COMPLEMENTATION OF RATIONAL SETS ON COUNTABLE SCATTERED LINEAR ORDERINGS In a preceding paper (Bruyère and Carton, automata on linear orderings, MFCS'01), automata have been introduced for words indexed by linear orderings. These automata are a generalization of automata for finite, infinite, bi-infinite and even transfinite words studied by Büchi. Kleene's theorem has been generalized to these words. We prove that rational sets of words on countable scattered linear orderings are closed under complementation using an algebraic approach. In his seminal paper [14] , Kleene showed that automata on finite words and regular expressions have the same expressive power. Since then, this result has been extended to many classes of structures like infinite words [7, 17] , bi-infinite words [12, 18] , transfinite words [9, 1] , traces, trees, pictures.... In [5] , automata accepting linear-ordered structures have been introduced with corresponding rational expressions. These linear structures include finite words, infinite, transfinite words and their mirrors. These automata are usual automata on finite words, extended with limit transitions. A Kleene-like theorem was proved for words on countable scattered linear orderings. Recall that an ordering is scattered if it does not contain a dense sub-ordering.. For many structures, the class of rational sets is closed under many operations like substitutions, inverse substitutions and boolean operations. As for boolean operations, the closure under union and intersection are almost always easy to get. The closure under complementation is often much more difficult to prove. This property is important both from the practical and the theoretical 1 point of view. It means that the class of rational sets forms an effective boolean algebra. It is used whenever some logic is translated into automata. For instance, in both proofs of the decidability of the monadic second-order theory of the integers by Büchi [8] and the decidability of the monadic second-order theory of the infinite binary tree by Rabin [21] , the closure under complementation of automata is the key property.. In [5] , the closure under complementation was left as an open problem. In this paper, we solve that problem in a positive way. We show that the complement of a rational set of words on countable scattered linear orderings is also rational.. The classical method to get an automaton for the complement of a set of finite words accepted by an automaton A is through determinization. It is already non-trivial that the complement of a rational set of infinite words is also rational. The determinization method cannot be easily extended to infinite words. In his seminal paper [8] , Büchi used another approach based on a congruence on finite words and Ramsey's theorem. This method is somehow related to our algebraic approach. McNaughton extended the determinization method to infinite words [15] proving that any Büchi automaton is equivalent to a deterministic Muller automaton. Büchi pushed further this method and extended it to transfinite words [9] . It is then very complex. In [4] , the algebraic approach was used to give another proof of the closure under complementation for transfinite words. In [11] , we have already proved the result for words on countable scattered linear orderings of finite ranks. The determinization method cannot be applied because any automaton is not equivalent to a deterministic one. In that paper, we extended the method used by Büchi in [8] using an additional induction on the rank. Since ranks of countable scattered linear orderings range over all countable ordinals, this approach is not suitable for words on all these orderings. In this paper, we prove the whole result for all countable scattered linear orderings using an algebraic approach. We define a generalization of semigroups, called -semigroups. We show that, when finite, these -semigroups are equivalent to automata. We also show that, by analogy with the case of finite words, a canonical -semigroup, called the syntactic -semigroup, can be associated with any rational set X. It has the property of being the smallest -semigroup recognizing X. A continuation of this paper would be to extend the equivalence between star-free sets, first order logic and aperiodic semigroups [24, 16, 3] and also between rational sets and the monadic second order theory.. Both hypotheses that the orderings are scattered and countable are really necessary. Büchi already pointed out that rational sets of transfinite words of length greater that ω 1 (the least non-countable ordinal) are not closed under complement. It can be proved that the set of all words on scattered linear orderings, viewed as a subset of words on all linear orderings, is not rational although its complement is rational.. Our proof of the complementation closure is effective. Given an automaton A, it gives another automaton B that accepts words that are not accepted by A. It gives another proof of the decidability of the equivalence of these automata [6] . This paper is organized as follows. Definitions concerning linear orderings and rational sets are first recalled in Sections 2 and 3. Then, Section 4 introduces the algebraic structure of -semigroup. Section 5 sketches the proof that any set accepted by a finte automaton is recognizable and the full proof of the converse is given in Section 6. Since rational sets are exactly those accepted by automata [5] , this proves that rational sets are exactly recognizable sets. This algebraic caracterisation proves trivially the closure under complementation of rational sets. Finally, the syntactic -semigroup corresponding to a rational set is defined in Section 7.

B 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 O O O O O O O O O O O O O O O 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 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 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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 B O 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 O O O O O O O O O O O O O O O O O O O O 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 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 B O O O O O O O O O O O O O O O O O


On algorithmically checking whether a Hilbert series comes from a complete intersection It is not possible to determine from the Hilbert series whether a graded Noetherian algebra is a complete intersection. Nevertheless, such Hilbert series satisfy very stringent conditions and we define a concept CI-type for formal power series, that embodies some of these necessary properties. This definition works for algebras that are not standard i. e. not generated in degree 1. For the class of formal power series that occur as the Hilbert series of Noetherian Cohen-Macualay algebras, the main result is a criterion for a series to be of CI-type, that is formulated in terms of properties of truncated power series. Hence it can be used as the basis for an algorithm that provides in a finite number of steps either a rational function expression of the formal power series, or the information that the truncated power series is not of CI-type. Also sample computations using this algorithm on some non-standard graded invariant algebras are described. The present study is motivated by the problem how to recognize whether a ring is a complete intersection or not, in terms of computable invariants of the ring. There has been several similar studies e. g. Avramov-Herzog [3] , characterizing complete intersections in homological terms, as well as work done with classes of special types of rings, e. g. rings of invariants [12] , and semi-group rings [7] .. We take a different approach; in the spirit of Macaulay and Stanley, we make our starting point the Hilbert series of a graded algebra. If the algebra is Noetherian the Hilbert series may be expressed as a rational function. Stanley showed for example that the condition of a standard algebra (i. e. all generators in degree 1) being Gorenstein, could be determined from the knowledge of its Hilbert series. Macaulay characterized Cohen-Macaulay algebras in a similar way, also in the case of standard algebras. Other authors have pursued this theme, both in order to characterize different properties of a ring in terms of their Hilbert series -e. g. integrality is discussed in [16] , as well as the related problem of which formal power series occur as Hilbert series of certain types of rings [8] .. As noted already by Stanley [15, Example 3.7 ] , it is not possible to decide whether an algebra is a complete intersection only by considering its Hilbert series. But on the positive side Stanley showed that it is possible, for standard algebras, to describe completely which formal power series occur as Hilbert series of complete intersections [15, . The possible Hilbert series will belong to a very restricted class of formal power series. Knowledge whether a Hilbert series belongs to this class, is then a strong necessary condition on an algebra for it to be a complete intersection.. However, many naturally occurring commutative algebras are not generated in degree 1, for example invariant rings or algebras that arise in algebraic geometry as section rings associated to line bundles. Hence it is important to see what can be done in the more general case.. We define a concept CI-type in this more general situation. It is formulated in terms of the existence of a special kind of rational function expression of a formal power series, and it embodies the most easily visible consequences for the Hilbert series of the fact that a graded algebra is a complete intersection. That the Hilbert series is CI-type is thus a necessary condition for a ring to be a CI, but not sufficient.. There is however a practical problem with the definition, in that it assumes the full knowledge of the Hilbert series as a rational function. In many calculations what is given is a partial knowledge of the Hilbert series, as a truncated series, and hence what is needed is a method for using this partial information effectively.. Complete intersections are always Cohen-Macaulay algebras, and this class of algebras has Hilbert series that have a precise description (see below) so we consider only this class of formal power series, called CM-type. Our main result is a characterization of CI-type CM-type formal power series in terms of their truncated Hilbert series. This is algorithmic in character and we formulate it below as an algorithm. In practice, its use will be to prove that a particular graded algebra cannot be a complete intersection, and as such we have illustrated its use on rings of invariants.. We will now give a more precise description of the contents of the paper. Suppose we have a truncated Hilbert series. of a noetherian graded algebra. It is natural to try to naively use our partial information to construct an expression of the series as a rational function by starting with. which equals the given Hilbert series up to degree 1, and then continuing with. which is equal to H(z) up to degree 2, and so on. This gives an algorithmic construction of a formal power series. which equals H(z) up to degree n. In the limit this uniquely expresses H(z) as an infinite product (well-defined as a formal power series). For a general series, this product is infinite, but if the Hilbert series stems from a (graded) complete intersection, only a finite product is needed, and the method produces a rational expression in a finite number of steps. There are strict restrictions on the finite products that can occur for a complete intersection R. Namely, in a presentation of R, the number of relations up to an arbitrary degree n must be less than the number of generators up to the same degree n. We give a name to the class of formal power series that satisfy a slightly more sophisticated version of this restriction.

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


Perception for Collision Avoidance and Autonomous Driving The Navlab group at Carnegie Mellon University has a long history of development of automated vehicles and intelligent systems for driver assistance. The earlier work of the group concentrated on road following, cross-country driving, and obstacle detection. The new focus is on short-range sensing, to look all around the vehicle for safe driving. The current system uses video sensing, laser rangefinders, a novel light-stripe rangefinder, software to process each sensor individually, a map-based fusion system, and a probability based predictive model. The complete system has been demonstrated on the Navlab 11 vehicle for monitoring the environment of a vehicle driving through a cluttered urban environment, detecting and tracking fixed objects, moving objects, pedestrians, curbs, and roads.During the decade of the 1990's, researchers from automotive engineering, from robotics, and from allied fields came together to start building intelligent vehicles [1, 2, 3, 4] . These vehicles use sensors, actuators, processors, and communications systems to either drive automatically, or to monitor a human driver and assist in navigation or warn in case of a developing dangerous situation.The field was driven by several market demand factors. First is an increasing interest in safety. While the accident rate has decreased steadily for 40 years, the total miles traveled have increased, with the net result that the number of road fatalities in the US has stayed approximately constant, averaging 40,000 / year [5] . Furthermore, there is an increasing sense that vehicles have become safer (air bags, anti-lock brakes, crumple zones); roadways have become safer (the Interstate highway system); societal pressures have become stronger (mandatory child safety seats, serious enforcement of drunk driving laws) but the drivers themselves have not necessarily improved. Currently, in the US, 70% of all crashes are primarily caused by the drivers, and in another 20% driver error is a major contributing factor [5, 6] .Beyond safety, the next major driving factors have to do with congestion and pollution. In the US, traffic continues to grow at 4% / year, while with the completion of the Interstate highway system, major new road construction greatly lags traffic growth. Computercontrolled vehicles promise to smooth out traffic flow, permitting more vehicles to travel in

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Developmental Stereo: Emergence of Disparity Preference in Models of the Visual Cortex Abstract-How our brains develop disparity tuned 1 and 2 cells and then integrate binocular disparity into 3-D perception of the visual world is still largely a mystery. Moreover, computational models that take into account the role of the 6-layer architecture of the laminar cortex and temporal aspects of visual stimuli are elusive for stereo. In this paper, we present cortex-inspired computational models that simulate the development of stereo receptive fields, and use developed disparity sensitive neurons to estimate binocular disparity. Not only do the results show that the use of topdown signals in the form of supervision or temporal context greatly improves the performance of the networks, but also results in biologically compatible cortical maps-the representation of disparity selectivity is grouped, and changes gradually along the cortex. To our knowledge, this work is the first neuromorphic, end-to-end model of laminar cortex that integrates temporal context to develop internal representation, and generates accurate motor actions in the challenging problem of detecting disparity in binocular natural images. The networks reach a subpixel average error in regression, and 0.90 success rate in classification, given limited resources.Index Terms-Binocular vision, neuromorphic modeling, spatiotemporal, six-layer laminar cortical architecture. T HE PAST few decades of engineering efforts to solve the problem of stereo vision proves that the computational challenges of binocular disparity are far from trivial. In particular, the correspondence problem is extremely challenging considering difficulties such as featureless areas, occlusion, etc. Furthermore, the existing engineering methods for binocular matching are not only computationally expensive, but also hard to integrate other visual cues to help the perception of depth. It is important to look at the problem from a different angle-How the brain solves the problem of binocular vision? In particular, what are the computational mechanisms that regulate the development of the visual nervous system, and what are the role of gene-regulated cortical architecture and spatiotemporal aspects of such mechanisms?. Although steropsis seems to be a spatial problem, the temporal information appears to help stereopsis due to the physical continuity underlying the physicality of dynamics. Biological agents exploit spatial and temporal continuity of the visual stimuli to enhance their visual perception. In the real world, objects do not come into and disappear from the field of view randomly, but rather, they typically move continuously across the field of view, given their motion is not too fast for the brain to respond. At the pixel level, however, values are very discontinuous as image patches sweep across the field of view. Our model assumes that visual stimuli are largely spatially continuous. Motivated by the cerebral cortex, it utilizes the temporal context in the later cortical areas, including the intermediate areas and motor output area, to guide the development of earlier areas, [In Section II-B, (4) the activation level of the neurons from the previous time step is used to supervise .] These later areas are more "abstract" than the pixel level, and thus provide needed information as temporal context. However, how to use such emergent information is a great challenge. Existing methods for stereo disparity detection fall into three categories.. 1) Explicit matching: Approaches in this category detect discrete features and explicitly match them across two views. Well-known work in this category include [8] , [13] , and [39] . 2) Hand-designed filters: Filters are designed to compute profile-sensitive values (e.g., Gabor filters [24] and [37] , and phase information [10] and [30] ) from images and then utilize these continuous values for feature matching. Then an algorithm or a network maps from the matched features to disparity output [14] . 3) Network learning models: These models develop disparity-selective filters (i.e., neurons) from experience, without doing explicit matching, and map the responses to disparity outputs (e.g., [11] , [16] , and [19] ). Categories (1) and (2) employ explicit left and right match through either an explicit search or implicit gradient-based search. They are generally called explicit matching approaches. Category (1) fails to perform well in image regions with weak texture or when a patch of the image is missing in either of left or right images (i.e., occlusion), as it requires searching for the best match using texture cues. Category (2) methods have the potentail advantage of detecting other visual information such as edges and shading, which can be used in an integrated visual recognition system. However, this category suffers from inability to adapt to experience-hand-designed filters cannot possibly capture the statistics of any new environment, regardless of how complicated their design is. Methods in Category (3) not only develop filters that integrate other visual information, but also adapt to changing visual environment. Moreover, in contrast with category (2), a unified neuromorphic network learns to deal with both feature matching and disparity computation.. Among the different stages of the explicit matching approaches, the correspondence problem is believed to be the most challenging step; i.e., the problem of matching each pixel of one image to a pixel in the other [22] . Solutions to the correspondence problem have been explored using area-based, feature-based, pixel-based, and phase-based as well as Bayesian approaches [8] . While those approaches have obtained limited success in special problems, it is becoming increasingly clear that they are not robust against wide variations in object surface properties and lighting conditions [10] .. The network learning approaches in category (3) do not require a match between the left and right elements. Instead, the binocular stimuli with a specific disparity are matched with binocular neurons in the form of neuronal responses. Different neurons have developed different preferred patterns of weights, each pattern indicating the spatial pattern of the left and right receptive fields. Thus, the response of a neuron indicates a degree of match of two receptive fields, left and right. In other words, both texture and binocular disparity are measured by a neuronal response-a great advantage for integration of binocular disparity and spatial pattern recognition.. However, existing networks that have been applied to binocular stimuli are either bottom-up self-organizing maps (SOM) type or error-back propagation type. There has been no biological evidence to support error back-propagation, but the Hebbian type of learning has been supported by the Spike-time dependent plasticity (STDP) [7] . SOM type of networks that use both top-down and bottom-up inputs has not be studied until recently [26] , [27] , [31] , [33] . In this paper we show that top-down connections that carry supervisory disparity information (e.g., when a monkey reaches an apple) enable neurons to self-organize according to not only bottom-up input, but also supervised disparity information. Consequently, the neurons that are tuned to similar disparities are grouped in nearby areas in the neural plane, forming what is called topographic class maps, a concept first discovered in 2007 [21] . Further, we experimentally show that such a disparity based internal topographic grouping leads to improved disparity classification.. Neurophysiological studies (e.g., [12] and [3] ) have shown that the primary visual cortex in macaque monkeys and cats has a laminar structure with a local circuitry similar to our model in Fig. 3 . However, a computational model that explains how this laminar architecture contributes to classification and regression was unknown. LAMINART [23] presented a schematic model of the 6-layer circuitry, accompanied with simulation results that explained how top-down attentional enhancement in can laterally propagate along a traced curve, and also how contrast-sensitive perceptual grouping is carried out in . Weng et al. 2007 [15] reported performance of the laminar cortical architecture for classification and recognition, and Weng et al. 2008 [33] reported the performance advantages of the laminar architecture (paired layers) over a uniform neural area. Franz and Triesch 2007 [11] studied the development of disparity tuning in toy objects data using an artificial neural network based on back-propagation and reinforcement learning. They reported a 90% correct recognition rate for 11 classes of disparity. In Solgi and Weng 2008 [28] , a multilayer in-place learning network was used to detect binocular disparities that were discretized into classes of 4 pixels intervals from image rows of 20 pixels wide. This classification scheme does not fit well for higher accuracy needs, as a misclassification between disparity class and class 0 is very different from that between a class and class 4. The work presented here also investigates the more challenging problem of regression with subpixel precision, in contrast with the prior scheme of classification in Solgi and Weng 2008 [28] .. For the first time, we present a spatio-temporal regression model of the laminar architecture of the cortex for stereo that is able to perform competitively on the difficult task of stereo disparity detection in natural images with subpixel precision. The model of the intercortical connections we present here was informed by the work of Felleman and Van Essen [9] , and that for the intracortical connections was informed by the work of Callaway [2] and Wiser and Callaway [38] , as well as others. Luciw and Weng 2008 [20] , presented a model for top-down context signals in spatio-temporal object recognition problems. Similar to their work, in this paper the emergent recursive topdown context is provided from the response pattern of the motor cortex at the previous time to the feature detection cortex at the current time. Biologically plausible networks (using Hebbian learning instead of error back-propagation) that use both bottom-up and top-down inputs with engineering-grade performance evaluation have not been studied until recently [15] , [28] , [33] .. It has been known that orientation preference usually changes smoothly along the cortex [1] . Chen et al. [4] has recently discovered that the same pattern applies to the disparity selectivity maps in monkey . Our model shows that defining disparity detection as a regression problem (as opposed to classification) helps to form similar patterns in topographic maps; disparity selectivity of neurons changes smoothly along the neural plane.. In summary, the work here is novel in the following aspects: 1) the first laminar model (paired layers in each area) for stereo; 2) the first utilization of temporal signals in a laminar model for stereo; 3) the first subpixel precision among the network learning models for stereo. Applying the novelties mentioned in 1) and 2) showed surprisingly drastic accuracy differences in performance. 4) The first study of smoothly changing disparity sensitivity map; 5) theoretical analysis that supports and provides insights into such performance differences.. One may question the suitability of supervised learning for autonomous mental development (AMD). However, the AMD literature goes beyond the traditional classification of machine learning types, and divides all the machine learning methods into eight categories [36] . The learning method used in this work falls in Type 2 of the classification proposed in [36] , and therefore, fits the autonomous mental development paradigm.. The extensive research literature in psychology supports the notion of developing visual capabilities via touch and interaction with the environment, also known as associative learning (e.g., [29] ). Here is a specific example of supervised learning via touch in disparity detection learning: Assume that a monkey sees a banana and touches it at the same time. The distance that the monkey has extended its hand to touch the banana serves as supervisory signal to guide learning the disparity of the banana in its visual field. In general, any previously categorized (known) stimulus (e.g., length of monkey's hand) can supervise any unknown stimulus (e.g., disparity of the banana), given they are presented at the same time (associative learning).. In a nutshell, the proposed stereoscopic network develops, in the feature detection cortex, a set of binocular features (templates for inner-product matching; see Fig. 9 ). These features are both profile-specific and disparity-specific. The best match from a binocular input means a match for both profile and disparity. The same mechanisms were used to develop the motor cortex neurons; as long as the top-matched neurons in the feature detection cortex and the corresponding motor cortex neurons fire together, they are connected (associated).. In the remainder of the paper, we first introduce the architecture of the networks in Section II. Section III provides analysis. Next, the implementation and results are presented in Section IV. Finally, we provide some predictions and concluding remarks in Sections V and VI. Presented is the first spatio-temporal model of the 6-layer architecture of the cortex which incorporated temporal aspects of the stimuli in the form of top-down context signals. It outper- 9 Marked as Level2 , layers 2 through 4B in [2] Fig. 2 . formed simpler single-layer models of the cortex by a significant amount. Furthermore, defining the problem of binocular disparity detection as a regression problem by training a few nearby neurons to relate to the presented stimuli (as opposed to only one neuron in the case of classification), resulted in biologically-observed smoothly changing disparity sensitivity along the neural layers.. Since the brain generates actions through numerical signals(spikes) that drive muscles and other internal body effectors (e.g., glands), regression (output signals) seems closer to what the brain does, compared to many classification models that have been published in the literature. The regression extension of the MILN [33] has potentially a wide scope of application, from autonomous robots to machines that can learn to talk. A major open challenge is the complexity of the motor actions to be learned and autonomously generated.. As presented here, an emergent representation based binocular system has shown disparity detection abilities with subpixel accuracy. In contrast with engineering methods that used explicit matching between the left and right search windows, a remarkable computational advantage of our work is the potential for integrated use of a variety of image information for tasks that require disparity as well as other visual cues.. Our model suggests a computational reason as to why there is no top-down connection from and to in laminar cortex; to prevent the top-down and bottom-up energies received at the cortex from mixing before they internally compete to sort out winners. Hence, we predict that the thick layer Layer 2/3 ( ) in laminar cortex carries out more functionality than what has been proposed in previous models-it provides sparse representation for top-down stimuli in , combines the topdown and bottom-up sparse representations in , and projects the output of the cortical region to higher cortices.. Utilization of more complex temporal aspects of the stimuli and using real-time stereo movies will be a part of our future work. The lack of computational experiments on real world data in previous works has led to the oversight of the role of sparse coding in neural representation in the models of laminar cortex. Sparse coding of the input is computationally advantageous both for bottom-up and top-down input, specially when the input is complex. Therefore, we hypothesize that the cortical circuits probably have a mechanism to sparsely represent top-down and bottom-up input. Our model suggests that the brain computes a sparse representation of bottom-up and top-down input independently, before it integrates them to decide the output of the cortical region. Thus, we predict the following.

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A comparison of line extraction algorithms using 2D range data for indoor mobile robotics This paper presents an experimental evaluation of different line extraction algorithms applied to 2D laser scans for indoor environments. Six popular algorithms in mobile robotics and computer vision are selected and tested. Real scan data collected from two office environments by using different platforms are used in the experiments in order to evaluate the algorithms. Several comparison criteria are proposed and discussed to highlight the advantages and drawbacks of each algorithm, including speed, complexity, correctness and precision. The results of the algorithms are compared with ground truth using standard statistical methods. An extended case study is performed to further evaluate the algorithms in a SLAM application. It is important for a mobile robot to be able to autonomously navigate and localize itself in a known or unknown environment. A precise position estimation always serves as the heart in any navigation systems, such as localization, map building or path planning. It is well known that pure dead-reckoning methods, e.g. odometry, are prone to errors that grow unbounded over time (Iyengar and Elfes 1991) . The problem gives rise to a variety of solutions using different exteroceptive sensors (sonar, infrared, laser, vision, etc.) . Among different types of sensors, 2D laser range finders are becoming increasingly popular in mobile robotics. For example, laser scanners have been used in localization (Cox 1991; Jensfelt and Christensen 1998) , dynamic map building (Lu and Milios 1994; Gutmann et al. 1998; Castellanos and Tardós 1996; Tomatis et al. 2003) or feature tracking (e.g. for collision avoidance) (Pears 2000) . There are many advantages of laser scanners compared to other sensors: they provide dense and more accurate range measurements, they have high sampling rates, high angular resolution, good range distance and resolution.. One primary issue is how to accurately match sensed data against information in a priori map or information that has been continuously collected. There are two common matching techniques that have been used in mobile robotics: pointbased matching and feature-based matching. The early work of Cox (1991) uses range data to help the robot localizing itself in a small polygonal environment. He proposes a matching algorithm between point images and target models in a priori map using an iterative least-squares minimization method. Another work done by Lu and Milios (1994) addresses the problem of self-localization in an unknown environment, not necessarily polygonal. The proposed approach is to approximate the alignment of two consecutive scans and then iteratively improve the alignment by defining and minimizing some distance between the scans.. Instead of working directly with raw measurement points, feature-based matching first transforms the raw scans into geometric features. The extracted features are then used for matching in the next step. This approach has been studied and employed intensively in recent research on feature extraction, feature tracking, robot localization, dynamic map building, etc. (Crowley 1985; Leonard et al. 1992; Castellanos and Tardós 1996; Gutmann and Schlegel 1996; Jensfelt and Christensen 1998; Schröter et al. 2002; Brunskill and Roy 2005) . Being more compact, they require much less memory and still provide rich and accurate information. Algorithms based on parameterized geometric features are therefore more efficient compared to point-based algorithms.. Among many geometric primitives, line segments are the simplest ones. It is easy to describe most office environment using line segments. Many algorithms have been proposed for mobile robotics using line features extracted from 2D range data. Castellanos and Tardós (1996) propose a line segmentation method inspired from an algorithm in computer vision, used with a priori map as an approach to robot localization. Vandorpe et al. (1996) introduce a dynamic map building algorithm based on geometrical features, e.g. lines and circles, using a laser scanner. Arras and Siegwart (1997) use a 2D scan segmentation method based on line regression in map-based localization. Jensfelt and Christensen (1998) present a technique for acquisition and tracking of the pose of a mobile robot in an office environment with a laser scanner by extracting orthogonal lines (walls). Pfister et al. (2003) suggest a line extraction algorithm using weighted line fitting for line-based map building. Finally, Brunskill and Roy (2005) propose an incremental probabilistic technique to extract segments for solving the SLAM problem.. Many work has been done on line extraction. However, there is a lack of comprehensive comparisons of the so far proposed algorithms. Selecting the best method to extract lines from scan data is the first task for anyone who is going to build a line-based navigation system using 2D laser scanners. In terms of speed, one would prefer the fastest algorithm for his real time application. In terms of quality, bad line extraction can seriously lead the system to divergence in line-based SLAM. Implementation complexity is also one of the main aspects to take into account.. The work done by Gutmann and Schlegel (1996) gives a brief comparison of three algorithms which are relatively out of date compared to ones found in recent research. Moreover, the uncertainty modeling of the used parameters is not introduced in their paper. Borges and Aldon (2004) present an extended version of split-and-merge and compare their method with a generic split-and-merge algorithm and a line tracking (incremental) algorithm. Sack and Burgard (2004) perform a comparison of three selected algorithms on range data. However, in both papers the evaluation results are indirectly observed and interpreted from the map built by the mapping process. A direct comparison of the extracted lines by the selected algorithms using probabilistic analysis is still missing.. This paper presents a throughout evaluation of six line extraction algorithms applied to laser range scans. This work is an extension of the one described in (Nguyen et al. 2005) . The six selected algorithms are the most commonly used in mobile robotics and computer vision. Several comparison criteria are proposed and discussed, including speed, complexity, correctness and precision. The experiments are performed on two datasets collected from the Autonomous Systems Laboratory-EPFL, Switzerland and the Intel Jones Farms Campus, Oregon with the environment size of 80 m × 50 m and 40 m × 40 m, respectively. The results of the algorithms are compared with ground truth using standard statistical methods. One case study is performed to evaluate the maps obtained from a SLAM application when using different line extraction algorithms. Finally, the conclusions are presented. This paper has presented an experimental evaluation of the six line extraction algorithms using 2D laser scanner which are commonly used for feature extraction in mobile robotics and computer vision. The basic versions of the algorithms are implemented and tested with two datasets taken from two office environments which have different structures, shapes and degrees of clutter. Line segments extracted by the algorithms are compared with the manually extracted lines using standard statistical methods. Several comparison criteria are proposed and used to discuss in details their advantages and drawbacks. Additionally, the line extraction algorithms are tested in the OrthoSLAM application and the results obtained individually are compared. We believe this is important, particularly in mobile robotics, that techniques or algorithms should be tested and verified their performance in real life application before we can make the final choice. The comparison result with the OrthoSLAM has been shown to agree with the findings in the first part, thus again verify the conclusions. Overall, the experimental results show that the two algorithms Split-and-Merge and Incremental have best performance because of their superior speed and correctness. For real-time applications, Split-and-Merge is clearly the best choice by its superior speed. It is also the first choice for localization problems with a priori map, where FalsePos is not very important. However, a right choice highly depends on the applications and implementation details as the case study showed, where correctness is favored over precision.. The first released version of the implementation is accessible to public at http://www.asl.ethz.ch/people/tnguyen/. The ASL dataset can also be downloaded from the same location for comparison purposes. Interested user can send inquiries to viet.nguyen@mavt.ethz.ch. Viet Nguyen is a Ph.D. student at the Swiss Federal Institute of Technology Lausanne (EPFL). He received his Bachelor in Software Engineering from the Australian National University, Australia in 1999. He worked as a research assistant in the Laboratory of Artificial Intelligence at EPFL in 2001. In 2003, he joined the Autonomous Systems Laboratory where started his Ph.D. study under the supervision of Professor Siegwart. Since July 2006, he has been working at the Autonomous Systems Laboratory at the Swiss Federal Institute of Technology Zurich (ETHZ). His research covered mobile robot navigation, SLAM, feature extraction, data association, constraint satisfaction and optimization.. Stefan Gächter received the Master's degree in electrical engineering from the École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, in 2001. After his master's studies, he spent three years as a research engineer in the field of active magnetic bearings at Koyo Seiko Co. Ltd, Japan. He joined the Autonomous Systems Lab (ASL), École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, in 2004, where he commenced work towards a Ph.D. degree. Since July 2006, the Autonomous Systems Lab has been based at the Eidgenössische Technische Hochschule Zürich (ETHZ), Switzerland. His research interest is in computer vision for mobile robotics with emphasis on probabilistic algorithms for object classification applied to range images.. Agostino Martinelli (1971) received the M.Sc. in theoretical Physics in 1994 from the University of Rome "Tor Vergat" and the PhD in Astrophysics in 1999 from the University of Rome "La Sapienza". During his PhD he spent one year at the University of Wales in Cardiff and one year in the School of Trieste (SISSA). His research was focused on the chemical and dynamical evolution in the elliptical galaxies, in the quasars and in the intergalactic medium. He also introduced models based on the General Relativity to explain the anisotropies on the Cosmic Background Radiation. After his PhD, his interests moved on the problem of autonomous navigation. He spent two years in the University of Rome "Tor Vergata" and, in 2002, he moved to the Autonomous Systems Lab, EPFL, in Lausanne as senior researcher, where he was leading several projects on multi sensor fusion for robot localization (with particular attention to the odometry sensors), simultaneous localization and odometry error learning, and simultaneous localization and map building. Since September 2006 he is First Researcher (CR1) at the INRIA Rhone Alpes in Grenoble. He has authored/co-authored more than 30 journals and conference papers.

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Expressive policy analysis with enhanced system dynamicity Despite several research studies, the effective analysis of policy based systems remains a significant challenge. Policy analysis should at least (i) be expressive (ii) take account of obligations and authorizations, (iii) include a dynamic system model, and (iv) give useful diagnostic information. We present a logic-based policy analysis framework which satisfies these requirements, showing how many significant policy-related properties can be analysed, and we give details of a prototype implementation. There is an obvious relationship between the expressiveness of a policy language and the ability to analyse its properties and impact on system behaviour. Without being expressive a policy language may not be able to regulate complex system behaviour, apply across heterogeneous components, or apply to systems involving frequent changes such as mobile systems. Yet without analysis much of the benefit of using policy-based techniques and declarative policy languages may be lost. Arguably, the lack of effective analysis tools accounts in part for the lack of wider adoption of policy-based techniques.. A policy framework needs several key properties. First, it should be expressive. We need to specify both authorization [23, 32] and obligation policies [21, 30, 31] formally, and to allow complex dependencies of one on the other-for instance, authorization to withdraw a library book may be denied if the obligation to return requested items has been repeatedly violated. To be expressive, a framework should also allow policy decisions to depend on aspects of the evolving system history, so that authorization can depend not only on a static assignment of roles, or the fixed location of a sensor, but will vary as the system state changes. Policies must also provide fine-grained defaults. Many policy languages rely on a simple, universal default of either permitting or denying requests not covered by any specific policy rule. SELinux [26] , for example, has blanket denials for actions not covered explicitly by policy rules. Whilst we support such defaults, there is a need for a much more nuanced control over the default behaviour, so that requests to delete a file may be denied by default, but requests to read a file would be authorized [22] . Defaults are also useful in the presence of conflicts: the policy combination rules of XACML [30] , for example, specify the response to a request which the explicit policy rules both authorize and deny. Our framework can represent both sorts of default easily and concisely.. Second, a powerful policy analysis component is essential. This lets the policies be checked for necessary or desirable properties. Existing analysis frameworks- [21, 7, 6 ]-rarely take into account the changing system state, or only allow the statement and analysis of temporal constraints and relationships amongst policy decisions. There is a strong relationship between the expressiveness of a policy language and its analysis, since a less expressive language simplifies the analysis but also limits the scope of properties that can be checked. For example, if the language does not allow the representation of an authorization's dependence on the fulfilment of two key obligations, then an analysis of whether it was even possible to jointly satisfy those two obligations and then obtain permission, would not be possible.. Yet, expressiveness in the representation of policies, in the way they rely on each other, and the way in which they interact with the system, is insufficient. Policy authors also need to check for a wide variety of properties on the policies and systems they define. This requires an expressiveness in the query language of the analysis component, and strength in the analysis algorithm itself. Analysis should be able to cope with the following tasks:. • Modality conflicts such as the joint authorization and denial of a request to perform some action, or the presence of an obligation to act without the permissions necessary for its fulfilment.. • Separation of duty conflicts, including static separation of duty, dynamic, and many other classes (see [33] for terminology and instances).. • Coverage gaps, where no policy exists to dictate the correct response to a request.. • Policy comparison, including whether two policies are equivalent, or one is subsumed by the other.. • Behavioural simulation provides specific sequences of requests and events to the policy-regulated system to determine which policy decisions arise.. Third, the output of the analysis component should be rich enough to provide useful diagnostic information to a policy writer or system engineer. The system traces, policy decisions, and actions related to a queried property should all be indicated by the analysis-in addition to properties of the actors or principals involved, and the policy rules used in making the decisions that led to the state reached. Alternative traces and decisions should also be suggested, and the user ought to be able to insert constraints which guide the search for diagnostic information.. Fourth, it is desirable that a policy framework is separated into a part which is used to describe the policies, and a part which specifies system behaviour-by which we mean, the system on which the policies are deployed, and whose requests and actions the policies govern and shape [14] . This permits analyzing the behaviour of policies on different systems-something which is crucial, given the increasing deployment of the same policy on heterogeneous platforms-and spares the user the effort of formalizing the policy again for each new system. This paper presents an expressive logical framework for policy specification, in which it is possible to analyse for the types of properties mentioned above. The framework caters for both authorization and obligation policies, and incorporates a model of the changing system state. Our algorithm gives policy authors rich diagnostic information on analyses. We use abductive, constraint logic programming (ACLP) systems as the basis of our analysis algorithms and implementation, and the Event Calculus (EC) [25] to describe how events and actions occurring in the system affect the system states, leading to circumstances in which a given policy rule is applicable. This information is an output of the analysis.. In contrast to other logic-based formalisms ( [20, 24, 22] ), our approach caters for more dynamic policy models and includes an explicit representation of time, with temporal variables governed by constraints, allowing policies to be sensitive to changing system state. In addition, we include a class of obligation policies which monitors when and how users or the system initiate actions. This is needed for managing security, but is also useful in other applications such as context-aware adaptation in ubiquitous computing and privacy. Our policy language is also expressive enough that existing policy notations such as Ponder2 [31] , XACML [30] and Cassandra [7] can automatically be translated into it; to provide analysis for specification notations which currently do not support this. Translation algorithms have been developed for a large class of Ponder2 policies, and we are currently working on such schemes for XACML. We have developed a prototype implementation, 1 of our analysis framework.. The paper is organized as follows. Section 2 considers related work. Section 3 gives the syntax and semantics of the language, including a number of illustrative examples. Section 4 discusses the kinds of analysis our language permits, together with a discussion of the implementation and complexity properties. Conclusions and future research are in Section 5. A formal policy framework must incorporate obligations as well as authorizations, include an analysis component using information about changing system state for accurate proof of significant properties, provide rich diagnostic information as output, separate the representation of system from policy, and include policies which depend on each other and contain fine-grained defaults. Many languages aim to achieve some of these goals, but none succeed in achieving all in a way which balances expresiveness with efficiency of evaluation and analysis.. Our framework was designed to meet these requirements. We defined the structure of the policy language, and described how we use the EC to depict and reason about changing properties of the system. We gave examples of authorization and obligation rules, and described how abductive algorithms lying at the heart of our framework can be used in the analysis, discussing the current implementation.. By separating the representation of the laws of system evolution, and constraints on the system state, from the authorizations and obligations which define policy decisions we gain clarity in the representation but also the ability to switch domain descriptions easily and study the behaviour of policies on different systems.. The choices we have made in the design of the language show that it is possible to encode subtle default relationships and decisions without sacrificing efficiency, readability or concision. The use of temporal constraints and an explicit representation of time has enabled us to express complex dependences of policy decisions on changing system states, as well as on other policies.. Abductive Constraint Logic Programming is a suitable paradigm for the kinds of analysis task we wish to perform on policies. We have used it successfully to provide rich diagnostic information on the system traces and initial conditions which give rise to properties of policies in heterogenous environments: in this way, the use of ACLP with the Event Calculus and separable policies and system representations has been shown to be an effective combination for policy analysis. We have also used abduction, in our analysis framework, to fill in a partially-specified system, so that initial conditions which might give rise to e.g. modality conflicts are generated as hypotheses.. Further work is ongoing both at the implementation and at the theoretical level. At the moment, all suitable ACLP systems use integers as a basis of their constraints, but the modularity of the abductive approach we have taken means that an implementation based on reals is entirely feasible. We are also completing the work on translations between our framework and other languages for policies representation. We currently have translation schemes for Ponder2 [31] , and are working on schemes for XACML [30] and others.. Our broader objective is to define a refinement framework, of which the analysis framework will form a part. Within this context, an expressive abstract policy language is necessary both to represent a broad spectrum of high-level policies but also to accommodate different concrete mechanisms on which policies need to be implemented. Our previous work on policy refinement [3] for network quality of service management suggests that many of the properties we have built into our analysis framework (expressivity, separation of the laws for system change from policies, flexible expression of defaults, etc.) are also valuable for policy refinement. The Lithium language [20] is a logical formalism for policy representation and analysis; however, the authors work in pure first-order logic which imposes on the policy author the burden of specifying complete definitions (every request has a decision) since default decision policies are not expressible. For example, representing that all and only faculty members are permitted to chair committees; students are not [20] requires a complete specification of faculty and student body members, which may change dynamically, thus raising the well-known problem of elaboration tolerance [27] . The use of default rules-of the kind that our formalism supports-can simplify specifications and changes to the specification. Another important difference in our work is that we perform hypothetical analysis through abduction, letting the engineer specify initial conditions and sequences of requests or events in a system only partially; our analysis algorithm then supplies the additional information which makes a property true or false.. Our treatment of obligations is based on our experience with Ponder [13] and deontic logic; the result is similar to [21] . However, we have adapted obligation policies to produce a more general language that allows more complex policies to be represented, and our framework can support analyses such as the strong accountability checking presented in [21] . Dougherty et al. [15] present a model in which obligations are tied to authorizations, as conditions on acquiring permission to access a given resource. The model we use is more general, allowing obligations that are not tied to authorizations, as well as mutual dependence. [15] also includes a system model, though this is conceived abstractly as a set of state traces, which would need to be defined in full-our use of EC domain descriptions allows us to generate traces of actions which lead to the holding or violation of policy-related properties, from concise system descriptions.. Barker presents in [4] a language that represents access control policies using stratified clausal-form logic, with emphasis on RBAC policies. However, this work does not discuss analysis. The Authorization Specification Language (ASL) [24] , the Flexible Authorization Framework (FAF) [23] and the extension to handle dynamic authorizations discussed in [11] are also based on stratified clausal-form logic. They offer techniques for detecting modality conflicts and some application-specific conflicts in authorization policies. However, they work with a fixed domain model; in contrast, our framework does not presume a predefined domain model and can cater for varying system descriptions.. An access control policy language is presented in [5] ; it has an associated analysis framework based on a subset of transaction logic programs and in these respects the approach is similar to our own. However, although the authors do take into account the fact that some policy-governed actions can change role activations, and thus there is some dynamicity in their framework, they limit the specification to sequences of operations. Further, they cannot represent explicit prohibitions, and are thus forced into an unchangeable default assumption that anything not explicitly allowed is to be denied. Our formalism is more expressive: it has explicit prohibitions, and a great degree of control can be exercised in the way defaults cover policy gaps, or legislate between conflicts. In [6] , the authors use abduction to analyse authorization policies, focussing on finding explanations for the denial of access requests. They provide soundness, completeness and termination results. However, as with [5] , there is no fully dynamic system model. So although credentials can be abduced which would have led to the granting of access, it is not possible to see which policy-regulated actions, or system events, would have led to those credentials being present.. Fisler et al. [17] present an approach for the analysis of role-based access control policies written in XACML. The underlying formalism is MTBDDs (multi-terminal binary decision diagrams), and the method supports the analysis of the impact of changes on policies. There are, however, a number of limitations. Obligation policies are not supported, and there is no scope for policies that simultaneously permit and deny a given access request (a direct and oft-noted consequence of the nature of XACML's combination rules). We regard support, especially of the latter, as essential for any generic policy analysis tool. The query language (for expressing properties) is somewhat cumbersome, though the authors acknowledge this as a theme for future work. Further, though environmental constraints can be included, there is no explicit dynamic system model, and so analysis does not show system traces and policy decisions which lead to properties of interest.. Finally, in [9, 10] the authors define a simple but powerful framework for representing and reasoning about accesscontrol policy composition. The semantics for access requests is four-valued: permit, deny, undefined, and conflict. Analysis is performed by transforming properties to be checked into constraints which can be fed to a modelchecker; the approach can support coverage-gap, modality conflict, and policy comparison analysis. The emphasis of this work is on the definition of an expressive, generic semantics for policy composition and related analysis, and thus A prototype implementation of our formal analysis framework is freely available to download. 6 The implementation uses the open-source abductive constraint logic programming ASystem [34] . Tests have enabled us to find modality conflicts, coverage problems, and other interesting properties of policies in conjunction with system descriptions, such as those earlier in this section.. The ASystem is based on finite domains. For this reason, we adapted our axioms to work on an integer base for Time, and chose a maximum time to consider in order to make the Time domain finite. In all cases we examined, analysis results under these modifications would hold under the original version of the axioms with R. However, the systems is modular, so that a solver based on the real numbers could simply be 'plugged in' to the algorithm instead. This is an area of current investigation.

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A CASE STUDY IN PARTICIPATORY PRIORITY SETTING For A Scandinavian Research Program Continuing attempts to align science and technology policies with industrial and societal needs have aroused interest in the determination of research priorities. In this paper, we report a case study where leading experts from industry and public administration were assisted by multicriteria decision analysis in the planning of a collaborative research program for Scandinavian forestry and forest industries. We also address processual and methodological challenges in the deployment of multicriteria methods, and argue that such methods can contribute to the quality of decision support processes in related contexts. The development of research priorities is a central concern in the preparation of publicly supported research programs (cf. Hartwich and Janssen, 1 Keenan 2 and OECD 3 ). This task is complicated by considerations such as major uncertainties, vested interests, lack of unequivocal "alternatives" and asymmetric distribution of relevant information, among others. Arguably, these complications have grown over the past few years, partly due to increasing pressures on the demonstration of the benefits of public science and technology (S&T) expenditure and the recognition of an ever broadening range of concerns in the assessment of these benefits (see, e.g. Smits and Kuhlmann 4 ). Because these pressures are likely to persist, there is a demand for decision-aiding processes through which these priorities can be established in a defensible and transparent manner, in view of the concerns that must be brought to bear on them.. In this paper, we describe a case study in which novel methods of multicriteria decision analysis were deployed in the planning of a research program for the Scandinavian forestry and forest industries. To a considerable extent, this case study was based on a participatory workshop where relevant stakeholders from Finland, Norway and Sweden evaluated complementary research themes with the help of a tailored group support system (GSS). Specifically, this GSS was employed to solicit both quantitative and qualitative inputs in order to inform the shaping of the research program on wood materials science, launched in 2003 with the aim of fostering the long-term industrial competitiveness of forestry and forest industries in Scandinavia. The rationale for this program can be seen in relation to major industrial trends: for example, after numerous mergers and acquisitions, many firms are no longer "national", wherefore the innovation policies of the countries they operate in need to be better coordinated too.. Apart from the novel use of methodological support, there are also other reasons that suggest that our case study is of broader interest. First, the resulting program is truly international in terms of its funding structure, scope of topics and participating organizations, although much of the earlier literature on research priority setting has focused on either national or regional exercises (see, e.g. Grupp and Linstone 5 ). Second, the priority setting process was supported by a GSS through which both formal evaluative statements and informal verbal comments were solicited; our concern with the complementary roles of quantitative and qualitative analysis can thus be contrasted with earlier accounts that have tended to emphasize the quantitative aspects of multicriteria analyzes (see, e.g. Henriksen and Traynor 6 ). Third, the process in Finland was organized hierarchically so that preliminary results from three national workshops were injected into the Scandinavian workshops for elaboration and validation. The process outline is therefore potentially applicable also in other settings where research priorities need to be synthesized through a hierarchical approach.. The rest of this paper is organized as follows. Section 2 discusses concerns in the development of research priorities and reports experiences from the use of multicriteria methods in the preparation of publicly supported research programs. Section 3 outlines the objectives that were placed on the research program on wood material research and describes the participatory workshops. Drawing upon experiences from this case study, Sec. 4 outlines methodological recommendations and considers the role of systematic methodologies in attaining quality attributes such as transparency, comparability and repeatability. In this paper, we have reported a case study of the application of novel multicriteria methods to the planning of a Scandinavian research program on wood material science. Apart from describing these methods and the corresponding decision support tools, we have discussed challenges in priority formation and discussed methodological considerations that may improve the quality of these processes: for example, due to the presence of high uncertainties and the need to account for multiple perspectives, these processes may benefit from the deployment of multiple approaches, a combination of both top-down and bottom-up approaches, explicit modeling of the participants' degree of expertise and the use of mechanisms for de-biasing possibly exaggerated statements about the beneficial impacts of proposed research themes.. Based on the positive feedback from this case study, we conjecture that a similar approach may be suitable for the preparation of research programs in other fields, or even for the design of other policy instruments where priorities must be developed as a precursor to the solicitation of project proposals. In such contexts, the benefits from the deployment of systematic multicriteria methods relate to (i) the transparency of decision support activities; (ii) the repeatability of the planning process, whereby additional research themes can be addressed through the same format and -perhaps most importantly -(iii) the requirement for equitability in addressing alternative research themes, which helps ensure that these themes are treated equally and receive the same amount of attention.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 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