Pseudo-NK: an Enhanced Model of Complexity

This paper is based on the acknowledgment that NK models are an extremely usefu l tool in order to represent and study the complexity stemming from interactions among components of a system. For this reason NK models have been applied in many domains, such as Organizational Sciences and Economics, as a simple and powerful tool for the representation of complexity. However, the paper suggests that NK suffers from un-necessary limitations and difficulties due to its peculiar implementation, originally devised for biological phenomena. We suggest that it is possible to devise alternative implementations of NK that, though maintaining the core aspects of the NK model, remove its major limitations to applications in new domains. The paper proposes one such a model, called pseudo-NK (pNK) model, which we describe and test. The proposed model appears to be able to replicate most, if not all, the properties of standard NK models, but also to offer wider possibilities. Namely, pNK uses real-valued (instead of binary) dimensions forming the landscape and allows for gradual levels of interaction among components (instead of presence-absence). These extensions provide the possibility to maintain the approach at the original of NK (and therefore, the compatibility with former results) and extend the application to further domains, where the limitations posed by NK are more striking.NK model, Simulation models, Complexity, Interactions

Laboratory for Simulation Development

This document contains a description of the main purposes and characteristics of Lsd. It discusses the problems related to the use of simulations in social sciences and describes how Lsd tackles these problems. In general, the use of simulations is constrained by two kinds of problems: difficulties in building the programs and difficulties to make use of other people’s programs. Lsd proposes a system to facilitate both aspects of the use of simulation models. This document is mainly concerned with the use of simulations by unskilled computer users, and describes in detail how Lsd can be successfully used to explore and use a model without requiring any programming knowledge. Though it is not the main concern of the document, there are also few hints on the aspect of simulation program building.Programming, Simulation models

Markets fo Heterogeneous Products: a Boundedly Rational Consumer Model

The paper is based on the acknowledgement that properties of markets stemming from features of demand are too frequently overlooked in the economic literature, and a re-balancing is necessary to properly account for theoretical and empirical phenomena. We sustain that one of the most relevant reasons for the neglect of the role of demand is the lack of an adequate representation of consumers. This claim is particu- larly relevant for evolutionary economics since its critique to the mainstream approach stopped at the representation of firms. The standard utility maximization approach to consumers? theory is even less defensible than the related assumption of producers? rationality, given the lack of competitive pressure on consumers. As a contribution to this theoretical gap, the paper presents a model for consumer based on the assumption of bounded rationality and inspired to the literature on experimental psychology. The proposed model can be applied to multi-dimensional products/services and relies on intuitive and potentially observable parameters, allow- ing for a wide range of theoretical and empirical applications. Moreover, the intrinsic structure of the model provides a clear definition of preferences, meant as ex-ante decisional criteria, distinguished from post-hoc justification of any decisional result. Though structurally simple, the proposed model is very flexible and allows for a clear exploration of the impact of specific demand features on the produced results. Several experiments show that the model can be successfully applied both to generate standard results and to implement complex configurations such as those of generated by large markets with heterogeneous products. Among the results presented, the most relevant concerns the identification of two classes of market segmentation, generated by the identical suppliers and demand?s ex- ogenous factors, but different consumers? decisional mechanisms. The results produced are observationally equivalent, but are shown to have radically different properties, and are proposed as initial elements of a taxonomy for the classification demand classes, likely to explain common properties across different markets.Evolutionary Economics, Consumer Theory, Bounded Rationality, Marketing and Preferences, Simulation Models, Market Structure

Laboratory for Simulation Develpment - LSD

LSD is one of many programming languages designed to develop agent-based models. LSD implements time-driven models expressed in formats equivalent to discrete systems of equations, where each equation computes the value of a generic instance of a variable at a generic time step. LSD models are therefore extremely parsimonious in terms of details that users must provide to the system. When a model has been described, the system automatically generates a working program implementing the model, endowed with a complete set of interfaces for any possible operation on the model. The major feature of is that users can rely on an automatic scheduling system and on automatic retrieval of data required for the equations. Such features are particularly attractive in complex, multi-herarchical models. They permit even non- expert programmers to develop even relatively complex models with minimal training. The systems interfaces guarantee the complete control of the model at building, at run-time and at post-simulation analysis, facilitating debugging, revisions and detailed analysis of model results, which are useful properties especially when developing large models for ambitious projects. The design of LSD is based on an "open architecture", so that LSD can be used to implement any type of model, including even-driven models and models based on customized data structures. The intrinsic modularity of LSD models make them easily scalable facilitating the development of highly complex models by demanding users. The underlining layer of C++, accessible by the users, allows the inclusions of external libraries or of complex data structures, besides an extreme speed and dimensions of the model. This work reports on the major features of the design of LSD outlining its most prominent advantages for users of simulation models in research, particularly for agent- based simulations.Simulations models, programming languages

Rubber/crete: mechanical properties of scrap to reuse tire-derived rubber in concrete. A review

The recycling of waste tires is of paramount importance for the environment protection and for economic reasons too. The amount of scrapped tires in USA reached 550 million tires per year and it is still raising. In the EU even higher numbers are estimated reaching the value of 1 billion tires per year. Disused tires are transformed into wastes, causing a highly negative environmental impact. Tire disposal mainly involves highly polluting treatments (e.g. combustion processes for the production of fuel oil), while only a small percentage of waste (from 3% to 15%) is destined for less invasive treatments such as powdering. In this work we will see some previous study in which waste tire powder of different ranges used in combination with cement concrete mixture, providing a final product with suitable mechanical properties for the chosen engineering application. As results of previous work recorded that reaching a good compressive strength can be achieved through replacing 30% of powder tire with crush sand. First, the percentage of aggregation between crumb rubber and crushed sand increases the compressive strength will drop extremely. Second, aggregation replacement between crumb rubber and crushed sand lower than 30 % can show reduction in density at around 10% leading lower in its weight. Third, modulus of elasticity depends on the percentage of addition, the more rubber added to concrete the lesser it will be. In addition to that, the lower the toughness of concrete means the higher strength. Moreover; addition of rubber to concrete increases the toughness value of it (1)

Production structure and economic fluctuations

We aim at contributing to the debate on the mechanisms and properties of economic fluctuations. We consider a crucial aspect among many thought to influence this ubiquitous and extremely relevant phenomenon: the interaction structure that characterises the organisation of production, that is, the production relation among sectors of a system. We build — and simulate — a very simple model representing an input–output system where sectors/firms adapt production and desired levels of stocks. Their output serves both an exogenous final demand and the intermediate demand solicited by the other sectors of the system. Series of simulation runs allow to derive relevant and non–obvious conclusions concerning the levels and, more importantly, the volatility of economic activity, as an outcome of the same, inherent, economic structure. We claim that the results that we obtain through the highly abstract representation we use, provide useful intuitions on the working of economic cycles, to be later integrated by further studies. As a by–product of our analysis, we also suggest that the methodology we adopt can provide valuable insights by allowing a detailed analysis of the time path generated in the artificial systems, and there- fore assessing with precisions the same mechanisms that affect real–world systems. The natural following step, left for further research, is to investigate how those mechanisms are empirically generated

Basalt short fibers dispersion and fabric impregnation with Magnesium alloy (AZ63). First results

Magnesium is one of the lightest structural metals used in different industrial sectors and many works in the literature have studied its reinforcement by filler addition. Basalt fibers are natural fillers that have good mechanical properties, excellent resistance to high temperatures, and lower cost than carbon fibers. Considering this, in recent years, they have been increasingly used in the production of composite materials with polymericmatrices. However, very little information is available in the literature about the use of basalt fibers as reinforcement inmetalmatrix compositematerials. It is well known that the impregnation of fiber reinforcement affects the mechanical behavior of the composite materials. The aim of this study was to investigate the impregnation and the behavior of basalt fibers in a magnesium alloy composite material manufactured by a centrifugal casting technique

RefDiff: Detecting Refactorings in Version Histories

Refactoring is a well-known technique that is widely adopted by software engineers to improve the design and enable the evolution of a system. Knowing which refactoring operations were applied in a code change is a valuable information to understand software evolution, adapt software components, merge code changes, and other applications. In this paper, we present RefDiff, an automated approach that identifies refactorings performed between two code revisions in a git repository. RefDiff employs a combination of heuristics based on static analysis and code similarity to detect 13 well-known refactoring types. In an evaluation using an oracle of 448 known refactoring operations, distributed across seven Java projects, our approach achieved precision of 100% and recall of 88%. Moreover, our evaluation suggests that RefDiff has superior precision and recall than existing state-of-the-art approaches.Comment: Paper accepted at 14th International Conference on Mining Software Repositories (MSR), pages 1-11, 201

Modeling Directed Local Search Strategies on Technology

NK Model, Technology Landscape, Depth and Breadth of Search, Simulation Analysis