Validating the random search model for a double-target search task

A random visual search model was fit to 2980 search times obtained from a double-target search task. The overall adequacy and prediction accuracy of the model for various search time parameters like mean and median search times, and response times for both individual and pooled data show that subjects' search strategy may reasonably be inferred from search time distributions. The results also suggest the general applicability of the random search model for describing the search behaviour of a large number of subjects performing the type of search task used here, and the practical feasibility of its application for determination of stopping policy in optimization of inspection system design. Notwithstanding the general conformity of the data with the model, some extremely long search times were found, and this was accounted for by the characteristics of visual lobes, nonoptimum interfixation distances and inappropriate overlapping of lobes previously reported. An interpretation of temporal changes of subjects' search strategies during target detection was made by considering the cross-over phenomenon exhibited by the two cumulative detection percentage curves.     

Sensitivity and validity of visual search models for multiple targets

This study proposes two search models for multiple targets (random search and systematic search) in an unstructured search field, derived by generalizing search models for single target search. Whilst the probability of locating a single target in the random search model is typically exponentially distributed, the probability of locating multiple targets was found to be distributed hypo-exponentially. The systematic search model was extended from a piecewise-linear function for a single target to a piecewise-curve function for multiple targets. To test whether these search models could predict human search performance, first, visibility area in a fixation, a main component of search models, was investigated at various fixation durations. Sensitivity analysis of this data indicated that using short fixation duration and a small fixation overlap would produce better search performance. Next, the visibility area data was combined with the search models and compared to human performance on a free search field with three targets. The systematic and random models provided upper and lower boundaries of actual human search performance. Additionally, at the start of the search task for multiple targets, search performance was close to the systematic search model, while for late targets, performance approached the random search model. Observers may have changed their search strategy during this multiple-target visual search task.     

利用VB5实现旋转体包装容器参数化设计

利用 VB5进行旋转体包装容器的外轮廓造型的参数设计 ,设计者可以通过输入参数或直接拖拽鼠标来改变旋转体包装容器的外轮廓造型 ,为旋转体包装容器三维造型设计打下了良好基础     

A decision model for the analysis of ergonomic investments

Costs associated with worker injuries can be high and some suggest investments in ergonomic solutions can lower those costs. However, many employers are still unsure if investing in various ergonomic solutions will generate benefits such as increased production and/or reduce workmen's compensation expenses. Estimating current losses and predicting possible gains provide most of the information needed to decide upon ergonomic investment. This paper presents a model employers can use to predict cost savings from ergonomic investments given certain input factors, including current losses, cost of implementation, and success of implementation.     

Value-driven maintenance planning for a production plant

Maintenance involves maintaining and securing the equipment and systems in, or restoring them to, a state in which they can perform the required functions. The challenge for maintenance planning is to identify appropriate objects and tasks for preventive maintenance and ensure that there are adequate resources for the repair actions. In this paper we will present a maintenance planning approach, called value-driven maintenance planning (VDMP), to emphasise the fact that the objectives of the plant are the reference points for specifying functional requirements for the equipment locations and equipment.The three basic phases of the VDMP planning approach are:

(i)

the definition of the fundamental, strategic and maintenance (means) objectives of the production plant,

(ii)

the classification of equipment locations (including one or several equipment items) into maintenance classes, each associated with a functional requirement specification, and

(iii)

the selection of maintenance strategies and maintenance tasks (including timing) for equipment assigned to the equipment locations.

Feedback of the operational experience is crucial for the application of the maintenance planning approach. As a consequence, the approach is developed to support the continuous improvement of the cost effectiveness of maintenance rather than planning of the initial maintenance programme of a new plant. Analysis techniques are presented and challenges of application are discussed. The application of the VDMP approach to a gasification plant in Finland is also presented.     

Optimal condition based maintenance with imperfect information and the proportional hazards model

Condition based maintenance (CBM) is based on collecting observations over time, in order to assess equipment's state, to prevent its failure and to determine the optimal maintenance strategies. In this paper, we derive an optimal CBM replacement policy when the state of equipment is unknown but can be estimated based on observed condition. We use a proportional hazards model (PHM) to represent the system's degradation. Since equipment's state is unknown, the optimization of the optimal maintenance policy is formulated as a partially observed Markov decision process (POMDP), and the problem is solved using dynamic programming. Practical advantages of combining the PHM with the POMDP are shown.     

基于扎根理论的明式家具造型组合规律提取

目的 推动当代中式家具在造型设计上对传统家具文化的继承与创新,促进传统家具与现代家具的融合发展。方法 运用了文献综述、扎根理论和统计学相结合的研究方法,收集大量与明式家具相关的绘画、书籍和期刊等资料信息,对其进行分类整理,再运用扎根理论三级编码的研究方法提取明式家具造型特征,最后运用统计分析方法提炼出明式桌案类家具的造型组合规律。结论 获取了包括腿部造型、足部造型、牙子造型、枨子造型、束腰造型和其他类造型共6大类明式家具造型元素,并提取到29组经典明式桌案类家具造型元素组合方式,以此倡议当代中式家具设计在借鉴明式家具的造型元素时,应遵循明式家具造型组合的规律,在保留经典特色的基础上推陈出新。     

Optimal inspection decisions for the block mats of the Eastern-Scheldt barrier

To prevent the southwest of The Netherlands from flooding, the Eastern-Scheldt storm-surge barrier was constructed, has to be inspected and, when necessary, repaired. Therefore, one is interested in obtaining optimal rates of inspection for which the expected maintenance cost is minimal and the barrier is safe. For optimisation purposes, a maintenance model was developed for part of the sea-bed protection of the Eastern-Scheldt barrier, namely the block mats. This model enables optimal inspection decisions to be determined on the basis of the uncertainties in the process of occurrence of scour holes and, given that a scour hole has occurred, of the process of current-induced scour erosion. The stochastic processes of scour-hole initiation and scour-hole development was regarded as a Poisson process and a gamma process, respectively. Engineering knowledge was used to estimate their parameters.     

Optimal control of epidemics in metapopulations

Little is known about how best to deploy scarce resources for disease control when epidemics occur in different but interconnected regions. We use a combination of optimal control methods and epidemiological theory for metapopulations to address this problem. We consider what strategy should be used if the objective is to minimize the discounted number of infected individuals during the course of an epidemic. We show, for a system with two interconnected regions and an epidemic in which infected individuals recover and can be reinfected, that equalizing infection in the two regions is the worst possible strategy in minimizing the total level of infection. Treatment should instead be preferentially directed at the region with the lower level of infection, treating the other subpopulation only when there is resource left over. The same strategy holds with preferential treatments of regions with lower levels of infection when quarantine is introduced.     

面向并行工程的智能型约束网络管理系统

在前期研究工作的基础上，提出了一个面向并行工程管理模式的智能约束网络管理系统的功能结构。     

Measurements of street-crossing decision-making in pedestrians with low vision

Purpose

Crossing the street is an important but risky activity of daily living. If a pedestrian makes a poor street-crossing decision, the consequence could be serious injury or death. In order to advance our understanding of how visual and auditory information is sampled and processed to make street-crossing decisions, an accurate, reliable, and sensitive psychophysical and/or psychometric method of measurement of the street-crossing decision variable must first be developed and validated. The aim of this paper is to develop and validate a new metric for this variable.

Methods

Using a 5 point rating scale, safety ratings for eight different vehicular gap times of different durations were recorded along an unsignalized, two-lane street of one-way traffic. Safety ratings were collected from 12 normally sighted and 10 visually impaired subjects. Receiver Operating Characteristic (ROC) curves were estimated for all possible gap pairs and the discriminability (d′) of the street-crossing decision variable for all gap pairs was estimated from the area under the ROC curve.

Results

We found that our data conform with the assumptions that the underlying distributions of the decision variable are continuous, monotonic and unbounded. Using the dissimilarity matrix of d’ values for each person (which were computed for all pairings of gap times) in a one-dimensional scaling model, we estimated the means of each distribution of the decision variable relative to a center of gravity (COG) for the person. When plotting the means of the distributions against vehicular gap time, the data are best described as a non-linear function symmetric about the COG. We showed that the x-intercept (t_COG) and slope from the non-linear function can be used to assess a person's street-crossing decision-making performance for different amounts of sensory information. Using our newly developed metrics, we found no significant difference in t_COG (p = 0.30) and in the slopes of the model (p = 0.85) between normally sighted and visually impaired subjects. In addition, both subject groups centered their t_COG close to their actual crossing time.

Conclusions

A newly developed model for measuring a street-crossing decision variable functions as a valid metric that can be used to quantify street-crossing decision-making performance in pedestrians. Using this new metric, we observed that visually impaired subjects who travel independently are able to make street-crossing judgments that are comparable to those of normally sighted subjects.     

Explicit formulas for the variance of discounted life-cycle cost

In life-cycle costing analyses, optimal design is usually achieved by minimising the expected value of the discounted costs. As well as the expected value, the corresponding variance may be useful for estimating, for example, the uncertainty bounds of the calculated discounted costs. However, general explicit formulas for calculating the variance of the discounted costs over an unbounded time horizon are not yet available. In this paper, explicit formulas for this variance are presented. They can be easily implemented in software to optimise structural design and maintenance management. The use of the mathematical results is illustrated with some examples.     

A mathematical model to evaluate the role of agility enablers and criteria in a manufacturing environment

Modern manufacturing arena necessitates the need for responsiveness by practicing agile manufacturing (AM) principles. AM imposes the transformation of the manufacturing organisation so as to respond to dynamic market changes. This article focuses towards the application of graph theory (GT) for conceptual modelling the agile system and to compute the dependencies among the individual agile enabler, criteria and attributes as a top-down approach. Using GT approach, digraphs were systematically constructed for agile enablers and variable permanent matrix values were computed for different scenarios and the relative importance of agility enablers were determined. The permanent values of ‘Management responsibility’ enabler and technology enabler are found to be 920 (minimum) and 3529?×?10¹⁴, respectively for the existing situation, whereas for the practically base case situation, it was found to be 1185 (minimum) and 5081.17?×?10¹⁴ (maximum), respectively. The Comprehensive Agility Index was found to be 1.3996?×?10⁴⁵, which can be even used to benchmark with other best-in-class agile organisations.     

A comparison of models for measurable deterioration: An application to coatings on steel structures

Steel structures like bridges, tanks and pylons are exposed to outdoor weathering conditions. In order to prevent them from corrosion they are protected by organic coating systems. This paper focuses on modelling the deterioration of the organic coating layer that protects steel structures from corrosion. Only if there is sufficient knowledge of the condition of the coating on these structures, maintenance actions can be done in the most efficient way. Therefore the course of the deterioration of the coating system and its lifetime, which is also of importance for doing maintenance, have to be assessed accurately. In this paper, three different stochastic processes, viz. Brownian motion with non-linear drift, the non-stationary gamma process and a two-stage hit-and-grow physical process, are fitted to two real data sets. In this way we are the first who compare the three stochastic processes empirically on criteria such as goodness-of-fit, computational convenience and ease of implementation. The first data set is based on expert judgement; the second consists of inspection results. In the first case the model parameters are obtained by a least-squares approach, in the second case by the method of maximum likelihood. A meta-analysis is performed on the two-stage hit-and-grow model by means of fitting Brownian motion and gamma process to the outcomes of this model.     

Modelling the heart as a communication system

Electrical communication between cardiomyocytes can be perturbed during arrhythmia, but these perturbations are not captured by conventional electrocardiographic metrics. We developed a theoretical framework to quantify electrical communication using information theory metrics in two-dimensional cell lattice models of cardiac excitation propagation. The time series generated by each cell was coarse-grained to 1 when excited or 0 when resting. The Shannon entropy for each cell was calculated from the time series during four clinically important heart rhythms: normal heartbeat, anatomical reentry, spiral reentry and multiple reentry. We also used mutual information to perform spatial profiling of communication during these cardiac arrhythmias. We found that information sharing between cells was spatially heterogeneous. In addition, cardiac arrhythmia significantly impacted information sharing within the heart. Entropy localized the path of the drifting core of spiral reentry, which could be an optimal target of therapeutic ablation. We conclude that information theory metrics can quantitatively assess electrical communication among cardiomyocytes. The traditional concept of the heart as a functional syncytium sharing electrical information cannot predict altered entropy and information sharing during complex arrhythmia. Information theory metrics may find clinical application in the identification of rhythm-specific treatments which are currently unmet by traditional electrocardiographic techniques.     

Training of the maintenance personnel to prevent failures in aircraft systems

The aircraft maintenance process plays a vital role in aviation safety. The quality of the maintenance process and the qualifications of the aircraft maintenance personnel are important factors in the safety of aircraft.In this study the aircraft maintenance training model has been developed by especially taking in to account the EASA Part 66 regulations. The progression of the aircraft maintenance personnel training was investigated and suggestions to improve training process were given so as to prevent failures in aircraft systems.