Parallel Simulation of Individual-Based, Physiologically-Structured Population and Predator-Prey Ecology Models

Utilizing as testbeds physiologically-structured, individual-based models for fish and Daphnia populations, techniques for the parallelization of the simulation are developed and analyzed. The techniques developed are generally applicable to individual-based models. For rapidly reproducing populations like Daphnia which are load balanced, then global birth combining is required. Super-scalar speedup was observed in simulations on multi-core desktop computers. The two populations are combined via a size-structured predation module into a predator-prey system with sharing of resource weighted by relative mass. The individual-based structure requires multiple stages to complete predation. Two different styles of parallelization are presented. The first distributes both populations. It decouples the populations for parallel simulation by compiling, at each stage, tables of information for each of the distributed predators. Predation is completed for all fish at one time. This method is found to be generally applicable, has near perfect scaling with increasing processors, and improves performance as the workload to communications ratio improves with increasing numbers of predator cohorts. But it does not take best advantage of our testbed models. The second design decouples the workload for parallel simulation by duplicating the predator population on all nodes. This reduces communications to simple parallel reductions similar to the population models, but increases the number of cycles required for predation. The performance of the population models is mimicked. Finally, the extinction and persistence behaviors of the predator-prey model are analyzed. The roles of the predation parameters, individual models, and initial populations are determined. In the presence of density-dependent mortality moderating the prey population, competition via resource of the larger fish versus the smaller is found to be a vital control to prevent extinction of prey population. If unconstrained, the juvenile fish classes can — through their rapid initial growth and predation upon the juvenile prey classes — push the prey population to extinction. Persistence of the predator-prey community is thus threatened when the fish population is dominated by juveniles. Conversely, the presence of larger fish moderates the juveniles and stabilizes the community via competition for shared resource

Design and application of a wireless torque sensor for CNC milling

A Smart Machining System for Computer Numerical Control (CNC) Milling continually adjusts the cutting process parameters to optimize for cutting tool life and material removal rate. The system depends on sensors to gather information from the machine during cutting, but commercially available sensors detract from the effectiveness of the cutting system by lowering the system stiffness. This research focuses on the development of the electronics for a Smart Tool Holder (STH) and potential applications such as measurement of mechanical cutting power and suppression of chatter. The STH is a standard milling tool holder modified to hold a torque strain gauge bridge, a thermocouple and a Bluetooth radio transmitter. The STH is meant to overcome some of the different limitations imposed by bed dynamometers, microphones and spindle power sensors without reducing the system stiffness. Comparison of the mechanical power estimates from the STH and a conventional power sensor showed 10% difference

Who Will Retweet This? Automatically Identifying and Engaging Strangers on Twitter to Spread Information

There has been much effort on studying how social media sites, such as Twitter, help propagate information in different situations, including spreading alerts and SOS messages in an emergency. However, existing work has not addressed how to actively identify and engage the right strangers at the right time on social media to help effectively propagate intended information within a desired time frame. To address this problem, we have developed two models: (i) a feature-based model that leverages peoples' exhibited social behavior, including the content of their tweets and social interactions, to characterize their willingness and readiness to propagate information on Twitter via the act of retweeting; and (ii) a wait-time model based on a user's previous retweeting wait times to predict her next retweeting time when asked. Based on these two models, we build a recommender system that predicts the likelihood of a stranger to retweet information when asked, within a specific time window, and recommends the top-N qualified strangers to engage with. Our experiments, including live studies in the real world, demonstrate the effectiveness of our work

MRTF specifies a muscle-like contractile module in Porifera

Muscle-based movement is a hallmark of animal biology, but the evolutionary origins of myocytes are unknown. Although believed to lack muscles, sponges (Porifera) are capable of coordinated whole-body contractions that purge debris from internal water canals. This behavior has been observed for decades, but their contractile tissues remain uncharacterized with respect to their ultrastructure, regulation, and development. We examine the sponge Ephydatia muelleri and find tissue-wide organization of a contractile module composed of actin, striated-muscle myosin II, and transgelin, and that contractions are regulated by the release of internal Ca2+ stores upstream of the myosin-light-chain-kinase (MLCK) pathway. The development of this contractile module appears to involve myocardin-related transcription factor (MRTF) as part of an environmentally inducible transcriptional complex that also functions in muscle development, plasticity, and regeneration. As an actin-regulated force-sensor, MRTF-activity offers a mechanism for how the contractile tissues that line water canals can dynamically remodel in response to flow and can re-form normally from stem-cells in the absence of the intrinsic spatial cues typical of animal embryogenesis. We conclude that the contractile module of sponge tissues shares elements of homology with contractile tissues in other animals, including muscles, indicating descent from a common, multifunctional tissue in the animal stem-lineage.publishedVersio

Thomas H. Charlton (1938–2010)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/88059/1/j.1548-1433.2011.01388.x.pd