3D simulations of self-propelled, reconstructed jellyfish using vortex methods

We present simulations of the vortex dynamics associated with the self-propelled motion of jellyfish. The geometry is obtained from image segmentation of video recordings from live jellyfish. The numerical simulations are performed using three-dimensional viscous, vortex particle methods with Brinkman penalization to impose the kinematics of the jellyfish motion. We study two types of strokes recorded in the experiment1. The first type (stroke A) produces two vortex rings during the stroke: one outside the bell during the power stroke and one inside the bell during the recovery stroke. The second type (stroke B) produces three vortex rings: one ring during the power stroke and two vortex rings during the recovery stroke. Both strokes propel the jellyfish, with stroke B producing the highest velocity. The speed of the jellyfish scales with the square root of the Reynolds number. The simulations are visualized in a fluid dynamics video.Comment: 1 page, 1 figur

Aqueous Free-Radical Polymerization of Non-Ionized and Fully Ionized Methacrylic Acid

Water-soluble, carboxylic acid monomers are known to exhibit peculiar kinetics when polymerized in aqueous solution. Namely, their free-radical polymerization rate is affected by several parameters such as monomer concentration, ionic strength, and pH. Focusing on methacrylic acid (MAA), even though this monomer has been largely addressed, a systematic investigation of the effects of the above-mentioned parameters on its polymerization rate is missing, in particular in the fully ionized case. In this work, the kinetics of non-ionized and fully ionized MAA are characterized by in-situ nuclear magnetic resonance (NMR). Such accurate monitoring of the reaction rate enables the identification of relevant but substantially different effects of the monomer and electrolyte concentration on polymerization rate in the two ionization cases. For non-ionized MAA, the development of a kinetic model based on literature rate coefficients allows us to nicely simulate the experimental data of conversion versus time at a high monomer concentration. For fully ionized MAA, a novel propagation rate law accounting for the electrostatic interactions is proposed: the corresponding model is capable of predicting reasonably well the electrolyte concentration effect on polymerization rate. Nevertheless, further kinetic information in a wider range of monomer concentrations would be welcome to increase the reliability of the model predictions

Coplanar back contacts for thin silicon solar cells

The type of coplanar back contact solar cell described was constructed with interdigitated n(+) and p(+) type regions on the back of the cell, such that both contacts are made on the back with no metallization grid on the front. This cell construction has several potential advantages over conventional cells for space use namely, convenience of interconnects, lower operating temperatures and higher efficiency due to the elimination of grid shadowing. However, the processing is more complex, and the cell is inherently more radiation sensitive. The latter problem can be reduced substantially by making the cells very thin (approximately 50 micrometers). Two types of interdigitated back contact cells are possible, the types being dependent on the character of the front surface. The front surface field cell has a front surface region that is of the same conductivity type as the bulk but is more heavily doped. This creates an electric field at the surface which repels the minority carriers. The tandem junction cell has a front surface region of a conductivity type that is opposite to that of the bulk. The junction thus created floats to open circuit voltage on illumination and injects carriers into the bulk which then can be collected at the rear junction. For space use, the front surface field cell is potentially more radiation resistant than the tandem junction cell because the flow of minority carriers (electrons) into the bulk will be less sensitive to the production of recombination centers, particularly in the space charge region at the front surface

Un método de paneles para el cálculo de la resistencia de ola en barcos

Presentamos un método de paneles para el cómputo linealizado del flujo potencial con una superficie libre, y el de la curva de resistencia de olas sobre un cuerpo con formas hidronavales en función del número de Fi-oude. Las ecuaciones gobernantes del flujo potencial con una superficie libre son, la ecuación de Laplace para el potencial de velocidad, con condiciones de borde apropiadas, y la condición de superficie libre basada en la ecuación de Bernoulli. Sin embargo, el problema hidrodinámico resulta incompletamente formulado, en el sentido de Birkhoof , porque permite soluciones con ondas de superficie viajeras, que se propagan en ambas direcciones (corriente arriba y corriente abajo), donde las primeras son consideradas como sin significado físico y deben ser descartadas. La unicidad de la solución es recuperada mediante una extensión de la técnica de Dawson2We present a panel method for a linearized computation of the potential flow with a free surface, and the wave-resistance curve over a ship-like body as a function of the F'roude number. The governing equations of the potential flow with a free surface are, the Laplace equation for the velocity potential with appropriate boundary conditions and the free surface condition based on the Bernoulli equation. However, the hydrodynamic problem is incompletely-posed, in the Birkoof'sensel, because allows solutions with trailing waves propagating in both (upstream and downstream) directions, where the first should be considered as non-physical and should be discarded. The unicity of the solution is recovered by means of an extension of the Dawson's technique2.Peer Reviewe

Forma simétrica de la condición de contorno absorbente DNL para el problema de la resistencia de ola en barcos

En la ref.' hemos presentado un esquema numérico basado en elementos finitos centrados con condición de contorno absorbente (la cual llamamos DNL, por Discrete Yon-Local) para el problema de la resistencia de ola en barcos. Al no agregar viscosidades numéricas este método da curvas de resistencia en función del Froude mejor definidas y posibilita el cálculo de la resistencia por el balance de flujo de momento a la salida. Sin embargo, debido a la naturaleza de la condición absorbente, el sistema resultante es no simétrico y en principio el sistema lineal resultante presenta ciertas dificultades para la factorización. En este trabajo se describe un método por el cual sólo es necesario factorizar una matriz simétrica y con el mismo ancho de banda que una matriz de elementos finitos típica, con el consecuente ahorro de memoria central (RAM).Peer Reviewe

A virtual sensor for electric vehicles’ state of charge estimation

The estimation of the state of charge is a critical function in the operation of electric vehicles. The battery management system must provide accurate information about the battery state, even in the presence of failures in the vehicle sensors. This article presents a new methodology for the state of charge estimation (SOC) in electric vehicles without the use of a battery current sensor, relying on a virtual sensor, based on other available vehicle measurements, such as speed, battery voltage and acceleration pedal position. The estimator was derived from experimental data, employing support vector regression (SVR), principal component analysis (PCA) and a dual polarization (DP) battery model (BM). It is shown that the obtained model is able to predict the state of charge of the battery with acceptable precision in the case of a failure of the current sensor

Implementation and Assessment Methodologies of Teachers' Training Courses for STEM Activities

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Functionalized lactic acid macromonomers polycondensation

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S100B is not a reliable prognostic index in paediatric TBI.

Pediatr Neurosurg. 2007;43(4):258-64