Showing papers by "Polytechnic University of Milan published in 1983"
TL;DR: In this paper, the stiffness and the stresses of a beam section made of anisotropic and non-homogeneous materials such as the rotor blades of a modern helicopter or of a large wind generator are calculated.
415 citations
TL;DR: A simple access protocol is described which meets the bandwidth requirement and maximum packet delay constraint for voice communication at all times, while guaranteeing a minimum bandwidth requirement for data traffic.
Abstract: Expressnet is a local area communication network comprising an inbound channel and an outbound channel to which the stations are connected. Stations transmit on the outbound channel and receive on the inbound channel. The inbound channel is connected to the outbound channel so that all signals transmitted on the outbound channel are duplicated on the inbound channel, thus achieving broadcast communication among the stations. In order to transmit on the bus, the stations utilize a distributed access protocol which achieves a conflict-free round-robin scheduling. This protocol is more efficient than existing round-robin Schemes as the time required to switch control from one active user to the next in a round is minimized (on the order of a carrier detection time), and is independent of the end-to-end network propagation delay. This improvement is particularly significant when the channel data rate is so high, or the end-to-end propagation delay is so large, Or the packet size is so small as to render the end-to-end propagation delay a significant fraction of, or larger than, the transmission time of a packet. Moreover, some features of Expressnet make it particularly suitable for voice applications. In view of integrating voice and data, a simple access protocol is described which meets the bandwidth requirement and maximum packet delay constraint for voice communication at all times, while guaranteeing a minimum bandwidth requirement for data traffic. Finally, it is noted that the voice/data access protocol constitutes a highly adaptive allocation scheme of channel bandwidth, which allows data users to recover the bandwidth unused by the voice application. It can be easily extended to accommodate any number of applications, each with its specific requirements.
231 citations
TL;DR: The optimal distribution of a database schema over a number of sites in a distributed network is considered and the design is driven by user-supplied information about data distribution.
Abstract: The optimal distribution of a database schema over a number of sites in a distributed network is considered. The database is modeled in terms of objects (relations or record sets) and links (predefined joins or CODASYL sets). The design is driven by user-supplied information about data distribution. The inputs required by the optimization model are: 1) cardinality and size information about objects and links, 2) a set of candidate horizontal partitions of relations into fragments and the allocations of the fragments, and 3) the specification of all important transactions, their frequencies, and their sites of origin.
139 citations
TL;DR: In this paper, the performance of a single-photon avalanche photodiode particularly suitable for the detection of fast and ultra-weak light pulses is described, and the advantages of this device over other available detectors are discussed.
Abstract: The performance of a new single-photon avalanche photodiode particularly suitable for the detection of fast and ultraweak light pulses is described. The advantages of this device over other available detectors are discussed. The electronic circuitry developed allows the measurement of fluorescence decays with a time resolution of 70 ps FWHM (full-width at half-maximum) and a data acquisition rate of up to 50 kHz.
122 citations
TL;DR: In this paper, the kinetics of steam reforming of methanol, catalyzed by a commercial Cu-Zn catalyst, have been studied using a CSTR reactor, and it was shown that the decomposition was the rate determining step of the process.
119 citations
102 citations
TL;DR: In this article, the propagation of blunt smeared crack bands through a finite element mesh in plain or reinforced concrete structures is studied, which is satisfactorily accomplished by extending the previously proposed concept of free bond slip length for the cases of skew meshes and skew bars.
Abstract: The propagation of blunt smeared crack bands through a finite element mesh in plain or reinforced concrete. structures is studied. A previous work, which demonstrated (approximate) independence of results from the chosen mesh size, is extended by demonstrating the same for the changes in mesh orientation with regard to the crack band and to the steel bars. Bond slip of bars must also be considered. This is satisfactorily accomplished by extending the previously proposed concept of free bond slip length for the cases of skew meshes and skew bars. In the presence of reinforcement, the previous formula for the equivalent strength giving approximately the same results as the energy criterion must be expanded by a term which corresponds to the third term of the asymptotic expansion of displacements near the tip of a sharp crack. The energy criterion is shown to give consistent results for different types of fracture specimens. However, the equivalent strength calibrated for the center‐cracked tensile specimen ...
76 citations
TL;DR: In this article, the authors used high sensitivity moire interferometry for the determination of the fracture process zone in concrete, which is a difficult experimental problem because the resulting deformation is strongly localized and cannot be measured adequately by strain-gages or coarse moire techniques.
75 citations
01 Jan 1983
TL;DR: In this paper, the main lobe of the autocovariance of a block of picture elements of an image is first modeled as a paraboloid; afterwards, the comparison with the mutual covariance between two successive video frames, allows to determine their relative displacement.
Abstract: Small variations of the apparent velocity of objects imaged by television cameras can be efficiently measured comparing the frame differences with the spatial variations of the luminance. The main lobe of the autocovariance of a block of picture elements of an image is first modeled as a paraboloid; afterwards, the comparison with the mutual covariance between two successive video frames, allows to determine their relative displacement. The curvatures of the autocovariance taken at the origin are proportional to the m.s. slopes of the image along the coordinate axes; it can be shown that the slopes should be calculated using a centered differentiation, rather than a non centered one, to avoid bias in the estimation of the displacement. To be able to precisely measure the displacement along a given direction, it is necessary that the m.s. slope in that direction be high enough; in fact, the measure of temporal and spatial image derivatives only constrains the projection of the actual displacement along the image gradient. More complex, but continuous, motion fields can be estimated with simple extensions of the original formulation of the differential method. A stochastic model for the motion field is therefore introduced, in order to derive a recursive estimation technique. The component of the motion paralel to the local image gradient is updated, on a pel by pel basis, while the other one is approximately kept constant. The practical results are sufficient for image coding, but not good enough to get a nicely smooth velocity field in real situations.
71 citations
TL;DR: The results indicate different rates of maturation of the neuronal systems underlying the genesis of the various movement-related brain macropotentials in children ranging from 8 to 13 years of age.
56 citations
08 Aug 1983
TL;DR: In this article, the authors present a general framework in which the activity of error recovery can be automated by introducing a monitor program which identifies the appearance of any error and attempts to correct that error.
Abstract: Unexpected events can cause the failure of apparently "correct" robot programs. The interaction with the real world and its unpredictability make the problem of error recovery in robot programming specially important. The goal of the paper is to present a general framework in which the activity of error recovery can be automated. This is accomplished by introducing a monitor program which identifies the appearance of any error and attempt to correct that error. The correction is done using a knowledge base where the knowledge that the user has about error identification and correction is expressed in symbolic form. An inference mechanism allows extension of this knowledge base for use in complex and unanticipated situations.
TL;DR: In this article, the authors presented time-resolved fluorescence studies of hematoporphyrin in aqueous solution and in different organic solvents, which revealed the presence of a monomeric and aggregated (probably dimeric) form of the molecule as confirmed by absorption and fluorescence measurements.
Abstract: Time-resolved fluorescence studies of hematoporphyrin in aqueous solution and in different organic solvents are presented. The| observation of two exponential components in the fluorescence decay in aqueous solution reveals the presence of a monomeric and aggregated (probably dimeric) form of the molecule, as confirmed by absorption and fluorescence measurements. The slow component (~ 15 ns in aqueous solution) and the fast one (~ 3.8 ns in aqueous solution) are attributed to monomers and dimers, respectively. Higher aggregated species of hematoporphyrin are also present, which are essentially devoid of fluorescence properties.
TL;DR: This work extends to the multi-constrained, unweighted case, the analysis that was already made in a previous work for the one-conStrained, weighted case of undirected spanning tree problems from the viewpoint of their computational complexity.
TL;DR: In this article, the kinetics of acetic acid esterification with ethyl alcohol, in vapor phase, have been studied in the presence of decationized Y zeolite catalysts.
TL;DR: In this paper, the preparation of (S)-1-(1,3-dithian-2-yl)-2-hydroxypropane 3 and its transformation into (S,S)-(+)-grahamimycin A1, through intramolecular pinacolic coupling of dialdehyde 9, are described.
TL;DR: In this article, a finite element model for elastic-plastic analysis is presented, which is based on a minimum principle requiring the optimization of a functional with respect to the independent fields of displacements and plastic multipliers.
Abstract: A finite element model for elastic-plastic analysis is presented. The formulation is based on a minimum principle requiring the optimization of a functional with respect to the independent fields of displacements and plastic multipliers. Connections with traditional procedure are explored. Some deficiencies of the formulation, due to the independent modelling of the two distributions of variables, are also discussed and some consistency criteria able to overcome the above shortcomings are proposed. Simple examples illustrate the proposed procedure, which can be expected to be efficient and reliable.
TL;DR: In this article, the lattice dynamics of trans-polyacetylene as a perfect one-dimensional crystal is treated and the results of the calculations are used to propose a vibrational assignment for (CH) x, (CD) x and ( 13 CH) x.
01 Jan 1983
TL;DR: In this article, the KS-transformation introduced by Kustaanheimo and Stiefel into Celestial Mechanics is formulated in terms of hypercomplex numbers as the product of a quaternion and its antiinvolute.
Abstract: In this note the KS-transformation introduced by Kustaanheimo and Stiefel into Celestial Mechanics is formulated in terms of hypercomplex numbers as the product of a quaternion and its antiinvolute. Therefore it represents a particular morphism of the real algebra of quaternions-having for image a three-dimensional real linear subspace-and also anatural generalization of the Levi-Civita transformation. The quaternion matrix of the product leads to the KS-matrix; the bilinear relation and the two identities which play a central role in the KS-theory are easily derived. A suitable quaternion gauge-transformation is given which leads to the well-known fibration of the four-dimensional space. In addition several geometrical interpretations are brought out.
TL;DR: In this paper, the SAW voltage sensor versus voltage is experimentally evaluated for YZ, YX LiNbO 3 and (001) (110) Bi 12 GeO 20 substrates.
TL;DR: In this paper, the impact of information technology on organizations is reconsidered by applying a new analytical framework, and an enlargement of the framework to take into account alternative mechanisms for organizational participation, such as exit, voice and loyalty, allows to examine the impacts of IT on participation possibilities within organizations.
TL;DR: The problem of proving the correctness of execution strategies is reduced to the problem of proved the equivalence of two expressions of Multirelational Algebra, which constitutes a theoretical foundation for the design of such optimizers.
Abstract: A major requirement of a Distributed DataBase Management System (DDBMS) is to enable users to write queries as though the database were not distributed (distribution transparency). The DDBMS transforms the user's queries into execution strategies, that is, sequences of operations on the various nodes of the network and of transmissions between them. An execution strategy on a distributed database is correct if it returns the same result as if the query were applied to a nondistributed database.This paper analyzes the correctness problem for query execution strategies. A formal model, called Multirelational Algebra, is used as a unifying framework for this purpose. The problem of proving the correctness of execution strategies is reduced to the problem of proving the equivalence of two expressions of Multirelational Algebra. A set of theorems on equivalence is given in order to facilitate this task.The proposed approach can be used also for the generation of correct execution strategies, because it defines the rules which allow the transformation of a correct strategy into an equivalent one. This paper does not deal with the problem of evaluating equivalent strategies, and therefore is not in itself a proposal for a query optimizer for distributed databases. However, it constitutes a theoretical foundation for the design of such optimizers.
TL;DR: In this paper, a simple electrostatic model for the binding energy in weak intermolecular interaction is proposed, which requires the knowledge of atomic equilibrium charges which can be derived from molecular dipole moments and infrared intensities.
TL;DR: In this article, the quadratic valence force field derived in Part I of this study for perfect trans-polyacetylene is used and adapted for the study of the doping-induced IR absorption of polyacetylene.
TL;DR: Theoretical and experimental investigation has been carried out to determine the best working conditions of single or parallel combinations of field effect or bipolar transistors in low noise preamplifiers for processing times in the 10 ns range as mentioned in this paper.
Abstract: Theoretical and experimental investigation has been carried out to determine the best working conditions of single or parallel combinations of field-effect or bipolar transistors in low noise preamplifiers for processing times in the 10 ns range. The effects of diffusion capacitance and base spreading resistance in bipolar transistors have been put into evidence and a way of reducing the noise due to the latter is suggested and experimentally demonstrated.
TL;DR: In this article, the phase speed of infinitesimal disturbances in a relativistic gas is shown to be less than the speed of light by means of the kinetic theory of gases and is valid for any collision operator.
Abstract: The phase speed of infinitesimal disturbances in a relativistic gas is shown to be less than the speed of light. The result is obtained by means of the kinetic theory of gases and is valid for any collision operator. The treatment applies, in particular, to the speeds of propagation of sound, shear, and heat waves. These waves are further shown to be damped.
TL;DR: In this paper, the main task of the θ convergence promoter is to afford a better estimate of liquid and vapor molar fractions in each tray of the column, while the assumptions implied by the promoter prove to be reliable for conventional columns, while they may cause numerical instability when dealing with nonconventional configurations.
Abstract: The main task of the θ convergence promoter is to afford a better estimate of liquid and vapor molar fractions in each tray of the column.
The assumptions implied by the promoter prove to be reliable for conventional columns, while they may cause numerical instability when dealing with nonconventional configurations. In these cases, corrected molar fractions may be computed only after making a supplementary assumption, which in principle is not unique. So, the paper presents a new methodology which gives rather satisfactory results.
TL;DR: An optimal filter (a Kalman filter) has been developed which is intended to capture the disturbances of the electromyographic noise on the basis of an a priori modelling which considers a series of impulses with a temporal occurrence according to a Poisson distribution as a noise generating mechanism.
TL;DR: The Mansouri-Sexl and Sjodin point of view on clock synchronization in special relativity is maintained against various criticisms, taking into account also the recent view of stochastic electrodynamics as mentioned in this paper.
Abstract: The Mansouri-Sexl and Sjodin point of view on clock synchronization in special relativity is maintained against various criticisms, taking into account also the recent point of view of stochastic electrodynamics. Light speed invariance is also discussed in an intuitive way.
TL;DR: A new cytotoxic lanostane triterpene, named 3-β-acetyl-2-α(3′-hydroxy-3′methyl)glutarylcrustulinol, was isolated from Hebeloma crustuliniforme and H. sinapizans as discussed by the authors.