Showing papers by "Polytechnic University of Milan published in 1998"

Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review

Abstract: The open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed. Catalytic systems based on supported V2O5 (including the industrial TiO2-supported V2O5–WO3 and/or V2O5–MoO3 catalysts) and catalysts containing Fe2O3, CuO, MnOx and CrOx are considered. The results of spectroscopic studies of the adsorbed surface species, adsorption–desorption measurements, flow reactor and kinetic experiments are analyzed. The proposed reaction mechanisms are described and critically discussed. Points of convergence and of disagreement are underlined.

Understanding code mobility

Abstract: The technologies, architectures, and methodologies traditionally used to develop distributed applications exhibit a variety of limitations and drawbacks when applied to large scale distributed settings (e.g., the Internet). In particular, they fail in providing the desired degree of configurability, scalability, and customizability. To address these issues, researchers are investigating a variety of innovative approaches. The most promising and intriguing ones are those based on the ability of moving code across the nodes of a network, exploiting the notion of mobile code. As an emerging research field, code mobility is generating a growing body of scientific literature and industrial developments. Nevertheless, the field is still characterized by the lack of a sound and comprehensive body of concepts and terms. As a consequence, it is rather difficult to understand, assess, and compare the existing approaches. In turn, this limits our ability to fully exploit them in practice, and to further promote the research work on mobile code. Indeed, a significant symptom of this situation is the lack of a commonly accepted and sound definition of the term mobile code itself. This paper presents a conceptual framework for understanding code mobility. The framework is centered around a classification that introduces three dimensions: technologies, design paradigms, and applications. The contribution of the paper is two-fold. First, it provides a set of terms and concepts to understand and compare the approaches based on the notion of mobile code. Second, it introduces criteria and guidelines that support the developer in the identification of the classes of applications that can leverage off of mobile code, in the design of these applications, and, finally, in the selection of the most appropriate implementation technologies. The presentation of the classification is intertwined with a review of state-of-the-art in the field. Finally, the use of the classification is exemplified in a case study.

IEEE 802.11-saturation throughput analysis

Abstract: To satisfy the emerging need of wireless data communications, the IEEE is currently standardizing the 802.11 protocol for wireless local area networks. This standard adopts a CSMA/CA medium access control protocol with exponential backoff. We present a simple analytical model to compute the saturation throughput performance in the presence of a finite number of terminals and in the assumption of ideal channel conditions. The model applies to both basic and request-to-send/clear-to-send (RTS/CTS) access mechanisms. Comparison with simulation results shows that the model is extremely accurate in predicting the system throughput.

Measuring regularity by means of a corrected conditional entropy in sympathetic outflow.

Abstract: A new method for measuring the regularity of a process over short data sequences is reported. This method is based on the definition of a new function (the corrected conditional entropy) and on the extraction of its minimum. This value is taken as an index in the information domain quantifying the regularity of the process. The corrected conditional entropy is designed to decrease in relation to the regularity of the process (like other estimates of the entropy rate), but it is able to increase when no robust statistic can be performed as a result of a limited amount of available samples. As a consequence of the minimisation procedure, the proposed index is obtained without an a-priori definition of the pattern length (i.e. of the embedding dimension of the reconstructed phase space). The method is validated on simulations and applied to beat- to-beat sequences of the sympathetic discharge obtained from decerebrate artificially ventilated cats. At control, regular, both quasiperiodic and periodic (locked to ventilation) dynamics are observed. During the sympathetic activation induced by inferior vena cava occlusion, the presence of phase-locked patterns and the increase in regularity of the sympathetic discharge evidence an augmented coupling between the sympathetic discharge and ventilation. The reduction of complexity of the neural control obtained by spinalization decreases the regularity in the sympathetic outflow, thus pointing to a weaker coupling between the sympathetic discharge and ventilation.

Exploiting an event-based infrastructure to develop complex distributed systems

Abstract: The development of complex distributed systems demands for the creation of suitable architectural styles (or paradigms) and related run-time infrastructures. An emerging style that is receiving increasing attention is based on the notion of event. In an event-based architecture, distributed software components interact by generating and consuming events. The occurrence of an event in a component (called source) is asynchronously notified to any other component (called recipient) that has declared some interest in it. This paradigm holds the promise of supporting a flexible and effective interaction among highly reconfigurable distributed software components. We have developed an object-oriented infrastructure, called JEDI (Java Event-based Distributed Infrastructure), to support the development and operation of event-based systems. During the past year, JEDI has been used to implement a significant example of distributed system, namely, the OPSS workflow management system. The paper illustrates JEDI main features and how we have used it to implement the OPSS workflow management system. Moreover, it provides an initial evaluation of our experiences in using an event-based architectural style.

Identifying effective PMSs for the deployment of “green” manufacturing strategies

Abstract: Environmental issues are rapidly emerging as one of the most important topics in strategic manufacturing decisions. Growing public awareness and increasing government interest in the environment have induced many companies to adopt programmes aimed at improving the environmental performance of their operations. State of the art literature has proposed many models to support executives in the assessment of a company’s environmental performance. Unfortunately, none of these identifies operating guidelines on how the systems should be adapted to support the deployment of different types of “green” manufacturing strategies. The present paper seeks to illustrate techniques and architecture for performance measurement systems (PMSs) to support the implementation of feasible “green” manufacturing strategies.

Cryptographic Traces for Mobile Agents

Abstract: Mobile code systems are technologies that allow applications to move their code, and possibly the corresponding state, among the nodes of a wide-area network. Code mobility is a flexible and powerful mechanism that can be exploited to build distributed applications in an Internet scale. At the same time, the ability to move code to and from remote hosts introduces serious security issues. These issues include authentication of the parties involved and protection of the hosts from malicious code. However, the most difficult task is to protect mobile code against attacks coming from hosts. This paper presents a mechanism based on execution tracing and cryptography that allows one to detect attacks against code, state, and execution flow of mobile software components.

The consensus glossary of temporal database concepts — February 1998 version

Abstract: This document1 contains definitions of a wide range of concepts specific to and widely used within temporal databases. In addition to providing definitions, the document also includes explanations of concepts as well as discussions of the adopted names.

Organizing for technological collaborations: a managerial perspective

Abstract: Researchers and practitioners have recently paid great attention to technological partnering. In this paper, the problem of choosing which organizational form the technological collaboration should take is carefully examined. The aim is to support the decision-maker who, once it has been decided that a certain technology is to be acquired externally, has to identify the most appropriate mode for such an acquisition. This is not an easy task and is critical to the success of the collaboration. A framework is suggested to assist the decision-maker, based upon the preliminary results of a qualitative empirical study. It is then applied to two case studies. The framework is articulated into three logical steps. First, the characteristics of different organizational forms of collaboration are analysed in terms of integration and formalization. Second, the company's requirements from a specific collaboration are defined in similar terms within the context of objective, content, partner typology. Third, the characteristics of the organizational form are matched with the company's specific requirements so as to identify the most appropriate organizational form for the collaboration.

On stability and convergence of projection methods based on pressure Poisson equation

Abstract: We investigate the proper choices of spatial approximations for velocity and pressure in fractional-step projection methods. Numerical results obtained with classical finite element interpolations are presented. These tests confirm the role of the inf-sup LBB condition in non-incremental and incremental versions of the method for computing viscous incompressible flows

A Characterization Framework for Software Deployment Technologies

Abstract: Software applications are no longer stand-alone systems. They are increasingly the result of integrating heterogeneous collections of components, both executable and data, possibly dispersed over a computer network. Dier ent components can be provided by dier ent producers and they can be part of dier ent systems at the same time. Moreover, components can change rapidly and independently, making it dicult to manage the whole system in a consistent way. Under these circumstances, a crucial step of the software life cycle is deployment|that is, the activities related to the release, installation, activation, deactivation, update, and removal of components, as well as whole systems. This paper presents a framework for characterizing technologies that are intended to support software deployment. The framework highlights four primary factors concerning the technologies: process coverage; process changeability; interprocess coordination; and site, product, and deployment policy abstraction. A variety of existing technologies are surveyed and assessed against the framework. Finally, we discuss promising research directions in software deployment.

An Extension to SQL for Mining Association Rules

Abstract: Data mining evolved as a collection of applicative problems and efficient solution algorithms relative to rather peculiar problems, all focused on the discovery of relevant information hidden in databases of huge dimensions In particular, one of the most investigated topics is the discovery of association rules This work proposes a unifying model that enables a uniform description of the problem of discovering association rules The model provides a SQL-like operator, named MINE RULE, which is capable of expressing all the problems presented so far in the literature concerning the mining of association rules We demonstrate the expressive power of the new operator by means of several examples, some of which are classical, while some others are fully original and correspond to novel and unusual applications We also present the operational semantics of the operator by means of an extended relational algebra

On the approximation of the unsteady Navier–Stokes equations by finite element projection methods

Abstract: This paper provides an analysis of a fractional-step projection method to compute incompressible viscous flows by means of finite element approximations. The analysis is based on the idea that the appropriate functional setting for projection methods must accommodate two different spaces for representing the velocity fields calculated respectively in the viscous and the incompressible half steps of the method. Such a theoretical distinction leads to a finite element projection method with a Poisson equation for the incremental pressure unknown and to a very practical implementation of the method with only the intermediate velocity appearing in the numerical algorithm. Error estimates in finite time are given. An extension of the method to a problem with unconventional boundary conditions is also considered to illustrate the flexibility of the proposed method.

Statistical analysis of defects for fatigue strength prediction and quality control of materials

Abstract: A wide range of studies and experimental evidence have shown that the lower bound of fatigue properties can be correctly predicted by considering the maximum occurring defect size. The estimate of this dimension can be done by analysing the defect sizes using the statistics of extremes. The scope of this paper is to discuss and investigate the two key points in a successful application of this technique: the first is the choice of statistical method for the analysis of data; the second is the knowledge of the minimum number of defects needed to obtain a good estimate of extreme defects. The results obtained in this study allow one to formulate a procedure for estimating the extreme defects with a precision suitable for fatigue strength prediction.

Seeing ecology and “green” innovations as a source of change

Abstract: States that over the last few years, the growing importance of the ecological question has led many executives to modify their business policies. The integration of “green” issues in the process of strategy formation has significant financial, managerial and organizational implications for the corporate system, thus requiring firms to re‐design their value chain activities and processes. This paper aims at: analysing current patterns of environmental behaviour adopted by firms; discussing whether and how the ecological challenge must be seen as a major source of change, thus identifying specific implications on the corporate system of environmental entrepreneurship; presenting the basic triggers which may foster the introduction of innovative environmental programmes.

"Greening" SMEs' competitiveness

Abstract: Over the last few years, public institutions, the market, the financial community and non governmental associations have explicitly demanded that firms improve their environmental performance. However, in spite of the strong pressure from external stakeholders, recent studies have highlighted the fact that only large corporations adopt a pro-active environmental strategy, whereas SMEs tend to comply with external pressures, thus adopting a re-active strategy. In the light of these issues, the paper analyses the stakeholders' role in supporting SMEs' shift from a reactive to a proactive pattern of environmental behavior. In particular, the study seeks to: design a conceptual model which describes stakeholders' "direct role", i.e. providing SMEs with resources, as well as their "indirect role", i.e. encouraging SMEs to develop co-operative relationships and creating the necessary conditions for collaboration in improving their environmental performance, and verify empirically stakeholders' actual role in supporting SMEs' environmental development.

Spectrum folding and phase noise in LC tuned oscillators

Abstract: We present a theory of the noise transfer in LC tuned oscillators accounting for the nonlinear operation of the transconductor. We show that the transconductor switching causes a folding of the wide-band noise such as the thermal noise of the spreading resistance of the bipolar transistors and the noise of the tail current generator. The effect is similar to what happens in sampled systems, however, for a careful evaluation of the oscillator phase noise, the correlations between the folded terms is of chief importance. We show how to account for the effect, we assess the impact on the oscillator noise performance and we give the guidelines for the circuit optimization.

Address bus encoding techniques for system-level power optimization

Abstract: The power dissipated by system-level buses is the largest contribution to the global power of complex VLSI circuits. Therefore, the minimization of the switching activity at the I/O interfaces can provide significant savings on the overall power budget. This paper presents innovative encoding techniques suitable for minimizing the switching activity of system-level address buses. In particular, the schemes illustrated here target the reduction of the average number of bus line transitions per clock cycle. Experimental results, conducted on address streams generated by a real microprocessor, have demonstrated the effectiveness of the proposed methods.

Conceptual schema analysis: techniques and applications

Abstract: The problem of analyzing and classifying conceptual schemas is becomig increasingly important due to the availability of a large number of schemas related to existing applications. The purposes of schema analysis and classification activities can be different: to extract information on intensional properties of legacy systems in order to restructure or migrate to new architectures; to build libraries of reference conceptual components to be used in building new applications in a given domain; and to identify information flows and possible replication of data in an organization. This article proposes a set of techniques for schema analysis and classification to be used separately or in combination. The techniques allow the analyst to derive significant properties from schemas, with human intervention limited as far as possible. In particular, techniques for associating descriptors with schemas, for abstracting reference conceptual schemas based on schema clustering, and for determining schema similarity are presented. A methodology for systematic schema analysis is illustrated, with the purpose of identifying and abstracting into reference components the similar and potentially reusable parts of a set of schemas. Experiences deriving from the application of the proposed techniques and methodology on a large set of Entity-Relationship conceptual schemas of information systems in the Italian Public Administration domain are described

Electromyographic signals during gait : criteria for envelope filtering and number of strides

Abstract: The use of linear envelopes to represent the electromyographic (EMG) measurements obtained during locomotion has become common practice. Guidelines for designing envelope filters and specifying the minimum number of strides needed to produce valid EMG profiles have been developed. Electromyograms from eight major muscles of the lower leg are measured from five normal young adults during self-selected slow, free and fast walking speeds. 30 strides per task are measured. The 'ideal' EMG profile is defined from the ensemble average of the rectified EMG signal. An error measure is defined and used as a criterion to assess the appropriateness of various cut-off frequencies for envelope filters and the number of strides required for establishing a good EMG profile. It is found that between six and ten strides are needed to form a representative profile, and an envelope filter with a minimum cut-off frequency of approximately 9 Hz is necessary.

Functionally oriented and clinically feasible quantitative gait analysis method

Abstract: A protocol for clinical gait analysis is described, and data from 30 normal adult female subjects are presented. Extensive application to pathologic subjects has proven to be feasible and sufficiently accurate. The method is based on a particular location and attachment of retro-reflective markers on the body and on a particular arrangement of four TV cameras. A motion analyser measures the 3D coordinates of each marker. A modelling approach, based on individual anthropometric measurements, and a functional approach, based on kinematical considerations, are used to estimate the location of hip, knee, and ankle joint centers and the orientation of the flexion-extension axis of the knee. 3D relative and absolute movements of pelvis and lower limbs are obtained and shown to be consistent with functional anatomy.

Tolerating deviations in process support systems via flexible enactment of process models

Abstract: Process support systems (PSSs) support business organizations in modeling, improving and automating their business processes. Thanks to their ability in enacting process models, they can be used to guide people in performing their daily work and to automate the repetitive tasks that do not require human intervention. Given these potential benefits, it is surprising to observe that PSSs are not widely adopted. This is especially true in case of highly flexible and human-intensive processes, such as design processes in general and software processes in particular. This fact can be explained by observing that currently available PSSs do not fulfil some crucial needs of modern business organizations. One of their major drawbacks is that they do not offer adequate mechanisms to cope with unforeseen situations. They are good at supporting business processes if all proceeds as expected, but if an unexpected situation is met, which would require one to deviate from the process model, they often become more an obstacle than a help. This paper deals with the problem of managing unforeseen situations that require deviations from the process model during enactment in the context of the PROSYT (PROcess Support sYstem capable of Tolerating deviations) PSS. During process model enactment, PROSYT is capable of tolerating deviations from the process model by supporting users even when unexpected situations arise. Furthermore, it supports users in reconciling the process model with the process actually followed, if necessary.

Shaking table tests on 24 simple masonry buildings

Abstract: The paper presents the results of a large experimental programme carried out on models, scaled 1:2, of two-storey masonry buildings. After suffering damage, the models were repaired and strengthened and tested again. A total of 24 buildings were subjected to 119 shaking-table tests, by ISMES (Italy) and LEE (Greece) facilities. The results allow to assess the efficiency of the various strengthening techniques employed and to describe the change of dynamic properties of the systems at the increase of damage. © 1998 John Wiley & Sons, Ltd.