197,244 research outputs found
The gluon content of the pion from high-pt photon production
No full textAurenche P, Baier R, Fontannaz M, Kienzle-Focacci MN, Werlen M. The gluon content of the pion from high-pt photon production. Physics letters B. 1989;233(3-4):517-521
The role of the inferior frontal gyrus and of the uncinate and of the inferior frontal occipital fasciculi in the recognition of emotional facial expressions
No full textThe perception of faces expressing emotions is one of the most developed human visual abilities and involves various cortical and subcortical brain regions, such as some occipital and temporal areas, involved in the processing of pictorial aspects of the visual stimuli, and the amygdala, which plays a crucial role in assessing their emotional content. The first part of the article will review the classical models proposed to explain this particular perceptual process, while the second part will deal with the most recent evidence, which places emphasis on anatomical substrates not initially considered, and which leads to unprecedented interpretations of the processing of emotional facial expressions. Previous theoretical models described this brain function as the result of a modular analysis performed exclusively within the visual system and based on separate processing pathways for the recognition of the different visual features, such as identity and emotional expressions. Subsequent studies have suggested that the motor and prefrontal territories should be added to the classical regions considered as involved in the perception of faces. This evidence has prompted the proposal of new models that envisage an information processing not purely hierarchical but rather serial and/or based on top-down and simulation mechanisms. In line with this evidence, recent studies have emphasized the crucial role of the inferior frontal gyrus (IFG) for the explicit recognition of emotional facial expressions. While the anatomical pathways through which the occipital and temporal regions interact with each other are relatively well known, the connections between these regions and the IFG have not yet been studied in detail. Nonetheless, based on the data already present in the literature, it is possible to hypothesize that the inferior fronto-occipital and uncinate fasciculi represent the two preferential anatomical pathways through which this prefrontal region interacts with the visual regions during the processing of emotional faces. In particular, it is likely that the uncinate fasciculus is the route through which visual information from subcortical territories, including the colliculus, pulvinar, and amygdala, reaches the IFG, that in parallel receives further visual information from a cortical pathway constituted by temporal and the occipital areas and the inferior occipital fasciculus. Since lesion and functional studies suggest that the IFG plays a role in the conscious recognition of facial expressions, one intriguing hypothesis is that this ability emerges from the integration of purely visual cortical information with subcortical information, in which the visual aspects of stimuli are encoded unconsciously and in a rough way, but at the same time endowed with emotional content. The effects of the lesions of these fascicles support this hypothesis although specific studies are needed to test its actual validity..All this evidence suggests the intriguing hypothesis that the role of the IFG in the conscious recognition of facial expressions emerges from its capacity to integrate purely visual cortical information with subcortical one, in which the visual aspects of the stimuli are unconsciously and coarsely encoded, but at the same time endowed with emotional content. Although the effects of the lesions of these fasciculi support this hypothesis, specific studies are needed to test its actual validity
Cost-based domain filtering
No full textConstraint propagation is aimed at removing from variable domains combinations of values which cannot appear in any consistent solution. Pruning derives from feasibility reasoning. When coping with optimization problems, pruning can be performed also on the basis of costs, i.e., optimality reasoning. Propagation can be aimed at removing combination of values which cannot lead to solutions whose cost is better then the best one found so far. For this purpose, we embed in global constraints optimization components representing suitable relaxations of the constraint itself. These components provide efficient Operations Research algorithms computing the optimal solution of the relaxed problem and a gradient function representing the estimated cost of each variable value assignment. We exploit these pieces of information for pruning and for guiding the search. We have applied these techniques to a couple of ILOG Solver global constraints (a constraint of difference and a path constraint) and tested the approach on a variety of combinatorial optimization problems such as Timetabling, Travelling Salesman Problems and Scheduling Problems with setup. Comparisons with pure Constraint Programming approaches and related literature clearly show the benefits of the proposed approach. By using cost-based filtering in global constraints, we can optimally solve problems that are one order of magnitude greater than those solved by pure CP approaches, and we outperform other hybrid approaches integrating OR techniques in Constraint Programming
Approximate Evaluation of Maximum Force Transferable at FRP-Masonry Interface
No full textThe debonding phenomenon between fiber-reinforced polymer (FRP) composites and masonry is influenced by the presence of mortar joints that could reduce the bond capacity of the FRP-brick interface (i.e., in the absence of the joints). The actual estimate of the maximum load transferable at the FRP-masonry interface is cumbersome. Thus, the aim of this paper is twofold. First, the paper provides a set of useful key remarks to understand how the presence of joints influence the behavior of the FRP-masonry interface with respect to the FRP-brick interface. This is an important aspect of the paper because it summarizes previous work and provides guidance for designers and researchers. Secondly, this paper proposes a step-by-step procedure to obtain an approximate estimate of the maximum transferable load at the FRP-masonry interface provided that the characteristics of the FRP-brick and FRP-mortar interfaces are known or can be derived from codes and guidelines, and the thickness of brick and joints is assigned. To the best knowledge of the authors, an approximate formulation for the FRP-masonry interface is presented in this paper for the first time together with guidance to evaluate when an approximate formulation might be necessary based on the desired acceptable error. The comparison between the maximum load transferable at the FRP-masonry interface and its approximation presented in this paper provides a relative error of roughly 0.4% for case of practical interest. Finally, the paper provides an example application of the proposed procedure
Cutting planes in constraint programming: An hybrid approach
No full textIn recent years, a growing number of attempts have been performed in order to integrate well known Operations Research(OR) techniques in Constraint Programming (CP) tools. The aim of the integration is to maintain the modelling facilities of the CP paradigm, while improving its performances by exploiting effective OR techniques. In our previous work, we proposed the use of optimization constraints [9], embedding a linear relaxation of the constraint itself and performing pruning on the basis of costs. In particular, domain values can be removed whenever it can be shown that their assignment will necessarily lead to solutions worse than the best solution found. In this setting, the use of cutting planes in global constraints allows to tighten the relaxation so as to infer more accurate bounds on the problem. We propose different ways of using cutting-planes in optimization constraints achieving different levels of tightness of the integration and pruning power. Even if the proposed technique is general, we use as testing application the Travelling Salesman Problem (TSPs) and its time constrained variant. Computational results compare different relaxations in terms of pruning achieved and computational complexity
Embedding relaxations in global constraints for solving TSP and TSPTW
No full textConstraint Programming (CP) has been successfully applied to several combinatorial optimization problems. One of its advantages is the availability of complex global constraints performing efficient propagation and interacting with each other through shared variables. However, CP techniques have shown their limitations in dealing with optimization problems since the link between the objective function and problem decision variables is often quite loose and does not produce an effective propagation. We propose to integrate optimization components in global constraints, aimed at optimally solving a relaxation corresponding to the constraint itself. The optimal solution of the relaxation provides pieces of information which can be exploited in order to perform pruning on the basis of cost-based reasoning. In fact, we exploit reduction rules based on lower bound and reduced costs calculation to remove those branches which cannot improve the best solution found so far. The interest of integrating efficient well-known Operations Research (OR) algorithms into CP is mainly due to the smooth interaction between CP domain reduction and information provided by the relaxation acting on variable domains which can be seen as a communication channel among different techniques. We have applied this technique to symmetric and asymmetric Traveling Salesman Problem (TSP) instances both because the TSP is an interesting problem arising in many real-life applications, and because pure CP techniques lead to disappointing results for this problem. We have tested the proposed optimization constraints using ILOG solver. Computational results on benchmarks available from literature, and comparison with related approaches are described in the paper. The proposed method on pure TSPs improves the performances of CP solvers, but is still far from the OR state of the art techniques for solving the problem. However, due to the flexibility of the CP framework, we could easily use the same technique on TSP with Time Windows, a time constrained variant of the TSP. For this type of problem, we achieve results that are comparable with state of the art OR results
Optimization-oriented global constraints
No full textIn this paper, we propose a way of exploiting Operations Research techniques within global constraints for cost-based domain filtering. In Constraint Programming, constraint propagation is aimed at removing from variable domains combinations of values which are proven infeasible. Pruning derives from feasibility reasoning. When coping with optimization problems, pruning can be performed also on the basis of costs, i.e., optimality reasoning. Cost-based filtering removes combination of values which are proven sub-optimal. For this purpose, we encapsulate in global constraints optimization components representing suitable relaxations of the constraint itself. These components embed efficient Operations Research algorithms computing the optimal solution of the relaxed problem and a gradient function representing the estimated cost of each variable-value assignment. We exploit these pieces of information for pruning and for guiding the search. We have applied these techniques to a couple of ILOG Solver global constraints (a constraint of difference and a path constraint) and tested the approach on a variety of combinatorial optimization problems such as Timetabling, Travelling Salesman Problems and Scheduling Problems with sequence dependent setup times. Comparisons with pure Constraint Programming approaches and related literature clearly show the benefits of the proposed approach
Mathematical programming techniques in constraint programming: A short overview
No full textIn recent years, the integration of techniques from Artificial Intelligence and Operations Research has shown to improve the solutions of complex and large scale combinatorial optimization problems, in terms of efficiency, scalability and optimality. In this context, Constraint Programming is an emerging discipline situated at the confluence of the two fields that has been recognized as a suitable environment for achieving such an integration. This paper briefly presents the integration directions explored in the literature, and provides some pointers to relevant work in these directions
The effect of the shape of the cohesive material law on the stress transfer at the FRP-masonry interface
No full textDebonding of the fiber-reinforced polymer (FRP) from the substrate that occurs before its tensile strength is reached typically controls the effectiveness of the stress transfer mechanism between FRP composites and a quasi-brittle substrate, such as masonry. The FRP-substrate interface is usually modelled as a zero-thickness interface whose fracture Mode-II cohesive material law (CML) is defined in terms of shear stress and slip at the interface. In this paper, the effect of the shape of the CMLs of the FRP-brick and FRP-mortar interfaces on the stress transfer process will be presented and discussed. Several multi-linear CMLs, obtained from experimental data for both mortar and brick interfaces, will be adopted to obtain the load response of the FRP-masonry interface. It will be shown that the shape of the CMLs adopted does not strongly affect the load response if the fracture parameters are the same or similar among the CMLs. Finally, certain geometric relationships of brick and mortar joints imply more pronounced differences in terms of load response between the CMLs adopted
Exploiting Relaxations in CP
No full textIn this chapter, we present the integration of various forms of
problem relaxation in Constraint Programming (CP). The main
motivation for the integration proposed concerns the introduction
in CP languages of some form of {em optimality reasoning}. Indeed,
CP languages provide effective and powerful tools for
reducing the search space of the problem by removing infeasible
values. However, they barely consider the problem objective
function and implement a naive form of branch-and-bound which
poorly reduces the search space to be explored.
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Relaxations can be integrated in CP in different ways. Some approaches
propose to automatically translate the whole CP program in linear form,
while some other focus only on global constraints. In this perspective, a
further differentiation can be noted. Some approaches translate all global
constraints in a unique linear store, while others embed an optimization
component within each global constraint. In other approaches, the part of
the problem to be relaxed is decided by the user that explicitly states it
in the program. First, we provide an introduction on different kinds of
relaxation and we discuss many integration approaches, how they exploit
results coming from the relaxation, providing references to related
bibliography. In the second part of the chapter, we consider global
constraints as suitable software components to integrate relaxations in CP.
We discuss, as a case study, a particular global constraint, the path
constraint, and show different relaxations and their tightness
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