Characterization and Control of Conservative and Non-conservative Network Dynamics

Diffusion processes are instrumental to describe the movement of a continuous quantity in a network of interacting agents. Here, we present a framework for diffusion in networks and study in particular two classes of agent interactions depending on whether the total network quantity follows a conservation law. Focusing on probabilistic, asymmetric interactions between agents, we define how the dynamics of conservative and non-conservative networks relate to the weighted in-degree and out-degree Laplacians. For uncontrolled networks, we compare the convergence behavior of both types of networks as a function of the eigenvectors of the weighted graph Laplacians. For networks with exogenous controls, we also analyze convergence and provide a method to measure the difference between conservative and non-conservative network dynamics based on the comparison of their respective reachable sets. The presented network control framework enables the comparative study of the dynamic and asymptotic network behavior for conservative and non-conservative networks

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Non-linear electrophoresis of ideally polarizable particles

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 219-229).This thesis investigates the non-linear regime of electrophoresis, in particular the variation of electrophoretic velocity with electric field at high field strengths. Known theoretical approaches to the problem accounting for ion steric effects, dielectric decrement effects and charge-induced thickening are consolidated, further developed and validated using numerical simulations. In doing so, the influences of the relative strengths of surface conductivity and bulk conductivity and of the relative importance of advection to diffusive transport in the electrolyte are both investigated. In addition, further light is shed on the dependence of electrophoretic mobility on the ionic and particle sizes, and on the relevant ionic diffusivities.by Wai Hong Ronald Chan.S.B

Nonlinear electrophoresis of ideally polarizable particles

International audienceWe focus in this paper on the nonlinear electrophoresis of ideally polarizable particles. At high applied voltages significant ionic exchange occurs between the electric double layer which surrounds the particle and the bulk solution. In addition steric effects due to the finite size of ions drastically modify the electric potential distribution in the electric double layer. In this situation the velocity field the electric potential and the ionic concentration in the immediate vicinity of the particle are described by a complicated set of coupled nonlinear partial differential equations. In the general case these equations must be solved numerically. In this study we rely on a numerical approach to determine the electric potential the ionic concentration and the velocity field in the bulk solution surrounding the particle. The numerical simulations rely on a pseudo-spectral method which was used successfully by Chu and Bazant [J. Colloid Interface Sci.315(1) 319–329 (2007)] to determine the electric potential and the ionic concentration around an ideally polarizable metallic sphere. Our numerical simulations also incorporate the steric model developed by Kilic et al. [Phys. Rev. E75 021502 (2007)] to account for crowding effects in the electric double layer advective transport and for the presence of a body force in the bulk electrolyte. The simulations demonstrate that surface conduction significantly decreases the electrophoretic mobility of polarizable particles at high zeta potential and at high applied electric field. Advective transport in the electric double layer and in the bulk solution is also shown to significantly impact surface conduction