Showing papers by "Polytechnic University of Milan published in 2001"

Permanent scatterers in SAR interferometry

Abstract: Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used.

Present status and perspectives in de-NOx SCR catalysis

Abstract: This paper surveys the present status and the perspective of de-NO x SCR catalysis for stationary sources, that is based on the reduction of NO x by NH 3 to form water and nitrogen. After a brief description of the SCR chemistry the characteristics of commercial SCR catalysts, their physico-chemical properties and reactivity, and their performances in both NO x reduction and SO 2 oxidation are presented. The mechanism of the SCR reactions, the mathematical modeling of the reactor and the arrangements of the reactor and process are then described. Finally the emerging technologies for NO x removal and the future perspectives of the SCR catalysis are outlined.

The JEDI event-based infrastructure and its application to the development of the OPSS WFMS

Abstract: The development of complex distributed systems demands the creation of suitable architectural styles (or paradigms) and related runtime 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. An event is the occurrence of some state change in a component of a software system, made visible to the external world. The occurrence of an event in a component is asynchronously notified to any other component that has declared some interest in it. This paradigm (usually called "publish/subscribe", from the names of the two basic operations that regulate the communication) holds the promise of supporting a flexible and effective interaction among highly reconfigurable, distributed software components. In the past two years, we have developed an object-oriented infrastructure called JEDI (Java event-based distributed infrastructure). JEDI supports the development and operation of event-based systems and has been used to implement a significant example of distributed system, namely, the OPSS workflow management system (WFMS). The paper illustrates the main features of JEDI and how we have used them to implement OPSS. Moreover, the paper provides an initial evaluation of our experiences in using the event-based architectural style and a classification of some of the event-based infrastructures presented in the literature.

Absolute-phase phenomena in photoionization with few-cycle laser pulses

Abstract: Currently, the shortest laser pulses1 that can be generated in the visible spectrum consist of fewer than two optical cycles (measured at the full-width at half-maximum of the pulse's envelope). The time variation of the electric field in such a pulse depends on the phase of the carrier frequency with respect to the envelope—the absolute phase. Because intense laser–matter interactions generally depend on the electric field of the pulse, the absolute phase is important for a number of nonlinear processes2,3,4,5,6,7,8. But clear evidence of absolute-phase effects has yet to be detected experimentally, largely because of the difficulty of stabilizing the absolute phase in powerful laser pulses. Here we use a technique that does not require phase stabilization to demonstrate experimentally the influence of the absolute phase of a short laser pulse on the emission of photoelectrons. Atoms are ionized by a short laser pulse, and the photoelectrons are recorded with two opposing detectors in a plane perpendicular to the laser beam. We detect an anticorrelation in the shot-to-shot analysis of the electron yield.

Developing Products on Internet Time: The Anatomy of a Flexible Development Process

Abstract: Uncertain and dynamic environments present fundamental challenges to managers of the new product development process. Between successive product generations, significant evolutions can occur in both the customer needs a product must address and the technologies it employs to satisfy these needs. Even within a single development project, firms must respond to new information, or risk developing a product that is obsolete the day it is launched. This paper examines the characteristics of an effective development process in one such environment-the Internet software industry. Using data on 29 completed development projects we show that in this industry, constructs that support a more flexible development process are associated with better-performing projects. This flexible process is characterized by the ability to generate and respond to new information for a longer proportion of a development cycle. The constructs that support such a process are greater investments in architectural design, earlier feedback on product performance from the market, and the use of a development team with greater amounts of "generational" experience. Our results suggest that investments in architectural design play a dual role in a flexible process: First, through the need to select an architecture that maximizes product performance and, second, through the need to select an architecture that facilitates development process flexibility. We provide examples from our fieldwork to support this view.

LIME: a middleware for physical and logical mobility

Abstract: LIME is a middleware supporting the development of applications that exhibit physical mobility of hosts, logical mobility of agents, or both. LIME adapts a coordination perspective inspired by work on the Linda model. The context for computation, represented in Linda by a globally accessible, persistent tuple space, is represented in LIME by transient sharing of the tuple spaces carried by each individual mobile unit. Linda tuple spaces are also extended with a notion of location and with the ability to react to a given state. The hypothesis underlying our work is that the resulting model provides a minimalist set of abstractions that enable rapid and dependable development of mobile applications. In this paper, we illustrate the model underlying LIME, present its current design and implementation, and discuss initial lessons learned in developing applications that involve physical mobility.

Rectifiability and perimeter in the Heisenberg group

Abstract: In this paper, we fully extend to the Heisenberg group endowed with its intrinsic Carnot-Caratheodory metric and perimeter the classical De Giorgi's rectifiability divergence theorems.

FT-IR and TPD investigation of the NOx storage properties of BaO/Al2O3 and Pt-BaO/Al2O3 catalysts

Abstract: The interaction of NO, NO2, or NO/O2 mixtures with Pt/Al2O3, Ba/Al2O3, and Pt−Ba/Al2O3 catalysts has been investigated by IR spectroscopy and temperature-programmed desorption. Upon NO interaction, small amounts of nitrites, nitrates, and hyponitrite species were formed on the Ba-containing samples. The NOx storage capacity of the catalysts was highly enhanced upon adsorption of NO/O2 mixtures and further upon NO2 admission. Upon adsorption of NO/O2 on Pt/Al2O3 sample nitrites, nitrates and NO2δ+ species were mainly formed, showing a moderate thermal stability. Barium markedly increased the amount and stability of the stored NOx species, which were bidentate and monodentate nitrites and, in minor amounts, nitrates. Nitrites were removed below 750 K and/or transformed into ionic Ba nitrates, stable up to 800−900 K. Upon NO2 adsorption, huge amounts of nitrates, but no nitrites, were formed on all the samples. Also in this case, Ba increased the amount and stability of the stored NOx species. The nature and...

Crystal Engineering through Halogen Bonding: Complexes of Nitrogen Heterocycles with Organic Iodides

Abstract: X-ray analysis has revealed that 4,4‘-bipyridine, 1,2-bis(4-pyridyl)ethylene, and hexamethylenetetramine form donor−acceptor complexes with 1,4-diiodobenzene, 1,4-diiodotetrafluorobenzene, and tetraiodoethylene in which the N···I distance is longer than that for the corresponding I2 complexes. As opposed to the corresponding I2 complexes that are molecular adducts, these complexes have extended structures and longer N···I distances. Steric and electronic effects influence the strength of the N···I interaction and the crystal packing. An additional complex of 1,2-bis(4-pyridyl)ethane and 1,4-dibromotetrafluorobenzene has also been investigated for comparison of N···I and N···Br interactions.

Baroreflex effectiveness index: an additional measure of baroreflex control of heart rate in daily life

Abstract: In healthy subjects, progressive beat-to-beat increases or decreases in systolic blood pressure (SBP) ramps are not always accompanied by baroreflex-driven lengthening or shortening in pulse interv...

Model-based control of FES-induced single joint movements

Abstract: A crucial issue of functional electrical stimulation (FES) is the control of motor function by the artificial activation of paralyzed muscles. Major problems that limit the success of current FES systems are the nonlinearity of the target system and the rapid change of muscle properties due to fatigue. In this study, four different strategies, including an adaptive algorithm, to control the movement of the freely swinging shank were developed on the basis of computer simulations and experimentally evaluated on two subjects with paraplegia due to a complete thoracic spinal cord injury. After developing a nonlinear, physiologically based model describing the dynamic behavior of the knee joint and muscles, an open-loop approach, a closed-loop approach, and a combination of both were tested. In order to automate the individual adjustments cited, we further evaluated the performance of an adaptive feedforward controller. The two parameters chosen for the adaptation were the threshold pulse width and the scaling factor for adjusting the active moment produced by the stimulated muscle to the fitness of the muscle. These parameters have been chosen because of their significant time variability. The first three controllers with fixed parameters yielded satisfactory result. An additional improvement was achieved by applying the adaptive algorithm that could cope with problems due to muscle fatigue, thus permitting on-line identification of critical parameters of the plant. Although the present study is limited to a simplified experimental setup, its applicability to more complex and functional movements can be expected.

Three‐dimensional cohesive modeling of dynamic mixed‐mode fracture

Abstract: A cohesive formulation of fracture is taken as a basis for the simulation of processes of combined tension-shear damage and mixed-mode fracture in specimens subjected to dynamic loading. Our three-dimensional finite-element calculations account explicitly for crack nucleation, microcracking, the development of macroscopic cracks and inertia. In particular, a tension-shear damage coupling arises as a direct consequence of slanted microcrack formation in the process zone. We validate the model against the three-point-bend concrete beam experiments of Guo et al. (International Journal of Solids and Structures 1995; 32(17/18):2951–2607), John (PhD Thesis, Northwestern University, 1988), and John and Shah (Journal of Structural Engineering 1990; 116(3):585–602) in which a pre-crack is shifted from the central cross-section, leading to asymmetric loading conditions and the development of a mixed-mode process zone. The model accurately captures the experimentally observed fracture patterns and displacement fields, as well as crack paths and crack-tip velocities, as a function of pre-crack geometry and loading conditions. In particular, it correctly accounts for the competition between crack-growth and nucleation mechanisms.

Silicon drift detectors for high count rate X-ray spectroscopy at room temperature

Abstract: Silicon Drift Detectors (SDDs) combine a large sensitive area with a small value of the output capacitance and are therefore well suited for high resolution, high count rate X-ray spectroscopy. The low leakage current level obtained by the elaborated processing technology makes it possible to operate them at room temperature or with moderate cooling. A brief description of the device principle is followed by the presentation of first results of a new production of large area SDDs with external electronics. Performance and applications of the already established SDDs with on-chip amplification are summarised. Various shapes of Multichannel Drift Detectors are introduced as well as their use in new experiments like X-ray holography and in new systems like an Anger camera for γ-ray imaging.

Modeling of the Norwood circulation: effects of shunt size, vascular resistances, and heart rate

Abstract: Hypoplastic left heart syndrome is the most common lethal cardiac malformation of the newborn. Its treatment, apart from heart transplantation, is the Norwood operation. The initial procedure for t...

Spin-orbit coupling in the Mott insulator Ca2RuO4

Abstract: O $1s$ x-ray absorption study of the Mott insulator ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ shows that the orbital population of the $4d$ ${t}_{2g}$ band dramatically changes with temperature. In addition, spin-resolved circularly polarized photoemission study of ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ shows that a substantial orbital angular momentum is induced in the Ru $4d$ ${t}_{2g}$ band. Based on the experimental results and model Hartree-Fock calculations, we argue that the cooperation between the strong spin-orbit coupling in the Ru $4d$ ${t}_{2g}$ band and the small distortion of the ${\mathrm{RuO}}_{6}$ octahedra causes the interesting changeover of the spin and orbital anisotropy as a function of temperature.

Small firms under MICROSCOPE: international differences in production/operations management practices and performance

Abstract: Although the importance of operations in reaching world-class competitiveness has been highlighted in the operations management literature, small and medium-sized companies (SMEs) have been found to have a poor uptake of world-class practices. Reports on a study of 285 SMEs located in Italy, the UK, and other northern European countries. The data are taken from the MICROSCOPE facilitated self-assessment benchmarking database, which studied operations practices and performance in small firms. The level of world-class practices and performance was compared across companies by company size and by country of origin. Significant differences were found between “micro” companies (fewer than 20 employees) and larger companies (between 20 and 200 employees). Other significant differences were found by country, which may be attributed to differences in regional policies and infrastructures regarding small firms.

Efficient polling schemes for Bluetooth picocells

Abstract: Bluetooth is a new low-cost wireless technology that is going to play an important role in communications among small electronic devices and the access to wired networking infrastructure. Bluetooth stations that communicate directly form a piconet. In a piconet one station has the role of master and the others are slaves. The access to the medium is based on a TDD (time division duplexing) scheme controlled by the master. The master sends packets to slaves in even-numbered slots triggering a transmission from slaves in the subsequent slot. Slaves are allowed to send packets only in response to a master packet. The way in which the master schedules packets transmission to slaves or polls them determines system performance. We consider the problem of designing an efficient and simple polling and scheduling scheme for Bluetooth. We propose some practical schemes and compare their performance with some ideal schemes derived from known results for polling systems.

Inertial waves in a rotating spherical shell : attractors and asymptotic spectrum

Abstract: We investigate the asymptotic properties of inertial modes confined in a spherical shell when viscosity tends to zero. We first consider the mapping made by the characteristics of the hyperbolic equation (Poincare's equation) satisfied by inviscid solutions. Charac- teristics are straight lines in a meridional section of the shell, and the mapping shows that, generically, these lines converge towards a periodic orbit which acts like an attrac- tor (the associated Lyapunov exponent is always negative or zero). We show that these attractors exist in bands of frequencies the size of which decreases with the number of reflection points of the attractor. At the bounding frequencies the associated Lyapunov exponent is generically either zero or minus infinity. We further show that for a given frequency the number of coexisting attractors is finite. We then examine the relation between this characteristic path and eigensolutions of the inviscid problem and show that in a purely two-dimensional problem, convergence towards an attractor means that the associated velocity field is not square-integrable. We give arguments which generalize this result to three dimensions. Then, using a sphere immersed in a fluid filling the whole space, we study the critical latitude singularity and show that the velocity field diverges as 1/ √ d, d being the distance to the characteristic grazing the inner sphere. We then consider the viscous problem and show how viscosity transforms singularities into internal shear layers which in general betray an attractor expected at the eigenfre- quency of the mode. Investigating the structure of these shear layers, we find that they are nested layers, the thinnest and most internal layer scaling with E 1/3 -scale, E being the Ekman number; for this latter layer, we give its analytical form and show its simi- larity to vertical 1 -shear layers of steady flows. Using an inertial wave packet traveling around an attractor, we give a lower bound on the thickness of shear layers and show how eigenfrequencies can be computed in principle. Finally, we show that as viscosity decreases, eigenfrequencies tend towards a set of values which is not dense in (0,2), contrary to the case of the full sphere ( is the angular velocity of the system). Hence, our geometrical approach opens the possibility of describing the eigenmodes and eigenvalues for astrophysical/geophysical Ekman numbers (10 −10 − 10 −20 ), which are out of reach numerically, and this for a wide class of containers.

An Efficient Adaptive Procedure for Three-Dimensional Fragmentation Simulations

Abstract: We present a simple set of data structures, and a collection of methods for constructing and updating the structures, designed to support the use of cohesive elements in simulations of fracture and fragmentation. Initially all interior faces in the triangulation are perfectly coherent, i.e., conforming in the usual finite element sense. Cohesive elements are inserted adaptively at interior faces when the effective traction acting on those face reaches the cohesive strength of the material. The insertion of cohesive elements changes the geometry of the boundary and, frequently, the topology of the model as well. The data structures and methods presented here are straightforward to implement and enable the efficient tracking of complex fracture and fragmentation processes. The efficiency and versatility of the approach is demonstrated with the aid of two examples of application to dynamic fracture.

Compartmental analysis of breathing in the supine and prone positions by optoelectronic plethysmography.

Abstract: Optoelectronic plethysmography (OEP) has been shown to be a reliable method for the analysis of chest wall kinematics partitioned into pulmonary rib cage, abdominal rib cage, abdomen, and right and left side in the seated and erect positions. In this paper, we extended the applicability of this method to the supine and prone positions, typically adopted in critically ill patients. For this purpose we have first developed proper geometrical and mathematical models of the chest wall which are able to provide consistent and reliable estimations of total and compartmental volume variations in these positions suitable for clinical settings. Then we compared chest wall (CW) volume changes computed from OEP(deltaVCW) with lung volume changes measured with a water seal spirometer (SP) (deltaVSP) in 10 normal subjects during quiet (QB) and deep (DB) breathing on rigid and soft supports. We found that on a rigid support the average differences between deltaVSP and deltaVCW were -4.2% +/- 6.2%, -3.0% +/- 6.1%, -1.7% +/- 7.0%, and -4.5% +/- 9.8%, respectively, during supine/QB, supine/DB, prone/QB, and prone/DB. On the soft surface we obtained -0.1% +/- 6.0%, -1.8% +/- 7.8%, 18.0% +/- 11.7%, and 10.2% +/- 9.6%, respectively. On rigid support and QB, the abdominal compartment contributed most of the deltaVCW in the supine (63.1% +/- 11.4%) and prone (53.5% +/- 13.1%) positions. deltaVCW was equally distributed between right and left sides. In the prone position we found a different chest wall volume distribution between pulmonary and abdominal rib cage (22.1% +/- 8.6% and 24.4% +/- 6.8%, respectively) compared with the supine position (23.3% +/- 9.3% and 13.6% +/- 13.0%).

In vivo optical characterization of human tissues from 610 to 1010 nm by time-resolved reflectance spectroscopy.

Abstract: A fully automated system for time-resolved reflectance spectroscopy based on tunable mode-locked laser sources and on time-correlated single-photon counting for the detection of time-resolved reflectance data was applied to the evaluation of the optical properties of biological tissues (arm, abdomen and forehead) in vivo from 610 to 1010 nm. The scattering decreases progressively with increasing wavelength, while the absorption line shapes show the typical spectral features of the principal tissue components (haemoglobin, water and lipid), with different weights depending on the tissue type. The best fit of the absorption spectra measured in vivo with the spectra of the pure constituents yielded information on the percentage composition of the different tissues. The interpretation of transport scattering spectra with Mie theory provided information on tissue structure.

Product-service systems: using an existing concept as a new approach to sustainability

Abstract: Product Service Systems (PS systems), though not new, are relatively new to be used as an approach to reach sustainability This perspective of PS systems is presented A PS system can be defined as a business innovation strategy offering a marketable mix of products and services jointly capable of fulfilling a client's needs and/or wants - with higher added value and a smaller environmental impact as compared to an existing system or product A major element of a PS system is that a consumer's need is met by selling utility instead of providing a product In essence the right of product ownership is shifted from a client to the producer or service provider PS systems are reviewed in light of other environmental managementstrategies, and they are described in general Company examples illustrate the potential benefits and motivations for a company to consider a shift to PS systems The examples are classified in three categories: 1) Services providing value added to product: in which a company can sell additional services, such as a warrantee, to guarantee functionality and/or durability of a product which is owned by the consumer 2) Services providing final results: in which a company can offer a customised mix of services, as a substitute for the purchasing and use of single products providing of a specific final result with a low-level of client participation; and 3) Services providing enabling platforms: in which a company can offer access to products, tools, opportunities or capabilities (platforms) that enable clients to get the results they want Furthermore, it is discussed how PS systems are applicable in developing countries, and how PS systems, as an innovation strategy can present an opportunity to facilitate the process of industrialisation with less environmental impact, by jumping over or by passing the stage characterised by individual consumption/ownership of mass-produced goods towards the more advanced service-economy

Extending UML for modeling Web applications

Abstract: Web sites are progressively evolving from browsable, read-only information repositories to Web-based distributed applications. Compared to traditional Web sites, these Web applications do not only support navigation and browsing, but also operations that affect their contents and navigation states. Compared to traditional applications Web applications integrate operations with the built-in browsing capabilities of hypermedia. These novelties make Web application design a complex task that requires the integration of methods and techniques developed in different "worlds". This integration is achieved in this paper by extending and customizing the Unified Modeling Language (UML) with Web design concepts borrowed from the Hypermedia Design Model (HDM). Hypermedia elements are described through appropriate UML stereotypes. UML diagrams are also tailored to model operations and relate them with hypermedia elements. The approach is exemplified by describing the design of a Web-based conference manager.