Unifying Brillouin scattering and cavity optomechanics

So far, Brillouin scattering and cavity optomechanics were mostly disconnected branches of research -- although both deal with photon-phonon coupling. This begs for the development of a broader theory that contains both fields. Here, we derive the dynamics of optomechanical cavities from that of Brillouin-active waveguides. This explicit transition elucidates the link between phenomena such as Brillouin amplification and electromagnetically induced transparency. It proves that effects familiar from cavity optomechanics all have traveling-wave partners, but not vice versa. We reveal a close connection between two parameters of central importance in these fields: the Brillouin gain coefficient and the zero-point optomechanical coupling rate. This enables comparisons between systems as diverse as ultracold atom clouds, plasmonic Raman cavities and nanoscale silicon waveguides. In addition, back-of-the-envelope calculations show that unobserved effects, such as photon-assisted amplification of traveling phonons, are now accessible in existing systems. Finally, we formulate both circuit- and cavity-oriented optomechanics in terms of vacuum coupling rates, cooperativities and gain coefficients, thus reflecting the similarities in the underlying physics.Comment: published manuscript, minor change

Analysis of enhanced stimulated Brillouin scattering in silicon slot waveguides

Stimulated Brillouin scattering has attracted renewed interest with the promise of highly tailorable integration into the silicon photonics platform. However, significant Brillouin amplification in silicon waveguides has yet to be shown. In an effort to engineer a structure with large photon-phonon coupling, we analyzed both forward and backward Brillouin scattering in high-index-contrast silicon slot waveguides. The calculations predict that gradient forces enhance the Brillouin gain in narrow slots. We estimate a currently feasible gain of about $10^{5} \, \text{W}^{-1}\text{m}^{-1}$, which is an order of magnitude larger than in a stand-alone silicon wire. Such efficient coupling could enable a host of Brillouin technologies on a mass-producible silicon chip

Need for narrative

What do consumers need from a narrative? How can videographers satisfy those needs? Through semi-structured interviews with 55 Eurostar passengers from 14 countries, this film documents how people define narratives, why they need them, and how they experience the effects of need for narrative. The adjoining commentary contributes to the development of videography as an attractive method by introducing the videographer’s perspective and elucidating key story elements that can help satisfy viewers’ needs for narrative. The suggested approach maintains the vivid quality of videography and respects its methodological rigour, while increasing its effectiveness in close alignment with a consumer society that visual communication increasingly permeates. As such, the commentary and the film jointly unveil videographers’ etic and viewers’ emic use and evaluation of the videographic method

The effect of an optical network on-chip on the performance of chip multiprocessors

Optical networks on-chip (ONoC) have been proposed to reduce power consumption and increase bandwidth density in high performance chip multiprocessors (CMP), compared to electrical NoCs. However, as buffering in an ONoC is not viable, the end-to-end message path needs to be acquired in advance during which the message is buffered at the network ingress. This waiting latency is therefore a combination of path setup latency and contention and forms a significant part of the total message latency. Many proposed ONoCs, such as Single Writer, Multiple Reader (SWMR), avoid path setup latency at the expense of increased optical components. In contrast, this thesis investigates a simple circuit-switched ONoC with lower component count where nodes need to request a channel before transmission. To hide the path setup latency, a coherence-based message predictor is proposed, to setup circuits before message arrival. Firstly, the effect of latency and bandwidth on application performance is thoroughly investigated using full-system simulations of shared memory CMPs. It is shown that the latency of an ideal NoC affects the CMP performance more than the NoC bandwidth. Increasing the number of wavelengths per channel decreases the serialisation latency and improves the performance of both ONoC types. With 2 or more wavelengths modulating at 25 Gbit=s , the ONoCs will outperform a conventional electrical mesh (maximal speedup of 20%). The SWMR ONoC outperforms the circuit-switched ONoC. Next coherence-based prediction techniques are proposed to reduce the waiting latency. The ideal coherence-based predictor reduces the waiting latency by 42%. A more streamlined predictor (smaller than a L1 cache) reduces the waiting latency by 31%. Without prediction, the message latency in the circuit-switched ONoC is 11% larger than in the SWMR ONoC. Applying the realistic predictor reverses this: the message latency in the SWMR ONoC is now 18% larger than the predictive circuitswitched ONoC

The means to justify the end: How the way in which decisions to intervene are communicated to users can combat cyber harassment in social media

Cyber harassment does not only have harmful effects for social network sites, because victims tend to exit the service (Avery 2010; Martin and Smith 2008), but the emotional distress brought on by the online aggression has also caused victims to take their own lives (Parker 2012). At the same time, social media users are often upset when network providers intervene with the network and deem such an intrusion an unjust occurrence (Brunk 2012; Davis 2007; Pruitt 2003). The general aim of this paper is to answer the call for “making a difference” research that the Association for Consumer Research North American Conference 2013 has put out. Our intention has been to explore how the aforementioned catch-22 can be resolved through framing the ways in which decisions to intervene are communicated to users. This work expands on existing persuasion and victim identification effects. First, we contend that a decision to intervene based on a story has a more positive effect on user perception that the decision is just than an analytical, factual format. We further distinguish two main components of identity: personal and social (Dollinger et al. 1996; Reid and Deaux 1996). We explore whether the effect of the story over the analytical format holds across both components. Second, we further understanding of the mechanism underlying the presentation format effect. We examine whether the narrative transportation that people experience may lead to a justice perception that the story events imply. Third, we move beyond the prediction that presentation format will be associated with justice perception by exploring an intraindividual moderator that influences this relationship. The current research investigates why self-referencing may lead to either less or more positive justice perceptions under the framework of the story and analytical presentation forma