Multi-agent persistent surveillance under temporal logic constraints

This thesis proposes algorithms for the deployment of multiple autonomous agents for persistent surveillance missions requiring repeated, periodic visits to regions of interest. Such problems arise in a variety of domains, such as monitoring ocean conditions like temperature and algae content, performing crowd security during public events, tracking wildlife in remote or dangerous areas, or watching traffic patterns and road conditions. Using robots for surveillance is an attractive solution to scenarios in which fixed sensors are not sufficient to maintain situational awareness. Multi-agent solutions are particularly promising, because they allow for improved spatial and temporal resolution of sensor information. In this work, we consider persistent monitoring by teams of agents that are tasked with satisfying missions specified using temporal logic formulas. Such formulas allow rich, complex tasks to be specified, such as "visit regions A and B infinitely often, and if region C is visited then go to region D, and always avoid obstacles." The agents must determine how to satisfy such missions according to fuel, communication, and other constraints. Such problems are inherently difficult due to the typically infinite horizon, state space explosion from planning for multiple agents, communication constraints, and other issues. Therefore, computing an optimal solution to these problems is often infeasible. Instead, a balance must be struck between computational complexity and optimality. This thesis describes solution methods for two main classes of multi-agent persistent surveillance problems. First, it considers the class of problems in which persistent surveillance goals are captured entirely by TL constraints. Such problems require agents to repeatedly visit a set of surveillance regions in order to satisfy their mission. We present results for agents solving such missions with charging constraints, with noisy observations, and in the presence of adversaries. The second class of problems include an additional optimality criterion, such as minimizing uncertainty about the location of a target or maximizing sensor information among the team of agents. We present solution methods and results for such missions with a variety of optimality criteria based on information metrics. For both classes of problems, the proposed algorithms are implemented and evaluated via simulation, experiments with robots in a motion capture environment, or both

Manipulation of fermentation dynamics and its effect on silage production, rumen fermentation and animal performance

Corn silage was either left untreated (control) or treated with a-amylase (.05% wet basis, a fermentation stimulant), sorbic acid (.10% wet basis, a fermentation inhibitor), or both in a 2 x 2 factorial arrangement. Experiments were conducted to ascertain treatment effects on: 1) fermentation and aerobic deterioration dynamics, 2) rumen micirobial activity as estimated by in vitro gas production, and 3) the nutritive value of these silages by measuring performance and carcass characteristics of cattle. During a 9-day fermentation study, silages treated with sorbic acid appeared to be better preserved since no yeast or mold growth was observed and because more (P\u3c.02) water-soluble carbohydrates were retained as compared to the other silages (12.2 vs 9.0 % DMB). However, the concentrations of butyric (P\u3c.01) and isobutyric acids (P\u3c.01) were also elevated in sorbic acid-treated silages, indicating clostridial degradation. Silages treated with sorbic acid were more aerobically stable as exhibited by lower temperatures (P\u3c.01), fewer total aerobes (P\u3c.06) and more retention of water-soluble carbohydrates (P\u3c.01) as compared to the other silages. Dry matter loss during ensiling was not significantly affected by treatment. The average dry matter loss during ensiling was 9.7% and ranged from a low of 9.1% for the sorbic acidtreated silage to a high of 10.3% in the a-amylase-treated silage. Spoilage losses were significantly decreased (P\u3c.07) by sorbic acid treatment (7.5 vs 5.7%). Rumen microbes from cattle fed a-amylase-treated silages produced more (14.5 vs 13.0 μl/g/min, P\u3c.09) gas in vitro as did those from cattle fed sorbic acid-treated silages (14.4 vs 13.1, P\u3e.16). During an 85-day silage feeding trial with beef heifers, treatment with a-amylase resulted in no difference in DM intake (mean 5.7 kg/d), greater (P\u3c.01) average daily gain (.84 vs .79 kg/d), and increased weight gain per feed intake (.146 vs .137, P\u3c.01). This improved performance due to α-amylase treatment may have been caused partly by the increased microbial activity and partly by an increased (P\u3c.09) nitrogen-free extract content (45.0 vs 43.2% DMB) of the silage. Results from these studies indicate that sorbic acid treatment of silages resulted in improved preservation and protection from aerobic deterioration. Treatment with α-amylase resulted in improved animal performance. Therefore, better preservation may not result in improved animal performance

Effect of addition of fermentation aids to corn silage on dry matter recovery, performance of slaughter heifers and digestibility by sheep

The effects of corn silage fermentation aids on dry matter recovery of silage, performance, and subsequent carcass data of beef heifers fed the silages and nutrient digestibility of the silages by wethers were determined in this study. Corn green chop in the late dough to early dent stage was harvested during August of 1979 and 1980. For each year, two silos were assigned to one of four silage treatments with or without fermentation aids added. The four experimental corn silage treatments were: (1) an untreated control silage; (2) treated with Silabac, a live lactobacillus preparation; (3) treated with Culbac, a dead lactobacillus preparation; and (4) treated with Crop Cure, sodium diacetate. Samples of the ensiled materials were taken for later determination of dry matter recovery. The ensiled materials were allowed to ferment for approximately 140 to 150 days before the first silo of each treatment was opened. Fresh silage samples were taken during both years when the silos were opened and at 28-day intervals thereafter. In addition, a sample of spoiled silage was taken from one silo of each treatment in 1980. These samples were taken in order to determine the dry matter recovery and nutrient composition of each treatment. In the fall of 1979 and 1980, Angus beef heifer calves were pur-chased during the Tennessee fall feeder calf sales. In mid-December of each year heifers were allotted, using several parameters, to eight groups of five animals each, two groups per treatment, with the effort being made to have maximum equality of all parameters. Two feedlot trials, designated as the 1979-80 trial and the 1980-81 trial, were then begun. These trials were partitioned into two phases— the silage-feeding phase and the full-feeding phase. At approximately 28-day intervals throughout each phase and at the end of each phase body weights were taken. Utilizing these weights and the feed intakes of the heifers during these intervals, the gains and feed efficiencies of the heifers of each treatment were calculated. Backfat thicknesses of the heifers were measured using a somoscope prior to the beginning of the silage-feeding phase and at the end of the silage-feeding phase. Backfat was also measured during the full-feeding phase, initially at four-week intervals and later at two-week intervals as heifers approached 12 mm backfat thickness, which was predetermined as the criterion to send each heifer to slaughter. Backfat thickness data were also studied to determine if there were any treatment effects. After chilling the carcasses of the slaughtered heifers for 48 hours, several carcass parameters were either measured or calculated and the data compared to determine possible treatment effects. A total collection digestion trial was conducted concurrently with the 1979-80 feedlot trial. Some silage from one of the silos of each treatment was removed, stored, and then fed to mature wethers averaging 74.5 kg in body weight. Nutrient digestibility of the corn silage treat-ments by the wethers were determined and compared. Two-year means of the dry matter recoveries of each treatment were not significantly different (P\u3e.G6); however, the statistical analyses were considered to be inconclusive due to a low number of replicates. The dry matter recovery after ensiling losses, after spoilage losses, and total dry matter recovery for each corn silage treatment, respectively, were 88.3, 94.7, and 83.1% for the control; 89.3, 95.4, and 84.7% for Silabac; 94.9, 96.3, and 91.2% for Culbac; and 91.9, 93.3, and 85.2% for Crop Cure. It appears that, except for the Culbac-treated corn silage, addition of fermentation aids had little effect on improvement of dry matter recovery. The nutrient composition of the corn silage treatments of the 1979-80 trial was similar among treatments for all constituents. In the 1980-81 trial, silages with additives were lower (P\u3c.01) in dry matter as compared to the control. All other constituents, except lignin, were not different (P\u3e.05) among treatments. The Silabac-treated silage was higher (P\u3c.05) and the Crop Cure-treated silage was lower (P\u3c.05) in lignin content than the control, the reason for which is not understood. Fermentation aids added to the corn silages during ensiling did not significantly affect (P\u3e.05) intake, gain, or feed efficiencies of the slaughter beef heifers as compared to the control during the silage-feeding phase. Also, there were no significant (P\u3e.05) treatment effects in intake, gain, or feed efficiencies during the full-feeding phase. There were no significant differences (P\u3e.05) among treatments for two-year means of any of the backfat thicknesses, which were measured at various times, or for any of the carcass parameters, except for fat thickness and yield grades. Silabac and Culbac treatment backfat thick-nesses and yield grades were found to be significantly lower (P\u3c.05) than the control and Crop Cure treatments. Differences in fat thicknesses may have been due to changes in acetate levels in the silages due to the addition of fermentation aids and subsequent change in the rumen acetate levels of the heifers. Yield grade differences were probably a function of the fat thickness differences. In the total collection digestion trial, wethers fed the fermenta-tion aid-treated silages consumed significantly less (P\u3c.05) dry matter than wethers fed the control. No significant differences (P\u3e.05) were found among rations in apparent nutrient digestion coefficients for any of the nutrient constituents except for those of crude protein and ether extract. Differences in ether extract digestibilities were considered inconclusive due to low ether extract contents in the rations. Crude protein digestibilities by wethers were depressed significantly (P\u3c.05) in the Culbac- and Crop Cure-treated rations as compared to the control and Silabac-treated rations. Wethers offered the Crop Cure-treated ration had lower crude protein digestibility which was attributed to a low crude protein percentage in the ration and an increased acid-detergent fiber nitrogen percentage as compared to the other rations. Depression of crude protein digestibility by Culbac addition could not be explained

STL: Surprisingly Tricky Logic (for System Validation)

Much of the recent work developing formal methods techniques to specify or learn the behavior of autonomous systems is predicated on a belief that formal specifications are interpretable and useful for humans when checking systems. Though frequently asserted, this assumption is rarely tested. We performed a human experiment (N = 62) with a mix of people who were and were not familiar with formal methods beforehand, asking them to validate whether a set of signal temporal logic (STL) constraints would keep an agent out of harm and allow it to complete a task in a gridworld capture-the-flag setting. Validation accuracy was $45\% \pm 20\%$ (mean $\pm$ standard deviation). The ground-truth validity of a specification, subjects' familiarity with formal methods, and subjects' level of education were found to be significant factors in determining validation correctness. Participants exhibited an affirmation bias, causing significantly increased accuracy on valid specifications, but significantly decreased accuracy on invalid specifications. Additionally, participants, particularly those familiar with formal methods, tended to be overconfident in their answers, and be similarly confident regardless of actual correctness. Our data do not support the belief that formal specifications are inherently human-interpretable to a meaningful degree for system validation. We recommend ergonomic improvements to data presentation and validation training, which should be tested before claims of interpretability make their way back into the formal methods literature

Robust Multi-Agent Coordination from CaTL+ Specifications

We consider the problem of controlling a heterogeneous multi-agent system required to satisfy temporal logic requirements. Capability Temporal Logic (CaTL) was recently proposed to formalize such specifications for deploying a team of autonomous agents with different capabilities and cooperation requirements. In this paper, we extend CaTL to a new logic CaTL+, which is more expressive than CaTL and has semantics over a continuous workspace shared by all agents. We define two novel robustness metrics for CaTL+: the traditional robustness and the exponential robustness. The latter is sound, differentiable almost everywhere and eliminates masking, which is one of the main limitations of the traditional robustness metric. We formulate a control synthesis problem to maximize CaTL+ robustness and propose a two-step optimization method to solve this problem. Simulation results are included to illustrate the increased expressivity of CaTL+ and the efficacy of the proposed control synthesis approach.Comment: Submitted to ACC 202