Preserving the B-Cell Compartment Favors Operational Tolerance in Human Renal Transplantation

Transplanted individuals in operational tolerance (OT) maintain long-term stable graft function after completely stopping immunosuppression. Understanding the mechanisms involved in OT can provide valuable information about pathways to human transplantation tolerance. Here we report that operationally tolerant individuals display quantitative and functional preservation of the B-c ell compartment in renal transplantation. OT exhibited normal numbers of circulating total B cells, naive, memory and regulatory B cells (Bregs) as well as preserved B-cell receptor repertoire, similar to healthy individuals. In addition, OT also displayed conserved capacity to activate the cluster of differentiation 40 (CD40)/signal transducer and activator of transcription 3 (STAT3) signaling pathway in Bregs, in contrast, with chronic rejection. Rather than expansion or higher activation, we show that the preservation of the B-cell compartment favors OT. Online address: http://www.molmed.org doi: 10.2119/molmed.2011.00281

TUNGSTEN ISOTOPIC COMPOSITIONS IN STARDUST SiC GRAINS FROM THE MURCHISON METEORITE: CONSTRAINTS ON THE s-PROCESS IN THE Hf-Ta-W-Re-Os REGION

We report the first tungsten isotopic measurements in stardust silicon carbide (SiC) grains recovered from the Murchison carbonaceous chondrite. The isotopes (182,183,184,186)Wand (179,180)Hf were measured on both an aggregate (KJB fraction) and single stardust SiC grains (LS+ LU fraction) believed to have condensed in the outflows of low-mass carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. The SiC aggregate shows small deviations from terrestrial (= solar) composition in the (182)W/(184)Wand (183)W/(184)Wratios, with deficits in (182)W and (183)W with respect to (184)W. The (186)W/(184)W ratio, however, shows no apparent deviation from the solar value. Tungsten isotopic measurements in single mainstream stardust SiC grains revealed lower than solar (182)W/(184)W, (183)W/(184)W, and (186)W/(184)W ratios. We have compared the SiC data with theoretical predictions of the evolution of W isotopic ratios in the envelopes of AGB stars. These ratios are affected by the slow neutron-capture process and match the SiC data regarding their (182)W/(184)W, (183)W/(184)W, and (179)Hf/(180)Hf isotopic compositions, although a small adjustment in the s-process production of (183)W is needed in order to have a better agreement between the SiC data and model predictions. The models cannot explain the (186)W/(184)W ratios observed in the SiC grains, even when the current (185)W neutron-capture cross section is increased by a factor of two. Further study is required to better assess how model uncertainties (e. g., the formation of the (13)C neutron source, the mass-loss law, the modeling of the third dredge-up, and the efficiency of the (22)Ne neutron source) may affect current s-process predictions.

Definite integrals and operational methods

An operational method, already employed to formulate a generalization of the Ramanujan master theorem, is applied to the evaluation of integrals of various types. This technique provides a very flexible and powerful tool yielding new results encompassing different aspects of the special function theory. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.

A modified Primal-Dual Logarithmic-Barrier Method for solving the Optimal Power Flow problem with discrete and continuous control variables

The aim of solving the Optimal Power Flow problem is to determine the optimal state of an electric power transmission system, that is, the voltage magnitude and phase angles and the tap ratios of the transformers that optimize the performance of a given system, while satisfying its physical and operating constraints. The Optimal Power Flow problem is modeled as a large-scale mixed-discrete nonlinear programming problem. This paper proposes a method for handling the discrete variables of the Optimal Power Flow problem. A penalty function is presented. Due to the inclusion of the penalty function into the objective function, a sequence of nonlinear programming problems with only continuous variables is obtained and the solutions of these problems converge to a solution of the mixed problem. The obtained nonlinear programming problems are solved by a Primal-Dual Logarithmic-Barrier Method. Numerical tests using the IEEE 14, 30, 118 and 300-Bus test systems indicate that the method is efficient. (C) 2012 Elsevier B.V. All rights reserved.

New constraints on the genesis and long-term stability of Os-rich alloys in the Earth's mantle

A variety of seemingly unrelated processes, such as core-mantle interaction, desulfurization, and direct precipitation from a silicate melt have been proposed to explain the formation of Ru-Os-Ir alloys (here referred to as osmiridiums) found in terrestrial mantle rocks. However, no consensus has yet been reached on how these important micrometer-sized phases form. In this paper we report the results of an experimental study on the solubilities of Ru, Os and Ir in sulfide melts (or mattes) as a function of alloy composition at 1300 degrees C. Considering the low solubilities of Ru, Os, and Ir in silicate melts, coupled with their high matte/silicate-melt partition coefficients, our results indicate that these elements concentrate initially at the ppm level in a matte phase in the mantle source region. During partial melting, the extraction of sulfur into silicate melt leads to a decrease in fS(2) that triggers the exsolution of osmiridiums from the refractory matte in the residue. The newly formed osmiridiums may persist in the terrestrial mantle for periods exceeding billions of years. (C) 2012 Elsevier Ltd. All rights reserved.

GATA3 and a dominant regulatory gene expression profile discriminate operational tolerance in human transplantation

Some organ-transplanted patients achieve a state of "operational tolerance" (01) in which graft function is maintained after the complete withdrawal of immunosuppressive drugs. We used a gene panel of regulatory/inflammatory molecules (FOXP3, GATA3, 100, TGFB1, TGFBR1/TBX21, TNF and IFNG) to investigate the gene expression profile in peripheral blood mononuclear cells of renal-transplanted individuals experiencing OT compared to transplanted individuals not displaying OT and healthy individuals (HI). OT subjects showed a predominant regulatory (REG) profile with higher gene expression of GATA3, FOXP3, TGFB1 and TGFB receptor 1 compared to the other groups. This predominant REG gene expression profile displayed stability over time. The significant GATA3 gene and protein expressions in OT individuals suggest that a Th2 deviation may be a relevant pathway to OT. Moreover, the capacity of the REG/INFLAMMA gene panel to discriminate OT by peripheral blood analysis indicates that this state has systemic repercussions. (C) 2011 Elsevier Inc. All rights reserved.

Time constraints on magmatism along the Major Gercino Shear Zone, southern Brazil: Implications for West Gondwana reconstruction

The Dom Feliciano Belt, situated in southernmost Brazil and Uruguay, contains a large mass of granite-gneissic rocks (also known as Florianopolis/Pelotas Batholith) formed during the pre-, syn- and post-orogenic phases of the Brasiliano/Pan-African cycle. In the NE extreme of this granitic mass, pre-, syn- and post-tectonic granites associated with the Major Gercino Shear Zone (MGSZ) are exposed. The granitic manifestation along the MGSZ can be divided into pre-kinematic tonalitic gneisses, peraluminous high-K calcalkaline early kinematic shoshonitic, and metaluminous post-kinematic granites. U-Pb zircon data suggest an age of 649 +/- 10 Ma for the pre-tectonic gneisses, and a time span from 623 +/- 6 Ma to 588 +/- 3 Ma for the early to post-tectonic magmatism. Negative epsilon Hf (t) values ranging from -4.6 to -14.6 and Hf model ages ranging from 1.64 to 2.39 Ga for magmatic zircons coupled with whole rock Nd model ages ranging from 1.24 to 2.05 Ga and epsilon Nd (t) values ranging from -3.84 to -7.50, point to a crustal derivation for the granitic magmatism. The geochemical and isotope data support a continental magmatic arc generated from melting of dominant Paleoproterozoic crust, and a similar evolution for the granitic batholiths of the eastern Dom Feliciano Belt and western Kaoko Belt. (C) 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Enhancing spiral-wound ultrafiltration performance for direct drinking water treatment through operational procedures improvement: A feasible option for the Sao Paulo Metropolitan Region

This work aimed to evaluate the influence of specific operational conditions on the performance of a spiral-wound ultrafiltration pilot plant for direct drinking water treatment, installed at the Guarapiranga's reservoir, in the Sao Paulo Metropolitan Region. Results from operational tests showed that the volume of permeate produced in the combination of periodic relaxation with flushing and chlorine dosage procedures was 49% higher than the volume obtained when these procedures were not used. Two years of continuous operation demonstrated that the ultrafiltration pilot plant performed better during fall and winter seasons, higher permeate flow production and reduced chemical cleanings frequency. Observed behavior seems to be associated with the algae bloom events in the reservoir, which are more frequent during spring and summer seasons, confirmed by chlorophyll-a analysis results. Concentrate clarification using ferric chloride was quite effective in removing NOM and turbidity, allowing its recirculation to the ultrafiltration feed tank. This procedure made it possible to reach almost 99% water recovery considering a single 54-hour recirculation cycle. Water quality monitoring demonstrated that the ultrafiltration pilot plant was quite efficient, and that potential pathogenic organisms, Escherichia coil and total coliforms, turbidity and apparent color removals were 100%, 95.1%, and 91.5%, respectively. (C) 2012 Elsevier B.V. All rights reserved.

Modularity and evolutionary constraints in a baculovirus gene regulatory network

Abstract Background The structure of regulatory networks remains an open question in our understanding of complex biological systems. Interactions during complete viral life cycles present unique opportunities to understand how host-parasite network take shape and behave. The Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) is a large double-stranded DNA virus, whose genome may encode for 152 open reading frames (ORFs). Here we present the analysis of the ordered cascade of the AgMNPV gene expression. Results We observed an earlier onset of the expression than previously reported for other baculoviruses, especially for genes involved in DNA replication. Most ORFs were expressed at higher levels in a more permissive host cell line. Genes with more than one copy in the genome had distinct expression profiles, which could indicate the acquisition of new functionalities. The transcription gene regulatory network (GRN) for 149 ORFs had a modular topology comprising five communities of highly interconnected nodes that separated key genes that are functionally related on different communities, possibly maximizing redundancy and GRN robustness by compartmentalization of important functions. Core conserved functions showed expression synchronicity, distinct GRN features and significantly less genetic diversity, consistent with evolutionary constraints imposed in key elements of biological systems. This reduced genetic diversity also had a positive correlation with the importance of the gene in our estimated GRN, supporting a relationship between phylogenetic data of baculovirus genes and network features inferred from expression data. We also observed that gene arrangement in overlapping transcripts was conserved among related baculoviruses, suggesting a principle of genome organization. Conclusions Albeit with a reduced number of nodes (149), the AgMNPV GRN had a topology and key characteristics similar to those observed in complex cellular organisms, which indicates that modularity may be a general feature of biological gene regulatory networks.

Constraints on the origin of cosmics rays above '10 POT. 18' eV from large-scale anisotropy searches in data of the Pierre Auger observatory

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above '10 POT. 18' eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments.Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above '10 POT. 18' eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.

Temporal constraints in large optical flow estimation

[EN] The aim of this work is to propose a model for computing the optical flow in a sequence of images. We introduce a new temporal regularizer that is suitable for large displacements. We propose to decouple the spatial and temporal regularizations to avoid an incongruous formulation. For the spatial regularization we use the Nagel-Enkelmann operator and a newly designed temporal regularization. Our model is based on an energy functional that yields a partial differential equation (PDE). This PDE is embedded into a multipyramidal strategy to recover large displacements. A gradient descent technique is applied at each scale to reach the minimum.

Constraint handling rules. Compositional semantics and program transformation

This thesis intends to investigate two aspects of Constraint Handling Rules (CHR). It proposes a compositional semantics and a technique for program transformation. CHR is a concurrent committed-choice constraint logic programming language consisting of guarded rules, which transform multi-sets of atomic formulas (constraints) into simpler ones until exhaustion [Frü06] and it belongs to the declarative languages family. It was initially designed for writing constraint solvers but it has recently also proven to be a general purpose language, being as it is Turing equivalent [SSD05a]. Compositionality is the first CHR aspect to be considered. A trace based compositional semantics for CHR was previously defined in [DGM05]. The reference operational semantics for such a compositional model was the original operational semantics for CHR which, due to the propagation rule, admits trivial non-termination. In this thesis we extend the work of [DGM05] by introducing a more refined trace based compositional semantics which also includes the history. The use of history is a well-known technique in CHR which permits us to trace the application of propagation rules and consequently it permits trivial non-termination avoidance [Abd97, DSGdlBH04]. Naturally, the reference operational semantics, of our new compositional one, uses history to avoid trivial non-termination too. Program transformation is the second CHR aspect to be considered, with particular regard to the unfolding technique. Said technique is an appealing approach which allows us to optimize a given program and in more detail to improve run-time efficiency or spaceconsumption. Essentially it consists of a sequence of syntactic program manipulations which preserve a kind of semantic equivalence called qualified answer [Frü98], between the original program and the transformed ones. The unfolding technique is one of the basic operations which is used by most program transformation systems. It consists in the replacement of a procedure-call by its definition. In CHR every conjunction of constraints can be considered as a procedure-call, every CHR rule can be considered as a procedure and the body of said rule represents the definition of the call. While there is a large body of literature on transformation and unfolding of sequential programs, very few papers have addressed this issue for concurrent languages. We define an unfolding rule, show its correctness and discuss some conditions in which it can be used to delete an unfolded rule while preserving the meaning of the original program. Finally, confluence and termination maintenance between the original and transformed programs are shown. This thesis is organized in the following manner. Chapter 1 gives some general notion about CHR. Section 1.1 outlines the history of programming languages with particular attention to CHR and related languages. Then, Section 1.2 introduces CHR using examples. Section 1.3 gives some preliminaries which will be used during the thesis. Subsequentely, Section 1.4 introduces the syntax and the operational and declarative semantics for the first CHR language proposed. Finally, the methodologies to solve the problem of trivial non-termination related to propagation rules are discussed in Section 1.5. Chapter 2 introduces a compositional semantics for CHR where the propagation rules are considered. In particular, Section 2.1 contains the definition of the semantics. Hence, Section 2.2 presents the compositionality results. Afterwards Section 2.3 expounds upon the correctness results. Chapter 3 presents a particular program transformation known as unfolding. This transformation needs a particular syntax called annotated which is introduced in Section 3.1 and its related modified operational semantics !0t is presented in Section 3.2. Subsequently, Section 3.3 defines the unfolding rule and prove its correctness. Then, in Section 3.4 the problems related to the replacement of a rule by its unfolded version are discussed and this in turn gives a correctness condition which holds for a specific class of rules. Section 3.5 proves that confluence and termination are preserved by the program modifications introduced. Finally, Chapter 4 concludes by discussing related works and directions for future work.

Biomass Gasification - Process analysis and dimensioning aspects for downdraft units and gas cleaning lines

In such territories where food production is mostly scattered in several small / medium size or even domestic farms, a lot of heterogeneous residues are produced yearly, since farmers usually carry out different activities in their properties. The amount and composition of farm residues, therefore, widely change during year, according to the single production process periodically achieved. Coupling high efficiency micro-cogeneration energy units with easy handling biomass conversion equipments, suitable to treat different materials, would provide many important advantages to the farmers and to the community as well, so that the increase in feedstock flexibility of gasification units is nowadays seen as a further paramount step towards their wide spreading in rural areas and as a real necessity for their utilization at small scale. Two main research topics were thought to be of main concern at this purpose, and they were therefore discussed in this work: the investigation of fuels properties impact on gasification process development and the technical feasibility of small scale gasification units integration with cogeneration systems. According to these two main aspects, the present work was thus divided in two main parts. The first one is focused on the biomass gasification process, that was investigated in its theoretical aspects and then analytically modelled in order to simulate thermo-chemical conversion of different biomass fuels, such as wood (park waste wood and softwood), wheat straw, sewage sludge and refuse derived fuels. The main idea is to correlate the results of reactor design procedures with the physical properties of biomasses and the corresponding working conditions of gasifiers (temperature profile, above all), in order to point out the main differences which prevent the use of the same conversion unit for different materials. At this scope, a gasification kinetic free model was initially developed in Excel sheets, considering different values of air to biomass ratio and the downdraft gasification technology as particular examined application. The differences in syngas production and working conditions (process temperatures, above all) among the considered fuels were tried to be connected to some biomass properties, such elementary composition, ash and water contents. The novelty of this analytical approach was the use of kinetic constants ratio in order to determine oxygen distribution among the different oxidation reactions (regarding volatile matter only) while equilibrium of water gas shift reaction was considered in gasification zone, by which the energy and mass balances involved in the process algorithm were linked together, as well. Moreover, the main advantage of this analytical tool is the easiness by which the input data corresponding to the particular biomass materials can be inserted into the model, so that a rapid evaluation on their own thermo-chemical conversion properties is possible to be obtained, mainly based on their chemical composition A good conformity of the model results with the other literature and experimental data was detected for almost all the considered materials (except for refuse derived fuels, because of their unfitting chemical composition with the model assumptions). Successively, a dimensioning procedure for open core downdraft gasifiers was set up, by the analysis on the fundamental thermo-physical and thermo-chemical mechanisms which are supposed to regulate the main solid conversion steps involved in the gasification process. Gasification units were schematically subdivided in four reaction zones, respectively corresponding to biomass heating, solids drying, pyrolysis and char gasification processes, and the time required for the full development of each of these steps was correlated to the kinetics rates (for pyrolysis and char gasification processes only) and to the heat and mass transfer phenomena from gas to solid phase. On the basis of this analysis and according to the kinetic free model results and biomass physical properties (particles size, above all) it was achieved that for all the considered materials char gasification step is kinetically limited and therefore temperature is the main working parameter controlling this step. Solids drying is mainly regulated by heat transfer from bulk gas to the inner layers of particles and the corresponding time especially depends on particle size. Biomass heating is almost totally achieved by the radiative heat transfer from the hot walls of reactor to the bed of material. For pyrolysis, instead, working temperature, particles size and the same nature of biomass (through its own pyrolysis heat) have all comparable weights on the process development, so that the corresponding time can be differently depending on one of these factors according to the particular fuel is gasified and the particular conditions are established inside the gasifier. The same analysis also led to the estimation of reaction zone volumes for each biomass fuel, so as a comparison among the dimensions of the differently fed gasification units was finally accomplished. Each biomass material showed a different volumes distribution, so that any dimensioned gasification unit does not seem to be suitable for more than one biomass species. Nevertheless, since reactors diameters were found out quite similar for all the examined materials, it could be envisaged to design a single units for all of them by adopting the largest diameter and by combining together the maximum heights of each reaction zone, as they were calculated for the different biomasses. A total height of gasifier as around 2400mm would be obtained in this case. Besides, by arranging air injecting nozzles at different levels along the reactor, gasification zone could be properly set up according to the particular material is in turn gasified. Finally, since gasification and pyrolysis times were found to considerably change according to even short temperature variations, it could be also envisaged to regulate air feeding rate for each gasified material (which process temperatures depend on), so as the available reactor volumes would be suitable for the complete development of solid conversion in each case, without even changing fluid dynamics behaviour of the unit as well as air/biomass ratio in noticeable measure. The second part of this work dealt with the gas cleaning systems to be adopted downstream the gasifiers in order to run high efficiency CHP units (i.e. internal engines and micro-turbines). Especially in the case multi–fuel gasifiers are assumed to be used, weightier gas cleaning lines need to be envisaged in order to reach the standard gas quality degree required to fuel cogeneration units. Indeed, as the more heterogeneous feed to the gasification unit, several contaminant species can simultaneously be present in the exit gas stream and, as a consequence, suitable gas cleaning systems have to be designed. In this work, an overall study on gas cleaning lines assessment is carried out. Differently from the other research efforts carried out in the same field, the main scope is to define general arrangements for gas cleaning lines suitable to remove several contaminants from the gas stream, independently on the feedstock material and the energy plant size The gas contaminant species taken into account in this analysis were: particulate, tars, sulphur (in H2S form), alkali metals, nitrogen (in NH3 form) and acid gases (in HCl form). For each of these species, alternative cleaning devices were designed according to three different plant sizes, respectively corresponding with 8Nm3/h, 125Nm3/h and 350Nm3/h gas flows. Their performances were examined on the basis of their optimal working conditions (efficiency, temperature and pressure drops, above all) and their own consumption of energy and materials. Successively, the designed units were combined together in different overall gas cleaning line arrangements, paths, by following some technical constraints which were mainly determined from the same performance analysis on the cleaning units and from the presumable synergic effects by contaminants on the right working of some of them (filters clogging, catalysts deactivation, etc.). One of the main issues to be stated in paths design accomplishment was the tars removal from the gas stream, preventing filters plugging and/or line pipes clogging At this scope, a catalytic tars cracking unit was envisaged as the only solution to be adopted, and, therefore, a catalytic material which is able to work at relatively low temperatures was chosen. Nevertheless, a rapid drop in tars cracking efficiency was also estimated for this same material, so that an high frequency of catalysts regeneration and a consequent relevant air consumption for this operation were calculated in all of the cases. Other difficulties had to be overcome in the abatement of alkali metals, which condense at temperatures lower than tars, but they also need to be removed in the first sections of gas cleaning line in order to avoid corrosion of materials. In this case a dry scrubber technology was envisaged, by using the same fine particles filter units and by choosing for them corrosion resistant materials, like ceramic ones. Besides these two solutions which seem to be unavoidable in gas cleaning line design, high temperature gas cleaning lines were not possible to be achieved for the two larger plant sizes, as well. Indeed, as the use of temperature control devices was precluded in the adopted design procedure, ammonia partial oxidation units (as the only considered methods for the abatement of ammonia at high temperature) were not suitable for the large scale units, because of the high increase of reactors temperature by the exothermic reactions involved in the process. In spite of these limitations, yet, overall arrangements for each considered plant size were finally designed, so that the possibility to clean the gas up to the required standard degree was technically demonstrated, even in the case several contaminants are simultaneously present in the gas stream. Moreover, all the possible paths defined for the different plant sizes were compared each others on the basis of some defined operational parameters, among which total pressure drops, total energy losses, number of units and secondary materials consumption. On the basis of this analysis, dry gas cleaning methods proved preferable to the ones including water scrubber technology in al of the cases, especially because of the high water consumption provided by water scrubber units in ammonia adsorption process. This result is yet connected to the possibility to use activated carbon units for ammonia removal and Nahcolite adsorber for chloride acid. The very high efficiency of this latter material is also remarkable. Finally, as an estimation of the overall energy loss pertaining the gas cleaning process, the total enthalpy losses estimated for the three plant sizes were compared with the respective gas streams energy contents, these latter obtained on the basis of low heating value of gas only. This overall study on gas cleaning systems is thus proposed as an analytical tool by which different gas cleaning line configurations can be evaluated, according to the particular practical application they are adopted for and the size of cogeneration unit they are connected to.

Constraints on mantle melting from major and trace element systematics in residual abyssal peridotites

ZusammenfassungDie Bildung von mittelozeanischen Rückenbasalten (MORB) ist einer der wichtigsten Stoffflüsse der Erde. Jährlich wird entlang der 75.000 km langen mittelozeanischen Rücken mehr als 20 km3 neue magmatische Kruste gebildet, das sind etwa 90 Prozent der globalen Magmenproduktion. Obwohl ozeanische Rücken und MORB zu den am meisten untersuchten geologischen Themenbereichen gehören, existieren weiterhin einige Streit-fragen. Zu den wichtigsten zählt die Rolle von geodynamischen Rahmenbedingungen, wie etwa Divergenzrate oder die Nähe zu Hotspots oder Transformstörungen, sowie der absolute Aufschmelzgrad, oder die Tiefe, in der die Aufschmelzung unter den Rücken beginnt. Diese Dissertation widmet sich diesen Themen auf der Basis von Haupt- und Spurenelementzusammensetzungen in Mineralen ozeanischer Mantelgesteine.Geochemische Charakteristika von MORB deuten darauf hin, dass der ozeanische Mantel im Stabilitätsfeld von Granatperidotit zu schmelzen beginnt. Neuere Experimente zeigen jedoch, dass die schweren Seltenerdelemente (SEE) kompatibel im Klinopyroxen (Cpx) sind. Aufgrund dieser granatähnlichen Eigenschaft von Cpx wird Granat nicht mehr zur Erklärung der MORB Daten benötigt, wodurch sich der Beginn der Aufschmelzung zu geringeren Drucken verschiebt. Aus diesem Grund ist es wichtig zu überprüfen, ob diese Hypothese mit Daten von abyssalen Peridotiten in Einklang zu bringen ist. Diese am Ozeanboden aufgeschlossenen Mantelfragmente stellen die Residuen des Aufschmelz-prozesses dar, und ihr Mineralchemismus enthält Information über die Bildungs-bedingungen der Magmen. Haupt- und Spurenelementzusammensetzungen von Peridotit-proben des Zentralindischen Rückens (CIR) wurden mit Mikrosonde und Ionensonde bestimmt, und mit veröffentlichten Daten verglichen. Cpx der CIR Peridotite weisen niedrige Verhältnisse von mittleren zu schweren SEE und hohe absolute Konzentrationen der schweren SEE auf. Aufschmelzmodelle eines Spinellperidotits unter Anwendung von üblichen, inkompatiblen Verteilungskoeffizienten (Kd's) können die gemessenen Fraktionierungen von mittleren zu schweren SEE nicht reproduzieren. Die Anwendung der neuen Kd's, die kompatibles Verhalten der schweren SEE im Cpx vorhersagen, ergibt zwar bessere Resultate, kann jedoch nicht die am stärksten fraktionierten Proben erklären. Darüber hinaus werden sehr hohe Aufschmelzgrade benötigt, was nicht mit Hauptelementdaten in Einklang zu bringen ist. Niedrige (~3-5%) Aufschmelzgrade im Stabilitätsfeld von Granatperidotit, gefolgt von weiterer Aufschmelzung von Spinellperidotit kann jedoch die Beobachtungen weitgehend erklären. Aus diesem Grund muss Granat weiterhin als wichtige Phase bei der Genese von MORB betrachtet werden (Kapitel 1).Eine weitere Hürde zum quantitativen Verständnis von Aufschmelzprozessen unter mittelozeanischen Rücken ist die fehlende Korrelation zwischen Haupt- und Spuren-elementen in residuellen abyssalen Peridotiten. Das Cr/(Cr+Al) Verhältnis (Cr#) in Spinell wird im Allgemeinen als guter qualitativer Indikator für den Aufschmelzgrad betrachtet. Die Mineralchemie der CIR Peridotite und publizierte Daten von anderen abyssalen Peridotiten zeigen, dass die schweren SEE sehr gut (r2 ~ 0.9) mit Cr# der koexistierenden Spinelle korreliert. Die Auswertung dieser Korrelation ergibt einen quantitativen Aufschmelz-indikator für Residuen, welcher auf dem Spinellchemismus basiert. Damit kann der Schmelzgrad als Funktion von Cr# in Spinell ausgedrückt werden: F = 0.10×ln(Cr#) + 0.24 (Hellebrand et al., Nature, in review; Kapitel 2). Die Anwendung dieses Indikators auf Mantelproben, für die keine Ionensondendaten verfügbar sind, ermöglicht es, geochemische und geophysikalischen Daten zu verbinden. Aus geodynamischer Perspektive ist der Gakkel Rücken im Arktischen Ozean von großer Bedeutung für das Verständnis von Aufschmelzprozessen, da er weltweit die niedrigste Divergenzrate aufweist und große Transformstörungen fehlen. Publizierte Basaltdaten deuten auf einen extrem niedrigen Aufschmelzgrad hin, was mit globalen Korrelationen im Einklang steht. Stark alterierte Mantelperidotite einer Lokalität entlang des kaum beprobten Gakkel Rückens wurden deshalb auf Primärminerale untersucht. Nur in einer Probe sind oxidierte Spinellpseudomorphosen mit Spuren primärer Spinelle erhalten geblieben. Ihre Cr# ist signifikant höher als die einiger Peridotite von schneller divergierenden Rücken und ihr Schmelzgrad ist damit höher als aufgrund der Basaltzusammensetzungen vermutet. Der unter Anwendung des oben erwähnten Indikators ermittelte Schmelzgrad ermöglicht die Berechnung der Krustenmächtigkeit am Gakkel Rücken. Diese ist wesentlich größer als die aus Schweredaten ermittelte Mächtigkeit, oder die aus der globalen Korrelation zwischen Divergenzrate und mittels Seismik erhaltene Krustendicke. Dieses unerwartete Ergebnis kann möglicherweise auf kompositionelle Heterogenitäten bei niedrigen Schmelzgraden, oder auf eine insgesamt größere Verarmung des Mantels unter dem Gakkel Rücken zurückgeführt werden (Hellebrand et al., Chem.Geol., in review; Kapitel 3).Zusätzliche Informationen zur Modellierung und Analytik sind im Anhang A-C aufgeführt