Description of a Hydrogel-Based Micro-Valve As a Library Element for Matlab Simulink

We propose a planar hydrogel-based micro-valve design which is modeled as a library element for Matlab Simulink. For this test case, a pressure pump (voltage source) in series with a micro-valve model (variable fluidic resistance) is built up. The micro-valve subsystem is separated in four main parts. Based on the applied temperature stimulus, the equilibrium length is determined according to an experimentally verified fit function. Furthermore, the equilibrium length considers a static hysteresis effect which is modeled in analogy to the saturation of magnetization in electric transformers. In a second step, the transient behavior follows a first order differential equation, but the cooperate diffusion coefficient is size dependent affecting the rise time of the system. This causes a faster swelling than deswelling of the hydrogel. In the third section, the stiffness property is implemented to calculate the maximum sealing pressure and the resulting gap between the hydrogel and the wall. The fluidic resistance of the micro-valve considers a three-dimensional geometry and is calculated based on a look-up table, extracted from a fluid-structure-interaction (FSI) model generated from a finite element structure. The proposed model allows a full description of the fluidic hydrogel-based micro-valve and is part of an upcoming microfluidic toolbox for Matlab Simulink containing passive elements and optional chemical reactions like mixing fluids and enzyme reactions for future applications.

Kinesin-5 forms a stable bipolar spindle in a fast, irreversible snap

SUMMARYGRAPHICAL ABSTRACTSeparation of duplicated spindle poles is the first step in forming the mitotic spindle. Kinesin-5 crosslinks and slides anti-parallel microtubules, but it is unclear how these two activities contribute to the first steps in spindle formation. In this study we report that in monopolar spindles, the duplicated spindle poles snap apart in a fast and irreversible step that produces a nascent bipolar spindle. Using mutations in Kinesin-5 that inhibit microtubule sliding, we show crosslinking alone drives the fast, irreversible pole separation. Electron tomography revealed microtubule pairs in monopolar spindles have short overlaps that intersect at high angles and are unsuited for ensemble Kinesin-5 sliding. However, maximal extension of a subset of microtubule pairs approaches the length of nascent bipolar spindles and is consistent with a Kinesin-5 crosslinking driven transition. Finally, stochastic microtubule sliding by Kinesin-5 stabilizes the nascent spindle and sets a stereotyped equilibrium length.

Structural and Optical Properties of α-Quartz Cluster with Oxygen-Deficiency Centers

The structural and optical properties of α-quartz cluster with oxygen-deficiency centers (ODCs) defects have been investigated based on the density functional theory (DFT). For cluster models with ODC(I) defect, with the increasing of cluster size and shape, the equilibrium length of Si-Si bond decreases. The excitation peaks of cluster models with ODC(I) defect are from 6.87 eV to 7.39 eV, while the excitation peaks of cluster models with ODC(II) defect are from 5.20 eV to 5.47 eV. We also study the interconversion between ODCs (≡Si-Si≡ bond and divalent Si) induced by UV irradiation. Our study predicted the existence of a metastable structure of ODC(I) for the first time in literature. Our results are in good agreement with the previous results and provide strong theoretical support to the viability of the processes.

Bathymetric Influences on the Estuarine Equilibrium Length and Adjustment Time

Linear theories are extended to enable investigations of how exponentially convergent width and sloping bottom affect the sensitivity of estuarine equilibrium length and adjustment time. This study focuses on the response to river forcing and considers a regime dominated by gravitational circulation, but the results are generalizable. For a range of forcing and bathymetric profiles, the predicted equilibrium length and adjustment time compare favorably with numerical solutions from a width-averaged model. The main findings are that 1) convergent width and sloping bottom reduce the sensitivity of equilibrium length to river forcing. The sensitivity is governed by a dimensionless parameter that measures the degree of width and depth changes sampled by the intrusion length. Hence, the sensitivity is not a constant in a system but varies with forcing: when discharge increases, a shortened estuary experiences less bathymetric changes over its intrusion. The sensitivity therefore increases progressively toward the conventional −⅓ power law. An observational example of variable sensitivity from Delaware Bay is given. 2) Width convergence and bottom slope help accelerate the adjustment process. It is shown that the linear adjustment time is set by the ratio of salt content variations to the discharge perturbation. Hence, under the same forcing, the adjustment time is controlled by the salt content variations, which decrease monotonically with increasing convergence and slope. This means that, to achieve a given length change, a more strongly convergent and sloped system simply requires transport of less salt, thereby needing a shorter adjustment time.

An r-Adaptive Technique for Unstructured Grids Based on the Segment Spring Analogy Method

A simple and effective r-adaptive technique for unstructured grids based on the segment spring analogy method is proposed. The finite element method and a corresponding error estimate method using second derivatives are used for computation. The traditional segment spring analogy method is modified, based on an idea of controlling the equilibrium length of the fictitious springs, and used for mesh adjustment. The principle of making numerical errors distributed uniformly over all elements is applied. Three numerical examples involving the one-dimensional (1D) convection-diffusion equation, the two-dimensional (2D) linear parabolic equation and the 2D Euler equations are presented and the effectiveness of the proposed r-type grid adaptive technique is examined.

Numerical Study of the Elastic Pendulum on the Rotating Earth

The elastic pendulum is a simple physical system represented by nonlinear differential equations. Analytical solutions for the bob trajectories on the rotating earth may be obtained in two limiting cases: for the ideally elastic pendulum with zero unstressed string length and for the Foucault pendulum with an inextensible string. The precession period of the oscillation plane, as seen by the local observer on the rotating earth, is 24 hours in the first case and has a well-known latitude dependence in the second case. In the present work, we have obtained numerical solutions of the nonlinear equations for different string elasticities in order to study the transition from one precession period to the other. It is found that the transition is abrupt and that it occurs for a quite small perturbation of the ideally elastic pendulum, that is, for the unstressed string length equal to about 10−4 of the equilibrium length due to the weight of the bob.

Teaching Experience in Biotransport Course for Undergraduates of Biomedical Engineering

For undergraduate student in biomedical engineering, they usually have very limited background of thermodynamics, heat mass transfer. Fundamental concepts of heat and mass transfer, thermodynamics are necessary at the beginning of the course. For this purpose, we found that Prof. John Chato’s book “Fundamentals of Bioheat Transfer” provides good text and it has been used successfully through our teaching. For example, after introducing the energy conservation law, a focused discussion on how the law is used in biological systems (how energy is generated from bio-chemical reactions, et.al) can be launched. Thermal resistance method and radiation network are easily accepted by the BME students as they have strong electrical background. Vasculature is one of the most important factors in bioheat transfer. It is also important in biomedical engineering field. Thus, the anatomic structure, quantification, thermal equilibrium length of blood vessels, are all taught in details. The Pennes equation and its applications are certainly necessary topics and taught right after the temperature measurement technique session. Medical applications, including hyperthermia, thermal ablation, cryosurgery, cryopreservation, burn evaluation etc. are given from both experimental and theoretical points of view. At the end, successful commercial products and models are also introduced.