344 research outputs found
Competing tunneling trajectories in a 2D potential with variable topology as a model for quantum bifurcations
We present a path - integral approach to treat a 2D model of a quantum
bifurcation. The model potential has two equivalent minima separated by one or
two saddle points, depending on the value of a continuous parameter. Tunneling
is therefore realized either along one trajectory or along two equivalent
paths. Zero point fluctuations smear out the sharp transition between these two
regimes and lead to a certain crossover behavior. When the two saddle points
are inequivalent one can also have a first order transition related to the fact
that one of the two trajectories becomes unstable. We illustrate these results
by numerical investigations. Even though a specific model is investigated here,
the approach is quite general and has potential applicability for various
systems in physics and chemistry exhibiting multi-stability and tunneling
phenomena.Comment: 11 pages, 8 eps figures, Revtex-
Subduction metamorphism of serpentiniteāhosted carbonates beyond antigorite-serpentinite dehydration (NevadoāFilĆ”bride Complex, Spain)
I. MartĆnez Segura and M. J. RomĆ”n Alpiste are thanked for their kind assistance during sample preparation and SEM operation, and M. T. GĆ³mezāPugnaire and A. Jabaloy for early work on Almirez ophicarbonates. We are grateful to the Sierra Nevada National Park for providing permits for fieldwork and sampling at the Almirez massif. We further acknowledge the editorial handling by D. Whitney and D. Robinson and the reviews of M. Galvez and T. Pettke, whose comments and constructive criticism helped to improve the manuscript.
We acknowledge funding from the European Union FP7 MarieāCurie Initial Training Network ABYSS under REA Grant Agreement no. 608001 in the framework of M.D.M.'s PhD project, the Spanish āAgencia Estatal de InvestigaciĆ³nā (AEI) grants no. CGL2016ā75224āR to V.L.S.āV and CGL2016ā81085āR to C.J.G and C.M and grant no. PCINā2015ā053 to C.J.G. The āJunta de AndalucĆaā is also thanked for funding under grants no. RNMā131, RNMā374 and P12āRNMā3141. C.M. thanks MINECO for financing a RamĆ³n y Cajal fellowship no. RYCā2012ā11314 and K.H. for a Juan de la Cierva Fellowship no. FPDIā2013ā16253 and a research contract under grant no. CGL2016ā81085āR. This work and the research infrastructure at the IACT have received (co)funding from the European Social Fund and the European Regional Development Fund.At subāarc depths, the release of carbon from subducting slab lithologies is mostly
controlled by fluid released by devolatilization reactions such as dehydration of antigorite (Atgā) serpentinite to prograde peridotite. Here we investigate carbonateāsilicate rocks hosted in Atgāserpentinite and prograde chlorite (Chlā) harzburgite in the
Milagrosa and Almirez ultramafic massifs of the palaeoāsubducted NevadoāFilĆ”bride
Complex (NFC, Betic Cordillera, S. Spain). These massifs provide a unique opportunity to study the stability of carbonate during subduction metamorphism at PāT
conditions before and after the dehydration of Atgāserpentinite in a warm subduction
setting. In the Milagrosa massif, carbonateāsilicate rocks occur as lenses of Tiāclinohumiteādiopsideācalcite marbles, diopsideādolomite marbles and antigoriteādiopsideādolomite rocks hosted in clinopyroxeneābearing Atgāserpentinite. In Almirez,
carbonateāsilicate rocks are hosted in Chlāharzburgite and show a highāgrade assemblage composed of olivine, Tiāclinohumite, diopside, chlorite, dolomite, calcite, Crā
bearing magnetite, pentlandite and rare aragonite inclusions. These NFC
carbonateāsilicate rocks have variable CaO and CO2 contents at nearly constant Mg/
Si ratio and high Ni and Cr contents, indicating that their protoliths were variable
mixtures of serpentine and Caācarbonate (i.e., ophicarbonates). Thermodynamic
modelling shows that the carbonateāsilicate rocks attained peak metamorphic conditions similar to those of their host serpentinite (Milagrosa massif; 550ā600Ā°C and
1.0ā1.4 GPa) and Chlāharzburgite (Almirez massif; 1.7ā1.9 GPa and 680Ā°C).
Microstructures, mineral chemistry and phase relations indicate that the hybrid carbonateāsilicate bulk rock compositions formed before prograde metamorphism,
likely during seawater hydrothermal alteration, and subsequently underwent subduction metamorphism. In the CaOāMgOāSiO2 ternary, these processes resulted in a
compositional variability of NFC serpentiniteāhosted carbonateāsilicate rocks along
the serpentineācalcite mixing trend, similar to that observed in serpentiniteāhosted
carbonateārocks in other palaeoāsubducted metamorphic terranes. Thermodynamic modelling using classical models of binary H2OāCO2 fluids shows that the compositional variability along this binary determines the temperature of the main devolatilization reactions, the fluid composition and the mineral assemblages of reaction
products during prograde subduction metamorphism. Thermodynamic modelling
considering electrolytic fluids reveals that H2O and molecular CO2 are the main fluid
species and charged carbonābearing species occur only in minor amounts in equilibrium with carbonateāsilicate rocks in warm subduction settings. Consequently, accounting for electrolytic fluids at these conditions slightly increases the solubility of
carbon in the fluids compared with predictions by classical binary H2OāCO2 fluids,
but does not affect the topology of phase relations in serpentiniteāhosted carbonateā
rocks. Phase relations, mineral composition and assemblages of Milagrosa and
Almirez (meta)āserpentiniteāhosted carbonateāsilicate rocks are consistent with local
equilibrium between an infiltrating fluid and the bulk rock composition and indicate
a limited role of infiltrationādriven decarbonation. Our study shows natural evidence
for the preservation of carbonates in serpentiniteāhosted carbonateāsilicate rocks beyond the Atgāserpentinite breakdown at subāarc depths, demonstrating that carbon
can be recycled into the deep mantle.Funding from the European Union FP7 MarieāCurie Initial Training Network ABYSS under REA Grant Agreement no. 608001Spanish āAgencia Estatal de InvestigaciĆ³nā (AEI) grants no. CGL2016ā75224āR to V.L.S.āV and CGL2016ā81085āR to C.J.G and C.M and grant no. PCINā2015ā053 to C.J.GJunta de AndalucĆa Funding under grants no. RNMā131, RNMā374 and P12āRNMā3141MINECO for financing a RamĆ³n y Cajal fellowship no. RYCā2012ā11314 and K.H. for a Juan de la Cierva Fellowship no. FPDIā2013ā16253 and a research contract under grant no. CGL2016ā81085ā
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Populations of Radial Glial Cells Respond Differently to Reelin and Neuregulin1 in a Ferret Model of Cortical Dysplasia
Radial glial cells play an essential role during corticogenesis through their function as neural precursors and guides of neuronal migration. Both reelin and neuregulin1 (NRG1) maintain the radial glial scaffold; they also induce expression of Brain Lipid Binding Protein (BLBP), a well known marker of radial glia. Although radial glia in normal ferrets express both vimentin and BLBP, this coexpression diverges at P3; vimentin is expressed in the radial glial processes, while BLBP appears in cells detached from the ventricular zone. Our lab developed a model of cortical dysplasia in the ferret, resulting in impaired migration of neurons into the cortical plate and disordered radial glia. This occurs after exposure to the antimitotic methylazoxymethanol (MAM) on the 24th day of development (E24). Ferrets treated with MAM on E24 result in an overall decrease of BLBP expression; radial glia that continue to express BLBP, however, show only mild disruption compared with the strongly disrupted vimentin expressing radial glia. When E24 MAM-treated organotypic slices are exposed to reelin or NRG1, the severely disrupted vimentin+ radial glial processes are repaired but the slightly disordered BLBP+ processes are not. The realignment of vimentin+ processes was linked with an increase of their BLBP expression. BLBP expressing radial glia are distinguished by being both less affected by MAM treatment and by attempts at repair. We further investigated the effects induced by reelin and found that signaling was mediated via VLDLR/Dab1/Pi3K activation while NRG1 signaling was mediated via erbB3/erbB4/Pi3K. We then tested whether radial glial repair correlated with improved neuronal migration. Repairing the radial glial scaffold is not sufficient to restore neuronal migration; although reelin improves migration of neurons toward the cortical plate signaling through ApoER2/Dab1/PI3K activation, NRG1 does not
Perceived economic selfāsufficiency: a countryand generationācomparative approach
We thank Michael Camasso and Radha Jagannathan as well as Asimina Christoforou,
Gerbert Kraaykamp, Fay Makantasi, Tiziana Nazio, Kyriakos Pierrakakis, Jacqueline OāReilly
and Jan van Deth for their contribution to the CUPESSE project (Seventh Framework Programme; Grant
Agreement No. 61325). CUPESSE received additional funding from the Mannheim Centre for European
Social Research (MZES) and the Field of Focus 4 āSelf-Regulation and Regulation: Individuals and
Organisationsā at Heidelberg University. We further acknowledge helpful comments on this article by
two anonymous reviewers. Julian Rossello provided valuable research assistance.Electronic supplementary material The online version of this article (https ://doi.org/10.1057/
s4130 4-018-0186-3) contains supplementary material, which is available to authorized users.Existing datasets provided by statistical agencies (e.g. Eurostat) show that the economic and financial crisis that unfolded in 2008 significantly impacted the lives and livelihoods of young people across Europe. Taking these official statistics as a starting point, the collaborative research project āCultural Pathways to Economic Self-Sufficiency and Entrepreneurship in Europeā (CUPESSE) generated new survey data on the economic and social situation of young Europeans (18ā35 years). The CUPESSE dataset allows for country-comparative assessments of young peopleās perceptions about their socio-economic situation. Furthermore, the dataset includes a variety of indicators examining the socio-economic situation of both young adults and their parents. In this data article, we introduce the CUPESSE dataset to political and social scientists in an attempt to spark a debate on the measurements, patterns and mechanisms of intergenerational transmission of economic self-sufficiency as well as its political implications.CUPESSE project (Seventh Framework Programme; Grant Agreement No. 61325
Recent visible light and metal free strategies in [2+2] and [4+2] photocycloadditions
When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as wellFinancial support was provided by the European Research Council (ERC-CoG, Contract Number: 647550), the Spanish Government (RTI2018-095038-B-I00), the āComunidad de Madridā and European Structural Funds (S2018/NMT-4367). R. I. R thanks FundaciĆ³n Carolina for a graduate fellowshi
Role of cytoskeletal abnormalities in the neuropathology and pathophysiology of type I lissencephaly
Type I lissencephaly or agyria-pachygyria is a rare developmental disorder which results from a defect of neuronal migration. It is characterized by the absence of gyri and a thickening of the cerebral cortex and can be associated with other brain and visceral anomalies. Since the discovery of the first genetic cause (deletion of chromosome 17p13.3), six additional genes have been found to be responsible for agyriaāpachygyria. In this review, we summarize the current knowledge concerning these genetic disorders including clinical, neuropathological and molecular results. Genetic alterations of LIS1, DCX, ARX, TUBA1A, VLDLR, RELN and more recently WDR62 genes cause migrational abnormalities along with more complex and subtle anomalies affecting cell proliferation and differentiation, i.e., neurite outgrowth, axonal pathfinding, axonal transport, connectivity and even myelination. The number and heterogeneity of clinical, neuropathological and radiological defects suggest that type I lissencephaly now includes several forms of cerebral malformations. In vitro experiments and mutant animal studies, along with neuropathological abnormalities in humans are of invaluable interest for the understanding of pathophysiological mechanisms, highlighting the central role of cytoskeletal dynamics required for a proper achievement of cell proliferation, neuronal migration and differentiation
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