Verifying plans for multiple agents

Abstract

Research in distributed artificial intelligence planning has historically focused on two distinct classes of problems. One paradigm has been that of 'planning for multiple agents', which considers issues inherent in centrally directed multi-agent execution. The second paradigm has been 'distributed planning', where multiple agents more autonomously participate in coordinating and deciding upon their own actions. The work described in this paper is in the first category, planning for multiple agents. Taking the STRIPS representation of actions, and directed acrylic graphs (DAGs) as plan representations particularly well suited to parallel execution, it formally analyses the following question: how can a DAG plan be verified (i.e. how can we be sure such a plan will be correct, given our uncertainty about exactly when unconstrained parallel actions will be performed)? A method is presented for verifying the correctness of plans for multiple agents, represented as DAGs. The technique allows for the efficient analysis of a plan, despite its many potential execution histories.     

ELECTROSTATIC EFFECTS ON PHYSICAL PROPERTIES OF PARTICULATE WHEY PROTEIN ISOLATE GELS

Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2‐5.8) with no added NaCl and adjusting the NaCl (0.2‐0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (γ_f), fracture stress (σ_f), and a measure of strain hardening (R_0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (B_gel). Overlaying σ_f and γ_f curves for pH and NaCl treatments demonstrated an overlap where gels of equal σ_f and γ_f could be formed by adjusting pH or NaCl concentration. The high fracture stress (σ_f～ 23 kPa and γ_f～ 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (σ_f～ 13 kPa and γ_f～ 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R_0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n‐ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties.     

A MODIFIED PATTERN SEARCH METHOD WITH RELAXED LEXICOGRAPHIC MINIMIZATION FOR ENGINEERING DESIGN

In engineering design, many design problems have multiple constraints and objectives, which may be non-differentiable. For this problem type, only zero-order solution methods are applicable. In this paper, a relaxed lexicographic pattern search method is presented for solving this design problem type, where the objectives are preferenced in either an Archimedean or preemptive formulation. The Hooke-Jeeves (HJ) pattern search method is the basis of this method, which is implemented as the MORPS (Multi-Objective Randomized Pattern Search) algorithm. The HJ pattern search method is used because it requires only function values and has an intuitive graphical interpretation through which to gain insight into the nature of complex design spaces. A relatively new class of simultaneous product/process design problem utilizing virtual prototypes to support design for disassembly is introduced to motivate the need for the MORPS algorithm. An example, based on the design of an automotive center console for disassembly, illustrates the application of the MORPS algorithm.     

CITY MANAGERS: Do They Promote Fiscal Efficiency?

ABSTRACT: Debate over the virtues of one or another form of municipal government has raged since the early days of the reform movement. Proponents of professional municipal management have based their argument on the virtues of having a person trained and practiced in the skills needed to manage the diverse operations and functions that make up the modern city. This line of reasoning encompasses the premise that professional management brings efficiency to municipal management. However, little research has focused on this aspect of professional management. This study uses data from a nationwide survey of cities to test the hypothesis that cities with professional management achieve measurable efficiencies compared to cities without such management. These efficiencies include reduced levels of municipal expenditures and property taxes. The results of this analysis provide significant new information for both scholars and practitioners.     

INVESTORS: THE MISSING PIECE IN THE FORECLOSURE RACIAL GAP DEBATE

ABSTRACT: Foreclosures have become one of the most important problems facing cities and the U.S. economy. However, not all communities are affected equally. Our goal is to better understand factors that affect variation in neighborhood foreclosures in a typical, mid‐sized U.S. city—Louisville, Kentucky. While previous findings indicate that a key explanatory variable leading to rising neighborhood foreclosures is the proportion of racial minorities, our analysis finds that in a fully specified model, race does not predict differences between black and white homeowners. On the other hand, an analysis of investors predicts high foreclosure rates in African‐American neighborhoods. The effect of percent nonwhite is caused by several key intervening variables, including the presence of investor foreclosures, the absence of neighborhood walkability, and the prevalence of high‐cost loans. In the past, walkability and investor behavior have largely been ignored by social scientists studying neighborhood variation in foreclosures and the role of race in rising foreclosures. In this article, we examine how speculation by investors in majority African‐American neighborhoods along with degree of walkability and the concentration of high‐priced loans have contributed to recent increases in foreclosures and variation across neighborhoods. Together, the findings demonstrate that these three factors help to better explain the contemporary causes of greater foreclosures in African‐American neighborhoods.     

Experimental Results for a Heat-Sink Mechanical Seal

This work presents experimental results for a heat-sink mechanical seal installed in a 1 × 1.5 × 6 in. ANSI centrifugal water pump. The heat-sink seal is constructed of a stainless steel substrate with an electrodeposited pin fin micro-heat sink located within 3 mm of the end face. Each pin has a ten-sided polygon cross section with a flat-to-flat diameter of 675 μm, a height of 856 μm, and a 300-μm edge-to-edge spacing. The end face is coated with a WC thin film that forms the wear surface for the rotating ring. The heat-sink seal's effectiveness is demonstrated in a significant reduction of both the seal interface and seal chamber temperature when compared to a similar industry standard seal. The heat-sink seal removes 750 W of heat and reduces the stationary ring temperature by 80°C under dead-head conditions using only 1.6 W of coolant pumping power.     

Quantifying the search space for multi-agent system decision-making organizations

When a group comes together to pursue a goal, how should the group interact? Both theory and practice show no single organization always performs best; the best organization depends on context. Therefore, a group should adapt how it interacts to fit the situation. In a multi-agent system (MAS), a decision-making framework (DMF) specifies the allocation of decision-making and action-execution responsibilities for a set of goals among agents within the MAS. Adaptive decision-making frameworks (ADMFs) is the ability to change the DMF, changing which agents are responsible for decision-making and action-execution for a set of goals. Interesting questions remain about the ability of an agent to find the 'best,' or 'near optimal' or 'sufficient' DMF among all the possible DMFs. This paper presents initial exploration of this investigation by asking, 'How does the state space of MAS decision-making organizations scale with growth in the number of agents, number of goals and complexity of the organization structure?' This paper presents tight computational bounds on the size of the search space for DMFs by applying combinatorial mathematics. The DMF representation is also shown to be a factor in the size of this search space.     

Changes in Connective Tissue Histology in Freeze-Thaw Cycled and Refrigerated Pork Liver

Alterations in the connective tissue of pork liver during storage were examined histologically. The connective tissue outlining the lobule of pork liver was apparently unaltered during refrigerated storage (R-S), but showed extensive crimping or waviness during freeze-thaw (F-T) cycling. Intralobular connective tissue (reticulin) disappeared during R-S but was still visible after six F-T cycles. The existence of a proteolytic enzyme active against Type III collagen at refrigerator temperatures but irreversibly inactivated by freezing was postulated.     

ROLE OF HOST PLANT VOLATILES IN MATE LOCATION FOR THREE SPECIES OF LONGHORNED BEETLES

Stressed woody plants represent an ephemeral and unpredictable resource for larvae of some species of longhorned beetles (Coleoptera: Cerambycidae) because prime subcortical tissues are rapidly degraded by a guild of xylophagous competitors. Selection favors efficient mechanisms of host and mate location to expedite colonization of hosts by larvae. Based on previous research, we hypothesize that mate location in some species of the subfamily Cerambycinae involves three sequential behavioral stages: (1) both sexes are attracted to larval hosts by plant volatiles; (2) males attract females over shorter distances with pheromones; and (3) males recognize females by contact pheromones in their epicuticular wax layer. We already have evidence of second-stage and third-stage behaviors in three species in this subfamily whose xylophagous larvae feed in hardwood trees: Xylotrechus colonus, Megacyllene caryae, and Neoclytus mucronatus mucronatus. In this report, we evaluate the first behavioral stage of mate location behavior (i.e., independent response of both sexes to host plant volatiles) for the same three species. Supporting our hypothesis, both males and females responded to volatiles emanating from hickory logs in Y-tube olfactometer bioassays.