Uncertainty drives deviations in normative foraging decision strategies

Nearly all animals forage to acquire energy for survival through efficient search and resource harvesting. Patch exploitation is a canonical foraging behaviour, but there is a need for more tractable and understandable mathematical models describing how foragers deal with uncertainty. To provide such a treatment, we develop a normative theory of patch foraging decisions, proposing mechanisms by which foraging behaviours emerge in the face of uncertainty. Our model foragers statistically and sequentially infer patch resource yields using Bayesian updating based on their resource encounter history. A decision to leave a patch is triggered when the certainty of the patch type or the estimated yield of the patch falls below a threshold. The time scale over which uncertainty in resource availability persists strongly impacts behavioural variables like patch residence times and decision rules determining patch departures. When patch depletion is slow, as in habitat selection, departures are characterized by a reduction of uncertainty, suggesting that the forager resides in a low-yielding patch. Uncertainty leads patch-exploiting foragers to overharvest (underharvest) patches with initially low (high) resource yields in comparison with predictions of the marginal value theorem. These results extend optimal foraging theory and motivate a variety of behavioural experiments investigating patch foraging behaviour.     

Optimal foraging: Lévy pattern or process?

Many different species have been suggested to forage according to a Lévy walk in which the distribution of step lengths is heavy-tailed. Theoretical research has shown that a Lévy exponent of approximately 2 can provide a higher foraging efficiency than other exponents. In this paper, a composite search model is presented for non-destructive foraging behaviour based on Brownian (i.e. non-heavy-tailed) motion. The model consists of an intensive search phase, followed by an extensive phase, if no food is found in the intensive phase. Quantities commonly observed in the field, such as the distance travelled before finding food and the net displacement in a fixed time interval, are examined and compared with the results of a Lévy walk model. It is shown that it may be very difficult, in practice, to distinguish between the Brownian and the Lévy models on the basis of observed data. A mathematical expression for the optimal time to switch from intensive to extensive search mode is derived, and it is shown that the composite search model provides higher foraging efficiency than the Lévy model.     

改进的细菌觅食优化算法及其在框架结构设计中的应用

在细菌觅食算法(bacterial foraging algorithm,BFA)基本原理的基础上,结合“和声搜索”算法,提出了一种改进的细菌觅食算法,并应用于框架结构优化.采用该优化算法分别对一单跨8层框架和双跨5层框架结构进行离散变量的质量优化设计,并与细菌觅食算法的计算结果进行了比较.计算结果表明改进的细菌觅食算法应用在结构优化中具有较好的收敛速度和精度,可应用于工程结构的优化设计.     

Solving cell formation and task scheduling in cellular manufacturing system by discrete bacteria foraging algorithm

We consider a joint decision model of cell formation and task scheduling in cellular manufacturing system under dual-resource constrained (DRC) setting. On one hand, machines and workers are multi-functional and/or multi-skilled, and they are grouped into workstations and cells. On the other hand, there is a processing sequence among operations of the parts which needs to be dispatched to the desirable workstations for processing. Inter-cell movements of parts can reduce the processing times and the makespan but will increase the inter-cell material handling costs. The objective of the problem is to minimise the material handling costs as well as the fixed and operating costs of machines and workers. Due to the NP-hardness of the problem, we propose an efficient discrete bacteria foraging algorithm (DBFA) with elaborately designed solution representation and bacteria evolution operators to solve the proposed problem. We tested our algorithm using randomly generated instances with different sizes and settings by comparing with the original bacteria foraging algorithm and a genetic algorithm. Our results show that the proposed DBFA has better performance than the two compared algorithms with the same running time.     

Social information use and the evolution of unresponsiveness in collective systems

Animal groups in nature often display an enhanced collective information-processing capacity. It has been speculated that natural selection will tune this response to be optimal, ensuring that the group is reactive while also being robust to noise. Here, we show that this is unlikely to be the case. By using a simple model of decision-making in a dynamic environment, we find that when individuals behave rationally and are subject to selection based on their accuracy, optimality of collective decision-making is not attained. Instead, individuals overly rely on social information and evolve to be too readily influenced by their neighbours. This is due to a classic evolutionary conflict between individual and collective interest. The result is a sub-optimal system that is poised on the cusp of total unresponsiveness. Individuals in the evolved group exhibit delayed reactions to changes in the environment, before responding with rapid, socially reinforced transitions, reminiscent of familiar human and animal social systems (markets, stampedes, fashions, etc.). Our results demonstrate that behaviour of this type may not be pathological, but instead could represent an evolutionary attractor for such collective systems.     

Mesoscale fronts as foraging habitats: composite front mapping reveals oceanographic drivers of habitat use for a pelagic seabird

The oceanographic drivers of marine vertebrate habitat use are poorly understood yet fundamental to our knowledge of marine ecosystem functioning. Here, we use composite front mapping and high-resolution GPS tracking to determine the significance of mesoscale oceanographic fronts as physical drivers of foraging habitat selection in northern gannets Morus bassanus. We tracked 66 breeding gannets from a Celtic Sea colony over 2 years and used residence time to identify area-restricted search (ARS) behaviour. Composite front maps identified thermal and chlorophyll-a mesoscale fronts at two different temporal scales—(i) contemporaneous fronts and (ii) seasonally persistent frontal zones. Using generalized additive models (GAMs), with generalized estimating equations (GEE-GAMs) to account for serial autocorrelation in tracking data, we found that gannets do not adjust their behaviour in response to contemporaneous fronts. However, ARS was more likely to occur within spatially predictable, seasonally persistent frontal zones (GAMs). Our results provide proof of concept that composite front mapping is a useful tool for studying the influence of oceanographic features on animal movements. Moreover, we highlight that frontal persistence is a crucial element of the formation of pelagic foraging hotspots for mobile marine vertebrates.     

An information trail model for capturing human behaviour in artefact creation and use in complex work systems

This article presents an information trail model. The model is a method for uncovering information transformation using artefacts in complex work systems. We use a patient care scenario in a hospital emergency department to illustrate theoretical, methodological and design elements of the model. In a complex system, humans create and manage complexity, a paradox. The information trail model proposes that humans manage the paradox by creating and evolving artefacts and information cues. They organise purposefully through self-organisation and stigmergical behaviour. Information trail model states that humans leave trails of information as signs or symbols, and the piecing together and transformation of which will lead to final goals. Information trails contain work attributes and strategies, which can be utilised in work system design.     

Determinants of internal and external R&D offshoring: evidence from Spanish firms

This paper analyses the determinants of R&D offshoring of Spanish firms using information from the Panel of Technological Innovation. We find that being an exporter, international technological cooperation, continuous R&D engagement, applying for patents, being a foreign subsidiary, and firm size are factors that positively affect the decision to offshore R&D. In addition, we find that a lack of financing is an obstacle relatively more important for independent firms than for firms that belong to business groups. For these latter, we also obtain that the factors that influence the decision to offshore R&D differ depending on whether the firm purchases the R&D services within the group or through the market: a higher degree of importance assigned to internal sources of information for innovation as compared to market sources increases (decreases) the probability of R&D offshoring only through the group (market).     

Optimal use of simplified social information in sequential decision-making

Social animals can improve their decisions by attending to those made by others. The benefit of this social information must be balanced against the costs of obtaining and processing it. Previous work has focused on rational agents that respond optimally to a sequence of prior decisions. However, full decision sequences are potentially costly to perceive and process. As such, animals may rely on simpler social information, which will affect the social behaviour they exhibit. Here, I derive the optimal policy for agents responding to simplified forms of social information. I show how the behaviour of agents attending to the aggregate number of previous choices differs from those attending to just the most recent prior decision, and I propose a hybrid strategy that provides a highly accurate approximation to the optimal policy with the full sequence. Finally, I analyse the evolutionary stability of each strategy, showing that the hybrid strategy dominates when cognitive costs are low but non-zero, while attending to the most recent decision is dominant when costs are high. These results show that agents can employ highly effective social decision-making rules without requiring unrealistic cognitive capacities, and indicate likely ecological variation in the social information different animals attend to.     

Relationships between multiaxial stress states and internal fracture patterns in sphere-impacted silicon carbide

Internal fracture patterns developed in silicon carbide cylindrical targets as a result of dynamic indentation (63–500 m/s) by tungsten carbide spheres are defined. Microscopy of recovered and sectioned targets delineate into three regions, each associated with distinct cracking modes, i.e., shallow cone macrocracking at and near the impact surface, steep interior cone macrocracks that radiate into the target from the impact region and local grain-scale microcracking directly underneath the impact region. The observed fracture patterns are found to maintain a noticeable degree of self-similarity upto the impact velocity of 500 m/s. Linear elastic analysis of the full (surface and interior) stress field developed under static (Hertz) contact loading delineate the target into four regions, based on the number of principal stresses that are tensile (none, 1, 2 or all 3). A strong correlation is found between the principal stress conditions within each region and the forms of cracking, their locations and orientations present therein. This correlation has a number of implications, including non-interaction of crack systems, which are discussed. Illustrative linear elastic fracture mechanics analyses are performed for three regions, and calculated and observed macrocrack lengths are found to be in reasonable agreement.     

Optoelectronics — past,present, and future

Considerable progress has been made in the field of optoelectronics in the last thirty years. The two principal drivers for this progress have been the invention of the laser and low-loss optical fibres. But what is optoelectronics? Optoelectronics is more than just a marriage of electronics and optics. It represents the higher order integration of technical achievements in electronics and photonics to allow one to chose what, where, when, and how to address both old and new problems and opportunities for increasing customer satisfaction in the areas of information movement and management. I will review the progress in the field and share my insights into where the future lies. The important question no longer is if optics will replace electronics in many of the technologies underlying information movement and management; it is when and to what degree. The limitation no longer arises from the technical capabilities, it comes from economics and social values provided by the increased capabilities in communications and computers.     

Impact of sharing full versus averaged social information on social influence and estimation accuracy

The recent developments of social networks and recommender systems have dramatically increased the amount of social information shared in human communities, challenging the human ability to process it. As a result, sharing aggregated forms of social information is becoming increasingly popular. However, it is unknown whether sharing aggregated information improves people’s judgments more than sharing the full available information. Here, we compare the performance of groups in estimation tasks when social information is fully shared versus when it is first averaged and then shared. We find that improvements in estimation accuracy are comparable in both cases. However, our results reveal important differences in subjects’ behaviour: (i) subjects follow the social information more when receiving an average than when receiving all estimates, and this effect increases with the number of estimates underlying the average; (ii) subjects follow the social information more when it is higher than their personal estimate than when it is lower. This effect is stronger when receiving all estimates than when receiving an average. We introduce a model that sheds light on these effects, and confirms their importance for explaining improvements in estimation accuracy in all treatments.     

Identifying and classifying force-generation strategies for one-hand isometric force exertion tasks with bracing availability

Obstructions within a task environment provide opportunities for people to brace themselves with the non-task hand, thigh, or other body part. Previous research has shown that bracing can increase one-hand isometric force-exertion capability in standing tasks. The current laboratory study examined the patterns of force on the bracing surfaces as a function of task and human characteristics. Twenty-two men and women exerted static forces with their right hands. Bracing opportunities were provided at the thigh, contralateral hand, or both. Using the task hand force as a reference, bracing forces were decomposed into opposing and non-opposing components and normalised relative to task hand force magnitude. Five distinct patterns of bracing force, termed force-generation strategies (FGSs), emerged.     

运输包装设计信息查询系统的研究与开发

采用Visual C++工具开发了一款运输包装设计信息查询系统,介绍了该系统的体系结构、系统功能的开发与实现方法,并进行了实例演示。结果表明:使用该系统能够快速、准确并完整地查询设计信息,将人们从繁杂的手工查询中解放出来,大大提高了工作效率和质量,避免了对产品的破坏性试验,具有实际应用价值。     

Identification of information sources and citation patterns in the field of reciprocating internal combustion engines

Processes and technology of reciprocating internal combustion engines (ICE) constitute a research field whose characteristics regarding information production and diffusion are determined by multidisciplinarity, the existence of pseudo-technical literature and the influence of confidentiality on the presentation of research outputs. The objective of this study is to provide a quantitative and objective basis for the evaluation of research in this field. This has been accomplished by identifying the most productive journals and the most cited sources, using the SCI and citation analysis. From this analysis, core journals have been identified, showing that their importance in this research area does not correlate with their impact factor. Moreover, conference proceedings (particularly those published by the Society of Automotive Engineers) are shown to be the most important information source in this field. This revised version was published online in June 2006 with corrections to the Cover Date.     

SSCM:一种语义相似度计算方法

分析了实例多重继承和实例属性层次关系对实例相似性的影响,针对原有的实例语义相似度计算方法的不足,提出了一种语义相似度计算方法SSCM,该方法综合考虑了实例多重继承关系和属性及属性值的层次关系,并利用继承关系的树状结构特点对计算过程进行了优化.实验表明,该方法在本体知识库的多种组成情况下,均能有效提高语义相似度计算的准确率.在实例多重继承关系相对复杂的情况下,准确率提高更加明显.     

构建创意空间的设计要素及策略研究

目的对发展智慧城市语境下的创意空间的必要性与意义展开深入分析,理清构建实体创意空间以及线上创意空间所需的设计要素以及发展策略,并提出解决方案。方法基于智慧城市对于创意社区的多样化需求,分析创意空间的功能承载以及设计定位;结合创意空间的发展现状以及信息技术的应用特点,分别从实体创意空间与线上创意空间的设计要素进行分类表述,并在此基础上探讨创意空间的运行模式以及发展趋势。结论从设计师角度将创意空间设计要素从实体创意空间与线上创意空间分别进行了探讨,依照创意分享、协作、实践与创新的逻辑关系组织,建立了创意空间信息系统的运行框架。     

架构和模式在水声信息流仿真软件中的应用

水声信息流仿真软件系统涉及多目标、多声纳以及多变的海洋环境．仿真软件的复用性是现代软件工程的重要性能指标．针对系统开放性的特点，在领域分析模型的基础上，采用了面向对象方法设计仿真软件模型．为了满足软件多层次复用的需求，应用软件架构技术和设计模式设计仿真软件．根据水声信息流仿真软件需求，系统划分为四层结构；按功能，层又可分解为包．可复用的设计模式用于设计不同层和包中类之间的关系．提出的仿真软件模型具有良好的可扩充性与可复用性．