Quantitative predictions on auxin-induced polar distribution of PIN proteins during vein formation in leaves

The dynamic patterning of the plant hormone auxin and its efflux facilitator the PIN protein are the key regulator for the spatial and temporal organization of plant development. In particular auxin induces the polar localization of its own efflux facilitator. Due to this positive feedback auxin flow is directed and patterns of auxin and PIN arise. During the earliest stage of vein initiation in leaves auxin accumulates in a single cell in a rim of epidermal cells from which it flows into the ground meristem tissue of the leaf blade. There the localized auxin supply yields the successive polarization of PIN distribution along a strand of cells. We model the auxin and PIN dynamics within cells with a minimal canalization model. Solving the model analytically we uncover an excitable polarization front that triggers a polar distribution of PIN proteins in cells. As polarization fronts may extend to opposing directions from their initiation site we suggest a possible resolution to the puzzling occurrence of bipolar cells, such we offer an explanation for the development of closed, looped veins. Employing non-linear analysis we identify the role of the contributing microscopic processes during polarization. Furthermore, we deduce quantitative predictions on polarization fronts establishing a route to determine the up to now largely unknown kinetic rates of auxin and PIN dynamics.Comment: 9 pages, 4 figures, supplemental information included, accepted for publication in Eur. Phys. J.

Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin

The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors onsedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonicallyactive arca, soils were weakly developed in aggrading alluvial fans, dominated by mass flows. reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed: the former were associated with Mg-poor fan sediments whitc: the latter formed on Mg-rich lake clays exposed during minar lake lowstands. The nonh-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream Aood deposits, sourced by carbonate terrains. Floodplain and freshwater lakc deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential developmenl on calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quatemary fans. Which are characterized by climatically induced periods of stability and instability

Middle-Late Permian mass extinction on land

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148626/1/Retallack_et_al_2006_GSA_Bulletin-PTr.pd

The Permian-Triassic boundary in Antarctica

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148634/1/Retallack_et_al_2005_Antarctic_Science-PTr_boundary_in_Antarctica.pd

Middle-Late Permian mass extinction on land

Este trabajo de investigación tuvo como objetivo comparar las complicaciones de cirugía laparoscópica y cirugía abierta en los casos de apendicitis aguda complicada en menores de catorce años en el hospital Sabogal durante los años 2012 a 2016 y cuál de estas técnicas presentó menores complicaciones. En cuanto a materiales y métodos, se revisó las historias clínicas de 201 casos de apendicitis aguda complicada, operados por cirugía laparoscópica y 160 casos operados por cirugía abierta. Fue un estudio cuantitativo, correlacional, observacional, retrospectivo, transversal. Para comparar las complicaciones se utilizó la prueba estadística del Chi cuadrado, con un nivel de significancia de 95%. Se excluyeron pacientes con comorbilidad asociada, operados en otros hospitales y conversión de técnica laparoscópica a abierta. En los resultados obtenidos, no hubo diferencia significativa en las complicaciones de cirugía abierta y laparoscópica, p= 0.493. Las infecciones de herida operatoria se presentaron más frecuentemente en los casos de cirugía abierta (p=0.004) y el íleo posoperatorio más frecuentemente en la técnica laparoscópica (p=0.035). No hubo diferencia estadística en relación a absceso residual, la edad, género, grupo etario y estancia hospitalaria (p>0.05). Se concluye que la prevalencia de complicaciones es elevada, tanto en la cirugía abierta como en la técnica laparoscópica, no existiendo diferencia significativa. La infección de herida operatoria, como complicación si tuvo diferencia estadísticamente significativa, y fue más frecuente en la técnica abierta. El íleo posoperatorio es un hallazgo resaltante en este estudio y se presentó más en la técnica laparoscópica. La edad, género, grupo etario y estancia hospitalaria no incrementan el riesgo de complicaciones

A mixed-age classed ‘pelycosaur’ aggregation from South Africa: earliest evidence of parental care in amniotes?

Living species of mammals, crocodiles and most species of birds exhibit parental care, but evidence of this behaviour is extremely rare in the fossil record. Here, we present a new specimen of varanopid ‘pelycosaur’ from the Middle Permian of South Africa. The specimen is an aggregation, consisting of five articulated individuals preserved in undisturbed, close, lifelike, dorsal-up, subparallel positions, indicating burial in ‘life position’. Two size classes are represented. One is 50% larger than the others, is well ossified, has fused neurocentral sutures and is distinguished by a coat of dermal ossifications that covers the neck and shoulder regions. We regard this individual to be an adult. The remaining four skeletons are considered to be juveniles as they are approximately the same size, are poorly ossified, have open neurocentral sutures and lack dermal ossifications. Aggregates of juvenile amniotes are usually siblings. Extant analogues of adult and juvenile groupings suggest that the adult is one of the parents, leading us to regard the aggregation as a family group. The Late Middle Permian age of the varanopid family predates the previously known oldest fossil evidence of parental care in terrestrial vertebrates by 140 Myr

Fluvial point‐bar architecture and facies heterogeneity and their influence on intra‐bar static connectivity in humid coastal‐plain and dryland fan systems

Many published studies detail the sedimentology and stratigraphic architecture of meandering fluvial systems and their preserved successions based on data from modern systems, outcrops or subsurface. However, the broader understanding of the behaviour of depositional systems and its role in determining the nature of the resultant depositional units remains limited due to difficulties associated with the collection of appropriate data on three‐dimensional sedimentary‐facies distributions and on the temporal evolution of the form of architectural elements. To overcome such limitations, numerical lithofacies and stratigraphic modelling approaches provide a valuable suite of tools to examine the sensitivity of intrinsic system behaviour to different controls that operate at varying spatial and temporal scales. This study utilises a three‐dimensional forward stratigraphic model, the ‘Point‐Bar Sedimentary Architecture Numerical Deduction’ (PB‐SAND), informed by data and relationships extracted from a sedimentological database, to model the facies architecture and heterogeneity of fluvial point‐bar elements in two contrasting environmental settings: humid coastal plains vs. dryland fluvial fans. This study demonstrates a workflow that uses high‐resolution seismic imagery to constrain the planform evolution of preserved point‐bar elements, in combination with data from appropriate geological analogues (five humid coastal‐plain and eight dryland fluvial‐fan systems) to constrain modelling parameters (i.e. bar thickness, facies proportion and mud‐drape geometry). The method applies a statistical analytical approach to constrain the ranges and types of sedimentary architectures and facies heterogeneity known for humid and dryland meandering fluvial depositional systems. Modelling results demonstrate the effects of increasing compartmentalisation of sand geo‐bodies by mud drapes, whose density increases vertically towards the bar top of point‐bar architectural elements. Modelling results also demonstrate how the compartmentalisation of point‐bar elements in the models constrained on humid coastal‐plain analogues, compared to those based on dryland‐fan analogues, exhibits a larger variation in response to the spatial distribution of mud drapes and their discontinuity in three dimensions. The modelling outputs are able to represent realistic architectural geometries, capture the three‐dimensional complexity of sedimentary architecture and incorporate styles of facies heterogeneity that can be employed in the quantitative analysis of connectivity. The PB‐SAND simulations can, therefore, be used to enhance conventional reservoir models and thereby to improve the realism of fluid‐flow models