Showing papers by "Polytechnic University of Turin published in 1981"

Unsteady compressible flow - A computational method consistent with the physical phenomena

Abstract: A methodology for the numerical prediction of 2-D and 3-D unsteady, in viscid, compressible flows is presented. The primitive Euler equations are recast in terms of compatibility equations on characteristic surfaces. In such a way the evolution in time of the flow properties is described explicitly as the interaction of signals corresponding to the physical wave-propagation phenomenon. The equations are discretized through a finite-difference method where the proper domain of dependence of each computed point is preserved, by approximating the space-derivatives with one-sided differences, according to the velocity of propagation of signals along bicharacteristics. Results of the application of the proposed method to subsonic and transonic flow past airfoils are shown and compared with different methods.

A new approach to the study of loss anomaly in SiFe

Abstract: The behavior of energy losses per cycle P/f m vs. magnetizing frequency has been investigated on a

Experimental strain analysis on the mandibular condyle under various conditions.

Abstract: Four human adult mandibles were selected, a rosette strain guage was applied in the angle region bilaterally and a single element strain gauge on the posterior surface of both condyles and condylar necks. Each mandible, together with a brass replica of the upper arch and the glenoid fossa, were placed together on a supporting frame and loads were applied to simulate the action of the anterior temporal, masseter and internal pterygoid muscles. Strains were recorded in maximum intercuspation and after insertion of a rubber frame between the lateral teeth. Strains in the angle region were greater on the working side than on the balancing side. However, in the condylar region the balancing side strains were higher than on the working side. This can be attributed to the different orientation of strains on the two sides.

On the vanishing viscosity limit for acoustic phenomena in a bounded region

Abstract: The problem of the linearized vibrations of a viscous, barotropic fluid in a bounded vessel is studied under various boundary conditions. It is shown that the essential spectrum is formed by one or two points that tend to infinity as the viscosity coefficients tend to zero. The asymptotics of solutions of the initialboundary value problem as the viscosity coefficients tend to zero is established. Some remarks about the physical properties of the associated sound waves are given.

Composition and structure of two hitherto unidentified phases in the system La2O3-NiO-O

Abstract: The compound La4Ni3O10 can be obtained in a mechanical mixture with NiO by heating LaNiO3 at 1100°C in air. It has an orthorhombic structure of the Sr4Ti3O10 modified type. By heating La(NO3)3 and Ni(NO3)2 in a molecular ratio of 4 3 at 1100°C at first a mixture of NiO and a compound with the formula La3Ni2O7 is obtained which slowly changes to La4Ni3O10. The compound La3Ni2O7 also belongs to the orthorhombic system with a structure of the Sr3Ti2O7 modified type.

Quantisation of motion in a velocity dependent field: the v2 case

Abstract: The case of the quantum unidimensional motion of a point particle subject to a viscous force proportional to the square of the speed of the particle is treated. Once a suitable Lagrangian has been chosen, the canonical quantization procedure is applied leading to a Schr\"odinger equation for quadratic friction and an arbitrary potential. The cases of an exponentially decreasing potential plus a linearly increasing term is explicitly solved.

Automobile Aerodynamic Drag on the Road Compared With Wind Tunnel Tests

Abstract: This investigation was performed with the purpose of comparing the arodynamic drag of an automobile as measured in a full-scale wind tunnel with the drag as measured on the road. A definition of the drag coefficient as measured both on the road and in the wind tunnel is given in advance in order to allow a comparison to be made between the two operating conditions. Three medium size european cars were selected, one notch-back type and two hatch-back types. Road testing was mainly based on the coast-down method. The total resistance was determined by statistical analysis of the experimental results. The theoretical basis and the specifications of the procedure are investigated and justified. Additional outdoor and indoor tests were carried out in order to isolate the aerodynamic drag. The wind tunnel tests were conducted on the same cars fully equipped as tested on the road and in the same speed range. The wind tunnel tests being executed at steady speeds, however, supplementary road tests were performed in order to determine the effect of the deceleration on the aerodynamic drag. The final results show only small differences between the aerodynamic drag coefficients as measured in the wind tunnel and on the road with the procedure here described

On a weakly singular volterra integral equation

Abstract: The need for providing reliable numerical methods for the solution of weakly singular Volterra integral equations ofIst Kind stems from the fact that they are connected to important problems in the theory and applications of stochastic processes. In the first section are briefly sketched the above problems and some peculiarities of such equations. Section 2 described the method for obtaining an approximate solution whose properties are described in section 3: such properties guarantee that our approximate solution always oscillates around the rigorous one. Section 4 discusses the applicability to our case of some classical bounds on the errors. The remaining sections are all devoted to the construction of upper bounds on the oscillating error in order to reach a high degree of reliability for our solution. All the bounds are independent on the numerical method which is employed for obtaining the numerical solution. In section 5 is derived a Volterra II Kind integral equation by subtracting to the original kernel the weak singularity, while in section 6 is given an upper bound to the error in the case of Wiener and Ornstein-Uhlenbeck kernels with constant barriers. Such a bound is generalized to other kinds of barriers in section 7 while in section 8 is suggested an approximation of the Kernel for the O. U. case with constant barriers and by means of it is given an explicit bound for the error in terms of Abel's transform of the known term in the original integral equation. A rough estimation of the error is also given under the assumption that\(y(t) - \int\limits_0^t {K(t,\tau )\tilde x(\tau )d_\tau [\tilde x(\tau )} \) denotes any approximate solution of (1a) obtained by any method] can be approximated by means of a sinusoidal function.

Tellurium-Cerium Oxides

Abstract: Phase equilibria in the (Ce, Te) O system, originating from interaction between Ce(NO3)3 · 6 H2O and H6TeO6 followed by calcination up to 700°C, have been studied by methods of physico-chemical analysis (DTA, TGA, x-ray diffraction, XPS). Evidence is given for the formation of non-stoichiometric fluorite-type mixed-crystals (Ce, Te)O2 in the 450–500°C range, up to a tellurium solubility limit corresponding to a lattice parameter of 5.666(3) A. At higher temperatures (500–600°C) Ce2(TeO4)3 is stable and Ce(TeO3)2 is formed above about 550°C. Ce(TeO3)2 is also obtained by solid-state interaction between CeO2 and TeO2 and is identical with the previously reported CeTe3O8 phase. Preparative conditions of the various compounds are described and x-ray diffraction data are reported. The TeO2CeO2 phase diagram was established in the temperature interval from about 650 to 1100°C. Eutectic temperatures are 689°C and 794°C at the TeO2 and CeO2-rich sides, respectively. Tellur-Cer-Oxide Die Phasengleichgewichte im (Ce, Te)O-System, erhalten aus Ce(NO3)3 · 6 H2O und H6TeO6 und Temperung bis 700°C, wurden durch physikalisch-chemische Analysen (DTA, TGA, Rontgenbeugung, XPS) untersucht. Offensichtlich bilden sich nicht-stochiometrische Mischkristalle (Ce, Te)O2 vom Fluorittyp im Temperaturbereich von 450–500°C bis zu einer Tellur-Loslichkeitsgrenze entsprechend einem Gitterparameter von 566,6(3) pm. Bei hoheren Temperaturen (500–600°C) ist Ce2(TeO4)3 stabil und Ce(TeO3)2 wird uber etwa 550°C gebildet. Ce(TeO3)2 wird auch durch Festkorperreaktion zwischen CeO2 und TeO2 erhalten und ist identisch mit der bereits mitgeteilten CeTe3O8-Phase. Praparative Bedingungen fur die verschiedenen Verbindungen und Rontgenbeugungsdaten werden mitgeteilt. Das TeO2CeO2-Phasendiagramm im Temperaturbereich von 650–1100°C wird aufgestellt. Eutektische Temperaturen sind 689°C bzw. 794°C fur die TeO2- bzw. CeO2-reiche Seite.

The An method in monokinetic neutron transport theory: Convergence and numerical applications

Abstract: The convergence of the approximate method, referred to as An, to study the solution of the monokinetic transport equation is fully investigated, when it is applied to the description of the neutron population in both infinite and finite media. The basic features of the method and the analytical and numerical implications are then analysed, in plane and curved geometries. The approximation is inserted within the other today available approximate methods panorama, such as discrete ordinates, SN and PN and its particular features are briefly pointed out. Finally, some typical numerical applications and results to study its performance and reliability are presented, such as calculations of critical dimensions, of Green functions in the infinite medium, and of space neutron distributions in infinite bodies injected by cylindrically symmetric sources.

The μ-size Schottky diodes as detectors and harmonic generators in the 100 GHz–1 THz range

Abstract: This paper is mainly concerned with a theoretical model of a μ-size Schottky-barrier junction which could explain the responsivity roll-off and the cut-off frequencies experimentally observed in different types of detector mounts. The model assumed can also explain the observed frequency dependence of the bias current peaking the responsivity.

Magneto-Optical Effects in the Paramagnetic and Ferromagnetic Phases of Cr Br 3

Abstract: We report new measurements of thermoreflectance spectra of Cr${\mathrm{Br}}_{3}$ in the paramagnetic and ferromagnetic phases in the 2.5-4 eV region. The spectra obtained with use of unpolarized and circularly polarized light, with and without external magnetic field, allow one to identify the dominating modulation mechanisms: electron-phonon interaction modulation (shift and broadening effects) in the paramagnetic phase, and exchange interaction modulation (splitting effects) in the ferromagnetic phase.

DEFASM: a microprogram meta-assembler with semantic capability

Abstract: A microprogram assembler which can assemble code for any user-defined target machine, i.e. a metamicroassembler, is described. Its most important feature is a definition phase where a description of the actual microinstruction set is given once for all, using a simple definition language. Within this definition phase, simple semantic controls may be introduced to facilitate the detection of errors that microprogram writers tend to make when the target machine has a high degree of parallelism, i.e. when long microinstructions are used.

Tomographic evaluation of size and X-ray density of normal and denervated human muscles.

Abstract: SummaryNeuromuscular disease will lead to size changes, degeneration or destruction of muscle fibres. However, fat or connective tissue infiltration occurs and this prevents the use of simple measures to assess wasting. Computerized tomography will allow accurate assessment of this wasting. Five normal subjects and five patients with total traumatic denervation of radial or peroneal origin were examined. Denervated muscle was shown to have lower than normal cross-section and X-ray density. These reductions were not paralleled in circumference or limb volume. Recovery could be followed by tomography.ResumeLes maladies neuromusculaires entraiˇnent le changement de taille, la degenerescence ou la destruction des fibres musculaires. Toutefois, l'infiltration de graisse ou de tissu connectif a lieu et rend impossible l'utilisation de mesures simples pour evaluer le degre de degenerescence. La tomographie informatisee permet l'evaluation exacte de cette degenerescence. Cinq sujets normaux et cinq patients ayant...

On form ideals and Artin-Rees condition

Abstract: We look for conditions which make two ideals and in a noetherian ring A have the same form ideal in an associated graded ring GA(α). More precisely, when and and fi−f'ieα m m≫0, ∀ i , we give a necessary and sufficient condition to have , involving the first syzygies modules both of (f1,...,fn) and (f'1,...,f'n); our proof is based on the Artin-Rees lemma. Finally we show that, when the sequence f1,...,fn is regular and for an integer q, then f1−f'i ɛ αq+1 ∀ i implies .