Littérature scientifique sur le sujet « Path Equilibration »

The equilibration of two coupled reservoirs is studied using a Green function approach that is suitable for future development with the closed time path method. The problem is solved in two parameterizations, to demonstrate the nontrivial issues of parameterization in both the intermediate steps and the interpretation of physical quantities. We use a covariant approach to find self-consistent solutions for the statistical distributions as functions of time. We show that by formally introducing covariant connections, one can rescale a slowly varying nonequilibrium theory so that it appears to be an equilibrium one, for the purposes of calculation. We emphasize the importance of properly tracking variable redefinitions to correctly interpret physical quantities. PACS Nos.: 11.10-z, 03.70+k, 05.70ln

Our contemporary civilization increasingly relies on creative approaches and solutions. This growing dependence makes issues of control, regulation, and management of the process of creation ever more important. This article finds two major current theoretical perspectives on creativity and the process of creation to be vulnerable in one important respect: their explanation of the production of disequilibrium, which plays a singularly important role in the process of creation, does not pass the test of rational justification. This article suggests that the production of disequilibrium is intimately related to equilibration—the essential operation of rational thought processes. The emphasis on the role equilibration makes a rational justification of the production of disequilibrium possible. The new theoretical perspective opens the path toward a comprehensive and objective understanding of the process of creation, which is the main condition for regulating, controlling, and managing this process.

Abstract The insensitivity of the Antarctic Circumpolar Current (ACC)’s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind-driven Ekman overturning—a framework verified in zonally symmetric circumpolar flows. Substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the ACC. Analysis of an eddy-resolving ocean GCM shows that the ACC can be broken into broad regions of weak eddy activity, where surface winds steepen isopycnals, and a small number of standing meanders, across which the isopycnals relax. Meanders are coincident with sites of (i) strong eddy-induced modification of the mean flow and its vertical structure as measured by the divergence of the Eliassen–Palm flux and (ii) enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions. Within meanders, the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence, providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification. Temporal fluctuations in these diagnostics are correlated with variability in both the Eliassen–Palm flux and bottom speed, implying a link to dissipative processes at the ocean floor. At larger scales, bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity, which links to variations in meander structure. From these results, it is proposed that the “flexing” of standing meanders provides an alternative mechanism for reducing the sensitivity of the ACC’s baroclinicity to changes in forcing, separate from an ACC-wide change in transient eddy characteristics.

Abstract. Better knowledge of spatial and temporal delivery of dissolved organic Carbon (DOC) in small catchments is required to understand the mechanisms behind reported long-term changes in C fluxes from some peatlands. We monitored two storms with contrasting seasons and antecedent conditions in a small upland UK moorland catchment. We examined DOC concentrations and specific UV absorbance (SUVA at 285 nm), together with solute concentrations required to undertake end member mixing analyses to define dominant flow paths contributing to streamflow. This was combined with laboratory soil-solution equilibrations. We aimed to resolve how seasonal biogeochemical processing of DOC and flowpath changes in organo-mineral soils combine to affect DOC exported via the stream. An August storm following a dry period gave maximum DOC concentration of 10 mg l−1. Small DOC:DON ratios (16–28) and SUVA (2.7–3.6 l mg−1 m−1) was attributed to filtration of aromatic compounds associated with up to 53% B horizon flow contributions. This selective filtration of high SUVA DOC was reproduced in the experimental batch equilibration system. For a November storm, wetter antecedent soil conditions led to enhanced soil connectivity with the stream and seven times greater DOC stream-load (maximum concentration 16 mg l−1). This storm had a 63% O horizon flow contribution at its peak, limited B horizon buffering and consequently more aromatic DOC (SUVA 3.9–4.5 l mg−1 m−1 and DOC:DON ratio 35–43). We suggest that simple mixing of waters from different flow paths cannot alone explain the differences in DOC compositions between August and November and biogeochemical processing of DOC is required to fully explain the observed stream DOC dynamics. This is in contrast to other studies proposing hydrological controls and provides evidence that DOC biogeochemistry must be incorporated in modelling to predict the impacts of changes in DOC delivery to aquatic systems.

In the upper Tesso Valley the folded contact between Piemonte Zone ophiolites and Sesia-Lanzo Zone continental crust is exposed. Here serpentinites, metabasites, calcschists and fine-grained gneisses are deformed by four ductile superposed groups of structures, associated with different mineral assemblages. Different serpentinite lithologies have been recognized and studied in detail. Mylonitic D2 structures are pervasive and mineral assemblages point to re-equilibration at T of 450 ± 50 ∘C and P of 0.8 ± 0.3 GPa, under blueschist/epidote amphibolite-facies conditions. Pre-D2 structures and mineral assemblages are relics within S2 and indicate a re-equilibration under eclogite-facies conditions, at T of 570 ± 50 ∘C and P > 1.8 GPa. Post-D2 occurs under greenschist-facies conditions. Numerical modeling of a subduction zone allows exploration of the geodynamic context in which such PT path could have developed, and to make hypotheses about the possible timing of such a scenario, in agreement with the timing generally proposed for the Alpine subduction and collision. Model predictions indicate that pre-D2 mineral assemblages may have developed during Paleocene at 60–90 km depth and 115–145 km from the trench, or, alternatively, during lower Eocene at ca. 70–90 km depth, and 135–160 km from the trench.

Titanomagnetite from Fe-Ti-V ores of the Lanjiahuoshan deposit, Panzhihua layered intrusion, Southwest China, was investigated at the nanoscale. The objectives were to establish the composition of exsolution phases and their mutual relationships in order to evaluate the sequence of exsolution among oxide phases, and assess mechanisms of ore formation during magma emplacement. At the micron-scale, titanomagnetite shows crosscutting sets of exsolutions with ilmenite and Al-Mg-Fe-spinel (pleonaste), as well as overprint, both in terms of phase re-equilibration and remobilization of trace elements. Most complex textures were found in titanomagnetite surrounded by ilmenite and this was selected for high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) imaging and STEM energy-dispersive X-ray spectrometry (EDS) spot analysis and mapping on a thin foil prepared in situ on a focused ion beam scanning electron microscope platform. Titanomagnetite revealed two sequential sets of exsolutions, {111} crosscutting {100}, which are associated with changes in phase speciation and trace element distribution patterns. Qandilite is the dominant spinel phase inside titanomagnetite; magnesioferrite is also identified. In contrast, Fe-poor, Al-rich, Mg-bearing spinel is present within ilmenite outside the grain. Vanadium enrichment in newly-formed magnetite lamellae is clear evidence for trace element remobilization. This V-rich magnetite shows epitaxial relationships with ilmenite at the contact with titanomagnetite. Two-fold super-structuring in ilmenite is evidence for non-redox re-equilibration between titanomagnetite and ilmenite, supporting published experimental data. In contrast, the transformation of cubic Ti-rich spinel into rhombohedral ilmenite imaged at the nanoscale represents the “oxy-exsolution” model of titanomagnetite–ilmenite re-equilibration via formation of a transient ulvöspinel species. Nanoscale disorder is encountered as vacancy layers in Ti-rich spinel, and lower symmetry in the Fe-poor, Al-Mg phase, suggesting that slow cooling rates can preserve small-scale phase equilibration. The cooling history of titanomagnetite ore can be reconstructed as three distinct stages, concordant with published models for the magma plumbing system: equilibrium crystallization of Al-rich, Mg-bearing titanomagnetite from cumulus melts at ~55 km, with initial exsolutions occurring above 800 °C at moderate fO2 conditions (Stage 1); crosscutting {111} exsolutions resulting in formation of qandilite, attributable to temperature increase due to emplacement of another batch of melt affecting the interstitial cumulus during uplift. Formation of 2-fold superstructure ilmenite + V-rich magnetite exsolution pairs representing non-redox equilibration indicates resetting of the cooling path at this stage (Stage 2); and ilmenite formation from pre-existing Ti-rich spinel and ulvöspinel, illustrative of redox-driven cooling paths at <10 km (Stage 3). HAADF STEM provides direct imaging of atomic arrangements, allowing recognition of processes not recognizable at the micron-scale, and can thus be used to constrain exsolution models during ore formation.

Abstract. Better knowledge of spatial and temporal delivery of dissolved organic carbon (DOC) in small catchments is required to understand the mechanisms behind reported long-term changes in C fluxes from some peatlands. We monitored two storms with contrasting seasons and antecedent conditions in a small upland UK moorland catchment. We examined DOC concentrations and specific UV absorbance (SUVA at 285 nm), together with solute concentrations required to undertake end-member mixing analyses to define dominant flow paths contributing to streamflow. This was combined with laboratory soil-solution equilibrations. We aimed to resolve how seasonal biogeochemical processing of DOC and flowpath changes in organo-mineral soils combine to affect DOC exported via the stream. An August storm following a dry period gave maximum DOC concentration of 10 mg l−1. Small DOC:DON ratios (16–28) and SUVA (2.7–3.6 l mg−1 m−1) was attributed to filtration of aromatic compounds associated with up to 53% B horizon flow contributions. This selective filtration of high SUVA DOC was reproduced in the experimental batch equilibration system. For a November storm, wetter antecedent soil conditions led to enhanced soil connectivity with the stream and seven times greater DOC stream-load (maximum concentration 16 mg l−1). This storm had a 63% O horizon flow contribution at its peak, limited B horizon buffering and consequently more aromatic DOC (SUVA 3.9–4.5 l mg−1 m−1 and DOC:DON ratio 35–43). We suggest that simple mixing of waters from different flow paths cannot alone explain the differences in DOC compositions between August and November and biogeochemical processing of DOC is required to fully explain the observed stream DOC dynamics. This preliminary evidence is in contrast to other studies proposing hydrological controls on the nature of DOC delivered to streams. Although our study is based only on two storms of very different hydrological and biogeochemical periods, this should promote wider study of DOC biogeochemical alteration in headwaters so that this be better incorporated in modelling to predict the impacts of changes in DOC delivery to, and fate in, aquatic systems.

AbstractA lenticular metagabbro crops out in an early Palaeozoic metasedimentary sequence at Nurra, northwest Sardinia. The metagabbro consists of variable proportions of early-formed coarse-grained albite, chlorite, epidote and apatite, later biotite and amphibole, and late stilpnomelane. Clinopyroxene and ilmenite are rare relict igneous minerals; albite has completely replaced primary plagioclase.The metamorphic evolution of the Nurra metagabbro has been investigated by pseudosection modelling for a fixed bulk-rock composition in the Na2O—CaO—K2O—FeO—MgO—A12O3—SiO2—H2O (NCKFMASH) model system with added Ti and Mn in the P-T range 1-11 kbar and 150-450°C. The P—T path of the metagabbro is a loop with a prograde segment overprinted by later metamorphic re-equilibration. The pressure peak was at ⩽7 kbar and ∼400°C. The subsequent temperature peak, at ∼440°C, was accompanied by a decrease in pressure to ∼3 kbar. The final P—T evolution of the metagabbro is characterized by near-isobaric cooling to 250—300°C, with the formation of stilpnomelane. The P—T path of the Nurra gabbro is typical of continental orogenic belts that have undergone crustal thickening.

Paleozoic platform carbonate rocks of the Rocky Mountains host Mississippi Valley-type (MVT), magnesite, barite, and REE-barite-fluorite deposits. Farther west, platform carbonate rocks of the Kootenay Arc host MVT and fracture-controlled replacement (FCR) deposits. This is the first systematic LA-ICP-MS study of carbonates in MVT and FCR deposits. We investigated seven MVT deposits in the Rocky Mountains, and five MVT deposits in the Kootenay Arc. None of the post-Archean Australian shale (PAAS)-normalized REE profiles show light REE (LREE) depletion and strong negative Ce anomalies characteristic of modern seawater: some profiles are nearly flat; others show depletion in LREE similar to seawater but without negative Ce anomalies; others are middle REE enriched. Carbonates with a strong positive Eu anomaly precipitated from or interacted with different fluids than carbonates with flatter profiles without a strong positive Eu anomaly. REE signatures reflect crystallization conditions of primary carbonates, and crystallization and re-equilibration conditions of carbonates with ambient fluids during diagenesis, deep burial, and/or metamorphic recrystallization. Chemical evolution of fluids along their migration path, fluid-to-rock ratio, fluid acidity, redox, and temperature also influence REE profile shape, which helps establish genetic and timing constraints on studied deposits and improves knowledge of the metallogeny of the Kootenay Arc and Rocky Mountains.