Showing papers by "Sapienza University of Rome published in 1985"

Path integral approach to birth-death processes on a lattice

Abstract: The Fock space formalism for classical objects first introduced by Doi is cast in a path integral form and applied to general birth-death processes on a lattice. The introduction of suitable auxiliary variables allows one to formulate random walks with memory and irreversible aggregation processes in a Markovian way, which is treatable in this formalism. Existing field theories of such processes are recovered in the continuum limit. Implications of the method for their asymptotic behaviour are briefly discussed.

Effects of thermal fluctuations on systems with small surface tension.

Abstract: We consider the influence of thermal fluctuations on systems with negligible surface tension ("membranes"), whose behavior is determined by curvature effects. Fluctuations change the effective rigidity and other relevant parameters. Two-dimensional membranes appear rigid at short distances and crumpled at long distances. For more than two-dimensional membranes (or in presence of long-range forces) a crumpling transition separates a rigid low-temperature phase from a crumpled high-temperature one.

Constructive proof of localization in the Anderson tight binding model

Abstract: We prove that, for large disorder or near the band tails, the spectrum of the Anderson tight binding Hamiltonian with diagonal disorder consists exclusively of discrete eigenvalues. The corresponding eigenfunctions are exponentially well localized. These results hold in arbitrary dimension and with probability one. In one dimension, we recover the result that all states are localized for arbitrary energies and arbitrarily small disorder. Our techniques extend to other physical systems which exhibit localization phenomena, such as infinite systems of coupled harmonic oscillators, or random Schrodinger operators in the continuum.

Chromosomal inversion intergradation and incipient speciation in Anopheles gambiae

Abstract: Polytene chromosome studies on the Afrotropical mosquitoes of the Anopheles gambiae complex show that the rearrangements of the banding pattern are all based on paracentric inversions. Some of these occur at the homozygous state only (fixed inversions) and are used for cytotaxonomic identification of the six sibling species. Others occur as intraspecific chromosomal polymorphisms which are frequent particularly in An. gambiae and An. arabiensis, the two taxa showing the widest distribution and the closest association with man and man-made breeding places. A particularly high level of chromosome differentiation has been recorded in Anpoheles gambiae (the most anthropophilic taxon of the complex and possibly the one most recently evolved) which can be split into forest and savanna chromosomal forms. The forest form seems chromosomally uniform, being characterized in all the rain forest areas by the chromosome-2 standard arrangement, probably one of the most primitive in the complex. The forest form...

Differentiation of PC12 phaeochromocytoma cells induced by v-src oncogene.

Abstract: PC 12 rat phaeochromocytoma cells1,2 are a model system that can be used to study both neuronal differentiation and the mechanism of action of nerve growth factor (NGF)3. PC12 cells respond to NGF protein by shifting from a chromaffin-cell-like phenotype to a neurite-bearing sympathetic neurone-like phenotype2,4,5. Here we present data on the effect of infection of PC 12 cells with retroviruses carrying the src oncogene of Rous sarcoma virus6. Previous studies have demonstrated that the expression of src severely affects the synthesis and accumulation of differentiated cell products in a variety of cell types7–9. We show that in the PC 12 cell system, expression of v-src appears to have an inductive effect on differentiation that resembles the action of a ‘physiological’ growth factor.

Voltage-dependent scanning-tunneling microscopy of a crystal surface: Graphite

Abstract: Scanning Tunneling Microscopy is now well established as a powerful technique for surface structural studies(1). Our aim is to demonstrate how this technique might also become useful for the spectroscopy of surfaces, and in particular of surface electronic states. We do this by direct calculation of the tunneling current flowing into, or out of, a graphite surface, as a function of an applied voltage V, illustrating the direct relationship between the current J(V) and the surface electronic structure at energy E-EF=V. Graphite has been chosen because it is an important surface, with perfectly known atomic structure, and a simple and well-known electronic structure, where localized σ and π states coexist with fairly delocalized interlayer bulk states(2), and with recently discovered empty surface states(3,4). Most of these interesting features lie several eV away from the Fermi energy. We do not concern ourselves here the the technical difficulties of achieving such a high tunneling voltage on a semimetallic surface. Our calculation, however, shows that the outcome would be very worthwhile, in terms of information on the surface electronic structure.

On the stochastic quantization of field theory

Abstract: We give a rigorous construction of a stochastic continuumP(φ)2 model in finite Euclidean space-time volume. It is obtained by a weak solution of a non-linear stochastic differential equation in a space of distributions. The resulting Markov process has continuous sample paths, and is ergodic with the finite volume EuclideanP(φ)2 measure as its unique invariant measure. The procedure may be called stochastic field quantization.

Haemoglobin switching in human embryos: asynchrony of ζ → α and ε → γ-globin switches in primitive and definitive erythropoietic lineage

Abstract: Haemoglobin switching in humans provides a unique model for investigating the mechanisms underlying expression of a developmentally regulated gene family. Numerous studies have focused on the switch from fetal to adult (that is, gamma----beta) globin, but little is known about the embryonic----fetal (that is, zeta----alpha and epsilon----gamma) switches, as well as the transition from 'primitive' yolk sac to 'definitive' liver erythropoiesis. Here we have studied the embryonic----fetal haemoglobin switches in yolk sac, liver and circulating blood erythroblasts from 25 embryos and 6 fetuses. Globin synthesis was also evaluated in purified 'primitive' and 'definitive' erythroblasts. Primitive erythroblasts synthesize essentially zeta and epsilon chains at 5 weeks and alpha- and epsilon-globin with a minor aliquot of zeta and gamma chains at 6-7 weeks, whereas definitive erythroblasts produce alpha and epsilon + gamma + beta-globin at 6 weeks but only alpha and gamma + beta chains from 8 weeks onward. In both lineages the zeta----alpha and the epsilon----gamma switches are asynchronous, the former preceding the latter. Furthermore, zeta- and beta-globin synthesis is restricted to primitive and definitive erythroblasts respectively. These findings are discussed in terms of a monoclonal model for haemoglobin switching in early human ontogeny.

Equipartition threshold in nonlinear large Hamiltonian systems: The Fermi-Pasta-Ulam model

Abstract: Etude du modele β de Fermi-Pasta-Ulam, par integration numerique des equations de mouvement pour un systeme de N oscillateurs couples non lineairement, N allant de 64 a 512. Le nombre Δn de modes initialement excites est tel que le rapport Δn/N est maintenu constant. On considere le systeme comme un gaz de phonons faiblement couples (modes normaux). Avec Δn/N constant, on trouve une analogie avec la limite thermodynamique de la mecanique statistique, ou le rapport M/V est constant quand le volume V et le nombre de particules M deviennent infinis

Continuous Non Invasive Monitoring of Human Brain by Near Infrared Spectroscopy

Abstract: Precise time-and space-resolved measurement of brain energy metabolism and circulation in vivo would provide important information on the cerebral physiology and pathophysiology, Consequently different optoelectronic techniques based on spectroscopic signals of the normoxic-anoxic transition of pyridine nucleotide (NADH), flavoprotein (Fp) and cytochrome-c-oxidase (cyt a,a3) have been developed (Tab. 1). Cyt a,a3 which catalyzes more than 90% of cellular oxygen consumption, has a greater visible absorption in the reduced than in oxidized form; it is characterized by a broad band in the near infrared (I.R.) centered at 830 nm and attributable to the copper component of oxidized enzyme.

Topographic lineament swarms - clues to their origin from domain analysis of italy

Abstract: Regional-scale, subparallel linear topographic features characterize almost all planetary surfaces. This experiment concerns their tectonic meaning by focusing on map limits or domains through which individual swarms of these linear features are developed. These domain limits are contrasted with map boundaries of better-known structural features in a tectonically active region (Italy) to seek clues to stress environments and times of origin of the lineaments. The study uses regional raised relief maps to filter the lineament data to a very simple subset: those strictly topographic features of a length and prominence capable of retaining detectability through generalizations required by relief-map production. A total of 5,372 lineaments were drawn using 4 differently lighted images of 1:1,000,000 scale relief maps of Italy. Seven different tests were used for reliability and reproducibility of the data. Rose diagrams were prepared for 86 subareas by computer fitting of gaussians to azimuth-frequency histograms. Individual azimuthal “petals” of these roses were then correlated to delimit the general area over which a given azimuthal swarm is developed. The precise swarm boundaries were then located by computer contouring the population density of lines of each swarm on the original data set. In this way, 48 local swarms were mapped. Boundaries of these swarms correlate poorly with traditional litho-tectonic provinces. Instead, they seem to be associated with basin axes, broad arches, coastal flexures, areas of normal fault swarms, and projections of structural grain from adjacent sea floors. The 48 domains may be grouped into 8 noncontiguous but azimuthally compatible super-swarms covering much of Italy. The most prominent of the super-swarms are greatly expanded versions of regional structural grains: trend of the Po Basin, axis of the upper Adriatic Basin, zone of south Alpine underthrusting, and landward extensions of structural grain of the Tyrrhenian Sea. From these relationships, a model for lineament-swarm origins is proposed, involving very minor regional stretching of the thin, brittle carapace of extremely large, sometimes subtle, structures deforming by ductile mechanisms at depth.

On the sampling of a linear analytic control system

Abstract: In the present work we characterize the discrete time system which reproduces exactly the evolutions in the state of a given vector input linear analytic continuous time system driven by inputs which are constant on time intervals of fixed amplitude. This is achieved by comparing the Volterra series associated respectively to the sampled and continuous input state functionals. Moreover we give a compact Lie formula for the solution of a parametrized nonlinear differential equation which enables to characterize the nonlinear difference equation which solves the problem in terms of formal Lie series. On these bases, it becomes very natural to introduce a notion of approximated sampling of main efficiency in practical situations for computing purpose.

The natural history of jumper's knee. Patellar or quadriceps tendonitis.

Abstract: We have reviewed the clinical records and the results of conservative and surgical treatment of 125 out of 172 cases of Jumper's Knee followed for at least 2 years since the onset of symptoms. All were athletes involved in various sporting activities. At follow up 15 patients had given up sport and the lesion had healed spontaneously.

Opiate receptors are present in the rat testis. identification and localization in sertoli cells

Abstract: We have characterized opioid binding sites in the Sertoli cells of adult and 18-day-old rat testes. Maximal specific etorphine binding was attained affer 30 min. at 4 C. The binding was reversible, with association and dissociation rate constants of 0.98 × 105 m−1 min−1 and 0.33 min−1, respectively. Scatchard analyses and saturation curves revealed a single class of high-affinity, low-capacity binding sites. No opioid binding was observed in Leydig cell cultures. Exposure to opioids for 3 days caused a significant increase in [3H] etorphine specifically bound to the Sertoli cells that was completely prevented by naloxone, demonstrating opioid up-regulation of its own receptor. Chronic opioid treatment of the cultures significantly inhibited androgen-binding protein production, and this effect was prevented by naloxone. Since the circulating concentrations of endorphins (10−12 m) are lower than the Kd of testis opiate receptors, it is conceivable that opioids of Leydig cell origin act on the specific high-...

Control of robot arm with elastic joints via nonlinear dynamic feedback

Abstract: It is known that control of a rigid robot arm can easily be achieved via static state-feedback compensation of the nonlinearities. However, in many practical situations, the elasticity in gear boxes is not negligible. If this is the case, the use of such a control technique is not possible anymore because neither is the system feedback equivalent to a controllable linear one, nor its input-output behavior can be decoupled via static state-feedback. The purpose of this paper is to show how dynamic state-feedback compensation may be used in order to obtain full state-space iinearity, and to present an application to the model of a three link robot arm with elastic joints.

The CO bond angle of carboxymyoglobin determined by angular-resolved XANES spectroscopy.

Abstract: Our knowledge of the structure of condensed matter has been based primarily on spectroscopic methods that measure first-order pair correlations of atomic arrangements and thus provide interatomic distances (for example neutron and X-ray scattering). Bond angles are given by higher-order correlation functions, and such information can be provided by X-ray absorption near-edge structure (XANES) spectroscopy, the features of which are determined by multiple scattering of photoelectrons whose paths begin and end at the selected absorbing atom. We report here angular-resolved XANES spectroscopy of a single crystal of carboxymyoglobin (MbCO). The large dichroism of the X-ray absorption of the crystal can be fully interpreted by multiple-scattering theory which allows the determination of Fe-ligand bond angles. The analysis of the identified multiple scattering features due to CO in high signal-to-noise-ratio spectra of protein in solution has allowed the determination of the variation of CO bond angles. This opens the way to the determination of subtle structural features due to bond angle variations in proteins in solution which are relevant to an understanding of the characteristics of proteins at the atomic scale.

Reduction techniques for infinite-dimensional Hamiltonian systems: some ideas and applications

Abstract: In the language of tensor analysis on differentiable manifolds, we present a reduction method of integrability structures, and apply it to recover some well-known hierarchies of integrable nonlinear evolution equations.

Planar Circuits, Waveguide Models, and Segmentation Method

Abstract: The planar-circuit approach to the analysis and design of microwave integrated circuits (MIC's), with specific reference to microstrip circuits, is reviewed. The planar approach overcomes the limitations inherent to the more conventional transmission-line approach. As the operating frequency is increased and/or Iow-impedence levels are required, in fact, the transverse dimensions of the circuit elements become comparable with the wavelength and/or the longitudinal dimensions. In such cases, one-dimensional analyses give inaccurate or even erroneous results. The analysis of planar elements is formulated in terms of an N-port circuit and results in a generalized impedance-matrix description. Analysis techniques for simple geometries, such as the resonant mode expansion, and for more complicated planar configurations, such as the segmentation method, are discussed along with planar models for accounting for fringing fields effects and radiation loss.

Antifungal activity of ovotransferrin towards genus Candida.

Abstract: The inhibiting activity of ovotransferrin was tested towards different species belonging to genus Candida. Of one hundred strains tested, only C. krusei showed a noticeable resistance, while the other species appeared to be more sensitive than bacteria to the action of ovotransferrin. The influence of anions, such as bicarbonate and citrate, on the inhibiting activity of ovotransferrin was also investigated. Moreover it was observed that iron saturated ovotransferrin retained its activity, thus suggesting an interaction between the protein and Candida cells.