Measuring Burstiness in Data Center Applications

Buffer sizing is a tricky task --- it depends on a large number of variables, ranging from congestion control to traffic engineering. Still, the most unpredictable contributors are the workloads running in the network. The link utilization and burstiness of these workloads dictate the buffer depth needed by a switch. But what is a burst? Do traditional definitions still apply in the age in which switches transfer terabits of data and billions of packets every second? Unless we assess bursts correctly, we are unlikely to size buffers appropriately. In this work, we present a measurement-led evaluation of the burstiness of different data center applications. We address the question of ``what is a burst?'' and assert that common techniques cannot answer this question in modern data centers. We quantify the change in burstiness of the studied applications across multiple vectors, including latency and network perspective, and generalize our results to the common case. Our observations can inform future buffer sizing efforts and guide switch configurations. Our dataset is openly available for the benefit of the community.Leverhulme Trust Isaac Newton Trus

Topological Defects from First Order Gauge Theory Phase Transitions

We investigate the mechanism by which topological defects form in first order phase transitions with a charged order parameter. We show how thick superconductor vortices and heavy cosmic strings form by trapping of magnetic flux. In an external magnetic field, intermediate objects such as strips and membranes of magnetic flux and chains of single winding defects are produced. At non-zero temperature, a variety of spontaneous defects of different winding numbers arise. In cosmology, our results mean that the magnetic flux thermal fluctuations get trapped in a primordial multi-tension string network. The mechanism may also apply to the production of cosmic-like strings in brane collisions. In a thin type-I superconductor film, flux strips are found to be meta-stable while thick vortices are stable up to some critical value of the winding number which increases with the thickness of the film. In addition, a non-dissipative Josephson-like current is obtained across the strips of quantized magnetic flux.Comment: Corrections made on sections 4,5. Higher quality figures in published versio

Quantum Phases of Vortices in Rotating Bose-Einstein Condensates

We investigate the groundstates of weakly interacting bosons in a rotating trap as a function of the number of bosons, $N$, and the average number of vortices, $N_V$. We identify the filling fraction $\nu\equiv N/N_V$ as the parameter controlling the nature of these states. We present results indicating that, as a function of $\nu$, there is a zero temperature {\it phase transition} between a triangular vortex lattice phase, and strongly-correlated vortex liquid phases. The vortex liquid phases appear to be the Read-Rezayi parafermion states

Novel colours and the content of experience

I propose a counterexample to naturalistic representational theories of phenomenal character. The counterexample is generated by experiences of novel colours reported by Crane and Piantanida. I consider various replies that a representationalist might make, including whether novel colours could be possible colours of objects and whether one can account for novel colours as one would account for binary colours or colour mixtures. I argue that none of these strategies is successful and therefore that one cannot fully explain the nature of the phenomenal character of perceptual experiences using a naturalistic conception of representation