Momentum conservation and correlation analyses in heavy-ion collisions at ultrarelativistic energies

Global transverse-momentum conservation induces correlations between any number of particles, which contribute in particular to the two- and three-particle correlations measured in heavy-ion collisions. These correlations are examined in detail, and their importance for studies of jets and their interaction with the medium is discussed.Comment: 5 pages, 2 figures. v2: corrected typos and added a paragrap

Phase space constraints and statistical jet studies in heavy-ion collisions

The effect of the correlation induced by global momentum conservation on the two-particle distribution in nucleus-nucleus collisions is discussed, with a focus on the generic case of collisions with a non-vanishing impact parameter.Comment: 5 pages, invited talk at the RHIC & AGS Annual Users' Meeting, Brookhaven Nat. Lab. (USA) and at the EPS HEP 2007 Conference, Manchester (UK

Listening Effort During Sentence Processing Is Increased for Non-native Listeners: A Pupillometry Study

Current evidence demonstrates that even though some non-native listeners can achieve native-like performance for speech perception tasks in quiet, the presence of a background noise is much more detrimental to speech intelligibility for non-native compared to native listeners. Even when performance is equated across groups, it is likely that greater listening effort is required for non-native listeners. Importantly, the added listening effort might result in increased fatigue and a reduced ability to successfully perform multiple tasks simultaneously. Task-evoked pupil responses have been demonstrated to be a reliable measure of cognitive effort and can be useful in clarifying those aspects. In this study we compared the pupil response for 23 native English speakers and 27 Italian speakers of English as a second language. Speech intelligibility was tested for sentences presented in quiet and in background noise at two performance levels that were matched across groups. Signal-to-noise levels corresponding to these sentence intelligibility levels were pre-determined using an adaptive intelligibility task. Pupil response was significantly greater in non-native compared to native participants across both intelligibility levels. Therefore, for a given intelligibility level, a greater listening effort is required when listening in a second language in order to understand speech in noise. Results also confirmed that pupil response is sensitive to speech intelligibility during language comprehension, in line with previous research. However, contrary to our predictions, pupil response was not differentially modulated by intelligibility levels for native and non-native listeners. The present study corroborates that pupillometry can be deemed as a valid measure to be used in speech perception investigation, because it is sensitive to differences both across participants, such as listener type, and across conditions, such as variations in the level of speech intelligibility. Importantly, pupillometry offers us the possibility to uncover differences in listening effort even when those do not emerge in the performance level of individuals

Melting relations of anhydrous olivine-free pyroxenite Px1 at 2 GPa

The reaction between melt derived by mafic heterogeneities and peridotites in an upwelling mantle may form hybrid olivine-free pyroxenites. In order to evaluate the impact of these lithologies on the chemistry of primitive magmas and their ability to give rise to new mantle heterogeneities, we experimentally investigate the melting relations at 2 GPa of the model olivine-free pyroxenite Px1 (X-Mg = 0.81, SiO2 = 52.9 wt %, Al2O3 = 11.3 wt %, CaO = 7.6 wt %). The subsolidus assemblage consists of clinopyroxene, orthopyroxene, and garnet. At 2 GPa, the solidus of Px1 is located between 1250 and 1280 degrees C, at a temperature about 70 degrees C lower than the solidus of fertile lherzolite. At increasing melt fraction, the sequence of mineral phase disappearance is garnet-clinopyroxene-orthopyroxene. Across the solidus, partial melting of Px1 is controlled by reaction garnet + clinopyroxene = liquid + orthopyroxene, and above 1300 degrees C, once garnet is completely consumed, by reaction clinopyroxene + orthopyroxene = liquid. Orthopyroxene is the liquidus phase, and at 1480 degrees C olivine-free pyroxenite Px1 is completely molten indicating a melting interval of about 200 degrees C. Isobaric melt productivity is similar to garnet clinopyroxenites, and it is more than 3 times that of a fertile lherzolite at 1400 degrees C. Px1 partial melts cover a wide range of X-Mg (0.57-0.84), with SiO2, Al2O3 and Na2O decreasing and Cr2O3 increasing with the degree of melting. CaO content in partial melts increases as long as clinopyroxene is involved in melting reactions and decreases after its exhaustion. At 2 GPa and for melting degrees higher than 10 %, Px1 produces MgO-rich basaltic andesites matching the composition of eclogitic melts in terms of silica and alkali contents but with significantly higher X-Mg values. These melts differ from those derived from lherzolites at 2 GPa by higher SiO2 and lower CaO contents. Their high silica activity makes them very reactive with mantle peridotite producing hybrid orthopyroxene-rich lithologies and residual websterites. Melt-rock reactions likely prevent direct extraction of melts produced by olivine-free pyroxenites

H2O and Cl in deep crustal melts: the message of melt inclusions in metamorphic rocks

The use of NanoSIMS on primary melt inclusions in partially melted rocks is a powerful approach to clarify the budget of volatiles at depth during crust formation and its reworking. Anatectic melt inclusions are indeed gateways to quantify H2O, halogens and other species (e.g. CO2, N) partitioned into the deep partial melts generated during metamorphism of the continental crust. Here we present new datasets of NanoSIMS measurements of H2O and Cl in preserved melt inclusions from metamorphic rocks with different protoliths – magmatic or sedimentary – which underwent partial melting at different pressure–temperature–fluid conditions. These new datasets are then compared with similar data on natural anatectic melts available in the literature to date. Our study provides novel, precise constraints for the H2O content in natural melts formed at high pressure, a field previously investigated mostly via experiments. We also show that H2O heterogeneities in partial melts at the microscale are common, regardless of the rock protolith. Correlations between H2O contents and P–T values can be identified merging new and old data on anatectic inclusions via NanoSIMS. Overall, the data acquired so far indicate that silicate melt generation in nature always requires H2O, even for the hottest melts found so far (&gt;1000 ∘C). Moreover, in agreement with previous work, preserved glassy inclusions always appear to be poorer in H2O than crystallized ones, regardless of their chemical system and/or P–T conditions of formation. Finally, this study reports the very first NanoSIMS data on Cl (often in amounts &gt;1000 ppm) acquired in situ on natural anatectic melts, showing how anatectic melt inclusions – additionally to magmatic ones – may become a powerful tool to clarify the role of halogens in many geological processes, not only in crustal evolution but also in ore deposit formation.</p

the stability of plagioclase in the upper mantle subsolidus experiments on fertile and depleted lherzolite

Plagioclase peridotites are important markers of processes that characterize the petrological and tectonic evolution of the lithospheric mantle in extensional tectonic settings. Studies on equilibrated plagioclase peridotites have documented continuous chemical changes in mantle minerals in response to plagioclase crystallization, potentially tracing the re-equilibration of mantle peridotites up to very low pressure.This experimental study provides new constraints on the stability of plagioclase in mantle peridotites as a function of bulk composition, and the compositional and modal changes in minerals occurring within the plagioclase stability field as a function of P^T^bulk composition. Subsolidus experiments have been performed at pressures ranging from 0·25 to 1·0 GPa, and temperatures ranging from 900 to 12008C on fertile and depleted anhydrous lherzolites modelled in the system TiO2^Cr2O3^Na2O^CaO^FeO^ MgO^Al2O3^SiO2 (Ti,Cr-NCFMAS). In the fertile lherzolite (Na2O/CaO 1⁄4 0·08; XCr 1⁄4 0·07) a plagioclase-bearing assemblage is stable up to 0·7 GPa, 10008C and 0·8 GPa, 11008C, whereas in the depleted lherzolite (Na2O/CaO 1⁄4 0·09; XCr 1⁄4 0·10) the upper limit of plagioclase stability is shifted to lower pressure.The boundary between plagioclase lherzolite and spinel lherzolite has a positive slope in P^T space. In a complex chemical system, the plagioclase-out boundary is multivariant and sensitive to the XCr value [XCr 1⁄4 Cr/(Cr þAl)] of spinel.This latter is controlled by the reaction MgCr2O4 þ CaAl2Si2O8 1⁄4 MgCrAlSiO6 þ CaCrAlSiO6, which is a function of the Cr^Al partitioning between spinel and pyroxenes, and varies with the XCr value and chromite/ anorthite normative ratio of the bulk composition. Within the plagioclase stability field, the Al content of pyroxenes decreases, coupled with an increase in the anorthite content in plagioclase, and Ti and XCr in spinel with decreasing pressure; these chemical variations are combined with systematic changes in modal mineralogy governed by a continuous reaction involving both plagioclase and spinel. As a consequence, the composition of plagioclase varies significantly over a rather narrow pressure range and is similar at the same P^T conditions in the investigated bulk-rocks.This suggests the potential application of plagioclase composition as a geobarometer for plagioclase peridotites

Factors affecting the quality of XBT data - results of analyses on profiles from the Western Mediterranean Sea

EXpendable BathyThermograph (XBT) temperature profiles collected in the framework of the Mediterranean Forecasting System - Toward Environmental Prediction (MFS-TEP) project have been compared with CTD measurements. New procedures for the quality control of recorded values have been developed and checked. Some sources of possible uncertainties and errors, such as the response time of the apparatus (XBT probe, thermistor and readout chain), or the influence of initial conditions are also analysed. To deal with the high homogeneity of Mediterranean waters, a new technique to compute the fall rate coefficients, that give a better reproduction of the depth of thermal structures, has been proposed, and new customized coefficients have been calculated. After the application of a temperature correction, the overall uncertainties in depth and in temperature measurements have been estimated

Improved quality check procedures of XBT profiles in MFS-VOS

International audienceSippican T4/DB XBT profiles, collected in the framework of Mediterranean Forecasting System ? Toward Environmental Prediction, are analysed, namely the possible influence of launching position height, ship speed and of probes' characteristics. Comparison of XBT vs CTD profiles have suggested some changes in quality control procedures and, more important, in the values of fall rate coefficients customised for the Mediterranean. The effects of these new procedures on the overall uncertainty on depth and on temperature measurements are estimated

Relationships and events: towards a general theory of reification and truthmaking.

We propose a novel ontological analysis of relations and relationships based on a re-visitation of a classic problem in the practice of knowledge repre- sentation and conceptual modeling, namely relationship reification. Our idea is that a relation holds in virtue of a relationship's existence. Relationships are therefore truthmakers of relations. In this paper we present a general theory or reification and truthmaking, and discuss the interplay between events and rela- tionships, suggesting that relationships are the focus of events, which emerge from the context (the scene) they occur in

Origin of pyroxenites in the oceanic mantle and their implications on the reactive percolation of depleted melts

Pyroxenites are diffuse in fertile mantle peridotites and considered an important component in the mantle source of oceanic basalts. They are rarely documented in abyssal and ophiolitic peridotites representing residual mantle after melt generation, and few studies defining their origin are to date available. We present a field-based microstructural and geochemical investigation of the pyroxenite layers associated with depleted peridotites from the Mt. Maggiore ophiolitic body (Corsica, France). Field and petrographic evidence indicate that pyroxenite formation preceded the melt\u2013rock interaction history that affected this mantle sector during Jurassic exhumation, namely (1) spinel-facies reactive porous flow leading to partial dissolution of the pyroxenites, and (2) plagioclase-facies melt impregnation leading to [plagioclase + orthopyroxene] interstitial crystallization. Pyroxenes show major element compositions similar to abyssal pyroxenites from slow-spreading ridges, indicative of magmatic segregation at pressures higher than 7 kbar. Both the parental melts of pyroxenites and the melts involved in the subsequent percolation were characterized by Na2O-poor, LREE-depleted compositions, consistent with unaggregated melt increments. This implies that they represent the continuous evolution of similarly depleted melts leading to different processes (pyroxenite segregation and later melt\u2013rock interaction) during their upward migration. To support the genetic relation and the continuity between the formation of pyroxenites and the subsequent melt\u2013rock interaction history, we modeled all the documented processes in sequence, i.e.: (1) formation of single-melt increments after 6% mantle decompressional fractional melting; (2) high-pressure segregation of pyroxenites; (3) spinel-facies reactive porous flow, (4) plagioclase-facies melt impregnation. The early fractionation of pyroxenites leads to a decrease in pyroxene saturation that is necessary for the subsequent reactive porous flow process, without any significant change in the melt REE composition