Geostatistical mapping and spatial variability of surficial sediment types on the Beaufort Sea shelf based on grain size data

The nearshore Beaufort Sea is a sensitive marine environment that is also the focus of oil and gas exploration. Offshore, the Beaufort Sea contains large potential reserves of hydrocarbons. Any future exploitation of these resources will present unique engineering challenges and will require an understanding of the processes that govern stability, nearshore morphology and sediment properties in the extensive shallow coastal zone of the Beaufort Sea shelf. Knowledge of the surficial sediment distribution is, therefore, necessary to provide a framework for understanding sediment stability, sediment transport, platform foundation conditions and to balance engineering challenges with environmental concerns, resource development and precautionary sustainable management. We describe an approach for a quality controlled mapping of grain sizes and sediment textures for the Beaufort Sea shelf in the Canadian Arctic. The approach is based on grain size data sampled during the period 1969-2008. A replenishment of grain size data since the 1980’s, as well as the consideration of correlating parameters (bathymetry, slope and sediment input) to a cokriging algorithm, amends the former way of mapping the surficial sediments of the Beaufort Sea shelf. Subsequent to data processing and applying autocorrelation, four single grids (clay, silt, sand and gravel) were generated from grain size data by ordinary kriging and cokriging. Cokriging also considered parameters that influence sediment texture such as bathymetry, slope, cost distance from the Mackenzie River and data anisotropy (directional dependency). The cokriging algorithm expressed as a variogram was quality controlled by cross-validation and predicted standard errors (PSEs). PSE values express a maximum deviation of modeled from the real values and therefore help to estimate the quality in these regions regarding the interpolation results for each grain size range. A sediment type classification scheme applied to the set of clay, silt, sand and gravel content maps resulted in a sediment type map of the Beaufort Sea shelf. The PSEs of ordinary kriging and cokriging have been compared and showed that the cokriging technique provided superior interpolation results for silt and slightly improved results for clay and sand. Cokriging was able to capture most of the small variations in the sediment texture distribution. Furthermore, reduced nugget effects confirmed that the cost distance grid was a better indicator for sediment texture when compared to bathymetry and slope. For gravel, ordinary kriging achieved better prediction probabilities and was, therefore, used for generation of the distribution map for this grain size class. The use of cokriging and ordinary kriging greatly enhanced interpolation estimates without additional sampling. Especially in nearshore regions, like the Beaufort Sea shelf, geostatistical interpolation techniques are very useful for evaluating seabed sediment texture because sampling is often difficult or impossible due to ice conditions or even prohibited near oil platforms. The described methodology along with the inclusion of recent data, provided an improved mapping of the surficial sediments of the Beaufort Sea shelf

Magnetic dynamic effects in TbMn1-x(Ga/Sc)xO 3 samples (x=0.4, 0.5, 0.6)

The magnetic properties of strongly doped TbMnO3 with non-magnetic ions, such as Ga and Sc, has been studied focused in the intermediate region (0.4=x=0.6) where long range ferromagnetic ordering was reported for La-based compounds. All samples are single phase and show a perovskite structure with orthorhombic unit cell, space group Pbnm. The Tb-based compounds do not show long range magnetic order but magnetic anomies are noticeable at low temperature. These anomalies show magnetic irreversibility and dynamic effects typical of magnetic glassy systems. These features have been studied in detail using ac magnetic susceptibility and the analysis shows the largest magnetic correlations for x=0.5 in both type of substitutions

Non-coboundary Poisson-Lie structures on the book group

All possible Poisson-Lie (PL) structures on the 3D real Lie group generated by a dilation and two commuting translations are obtained. Its classification is fully performed by relating these PL groups with the corresponding Lie bialgebra structures on the corresponding "book" Lie algebra. By construction, all these Poisson structures are quadratic Poisson-Hopf algebras for which the group multiplication is a Poisson map. In contrast to the case of simple Lie groups, it turns out that most of the PL structures on the book group are non-coboundary ones. Moreover, from the viewpoint of Poisson dynamics, the most interesting PL book structures are just some of these non-coboundaries, which are explicitly analysed. In particular, we show that the two different q-deformed Poisson versions of the sl(2,R) algebra appear as two distinguished cases in this classification, as well as the quadratic Poisson structure that underlies the integrability of a large class of 3D Lotka-Volterra equations. Finally, the quantization problem for these PL groups is sketched.Comment: 15 pages, revised version, some references adde

Semisimple types for p -adic classical groups

a

Atomic-scale mechanisms for magnetostriction in CoFe2O4 and La0.5Sr0.5CoO3 oxides determined by differential x-ray absorption spectroscopy

The atomic environments involved in the magnetostriction effect in CoFe2O4 and La0.5Sr0.5CoO3 poly-crystalline samples have been identified by differential extended x-ray absorption fine structure (DiffEXAFS) spectroscopy. We demonstrate that cobalt atoms at octahedral sites are responsible for their magnetostriction. The analysis of DiffEXAFS data indicates that the local-site magnetostrictive strains of Co atoms are reversed in these two oxides, in agreement with the macroscopic magnetostriction. For the CoFe2O4 spinel, a large negative strain along the (100) direction has been determined for the CoO6 octahedron causing a tetragonal contraction in contrast with the La0.5Sr0.5CoO3 perovskite, where a positive moderate strain along the (100) direction was found resulting in a tetragonal expansion. The different local-site magnetostriction is understood in terms of the different valence and spin state of the Co atoms for the two oxides. The macroscopic magnetostriction would be explained then by the relative change in volume, either contraction in CoFe2O4 or expansion in La0.5Sr0.5CoO3, when the tetragonal axis of the Co site is reoriented under an externally applied magnetic field

Metamagnetic transition in Tb2MnCoO6

The magnetic properties of the double perovskite Tb2MnCoO6 have been studied. The refinement of neutron pattern reveals antisite defects in the ordered array of Mn4+ and Co2+ cations. The temperature dependence of dc magnetization exhibits a magnetic transition at ~100 K with a strong irreversibility between ZFC and FC conditions. The ac magnetic susceptibility curve shows a strong peak at the same temperature whose position and intensity slightly depends on the field frequency. These features are typical of a spin-glasslike phase but neutron diffraction shows the onset of a ferromagnetic contribution at the same temperature. Ferromagnetism in this sample is associated to superexchange interaction between Mn4+ and Co2+ cations. The most striking property of Tb2MnCoO6 is the presence of field induced transitions. This is observed in the magnetic hysteresis loops below 100K. The metamagnetic transition was studied by powder neutron diffraction at different temperatures and magnetic fields. At low temperature, the magnetic field induces a long range magnetic ordering of Tb3+ moments in the ab-plane. The magnetic peaks of Tb moments at 30 kOe vanish at 60 K. Above this temperature, the metamagnetic transition is ascribed to the field induced transition from short to long range ferromagnetic ordering in the Mn-Co sublattice

El Paleolítico Medio en el territorio valenciano y la variabilidad tecno-económica de la Cova del Bolomor

En el presente artículo se exponen las principales características de las industrias líticas del Paleolítico Medio en el territorio valenciano. Se hace especial hincapié en la variabilidad tecno-económica observada en la secuencia estratigráfica de la Cova del Bolomor. Con dicho análisis se pretende contribuir al establecimiento de los rasgos evolutivos de las industrias asociadas a los grupos de neandertales. En este sentido, el estudio pone de manifiesto que en estas sociedades se produjo, en los momentos finales, cierto progreso tecnológico, en un contexto arqueológico en el que es difícil precisar si hubo, o no, influencia externa o aculturación por parte de las poblaciones de cromañones en el territorio valenciano.En el present article s'exposen les principals característiques de les indústries lítiques del Paleolític Mitjà en el territori valencià. Es posa especial atenció a la variabilitat tecno-econòmica observada en la seqüència estratigràfica de la Cova del Bolomor. Amb aquesta anàlisi es pretén contribuir a l'establiment dels trets evolutius de les indústries associades als grups de neandertals. En aquest sentit, l'estudi posa de manifest que en aquestes societats es va produir, en els moments finals, un cert progrés tecnològic, en un context arqueològic en el qual és difícil precisar si va haver-hi, o no, influència externa o aculturació per part de les poblacions de cromanyons en el territori valencià.Dans l'article ci-dessous, s'exposent les principales caractéristiques des industries lithiques du Paléolithique Moyen dans le territoire valencien. On veut mettre en relief la variabilité techno-économique observée dans la séquence stratigraphique de la Cova del Bolomor. Avec cette analyse, on cherche à établir les traits évolutifs des industries associées aux groupes néandertaliens. Dans ce sens, l'étude met en relief que ces sociétés ont probablement connu, dans un dernier temps, un certain progrès technologique, dans un contexte archéologique où il est difficile de préciser s'il y a eu ou pas une influence externe ou une acculturation venue des populations cromagnones dans la région de Valence.In this paper main characteristics of the Middle Palaeolithic lithic industries from the territory of Valencia are presented. Particular attention is paid to the techno-economical variability of the archaeological record in Cova del Bolomor. This study aims to discuss the evolutionary features of Neanderthal industries; our analysis shows that there was some technological progress at the end of the Middle Palaeolithic, in an archaeological context in which it is uncertain whether or not there was external influence or acculturation from Cro-Magnon populations in the valencian territory

Dependence of the Jahn-Teller distortion in LaMn1-xScxO3 on the isovalent Mn-site substitution

We investigated the relative importance of removing the Mn3+ Jahn-Teller distortion in driving ferromagnetism in LaMn1-xScxO3 combining x-ray powder diffraction and x-ray absorption spectroscopy at the Mn and Sc K-edges. By increasing the Sc content, the orthorhombic distortion of the Pbnm cell in LaMnO3 decreases but the unit-cell remains slightly distorted in LaScO3. Besides, the nearly tetragonal-distorted MO6 in LaMnO3 continuously evolves into a nearly regular one in LaScO3. On the other hand, x-ray absorption spectra show that the MnO6 octahedron remains Jahn-Teller distorted and the ScO6 octahedron is nearly regular along the whole series. Moreover, the ordering of the Mn3+ Jahn-Teller distortion is not disrupted in the ab plane for any Sc concentration. This contrasts with the Gasubstituted compounds, where a regular MnO6 is found for x > 0.5. However, both LaMn0.5Sc0.5O3 and LaMn0.5Ga0.5O3 show ferromagnetic behavior independently of the presence (or not) of Jahn-Teller distorted Mn3+. Thus, our results point to the Mn-sublattice dilution as the main effect in driving ferromagnetism in these manganites over local structure effects previously proposed by the spin flipping or the vibronic superexchange models

Rotura de cotilo en artroplastia total de cadera

Describimos dos casos de rotura de cotilos de expansión de prótesis de cadera tipo CLS de origen no traumático. Ambos casos sucedieron a los seis años de cirugía y no se apreció desgaste o rotura del polietileno en ninguno de ellos. En nuestra opinión la hipótesis más probable es que la falta de contacto entre la zona polar del cotilo y el fondo del acetábulo produzca una zona de inestabilidad en los segmentos de la prótesis y rotura por fatiga del material. Creemos que es obligado su recambio aunque el paciente no presente sintomatología actual, ya que la rotura del acetábulo conducirá a un aflojamiento y a una osteolisis secundaria.We describe two cases of breakage of expansion cups in a CLS uncemented total hip arthroplasty wihtout traumatic etiologic. Both cases occurred six years after the surgery and none had breakage or polyethylene wear. We postulate that the lack of contact between the polar area of the cup and the acetabulum produces a zone of instability in the segments of the prosthesis and increases the risk of fatigue of the material. In our opinion acetabular revision is mandatory in this situation, even in asymptomatic cases, because cup rupture leads to implant loosening with secondary short-team osteolysis

Structural, Magnetic, and Electronic Properties of CaBaCo4- xMxO7 (M = Fe, Zn)

The effect of substituting iron and zinc for cobalt in CaBaCo4O7 was investigated using neutron diffraction and X-ray absorption spectroscopy techniques. The orthorhombic distortion present in the parent compound CaBaCo4O7 decreases with increasing the content of either Fe or Zn. The samples CaBaCo3ZnO7 and CaBaCo4-xFexO7 with x = 1.5 are metrically hexagonal, but much better refinements in the neutron diffraction patterns are obtained using an orthorhombic unit cell. The two types of substitution have opposite effects on the structural and magnetic properties. Fe atoms preferentially occupy the sites at the triangular layer. Thus, the replacement of Co by Fe suppresses the ferrimagnetic ordering of the parent compound, and CaBaCo4-xFexO7 (0.5 = x = 2) samples are antiferromagnetically ordered following a new propagation vector k = (1/3, 0, 0). However, the Zn atoms prefer occupying the Kagome layer, which is very detrimental for the long-range magnetic interactions giving rise to a magnetic glass-like behavior in the CaBaCo3ZnO7 sample. The oxidation states of iron and zinc are found to be 3+ and 2+, respectively, independently of the content, as confirmed by X-ray absorption spectroscopy. Therefore, the average Co oxidation state changes accordingly with the Fe3+ or Zn2+ doping. Also, X-ray absorption spectroscopy data confirm the different preferential occupation for both Fe and Zn cations. The combined information obtained by neutron diffraction and X-ray absorption spectroscopy indicates that cobalt atoms can be either in a fluctuating Co2+/Co3+ valence state or, alternatively, Co2+ and Co3+ ions being randomly distributed in the lattice. These results explain the occurrence of local disorder in the CoO4 tetrahedra obtained by EXAFS. An anomaly in the lattice parameters and an increase in the local disorder are observed only at the ferrimagnetic transition for CaBaCo4O7, revealing the occurrence of local magneto-elastic coupling