Transient Analysis and Control for Scalable Network Systems

The rapidly evolving domain of network systems poses complex challenges, especially when considering scalability and transient behaviors. This thesis aims to address these challenges by offering insights into the transient analysis and control design tailored for large-scale network systems. The thesis consists of three papers, each of which contributes to the overarching goal of this work.The first paper, A closed-loop design for scalable high-order consensus, studies the coordination of nth-order integrators in a networked setting. The paper introduces a novel closed-loop dynamic named serial consensus, which is designed to achieve consensus in a scalable manner and is shown to be implementable through localized relative feedback. In the paper, it is shown that the serial consensus system will be stable under a mild condition — that the underlying network contains a spanning tree — thereby mitigating a previously known scale fragility. Robustness against both model and feedback uncertainties is also discussed.The second paper, Closed-loop design for scalable performance of vehicular formations, expands on the theory on the serial consensus system for the special case when n=2, which is of special interest in the context of vehicular formations. Here, it is shown that the serial consensus system can also be used to give guarantees on the worst-case transient behavior of the closed-loop system. The potential of achieving string stability through the use of serial consensus is explored.The third paper, Input-output pseudospectral bounds for transient analysis of networked and high-order systems, presents a novel approach to transient analysis of networked systems. Bounds on the matrix exponential, coming from the theory on pseudospectra, are adapted to an input-output setting. The results are shown to be useful for high-order matrix differential equations, offering a new perspective on the transient behavior of high-order networked systems

Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s).Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035]info:eu-repo/semantics/publishedVersio

A Frequency Domain Analysis of Slow Coherency in Networked Systems

Network coherence generally refers to the emergence of simple aggregated dynamical behaviours, despite heterogeneity in the dynamics of the subsystems that constitute the network. In this paper, we develop a general frequency domain framework to analyze and quantify the level of network coherence that a system exhibits by relating coherence with a low-rank property of the system's input-output response. More precisely, for a networked system with linear dynamics and coupling, we show that, as the network's \emph{effective algebraic connectivity} grows, the system transfer matrix converges to a rank-one transfer matrix representing the coherent behavior. Interestingly, the non-zero eigenvalue of such a rank-one matrix is given by the harmonic mean of individual nodal dynamics, and we refer to it as the coherent dynamics. Our analysis unveils the frequency-dependent nature of coherence and a non-trivial interplay between dynamics and network topology. We further show that many networked systems can exhibit similar coherent behavior by establishing a concentration result in a setting with randomly chosen individual nodal dynamics.Comment: arXiv admin note: substantial text overlap with arXiv:2101.0098

The RNA binding protein KSRP destabilizes GAP-43 mRNA to limit axonal elongation in cultured hippocampal neurons

The KH-type splicing regulatory protein (KSRP) promotes the decay of AU-rich element (ARE) containing mRNAs. Although KSRP is expressed in the developing and mature nervous system, very little is known about its role in regulating gene expression in the brain. In this study, we utilized in vitro binding and decay studies to examine whether KSRP regulates the stability of the GAP-43 transcript, an ARE-containing neuronal mRNA whose protein product plays a role in axonal growth and synaptic plasticity. We found KSRP destabilizes GAP-43 mRNA by binding to the GAP-43 ARE, a process that depends on the presence of the fourth KH domain in the protein. Furthermore, KSRP competed with another GAP-43 mRNA binding protein, the stabilizing factor HuD, for binding to these ARE sequences. Given that GAP-43 expression is crucial for accurate axonal outgrowth during neuronal development, we also examined the functional consequences of KSRP overexpression and depletion on the axonal outgrowth from primary hippocampal neurons. Overexpression of either full length KSRP or KSRP without the nuclear localization signal hindered axonal outgrowth in these cultures, while overexpression of a mutant protein without the KH4 domain did not have any effect. In contrast, depletion of KSRP led to a dramatic increase in axonal length. Concurrent overexpression of GAP-43 and KSRP rescued the axonal outgrowth deficits seen with KSRP overexpression, but only when the GAP-43 mRNA was targeted to axons using GAP-43 or amphoterin 3 UTR sequences. Together, our results suggest that KSRP is an important regulator of GAP-43 mRNA stability and neuronal differentiation that works in direct opposition to HuD

The World Social Forum as a Portal of Globalization:: Complex Spatialities in Social Movement Studies

Anhand des Konzeptes „Portale der Globalisierung“ soll die Bedeutung des Weltsozialforums (WSF) für die globalisierungskritische Bewegung aufgezeigt werden. Seit 200 bringt das Forum soziale Bewegungen und andere zivilgesellschaftliche Akteure aus verschiedensten Regionen der Welt zusammen, die zudem oft von einem unterschiedlichen ideologischen Hintergrund geprägt sind. Das Forum bietet dieser heterogenen Teilnehmerschaft einen transnationalen Ort für den Erfahrungs- und Ideenaustausch über Globalisierungsprozesse und wie diese beeinlusst werden können. Dieser Artikel analysiert die politischen Dimensionen von Raum, Netzwerk, Ort und räumliche Maßstabsebenen im WSF und zeigt, dass das Konzept „Portale der Globalisierung“ nützlich ist, die Komplexität des Forums zu erfassen. Zudem zeigt der Artikel, dass das WSF ein Portal der Globalisierung ist, in welchem verschiedene Akteure um die Anerkennung ihrer Interpretation des Wesens der Globalisierung ringen.Applying the concept of portals of globalization, the goal of this paper is to capture the signiicance of the World Social Forum (WSF) for the alter-globalization movement. Since 200, the WSF brings together social movements and other civil-society actors that are ideologically or geographically disconnected. It ofers a transnational space for sharing experiences about globalization processes and for facilitating the lows of ideas on how to inluence the course of globalization. Analysing the politics of space, place, network, and scale in the WSF, the paper shows that the concept of portals of globalization helps to capture the spatial complexity of the forum. I argue that the WSF is not simply a place of anti-neoliberalism but a portal of globalization that inhabits diferent actors competing for the recognition of their interpretation of the nature of globalization

Frustration in Biomolecules

Biomolecules are the prime information processing elements of living matter. Most of these inanimate systems are polymers that compute their structures and dynamics using as input seemingly random character strings of their sequence, following which they coalesce and perform integrated cellular functions. In large computational systems with a finite interaction-codes, the appearance of conflicting goals is inevitable. Simple conflicting forces can lead to quite complex structures and behaviors, leading to the concept of "frustration" in condensed matter. We present here some basic ideas about frustration in biomolecules and how the frustration concept leads to a better appreciation of many aspects of the architecture of biomolecules, and how structure connects to function. These ideas are simultaneously both seductively simple and perilously subtle to grasp completely. The energy landscape theory of protein folding provides a framework for quantifying frustration in large systems and has been implemented at many levels of description. We first review the notion of frustration from the areas of abstract logic and its uses in simple condensed matter systems. We discuss then how the frustration concept applies specifically to heteropolymers, testing folding landscape theory in computer simulations of protein models and in experimentally accessible systems. Studying the aspects of frustration averaged over many proteins provides ways to infer energy functions useful for reliable structure prediction. We discuss how frustration affects folding, how a large part of the biological functions of proteins are related to subtle local frustration effects and how frustration influences the appearance of metastable states, the nature of binding processes, catalysis and allosteric transitions. We hope to illustrate how Frustration is a fundamental concept in relating function to structural biology.Comment: 97 pages, 30 figure

Jamming graphs: A local approach to global mechanical rigidity

We revisit the concept of minimal rigidity as applied to frictionless, repulsive soft sphere packings in two dimensions with the introduction of the jamming graph. Minimal rigidity is a purely combinatorial property encoded via Laman’s theorem in two dimensions. It constrains the global, average coordination number of the graph, for example. However, minimal rigidity does not address the geometry of local mechanical stability. The jamming graph contains both properties of global mechanical stability at the onset of jamming and local mechanical stability. We demonstrate how jamming graphs can be constructed using local moves via the Henneberg construction such that these graphs fall under the jurisdiction of correlated percolation. We then probe how jamming graphs destabilize, or become unjammed, by deleting a bond and computing the resulting rigid cluster distribution. We also study how the system restabilizes with the addition of new contacts and how a jamming graph with extra (redundant) contacts destabilizes. The latter endeavor allows us to probe a disk packing in the rigid phase and uncover a potentially new diverging length scale associated with the random deletion of contacts as compared to the study of cut-out (or frozen-in) subsystems