MULTI-ROBOT COVERAGE WITH DYNAMIC COVERAGE INFORMATION COMPRESSION

This work considers the problem of coverage of an initially unknown environment by a set of autonomous robots. A crucial aspect in multi-robot coverage involves robots sharing information about the regions they have already covered at certain intervals, so that multiple robots can avoid repeated coverage of the same area. However, sharing the coverage information between robots imposes considerable communication and computation overhead on each robot, which increases the robots’ battery usage and overall coverage time. To address this problem, we explore a novel coverage technique where robots use an information compression algorithm before sharing their coverage maps with each other. Specifically, we use a polygonal approximation algorithm to represent any arbitrary region covered by a robot as a polygon with a fixed, small number of vertices. At certain intervals, each robot then sends this small set of vertices to other robots in its communication range as its covered area, and each receiving robot records this information in a local map of covered regions so that it can avoid repeat coverage. The coverage information in the map is then utilized by a technique called spanning tree coverage (STC) by each robot to perform area coverage. We have verified the performance of our algorithm on simulated Coroware Corobot robots within the Webots robot simulator with different sizes of environments and different types of obstacles in the environments, while modelling sensor noise from the robots’ sensors. Our results show that using the polygonal compression technique is an effective way to considerably reduce data transfer between robots in a multi-robot team without sacrificing the performance and efficiency gains that communication provides to such a system

Using extreme value theory for the estimation of risk metrics for capacity adequacy assessment

This paper investigates the use of extreme value theory for modelling the distribution of demand-net-of-wind for capacity adequacy assessment. Extreme value theory approaches are well-established and mathematically justified methods for estimating the tails of a distribution and so are ideally suited for problems in capacity adequacy, where normally only the tails of the relevant distributions are significant. The extreme value theory peaks over threshold approach is applied directly to observations of demand-net-of-wind, meaning that no assumption is needed about the nature of any dependence between demand and wind. The methodology is tested on data from Great Britain and compared to two alternative approaches: use of the empirical distribution of demand-net-of-wind and use of a model which assumes independence between demand and wind. Extreme value theory is shown to produce broadly similar estimates of risk metrics to the use of the above empirical distribution but with smaller sampling uncertainty. Estimates of risk metrics differ when the approach assuming independence is used, especially when data across different historical years are pooled, suggesting that assuming independence might result in the over- or under-estimation of risk metrics.Comment: 8 pages, 4 figure

In situ imaging of vortices in Bose-Einstein condensates

Laboratory observations of vortex dynamics in Bose-Einstein condensates (BECs) are essential for determination of many aspects of superfluid dynamics in these systems. We present a novel application of dark-field imaging that enables \texttt{\it in situ} detection of two-dimensional vortex distributions in single-component BECs, a step towards real-time measurements of complex two-dimensional vortex dynamics within a single BEC. By rotating a $^{87}$Rb BEC in a magnetic trap, we generate a triangular lattice of vortex cores in the BEC, with core diameters on the order of 400 nm and cores separated by approximately 9 $\mu$m. We have experimentally confirmed that the positions of the vortex cores can be determined without the need for ballistic expansion of the BEC.Comment: 5 pages, 4 figure

Evaluation of Protein from Distillers Grains in Finishing Diets on Nutrient Digestibility

A metabolism trial was conducted to evaluate protein from modified distillers grains plus solubles (MDGS) in finishing diets on nutrient digestibility and ruminal fermentation characteristics. Isolated protein from corn was not different than MDGS for dry matter, organic matter, or neutral detergent fiber digestibility. However, steers fed MDGS tended to have lower total tract organic matter digestibility compared to corn and protein from corn. Protein had greater total tract organic matter and starch digestibility than MDGS. Protein from corn did not contribute towards the lower digestibility of MDGS. Protein is more easily digestible than the other components in distillers grains plus solubles

Evaluation of Protein from Distillers Grains in Finishing Diets on Nutrient Digestibility

A metabolism trial was conducted to evaluate protein from modified distillers grains plus solubles (MDGS) in finishing diets on nutrient digestibility and ruminal fermentation characteristics. Isolated protein from corn was not different than MDGS for dry matter, organic matter, or neutral detergent fiber digestibility. However, steers fed MDGS tended to have lower total tract organic matter digestibility compared to corn and protein from corn. Protein had greater total tract organic matter and starch digestibility than MDGS. Protein from corn did not contribute towards the lower digestibility of MDGS. Protein is more easily digestible than the other components in distillers grains plus solubles

Generation of high-winding-number superfluid circulation in Bose-Einstein condensates

We experimentally and numerically demonstrate a method to generate multiply quantized superfluid circulation about an obstacle in highly oblate Bose-Einstein condensates (BECs). We experimentally achieve pinned superflow with winding numbers as high as 11, which persists for at least 4 s. Our method conceptually involves spiraling a blue-detuned laser beam, around and towards the center of the BEC, and is experimentally implemented by moving the BEC in a spiral trajectory around a stationary laser beam. This optical potential serves first as a repulsive stirrer to initiate superflow, and then as a pinning potential to transport the superfluid circulation within the BEC. The spiral technique can be used either to generate a high-winding-number persistent current, or for controlled placement of a cluster of singly quantized vortices of the same circulation. Thus, the technique may serve as a building block in experimental architectures to create on-demand vortex distributions in BECs