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Showing papers by "Polytechnic University of Turin published in 1992"


Journal ArticleDOI
TL;DR: In this paper, a new operatorial approach to the study of turbulence is described, based on the general algebraic properties of the filtered representations of a turbulence field at different levels.
Abstract: The paper describes a new operatorial approach to the study of turbulence, based on the general algebraic properties of the filtered representations of a turbulence field at different levels. The main results of this analysis is the averaging invariance of the filtered Navier-Stokes eaquations in terms of the generalized central moments, and an algebraic identity that relates the turbulent stresses at different levels. The resolved turbulence is defined, the algebraic consistency rules that relate these resolved quantities to the turbulent stresses at different levels are derived, and their possible uses in subgrid modeling is discussed.

1,094 citations


Journal ArticleDOI
TL;DR: A procedure performed by using a genuine two-port reciprocal network instead of a standard 'thru' in a full two- port error correction of an automatic network analyzer is presented and provides a great degree of accuracy.
Abstract: A procedure performed by using a genuine two-port reciprocal network instead of a standard 'thru' in a full two-port error correction of an automatic network analyzer is presented. Although it can be applied to any type of waveguide system, the proposed technique is particularly useful with noninsertable coaxial or one-wafer devices. Experimental comparisons show that the suggested procedure provides a great degree of accuracy. >

264 citations



Journal ArticleDOI
TL;DR: In this article, the authors developed the equations governing the elastodynamic behavior of moderately thick multilayered anisotropic plates by making use of a displacement field which allows a nonlinear variation of the inplane displacements through the laminate thickness and fulfils a priori the static and geometric continuity conditions.

244 citations


Journal ArticleDOI
TL;DR: A rigorous analysis of digital coherent optical modulation schemes using the state of polarization as the modulating parameter obtains the exact performance of all the polarization-based modulation schemes proposed in the literature so far, including a differential demodulation scheme, named DPOLSK, which does not require either electrooptic or electronic polarization tracking.
Abstract: A rigorous analysis of digital coherent optical modulation schemes using the state of polarization as the modulating parameter is presented. The analysis obtains the exact performance of all the polarization-based modulation schemes proposed in the literature so far, including a differential demodulation scheme, named DPOLSK, which does not require either electrooptic or electronic polarization tracking. Preliminary results involving multilevel transmission schemes based on the state of polarization are introduced. A spectral analysis of POLSK signals is also proposed. >

223 citations


Proceedings ArticleDOI
TL;DR: In this paper, a dynamic generalization of the Preisach hysteresis model is proposed, in which the rate of change of the flux associated with each elementary preisach loops is not infinite, as in the standard PreISach model, but proportional to the difference between the external field and the loop threshold fields.
Abstract: A dynamic generalization of the Preisach hysteresis model is proposed, in which the rate of change of the flux associated with each elementary Preisach loops is not infinite, as in the standard Preisach model, but proportional to the difference between the external field and the loop threshold fields. With this assumption, the shape of the elementary Preisach loops, as well as of the macroscopic hysteresis loops, becomes dependent on the magnetizing frequency f. In particular, it is found that the loop area follows a law of the form C/sub 0/+C/sub 1/ square root f. The model is well suited to applications in the field of power loss calculations in soft magnetic materials. >

196 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the functions on a Siegel domain that depend only on the distance from the identity form a commutative convolution algebra, which makes S an example of a harmonic manifold, not necessarily symmetric.
Abstract: To each groupN of Heisenberg type one can associate a generalized Siegel domain, which for specialN is a symmetric space This domain can be viewed as a solvable extensionS =NA ofN endowed with a natural left-invariant Riemannian metric We prove that the functions onS that depend only on the distance from the identity form a commutative convolution algebra This makesS an example of a harmonic manifold, not necessarily symmetric In order to study this convolution algebra, we introduce the notion of “averaging projector” and of the corresponding spherical functions in a more general context We finally determine the spherical functions for the groupsS and their Martin boundary

175 citations


Journal ArticleDOI
TL;DR: Theoretical and phenomenological aspects of trickle-bed reactors as reported in a wide number of papers of the last 35 years have been reviewed in this article, where several engineering topics have been focused by trying a critical interpretation of the attained results.

169 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that a first-order compensator is necessary and sufficient to stabilize only sixteen of the extreme plants, and when additional information about the compensator was specified (sign of the gain and signs and relative magnitudes of the pole and zero), then, in some cases, it was sufficient and sufficient for stabilizing eight critical plants, while, in other cases, the compensators were sufficient and necessary to stabilize twelve critical plants.
Abstract: It has been shown previously that a first-order compensator robustly stabilizes an internal plant family if and only if it stabilizes all of the extreme plants. These extreme plants are obtained by considering all possible combinations for the extreme values of the numerator and denominator coefficients. In this work, the authors prove a stronger result, namely, that it is necessary and sufficient to stabilize only sixteen of the extreme plants. These sixteen plants are generated using the Kharitonov polynomials associated with the numerator and denominator. Furthermore, when additional information about the compensator is specified (sign of the gain and signs and relative magnitudes of the pole and zero), then, in some cases, it is necessary and sufficient to stabilize eight critical plants, while, in other cases, it is necessary and sufficient to stabilize twelve critical plants. >

168 citations


Journal ArticleDOI
TL;DR: In this article, a morphous solids belonging to the systems Al2O3-Me2O (Me = Na, K) and Al6-xBxO9 (1 x 3) were prepared by nitrate decomposition, introducing boron in the form of boric acid.
Abstract: A morphous solids belonging to the systems Al2O3–Me2O (Me = Na, K) and Al2O3–B2O3 were prepared by nitrate decomposition, introducing boron in the form of boric acid. Crystalline metastable solids with pseudotetragonal symmetry were obtained from thermal treatment at 850° to 900°C for the compositions Al6MexO(9+0.5x) (x≅ 1; Me = Na, K) and Al6-xBxO9 (1 x 3). The resultant solids were stable only within a difinite temperature range and transformed, with further treatment increases, into stable equilibrium phases. The structures of the metastable phases were examined by X-ray diffraction and Fourier transform infrared spectroscopy, and both analyses showed a mullite type of framework, inside of which the atomic coordinates were refined in the Pbam (no. 55) space group. The present results indicate that these silica-free mullite structures are stabilized by two different mechanisms: (1) interstitial occupation of bulky cations (Na+, K+) or (2) substitution of B for Al in some of the tetrahedral positions.

117 citations


Journal ArticleDOI
TL;DR: The curve-fitting process is explained with reference to the main factors affecting the wind pressure distribution on a building envelope: terrain roughness, surrounding buildings, aspect ratios, and wind direction.

Journal ArticleDOI
TL;DR: In this article, a generalized multiport network analyzer implemented using commercially available hardware is presented, where measurement calibration is accomplished through a novel calibration procedure which requires only conventional standards used for two-port calibrations.
Abstract: A generalized multiport network analyzer implemented using commercially available hardware is presented. Measurement calibration is accomplished through a novel calibration procedure which requires only conventional standards used for two-port calibrations. The calibration theory accounts for the errors due to the signal switching network but does not systematically remove errors due to signal switching leakage between port pairs. The approach is verified on a three-port test set implementation, and the measuring system can be expanded to n ports with additional hardware in a straightforward manner. Experimental verification was carried out through measurement of one-, two-, and three-port devices connected to the test set ports in several different ways. Excellent agreement of the same corrected S-parameters measured at different test set ports was observed, and confidence in system accuracy is established through measurement of two-port verification standards. >

Journal ArticleDOI
TL;DR: In this paper, a reluctance motor drive with high dynamic performances is proposed, which is sinusoidally wound and the rotor belongs to the axially laminated type, and the vector control technique used (utilizing a flux observer) is described.
Abstract: A reluctance motor drive giving high dynamic performances is proposed. The machine is sinusoidally wound, and the rotor belongs to the axially laminated type. The vector control technique used (utilizing a flux observer) is described. A prototype system has been realized, and the practical results obtained are given. >

Journal ArticleDOI
13 Apr 1992
TL;DR: In this article, a loss model based on a dynamic generalization of the Preisach hysteresis model, in which the standard preisach algorithm is coupled to an equation for the rate of change of the flux associated with each elementary PreisACH loop, is presented.
Abstract: A loss model based on a dynamic generalization of the Preisach hysteresis model, in which the standard Preisach algorithm is coupled to an equation for the rate of change of the flux associated with each elementary Preisach loop, is presented. The model is able to predict loss features not explained by previous treatments and provides a general interpretative frame for the study of the connection between power losses and microstructure of soft magnetic materials. >

Book ChapterDOI
07 Sep 1992
TL;DR: SPELL is a language fot software process modeling based on a structurally object-oriented data-model with relations that extends the underlying versioned EPOSDB, and is based on Prolog with full object-orientation, concurrency, persistency, distribution, and tool invocation facilities.
Abstract: SPELL is a language fot software process modeling based on a structurally object-oriented data-model with relations. It extends the underlying versioned EPOSDB, and is based on Prolog with full object-orientation, concurrency, persistency, distribution, and tool invocation facilities. SPELL can express multiple level of abstraction/composition of process information. A process model is a set of types to describe activities (tasks), products, tools and projects (management information). Task instantiation can be partly automatized. SPELL also provides a platform for modeling and experimenting with software meta-activities to model, analyze, and support software processes.

Proceedings ArticleDOI
16 Dec 1992
TL;DR: In this paper, the performance robustness of control systems in the presence of both parametric perturbations and unmodeled dynamics is investigated, and a novel algorithm based on the Bernstein polynomial expansion is proposed.
Abstract: The performance robustness of control systems in the presence of both parametric perturbations and unmodeled dynamics is investigated. Assuming polynomial parametric perturbations and H/sub infinity / performances, the problem is reduced to checking the positivity of suitable polynomials. A novel algorithm based on the Bernstein polynomial expansion is proposed. A Bernstein branch and bound (B/sup 3/) algorithm has been implemented using the formulas of Bernstein coefficients on subdivisions in the parameter space. The efficiency of the algorithm is demonstrated on some examples taken from the literature on the robustness analysis of nonlinearity perturbed control systems. >

Journal ArticleDOI
TL;DR: In this paper, a method for deducing the [${\mathit{sp}}^{3}$]/[${m{m} √ √ m} ratio from the experimental values of the complex dielectric constant as obtained by optical transmittance and reflectance measurements is presented.
Abstract: The evaluation of the amount of tetrahedral and trigonal cross-linking, that is, the ${\mathit{sp}}^{3}$- and ${\mathit{sp}}^{2}$-hybridized carbon, is of great importance in understanding the properties of amorphous carbon films. In this paper we report a method for deducing the [${\mathit{sp}}^{3}$]/[${\mathit{sp}}^{2}$] ratio from the experimental values of the complex dielectric constant as obtained by optical transmittance and reflectance measurements. We assume a Gaussian-like distribution of \ensuremath{\pi} and ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ electronic densities of states in order to fit the contribution of \ensuremath{\pi}\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ to the imaginary part, ${\mathrm{\ensuremath{\epsilon}}}_{2}$, of the dielectric constant in the low-energy region. Through the Kramers-Kronig relationships we deduce the corresponding values of the real part ${\mathrm{\ensuremath{\epsilon}}}_{1}$ of the dielectric constant for such transitions. By subtracting these values from the measured ${\mathrm{\ensuremath{\epsilon}}}_{1}$ we deduce the contribution of \ensuremath{\sigma}\ensuremath{\rightarrow}${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ to ${\mathrm{\ensuremath{\epsilon}}}_{1}$. The Wemple-Didomenico model has been used to obtain the dispersion energy and the average excitation energy. Knowing the plasmon energies, we apply the ``f-sum rule'' to deduce the [${\mathit{sp}}^{3}$]/[${\mathit{sp}}^{2}$] ratio. The method applied to a-C:H films deposited by rf diode sputtering provides results in agreement with those obtained by other techniques.

Journal ArticleDOI
TL;DR: In this article, the state of the art and future trends in physics-based electron device modelling for the computer-aided design of monolithic microwave ICs are provided. But the authors focus on the use of state-of-the-art physics-and analytical or numerical models for circuit analysis, with particular attention to the role of intermediate behavioral models in linking multidimensional device simulators with circuit analysis tools.
Abstract: On overview on the state of the art and future trends in physics-based electron device modelling for the computer-aided design of monolithic microwave ICs is provided. After a review of the main physics-based approaches to microwave modeling, special emphasis is placed on innovative developments relevant to circuit-oriented device performance assessment, such as efficient physics-based noise and parametric sensitivity analysis. The use of state-of-the-art physics-based analytical or numerical models for circuit analysis is discussed, with particular attention to the role of intermediate behavioral models in linking multidimensional device simulators with circuit analysis tools. Finally, the model requirements for yield-driven MMIC design are discussed, with the aim of pointing out the advantages of physics-based statistical device modeling; the possible use of computationally efficient approaches based on device sensitivity analysis for yield optimization is also considered. >

Journal ArticleDOI
TL;DR: New theorems on fault equivalence and dominance, forming the basis of an algorithm that collapses all the structurally equivalent faults in a circuit, plus many of the functionally equivalent faults, are presented.
Abstract: The partitioning of faults into equivalence classes so that only one representative fault per class must be explicitly considered in fault simulation and test generation, called fault collapsing, is addressed. Two types of equivalence, which are relevant to the work reported, are summarized. New theorems on fault equivalence and dominance, forming the basis of an algorithm that collapses all the structurally equivalent faults in a circuit, plus many of the functionally equivalent faults, are presented. Application of the algorithm to a set of benchmark circuits establishes that identification of functionally equivalent faults is feasible, and that, in some cases, they are a large fraction of the faults in a circuit. The collapsing algorithm applies not only to combinational designs but to synchronous sequential circuits as well. >

Journal ArticleDOI
TL;DR: In this article, the scattering of an arbitrarily polarized plane wave by impenetrable (e.g., metallic) or penetrable (i.e., chiral) cylinders coated with an arbitrary number of layers of different chiral materials is considered.
Abstract: The scattering of an obliquely incident and arbitrarily polarized plane wave by impenetrable (e.g., metallic) or penetrable (i.e., chiral) cylinders coated with an arbitrary number of layers of different chiral materials is considered. The constitutive relations within each homogeneous layer are given in terms of the chirality admittance. A cylindrical wave expansion is used to express the fields in each layer and in free-space, while a chain-matrix algorithm is used to expedite the numerical evaluation of the scattered field. The radar cross-section is analyzed over a wide frequency band.

Proceedings ArticleDOI
04 Oct 1992
TL;DR: In this paper, a Universal Field Oriented (UFO) controller operating in the air gap flux reference frame is applied to a current regulated PWM induction motor drive, which is measured by the stator third harmonic voltage component.
Abstract: The universal field oriented (UFO) controller operating in the air gap flux reference frame is applied to a current regulated PWM induction motor drive. The air gap flux is measured by the stator third harmonic voltage component. It is shown in the paper that due to motor saturation, a third harmonic flux component is generated in the air gap. Since the third harmonic flux component is a function of the fundamental air gap flux and is always in phase with it for any load condition, it constitutes an accurate way to measure the fundamental air gap flux. This harmonic flux component induces a third harmonic in each one of the motor phase voltages, and the paper shows how this voltage is processed for the measurement of the air gap flux and consequent implementation of the UFO controller. Due to the robustness of the third harmonic sensing method and to the structure of the UFO controller, the resulting drive is not affected by detuning errors in steady state operation. In addition, the UFO drive has excellent dynamic performance even under strongly detuned conditions. To avoid any transition between the indirect universal field orientation (IUFO) (suitable controller structure for low speed) and the direct universal field orientation (DUFO) (suitable controller structure for high speed), a new type of UFO, i.e. a combination of the two methods is presented. >

Journal ArticleDOI
01 Jan 1992
TL;DR: In this paper, the restoring force surface method of non-linear system identification is applied in order to determine the nonlinear characteristics of the absorbers in an easily visualizable manner, which provides a more realistic representation of the stiffness characteristics than previous simple models.
Abstract: The objectives of this paper are essentially twofold. In the first case an experimental study of a number of shock absorbers is presented; the restoring force surface method of non-linear system identification is applied in order to determine the non-linear characteristics of the absorbers in an easily visualizable manner. In the second part, a new physical model for the absorber is presented which incorporates effects due to compressibility of the fluid in the absorber; this provides a more realistic representation of the stiffness characteristics than previous simple models. The new model is compared with the experimental data.

Journal ArticleDOI
TL;DR: In this paper, the relationship between classical and quantum structures for a map on the sphere whose behavior can be chaotic in the classical limit is studied, and the scarring phenomena related to the short periodic orbits and their homoclinic neighborhoods are discussed.
Abstract: We study the relationship between classical and quantum structures for a map on the sphere whose behavior can be chaotic in the classical limit. On the classical side we implement an efficient method to locate periodic points on symmetry lines. On the quantum side we show how matrix elements of the propagator in the coherent-state representation are connected to classical structures. Diagonal and off-diagonal matrix elements are related to periodic points, symmetry lines, and other invariant structures in phase space, both in the time and in the energy domains. The scarring phenomena related to the short periodic orbits and their homoclinic neighborhoods are discussed.

Proceedings ArticleDOI
06 Dec 1992
TL;DR: An analysis of the main parameters determining the performance of a trellis-coded modulation (TCM) scheme, together with a comparison of the algorithms used in evaluating these performances in a computationally efficient and fast way, is presented.
Abstract: An analysis of the main parameters determining the performance of a trellis-coded modulation (TCM) scheme, together with a comparison of the algorithms used in evaluating these performances in a computationally efficient and fast way, is presented. Performance evaluation methods are matched to the symmetry degree of the TCM scheme so as to take advantage of it in reducing the algorithms' complexity. New examples of application are also included. >

Proceedings ArticleDOI
04 Oct 1992
TL;DR: In this paper, the design problems of high-frequency machines are analyzed from the electromagnetic, mechanical, and thermal points of view, and the possibility of using the classical relations adopted to calculate the equivalent circuit parameters for standard motors at 50 Hz is examined.
Abstract: Induction motors used in electrical spindles and fed by high-frequency inverters are considered. The design problems of high-frequency machines are analyzed from the electromagnetic, mechanical, and thermal points of view. The possibility of using the classical relations adopted to calculate the equivalent circuit parameters for standard motors at 50 Hz is examined, and the results are compared with experimental ones. A brief overview of problems related to the mechanical design (bearings, lubrication, and shaft stiffness) and to the thermal design is presented. Finally, based on simulation and experimental results, some specific criteria for the electromagnetic design are developed. >

Journal ArticleDOI
TL;DR: In this article, deep catalytic oxidation over a commercial platinum catalyst of benzene, enthenylbenzene (styrene) and their mixtures is investigated. And the authors show that strong inhibition effects are observed when binary mixtures are oxidized.

Journal ArticleDOI
TL;DR: In this paper, the artificial aging characteristics at 177 °C of Mg-Al-Zn (AZ80A) alloy and its composite reinforced by B4C particles were compared.
Abstract: The artificial aging characteristics at 177 °C of MgAlZn (AZ80A) alloy and its composite reinforced by B4C particles were compared. The morphology and the different distributions of the hardening precipitate (Mg17Al12) were observed by optical microscopy in these two materials. The aging sequence was studied by differential scanning calorimetry. This technique coupled with X-ray diffraction analyses allowed us to evaluate both the precipitation kinetics and the amount of Mg17Al12 obtained as a function of the aging time. The mechanical characteristics were evaluated by hardness measurements. The ceramic reinforcement was found to increase the aging rate of the composite with respect to that of the unreinforced alloy. Furthermore B4C particles affect the precipitation mechanism and the precipitate-strengthening distribution. In fact the heterogenous nucleation of Mg17Al12 close to the interface between ceramic and metal matrix is greatly enhanced in the composite. As a consequence the hardness increase is slightly lower for composite than for the alloy, because of the different precipitate distributions in the matrix.

Book ChapterDOI
01 Jan 1992
TL;DR: This is the third report on the development of a local interaction simulation approach (LISA), based on the use of the Connection Machine, a massively parallel computer with a large number of processors connected in a programmable way, in the framework of a fixed physical wiring scheme.
Abstract: This is our third report on the development of a local interaction simulation approach (LISA), based on the use of the Connection Machine(CM) The CM is a massively parallel computer with a large number of processors (many thousands or even millions, if virtual processors are also included), connected in a programmable way, in the framework of a fixed physical wiring scheme

Journal ArticleDOI
TL;DR: The effect of the inclusion of silicon atoms in the network of diamond-like carbon (amorphous carbon and hydrogenated amorphous carbon) is studied in this article, where it is shown that initially the effect of silicon inclusion is to reduce the size of the graphitic-like islands.
Abstract: The effect of the inclusion of silicon atoms in the network of diamond-like carbon (amorphous carbon and hydrogenated amorphous carbon) is studied. Samples of amorphous hydrogenated CSi are deposited by means of a sputter-assisted plasma chemical vapour deposition system in which a carbon target is sputtered in an atmosphere composed of silane-diluted argon, where the silane flow rate is varied. It is shown that initially the effect of silicon inclusion is to reduce the size of the graphitic-like islands. When the amount of silicon is increased over a critical value, the network assumes the characteristic of the semiconductor-type amorphous hydrogenated SiC, where the properties of silicon are predominant.

Journal ArticleDOI
TL;DR: In this paper, compliance change and crack tip stress intensity factor are applied to study the failure behavior of a reinforced beam with an edge crack in the matrix to simulate the constraint of the reinforcement.