox is helpful for the growth of perovskite layers with larger grains and higher crystallinity compared with the pristine niox. furthermore, the perovskite films deposited on mn-doped niox exhibit lower recombination and shorter carrier lifetime. the device based on 0.5 mol% mn-doped niox as the htl displayed the best power conversion efficiency (pce) of 17.35% and a high fill factor (ff) of 81%, which were significantly higher than those of the one using the pristine niox htl (pce = 14.71%, ff = 73%). moreover, the device retained 70% of its initial efficiency after 35 days' storage under a continuous halogen lamp matrix exposure with an illumination intensity of 1000 w m−2. our results widen the development of pscs for future production. | efficient and stable perovskite solar cells using manganese-doped nickel oxide as the hole transport layer |
we report effects of controlled humidity in ambient condition on grain boundary potential and charge transport within the grains of pervoskite films prepared by sequential deposited technique. grain boundary exhibited variation of their electronic properties with change in humidity level from sample kept inside glove box to 75% rh. x-ray diffraction (xrd) indicates the formation of pbi2 phase with increasing humidity level. the degradation of pervoskite solar cell is mainly associated with the increase of pbi2 phase with increase in humidity level and hydration of the grain boundaries with the formation of hydrated phases. spatial mapping of surface potential in the perovskite film exhibits higher positive potential at grain boundaries compared to the surface of the grains. grain boundary potential barrier were found to increase from 35 mev to 80 mev for perovskite film exposed to 75% rh level compared to perovskite film kept inside glove box. nanoscale current sensing measurement (cs-afm) shows that charge transport in perovskit solar cell strongly depends in humidity level. performances of the solar cell was maximum for 25% humidity with 14.01 %. transient measurement shows decrease in charge carrier life time and charge transport time with increase in humidity level. our results show strong correlation between humidity level, electronic grain boundary properties and device performance. | nanoscale potential distribution of grain boundary dependence on humidity of high performance perovskite (ch3nh3pbi3) solar cell(conference presentation) |
examining the compositional effect of aeolian transport and sorting processes on basaltic sands is significant for understanding the evolution of the bagnold dune field, as well as other martian soils and sedimentary units. we use the askja sand sheet, iceland, as a testbed to quantify the nature of soil production and aeolian transport processes in a mafic system. basalts from askja and surrounding volcanic units, which can have high mgo (5-18 wt %) and high fe2o3 (5-18 wt %), have been weathered to form mafic volcaniclastic deposits which are incorporated into a 40-km long sand sheet to the e-se of the caldera, ranging from 10 cm to 10 m thick, and covering 240 km2. ash and lava from the 2014-2015 holuhraun eruption were emplaced onto the southeastern part of the sand sheet. the sw section is deflationary and defined by very fine to medium grained basaltic sand with ventifact cobbles and boulders. the central part is inflating and dominated by very fine-grained sand, relict lava fields, and small to large sand ripples (1 to 30 cm). the ne portion is also inflating but accumulation is limited to topographic depressions. bulk chemistry of >200 sand samples are similar to martian crust (sio2: 48-52 wt %, mgo: 5-8 wt %, fe2o3: 13-15 wt %). mgo concentrations vary with distance along the sand sheet, increasing by 1.5% over 10 km in the downwind direction (e, ne), then maintaining a relatively consistent concentration of 6.75 wt % over 18 km. mean equancy of grains decreases 15 % to the e over 10 km followed by a plateau at 65 to 75 %. material at depth tends to be of higher sphericity than material on or near the surface. notably, mgo increases while the sphericity decreases and both data sets level off at 10 km, which suggests these two variables are related. these indicate input of material with prismoidal morphology around 10 km, and may be due to the holuhraun eruption. | insights from askja sand sheet, iceland, as a depositional analogue for the bagnold dune field, gale crater, mars. |
polar faculae (pfe) are bright points at the edges of granules that illuminate where magnetic field lines intersect the solar surface near the suns poles. we previously reported the average pf lifetime determined from the helioseismic and magnetic imager (hmi) on solar dynamics observatory (sdo) is 6.0 2.7 hours. we also showed that the number of pfe in solar cycle 24 is correlated with the strength of the polar magnetic field and anti-correlated with the sunspot number. those correlations had been known before but, as with any solar activity variable, the time dependence is more complicated than a linear correlation. we report on our continuing analysis of hmi pf data, extending the time coverage of the number of pfe and measuring the magnetic field associated with a sample of those pfe. we will map the proper motion of those pf that appear to move in latitude. this proper motion confirms that faculae participate in convective motions at the poles. by measuring the presence, trajectory, and magnetic field strength of a large sample of faculae, we can better understand polar faculae and therefore the polar magnetic field and its evolution, as well as conditions and convective motions at the poles. these observations will help design space missions to observe the solar polar regions. | properties of polar faculae |
despite the fact that polycrystalline photovoltaics materials such as cdte and cigs are an established commercial technology, the precise role of grain boundaries in their performance remains poorly understood. the high defect density at grain boundaries is generally detrimental to carrier lifetime, however the electric fields surrounding charged grain boundaries may separate electrons and holes, effectively passivating the grain boundary. one difficulty in ascertaining the properties of grain boundaries is that high spatial resolution experimental techniques needed to probe individual grain boundaries are generally surface sensitive. for this reason, extracting quantitative grain boundary and other material properties from this data requires a quantitatively accurate model of the exposed surface. motivated by these considerations, we present a theoretical analysis of the response of a polycrystalline semiconductor to a localized excitation near a grain boundary, and near the surface. we use our analytical results to interpret electron beam induced current (ebic) data on polycrystalline cdte solar cells. | grain boundaries and surfaces in polycrystalline photovoltaics |
the detection of planets using the radial velocity (rv) method is hampered by astrophysical processes on the surfaces of stars. these processes induce noise, or "jitter", which can drown out or even mimic the signal due to planets. in an effort to better understand what drives rv jitter, we empirically investigate the rv jitter of more than 650 stars from the california planet search (cps) sample with precise stellar properties. using a careful vetting process, we isolate the rv jitter intrinsic to the star for each star in our sample and examine trends with activity and with evolutionary state. we find that rv jitter ultimately tracks stellar evolution and that in general, stars evolve through different stages of rv jitter: younger main sequence stars are dominated by jitter that is driven by magnetic activity until they have aged and sufficiently spun down to the point where convectively-driven jitter (granulation, oscillations) becomes dominant. from this, we identify the "jitter minimum" - where activity-driven and convectively-driven components have similar amplitudes - for stars between 0.7 and 1.7 solar masses. we show that as a result of their more rapid evolution, more massive stars reach this jitter minimum later in their lifetime, in the subgiant or even giant phases. | astrophysical insights into radial velocity jitter from an analysis of 650 planet-search stars |
its not easy being a speeding rock in our solar system.illustration of an asteroid breaking apart into smaller fragments. [nasa/jpl]over their lifetimes, the millions of minor rocky bodies of our solar system asteroids are subject to extreme conditions. some experience dramatic collisions, some are spun up to such high rotation speeds that they fly apart, and some venture so close to the sun that our stars heat cracks them into pieces.over time, these violent processes create families of asteroids that dance around our solar system on similar paths. where one rock once orbited, there might now be a group of genetically linked asteroids that follow similar trajectories all produced by the splitting of one parent rock.in a new study, scientists have explored two especially nearby asteroids to determine whether they might be linked.a visit to a potentially hazardous neighborthe orbital path of the near-earth asteroid phaethon. [skytel]asteroids whose orbits bring them close to the earth are of particular interest to us: we like to keep an eye on those bodies that might threaten our planet.perhaps 22,000 near-earth asteroids are currently known, with just over 2,000 that are large enough and swing close enough to earths orbit to be considered potentially hazardous though it should be noted that the vast majority of these have been ruled out as being an impact threat in at least the next 100 years.artists illustration of the destiny+ spacecraft. [jaxa]to learn more about these nearby bodies, the japanese aerospace exploration agency is sending a spacecraft, destiny+, to fly by a large (~5-km) near-earth asteroid. the target is 3200 phaethon an unusual blue-toned, dust-producing asteroid thought to be the source of the geminid meteor stream and other minor bodies that might be associated with it.as destiny+ is currently scheduled to launch in 2022, scientists are currently preparing by learning all they can about the possible mission targets using ground- and space-based observatories. in a new study led by maxime devogle (lowell observatory), a team of scientists presents detailed observations of (155140) 2005 ud, another near-earth object and potential destiny+ target that might be related to phaethon.signs point to a linked pairdevogle and collaborators gathered an impressive array of observations of 2005 ud, using dozens of telescopes to obtain photometry, polarimetry, and spectroscopy, and also reanalyzing thermal imaging.2005 ud and phaethon exhibit very similar spectra, including rare spectroscopic (b-type) signatures. [devogle et al. 2020]by combining new observations with archival data and detailed modeling, the team constrained 2005 uds size (just over 1 km across) and rotation rate (it spins roughly once every 5.2 hours), as well as many other properties like its albedo, spectroscopic class, and even the size of the grains on its surface knowledge that will all help with mission planning for destiny+.but what about 2005 uds potential link to phaethon? based on devogle and collaborators observations, 2005 ud and phaethon appear to share more than just orbital characteristics. they also have very similar and rare, among asteroids physical properties as shown by their spectroscopy and polarimetry.more study is needed, but the data suggest that the two are, indeed, genetically linked perhaps 2005 ud and phaethon both split from the same parent thousands of years ago. with any luck, destiny+ will soon reveal more about these close-swinging rocky bodies!citationnew evidence for a physical link between asteroids (155140) 2005 ud and (3200) phaethon, maxime devogle et al 2020 planet. sci. j. 1 15. doi:10.3847/psj/ab8e45 | exploring links between nearby asteroids |
dye-sensitized solar cells (dsscs) have attracted great attention due to environmentally friendly low-cost processing, excellent working ability in diffuse light, and potential to meet the power demands of future buildings due the true class of building integrated photovoltaics (bipv). nevertheless, dsscs have relatively low photoconversion efficiency (pce) due to multiple issues. several strategies have been employed to enhance its pce. for instance, bi-layered structure of photoelectrode i.e., mesoporous tio2 transparent layer with top scattering layer was introduced which scatter light inside on large angles improves the harvesting ability of photoelectrode thus enhanced pce. however, scattering layer is composed of aggregated small particles which offer sluggish electron transport due to multiple grain boundaries, consequently, unwanted recombination reaction which leads to poor pce. this issue has been addressed for transparent layer immensely but ignored for scattering layer. mostly for scattering layer in previous studies novel structures have been proposed to enhance scattering properties and dye adsorption only. therefore, in this study for the first time presenting dual functional graphene/tio2 scattering layer in which solvent exfoliated graphene is incorporated in tio2 submicron spheres which enhanced electron transport properties, while submicron spheres scatter light effectively. scattering and electron transport characteristics of dsscs are thoroughly investigated with the function of graphene loading. electrochemical impedance spectroscopy (eis) has revealed that diffusion coefficient length and coefficient and conductivity attained maximum value at 0.01 wt%. while other important parameters such as electron lifetime and electron density in conduction band have been improved till 0.020 wt% graphene loading. however, results indicated that with 0.01 w% graphene 33% higher pce was achieved than without scattering layer and 13% higher than scattering layer without graphene. the depraving in pce at >0.01 wt% graphene despite of excellent electron transport improvement is attributed to the loss of diffuse reflectance and higher optical absorption by graphene. | graphene loaded tio2 submicron spheres scattering layer for efficient dye-sensitized solar cell |
the sheepbed mudstone forms the base of the succession examined by the curiosity rover and is also the first bona fide mudstone known on another planet. many initial papers have discussed a lacustrine depositional setting, geochemical features, and implications for habitability. careful review of all collected images and associated data prompts us to update interpretations of depositional regime, diagenesis, and burial history. the lake basin received sediment pulses associated with localized scouring, lateral thinning of beds, and decelerating flows. bed cross sections suggest mm-cm scale layering to be the norm, probably recording distal pulses of fluvial sediment injections (fine grained hyperpycnites), fall-out from river plumes, and some eolian supply. prior diagenesis studies focused on synaeresis cracks and mm-scale nodules but contrary to other genetic models we consider centrifugal diffusion could have formed hollow nodule shells, some continuing until filled. there is also an element of stratiform cementation and formation of thin, laterally extensive concretions that establish outcrop appearance of the uppermost meter of the sheepbed mudstone. typical surface mud with 80 vol% water has a water/rock ratio of about 1.4 (assuming basaltic debris), and this ratio declines with further compaction. given that clay formation is thought to require rather higher w/r, the observation of around 20% clays in these rocks seems to argue against in situ clay generation, and instead suggests that they were derived from the crater's periphery and carried into the basin by fluvial discharge. this view is also supported by the presence of significant amounts (>30%) of likely highly reactive amorphous component(s) and fe-forsterite in john klein, and the need for an initial presence of clay minerals to enable synaeresis. the virtual lack of fe-forsterite in cumberland is more supportive of in situ alteration, although significant amorphous material exists in cumberland. | revisiting the sheepbed mudstone of gale crater, mars - a comprehensive reappraisal of its depositional, diagenetic, and burial history |
lunar xenon from ancient earth-wind the apparent secular variability of the xe/kr abundance ratio in the solar wind implanted in grains of the lunar regolith is a long-standing problem (wieler, 2016): recently irradiated soils (<100 ma ago) show xe/kr ratios comparable to the ratio found in solar wind targets of the genesis mission (meshik et al. 2014, vogel et al. 2011), while lunar samples exposed billions of years ago to the solar wind exhibit a xe/kr ratio about twice as high. it has been argued that this observation is the consequence of the variability of the solar wind composition. more recently it has also been suggested that, over time, cometary impacts have contributed significantly to the inventory of noble gases and other volatiles of the lunar regolith.from our understanding of the development of typical g-stars, such as the sun, we consider it unlikely that such a strong variation could have occurred several 100 my after the lunar regolith had started to build up. today, variations of this ratio even in very different solar wind regimes are marginally distinguishable (vogel et al. 2019). on the other hand, it seems also unlikely that early cometary impacts could have implanted sufficient amounts of xe to noticeably modify the xe/kr inventory in the regolith with the correct isotopic compositions.while we are currently unable to clearly outrule any of the above hypotheses, we here propose an alternative explanation: the ancient lunar regolith has been exposed to a xenon-rich earth-wind. an ancient earth-wind has been invoked previously (e.g., geiss and bochsler, 1991, ozima et al. 2005) in order to explain the secular variability of the isotopic composition of nitrogen in the lunar regolith.the apparent secular depletion of light isotopes of atmospheric xenon combined with the presumed large deficit of xe in the atmosphere (avice et al. 2018) recently led zahnle et al. (2019) to postulate a loss of xe ions over the first 3 gy from the upper atmosphere, concomitant with the hydrogen escape and the oxygenation of the atmosphere. the loss mechanism devised by zahnle and co-authors selectively involves xe without affecting the other noble gases. it operates through resonant charge exchange of h+ with xe, leading to a low-lying excited state of xe+.we believe that escaping terrestrial xe ions will undoubtedly be incorporated into the flow of the magnetotail of the earth and impact the lunar surface, whenever the moon crosses the tail directed away from the sun. from the present cross section of the magnetotail near the orbit of the moon and the amount of xenon lost from the terrestrial atmosphere over the first few gy, we conclude that the xe-fluence of the earth-wind could be sufficient to account for the apparent secular variation of the lunar xe/kr ratio. since we expect earth-wind-xenon to be strongly fractionated in favour of light isotopes, we expect its isotopic composition to deviate significantly from the present-day terrestrial atmosphere, approaching the composition of the solar wind. unfortunately, given the experimental uncertainties of the isotopic composition of xenon in ancient lunar soil, it is difficult to obtain conclusive evidence in favour or against the earth-wind hypothesis from isotopic abundances. in a simple box model as outlined in figure 1, we investigate the potential contribution of the earth-wind to the lunar regolith using the compilation of data on the isotopic composition of xe in the ancient atmosphere of avice et al. (2018) and the abundance of xe in the mantle to determine free parameters. our first results indicate that the earth-wind is a viable alternative to explain the apparent secular decrease of the xe/kr ratio in the lunar regolith, even if the solar wind has decreased in intensity over the life-time of the sun.the earth-wind hypothesis could be tested by investigation of ancient lunar regolith samples with present-day state-of-the-art mass spectrometry and by analysis of lunar samples at different lunar longitudes, particularly from the lunar backside, which at least at present, is mostly shielded from the ion-flow in the geotail. references:avice g. et al. (2018) geochimica et cosmochimica acta 232, 82-100.geiss j., and bochsler p. (1991) in: the sun in time, the university of arizona press, 98-117.meshik a. et al. (2014) geochimica et cosmochimica acta 127, 326-347.ozima m. et al. (2005) nature 436, 655-659.vogel n. et al. (2011) geochimica et cosmochimica acta 75, 3057-3071.vogel n. et al. (2019) geochimica et cosmochimica acta 263, 182-194.wieler r. (2016) chemie der erde - geochemistry 76, 463-480.zahnle k.j., gacesa m., and catling d.c. (2019), geochimica et cosmochimica acta 244, 56-85. | lunar xenon from ancient earth-wind |
we live in a molecular universe full of complex, carbon-rich molecules and dust grains. emission from large pah (polycyclic aromatic hydrocarbon) molecules, carbon clusters, and carbon nanograins dominates the infrared spectrum from almost all objects in the universe. however the relationship, if any, between the large pahs (50-100 carbon atoms) believed to be present in the ism and the organic content a planetary system, is not understood. can the large pahs survive a proto-solar nebula, and serve as chemical feedstock for the organic content of a planetary system? are the complex organic molecules (coms) found within our solar system the result of a "bottom-up" synthesis from smaller molecules? recent experimental evidence involving large pahs and high energy radiation provides new insight into these questions. this presentation will discuss these results and their implications for the organic content of planetary systems and astrobiology. | formation of complex organic materials (coms) from pahs |
the saturnian moon enceladus presents a remarkable opportunity in our solar system for searching for evidence of life, given its habitable ocean and active plume that deposits organic-bearing ocean material onto the icy surface. organic ocean material could be sampled by a lander mission on the surface of enceladus. it is of interest to understand the amount of relatively pristine, unaltered organics present on the surface, given the uv and plasma environment. here we provide estimates of exposure ages of plume deposits - and the organic material therein - using the uv spectral signature of enceladus to understand the penetration depth of solar uv photons into the icy regolith. we investigate the resultant effective exposure ages for various regions on enceladus, considering the rate of resurfacing by plume fallout. in high plume fallout regions near the south pole, we find that plume grains are buried by fresher grains within years, resulting in low levels of exposure of surface grains to solar uv, which penetrates only ~100 microns. regions at latitudes south of ~40°s can have exposure ages <100 years, translating to relatively high abundances of pristine organic material preserved in the icy regolith. | low effective uv exposure ages for enceladus surface organics |
earth is the only known inhabited world in our solar system. criteria essential for planetary habitability include surface liquid water, a stable atmosphere, and a magnetic field. while the rock record suggests earth has fulfilled these criteria for at least 4 billion years (ga), both its environment and life have evolved over time. the great oxygenation event (goe), which occurred ~2.5 ga ago, drastically altered the chemistry of the oceans and atmosphere. decoding environmental and magnetic signals recorded in rocks prior to the goe is essential for understanding the conditions under which life first emerged.an ideal target for investigating surface conditions prior to the goe are banded iron formations (bifs), which precipitated directly from ancient oceans. however, bifs have been significantly altered since their formation, and it is unclear whether a record of their depositional environment remains. the present day mineralogy is dominated by magnetite, but it remains to be established how this relates to the precipitates deposited on the seafloor. additionally, in spite of magnetite's ideal magnetic properties, bifs are avoided for paleomagnetic analysis because the timing of magnetization is uncertain. it is vital to constrain the magnetic field record leading up to the goe because it may have influenced atmospheric hydrogen loss, contributing to rapid surface oxidation.we present paleomagnetic field tests from the isua supracrustal belt that suggest a record of earth's 3.7-billion-year (ga) old (eoarchean) magnetic field is preserved in the banded iron formation in the northernmost northeast region of the belt. our results are supported by radiometric pb-pb dating of magnetite from the same banded iron formation. we show that the pb-magnetite system has a closure temperature below 400 °c for the magnetite grain size range observed in the banded iron formation, suggesting the rocks have not been significantly heated since magnetization was acquired. this temperature range is well below the curie temperature of magnetite (580 °c), suggesting eoarchean magnetization has not been thermally overprinted by subsequent metamorphism. passed paleomagnetic field tests suggest the rocks have also avoided chemical overprints. we recover an ancient magnetic field strength, supporting previous studies that argue earth's magnetic field has been active throughout most of its history although variations in its strength remain poorly constrained. | using banded iron formations to understand habitable conditions on the early earth |
this dissertation combines three perspectives on the potential of cost reductions of renewable energy--a relevant topic, as high energy costs have traditionally been cited as major reason to vindicate developments of fossil fuel and nuclear power plants, and to justify financial support mechanisms and special incentives for renewable energy generators. first, i highlight the role of market and policy drivers in an international comparison of upfront capital expenses of residential photovoltaic systems in germany and the united states that result in price differences of a factor of two and suggest cost reduction opportunities. in a second article i examine engineering approaches and siting considerations of large-scale photovoltaic projects in the united states that enable substantial system performance increases and allow thus for lower energy costs on a levelized basis. finally, i investigate future cost reduction options of wind energy, ranging from capital expenses, operating expenses, and performance over a project's lifetime to financing costs. the assessment shows both substantial further cost decline potential for mature technologies like land-based turbines, nascent technologies like fixed-bottom offshore turbines, and experimental technologies like floating offshore turbines. the following paragraphs summarize each analysis: international upfront capital cost comparison of residential solar systems: residential photovoltaic (pv) systems were twice as expensive in the united states as in germany in 2012. this price discrepancy stems primarily from differences in non-hardware or "soft" costs between the two countries, of which only 35% be explained by differences in cumulative market size and associated learning. a survey of german pv installers was deployed to collect granular data on pv soft costs in germany, and the results are compared to those of a similar survey of u.s. pv installers. non-module hardware costs and all analyzed soft costs are lower in germany, especially for customer acquisition, installation labor, and profit/overhead costs, but also for expenses related to permitting, interconnection, and inspection procedures. additional costs occur in the united states due to state and local sales taxes, smaller average system sizes, and longer project-development times. to reduce the identified additional costs of residential pv systems, the united states could introduce policies that enable a robust and lasting market while minimizing market fragmentation. regularly declining incentives offering a transparent and certain value proposition might help accelerate pv cost reductions in the united states. performance analysis of large-scale solar installations in the united states: this paper presents the first known use of multi-variate regression techniques to statistically explore empirical variation in utility-scale pv project performance across the united states. among a sample of 128 utility-scale pv projects totaling 3,201 mwac, net capacity factors in 2014 varied by more than a factor of two. regression models developed for this analysis find that just three highly significant independent variables can explain 92% of this project-level variation. adding the commercial operation year as a fourth independent variable and three interactive variables improves the model further and reveals interesting relationships. taken together, the empirical data and statistical modeling results presented in this paper can provide a useful indication of the level of performance that solar project developers and investors can expect from various project configurations in different regions of the united states. moreover, the tight relationship between fitted and actual capacity factors should instill confidence among investors that the utility-scale projects in this sample have largely performed as predicted by our models, with no significant outliers to date. holistic assessment of future cost reduction opportunities of wind energy applications: wind energy supply has grown rapidly over the last decade. however, the long-term contribution of wind to future energy supply, and the degree to which policy support is necessary to motivate higher levels of deployment, depends on the future costs of both onshore and offshore wind. here, i summarize the results of an expert elicitation survey of 163 of the world's foremost wind experts, aimed at better understanding future costs and technology advancement possibilities. results suggest significant opportunities for cost reductions, but also underlying uncertainties. costs could be even lower: experts predict a 10% chance that reductions will be more than 40% by 2030 and more than 50% by 2050. the main identified drivers for near term cost reductions are rotor-related advancements and taller towers for onshore installations, fixed-bottom offshore turbines can benefit from an upscaling in generator capacity, streamlined foundation design and reduced financing costs, while floating offshore turbines require further progress in buoyant support structure design and installation process efficiencies. insights gained through this expert elicitation complement other tools for evaluating cost-reduction potential, and help inform policy, planning, r&d, and industry strategy. (abstract shortened by proquest.). | socio-economic and engineering assessments of renewable energy cost reduction potential |
ocean worlds in the solar system are prime targets for the search for life. we conducted laboratory laser-based experiments for the identification of bacterial cells on ocean worlds using mass spectrometry during spacecraft flybys. our results show that, using this approach, signatures of the investigated bacteria could be clearly identified on ocean worlds with a surface dust analyzer (suda)-type instrument. | laboratory predictions for the identification of bacterial cells in ice grains from ocean worlds |
interstellar gas and dust can condense into clouds of very different size, ranging from giant molecular cloud complexes to massive, isolated, dark cloudlets, called globules with a few solar masses. this thesis focuses on a new category of small globules, named globulettes. these have been found in the bright surroundings of h ii regions of young, massive stellar clusters. the globulettes are much smaller and less massive than normal globules. the analysis is based on h-alpha images of e.g., the rosette nebula and the carina nebula collected with the nordic optical telescope and the hubble space telescope. most globulettes found in different h ii regions have distinct contours and are well isolated from the surrounding molecular shell structures. masses and densities were derived from the extinction of light through the globulettes and the measured shape of the objects. a majority of the globulettes have planetary masses, <13 m_j (jupiter masses). very few objects have masses above 100 m_j ≈ 0.1 m (solar masses). hence, there is no smooth overlap between globulettes and globules, which makes us conclude that globulettes represent a distinct, new class of objects. globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. at a later stage, globulettes expand, disrupt or evaporate. however, preliminary calculations of their lifetimes show that some might survive for a relatively long time, in several cases even longer than their estimated contraction time. the tiny high density globulettes in the carina nebula indicate that they are in a more evolved state than those in the rosette nebula, and hence they may have survived for a longer time. it is possible that the globulettes could host low mass brown dwarfs or planets. using the virial theorem on the rosette nebula globulettes and including only the thermal and gravitational potential energy indicated that the 133 found globulettes are all either expanding or disrupting. when the ram and the radiation pressure were included, we found that about half of our objects are gravitationally bound or unstable to contraction and could collapse to form brown dwarfs or free floating planets. we also estimated the amount of globulettes and the number of free floating planetary mass objects, originating from globulettes, during the history of the milky way. we found that a conservative value of the number of globulettes formed is 5.7×10^10. a less conservative estimate gave 2 × 10^11 globulettes and if 10% of these forms free floating planets then the globulettes have contributed about 0.2 free floating planets per star. in the crab nebula, which is a supernova remnant from the explosion of a massive old star, one can find dusty globules appearing as dark spots against the background nebulosity. these globules are very similar to the globulettes we have found in h ii regions. the total mass of dust in globules was estimated to be 4.5×10^-4 m, which corresponds to .2% of the total dust content of the nebula. these globules move outward from the center with transversal velocities of 60-1600 km s-1. using the extinction law for globules, we found that the dust grains are similar to the interstellar dust grains. this means that they contribute to the ism dust population. we concluded that the majority of the globules are not located in bright filaments and we proposed that these globules may be products of cell-like blobs or granules in the atmosphere of the progenitor star. theses blobs collapse and form globules during the passage of the blast wave during the explosion. | dusty globules and globulettes |
oceanic ph and salinity are fundamental indices, needed for describing both chemistry and biochemistry. earth, being relatively water-poor, is an end member of the ocean planet family. we study planets very rich in water. understanding both end members is important for establishing a global view on the ph and salinity of ocean worlds. we find it likely that the ocean floor is rich in co2 clathrates. their density implies gravitational stability only for nacl concentrations less than ≈0.56 molal. in addition, in our studied planets a desalination pump is at work, with a timescale τd. high-pressure ice, devoid of salt, upwells and melts below ridges along the ocean floor. therefore, an ocean in steady-state experiences solidification at the same rate ( 108 kg/s). this solidification partitions hydrated ions of salt out of the ocean and into the ocean floor. overturn of the ice mantle causes the newly formed floor to downwell. in the deep ice mantle the interstitial ions are exsolved out of the ice (for t>500k). the highly-dense grains of salt sediment onto the rocky core. in regions of downwelling, if there is no macroscopic entrapment of oceanic water, and local temperatures can stabilize ice vii, we find τd ≈ 20 myr. for an ocean floor composed of ice vi we find τd ≈ 860 myr. if macroscopic entrapment can account for 1% of the reprocessing of ocean water than the latter reduces to 290 myr. thus, the desalination of the ocean is efficient, with fundamental implications for its habitability. after 5 gyr (age of kepler planets) the maximal concentration of oceanic nacl is ≈0.001 molal. we find that freely dissolved co2 is the most abundant form of inorganic carbon (≈1.3 molal), independent of depth. we find no substantial difference between the concentrations of h+ and bicarbonate (0.0006 - 0.01 molal). carbonate and hydroxide exist only in trace amounts. our studied ocean worlds, are likely rich in volatiles, though poor in salts. these oceans are acidic and stably stratified. their ph decreases with depth from 4 to 2. only a few extremophiles inhabit our low temperature and acidic regime. their scarcity may be due to the high stress imposed by these conditions. however, it may also be the result of the rarity of such an environment on earth. our studied oceans impose additional stressors on life, such as high pressure and low salinity. | the ph and salinity of ocean worlds: when high-pressure ice separates the ocean from the rocky interior |
nasa's mars exploration rovers (mer) and mars science laboratory curiosity rover (msl) are proxies for field geologists on mars, taking high resolution imagery of rock formations and landscapes which is analysed in detail on earth. panoramic digital cameras (pancam on mer and mastcam on msl) are used for characterising the geology of rock outcrops along rover traverses. a key focus is on sedimentary rocks that have the potential to contain evidence for ancient life on mars. clues to determine ancient sedimentary environments are preserved in layer geometries, sedimentary structures and grain size distribution. the panoramic camera systems take stereo images which are co-registered to create 3d point clouds of rock outcrops to be quantitatively analysed much like geologists would do on earth. the eu fp7 provide project is compiling all mars rover vision data into a database accessible through a web-gis (progis) and 3d viewer (pro3d). stereo-imagery selected in progis can be rendered in pro3d, enabling the user to zoom, rotate and translate the 3d outcrop model. interpretations can be digitised directly onto the 3d surface, and simple measurements can be taken of the dimensions of the outcrop and sedimentary features. dip and strike is calculated within pro3d from mapped bedding contacts and fracture traces. results from multiple outcrops can be integrated in progis to gain a detailed understanding of the geological features within an area. these tools have been tested on three case studies; victoria crater, yellowknife bay and shaler. victoria crater, in the meridiani planum region of mars, was visited by the mer-b opportunity rover. erosional widening of the crater produced <15 m high outcrops which expose ancient martian eolian bedforms. yellowknife bay and shaler were visited in the early stages of the msl mission, and provide excellent opportunities to characterise martian fluvio-lacustrine sedimentary features. development of these tools is crucial to exploitation of vision data from future missions, such as the 2018 exomars rover and the nasa 2020 mission. the research leading to these results has received funding from the european community's seventh framework programme (fp7/2007-2013) under grant agreement n° 312377 provide. | pro3d®: a tool for high resolution rendering and geological analysis of martian rover-derived digital outcrop models. |
glacier movement has been measured over the years using commercial units such as those from leica. the aim is to measure point movements on the glacier surface in order to capture fine-grained data about its movement. this can also help to calibrate satellite-based approaches which have much lower resolution. commercial dgps recorders cost thousands of euros so our project is creating a solution using new lower cost dgps boards which could enable their use by more earth scientists.the u-blox zed-f9p based boards from sparkfun can be used as a base station to send dgps corrections to "rover" units on the glacier via a radio link. each measurement is accurate to about 2cm depending on conditions. in our design the radio is used by the rovers to forward good fixes back to the base station, which then uses off-site communications to send the data home. two types of internet link have been enabled: using a nano-satellite board (by swarm) and a more traditional gsm mobile phone board (for locations with coverage). both these boards are also available from sparkfun - making most of the modules off-the-shelf. however our power supply is optimised to save power and charge the lithium ion battery from a solar panel. a real-time clock chip is used to wake up the system to take readings and transmit data, so the sleep power is only 0.03 mw enabling a year-long lifetime. the whole system is controlled by a sparkfun thing plus samd51 which provides the required four serial connections and a circuitpython environment. the full system will be installed in iceland in the summer of 2023 and replace the previous prototype based on swift piksi multi units which had shown the measurement principle to be sound. | a low cost real-time kinematic dgps system for measuring glacier movement |
halide perovskite materials have emerged in the past few years as promising materials in the absorption layer of photovoltaic cells and new emissive materials for use in light emitting diodes (leds). this is due to their rapidly increasing efficiencies and brightness. in photovoltaic applications they show promise to lower cost and improve efficiency of photovoltaic cells. their low temperature processability also may lead to interesting new applications in existing solar cell technologies. in led applications, they exhibit other desirable properties such as color tunability, simple device structures, and facile processability. however, a common problem that is observed in perovskite thin films is a hysteresis in their i-v characteristics, and short device lifetimes. it is hypothesized this is due to ion migration within the crystal and along the grain boundaries between crystals. this thesis addresses this issue by exploring methods to restrict ionic motion. one highly promising method was controlling nucleation to reduce the grain boundary density in the perovskite thin films. a deterministic nucleation process was developed using standard lithography techniques to prepattern a substrate followed by solution processing of the halide perovskite layer. it was found the grain size, grain boundary density, and final crystal shape could be well controlled using this process. in addition, it was found the hysteresis behavior was well controlled, and the stability of the final film was increased due to lower grain boundary density. in addition, further methods to restrict ionic motion were explored using ruddlesden-popper perovskites that form a quasi 2d structure. these perovskites were examined and characterized due to their ability to restrict ionic motion within the perovskite crystal. these perovskites also allowed for further flexibility in tuning device electrical and optical properties and offered greater stability compared to their 3d counterparts. | deterministic nucleation and structural control of halide perovskite thin films for optoelectronic devices |
we present time-dependent simulations to study evaporative transmission spectra at candidate exo-io systems. several close-in gas giant systems are now known to possess minimum column densities, of neutral sodium and potassium, <n>min ≥ ~1010 - 1011 cm-2, that are able to be sustained in the planetary exosphere via the evaporation of rocky exomoons or exoring grains, during transit. however, the proximity of the stellar tide, along with the photoionization lifetime of τna < 5 minutes within an orbit <10 rsun, strongly suggest any jupiter-io interaction should display time-dependent behavior in individual exposures associated with the close-in orbit of a putative third body. time-series data from 2011-2021 of wasp-49, a g6v star (k = 9.75) taken by the high-resolution spectrographs: espresso/vlt, keck/hires, and harps/eso-3.6-m, are analyzed before, during, and after the transit of wasp-49 b, a hot saturn orbiting at 2.8 days. we report a transient sodium signature occulting 3.53% of nad2 light at 3.1σ confidence, far larger than <n>min , during the transit of the gas giant's hill sphere ~ 100 minutes before transit begins. transient and sustained alkali line absorption depths are systematically compared with several other exo-io candidate systems to test the validity of the interpretations, as d2/d1 and na/k ratios are known to characterize evaporative rock and ice processes in the solar system. we discuss conundrums with an exomoon-cloud scenario, and how alkali signatures at certain exoplanets may not be planetary, as recently suggested at hd-209458 b. future infrared observatories may identify progenitor molecules of the evaporating atoms we observe here (e.g. dusty exorings/exomoons), as well as the thermal emission of tidally-heated molten rock. | transient sodium and potassium clouds at candidate exomoon systems |
enceladus's subsurface global ocean (1) can be probed by sampling the gaseous and icy material the moon expels into its cryovolcanic plume and - even further out - into saturn's e ring (2,3,4,5). hydrothermal outflows caused by tidal heating (4,5,6), together with rich organic chemistry (7,8) imply that the moon appears to be one of most habitable places in our solar system. among the critical elements c, h, n, o, p and s that are considered to be essential for life, all except phosphorous have either been identified (5,7,8) or - in the case of sulfur - tentatively detected (9). recent geochemical modelling claims that p will be severely depleted in ocean worlds and thus p could be a bottle neck for the emergence of life in subsurface oceans (10).here we present results from a re-analysis of mass spectrometric data from cassini's cosmic dust analyzer (cda), showing proof of sodium-phosphate salts in ice grains originating from enceladus's subsurface ocean. we found a small number of ice grains whose spectra clearly indicate the presence of at least two sodium orthophosphates: na3po4 and na2hpo4. these cda spectra have been subsequently reproduced in the laboratory which enables the quantitative evaluation of cda spectra (11). we infer phosphate concentrations in the enceladus ocean in the order of a few mm, at least 100-times higher concentrations than in earth's ocean.we carried out geochemical experiments and calculations showing that such high phosphate abundances can be achieved in enceladus, either at the cold seafloor or in hydrothermal environments with moderate temperatures. the driver enabling the abundant availability of phosphate is the high observed concentration of dissolved carbonate species, which shift phosphate-carbonate mineral equilibria toward dissolution of solid phosphates into enceladus' ocean. we show that interactions between chondritic rocks and co2-rich fluids generally lead to conditions where dissolved phosphate concentrations tend to maximize. therefore p-rich oceans would commonly occur in ocean worlds beyond in the outer solar system beyond the co2 snow line.these results demonstrate that enceladus has a high availability of dissolved p, which is thus likely not a limiting factor for development of putative life on enceladus and probably on other ocean worlds in the outer solar system. since phosphate plays many roles in organic synthesis (12), enceladus and other icy bodies could moreover serve as natural analogs of p-rich environments on early earth, where chemical evolution might have been promoted.1 thomas et al., icarus 264 (2016), 2 postberg et al., nature 459 (2009), 3 postberg et al., nature 474 (2011), 4 hsu et al., nature 519 (2015), 5 waite et al., science 356 (2017), 6 choblet et al. , nat astron 1 (2017), 7 postberg et al., nature 558 (2018) , 8 khawaja et al., mnras 489 (2019), 9 postberg et al., isbn: 9780816537075 (2018), 10 lingam & loeb, astron. j., 2018., 11 klenner et al., rapid commun mass spectrom 33 (2019), 12 powner et al., nature 459 (2009) | detection of phosphate in enceladus' ocean with implications for geochemistry and habitability in the outer solar system |
for more than 300 sols, the mars science laboratory team has been exploring vera rubin ridge (vrr), a prominent topographic feature on the lower northwest slope of aeolis mons. curiosity's investigation of the ridge began with an ascent starting around sol 1800, and subsequent traverse through several key waypoints which were identified based on data from orbiting instruments. here we review the sedimentary facies and stratigraphy observed during sols 1800-2115, covering more than 100 m of stratigraphic thickness. curiosity's traverse includes two distinct transects across the ridge, which enables studies of lateral variability over a distance of 300 m. three informally-named stratigraphic members of the murray formation are described: blunts point, pettegrove point, and jura, with the latter two forming the topographic feature known as vrr. the blunts point member, exposed on the north-facing slope just below the ridge, is characterized by a recessive, fine-grained facies that exhibits extensive planar lamination and is crosscut by abundant curviplanar calcium sulfate veins. the pettegrove point member is more resistant, fine-grained, thinly planar laminated, and contains a higher abundance of diagenetic concretions compared to the blunts point member. conformable above the pettegrove point member is the jura member, which is also fine-grained and parallel stratified, but shows much more variability in color and includes meter-scale inclined strata and occasional diagenetic crystal molds, suggestive of former gypsum based on their geometry consistent with swallowtail twinning. all three members record deposition in a dominantly low-energy lacustrine environment, consistent with prior observations of the murray formation earlier in the mission. uncommon outcrops of low-angle stratification suggest possible influences by subaqueous currents, and steeply inclined beds may be the result of slumping. collectively, the rocks exposed at vrr provide additional evidence for a long-lived lacustrine environment (in excess of 106 years via comparison to terrestrial records of sedimentation), which extends our understanding of the duration of habitable conditions in gale crater. | a lacustrine environment recorded at vera rubin ridge: overview of the sedimentology and stratigraphy observed by the mars science laboratory curiosity rover |
comet neowise (c/2020 f3) displayed a highly structured dust tail, exhibiting the most prominent dust tail features visible from earth since comet mcnaught (c/2006 p1) in the southern hemisphere and comet hale-bopp (c/1995 o1) in the northern hemisphere. using images taken by the amateur astronomer community, this dust tail is analysed using the finson-probstein model. the comet's position in the sky in amateur images is calculated using an open source algorithm [1], the position and exact time then calculated, and the dust tail is simulated. this modelled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. using the novel analysis method of mapping the image to a plot of dust grain beta against ejection time[2], tail structures can be more easily identified, analysed and tracked over time (where beta is the ratio of force due to solar radiation pressure and that due to the sun's gravity).dust tail structures such as syndynic bands and striae (near-parallel linear features) have been identified and characterised in terms of dust ejection time and dust beta values. these structures are tracked over time, and compared to the analysis of similar structures seen in c/2006 p1 (mcnaught) [2]. there are some clear differences between the two comets, particularly in the alignment and arrangement of their striae, most likely due to different heliospheric conditions during each comet's perihelion passage. these results, all based on amateur observations, provide a thorough description of comet neowise's dust tail to contribute to the collection of cometary dust tail profiles currently available. this will enable convenient comparison between comets in the future, and will eventually enable population studies on cometary dust tails and their features. due to the comet's very high activity, it also exhibited a rarely seen tail of neutral sodium atoms. this sodium tail has also been parameterised in this work, with an estimated ionization lifetime of the sodium atoms of 17 hours ± 2 hours. [1] lang, dustin, david w. hogg, keir mierle, michael blanton, and sam roweis. 2010."astrometry.net: blind astrometric calibration of arbitrary astronomical images". the astronomical journal 139 (5): 1782-1800. doi:10.1088/0004-6256/139/5/1782.[2] price, oliver, geraint h. jones, jeff morrill, mathew owens, karl battams, huw morgan, miloslav drückmuller, and sebastian deiries. 2019. "fine-scale structure in cometary dust tails i: analysis of striae in comet c/2006 p1 (mcnaught) through temporal mapping". icarus 319: 540-557. doi:10.1016/j.icarus.2018.09.013. | structural analysis of the dust tail of comet neowise (c/2020 f3) |
many factors have conspired to make earth a home to complex life. earth has abundant water due to a combination of factors, including orbital distance and the climate regulating feedbacks of the long-term carbon cycle. earth has plate tectonics, which is crucial for maintaining long-term carbon cycling and may have been an important energy source for the origin of life in seafloor hydrothermal systems. earth also has a strong magnetic field that shields the atmosphere from the solar wind and the surface from high-energy particles. synthesizing recent work on these topics shows that water, a temperate climate, plate tectonics, and a strong magnetic field are linked together through a series of negative feedbacks that stabilize the system over geologic timescales. although the physical mechanism behind plate tectonics on earth is still poorly understood, climate is thought to be important. in particular, temperate surface temperatures are likely necessary for plate tectonics because they allow for liquid water that may be capable of significantly lowering lithospheric strength, increase convective stresses in the lithosphere, and enhance the effectiveness of "damage" processes such as grainsize reduction. likewise, plate tectonics is probably crucial for maintaining a temperate climate on earth through its role in facilitating the long-term carbon cycle, which regulates atmospheric co2 levels. therefore, the coupling between plate tectonics and climate is a feedback that is likely of first order importance for the evolution of rocky planets. finally, plate tectonics is thought to be important for driving the geodynamo. plate tectonics efficiently cools the mantle, leading to vigorous thermo-chemical convection in the outer core and dynamo action; without plate tectonics inefficient mantle cooling beneath a stagnant lid may prevent a long-lived magnetic field. as the magnetic field shields a planet's atmosphere from the solar wind, the magnetic field may be important for preserving hydrogen, and therefore water, on the surface. thus whole planet coupling between the magnetic field, atmosphere, mantle, and core is possible. we lay out the basic physics governing whole planet coupling, and discuss the implications this coupling has for the evolution of rocky planets and their prospects for hosting life. | whole planet coupling from climate to core: implications for the evolution of rocky planets and their prospects for habitability |
neutral aqueous flow batteries with common traits of the redox flow batteries, such as the independence of energy and power, scalability and operational flexibility, and additional merits of outstanding safety and low corrosivity show great promise for storing massive electrical energy from solar and wind energy. particularly, the ferricyanide/ferrocyanide ([fe(cn)6]3−/4−) couple has been intensively employed as redox mediator to store energy in the catholyte ascribed to its abundance, low corrosivity, remarkable redox reversibility and stability. however, the low energy density arising from poor solubility of [fe(cn)6]3−/4− restricts their commercial applications for energy storage systems. in this study, the practical energy density of a [fe(cn)6]3−/4−‑based catholyte is significantly boosted from 10.5 to 92.8 wh l−1 by combining the counter‑ion effect and the single‑molecule redox‑targeting (smrt) reactions between [fe(cn)6]3−/4− and prussian blue (fe4[fe(cn)6]3, pb)/prussian white (pw). paired with concentrated k2s anolyte, we demonstrate a neutral aqueous smrt‑based pb−fe/s flow battery with ultra‑long lifespan over 7000 cycles (4500 h) and ultra‑low chemical cost of electrolytes in the cell as 19.26 $ kwh−1. remarkably, under the influences of smrt reactions in the presence of pb granules in the catholyte, the capacity after 7000 cycles of the pb−fe/s flow battery is 181.8 % of the initial capacity without pb. | redox targeting‑based neutral aqueous flow battery with high energy density and low cost |
opportunity has been exploring exposures of noachian-age rocks along the rim of endeavour crater since august 2011, motivated by orbital spectral evidence for phyllosilicates at multiple locations along the crater's rim. as reported previously, opportunity discovered multiple bright linear features at "cape york" that have been interpreted as veins of ca sulfate deposited in bedrock fractures, and in-situ measurements are consistent with the presence of smectite clays in rocks and veneers on the east side of cape york. the inferred neutral ph and relatively low temperature of the fluids involved in multiple phases of alteration would have provided a habitable environment if life existed on mars at that time. because opportunity can no longer directly sense phyllosilicate mineralogy with the minites or mössbauer spectrometers, it is focusing on characterizing outcrop multispectral reflectance with pancam, chemistry with the alpha particle x-ray spectrometer and microtexture with the microscopic imager (mi) of potential phyllosilicate host rocks. while traversing the western side of "murray ridge," opportunity found outcrops of breccia that are similar in texture and chemical composition to the shoemaker formation rocks exposed at cape york. mi images of the breccias show cm-size angular clasts in fine-grained matrix, consistent with an impact origin. at "cook haven," the rover wheels overturned a few rocks, exposing dark mn-rich coatings and haloes on brighter sulfates (figure 1), which suggest aqueous precipitation followed by interaction with a strong oxidant. the dark, resistant coatings on "thessaloniki" are less than about 0.1 mm thick, barely resolved in places by mi stereogrammetry. opportunity's mission continues, with the rover exploring more exposures of phyllosilicates detected from orbit on "cape tribulation." the latest mi results, including observations in "marathon valley," will be presented at the conference. | opportunity microscopic imager results from the western rim of endeavour crater, mars |
summary. grain boundaries in perovskites are a major source of degradation in perovskite solar cells. here, we report selective passivation of perovskite grain boundaries with the aid of biphenyl-containing moieties. we find that biphenyl ligands selectively react with pbi2-rich interfaces but not with perovskite itself. such targeted defect deactivation of grain boundaries leads to extended radiative recombination lifetime from 1 to 2.7 μs while allowing for efficient charge transfer from grains. the hydrophobic nature of benzene ring present in biphenyl improves the stability of perovskite in direct reaction with water by a factor of 3. the devices, all fabricated in ambient air, show significantly improved reproducibility (17%-21% efficiency) and increased open-circuit voltage of 1.11 v. this work offers a design principle for selective passivation of grain boundaries and chemical stabilization of hybrid structures. | selective deactivation of perovskite grain boundaries |
cinematic visualization of a solar system mission and its environment can lead to new insights for both general audiences and mission scientists and engineers. for its most recent planetarium show, the california academy of sciences chose to address the topic of searching for signs of life on enceladus. working closely with the exobiology extant life surveyor (eels) team at jpl, the academys visualization studio created a scene in which enceladus and its geysers are seen at a global scale before diving into a simulated ocean environment with physically reasonable hydrothermal ventsand emerging through a crevasse near the south pole, where viewers encounter the eels robot snaking its way downward to search for signs of life. at each point in that virtual journey, physical considerations were taken into account that informed not just the appearance of the scene, but also the characteristics of the mission parameters. how rapid is the flow of gas and grains around the eels robot during its descent? how many particulates would be seen in the flow, and how might this affect navigation of the robot? how do the reduced gravity of enceladus and the high-saline buoyancy affect the rate at which material rises from putative hydrothermal vents? those and many other questions came to the fore in developing the planetarium show. this collaboration points to new ways of fostering educational partnerships that can benefit mission team members and the general public. | visualizing enceladus: designing a scene for an immersive planetarium show |
spatially sharpened, along-track oversampled crism data show horizons of hematite distributed non-uniformly throughout mudstones of the murray formation, the oldest unit of mt. sharp, and curiosity drill samples from three locations within this unit contain 5-20 wt.% hematite. due to the redox chemistry and solubility of ferric iron, this phase likely formed at a redox interface, and understanding its formation is critical for reconstructing past geochemical environments at mt. sharp and may provide insight into mars' ancient atmosphere. one key question is whether hematite (or a precursor ferric phase) precipitated syndepositionally with the murray formation, or if it is a product of post-depositional processes. we used mastcam multispectral and chemcam passive spectral data to map the presence of hematite and other iron oxides at the outcrop-scale along curiosity's traverse, and combined these results with larger scale crism context mapping to provide insight into the stratigraphic setting, timing, and mechanism(s) of hematite formation. the locations of hematite, and possibly other less crystalline ferric phases, seen by curiosity and crism data roughly coincide, confirming the validity of crism mapping and supporting the conclusion that iron oxides are non-uniformly present throughout the murray formation. the shape of mastcam and chemcam hematite-like spectral signatures vary along the traverse, and may reflect differences in grain size, crystallinity, and/or abundance. mastcam images at the outcrop scale show that iron oxides are not associated with later-stage diagenetic features such as veins or concretions, so this phase is probably present as a cement, coating, or fine-scale grains. notably, hematite-like spectral signatures are never observed in the younger, overlying stimson formation, suggesting these phases formed prior to the deposition of this unit. | distribution of iron oxides in lower mt. sharp from curiosity and orbital datasets, and implications for their formation |
most dunes in the netherlands are phytogenic, which means that plants are essential in their formation. this applies also to the dunes of the inland drift sand areas, which are nicknamed atlantic deserts on account of their extreme climatic conditions. daily temperatures on the bare sand surfaces may run up to 60° c on sunny summer days, dropping as low as below freezing point at night. apart from blue and green algae, corynephorus canescens, grey hair-grass, it is the first conqueror of these active sands and plays an important role in the geomorphological development of the inland drift sands. c. canescens is a rapid colonizer and flourishes when it receives a regular supply of fresh sand, but is soon succeeded by competitor species. like ammophila arenaria (marram grass), its vigour declines after some time, because its roots are affected. therefore the plant requires a regular supply of fresh sand to outgrow the affected root zone. the growth of c. canescens is stimulated by two different geomorphological processes: aeolian and pluvial processes. aboveground, the tussock architecture of the plant helps to trap sand and form small initial dunes. when formed by wind, these are called nabkahs; when formed by splash bush mounds. in a micro-morphological thin section both processes can often be recognized in one dune. the decline of c. canescens is caused by two soil-forming processes: reduction of permeability and accumulation of organic matter. poor aeration and compaction restrict the growth of its roots. increase in organic matter hampers the rate of root respiration and promotes conditions for the establishment of competitor species. in the nabkahs, thin slides show on the positive side for c. canescens there is little blown-in organic matter, but on the negative side that the grains upon aging develop a colourless organic coating formed by cyanobacteria (algae. for splashed sands on the positive side for grey hairgrass there are few organic coatings, but on the negative side there are many organic fragments. so although different both sediments have the same effect. under the present climate and level of air pollution, the phase of c. canescens is short-lived. its disappearance marks the end of dune formation and after its decline slope development changes drastically. in conclusion, the interaction between corynephorus canescens and the geomorphological and soil processes are important in the development and the geodiversity of inland drift sands. | the contribution of corynephorus canescens to the geodiversity of inland drift sands |
molecules that are important for life on earth or elsewhere are called astrobiologically relevant molecules. one of the theories of the origin of life on earth is that comets and asteroids brought these astrobiologically relevant molecules to earth during the late heavy bombardment in the early stages of our solar system formation. comets are thought of preserving the primordial interstellar composition in their interior. in order to understand how and when simple interstellar molecules such as h2o, co, co2, ch4, nh3, ocs, etc., have been transformed into complex astrobiologically relevant molecules, we developed a laboratory method. using two lasers we scoop and analyze very cold ice in one step without having to process the sample. our work showed that astrobiologicall relevant molecules can be synthesized in interstellar ice grains at temperatures as low as 5 k, confirming that interstellar ice grains generate these molecules (that would have eventually made to earth and riggered origin of life). | in-situ interrogation of astrophysical ice analogs to understand the origins of astrobiologically relevant molecules |
one of the leading hypotheses for the emergence of life suggests that the building blocks of life were delivered to earth at an early phase by comets and asteroids. protoplanetary disks around young stars offer a unique window into the physical and chemical processes that may have occurred in the early solar system. although only a limited number of atoms and molecules have been observed in these objects, high resolution observations with the atacama large millimeter/sub-millimeter array (alma) have revolutionized the study of protoplanetary disks. these observations indicate that local physical conditions strongly affect the molecular content of disks. molecules such as n2h+, c2h and h2co show ring-like structures suggesting an active gas-grain chemical coupling. evidence for gas-grain chemistry has been further strengthened by the recent detection of two complex organic molecules, methanol and methyl cyanide. in this presentation i will show results obtained from new detailed models of protoplanetary disks. i will show that complex organic molecules efficiently form at the surface of grains in the dense, shielded midplane of disks and discuss the effect of radial and vertical variations of the physical conditions on the spatial distribution of these molecules. | theoretical investigations on the production of organic molecules in protoplanetary disks |
since its departure from the plains of aeolis palus, the curiosity rover has traversed through a number of new geologic units at the base of mount sharp in gale crater. these have included both units inferred to comprise the lower strata of mount sharp itself, along with units that appear to superpose mount sharp. over the last 100 sols, curiosity has documented several occurrences of a stratigraphic contact between fine-grained mudstones of the murray formation, and coarser sandstones of the overlying stimson unit. detailed mapping from both orbital and rover image and topographic data suggests an unconformable relationship between the two units. from orbit, inferred exposures of the unconformity span at least several tens of meters, climbing up the lowermost slopes of mount sharp. although the absolute timing of the two units is poorly constrained, this unconformity between likely represents a geologically significant gap in time. deposition of the overlying stimson unit is inferred to post-date the large-scale erosion of mount sharp, likely requiring late stage aqueous interaction in the lithification of the stimson unit. from the rover, stereo imaging reveals the small-scale topography preserved at the murray-stimson contact, and allows the determination of bedding geometries within the units. where laminations are expressed, the basal mount sharp rocks exhibit planar stratification at low angles to horizontal. in contrast, the coarser-grained stimson unit exhibits large-scale cross stratification. three dimensional bedding geometry within this unit indicates a predominant southward transport direction uphill towards mount sharp. the observation of rounded calcium sulfate clasts in the lowermost stimson unit, interpreted to be reworked veins from the underlying murray formation, supports the interpretation of an erosional unconformity. investigations at the boundary between these two distinct units present a unique opportunity to probe the long-term environmental history of the gale crater basin. | investigation of a major stratigraphic unconformity with the curiosity rover |
introduction the reliable identification of biosignatures on extraterrestrial ocean worlds is key to the search for life in our solar system. saturn's moon enceladus, and potentially jupiter's moon europa, emit plumes of gas and ice grains formed from subsurface water into space (e.g. spahn et al. 2006, roth et al. 2014). the compositions of individual ice grains in such a plume can be analyzed during spacecraft flybys by impact ionization mass spectrometers, such as the cosmic dust analyzer (cda; srama et al. 2004) on board the past cassini mission, the surface dust analyzer (suda; kempf et al. 2014) on board the upcoming europa clipper mission (howell & pappalardo 2020), or the enceladus ice analyzer (enia), proposed for future enceladus missions (reh et al. 2016). analysis of cda mass spectra collected in the saturnian system revealed that enceladus's ocean is salty (postberg et al. 2009) and contains a variety of organic material, including complex macromolecules (postberg et al. 2018) as well as low-mass volatile compounds (khawaja et al. 2019). our recent detection of phosphates in ice grains emitted by enceladus (postberg et al. 2022, under review) further enhances enceladus's potential as a habitable environment, possibly able to support microbial life in its subsurface ocean. impact ionization detectors, such as suda or enia, are the only instruments capable of determining the compositions of single µm- or sub-µm-sized ice grains emitted by ocean world plumes. cassini cda results showed that refractory organics occur in only a few percent of plume ice grains and are believed to form from an organic film covering the oceanic surface (postberg et al., 2018). if cell material is indeed present, it would likely reside in even fewer ice grains, potentially as many as just one in a thousand. on earth, 70% of the planetary surface is covered by a biofilm, the surface microlayer on top of the ocean water (flemming and wuertz, 2019), which hosts a distinct microbial community at cell densities 3 – 5 orders of magnitude higher than in the bulk water phase (franklin et al. 2005). after lifting, organics and cells from this surface layer can initiate ice crystal formation in clouds (pratt et al. 2009). methods and results to simulate a scenario, in which biosignatures are present only in a small fraction of emitted grains, but with relatively high cell densities, we conducted laboratory analogue experiments with sphingopyxis alaskensis, an ultrasmall (volume of <0.1 µm3) bacterium, extracted from various cold marine environments (ting et al. 2010). we simulated the case of an individual ice grain of 15 µm in diameter - constituting an extremely low cell density case for enceladus where ice grains are generally much smaller (1-5 µm in diameter) - formed from a nucleation core of a single inactivated bacterial cell. we used laser induced liquid beam ion desorption (lilbid) – a proven technique to accurately simulate impact ionization mass spectra of ice grains recorded byin space (klenner et al. 2019, 2020, 2020a). recent lilbid experiments demonstrated that trace amounts of dna and lipids extracted from bacterial cultures will produce characteristic signals in the mass spectra of ice grains emitted from ocean worlds (dannenmann et al. 2022, under review). here we present the next steps – lilbid experiments with untreated lysed bacterial cells, simulating the appearance of these microbial life forms in impact ionization mass spectra of single 15 µm ice grains. in both polarity mass spectra, we clearly identify signatures of s. alaskensis. cationic mass spectra exhibit features due to protonated amino acids, either fragments of the bacteria's proteins or metabolic intermediates. sequences of deprotonated fatty acids, fragments of bacterial lipids, are identifiable in anionic mass spectra. our experiments show that even if less than 0.1% of the constituents of a single cell would form a nucleation core of a 15µm ice grain, the bacterial signature would be apparent in the data. the signal-to-noise ratio would be even higher in smaller ice grains. conclusions our results show that biosignatures deriving from a single bacterial cell – or small fractions thereof - embedded as a nucleation core in a single µm ice grain will be clearly identifiable in impact ionization mass spectra from suda-type instruments. this demonstrates the advantage of analyzing individual ice grains in a plume over analyzing the average composition of all plume material encountered during a flyby. a modern impact ionization instrument like suda or enia would be capable of recording 10,000 – 100,000 ice grain spectra (cationic and anionic) during a single plume passage, allowing the detection of biosignatures present in only 1 out of 100,000 grains during a multiple flyby mission. such low abundances would be out of reach for other analytical methods that measure the integrated - and thus extremely diluted - concentrations of such biosignatures in a plume. the recorded spectra complement a comprehensive database containing analogue data for impact ionization mass spectrometers on board spacecraft (klenner et al. 2022, under review), thereby aiding planning for future space missions to enceladus or europa. references dannenmann, m. et al. 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(2010) environ microbiol 12, 2658–267. | one is enough: identifying cell material in a single µm-sized ice grain emitted by enceladus or europa |
the formation of small-scale strong magnetic features in the quiet sun was studied for a long time. it is likely that magnetic field on the solar surface is collected in the intergranular lanes by the horizontal flows in granules, and then a convective instability (collapse), which leads to downflow in the flux tube and a reduction of the internal gas pressure, intensifies them to kg levels. however, a static equilibrium with such a strong field would not be realized and open question remained is the evolution including the possible rebounding upflow and the associated chromospheric responses, which may show up as shocks and subsequent heating. using high resolution time series of hinode/sot filter images in na d1 line, g-band and ca ii h band at the quiet sun disk center, we were able to identify many point-like downflow (convective collapse) events in the photosphere and corresponding chromospheric bright points. for each events, we investigated temporal variations of, photospheric vertical flow velocities, magnetic flux, g-band intensity (proxy of kg field) and ca ii h intensity (chromospheric brightening) to see the implications of convective collapse on the photospheric and chromospheric dynamical processes.in 500 point-like downflow events studied, most cases indicate a signature of convective collapse (g-band brightening). typical lifetime of downflow is about a few minutes irrespective of strength of magnetic flux, strong downflows are always associated with ca ii h bright points which appear about a minute later, implying a rebound shock heating of the low chromosphere. | chromospheric heating associated with strong photospheric downflow events in photospheric flux tubes |
several icy bodies of the solar system host, or are suspected to host, an ocean of liquid water beneath their icy crust. the most prominent two examples of these "ocean worlds" are jupiter's moon europa (target of the future europa clipper mission) and saturn's moon enceladus (object of abundant observations by the cassini mission). the presence of liquid water raises the question of whether these bodies could host life as we know it. the first step in answering this question is to investigate their habitability: do these oceans offer suitable conditions for life to emerge and sustain itself? habitability requires not only water, but a source of energy (chemical redox disequilibrium) and the availability of chnops elements (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur). determining habitability can be done only through a comprehensive understanding of the chemical composition of these oceans beneath the ice. we discuss several processes that can affect our understanding of compounds related to the habitability of a subglacial ocean, with a focus on enceladus. this moon of saturn offers an extraordinary opportunity to astrobiologists as its south pole is geologically active, with geysers that allowed cassini to sample its ocean.. however, analysis of these samples requires extensive interpretation to constrain the conditions in the ocean. clathrate formation can alter the abundance of volatile molecules in the ocean by trapping them in the ice shell. we use a statistical thermodynamic model to investigate this alteration and find that the abundance of methane relative to other volatiles in the plumes is higher than expected, indicating either a fast rate of production of methane in the ocean, an ongoing destabilization of clathrate releasing their content into the ocean or the plumes, or a non-saturated ocean that is not favorable to clathrate formation. the presence of molecular hydrogen (h2) in an ocean world is crucial for astrobiological considerations as it is a reactant in the metabolic process of methanogenesis, and only an ongoing production can ensure its presence in a small icy moon incapable of trapping a sizeable reservoir of this light molecule. we analyze the data of cassini's ion and neutral mass spectrometer at enceladus to disentangle the detection of h2 in the plumes from instrumental effects, and uncover several unresolved issues in our understanding of the instrument's response in this complex environment. we then investigate the role of endogenic radiolysis - the radiation chemistry of water induced by radioactive elements present in the rocky core - in the production of h2 in ocean worlds of the solar system. this process is a small but steady supplement to the hydrothermal production necessary to explain the amount of h2 seen at enceladus. enceladus' plumes are generated by a system of cracks between the ocean and the surface, in which compounds in gas phase interact with the cold crack walls and the ice grains of the plumes. various organics can adsorb onto the icy surfaces, with the stickiest compounds detectable mostly on the surface of ice grains rather than in gas phase. this bears consequences on what would be the most adequate type of observation for detecting these compounds, between remote observation, analysis of grains, or mass spectrometry focused on the gas phase. we model the adsorption of several light organics and find how oxygen-bearing compounds are more likely to be affected by adsorption, which has to be accounted for in our interpretation of cassini data and of future observations of any ocean world. | processes affecting the abundance of astrobiologically relevant compounds from icy bodies within the solar system |
the plume material emerging from enceladus' south-pole has contributions from many sources distributed along four distinct fissures designated as alexandria, cairo, baghdad and damascus. in principle, the properties of the material escaping into the plume would depend upon the conditions within these individual fissures. therefore, the particles emitted from different sources could have different properties. indeed, observations made by the visual and infrared mapping spectrometer (vims) and cosmic dust analyzer (cda) instruments indicate differences in the water-ice grain sizes and abundance of organic-rich particles along the various fissures. these differences can be detected in both the plume surface deposits around the fissures [e.g. brown et al., 2006; jaumann et al, 2008] as well as in the active plume eruptions [postberg et al., 2011; dhingra et al., 2015, 2016]. furthermore, these variations may represent systematic trends in particle size and organic content across the south polar terrain. we are analyzing these spatial correlations between different parameters and what they mean for the sub-surface environment in the active south polar terrain of enceladus. brown et al. (2006) science, 311, 1425-1428dhingra at al. (2015) 46th lunar planet. sci. conf., abst#1648dhingra et al. (2016) icarus, under reviewjaumann et al. (2008) icarus, 193, 407-419postberg et al. (2011) nature, 474, 620-622 | spatial variability in enceladus' plume material properties across tiger stripes: observed correlations and implications |
microscopic imaging has long been an essential tool in the robotic exploration of planetary surfaces. spatially correlated microscale texture and composition are essential for properly identifying rocks and soils in situ and interpreting their geologic histories. future ocean world missions will need microscopic imaging capabilities for characterizing textural and structural properties of collected material, and searching for cells and other biosignatures. in support of determining the habitability and search for potential biosignatures on europa and other ocean worlds such as enceladus and titan, we have developed the advanced multispectral infrared microimager (amim). amim combines microscopic imaging with visible-infrared microspectroscopy to enable the non-destructive first-reconnaissance of collected samples in situ. amim generates a visible-infrared spectrum at each pixel to provide spatially-correlated composition of minerals and ices within microtexture at the microscale. amim can also detect the presence of organics via uv fluorescence and absorptions in the infrared as well as operate in low light environments. we have developed an amim prototype that features compact illumination system composed of low-power multispectral led arrays (> 25 wavelengths with fwhm ≤ 50 nm), an adjustable focus mechanism that provides in-focus images (spatial resolution ≤ 6 µm/pixel) with z-stacking, and a visible-infrared camera capable of imaging from the visible to the infrared (vis-ir, 0.4 to 2.6 µm; expandable to 3.6 µm). within this wavelength range, amim provides imaging/ spectroscopic measurements to detect hydrated minerals, salts, and other biominerals, characterize the crystallinity and grain size of ice, and search for potential organic biosignatures. amim's dpu merges multiple frames of each wavelength to remediate radiation, co-registers images from different bands, and uses onboard processing to reduce image cubes to a few "summary products" that measure key absorptions and are downlinked to provide a context for samples analyzed with other onboard instruments. | advanced multispectral infrared microimager (amim) for ocean worlds exploration |
salts are found throughout the solar system, and are an important factor in the stability of water, as well as potential habitability. different salts will affect the stability of water to varying degrees. chlorine salts (chlorides, perchlorates, and chlorates), can suppress the freezing temperature of water down to ~200 k. they also slow down the evaporation rate, extending the lifetime of the liquid water solution. the local relative humidity plays a significant role in the stability of these salts, in both their liquid and solid phases. salts can undergo deliquescence when the relative humidity exceeds a given threshold, forming liquid droplets. some halophiles have been known to utilize these droplets for active metabolism. on mars, chlorides have been found at every landing site, and perchlorates have been detected by phoenix in the north polar plains, by curiosity at gale crater, and by perseverance in jezero crater. reanalysis of viking data suggests perchlorates could have been present there as well. chlorates, which are almost as stable as perchlorates, are found on earth everywhere that perchlorates exist, making them likely to be present on mars too. other oxidized chlorine salts may be present in limited quantities as precursors to the formation of perchlorate. chlorine salts may also play a role in the mechanical properties of the regolith, as well as the stability of subsurface water. high soil cohesion was encountered at the phoenix landing site making sample analysis challenging; such cohesion may result from hydrated salts and eutectic brines bonding grains together at their contacts by wetting, or from dehydrated salts crystallizing at grain contacts. changes in hydration state with time (such as diurnally or seasonally) may then result in correlated changes in cohesive properties with time. it is imperative to study not only how these salts interact with their environment, but also how we detect and distinguish them. reference spectra of surface materials at relevant temperatures are critical for deriving abundance estimates through spectral modeling. i will present laboratory measurements and modeling of salt, water and/or regolith interactions, as well as spectra of various chlorine-salt hydrates to aid in their identification. | mars with a pinch of salt |
the remarkable performance of organic-inorganic perovskite solar cells (pscs) is challenging the dogma that solution-processed thin films are inevitably associated with inferior energy conversion efficiencies. the surprisingly low impact of polycrystallinity on the film quality highlights the unusual photo-response of intrinsic defects and grain boundaries in these materials. here, we report the first quantitative nanoscale photoconductivity imaging on methylammonium lead triiodide (mapbi3) thin films by microwave impedance microscopy with light stimulation. the local photoconductivity as a function of the above-gap laser power is consistent with the high carrier mobility and long lifetime of mapbi3. the photo-response is largely uniform across grains and grain boundaries, which is direct evidence on the inherently benign nature of microstructures in the perovskite thin films. for encapsulated mapbi3 films, the observed long-term degradation in photoconductivity begins with the disintegration of large grains due to the diffusion of water molecules through the capping layer. our work suggests that the striking psc performance is deeply rooted in the nanoscale optoelectronic properties of mapbi3. we gratefully acknowledge financial support from nsf efma-1542747. | unconventional nanoscale photoresponse and degradation process in hybrid organic-inorganic perovskites. |
asteroids are the most numerous objects in the solar system and as such act as tracers of the dynamical and physical evolution of our planetary system. at present, there are nearly 800,000 known asteroids — primarily in the main belt — and there are probably around 1 million asteroids larger than 1 km. a comprehensive understanding of the evolution of our solar system can therefore use the individual properties of asteroids as the fine-grained measurements from which broader conclusions can be drawn. asteroids can be used to understand the dynamical and collisional history of the solar system, the intrinsic material properties of primitive bodies, and help unravel the origin of life on earth through understanding the degree to which asteroids brought water and organics to the early earth. the vera c. rubin observatory will carry out the legacy survey through space and time (lsst) will observe more than 5 million main belt asteroids, an order of magnitude increase over present catalogs. however, the lsst data by itself (time, brightness, position) will not provide new insight into the processes that have driven the evolution of our solar system. to reap the scientific reward from this data set, the physical properties of each asteroid must be derived, so that the ensemble properties can be used for scientific investigations. in this talk i will present our ongoing project entitled the solar system notification alert processing system (snaps). we are presently ingesting the ztf data stream as a pathfinder for lsst alerts. we derive physical properties for each asteroid and are constructing a value-added publicly accessible database that enables a wide range of science cases. these tasks will provide the missing steps between survey-provided measurements and detailed science investigations. | the solar system notification alert processing system (snaps) |
nowadays the use of species distribution models (sdm) is common to predict in space and time the distribution of organisms living in the critical zone. the realized environmental niche concept behind the development of sdm imply that many environmental factors must be accounted for simultaneously to predict species distributions. climatic and topographic factors are often primary included, whereas soil factors are frequently neglected, mainly due to the paucity of soil information available spatially and temporally. furthermore, among existing studies, most included soil ph only, or few other soil parameters. in this study we aimed at identifying what are the most crucial soil factors for explaining alpine plant distributions and, among those identified, which ones further improve the predictive power of plant sdms. to test the relative importance of the soil factors, we performed plant sdms using as predictors 52 measured soil properties of various types such as organic/inorganic compounds, chemical/physical properties, water related variables, mineral composition or grain size distribution. we added them separately to a standard set of topo-climatic predictors (temperature, slope, solar radiation and topographic position). we used ensemble forecasting techniques combining together several predictive algorithms to model the distribution of 116 plant species over 250 sites in the swiss alps. we recorded the variable importance for each model and compared the quality of the models including different soil proprieties (one at a time) as predictors to models having only topo-climatic variables as predictors. results show that 46% of the soil proprieties tested become the second most important variable, after air temperature, to explain spatial distribution of alpine plants species. moreover, we also assessed that addition of certain soil factors, such as bulk soil water density, could improve over 80% the quality of some plant species models. we confirm that soil ph remains one of the most important soil factor for predicting plant species distributions, closely followed by water, organic and inorganic carbon related properties. finally, we were able to extract three main categories of important soil properties for plant species distributions: grain size distribution, acidity and water in the soil. | what are the most crucial soil factors for predicting the distribution of alpine plant species? |
we developed a direct mapping approach to overlay the image of a polycrystalline perovskite film obtained from the transient absorption microscope (tam) with that from the scanning electron microscope (sem). by mapping these imaging data pixel by pixel, we are able to observe the relaxation dynamics of the photo‑generated charge carriers on varied regions of the film. the carrier relaxation dynamics contain a dominated single‑exponential decay component owing to the recombination of charge carriers. the lifetime distribution of charge recombination shows a bimodal feature, for which the rapid and slow distributions are assigned as free and trapped carriers, respectively. the charge recombination was slower in the grain boundary (gb) region than in the grain interior (gi) region. the small grains have longer lifetimes than the large grains for the crystal size smaller than 500 nm. therefore, gb with retarded charge recombination might play a positive role in a perovskite solar cell. | a direct mapping approach to understand carrier relaxation dynamics in varied regions of a polycrystalline perovskite film |
we have analysed of the complete visual and infrared mapping spectrometer data set of titan covering the 2004-2017 period with two objectives: the first is to document the atmospheric seasonal changes over the poles. the second is to merge all the observations in synthetic global color maps of the surface. for the study of the poles, we have computed individual mosaics for each of the 127 targeted flybys, using vims wavelengths sensitive both to clouds and surface features. these maps reveal the systematic changes that occurred in the 2004-2017 timeframe [1]. the north pole appeared fully covered by a huge cloud system as soon as the first flybys in 2004 [2]. this vast north polar feature progressively vanished around the equinox in 2009 [3, 4, 5, 6], in agreement with the predictions of global circulation models [7], revealing the underlying lakes and seas. a reverse situation has been observed over the south pole, which was mostly clear of clouds and haze up to the equinox, and started to develop a giant atmospheric cloud in may 2012. this feature grew up month after month until the end of the mission in 2017, with a poleward latitudinal extent of 75°s in 2013 and up to 58°s in april 2017. thanks to the spectral capabilities of vims, we have detected hcn spectral signatures over the north pole in almost all flybys between 2004 and 2008. these hcn signatures then started to show up over the south pole in almost all flybys between 2012 and 2017 [1]. for the study of the surface, we focused our efforts on data cubes acquired in the most favourable observing geometries (i.e. incidence and emergence angles lower than 80° for example). we have developed an empirical approach to mitigate the effects of the atmosphere, which otherwise induces significant seams between individual images due to the scattering and absorption of gases and aerosols. we use in particular band ratios to emphasize subtle spectral variations linked either to composition or grain size variations. global maps at 32 pixels per degrees have been produced at specific wavelengths, revealing the surface heterogeneity of titan. [1] le mouélic et al., icarus, 311, 2018 [2] griffith et al., science, 310, 2006. [3] le mouélic et al., pss, 60, 2012. [4] rodriguez et al., nature, 459, 2009. [5] rodriguez et al., icarus 216,2011. [6] turtle et al., grl, 45, 2018, [7] rannou et al., science 311, 2005. | evolution of the polar clouds and global mapping of the surface derived from the vims archive of titan |
metal halide perovskites have received much attention for their application in light-emitting diodes (leds) and solar cells in the past several years. among them, 2d and quasi-2d perovskite with organic long-chain cations introduced have drawn significant attention. however, while improving wet and thermal stability, as the grain size becomes smaller, more defects introduced at the grain boundary and surface, resulting in the increase of non-radiative recombination is becoming the main problem which should be faced by 2d/quasi-2d perovskite materials. here, we report a new strategy employing ionic liquid named 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(emb).by adding a small amount of ionic liquid to the precursor, the defect was effectively passivated and the photoluminescence intensity was increased by 11 times and the fluorescent lifetime was increased by about 1.5 times. the flatness of the prepared perovskite thin films has also been effectively improved. | improvement of photoluminescence intensity and film morphology of perovskite by ionic liquids additive |
planetary science is naturally focussed on the issues of the origin and history of solar systems, especially our own. the implications of an early turbulent history of our solar system reach into many areas including the origin of earth's oceans, of ores in the earth's crust and possibly the seeding of life. there are however other areas of science that stand to be developed greatly by planetary missions, primarily to small solar system bodies. the physics of granular materials has been well-studied in earth's gravity, but lacks a general theory. because of the compacting effects of gravity, some experiments desired for testing these theories remain impossible on earth. studying the behavior of a micro-gravity rubble pile -- such as many asteroids are believed to be -- could provide a new route towards exploring general principles of granular physics. these same studies would also prove valuable for planning missions to sample these same bodies, as techniques for anchoring and deep sampling are difficult to plan in the absence of such knowledge. in materials physics, first-principles total-energy calculations for compounds of a given stoichiometry have identified metastable, or even stable, structures distinct from known structures obtained by synthesis under laboratory conditions. the conditions in the proto-planetary nebula, in the slowly cooling cores of planetesimals, and in the high speed collisions of planetesimals and their derivatives, are all conditions that cannot be achieved in the laboratory. large samples from comets and asteroids offer the chance to find crystals with these as-yet unobserved structures as well as more exotic materials. some of these could have unusual properties important for materials science. meteorites give us a glimpse of these exotic materials, several dozen of which are known that are unique to meteorites. but samples retrieved directly from small bodies in space will not have been affected by atmospheric entry, warmth or weathering. we give examples from both of these fields of enquiry. | non-planetary science from planetary missions |
in perovskite solar cells (pscs), rapid charge transfer at the interfaces between photoactive layer and charge transport layers is very important. various defects and energy barriers at the interfaces will lead to non-radiative recombination of charge carriers in the charge transfer process, which is not conducive to charge collection and eventually hinder the improvement of power conversion efficiency (pce) and stability of pscs. herein, we report a dual interface modification strategy by using different phosphonic acid molecules to modify the interface between sno2 layer and perovskite layer and the interface between perovskite layer and hole transport layer, respectively. acidic diphenylphosphinate chloride (dpc) with uv resistance is employed to modify sno2 surface before depositing perovskite layer to alleviate the corrosion of oh- in sno2 to perovskite film and regulate the crystal growth process of perovskite. methyldiphenylphosphine oxide (mpo) that can coordinate with pb2+ is used to post-treat the surface of perovskite film to passivate defects at the film surface and grain boundary. the effects of organic interface modifiers on charge transport and charge recombination are comprehensively studied by photoluminescence spectra and electrical measurement. the optimal fa0.85cs0.15pbi3 device with active area of 0.255 cm2 obtained a pce of 23.37 %. in addition, the device with working area of 1 cm2 achieved the best pces of 20.29 %. more interestingly, owing to the strong ultraviolet light absorption ability of dpc, the final device with the dual interface modification can still maintain 91.4 % of the initial efficiency after 1000 h in air and 87.8 % when placed in am1.5g light for 500 h. | synergistic enhancement of efficiency and stability of perovskite solar cells via dual interface modification |
impact ionization time of flight mass spectrometer (tof-ms) instruments (such as the suda instrument on the europa clipper) study molecular composition of space-borne dust grains by impacting them at several km/s to ionize molecules for tof-ms analysis. however, there have been questions about whether flyby impacts can shatter organics, if there is some critical velocity below which fragmentation is minimized, and if water ice reduces fragmentation. in particular, it would be beneficial to know if amino acids or other organics can be studied with this type of instrument during flybys of enceladus or europa. more generally, the ability of these instruments to assess the inventory and distribution of organics is important for understanding habitability across the solar system and the origins of terrestrial life. here we describe experiments using a novel airbrushing technique for ice creation at the colorado dust accelerator. experiments were performed with a pure surface of histidine mono-hydrochloride and with an identical pure surface with 60 nm of water ice deposited on top. these surfaces were kept at ~80 kelvin and impacted by <2 um iron dust particles at velocities >3km/s. the resulting impact plumes were studied using tof-ms. a plot of the ion yields of breakup products relative to the parent molecule ions as a function of velocity is shown in figure 1. purple triangles denote bare histidine data, while blue circles denote histidine under 60 nm of water ice. the dotted lines represent linear fits to the first three data points, below 6 km/s. the solid lines represent linear fits to the high velocity data. fragmentation is minimal below 6 km/s, with little variation between datasets. with bare histidine, the fragmentation rises significantly beyond 6.1 km/s, while ice-covered histidine shows significant increases beyond 8.5 km/s. these results imply that there is a critical flyby velocity between 6 and 8.5 km/s and that water ice layers reduce fragmentation rates, both in absolute terms and as a function of velocity. we further observe characteristic fragmentation products at 81-83 and 110 amu, the dominant breakup products associated with histidine in existing literature. this would indicate that fragmentation products may be used to enhance detection of organics when they are observed alongside the parent molecule. | detection of the amino acid histidine and fragmentation products in hypervelocity impact ice spectra: implications for flyby mission velocities |
the outstanding performance of organometal trihalide solar cells benefits from the exceptional photo-physical properties of both electrons and holes in the material. here, we directly probe the spatial diffusion and temporal dynamics of photo-generated free carriers in cs-doped fapbi3 thin films by nanoscale microwave impedance microscopy. the sample exhibits two relaxation times on the order of 1 μs and 10 μs, which are uniform across grains and grain boundaries. using charge transport layers to selectively quench one type of carriers, we are able to attribute the short and long lifetimes to that of electrons and holes, respectively. both types of carriers display a long diffusion length of 3 ~ 5 μm, indicating that the difference in lifetimes is compensated by their distinct mobility. the spatiotemporal microwave imaging provides the most direct method to accurately determine photo-physical properties, which are crucial for the development of perovskite solar cells. nsf mrsec under dmr-1720595 welch foundation grant f-1814 and f-1662. us army research laboratory and the us army research office under grants w911nf-16-1-0276 and w911nf-17-1-0190. u.s. doe under contract no. de-ac36-08go28308 with alliance for sustainable energy, limited liability company (llc). | spatiotemporal dynamics of photo-excited electrons and holes in organometal trihalide perovskites by microwave impedance microscopy |
comets hold the key to the understanding of our solar system, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. a comet nucleus emits gas as it is heated by the sunlight. the gas forms the coma, where it is ionised, becomes a plasma and eventually interacts with the solar wind. besides these neutral and ionised gases, the coma also contains dust grains, released from the comet nucleus and influenced by the electric charges in the plasma. as a cometary atmosphere develops when the comet travels through the solar system, large-scale structures, such as the plasma boundaries, develop and disappear, while at planets such large-scale structures are only accessible in their fully grown, quasi-steady state. in situ measurements at comets enable us to learn both how such large-scale structures are formed or reformed and how small- scale processes in the plasma affect the formation and properties of these large scale structures. furthermore, a comet goes through a wide range of parameter regimes during its life cycle, where either collisional processes, involving neutrals and charged particles, or collisionless processes are at play, and might even compete in complicated transitional regimes. thus a comet presents a unique opportunity to study this parameter space, from an asteroid-like to a mars- and venus-like interaction. however, these processes are integral to understanding the composition and surface features. much of the interaction between the plasma and the cometary nucleus remains poorly explored as well as the plasma's influence on surface features and dust grains in the coma. the rosetta mission and previous fast flybys of comets have together made many new discoveries, but the most important breakthroughs in the understanding of cometary plasmas are yet to come. the comet interceptor mission will provide a sample of multi-point measurements at a comet, setting the stage for a multi-spacecraft mission to accompany a comet on its journey through the solar system. these deliberations were submitted as a white paper to the european space agency's voyage 2050 effort and reviews the present-day knowledge of cometary plasmas, discusses the many questions that remain unanswered. it outlines a multi-spacecraft esa mission to accompany a comet that will answer these questions by combining both multi-spacecraft observations and a rendezvous mission, and at the same time advance our understanding of fundamental plasma physics and its role in planetary systems. | cometary plasma science - a white paper in response to the voyage 2050 call by the european space agency |
the curiosity rover is finishing exploration of vera rubin ridge (vrr), a topographic feature in lower aeolis mons (informally, mt. sharp). vrr is relatively resistant to erosion as compared with underlying strata and consists largely of finely laminated mudstones. diagenetic features, including veins, concretions, and crystal molds, are variably present throughout. in situ data show the majority of the vrr rocks have ferric spectral signatures, as do the rocks in most of the underlying murray formation previously investigated by curiosity. the sedimentary facies at vrr were deposited in a lacustrine environment, consistent with prior observations of the murray formation. the reason for the ridge's erosional resistance is not yet clear, but variations in grain size, cement, porosity, or mineralogy of ridge rocks likely play a key role. the intimate association of ferric spectral signatures with the vrr and rocks below suggests that hematite or a precursor ferric phase formed either as a primary depositional phase at a redox interface in the lacustrine setting, or via pervasive and relatively uniform diagenetic oxidation. in situ spectral data are being used to model how dust and surface texture govern visibility of the hematite spectral signatures in crism orbital data. one of the most surprising findings occurred at the top of vrr, when curiosity explored areas that were visible as small ( 10 m diameter) bright patches in hirise orbiter images. these patches are almost always found in local topographic depressions, and curiosity discovered they contained gray rocks with no spectral evidence for ferric phases. the walls of these depressions expose a geological boundary between typical red ferric vrr rocks and gray rocks. this color change may mark a facies change within the murray formation, but, based on their geologic settings, more likely records redox transformations caused by diagenetic fluids. both the lake setting of the primary vrr rocks and evidence for redox-driven processes are favorable for habitability. | curiosity at vera rubin ridge: major findings and implications for habitability |
the occurrence of sets of regularly spaced, linear ridges at numerous locations on the surface of mars has been recognized for two decades via high spatial resolution orbiter images. many of these landforms have been interpreted as inactive, possibly indurated aeolian bedforms. an alternative proposed by montgomery et al. (2012, doi:10.1029/2011je003970) is that some of these ridges are erosional 'periodic bedrock ridges' carved into bedrock by wind and elongated transverse to the dominant wind direction. although the erosional interpretation for some of these ridges is compelling, the mechanism and process by which periodic bedrock ridges form on mars remains uncertain, in part, because analogs on earth are rare. this study focuses on a 2.5 km2 field of linear, parallel northeast-southwest trending ridges that occur within clay-bearing strata of the glen torridon trough on lower north aeolis mons within gale crater. as measured in hirise orbiter images and digital terrain models, ridge length varies from a few meters to several hundred meters, ridge height ranges from <1 m to several meters, and wavelengths of ~20 m are typical. ridge orientation is consistently discordant to the strike of sedimentary bedding. curiosity image observations show that the bedrock comprising the ridges is predominantly finely laminated mudstone or fine-grained sandstone that has eroded to cm-scale pebbles at the surface. these mudstones and sandstones are interpreted to record a continuation of lacustrine deposition seen throughout the murray formation. although origins as lithified aeolian bedforms and erosional landforms were both previously proposed to explain these ridges, this study's analysis supports an interpretation that these are erosional periodic bedrock ridges. we are currently using the glen torridon ridges to gain further insights into the depositional context and erosional history of this interval of aeolis mons stratigraphy, and to advance understanding of the processes by which periodic bedrock ridges form on mars. | in-situ investigation of periodic bedrock ridges in the glen torridon area with the msl curiosity rover, gale crater, mars |
this thesis presents a study of quiet-sun magnetic features in the solar photosphere. magnetic fields in the quiet sun organize on small spatial scales, evolve very rapidly, and produce weak polarization signals. with these properties their observation requires high spatial and temporal resolution together with sensitive and accurate polarimetric measurements. it is for these instrumental limitations that the origin and evolution of these features remains elusive. the imaging magnetograph experiment (imax) is an imaging spectropolarimeter that flew over the artic circle aboard the sunrise balloon-borne stratospheric mission. imax was designed to mitigate the above mentioned issues and has provided polarimetric observations with unprecedentedly high spatial resolution of a hundred kilometers. flying in the stratosphere, it obtained stable, nearly seeing-free time series, and its imaging capabilities allowed to cover large areas of the sun simultaneously. all these features are indeed crucial when studying the highly dynamic nature of the quiet-sun magnetism. the thesis gathers empirical evidence of magnetoconvection at the smallest scales ever observed. the evolutionary tracks of several different quiet-sun magnetic structures in a continuous interaction with photospheric convection are presented. specifically, we study 1) the formation and evolution of an isolated magnetic element; 2) the dynamics of multi-core magnetic structures; and 3) the relation between magnetic features and convectively driven, long living sinks at the junctions of several mesogranular cells. seen at a scale of one hundred kilometers, we find that the evolution of an isolated quiet-sun magnetic element is a complex process where many phenomena are involved. the formation starts when a small-scale magnetic loop emerges through the solar surface in a granular upflow. its footpoints are soon swept to nearby intergranular lanes where some, weak positive polarity patches are already present. the negative polarity footpoint cancels out with an opposite polarity feature while the positive one and other remaining patches are advected by converging granular flows toward a long-living sink. the magnetic fields agglomerate in the sink and a new element with a magnetic field strength in equipartition with the kinetic energy density of convective motions is formed. the intergranular downflow then begins to increase within the magnetic feature while the surrounding granules compress it until kilogauss field strengths are reached. during this process, a bright point appears at the edge of the flux concentration almost co-spatial with an upflow plume. the development of the magnetic element does not stop here since we discover that is indeed unstable. the magnetic element displays an oscillatory behavior as the field strength weakens and rises again with time. focusing on extended magnetic structures that harbor multiple bright points in their interiors, we find that they are resolvable into a series of more elemental inner magnetic cores, each of which appears related with a single bright point. the inner cores are strong and vertical. they all are surrounded by common, weaker, and more inclined fields. we interpret these structures as bundles of flux concentrations in the lower photosphere that expand with height to merge into a common canopy in the upper photospheric layers. the evolution of the individual magnetic cores is completely governed by the local granular convection flows. through this interaction, they continuously intensify, fragment, and merge in the same way that chains of bright points in photometric observations have been reported to do. this evolutionary behavior results in magnetic field oscillations of the global entity. we conclude that the magnetic field oscillations previously discovered in small quiet-sun magnetic elements correspond to the forcing by granular motions and not to characteristic oscillatory modes of thin flux tubes. finally, we analyze the relation between mesogranular flows, localized downdrafts, and quiet-sun magnetic fields. we study first the statistical properties of the sinks. some of them manifest as whirlpools while the others display radially symmetrical converging flows. their spatial distribution reveals that they are located at the vertices between neighboring mesogranules. we quantitatively proof that the strongest fields tend to concentrate at sinks. meanwhile, the small-scale magnetic loops do not show any preferential distribution at mesogranular scales. we also analyze one of the mesogranules in more detail and observe that magnetic loops appearing inside the mesogranular cell can be advected by horizontal flows toward its vertex. if confirmed by new observations, these results can imply that the formation of magnetic elements through the concentration of loop footpoints in mesogranular vertices is ubiquitous over the solar surface. | evolutionary tracks of quiet-sun magnetic features |
chemical passivation of defective perovskite surface is a fundamental strategy to stabilize solar cell operation by impeding the defect-dominant surface ion migration. here, we show that the configuration of organic cations plays a key role in determining their surface adsorption energetics at various perovskite facets, which will strongly impact the spatial uniformity of the low-dimensional perovskite passivation layer (ldpl). a weak-anisotropic adsorption behavior is demonstrated for tertiary ammonium that can enable a conformal ldpl on the perovskite grain surface. benefiting from comprehensive surface passivation, the migration of ionic perovskite species was suppressed and the as-fabricated p-i-n solar cells yielded an optimized power conversion efficiency of 22.6% with an expected t80 lifetime of about 4,000 h under continuous 1-sun illumination. our findings give insight into the design and preparation of heterostructured perovskite films toward efficient and stable solar cells. | non-selective adsorption of organic cations enables conformal surface capping of perovskite grains for stabilized photovoltaic operation |
one of highest priority science objectives for astrobiology is to characterize habitability and detect signatures of life in the solar system. the development of new, compact, and energy-efficient technologies capable of facilitating that objective is necessary for surface exploration of ocean worlds and other planetary bodies. the habitable potential of the ocean beneath the icy shell of europa has been inferred by geophysical geothermal features, indicating the presence of brines and materials conducive to life macromolecular organics, and organic-enriched ice grains have been detected in ejected plume material on enceladus. raman spectroscopy has established itself in current missions as an information-rich, non-contact, non-destructive method for identifying and characterizing inorganic and organic compounds and characterizing structural features in a wide variety of planetary materials. ultra-violet detector innovation for raman exploration and characterization (uv-direct) of ocean worlds enables the identification of minerals, volatiles, organic molecules, biopolymers, water, and other hydrous phases in planetary materials. uv-direct utilizes a silicon-carbide (sic) avalanche photodiode (apd), with high internal gain, specifically targeted for the identification of ocean world-relevant compounds utilizing uv/nuv (266-340 nm) raman spectroscopy with ppb sensitivity. excitation in the uv range permits the acquisition of raman spectra without the signal-interfering fluorescence that is typical under longer excitation wavelengths. sic detectors are radiation hard and are also "blind" to visible light, i.e., solar background, that can completely obscure the raman signal. unlike most mission-relevant raman detectors that only support the acquisition of point spectra, the architecture of uv-direct enables raman spectroscopic imaging. acquiring point spectra can provide information about what compounds are present; raman imaging enables the full characterization of target areas revealing spatial relationships between compounds, improving the capability of detecting biosignatures. for life detection this is important because while abundant in the solar system, the mere presence of organics does not indicate life, but the complexity of that material may be a biosignature. the sic apd technology in uv-direct is applicable for stand-off or in situ raman applications, enabling compact, robust instrumentation for planetary surface exploration using raman spectroscopy. | ultra-violet detector innovation for raman exploration and characterization (uv-direct) of ocean worlds |
asteroids, and more globally small bodies, are keys to unravel the origin and the evolution of our solar system. remnants of the material which formed planets early on, they captured the composition and the conditions of formation of the latter at that time, since they did not undergo too harsh internal alteration during their lifetimes. the hayabusa2 spacecraft explored the cb-type asteroid (162173) ryugu between june 2018 and november 2019, notably collecting data with its near-infrared spectrometer (nirs3) in the 1.8-3.2 μm range. we selected five nirs3 datasets among the ones having the highest spatial resolution on which we applied the g-mode multivariate statistical analysis, in order to spot small heterogeneities at the surface of ryugu. both global scale and local scale cases were investigated. with a confidence level of 3σ, we obtained two classes at global and local scales, while decreasing to 2σ results in the identification of more classes (five at global scale, four at local scale). overall, our results are consistent among them and with previous studies. in particular, terrains spectrally redder as well as terrains spectrally bluer than the average surface are newly identified by our analysis. the floors of all main craters at the surface of ryugu appear redder than their surroundings, and are associated with a probable smaller grain size material. a large depression of the northern hemisphere may contain bluer heterogeneities likely due to a more packed or/and fresher, subsequently deposited material. finally, a comparison with data from the hayabusa2 optical camera onc-t shows no evident correlation between the spectral properties in the near-infrared and in the visible. | clustering analysis of high spatial resolution spectra of asteroid (162173) ryugu from hayabusa2/nirs3 |
ganymede is the largest icy moon in the solar system. the galileo spacecraft discovered the presence of a magnetic field that is generated in an iron-rich core (kivelson et al., 1996). gravity data from the galileo mission suggest a low value of the reduced moment of inertia (moi) of 0.3115 (anderson et al., 1996), which indicates a high degree of differentiation. schubert et al. (1996) proposed a three-layer structure: an iron-rich liquid core, coherent with magnetic data, a silicate mantle, and a hydrosphere. the present work investigates the thermal evolution of ganymede"s rocky core to assess the conditions under which the rocky interior can differentiate, leading to the formation of an iron core. the first step of the study addresses the possible end-members for the rocky composition. two chondritic compositions have been proposed for ganymede"s rocky interior: ll chondrite (kronrod, kuskov, 2006) that can explain the low fe/si ratio inferred from the density derived from mass and moment of inertia (moi) or a carbonaceous chondrite (ci type) which is more probable during the accretion beyond the snow line (néri et al., 2020). using the bulk elementary composition and the abundances of the different phases, the elementary composition of each phase is calculated. the silicate fractions have a very similar mg# and the main difference is the much larger fraction of iron-rich phases in the ci chondrite. perple_x,a thermodynamic calculation tool that determines the phases from elementary composition,was used to study the mineralogical evolution of the silicate phase in the (p,t) domain relevant to ganymede. in the case of the ll composition, we consider the hydration of the rock during the accretion and differ- entiation between the rocky core and the hydrosphere. the second step simulates the thermal evolution of the rocky core starting after the differentiation of the hydrosphere (primitive core). the decay of long-lived radioactive elements (k, u, th) provides thermal energy that heats up the interior. thermal energy can be transferred by either conduction or convection. the onset of convection in a solid material depends on its viscosity (ratio of stress to strain rate) that depends on parameters such as pressure, temperature, grain size, and stress. hydrated silicates have a viscosity that strongly depends on stress whereas dry silicates have a viscosity that depends mainly on temperature. more than 30 numerical simulations were performed to investigate the effect of parameters including the time of formation of the primitive core (or time of differentiation of the hydrosphere), the type of chondrite origin (ll chondrites have a larger amount of radioactive elements), the initial temperature profile, and the sensitivity to the rheology parameters. the effect of numerical parameters such as initial perturbations in temperature and strain rate and maximum viscosity contrasts were also investigated.simulations performed in 3d spherical geometry show that, in the domain of investigated parameters, convection does not happen in the hydrated silicates before dehydration. dehydration occurs in the center leading to a structure in two layers: an upper layer, about 150 km thick, of hydrated silicates sitting on top of a dry silicates core. as temperature increases in the core, the eutectic temperature of the fe-fes sys- tem (buono, walker, 2011) is reached before convection in the dry silicates starts. such an event happens between 1.5 and 2.5 gyr, leading to a potential formation of the iron-rich liquid core. the percolation of the iron-rich liquid phase would have significant effect on the core dynamics as the deep silicates would become less dense than the upper layer of hydrated silicates. even without this effect, we observe an onset of convection when the temperature in the core reaches 1600 k when dry silicates have a viscosity low enough for convection to start. we note that convection does not start in all models: when the differentiation of the hydrosphere is late the rocky interior remains in a con- ductive state until present, the rocky interior remains in a conductive state until present. the differentiation of the iron core and its effect on the interior dynamics is not yet implemented in the model. it would lead to an earlier onset of the convection. the convection step is short on geological time steps (a few 10s to 100s of myr). it has two consequences. first, it dehydrates the upper layer and eventually allows for silicate melt- ing. second, it cools down the interior very efficiently, reducing the temperature and stopping the convection process. by bringing the newly dehydrated iron-rich silicates in the center, it may lead to a second step in the formation of the iron core. it also creates a pulse in heat flux that may have a major consequence on ganymede"s global interior dynamics. the upcoming esa mission juice that will orbit ganymede will provide additional information on the interior structure of ganymede that will help understand the evolution of its core. such models can be extended to the evolution of the silicate cores of other icy moons such as titan and europa that will be visited by the dragonfly mission and the europa clipper mission, respectively. anderson jd, lau el, sjogren wl, schubert g, moore wb., 1996. nature. 384, 6609. 541- 543.buono as, walker d, 2011.geochimica et cosmochimica acta. 75, 8. 2072-2087.kivelson mg, khurana kk, russell ct, walker rj, warnecke j, coroniti fv, polanskey c, southwood dj, schubert g. 1996. nature. 384, 6609. 537-541.kronrod va, kuskov ol., 2006. geochemistry international. 44, 6. 529-546.néri a, guyot f, reynard b, sotin c, 2020. earth and planetary science letters. 530. 115920.schubert g, zhang k, kivelson mg, anderson jd, 1996. nature. 384, 6609. 544-545. | thermal and chemical evolution of ganymede's primitive core |
semiconductor heterostructures are used in high-efficiency solar cells and in other electronic devices. solar cells can't reach thermodynamic efficiency limits in part due to the charge carrier recombination, and efforts are applied to understand and reduce recombination. we describe a novel experimental approach to identify and quantify recombination losses at semiconductor interfaces. using time-resolved two-photon excitation microscopy, we generate carriers at well-defined absorber depths and find that the red spectral shift of the photoluminescence (pl) emission can be used as a "spectroscopic ruler" to identify recombination depth up to 30 μm. we apply this analysis to quantify shockley-read-hall recombination at the buried cdte/cdte interface, where 15 μm thick epitaxial cdte is grown by the molecular beam epitaxy on the single crystal cdte substrate. we also measure luminescent coupling between the gainp and gaas layers in heterostructures grown by the metal-organic chemical vapor deposition. our results resolve important limitations for accurate 3d charge carrier lifetime tomography. earlier we analyzed recombination due to extended defects and grain boundaries with the lateral resolution sufficient to resolve such features (approximately 0.5 μm), but interpretation of the carrier lifetime microscopy data for buried interfaces and buried semiconductor layers was a challenge. using methods described here, the axial (z) coordinate for the pl microscopy measurements becomes as well defined as the lateral (x, y) coordinates, enabling accurate 3d identification and analysis of the charge carrier recombination locations in semiconductor heterostructures. | buried interface and luminescent coupling analysis with time-resolved two-photon excitation microscopy in ii-vi and iii-v semiconductor heterostructures |
identifying habitable environments on mars is one of the key drivers in the mars exploration program. in order to support life, an environment must have a source of energy. a geochemical process that supports microbial communities in some terrestrial environments is water radiolysis, the decomposition of water molecules due to ionizing radiation. radiolysis produces compounds, such as hydrogen, that can be metabolized by a variety of organisms for energy. to assess the extent to which water radiolysis may support life on mars, we calculate the potential range of radiolytic h2 produced by contact of water with different martian lithologies. our calculations assume a constant th/u ratio and use gamma ray spectrometer concentration data for thorium and potassium collected by the 2001 mars odyssey mission. we calculate rates using separate protocols for hard-rock fractures and for fine-grained sediment. the range in radionuclide concentrations from one lithology to another corresponds to about 6-fold variation in h2 production rates. the lowest apparent yield occurs at the northern pole, where it may be biased by low radionuclide estimates due to ice cover. variation is 3.5-fold for regions restricted to ±75° latitude. the lowest h2 production rate within ±75° of the equator is associated with promethei terra while the highest rate is associated with acidalia plantia. the highest rate for acidalia plantia, 0.4 nm h2 yr-1, is produced in microfractured rock with fractures less than 10 μm wide. the rate for fine-grained sediment at acidalia plantia is 0.2 nm h2 yr-1. these yields for acidalia plantia are consistent with h2 production rates in earth's oceanic basement. if minerals that amplify radiolytic h2 production rates, such as zeolites, are present, radiolytic h2 production is at least a factor of 5 higher than these estimates. in this case, they match rates that sustain microbial life in earth's ocean-gyre sediment. | radiolytic h2 production in different martian environments |
the development of perovskite-based solar cells has recently attracted the attention of many researchers because the efficiency value increases rapidly in a short span of time. third generation solar cells have the potential to achieve shockley-queisser limit of 31% for single energy bandgap solar cells. besides that, this solar cell technology is economically very promising because the manufacturing costs are cheaper. the main drawback of this solar cell is its low stability (lifetime), which is caused by degradation over its lifetime. in addition, most of the high efficiency perovskite-based solar cells still use lead (pb), so they are not environmentally friendly. another alternative perovskite material is required. one promising material is barium titanate (batio3). as a material for solar cells, not much research has been done. batio3 film has been successfully made, which is then given annealing treatment at temperature of 500 °c, with annealing time of 30 minutes, 60 minutes, 90 minutes, and 120 minutes. in general, increasing the annealing time increases absorbance, decreases film thickness, decreases energy bandgap, and tends to reduce grain size of film. energy bandgap tends to decrease with the increasing grain size. the grain size of film decreases with the decreasing thickness. more in-depth characterization and analysis are needed, especially those related to microstructure analysis. | effect of annealing hold time on thickness and optical properties of barium titanate solar cell material |
the surrogate-reaction method can improve our understanding of s-process nucleosynthesis. branch-point nuclei are a crucial feature of the s-process that highly impact the elemental abundances. knowing the (n, γ) cross sections of these nuclei allows for powerful constraints to be placed on the stellar conditions of the parent stars in which the elements originated. however, a large number of branch-point nuclei have half-lives on the order of months or less, making the use of direct-measurement techniques challenging, if not impossible. an experiment was performed in which the surrogate-reaction method was used to obtain the (n, γ) cross section for 95zr (64-day half-life), whose branching has been observed in presolar stardust grains. inelastic proton scattering from the stable isotope 96zr served as the surrogate. the measurement was carried out at the texas a&m university k150 cyclotron. an enriched 96zr foil was bombarded with 20-mev protons. scattered protons and coincident γ rays were measured with the llnl hyperion array, which consists of three segmented annular silicon detectors in a de-e1-e2 configuration surrounded by an array of bgo compton-suppressed hpge clover detectors. a benchmark was also performed using 94zr(p, p') to determine the 93zr(n, γ) cross section, which has been previously measured via direct methods. details of the experiment and preliminary results will be discussed. prepared by llnl under contract de-ac52-07na27344 and ldrd 20-erd-030. | determining the 95zr(n, γ) and 93zr(n, γ) cross sections via 96zr(p, p') and 94zr(p,p')surrogate reactions |
water plays a key role in many astrophysical environments (star-forming regions, outflows, prestellar cores, comets, asteroids, …) as well as for the emergence of life as we know it. its detection in the inner regions of low-mass protostars raises the question whether this is similar to the water that is incorporated into comets and asteroids that may deliver it to earth-like planets. the water deuterium fractionation is very helpful to understand how it forms and evolves. for example, cleeves et al. (2014) showed that a contribution of water formed in the primordial cloud is necessary to explain the hdo/h2o ratio of the terrestrial oceans. observations of the deuterated and non-deuterated forms of water at an early stage of star formation may therefore potentially be an important tool to describe the origin of water on earth.we here present recent interferometric measurements of the distribution and deuteration of water on solar system scales. during the last few years, a few hdo and h218o lines were observed in the inner regions of class 0 protostars with interferometers (jørgensen & van dishoeck 2010, codella+2010, persson+ 2012, 2013, 2014, taquet+ 2013), which enables estimates of the hdo/h2o ratios. our recent detection of d2o with the plateau de bure interferometer towards the low-mass protostar ngc1333 iras2a leads to a surprisingly high d2o/hdo ratio compared with the hdo/h2o ratio (coutens+ 2014). these results contradict the predictions of current grain surface chemical models and indicate that either an ingredient is missing in our understanding of the surface deuteration process or that both sublimation of grain mantles and water formation at high temperature (t > 230k) take place in the inner regions of protostars. we also present the first results of an alma cycle 2 program (pi: a. coutens) to target several hdo, h218o and d2o lines at a spatial resolution of ~0.3" (40 au) toward the nearby protostellar binary iras16293-2422. these observations will reveal the dynamics of water in the warm inner regions of protostars and determine if the high d2o/hdo ratio derived in ngc1333 iras2a is specific to this source or common among low-mass protostars. | water in the warm inner regions of class 0 protostars |
a survey was conducted in ada'a, sululta, and debre birhan districts. the districts are located in the vicinity of brewery factories. a semi-structured questionnaire was used to collect data from purposively selected dairy farmers (160). data were analyzed with a statistical package for social sciences (version 21). the majority of farmers (69.4%) used wet brewery-spent grain (wbsg), whereas 30% of them used both wbsg and wet brewery spent yeast (wbsy). farmers obtained wbsg and wbsy only in fresh form from the distributors. the majority of farmers (66.67%) blended wbsg and wbsy with concentrate and roughage feed before feeding it to their animals, while 14.47% fed the by-products alone to their animals. several farmers (60.1%) responded that the key reason for providing wbsg and wbsy to their livestock was higher production (increased milk and growth rates). the majority (82.78%) of farmers used common salt to extend the shelf life of wbsg and wbsy. out of 128 (80%) farmers who reported spoilage in wbsg, 49 (38.28%) farmers observed sever mold development, while the remaining 12 (9.38%) and 28 (21.88%) saw change in colour and unpleasant odor. according to 68 (53.13%) of the farmers who experienced in wbsg spoiling, the amount of spoilt was less than 9% and 10-20% of the total purchased. the majority of farmers (87.8%) reported that storage time and storage conditions (temperature, moisture, and humidity) were the primary reasons of wbsg spoilage, whereas 12.2% of the farmers reported that inadequate sanitation of feeding troughs, transportation, and storage facilities were the primary causes of spoilage. the key restrictions of brewery by-product utilization were found as scarcity and high purchasing costs. farmers (44.38% and 41.86%) believed that feeding wbsg and wbsy to dairy cattle have negative health effect, respectively. in conclusion, insufficient and irregular supply, rising cost of material and transport, spoilage, and health-related hazards are the main constraints of wbsg and wbsy usage. it is suggested that there is a dire need for consistent supply, staying away from the brokers, and preserving the brewery by-products through sun drying, and ensiling. additionally, more research is required to determine the negative health impact of feeding brewer by-products for dairy cattle. | dairy farmer's perception on feeding, conservation, and constraints of brewery by-products utilization in selected districts of ethiopia |
the cosmic dust analyzer (cda) instrument onboard the cassini mission found complex macromolecular organic material in ice grains erupting from the plume of enceladus [1]. while [1] suggested that these organics could be primordial material processed in enceladus' core and delivered to the ocean by hydrothermal activity, it has been demonstrated that complex organics can also be synthesized abiotically from the reduction of inorganic carbon species by molecular hydrogen (h2) during hydrothermal reactions on earth [2-4]. here, we use the kerogens described in [5] as analogs for the high-mass organics detected on enceladus to explore this hypothesis. we generate stability diagrams for kerogens relative to oceanic carbonate species at temperatures from 50°c to 300°c as functions of oxidation state (represented by hydrogen activity, ah2) and ph. we apply constraints from [6] and [7] on the temperature, oxidation state and ph of the hydrothermal fluid to test whether the kerogens could be formed under these conditions. we find that, within our lower allowed temperature range (t ~ 100°c) , kerogen formation from ∑co2 and h2 is thermodynamically favorable within the entire constrained ph and ah2 boundaries. as temperature increases, the ah2 required to form kerogens increases more rapidly than our predicted ah2 range for enceladus' interior. thus, we find that kerogens could only form within a small region of the constrained parameter space at higher temperatures, and would be unlikely to form at all at the high end of our temperature range (t ~ 300°c). we present the implications of our findings for the plausibility of abiotic synthesis of complex organic material in the enceladus interior, and motivate the need to measure carbon isotopes on enceladus to further constrain the origin of this material. [1] postberg et al. (2018), nature, 558, 564 [2] mccollom & seewald (2007), chemical reviews, 107(2), 382-401 [3] sforna et al. (2018), nature communications, 9(1), 1-8. [4] milesi et al. (2016). geochim. cosmochim. acta, 189, 391-403. jgr: planets, 104(e6), 14033-14049. [5] helgeson et al. (2009), geochim. cosmochim. acta, 73, 594-695 [6] hsu et al. (2015), nature, 519, 207-210 [7] glein et al. (2018), enceladus and the icy moons of saturn, p. 39 | abiotic synthesis as a new source of organic matter on enceladus |
the mars science laboratory curiosity rover has been exploring sedimentary rocks at the foothills of mount sharp since august 2014. robust interpretation of the paleoenvironmental contexts requires detailed facies analysis of these rocks including analysis and interpretation of sedimentary structures and sediment body geometries. here, we describe some of the detailed sedimentary structures and sedimentary geometries observed by curiosity between the pahrump_hills field site and its current location at marias pass. the pahrump hills sedimentary section comprises a succession dominated by finely laminated mudstones of the murray formation that are interpreted to have been deposited in an ancient lake within gale crater. toward the top of the pahump hills succession, we observe the appearance of coarser-grained sandstones that are interstratified within the lacustrine mudstones. these sandstones that include whale rock and newspaper rock show lenticular geometries, and are pervasively cross-stratified. these features indicate that currents eroded shallow scours in the lake beds that were then infilled by deposition from migrating subaqueous dunes. the paleoenvironmental setting may represent either a gullied delta front setting or one in which lake level fall caused fluvial erosion and infilling of the shallow scours. since leaving pahrump_hills, curiosity has imaged extensive exposures of strata that are partly correlative with and stratigraphically overlie the uppermost part of the pahrump section. isolated cross-bedded sandstones and possible interstratified conglomerates beds occur within murray formation mudstones. capping sandstones with a likely variety of environmental contexts overlie mudstones. where imaged in detail, sedimentary structures, such as trough-cross bedding and possible eolian pinstriping, provide constraints on plausible sedimentary processes and bounds on depositional setting. | sedimentary structures and stratal geometries at the foothills of mount sharp: their role in paleoenvironmental interpretation |
we present numerical experiments to determine quantitatively the effects of mineral particle clustering on mars spacecraft spectral signatures and to improve upon the values of refractive indices (optical constants n, k) derived from mars dust laboratory analog spectra such as those from relab and mro crism libraries. whereas spectral properties for mars analog minerals and actual mars soil are dominated by aggregates of particles smaller than the size of martian atmospheric dust, the analytic radiative transfer (rt) solutions used to interpret planetary surfaces assume that individual, well-separated particles dominate the spectral signature. both in rt models and in the refractive index derivation methods that include analytic rt approximations, spheres are also over-used to represent nonspherical particles. part of the motivation is that the integrated effect over randomly oriented particles on quantities such as single scattering albedo and phase function are relatively less than for single particles. however, we have seen in previous numerical experiments that when varying the shape and size of individual grains within a cluster, the phase function changes in both magnitude and slope, thus the "relatively less" effect is more significant than one might think. here we examine the wavelength dependence of the forward scattering parameter with multisphere t-matrix (mstm) and discrete dipole approximation (ddscat) codes that compute light scattering by layers of particles on planetary surfaces to see how albedo is affected and integrate our model results into refractive index calculations to remove uncertainties in approximations and parameters that can lower the accuracy of optical constants. by correcting the single scattering albedo and phase function terms in the refractive index determinations, our data will help to improve the understanding of mars in identifying, mapping the distributions, and quantifying abundances for these minerals and will address long-standing questions on fundamental physics in the martian surface (e.g., what is the fundamental scattering unit for closely packed dust or regolith grains?). this work was supported by nasa's mars fundamental research program and performed with the pleiades cluster courtesy of nasa's advanced supercomputing division. | improving estimated optical constants with mstm and ddscat modeling |
a thousand times smaller in mass than ganymede, enceladus was known from voyager data to be extremely bright and a dearth of craters on some parts of its surface suggested geologic activity. cassini discovered the presence and composition of a plume erupting from the south polar terrain of enceladus, approximately 100 narrow, distinct "geysers" or "jets" that feed it, and anomalous thermal signatures along fractures from which the geysers erupt. cassini discovered organic and nitrogen-bearing molecules in the plume vapor, and detected salts in the plume icy grains, arguing strongly for ocean water being in contact with a rocky core. as much as cassini has done, it cannot tell us whether the ocean of enceladus hosts an active biota today. enceladus life finder (elf) is a discovery-class solar-powered saturn orbiter designed to fly multiple times through the plume of enceladus. it carries two state-of-the-art mass spectrometers designed to analyze the gas and grains in the plume. the goals of the mission are derived directly from the most recent decadal survey: first, to determine primordial sources of organics and sites of organic synthesis today, second, to determine if there are modern habitats in the solar system beyond earth where the conditions for life exist today and third, if life exists there now. elf conducts three tests for life. the first test looks for a non-abiotic distribution of amino acids, the second determines whether the carbon number distribution in fatty acids or isoprenoids is biased toward a particular rule, and the third measures carbon and hydrogen isotopic ratios, together with the abundance of methane relative to other alkanes, to assess whether the values fall in the range for biological processes. the elf mission spacecraft conducts ten science plume fly-throughs; the baseline science is completed in the first five plume passages. | enceladus life finder: search for life in a habitable moon. |
organic matter in asteroids and comets records the chemical history from the protosolar molecular cloud to the early solar system. they are thought to have contributed to the formation of our habitable planet earth, through exogenous delivery. therefore, it is important to reveal the chemical evolution of organic compounds in primitive small bodies for understanding the origins of planets and life. jaxa's hayabusa2 mission explored the carbonaceous asteroid ryugu and collected its sands and pebbles (tachibana et al. 2022). on december 6, 2020, the asteroid sample was returned to the earth. through the curatorial work at jaxa, it was reported that the ryugu samples contain high abundances of hydrous minerals and organic matter (yada et al. 2021; pilorget et al. 2021). afterward, the initial sample analysis has started from june 2021 to classify and characterize the ryugu samples in the context of the solar system formation. the initial analysis iom (insoluble organic matter) team has aimed to unveil the chemical, isotopic, and morphological compositions of macromolecular organic solids from the ryugu samples by coordinating spectromicroscopies, electron microscopy, and isotopic microscopy. the initial analysis som (soluble organic matter) team has investigated the distributions of soluble organic molecules from the ryugu samples using high-sensitive and high-resolution mass spectrometry techniques. chamber a aggregates and chamber c aggregates collected at the first and second touchdown sites, respectively, have been analyzed. bulk c, h, n and s compositions of the ryugu samples were consistent with those of primitive carbonaceous chondrites. macromolecular organic solids were abundant and had complex structures consisting of aromatic carbons, aliphatic carbons, ketones and carboxyls. the functional group compositions correlated with the morphologies of nano-sized organic matter, such as organic nanoglobules and diffuse carbon. these organic microstructures were associated with phyllosilicates and carbonates. thus the observed functional group diversity likely resulted from aqueous alteration on the asteroid parent body without significant heating event. the δd distributions of the isolated organic solids from the ryugu samples were within the δd range of primitive carbonaceous chondrites. the δ 15n of bulk c and organic solids from the ryugu samples showed similar values to those in ci chondrites. extreme d and/or 15n enrichments or depletions in some c-rich grains could possibly have been derived from the solar nebula or protosolar molecular cloud. the solvent extracts of the ryugu aggregates yielded a variety of plausibly prebiotic organic molecules including amino acids as well as aliphatic carboxylic acids and amines. more than 10 proteinogenic and non-proteinogenic amino acids were present as racemic mixtures (d/l ~1), indicating non-biological and extraterrestrial origins. n-containing heterocyclic compounds were also identified as their alkylated homologues, including pyridine-, pyrimidine- and imidazole-containing species. these n-heterocycles could have been synthesized in the parent body from ammonia and simple aldehydes. alkylated aromatic hydrocarbons including polycyclic aromatic hydrocarbons were also present. in-situ mass spectrometry imaging showed heterogenous spatial distribution of organic compounds in the ryugu grain. organic molecules in ryugu samples are intact without suffering significant terrestrial contamination and/or weathering, and will be the best sample to investigate the organic evolution, including synthesis of prebiotic molecules, in the early solar system. | hayabusa2 initial analyses of organic matter in the asteroid ryugu samples |
since the first but ambiguous evidence of water sublimation activity on ceres was reported more than two decades ago [1] and the negative results in a number of follow up observations [2], water vapor has recently been unambiguously detected by the herschel space observatory observations [3]. the mechanism of water sublimation on ceres is still unclear, but the most probable mechanisms include cometary-like sublimation and cryovolcanism. such sublimation activity could entrain dust grains in the outgassing, resulting in either a dust envelope or dust plumes above the surface of ceres. given the much higher escape velocity of ~0.5 km/s on the surface of ceres compared to those on comets (a few m/s), any dust around ceres might be short-lived, and/or close to the surface of ceres. the implications of possible dust around ceres motivated nasa's dawn mission to perform a high-sensitivity, high-resolution search for dust around ceres. the dawn spacecraft, during its first science orbit around ceres, will have an excellent opportunity to search for dust at a pixel scale of 1.4 km/pixel from the night-side of ceres looking close to the direction of the sun. this observing geometry is the most favorable to search for dust around ceres due to the significant increase of dust brightness and decrease in the surface brightness of ceres towards high solar phase angle. here we report the results of this search for dust around ceres with dawn's framing camera (fc) [4]. | search for dust around ceres |
the study of photochemistry in the solar system is of prime importance to assess complex organic chemistry in any extraterrestrial environment. among those environments, comets and grains ejected from their nuclei are of particular interest in the context of astrobiology as they could have brought organic matter on the primitive earth, and hence contribute to the emergence of life. furthermore, they can provide precious information on the physico-chemical parameters prevailing in the primitive solar nebula during its formation. in this context, we are studying the extent to which organic matter within grains may survive to solar radiation and the fraction of these organic molecules destroyed when it is subjected to sunlight. | photostability of glycine and nitrogen basis in cometary grains : application to the transport of organic matter within the primitive earth |
vegetation plays a leading role in ecosystems. plant communities are the main components of ecosystems. green plants in ecosystems are the primary producers, and they provide the living organic matter for the survival of other organisms. the dynamics of most landscapes are driven by both natural processes and human activities. in this study, the growing season gimms ndvi3g and climatic data were used to analyse the vegetation trends and drivers in beijing-tianjin-hebei region from 1982 to 2013. result shows that, the vegetation in beijing-tianjin-hebei region shows overall restoration and partial degradation trend. the significant restoration region accounts for 61.5 % of beijing-tianjin-hebei region, while the significant degradation region accounts for 2.1 %. the dominant climatic factor for time series ndvi were analyzed using the multi-linear regression model. vegetation growth in 17.9 % of beijing-tianjin-hebei region is dominated by temperature, 35.5 % is dominated by precipitation, and 11.68 % is dominated by solar radiance. human activities play important role for vegetation restoration in beijing-tianjin-hebei region, where the large scale forest restoration programs are the main human activities, such as the three-north shelterbelt construction project, beijing-tianjin-hebei sandstorm source control project and grain for green projects. | the vegetation trends and drivers in beijing-tianjing region from 1982 to 2013 based on time series gimms ndvi3g |
nasa is committed to landing humans again on the moon by 2025 to a long-term goal of a sustaining presence. a major component of this mission is nasa's orbiting lunar outpost, gateway, that will be subjected to the harsh environment of space during the planned 15-year lifespan in the cis-lunar environment. one aspect of this environment that is not well quantified is microscopic lunar regolith particles, or simply, lunar dust. dust particles, most of which are smaller than the width of two human hairs and generally irregularly shaped, are widely influenced by the following electrostatic characteristics: volume resistivity, charge decay, chargeability, and dielectric properties of the dust. such characteristics can allow the dust particles to collect electric charge from the surrounding environment, resulting in electrostatic interactions between the dust, electromagnetic fields, and electrically charged surfaces. due to the nature of these fields, dust can collect on and contaminate charged surfaces. lunar dust introduced into the gateway environment by a lunar ascent vehicle element returning from the surface of the moon presents risks to gateway hardware such as radiators, solar arrays, external robotic systems, antennae, and docking mechanisms. to quantify this risk and inform nasa, international partner, and commercial provider stakeholders, a comprehensive physics-based model is in development to investigate the interaction of charged lunar dust particles with the cis-lunar, deep-space environments, and spacecraft. it is comprised of a set of models of the space plasma and solar radiation environment and electromagnetic interaction of spacecraft and lunar dust. spacecraft charging and plasma environment are solved using the open-source code from the french aerospace research laboratory (onera) and the european space agency (esa), known as spacecraft plasma interaction software (spis). the physics of particle charging and transport is modeled as an equilibrium implementation of shifted-orbital-motion-limited (soml) theory which accounts for plasma flows and positive potential grains, using siemens star-ccm + as the framework. model validation includes lab experiments by nasa experts and academia, as well as future on-orbit dust detecting and dust collecting payloads on the exterior of gateway. the results and analyses will inform gateway program system owners at risk for lunar dust contamination. | development of a comprehensive physics-based model for study of nasa gateway lunar dust contamination |
a ray of state of existence gives a tree of limit experience that can be traced from literal calculus and, in s-language, propagates heterocycles in not equivalent syntactic replica beyond page curve tautology. stratifying semantic stability in space i prospect irrational unbalance as s-flare precession and a tree of unfolding of granular life as astrobiology solution of hawking paradox. | remote sensing of heterocyclic life in solar system and in generalized clusters unfolding |
i present results from three theoretical numerical studies relating to destructive events in the lives of outer solar system satellites and smaller bodies. the first project is a study of the implications that a late heavy bombardment in the outer solar system, such as predicted by the nice model, might have had for the mid sized moons of jupiter, saturn, and uranus. a monte carlo calculation shows that mimas, enceladus, tethys, and miranda each would almost certainly have experienced at least one catastrophic collision after formation. if true, these bodies would have disrupted and then reaccreted as scrambled mixtures of rock and ice---potentially preserving this signature in their present day structure. conversely, if these satellites are fully differentiated today then they would have required a heat source sufficient for melting and differentiation in the absence of short half life radioactive elements. tidal heating may have been sufficient for tethys, enceladus, and miranda, but a differentiated mimas would present a difficulty to either the nice model or to the classical formation model of the saturn system. the second study is a numerical investigation of the expected outcome of destructive collisions between gravity-dominated bodies; in particular of the conditions required for a collision to be catastrophic, defined as one that leaves behind a surviving body with less than half the total colliding mass. in this study i focus on bodies with radii between 100 and 1000 km, a previously neglected size range, and derive a simple scaling law for the threshold impact energy required for disruption in this size range. this scaling law is expected to hold for all projectile-to-target size ratios and is independent of material, so long as elastic strength may be ignored. compared with scaling laws existing in the literature the newly derived scaling generally predicts lower threshold energy for disruption, except for highly oblique impacts by projectiles much smaller than the target. the third project is a study of the tidal breakup of rubble piles by modeling the breakup of comet shoemaker-levy 9 in a rigid body code that, for the first time, treats non-spherical rubble pile elements. this introduces dilatation and grain locking as the major forces acting against gravity tides during the comet's close approach to jupiter and changes the outcome of tidal encounters compared with that predicted by models using spherical elements. by comparing simulation results to the well-studied post-breakup morphology of comet sl9 we were able to constrain the progenitor's bulk density at 300--400 kg/m3, half that of previous estimates. | destructive gravitational encounters: outcome and implications of catastrophic collisions and tidal splitting in the post-formation outer solar system |
the curiosity rover team has explored several different eolian sand targets in gale crater, including dunes and ripples. using curiosity's mars hand lens imager (mahli), we measured the size of grains on or near ripple crests within dunes, ripple fields, and in isolated ripples. the barby target (sol 1184) is on the crest of a ripple on the lower stoss slope of the barchan high dune. flume ridge (sol 1604) and avery peak (sol 1651) are smaller ripples on the nathan bridges and mount desert island linear dunes. schoolhouse ledge (sol 1688) is an isolated megaripple not associated with either a dune or ripple field. enchanted island (sol 1751) is a ripple contained within a larger ripple field near the vera rubin ridge. our results show the grains of the avery peak and flume ridge targets are mostly 75-150 µm in size and grain motion was observed during each mahli imaging sequence. barby is dominated by 250-450 µm grains assumed to be active based upon the lack of a dust coating, though grain motion was not observed. the enchanted island target has slightly larger grains than barby, with most between 300-500 µm. the grains have some dust aggregates on their surfaces, suggesting they have been less active in recent months or years relative to the ripples examined within the bagnold dune field. finally, grains along the crest of schoolhouse ledge are the largest, 400-600 µm, and all of the grain surfaces have a thin dust coating, indicating the ripple is not currently active. some of the ripple crests have similar grain sizes on both the stoss and lee sides (schoolhouse ledge, barby) whereas other ripples showed larger grains concentrated on the stoss side (enchanted island, avery peak, flume ridge). scuffing by the rover's front wheel revealed both schoolhouse ledge and enchanted island had coarser grains dominating the ripple surface with finer grains within the ripple interior. in general, the surfaces of active sand ripples have smaller grains compared to the inactive ripples which exhibit an armor of larger grains. our results indicate grain sizes vary widely depending upon such factors as ripple activity, location along the ripple, ripple size, dune type, and orientation relative to the wind direction. | grain size measurements of eolian ripples in gale crater, mars |
through laboratory analyses it is possible to study the physical and chemical processes involving prebiotic molecules, the building blocks of life. today thanks to the advent of new generation of (sub-) millimeter and centimeter interferometers (alma, noema, ngvla), an increasing number of interstellar complex organic molecules (icoms) is observed in star forming regions, pre-stellar dense cores, hot corinos, jets and outflow ardound protostars [1, 2, 3]. hot corinos are inner compact (<100 au) and hot (>100 k) regions of some protostars [4]. in these high-temperature regions, thermal desorption is the physical process responsible for the sublimation of frozen mantles into the gas phase and so for the presence of a rich chemistry [5] in the gas phase. on the other hand, icoms are difficult to observe in protoplanetary disks, where, for a solar-type star, the region where the temperature reaches the values for the desorption and release into the gaseous phase of water and icoms (water snow line) is too close to the star (≤5 au). this region is difficult to solve but a new perspective is provided by objects such as the fu ori systems in which the young central star undergoes a sudden increase in brightness which leads to heating of the disk and quick expansion of the snow lines to large radii. this phenomenon has been observed in the protoplanetary disk around the protostar v883 ori [6]. thanks to the increase in temperature of the disk and the consequent thermal desorption of the molecules, five icoms were recently detected: methanol, acetone, acetonitrile, acetaldehyde, and methyl formate [7]. moreover, outbursting young stars are good new targets for looking for organic complex molecules that thermally desorb from icy mantles. the interpretation of observations can benefit from laboratory activities, where it is possible to simulate the thermal desorption process and uv irradiation of complex molecules under simulated space conditions. furthermore, laboratory studies on thermal desorption are fundamental to constrain parameters such as the thermal desorption temperature of a given molecule and its fragments, and the binding energies involved. here we reported the results that we have recently published about temperature-programmed desorption (tpd) analysis of pure formamide (hconh2) ice and in the presence of tio2 dust, before and after uv irradiation. we found that pure formamide desorbed at 220 k in high vacuum regime and after uv irradiation it fragmented mainly into nh2, hco and ch2no. these fragments are more volatile and desorbed before formamide (~180 k) at the same desorption temperature of water. the presence of water was due to residual deposition in the high vacuum chamber. it is reasonable to think, therefore, that the sublimation of water ice was responsible for releasing more volatile species. the same phenomenon probably occurs in the space where water is the most abundant molecule. going forward with our investigation, we reproduced the condensation, irradiation, and desorption experiments with a substrate of tio2 dust. in presence of grains, we observed evidence for a change in desorption temperature. formamide desorption from tio2 dust occurred at higher temperatures, that is, around 30 k above the temperature at which desorption takes place for pure formamide. a higher desorption temperature is direct evidence of the interactions described by the van der waals forces that were occurring between the molecule and the grains. the molecule interacts and diffuses into the grains and this is confirmed by the values of the binding energy that we found. when formamide desorbed directly from the cold finger of the cryostat (copper chromate surface), the binding energy found was (5.9 ± 0.3)·103 k; while when it desorbed from tio2 dust, the binding energy found was (1.35 ± 0.08)·104 k, a value two times higher [8]. therefore, in the chemical models of sublimation, it is essential to take into account physisorption of icoms on grain surfaces and their diffusion to correctly describe the desorption process, that is, to constrain desorption temperatures and binding energies [8]. furthermore, our experiments show something more than the desorption temperature and the binding energy of formamide. the molecular fragments observed in laboratory (nh2, hco and ch2no) can be used to indirectly measure the presence of formamide through detection of relative abundance (e.g., [nh2]/[hco]∼4).we reported also preliminary results on laboratory studies about thermal desorption of ice mixtures of acetaldehyde and acetonitrile from crystalline olivine grains.these studies offer support to observational data and improve our understanding of the role of the grain surface in enriching the chemistry in space. references[1]beltrán, m. t. et al. 2009, the astrophysical journal letters, 690 [2] rivilla, v. m. et al. 2017, astronomy & astrophysics, 598 [3] codella, c. et al. 2015, mon. not. r. astron. soc., 449 [4]ceccarelli, c. et al. 1999, astronomy and astrophysics, 342[5] lópez-sepulcre, a. et al. 2015, mnras, 449[6] cieza, l. a. et al. 2016, nature, 535, issue 7611[7] lee, j. et al. 2019, nature astronomy,3, 314[8] corazzi, m. a. et al. 2020, a&a, 636, a63 | laboratory studies on temperature-programmed desorption analyzes of prebiotic molecules in space |
the basic structure of the solar system is set by the presence of low-mass terrestrial planets in its inner part and giant planets in its outer part. this is the result of the formation of a system of multiple mars-mass embryos in the inner disk and of a few multi-earth-mass cores in the outer part, within the lifetime of the gaseous component of the protoplanetary disk. what was the origin of this dichotomy in the mass distribution of embryos/cores? we show in this paper that the classic processes of runaway and oligarchic growth from a disk of planetesimals can not explain this dichotomy, even if the original surface density of solids increased at the snowline. instead, the accretion of drifting pebbles by embryos/cores can explain the dichotomy, provided that some assumptions hold true. we propose that the mass flow of pebbles is two-times lower and the characteristic size of the pebbles is ten times smaller within the snowline than beyond the snowline (respectively at r < r_ice and r > r_ice, where r_ice is the snowline heliocentric distance), due to ice sublimation and the splitting of icy pebbles into a collection of chondrule-size silicate grains. in this case, objects of original sub-lunar mass would grow at drastically different rates in the two regions of the disk. within the snowline these bodies would reach approximately the mass of mars while beyond the snowline they would grow to 20 earth masses. the results may change quantitatively with the assumed parameters, but the establishment of a clear dichotomy in the mass distribution of protoplanets appears robust. | origin of the great dichotomy of the solar system: small terrestrial embryos and massive giant planet cores |
enceladus offers a unique opportunity in the solar system in that material derived from its potentially habitable ocean is accessible without the need to dig, drill, or even land. in situ sampling of the enceladus plume will likely be required to determine whether life is present in the subsurface ocean. this can be achieved via orbit or flyby; such encounters occur at speeds determined by the velocity of the spacecraft and can range from hundreds of m/s to tens of km/s. here we focus on impact-induced ionization, a technique to analyze putative biomolecules in ice grains with minimal sample processing. grains hit a metal plate and their contents are ionized and volatilized upon impact; the resulting ions can then be queried using a time-of-flight (tof) mass spectrometer (ms). this technique was employed by the cosmic dust analyzer aboard cassini and will also be used by the surface dust analyzer (suda) on europa clipper. at high velocities, potential biosignature molecules may undergo fragmentation or chemical modification, making identification difficult. we therefore seek to determine the maximum spacecraft velocity where astrobiology investigations could be performed, i.e., the 'speed limit' of biosignature detection via plume flythrough. two experimental systems were built and tested to replicate hypervelocity sampling of the enceladus plume: the hypervelocity ice grain system (higs) at jpl and the aerosol impact spectrometer (ais) at uc san diego. we also used reactive molecular dynamics and quantum mechanics simulations at caltech to determine the fragmentation dynamics and pathways for amino acids and fatty acids up to 12 km/s inside hexagonal ice grains up to tens of nm in diameter. we achieved ice grain velocities up to 6.3 and 4.1 km/s for higs and ais, respectively, and were able to establish experimentally that organic molecules such as amino acids, fatty acids, and peptides do indeed survive impacts at these velocities. modeling suggests that biomolecules encased within ice grains are more protected, increasing the fragmentation threshold from 3-5 km/s for bare molecules to 4-6 km/s when in ice grains for most species. any future spacecraft sampling the plume of enceladus (or possibly europa) with a cda- or suda-like instrument should therefore target 3-6 km/s for biosignature searches. | searching for biosignatures in the plume of enceladus at hypervelocity: experimental and theoretical validation |
saturn's icy moon enceladus emits into space a plume of gas and ice grains formed from a subsurface salt-water ocean that interacts with a porous rocky core via hydrothermal vents. a similar plume phenomenon is suspected to occur on jupiter's moon europa. such plume material enables the internal exploration of satellites by spacecraft flybys, as undertaken at enceladus by the cassini spacecraft's mass spectrometers, the cosmic dust analyzer (cda) and the ion and neutral mass spectrometer (inms). cda and inms detected h2, ch4 [1] and nano-silica [2], confirming active alkaline hydrothermal activity at enceladus' ocean-core interface, believed to be similar to the lost city hydrothermal vent systems on earth. the discovery of insoluble high-mass organic macromolecules [3] as well as soluble n-, o-, and aromatic low-mass organic compounds [4], some of which could act as amino acid precursors, revealed complex and reactive organic chemistry within the moon. interpreting ice grain mass spectra and inferring the biogeochemistry of enceladus requires terrestrial calibration. here, we report our results from laser-induced liquid beam ion desorption (lilbid) time-of-flight mass spectrometry in the laboratory, a proven analogue for cda in situ ice grain mass spectrometry [5]. geochemically-relevant salts and biologically-relevant organics, such as amino acids, fatty acids and peptides, have been tested and characteristic spectral signatures of these compounds could be identified [6]. abiotic and biotic mass spectral fingerprints could be discriminated and detection limits of the organics were found to be at the μm or nm level in enceladus-like solutions [7], while those for salts (including sulfates and phosphates) are currently being determined. further biological samples, such as dna and lipids extracted from bacterial cell cultures, are also under evaluation. the results reported here aid planning for future space missions to enceladus and other ocean worlds, such as the europa clipper mission to europa. references [1] waite et al., 2017 (science) [2] hsu et al., 2015 (nature) [3] postberg et al. 2018 (nature) [4] khawaja et al. 2019 (mon not r astron soc) [5] klenner et al. 2019 (rapid commun mass spectrom) [6] klenner et al. 2020a (astrobiology) [7] klenner et al. 2020b (astrobiology) | exploring enceladus and other ocean worlds using mass spectrometry |
one of the most pressing questions in exploration is whether life exists or existed anywhere else in the solar system. water is a critical prerequisite for life as we-know it; thus, targets in the search for extraterrestrial life are bodies that have or had liquid water, e.g. ceres, enceladus and europa (ocean worlds), or mars. due to significant radiation fluxes, or the possibility for burial by later materials, the search for life requires subsurface access. solar system life detection, further, requires a sampling system to deliver subsurface samples to state-of-the-art instruments as remote sensing approaches alone are insufficient. a sampling operation normally has six steps: 1. sampler deployment, 2. material excavation, 3. sample capture, 4. sample transport, 5. sample metering and verification, 6. sample delivery. in the recent past, significant efforts have been undertaken to increase technology readiness of steps 1, 2 and 6. however, steps 3 - 5 have seen more limited development efforts, in spite of these steps (3 - 5), being more challenging. frozen regolith observation and sampling tool (frost) is a sample acquisition and delivery system suitable for ices and rocky regolith on airless bodies. frost covers steps 2-6 outlined above (frost architecture does not need step 1) and is suitable for ceres, enceladus, europa, and other airless bodies, as well as mars. frost captures the most promising approaches into a single, fully integrated system. it includes a drill to excavate and reach up to 20 cm below the surface (step 2), planetvac to capture and pneumatically move material (step 3 and 4), a diverter and a cup for metering (step 5) and a carousel with leveler to deliver samples to instruments (step 6). since the drill and planetvac are mounted on the footpad/leg of a lander, step 1 (deployment) is eliminated, reducing system mass and risk. since planetvac (without a use of a drill) can be used as excavation system for granular material, it offers system level redundancy. | frost: frozen regolith observation and sampling tool |
perovskite solar cells are sensitive to subtle changes in atmospheric conditions, resulting in problems such as the collapse of the perovskite structure and sharp drops in efficiency. internal defects are also a big obstacle for high‑quality polycrystalline perovskites. at present, it is difficult to control the density of the trapping sites. by using the bidentate chelating agent thenoyltrifluoroacetone (ttfa), the crystallization kinetics, grain sizes, and crystal defect of cs‑, methylammonium‑, and formamidinium‑based perovskite materials can be to effectively controlled through a nucleation and growth process for the preparation of perovskite crystals. crystalline‑state tuning during the crystallization process to obtain better quality perovskite thin films can be achieved with no additional operation, which is suitable for the needs of modern industrial production and management. the chelating agent can effectively passivate the defects in perovskite films, leading to a low defect density and a long charge carrier lifetime. as a result, the ttfa‑passivated perovskite solar cell demonstrated a high power conversion efficiency of 19.70 % with superior stability retention of 64 % of the initial power conversion efficiency after two weeks unencapsulated storage in an adverse atmosphere with approximately 50 % relative humidity. | highly efficient and stable perovskite solar cells using an effective chelate‑assisted defect passivation strategy |
amides are a regularly recurring chemical structure in biomolecules, such as peptides, nucleobases, and lipids, and therefore essential to life as we know it. simple amides, such as formamide (nh$ _{2}$cho) and acetamide (ch$ _{3}$conh$ _{2}$), are detected in space, thus making it possible that such molecules are involved in prebiotic chemistry leading to biomolecules. at the same time, the structural similarity between these molecules raises the question if and how these molecules are related to each other in interstellar chemical networks. in this talk, i will present the recent laboratory and observational results of this class of molecules. cryogenic laboratory experiments are used to simulate interstellar icy dust grains and to elucidate the formation pathways of small amide in these ice mantles. alma observations of the sun-like protostar iras16293-2422b and the high-mass star-forming region ngc 6334i are used to constrain the interstellar presence of small amides and to determine correlations between these species. | the interstellar chemistry of amides |
the basal siccar point group unconformity observed at the greenheugh pediment is a major regional break in sedimentation within gale crater. below the unconformity, mudstones and sandstones of the murray formation records a predominantly lacustrine palaeoenvironment that was likely habitable. overlying the unconformity is a distinctive fan-shaped, erosion-resistant, tabular stratal unit (~2-6 m thick) informally called the greenheugh pediment capping unit. this unit has been identified as part of the stimson formation, which encodes the signature of surfaces processes and the climate in gale crater postdating the formation of the unconformity. between sols 2633 and 2781, the curiosity rover was used to investigate the pediment capping unit, where detailed observations of sedimentary architecture, facies and sediment texture were obtained. textural and grain-size analyses of the sandstone show that it comprises a well-sorted, medium-grained, well-rounded sandstone with an average grainsize of ~425 μm, which suggests aeolian transport processes the dominant sedimentary structure are cross-bedded sandstones composed of 2-4 mm thick, uniform-thickness cross-laminations, that are typical of wind ripple stratification. architectural observations reveal that the unit is composed of compound cross-sets, with sets that are 0.2-0.7 m thick, that form cosets up to 2.5 m thick. these observations lead us to conclude that the pediment capping unit accumulated as the result of aeolian processes, where wind-blown dunes migrated across the unconformity, leaving preserved aeolian cross strata. further to this, our observations of sedimentary texture, facies and architecture are consistent with stimson formation sandstones observed in the emerson plateau, naukluft plateau and murray buttes areas. we conclude that the pediment-capping unit is an up-slope equivalent of the stimson formation, and that the stimson formation drapes the unconformity over a ~500 m elevation range. the stimson formation is the preserved expression of a dry aeolian dune field, that accumulated in a climate of extreme aridity, when gale crater would likely have been devoid of surface water. the juxtaposition of desert deposits overlying lake deposits indicates a major change in palaeoclimate in gale crater. | reconstructing martian environmental change across a major unconformity at gale crater: sedimentology of the stimson formation at the greenheugh pediment |
inferior morphology of perovskite films and suppressed hole extraction restricts the performance of perovskite solar cells (pscs) with a pedot:pss hole transporting layer (htl). in this work, poly-tpd is used to modify the surface of pedot:pss films in psc. the presence of hydrophobic poly-tpd decreases the nucleation sites, and as a result, perovskite films with larger grains are obtained. improved energy level alignment in the presence of poly-tpd results in enhanced hole extraction from the perovskite layer to the htl. the improved morphology and charge extraction resulted in improved photovoltaic performance. the power conversion efficiency (pce) of pscs was increased from 13.6% to 16.1% with the incorporation of poly-tpd. also, the shelf life of the pscs has exhibited considerable improvement due to the presence of hydrophobic poly-tpd and fewer number of grain boundaries. after 66 days, the psc with poly-tpd maintained 96% of its initial pce, whereas the pce of the control device degraded to 72% of its initial value. | hydrophobic poly-tpd modified pedot pss surface for improved and stable photovoltaic performance of mapbi3 based p-i-n perovskite solar cells |
images acquired by the mars hand lens imager (mahli) and the chemcam remote micro imager (rmi) onboard the mars science laboratory (msl) curiosity rover provide grain-scale data that are critical for interpreting sedimentary deposits. at the location informally known as marias pass, curiosity used both cameras to image the nine rock targets used in this study. we used manual point-counts to measure grain size distributions from those images to compare the abilities of the two cameras. the manually derived results were compared to automated grain size data obtained using pydgs (digital grain size), an open-source python program. grain size analyses were used to test the lacustrine and aeolian depositional hypotheses for the murray and stimson formations at marias pass. results indicate that the mahli and rmi instruments, despite their different fields of view and properties, provide comparable grain size measurements. additionally, pydgs does not account for grains smaller than a few pixels and thus does not report representative grain size data and should not be used on images with a large fraction of unresolved grains. finally, the data collected at marias pass are consistent with the existing interpretations of the murray and stimson formations. the fine-grained results of the murray formation analyses support lacustrine deposition, while the mean grain size of the stimson formation is fine to medium sized sand, consistent with aeolian deposition. however, directly above the contact with the murray formation, larger rip-up clasts of the murray formation are present in the stimson formation. it is possible that water was involved at this stage of erosion and re-deposition, prior to aeolian deposition. additionally, the grain-scale analyses conducted in this study show that the dust removal tool on curiosity should be used prior to capturing images for grain-scale analysis. two images of the target informally named ronan, taken before and after brushing, resulted in dramatically different grain size results, suggesting that the common, thin layer of dust obscured the true grain size distribution. these grain-scale analyses at marias pass have important implications for the collection and processing of image data, as well as the depositional environments recorded in gale crater. funded by nsf grant ast-1461200 | grain-scale analyses of curiosity data at marias pass, gale crater, mars: methods comparison and depositional interpretation |
the subsurface oceans of icy moons in the outer solar system are potential sites for the search of extraterrestrial life [1]. understanding the chemical properties of the subsurface ocean material emitted into the moons' cryo-volcanic plumes in the form of gas and ice grains is key to finding out whether or not signs of life exist in these oceans [2]. during cassini's entire mission, its onboard mass spectrometers — the cosmic dust analyzer (cda, [3]) and the ion and neutral mass spectrometer (inms, [4]) — frequently sampled ice grains and gas in enceladus plume and saturn's e ring. the detections of various salts [5], nanophase silica (sio _{2}; [6]) particles and molecular hydrogen (h _{2}; [7]) strongly indicated the presence of a subsurface liquid water ocean interacting with the moon's rocky core via the sea floor, with, for example, the products of serpentinization reactions cycling into the ocean through hydrothermal vent systems. here, we present an overview of the inventory of enceladean organic material, as detected by cassini's inms and cda instruments, as well as future plans for simulating their production and evolution. inms detected a number of unidentified o- and n-bearing volatiles, as well as hydrocarbon compounds [8, 9], in the gas plume. these particularly volatile organic species have low ice adsorption energies [10] and did not condense onto ice grains in the icy vents before their ejection into the plume. in contrast, cda was also able to detect refractory compounds by recording time of flight mass spectra from ions created by ice grains imping the instrument's metal target at hypervelocities ≥ 1 km/s. one class of spectra commonly generated by ice grains impacts in the e ring and plume, are the so-called type-2 spectra, which indicate the presence of organic compounds within the grains. with the help of laboratory analogue experiments [11], a detailed analysis of cda type 2 spectra revealed a significant diversity of organic compounds in the ice grains. this led to the further classification of type 2 spectra into: (i) type 2 hmoc, indicating the presence of complex, hydrophobic, solid, macromolecular organic compounds with molecular masses > 200 u [12]. the spectra generating ice grains probably formed around organic condensation cores created by the dispersion of an organic-rich layer at the top of enceladus's ocean water surface by bubble bursting [12]; and (ii) so-called volatile organic compound (voc) bearing ice grains, the dominant fraction of the type 2 class, which produce spectral features due to low mass (< 100 u molecular mass) nitrogen-, oxygen- or single aromatic-ring bearing compounds (type 2 n, o and a, respectively [13]). vocs evaporate at ≍ 272 k from the water surface, but those with water-ice binding energies ≥ 0.5—0.7 ev can then adsorb onto pre-existing water ice grains (and the fracture walls) at the much cooler temperatures inside the ice vents, being subsequently detected by cda [10, 13], while those with a lower tendency to adsorb remain in the plume gas, as detected by inms [8, 10]. the organic compounds in enceladus's plume material indicate the presence of rich organic chemistry in the moon's subsurface ocean (e.g. friedel-crafts-type reactions, which are known to be able to hydrothermally synthesize potential biogenic compounds [14]). ongoing analyses of cda type 2 spectra indicate the presence of further classes of organic compounds. to relate the composition of organic enriched ice grains with the composition of the subsurface ocean and hydrothermal fluids, an understanding of the possible chemical alteration of these species during their ascent from enceladus's core to the vacuum of space is required. [1] schenk et al. (2018) enceladus and the icy moons of saturn, univ. arizona press [2] mckay et al. (2018) in enceladus and the icy moons of saturn, (ed schenk et al.) univ. arizona press [3] srama et al. (2004) space sci. rev. 114 (1-4), 465-518 [4] waite et al. (2004) space sci. rev. 114 (1-4), 113-231 [5] postberg et al. (2009) nature 459, 1098-1101 [6] hsu et al. (2015) nature 519, 207-210 [7] waite et al. (2017) science 356, 155-159 [8] magee and waite (2017) lpsc xlviii, 2974 [9] postberg et al. (2018a) in enceladus and the icy moons of saturn, (ed schenk et al.) univ. arizona press [10] bouquet et al. (2019) apj 873, 28 [11] klenner et al. (2019) rcms 33(22), 1751-1760 [12] postberg et al. (2018b) nature 558(7711), 564-568 [13] khawaja et al. (2019) mnras 489(4), 5231-5243 [14] barge et al. (2019) pnas 116(11), 4828-4833 | on the organic material emitted by enceladus |
hydrated silicates on mars have been studied extensively at the surface, however, many exposures are associated with basins/tectonic features: this hints at a record extending deep into the subsurface. as well, recent work suggests astonishingly low bulk crustal densities of 1,800-2,400 kg/m3 for ancient terrains [1], which is difficult to reconcile with grain densities of unaltered basalt combined with reasonable porosity values. here, i extend modeling work on primordial clays [2] to assess the spatial and temporal evolution of hydrated silicates (clays) formed in multiple environments in the first gyr after the crust formed. the entire crust of mars is modeled as a 3d grid, with parameterized impacts, volcanism, and aqueous alteration. primordial-type clays form during the first 10 ma due to a dense outgassed atmosphere [2]; after this, geothermal-type clays [3] form at depth from crustal heating, and surface weathering-type clays form during transient warming [4] linked to climate forcing from basins/volcanism. updated models show a strong dichotomy: the upper surface is dominated by weathering-type, noachian clays ( 80% of clay budget), while the subsurface is mostly pre-noachian geothermal- and primordial-type clays. assuming a 70% alteration extent for clay grid cells, 20-30% porosity (macro+micro), and 3 wt.% h2o in clays, the upper 5 km of crust in the models can sequester 190-260 m gel of water consistent with the intermediate d/h reservoir of [5], and would have a low density around 1,900-2,300 kg/m3 consistent with [1]. subsurface pods/layers of clays thus represent a significant water resource for isru, and these clays likely date back to pre-noachian times that were most suitable for abiogenesis in hot lakes/seas that may have condensed after the planet cooled. nwa 7034 shows that pre-noachian material is present in the upper few km of crust [6], but it contains few hydrated minerals. future deep drilling missions or missions to large basins should easily find ancient clays, and pervasive hydration in the entire crust should be considered when interpreting insight data. [1] goossens, s. et al. (2017), grl.[2] cannon, k. m. et al. (2017), nature.[3] ehlmann, b. l. et al. (2011), nature.[4] bishop, j. l. et al. (2018), nature astron.[5] usui, t. et al. (2017), lpsc. [6] cassata, w. s. et al. (2018), sci. adv. | ancient hydrated silicates in the martian deep: crustal density, water budget, and astrobiology |
as the world energy consumption increases, the necessity for clean energy proves vital and urgent as catastrophic effects of global climate change are imminent. the sun delivers more energy to earth in just over an hour than we have consumed over the course of last year, making solar technology a most promising candidate for a sustainable future. currently, state-of-the-art silicon-based solar technologies dominate the market owed to their maturity in processing knowledge, performance reliability, and lifetime. despite lower costs in recent years, the levelized cost of electricity of silicon-based solar pv technologies is still much greater than conventional fossil fuel sources, providing large incentive to find more cost-effective alternative solar pv technologies. solution-processed solar technologies are appealing as a low-cost alternative, among which, hybrid perovskites have recently risen as a high performance solution-processed pv technology achieving laboratory scale efficiencies >23%, which are rapidly approaching those of conventional si-based pv (∼26%). however, owed to the solution-processed nature of perovskites, there are many associated defects and grain boundary regions that can adversely affect performances and lifetimes. in this dissertation, i will focus on addressing defect and grain boundary engineering, taking advantage of the wet chemical environment of perovskite thin film processing to manipulate crystallization dynamics and modulate defect and grain boundary properties. in chapter 4, the guanidinium molecule was first discovered for use in hybrid perovskites. it was found that inclusion of guanidinium can provide extraordinary enhancements in photoluminescent properties of the thin film and enhanced open-circuit voltage of the devices. based on further experimental analyses and results, we believe that the guanidinium ion serves to suppress formation of defects via lattice strain relaxation and also may serve as a passivant at grain boundaries, giving rise to these impressive improvements. this work opened the door to future works throughout my ph.d. to control crystallization and defect properties. to further investigate the nature of controlling crystal growth and associated defect natures, a lewis acid-base adduct approach was developed and is discussed in chapter 5. the strength of interactios between the lewis acid perovskite precursors and lewis base additives were shown to greatly influence nucleation and growth dynamics. the lewis base urea was found to provide great enhancement in crystal growth, producing larger sized grains and enhanced photoluminescent properties, alongside a greater performance and stability of the device. lastly, in chapter 6, the intrinsic stability of the perovskite thin film is addressed by utilizing the compositional and dimensional tenability of hybrid perovskite materials, utilizing a hybrid 3- and 2-dimensionality of the perovskite structure to lead to even further enhanced performances and long-term lifetimes. it was found that the 2-d perovskite forms around grains (at grain boundaries) to facilitate the production of high quality 3-d grains and serve as passivating layers to grain boundaries. these works provide important future directions for hybrid perovskite pv research to realize commercial technologies with competitive efficiencies, long lifetimes, and low costs. conclusions and future outlooks of these works are discussed in chapter 7. | defect and grain boundary engineering for enhanced performances and lifetimes of hybrid perovskite solar cells |
the low temperatures and densities in the extended outer layers of asymptotic giant branch (agb) stars foster a rich chemistry, enabling the synthesis of a variety of both simple and complex molecules. however, due to the increasing flux of ultraviolet (uv) photons over the course of the star's late stage evolution, chemical models have predicted that the abundances of these species should be significantly depleted shortly after the onset of the planetary nebula (pn) stage. millimeter- and submillimeter-wave observations of a variety of pne of varying morphologies and kinematic ages have been conducted in order to explore the molecular composition of these objects and how the abundances of these molecules evolve over the course of the nebular lifespan. observations of hcn and hco+ in seventeen pne using the 12-m telescope and submillimeter telescope (smt) of the arizona radio observatory (aro) resulted in an overall detection rate of 76%, while subsequent measurements of hnc and cch in the 11 nebulae in which hcn had been identified yielded detection rates of 100% and 82%, respectively. these results strongly support the argument that polyatomic molecular material is a common constituent of pn ejecta. further, the abundances of these molecular species do not vary significantly with nebular age, in contrast to the predictions of chemical models, and they are consistently orders of 1 to 2 magnitudes greater than the abundances measured for diffuse clouds, a strong indication that these compounds are shielded from incident uv radiation in dense clumps of gas and dust which slowly disperse and seed the surrounding interstellar medium (ism) with molecular material. these conclusions are strengthened by the results of observations of hcn, hnc, cch, and c-c3h2 at eight positions across the helix nebula. other implications of these studies, particularly with regard to their impact on molecular synthesis, are discussed. molecular observations of the pn k4-47 using both aro facilities as well as the institut de radioastronomie millimetrique (iram) 30-m telescope are also presented. a plethora of molecules has been identified in this relatively unstudied source, including ch3cn, h2cnh, and ch3cch, all of which have been detected for the first time in a pn, as well as numerous 13c-containing species, including all singly- and doubly-13c-substituted variants of hc3n. particularly unusual are the incredibly low 12c/13c, 14n/15n, and 16o/17o ratios measured in this nebula (2.2 ± 0.8, 13.6 ± 6.5, and 21.4 ± 10.3, respectively), the lowest thus far measured in interstellar gas. the implications of these results on stellar nucleosynthesis and the sources of particular sic presolar grains are discussed. finally, modeling results of detections of phosphorus mononitride (pn) and phosphorus monoxide (po) made in several agb and supergiant stars are presented, along with the impact of these results on phosphorus chemistry. | the unexpected molecular complexity of planetary nebulae as revealed by millimeter-wave observations |
semi-transparent solar cells are the next step for photovoltaics into our daily life. over the last years, kesterite-type material has attracted a special attention to be used as an absorber in thin-film solar cells because of its low toxicity and earth abundant constituents. here, cu2zngese4 (czgse) thin films are grown by co-evaporation and subsequent annealing at a maximum temperature of 480 °c or 525 °c onto mo/v2o5/fto/glass stacks. the goal of this work is to investigate the influence of the annealing temperature on the composition, morphology, vibrational properties, and transmittance of czgse layers, the formation of secondary phases, and distribution of elements within the absorber layer as well as on the optoelectronic properties of the corresponding solar cell devices. raising the annealing temperature to 525 °c leads to a more uniform distribution of cu, zn, ge and se throughout the absorber layer, a reduction of the presence of the gese2 secondary phase, which is mainly detected at 480 °c, a larger grain size and the formation of a thicker mose2 layer at the czgse/back contact interface. the strategy of increasing the annealing temperature allows for improved j-v characteristics and higher spectral response resulting in an enhanced device performance of 5.3% compared to 4.2% when using 525 °c and 480 °c, respectively. both absorber layers present an optical band gap energy of 1.47 ev. furthermore, higher annealing temperature has beneficial effect to the czgse-based devices without losses in total transmitted light because of the higher diffuse transmittance. this work shows first promising semi-transparent czgse-based solar cells possibly open up new routes of applications. | the effect of annealing temperature on cu2zngese4 thin films and solar cells grown on transparent substrates |
since landing, the mars science laboratory curiosity rover climbed 300 meters in elevation from the floor of north gale crater up the lower northwest flank of aeolis mons ("mount sharp"). nearly 200 meters of this ascent was accomplished in the 1.5 years alone, as the rover was driven up-section through the sedimentary rocks of the informally designated "murray" formation. this unit comprises a large fraction of the lower strata of mt. sharp along the rover traverse. our exploration of the murray formation reveals a diverse suite of fine-grained facies. grain sizes range from finer grains than can be resolved by the mahli imager (particles <62.5 microns) up to medium sand; the finer fraction comprises the bulk of the stratigraphy. layering occurs at a range of scales; the majority is expressed as parallel laminae of mm-scale. some sandy stratigraphic intervals exhibit cross-stratification at ripple (cm) and dune (m and larger) scales; the inferred bedforms are consistent with a range of subaqueous and aeolian depositional settings. diagenetic features include locally variable occurrences of concretions and near-ubiquitous ca-sulfate veins; these attest to extended interaction of the sediment with aqueous fluids in the subsurface. as a whole, the sedimentary facies of the murray formation have been interpreted to record a predominately lacustrine paleo-environment, with likely subaerial aeolian and fluvial intervals. further exploration, including the campaign at the hematite-bearing vera rubin ridge, continues to reveal the complex and long-lived depositional history of the gale crater basin. | paleo-environmental setting of the murray formation of aeolis mons, gale crater, mars, as explored by the curiosity rover |
the purpose of this research is to create a high-resolution geologic map of henry crater on mars using interpretations made from hirise and ctx images. henry crater is located within the arabia terra region of mars at 0.9° north and 23.3° east. henry crater is roughly 170 km in diameter and is known for having a large mound located within the center of the crater. this large mound preserves a >2 km thick section of layered sedimentary rock thought to record evidence of early martian climate. phase 1 of the research primarily focused on obtaining an accurate account of the number of smaller craters present within henry crater. craters were identified in ctx images and their size and location documented. the ctx image resolution (6 meters per pixel) limited the size of the craters that could be documented. an estimated 2,612 craters are located within henry crater. these craters range from 70 m to 11.53 km in diameter. the mound located within the center of henry crater has a superimposed crater that is 8.54 km in diameter. phase 2 of this research was to map the different units within the crater and the mound. the mound layers vary in thickness and can range anywhere from meters to tens of meters in thickness. units were defined by visible changes in lithology, such as changes in grain size and layer thickness. the units that are found on the central mound were then correlated to the interior crater rim, suggesting large-scale erosion has taken place. this geologic map of henry crater can be used to understand the origin of the layered mound and the history of deposition in other similar craters in arabia terra. . | geologic mapping in henry crater, mars |
complex organic molecules (coms) play an essential role in the emergence of life. understanding how, when and where coms (including potentially prebiotic molecules) are formed is one of the most critical questions in the "cradle of life" science theme of astronomy. coms have been detected in prestellar cores, protostars, and protoplanetary disks. is it possible to preserve part of the molecular content during protostellar stage which can be incorporated into comets? by looking at the cometary compositions, observations of solar-type protostars can help to address this fundamental question. in this context, here we will present our observations towards the solar-type protostar iras 16293-2422 in the 3mm band of the iram 30m telescope along with current alma observations. we will describe how an integrative study using observations and chemo-dynamical simulations (using the state-of-the-art gas-grain-bulk (3 phase) chemical-kinetic model) can help us to understand the chemical composition both on the surface as well as on the coma of comet 67p/c-g observed by the cosac and rosina instruments onboard rosetta spacecraft. | possibility of protostellar inheritance of organics to jupiter-family comet 67p/c-g |
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