Protocol design contests

In fields like data mining and natural language processing, design contests have been successfully used to advance the state of the art. Such contests offer an opportunity to bring the excitement and challenges of protocol design---one of the core intellectual elements of research and practice in networked systems---to a broader group of potential contributors, whose ideas may prove important. Moreover, it may lead to an increase in the number of students, especially undergraduates or those learning via online courses, interested in pursuing a career in the field. We describe the creation of the infrastructure and our experience with a protocol design contest conducted in MIT's graduate Computer Networks class. This contest involved the design and evaluation of a congestion-control protocol for paths traversing cellular wireless networks. One key to the success of a design contest is an unambiguous, measurable objective to compare protocols. In practice, protocol design is the art of trading off conflicting goals with each other, but in this contest, we specified that the goal was to maximize \log(\mbox{throughput}/\mbox{delay}). This goal is a good match for applications such as video streaming or videoconferencing that care about high throughput and low interactive delays. Some students produced protocols whose performance was better than published protocols tackling similar goals. Furthermore, the convex hull of the set of all student protocols traced out a tradeoff curve in the throughput-delay space, providing useful insights into the entire space of possible protocols. We found that student protocols diverged in performance between the training and testing traces, indicating that some students had overtrained ("overfitted") their protocols to the training trace. Our conclusion is that, if designed properly, such contests could benefit networking research by making new proposals more easily reproducible and amenable to such "gamification," improve networked systems, and provide an avenue for outreach

Genotoxicity biomonitoring of sewage in two municipal wastewater treatment plants using the Tradescantia pallida var. purpurea bioassay

The genotoxicity of untreated and treated sewage from two municipal wastewater treatment plants (WTP BN and WTP SJN) in the municipality of Porto Alegre, in the southern Brazilian state of Rio Grande do Sul, was evaluated over a one-year period using the Tradescantia pallida var. purpurea (Trad-MCN) bioassay. Inflorescences of T. pallida var. purpurea were exposed to sewage samples in February (summer), April (autumn), July (winter) and October (spring) 2009, and the micronuclei (MCN) frequencies were estimated in each period. The high genotoxicity of untreated sewage from WTP BN in February and April was not observed in treated sewage, indicating the efficiency of treatment at this WTP. However, untreated and treated sewage samples from WTP SJN had high MCN frequencies, except in October, when rainfall may have been responsible for reducing these frequencies at both WTPs. Physicochemical analyses of sewage from both WTPs indicated elevated concentrations of organic matter that were higher at WTP SJN than at WTP BN. Chromium was detected in untreated and treated sewage from WTP SJN, but not in treated sewage from WTP BN. Lead was found in all untreated sewage samples from WTP SJN, but only in the summer and autumn at WTP BN. These results indicate that the short-term Trad-MCN genotoxicity assay may be useful for regular monitoring of municipal WTPs

Mineral dust increases the habitability of terrestrial planets but confounds biomarker detection

Identification of habitable planets beyond our solar system is a key goal of current and future space missions. Yet habitability depends not only on the stellar irradiance, but equally on constituent parts of the planetary atmosphere. Here we show, for the first time, that radiatively active mineral dust will have a significant impact on the habitability of Earth-like exoplanets. On tidally-locked planets, dust cools the day-side and warms the night-side, significantly widening the habitable zone. Independent of orbital configuration, we suggest that airborne dust can postpone planetary water loss at the inner edge of the habitable zone, through a feedback involving decreasing ocean coverage and increased dust loading. The inclusion of dust significantly obscures key biomarker gases (e.g. ozone, methane) in simulated transmission spectra, implying an important influence on the interpretation of observations.We demonstrate that future observational and theoretical studies of terrestrial exoplanets must consider the effect of dust