Path Length Metric Research Articles

A Deep Reinforcement Learning Approach to Optimal Morphologies Generation in Reconfigurable Tiling Robots

Reconfigurable robots have the potential to perform complex tasks by adapting their morphology to different environments. However, designing optimal morphologies for these robots is challenging due to the large design space and the complex interactions between the robot and the environment. An in-house robot named Smorphi, having four holonomic mobile units connected with three hinge joints, is designed to maximize area coverage with its shape-changing features using transformation design principles (TDP). The reinforcement learning (RL) approach is used to identify the optimal morphologies out of a vast combination of hinge angles for a given task by maximizing a reward signal that reflects the robot’s performance. The proposed approach involves three steps: (i) Modeling the Smorphi design space with a Markov decision process (MDP) for sequential decision-making; (ii) a footprint-based complete coverage path planner to compute coverage and path length metrics for various Smorphi morphologies; and (iii) pptimizing policies through proximal policy optimization (PPO) and asynchronous advantage actor–critic (A3C) reinforcement learning techniques, resulting in the generation of energy-efficient, optimal Smorphi robot configurations by maximizing rewards. The proposed approach is applied and validated using two different environment maps, and the results are also compared with the suboptimal random shapes along with the Pareto front solutions using NSGA-II. The study contributes to the field of reconfigurable robots by providing a systematic approach for generating optimal morphologies that can improve the performance of reconfigurable robots in a variety of tasks.

Structural covariance in the affective pain network in Alzheimer’s disease

AbstractBackgroundPain consists of both sensory and affective networks. Literature exploring the effect of Alzheimer’s disease (AD) on pain is limited. Some evidence suggests that the affective networks are impacted earlier while the sensory networks are preserved until late in the course of disease (Cole 2006). To examine the preservation of networks underlying pain perception in AD, we examined the structural covariance of regions in the pain network. Using structural MRI (sMRI) data, we investigated structural covariance by modeling a network from the correlation of volume between regions. In structural covariance, path length represents the minimum number of steps that must be taken to travel between two nodes and may serve as a proxy for structural brain integrity. Characteristic path length averages together the path lengths for all nodes in a given a priori network to create a global network metric (Paldino 2017). We hypothesized that there would be alterations in altered characteristic and nodal path length in individuals with AD.MethodAs part of a larger study, cortical volume measurements were obtained for 78 participants (39 AD, 39 HC) via Ma‐CRUISE mutli‐atlas segmentation (Huo 2016). The affective pain network consisted of bilateral: anterior and posterior insula, amygdala, anterior cingulate cortex (ACC), and dorsolateral pre‐frontal cortex (dlPFC, specifically the superior frontal and medial frontal gyri, Woo 2017). The analysis was conducted in BRAPH using a undirected weighted graph with negative correlations set to zero. (Mijalkov 2017). Only characteristic and nodal path length were included in this analysis as these metrics are more robust for discriminating differences in AD (Mårtensson 2018).ResultNo significant differences were found for characteristic path length between groups (p = > 0.05). Additionally, no significant differences were found in path length for any of the nodes analyzed following correction with the Benjamini‐Hochberg procedure (Q = 0.05).ConclusionPreservation of characteristic and nodal path length metrics in the affective pain network provides preliminary evidence that this network may be preserved in mild to moderate AD. This clinically meaningful finding provides further evidence indicate that affective pain may be preserved longer than originally thought during the course of AD.

Planning Under Non-Rational Perception of Uncertain Spatial Costs

This work investigates the design of risk-perception-aware motion-planning strategies that incorporate non-rational risk associated with uncertain spatial costs. Our proposed method employs the Cumulative Prospect Theory (CPT) to generate a perceived risk map over a given environment. CPT-like perceived risks and path-length metrics are then combined to define a cost function that is compliant with the requirements of asymptotic optimality of sampling-based motion planners (RRT*). The modeling power of CPT is illustrated in theory and in simulation, along with a comparison to other risk perception models like Conditional Value at Risk (CVaR). Theoretically, we define a notion of expressiveness for a risk perception model and show that CPT's is higher than that of CVaR and expected risk. We then show that this expressiveness translates to our path planning setting, where we observe that a planner equipped with CPT together with a simultaneous perturbation stochastic approximation (SPSA) method can better approximate arbitrary paths in an environment. Additionally, we show in simulation that our planner captures a rich set of meaningful paths, representative of different risk perceptions in a custom environment. We then compare the performance of our planner with T-RRT* (a planner for continuous cost spaces) and Risk-RRT* (a risk-aware planner for dynamic human obstacles) through simulations in cluttered and dynamic environments respectively, showing the advantage of our proposed planner.

Medians are Below Joins in Semimodular Lattices of Breadth 2

Let L be a lattice of finite length and let d denote the minimum path length metric on the covering graph of L. For any xi =(x_{1},dots ,x_{k})in L^{k}, an element y belonging to L is called a median of ξ if the sum d(y,x1) + ⋯ + d(y,xk) is minimal. The lattice L satisfies the c1-median property if, for any xi =(x_{1},dots ,x_{k})in L^{k} and for any median y of ξ, yleq x_{1}vee dots vee x_{k}. Our main theorem asserts that if L is an upper semimodular lattice of finite length and the breadth of L is less than or equal to 2, then L satisfies the c1-median property. Also, we give a construction that yields semimodular lattices, and we use a particular case of this construction to prove that our theorem is sharp in the sense that 2 cannot be replaced by 3.

Multiple-Target Homotopic Quasi-Complete Path Planning Method for Mobile Robot Using a Piecewise Linear Approach.

The ability to plan a multiple-target path that goes through places considered important is desirable for autonomous mobile robots that perform tasks in industrial environments. This characteristic is necessary for inspection robots that monitor the critical conditions of sectors in thermal, nuclear, and hydropower plants. This ability is also useful for applications such as service at home, victim rescue, museum guidance, land mine detection, and so forth. Multiple-target collision-free path planning is a topic that has not been very studied because of the complexity that it implies. Usually, this issue is left in second place because, commonly, it is solved by segmentation using the point-to-point strategy. Nevertheless, this approach exhibits a poor performance, in terms of path length, due to unnecessary turnings and redundant segments present in the found path. In this paper, a multiple-target method based on homotopy continuation capable to calculate a collision-free path in a single execution for complex environments is presented. This method exhibits a better performance, both in speed and efficiency, and robustness compared to the original Homotopic Path Planning Method (HPPM). Among the new schemes that improve their performance are the Double Spherical Tracking (DST), the dummy obstacle scheme, and a systematic criterion to a selection of repulsion parameter. The case studies show its effectiveness to find a solution path for office-like environments in just a few milliseconds, even if they have narrow corridors and hundreds of obstacles. Additionally, a comparison between the proposed method and sampling-based planning algorithms (SBP) with the best performance is presented. Furthermore, the results of case studies show that the proposed method exhibits a better performance than SBP algorithms for execution time, memory, and in some cases path length metrics. Finally, to validate the feasibility of the paths calculated by the proposed planner; two simulations using the pure-pursuit controlled and differential drive robot model contained in the Robotics System Toolbox of MATLAB are presented.

Objective assessment based on motion-related metrics and technical performance in laparoscopic suturing.

The aim of this study is to present the construct and concurrent validity of a motion-tracking method of laparoscopic instruments based on an optical pose tracker and determine its feasibility as an objective assessment tool of psychomotor skills during laparoscopic suturing. A group of novice ([Formula: see text] laparoscopic procedures), intermediate (11-100 laparoscopic procedures) and experienced ([Formula: see text] laparoscopic procedures) surgeons performed three intracorporeal sutures on an ex vivo porcine stomach. Motion analysis metrics were recorded using the proposed tracking method, which employs an optical pose tracker to determine the laparoscopic instruments' position. Construct validation was measured for all 10 metrics across the three groups and between pairs of groups. Concurrent validation was measured against a previously validated suturing checklist. Checklists were completed by two independent surgeons over blinded video recordings of the task. Eighteen novices, 15 intermediates and 11 experienced surgeons took part in this study. Execution time and path length travelled by the laparoscopic dissector presented construct validity. Experienced surgeons required significantly less time ([Formula: see text]), travelled less distance using both laparoscopic instruments ([Formula: see text]) and made more efficient use of the work space ([Formula: see text]) compared with novice and intermediate surgeons. Concurrent validation showed strong correlation between both the execution time and path length and the checklist score ([Formula: see text] and [Formula: see text], [Formula: see text]). The suturing performance was successfully assessed by the motion analysis method. Construct and concurrent validity of the motion-based assessment method has been demonstrated for the execution time and path length metrics. This study demonstrates the efficacy of the presented method for objective evaluation of psychomotor skills in laparoscopic suturing. However, this method does not take into account the quality of the suture. Thus, future works will focus on developing new methods combining motion analysis and qualitative outcome evaluation to provide a complete performance assessment to trainees.

AN APPROACH TO EVALUATE QUALITY OF WEBSITE STRUCTURE

The primary goal of this paper is to identify the elements involved in quality assessment of website structure. Always quality of website structure is based on its navigability, average number of clicks and structural complexity. The web tool PowerMapper is used to establish the sitemap for the website, path length metric is used to evaluate average number of clicks to get desired web page and web site structural complexity is determined with cyclomatic complexity. The quality of web site structure is measured in 10point scale and scale is formulated by considering various levels of website tree structure. The status of web site structure is determined in 10 point scale and the value suggests the improvement of the site structure.

A Qualitative and Quantitative Frame Work for effective Website Design

The primary goal of this paper is to investigate various elements of website and evaluate quality of website design. The quality of website depends on various components such as download time, website size, broken links and website structure. The quality of website structure is based on its navigability, average number of clicks and structural complexity. Different kinds of tools are used to examine the components of website. These tools include: W3C Link Checker, W3C Markup Validation Service, Webpage Analyzer and Website Extractor. The W3C Link checker accepts URL address of Web page and parses each and every hyperlink to find broken links in the page. The W3C Markup Validation Service finds the errors regarding HTML tags', usage errors, properties of Web page and standards of the Web page mentioned by W3C Consortium. The errors of each web site are grouped into major and minor errors. A set of qualitative measures are identified based on these errors. The web tool PowerMapper is used to establish the sitemap for the website and path length metric is used to evaluate average number of clicks to get desired web page and web site structural complexity is determined with cyclomatic complexity. The quality of website design is measured in 10-point scale and the value suggests the improvement of the site design.

Path-Length as a Metric for Subject Motion

Path-Length as a Metric for Subject Motion

Medians for weight metrics in the covering graphs of semilattices

We consider the undirected covering graph G of a finite (meet) semilattice X endowed with a lower valuation. More precisely, our main concerns are the lower valuations associated to a weighting of the join-irreducible elements of X and the corresponding minimum path length metrics in G, which are frequently considered in the literature. Some results on the medians for such metrics are obtained, in relation with a lattice majority rule. Especially, these medians are characterized in the case where X is distributive. The unanimity, or Pareto, property is also investigated for such medians.