Zero Hausdorff dimension spectrum for the almost Mathieu operator

We study the almost Mathieu operator at critical coupling. We prove that there exists a dense $G_\delta$ set of frequencies for which the spectrum is of zero Hausdorff dimension.Comment: v1: 24 pp. v2: 25 pp, corrected the statement of Theorem 3 and added explanations in the proof of Theorem

Localisation for non-monotone Schroedinger operators

We study localisation effects of strong disorder on the spectral and dynamical properties of (matrix and scalar) Schroedinger operators with non-monotone random potentials, on the d-dimensional lattice. Our results include dynamical localisation, i.e. exponentially decaying bounds on the transition amplitude in the mean. They are derived through the study of fractional moments of the resolvent, which are finite due to resonance-diffusing effects of the disorder. One of the byproducts of the analysis is a nearly optimal Wegner estimate. A particular example of the class of systems covered by our results is the discrete alloy-type Anderson model.Comment: 21pp; expanded introduction, added references, fixed typo

Auditable and performant Byzantine consensus for permissioned ledgers

Permissioned ledgers allow users to execute transactions against a data store, and retain proof of their execution in a replicated ledger. Each replica verifies the transactions’ execution and ensures that, in perpetuity, a committed transaction cannot be removed from the ledger. Unfortunately, this is not guaranteed by today’s permissioned ledgers, which can be re-written if an arbitrary number of replicas collude. In addition, the transaction throughput of permissioned ledgers is low, hampering real-world deployments, by not taking advantage of multi-core CPUs and hardware accelerators. This thesis explores how permissioned ledgers and their consensus protocols can be made auditable in perpetuity; even when all replicas collude and re-write the ledger. It also addresses how Byzantine consensus protocols can be changed to increase the execution throughput of complex transactions. This thesis makes the following contributions: 1. Always auditable Byzantine consensus protocols. We present a permissioned ledger system that can assign blame to individual replicas regardless of how many of them misbehave. This is achieved by signing and storing consensus protocol messages in the ledger and providing clients with signed, universally-verifiable receipts. 2. Performant transaction execution with hardware accelerators. Next, we describe a cloud-based ML inference service that provides strong integrity guarantees, while staying compatible with current inference APIs. We change the Byzantine consensus protocol to execute machine learning (ML) inference computation on GPUs to optimize throughput and latency of ML inference computation. 3. Parallel transactions execution on multi-core CPUs. Finally, we introduce a permissioned ledger that executes transactions, in parallel, on multi-core CPUs. We separate the execution of transactions between the primary and secondary replicas. The primary replica executes transactions on multiple CPU cores and creates a dependency graph of the transactions that the backup replicas utilize to execute transactions in parallel.Open Acces

Media and Message in Modern Political Thought: From the Age of Print to the Age of Digital Reproduction

The dissertation investigates the relationship between media and message in modern political thought. In the research I situate the ideas of three modern political theorists Jean-Jacques Rousseau, Karl Marx, and Theodor Herzl in the material conditions prevailing in the printing industry of their times. I investigate in each case how the media culture the thinker was working in influenced his political ideas. My findings indicate that in all three cases the political ideas were shaped and conditioned by the particular position of the author, the prevailing attitude to the printed word, and the existing media technologies. Based on the historical research, in the last part of the study I explore the future of political ideas in the age of digital hypertexts. Overall, the findings of the research lead me to call for a broadening of conventional analysis of political ideas: Political ideas must be seen as part of the highly regulated streams of information that flow between author and reader in any given historical period