The representation of manufacturing requirements in model-driven parts manufacturing Today there is a need to make process and production planning more cost-effective while not compromising the quality of the product. Manufacturing requirements are used to ensure producibility in early development phases and also as a source for continuous improvement of the manufacturing system. To make this possible it is essential to have correct, updated information available and to be able to trace the relations between requirements and their origin and subjects. To trace requirements' origin in resources or processes is today very difficult owing to system integration problems. This article discusses the relations that need to be represented and proposes the use of modelbased methods to enable traceability of requirements. Because requirements are a collaborative effort a standard for information exchange is needed. The ISO10303 STEP application protocol AP233 System Engineering is proposed for this purpose. One of the biggest challenges in early development phases of a product is the management of requirements. (Kerr et al. 2006 ) A great effort is put on maintaining and managing requirements. The requirements must be attainable; stated in an unambiguous way; consistent, meaning that they do not contradict each other; and in the end verifiably to ensure the fulfilment of requirements (Harwell et al. 1993 , Gilb 1997 . In addition to this there is the complexity of requirements' relationships; in collaborative development environments, requirements will originate from different domains and state different stakeholders' needs (Rogstrand and Kjellberg 2004) . Manufacturing is one of the stakeholders (INCOSE 2004) . In the era of cutting time-to-market at lower cost, manufacturing systems' life-span exceeds the product life on the market. Therefore, companies must meet the challenge of reusing existing manufacturing systems. This has led to a desire to secure the producibility of new products in the available manufacturing system through the use of requirements in early development phases, making the stakeholder manufacturing even more important. These requirements (henceforth referred to as manufacturing requirements) are complex, because some act on the product and originate from manufacturing while others act on the production itself (more thoroughly explained in section 3).. Most requirements are still text-based, meaning that they are defined as sentences in documents or systems. The management of requirements is therefore mainly handled through manual editing of documents. The large number of requirements makes the requirement documents endless and requirement management and verification time-consuming and difficult, described by (Melchisedech 1998 , Rogstrand and Kjellberg 2004 , Nilsson 2004 , Kerr et al. 2006 . Therefore, more effort is now being exerted on management of requirements by dynamic methods that facilitate updating, derivation, decomposition, verification, etc. of requirements. This has led to an increasing use of requirement management tools to manage manufacturing requirements. Requirements management tools facilitate access, structuring and derivation of requirements (Nilsson 2004) .. However, existing commercial requirement management tools mostly support text-based requirements. They are often poorly integrated with data in other systems, e.g. PLM-data (Bailey 2004 , Kerr et al. 2006 . Together, this makes the process of verifying the requirements difficult and time-consuming. (Rogstrand and Kjellberg 2004) have showed that the poor support and variety of data makes it necessary to be an area expert in order to be able to understand and verify the requirements. The importance of all stakeholders being able to understand the requirements have also been emphasised by (Lang and Duggan 2001) .. Furthermore, in the case of manufacturing requirements there is also the issue that manufacturing requirements often secure producibility in an actual manufacturing system that is changing through time owing to normal wear, maintenance and upgrades. The information about the manufacturing system and its processes is created and maintained in a variety of systems. The information is at different levels of details and the nomenclature of different domains varies a lot. Therefore, requirements from different stakeholders are neither consistent, nor homogenous during the product development process. (Kerr et al. 2006) .. The objective of the research was to determine the information needs of manufacturing requirements. Another objective was to examine what support is available for model-driven information representation of manufacturing requirements. The study showed that it is possible to achieve a higher degree of accuracy during decision-making when limitations of existing manufacturing processes or equipment are known in early phases of product development. But to get a full change impact evaluation all aspects must be known. Access to all relevant information requires a lifecycle representation that includes information about products, processes and resources.. The following hypotheses were stated:. Complete and integrated information structures of the product, process, and resource domain is a prerequisite for performing a change impact evaluation.. Requirement information regarding the different domains and the relationships between them is necessary in order to make informed decisions based on the impact evaluation.. The research shows that both AP233 System Engineering and AP239 PLCS may be used for manufacturing requirements representation. However AP233 System Engineering has a richer requirement representation. AP233 System Engineering enables full property-based requirement representation while AP239 PLCS has limited support for requirements. This indicates that AP233 System Engineering is more suitable for the manufacturing requirement representation presented in this research article. The next step is to test the hypotheses by implementing manufacturing requirement data in the chosen application protocol of STEP. The use of AP233 System Engineering to represent manufacturing requirements will be tested in an ongoing Swedish research project. The representation of manufacturing requirements will also be tested in two different requirement management and PLM-systems. The purpose is to evaluate how the information models may be implemented and what additional support is needed. Communication of these types of requirements between different systems using AP233 System Engineering will also be tested. The work is scheduled to be finished in December 2008. Model-based requirements as presented in this research article would be beneficial to manufacturing requirement management, but this approach is far from the way requirements are managed today.. A common view regarding property-based requirements is that they are difficult to create; it is difficult to quantify the requirement in a property that may be automatically evaluated.. Using the model-based approach presented here may alleviate some of this difficulty but will introduce others, e.g. version management of requirements based on parts of a geometry definition.. Furthermore, the problem with defining propertybased requirements may stem from the fact that the quantification highlights the fact that the requirement is not stated clearly enough, or not stated in an unambiguous way. A case study was performed with the aim of investigating the information needs for robust information management of requirements. Robust information is defined in this research article as updated, accurate information which is always available and interpretable by all concerned systems (Rogstrand and Kjellberg 2005) . Based on the needs for a representation of manufacturing requirements, a study of the information standard ISO 10303, STEP, STandard for the Exchange of Product model data, has been conducted to evaluate if STEP may represent the necessary information about manufacturing requirements identified by the case study.

O O O B B O O O B O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O B O O O O B O O O O B B O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O B B B O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O B B O O O O O O B B O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O


There is more to green reading than meets the eye! Exploring the gaze behaviours of expert golfers on a virtual golf putting task Abstract Gaze patterns and verbal reports of golfers at three skill levels (professional, elite amateur and club) were recorded as they read the slope of a virtual golf green from six different positions. The results showed that the professional golfers used a more economical gaze pattern consisting of fewer fixations of longer duration than the amateur and club players. Gaze pattern was accompanied by verbal reports that were not significantly more accurate in terms of aiming accuracy, although the professionals were accurate on 76.5 % of putts compared to 57.1 % for the elite and club groups. Two read positions lead to more accurate predictions by the professional golfers only, suggesting distinctive periods of visual perceptual-cognitive attention may underly higher levels of putting skill. Theoretical implications of these results are discussed in relation to the application of visual attention theory to practise, as well as suggestions provided for further research. Expertise in sport, or the growth of specialist athletic knowledge and skills through instruction and experience, has attracted increasing interest from researchers in cognitive science (Bilalic et al. 2009; Ross 2006) , cognitive psychology (Kahnemann and Klein 2009; Rey and Buchwald 2011) and sport psychology (Causer et al. 2011; Hodges et al. 2006 ) in recent years. The upsurge in popularity of this topic is attributable to a combination of theoretical and methodological factors. Theoretically, a significant benefit of studying athletic expertise is that it provides a window on knowledge-based perception. Specifically, studies in this field reveal the role of cognitive processes in mediating the relationship between visual perception and skilled action in dynamic environments characterised by severe time constraints (see the work of Libet 2004; Müller et al. 2006 for examples) .. Methodologically, the domain of competitive sport (like chess) appeals to expertise researchers because it supplies a wealth of objective rating and ranking systems to facilitate the measurement of skilled performance. In view of these factors, a considerable amount of research evidence has accumulated on expert-novice differences in visual perception in sport (see Hodges et al. 2006; Williams et al. 1999) . Typically, studies in this field have employed eyetracking systems to compare the visual search behaviour of two samples of participants engaged in simulated performance in a given sport (see review by Ward et al. 2006) . These samples comprise ''experts'' or elite performers and ''novices'' or relative beginners. Using this group comparison paradigm, investigators have discovered that expert athletes tend to display more efficient search strategies than novices when inspecting sport-specific visual displays in rapid dynamic activities such as soccer (Helsen and Starkes 1999) , tennis (Singer et al. 1996) , cycling (Parry et al. 2012) , boxing (Ripoll et al. 1993 ) and basketball (Vickers 1996) . Such efficiency is usually evident in characteristic quantitative and qualitative differences between expert and novice groups. Specifically, proficient performers tend to display fewer visual fixations than novices while engaged in their sport skills (e.g. Abernethy 1990 ), but these fixations are often of longer duration than those of their less skilled counterparts (Gegenfurtner et al. 2011) .. There are also reliable qualitative differences in visual search behaviour between these groups with experts tending to fixate more than novices on ''information rich'' areas of the visual display in question (Hodges et al. 2006) . Taken together, such findings suggest that experts in dynamic sporting domains are capable of extracting more information than novices from a single glance at a pattern relevant to their field even when the dynamic environment is a virtual reality computerised task (Correia et al. 2012 ). Unfortunately, due to a paucity of relevant research, it is unclear whether this latter finding applies to self-paced skills performed in relatively static environments (e.g. the golf putt) as much as to reactive skills performed in dynamic environments (e.g. the tennis volley). Given this unresolved issue, the purpose of the present paper is to address this gap in the research literature by investigating the visual search patterns of skilled golfers, while they perform a crucial but hitherto neglected perceptual skillnamely ''green-reading'' or trying to determine the slope of the putting surface prior to aiming the ball towards the hole. At this stage, it is important to consider in more detail what this skill of green reading or slope perception involves in the context of golf putting.. ''Putting'', or attempting to strike the ball along the ground from its resting position into the hole on the green, is one of the most important skills in golf. Specifically, it requires fine motor control, sound technique and precise judgement and accounts for an estimated 41 % of all strokes made during an average round of tournament golf (Professional Golfers Association 2011) . But what makes this skill especially difficult to perform successfully is the fact that golf putting greens are never flat surfaces but instead contain built-in slopes and undulations (designed traditionally to facilitate drainage of water off the surface)-many of which are subtle or disguised. Faced with such uncertain terrain, a golfer's putting performance depends on three skills (MacKenzie and Sprigings 2005) . First, appropriate club-head speed in striking the ball and second, at a biomechanical level, the golfer must ensure that his or her putting stroke will have only horizontal velocity in the chosen target line towards the hole. Finally, and arguably most importantly, accurate perceptual judgement is required when the golfer attempts to predict the proposed path of the putt in relation to the slope of the green. Specifically, the golfer must be able to determine the degree of break or swing in the putt when directing the ball towards the hole across the uneven putting surface.. This process of green-reading varies considerably from golfer to golfer but typically takes between 30 and 120 s, and indeed, golfers themselves highlighted this inspection time as an important pre-requisite to making a good decision on where to aim and subsequent stroke execution (Campbell 2006) . During this period of time, golfers invariably walk around the green and visually inspect the position of the ball in relation to the hole from a number of different angles and positions before making a final decision about the optimal line or aim of the putt and the corresponding force required to execute the shot.. Unfortunately, despite its importance in golf, proficiency in green-reading or slope perception has received little or no published scientific attention from researchers. A possible reason for this neglect is that there appears to be little agreement as to the most effective method for assessing the slope of a given golf green (MacKenzie and Sprigings 2005) . Against this background, the purpose of the present paper is to investigate for the first time expertise differences in the gaze behaviour of skilled golfers faced with the task of reading putts.. Although golf putting is a complex skill, it can be measured relatively easily in the laboratory. Accordingly, a number of psychological studies have been conducted on various aspects of this skill. For example, research in this field has examined such topics as gaze control and putting (Vickers 1992; Vine et al. 2011) , the effect of putting grip on eye and head movements (Hung 2003) , mental imagery in putting (Beilock et al. 2001; Short et al. 2002; Kornspan et al. 2004) , vibrotactile sensations in the ''feel'' of a putt (Roberts et al. 2005) , attentional processes in putting (Beilock et al. 2002a (Beilock et al. , b, 2003 Perkins-Ceccato et al. 2003) , EEG measures of attentional patterns prior to putt execution (Crews and Landers 1993) and brain imaging of people imagining putting (Ross et al. 2003) .. Unfortunately, none of these studies has addressed the specific issue of what golfers actually look at during their pre-putt routine, while they inspect the slope of the putting surface. Faced with such inherent perceptual uncertainties, where golfers have to look and attend to should be a matter of importance and critically has been highlighted as largely ignored but deserving of empirical scrutiny (Craig et al. 2000) . Indeed, van Lier and colleagues summed it up when they said that ''…successful putting entails more than proficient movement control, but requires…skillful perception' ' (van Lier et al. 2011, p. 349) . Van Lier et al. (2011) demonstrated that systematic perceptual errors in relation to the direction of a line are made in golf putting, and they looked at how golfers overcome this perceptual distortion. Importantly, they highlighted the following: ''Before actually executing a putt, it is important for the player to read the green before addressing the ball (i.e. preparing the actual swing). By reading the green, the golfer can gather information over and beyond information used to control the direction of the swing' ' (p. 366) . Such a strategy they recommend can reduce biases evident in perceived direction of golfers. Finally, they concluded that ''the present results suggest that novices would benefit more … than high skilled players' ' (p. 366) . In a further related study of 407 golfers, Pelz (1994) found that ''men, women, pros and amateurs, indeed all golfers, consistently and substantially underestimate the amount a putt breaks' ' (p. 180) . This underestimation is realised in golfers missing putts on the ''low'' side, i.e. the side away from the break or slope. Importantly, Pelz (1994 Pelz ( , 2000 posited that golfers have to compensate for this under-read/underestimation during their preparation of the stroke. The gaze behaviours of golfers may therefore serve an important function of cognitively processing this underestimation with an appropriate compensatory aiming and motor action. Vickers (1992 Vickers ( , 2007 has provided some insights into a similar perceptual process-the visual search behaviour of golfers as they stood over the ball, about to strike their putts. Briefly, she explored expert-novice differences in the eye movements of golfers as they performed a series of golf putts in the laboratory. Results revealed significant differences between these groups in the number and duration of visual fixations displayed during the preparation and executing of the putting action. Specifically, in comparison with the less skilled players, the more expert golfers displayed significantly fewer fixations per putt. Finally, Wilson and Pearcy (2009) conducted a study examining golfers gaze behaviour in both the preparation (line reading) and execution of putts with different break characteristics as golfers stood over the golf ball ready to address it and execute their putts. They found that the only gaze variable to distinguish between successful and unsuccessful putting outcome was the quiet eye (QE) period. This QE period equated to a significantly longer period of gaze fixation immediately prior to onset of putting stroke. Additionally, Wilson and Pearcy (2009) also found that golfers displayed more aiming fixations on sloped putts than straight putts. This they argued was because of the demands of specifying an abstract target on a sloping putt.. Perhaps the most intriguing finding of this study, however, was the discovery that the expert players spent significantly longer than their novice counterparts in looking at the target (in this case the golf ball) as the last step before initiating their putting stroke. Vickers (1996) coined the term QE for this finding, and specifically, she used this term to designate a phenomenon whereby sport performers who are aiming at something tend to display a final visual fixation at the target of their aim before executing the relevant motor action (e.g. striking the golf ball towards the hole or throwing the basketball at the hoop). This QE period, which can last from 300 to 2,000 ms depending on the sport, is thought to reflect the performer's attempt to establish cognitive control of relevant visual parameters prior to skill execution. It is also believed to facilitate the ''dampening'' of unwanted variability in the performer's motor system before task execution (Vickers 2006 (Vickers , 2007 . Perhaps not surprisingly, QE phenomena have been discovered in the performance of aiming skills in other sports such as basketball (Harle and Vickers 2001; Vickers 1996) , ice hockey (Martell and Vickers 2004) , golf putting (Vickers 1992) , table tennis (Vickers and Adolphe 1997), billiards (Williams et al. 2002) and darts (Vickers et al. 2002) .. Although Vickers' (1992 Vickers' ( , 2007 ) research on golfers gaze behaviours was seminal in the field of expertise and visual perception in athletes, it has at least two key limitations that need to be addressed. First, it was based on data collected from participants, while they were executing their skills-not while they were planning them. Indeed, as she noted, we do not ''understand … the manner in which golfers move their eyes about the putting environment'' (p. 117). A second limitation of Vickers' (1992) study stems from the number and classification of the participants tested. Specifically, her sample size (n = 12) was small and somewhat idiosyncratically defined. To explain, the highly skilled golfers in her study were not ''experts'' in any conventional sense because their mean handicap (of 6.2) indicated that they played at a proficient rather than excellent competitive level. In an effort to rectify this performer classification problem, three groups of golfers will be employed in the present study-two samples of experts (from touring professionals to so called lesser skilled experts; elite amateurs) and a group of club-level players. In summary, the purpose of the study was to investigate expertise differences in the visual search behaviour of golfers of different levels of ability as they engaged in a simulated green-reading task. The present study is the first empirical investigation of expertise and eye-tracking in golf green-reading. Extending previous research on expert-novice differences in planning and perception in sport, we suggest that there are significant differences between professional golfers and club-level players in the number and duration of the visual fixations displayed while engaged in the inspection of a golf putt during a virtual tour of a simulated golf green. Specifically, two findings can be highlighted as follows. First, we discovered that the less skilled golfers in our sample displayed significantly more fixations than the more expert players in three of the six predetermined viewing positions on the virtual tour of the golf green. Second, we found that average visual fixation times increased among expert players in two of the six predetermined viewing positions. Taken together, we interpreted these findings to indicate that relative to less skilled performers, expert golfers display distinctive periods of visual cognitive activity while inspecting aspects of the golf putt that they face. In general, these findings are broadly consistent with previous research on expert-novice differences in the perceptual processes of athletes. Specifically, they corroborate Vickers' (1992) speculation that expertise in golf putting is ''characterised by economy in the number of gaze shifts'' (p. 117) during the stroke planning process. Economical search patterns among expert athletes have also been reported in previous studies with athletes from other sports. For example, Moran et al. (2002) found that expert gymnasts and equestrian performers displayed an economical search strategy that was characterised by a relatively low number of short duration fixations and a relatively greater number of longer duration fixations directed at task relevant areas. In relation to planning of skills, Williams et al. (2002) found that skilled billiards players exhibited longer visual fixations on the target during the preparatory phase of their stroke than their less skilled counterparts.. In the present study, the lesser skilled club-level golfers displayed more fixation numbers of shorter duration on average than their more skilled professional counterparts. The expertise and eye-tracking literature has no fixed agreement on whether this is more ''expert'' like or not. Some authors have reported that experts have more fixations of shorter duration than novices (Konstantopoulos 2009; Litchfield et al. 2008) , while others have reported the opposite direction (Bertrand and Thullier 2009; Vogt and Magnussen 2007) . One ongoing problem with eye-tracking methodology in expertise research is the typically small sample size (Gegenfurtner et al. 2011 ) and possible sampling error arising from this. The current study with a very large number of participants (N = 45) aimed to avoid this traditional problem. The preceding conclusions must be tempered by acknowledgement of certain limitations of our research, however. For example, the green-reading task that we used was a computer simulation whose ecological validity is unknown. Perceptual-cognitive judgements can be adversely affected by the demands and/or set-up of the task (Dicks et al. 2010 ). Thus, critics may argue that the threedimensional software used to create the virtual greens does not mimic adequately the appearance of an actual golf green. The benefits of using a real golf green in a field setting must be balanced against the difficulty and inconvenience of measuring eye movements in such environments. A second limitation of the present study stems from the fact that we did not address the issue of proprioceptive feedback which walking on a surface can provide about its possible slope. Thirdly, problems arise from the fact that we used a predetermined sequence of viewing positions in the virtual tour of the green. In reality, considerable individual differences can exist among golfers in pre-putting visual inspection routines. These individual differences are ignored by the use of a standard sequence of viewing positions. In our defence, however, we decided to use a standard 6-step virtual tour for participants because a previous qualitative study (reported in Campbell 2006 ) and various coaching instruction books (Pelz 2000; Utley and Rudy 2006) had shown that professional golfers tended to favour a consistent pre-putt inspection routine-involving a combination of the six positions that formed the basis of our virtual tour. Turning to suggestions for future research, it is important to explore more precisely the cognitive processes and theoretical mechanisms that underlie the ''quiet eye'' (QE) effect in target sports. Also it would be very pertinent to examine the gaze behaviour of golfers as they engage in the pre-shot routines and to marry this up with the subsequent skill execution. This way a link can be made between QE findings and earlier visual perceptualcognitive periods of activity. This could then provide a more robust examination of a complete perception-action cycle in a sensori-motor skill such as golf. Finally, subsequent research may investigate the benefits of a structured visual perceptual training programme or a programme that instructs performers in obtaining knowledge about the type of reading or perceptual errors that they make as this may facilitate adaptive changes in alignment, aiming and shot selection.. To summarise, our research provides the first empirical evidence of expertise differences in visual perceptual processes on a simulated green-reading task. It also suggests that distinctive periods of visual perceptual-cognitive activity may be evident in athletes' pre-performance routines-as they ''toured'' the environment in which skill execution was required. Before conducting inferential statistical tests on these data, it may be helpful to note that firstly not all golfers identified some green-reading positions as part of their specific green-reading routine; therefore, only four viewing positions were consistently deemed of importance in the sequence (behind the ball and behind the hole crouching and standing). Therefore, main effects will be examined for the viewing positions in relation to the two dependent variables. Secondly, an economical or efficient eye-tracking search rate is usually indicated by a relatively low number of visual fixations of longer duration.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O


Modeling Signal Transduction in Enzyme Cascades with the Concept of Elementary Flux Modes Concepts such as elementary flux modes (EFMs) and extreme pathways are useful tools in the detection of non-decomposable routes (metabolic pathways) in biochemical networks. These methods are based on the fact that metabolic networks obey a mass balance condition. In signal transduction networks, that condition is of minor importance because it is the flow of information that matters. Nevertheless, it would be interesting to apply pathway detection methods to signaling systems. Here, we present a formalism by which this can be achieved in the case of enzyme cascades operating, for example, by phosphorylation and dephosphorylation. It is based on the ideas that the signal is not diminished along each route and that the system has to return to its original state after each signaling event. We illustrate the method by several simple prototypic single-phosphorylation and double-phosphorylation cascades, including convergent and divergent branching. Moreover, it is applied to a specific example from insulin signaling. (See online Supplementary Material at www.liebertonline.com.) Here, we have presented an approach for detecting elementary signaling routes in enzyme cascades (e.g., phosphorylation cascades). To this end, we adapted elementary flux modes (EFM) analysis, which had been established earlier for detecting pathways in metabolism (Schuster et al., 1999 (Schuster et al., , 2000 . A schematic application of the concept of EFMs to enzyme cascades would lead to the trivial result that the EFMs reflect particular enzyme cycles (e.g., phosphorylation-dephosphorylation cycles) rather than the routes of information transfer. In order to describe the latter in a suitable way, we have started from the reasoning that signaling usually implies signal amplification or at least a constant signal strength, but never a diminuition. In the limit case of constant signal strength, each active enzyme molecule should activate exactly one enzyme molecule at the next level of the cascade. By this coupling, we can write reaction equations that lead to EFMs representing routes of information transfer. The same routes are relevant when signal amplification occurs. By this reasoning, the application of elementary flux modes analysis and related methods such as extreme pathway analysis (Schilling et al., 2000) and minimal T-invariants (Starke, 1990) to intracellular signaling systems has been put on a firm theoretical basis. Thus, EFMs can be calculated, for example, by the program Metatool (von Kamp and Schuster, 2006 ) also for enzyme cascades. Earlier, these analyses have been applied in a formal way to such systems without a theoretical justification (Xiong et al., 2004; Heiner et al., 2004; Sackmann et al., 2006) .. As a proof of concept, we have applied the presented method to part of the insulin signaling network. The three resulting EFMs can be interpreted in biochemical terms. The first EFM leads to a serine phosphorylated and thus active 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase (EC 3.1.3.46/EC 2.7.1.105). This bifunctional enzyme is part of the fructose and mannose metabolism, where it catalyzes the reaction from b-D-fructose 6-phosphate to b-D-fructose 2,6-bisphosphate, and back. The output of the second EFM is the activated transcription factor CREB(PS), which regulates (together with the transcription factor forkhead box O1A) the expression of the insulin-like growth factor binding protein 1. That protein is neccessary for binding the insulin-like growth factor 1, which in turn regulates cell growth, glucose metabolism, and several other processes. The third EFM results in the phosphorylated ribosomal protein S6. Hence, the further outcome of this signaling route is activation of protein synthesis. For all of these functions, see the Transpath database (Krull et al., 2006) .. Of course, the entire insulin signaling network has many more functions, such as activation of glycogenesis and enhancing glucose uptake in muscle cells and adipocytes by increasing the number of GLUT4 transporters in their membranes.. The enzyme cascades analyzed here can be considered as relay races with changing batons because it might appear as if the phosphates were transferred along the cascades, but they are replaced at each level. This situation differs from group transfer pathways such as the phophotransferase system (PTS) for which the analogy to a relay race is more appropriate because the ''baton'' is not replaced. Papin and Palsson (2004) have studied the latter type of systems.. The enzyme Ras, which we have included in our model, belongs to the G-proteins and in particular to the family of small GTPases. Such enzymes are activated by replacing the GDP they are complexed with in their inactive form, by GTP. The substitution is catalyzed by so-called guanine nucleotide exchange factors (GEFs) (Krauss, 2003) . In our case, this is IIR(PY)_Shc(PY)_Grb-2_Sos, the complex of insulin, insulin receptor, Src homologous and collagen protein, growth-factor receptor-binding protein 2, and the enzyme Son of Sevenless. The inactivation of these activated G-proteins is triggered by their intrinsic ability to hydrolyze GTP to GDP and phosphate (Gomperts et al., 2002) . From the point of view of the biochemical structure of the active form of the G-protein, the replacement of GDP by GTP is equivalent to a phosphorylation. Therefore, our formalism is also applicable to this class of signaling proteins.. Our analysis differs from the approach proposed by Alon (2007) in that we determine routes going through the entire signaling network, starting from an initial signal and leading to some cellular response. In contrast, Alon (2007) extracts modular (non-overlapping) network motifs, which are smaller than the signaling routes determined here, which can have subroutes in common.. It is promising to apply robustness analysis (Wilhelm et al., 2004; Behre et al., 2008) and the concept of minimal cut sets (Klamt and Gilles, 2004; Klamt, 2006) proposed earlier for metabolic networks to enzyme cascades. Since these methods use EFMs, their application is straightforward. Also the concept of enzyme subsets (Pfeiffer et al., 1999) and the refined concepts in flux coupling analysis (Burgard et al., 2004 ) can be applied. On Boolean networks, information transfer has been analyzed, and minimal intervention sets have been defined without explicitly considering mass balance constraints . It would be interesting to investigate the interrelations between these approaches.

O O O O O O O O O O B I I O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A direct evaluation of stress intensity factors using the Extended Dual Boundary Element Method The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract We introduce an alternative method in computational fracture mechanics to evaluate Stress Intensity Factors (SIFs) directly using the Extended Dual Boundary Element Method (XBEM) for 2D problems. Like other enrichment approaches, the new approach is able to yield accurate results on coarse discretisations, and the enrichment increases the problem size by only two degrees of freedom per crack tip. The BEM equations formed by collocation at nodes are augmented by two additional equations that enforce continuity of displacement at the crack tip. The enrichment approach provides the values of SIFs KI and KII directly in the solution vector and without any need for postprocessing such as the J-integral. Numerical examples are used to compare the accuracy of these directly computed SIFs to J-integral processing of both conventional and enriched boundary element approximations. In making fracture assessments, and in particular the prediction of crack propagation, it is of great importance to have an accurate understanding of the stress field in the vicinity of the crack tip. In Linear Elastic Fracture Mechanics (LEFM), the Stress Intensity Factors (SIFs) play a major role in the description of the the singular stress field, and can be seen in the stress and displacement expansions introduced by Williams [1] . SIFs can be determined from handbooks (e.g. [2] ) for some simple cases of geometry and loading. For complicated shapes or applied boundary conditions, engineers can make use of numerical methods to resolve the stress fields and thereby give the SIFs K I and K II for modes I and II, respectively. It is well known that a singularity appears at the crack tip in LEFM, making numerical methods such as Finite Element Method (FEM) and Boundary Element Method (BEM) inefficient without modification. Watwood [3] noted the need for using a very refined mesh near the crack tip. Much of the computational fracture mechanics research work since then has involved developing algorithms that, in one way or another, offer a more efficient solution. In an early example of enriched FEM formulations, Benzley [4] successfully determined SIFs using isoparametric finite elements enriched locally with functions to 1 capture point singularities. Henshell and Shaw [5] presented the use of quarterpoint elements, in which the desired √ r (where r is the distance from the crack tip) variation in displacements could be achieved by moving the mid-nodes of elements to quarter-point positions.. Contributions to computational fracture mechanics continued with the hybrid crack element introduced by Tong et al. [6] and extended by Xiao and Karihaloo [7] , showing how it can be used for direct evaluation of singular and higher order coefficients. In parallel, Leung and Su [8, 9] introduced the fractal finite element method which divides the domain into a regular and a singular region, where the crack tip is the centre of similarity of the singular region. The method was applied to modes I, II and III successfully and has shown an accuracy of (1%) [10] . Recently, extensions of the method have been added including fractal hybrid finite elements [11] and fractal-like FEM [12] for bi-material problems. The Scaled Boundary Finite Element Method (SBFEM) [13] benefits from its semianalytical formulation to provide highly accurate approximations for the SIFs. The method suffers from its restriction to star-shaped domains (i.e. those exhibiting a line-of-sight to all boundary points from the "scaling centre" which is placed at the crack tip in fracture problems) or models comprising a set of star-shaped subdomains. This restriction has been overcome by coupling the SBFEM to the BEM [14] .. The partition of unity method was introduced as a general technique to allow enrichment of FEM approximations. Melenk & Babuška [15] showed how the traditional piecewise polynomial approximation basis can be enriched by the use of functions (or sets of functions) that offer better approximation properties. This idea has been applied to computational fracture mechanics in the form of the Extended Finite Element Method (XFEM) [16] . The use of XFEM enrichment led to a reduction in the need for mesh refinement, and also separated the mesh from the crack path so crack propagation analysis could proceed with the need for remeshing, and for these reasons it has spawned a considerable volume of literature.. In parallel with the development of finite element methods, the Boundary Element Method (BEM) also gained popularity because of its boundary-only meshing (offering a reduction in dimensionality of the problem) and because of its ability to capture discontinuous functions. It also offered good accuracy of solutions on the domain boundary whereas finite element methods offered their greatest accuracy at integration points within the element. However, using the classical BEM to collocate on coincident points on opposing crack surfaces gives rise to degenerate linear systems [17] . Many methods have been proposed offering various treatments including special Green's functions [18] and the subregion technique [19] . Hong and Chen [20, 21] introduced the idea of Dual Boundary Integral Equations, in which a combination of the standard Boundary Integral Equation and its derivative can be used to provide independent equations in order to overcome the problem of degeneracy. They showed how the Displacement Boundary Integral Equation (DBIE) can be differentiated and Hookes law applied to derive the Traction Boundary Integral Equation (TBIE). Chen and Hong [22] for the first time solved a system formed from a combination of the two integral equations in the context of a Darcy problem, but Portela et al. [23] were the rst to implement the combined use of the DBIE and TBIE in a single system to solve crack problems. They named this the Dual Boundary Element Method. Hong and Chen [24] reviewed the Dual BEM development up to the end of the 1990s. Portela et al [23] also described how the use of the TBIE imposes certain conditions on the selection of elements used for the discretisation of crack surfaces. These conditions arise because of the continuity requirements of the field variables for the existence of Cauchy and Hadamard principal value integrals. It is routine to overcome the problem while still using collocation by using discontinuous elements, in which the nodes are located within the body of the element, and not at its ends. Collocation at these nodes satisfies the Holder continuity requirements of the hypersingular integral equation since the shape functions are continuously differentiable at these points. There is considerable literature describing the application of discontinuous element for this purpose e.g. [23, 25, 26, 27] . These elements also permit the analysis of wide variety of crack geometries including kinked cracks.. The use of the Williams expansions in the BEM has been presented by Portela et al. [28] to subtract the singularity by dividing the domain into singular and regular fields. The technique was able to solve for K I and K II directly. Recently, the partition of unity approach was used by Simpson and Trevelyan [29] , who presented a boundary element method enriched in a similar fashion to XFEM (giving a technique that could be called XBEM, as we continue to call it henceforth). This work extended the benefits of XFEM to provide high accuracy of SIFs from coarse boundary-only discretisations. Their method was soon extended to curved cracks [30] . Both implementations relied on the use of the J-integral [31] to calculate the SIFs. In the current paper, we extend this XBEM approach by using a modified form of enrichment in combination with crack tip displacement constraint equations to provide values of SIFs directly. The aim is to enable the solution of large problems, particularly when the enrichment is extended to 3D, by making a considerable reduction in the number of degrees of freedom required to achieve results of a prescribed accuracy. We note that other approaches to acceleration of BEM simulations have been developed, e.g. the Fast Multipole Method (FMM), which has been applied successfully to speed up the evaluation for thousands of cracks [32] . The authors believe the enriched XBEM approach described in this article could be further accelerated with the FMM to provide a powerful solution. Unlike [32] the proposed method is able to evaluate SIFs directly at a cost of two additional degrees of freedom per crack tip. This is an interesting subject for further research.. A similar square root enrichment was earlier introduced into the shape functions for special crack tip elements by Li et al. [33] , and applied to the relative crack face displacements in a symmetric Galerkin BEM based on weak form integral equations. Like [29, 30] this technique was shown to give good accuracy from coarse meshes. The approach of [29, 30] is adopted in the current work as it offers similar accuracy benefits but can be more easily implemented by making a relatively simple modification to a pre-existing DBEM code.. In general determination of SIFs can be categorized into direct and post-processing methods. Direct methods offer speed and flexibility to evaluate higher order terms [7] . On the other hand, the J-integral, taken over a closed independent integral path and based on energy approach, is the most used postprocessing technique and is available to general purpose FEM and BEM codes that do not have any special formulations injected to deal directly with the stress singularity.. In this paper, we introduce a direct, highly accurate evaluation of SIFs by enriching crack surface elements. Moreover, it has potential for extension to 3D, where the use of the J-integral type approaches become more cumbersome than in 2D.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Decentralized management of building indoors through embedded software agents Abstract. In order to support personalized people comfort and building energy efficiency as well as safety, emergency, and context-aware information exchange scenarios, next-generation buildings will be smart. In this paper we propose an agent-oriented decentralized and embedded architecture based on wireless sensor and actuator networks (WSANs) for enabling efficient and effective management of buildings. The main objective of the proposed architecture is to fully support distributed and coordinated sensing and actuation operations. The building management architecture is implemented at the WSAN side through MAPS (Mobile Agent Platform for Sun SPOTs), an agent-based framework for programming WSN applications based on the Sun SPOT sensor platform, and at the base station side through an OSGi-based application. The proposed agent-oriented architecture is demonstrated in a simple yet effective operating scenario related to monitoring workstation usage in computer laboratories/offices. The high modularity of the proposed architecture allows for easy adaptation of higher-level application-specific agents that can therefore exploit the architecture to implement intelligent building management policies. Nowadays, due to advances in communication and computing technologies, the need to have high comfort levels together with an optimization of the energy consumption is becoming important for inhabitants of buildings. Moreover, buildings should also support their inhabitants with automatic emergency and safety procedures as well as context aware information services. To meet all these requirements, future buildings have to incorporate diversified forms of intelligence [7] .. We believe that agent-based computing [20] can be exploited to implement the concept of intelligent buildings due to the agent features of autonomy, proactiveness, reactiveness, learnability, mobility and social ability. Specifically agents can continuously monitor building indoors and their living inhabitants to gather useful data from people and environment and can cooperatively achieve even conflicting specific goals such as personalized people comfort and building energy efficiency.. A few research efforts based on agents have been to date proposed to design and implement intelligent building systems [25] [17] [8] [28] [27] [23] . However, none of them provide agents embedded in the sensor and actuator devices that would introduce intelligence decentralization and improve system efficiency. This is due to the exploitation of conventional sensing and actuation systems that do not offer distributed computing devices for sensing and actuation. To overcome this limitation, wireless sensor and actuator networks (WSAN) [26] can be adopted. WSANs represent a viable and more flexible solution to traditional building monitoring and actuating systems (BMAS), which require retrofitting the whole building and therefore are difficult to implement in existing structures. In contrast, WSAN-based solutions for monitoring buildings and controlling equipment, such as electrical devices, heating, ventilation and cooling (HVAC), can be installed in existing structures with minimal effort. This should enable monitoring of structure conditions, and space and energy (electricity, gas, water) usage while facilitating the design of techniques for intelligent device actuation.. The implementation of the proposed architecture is based on MAPS (Mobile Agent Platform for Java Sun SPOTs) [3] at sensor/actuator node side and on Jade [5] OSGi-based application at coordinator side.. The main contribution of this paper is the definition of A-BMF (Agent based Building Management Framework), a decentralized and embedded agent oriented architecture for the management of intelligent buildings that is based on WSANs and overcomes the limitations of the aforementioned solutions [25] [17] [8] [28] [27] [23] . In particular, the aim of our architecture is to optimize and fully decentralize the sensing and actuation operations through distributed cooperative agents both embedded in sensor/actuator devices and running on more capable coordinators (PC, plug computers, PDA, smartphones). This would enable more effectiveness in programming the sensing and actuation operations and more efficiency in the management of distributed sensor and actuator nodes. Moreover, the proposed architecture can be easily programmed to support a wide range of building management applications integrating comfort, energy efficiency, emergency, safety, and context-aware information exchange aspects.. The rest of this paper is organized as follows. Section 2 describes approaches related to our work. In Section 3 the proposed agent-based architecture for building management is defined. Section 4 presents the MAPS-based implementation of the low-level architecture, specifically the sensor/actuator agents. Section 5 shows the system GUI and a system deployment for monitoring the workstation usage in computer laboratories. Finally, conclusions are drawn and directions of future work elucidated. In this paper we have proposed A-BMF, an agent-based architecture for flexible, efficient and embedded sensing and actuation in buildings. Specifically, the distributed software architecture is embedded into both WSANs and more capable computing devices (e.g. PCs, smartphones, plug computers). The proposed architecture can be seen as basic middleware for developing intelligent building management systems to achieve the Smart Building concept. Currently the proposed architecture is exploited to monitor the space occupation and energy expenditure in computer laboratories for students to analyze energy consumption patterns with respect to users' behavior so as to semi-automatically implement behavior policies. In the current implementation, BMA and CA are merged into a component-based application implemented through OSGi [24] . Moreover, only one cluster can be deployed. On-going work is aimed at completing the JADE-based implementation of the multi-cluster architecture founded on the BMA and on multiple coordinated CAs. Future work will be devoted to: (i) the design of a higher-level agent-based architecture for Smart Buildings atop the proposed architecture to trade off inhabitants' personal comfort and building energy expenditure; (ii) the support of user mobility in buildings based on the interoperation between body sensor network worn by users and the intelligent agent based building infrastructure; (iii) the formalization of the A-BMF system through communicating real time state machine-based formalisms [14] for verification of A-BMF-based application scenarios; (iv) the exploitation of streaming techniques [13] to enhance sensor data collecting at application and network level. In [25] the authors present the MASBO (Multi-Agent System for Building cOntrol) architecture that aims to provide a set of software agents to support both on-line and off-line applications for intelligent work environments. MASBO is used to develop a multi-agent system (MAS) able to tradeoff energy saving and inhabitants' preferences where preferences can be learnt and predicted through an unsupervised online real-time learning algorithm (analyzing inhabitants' behavior). MASBO agents reside on a server and constantly monitor data from sensors and eventually actuate some commands. MASBO works as an enhancement to an existing building automation system by adding learning, reasoning and autonomous capabilities. The responsibility of controlling sensors and actuators, and keeping a requested environmental value constant is not addressed by MASBO.. In [17] the authors propose a working solution to the problem of thermal resource distribution in a building using a market-based MAS. Computational agents representing individual temperature controllers bid to buy or sell cool or warm air. The agents, running in a monolithic process on a workstation, are able to distribute the thermal resources so that all the building offices have an equitable temperature distribution. Temperature sensors and air flow actuators are all accessible directly through distributed hardware modules via a network connection.. In [8] the authors describe a MAS that monitors and controls an office building in order to provide added values like energy saving together with the delivery of energy. The developed system is distributed in the sense that some agents are located on PDAs and others run on the Bluetooth access points (workstations) that communicate with the PDAs. The system makes use of the existing power lines for communication between the agents and the sensing and actuation system controlling lights, heating, ventilation, etc.. In [28] a conceptual framework, namely Cyber-enabled Efficient Building Energy Management System (CEBEMS), is presented. Its intent is increasing energy efficiency, lowering dependence on the energy grid, and providing an economic incentive for the end user. It enables distributed control methodology using MAS for efficient management of both electrical and thermal energy systems for realizing maximum efficiency energy management. MAS aim to achieve system-wide objectives, which may not be solved using a single agent, but by coordination and communication among the agents.. In [27] authors do a demonstration of data gathering from a WSN. In the system proposed, users can query and view the local data in an ad-hoc manner, and possibly remotely configure and manipulate the data capture process. For the purposes of this demonstration, authors adopted Agent Factory Micro Edition (AFME) [22] . The Agents, implemented on AFME, are programmed to answer users' requests.. In [23] a simulation of a building environment where agents can manage the allocation of resources and facilitate the residents' lives is presented. In the designed system, sensors deployed in a building send their information to agents. Agents, that reside on workstations, process information and send them to a fuzzy controller [16] that eventually transmits a proper signal to switches, valves or other actuators.. Differently from the described approaches, our agent-based architecture embeds agents both into the wireless sensor and actuator network used as infrastructure for building monitoring and control and on more capable coordinators. This important feature would provide decentralized intelligence and improve system efficiency. Table 1 summarizes the characteristics of the works reported above.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O