The role of ongoing dendritic oscillations in single-neuron dynamics

The dendritic tree contributes significantly to the elementary computations a neuron performs while converting its synaptic inputs into action potential output. Traditionally, these computations have been characterized as temporally local, near-instantaneous mappings from the current input of the cell to its current output, brought about by somatic summation of dendritic contributions that are generated in spatially localized functional compartments. However, recent evidence about the presence of oscillations in dendrites suggests a qualitatively different mode of operation: the instantaneous phase of such oscillations can depend on a long history of inputs, and under appropriate conditions, even dendritic oscillators that are remote may interact through synchronization. Here, we develop a mathematical framework to analyze the interactions of local dendritic oscillations, and the way these interactions influence single cell computations. Combining weakly coupled oscillator methods with cable theoretic arguments, we derive phase-locking states for multiple oscillating dendritic compartments. We characterize how the phase-locking properties depend on key parameters of the oscillating dendrite: the electrotonic properties of the (active) dendritic segment, and the intrinsic properties of the dendritic oscillators. As a direct consequence, we show how input to the dendrites can modulate phase-locking behavior and hence global dendritic coherence. In turn, dendritic coherence is able to gate the integration and propagation of synaptic signals to the soma, ultimately leading to an effective control of somatic spike generation. Our results suggest that dendritic oscillations enable the dendritic tree to operate on more global temporal and spatial scales than previously thought

Fast, non-monte-carlo estimation of transient performance variation due to device mismatch

This paper describes an efficient way of simulating the effects of device random mismatch on circuit transient characteristics, such as variations in delay or in frequency. The proposed method models DC random offsets as equivalent AC pseudo-noises and leverages the fast, linear periodically time-varying (LPTV) noise analysis available from RF circuit simulators. Therefore, the method can be considered as an extension to DC match analysis and offers a large speed-up compared to the traditional Monte-Carlo analysis. Although the assumed linear perturbation model is valid only for small variations, it enables easy ways to estimate correlations among variations and identify the most sensitive design parameters to mismatch, all at no additional simulation cost. Three benchmarks measuring the variations in the input offset voltage of a clocked comparator, the delay of a logic path, and the frequency of an oscillator demonstrate the speed improvement of about 100-1000x compared to a 1000-point Monte-Carlo method

Parametric study of the fluid behaviour in a simplified Vortex-Cooled Rocket Engine through numerical simulations

Humans have always looked at the heavens and wondered about the nature of the objects seen in the night sky. Discovering the secrets of space has been and is one of humanity’s greatest desires, however, each rocket launch involves a great economic cost. With the development of lighter rockets and the advances in electronics and other technologies in the 20th century, it became possible to lower costs and make rocket launches a common practice. Several methods to reduce the weight of the rockets have been proposed. This document is based on the Vortex-Cooling technique, a variant of film cooling which aims to cool the walls of the combustion chamber by means of a vortex flow in order to reduce its thickness. The main objective is to study the flow behavior of such a simplified vortex-cooled rocket engine in different configurations through numerical simulations. Firstly, a 3D model of Rocketdyne RS-25 (SSME) geometry is created from data sheets published by NASA. Besides, six different geometries of vortex-cooled rocket engines (VCRE) have been 3D modeled in order to carry out four analyses. Secondly, the characteristics of the mesh, a turbulent model for high-velocity flows, as well as the boundary conditions and all the parameters that allow computing the simulations of the SSME and vortex-cooled rocket engine have been selected. Using computational fluid dynamics (CFD) studies on the SSME it has been possible to verify the simulations obtained with Ansys Fluent. Once the parameters used in Fluent have been verified, it is proceeded to compute the simulations of 8 VCRE, modifying the number of inlets that generate the vortex; the angle of incidence of the inlets with respect to the axial direction; the diameter of the inlets; and finally, inlet velocity. After drawing conclusions from each analysis, the VCRE configuration chosen among the 8 cases studied is presented in more detail. The choice is based on the characteristics of the generated vortex, being the one that best meets the purpose of the vortex cooling technique. Comparing this rocket engine with the SSME, an 83% reduction of the flow temperature in the combustion chamber wall stands out. Nevertheless, apart from temperature, results are presented for other physical properties of the flow, such as velocity and pressure

CFD analysis of co-firing of coke and biomass in a parallel flow regenerative lime kiln

The lime industry is a highly energy intensive industry, with a huge presence worldwide. To reduce both production costs and pollutants emissions, some lime production plants are introducing more environmentally-friendly energy sources, such as local agro-industry residues. In this paper, a numerical tool is presented, which simulates a large-scale Parallel Flow Regenerative (PFR) kiln that currently uses coke as main fuel. The developed tool aims at investigating the combustion process under conditions of co-firing of coke and biomass and to assist the plant operators in the optimization of such operating conditions. To achieve this goal, a two-way coupling Euler–Lagrange approach is used to model the dynamics of the particulate phase and their interaction with the gas phase. Pyrolysis, volatiles oxidation and char oxidation are modelled by kinetics/diffusion-limited model (for heterogeneous reactions) and mixture fraction approach (for homogeneous reactions). Moreover, two methods are investigated for representing the limestone bed: a porous medium (PM) approach and a “solid blocks” (BM) tridimensional mesh. Comparison of the results for the case of 100% coke showed that the ideal “blocks” method is more accurate as it adequately simulates the scattering of fuel particles through the PFR kiln anchor, which is limited with the PM approach. Moreover, the temperature profile, maximum and minimum temperatures, as well as CO2 and O2 concentrations at outlet, are comprised in the expected range for this technology, according to available literature. Finally, the predicted results of a co-firing case with 60% biomass (in mass) were validated with measurements in an industrial facility, with production capacity of 440 calcium oxide tons per day. The results suggest that the model is fairly accurate to predict gas temperature, as well as O2 and NOX concentrations at the kiln outlet. Although some improvements are recommended to refine the CFD predictions, these promising results and the high computational efficiency laid the foundation for future modelling of co-firing of coke and biomass, as well as the modelling of the lime calcination process. It also paves the way for facilitating the reduction of pollutant emissions thus contributing to a more sustainable lime production

The Mental Landscape of Imagining Life Beyond the Current Life Span : Implications for Construal and Self-Continuity

© The Author(s) 2020. Published by Oxford University Press on behalf of The Gerontological Society of America. Funding Funding for Mechanical Turk Participants was provided by Seattle Pacific University School of Psychology, Family and Community. Acknowledgments Life-extension supporters were recruited by A. Csordas at the Undoing Aging conference held in Berlin, Germany, on March 15–17, 2018. No incentives were offered for participation. Data from the present manuscript were not published in any form prior to the submission of the manuscript for publication.Peer reviewedPublisher PD

Conjugate Heat Transfer Analysis of Combined Regenerative and Discrete Film Cooling in a Rocket Nozzle

Conjugate heat transfer analysis has been carried out on an 89kN thrust chamber in order to evaluate whether combined discrete film cooling and regenerative cooling in a rocket nozzle is feasible. Several cooling configurations were tested against a baseline design of regenerative cooling only. New designs include combined cooling channels with one row of discrete film cooling holes near the throat of the nozzle, and turbulated cooling channels combined with a row of discrete film cooling holes. Blowing ratio and channel mass flow rate were both varied for each design. The effectiveness of each configuration was measured via the maximum hot gas-side nozzle wall temperature, which can be correlated to number of cycles to failure. A target maximum temperature of 613K was chosen. Combined film and regenerative cooling, when compared to the baseline regenerative cooling, reduced the hot gas side wall temperature from 667K to 638K. After adding turbulators to the cooling channels, combined film and regenerative cooling reduced the temperature to 592K. Analysis shows that combined regenerative and film cooling is feasible with significant consequences, however further improvements are possible with the use of turbulators in the regenerative cooling channels