The Effect of Molecular Isomerism on the Induced Circular Dichroism of Cadmium Sulfide Quantum Dots

Post-synthetic phase transfer ligand exchange has been established as a simple, reliable, and versatile method for the synthesis of chiral, optically active colloidal nanocrystals displaying circular dichroism (CD) and circularly...

Rippite, K2(Nb,Ti)2(Si4O12)O(O,F), a New K-Nb-Cyclosilicate from Chuktukon Carbonatite Massif, Chadobets Upland, Krasnoyarsk Territory, Russia

Rippite K2(Nb,Ti)2(Si4O12)(O,F)2, a new K-Nb-cyclosilicate, has been discovered in calciocarbonatites from the Chuktukon massif (Chadobets upland, SW Siberian Platform, Krasnoyarsk Territory, Russia). It was found in a primary mineral assemblage, which also includes calcite, fluorcalciopyrochlore, tainiolite, fluorapatite, fluorite, Nb-rich rutile, olekminskite, K-feldspar, Fe-Mn–dolomite and quartz. Goethite, francolite (Sr-rich carbonate–fluorapatite) and psilomelane (romanèchite ± hollandite) aggregates as well as barite, monazite-(Ce), parisite-(Ce), synchysite-(Ce) and Sr-Ba-Pb-rich keno-/hydropyrochlore are related to a stage of metasomatic (hydrothermal) alteration of carbonatites. The calcite–dolomite coexistence assumes crystallization temperature near 837 °C for the primary carbonatite paragenesis. Rippite is tetragonal: P4bm, a = 8.73885(16), c = 8.1277(2) Å, V = 620.69(2) Å3, Z = 2. It is closely identical in the structure and cell parameters to synthetic K2Nb2(Si4O12)O2 (or KNbSi2O7). Similar to synthetic phase, the mineral has nonlinear properties. Some optical and physical properties for rippite are: colorless; Mohs’ hardness—4–5; cleavage—(001) very perfect, (100) perfect to distinct; density (meas.)—3.17(2) g/cm3; density (calc.)—3.198 g/cm3; optically uniaxial (+); ω = 1.737-1.739; ε = 1.747 (589 nm). The empirical formula of the holotype rippite (mean of 120 analyses) is K2(Nb1.90Ti0.09Zr0.01)[Si4O12](O1.78OH0.12F0.10). Majority of rippite prismatic crystals are weakly zoned and show Ti-poor composition K2(Nb1.93Ti0.05Zr0.02)[Si4O12](O1.93F0.07). Raman and IR spectroscopy, and SIMS data indicate very low H2O content (0.09–0.23 wt %). Some grains may contain an outermost zone, which is enriched in Ti (+Zr) and F, up to K2(Nb1.67Ti0.32Zr0.01)[Si4O12](O1.67F0.33). It strongly suggests the incorporation of (Ti,Zr) and F in the structure of rippite via the isomorphism Nb5+ + O2− → (Ti,Zr)4+ + F1−. The content of a hypothetical end-member K2Ti2[Si4O12]F2 may be up to 17 mol. %. Rippite represents a new structural type among [Si4O12]-cyclosilicates because of specific type of connection of the octahedral chains and [Si4O12]8− rings. In structural and chemical aspects it seems to be in close with the labuntsovite-supergroup minerals, namely with vuoriyarvite-(K), K2(Nb,Ti)2(Si4O12)(O,OH)2∙4H2O.

2.5D retrieval of atmospheric properties from exoplanet phase curves: application to WASP-43b observations

ABSTRACT We present a novel retrieval technique that attempts to model phase curve observations of exoplanets more realistically and reliably, which we call the 2.5-dimensional (2.5D) approach. In our 2.5D approach we retrieve the vertical temperature profile and mean gaseous abundance of a planet at all longitudes and latitudes simultaneously, assuming that the temperature or composition, x, at a particular longitude and latitude (Λ, Φ) is given by $x(\Lambda ,\Phi) = \bar{x} + (x(\Lambda ,0) - \bar{x})\cos ^n\Phi$, where $\bar{x}$ is the mean of the morning and evening terminator values of x(Λ, 0), and n is an assumed coefficient. We compare our new 2.5D scheme with the more traditional 1D approach, which assumes the same temperature profile and gaseous abundances at all points on the visible disc of a planet for each individual phase observation, using a set of synthetic phase curves generated from a GCM-based simulation. We find that our 2.5D model fits these data more realistically than the 1D approach, confining the hotter regions of the planet more closely to the dayside. We then apply both models to WASP-43b phase curve observations of HST/WFC3 and Spitzer/IRAC. We find that the dayside of WASP-43b is apparently much hotter than the nightside and show that this could be explained by the presence of a thick cloud on the nightside with a cloud top at pressure <0.2 bar. We further show that while the mole fraction of water vapour is reasonably well constrained to (1–10) × 10−4, the abundance of CO is very difficult to constrain with these data since it is degenerate with temperature and prone to possible systematic radiometric differences between the HST/WFC3 and Spitzer/IRAC observations. Hence, it is difficult to reliably constrain C/O.

The validity of a person’s authentication using an electrocardiogram with a limited number of channels

The concept of mobile and home telemedicine for screening and early diagnostics of cardiovascular dis-eases is being expanded due to the emergence of mobile diagnostic devices and smartphones. In the course of such telemedicine consultations, the doctor must be sure that the digital electrocardiogram (ECG) be-longs to the patient who was registered. Both multi-channel and single-channel ECG-recording devices are available on the telemedicine consulting market now. Single-channel electrocardiographs are more eco-nomic feasible for home use. Previously, the authors have developed and experimentally tested the algo-rithms for patient authentication by his/her multi-channel ECG. These algorithms are based on the analysis of the shape of QRS complex in three-dimensional phase space of coordinates. Therefore, it is reasonable to adapt these algorithms to single-channel ECG. In case of multi-channel ECG, we can construct a three-dimensional phase space of coordinates by obtaining all the necessary data from the ECG leads. In a case of the single-channel ECG it is necessary to create two additional signals artificially and then it will be possible to form a synthetic phase space. In general, the question of the validity of biometric person au-thentication algorithms by his/her ECG with a limited number of channels is discussed in this paper. Be-sides the algorithms for solving the problem of authentication, the comparison of sensitivity and specificity indicators, calculated on the results of experiments for multi-channel and single-channel ECG, are also given in this paper. The results of experiments with multi-channel and single-channel ECG of a larger number of patients are given in comparison to the previous experiments. The results of the experiments for the case of recording ECG signals by different devices are given as well.

Alkali sulfates with aphthitalite-like structures from fumaroles of the Tolbachik Volcano, Kamchatka, Russia. I. MetathÉnardite, a natural high-temperature modification of Na2SO4

A new mineral, metathénardite, ideally Na2SO4, the high-temperature hexagonal dimorph of thénardite, a natural analogue of the synthetic phase Na2SO4(I), was found in the sublimates of active fumaroles at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure eruption, Tolbachik volcano, Kamchatka, Russia. The holotype originates from the Glavnaya Tenoritovaya fumarole in which metathénardite is associated with hematite, tenorite, fluorophlogopite, sanidine, anhydrite, krasheninnikovite, vanthoffite, glauberite, johillerite, and lammerite. The cotypes 1 and 2 are from the Arsenarnaya (with hematite, tenorite, fluorophlogopite, sanidine, euchlorine, wulffite, anhydrite, fluoborite, johillerite, nickenichite, calciojohillerite, badalovite, tilasite, cassiterite, and pseudobrookite) and the Yadovitaya (with tenorite, euchlorine, fedotovite, dolerophanite, langbeinite, krasheninnikovite, anhydrite, and hematite) fumaroles, respectively. All specimens with metathénardite were collected from areas with temperatures of 350–400 °C. Metathénardite forms hexagonal tabular, lamellar, or dipyramidal crystals (forms: {001}, {100}, {102}, and {201}) up to 3 mm combined in crusts up to several hundred cm2 in area. The mineral is transparent to semitransparent, colorless, white, light-blue, greenish, yellowish, grayish or brownish, with vitreous luster. Dmeas. = 2.72(1), Dcalc. = 2.717 g/cm3. Metathénardite is optically uniaxial (–), ω = 1.489(2), ε = 1.486(2). The empirical formulae are (Na1.92K0.05Ca0.02Zn0.01)[S0.99O4] (holotype), (Na1.54K0.22Ca0.09Cu0.01Mg0.01)[S1.00O4] (cotype 1), and Na1.65K0.11Ca0.05Cu0.04Mg0.01)[S1.01O4] (cotype 2). Admixed K and bivalent cations probably stabilize the hexagonal aphthitalite-like structure of metathénardite at room temperature. The crystal structure was solved using single crystals of all three samples, R1 = 0.0852, 0.0452, and 0.0449 for holotype and cotypes 1 and 2, respectively. The space group is P63/mmc, and the unit-cell parameters of the holotype are a = 5.3467(9), c = 7.0876(16) Å, V = 157.47(6) Å3, and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 4.667(27)(100), 3.904(89)(101), 3.565(33)(002), 2.824(94)(102), 2.686(100)(110), and 1.939(35)(202). Metathénardite and thénardite clearly differ from one another in X-ray diffraction data and infrared and Raman spectra.

Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite

Edscottite (IMA 2018-086a), Fe5C2, is a new iron carbide mineral that occurs with low-Ni iron (kamacite), taenite, nickelphosphide (Ni-dominant schreibersite), and minor cohenite in the Wedder-burn iron meteorite, a Ni-rich member of the group IAB complex. The mean chemical composition of edscottite determined by electron probe microanalysis, is (wt%) Fe 87.01, Ni 4.37, Co 0.82, C 7.90, total 100.10, yielding an empirical formula of (Fe4.73Ni0.23Co0.04)C2.00. The end-member formula is Fe5C2. Electron backscatter diffraction shows that edscottite has the C2/c Pd5B2-type structure of the synthetic phase called Hägg-carbide, χ-Fe5C2, which has a = 11.57 Å, b = 4.57 Å, c = 5.06 Å, β = 97.7 °, V = 265.1 Å3, and Z = 4. The calculated density using the measured composition is 7.62 g/cm3. Like the other two carbides found in iron meteorites, cohenite (Fe3C) and haxonite (Fe23C6), edscottite forms in kamacite, but unlike these two carbides, it forms laths, possibly due to very rapid growth after supersaturation of carbon. Haxonite (which typically forms in carbide-bearing, Ni-rich members of the IAB complex) has not been observed in Wedderburn. Formation of edscottite rather than haxonite may have resulted from a lower C concentration in Wedderburn and hence a lower growth temperature. The new mineral is named in honor of Edward (Ed) R.D. Scott, a pioneering cosmochemist at the University of Hawai‘i at Manoa, for his seminal contributions to research on meteorites.