Strongly rigid tensegrity graphs on the line Tensegrity frameworks are defined on a set of points in R d and consist of bars, cables, and struts, which provide upper and/or lower bounds for the distance between their endpoints. The graph of the framework, in which edges are labeled as bars, cables, and struts, is called a tensegrity graph. It is said to be strongly rigid in R d if every generic realization in R d as a tensegrity framework is infinitesimally rigid. In this note we show that it is NP-hard to test whether a given tensegrity graph is strongly rigid in R 1 . A tensegrity graph T = (V ; B, C, S) is a graph on vertex set V = {v 1 , v 2 . . . , v n } whose edge set is partitioned into three sets B, C, and S, called bars, cables, and struts, respectively. The elements of E = B ∪ C ∪ S are the members of T . A tensegrity graph containing no bars is called a cable-strut tensegrity graph 1 . The underlying graph of T is the (unlabeled) graph T = (V ; E). A d-dimensional tensegrity framework is a pair (T, p), where T is a tensegrity graph and p is a map from V to R d . We will also refer to (T, p) as a realization of T . If T has neither cables nor struts then we call it a bar graph and a realization (T, p) is said to be a bar framework.. An infinitesimal motion of a tensegrity framework (T, p) is an assignment q : V → R d of infinitesimal velocities to the vertices, such that. where p(v i ) = p i and q(v i ) = q i for all 1 ≤ i ≤ n. An infinitesimal motion is trivial if it can be obtained as the derivative of a rigid congruence of all of R d restricted to the vertices of (T, p). The tensegrity framework (T, p) is infinitesimally rigid in R d if all of its infinitesimal motions are trivial. It is well-known that the infinitesimal rigidity of tensegrity frameworks is not a generic property: the same tensegrity graph may possess infinitesimally rigid as well as infinitesimally non-rigid generic realizations in any fixed dimension d ≥ 1. Thus we may define two (different) families of tensegrity graphs in dimension d: we say that a tensegrity graph T is rigid in R d if it has an infinitesimally rigid generic realization (T, p) in R d and strongly rigid if all generic realizations (T, p) in R d are infinitesimally rigid. We refer the reader to [1, 2, 6, 7] for more details on the rigidity of tensegrity frameworks.. It is not known whether the rigidity of tensegrity graphs can be tested in polynomial time for d ≥ 2. (The solution for d = 1 can be found in [5] .) The special case of rigid bar graphs has been solved for d = 2, but the 3-dimensional version remains one of the major open problems in combinatorial rigidity.. In this note we show that it is co-NP-complete to test whether a tensegrity graph is strongly rigid in R 1 . The proof of Theorem 2.1 shows that if we replace 'generic' by 'general position' in the definition of strong rigidity in R 1 then the family of strongly regular graphs will reamin the same. This is not true when d ≥ 2, even for bar graphs.. Let G = (V ; C, S) be a 2-edge-labeled graph and let B be a set of bars corresponding to the alternating 2-cycles of G. Theorem 2.1 implies that if G is strongly rigid in R 1 then each vertex of G is incident with an edge of B. Let c be the number of components of the graph (V, B). Theorem 2.1 gives a polynomial algorithm for checking if G is strongly rigid when c is fixed since we need only check 2 c bipartite graphs for alternating cycles (which can be done by checking if the associated digraph is acyclic).. We can use Theorem 2.1 to construct graphs which are not strongly rigid in R 1 and for which the connectivity of both (V, C) and (V, S) is arbitrarily large. For example let (V, B) consist of two large complete graphs and join them by 2k independent edges, half in C and half in S.. A natural open question is whether our hardness result concerning strong rigidity extends to higher dimensions d ≥ 2.. Another question is whether the corresponding labeling problem is hard: given a graph G, decide whether the edges set of G can be 2-edge-labeled so that the resulting cable-strut tensegrity graph is strongly rigid in R 1 (and find a good labeling, if it exists). If we replace strongly rigid by rigid, we obtain a labeling problem which is polynomially solvable in R d for d = 1, 2, see [4] .

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Reduced-cost microwave filter modeling using a two-stage Gaussian process regression approach ABSTRACT: A technique for the reduced-cost modeling of microwave filters is presented. Our approach exploits variable-fidelity electromagnetic (EM) simulations, and Gaussian process regression (GPR) carried out in two stages. In the first stage of the modeling process, a mapping between EM simulation filter models of low and high fidelity is established. The mapping is subsequently used in the second stage, making it possible for the final surrogate model to be constructed from training data obtained using only a fraction of the number of high-fidelity simulations normally required. As demonstrated using three examples of microstrip filters, the proposed technique allows us to reduce substantially (by up to 80%) the central processing unit (CPU) cost of the filter model setup, as compared to conventional (single-stage) GPR-the benchmark modeling method in this study. This is achieved without degrading the model generalization capability. The reliability of the two-stage modeling method is demonstrated through the successful application of the surrogates to surrogate-based filter design optimization. Full-wave electromagnetic (EM) analysis has become a primary design tool of contemporary microwave engineering. High-fidelity EM simulation ensures accurate design verification but it is normally computationally expensive. This might present a bottleneck to carrying out EM simulation-driven design tasks, such as parametric optimization, statistical analyses, and robust (e.g., toleranceaware) design that require numerous evaluations of the structure of interest. This is particularly true not only for conventional optimization techniques, both gradient-based and derivative free [1, 2] , but also for global optimization sing metaheuristics (e.g., genetic algorithms [3, 4] , and particle swarm optimizers [5] ) that usually require a large number (thousands or more) of high-fidelity EM simulations of the candidate geometries. Rapid development of computational tools and the presence of massive computing resources alleviate this difficulty to some extent only. This is because growing demand for accuracy (e.g., by including multiphysics and using finer discretization), as well as the necessity of accounting for various interactions and couplings between the structure of interest and its environment (e.g., antenna housing) tend to increase the computational complexity of the simulation process.. For the reasons elaborated above, fast and yet accurate models (also referred to as surrogates) become indispensable in microwave design. Perhaps the most popular way of creating such models is response surface approximation, where the surrogate is identified using a (training) set consisting of suitably selected input-output data samples. Properly trained response surface models exhibit good generalization capability, that is, allow for reliable prediction of the system/device response for the input parameter vectors that were not used in the training stage.. One of the most powerful approaches for constructing approximation-based surrogate models is Gaussian process regression (GPR) [6] . GPR has been shown to be a particularly effective modeling technique for performance characteristics such as antenna reflection coefficient and filter transmission coefficient responses against frequency [7] [8] [9] . Other kernel-based machine learning methods that have been used in this context include standard support vector regression, for example, [10] , and the more flexible, GPR-based Bayesian support vector regression [11] .. A Gaussian process (GP) is a stochastic process that generalizes the notion of Gaussian probability distribution to functions. Due to the Gaussian nature of the distribution, the calculations necessary in the learning and inference processes become tractable. Under suitable conditions, GPs can be considered equivalent to neural networks, but GPs are generally easier to implement and interpret-one reason is that training of far fewer parameters (in the order of the dimension of the input vectors) is required compared to the number of weights in a neural network (e.g., multilayer perceptron).. A drawback shared by response surface modelling techniques, including GPR (but also neural networks [12] , support vector regression [13] , and radial basis function interpolation [14] ), is the usually large number of training points necessary to ensure sufficient predictive power of the model. In a typical setup, a few hundred to several thousand points might be required, which results in considerable computational overhead related to data acquisition, normally through massive EM simulations of the respective microwave structure. In many situations, such an overhead may be impractical or even prohibitive.. There have been various attempts to reduce the computational cost of creating the surrogate model setup cost. Adaptive sampling is perhaps the most popular approach, where the number of training data samples required to secure sufficient model accuracy is obtained in an iterative process consisting of model identification and subsequent generation of new samples using a suitable strategy. The strategies may be based on the actual modelling error at the testing locations [15] , or the predicted error [16] . The methods described in [15] and [16] are developed to work as local ones, usually in an optimization context. Our focus is on the development of global surrogates (to be used as library models), where accurate prediction over the entire design space is of concern. Such models can be used in a wide range of applications, including parametric optimization or statistical analysis. Another approach to reduce the computational cost of surrogate model setup was presented in [17] , where only the support vectors of an initial (global) Bayesian support vector regression model trained on low-fidelity data were selected for finely meshed simulation. A 31-to-48 percent reduction in model setup costs could be achieved without adversely affecting predictive ability.. In this work, we demonstrate that the central processing unit (CPU) cost of surrogate model setup can be substantially reduced by means of variable-fidelity EM simulations in combination with GPR. In particular, we propose a two-stage modeling scheme, where-in the first stagewe generate by full-wave simulation a low-fidelity (coarse) training dataset of n points, and n aux < n points of the corresponding (computationally expensive) high-fidelity (fine) training set. These n aux high-fidelity points are used to learn a model that maps low-fidelity training targets (either of Re{S 21 }, Im{S 21 }, or |S 21 |) to the corresponding highfidelity ones. The mapping is subsequently used to predict the remaining n 2 n aux high-fidelity targets that were not simulated. The n aux simulated high-fidelity targets and the n 2 n aux predicted ones (together with the input vectors) form the n-point "approximate" high-fidelity training set. In the second stage, a final GPR model is constructed using the latter training set. The proposed two-stage modelling methodology exhibits substantial novelty with respect to the conventional GPR approach. It not only blends EM simulations of various level of fidelity into one surrogate model, but also does it in a parameter-less fashion (in contrast with, e.g., space mapping, SM [18] [19] [20] [21] ). While it has recently been applied with good effect to the modelling of antenna input characteristics [22] , this study shows that the method is general enough to hold for filter responses too, which can be more challenging to model due to the sharp transitions explicitly required between, for example, passband and stopband portions of responses.. The article is organized as follows. In Section II we provide a brief theoretical overview of GPR following [6] , and describe the two-stage modeling procedure. In Section III our approach is illustrated using three examples of microstrip filters. We demonstrate that exploitation of the knowledge embedded in the low-fidelity model allows for considerable (up to 80%) computational savings as compared to conventional GPR modelling, and without compromising modelling accuracy. Section IV demonstrates that the two-stage GPR surrogates are sufficiently accurate to be used for filter optimization within a surrogate-based optimization scheme involving output SM [19, 21] . Conclusions are presented in Section 5. A method has been presented for the efficient modeling of highly challenging nonlinear microwave filter responses using variable-fidelity EM simulations and GPR within a two-stage framework. The knowledge embedded in the low-fidelity filter simulations is used in the first modeling stage, where the mapping between the EM models of different fidelity is established. This leads to substantial reduction of the number of high-fidelity simulations necessary to construct-in the second stage-the surrogate model of the filter of interest. These computational savings are achieved without compromising the predictive power of the final surrogate. Our approach has been verified using three examples of microstrip filters with satisfactory results obtained even for very limited high-fidelity simulations, corresponding to only 20-40% of what is required in setting up highfidelity training sets for conventional GP modeling. The two-stage surrogates have been also successfully used for filter optimization, proving their usefulness in the design context. The results presented in the previous section indicate that combining low-and high-fidelity EM simulation data using the proposed modeling technique allows for very significant reduction-compared to conventional GPR modeling-of the computational overhead related to training data acquisition without compromising the predictive power of the surrogate model.. It should be emphasized that modeling of filter characteristics is a difficult task because of the high nonlinearity of the responses. In practice, this can be effectively realized only if the number of design variables is relatively low, or the design space is small (in terms of the range of variability of the geometry/material parameters). Thus, the presented examples are quite representative of what can be accomplished using approximation techniques such as GPR. For the sake of illustration, we focused on modeling the transmission characteristics of the filters. Modeling of return loss would be actually much more challenging mostly due to the nonlinearity issues.

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


The use of a virtual instruction set for the software synthesis of Hw/Sw embedded systems The application range of the embedded computing is going to The increasing pressure of the embedded system market to shrink time-to-market, size, power and cost of products is facing the designers with the problem of managing the entire synthesis flow of architectures composed of programmable software and hardware engines [l] . In this paper we refer to dedicated designs as those embedded in equipment for automotive, process control and telecom applications such as public switching and networking systems. For this class of systems, the function to be implemented is well known in advance and it will never change during their operational life, apart from possible minor adjustments. As opposed to the general purpose computer systems, embedded applications do not require a significant degree of flexibility once they are running. They are usually produced in large volumes and sophisticated analyses and optimizations can be carried out to meet the design requirements. According to the particular data on which the design is focused, the system can be roughly classified into: data dominated and control dominated [l, 21. We devote our attention mainly to the control-dominated applications whose purpose is to react to external stimuli, possibly within some tight deadlines, but where data intensive functions play a secondary role [2, The challenge of finding out a methodology to develop cost-effective hardware-software systems has been driven by extending the research in high-level synthesis to cover the particular requirements of buildings blocks and specification formalisms for mixed hardware-software architectures [5] . Our goal is to identify a pragmatic design methodology for control dominated embedded systems to be actually used, and therefore interfaced with the industrial requirements, of an Italian telecom company whose main products are in the area of public switching.. This project, named TOSCA (Tools for System Codesign Automation), started some years ago and is currently under development at the CEFRIEL research center [6] . The aim is to define a methodology and the related CAD support to cover a complete co-design flow: the capturing of uncommitted process-level specification including the designer' objectives and constraints (co-specfzcation), the identification of a suitable system-level modularization of the initial specification (design-space exploration and binding) to be mapped onto the hardware or software components composing the target hardware-software architecture (co-synthesis). Hence, before committing to a specific implementation, the initial system specification can be manipulated to fulfill the target design requirements. This partitioning process, can be viewed as an incremental activity of modification of the initial specification through the application of transformations under the driving of metrics for system quality evaluation [6] . The internal model is based on a customization of the Occam11 [7] computational model. The specifications and constraints can be captured through a built-in mixed textual/graphical editor. Direct import fron existing design entry tools (such as speedCHART) is also supported, based on the use of suitable OccamII process templates.. After the identification of the optimal system partitioning and binding, the following stage is the mapping of the system description onto an actual digital architecture. The TOSCA co-synthesis is performed by two different tools: a tool for VHDL generation for hardware-bound architectural units including interface generation, and a software synthesis tool for software-bound architectural units, including a lightweight 3,41.. Operating System. Interfaces are generated with respect to the adopted model of communication, currently a fixed protocol is available, consistent with the target architecture adopted.. This paper emphasizes the problem of the modeling and synthesis of the software programs running on the microprocessor. The presented approach aims at providing a complete solution by taking into account the operating system including CPU scheduling and I/O management, direct generation of the software at assembly level, and the definition of a model of the software for co-design purposes to allow code retargeting and VHDL-based co-simulation of hardware-software systems.. In literature, the identification of the software side of the system is frequently unbalanced between hardware and software, since typically it is considered at a higher level such as the C language. A comprehensive analysis of the proposals can be found in [8] . For many dedicated applications, it is becoming important to consider the real time constraints not only during the hardware generation but also during the system-level partitioning and software synthesis. Recent works have considered the sofhvare properties at a finer granularity [9, IO] . Specific scheduling algorithms are emerging to manage the coexistence of interacting hardware and software parts in the global design [4, 111 as well as to optimize the interfaces [9] . Software performance modeling and compiling techniques are now entering as a substantial stage of the co-design flow both for reactive systems [ For our target application field, frequently requiring hard real-time performance and low-level characterization of U 0 interfaces, we found advantageous to consider the software at a lower level of detail with respect to C to predict the effects of the compiler and of the operating system.. The software generation is based on the use of a generic Virtual Instruction Set (VIS) acting as an intermediate language between OCCAMII and the target CPU assembly aiming at capturing the minimum set of features shared by microcontrollers for embedded applications. According to the needs of the application field, requiring simplicity and predictability, a static schedule approach with a coroutine scheme has been adopted as the target software structure. The VIS model is useful both for evaluation and synthesis purposes and it is conceived to achieve the following goals: 0 simulation of the mixed hardware-software system within the same VHDL simulation environment by using simplified non-proprietary microprocessor models [ 151. extension of the analysis to cover also multiple processor families with minimal user intervention; good predictability of the final running software behavior and cost; integrated design flow able to cover the entire system synthesis in terms of hardware, interfaces and software. The actual use of VIS within the TOSCA environment provides similar properties of flexibility and retargeting typically reserved to high level programming languages, In fact, it is possible to map the VIS code onto different target assembly instruction sets while accurately predicting the performance of the CPU and I/O. Even if the VIS code is readable, it has to be pointed out that user should interact with it only during the final system-level co-simulation, the maintenance of the system has to be performed at system-level.. The paper is organized as follows. After a brief description of the target architecture we are considering to physically implement the system, the problem of scheduling the software-bound modules identified during the system exploration is detailed. In particular, section 3 presents an overview of our solution based on a static scheduling using the information obtained during the VIS generation, detailed in section 4. The main features of the VIS notation are introduced by means of a small illustrative example. The paper is concluded by an outline of the results of our researches in the field of software modeling and generation for embedded systems and by the guidelines of current investigation effort. A design methodology (which is currently part of the TOSCA co-design environment) to synthesize the software-bound sub-systems of control dominated embedded applications has been presented.. The model adopted to represent the software has been discussed, based on the concept of Virtual Instruction Set.. Such a level of representation has been adopted since it provides the following advantages with respect to the use of high-level languages: fine-grain predictability of software cost and performance; code retargeting; hw-sw co-simulation for different microprocessor families with minimal customization effort based on the use of VHDL models (see [ 151 for more details). The operating system has been also discussed in the paper. A static schedule algorithm has been adopted, based on the use of the information derived from the VIS model to assure the fulfillment of real-time constraints.. Evaluation of these strategies has been performed on a number of medium size examples, allowing the identifi cation of the optimal solution in a reduced time. We are currently developing a large telecom example to test all features of the proposed approach. Furthermore we are extending the model to consider also pipelined microprocessors and to analyze the power consumption of the software as one of the figures of merit driving the co-design activity.

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


Supporting effective health and biomedical information retrieval and navigation: A novel facet view interface evaluation Exploratory searching Biomedical information retrieval systems Cluster and facet view Search interface evaluation a b s t r a c tThere is a need to provide a more effective user interface to facilitate non-domain experts' health information seeking in authoritative online databases such as MEDLINE. We developed a new topic cluster based information navigation system called SimMed. Instead of offering a list of documents, SimMed presents users with a list of ranked clusters. Topically similar documents are grouped together to provide users with a better overview of the search results and to support exploration of similar literature within a cluster. We conducted an empirical user study to compare SimMed to a traditional document list based search interface. A total of 42 study participants were recruited to use both interfaces for health information exploration search tasks. The results showed that SimMed is more effective in terms of users' perceived topic knowledge changes and their engagement in user-system interactions. We also developed a new metric to assess users' efforts to find relevant citations. On average, users need significantly fewer clicks to find relevant information in SimMed than in the baseline system. Comments from study participants indicated that SimMed is more helpful in finding similar citations, providing related medical terms, and presenting better organized search results, particularly when the initial search is unsatisfactory. Findings from the study shed light on future health and biomedical information retrieval system and interface designs. More people search for health related information through the Internet [1] . The large number of health websites and broad range of topics covered make the web an important resource for people seeking health or biomedical information. Some medical information websites such as PubMed, 1 which traditionally target healthcare practitioners and professional researchers, are now more frequently visited by general users looking for authoritative biomedical information [2, 3] . According to the National Library of Medicine, in 2002 one third of PubMed's users were general public users [4] . Studies have showed that general users search differently than practitioners and professionals, and lack the domain knowledge often necessary to search a medical database [4] . It is important for PubMed's interface to accommodate both professional and non-domain expert users. Many studies have been conducted examining how physicians and clinicians use medical databases [5] [6] [7] [8] . Their information needs and concerns are different than general users [4, 8] . For example, medical terminology is a main problem for the general users when researching health information [9] . However, few studies have examined how biomedical database interfaces affect general users' health information search. Lau and Coiera have done some research regarding general users' health information seeking behaviors, but their area has focused on biases present when searching for information and methods to debias interfaces and interpretations in order for users to retrieve accurate health information [10, 11] . From a different perspective, in this study we explored how clustering technology based interface affects general users' health information access in navigational and exploratory search tasks.. According to Marchionini's model, exploratory searches involve learning and investigating, and are conducted for question investigation and topic exploration [12] . Exploratory searching allows users to find relationships between medical literatures and provides a more holistic view of the information [13] . A study of PubMed queries revealed that most users conduct ''informational queries'' [4] , which are similar to exploratory search in that users are looking for information on topic, not a specific citation. The research challenge is thus how to improve the interface design to support effective exploratory searches in health and biomedical databases [9, 14] .. In this paper we applied clustering technology in health and biomedical information retrieval to facilitate general users' exploratory searches, which to our knowledge has not been fully examined in previous research. The idea is to organize search results as a list of ranked topic clusters instead of a list of citations. This design offers both an overview of the results and a focus-view of a specific topic by allowing users to further mine an area of interest. Based on this model, we designed and implemented a new prototype cluster-based online search system, which we called SimMed. We evaluated the effectiveness of SimMed compared to a baseline system we developed in an empirical user study. We examined how SimMed influenced users' search behaviors and what new search strategies users applied in explorative health information retrieval.. The remainder of this paper is organized as follows: After a brief literature review for background information, we first introduce the SimMed system, including its user interface, search engine, and topic clustering algorithm. In the methodology section of the evaluation study, we describe the data corpus, study participants, and study procedure. Findings from the study are presented in the results and analysis section. We conclude the paper with discussions and implications. ''Research tools critical for exploratory search success involve the creation of new interfaces that move the process beyond predictable fact retrieval'' [12] .. The purpose of this study is to develop a new cluster ranking based health and biomedical information retrieval system and examine its advantages and disadvantages for exploratory search tasks. The new system, called SimMed, groups topic similar documents together in order to provide users with both over-and focus-views. Users not only were able to rapidly scan the result list organized by clusters for an overall understanding of the scope and nature of the results, but could also focus on an interesting topic and further explore related documents.. The results from our evaluation study with 42 participants indicated that the new interface is more effective and helpful than the traditional ranking list interface. Users spent significantly more time interacting with SimMed and reported more topic knowledge increases. User comments indicated that SimMed was helpful in finding more relevant documents, organizing search results, and providing related medical terms. This conclusion is particularly true when the initial search is unsatisfactory.. The novelty of our study is to develop a new cluster-based health and biomedical information retrieval system to facilitate non-domain expert users exploring medical information using authoritative databases such as MEDLINE. By supporting different views of the search results and richer user-system interactions, SimMed provides an effective alternative to the traditional document ranking list based search result presentation. In addition, the findings from our usability study reviewed the search strategies employed by non-domain expert users that can be helpful in future system and interface designs. Finally, our evaluation metrics, especially the proposed inversed minimum clicks (IMC) index, can be useful for performance evaluations on other similar health and biomedical information retrieval systems. In this study we compared SimMed with the traditional document ranking list interface for health and biomedical information exploratory search tasks. Both quantitative and qualitative data, as well as the relevant document accessibility measured by Inverted Minimum Clicks (IMC), were analyzed. In quantitative data analysis, we found that users' perceived topic knowledge changes when using SimMed were on average 20.19% higher than when using the baseline. Also, users were observed to engage more in user-system interactions in SimMed. Users spent significantly more time (10.89%) interacting with SimMed than with the baseline. An action analysis further supported this conclusion. An average of 3.55 more actions per topic search were observed when using SimMed. Cluster related operations attributed to most of these additional engagements. Furthermore, the user-system interaction component and shift pattern analysis also indicated that 46.76% of interaction shifts involved the cluster expanding operation.. Qualitative analysis from post-experiment questionnaires indicated that SimMed was more effective for the health information exploration tasks. We noticed that many participants frequently mentioned the helpfulness of SimMed in providing a better interface to find related terms. One challenge for general users (or non-domain expert users) who search for health information online is the vocabulary mismatch that occurs between consumers' natural language and the terminology used in professional medical literature [53] [54] [55] [56] . With relatively low domain knowledge regarding health and biomedical information, general users need assistance from the search system to better understand the related concepts and to optimize their search queries [57] . Studies have demonstrated that it is significantly difficult for general users to form effective queries using the traditional document ranking list interface [58] . In addition, users may not be able to discern how documents are related to each other, or know that unfamiliar terms contained in multiple documents discuss the same information [59] . By clustering similar documents into topic clusters with relevant keywords highlighted, SimMed helps in facilitating nonexpert users' information Searching and Browsing.. We codified user responses to find when they would expand a cluster to view more related documents. It is not surprising that users would click and open a cluster to further explore a topic when a relevant document was found. But we also noticed three other conditions under which users would like to open a cluster: when the relevant document failed to provide enough information, when the search results were unsatisfactory, and when the search subject was unfamiliar. These conditions were in line with Pratt's [27] research findings that categorization tools were more helpful when document ranking fails. From this perspective, we believe that SimMed also provides users with a better way to organize and more choices to manipulate the search results. When the results from the initial query were unsatisfactory, users took advantage of the additional cluster feature to do further exploration.. When navigating the search results, users may use two browsing strategies: depth-and breadth-first browsing [60] . With depthfirst strategy, users examine each item in the list starting from the top and decide immediately whether to open an interesting document to explore details. With breadth-first strategy, users look ahead at a number of list entities and then revisit the most promising ones for more details. SimMed supported both browsing strategies well. First, after a query search, in addition to the cluster representative document, the titles of three more top-ranked documents in the cluster were presented to improve the overview and facilitate the breadth-first browsing. Secondly, if users clicked the ''more relevant documents'' link, additional documents in the cluster were presented. It facilitated user's depth-first browsing by allowing users to drill down on a specific topic. Twenty-eight participants (66.67%) clicked the links and further expanded the clusters during the study. As compared to those who did not click the links, these 28 participants reported significant more topic knowledge changes and they spent much more time interacting with the search results. This implies that the retrieved documents organized in clusters were useful and helpful. For the 14 participants who did not expand clusters, nine of them (64.29%) still preferred SimMed to the baseline. Their comments showed that the additional three titles in each cluster are helpful. For example, one participant mentioned that she had ''more relevant answers on the first pages.'' In addition, users also appreciated the control and options offered by SimMed. One user commented that ''More choices just in case one would turn up to be relevant'' and ''at least made it seem like I had some leverage by suggesting related topics.'' In summary, SimMed helps users foraging for health information by providing a cluster-based overview of the search results and additional exploration opportunities through useful and relevant links. According to the Information Foraging Theory [61] , we believe SimMed was more attractive to users because of its information dense clusters. When users' initial search fails and they are not satisfied with the search results, SimMed gives an information ''scent'' encouraging users to expand to more relevant documents in the current information ''patch.'' Currently PubMed interface supports ''Also try'' and ''Related links'' functions to provide another type of ''scent'' to facilitate users' information foraging. If a query of ''breast cancer'' is issued, the ''Also try'' will provide ''metastatic breast cancer,'' ''breast cancer risk,'' ''breast cancer stem,'' ''triple negative breast cancer,'' and ''breast cancer review'' for users to further explore the related topics. After a document link is clicked, some more related links based on similarity to the selected document are provided under ''Related links.'' According to Lin et al., these links were accessed by roughly a fifth of all search sessions [29] . In addition to expanding the search scope, PubMed also supports ''Titles with your search terms'' function to allow users to effectively limit their search results. In SimMed we provide a different approach to encourage information foraging. We clustered the user's search results into groups based on similarity. These clusters provide users an overview of their search results. Users are encouraged to further explore related documents within a cluster by clicking the ''Click here to see more relevant documents'' link.. In this paper we introduced the concept of Inverted Minimum Clicks (IMC) to theoretically analyze the average cost to access relevant documents. The results indicated that on average significantly less clicks were needed to reach a relevant document using SimMed than using the baseline. This makes SimMed particularly effective and efficient for high recall search tasks (more exhaustive searches are needed). The improved relevant document accessibility was also supported by evidence from our analysis of search topic three and four, in which users spent less time on SimMed but obtained higher topic knowledge changes. Comments from users further confirmed such benefits. For example, ''I thought it brought more information up on the front screen and allowed me to drill down to relevant information quickly. It also allowed me to skip those results which did not relate to my search. '' As we mentioned previously, no training or tutorials were given for the new SimMed interface. In the study we found that users had no problem using the new cluster-based interface for their searches. We did not receive any complaints about SimMed from the participants' comments. Even though we did not ask questions in the study about the simplicity or difficulty of using SimMed, several participants indicated that it was more enjoyable to use SimMed than to use the baseline. For example, one participant commented that ''It made it easier to search because the database was being helpful in providing me related documents. It was a more pleasurable searching experience.' ' We also noticed a number of limitations of the study. One is that we only examined the effectiveness of SimMed design implemented based upon one clustering algorithm with one particular clustering number, and we only compared it to one type of baseline. It would be interesting to further investigate the best clustering algorithm in a specific retrieval context and compare its performance with other similar cluster or facet view interfaces.. Second, we chose to use OHSUMED dataset because of the large number of citations, the exploratory search tasks, and a set of ground truth for these tasks. We acknowledge that OHSUMED is not current but given the time and labor constraints, we were unable to create a dataset to specifically match our user group. Third, the tasks provided by OHSUMED asked study participants to imagine a given scenario, and their engagement with the system may have been affected by the level of role-playing. In hindsight, simpler, more relevant search tasks could have yielded better results. In the future we can further explore users' search behaviors in fact finding lookup search tasks using more straightforward yes/no questions such as those used in studies by Westbook et al. [7] and Lau and Coiera [11] .. The third limitation is that this study focused on health information exploratory tasks by general users with post-secondary education. Those users represent only a portion of the population that uses PubMed. In the future it would be informative to also look at other user groups' exploratory searches using SimMed. Users search the web to obtain information for knowledge acquisition, known item finding, comprehension and interpretation, comparison, aggregation and integration, verification, question answering, and socialization [12] . These different search tasks can be roughly classified into two main categories: lookup and exploratory searching. While lookup searches are related to finding an item, exploratory searches arise when users ''lack the knowledge or contextual awareness to formulate queries or navigate complex information spaces, [and] the search task requires browsing and exploration'' [15] . The usual strategy for exploratory searching is to submit a tentative query, explore the retrieved information, selectively browse interesting items, and then decide what to do next [12] . Two typical technologies that facilitate exploratory searching are facet view interface and similarity browsing.

O O O O O O O O O O O O O O O B I B I I I B I I I B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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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The square root law does not require a linear key Square root laws are theorems about imperfect steganography, embedding which fails to preserve all statistical properties of covers. They show that, in various situations, capacity of covers grows only with the square root of the available cover size. In a paper given at this conference last year [14], we showed an important caveat: when the sender's and recipient's shared embedding key determines the embedding path, its length must be at least linear in the size of the hidden payload to avoid their enemy exhausting over all possible sets of locations. It was left open to show that a linear key is sufficient.There is no necessity, however, for the recipient to know exactly which locations were changed during the embedding process. In this paper we remove that condition, allowing the embedder to combine more than one cover location to convey one bit of payload. As long as the embedder lives beneath the classic square root law bound, we can do more than prove the sufficiency of a linear key: we can even show that asymptotically perfect steganographic security is possible with no key at all. Furthermore, by computing Steganographic Fisher Information, we can show that the keyless embedding tends to perfect security at least as fast as the "ideal" embedding, which requires an unfeasibly large key to spread payload uniformly at random over the cover. Finally, we show asymptotic perfect security of a simple matrix embedding, which allows payload capacity of order √ n log n to be achieved. The square root law is a collection of mathematical results about imperfect steganography, which is when the embedding fails to preserve exactly all statistical properties of covers. They apply in different mathematical models, with the common theme that the capacity of covers grows only with the square root of the available cover size. Such theorems can be found, for example, in [10, 12] in the case of multiple independent covers and [5] in the case of single covers under the assumption that the source is a Markov chain satisfying certain conditions.. In a paper published at this conference last year [14] , we showed an important limitation to the simplest square root law for single covers, whose elements consist of independent and identically distributed (i.i.d.) elements, whereby the sender and recipient are required to share a large enough secret key to make it impossible for their enemy to guess the embedding locations used: it was shown that a secret key of size at least linear in the hidden payload is required, otherwise detection is asymptotically certain no matter how slowly the payload size grows with the cover size. We dubbed the result, and the paper,"the square root law requires a linear key." It was conjectured, but not proved, that a secret key linear in the payload is sufficient; at that stage, all that could be proved was that a key of order m log m bits, where m indicates the payload size, is sufficient. This paper changes the hypotheses very slightly, allowing the embedder to combine more than one cover location to convey one bit of payload. This means that the recipient, and hence the enemy, need not know the exact locations which were changed. In this situation we can go even further than proving the sufficiency of a linear key, in fact showing that no key is required for steganographic security as long as the embedder lives below the square root law bound. (A cryptographic secret key would still be needed to keep the content of the payload from the enemy.) This parallels a result by Ryabko [16] , which applies in the very different context of perfect steganography. The results in [16] demonstrate that no stego key is needed even when embedding an asymptotically maximum capacity payload, though the case of perfect steganography is completely different and the capacities are linear in the cover size.. The paper proceeds as follows. We outline our notation (Subsect. 1.1) and prove a useful convergence result from pure probability theory (Subsect. 1.2). In Sect. 2 we recapitulate the classic square root law for i.i.d. covers, along with its caveat about key length, as described in [14] . We examine options for locating the payload without informing the recipient (or enemy) exactly where it can be found, and prove new results about an old embedding scheme for which no steganographic key is required at all, in Sect. 3 . The rate of convergence to perfect security is related to Steganographic Fisher Information [13, 4] , and we examine this in Sect. 4: we are able to prove that the keyless embedding is equally secure as uniform embedding requiring unfeasibly large keys, so that no security is lost. The keyless embedding also adapts naturally to a more efficient encoding, allowing payload size superlinear in the number of embedding changes via matrix embedding [8] , and this is examined in Sect. 5. Finally, Sect. 6 closes the paper with a discussion of the new results' significance, and possible extensions.

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Eco-innovative design method for process engineering Due to the environmental issues, innovation is one way to challenge eco-friendly technologies, create new process options which are needed to meet the increasing demands for sustainable production. To accelerate and improve eco-innovative design, there is a need for the computer aided eco-innovation tools to support engineers in the preliminary design phase. Currently, several computer aided innovation tools with a clear focus on specific innovation tasks exist but very few of them deal with the eco-innovation issues. Therefore the purpose of this paper is to present the development of a computer aided model based preliminary design methodology focused on technological eco-innovation for chemical engineering. This methodology is based on modified tools of the structured TRIZ theory. The general systematic framework gives the same level of importance, to the technological and environmental requirements during the conceptual design phase. Integrating environment oriented design approach at the earliest, in the design phase, is essential for product effectiveness and future development. The methodology employs a decomposition based solution approach in hierarchical steps by analysing the problem faced, formulation of the problem and the generation of possible and feasible ideas. At each step, various methods and tools will be needed. In this paper some existing tools are adapted to chemical engineering and some tools of the structured TRIZ theory are modified and improved to build a specific methodology oriented towards the increasing technological complexity and environmental issues of current designs. Undoubtedly, the selection of materials and substances for a particular generated concept, mainly affects the structure, mechanical factors (processability and dimensions) and the environmental impact. In order to deal with these environmental criteria, the resources and their impacts are considered in the upstream phase of the design process and are introduced as constraints in our model. To highlight its capabilities, the methodology is illustrated through a case study dedicated to tars and ashes issues in biomass gasification.

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


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Mechanism change in a simulation of peer review: from junk support to elitism Abstract Peer review works as the hinge of the scientific process, mediating between research and the awareness/acceptance of its results. While it might seem obvious that science would regulate itself scientifically, the consensus on peer review is eroding; a deeper understanding of its workings and potential alternatives is sorely needed. Employing a theoretical approach supported by agent-based simulation, we examined computational models of peer review, performing what we propose to call redesign, that is, the replication of simulations using different mechanisms. Here, we show that we are able to obtain the high sensitivity to rational cheating that is present in literature. In addition, we also show how this result appears to be fragile against small variations in mechanisms. Therefore, we argue that exploration of the parameter space is not enough if we want to support theoretical statements with simulation, and that exploration at the level of mechanisms is needed. These findings also support prudence in the application of simulation results based on single mechanisms, and endorse the use of complex agent platforms that encourage experimentation of diverse mechanisms. Peer review at the center of the research process Science has developed as a specific human activity, with its own rules and procedures, since the birth of the scientific method. The method itself brought upon unique and abundant rewards, giving science a special place, distinct from other areas of human thinking. This had been epitomized in the 1959 ''two cultures'' lecture, whose relevance is testified by countless reprints (see Snow 2012), presenting the natural sciences and the humanities as conflicting opposites, evidenced by their misunderstandings and the resulting animosity in the world of academia. 1 Famous studies on science (the first example that comes to mind is that of Kuhn 1996) have been carried out with the tools of sociology and statistics. In the meantime science, co-evolving with society, has developed and refined a set of procedures, mechanisms and traditions. The most prominent about them is the mechanism of paper selection by evaluation from colleagues and associates-peers, from which the name peer review-, which is so ingrained in everyday research process to make scientists forget its historical, immanent nature (Spier 2002) .. Nowadays, simulation techniques, and especially social simulations, have been proposed as a new method to study and understand societal constructs. Time is ripe to apply them to science in general and to peer review in particular. Simulations of peer review are starting to blossom, with several groups working on them, while the whole field of scientific publications is undergoing remarkable changes due, for instance, to the diffusion of non-reviewed shared works, 2 and to the open access policies being enacted after the 2012 approval of the Finch report from the UK government. These are only symptoms of the widespread changes brought about by the information revolution, which has transformed general access and dissemination of content, and specifically access and dissemination of science. In the future, the paper as we know it might be superseded by new forms of scientific communication (Marcus and Oransky 2011) . The measures we use to evaluate scientific works will also keep changing. Consider for instance the impact factor, not yet fully superseded by the h-index, which in turn is likely to be substituted by alternatives as the P top 10 % index (Bornmann 2013) , or complemented by usage metrics. The simplest of the latter, paper downloads, has already been shown to exhibit unique patterns; reading and citing, apparently, are not the same (Bollen et al. 2009 ).. In the meantime, collective filtering (e.g. reddit) and communal editing (e.g. Wikipedia) have found a way to operate without the need of the authority figures that constitute the backbone of peer review. Academia, on the contrary, still shows a traditional structure for the management of paper acceptance, maintaining a ''peer evaluation'' mechanism that is the focus of the present work. We note in passing that the peer review mechanism is only one of the many aspects of collective scientific work, which has been little studied as such (see for a recent exception Antonijevic et al. 2012) ; it is only one of a number of intersected feedback loops, serving the purpose of quality assurance between others.. Peer review, as a generic mechanism for quality assurance, is contextualized by a multiplicity of journals, conferences and workshops with different quality requests, a kind of multilevel selection mechanism where the pressure to improve quality is sustained through the individualization of a container-for now we will consider only journals as representative of this-and the consequent pressure to defend its public image (see Camussone et al. 2010 , for a similar analysis).. Journals as aggregates of papers, then, play two other important roles: first, as one of the most important (although indirect) elements in deciding researchers' career, at least for the current generation of researchers, that are often evaluated on the basis of their publications on selected journals. Second, journals play a role in the economy of science: their economic sustainability-or profit, as shown by the recent campaign on subscription prices 3 -depends on quality too, but just indirectly; profits would be warranted as well in a selfreferential system, based not on quality but on co-option.. At the core of the above intersected feedback loops lies the mechanism of peer evaluation, that is based on custom and tradition, leveraging on shared values and culture. The operation of this mechanism has been the target of much criticism, including accusations of poor reliability, low fairness and lack of predictive validity (Bornmann and Daniel 2005) even if this calculation often lacks a good term of comparison. Declaring a benchmark poor/low with respect to perfect efficiency is an idealistic perspective, while a meaningful comparison should target other realistic social systems. All the same, we must mention that some studies have demonstrated the unreliability of the journal peer review process, in which the levels of inter-reviewer agreement are often low, and decisions can be based on procedural details. An example is reported by Bornmann and Daniel (2009) , who show how late reviews-that is, reviews that come after the editors have made a decision-, would have changed the evaluation result in more than 20 % of the cases. Although a high level of agreement among the reviewers is usually seen as an indicator of the high quality of the process, many scientists see disagreement as a way of evaluating a contribution from a number of different perspectives, thus allowing decision makers to base their decisions on much broader information (Eckberg 1991; Kostoff 1995 ). Yet, with the current lack of widely accepted models, the scientific community has not hitherto reached a consensus on the value of disagreement (Lamont and Huutoniemi 2011; Grimaldo and Paolucci 2013) .. Bias, instead, is agreed to be much more dangerous than disagreement, because of its directional nature. Several sources of bias that can compromise the fairness of the peer review process have been pointed out in the literature (Hojat et al. 2003; Jefferson and Godlee 2003) . These have been divided into sources closely related to the research (e.g. reputation of the scientific institution an applicant belongs to), and sources irrelevant to the research (e.g. author's gender or nationality); in both cases the bias can be positive or negative. Fairness and lack of bias, indeed, is paramount for the acceptance of the peer review process from both the community and the stakeholders, especially with regard to grant evaluation, as testified by empirical surveys.. Finally, the validity itself of judgments in peer review has often been questioned against other measures of evaluation. For instance, evaluations from peer review show little or no predictive validity for the number of citations (Schultz 2010; Ragone et al. 2013) . Also, anecdotal evidence of peer review failures abound in the literature and in the infosphere; since mentioning them contributes to a basic cognitive bias-readers are bound to remember the occasional failures more vividly than any aggregated data-we will not delve on them, striking as they might be. 4 Some of the most hair-rising recent failures (Wicherts 2011) recently raised the attention to the emerging issue of research integrity, that converged in documents such as the Singapore statement.. 5 These documents highlight the hazard of cheating in science, by exploiting the loopholes of peer review. This behavior goes under the name of rational cheating.. Rational cheating is defined in (Callahan 2004 ) as a powerful force, often augmented by rational incentives for unethical misconduct. Factors like large rewards for winners, perception of diffused cheating, limited or non-existing punishments for breaking the rules put pressure on researchers to work against the integrity and fairness required from themselves. Rational cheating is currently believed to be an important factor, potentially contributing to the failure of peer review and with that, to the tainting of science by cronyism. In this work, we aim to contribute to the understanding of rational cheating in peer review. Before moving on, however, we point out how the peer review mechanism has never been proved-or, for the matter, disproved-to work better than chance. Indeed, at present, little empirical evidence is available to support the use of editorial peer review as a mechanism to ensure quality; but the lack of evidence on efficacy and effectiveness cannot be interpreted as evidence of their absence (Jefferson et al. 2002) .. This might sound strange, given the central position of peer review in the scientific research process as it is today. Why this lack of attention for such a crucial component? The answer, besides the habituation component, is probably to be found in the nature of the peer review as a complex system, based on internal feedback, whose rules are determined by tradition in a closed community. In this paper, we aim to contribute to an undergoing collective effort to understand peer review, in order to improve it, preparing the ground for its evolution by reform. In this paper, we replicated results from Thurner and Hanel (2011) by using a different approach: we employed independent agents (Wooldridge 2009; Bordini et al. 2007 ), a different structure of multiple conferences , and different quality distributions: we call this approach redesign. Notwithstanding those differences, we obtained a clear qualitative replication of the original results.. Once the replication is established, our approach to modeling (with explicit, ''intelligent'' agents as opposed to spin-like agents) naturally made us want to test the solidity of the result with respect to the employed mechanisms. With respect to mechanism change, the result showed surprisingly fragile. Simple, plausible changes in the mechanisms showed that peer review can withstand a substantial amount of cheaters, causing just a graceful decline in total quality. By not favoring the publication of low-quality papers, peer review becomes more robust and less random. By moving from an accept/reject review to a numerical score, hence accepting those papers whose average review value is greater than the acceptance value of the conference, the initial drop disappears as well. Remarkably, a further change that enables a plausible restraint mechanism for cheaters results in an inversion of the tendency, from decrease to increase, generating an unexpected elitist effect (see Fig. 8 for a summary of these results).. Our conclusion is then twofold. First, peer review and rational cheating show in our model a complex interaction: depending on the mechanisms employed, it can cause a quality collapse, a graceful decay, or even a slight quality increase (elitist effect).. Secondly, we point out mechanism exploration as a key challenge for agent-based modeling and simulation. Especially for social simulation, models should always control for mechanism effect, at least for those mechanisms that appear to be plausible at the micro level, in the description of the agent processes. The above presented results give indications in two main directions, concerning the object of study, and the method applied; peer review, and agent-based modeling.. For peer review, we have confirmed that unfair play (here, rational cheating), in a first approximation, is likely to impact the performance of the review process rather heavily. However, by modifying the mechanisms employed (see a comparison for all scenarios in Fig. 8 ), we have also been able to lessen this impact, and even to reverse it when we come to a specific scenario (see ''Restrained cheaters'' section). This evidence points out to a more complex role of cheating in an evaluation system, ranging from sabotaging effect, to a sort of ''useful idiot'' role. In turn, this suggests a multi-level approach for containment of cheaters. Indeed, cheating behavior could be directly addressed at the individual level with enforced norms, and/or it could be made harmless by using the opportune mechanism at the collective level.. Concerning its applicability to concrete situations, we are aware that the model presents some important weaknesses; first of all, the attribution of a single quality value to papers, which in this version of the model is directly accessible, without noise, to the reviewers. We nevertheless believe that these weaknesses are justified as first approximations; in Fig. 8 Average quality of papers for different mechanisms. Only the replication scenario drops sharply for a small amount of rational cheaters addition, they have been required for comparability with the TH-HA model that inspired us. Removing some of these weaknesses, for example by carrying on validation with data collected from a journal or conference, would be an interesting topic for future studies. However, notwithstanding the extensive informatization of the peer review process, actual data are still hard to obtain due to privacy issues and to uncertain copyright status. Peer review text and evaluations remain, curiously, one of the few online activities that are performed, for the most part, without explicit acceptance of copyright/ownership transfer clauses. As a consequence, published data for validation appears limited and highly aggregated (see Ragone et al. 2013 for a discussion).. Should we be reassured and conclude that cheating is manageable? Hardly so. When reading the results under the light of an evolutionary approach, it is not easy to say which situation-between the one in Fig. 3 and in Fig. 5 , for example-is the most dangerous. While in the first one the sharp decrease is easily detectable, the second case gives ''generous'' rational cheating a chance to invade the system being undetected until a large amount of reviewers are turned into rational cheaters, reminding of the cooperative invasions of TFT populations by genetic drift (Nowak and Sigmund 1992) . The study of this phenomenon requires an evolutionary simulation, perhaps under group selection, and will be the object of future work.. For what concerns the applied methodology, that is, agent-based modeling, and in particular a BDI approach, we found it to be crucial for letting us focus on the mechanisms as defined above (see ''Agent-based simulation and mechanisms'' section). Mechanismbased redesign motivated us to explore the variations presented above, pointing out the fragility of the initial result against this class of changes.. In our exploration, we did not check only the mechanisms that we have illustrated in this paper. The results that we have presented are a representative sample of a much larger set of experiments that we have been running, introducing variations in the mechanisms; in general, results follow one of the presented patterns. Other mechanisms that we have tested but not reported for matters of space include using three reviewers (rp = 3) or requiring unanimous consensus from reviewers before accepting a paper. Using three reviewers invalidates substantially the Thurner and Hanel (2011) mechanism that applies dice rolling when the result is uncertain (with two yes/no reviews, uncertain results are bound to happen frequently) and that was one of the causes of the sharp drop in Fig. 3 . In this paper, this already happens for the scenario where conferences decide (''Conferences decide '' section, results in Figs. 5, 6) . Requiring unanimity does not change the results qualitatively.. This begs the general questions: is mechanism exploration useful? Is it necessary? Is it feasible? In the case that we present, analyzing the results obtained with different mechanisms has been certainly useful. More in general, we believe it to be necessary for all the simulations aimed to describe society. Indeed, society consists for large part of evolved and/or agreed upon mechanisms. Thus, in order to get a better simulative understanding of society, in the spirit of recent attempts as the FuturICT initiative (Helbing et al. 2012; Paolucci et al. 2013) , exploration of alternative mechanisms should necessarily be performed. The last question is perhaps more difficult to answer. Running consistent exploration of the parameter space gives agent-based simulation a hard time -and parameters are, after all, just numbers: what about the much wider space of possible algorithms?. A tentative answer, which is all we can offer here, would touch the difference between all possible mechanisms and the likely ones, perhaps leaning on a micro level plausibility argument. In perspective, simulations that explore different plausible mechanisms, perhaps supported by crowdsourcing mechanisms (Paolucci 2012) .

B I O O O O B I 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 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 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 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 B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 O O O O O O 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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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 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 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 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 B I O O O O O O O B I 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 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 B I O B I O O O O O 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Life cycle data management: first step towards a new product lifecycle management standard Nowadays, companies need to focus on efficiency problems, assuring, at the same time, products to be compliant with quality standards, providing a full product support and managing suppliers' and customers' relationships. According to these needs, product is reassuming a central role as enterprise value creator. In literature, many authors agree that a correct and effective management of the product lifecycle could reduce costs by gaining, meanwhile, a higher customer satisfaction and brand loyalty. This kind of approach needs an integrated management of all product-related information and calls for a wide standardisation activity. Today, a data model, capable of collecting all the information regarding the product along its lifecycle, is still missing. This article aims at providing a concrete answer to this urgent industrial need, presenting the steps taken towards the creation of a new product lifecycle management standard, named life cycle data management. The development of this new standard is an effort to provide an effective and reliable information model to manage all product lifecycle data and information. In today's competitive world, companies are ever more stressed and subjected to high market requests. Customers pay more and more attention to products' quality and related services. The best product, at the lowest price, at the right time and place is the only key factor for success for the modern global enterprise. In order to maintain or gain the needed competitive advantages, modern companies have to manage themselves along the two main directions: (1) improve internal and external efficiency, reducing all the nonrelevant costs and (2) foster innovation of product, process and organisation (Stark 2006) .. According to these needs, enterprises are refocusing on their core competences, while the product is becoming again, after the 1990s new economy experiences, the enterprise value creator and the whole production process is reassuming its role. In this way, within the globally scaled scenario, product management is composed of complex, overlapped processes. Product development might ever more take into account improved customers' tastes and requests in a shorter time-to-market, while the related engineering activities are consequently stressed and inefficiencies in the production and distribution functions are not tolerated.. Thus, the 'product' management is becoming unavoidably a key aspect, creating such a 'product centric' or 'product-driven' approach. This kind of approach needs an integrated management of all the information regarding the product (Garetti and Terzi 2004) .. Unfortunately, today a data model, capable to collect and manage in an effective and easy way all product-related information along the entire lifecycle, is still missing. Namely, only few existing standards are capable of supporting the whole set of product lifecycle phases and where it is possible their use is fairly complex (Cassina et al. 2009 ).. The purpose of this article is to provide a concrete answer to this gap, moving the first step towards the creation of new product lifecycle management (PLM) standard capable to manage all product information along its lifecycle. Section 2 presents the state of the art of product lifecycle modelling, focusing on the standards for product data representation. Section 3 focuses on the overall framework and the process used for the creation of the new standard, describing in detail the three proposed developing phases.. Then, Section 4 provides a deep description of the developed standard, focusing on its aim, scope and structure. Section 5 presents standard validation, focusing on one of the 10 application scenarios that have been used in testing the data model. Finally, Section 6 concludes the article, giving also a view of the further developments that can be done. This article has presented the first step taken towards the creation of a new PLM standard: LCDM AP, capable to follow the product along its entire life.. Firstly, it has provided a detailed comparison between objects of data model developed within the PROMISE project and semantic constructs of the IRs of ISO 10303, which are standardised building blocks for the representation of product lifecycle data.. Then, it focuses on the development of data structures, which are the fundamental parts of the new AP, aiming at collecting all information needed for the various actors involved in different product lifecycle stages.. This standardisation effort can be seen as a concrete starting point towards a widespread standardisation activity, aiming at fully developing the proposed AP.

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