Showing papers by "Sapienza University of Rome published in 1984"

Value and distribution in the classical economists and marx

Abstract: 1. THE theory of value and distribution is at present in a situation of unease and uncertainty: we no longer find the same general agreement about its basic elements which obtained until a few decades ago. Two main theoretical developments have undermined the dominant theory which explained distribution and relative prices by means of the "equilibrium" of the two "opposing sets of forces", demand and supply for factors of production. The first development in order of time has been Keynes's refutation of the doctrine according to which a competitive economic system tends towards the full employment of labour, i.e. towards that equilibrium between "demand and supply" of labour, which was to determine the wage. Keynes' concentration on the short period, and the persistence in the General Theory of many traditional premises favoured the successive attempts to reconcile his results with orthodox long-period analysis: but the weakening of the dominant theory which nonetheless resulted from his work can be seen both in the uneasiness which, in ever-changing forms, characterizes the renewed orthodoxy, and in the tendency of Keynes' direct followers towards a more radical departure from traditional theory. The second development consists in the critique of the notion of capital as a "factor of production" measurable independently of distribution.2 This critique has shown the invalidity of some propositions of the theory, like the inverse relation between the rate of interest (rate of profit) and the "quantity of capital" per worker, which are basic for the explanation of distribution in terms of demand and supply for "factors of production". The uncertainty which has resulted from these developments finds its expression in authors who think that new theoretical approaches should be explored. It is also revealed by the nature of some of the work carried out by those who adhere to the traditional approach.3 1 This paper which develops under the impact of Sraff a's production of commodities by means of commodities some propositions contained in a Ph.D dissertation of 1955-1958, is based on notes delivered at a conference on "Marx's Transformation of Values into Prices of Production" held in Siena in 1972, and used then for lectures given in Cambridge and elsewhere since

Replica symmetry breaking and the nature of the spin glass phase

Abstract: A probability distribution has been proposed recently by one of us as an order parameter for spin glasses. We show that this probability depends on the particular realization of the couplings even in the thermodynamic limit, and we study its distribution. We also show that the space of states has an ultrametric topology Etude d'une distribution de probabilite, proposee recemment, comme parametre d'onde pour les verres de spin: la probabilite depend de la realisation particuliere des couplages, meme a la limite thermodynamique. Etude de la distribution de cette probabilite. Mise en evidence de la topologie ultrametrique de l'espace des etats

Nonlinear feedback in robot arm control

Abstract: Nonlinear feedback control is proposed for implementation of an advanced dynamic control strategy for robot arms. Using differential geometric system theory we obtained necessary and sufficient conditions for the existence of a nonlinear feedback control for a general nonlinear system to be externally linearized and simultaneously output decoupled. An algorithm is given for the construction of the required nonlinear feedback. To design a dynamic control for robot arms we apply the above result to the JPL-Stanford arm and propose a new control strategy, which also contains an optimal error-correcting feedback. Simulation results show great promise for the obtained dynamic control strategy.

Ground deformation and gravity changes accompanying the 1982 Pozzuoli uplift

Abstract: During the summer of 1982 a continuous uplift began at Phlegraean Fields, an active volcanic area in southern Italy (Fig. 1), that persisted up to September 1984. The uplift, which reached a maximum value of about 160 cm in the central part of the Phlegraean caldera, was characterized by variable velocity and occurred within an area that extended about 7 km outward from the town of Pozzuoli (Fig. 1); the surface deformation performs a bell-shape pattern. The uplift was accompanied by horizontal displacements and gravity changes that closely correlate with the described elevation changes. The horizontal displacements displayed an anomalous pattern within a narrow belt about 1 km from the center of the uplift and approximately coincident with the area of maximum seismic activity. The change in gravity is attributed primarily to a free-air effect to which a small Bouguer effect must be added. Several models have been invoked in order to explain the observed phenomenon. The one which gives the best fit to the observed data is an increasing pressure source of radial simmetry, at a constant depth of about 3 km beneath the town of Pozzuoli, and having a diameter of several hundred meters. Migration of magma at depth is believed to be responsible for the observed activity in the Phlegraean Fields caldera.

Interaction-driven metal-insulator transitions in disordered fermion systems

Abstract: We study the effects of electron-electron interactions in disordered metals in and close to two dimensions (2D). We consider physical situations in which localization effects are suppressed. The field-theoretical renormalization-group (RG) calculation performed recently by Finkelstein is interpreted and rederived in terms of perturbative results. Surprisingly, except for the density of states, the scaling behavior is independent of the interaction range. We further extend the model to several new universality classes. In the presence of a strong magnetic field the metal is unstable in 2D and undergoes a metal-insulator transition in $d=2+\ensuremath{\epsilon}$. The conductivity exponent, defined by $\ensuremath{\sigma}\ensuremath{\sim}{(n\ensuremath{-}{n}_{c})}^{\ensuremath{\mu}}$, is universal with $\ensuremath{\mu}=1+O(\ensuremath{\epsilon})$ but $N({E}_{F})$ depends not only on the range of the interaction but also on its strength for short-ranged interactions. In 2D the conductivity has a universal temperature dependence [$\ensuremath{\delta}\ensuremath{\sigma}(T)={\ensuremath{\sigma}}_{N}(2\ensuremath{-}2\mathrm{ln}2)\mathrm{ln}(T\ensuremath{\tau})$, ${\ensuremath{\sigma}}_{N}=\frac{{e}^{2}}{2{\ensuremath{\pi}}^{2}\ensuremath{\hbar}}$] if the interaction is Coulombic. If magnetic impurities (or strong spin-orbit scattering with a weak magnetic field) are present instead, the noninteracting fixed point is stable for short-ranged interactions ($\ensuremath{\mu}=\frac{1}{2}$). For the Coulomb interaction the interaction is relevant and drives a metal-insulator transition in $d=2+\ensuremath{\epsilon}$ with universal critical properties ($\ensuremath{\mu}=1$). In 2D the conductivity also has a universal temperature dependence [$\ensuremath{\delta}\ensuremath{\sigma}(T)={\ensuremath{\sigma}}_{N}\mathrm{ln}(T\ensuremath{\tau})$]. We also discuss the behavior of the dielectric constant on the insulator side and the frequency (temperature) dependence of the conductivity at criticality. Remarks are made on the relationship of the above to experiments.

Effects of dynamical screening on resonances at inner-shell thresholds in semiconductors

Abstract: A theory of core excitons in semiconductors is formulated, taking into account the frequency dependence of the dielectric matrix which screens the electron-hole attraction. The present approach combines standard many-body techniques (which reduce the Bethe-Salpeter equation for the two-particle Green's function to an effective eigenvalue problem) with elements drawn from Fano's formalism for discrete states interacting with continuum channels. The positions and the widths of core-exciton resonances are affected by dynamical screening, which increases the binding energy above its value for static screening and decreases its Auger width below its value for a core hole. The latter effect is peculiar to a dynamical theory and has recently been confirmed experimentally.

A Methodology for Data Schema Integration in the Entity Relationship Model

Abstract: The conceptual design of databases is usually seen as divided into two steps: view modeling, during which user requirements are formally expressed by means of several user oriented conceptual schemata, and schema integration, whose goal is to merge such schemata into a unique global conceptual schema. This paper is devoted to describe a methodology for schema integration. An enriched entity relationship model is chosen as the data model. The integration process consists of three steps: first, several types of conflicts between the different user schemata are checked and solved; second, schemata are merged into a draft integrated schema, that is, third, enriched and restructured according to specific goals.

Spectroscopic evidence for Davydov-like solitons in acetanilide

Abstract: Detailed measurements of infrared absorption and Raman scattering on crystalline acetanilide [${(\mathrm{C}{H}_{3}\mathrm{CONH}{C}_{6}{H}_{5})}_{x}$] at low temperature show a new band close to the conventional amide I band. Equilibrium properties and spectroscopic data rule out explanations based on a conventional assignment, crystal defects, Fermi resonance, and upon frozen kinetics between two different subsystems. Thus we cannot account for this band using the concepts of conventional molecular spectroscopy, but a soliton model, similar to that proposed by Davydov for $\ensuremath{\alpha}$-helix in protein, is in satisfactory agreement with the experimental data.

Differential Reflectivity of Si(111)2×1 Surface with Polarized Light: A Test for Surface Structure

Abstract: The polarization dependence of the differential reflectivity of the Si(111)2\ifmmode\times\else\texttimes\fi{}1 single-domain surface has been studied experimentally. A marked anisotropy of the optical peak at 0.45 eV associated with dangling bonds is observed with maximum absorption along $[0\overline{1}1]$ directions. The chain model is in good agreement with the experimental result.

Secretion of androgen binding protein by Sertoli cells is influenced by contact with germ cells.

Abstract: Sertoli cells were cultured alone or with germ cells to evaluate the effect of the association with germ cells on the secretory activity of Sertoli cells. Secretion of androgen-binding protein, which is specifically secreted by Sertoli cells, was measured under several experimental conditions. The following experimental models were utilized: 1) cultures of explants of seminiferous epithelium from prepubertal animals in which germ cells adherent to Sertoli cells are present (Sertoli cell enriched cultures); 2) monolayers formed only by Sertoli cells, obtained by removing germ cells from Sertoli cell enriched cultures, and 3) cocultures of Sertoli cell only cultures and germ cell populations at defined stages of differentiation. The results obtained indicated that FSH-induced ABP secretion was greatly reduced in Sertoli cell only cultures as compared to enriched Sertoli cell cultures, and that this difference was stable throughout the first eight days of culture. In addition, cocultures of Sertoli cell only cultures with germ cells induced an increase of ABP when cocultured germ cells were at differentiation stages, such as pachytene spermatocytes, which are able to recognize and firmly adhere to the Sertoli cell monolayers. Cocultures with round spermatids, which do not adhere to Sertoli cells, did not increase the amount of FSH-induced ABP production. The addition of nongerminal cells such as lymphocytes and fibroblasts were also not effective in stimulating ABP secretion. Surface interaction between Sertoli cells and cocultured germ cells seemed to be necessary for this FSH-induced ABP production.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytogenetic analysis of a segment of the Y chromosome of Drosophila melanogaster.

Abstract: Males carrying a large deficiency in the long arm of the Y chromosome known to delete the fertility gene kl-2 are sterile and exhibit a complex phenotype: (1) First metaphase chromosomes are irregular in outline and appear sticky; (2) spermatids contain micronuclei; (3) the nebenkerns of the spermatids are nonuniform in size; (4) a high molecular weight protein ordinarily present in sperm is absent; and (5) crystals appear in the nucleus and cytoplasm of spermatocytes and spermatids. In such males that carry Ste+ on their X chromosome the crystals appear long and needle shaped; in Ste males the needles are much shorter and assemble into star-shaped aggregates. The large deficiency may be subdivided into two shorter component deficiencies. The more distal is male sterile and lacks the high molecular weight polypeptide; the more proximal is responsible for the remainder of the phenotype. Ste males carrying the more proximal component deficiency are sterile, but Ste + males are fertile. Genetic studies of chromosome segregation in such males reveal that (1) both the sex chromosomes and the large autosomes undergo nondisjunction, (2) the fourth chromosomes disjoin regularly, (3) sex chromosome nondisjunction is more frequent in cells in which the second or third chromosomes nondisjoin than in cells in which autosomal disjunction is regular, (4) in doubly exceptional cells, the sex chromosomes tend to segregate to the opposite pole from the autosomes and (5) there is meiotic drive; i.e., reciprocal meiotic products are not recovered with equal frequencies, complements with fewer chromosomes being recovered more frequently than those with more chromosomes. The proximal component deficiency can itself be further subdivided into two smaller component deficiencies, both of which have nearly normal spermatogenic phenotypes as observed in the light microscope. Meiosis in Ste + males carrying either of these small Y deficiencies is normal; Ste males, however, exhibit low levels of sex chromosome nondisjunction with either deficient Y. The meiotic phenotype is apparently sensitive to the amount of Y chromosome missing and to the Ste constitution of the X chromosome.

Transverse Resonance Analysis Discontinuities of Finline

Abstract: A method of analysis is proposed for characterizing finline discontinuities. Two conducting or magnetic planes are inserted at some distances away from the discontinuity so as to obtain a closed resonant structure. A transverse resonance technique is then used to compute the resonant frequencies and, from these, the equivalent circuit parameters of the discontinuity. In the particular case when the discontinuity is removed, the method can be used to characterize uniform finlines.

Characteristics of Metal-Insulator-Semiconductor Coplanar Waveguides for Monolithic Microwave Circuits

Abstract: Using a full-wave mode-matching technique, an extensive analysis is presented of the slow-wave factor, attenuation, and characteristic impedance of a metal-insulator semiconductor coplanar waveguide (MISCPW) as functions of the various structural parameters. Design criteria are given for low-attenuation slow-wave propagation. By a proper optimization of the structure, performances comparable with or even better than those of alternative structures proposed in the literature are theoretically predicted.

Genesis, evolution and tectonic significance of K-rich volcanics from the Alban Hills (Roman comagmatic region) as inferred from trace element geochemistry

Abstract: Trace element data are reported in 21 lava samples from the Alban Hills, one of the most important volcanic complexes of the Roman comagmatic region. The samples consist mostly of tephritic leucitites with minor phonolitic tephrites and tephritic phonolites emplaced during two distinct phases of activity, separated by a caldera collapse.

Planar Circuit Analysis of Microstrip Radial Stub (Short Paper)

Abstract: Radial-line stubs have been found to work better than low-impedance rectangular stubs when an accurate localization of a zero-point impedance is needed. In this paper, microstrip radial-line stubs are analyzed using a planar circuit technique and characterized for design purposes. Experiments performed on various structures are in excellent agreement with the theory and confirm the suitability of such a structure as an altenative to a conventional straight stub.

Macroscopic dielectric tensor at crystal surfaces

Abstract: We formulate the theory of the macroscopic dielectric tensor for crystals of lower-than-cubic symmetry, using the local-orbital approach to the dielectric response. In the case of noncubic infinite crystals we give a definition of the macroscopic dielectric tensor that is simpler than any previous formulation and allows us to perform realistic calculations with roughly the same computational effort needed in cubic crystals. In the case of semi-infinite crystals, we give for the first time a definition of the macroscopic dielectric tensor and outline a way of computing it from the two-particle Green's function, which can be computed according to the method of Hanke and Sham, including local-field and excitonic effects. A remarkable result is that in both cases the long-range part of the Coulomb interaction does not affect the macroscopic dielectric tensor. Previous formulations of the optical properties of surfaces, which neglected local-field effects, are shown to be yet valid, provided that the macroscopic dielectric tensor replaces the microscopic one.