375 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 serpentiniteâhosted carbonates beyond antigorite-serpentinite dehydration (NevadoâFilĂĄbride Complex, Spain)
I. MartĂnez Segura and M. J. RomĂĄn Alpiste are thanked for their kind assistance during sample preparation and SEM operation, and M. T. GĂłmezâPugnaire 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 MarieâCurie Initial Training Network ABYSS under REA Grant Agreement no. 608001 in the framework of M.D.M.'s PhD project, the Spanish âAgencia Estatal de InvestigaciĂłnâ (AEI) grants no. CGL2016â75224âR to V.L.S.âV and CGL2016â81085âR to C.J.G and C.M and grant no. PCINâ2015â053 to C.J.G. The âJunta de AndalucĂaâ is also thanked for funding under grants no. RNMâ131, RNMâ374 and P12âRNMâ3141. C.M. thanks MINECO for financing a RamĂłn y Cajal fellowship no. RYCâ2012â11314 and K.H. for a Juan de la Cierva Fellowship no. FPDIâ2013â16253 and a research contract under grant no. CGL2016â81085âR. 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 subâarc depths, the release of carbon from subducting slab lithologies is mostly
controlled by fluid released by devolatilization reactions such as dehydration of antigorite (Atgâ) serpentinite to prograde peridotite. Here we investigate carbonateâsilicate rocks hosted in Atgâserpentinite and prograde chlorite (Chlâ) harzburgite in the
Milagrosa and Almirez ultramafic massifs of the palaeoâsubducted NevadoâFilĂĄbride
Complex (NFC, Betic Cordillera, S. Spain). These massifs provide a unique opportunity to study the stability of carbonate during subduction metamorphism at PâT
conditions before and after the dehydration of Atgâserpentinite in a warm subduction
setting. In the Milagrosa massif, carbonateâsilicate rocks occur as lenses of Tiâclinohumiteâdiopsideâcalcite marbles, diopsideâdolomite marbles and antigoriteâdiopsideâdolomite rocks hosted in clinopyroxeneâbearing Atgâserpentinite. In Almirez,
carbonateâsilicate rocks are hosted in Chlâharzburgite and show a highâgrade assemblage composed of olivine, Tiâclinohumite, diopside, chlorite, dolomite, calcite, Crâ
bearing magnetite, pentlandite and rare aragonite inclusions. These NFC
carbonateâsilicate 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 Caâcarbonate (i.e., ophicarbonates). Thermodynamic
modelling shows that the carbonateâsilicate rocks attained peak metamorphic conditions similar to those of their host serpentinite (Milagrosa massif; 550â600°C and
1.0â1.4 GPa) and Chlâharzburgite (Almirez massif; 1.7â1.9 GPa and 680°C).
Microstructures, mineral chemistry and phase relations indicate that the hybrid carbonateâsilicate bulk rock compositions formed before prograde metamorphism,
likely during seawater hydrothermal alteration, and subsequently underwent subduction metamorphism. In the CaOâMgOâSiO2 ternary, these processes resulted in a
compositional variability of NFC serpentiniteâhosted carbonateâsilicate rocks along
the serpentineâcalcite mixing trend, similar to that observed in serpentiniteâhosted
carbonateârocks in other palaeoâsubducted metamorphic terranes. Thermodynamic modelling using classical models of binary H2OâCO2 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 carbonâbearing species occur only in minor amounts in equilibrium with carbonateâsilicate 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 H2OâCO2 fluids,
but does not affect the topology of phase relations in serpentiniteâhosted carbonateâ
rocks. Phase relations, mineral composition and assemblages of Milagrosa and
Almirez (meta)âserpentiniteâhosted carbonateâsilicate rocks are consistent with local
equilibrium between an infiltrating fluid and the bulk rock composition and indicate
a limited role of infiltrationâdriven decarbonation. Our study shows natural evidence
for the preservation of carbonates in serpentiniteâhosted carbonateâsilicate rocks beyond the Atgâserpentinite breakdown at subâarc depths, demonstrating that carbon
can be recycled into the deep mantle.Funding from the European Union FP7 MarieâCurie Initial Training Network ABYSS under REA Grant Agreement no. 608001Spanish âAgencia Estatal de InvestigaciĂłnâ (AEI) grants no. CGL2016â75224âR to V.L.S.âV and CGL2016â81085âR to C.J.G and C.M and grant no. PCINâ2015â053 to C.J.GJunta de AndalucĂa Funding under grants no. RNMâ131, RNMâ374 and P12âRNMâ3141MINECO for financing a RamĂłn y Cajal fellowship no. RYCâ2012â11314 and K.H. for a Juan de la Cierva Fellowship no. FPDIâ2013â16253 and a research contract under grant no. CGL2016â81085â
ApoE Receptor 2 Regulates Synapse and Dendritic Spine Formation
Apolipoprotein E receptor 2 (ApoEr2) is a postsynaptic protein involved in long-term potentiation (LTP), learning, and memory through unknown mechanisms. We examined the biological effects of ApoEr2 on synapse and dendritic spine formation-processes critical for learning and memory.In a heterologous co-culture synapse assay, overexpression of ApoEr2 in COS7 cells significantly increased colocalization with synaptophysin in primary hippocampal neurons, suggesting that ApoEr2 promotes interaction with presynaptic structures. In primary neuronal cultures, overexpression of ApoEr2 increased dendritic spine density. Consistent with our in vitro findings, ApoEr2 knockout mice had decreased dendritic spine density in cortical layers II/III at 1 month of age. We also tested whether the interaction between ApoEr2 and its cytoplasmic adaptor proteins, specifically X11α and PSD-95, affected synapse and dendritic spine formation. X11α decreased cell surface levels of ApoEr2 along with synapse and dendritic spine density. In contrast, PSD-95 increased cell surface levels of ApoEr2 as well as synapse and dendritic spine density.These results suggest that ApoEr2 plays important roles in structure and function of CNS synapses and dendritic spines, and that these roles are modulated by cytoplasmic adaptor proteins X11α and PSD-95
Lrp12/Mig13a Reveals Changing Patterns of Preplate Neuronal Polarity during Corticogenesis that Are Absent in Reeler Mutant Mice
During corticogenesis, the earliest generated neurons form the preplate, which evolves into the marginal zone and subplate. Lrp12/Mig13a, a mammalian gene related to the Caenorhabditis elegans neuroblast migration gene mig-13, is expressed in a subpopulation of preplate neurons that undergo ventrally directed tangential migrations in the preplate layer and pioneer axon projections to the anterior commissure. As the preplate separates, Lrp12/Mig13a-positive neurons polarize in the radial plane and form a pseudocolumnar pattern, prior to moving to a deeper position within the emerging subplate layer. These changes in neuronal polarity do not occur in reeler mutant mice, revealing the earliest known defect in reeler cortical patterning and suggesting that the alignment of preplate neurons into a pseudolayer facilitates the movement of later-born radially migrating neurons into the emerging cortical plate
The Reelin Receptors Apoer2 and Vldlr Coordinate the Patterning of Purkinje Cell Topography in the Developing Mouse Cerebellum
The adult cerebellar cortex is comprised of reproducible arrays of transverse zones and parasagittal stripes of Purkinje cells. Adult stripes are created through the perinatal rostrocaudal dispersion of embryonic Purkinje cell clusters, triggered by signaling through the Reelin pathway. Reelin is secreted by neurons in the external granular layer and deep cerebellar nuclei and binds to two high affinity extracellular receptors on Purkinje cells-the Very low density lipoprotein receptor (Vldlr) and apolipoprotein E receptor 2 (Apoer2). In mice null for either Reelin or double null for Vldlr and Apoer2, Purkinje cell clusters fail to disperse. Here we report that animals null for either Vldlr or Apoer2 individually, exhibit specific and parasagittally-restricted Purkinje cell ectopias. For example, in mice lacking Apoer2 function immunostaining reveals ectopic Purkinje cells that are largely restricted to the zebrin II-immunonegative population of the anterior vermis. In contrast, mice null for Vldlr have a much larger population of ectopic Purkinje cells that includes members from both the zebrin II-immunonegative and -immunopositive phenotypes. HSP25 immunoreactivity reveals that in Vldlr null animals a large portion of zebrin II-immunopositive ectopic cells are probably destined to become stripes in the central zone (lobules VIâVII). A small population of ectopic zebrin II-immunonegative Purkinje cells is also observed in animals heterozygous for both receptors (Apoer2+/â: Vldlr+/â), but no ectopia is present in mice heterozygous for either receptor alone. These results indicate that Apoer2 and Vldlr coordinate the dispersal of distinct, but overlapping subsets of Purkinje cells in the developing cerebellum
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 selfâsufficiency: a countryand generationâcomparative approach
We thank Michael Camasso and Radha Jagannathan as well as Asimina Christoforou,
Gerbert Kraaykamp, Fay Makantasi, Tiziana Nazio, Kyriakos Pierrakakis, Jacqueline OâReilly
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 âSelf-Regulation and Regulation: Individuals and
Organisationsâ 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 âCultural Pathways to Economic Self-Sufficiency and Entrepreneurship in Europeâ (CUPESSE) generated new survey data on the economic and social situation of young Europeans (18â35 years). The CUPESSE dataset allows for country-comparative assessments of young peopleâs 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
Patterns of Neurogenesis and Amplitude of Reelin Expression Are Essential for Making a Mammalian-Type Cortex
The mammalian neocortex is characterized as a six-layered laminar structure, in which distinct types of pyramidal neurons are distributed coordinately during embryogenesis. In contrast, no other vertebrate class possesses a brain region that is strictly analogous to the neocortical structure. Although it is widely accepted that the pallium, a dorsal forebrain region, is specified in all vertebrate species, little is known of the differential mechanisms underlying laminated or non-laminated structures in the pallium. Here we show that differences in patterns of neuronal specification and migration provide the pallial architectonic diversity. We compared the neurogenesis in mammalian and avian pallium, focusing on subtype-specific gene expression, and found that the avian pallium generates distinct types of neurons in a spatially restricted manner. Furthermore, expression of Reelin gene is hardly detected in the developing avian pallium, and an experimental increase in Reelin-positive cells in the avian pallium modified radial fiber organization, which resulted in dramatic changes in the morphology of migrating neurons. Our results demonstrate that distinct mechanisms govern the patterns of neuronal specification in mammalian and avian pallial development, and that Reelin-dependent neuronal migration plays a critical role in mammalian type corticogenesis. These lines of evidence shed light on the developmental programs underlying the evolution of the mammalian specific laminated cortex
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 âComunidad de Madridâ and European Structural Funds (S2018/NMT-4367). R. I. R thanks FundaciĂłn Carolina for a graduate fellowshi
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