The Ability of UK Offshore Workers of Different Body Size and Shape to Egress through a Restricted Window Space 404 male offshore workers aged 41.4 ± 10.7 y underwent 3D body scanning and an egress task simulating the smallest helicopter window emergency exit size. The 198 who failed were older (P < 0.01), taller (P < 0.05) and heavier (P < 0.0001) than the 206 who passed. Using all extracted dimensions from the scans, binary logistic regression identified a model (refined using backward elimination) which predicted egress outcome with 75.2% accuracy. Using only weight, bideltoid breadth and maximum chest depth, the model achieved ∼70% accuracy. When anatomical dimensions categorise individuals for small window egress, 25% or more will be misclassified, with false positives (those predicted to fail, but pass) slightly outnumbering false negatives (those predicted to pass, but fail), highlighting the limitations of a predictive approach which treats the body as a rigid object. Differences in flexibility and technique may explain these observations, which may be important considerations for future research. The ability of UK offshore workers of different body size and shape to egress through a restricted window space. Although the stature of humans has increased for the last six generations, in many northern European countries it has largely stabilised, while in southern and eastern European countries, it continues to rise (Cole, 2002) . Alongside increased stature are increased girths, breadths and depths, although these do not precisely follow a pattern of geometric similarity (Nevill et al., 2004) . Observed secular body weight increase necessarily reflects height and other dimensional increases, but in addition, the rising prevalence of global obesity (WHO, 2000) . In addition to being a health risk, excess fat enlarges the body laterally, affecting posture, compromising locomotion (Wearing et al., 2006) , and increasing the likelihood of adopting unusual or restricted postures in restricted space, with consequences for musculo-skeletal health (Gallacher, 2005) . Physical body size and shape affects the ability of a person to function in any environment where space is restricted. The built environment, examples of which endure for centuries, if not millennia, expresses designs which never anticipated the physical size of adults today.. In addition to the underlying trends for size to increase, certain professions are associated with larger individuals, such as truck drivers (Guan & Hsaio, 2012) and firefighters (Hsaio et al., 2014) . Whether or not such enlarged dimensions arise via preferential recruitment of larger candidates, or result from wider cultural aspects of the role, these will add to any size burden imposed by the secular trend, and may present specific challenges for ergonomic applications such as accessibility, signage or comfort. Over more than four decades of operations, the UK offshore work environment has borne witness to a progressive size increase of its workers. The male UK offshore population has previously been surveyed (Light and Dingwall, 1985) and reported to be heavier and fatter than their onshore counterparts (Light and Gibson, 1986) . At the time, offshore workers were approximately 3% heavier than the equivalent UK onshore population, but this discrepancy varied according to age. Since this time, the average discrepancy has nearly trebled in magnitude.. Comparing the Size and shape of the UK Offshore Workforce 2014 (SASOW) findings to those of Light & Dingwall, show that offshore workers are, on average, 19% heavier, 2% taller, and have 17% greater waist girth, 14% greater neck girth, 12% greater chest and hip girths and 11% greater wrist girth. The theoretical modelling of ability to pass in a narrow corridor using SASOW data suggested that male UK workers were 28% less likely to be able to pass one another than the general male population .. The ergonomic consequences of increased body size for emergency escape planning include all aspects of transportation, locomotion, mustering and personal protective equipment (Ledingham and Stewart, 2013) . This is perhaps most apparent in helicopter window egress. Research performed in a military facility determined the minimum dimensions of rectangular opening which could be used as a secondary exit in an emergency (Allan & Ward, 1986) . Four individuals of varying body size exited progressively smaller apertures underwater in a simulated helicopter escape exit, and the study concluded that an exit of 432 x 356 mm was compatible with the 99 th centile of bidletoid breadth, (based on 1970-71 Royal Air Force aircrew size data). How highly trained such individuals were, and other demographic data were not included in the report. While the conclusions may be robust for military aircrew, the applicability to civilians assumes no underlying size difference between the two populations. While a range of human factors other than anatomical ones will govern the response to the successful escape from helicopters ditching in water (Brooks, 1989) , it is virtually impossible to recreate authentic emergency situations experimentally due to unassailable practical and ethical considerations, and sizerelated factors have not been prominent in this consideration due to a lack of current information. As a result, the aim of this study was to provide current, context-specific information for the civilian UK male offshore workforce, relating body dimensions to simulated helicopter window egress. Successful egress through a small window frame is based on a number of factors. Anatomical factors account for the majority of the variability in outcome, however there are limitations of a predictive approach which treats the body as a rigid object because non-morphological factors may also be influential. Bideltoid breadth remains useful in predicting egress, and its accuracy is enhanced with the addition of chest depth and body weight. Descriptive statistics of the physical characteristics of the participants are provided in table 1. For the window egress, those who succeeded in passing through the window frame were younger, shorter and lighter, in terms of absolute and relative weight. The measurements themselves were assessed for reliability, which are illustrated in table 2. The analysis used only the first measurement of paired measurements, in the case of the 28 individuals selected for duplicate measures.. Effect size comparison of passes / fails with a representative sample of the offshore workforce (n=588), as selected by the SASOW study, is illustrated in figure 3 . Figure 3 . Effect size of passes and fails' extracted measurements from 3D scans Figure 3 shows the standardised effect size (ES) when comparing the difference in means for each dimension for those who passed or failed to the entire offshore sample (n=588). (Note: body weight measures and stature are not included). The upper figure compares those who passed to the offshore sample and the lower figure compares those who failed to the offshore sample. The dimensions for each have been ranked from highest ES to lowest ES (black circles) and 95% CI, with the middle vertical line representing 0 (or no difference). A negative ES represents a dimension for which those who passed/failed are typically smaller than the offshore sample. A positive ES represents a dimension for which those who passed/failed are typically larger than the offshore sample. Effect sizes and 95% CIs for each dimension are listed down the right-hand-side of the figure. A comparison of CV ratios of passes v fails is illustrated in figure 4 . This figure shows the CV ratios comparing those who passed to those who failed the small window egress test (Note: body weight measures and stature are not included). Dimensions ranked from highest CV ratio to the lowest. All CV ratios have been extended from unity, and anything to the left of 1 represents dimensions for which those who passed are typically less variable than those who failed (only dimensions with a CV ratio less than 0.9, represented by the dashed line, are considered to be substantially less variable). Anything to the right of 1 represents dimensions for which those who passed are typically more variable than those who failed (only dimensions with a CV ratio greater than 1.1, represented by the dashed line, are considered to be substantially more variable).. Binary Logistic Regression yielded results which were broadly similar, in terms of their predictive capability of discriminating those able to pass through the small window frame and those who were not. Using all 30 measures in the backward elimination process yielded the optimal model. These input measures were: shoulder girth, bideltoid breadth, height of deltoid, chest depth at deltoid, maximum chest depth, neck girth, chest depth at deltoid wearing survival suit, maximum depth wearing a survival suit, maximum breadth wearing a survival suit, chest breadth at axilla, chest girth, chest breadth at nipple height, waist girth (minimum), waist girth (umbilicus), abdominal depth, hip girth, hip breadth, wrist girth, total volume, abdominal volume, arm volume, leg volume, total volume wearing a survival suit, hip breadth sitting, buttock to knee, deltoid to thorax, weight (clothing), weight (survival suit), weight (form-fitting) and age.. Using measures of body weight, namely the weight category (1 to 7, lightest to heaviest), weight in form fitting shorts, weight in indoor clothing (without shoes) and weight in survival suit / re-breather, the model selected the indoor clothed weight. ROC analysis was performed to consider the readily-measurable variables separately, to identify the probability of a randomly selected offshore worker failing the test being larger or heavier than one passing the test. This probability is represented by the area under the curves for weight (in indoor clothing), bideltoid breadth and maximum chest depth (measured against the body surface), which were 77, 71 and 76% respectively, as illustrated in figure 5. With the average TEM for repeated measurement extractions close to 1% of the measurement value, the extracted dimensional data, with the exception of segmental volumes, compare very well with conventional anthropometry. Better reproducibility of segmental volumes was obtained using manually landmarked participants (Schranz et al., 2010) which was not practical in the present study. Poorer reliability relates to the variability in the location of the slice plane used to divide the arm and leg segments from the torso. Accepting that we did not reposition individuals and scan twice, but manually extracted dimensions from the same scans on two separate occasions, the key measurements readily made on offshore workers, such as the bideltoid breadth, are very encouraging. Crucially, these involve error which equates to or even outperforms that of experienced anthropometrists' manual measurements (Marfell-Jones et al., 2013) .. Consideration of the effect size of passes and fails of small window egress, relative to the entire sample, shows all dimensions with the exception of the height of the deltoid to affect the likelihood of passing. Examination of the CV ratios shows that individuals who pass have less variable dimensions than those who fail for shoulder girth, hip breadth, waist girth (umbilicus), bideltoid breadth, abdominal volume, abdominal depth and hip girth. There was the suggestion of greater variability in dimensions of depth in those who passed as compared with those who failed, but these were not considered substantial (i.e. CV ratios < 1.1). Smaller physiques may have less scope for variability, and this, together with smaller absolute dimensions may explain these findings. Larger individuals, by contrast, have greater potential for variability.. Close inspection of the optimised model revealed some predictor variables that have the opposite sign to the majority of body size dimensions in the prediction. This was the case with stature, suggesting a greater height was associated with passing the test. This is plausible because being taller allows for greater quantities of tissue to be more evenly distributed along the skeleton, an observation noted in a general population sample at sites of fat accumulation (Nevill et al., 2010) , enhancing the ability of the individual to achieve a successful escape through the window. Similarly, leg length has been observed to be inversely proportional to cross sectional area (Burton et al., 2012) which could be explained by mechanical work achieved either through a longer contraction distance or a larger cross sectional area.. Weakly positive coefficients also prevailed for waist and hip girth, suggesting that a larger girth led to a greater chance of successful egress, whereas the shoulder girth had a more strongly negative coefficient (suggesting a larger shoulder girth reduces successful egress). More challenging to explain is why the bideltoid breadth also reveals a positive coefficient. The fact that a larger bideltoid breadth is associated with a poorer chance of successful window egress on its own, and yet when, in conjunction with a given bideltoid girth favours a successful outcome is perplexing. Our interpretation is that for a given shoulder girth, a relatively large breadth, but small depth seems favourable. Because the shoulder girdle can elevate or depress relative to the spinal axis, provided sufficient spinal and shoulder flexibility exist, a wide-framed yet flexible person might be favoured. No equivalent effect could influence the dimensions of the thorax, which move only a modest amount during ventilation.. In a recent safety review of helicopter operations the UK Civil Aviation Authority highlighted the mis-match between escape time from a submerged helicopter and breath hold time (CAA, 2014). Of particular concern was the possibility of passengers awaiting the egress of another occupant, prior to making their own escape. It acknowledged the need to ensure compatibility of passenger body morphology and exit window size, and prior to implementation of a CAA recommendation on 1 st April 2015, an ambitious measuring programme of bideltoid breadth (via manual anthropometry) of all offshore workers was undertaken, informed by old aviation data (Allen & Ward, 1986) and preliminary data of the SASOW study. A 'cut-off' value of bideltoid breadth was chosen above which passengers were categorised as 'extra-broad' or 'XBR', and the practice implemented that 'extra-broad' persons are only seated next to the largest windows in the helicopter. With the proportion of large windows in the current helicopter fleet being much higher than the 3-4% of workers measured as XBR, there is considerable contingency built into this process.. However, it should be noted that while this study was of persons wearing a 'rebreather' lifejacket (standard issue for years prior to and during the study), an additional CAA recommendation regarding the type of emergency breathing apparatus to be used on offshore helicopter flights had resulted in the removal of this 're-breather' system from service and the introduction of a new system. The new system has different physical characteristics which may themselves influence ability to exit through a window, and a clear mandate therefore exists to investigate all aspects of the implementation of the new emergency breathing apparatus, in terms of egress.. The current study, with more complete data than those available at the time the April 2015 decision was taken, identifies that the maximum chest depth would perform slightly better than bideltoid breadth as a predictor of ability to exit a window of given size, and that a combination of measures including body weight and both these would perform better still. In its favour, bideltoid breadth can be measured more reliably than many other measures by virtue of its lower %TEM. Furthermore, all extracted data were based on the same scans, and this the same phase of the breathing cycle captured. While most of the thoracic movement during breathing is vertical, the effect of breathing artefact may affect chest depth more than bideltoid breadth. Importantly, maximum chest depth would not be straightforward to measure on females, who comprise 3-4% of offshore workers. Inspection of the effect size chart (figure 3) reveals that many of the parameters which have larger effects than bideltoid, are not practical to measure.. The question remains as to what might explain the likelihood of successful egress through a small window, other than anatomy. The issue of the fit of the survival suit and rebreather is important, as the potential for different shapes and juxtapositions may have an influence, both on snag hazard and buoyant force on immersion, which are beyond the scope of this investigation. Three further factors may influence egress, which have not been assessed in the current investigation: compressibility, flexibility and motivation. The methodology of capturing body shape as a 3D scan involves considering the body as a rigid object -as if it were a mannequin. The reality is that the body surface is compressible, but to a different extent within and between individuals, depending upon individual muscularity and adiposity. Ultrasonography of the superficial tissues shows adipose tissue compression of up to 37% with a modest force of only 11.2 N, and only very slightly less compression with half the applied force (Toomey et al., 2011) . Given the likely strength of offshore workers, and the forces generated in an emergency situation, there is potential for compressibility to be considerably greater.. Age was significantly greater in those who failed, as compared to those who passed, and this may be associated with factors including increased adiposity and increased thoracic depth. A loss of compliance of the chest wall results in decreased lung volumes with age (Mittman et al., 1965) , and structural changes include increased anterio-posterior depth. Flexibility has been shown to decrease with age, but the effect is joint-specific (Medeiros et al., 2013) . In their study, a deterioration of the shoulder and trunk flexibility commencing in the 4 th or 5 th decade, was more marked than at other joints, a finding the authors attribute to the lack of use of regular full range of movement of these joints in the tasks of daily living. Shoulder flexibility may limit egress when wearing a survival suit, and may be reduced according to prior activity or injury.. Motivation to egress the window frame may have not been uniform across all participants. This may be because it was not a genuine emergency situation, and that some individuals may have experienced discomfort during the attempt. While the wooden frame does not reproduce the conditions in an emergency, such conditions would be very challenging to recreate both practically and ethically. At present helicopter underwater escape training does not require participants to attempt to egress through a push-out window of dimensions as small as those of the window used in this study. Nevertheless, anecdotal evidence suggests some workers experience heightened arousal when exiting a much larger window underwater. The industry needs to strike a balance between the need to quantify as accurately as possible the relationship between large individuals and space or exit size provision, and the physical and psychological discomfort associated with the periodic helicopter underwater escape training for a civilian workforce.. The optimal model from 3D scanning yielded 75.2% accuracy. The rationale of the study was to seek to approach its performance using measures which may be feasible in practice. With the two favoured anatomical variables, bideltoid breadth and maximum chest depth, the test accuracy was 68.8%, which reached 72.5% using derived variables from easily-made measurements. In practical terms the reduction in accuracy from the optimal model is likely to be of no consequence, and the suitability of measuring women favours the bideltoid breadth, with the inclusion of clothed weight. This lends support to the strategy of measuring bideltoid breadth favoured by the CAA. Nevertheless, some examples of very large individuals who successfully exited, and, more worryingly, much smaller ones who failed, raises the possibility of a workforce testing regime involving an actual exit test itself. While the logic of such an approach is salient, its value in relation to its cost and time to implement, would present major challenges to the industry. The affordability and practicality of predictive testing justify its continued use meantime. However, questions remain as to whether other factors should be measured which could enhance the predictive accuracy of an egress test, and as an alternative to a mandatory window egress task for all offshore workers, further study of flexibility and compressibility might cast valuable light on this in a cost-effective way. Participants comprised a subset of the larger Size and shape of offshore workers (SASOW) study , and were the 404 'core crew' (who worked at least 50% time offshore) for whom all required data were available, recruited via a range of media from Oil & Gas UK and key stakeholders. Measurements were made in appointments lasting ~ 20 minutes mostly at Aberdeen heliports but also in Norfolk which services the Southern North Sea sector. Participants wore lycra shorts for some scans, and a survival suit of standard type in one of 11 available sizes (over regular indoor clothing), according to manufacturer's instructions based on stature and chest girth. Each volunteer underwent a 'window frame' egress test by passing a wooden window frame over himself, when wearing survival suit and re-breather lifejacket. The frame was sized 432 x 356 mm (precisely to replicate the minimum acceptable size for an escape window (CAA, 2006) , and smaller than all emergency exit sizes. Three-dimensional (3D) body scans using an Artec L scanner (Artec Group, Luxembourg) wearing form-fitting shorts, and also with a full survival suit and lifejacket over their regular indoor clothing, in two standing and one sitting postures. Examples of scans are depicted in figure 1. Scans were processed using Artec studio 9 software (Artec Group, Luxembourg). This involved global registration, fusion and hole-filling processes, which rendered the scans into 3D objects suitable for measurement extraction. Scans were oriented using a positioning tool which standardised the presentation in 3D xyz space, with the x axis anterior-posterior, y axis lateral and z axis vertical, which enabled coordinates to be calculated for all placed landmarks.. The requirement to constrain measurements to a short enough time to attract a large sample, precluded manual landmarking. Instead, extracted measurements relied on visually identifiable landmark locations placed digitally on the scan surface, such as the axilla, nipple, naval and anterior knee, together with the most anterior, posterior or lateral aspects of convex surfaces. From these locations, planes for measurements were constructed and dimensional analyses performed using direct measurements, or the x-x, y-y, or z-z co-ordinate differences between landmarks. A total of 25 dimensional measurements were extracted which include linear distances, girths and segmental volumes, which are fully described in Ledingham et al. (2015) . These are: shoulder girth, bideltoid breadth, height of deltoid, chest depth at deltoid, chest depth at deltoid (in survival suit), maximum chest depth, neck girth, maximal breadth (in survival suit), maximal depth (in survival suit), chest breadth (axilla), chest breadth (nipple), chest girth, waist girth (minimum), waist girth (umbilicus), abdominal depth, hip girth, hip breadth (standing), hip breadth (sitting), wrist girth, buttock to knee (seated), abdominal volume, arm volume, leg volume, total volume, total volume (in survival suit). All linear measurements were in cm, and volumes in l. Measurements acquired when wearing the survival suit were located using landmarks identified by xyz coordinates from the equivalent scans acquired when subjects wore shorts, and such landmarks were readily observable.. After scans were processed, data were all extracted by the same researcher. Reproducibility for measurement extraction was established using blinded re-analysis of the same scans of 28 individuals, four from each of the seven weight categories of the SASOW study, and calculating the technical error of measurement (TEM). Technical error of measurement was calculated by replicate measurement extractions (in cm, or l for linear dimensions and volumes, respectively) for all variables according to the formula:. where x 1 and x 2 are replicate measures, and n is the number of measurement pairs. This gives the absolute error in the same units as the measurement.. The percentage TEM is value is more widely reported, and is given by the formula:. Effect size (ES) differences and coefficients of variation (CV) were calculated for each variable, to facilitate comparison of those who passed and failed with the general offshore workforce. Dimensional data were entered into a model with all candidate variables subjected to backwards elimination binary logistic regression to discriminate those who passed from those who failed the window egress. In addition, models which used the variables most easily assessed in practice were also used, including body weight, bideltoid breadth, maximum chest depth (measured against the body surface), and also the maximum breadth and depth when wearing the survival suit and lifejacket. Further receiver operator characteristic tests were performed individually on selected variables retained by the optimised model, or by variables used within the literature on egress, which explained the probability of a single variable correctly predicting an egress test outcome. Examples of some measurements extracted are illustrated in figure 2. The study was approved by Robert Gordon University Research Ethics Subcommittee.

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O O O O O O O O O O O O O O O O O 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 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 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 B I 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 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 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Stability SCAD: a powerful approach to detect interactions in large-scale genomic study Background: Evidence suggests that common complex diseases may be partially due to SNP-SNP interactions, but such detection is yet to be fully established in a high-dimensional small-sample (small-n-large-p) study. A number of penalized regression techniques are gaining popularity within the statistical community, and are now being applied to detect interactions. These techniques tend to be over-fitting, and are prone to false positives. The recently developed stability least absolute shrinkage and selection operator ( S LASSO) has been used to control family-wise error rate, but often at the expense of power (and thus false negative results). Results: Here, we propose an alternative stability selection procedure known as stability smoothly clipped absolute deviation ( S SCAD). Briefly, this method applies a smoothly clipped absolute deviation (SCAD) algorithm to multiple sub-samples, and then identifies cluster ensemble of interactions across the sub-samples. The proposed method was compared with S LASSO and two kinds of traditional penalized methods by intensive simulation. The simulation revealed higher power and lower false discovery rate (FDR) with S SCAD. An analysis using the new method on the previously published GWAS of lung cancer confirmed all significant interactions identified with S LASSO, and identified two additional interactions not reported with S LASSO analysis.Conclusions: Based on the results obtained in this study, S SCAD presents to be a powerful procedure for the detection of SNP-SNP interactions in large-scale genomic data. We developed a variable selection procedure (referred to as S SCAD selection). This procedure could control the FDR while maintaining the power to detect SNP-SNP interactions in association studies. In the pure interaction model, this procedure seems to overcome the conservativeness of S LASSO. The end result is that S SCAD, as a new technique in detecting interactions, can benefit the selection of S LASSO. Identifying interactions among multiple SNPs is both statistically and computationally challenging in large-scale association studies. The challenges include high-dimensional problems, computational capability, multiple testing problems, and genetic heterogeneity [20] . Many stochastic and heuristic detecting epistasis methods [21] could be used to analyze GWAS dataset. Wang et al. used AntEpiSeeker, a two-stage ant colony optimization algorithm (ACO), to identify epistasis [22] . Wan et al. proposed SNPRuler [23] based on both predictive rule inference, and two-stage design. Boolean operation-based screening and testing (BOOST) [24] involves only Boolean values, and allows the use of fast logic operations to obtain contingency tables. TEAM [25] exploits properties of test statistics to mitigate multiple testing problems. To date, there appears to be no one method free from model sensitivity.. In addition to non-parametric and model-free methods, many LASSO-based penalized parametric methods provide the estimation of parameter as the dimensionality increases, even if the number of variables is greater than the sample size. The coefficients of those none diseaseassociated SNPs will be zero in the penalized multivariate regression model. Thus, detecting interactions is equivalent with the variable selection problem under the framework of regression analysis. A broad range of simulations has demonstrated that the penalized regression method is a useful tool for detecting gene-gene interactions. However, the regularization choice in penalized regression is usually made by cross-validation that maximizes predictive accuracy in finite samples; although it does not necessarily induce the correct sparseness pattern for variable selection [26] . In our simulations, cross-validation often leads to the inclusion of too many noise variables, and induces instability of variable selection for the ordinary penalized regression method, such as LASSO or SCAD. A major hurdle for studying interactions in GWAS is the lack of efficient algorithms that can map different forms of interactions while keeping FDR under control [27] . S LASSO introduces stability selection into traditional LASSO. The stability selection procedure combines selection algorithms for high dimensional problems by sub-sampling. S LASSO dramatically reduces the number of false discovery rate, and could accurately identify crucial regions of GWAS; however, it is overly conservative, and may miss some important regions. S SCAD procedure increases the power of detecting the interactions while controlling FDR. It attempts to provide more true interactions, but less noise terms than S LASSO. The above advantage could be attributed to the fact that running the LASSO-penalized procedure within stability selection results in more false positives than SCAD for each random sub-sample. Thus, the interactions causing noise as well as true interactions in the region both satisfy the threshold condition π thr for selection. To control the number of falsely selected variables, the threshold must be very stringent. As a result, the S LASSO selection suffers a loss of power.. We analyzed a previously reported lung cancer dataset in Han Chinese, and confirmed significant interactions in the achPathway pathway, which supported the appropriate use of the proposed method. The observation of interactions between two closely located SNP pairs supports the hypothesis that some genetic variation in complex traits may hide in interactions between linked SNPs [28] .. Application of the proposed procedure to GWAS data may ensure that the power of detection is reduced when over-stringent threshold π thr conditions exist for the much increased ratio of SNPs to samples. A good alternative to derive genome-wide significant threshold is permutation. Unfortunately, genome-wide permutation in real GWAS of interactions is computationally prohibitive for the S SCAD selection. Partial search strategies based on biological knowledge [29] or the filtering of unimportant SNPs prior to analysis [30] could be adopted to reduce excessive computing burdens in early stage of genome-wide scale. These strategies are also necessary for the proposed method.. Under our current approach, high-dimensional data were primarily managed with sparse models. High correlations (individual SNPs that have a variance inflation factor (VIF) > 2 with other markers) were excluded. The chip data were pruned, and then analyzed with regression model method using a sparse constraint. Many common diseases may be associated with many SNPs with small to moderate effects. In this situation, we are considering group penalized methods in another paper. High-dimensional genomic data are becoming increasingly available to assist in the identification of genetic factors for complex diseases such as lung cancer. In particular, genome-wide association studies (GWAS) have implicated a variety of genetic variants in many diseases, while only a small fraction of phenotypic variation was explained by those. This suggests that multi-locus gene-gene or gene-environment interactions must be considered [1] .. Gene-gene interactions could be detected using a variety of methods [2] . For example, multifactor dimensionality reduction (MDR, [3] ) is a non-parametric and model-free method that does not require any assumption of genetic mode of inheritance. However, MDR is inefficient in handling large scale genetic datasets [4] . Penalized regression methods such as least absolute shrinkage and selection operator (LASSO) [5] and smoothly clipped absolute deviation (SCAD) [6] are also widely used for high-dimensional data. LASSO is a useful tool for detecting gene-gene interactions with a broad range of simulations [7] . SCAD penalty has an oracle property, and thus it is more consistent with the actual effects than LASSO [6] . The crossvalidation is usually used for the choice of the amount of regularization in penalized regression methods (e.g., LASSO and SCAD), but it often includes too many noise variables. In an attempt to minimize such a problem, a modified LASSO penalized method, stability LASSO ( S LASSO), has been proposed to unify optimal shrinkage and variable selection in GWAS ( [8] ). Stability selection controls false discovery rate and renders crossvalidation practically unnecessary. Alexander and Lange (2011) claimed that S LASSO could accurately identify the most important regions of GWAS, but in a simulation study S LASSO offers less power than the simpler and less computationally intensive methods of marginal association testing [8] .. It has been shown that the LASSO penalty could produce a bias even in the simple regression setting due to its linear increase of penalty on regression coefficients. To remedy this bias issue, a non-concave penalty such as SCAD penalty was proposed. SCAD has the so-called oracle property, meaning that, in the asymptotic sense, it performs as effectively as if an analyst had known in advance which coefficients were zero and which ones were nonzero [6] . SCAD is capable of achieving the sparse estimator in combination with smaller biases in linear regression than LASSO. Here, we propose a new stability selection procedure in combination with SCAD penalization ( S SCAD). The new method was compared to S LASSO using systematic simulations and a published GWAS study.

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


Strategic innovation through outsourcing: The role of relational and contractual governance ABSTRACTThere is growing evidence that client firms expect outsourcing suppliers to The last fifteen years have witnessed significant growth in the outsourcing industry (Oshri et al. 2015) .. While the early years of Information Technology (IT) and business process outsourcing (BPO) were mainly characterized by a quest for costs savings (Loh and Venkatraman 1992; Lacity and Hirschheim 1993 ) and a focus on core competences (Quinn and Hilmer 1994) , recent evidence suggests that client firms now seek to achieve added value from outsourcing by accessing suppliers' competences (e.g. Dyer and Nobeoka 2000; Quinn 2000; Whitley and Willcocks 2011) . Mol (2005: 571) argues that "firms are increasingly relying on partnering relationships with outside suppliers that can act as an effective substitute to the internal generation of knowledge and innovation". Similarly, Linder et al. (2003) and Weeks and Feeny (2008) argue that client firms rely on external suppliers in the search for new ideas.. More recently, accepting that innovation is outsourced and offshored, Lewin et al. (2009) studied the determinants driving firms to offshore innovations only to conclude that firms have been entering a global race for talent in which solutions will be sought wherever skills are available. Such observations suggest that innovation may be considered as one of the possible outcomes of outsourcing engagements.. Indeed, several recent studies have examined the practices through which innovation can be achieved in outsourcing settings (Weeks and Feeny 2008; Whitley and Willcocks 2011; Lacity and Willcocks 2014) . Weeks and Feeny (2008) offer a taxonomy of forms of innovation through outsourcing that distinguishes between IT operational and business process innovations, and strategic innovations. The former corresponds with incremental forms of innovation (Dewar and Dutton 1986) , while the latter matches the definition of radical innovation (Droege et al. 2009 ). Defined as ways to "significantly enhance the firm's product or service offerings for existing target customers, or enable the firm to enter new markets" (Weeks and Feeny 2008: 131) , strategic innovations have been traditionally perceived to be more challenging to achieve (Weeks and Feeny 2008) and therefore will be the focus of this study. Strategic innovation requires significant product or service development and its success can be challenged by lack of cooperation, low levels of trust and information asymmetry between the supplier and client (Weeks and Feeny 2008) . Similarly, the lack of appropriate incentives for both client and supplier may inhibit the sides from developing collaborative innovation through outsourcing (Lacity and Willcocks 2014) . The limited literature on innovation in the outsourcing context has persistently highlighted the key role that relational governance plays in creating favourable conditions for strategic innovation through outsourcing (Whitley and Willcocks 2011; Weeks and Feeny 2008) . We concur with such observations; however, we seek to advance and contribute to the Information Systems (IS) outsourcing literature by examining the role that relational and contractual governance plays in fostering strategic innovation through outsourcing.. In particular, we seek to verify whether high-quality relationships between clients and suppliers do lead to strategic innovation, and whether certain contract types positively or negatively affect the impact of highquality client-supplier relationships on the ability to achieve strategic innovation. Relational governance will be examined in this study as the quality of the client and supplier relationships (Lacity et al. 2010), while contractual governance will be explored through three contract types commonly used in outsourcing engagements: fixed-price, time and materials (Gopal et al. 2003; Gefen et al. 2008 ) and partnership-based (Willcocks and Choi 1995; Dibbern et al. 2004) , and the combinations of these contract types. This research relies on a pan-European cross-industry survey that included representatives of 248 firms that are buyers of IT and business process outsourcing services. Respondents were senior managers involved in the execution of outsourcing projects or programmes who were selected in accordance to the "key informant" methodology (e.g. ).. The contributions of this study are twofold. First, our paper is one of the early attempts to shed light on the link between a governance approach and strategic innovation through outsourcing. In this regard, our empirical results confirm a positive effect of the client-supplier relationships on the likelihood of achieving strategic innovation. Second, this study shows that the interaction of contractual governance with relational governance is central to achieving strategic innovation through outsourcing. We found that a partnership contract, when included in the client contract portfolio alongside a fixed-price or time and materials contract magnifies the positive effect of the client-supplier relationships on the possibility to achieve strategic innovation, but no effect for fixed-price and time and materials contracts, as stand-alone contracts.. The rest of the paper is organized as follows: first the literature on innovation in the context of strategic IT and business process outsourcing is reviewed; then we theorize about the role of relational and contractual governance in achieving strategic innovation. This is followed by an explanation of methods and results and a discussion of our findings in the light of the existing literature. We conclude with theoretical and practical contributions.

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


An inter-FPGA communication bus with error detection and dynamic clock phase adjustment Background: Nowadays, systems involving multiple FPGAs are used for various scientific applications. Such systems require a data bus dedicated to the communication between FPGAs, which could be done through a LVDS type. Another important factor is that the routing that interconnects the LVDS pins on the platform should be precisely developed to avoid instabilities in communication. Unfortunately, many platforms available in the market do not observe such restrictions, limiting the throughput of the bus. Methods: This paper presents an inter-FPGAs communication channel based on a DDR interface directed to this kind of platform. This approach promotes a stable communication between these devices without the use of LVDS pins. An error detection module was also designed to ensure the sending integrity and correct any errors on the bus. A mechanism for dynamic and automatic clock phase adjustment used on the bus was also implemented to ensure that the developed modules were compatible with other platforms. Results: The channel has been implemented in a PROCStarIII platform and rates of 4.76 Gbps were achieved.The channel has been validated on a commercial platform with success and the synthesis results, as well as the performance results obtained by using it in a real implementation of the RTM algorithm, are also presented. The use of multi-FPGA platforms enables the application of performance increase, as multiple reconfigurable devices can be used to perform the same task or work in cooperation. The use of several FPGAs integrated on a single board demands the establishment of a communication channel among such devices.. The presented work describes a bi-directional inter-FPGA communication bus using a DDR interface for data transmission. An architecture was designed as a reconfigurable platform, requiring only few parameter settings on the transmitter and receiver to port for different configurations.. A detection error module was also implemented. It was based on the CRC method and has also a dynamic clock phase shift adjustment in order to ensure a stable communication. The proposed architecture has been tested and validated on the GiDEL PROCStarIII platform.. The proposed communication channel achieved an excellent performance on platforms that do not have advanced features like LVDS interfaces and transceivers. The next step will be to implement it in another platform, the GiDEL PROCStarIV. This platform is based on Altera Stratix IV FPGAs and more advanced features. Thus, the authors expect to achieve higher frequencies with the use of the presented communication channel. The presented implementation obtained transfer rates on the order of magnitude of Gbps. At 150 MHz, the communication bus achieved transfer rates of up to 4.76 Gbps. [16] . However, it is essential that the PCB track routing that will accommodate these devices is done carefully, avoiding communication instabilities. The communication channel was tested on a GiDEL PROCStarIII platform connected to an Intel Xeon 3 GHz computer with 4 GB of DDR memory through a PCIex8 bus. Different clock rates and package sizes were tested. Each test was performed considering at least 1 h of continuous data transfer between the FPGAs on the platform.. The data to be transferred is generated by an application at high level and sent to the host platform through the PCIex8 bus. A specific memory controller from GiDEL (GiDEL PROCMultiPort [15] ) is used to transfer the data sent from the application to the transmitter. For testing purposes and correct analysis, the data received by the receiver is sent back to the host, and there, it is compared to the previously sent data.. The times presented in the result tables refer only to the effective data transmission time on the bus. The time of sending data to the host platform, the time to transfer data from the DDR2 memory (located on the platform) to the FPGA transmitter, and the time of data transmission from the receiver on the FPGA to the host were not taken into account.. As a basis for testing, the amount of transferred data during 1 h and a package size of 8 words was adopted. With the data amount transferred in this configuration, it was possible to repeat the tests varying the package size and measuring the transfer time. Tables 1, 2, 3, and 4 show the results obtained for transmissions at frequencies of 50, 100, 120, and 150 MHz, respectively.. All the tests with the configurations presented in Tables 1, 2, 3, and 4 were successfully performed, and no transmission error was detected. For all results, a higher data rate was observed when the package size is increased from 8 to 16 words, and then from 16 to 32 words. This occurs due to the clock cycles required to generate and check the CRC at the transmitter and receiver. Once the data package becomes smaller, more cycles will be required to generate the CRC check, consequently increasing the overall transmission time. Figure 5 shows a transmission flow for a package size equal to 4 words. Note in the diagram that after sending the It is important to mention that the same architecture developed and tested in PROCStarIII may have different transmission rates when instantiated on other platforms. Inherent characteristics to the platform design can directly influence the communication performance. In this section, some studies focusing on inter-FPGA communication are presented. The paper [8] presents an architecture for this purpose, and the work [9] proposes a solution for optimizing communication between different FPGA devices.. The work [8] presents an architecture for inter-FPGA full-duplex communication with 18 LVDS transmission tracks. The architecture is based on DDR interface and consists of a transmitter and a receiver. The authors demonstrate that it is possible to reach transfer rates of about 10 Gbps by using this approach. The architecture is designed to be implemented in a high-performance cluster (PARAMNet-3) [10] . The architecture comprises a network switch allowing package routing to be performed at high speed. Each board being part of the switch consists of four FPGAs from Xilinx Virtex-4 and transceivers (multi-gigabit transceivers) available inside each FPGA. These transceivers are used for communication with the other system boards.. The transmitter consists of a control unit, LVDS I/O buffers, and a serializer/deserializer (SERDES) module. These last two features are I/O already available in the Xilinx Virtex-4 FPGA. The SERDES module is a serializer/deserializer that receives the application data in parallel and serializes it. The LVDS output buffers receive this serialized data and implement the output to 18 tracks of differential pairs. Each track has a transfer rate of 625 Mbps, summing up a total rate of about 10 Gbps.. The receiver has its clock generated by the transmitter. This allows synchronization of both sides. It consists of a control module, delays, SERDES I/O buffers, and LVDS module. The delay modules are responsible for introducing a 5-10 ps jitter on the clock input from the transmitter. This strategy respects the valid data window and is necessary to ensure that signals are received in the receiver correctly. The clock used in the receiver is of 312.5 MHz and is synchronized with the transmitter.. Communication error detection is performed on the network layer of the switch, and the authors have developed a test engine to generate errors in the communication channel. This engine is responsible for testing each LVDS track, and two instances were implemented in each FPGA. The testing environment consists of a PowerPC processor executing an application that communicates with the architecture via a UART interface. It can be configured with test parameters and statistics view on the application.. In [9] , a solution for optimizing inter-FPGA communication using channel adaptation is shown. The work demonstrates that each platform has its own characteristics, and to migrate up the project to another platform, you often need to change the architecture to adapt to necessary changes. The communication bus width, pointto-point broadcast, or LVDS are some of the options that could be parameterized by abstracting from the users that need to change theirs. In that sense, the authors of the work propose a definable channel and one that is able to self-adapt the target architecture.. Initially, it seems to be an architecture that consists of a base control module, FIFOs (First In, First Out), and PHY modules transmit (TX) and receive (RX). The architecture supports SDR/DDR interfaces and point-to-point transmission or LVDS. It can therefore be used for SERDES modules, serialization/deserialization of data, and it can be defined whether the communication is unidirectional or bidirectional. Finally, the architecture allows the bus width to be configurable.. The channel adaptation, called chAdapt, consists of a hardware module that self-configures the transmission according to the platform characteristics. For this, a transmission of a bit sequence occurs repeatedly between the transmitter and receiver, initially to identify possible delays in the communication form. At that time, all the controls are optimized and clock alignment is performed by dynamically adjusting its phase.. The architecture has been tested in different FPGAs by using the RAPTOR [11] module platform as base. This platform allows the adaptation of different reconfigurable modules that consist of Xilinx FPGAs. The tests were performed with the following FPGAs: Spartan-3A, Spartan-6, Virtex-4, and Virtex-5. Several combinations were analyzed in order to find possible optimizations in the communication. As a result, the authors demonstrate a comparative table between combinations used, highlighting the relative optimization after the addition of chAdapt module architecture. The tests performed with the communication between Virtex-4 and Spartan-6 are noteworthy. A significant improvement in communication was observed after the introduction of chAdapt in these scenarios. The results indicate that although it was not possible to align the bus width for these tests, the channel offers a great way when implemented for the communication link validation and identifying best parameters for data transfer. Platforms that involve multiple field-programmable gate arrays (FPGAs) have been the target of several study fields such as prototyping of MPSoCs (multiprocessor system-on-chip), acceleration, and encryption algorithms [1, 2] . For these systems to work efficiently using existing resources in FPGAs, an efficient communication must exist between the FPGAs available on the platform. This type of communication in next-generation FPGAs is usually established through type interfaces low-voltage differential signaling (LVDS) [3] . This type of signaling allows signal sending at high speed through a differential pair of parallel wire. The use of this feature enables data The communication system proposed by this work is defined as a parallel communication channel, synchronized and 32 bits wide. Each controller is comprised of two main modules: a transmitter and a receiver. A common clock synchronizes the communication in the channel. This system can then be coupled in each FPGA to allow data communication between these devices on the platform.. The entire system was designed to facilitate its adaptation to different projects. To make this possible, a FIFO input on the transmitter and a FIFO output on the receiver were used, making the design transparent to the user. The adjustments for each application should be made through few adjustments in the input and output parameters of each FIFO. One signal of 33 bits (data_bus) was defined for transferring data between devices. One bit of data_bus signal is intended for a valid signal, which indicates to the receiver that the data sent is valid and that it can be received and forwarded to the CRC check module and later to the FIFO output. Thus, the communication channel enables a data transfer with a width of 32 bits between the FPGAs.. The critical clk_bus signal is used to feed the clock signal to the receiver. The clock signal is generated in the transmitter through a PLL (Phase-Locked Loop) and sent to the receiver through a path reserved for this purpose. This ensures that both the transmitter and receiver are synchronized allowing the communication channel to operate stably. The synchronization and transmission failure signals that also incorporate the bus will be discussed in the next sections.

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A common framework and taxonomy for multicriteria scheduling problems with interfering and competing jobs: Multi-agent scheduling problems Most classical scheduling research assumes that the objectives sought are common to all jobs to be scheduled. However, many real-life applications can be modeled by considering different sets of jobs, each one with its own objective(s), and an increasing number of papers addressing these problems has appeared over the last few years. Since so far the area lacks a unified view, the studied problems have received different names (such as interfering jobs, multi-agent scheduling, mixed-criteria, etc), some authors do not seem to be aware of important contributions in related problems, and solution procedures are often developed without taking into account existing ones. Therefore, the topic is in need of a common framework that allows for a systematic recollection of existing contributions, as well as a clear definition of the main research avenues. In this paper we review multicriteria scheduling problems involving two or more sets of jobs and propose an unified framework providing a common definition, name and notation for these problems. Moreover, we systematically review and classify the existing contributions in terms of the complexity of the problems and the proposed solution procedures, discuss the main advances, and point out future research lines in the topic. The existence of several objectives is consubstantial to scheduling problems, as it can be seen from different definitions of the field, such as Pinedo (1995) , where scheduling is defined as a decision-making process that has as a goal the optimization of one or more objectives. Therefore, it is not surprising that multicriteria scheduling problems have been widely studied in the scheduling literature (see e.g. the reviews by Billaut, 2001, 2002; Hoogeveen, 2005 and Minella et al., 2008) . In all the problems analyzed in these surveys the criteria considered affect all jobs to be scheduled. Only Hoogeveen (2005) mentions the case of multicriteria scheduling problems with two or more sets of jobs. In these problems, two or more sets of jobs (not necessarily disjoint) have to be scheduled, each one with its own objective(s). Although this is a special case of multicriteria scheduling problems, the existence of several sets makes the problems rather different than their one-set counterpart as, in general, the complexity of these problems changes even if the objective functions are the same (Agnetis et al., 2004) .. As discussed later in this paper, this type of scheduling problems arise in a number of real-life applications and therefore have been subject of interest by researchers and practitioners in the last few years. However, the lack of a unified framework has been a major deterrent for research advances in the field. There is not even a common name which has caused some contributions to ignore past works on the topic, as the keywords and title of the existing results make it difficult to conduct an extensive search (for instance, the same conclusion regarding a specific problem is independently shown by Agnetis et al., 2007a and Nong et al., 2011) . Without a common definition and name, the notation and limits for this kind of problems are not clear, which may have hidden valuable contributions and makes the comparison among similar problems very difficult. In addition, this has caused that some scheduling problems dealing with two types of jobs, but with no interference among them, were considered part of the topic. For instance, in some problems described in Leung et al. (2010) , the jobs in one set have their due date to be equal to their release date plus their processing times. Therefore, these jobs have to be processed in a specific (fixed) time interval and the remaining scheduling problem is how to schedule the jobs in the other set, which can be assimilated to a traditional scheduling problem with machine unavailability.. In this paper we will try to move towards an unified view on the topic that allows overcoming the above problems. More specifically, we 1) discuss the different definitions and approaches for the problem and provide a framework consisting of a single definition and notation, 2) give some complexity results and general properties, 3) review and classify the different contributions and results on the topic based on the aforementioned framework, and 4) point out the main research avenues in the field. By doing so, we expect to foster the research in this interesting and challenging scheduling area.. The remainder of the paper is structured as follows: Section 2 discusses the problems, their applications and the different names used in the literature. In Section 3 we present the notation and adapt the taxonomy presented by T'kindt and Billaut (2002) for multicriteria scheduling problems. The relationship among the complexities, single criteria and multicriteria scheduling problems is outlined in Section 4, where some general properties are presented as well. Literature is reviewed by classifying the problems into basic problems (discussed in Section 5) if there are no conditions for the machines or jobs, i.e. the most general case indicating only the machine environment and the objectives considered for each set of jobs; and extended problems (discussed in Section 6), where specific conditions are imposed. Finally, Section 7 contains the conclusions and future research lines. In this work, we have reviewed a high number of papers containing different contributions to the field of multicriteria scheduling problems considering two or more sets of jobs. Up to 75 papers have been identified as related to the problem in the sense presented in this work, including only those papers written in English.. Doing an analysis of the literature we concluded that the most suitable name for this kind of problems is interfering jobs scheduling problem. However, the most used term is multiagent scheduling problem (MASP).. Problems have been classified in basic or extended problems, indicating the approach considered (Linear Convex Combination approach; ϵ-constraint and Pareto approach). In the following, we will highlight the main conclusions and try to set some possible future research avenues.. The first comment refers to the fact that there are much more works solely devoted to extended problems (47) than to basic problems (20). Moreover, eight references consider both types of problems. This may be seen as an indicator that the research has been so far conducted by specific application areas rather than for a systematic approach, which is not surprising given the lack of an integrated framework that hopefully our paper may help to build. While there are clear advantages for the application-oriented approach (such as providing sound, real-life justification for research in the area) more research on the basic problems would set the foundations for gaining further advances on extended problems. Then, extensions of the solution procedures for the former can be implemented in the latter.. A second general comment is that most of the works refer to the one machine setting, which is clearly an indication of the fact that we are on the early stages of the research. Moreover, most of the single machine problems are NP-hard, so we can expect that a big number of problems are NP-hard. Therefore, in the next years, the number of contributions addressing other settings would increase. Interestingly, the proportion of works dealing with layouts different than the one-machine is higher for the extended problems than for the basic problems. Again, this point out the direction that most research has been application-driven.. Regarding basic problems, the case of disjoint sets of jobs has been the one receiving more attention.. Some comments about the main results can be done:. • In the one-machine layout, the LCC approach has been found to be polynomially solvable for many objectives, and only some specific cases of weighted objectives are shown not to be polynomial. Outside this layout, only the permutation flowshop with two machines has been studied for a very simple case (max C A j and max C B j ), which is already NP-hard.. • The ϵ-constraint approach has been found not to be polynomially solvable except for a very simple case, even for one machine and two objectives. However, relatively few approximate algorithms have been proposed for these problems. The cases with three or more objectives have been addressed only for specific rescheduling-related objective functions.. • With respect to the Pareto approach, less work has been done, bounding the number of non-dominated solutions for most of the problems, mainly because the complexity of this approach.. Basic problem with non disjoint sets of jobs have been addressed only for the case where one of the sets contains all jobs (called interfering jobs problems with global objective function). An interesting future research line could be to analyse the complexity for the more general case of non-disjoint (interfering) sets of jobs (i.e. when one of sets does not contain all jobs). The contributions with global objective function consider the ϵ-constraint and LCC approaches, and they are due to two groups of authors, analysing complexities for a great number of problems. There are hardly any algorithm proposed for these problems, so it is a open issue for this approach. In contrast, such algorithms have been proposed for the Pareto approach.. Regarding the extended problems, the case considering only one constraint has been scarcely studied, and a research avenue could be initiated in this area. Most of the works have been done for the case of disjoint sets of jobs under the LCC approach. In this type of problems, some general results have been presented regarding the learning effect. In contrast, those obtained for controllable processing times are very specific, focusing on the determination of the polynomially solvable cases. Regarding the Pareto approach, it is worth to note that many problems have been found not to be polynomially solvable, and several approximate algorithms (mostly based on metaheuristics) have been presented. Extended problems with non-disjoint sets of jobs have been scarcely studied, all of them for one machine.. Regarding solution procedures, there is an extensive contribution on studying the complexity, and a considerable number of one machine problems providing exact procedures have been found. It would be interesting to extend these results to other, more complex, machine layouts, even if it is likely that the complexity would increase. In contrast, there are relatively few approximate procedures available for the rest of the problems addressed with higher complexity (although it can be observed a concentration of similar methods for similar problems, for example some papers considering deteriorating and learning constraints).. The relative scarcity of solution procedures is again another sign of a research field in its earliest stages, and it makes difficult to apply the research results. Another consequence of this fact is that there are only a handful of test beds to generate problem instances in which the solution procedures can be tested. Most of them consider the same size of the sets of jobs, avoiding extreme cases. Therefore, it may be interesting to generate a common and exhaustive test bed, considering different cases for the sizes of the jobs, in order to facilitate the comparison among solution procedures.. Finally, it is also worth mentioning that, in the case of more than two sets of jobs, most of the work is preliminary and for some specific cases, pointing at other future area of research.

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


Emitter Localisation from Reception Timestamps in Asynchronous Networks We address the problem of localising a mobile terrminal ("blind" node) in unknown position from a set of "anchor" nodes in known positions. The proposed method does not require any form of node synchronisation nor measurement (or control) of the transmission times, which is difficult or anyway costly to achieve in practice. It relies exclusively on reception timestamps collected by the anchor nodes, according to their local clocks, that overhear packets transmitted by the blind node and by (at least one) other transmitting node(s) in known position, e.g., other anchors. The clock differences between the nodes are not eliminated ex ante through clock synchronisation, as in traditional ToA and TDoA methods. Instead, they are counteracted ex post, during the data processing stage, leveraging the data redundancy that is intrinsic to the multiple reception of the same packet by different (anchor) nodes. We validate the proposed method in two experimental setting, indoor and outdoor, using exclusively low-cost Commercial-Off-The-Shelf WiFi devices, and obtain sub-meter accuracy in Line-of-Sight conditions. The proposed method does not require that the blind node participate actively to the localisation procedure and can use "opportunistically" any legacy signal or packet available over-the-air for communication purposes. Considering the very minimal requirement on the system -basically, only that anchors in known positions are able to collect and share reception timestamps -the proposed approach can enable practical adoption of opportunistic and/or cooperative localisation on top of existing radio communication systems. Despite the widespread success of Global Navigation Satellite Systems (GNSS), alternative radio-based positioning systems remain of interest for those applications where GNSS signals are not available (e.g., indoor, tunnels, urban canyon) and/or the integration of GNSS receivers is not feasible due to size, energy or cost constraints. In order to preserve cost-effectiveness and ease of adoption, it would highly desirable to develop localisation methods that reuse opportunistically the legacy radio signals, protocols and receivers which are anyway available for communication purposes. We consider the problem of localising a transmitting node in unknown position, called "blind node" hereafter, based on the reception measurements collected by a set of nodes in known positions, called "anchors".. One possible approach is to rely on power measurements, leveraging the Received Signal Strength Indicator (RSSI) available today in almost all Commercial-Off-The-Shelf (COTS) transceivers to deploy RSSI-based localisation functions on top of existing wireless communication systems. Both commercial and open-source tools are available for several technologies, including WiFi, Bluetooth, and IEEE 802.15.4 (e.g. [1] , [2] , [3] ). Generally speaking, RSSI-based methods exhibit low accuracy, since in real environments the received power is heavily affected by other factors than the distance from the transmitter, for instance multipath propagation and antenna patterns. Several previous work seek to improve accuracy of RSSI-based methods using machine learning techniques that create and use detailed power loss pattern models for specific environments [4] , [5] , [6] , [7] , in the direction of so called "RSSI fingerprinting" techniques.. Another class of approaches is based on time measurements. As signals travel at constant speed, the relation between reception time and distance is tighter than for received power, therefore time-based localisation is intrinsically superior to RSSI-based methods in terms of potential accuracy [8] . However, the traditional approaches to time-based localisation require the system to support some form of node synchronisation and/or accurate measurement of transmission times. Both these functionalities are difficult or costly to achieve in practice [9] . Node synchronisation requires the distribution of synchronisation signals, either via additional wired infrastructure or wireless protocols, and the implementation of dedicated functions into the devices which consume additional energy, bandwidth, and computation resources [9] . Controlling or measuring the actual transmission time is also difficult with standard hardware, due to unpredictable delay components between the construction of the packet and the transfer to the network interface, not to mention the variability of channel access delays due, e.g., to MAC dynamics [9] .. In Time-of-Arrival (ToA) methods all nodes must use a common synchronous clock reference and must take active part into the localisation procedure [8] , [10] , [11] . The transmitting node attaches the transmission timestamp to the packet to allow the receiver to compute the travel time (time of flight), and from there derive the distance from the transmitter (one-way ranging). In two-way ranging methods instead, node A sends a probe packet to node B and the latter answers back with a reply packet that includes the information about the elapsed time between the reception of the probe and the transmission of the reply packet. By subtracting this value from the elapsed time between the transmission of the probe packet and reception of the reply packet, node A is able to compute the distance (range) to B. Two-way ranging does not need clock synchronisation between the nodes, however it still requires accurate knowledge of both transmission and reception times for every packet. Moreover, it requires that the node to be localised ("blind node") take active part into the ranging phase. With Time-Difference of Arrival (TDoA) methods an emitter node can be localised by a set of anchors in known positions that measure exclusively the reception times of the signals transmitted by the blind node [12] . This method relaxes the requirement on the transmission times, but still needs tight synchronisation between the anchor nodes for accurate localisation [13] .. Due to the requirements on node synchronisation and/or transmission time measurement, it turns out that deploying these methods on COTS devices is impractical [14] , [15] , [16] , [17] . To overcome these limitations, we develop here a localisation method that relies exclusively on reception timestamps and does not require any form of node synchronisation. The proposed method can passively localise a (possibly unaware) blind node while it is executing standard communication operations, i.e., exchanging packets with a neighbouring node, without requiring its active participation to the localisation procedure. In other words, our method meets the following system-level requirements:. • The blind node transmits beacons and/or packets (e.g. towards one or more other nodes, mobile or fixed) but it does not take any active part to the localisation process. The localisation procedure involves exclusively a set of "anchor" nodes in known positions.. • No synchronisation mechanism is in place between the anchor nodes nor between blind and anchors, i.e., we assume asynchronous nodes.. • Anchor nodes can measure only local reception times (i.e., timestamps) while the transmission times are unknown and can not be controlled, i.e., we assume asynchronous signals. It can be easily seen that the above requirements do not allow to adopt ToA, two-way ranging, TDoA nor other hybrid variants proposed recently in the literature (e.g. [18] , [19] , [20] ) that anyway demand some combination of node synchronisation and/or control of transmission times.. By force of the above requirements, the method described here can be adopted in a wide range of practical applications to localise passively a mobile transmitter based exclusively on the local reception timestamps collected by other nodes placed in the surrounding environment. Waiving the requirement of node and signal synchronisation enables the implementation of localisation capabilities in legacy communication systems, which are typically completely asynchronous. Possible applications of the proposed method include indoor localisation of smartphones, localisation in Wireless Sensor Networks (WSN), and extension (augmentation) of GNSS positioning in Cooperative Intelligent Transportation Systems (C-ITS) [21] .. While in traditional localisation systems clock differences are eliminated ex-ante by the synchronisation mechanism, we consider a model where clock differences are accounted for ex-post, i.e., they are estimated (or directly eliminated) during the data processing stage, jointly with the estimation of the (unknown) blind position. Only a few recent pioneering works have started to consider this class of techniques [22] , [23] , [24] , [25] , [26] , [27] . The basic form of the method considered here belongs to the class of so-called Differential Time-Difference of Arrival (DTDoA). A detailed review of previous DTDoA literature is given later in the Related Work section. The proposed method is validated by means of experimental measurements in two different environments, indoor and outdoor, with a testbed setting consisting exclusively of COTS WiFi devices. The complete experimental dataset used in this work, together with the software developed to setup the testbed, will be made publicly available in order to allow for independent replication of the experiments and validation of our results, and to facilitate the progress of the research by the scientific community (visit http://www.ing.unibs.it/ ∼ openfwwf/localisation).. The rest of this paper is organised as follows. In Sec. II we formalise the system model and describe step-by-step the proposed methodology in the basic case of receive-only anchors. In Sec. III we provide experimental results with COTS WiFi devices in two different testbed scenarios, indoor and outdoor, achieving meter-level accuracy. In Sec. IV we extend the method to work in scenarios with multiple active anchors that are able also to transmit (in addition to receive) packets: our experimental results show that the positioning accuracy can be improved down to sub-meter level in this case. In Sec. V we discuss future research directions for progressing and extending the work. In Sec. VI we position our method with respect to existing literature. Finally, we conclude in Sec. VII.

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