PathFinder Model Research Articles

An optimal path finding strategy in networks based on random walk

In this paper, we study a path finding strategy based on random walk in which we allow multiple particles to set out from different but neighboring sources to their common destination. Three path finding models, the single-particle-form-one-source, the multiple-particles-from-one-source, and the last multiple-particles-form-multiple-sources (MSMP) are described. Then we apply the three models to different simulation networks. The experiment results show that the MSMP schema can decrease the path finding cost. Furthermore, we propose an absorption strategy to deal with the additional Brownian particles in networks. The experiment results on BA networks show that the absorption strategy can increase the probability of a successful path finding. In the end, we find he path found out by above methods may be the shortest theoretically, but may not be optimal in the practical application. To overcome this, we put forward a method to calculate the optimal path based on arrival reliability and verify its correctness by enumeration.

공간의 의미를 연산하는 가상 사용자 모델이 건축설계 전공학생들의 인간행동 시뮬레이션 운용과 이해도에 미치는 효과에 관한 연구

The previous studies argue that using the semantic properties of BIM objects is efficient for simulating the behaviors of autonomous, computer agents, called virtual-users, but such assumption is not proven via evidence-based research approaches. Hence, this present study aims to investigate the empirical effects of a human behavior simulation model equipped the semantics of spaces on the architecture-major students' operation and understanding of the simulation system, compared to a typical path-finding model. To achieve the aim, this study analyzed the survey and interview data, collected in the authentic design projects. The analysis indicates that (1) using a simulation model equipped the semantics of spaces helps the students' operation of the simulation, and (2) it also aids understanding the relationship between the variables of spaces and virtual-users (<TEX>${\alpha}=0.74$</TEX>). In addition, the qualitative data inform that the advantages of the simulation model that computes the semantics of spaces stem in the automatic behavioral changes of massive numbers of virtual-users, and efficient detection and activation on the what-if situations. The analysis also reveals that the simulation model has shortcomings in orchestrating the complex data structure between the semantics properties of spaces and virtual-users under multi-sequential scenarios. The results of this study contribute to develop a future design system combining BIM with human behavior simulation.

A Formal Approach to implement java exceptions in cooperative systems

The increasing number of systems that work on the top of cooperating elements have required new techniques to control cooperation on both normal and abnormal behaviors of systems. The controllability of the normal behaviors has received more attention because they are concerned with the users expectations, while for the abnormal behaviors it is left to designers and programmers. However, for cooperative systems, the abnormal behaviors, mostly represented by exceptions at programming level, become an important issue in software development because they can affect the overall system behavior. If an exception is raised and not handled accordingly, the system may collapse. To avoid such situation, certain concepts and models have been proposed to coordinate propagation and recovering of exceptional behaviors, including the Coordinated Atomic Actions (CAA). Regardless of the effort in creating these conceptual models, an actual implementation of them in real systems is not very straightforward. This article provides a reliable framework for the implementation of Java exceptions propagation and recovery using CAA concepts. To do this, a Java framework (based on a formal specification) is presented, together with a set of properties to be preserved and proved with the Java Pathfinder (JPF) model checker. In practice, to develop new systems based on the given coordination concepts, designers/programmers can instantiate the framework to implement the exceptional behavior and then verify the correctness of the resulting code using JPF. Therefore, by using the framework, designers/programmers can reuse the provided CAA implementation and instantiate fault-tolerant Java systems.

Avoiding hepatic metastasis naturally: Lessons from the cotton top tamarin (Saguinus oedipus).

Much has been written about hepatic metastasis and animal models abound. In terms of the human experience, progress in treating this final common pathway, a terminal event of many human malignancies has been relatively slow. The current thinking is that primary prevention is best served by early detection of cancer and eradication of early stage cancers by screening. Some cancers spread early in their course and the role of screening may be limited. Until relatively recently there has not been a pathfinder model that makes the evasion of this unfortunate event a reality. This review discusses such an animal model and attempts to relate it to human disease in terms of intervention. Concrete proposals are also offered on how scientists may be able to intervene to prevent this deadly progression of the cancer process.

Roads Less Traveled: Finding a Path to Using Complementary and Alternative Medicine.

An increasing number of health seekers in the United States are looking outside conventional medicine to address their health needs. It is estimated that in the United States, 38% of adults use complementary and alternative medicine (CAM). Extant research characterizes CAM users as a unified homogeneous group, with little understanding of the differences among them in terms of attitudes toward body, wellness, disease, and pivotal aspects of their personal histories. In this article, we seek to better understand the nuances of who uses CAM and why, using the following questions: How do people communicate their life stories that explain their decision to use CAM? How do the life stories enable us to understand the similarities and differences among CAM users? Based on analysis of the narratives of 18 individuals, three clusters or types of CAM users emerged: natives, immigrants, and tourists. In an effort to push our analysis further, we theorized three dimensions that help to explain CAM users' objectives, motives, and resultant sense of empowerment. Together, these dimensions comprise The Pathfinder Model of CAM Usage. The Pathfinder Model can be useful to clarify self-understanding among CAM users themselves, as well as for conventional and alternative practitioners, as they establish a working relationship and communicate with their patients during medical encounters. Understanding the path of the health seeker can help influence the quality of the relationship and the communicative strategies providers use to educate and influence.

An anticipation mechanism for the shortest path problem based on Physarum polycephalum

In this paper, we put forward an anticipation mechanism for the existing Physarum-inspired shortest path finding method. The Physarum-based shortest path finding model can be implemented by an iterative algorithm and has wide applications in many fundamental network optimization problems. In this paper, we mainly focus on the Physarum-inspired shortest path tree model. Normally, we stop the program when the difference between two consecutive iterations is less than a predefined threshold. However, we do not know how to set the specific value for the threshold variable. In order to find out the optimal solution, we need to set the threshold as a very small number. This in turn will consume a lot of time. From this point of view, this algorithm lacks an efficient and reliable mechanism to judge when the optimal solution will be found. In this paper, we introduce an anticipation mechanism to address this issue. Numerical examples are used to demonstrate its reliability and efficiency.

Multi-objective path finding in stochastic time-dependent road networks using non-dominated sorting genetic algorithm

In this paper, a new multi-objective path-finding model is proposed to find optimal paths in road networks with time-dependent stochastic travel times. This study is motivated by the fact that different travelers usually have different route-choice preferences, often involving multiple conflicting criteria such as expected path travel time, variance of path travel time and so forth. However, most of the existing studies have only considered the expected value of path travel time as the sole decision criterion. In order to solve the multi-objective model, the non-dominated sorting genetic algorithm is employed and its parameters are tuned by the Taguchi method. Moreover, a dynamic n-point crossover operator is developed to enhance the search capability of the genetic algorithm. Experimental results on a grid network demonstrate that the proposed approach is able to provide a set of non-dominated paths from which travelers can choose their paths based on their attitudes toward travel time uncertainty. Statistical analysis confirms that the dynamic n-point crossover operator outperforms the traditional one-point crossover operator.

An improved bio-inspired algorithm for the directed shortest path problem

Because most networks are intrinsically directed, the directed shortest path problem has been one of the fundamental issues in network optimization. In this paper, a novel algorithm for finding the shortest path in directed networks is proposed. It extends a bio-inspired path finding model of Physarum polycephalum, which is designed only for undirected networks, by adopting analog circuit analysis. Illustrative examples are given to show the effectiveness of the proposed algorithm in finding the directed shortest path.

Rapid Physarum Algorithm for shortest path problem

As shortest path (SP) problem has been one of the most fundamental network optimization problems for a long time, technologies for this problem are still being studied. In this paper, a new method by integrating a path finding mathematical model, inspired by Physarum polycephalum, with extracted one heuristic rule to solve SP problem has been proposed, which is called Rapid Physarum Algorithm (RPA). Simulation experiments have been carried out on three different network topologies with varying number of nodes. It is noted that the proposed RPA can find the optimal path as the path finding model does for most networks. What is more, experimental results show that the performance of RPA surpasses the path finding model on both iterations and solution time.

Towards a lazier symbolic pathfinder

To explore the state space of programs with complex user-defined data structures, most symbolic execution engines use the lazy initialization algorithm. Symbolic Pathfinder (SPF) is the symbolic execution engine for the Java PathFinder (JPF) model checker; SPF too contains an implementation of the lazy initialization algorithm. A number of extensions to the original lazy initialization algorithm have since been published. One such extension is the lazier# algorithm which demonstrated dramatic performance gains over the other algorithms. There is, however, no open-source implementation of the lazier# algorithm available. This work is an implementation of the the lazier# algorithm within the Symbolic PathFinder framework. In addition, this work describes the implementation of two heap bounding techniques in SPF, namely k-bounding and n-bounding. The purpose of this paper is to discuss the nature of the improvements, implementation details, usage and performance test results.

Performance-Based Evaluation of Large Steel-Framed Structures in the Overall Fire Process

This paper proposes a systematic analysis of fire hazards within an oversized steel-framed building that is taller and wider than usual, using a performance-based approach. We put forth both the method and the performance criteria for performance-based fire design of oversized steel-framed buildings and quantitatively evaluate the hazard factors (smoke temperature, smoke visibility, smoke toxicity, and structural collapse) in fire condition. FDS large eddy simulation and a modified temperature rise model of oversized steel structures were proposed for the quantitative analysis of hazard factors. Furthermore, we also studied evacuation process from oversized buildings and found that the Pathfinder model (developed based on water conservation model and behavior model) can accurately predict the evacuation process from oversized buildings based on our experimental study of an evacuation from a stadium. By comparing the time of occurrence of fire hazard factors (smoke temperature, smoke visibility, smoke toxicity, and structural collapse) and the time needed for safe evacuation, we could conduct a quantitative fire risk assessment on personal evacuation. And the time of occurrence of fire hazard factors can also provide a theoretical reference for emergency rescuers.

A biologically inspired solution for fuzzy shortest path problems

By considering the uncertainty that exists in the edge weights of the network, fuzzy shortest path problems, as one of the derivative problems of shortest path problems, emerge from various practical applications in different areas. A path finding model, inspired by an amoeboid organism, Physarum polycephalum, has been shown as an effective approach for deterministic shortest path problems. In this paper, a biologically inspired algorithm called Fuzzy Physarum Algorithm (FPA) is proposed for fuzzy shortest path problems. FPA is developed based on the path finding model, while utilizing fuzzy arithmetic and fuzzy distance to deal with fuzzy issues. As a result, FPA can represent and handle the fuzzy shortest path problem flexibly and effectively. Distinct from many existing methods, no order relation has been assumed in the proposed FPA. Several examples, including a tourist problem, are given to illustrate the effectiveness and flexibility of the proposed method and the results are compared with existing methods.

Modeling class loaders in Java PathFinder version 7

The class loading mechanism is one of the essential components of the Java runtime environment. Java class loading is performed on-demand, allows multiple, user extensible class loaders, and can associate a separate type namespace with each class loader. Previous versions of the Java Pathfinder (JPF) model checker only provided a single, hardcoded class loading mechanism. As one of the cornerstones of the upcoming JPF version 7 (JPF v7), we have implemented a standard Java conforming class loader infrastructure. Our implementation does not only support different class loaders and type namespaces, but also allows explicit instantiation of multiple bootstrap class loaders which is essential for model checking of distributed applications - the primary motivation for our work. With the new class loading mechanism, such applications can be mapped to threads using different bootstrap class loaders, thus effectively separating all static fields between application threads. In addition, the JPF v7 class loading is considered to be the basis for future verification of Java security properties.

Ranged Model Checking

We introduce ranged model checking, a novel technique for more effective checking of Java programs using the Java PathFinder (JPF) model checker. Our key insight is that the order in which JPF makes non-deterministic choices denes a total ordering of execution paths it explores in the program it checks. Thus, two in-order paths define a range for restricting the model checking run by defining a start point and an end point for JPF's exploration. Moreover, a given set of paths can be linearly ordered to define consecutive, (essentially) non-overlapping ranges that partition the exploration space and can be explored separately. While restricting the run of a model checker is a well-known technique in model checking, the key novelty of our work is conceptually to restrict the run using vertical boundaries rather than the traditional approach of using a horizontal boundary, i.e., the search depth bound. Initial results using our prototype implementation using the JPF libraries demonstrate the promise ranged model checking holds.

Optimal path finding in direction, location, and time dependent environments

AbstractThis article examines optimal path finding problems where cost function and constraints are direction, location, and time dependent. Recent advancements in sensor and data‐processing technology facilitate the collection of detailed real‐time information about the environment surrounding a ground vehicle, an airplane, or a naval vessel. We present a navigation model that makes use of such information. We relax a number of assumptions from existing literature on path‐finding problems and create an accurate, yet tractable, model suitable for implementation for a large class of problems. We present a dynamic programming model which integrates our earlier results for direction‐dependent, time and space homogeneous environment, and consequently, improves its accuracy, efficiency, and run‐time. The proposed path finding model also addresses limited information about the surrounding environment, control‐feasibility of the considered paths, such as sharpest feasible turns a vehicle can make, and computational demands of a time‐dependent environment. To demonstrate the applicability and performance of our path‐finding algorithm, computational experiments for a short‐range ship routing in dynamic wave‐field problem are presented. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012

워게임 시뮬레이션에서 온톨로지 기반의 경로탐색 모델링 및 시뮬레이션

워게임 시뮬레이션은 전장의 상황을 모델링하고 전력 평가나 임무 분석을 위해 사용되고 있다. 그러나 워게임 시뮬레이션에서 실제 전장에서 받을 수 있는 영향을 모두 고려하는 것은 매우 복잡하다. 이를 해결하기 위해 우리는 온톨로지 기반의 경로탐색 모델을 제안한다. 이 모델은 전장 상황 데이터를 개념화하고 그 관계를 표현할 수 있는 온톨로지를 사용한다. 또한, 몇 가지 추론 규칙을 정의하여 온톨로지로 부터 새로운 지식을 만들거나 기존의 규칙을 통해 지식을 공유한다. 제안하는 모델의 성능 평가를 위해 우리는 제한된 시뮬레이션 환경을 구성하고 부대 이동 시간, 부대의 전투력, 부대 이동간 소요 비용을 측정한다. 측정된 실험의 결과는 제안하는 모델이 이동 시간과 전투력 손실, 소요 비용 측면에서 이점을 제공한다는 것을 보여준다. War-game simulation models the situation of a battlefield and has been used for evaluating fighting power and analyzing the occupation of a troop. However, in war-game simulation environment, it is very complex to consider all factors which can be influenced in real battlefields. To solve the problem of the consideration, we propose an ontology-based path finding model. This model uses an ontology to conceptualize the situation data of a battlefield and represents the relations among the concepts. In addition, we extract new knowledge from the war-game ontology by defining some inference rules and share knowledge by the established rules. For the performance evaluation of the proposed model, we made a limitation on the simulation environment and measure the moving time of a troop, the fighting capability of a troop, and the necessary cost while a troop is moving. Experimental results show that this model provides many advantages in aspects of the moving time, a loss of fighting capability, and the necessary cost.

Biochip/laser cell deposition system to assess polarized axonal growth from single neurons and neuron/glia pairs in microchannels with novel asymmetrical geometries

Axon path-finding plays an important role in normal and pathogenic brain development as well as in neurological regenerative medicine. In both scenarios, axonal growth is influenced by the microenvironment including the soluble molecules and contact-mediated signaling from guiding cells and cellular matrix. Microfluidic devices are a powerful tool for creating a microenvironment at the single cell level. In this paper, an asymmetrical-channel-based biochip, which can be later incorporated into microfluidic devices for neuronal network study, was developed to investigate geometric as well as supporting cell control of polarized axonal growth in forming a defined neuronal circuitry. A laser cell deposition system was used to place single cells, including neuron-glia pairs, into specific microwells of the device, enabling axonal growth without the influence of cytophilic∕phobic surface patterns. Phase microscopy showed that a novel "snag" channel structure influenced axonal growth in the intended direction 4:1 over the opposite direction. In heterotypic experiments, glial cell influence over the axonal growth path was observed with time-lapse microscopy. Thus, it is shown that single cell and heterotypic neuronal path-finding models can be developed in laser patterned biochips.

Assume-guarantee verification of software components in SOFA 2 framework

A key problem in compositional model checking of software systems is that typical model checkers accept only closed systems (runnable programs) and therefore a component cannot be model-checked directly. A typical solution is to create an artificial environment for the component such that its composition forms a runnable program that can be model-checked. Although it is possible to create a universal environment that performs all possible sequences and interleavings of calls of the component's methods, for practical purposes it is sufficient to capture in this way just the use of the component in a particular software system – this idea is expressed by the paradigm of assume-guarantee reasoning. The authors present an approach to assume-guarantee-based verification of software systems in the context of the SOFA 2 component framework. They provide an overview of the approach to the construction of an artificial environment for the verification of SOFA 2 components implemented in Java with the Java PathFinder model checker. They also show the benefits of their approach on results of experiments with a non-trivial software system and discuss its advantages over other approaches with similar goals.

Mechanisms for transcellular diapedesis: probing and pathfinding by `invadosome-like protrusions'

Immune-system functions require that blood leukocytes continuously traffic throughout the body and repeatedly cross endothelial barriers (i.e. diapedese) as they enter (intravasate) and exit (extravasate) the circulation. The very earliest studies to characterize diapedesis directly in vivo suggested the coexistence of two distinct migratory pathways of leukocytes: between (paracellular pathway) and directly through (transcellular pathway) individual endothelial cells. In vivo studies over the past 50 years have demonstrated significant use of the transcellular diapedesis pathway in bone marrow, thymus, secondary lymphoid organs, various lymphatic structures and peripheral tissues during inflammation and across the blood-brain barrier and blood-retinal barrier during inflammatory pathology. Recently, the first in vitro reports of transcellular diapedesis have emerged. Together, these in vitro and in vivo observations suggest a model of migratory pathfinding in which dynamic 'invadosome-like protrusions' formed by leukocytes have a central role in both identifying and exploiting endothelial locations that are permissive for transcellular diapedesis. Such 'probing' activity might have additional roles in this and other settings.

Career Pathfinders: A Qualitative Study of Career Development

This paper examined the perceptions of career path and issues of MBA students in response to Lore's The Pathfinder, a comprehensive career-planning model. Using internet discussion boards, an interactive dialogue was mentioned by participants in response to the components of Lore's model. The sample consisted of 50 fully employed MBA students enrolled in a course on self-assessment and career planning. A total of 1,781 separate postings were made and analyzed, using inductive analysis derived from discussion threads based on Lore's categories: comments on Lore's Pathfinder model, living a life you love (what's the holdup, career fantasies, work and family issues, and career selection), how to get there from here (commitment and future from the present), and designing your future career. Findings indicated several interesting trends in the career planning of current MBA students, particularly the importance of self or self-reflective observations in real time as students who are also fully employed formulate career plans. Implications for psychologists and career counselors, career development models, and suggestions for research are presented.