5,737 research outputs found
A uniform framework for modelling nondeterministic, probabilistic, stochastic, or mixed processes and their behavioral equivalences
Labeled transition systems are typically used as behavioral models of concurrent processes, and the labeled transitions define the a one-step state-to-state reachability relation. This model can be made generalized by modifying the transition relation to associate a state reachability distribution, rather than a single target state, with any pair of source state and transition label. The state reachability distribution becomes a function mapping each possible target state to a value that expresses the degree of one-step reachability of that state. Values are taken from a preordered set equipped with a minimum that denotes unreachability. By selecting suitable preordered sets, the resulting model, called ULTraS from Uniform Labeled Transition System, can be specialized to capture well-known models of fully nondeterministic processes (LTS), fully
probabilistic processes (ADTMC), fully stochastic processes (ACTMC), and of nondeterministic and probabilistic (MDP) or nondeterministic and stochastic (CTMDP) processes. This uniform treatment of different behavioral models extends to behavioral equivalences. These can be defined on ULTraS by relying on appropriate measure functions that expresses the degree of reachability of a set of states when performing
single-step or multi-step computations. It is shown that the specializations of bisimulation, trace, and testing
equivalences for the different classes of ULTraS coincide with the behavioral equivalences defined in the literature over traditional models
PDDL2.1: An extension of PDDL for expressing temporal planning domains
In recent years research in the planning community has moved increasingly towards application of planners to realistic problems involving both time and many types of resources. For example, interest in planning demonstrated by the space research community has inspired work in observation scheduling, planetary rover ex ploration and spacecraft control domains. Other temporal and resource-intensive domains including logistics planning, plant control and manufacturing have also helped to focus the community on the modelling and reasoning issues that must be confronted to make planning technology meet the challenges of application. The International Planning Competitions have acted as an important motivating force behind the progress that has been made in planning since 1998. The third competition (held in 2002) set the planning community the challenge of handling time and numeric resources. This necessitated the development of a modelling language capable of expressing temporal and numeric properties of planning domains. In this paper we describe the language, PDDL2.1, that was used in the competition. We describe the syntax of the language, its formal semantics and the validation of concurrent plans. We observe that PDDL2.1 has considerable modelling power --- exceeding the capabilities of current planning technology --- and presents a number of important challenges to the research community
Comparing Common Procedures Used to Manipulate Reinforcer Magnitude
Reinforcer magnitude is one of several parameters of reinforcement. In the present study, it referred to the quantitative value of the reinforcer in terms of duration of access to a finite supply of grain pellets. Pigeons responded on concurrent-chain schedules earning one of several reinforcer durations depending on response allocation and experimental conditions. Experiment 1 consisted of relatively long reinforcer durations available for completing one chain compared to relatively short durations available on the other. Response allocation in the initial link determined the reinforcer duration, but responses in the terminal link produced no change in the upcoming reinforcer. This arrangement allowed for the comparison of response-correlated and experimenter-controlled changes in reinforcer magnitude in terms of the control by reinforcer magnitude they produced. Additional changes in reinforcer durations were programmed between experimental conditions to allow for comparisons of within-sessions and between-conditions changes in magnitude as well. Experiment 2 was procedurally similar to the first, but the total reinforcer duration was identical for each chan. Instead, reinforcer durations were segmented into bins on one chain and kept continuous on the other (e.g., two 4-s reinforcers separated by a brief blackout period compared to one, continuous 8-s reinforcer). Control by reinforcer magnitude was most apparent when changes were response correlated and within-sessions, but behavior change was also observed on the between-conditions scale. No magnitude effects were observed in changes in magnitude were experimenter controlled (i.e., not correlated to behavior). Further, the observed effects seemed to be mediated by eating efficiency. It is recommended that future research on reinforcer magnitude include thorough measurement of the consummatory chain to fully describe the role of eating efficiency in control by reinforcer magnitude
The Structure of Parent-Child Coping Interactions as a Predictor of Adjustment in Middle Childhood: A Dynamic Systems Perspective
This study applied a contemporary dynamic systems methodology (state space grids) to examine how the structure of parent-child coping interactions, above and beyond the content of such interactions, influences adjustment (i.e., internalizing problems, externalizing problems, and coping efficacy) over time in middle childhood. A community sample of children (N = 65) completed a stressful laboratory task with a parent present, during which parent and child behavior were observed. Parent behavior during the task was coded using a socialization of coping framework. Parents\u27 verbal suggestions to their child about how to cope with the stressful task were coded as primary control engagement suggestions (i.e., suggestions encouraging the child to directly address and attempt to change the stressor or the child\u27s associated emotions), secondary control engagement suggestions (i.e., suggestions encouraging the child to change their own reaction to their stressor), or disengagement suggestions (i.e., suggestions encouraging the child to take their attention away from the stressor). Child coping verbalizations and behavior during the task was coded as either engaging with the stressor or disengaging from the stressor. The structure of the parent-child coping interaction was measured in two ways: (a) dyadic flexibility, defined as the dispersion of parent and child behavior across all possible behaviors and the number of transitions between different parent or child behaviors during the task, and (b) attractor (i.e., parent-focused, child-focused, or dyad-focused interaction pattern) strength, defined as the number of visits, duration per visit, and return time to that interaction pattern. Child adjustment outcomes were measured using parent-report (internalizing and externalizing problems) and child-report (coping efficacy) at baseline and a 6-month follow-up. Linear regression analyses were conducted examining dyadic flexibility and the proposed attractors as predictors of child adjustment, while accounting for demographic variables, attractor content, and adjustment at baseline. Findings suggested that dyadic flexibility in the parent-child coping interaction was largely adaptive for child adjustment, whereas attractor strength demonstrated a more complex relationship with child adjustment outcomes. This study demonstrates the utility of applying state-space grids to examine the structure of parent-child coping interactions, in addition to content, as predictors of child adjustment. Furthermore, this study offers novel, detailed information about coping interactions in families with children in middle childhood. Clinical implications, limitations, and future directions are discussed
Different types of X-ray bursts from GRS 1915+105 and their origin
We report the X-ray observations of the Galactic X-ray transient source GRS
1915+105 with the PPCs of the Indian X-ray Astronomy Experiment(IXAE) onboard
the Indian satellite IRS-P3 during 1997 June - August, which have revealed the
presence of four types of intense X-ray bursts. All the observed bursts have a
slow exponential rise, a sharp linear decay, and they can broadly be put in two
classes: irregular and quasi-regular bursts in one class, and regular bursts in
another class. The regular bursts are found to have two distinct time scales
and they persist over extended durations. There is a strong correlation between
the preceding quiescent time and the burst duration for the quasi-regular and
irregular bursts. No such correlation is found for the regular bursts. The
ratio of average flux during the burst time to the average flux during the
quiescent phase is high and variable for the quasi- regular and irregular
bursts while it is low and constant for the regular bursts. We suggest that the
peculiar bursts that we have seen are charact- eristic of the change of state
of the source. The source can switch back and forth between the low-hard state
and the high-soft state near critical accretion rates in a very short time
scale. A test of the model is presented using the publicly available 13-60 keV
RXTE/PCA data for irregular and regular bursts concurrent with our
observations.Comment: 13 pages, 12 figures, Accepted in APJ, emulateapj style use
Effects of schedule segmentation on pausing and escape in the transitions between favorable and unfavorable schedules of reinforcement
Simple schedules of reinforcement typically are preferred to chained schedules of equal duration. In the current study, pigeons served in six experiments designed to test whether the juxtaposition of simple and chained schedules would engender the disruption in behavior typically observed in the transition from favorable to unfavorable conditions of reinforcement. In one set of experiments, a multiple schedule was employed in which a simple schedule alternated irregularly with a chained schedule. Whether fixed-ratio or fixed-interval schedules were employed, only half the subjects paused for an extended duration in the simple-to-chain transition, and this occurred only when the first segment of the chained schedule was short. When the option to turn off the stimuli correlated with the schedule in effect (escape) was available at the start of each component, escape occurred infrequently and inconsistently across pigeons. In another set of experiments, a (rich) schedule ending in a large reinforcer was juxtaposed with a (lean) schedule ending in a small reinforcer. In addition, either the rich or lean schedule was segmented across conditions. Inconsistent results were obtained when fixed-ratio schedules were employed; however, when fixed-interval schedules were employed, pausing was extended in the rich-to-lean transition and this effect was attenuated by segmenting the rich schedule and enhanced by segmenting the lean schedule. When the option to escape was available, escape was more frequent (or constituted a larger percentage of the session) in the rich-to-lean transition when simple schedules operated. Segmenting the lean schedule had inconsistent effects on escape. The fact that the predicted results were obtained only when fixed-interval schedules differed in reinforcer magnitude and schedule segmentation is attributed to two factors. First, perhaps it was only in this experiment that the difference in favorability across schedules was sufficient to produce noticeable disruptions in behavior. Second, response patterns suggest that the pigeons failed to respond differentially across the simple and chained fixed-ratio schedules. The results of the present study together with previous findings suggest the potential for basic research to contribute to the identification and manipulation of variables that control problem behavior in institutional settings and in everyday situations
Quantifying fisher responses to environmental and regulatory dynamics in marine systems
Thesis (Ph.D.) University of Alaska Fairbanks, 2017Commercial fisheries are part of an inherently complicated cycle. As fishers have adopted new technologies and larger vessels to compete for resources, fisheries managers have adapted regulatory structures to sustain stocks and to mitigate unintended impacts of fishing (e.g., bycatch). Meanwhile, the ecosystems that are targeted by fishers are affected by a changing climate, which in turn forces fishers to further adapt, and subsequently, will require regulations to be updated. From the management side, one of the great limitations for understanding how changes in fishery environments or regulations impact fishers has been a lack of sufficient data for resolving their behaviors. In some fisheries, observer programs have provided sufficient data for monitoring the dynamics of fishing fleets, but these programs are expensive and often do not cover every trip or vessel. In the last two decades however, vessel monitoring systems (VMS) have begun to provide vessel location data at regular intervals such that fishing effort and behavioral decisions can be resolved across time and space for many fisheries. I demonstrate the utility of such data by examining the responses of two disparate fishing fleets to environmental and regulatory changes. This study was one of "big data" and required the development of nuanced approaches to process and model millions of records from multiple datasets. I thus present the work in three components: (1) How can we extract the information that we need? I present a detailed characterization of the types of data and an algorithm used to derive relevant behavioral aspects of fishing, like the duration and distances traveled during fishing trips; (2) How do fishers' spatial behaviors in the Bering Sea pollock fishery change in response to environmental variability; and (3) How were fisher behaviors and economic performances affected by a series of regulatory changes in the Gulf of Mexico grouper-tilefish longline fishery? I found a high degree of heterogeneity among vessel behaviors within the pollock fishery, underscoring the role that markets and processor-level decisions play in facilitating fisher responses to environmental change. In the Gulf of Mexico, my VMS-based approach estimated unobserved fishing effort with a high degree of accuracy and confirmed that the regulatory shift (e.g., the longline endorsement program and catch share program) yielded the intended impacts of reducing effort and improving both the economic performance and the overall harvest efficiency for the fleet. Overall, this work provides broadly applicable approaches for testing hypotheses regarding the dynamics of spatial behaviors in response to regulatory and environmental changes in a diversity of fisheries around the world.General introduction -- Chapter 1 Using vessel monitoring system data to identify and characterize trips made by fishing vessels in the United States North Pacific -- Chapter 2 Paths to resilience: Alaska pollock fleet uses multiple fishing strategies to buffer against environmental change in the Bering Sea -- Chapter 3 Vessel monitoring systems (VMS) reveal increased fishing efficiency following regulatory change in a bottom longline fishery -- General Conclusions
Zone clearance in an infinite TASEP with a step initial condition
The TASEP is a paradigmatic model of out-of-equilibrium statistical physics,
for which many quantities have been computed, either exactly or by approximate
methods. In this work we study two new kinds of observables that have some
relevance in biological or traffic models. They represent the probability for a
given clearance zone of the lattice to be empty (for the first time) at a given
time, starting from a step density profile. Exact expressions are obtained for
single-time quantities, while more involved history-dependent observables are
studied by Monte Carlo simulation, and partially predicted by a
phenomenological approach
Biochemical, endocrine, and hematological factors in human oxygen tolerance extension: Predictive studies 6
The Predictive Studies VI (Biochemical, endocrine, and hematological factors in human oxygen tolerance extension) Program consisted of two related areas of research activity, integrated in design and performance, that were each based on an ongoing analysis of human organ oxygen tolerance data obtained for the continuous oxygen exposures of the prior Predictive Studies V Program. The two research areas effectively blended broad investigation of systematically varied intermittent exposure patterns in animals with very selective evaluation of specific exposure patterns in man
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