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New Constraints (new + constraint)
Selected AbstractsNeoproterozoic Tectonic Setting of Southeast China: New Constraints from SHRIMP U-Pb Zircon Ages and Petrographic Studies on the Mamianshan GroupACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2010Ganguo WU Abstract: Precambrian tectonic history of Zhejiang, Fujian, and Jiangxi provinces of south China is important for understanding the tectonic evolution of South China but its magmatic activity, petrogenesis, stratigraphic sequence of the Mamianshan Group is still strongly controversial. Here we present new sensitive high resolution ion micro-probe (SHRIMP) U-Pb zircon geochronological data for the Mamianshan Group and petrographical data to constrain the tectonic framework of the regions. Our results showed that the SHRIMP U-Pb zircon age of green schists of the Dongyan Formation is 796.544.3 Ma, the Daling Formation is 756.2±7.2 Ma, and mica-quartz schist of the Longbeixi Formation is 825.5±9.8 Ma. These data indicate that the Mamianshan Group was formed not in the Mesoproterozoic, but in the Neoproterozoic and its stratigraphic sequences should be composed of Longbeixi, Dongyan, and Daling Formations from the bottom to the top. Rocks from this Group, from Zhejiang, Fujian and Jiangxi provinces, constituted the upper basement of the Cathaysia Block that overlay the lower basement of the Mayuan Group. Detailed petrographic studies demonstrate that the amphibole schists of the Dongyan Formation in the Mamianshan Group were formed within an intra-arc rift setting rather than a continental rift as previously suggested. Rather, this island-arc type formation was developed by collision and/or subduction between various blocks resulting from the breakup of the supercontinent Rodinia at c.850,750 Ma. The Zhuzhou conglomerate, distributed near Dikou Town, Jian'ou City, Fujian Province and previously considered as evidence of the Mesoproterozoic Dikou movement, is shown here not to be the basal conglomerate above the angular unconformity between the upper and lower basements. Our conclusions have important implications for understanding the Precambrian tectonics of South China. [source] The P,T path of the ultra-high pressure Lago Di Cignana and adjoining high-pressure meta-ophiolitic units: insights into the evolution of the subducting Tethyan slabJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2009C. GROPPO Abstract The Lago di Cignana ultra-high-pressure unit (LCU), which consists of coesite,eclogite facies metabasics and metasediments, preserves the most deeply subducted oceanic rocks worldwide. New constraints on the prograde and early retrograde evolution of this ultra-high pressure unit and adjoining units provide important insights into the evolution of the Piemontese,Ligurian palaeo-subduction zone, active in Paleocene,Eocene times. In the LCU, a first prograde metamorphic assemblage, consisting of omphacite + Ca-amphibole + epidote + rare biotite + ilmenite, formed during burial at estimated P < 1.7 GPa and 350 < T < 480 °C. Similar metamorphic conditions of 400 < T < 650 °C and 1.0 < P < 1.7 GPa have been estimated for the meta-ophiolitic rocks juxtaposed to the LCU. The prograde assemblage is partially re-equilibrated into the peak assemblage garnet + omphacite + Na-amphibole + lawsonite + coesite + rutile, whose conditions were estimated at 590 < T < 605 °C and P > 3.2 GPa. The prograde path was characterized by a gradual decrease in the thermal gradient from ,9,10 to ,5,6 °C km,1. This variation is interpreted as the evidence of an increase in the rate of subduction of the Piemonte,Ligurian oceanic slab in the Eocene. Accretion of the Piemontese oceanic rocks to the Alpine orogen and thermal relaxation were probably related to the arrival of more buoyant continental crust at the subduction zone. Subsequent deformation of the orogenic wedge is responsible for the present position of the LCU, sandwiched between two tectonic slices of meta-ophiolites, named the Lower and Upper Units, which experienced peak pressures of 2.7,2.8 and <2.4 GPa respectively. [source] Formation of TiC core-graphitic mantle grains from CO gasMETEORITICS & PLANETARY SCIENCE, Issue 5 2006Yuki KIMURA 1996). Carbonaceous materials can be formed from C2H2 and its derivatives, as well as from CO gas. In this paper, we will demonstrate that large-cage-structure carbon particles can be produced from CO gas by the Boudouard reaction. Since the sublimation temperature for such fullerenes is low, the large cages can be deposited onto previously nucleated TiC and produce TiC core-graphitic mantle spherules. New constraints for the formation conditions and the time scale for the formation of TiC core-graphitic mantle spherules are suggested by the results of this study. In particular, TiC core-graphitic mantle grains that are found in primitive meteorites that have never experienced hydration could be mantled by fullerenes or carbon nanotubes rather than by graphite. In situ observations of these grains in primitive anhydrous meteoritic matrix could confirm or refute this prediction and would demonstrate that the graphitic mantle on such grains is a metamorphic feature due to interaction of the presolar fullerenes with water within the meteorite matrix. [source] New constraints from the H, line for the temperature of the transiting planet host star OGLE-TR-10,ASTRONOMISCHE NACHRICHTEN, Issue 6 2008M. Ammler-von Eiff Abstract The spectroscopic analysis of systems with transiting planets gives strong constraints on planetary masses and radii as well as the chemical composition of the systems. The properties of the system OGLE-TR-10 are not well-constrained, partly due to the discrepancy of previous measurements of the effective temperature of the host star. This work, which is fully independent from previous works in terms of data reduction and analysis, uses the H, profile in order to get an additional constraint on the effective temperature. We take previously published UVES observations which have the highest available signal-to-noise ratio for OGLE-TR-10. A proper normalization to the relative continuum is done using intermediate data products of the reduction pipeline of the UVES spectrograph. The effective temperature then is determined by fitting synthetic H, profiles to the observed spectrum. With a result of Teff = 6020 ± 140 K, the H, profile clearly favours one of the previous measurements. The H, line is further consistent with dwarf-like surface gravities as well as solar and super-solar metallicities previously derived for OGLE-TR-10. The H, line could not be used to its full potential, partly because of the varying shape of the UVES échelle orders after flat field correction. We suggest to improve this feature when constructing future spectrographs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A new path-following constraint for strain-softening finite element simulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2004E. Lorentz Abstract The application of strain-softening constitutive relations to model the failure modes of real-life structures is faced to numerical difficulties related to instabilities that appear as sharp snap-backs of the structural response. A path-following method has to complement the solution algorithm to achieve convergence despite these critical points. Because of the sharpness of the snap-backs, it is believed essential that the path-following constraint distinguish between a purely elastic unloading and a dissipative path. For that purpose, a new constraint based on the maximal value of the elastic predictor for the yield function is proposed. As it is highly non linear, a specific solution algorithm is required. The robustness of this constraint is illustrated by three applications: the study of crack propagations by means of a cohesive zone model, the failure of a structure submitted to nonlocal damage and the simulation of a nonlocal strain-softening plastic specimen. Copyright © 2004 John Wiley & Sons, Ltd. [source] Mating triggers dynamic immune regulations in wood ant queensJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2009G. CASTELLA Abstract Mating can affect female immunity in multiple ways. On the one hand, the immune system may be activated by pathogens transmitted during mating, sperm and seminal proteins, or wounds inflicted by males. On the other hand, immune defences may also be down-regulated to reallocate resources to reproduction. Ants are interesting models to study post-mating immune regulation because queens mate early in life, store sperm for many years, and use it until their death many years later, while males typically die after mating. This long-term commitment between queens and their mates limits the opportunity for sexual conflict but raises the new constraint of long-term sperm survival. In this study, we examine experimentally the effect of mating on immunity in wood ant queens. Specifically, we compared the phenoloxidase and antibacterial activities of mated and virgin Formica paralugubris queens. Queens had reduced levels of active phenoloxidase after mating, but elevated antibacterial activity 7 days after mating. These results indicate that the process of mating, dealation and ovary activation triggers dynamic patterns of immune regulation in ant queens that probably reflect functional responses to mating and pathogen exposure that are independent of sexual conflict. [source] Cross-spectral analysis of the X-ray variability of Markarian 421MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002Y. H. Zhang ABSTRACT Using the cross-spectral method, we confirm the existence of the X-ray hard lags discovered with cross-correlation function technique during a large flare of Mrk 421 observed with BeppoSAX. For the 0.1,2 versus 2,10 keV light curves, both methods suggest sub-hour hard lags. In the time domain, the degree of hard lag, i.e. the amplitude of the 3.2,10 keV photons lagging the lower energy ones, tends to increase with the decreasing energy. In the Fourier frequency domain, by investigating the cross-spectra of the 0.1,2/2,10 keV and the 2,3.2/3.2,10 keV pairs of light curves, the flare also shows hard lags at the lowest frequencies. However, with the present data, it is impossible to constrain the dependence of the lags on frequencies even though the detailed simulations demonstrate that the hard lags at the lowest frequencies probed by the flare are not an artefact of sparse sampling, Poisson and red noise. As a possible interpretation, the implication of the hard lags is discussed in the context of the interplay between the (diffusive) acceleration and synchrotron cooling of relativistic electrons responsible for the observed X-ray emission. The energy-dependent hard lags are in agreement with the expectation of an energy-dependent acceleration time-scale. The inferred magnetic field (B, 0.11 G) is consistent with the value inferred from the spectral energy distributions of the source. Future investigations with higher quality data that show whether or not the time-lags are energy-/frequency-dependent will provide a new constraint on the current models of the TeV blazars. [source] Delta Scuti Network observations of XX Pyx: detection of 22 pulsation modes and of short-term amplitude and frequency variationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000G. Handler We report multisite observations devoted to the main-sequence , Scuti star XX Pyx, conducted as the 17th run of the Delta Scuti Network. Over 125 nights a total of 550 h of usable time-series photometric B - and V -filter data were acquired involving both photoelectric and CCD measurements at eight observatories spread around the world, which represents the most extensive single time-series for any pulsating star other than the Sun obtained so far. We describe our observations and reduction methods, and present the frequency analysis of our new data. First, we detect six new pulsation and five new combination frequencies in the star's light curves. We also discover evidence for amplitude and/or frequency variations of some of the modes during the observations. These can occur on time-scales as short as 20 d and show quite diverse behaviour. To take them into account in the frequency analysis, a so-called non-linear frequency analysis method was developed, allowing us to quantify the temporal variability of the modes and to compensate for it. Following that we continue the frequency search and we also incorporate published multisite observations. In this way, we reveal three more pulsation and two more combination frequencies. In the end, we report a total of 30 significant frequencies , 22 of which correspond to independent pulsation modes. This is the largest number of independent modes ever detected in the light curves of a , Scuti star. The frequencies of the modes show preferred separations as already suggested by previous work on this star; they are also arranged in clear patterns. These results lead to a refinement of the stellar mean density and to a new constraint on the rotation rate of XX Pyx (,rot=1.1±0.3 d,1). However, our attempts to identify the modes by pattern recognition failed. Moreover, mode identification from multicolour photometry failed as well because the high pulsation frequencies make this method unfavourable. The diverse behaviour of the amplitude and frequency variations of some of the modes leaves resonances as the only presently known possibility for their explanation. [source] Dieback due to Lasiodiplodia theobromae, a new constraint to cocoa production in CameroonPLANT PATHOLOGY, Issue 2 2008M. Mbenoun No abstract is available for this article. [source] Ironies in Human Rights Protection in the EU: Pre-Accession Conditionality and Post-Accession ConundrumsEUROPEAN LAW JOURNAL, Issue 1 2009Anneli Albi In the wake of the extensive scrutiny of the human rights credentials of the new Member States under the EU pre-accession conditionality, which itself was riddled with paradoxes, this article considers a rather unexpected irony thrown up by the accession of these countries. It is that the post-communist constitutional courts, which have been applauded for vigorous protection of fundamental rights after the fall of the Communist regime that was marked by nihilism to rights, have come rather close to having to downgrade the protection standards after accession, due to the new constraints of supremacy of EC law. The article will consider the sugar market cases of the Hungarian and Czech Constitutional Courts and of the Estonian Supreme Court, which appear to add weight to the concerns that have been voiced in some older Member States about the fundamental rights protection in the EU. Indeed such concerns were recently also addressed in the concurring opinions to the Bosphorus judgment of the European Court of Human Rights. [source] A Pragmatic Response to an Unexpected Constraint: Problem Representation in a Complex Humanitarian EmergencyFOREIGN POLICY ANALYSIS, Issue 2 2009Thomas Knecht This paper elaborates a model of problem representation first presented by Billings and Hermann (1998). The foreign policy process begins when decision-makers specify policy goals and identify relevant constraints in response to a perceived problem. Although this initial problem representation often sets the course for subsequent policy, unanticipated constraints can arise that catch decision makers off-guard. Finding themselves in a context they did not anticipate to be in, decision makers may choose to alter their representation of the problem and/or change the course of policy. Billings and Hermann offer one piece of this puzzle by examining how decision makers re-represent problems; this paper provides the second piece by assessing how policies, not representations, change in response to new constraints. A case study of the U.S. response to the Ethiopian famine in the mid 1980s demonstrates that policy does not always follow problem representation. [source] A new policy-aware terminal for QoS, AAA and mobility managementINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 2 2004Hakima Chaouchi Policy-based management has been widely studied in recent years. The Internet Engineering Task Force (IETF) has recently introduced the policy-based networking as a means of managing IP networks according to the new constraints defined in the network, such as the guarantee of the quality of service (QoS). Network management based on policies, is modelled as a state machine, which moves from one state to another according to the enforced policy. The IETF policy-based networking is defined for application to network nodes. However, some recent work suggests extending the policy-based networking to the end-user terminals. In this paper, we present an analysis of such an extension and we propose some possible solutions to support new policy-aware terminals. In addition, we present AAA, QoS and mobility management that user such a policy-aware terminals.,Copyright © 2004 John Wiley & Sons, Ltd. [source] Reaction-induced nucleation and growth v. grain coarsening in contact metamorphic, impure carbonatesJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2010A. BERGER Abstract The understanding of the evolution of microstructures in a metamorphic rock requires insights into the nucleation and growth history of individual grains, as well as the coarsening processes of the entire aggregate. These two processes are compared in impure carbonates from the contact metamorphic aureole of the Adamello pluton (N-Italy). As a function of increasing distance from the pluton contact, the investigated samples have peak metamorphic temperatures ranging from the stability field of diopside/tremolite down to diagenetic conditions. All samples consist of calcite as the dominant matrix phase, but additionally contain variable amounts of other minerals, the so-called second phases. These second phases are mostly silicate minerals and can be described in a KCMASHC system (K2O, CaO, MgO, Al2O3, SiO2, H2O, CO2), but with variable K/Mg ratios. The modelled and observed metamorphic evolution of these samples are combined with the quantification of the microstructures, i.e. mean grain sizes and crystal size distributions. Growth of the matrix phase and second phases strongly depends on each other owing to coupled grain coarsening. The matrix phase is controlled by the interparticle distances between the second phases, while the second phases need the matrix grain boundary network for mass transfer processes during both grain coarsening and mineral reactions. Interestingly, similar final mean grain sizes of primary second phase and second phases newly formed by nucleation are observed, although the latter formed later but at higher temperatures. Moreover, different kinetic processes, attributed to different driving forces for growth of the newly nucleated grains in comparison with coarsening processes of the pre-existing phases, must have been involved. Chemically induced driving forces of grain growth during reactions are orders of magnitudes larger compared to surface energy, allowing new reaction products subjected to fast growth rates to attain similar grain sizes as phases which underwent long-term grain coarsening. In contrast, observed variations in grain size of the same mineral in samples with a similar T,t history indicate that transport properties depend not only on the growth and coarsening kinetics of the second phases but also on the microstructure of the dominant matrix phase during coupled grain coarsening. Resulting microstructural phenomena such as overgrowth and therefore preservation of former stable minerals by the matrix phase may provide new constraints on the temporal variation of microstructures and provide a unique source for the interpretation of the evolution of metamorphic microstructures. [source] Exhumation rates and age of metamorphism in the Sanbagawa belt: new constraints from zircon fission track analysisJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2004S. Wallis Abstract Zircon fission track dating and track length analysis in the high-grade part of the Asemigawa region of the Sanbagawa belt demonstrates a simple cooling history passing through the partial annealing zone at 63.2 ± 5.8 (2 ,) Ma. Combining this age with previous results of phengite and amphibole K,Ar and 40Ar/39Ar dating gives a cooling rate of between 6 and 13 °C Myr,1, which can be converted to a maximum exhumation rate of 0.7 mm year,1 using the known shape of the P,T path. This is an order of magnitude lower than the early part of the exhumation history. In contrast, zircon fission track analyses in the low-grade Oboke region show that this area has undergone a complex thermal history probably related to post-orogenic secondary reheating younger than c. 30 Ma. This event may correlate with the widespread igneous activity in south-west Japan around 15 Ma. The age of subduction-related metamorphism in the Oboke area is probably considerably older than the generally accepted range of 77,70 Ma. [source] The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O,FeO,MgO,Al2O3,SiO2,H2O,TiO2,Fe2O3JOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2000White Mineral equilibria calculations in the system K2O,FeO,MgO,Al2O3,SiO2,H2O,TiO2,Fe2O3 (KFMASHTO) using thermocalc and its internally consistent thermodynamic dataset constrain the effect of TiO2 and Fe2O3 on greenschist and amphibolite facies mineral equilibria in metapelites. The end-member data and activity,composition relationships for biotite and chloritoid, calibrated with natural rock data, and activity,composition data for garnet, calibrated using experimental data, provide new constraints on the effects of TiO2 and Fe2O3 on the stability of these minerals. Thermodynamic models for ilmenite,hematite and magnetite,ulvospinel solid solutions accounting for order,disorder in these phases allow the distribution of TiO2 and Fe2O3 between oxide minerals and silicate minerals to be calculated. The calculations indicate that small to moderate amounts of TiO2 and Fe2O3 in typical metapelitic bulk compositions have little effect on silicate mineral equilibria in metapelites at greenschist to amphibolite facies, compared with those calculated in KFMASH. The addition of large amounts of TiO2 to typical pelitic bulk compositions has little effect on the stability of silicate assemblages; in contrast, rocks rich in Fe2O3 develop a markedly different metamorphic succession from that of common Barrovian sequences. In particular, Fe2O3 -rich metapelites show a marked reduction in the stability fields of staurolite and garnet to higher pressures, in comparison to those predicted by KFMASH grids. [source] Constraining dark energy with X-ray galaxy clusters, supernovae and the cosmic microwave backgroundMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005David Rapetti ABSTRACT We present new constraints on the evolution of dark energy from an analysis of cosmic microwave background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state w0, the early-time equation of state wet, and the scalefactor at transition at. From a combined analysis of all three data sets, assuming a constant equation of state and that the Universe is flat, we measure w0=,1.05+0.10,0.12. Including wet as a free parameter and allowing the transition scalefactor to vary over the range 0.5 < at < 0.95 where the data sets have discriminating power, we measure w0=,1.27+0.33,0.39 and wet=,0.66+0.44,0.62. We find no significant evidence for evolution in the dark energy equation-of-state parameter with redshift. Marginal hints of evolution in the supernovae data become less significant when the cluster constraints are also included in the analysis. The complementary nature of the data sets leads to a tight constraint on the mean matter density ,m and alleviates a number of other parameter degeneracies, including that between the scalar spectral index ns, the physical baryon density ,bh2 and the optical depth ,. This complementary nature also allows us to examine models in which we drop the prior on the curvature. For non-flat models with a constant equation of state, we measure w0=,1.09+0.12,0.15 and obtain a tight constraint on the current dark energy density ,de= 0.70 ± 0.03. For dark energy models other than a cosmological constant, energy,momentum conservation requires the inclusion of spatial perturbations in the dark energy component. Our analysis includes such perturbations, assuming a sound speed c2s= 1 in the dark energy fluid as expected for quintessence scenarios. For our most general dark energy model, not including such perturbations would lead to spurious constraints on wet, which would be tighter than those mentioned above by approximately a factor of 2 with the current data. [source] Setting new constraints on the age of the UniverseMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001Ignacio Ferreras There are three independent techniques for determining the age of the Universe: via cosmochronology of long-lived radioactive nuclei, via stellar modelling and population synthesis of the oldest stellar populations, and, most recently, via the precision cosmology that has become feasible with the mapping of the acoustic peaks in the cosmic microwave background. We demonstrate that all three methods give completely consistent results, and enable us to set rigorous bounds on the maximum and minimum ages that are allowed for the Universe. We present new constraints on the age of the Universe by performing a multiband colour analysis of bright cluster ellipticals over a large redshift range , which allows us to infer the ages of their stellar populations over a wide range of possible formation redshifts and metallicities. Applying a prior to Hubble's constant of we find the age of the Universe to be (1,), in agreement with the estimates from Type Ia supernovae, as well as with the latest uranium decay estimates, which yield an age for the Milky Way of . If we combine the results from cluster ellipticals with the analysis of the angular power spectrum of the cosmic microwave background and with the observations of Type Ia supernovae at high redshift, we find a similar age: . Without the assumption of any priors, universes older than 18 Gyr are ruled out by the data at the 90 per cent confidence level. [source] Adversarialism versus legalism: Juridification and litigation in corporate governance reformREGULATION & GOVERNANCE, Issue 3 2009John W. Cioffi Abstract Recent reforms of corporate governance law and related litigation rules in the US and in Germany indicate that reports of the spread of adversarial legalism are greatly exaggerated. Politics and legislation in the US since the mid-1990s have turned quite decisively against shareholder litigation even as corporate governance and securities law reforms have expanded the role and scope of the regulatory state. Germany's extraordinary expansion of financial and corporate governance regulation since the early 1990s exemplifies juridification. Although these reforms included some liberalization of shareholder litigation rules, the changes reflected skepticism towards private litigation and imposed new constraints on the most prevalent forms of shareholder suits. Marketization of economic relations and the era of finance capitalism have produced far more legalism than adversarialism, more regulation than judicialization, and more ex ante transparency rules than ex post litigation remedies. [source] Ageing in granular aluminium insulating thin filmsANNALEN DER PHYSIK, Issue 12 2009J. Delahaye Abstract We present a new set of electrical field effect measurements on granular aluminium insulating thin films. We have explored how the conductance relaxations induced by gate voltage changes depend on the age of the system, namely the time elapsed since its quench at low temperature. A clear age dependence of the relaxations is seen, qualitatively similar to ageing effects seen in other well studied glassy systems such as spin glasses or polymers. We explain how our results differ from the previous ones obtained with different protocols in indium oxide and granular aluminium thin films. Our experimental findings bring new information on the dynamics of the system and put new constraints on the theoretical models that may explain slow conductance relaxations in disordered insulators. [source] Importance of predecessor basin history on sedimentary fill of a retroarc foreland basin: provenance analysis of the Cretaceous Magallanes basin, Chile (50,52°S)BASIN RESEARCH, Issue 5 2010B. W. Romans ABSTRACT An integrated provenance analysis of the Upper Cretaceous Magallanes retroarc foreland basin of southern Chile (50°30,,52°S) provides new constraints on source area evolution, regional patterns of sediment dispersal and depositional age. Over 450 new single-grain detrital-zircon U-Pb ages, which are integrated with sandstone petrographic and mudstone geochemical data, provide a comprehensive detrital record of the northern Magallanes foreland basin-filling succession (>4000-m-thick). Prominent peaks in detrital-zircon age distribution among the Punta Barrosa, Cerro Toro, Tres Pasos and Dorotea Formations indicate that the incorporation and exhumation of Upper Jurassic igneous rocks (ca. 147,155 Ma) into the Andean fold-thrust belt was established in the Santonian (ca. 85 Ma) and was a significant source of detritus to the basin by the Maastrichtian (ca. 70 Ma). Sandstone compositional trends indicate an increase in volcanic and volcaniclastic grains upward through the basin fill corroborating the interpretation of an unroofing sequence. Detrital-zircon ages indicate that the Magallanes foredeep received young arc-derived detritus throughout its ca. 20 m.y. filling history, constraining the timing of basin-filling phases previously based only on biostratigraphy. Additionally, spatial patterns of detrital-zircon ages in the Tres Pasos and Dorotea Formations support interpretations that they are genetically linked depositional systems, thus demonstrating the utility of provenance indicators for evaluating stratigraphic relationships of diachronous lithostratigraphic units. This integrated provenance dataset highlights how the sedimentary fill of the Magallanes basin is unique among other retroarc foreland basins and from the well-studied Andean foreland basins farther north, which is attributed to nature of the predecessor rift and backarc basin. [source] Direct Associations or Internal Transformations?COGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 1 2010Exploring the Mechanisms Underlying Sequential Learning Behavior Abstract We evaluate two broad classes of cognitive mechanisms that might support the learning of sequential patterns. According to the first, learning is based on the gradual accumulation of direct associations between events based on simple conditioning principles. The other view describes learning as the process of inducing the transformational structure that defines the material. Each of these learning mechanisms predicts differences in the rate of acquisition for differently organized sequences. Across a set of empirical studies, we compare the predictions of each class of model with the behavior of human subjects. We find that learning mechanisms based on transformations of an internal state, such as recurrent network architectures (e.g., Elman, 1990), have difficulty accounting for the pattern of human results relative to a simpler (but more limited) learning mechanism based on learning direct associations. Our results suggest new constraints on the cognitive mechanisms supporting sequential learning behavior. [source] | ||||||||||||||||||||||