SE Structures Research Articles

Geology, Geochemistry and Re–Os systematics of manganese deposits from the Santa Rosalía Basin and adjacent areas in Baja California Sur, México

The manganese ores in the Santa Rosalia region, western Mexico, are mainly stratiform horizons or mantos, constrained to the initial stages of sedimentary cycles of the Miocene Boleo Formation. The manganese mineralization is generally restricted to isolated paleo-basins and related to NW–SE faults formed during the early stages of the opening of the Gulf of California. Jasper, Fe, and Mn oxides associated to the NW–SE structures may represent feeder zones for the mineralized system. The manganese oxide minerals include pyrolusite, cryptomelane, todorokite, hollandite, jacobsite, and pyrochroite. Trace elements in the manganese ores indicate a hydrothermal origin for the deposits of the Santa Rosalia area. Rare earth elements (REE) patterns obtained for manganese minerals from the Lucifer and El Gavilan deposits also support a hydrothermal origin, whereas the middle REE enrichment observed in samples from the Boleo district indicates mixing between hydrothermal and hydrogenous sources. Osmium and rhenium concentrations of the manganese minerals range between 33–173 ppt and 0.14–89 ppb, respectively. The initial 187Os/188Os ratios in the manganese oxides from Lucifer and the Boleo district range between 0.43 to 0.51 and 0.70 to 0.74, respectively. These ratios are different from seawater at 7 Ma (0.84–0.89), which suggests important contributions of osmium from underlying rocks such as the Miocene volcanic rocks and the Cretaceous quartz–monzonite basement. Field evidence, manganese oxide mineralogy coupled with major and trace element geochemistry and Re–Os systematics support a hydrothermal origin for the manganese deposits from the Santa Rosalia region. The ore deposition style indicates an exhalative-intraformational environment restricted to isolated basins in a diagenetic stage related to the initial evolution of the Gulf of California.

The European Company under French Law: Main Features

The Regulation and the Directive on the Statute for a European company introduce a new corporate structure under French law justifying the inclusion of new chapters in both the Commercial Code and Labour Code of France. In order to assess the merits of this new alternative, the benefits offered by the SE structure and regime need to be examined in comparison with existing corporate structures under French law, in particular the SA, which is the structure that the SE most resembles. This article reviews the main features of the SE as a legal entity under French law facilitating the formation of European groups. It also looks at reasons for choosing the French SE regime from the point of view of corporate and employment law. The SE is clearly most valuable in cases where the scope of business is European, in which context it can facilitate transnational mergers and joint operations, make the transfer of registered offices possible and serve as a model for streamlining the corporate governance of European groups. If, on the whole, the French legislator has proved conservative with regard to the SE, even in implementing the Directive on labour side, he has nevertheless granted the ‘French’ SE plenty of freedom in the statutes regarding the definition of relationships among shareholders.

Imaging links between lithospheric architecture and surface geology in the Proterozoic Curnamona Province, Australia

Potential field (magnetic and gravity) analysis is an effective method to investigate crustal‐scale architecture and provides a means of linking continental‐scale geophysical data sets (e.g., seismic tomography) with detailed geological and geophysical studies. Here, we image deep‐crustal structure of the Proterozoic Curnamona Province, Australia, in aeromagnetic and gravity data sets and establish spatial and temporal links between deep structures and near surface geological features by superimposing first vertical derivative responses on upward continued images. Upward continued gravity and aeromagnetic data show NW–SE, NE–SW, E–W, and N–S oriented long‐wavelength discontinuities and boundaries to anomalies, which we interpret as deep‐seated structures. These structures predate the oldest known tectonic events recorded in outcropping rocks and appear to have been long‐lived, thereby influencing the tectonic history of the province. For example, outcropping Cambrian shear zones, evident in vertical derivative data, appear to have nucleated off displaced segments of a once continuous deep‐seated structure of Proterozoic origin that has been imaged in upward continued data. Long‐wavelength gradients defining E–W and NW–SE structures in upward continued aeromagnetic data intersect beneath the dominantly felsic Benagerie igneous province in the central province and are coincident with a large negative gravity anomaly interpreted as felsic igneous rocks that are coeval to the volcanic pile. Tectonic implications of this study include (1) deep‐seated structures in the Curnamona Province have protracted histories; (2) these structures appear to have controlled the location and distribution of younger shear zones, igneous activity, and possibly basin subsidence in the upper crust; (3) geophysical lineaments are likely to have evolved and propagated during multiple tectonic cycles and hence record the protracted evolution of a geological province.

Steric and electronic properties in bicyclic phosphines. Crystal and molecular structures of Se = Phoban-Q (Q = C 2, C 3Ph, Cy and Ph)

Reacting a series of the bicylic Phoban-Q (9-Q-9-phosphabicyclo[3.3.1]nonane and 9-Q-9-phosphabicyclo[4.2.1]nonane) derivatives (Q = alkyl, cyclo alkyl, aryl) with KSeCN results in the formation of the corresponding phosphine selenides. The first order phosphorus–selenium coupling constants, 1 J P–Se, ranges from 682 to 689 Hz for the [3.3.1] isomers and from 703 to 717 Hz for the [4.2.1] isomers indicating the former to be significantly more electron rich. The crystal structures of Se = Phoban[3.3.1]-Q (Q = CH 2CH 3, C 3H 6Ph, Cy, and Ph) and Se = Phoban[4.2.1]-Q (Q = Cy and Ph) are reported and reveal P Se bond distances ranging from 2.1090(9) to 2.1245(7) Å. For Q = Cy and Ph the two isomers ([3.3.1] and [4.2.1]) co-crystallise in the same crystal enabling the determination of the molecular structures for both from the same data collection. The cone angles for all ligand derivatives were determined according to the Tolman model but by using the actual P–Se bond distances and were found to be virtually identical ranging from 165° to 175°. Changes in the Q substituent have a minor effect on the overall steric and electronic properties of the Phoban family of ligands and can be used to manipulate physical properties without changing the chemical properties significantly.

Optical characterization of intersubband transitions in ZnxCd1−xSe∕Znx′Cdy′Mg1−x′−y′Se multiple quantum well structures by contactless electroreflectance

Contactless electroreflectance was measured at room temperature to characterize a wide range of the possible optical transitions in ZnxCd1−xSe∕Znx′Cdy′Mg1−x′−y′Se multi-quantum-well structures grown by molecular beam epitaxy. Based on these measurements, the authors predict and then verify the anticipated intersubband transition energies. They investigate a representative Zn0.5Cd0.5Se∕Zn0.20Cd0.19Mg0.61Se structure, for which the E1-E2 transition energy is predicted to be 178meV (6.97μm). Intersubband absorption using Fourier transform infrared spectroscopy exhibits a peak at 180meV (6.89μm), in excellent agreement with the contactless electroreflectance measurements.

Hydrogen storage capability of Se@C 120 system

A single-walled, capped and selenium doped, carbon nanotube, Se@C 120, was doped endohedrally with hydrogen molecules to obtain a series of ( n H 2 + Se ) @ C 120 , ( n: 0–11) systems. Then, they were subjected to quantum chemical treatment using PM3 method at the level of RHF approach. Calculations indicated that these systems were stable but endothermic in nature. In ( 10 H 2 + Se @ C 120 ) and ( 11 H 2 + Se @ C 120 ) systems, the hydrogen molecule nearest to the Se atom tends to dissociate to form a quasi- H 2 Se structure.

SRTM-based morphotectonic analysis of the Poços de Caldas Alkaline Massif, southeastern Brazil

An evaluation of SRTM 03″ data applicability in geomorphology and morphotectonic analysis is proposed, considering the morphometric parameters slope, aspect, surface roughness and isobase surface. The study area, in southeastern Brazil, comprises the Poços de Caldas Alkaline Massif, a 33 km-diameter Late Cretaceous collapsed volcanic caldera. Morphometric indices evaluated showed the correlation of landscape within the massif with NE–SW and NW–SE structures, as well as landforms related with recent tectonic influence. DEM-derived drainage presented satisfactory results when compared to a 1:50,000 topographic map. SRTM 03″ proved to be a good resource for geomorphological analysis, up to the semi-detail scale.

Direct energy transfer from photocarriers to Mn-ion system in II-VI diluted-magnetic-semiconductor quantum wells

The dynamical response of magnetic ion system to pulsed laser excitation is studied in $(\mathrm{Zn},\mathrm{Mn})\mathrm{Se}∕(\mathrm{Zn},\mathrm{Be})\mathrm{Se}$ and $(\mathrm{Cd},\mathrm{Mn})\mathrm{Te}∕(\mathrm{Cd},\mathrm{Mg})\mathrm{Te}$ quantum well structures. Contributions of a direct heating of the Mn system by photocarriers and an indirect heating via nonequilibrium phonons are distinguished. Their relative efficiency is measured at different excitation densities and over a wide range of Mn concentrations from 0.4 to 11%. For all studied regimes the direct energy transfer from carriers dominates in (Zn,Mn)Se structures. In (Cd,Mn)Te structures a regime where the direct heating is still prominent but weaker than the phonon contribution is found.

Tertiary phosphine abstraction from a platinum(II) coordination complex with SeCN −: Crystal and molecular structures of Se [dbnd]PTA and [Se [dbnd]PTA-Me]I · CH 3OH

Reacting [PtCl(PTA) 3]Cl(PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1 3,7]decane) with KSeCN in aqueous or MeOH medium results in the abstraction of the PTA ligands to yield Se PTA. The reaction also proceeds quantitatively by direct reaction of PTA and KSeCN in water or methanol. The methylated PTA ligand, [PTA-Me]I (1-methyl-1-azonia-3,5-diaza-7-phosphatricyclo[3.3.1.1 3,7]decane iodide), reacts accordingly with KSeCN, albeit significantly slower. The crystal structure of Se PTA, 1, and [Se PTA-Me]I · CH 3OH, 2, revealed P Se bond distances of 2.0991(19) and 2.100(2) Å, respectively. The first order phosphorous selenium coupling constants, 1 J P–Se (D 2O), of 722 and 788 Hz for Se PTA and [Se PTA-Me]I, respectively, indicates the latter is significantly less electron rich.

Pentamethylcyclopentadienylselenium derivatives VI: Synthesis and characterisation of ferrocenyl(pentamethylcyclopentadienyl)selenium

The novel mono(cyclopentadienyl)selenium derivatives, Se(C 5Me 4R)Fc (Fc = ferrocenyl, [Fe(η 5-C 5H 5)(η 5-C 5H 4)]; R = H or Me) have been prepared by treatment of diferrocenyl diselenide with LiC 5Me 4R, and characterised by NMR spectroscopy and mass spectrometry. The structure of Se(C 5Me 5)Fc has been confirmed by X-ray crystallography, and its redox properties have been examined by cyclic voltammetry. It reacts with [W(CO) 5(THF)] to form [W 2(μ-SeFc) 2(CO) 8] via C–Se bond cleavage.

Confinement of Selenium into Carbon Nanotubes

Filling of carbon nanotubes with metals or semi‐metals (such as Se, Bi, …) raises the possibility of novel nanomaterials synthesis with technologically interesting properties on a nanometric scale. Indeed it offers the possibility to enhance the physical properties of both the encapsulated and encapsulating materials. In the present study, multi‐walled nanotubes, synthesized by thermic decomposition of propylene in alumina membrane and catalytic decomposition of acetylene on solid solution and single‐walled nanotubes (from Rice University, Houston, Texas, USA) were filled with selenium, in order to study the influence of confinement on Se structure and the nanocomposite properties. The filling was performed in the vapor phase in a sealed reactor, and the control of selenium pressure allows us to control the nanotube filling rate, which depends also on the nanotube diameter. A filling rate up to 90% could be reached with this method.

Understanding the structural setting in the Southern Apennines (Italy): insight from Gravity Gradient Tensor

The Lucania Apennines form the frontal part of the Apennines in Southern Italy. This orogenic belt was formed in response to late Miocene–Early Pleistocene shortening and allochthon emplacement toward the northeast, and was subsequently affected by extensional faulting which migrated to northeast ahead of the thrust system. As a result, contraction structures are found associated to Pliocene–Early Pleistocene thrust-top basins in the NE part of the area, whereas extensional faults shape Middle Pleistocene–Holocene basin on the SW sector. The main structural grain of the belt is NW–SE, but E–W structures are widespread in the area as a result of phases of non-coaxial thrusting and strike-slip faulting. The analysis, one by one, of the components of the Gravity Gradient Tensor (GGT) has proved to yield a fine image of the structural setting of the investigated area. GGT is a second rank tensor containing the second spatial derivatives of the gravity potential and in this paper is used instead than the more traditional gravity data. The Tzz component allows an accurate description of the location and of the shape of basins and other structures, but different components of the GGT provide even more detailed insights for such structures. In particular, we found that the Tzy and Tyy locate well those structures trending closer to the E–W direction for both thrust-top and extensional basins, and their termination against the main NW–SE structures. The combined use of components of GGT provides a finer definition of the anomaly sources particularly if a good knowledge of their strike and depth is independently estimated with other geological and geophysical investigations.

Molecular structures of Se(SCH3)2 and Te(SCH3)2 using gas-phase electron diffraction and ab initio and DFT geometry optimisations

The molecular structures of Se(SCH(3))(2) and Te(SCH(3))(2) were investigated using gas-phase electron diffraction (GED) and ab initio and DFT geometry optimisations. While parameters involving H atoms were refined using flexible restraints according to the SARACEN method, parameters that depended only on heavy atoms could be refined without restraints. The GED-determined geometric parameters (r(h1)) are: rSe-S 219.1(1), rS-C 183.2(1), rC-H 109.6(4) pm; angleS-Se-S 102.9(3), angleSe-S-C 100.6(2), angleS-C-H (mean) 107.4(5), phiS-Se-S-C 87.9(20), phiSe-S-C-H 178.8(19) degrees for Se(SCH(3))(2), and rTe-S 238.1(2), rS-C 184.1(3), rC-H 110.0(6) pm; angleS-Te-S 98.9(6), angleTe-S-C 99.7(4), angleS-C-H (mean) 109.2(9), phiS-Te-S-C 73.0(48), phiTe-S-C-H 180.1(19) degrees for Te(SCH(3))(2). Ab initio and DFT calculations were performed at the HF, MP2 and B3LYP levels, employing either full-electron basis sets [3-21G(d) or 6-31G(d)] or an effective core potential with a valence basis set [LanL2DZ(d)]. The best fit to the GED structures was achieved at the MP2 level. Differences between GED and MP2 results for rS-C and angleS-Te-S were explained by the thermal population of excited vibrational states under the experimental conditions. All theoretical models agreed that each compound exists as two stable conformers, one in which the methyl groups are on the same side (g(+)g(-) conformer) and one in which they are on different sides (g(+)g(+) conformer) of the S-Y-S plane (Y = Se, Te). The conformational composition under the experimental conditions could not be resolved from the GED data. Despite GED R-factors and ab initio and DFT energies favouring the g(+)g(+) conformer, it is likely that both conformers are present, for Se(SCH(3))(2) as well as for Te(SCH(3))(2).

One-step fabrication of selenium and tellurium tubular structures

Single-crystal Se and Te tubular structures have been synthesized in one step by a hydrothermal method and characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). The hollow prismatic morphology of the tubular structures has been revealed and explained based on the nucleation and growth mechanism of the highly anisotropic crystal structures of Se and Te.

Spin and energy transfer between magnetic ions and freecarriers in diluted‐magnetic semiconductor heterostructures

In this paper we give a brief overview of our studies on dynamical processes in diluted-magnetic-semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. Presence of free carriers is an important factor which determines the energy- and spin transfer in a coupled systems of magnetic ions, lattice (the phonon system) and carriers. We report also new data on dynamical response of magnetic ions interacting with photogenerated electron-hole plasma. (Zn,Mn)Se/(Zn,Be)Se structures with relatively high Mn content of 11% provide spin-lattice relaxation time of about 20 ns, which is considerably shorter then the characterictic times of nonequilibrium phonons ranging to 1 μs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

EXAFS study of mechanical-milling-induced solid-state amorphization of Se

Complete solid-state amorphization has been realized in elemental selenium by means of mechanical milling of crystalline Se powder. Extended X-ray-absorption fine-structure measurements (EXAFS) indicated that the amorphization process of crystalline Se was accompanied with a decrease of the nearest neighboring coordination number and the bond length, and the increase of the Debye–Waller factor. Combined with the previous study, we conclude that the mechanical milling results in the strengthening of intra-chain and weakening of inter-chain interactions of Se during amorphization. Compared to the structure of the as-quenched amorphous Se, the first nearest neighbor coordination number of the as-milled amorphous Se becomes smaller, while the Debye–Waller factor is larger, which is caused by the milling process.

Thermoelectric Properties and Electronic Structure of CoSb3 Doped with Se and Te.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermoelectric properties and electronic structure of CoSb 3 doped with Se and Te

This work presents structural and electron transport properties of Se- and Te-doped CoSb 3 skutterudites in relation to results of electronic structure calculations performed for this system. The physical quantities were determined from crystal structure studies and measurements of transport coefficients: electrical conductivity, thermal conductivity and Seebeck coefficient as a function of composition and temperature. The electronic structure of CoSb 3 was calculated using the Korringa–Kohn–Rostoker method with the LDA framework. Dispersion curves E( k) in CoSb 3 computed for experimental crystallographic parameters exhibit a very narrow indirect energy gap at the Fermi level, which however strongly varies along different k-directions. The KKR valence and conduction band curvatures reflect effective masses estimated from experimental data well. The effect of doping CoSb 3 with Se and with Te as well as the dopants’ influence on density of electronic states was investigated by the KKR method combined with the coherent potential approximation (CPA). This method was also used to show an impact of various crystal defects on electronic structure in pure Se- and Te-doped CoSb 3.

Fault geometries from the space distribution of the 1990–1997 Sannio–Benevento earthquakes: inferences on the active deformation in Southern Apennines

In this study, we analyze the recent (1990–1997) seismicity that affected the northern sector (Sannio–Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method (BEM), which collapses hypocentral clouds, to the events of low energy ( M d max=4.1) seismic sequences in order to constrain the location and geometry of the seismogenetic structures. The results indicate that earthquakes aligned along three main structures: two sub-parallel structures striking NW–SE (1990–1992, Benevento sequence) and one structure striking NE–SW (1997, Sannio sequence). The southernmost NW–SE structure, which dips towards NE, overlies the fault that is likely to be responsible for a larger historical earthquake ( I o max= XI MCS, 1688 earthquake). The northernmost NW–SE striking structure dips towards SW. The NE–SW striking structure is sub-vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake. The spatio-temporal evolution of the 1990–1997 seismicity indicates a progressive migration from SE (Benevento) to NW (Sannio) associated to a deepening of hypocenters (i.e., from about 5 to 12 km). Hypocenters cluster at the interface between the major structural discontinuities (e.g., pre-existing thrust surfaces) or within higher rigidity layers (e.g., the Apulia carbonates). Available focal mechanisms from earthquakes occurred on the recognized NW–SE and NE–SW faults are consistent with dip-slip normal solutions. This evidences the occurrence of coexisting NW–SE and NE–SW extensions in Southern Apennines.

An XAFS study of the S–Se exchange during the reaction of selenophene over Mo sulfide catalysts

The S–Se exchange during the hydrode-selenium (HD-Se) reaction of selenophene was investigated over MoS 2/Al 2O 3 and intrazeolite Mo sulfide clusters. The local structure of Se incorporated into the Mo sulfide catalysts was studied by means of Se K-edge XAFS. It was found that the capacity of S–Se exchange during the HD-Se reaction and dynamic behavior of Se incorporation strongly depend on the cluster size of Mo sulfides.