New thermodynamic data for CoTiO3, NiTiO3 and CoCO3 based on low-temperature calorimetric measurements

The low-temperature heat capacities of nickel titanate (NiTiO3), cobalt titanate (CoTiO3), and cobalt carbonate (CoCO3) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO3 and 26 K for NiTiO3. From our data we calculate standard molar entropies (298.15 K) for NiTiO3 of 90.9 ± 0.7 J mol-1 K-1 and for CoTiO3 of 94.4 ± 0.8 J mol-1 K-1. For CoCO3, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO3 of 88.9 ± 0.7 J mol-1 K-1

The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths

We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks

Thermal history of Northwest Africa 5073--A coarse-grained Stannern-trend eucrite containing cm-sized pyroxenes and large zircon grains

International audienceWe report on the bulk chemical composition, petrology, oxygen isotopic composition, trace element composition of silicates, and degree of self-irradiation damage on zircon grains of the eucrite Northwest Africa (NWA) 5073 to constrain its formation and postcrystallization thermal history, and to discuss their implications for the geologic history of its parent body. This unequilibrated and unbrecciated meteorite is a new member of the rare Stannern-trend eucrites. It is mainly composed of elongated, zoned pyroxene phenocrysts up to 1.2 cm, plagioclase laths up to 0.3 cm in length, and is rich in mesostasis. The latter contains zircon grains up to 30 μm in diameter, metal, sulfide, tridymite, and Ca-phosphates. Textural observations and silicate compositions, coupled with the occurrence of extraordinary Fe-rich olivine veins that are restricted to large pyroxene laths, indicate that NWA 5073 underwent a complex thermal history. This is also supported by the annealed state of zircon grains inferred from μ-Raman spectroscopic measurements along with U and Th data obtained by electron probe microanalyses

PHOSPHORUS ZONING FROM SECONDARY OLIVINE IN MANTLE XENOLITH FROM MIDDLE ATLAS MOUNTAINS (MOROCCO, AFRICA): IMPLICATIONS FOR CRYSTAL GROWTH KINETICS

Συλλέχθηκαν δείγματα μανδυακών ξενολίθων σε επαφή με βασάλτες από το μάαρ Tafraoute του Μαρόκκου. Διαπιστώθηκε η ύπαρξη φλεβών τήγματος που τέμνουν την πρωτογενή στρωμάτωση και σχιστότητα. Για τον πετρογραφικό και χημικό χαρακτηρισμό των φλεβών τήγματος, εφαρμόστηκαν οι τεχνικές της οπτικής μικροσκοπίας και ηλεκτρονικής μικροανάλυσης. Οι φλέβες αποτελούνται από ύελο και κρυστάλλους ολιβίνη, κλινοπυροξένου, πλαγιοκλάστου, σπινελίου και απατίτη. Ο ολιβίνης είναι πλούσιος στην περιφέρειά του σε φώσφορο ~0,3 %κ.β (εκπεφρασμένο ως P2O5). Correlations between Al and P, as well as experimentally determined partition coefficient for P, point towards non-equilibrium partitioning during rapid crystal growth at the end of crystallization. Βασιζόμενοι σε συντελεστές κατανομής φωσφόρου μεταξύ ολιβίνη και τήγματος, και τη σχέση του αργιλίου με το φώσφορο, 1924 καταλήγουμε σε κατανομή σε συνθήκες μη ισορροπίας κατά τη διάρκεια ταχύτατης ανάπτυξης στο τέλος της κρυστάλλωσηςMantle xenolith samples in contact with basalt flows were collected from the Tafraoute maar in Morocco. Discrete melt veins are present in one xenolith sample, crosscutting primary layering and foliation. We used both optical microscopy and electron microprobe analysis to characterize the glasses and minerals in the melt veins. The melt veins consist of glass and crystals of olivine, clinopyroxene, plagioclase, spinel and apatite. The olivine in the melt veins is quite distinct from the same mineral within the matrix due to its characteristic P-enriched rims (up to 0.3 wt.%). Correlations between Al and P, as well as experimentally determined partition coefficient for P, point towards non-equilibrium partitioning during rapid crystal growth at the end of crystallization

Ego-Splitting and the Transcendental Subject. Kant’s Original Insight and Husserl’s Reappraisal

In this paper, I contend that there are at least two essential traits that commonly define being an I: self-identity and self-consciousness. I argue that they bear quite an odd relation to each other in the sense that self-consciousness seems to jeopardize self-identity. My main concern is to elucidate this issue within the range of the transcendental philosophies of Immanuel Kant and Edmund Husserl. In the first section, I shall briefly consider Kant’s own rendition of the problem of the Egosplitting. My reading of the Kantian texts reveals that Kant himself was aware of this phenomenon but eventually deems it an unexplainable fact. The second part of the paper tackles the same problematic from the standpoint of Husserlian phenomenology. What Husserl’s extensive analyses on this topic bring to light is that the phenomenon of the Ego-splitting constitutes the bedrock not only of his thought but also of every philosophy that works within the framework of transcendental thinking

Santorini volcano as a potential Martian analogue: The Balos Cove Basalts

The interpretation of geologic processes on Mars from sparse meteorite, remote sensing and rover data is influenced by knowledge gained from well-characterized terrestrial analogues. This calls for detailed study of candidate terrestrial analogues and comparison of their observable features to those encountered on the surface of Mars. We evaluated the mineralogical, geochemical, and physical properties of the Balos cove basalts (BCB) from the island of Santorini and compared them to Martian meteorites, Mars rover surface measurements, and other verified Martian analogues obtained from the International Space Analogue Rockstore (ISAR). Twenty rock samples were collected from the Balos cove area based on their freshness, integrity, and basaltic appearance in the field. Optical microscopy of BCB revealed a pilotaxitic to trachytic texture, with olivine and clinopyroxenephenocrysts in a fine groundmass of olivine, clinopyroxene, plagioclase, magnetite, and devitrified glass. All major minerals show normal zoning, including calcic plagioclase (An_(78–85) at the core and An_(60–76) at the rim), augite (En_(36-48)Wo_(41-44)Fs_(11–21)), and olivine (Fo_(74–88)). The dominant bands in the infrared-attenuated total reflectance (IR-ATR) spectra from BCB can be assigned to olivine (~875 cm−1), calcic plagioclase (~1130 cm^(−1)), and augite (~970 cm^(−1)). The whole-rock chemical compositions and mineralogy of the BCB are similar to published analyses of typical olivine-phyric shergottites and basalts and basaltic materials analyzed in Gusev and Gale craters on Mars. BCB porosity is in the range of 7–15% and is similar to the porosities of the ISAR samples. Although no terrestrial rock is ever a perfect match to Martian compositions, the differences in mineralogy and geochemistry between BCB and some classes of Martian samples are relatively subtle and the basalts of Santorini are as close a match as other accepted Mars basalt analogues. The Santorini site offers excellent field logistics that, together with the petrology of the outcrop, makes it a valuable locality for testing and calibration deployments, field training, and other activities related to current and future Mars exploration

Coexistent State of Charge Density Wave and Spin Density Wave in One-Dimensional Quarter Filled Band Systems under Magnetic Fields

We theoretically study how the coexistent state of the charge density wave and the spin density wave in the one-dimensional quarter filled band is enhanced by magnetic fields. We found that when the correlation between electrons is strong the spin density wave state is suppressed under high magnetic fields, whereas the charge density wave state still remains. This will be observed in experiments such as the X-ray measurement.Comment: 7 pages, 15 figure

Mechanistic relationship among mutagenicity, skin sensitization, and skin carcinogenicity.

Twenty organic Salmonella mutagens, seven of which (including benzo[a]pyrene) are established skin carcinogens, and one of which (2-chloroethanol) is a well-defined noncarcinogen to skin, have been evaluated for skin-sensitizing activity using the local lymph node assay. The relative mutagenicity of the agents to Salmonella was also established. Fourteen of the chemicals were positive in the local lymph node assay, including the seven skin carcinogens. 2-Chloroethanol was inactive as a sensitizing agent. We suggest that a variety of factors contributes to the lack of sensitizing activity of the remaining six bacterial mutagens: extremes of intrinsic chemical reactivity, high water solubility reducing dermal translocation, and inappropriate dermal metabolism. Two reference skin-sensitizing agents (an oxazolinone and fluorescein isothiocyanate) were established as in vitro clastogens after their recognition as nonmutagens to Salmonella. These data imply that mutagenicity, rather than simply activity in the Salmonella assay, is a primary stimulus for electrophilic sensitization and carcinogenic initiation in the skin. We conclude that genotoxicity data for an agent can provide indications of the agent's potential to induce skin sensitization and that genotoxins which are skin-sensitizing agents have an enhanced potential to initiate skin carcinogenesis. We suggest that common, albeit individually distinct, structure-activity relationships underpin genotoxicity, skin sensitization, and the initiation of skin carcinogenesis. These relationships should simplify the hazard evaluation of chemicals and contribute to a reduction in animal usage. Several predictions of skin carcinogenicity are made based on the data presented

The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths

We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks

First-principles study of the inversion thermodynamics and electronic structure of FeM2X4 (thio)spinels (M = Cr, Mn, Co, Ni; X = O, S)

FeM2X4 spinels, where M is a transition metal and X is oxygen or sulfur, are candidate materials for spin filters, one of the key devices in spintronics. We present here a computational study of the inversion thermodynamics and the electronic structure of these (thio)spinels for M = Cr, Mn, Co, Ni, using calculations based on the density functional theory with on-site Hubbard corrections (DFT+U). The analysis of the configurational free energies shows that different behaviour is expected for the equilibrium cation distributions in these structures: FeCr2X4 and FeMn2S4 are fully normal, FeNi2X4 and FeCo2S4 are intermediate, and FeCo2O4 and FeMn2O4 are fully inverted. We have analyzed the role played by the size of the ions and by the crystal field stabilization effects in determining the equilibrium inversion degree. We also discuss how the electronic and magnetic structure of these spinels is modified by the degree of inversion, assuming that this could be varied from the equilibrium value. We have obtained electronic densities of states for the completely normal and completely inverse cation distribution of each compound. FeCr2X4, FeMn2X4, FeCo2O4 and FeNi2O4 are half-metals in the ferrimagnetic state when Fe is in tetrahedral positions. When M is filling the tetrahedral positions, the Cr-containing compounds and FeMn2O4 are half-metallic systems, while the Co and Ni spinels are insulators. The Co and Ni sulfide counterparts are metallic for any inversion degree together with the inverse FeMn2S4. Our calculations suggest that the spin filtering properties of the FeM2X4 (thio)spinels could be modified via the control of the cation distribution through variations in the synthesis conditions