Showing papers by "Polytechnic University of Milan published in 1993"
TL;DR: The paper presents HDM (Hypertext Design Model), a first step towards defining a general purpose model for authoring-in-the-large, and the central advantages of HDM in the design and practical construction of hypertext applications is that the definition of a significant number of links can be derived automatically from a conceptual-design level description.
Abstract: Hypertext development should benefit from a systematic, structured development, especially in the case of large and complex applications. A structured approach to hypertext development suggests the notion of authoring-in-the-large. Authoring-in-the-large allows the description of overall classes of information elements and navigational structures of complex applications without much concern with implementation details, and in a system-independent manner. The paper presents HDM (Hypertext Design Model), a first step towards defining a general purpose model for authoring-in-the-large. Some of the most innovative features of HDM are: the notion of perspective; the identification of different categories of links (structural links, application links, and perspective links) with different representational roles; the distinction between hyperbase and access structures; and the possibility of easily integrating the structure of a hypertext application with its browsing semantics. HDM can be used in different manners: as a modeling device or as an implementation device. As a modeling device, it supports producing high level specifications of existing or to-be-developed applications. As an implementation device, it is the basis for designing tools that directly support application development. One of the central advantages of HDM in the design and practical construction of hypertext applications is that the definition of a significant number of links can be derived automatically from a conceptual-design level description. Examples of usage of HDM are also included.
736 citations
TL;DR: This paper applies the tabu-search technique to the job-shop scheduling problem, a notoriously difficult problem in combinatorial optimization and shows that the implementation of this method dominates both a previous approach with tabu search and the other heuristics based on iterative improvements.
Abstract: In this paper, we apply the tabu-search technique to the job-shop scheduling problem, a notoriously difficult problem in combinatorial optimization. We show that our implementation of this method dominates both a previous approach with tabu search and the other heuristics based on iterative improvements.
605 citations
TL;DR: In this article, the optimal and robust design of a four-section countercurrent adsorption separation unit is investigated in the frame of equilibrium theory, using a model where the ad-ption equilibria are described through the constant selectivity stoichiometric model, while mass transfer resistances and axial mixing are neglected.
Abstract: The separation of a binary mixture, using a third component having intermediate adsorptivity as desorbent, in a four section countercurrent adsorption separation unit is considered. A procedure for the optimal and robust design of the unit is developed in the frame of Equilibrium Theory, using a model where the adsorption equilibria are described through the constant selectivity stoichiometric model, while mass-transfer resistances and axial mixing are neglected. By requiring that the unit achieves complete separation, it is possible to identify a set of implicity constraints on the operating parameters, that is, the flow rate ratios in the four sections of the unit. From these constraints explicit bounds on the operating parameters are obtained, thus yielding a region in the operating parameters space, which can be drawn a priori in terms of the adsorption equilibrium constants and the feed composition. This result provides a very convenient tool to determine both optimal and robust operating conditions. The latter issue is addressed by first analyzing the various possible sources of disturbances, as well as their effect on the separation performance. Next, the criteria for the robust design of the unit are discussed. Finally, these theoretical findings are compared with a set of experimentalmore » results obtained in a six port simulated moving bed adsorption separation unit operated in the vapor phase.« less
370 citations
TL;DR: In this article, a photon emission efficiency of 2.9*10/sup 5/ photons with energy higher than 1.14 eV per carrier crossing the junction, independent of the lattice temperature down to 20 K, was measured.
Abstract: Spectrally resolved absolute measurements of hot-carrier-induced photon emission in silicon are reported. In order to avoid uncertainties in geometrical and physical parameters, the simplest conceivable device, an avalanching p-n junction, was used. A photon emission efficiency of 2.9*10/sup 5/ photons with energy higher than 1.14 eV per carrier crossing the junction, independent of the lattice temperature down to 20 K, was measured. On the basis of these results the bremsstrahlung origin of the hot-carrier-induced light emission is critically reviewed. >
326 citations
TL;DR: This work is devoted to the description of an efficient unstructured mesh generation method entirely based on the Delaunay triangulation, which has the distinctive characteristic of the proposed method is that point positions and connections are computed simultaneously.
291 citations
TL;DR: In this article, the authors present an overview of disassembly research at universities, research centers and industrial companies, pointing out ongoing topics and trends for future activities, including technological development, product design, process design, and system design.
243 citations
TL;DR: In this article, a classical predator-prey model is considered with reference to the case of periodically varying parameters and six elementary seasonality mechanisms are identified and analyzed in detail by means of a continuation technique producing complete bifurcation diagrams.
236 citations
TL;DR: The mechanisms a process language should possess in order to support changes are discussed and how the proposed mechanisms can be used to model different policies for changing a software process model are discussed.
Abstract: Software processes are long-lived entities. Careful design and thorough validation of software process models are necessary to ensure the quality of the process. They do not prevent, however, process models from undergoing change. Change requests may occur in the context of reuse, i.e. statically, in order to support software process model customization. They can also occur dynamically, while software process models are being executed, in order to support timely reaction as data are gathered from the field during process enactment. We discuss the mechanisms a process language should possess in order to support changes. We illustrate the solution adopted in the context of the SPADE environment and discuss how the proposed mechanisms can be used to model different policies for changing a software process model. >
235 citations
TL;DR: In this article, a round-robin program has been undertaken to assess the compatibility in the micromechanical techniques used to evaluate the interfacial shear strength of the fiber/matrix bond in composite materials.
225 citations
01 Jan 1993
TL;DR: Experiments show how behavior acquisition can be achieved by means of a learning coordination mechanism using an architecture based on learning classifier systems and on the structural properties of animal behavioral organization as proposed by ethologists.
Abstract: Intelligent robots should be able to use sensor information to learn how to behave in a changing environment. As environmental complexity grows, the learning task becomes more and more difficult. This problem is faced using an architecture based on learning classifier systems and on the structural properties of animal behavioral organization, as proposed by ethologists. After a description of the learning technique used and of the organizational structure proposed, experiments that show how behavior acquisition can be achieved are presented. The simulated robot learns to follow a light and to avoid hot dangerous objects. While these two simple behavioral patterns are independently learned, coordination is attained by means of a learning coordination mechanism. >
205 citations
TL;DR: The investigation shows the FEM is a versatile tool for studying the mechanics of vascular structures and enables the influence of various parameters on wall stress to be quantified in diagnostic settings, and so could be useful for predicting the rupture of AAA, although at present such predictions are limited by data leakage and by the approximations used in the model.
01 Sep 1993
TL;DR: A PID autotuning algorithm based on relay feedback has the capability of exploring different points of the process frequency response before performing the actual tuning procedure, and minimises the amount of a prioriinformation required on the process.
Abstract: A PID autotuning algorithm based on relay feedback has the capability of exploring different points of the process frequency response before performing the actual tuning procedure. In addition, the algorithm minimises the amount of a prioriinformation required on the process; in fact, the user is only asked to specify the minimum phase margin required for the closed-loop system. Some experimental results, obtained by laboratory simulation, are also presented.
TL;DR: A description that provides more precise definitions for terms such as tool, workbench, toolset, and environment is provided to provide a reference framework and an initial classification of existing technology as a solid starting point for continuous updating.
Abstract: A description that provides more precise definitions for terms such as tool, workbench, toolset, and environment is provided. The aim is to provide a reference framework and an initial classification of existing technology as a solid starting point for continuous updating. >
TL;DR: In this paper, the authors considered the cauchy-dirichlet problem for parabolic equations with vmo coefficients and proved the solvability of the problem for the case of vmo-coefficients.
Abstract: (1993). Wp 1,2solvability for the cauchy-dirichlet problem for parabolic equations with vmo coefficients. Communications in Partial Differential Equations: Vol. 18, No. 9-10, pp. 1735-1763.
TL;DR: In this paper, a phenomenological hypothesis of bread baking was developed, where the temperature, moisture, and volume were determined during the baking process of a leavened bread sample, and the variation in temperature and moisture of bread during baking were determined by the formation of an evaporation front at 100°C.
TL;DR: In this paper, it is shown that the nuclear relaxation following the excitation of the electrons by an intense electromagnetic field can be described in terms of the vibrational modes and can be related to the nuclear contributions to the non-linear optical responses of the material.
Abstract: New classes of polymers and oligomers whose backbone consists of a network of delocalized π electrons have recently been synthesized and show electrical and non-linear optical properties of great interest for new technologies. The vibrational spectra of these materials show peculiar features which, if properly interpreted, can provide unique structural information. The interpretation of the spectra requires the development of new theoretical tools. The theoretical and experimental aspects of the problem are presented. It is also shown that the nuclear relaxation following the excitation of the electrons by an intense electromagnetic field can be described in terms of the vibrational modes and can be related to the nuclear contributions to the non-linear optical responses of the material. In this case Raman intensities play a determining role.
TL;DR: A model-based approach to nonpreemptive multi-project management problems, based on a hierarchical two-stage decomposition of the planning and scheduling process, resulting in a hierarchy of integer programming models aimed at assisting the planners in understanding the interrelations among the allocation of resources, the timing of the activities, the cash flows.
01 Mar 1993-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a charge sensitive preamplifier with no resistor in parallel with the feedback capacitor is presented, which has no external device or circuit required to discharge the feedback capacitance.
Abstract: A novel charge sensitive preamplifier which has no resistor in parallel with the feedback capacitor is presented. No external device or circuit is required to discharge the feedback capacitor. The detector leakage and signal current flows away through the gate of the first JFET which works with its gate to source junction slightly forward biased. The DC stabilization of the preamplifier is accomplished by an additional feedback loop, which permits to equalize the current flowing through the forward baised gate to source junction and the current coming from the detector. An equivalent noise charge of less than 20 electrons r.m.s. has been measured at room temperature by using an input JFET with a transconductance to gate capacitance ratio of 4 mS/5.4 pF.
01 Jan 1993
TL;DR: Christaller's and Losch's central-place model as mentioned in this paper still remains the more elegant, abstract but consistent representation of the hierarchy of urban centres, even after the basic refinements introduced by Isard, Beckmann and McPherson, a huge literature has grown upon the same logical foundations and simplifying assumptions with the works of Parr, Beguin, Mulligan and others.
Abstract: According to textbooks of theoretical geography and urban economics, the analytical model which still better describes in strictly economic and locational terms the structure of the city system is Christaller’s and Losch’s central-place model developed in the 1930’s and 1940’s. After the basic refinements introduced by Isard, Beckmann and McPherson, a huge literature has grown upon the same logical foundations and simplifying assumptions with the works of Parr, Beguin, Mulligan and others, but it has not changed the basic economic characteristics of the initial model: it still remains the more elegant, abstract but consistent representation of the hierarchy of urban centres.1
TL;DR: The authors derive and discuss a new technique for increasing the across-track resolution of objects that do not change with time, using multiple surveys of the same area from different off-nadir angles.
Abstract: Across-track resolution of a spaceborne synthetic aperture radar (SAR) system is limited by power and data rate constraints. The authors derive and discuss a new technique for increasing the across-track resolution of objects that do not change with time, using multiple surveys of the same area from different off-nadir angles. Precise information on the spaceborne trajectories are not requested since they can be derived from SAR interferometry. Simulated data show that theoretical derivations are in good agreement with practice. >
TL;DR: In this paper, rainfall forecasting is approached assuming that hourly rainfall follows an autoregressive moving average (ARMA) process, which is based on the fact that the autocovariance structure of some point processes, such as hourly rainfall processes, is equivalent to the auto-coverage structure of certain low-order ARMA processes.
TL;DR: In this article, the authors present a computational theory of the cognitive processes underlying human communication, based on the assumption that two agents overtly reach a situation of shared mental states through shared beliefs and communicative intentions.
TL;DR: It is shown that the Classification of queueing is the main concept that enables the classification of nonblocking ATM switches and the ways in which two strategies can be jointly adopted in a switching fabric to result in the mixed queueing strategies input-output queueing, input-shared queues, and shared-output queues.
Abstract: General models for a class of nonblocking architectures of asynchronous transfer mode (ATM) switches are described. Hardware aspects are discussed to show the implementation feasibility of the proposed switch architectures by means of the current technology. Performance issues are studied to point out the traffic bottlenecks of the different structures. It is shown that the classification of queueing is the main concept that enables the classification of nonblocking ATM switches. Three main packet queueing strategies can be adopted in the switching fabric: input queueing, shared queueing, and output queueing. Switch architectures adopting only one of these strategies are described. The ways in which two strategies can be jointly adopted in a switching fabric to result in the mixed queueing strategies input-output queueing, input-shared queueing, and shared-output queueing are also discussed. >
TL;DR: In this article, the chemistry of the selective catalytic reduction (SCR) of NO x with ammonia over V 2 O 5 -TiO 2 and WO 3 - TiO 2 catalysts has been investigated by Fourier-Transform Infrared spectroscopy, temperature programmed desorption, temperature-programmed surface reaction and catalytic activity measurements.
01 Mar 1993-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a pn-CCD with an activa area of 3 × 1 cm2 was fabricated for ESA's X-ray multi-mirror mission (XMM).
Abstract: A new pn-CCD with an activa area of 3 × 1 cm2 was recently fabricated for ESA's X-ray Multi Mirror Mission (XMM). The front-end electronics has been integrated on the same chip as the detector, and its noise behaviour was investigated. X-rays from a 55Fe source have been used for the absolute calibration. The measured electronic Equivalent Noise Charge (ENC) of the on-chip amplifier was 8.8 e− at room temperature and 2.2 e− at the CCD operating temperature of 150 K. The improvements with respect to the last version with noise figures of 4.8 e− (at 150 K) are due to the reduction of the total input capacitance by a factor of 1.6, the improvement of the transistor transconductance by a factor of 2, and the reduction of 1 ƒ noise because of the different p-well implant with a better thermal annealing.
01 Jan 1993
TL;DR: In this paper, the Navier-Stokes equations have been used for the calculation of both steady and unsteady viscous flows using the various possible formulations of the problem, and an important aspect of the numerical methods for solving this class of problems is the proper specification of the boundary conditions.
Abstract: Methods for the approximate solution of the incompressible Navier-Stokes equations have been investigated rather extensively in the last two decades. Several numerical schemes have been developed for the calculation of both steady and unsteady viscous flows using the various possible formulations of the problem. An important aspect of the numerical methods for solving this class of problems is the proper specification of the boundary conditions, especially when solid walls are present. Of course, the appropriate treatment depends on which variables are chosen as unknowns and, from a numerical viewpoint, the specific form assumed by the boundary conditions may also depend on the method adopted for discretizing space and time.
TL;DR: In this article, the potential merits of cyclic polymethylsiloxanes, particularly those conventionally denominated D4 and D5, as working fluids for space power cycles are discussed.
Abstract: The potential merits of cyclic polymethylsiloxanes, particularly those conventionally denominated D4 and D5 , as working fluids for space power cycles are discussed. The attractive technical characteristics of these substances which are fully nontoxic, moderately flammable, and stable at high temperature are presented. Some experimental results on vapor pressure and on thermal stability are reported. A maximum operating temperature of about 400°C appears achievable. A comprehensive thermodynamic analysis comparing siloxanes with other classes of high temperature fluids is performed. The peculiar characters of siloxane cycles are found to be: a good overall efficiency achieved through a massive regeneration, a moderate expansion work, and an abundant volume flow at turbine exhaust. A number of two-stage turbines for two power levels (i.e., 30 and 5 kW) were designed using an appropriate optimization program. The resulting main features of such expanders were a satisfactory efficiency, a low rotating and peripheral speed, and a comparatively large wheel diameter. These characteristics seem of particular interest for low capacity systems where, with other fluids, turbines tend to be impractically small and fast rotating and where a high level of regeneration becomes more acceptable. In considering for the sake of comparison the thermodynamic performance of many classes of organic fluids, it becomes apparent that the full potential of organic power cycles in view of the variety of future needs has not yet been thoroughly investigated.
TL;DR: In this article, the effects of deliberate nonuniform distribution of the catalytic material within the support on the performance of a catalyst pellet started receiving attention in the late 1960's.
Abstract: A large fraction of the chemical and refinery processes are catalytic in nature. While the worldwide sales of catalysts are only about $4 billion annually, the economic impact of catalysis comes from the fact that approximately $200 worth of products are manufactured for every $1 worth of catalyst consumed [1]. The active materials used as catalysts are often expensive metals, and in order to be utilized effectively, they are deposited on high surface area supports. This approach in many cases introduces intrapellet activity gradients during the preparation process, which were traditionally thought to be detrimental to catalyst performance. However, the effects of deliberate nonuniform distribution of the catalytic material within the support on the performance of a catalyst pellet started receiving attention in the late 1960's (see Refs. 2–6). These, as well as later studies, both experimental and theoretical, demonstrated that nonuniformly distributed catalysts can offer superior conversion, se...
TL;DR: This paper starts by motivating the use of process modeling and its main objectives, then proposes a list of desirable features for process languages and reviews the main existing approaches and proposes a classification scheme.
Abstract: Process modeling is a rather young and very active research area. During the last few years, new languages and methods have been proposed to describe software processes. In this paper we try to clarify the issues involved in software process modeling and identify the main approaches. We start by motivating the use of process modeling and its main objectives. We then propose a list of desirable features for process languages. The features are grouped as either already provided by languages from other fields or as specific features of the process domain. Finally, we review the main existing approaches and propose a classification scheme.
TL;DR: In this work, an attempt is made at filling the apparent gap existing between the two major approaches evolved in the literature towards formulating space-time finite element methods.
Abstract: In this work, an attempt is made at filling the apparent gap existing between the two major approaches evolved in the literature towards formulating space-time finite element methods. The first assumes Hamilton's Law as underlying concept, while the second performs a weighted residual approach on the ordinary differential equations emanating from the semidiscretization in the space dimension. A general framework is proposed in the following pages, where the configuration space and the phase space forms of Hamilton's Law provide the general statements of the problem of motion. Within this framework, different families of integration algorithms are derived, according to different interpretations of the boundary terms. The bi-discontinuous form is obtained as the consequence of a consistent impulsive formulation of dynamics, while the discontinuous Galerkin form is obtained when the boundary terms at the end of the time interval are appropriately approximated.