Electronic structure and magnetism of Fe3−x_{3-x}Vx_{x}X (X = Si, Ga and Al) alloys by the KKR-CPA method

We present first principles charge- and spin-selfconsistent electronic structure computations on the Heusler-type disordered alloys Fe$_{3-x}$V$_{x}$X for three different metalloids X=(Si, Ga and Al). In these calculations we use the methodology based on the Korringa-Kohn- Rostoker formalism and the coherent-potential approximation (KKR-CPA), generalized to treat disorder in multi-component complex alloys.Comment: RevTeX, 17 pages, 15 figures, to appear in Phys. Rev. B on Nov. 15 199

Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes

We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re

Preliminary results of fluid inclusions investigation in euhedral quartz crystals from overlying sediments of the Wapno Dome (C1 borehole)

W obrębie utworów piaszczystych nadkładu znajdującego się nad wysadem i czapą gipsową Wapna (woj. wielkopolskie) występują automorficzne kryształy kwarcu (AKK). Dokładnej analizie poddano AKK wyseparowane z piasków kwarcowych średnioziarnistych (reprezentujących utwory miocenu i najprawdopodobniej oligocenu). Materiał ten pozyskano z otworu C1 zlokoalizowanego w NW części czapy. W tym miejscu jest ona rozcięta głęboką na około 120 m rynną wypełnioną osadami kenozoiku. AKK wyróżniają się od ziaren piasku kwarcowego automorficznym kształtem (mają prawidłową postać odpowiadającą odmianie niskotemperaturowej) i wysokim, diamentowym połyskiem. Osiągają od 0,1 do 2 mm długości; przeciętnie ok. 0,5 mm. Jedynie w niektórych AKK zaobserwowano inkluzje fluidalne (ciekło-gazowe). Występują one w formie: 1/ pojedynczych osobników, bezładnie rozmieszczonych, 2/ zespołów gęsto upakowanych przebiegających w postaci pasm lub obszarów o nieregularnym zasięgu. Rozmiary inkluzji sięgają od kilku do około 30 μm. Pomiary mikrotermometryczne inkluzji wykazały wąski zakres ich temperatur homogenizacji w przedziale od 86,4 do 126,5°C, a w jednym przypadku 158,8°C. W AKK oprócz inkluzji fluidalnych, stwierdzono także w mniejszej ilości inkluzje wypełnione substancją organiczną.Within sandy sediments overlaying the Wapno Salt Dome and its cap-rock (Middle Poland) occur euhedral quartz crystals (signed AKK). Those AKK subjected to a thorough analysis were separated from middle-grained quartz sands (of Miocene and probable Oligocene age). This material was obtained from C1 bore-hole which is located at NW part of cap-rock. In this place the cap-rock is cut by deep (about 120 m) trough filled with Cenozoic sediments. The AKK differ from grains of sand by euhedral shape (they display normal shape corresponding to the low-temperature variety) and very intensive diamond shine. Their length vary from 0.1 to 2 mm with average about 0.5 mm. Fluid (liquid-gas) inclusions occur only in some AKK. They are in form: 1/ randomly distributed single fluid inclusions, 2/ belts or irregular areas of densely packed inclusions. The size of inclusions vary from a few to about 30 μm. The microthermometric measurements show homogenization temperatures in the range of 86.4 – 126.5°C and in one case 158.8°C. In addition to the fluid inclusions in a smaller amount in the AKK were found inclusions filled by organic matter

Phase transitions in the borate minerals from the Kłodawa Salt Dome (Central Poland) as the indicators of the temperature processes in salt diapirs

The diapiric structures of the Polish Lowlands are tectonically deeply seated down to the autochthonous Zechstein strata at a depth of ca. 6 km. In the process of deep burial and halokinetic diapirism, the salt rocks were subjected to diagenetic and metamorphic transformations, with the temperature being an essential factor. Considering the thermal gradient, a temperature of up to ca. 200°C can be achieved in the salt dome within a depth range from several hundred metres to 6 km, which may lead to transformations of the majority of salt minerals. Phase transitions of two borate minerals – boracite and congolite from the Kłodawa salt dome – provide evidence for higher temperatures in the salt dome rocks. The authigenic euhedral crystals of those borate minerals display their external habitus in ambient temperature in the form of regular symmetry (F43c – pseudo-regular polyhedrons), whereas their internal structure is lower: orthorhombic (Pca21) for boracite and rhombohedral (R3C) for congolite. The heating and cooling of boracite and congolite crystals show reversible phase transition. At a temperature of ca. 270°C, boracite crystals change their symmetry: orthorhombic ↔ cubic. In the case of congolite three reversible phase transitions within a temperature range of 50–339°C can be observed: rhombohedral ↔ monoclinic ↔ orthorhombic ↔ cubic symmetry. Those phase transitions, confirmed experimentally in our study, clearly document at least local occurrences of temperatures exceeding 339°C in the Kłodawa salt dome

Evidence of high-temperature rock salt transformations in areas of occurrence of borate minerals (Zechstein, Kłodawa salt dome, Poland)

Occurrences of borate minerals in the Zechstein salt-bearing deposits of the Kłodawa salt dome (central Poland), and the manner of their development, suggest that the minerals were formed at high temperatures, that considerably exceed the temperature estimated from the thermal gradient (~180°C). Research on rock salt and potassium-magnesium salts containing congolite and boracite, respectively, are consistent with high-temperature processes of transformations affecting the salt rocks in certain sections of the salt dome. The chemical composition of, and daughter minerals occurring in, primary fluid inclusions in halite, originating from the congolite zone, indicated a very high proportion of potassium and magnesium in the brines from which the halite crystallised. The thermal transformations observed in inclusions indicate a halite crystallisation temperature exceeding 420°C. Anhydrite crystals, co-occurring with borate minerals, represent unique features as to the distribution and composition of solid and fluid inclusions. These features indicate crystallisation or recrystallisation in conditions that differed considerably from those typical of the salt dome, with the involvement of solutions of changing chemical compositions. The crystals contain multiple solid inclusions of transparent and non-transparent minerals, among which we have focused on carnallite. The relationships of carnallite with liquid and gaseous phases indicate, as in the congolite zone, migration of very highly concentrated brines with respect to potassium and magnesium, or even transport of carnallite in the form of melt (liquid). Measurements of fluid inclusion homogenization temperatures, within the range from 197.8 to 473.8°C, supported a high-temperature origin for these minerals in hydrothermal conditions

Theoretical Study of Substitution of Si for Ge in Mn5\text{}_{5}Ge3\text{}_{3}

The substitution of silicon for germanium in Mn$\text{}_{5}$Ge$\text{}_{3}$ leads to a decrease in the magnetization for x < 0.7 and then to phase transition toward a non-collinear antiferromagnetic order for Mn$\text{}_{5}$Si$\text{}_{3}$. The magnetic properties of Mn$\text{}_{5}$Ge$\text{}_{3}$ and Mn$\text{}_{5}$(Ge$\text{}_{0.5}$Si$\text{}_{0.5}$)$\text{}_{3}$ are analyzed by means of band structure calculations

The Electronic Structure of the RMn2\text{}_{2}Ge2\text{}_{2} (R = Ca, Y, La, Ba) Antiferromagnets

The electronic structure of the tetragonal RMn$\text{}_{2}$Ge$\text{}_{2}$ (R = Ca, Y, La, Ba) antiferromagnets is presented using the self-consistent Korringa-Kohn-Rostoker method. According to the neutron refinements, two types of collinear antiferromagnetic structure are taken into account: AF$\text{}_{1}$ for YMn$\text{}_{2}$Ge$\text{}_{2}$ and AF$\text{}_{2}$ for the other compounds. The calculated magnetic moments on Mn: 2.17μ$\text{}_{B}$ (YMn$\text{}_{2}$Ge$\text{}_{2}$), 2.84 μ$\text{}_{B}$ (CaMn$\text{}_{2}$Ge$\text{}_{2}$), 2.95 μ$\text{}_{B}$ (LaMn$\text{}_{2}$Ge$\text{}_{2}$), and 3.47 μ$\text{}_{B}$ (BaMn$\text{}_{2}$Ge$\text{}_{2}$) remain in good agreement with the neutron data (in μ$\text{}_{B}$) 2.20, 2.67, 3.05, and 3.66, respectively. As seen on antiferromagnetic density of states, all systems are metallic, however BaMn$\text{}_{2}$Ge$\text{}_{2}$ is found near semimetallic limit. The total energy Korringa-Kohn-Rostoker computations on CaMn$\text{}_{2}$Ge$\text{}_{2}$, performed in both antiferromagnetic phases, result in preferring of the AF $\text{}_{2}$ structure.za

Salinity of Quaternary sediments and halophytes at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

Interdisciplinary geophysical, geochemical and botanical studies were performed to recognize the problem of salinity of Quaternary sediments in the place, where woolly rhinoceroses were discovered at the beginning of the 20th century. Geoelectric methods (high resolution geoelectric research with electromagnetic conductivity meter) enabled construction of maps of the distribution of conductivity of near-surface sediments. Variation of conductivity with depth was recognized with penetrometer-based geoelectric measurements. Measured conductivity mainly depends on the level of mineralization (salinity) of underground water filling the pores and voids of poorly consolidated Quaternary sediments and partly underlying Miocene strata. Several samples were taken from geological boreholes. The analysis of these cores enabled estimation of salt (chloride ion) content in the solid phase of sediments. This content varies from place to place and with depth in an unpredictable way. The highest values reached 8.5 wt%. Generally, on the basis of a qualitative comparison, the salinity data gained from sampled cores correlate with distribution of apparent conductivity obtained with geoelectric methods. Nevertheless, in some places there is a discrepancy between geophysical and geochemical data, especially for penetrometer versus borehole data. It may be partly explained by an unavoidable difference in location of the geological borehole and penetrometer site (technically this cannot be the same place). During botanical field studies a group of vascular plants growing on saline soils (halophytes) was found. Halophytes indicate a higher salt concentration in the soil. Their aggregations are extremely rare in the Carpathian region. The pattern of halophytes distribution reflected the presence of saline water sources, and their flows and soils affected by them. Generally, the distribution of halophytes showed a good correlation with the distribution of high-conductivity anomalies determined with the surface geoelectric survey

Ro-vibrational excitation of SiS by He

International audienc