Theory-Motivated Benchmark Models and Superpartners at the Tevatron

Recently published benchmark models have contained rather heavy superpartners. To test the robustness of this result, several benchmark models have been constructed based on theoretically well-motivated approaches, particularly string-based ones. These include variations on anomaly and gauge-mediated models, as well as gravity mediation. The resulting spectra often have light gauginos that are produced in significant quantities at the Tevatron collider, or will be at a 500 GeV linear collider. The signatures also provide interesting challenges for the LHC. In addition, these models usually account for electroweak symmetry breaking with relatively less fine-tuning than previous benchmark models.Comment: 44 pages, 4 figures; some typos corrected. Revisions reflect published versio

The mid-infrared instrument for the James Webb space telescope, II: design and build

Instrumentatio

A computer simulation of the oxygen balance in a cold climate winter storage WSP during the critical spring warm-up period

The paper considers factors that determine the oxygen balance in extreme climate waste stabilisation ponds during the critical spring warm-up period. At this time BOD load on the pond is a maximum, due to accumulation of wastewater under the ice during the winter. The paper describes the operation of a typical cold climate WSP and the events leading to a balanced steady state system as spring develops into summer. A mathematical model to simulate conditions within a batch fed experimental pond over the transient period is described. To model temperature changes in the water body experimental data were fitted to a generalised equation based on diurnal fluctuations in air temperature. The results are plotted in a normalised form and show the diurnal fluctuation and time lapse as the depth of the pond increases. Maximum daily water temperature lags behind maximum light intensity. Bacterial growth is simulated by a Monod kinetic model in which growth rate depends on initial substrate concentration; temperature compensation is applied using a temperature activity coefficient. Oxygen utilisation is calculated from substrate removal. Algal growth rate is more complicated as it is affected by temperature and light availability. Algal oxygen production potential is considered in terms of its primary metabolite yield, which is then used in a Monod equation to estimate the growth rate. The model uses a mass balance approach to determine dissolved oxygen concentration in the pond. The model is still in a simple form but shows reasonable agreement, in terms of events and time lapses, to measured parameters in experimental ponds recovering from ice cover

Multi-armed bandits with metric switching costs

In this paper we consider the stochastic multi-armed bandit with metric switching costs. Given a set of locations (arms) in a metric space and prior information about the reward available at these locations, cost of getting a sample/play at every location and rules to update the prior based on samples/plays, the task is to maximize a certain objective function constrained to a distance cost of L and cost of plays C. This fundamental problem models several stochastic optimization problems in robot navigation, sensor networks, labor economics, etc. In this paper we consider two natural objective functions – future utilization and finite horizon. We develop a common duality-based framework to provide the first approximation algorithms in the metric switching cost model, the approximation ratios being small constant factors. Since both problems are Max-SNP hard, this result is the best possible. We also show an “adaptivity ” result, namely, there exists a policy which orders the arms and visits them in that fixed order without revisiting any arm and this policy gives at least Ω(1) fraction reward of the fully adaptive policy. The overall technique involves a subtle variant of the widely used Gittins index, and the ensuing structural characterizations will be independently of interest in the context of bandit problems with complicated side-constraints. This combines two papers [25, 26] appearing in STOC 2007 and ICALP 2009 conferences respectively