919 research outputs found
Criticismo trascendental
In this presentation, unpublished until now, Francisco Canals
establishes a dialogue between Kantian trascendentalism and
Aquinas' thought. The question concerning the ontology
of the knowing human subject, blocked by the presuppositions
of Kant, can in turn be formulated and find response in the
metaphysics of knowledge of Aquinas. In the face of the problems
raised by the Cartesian postulation of a perfect intellectual intuition
of the thinking self, and in the face of the separation of the
pure ego and the empirical ego which is operative in Kant, Canals
proposes an ontology of the subject based in the metaphysics of
knowledge of Thomas Aquinas, where the finite, intellectual, sensible
compound that is the human being is interpreted within the
plane of his intellectual nature
XY checkerboard antiferromagnet in external field
Ordering by thermal fluctuations is studied for the classical XY
antiferromagnet on a checkerboard lattice in zero and finite magnetic fields by
means of analytical and Monte Carlo methods. The model exhibits a variety of
novel broken symmetries including states with nematic ordering in zero field
and with triatic order parameter at high fields.Comment: 6 page
Chiral nature of magnetic monopoles in artificial spin ice
Micromagnetic properties of monopoles in artificial kagome spin ice systems
are investigated using numerical simulations. We show that micromagnetics
brings additional complexity into the physics of these monopoles that is, by
essence, absent in spin models: besides a fractionalized classical magnetic
charge, monopoles in the artificial kagome ice are chiral at remanence. Our
simulations predict that the chirality of these monopoles can be controlled
without altering their charge state. This chirality breaks the vertex symmetry
and triggers a directional motion of the monopole under an applied magnetic
field. Our results also show that the choice of the geometrical features of the
lattice can be used to turn on and off this chirality, thus allowing the
investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure
Sandstones from the Eureka Mine (Cu-U-V) (Central Pyrennees): observed textures versus proposed reactions
In situ thermochemical sulfate reduction during ore formation at the Itxaspe Zn-(Pb) MVT occurrence (Basque-Cantabrian basin, Northern Spain)
Organic matter is thought to play a role in the genesis of many Mississippi Valley-type (MVT) deposits, acting as a reducing agent during thermochemical sulfate reduction (TSR). Although TSR is an extremely slow reaction t low temperatures (<100ºC), under favorable conditions it may supply the necessary reduced sulfur during ore formation. To test this hypothesis, the Itxaspe Zn-(Pb) MVT occurrence in the Basque-Cantabrian basin (Northern Spain) was studied. Sphalerite, the main ore phase, is generally found disseminated in Urgonian (Lower Cretaceous) carbonates, and in close relationship with solid bitumen. The bitumen source rock was very likely deposited in a marine marginal setting. Differences in composition of the bitumen samples are attributed to a fractionation during hydrocarbon expulsion and/or migration. The fluids involved in ore deposition were low temperature (Th ~130ºC), Na-Ca-Cl-(K-Mg)-type brines (salinities ~12.5 equiv. mass % NaCl). The origin of brine solutes (including sulfate) is related to the dissolution of Mesozoic evaporite units, although the contribution of evaporated seawater brines cannot be ruled out. The temperatures of ore deposition, the close relationship between the bitumen and ore phases, the presence of aromatic sulfur-bearing compounds and the d34S of sulfides and sulfates are consistent with an in situ TSR during ore formation in the Itxaspe Zn-(Pb) occurrence. Therefore, at least for small mineralizations like Itxaspe, our conclusion is that the necessary reduced sulfur can be supplied by TSR during ore genesis at the site of metal deposition
Non-universality of artificial frustrated spin systems
Magnetic frustration effects in artificial kagome arrays of nanomagnets with
out-of-plane magnetization are investigated using Magnetic Force Microscopy and
Monte Carlo simulations. Experimental and theoretical results are compared to
those found for the artificial kagome spin ice, in which the nanomagnets have
in-plane magnetization. In contrast with what has been recently reported, we
demonstrate that long range (i.e. beyond nearest-neighbors) dipolar
interactions between the nanomagnets cannot be neglected when describing the
magnetic configurations observed after demagnetizing the arrays using a field
protocol. As a consequence, there are clear limits to any universality in the
behavior of these two artificial frustrated spin systems. We provide arguments
to explain why these two systems show striking similarities at first sight in
the development of pairwise spin correlations.Comment: 7 pages, 6 figure
In situ thermochemical sulfate reduction during ore formation at the Itxaspe Zn-(Pb) MVT occurrence (Basque-Cantabrian basin, Northern Spain)
International audienceOrganic matter is thought to play a role in the genesis of many Mississippi Valley-type (MVT) deposits, acting as a reducing agent during thermochemical sulfate reduction (TSR). Although TSR is an extremely slow reaction at low temperatures (<100ºC), under favorable conditions it may supply the necessary reduced sulfur during ore formation. To test this hypothesis, the Itxaspe Zn-(Pb) MVT occurrence in the Basque-Cantabrian basin (Northern Spain) was studied. Sphalerite, the main ore phase, is generally found disseminated in Urgonian (Lower Cretaceous) carbonates, and in close relationship with solid bitumen. The bitumen source rock was very likely deposited in a marine marginal setting. Differences in composition of the bitumen samples are attributed to a fractionation during hydrocarbon expulsion and/or migration. The fluids involved in ore deposition were low temperature (Th ~130ºC), Na-Ca-Cl-(K-Mg)-type brines (salinities ~12.5 equiv. mass % NaCl). The origin of brine solutes (including sulfate) is related to the dissolution of Mesozoic evaporite units, although the contribution of evaporated seawater brines cannot be ruled out. The temperatures of ore deposition, the close relationship between the bitumen and ore phases, the presence of aromatic sulfur-bearing compounds and the 34S of sulfides and sulfates are consistent with an in situ TSR during ore formation in the Itxaspe Zn-(Pb) occurrence. Therefore, at least for small mineralizations like Itxaspe, our conclusion is that the necessary reduced sulfur can be supplied by TSR during ore genesis at the site of metal deposition
Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice
Magnetic frustration effects in artificial kagome arrays of nanomagnets are
investigated using x-ray photoemission electron microscopy and Monte Carlo
simulations. Spin configurations of demagnetized networks reveal unambiguous
signatures of long range, dipolar interaction between the nanomagnets. As soon
as the system enters the spin ice manifold, the kagome dipolar spin ice model
captures the observed physics, while the short range kagome spin ice model
fails.Comment: 4 pages, 4 figures, 1 tabl
Insights into the structural evolution of the pre-Variscan rocks of the Eastern Pyrenees from La Molina quartz veins; constraints on chlorite and fluid inclusion thermometry
Quartz veins hosted in the infra and overlying series to the (Sardic) Upper Ordovician Unconformity provide new insights into the structural and thermal evolution of the pre-Variscan rocks of the Eastern Pyrenees. In the La Molina area (Canigó massif), two generations of metric quartz veins (V1 and V2) are distinguished by their distribution patterns and their relationships to the deformational macro, meso, and microstructures. P-T formation conditions are obtained by combining chlorite geothermometry and fluid inclusion microthermometry data. Discrepancy on formation temperature for chlorites located at different positions within the veins are discussed, concluding that veins grew in a low fluid/rock ratio regime. V1 veins can be related to the Late Ordovician syn-sedimentary faulting episode as revealed by their distribution patterns, formation mechanisms, and fluid-rock interactions. We propose an Alpine age for the V2 veins, based on their structure and the emplacement conditions of 318 ± 12°C and 2.4 ± 0.2kbar, with an estimated geothermal gradient of 34°C∙km-1 and a burial depth of ca. 9km. Results obtained here are compared with other quartz veins spread throughout the Paleozoic basement of the Eastern Pyrenees
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