Uniqueness, stability and global convergence for a discrete inverse elliptic Robin transmission problem

We derive a simple criterion that ensures uniqueness, Lipschitz stability and global convergence of Newton’s method for the finite dimensional zero-finding problem of a continuously differentiable, pointwise convex and monotonic function. Our criterion merely requires to evaluate the directional derivative of the forward function at finitely many evaluation points and for finitely many directions. We then demonstrate that this result can be used to prove uniqueness, stability and global convergence for an inverse coefficient problem with finitely many measurements. We consider the problem of determining an unknown inverse Robin transmission coefficient in an elliptic PDE. Using a relation to monotonicity and localized potentials techniques, we show that a piecewise-constant coefficient on an a-priori known partition with a-priori known bounds is uniquely determined by finitely many boundary measurements and that it can be uniquely and stably reconstructed by a globally convergent Newton iteration. We derive a constructive method to identify these boundary measurements, calculate the stability constant and give a numerical example.

Introduction: Ten years of WhatsApp: The role of chat apps in the formation and mobilization of online publics

This special issue, curated by Emma Baulch, Ariadna Matamoros-Fernández, and Amelia Johns, marks the end of the first decade of WhatsApp’s existence and offers a collection of essays on the importance of this technology in everyday life. Considering the rapid uptake and ubiquity of WhatsApp in places beyond the Anglophone world, including Brazil, Mexico, Malaysia, and Spain, the seven papers interrogate the opportunities and challenges that the app affords to activists and ordinary users through its main features: end-to-end encryption, groups, and the forward function.

ROUTING IMPLEMENTATION BASED-ON SOFTWARE DEFINED NETWORK USING RYU CONTROLLER AND OPENVSWITCH

Open Flow is a standard protocol for differentiating forward function and control functions to facilitate the management of big network of SDN. The research have been carried out before using the emulator SDN Mininet. However Mininet has many shortcomings, such as the performance of which is less than the maximum due to simulation. Then some researchers also use the Net-FPGA as device. This device is less suitable for small scale because the prices are quite expensive and programming is quite complicated. In this study, SDN implementation carried out using OpenvSwitch as forwarding function mounted on TP-Link that has modificated using openwrt as firmware and Raspberry Pi with Ryu SDN Controller as control functions. The result shows that routing static can be implemented on SDN Network which use Raspberry Pi with Ryu Controller as control function with average bandwith 536.0909 Mbits/sec and average uptime network is 10.45 second.

Research on Control Method of Grid-Connected Inverter Suppressing Grid-Voltage Background Harmonics

The traditional LCL-filter third-order system grid-connected inverter may cause the resonance phenomenon without damping. Also, it will be affected by the distorted grid-voltage background harmonics. In order to overcome these problems, based on the passive damping method, a new control strategy is proposed. The paper analyses the current waveform performance of grid-connected inverter in the condition of grid-voltage background harmonics, derives the feed-forward function for grid-connected inverter. The disadvantages of passive damping could be well solved by damping resistor virtualization of the original system, which realized the active damping suppression of resonance. Simulation results based on the Heric single-phase transformerless grid-connected inverter verify the correctness of the 2éQ: theoretical analysis"theoretical analysis.

Estimating basal properties of ice streams from surface measurements: a non-linear Bayesian inverse approach applied to synthetic data

We propose a new approach to indirectly estimate basal properties of ice streams, i.e. bedrock topography and basal slipperiness, from observations of surface topography and surface velocities. We demonstrate how a maximum a posteriori estimate of basal conditions can be determined using a Bayesian inference approach in a combination with an analytical linearisation of the forward model. Using synthetic data we show that for non-linear media and non-linear sliding law only a few forward-step model evaluations are needed for convergence. The forward step is solved with a numerical finite-element model using the full Stokes equations. The Fréchet derivative of the forward function is approximated through analytical small-perturbation solutions. This approximation is a key feature of the method and the effects of this approximation on model performance are analyzed. The number of iterations needed for convergence increases with the amplitude of the basal perturbations, but generally less than ten iterations are needed.