An Optimized Structure-Function Design Principle Underlies Efficient Signaling Dynamics in Neurons.

Dynamic signaling on branching axons is critical for rapid and efficient communication between neurons in the brain. Efficient signaling in axon arbors depends on a trade-off between the time it takes action potentials to reach synaptic terminals (temporal cost) and the amount of cellular material associated with the wiring path length of the neuron's morphology (material cost). However, where the balance between structural and dynamical considerations for achieving signaling efficiency is, and the design principle that neurons optimize to preserve this balance, is still elusive. In this work, we introduce a novel analysis that compares morphology and signaling dynamics in axonal networks to address this open problem. We show that in Basket cell neurons the design principle being optimized is the ratio between the refractory period of the membrane, and action potential latencies between the initial segment and the synaptic terminals. Our results suggest that the convoluted paths taken by axons reflect a design compensation by the neuron to slow down signaling latencies in order to optimize this ratio. Deviations in this ratio may result in a breakdown of signaling efficiency in the cell. These results pave the way to new approaches for investigating more complex neurophysiological phenomena that involve considerations of neuronal structure-function relationships

An all speed second order well-balanced IMEX relaxation scheme for the Euler equations with gravity

We present an implicit-explicit well-balanced finite volume scheme for the Euler equations with a gravitational source term which is able to deal also with low Mach flows. To visualize the different scales we use the non-dimensionalized equations on which we apply a pressure splitting and a Suliciu relaxation. On the resulting model, we apply a splitting of the flux into a linear implicit and an non-linear explicit part that leads to a scale independent time-step. The explicit step consists of a Godunov type method based on an approximative Riemann solver where the source term is included in the flux formulation. We develop the method for a first order scheme and give an extension to second order. Both schemes are designed to be well-balanced, preserve the positivity of density and internal energy and have a scale independent diffusion. We give the low Mach limit equations for well-prepared data and show that the scheme is asymptotic preserving. These properties are numerically validated by various test cases

The use of stable and radioactive sterol tracers as a tool to investigate cholesterol degradation to bile acids in humans in vivo

Alterations of cholesterol homeostasis represent important risk factors for atherosclerosis and cardiovascular disease. Different clinical-experimental approaches have been devised to study the metabolism of cholesterol and particularly the synthesis of bile acids, its main catabolic products. Most evidence in humans has derived from studies utilizing the administration of labeled sterols; these have several advantages over in vitro assay of enzyme activity and expression, requiring an invasive procedure such as a liver biopsy, or the determination of fecal sterols, which is cumbersome and not commonly available. Pioneering evidence with administration of radioactive sterol derivatives has allowed to characterize the alterations of cholesterol metabolism and degradation in different situations, including spontaneous disease conditions, aging, and drug treatment. Along with the classical isotope dilution methodology, other approaches were proposed, among which isotope release following radioactive substrate administration. More recently, stable isotope studies have allowed to overcome radioactivity exposure. Isotope enrichment studies during tracer infusion has allowed to characterize changes in the degradation of cholesterol via the “classical” and the “alternative” pathways of bile acid synthesis. Evidence brought by tracer studies in vivo, summarized here, provides an exceptional tool for the investigation of sterol metabolism, and integrate the studies in vitro on human tissue

Fundamental diagrams in traffic flow: the case of heterogeneous kinetic models

Experimental studies on vehicular traffic provide data on quantities like density, flux, and mean speed of the vehicles. However, the diagrams relating these variables (the fundamental and speed diagrams) show some peculiarities not yet fully reproduced nor explained by mathematical models. In this paper, resting on the methods of kinetic theory, we introduce a new traffic model which takes into account the heterogeneous nature of the flow of vehicles along a road. In more detail, the model considers traffic as a mixture of two or more populations of vehicles (e.g., cars and trucks) with different microscopic characteristics, in particular different lengths and/or maximum speeds. With this approach we gain some insights into the scattering of the data in the regime of congested traffic clearly shown by actual measurements

AnAll Speed SecondOrder IMEXRelaxation Scheme for the Euler Equations

We present an implicit-explicit finite volume scheme for the Euler equations. We start from the non-dimensionalised Euler equations where we split the pressure in a slow and a fast acoustic part. We use a Suliciu type relaxation model which we split in an explicit part, solved using a Godunov-type scheme based on an approximate Riemann solver, and an implicit part where we solve an elliptic equation for the fast pressure. The relaxation source terms are treated projecting the solution on the equilibrium manifold. The proposed scheme is positivity preserving with respect to the density and internal energy and asymptotic preserving towards the incompressible Euler equations. For this first order scheme we give a second order extension which maintains the positivity property. We perform numerical experiments in 1D and 2D to show the applicability of the proposed splitting and give convergence results for the second order extension

Burri: nelle parole (e nei quadri) di Guttuso

Nel corso del 2015-2016, a cento anni dalla sua nascita, la figura di Alberto Burri ha conosciuto un nuovo momento di affermazione a livello mondiale, che ha riportato in auge l\u2019attualit\ue0 della sua opera e ha permesso di tornare a fare i conti con essa in una prospettiva storica. Gli interventi dei dieci studiosi che si sono avvicendati nell\u2019occasione del convegno realizzato presso le Gallerie d\u2019Italia di Intesa Sanpaolo il 29 ottobre 2015 si sono impegnati ad apportare nuovi e originali contributi, che si collocano tra i documenti utili per la continuit\ue0 di attenzione che l\u2019opera di Burri richiede

Loopy Cuts: Surface-Field Aware Block Decomposition for Hex-Meshing.

We present a new fully automatic block-decomposition hexahedral meshing algorithm capable of producing high quality meshes that strictly preserve feature curve networks on the input surface and align with an input surface cross-field. We produce all-hex meshes on the vast majority of inputs, and introduce localized non-hex elements only when the surface feature network necessitates those. The input to our framework is a closed surface with a collection of geometric or user-demarcated feature curves and a feature-aligned surface cross-field. Its output is a compact set of blocks whose edges interpolate these features and are loosely aligned with this cross-field. We obtain this block decomposition by cutting the input model using a collection of simple cutting surfaces bounded by closed surface loops. The set of cutting loops spans the input feature curves, ensuring feature preservation, and is obtained using a field-space sampling process. The computed loops are uniformly distributed across the surface, cross orthogonally, and are loosely aligned with the cross-field directions, inducing the desired block decomposition. We validate our method by applying it to a large range of complex inputs and comparing our results to those produced by state-of-the-art alternatives. Contrary to prior approaches, our framework consistently produces high-quality field aligned meshes while strictly preserving geometric or user-specified surface features

BoolSurf: Boolean Operations on Surfaces

We port Boolean set operations between 2D shapes to surfaces of any genus, with any number of open boundaries. We combine shapes bounded by sets of freely intersecting loops, consisting of geodesic lines and cubic Bézier splines lying on a surface. We compute the arrangement of shapes directly on the surface and assign integer labels to the cells of such arrangement. Differently from the Euclidean case, some arrangements on a manifold may be inconsistent. We detect inconsistent arrangements and help the user to resolve them. Also, we extend to the manifold setting recent work on Boundary-Sampled Halfspaces, thus supporting operations more general than standard Booleans, which are well defined on inconsistent arrangements, too. Our implementation discretizes the input shapes into polylines at an arbitrary resolution, independent of the level of resolution of the underlying mesh. We resolve the arrangement inside each triangle of the mesh independently and combine the results to reconstruct both the boundaries and the interior of each cell in the arrangement. We reconstruct the control points of curves bounding cells, in order to free the result from discretization and provide an output in vector format. We support interactive usage, editing shapes consisting up to 100k line segments on meshes of up to 1M triangles

Alternativas de fertilización nitrogenada en maíz bajo riego por pivot central

Título alternativo : Alternativas de fertilização com nitrogênio no milho sob irrigação por pivô centralIn the last 15 years, there has been an expansion of the use of center-pivots for irrigation in Uruguay. This equipment allows the application of diluted fertilizer in the irrigation water. The study aimed to generate information on fertilization strategies with nitrogen (N) in irrigated maize crops. A study was performed where five treatments were evaluated: T0, without additional nitrogen fertilization to the basal sowing fertilization; C0, cover fertilization with 150 Kg N ha⁻¹ split in three (V3) and seven leaves (V7); F1, idem “C0” but with liquid fertilizer in water; F2, 150 Kg N ha⁻¹ as liquid fertilizer in water split weekly from V3 to reproductive stage (R1); F3, idem "F2" but with 225 Kg N ha⁻¹. Irrigation was done according to water balance and the soil moisture was measured with an FDR probe. The N plant level and biomass were evaluated in states V3, V6, R1 and physiological maturity (R6). The grain yield was determined at harvest. The correlation between the color values and Color Index (InCol) was analyzed in R1 using aerial photography and software, with: % N; biomass; Nitrogen Sufficiency Index (NSI); and grain yield (kg ha⁻¹). The yield was higher in the treatment with the highest N dose, with no significant differences. No differences were found between the sources of N (sulfur urea and Fertec®) for the evaluated variables. A high correlation was obtained between the colors and the InCol and the cultivation variables.En los últimos 15 años, ha habido una expansión del uso de pivotes centrales para riego en Uruguay. Estos equipos permiten la aplicación de fertilizante con el riego. El objetivo fue generar información sobre estrategias de fertilización con nitrógeno (N) en maíz regado. Se instaló un experimento con 5 tratamientos: T0, sin fertilización nitrogenada adicional a la basal de la siembra; C0, fertilización en cobertura con 150 kg N ha⁻¹ fraccionado en tres (V3) y siete hojas (V7) de estado de desarrollo; F1, ídem a “C0” pero con fertilizante diluido en agua; F2,150 kg N ha⁻¹ como fertilizante diluido en agua, fraccionado semanalmente desde V3 hasta estado reproductivo (R1); F3, ídem a “F2” pero con 225 kg N ha⁻¹. Se manejó el riego a partir de un balance hídrico y se midió la humedad en el suelo con sonda FDR. Se evaluó contenido de N en planta y biomasa en los estados V3, V6, R1 y madurez fisiológica (R6). A cosecha se determinó el rendimiento en grano. En R1 mediante foto aérea del cultivo y software se analizó la correlación entre los valores de color e Índice de Color (InCol) con: %N; biomasa; Índice de Suficiencia de Nitrógeno (ISN); y rendimiento de grano (kg ha⁻¹). El rendimiento fue superior en el tratamiento con mayor dosis de N, sin detectar diferencias significativas. No se encontraron diferencias entre las fuentes de N (urea azufrada y Fertec®). Se obtuvo alta correlación entre los colores e InCol y las variables del cultivo analizadas.Nos últimos 15 anos, no Uruguai, houve uma expansão do uso de pivôs centrais para irrigação. Esses equipamentos permitem a aplicação de fertilizantes diluídos nas irrigaçãoes. O objetivo foi gerar informações sobre estratégias de fertilização com nitrogênio (N) no milho irrigado. Foram avaliados 5 tratamentos: T0, sem fertilização com nitrogênio adicional à fertilização de base da semeadura; C0, adubação em cobertura com 150 kg N ha⁻¹ dividido em três (V3) e sete (V7) folhas do estádio de desenvolvimento; F1, igual a “C0” mas com fertilizante diluído em água; F2, 150 kg N ha⁻¹ como fertilizante diluído em água, fracionado semanalmente de V3 ao estado reprodutivo (R1); F3, idem para “F2” mas com 225 kg N ha⁻¹. Foi regado de acordo com o balanço hídrico e a umidade do solo foi medida com uma sonda FDR. A concentração de N da planta e biomassa foram avaliadas nos estágios V3, V6, R1 e maturidade fisiológica (R6). Na colheita, foi determinado o rendimento de grãos. No R1, por meio de foto aérea e software, foi analisada a correlação entre os valores de cor e o Índice de Cor (InCol) com:% N; biomassa; Índice de Suficiência de Nitrogênio (ISN); e rendimento de grãos (kg ha⁻¹). O desempenho foi superior no tratamento com a maior dose de N, sem detectar diferenças significativas. Não foram encontradas diferenças entre as fontes de N (enxofre uréia e Fertec®). Uma alta correlação foi obtida entre as cores e o InCol e as variáveis de cultivo analisadas