Roberto De Luca

Critical state in Josephson junction arrays as models of a bi-dimensional superconducting granular system

In order to analyze the diamagnetic properties of sintered granular superconductors, a circuital model consisting of a network of identical inductances (L0) and Josephson junctions is developed. In particular, the case of sufficiently high values of the maximum Josephson currents (Ij), such that L0Ij⪢Φ0, is considered. Neglecting thermal activation processes, the process of irreversible penetration of flux quanta is studied numerically. A critical state model follows.

Low‐field diamagnetic response of hollow cylindrical samples of sintered high‐Tc superconductors

Magnetization curves of hollow cylindrical samples of sintered high‐Tc superconductors are derived both numerically, by means of a Josephson junction array model, and analytically, by a critical‐state model. In both cases the field dependence of the critical current density Jc is assumed to have the following analytic form: Jc(h,T)=Jc0(T) H02(T)/[H0(T)2+h2]. The two descriptions are seen to be qualitatively equivalent.

Fronto-turbinalis Sinus Expansion and Headache

Headaches of rhinogenic origin illustrate an interesting paradox. Little is known about their pathophysiology, mechanisms, and prevalence; yet, the concept that these headaches are of importance is widely accepted. This article discusses the relationship between fronto-turbinalis sinus expansion and headaches, as well as headache outcomes after surgical approach.

Low field magnetization curves of cylindrical samples of high-Tc granular superconductors

Abstract Low field magnetization curves of cylindrical samples of high- T c granular superconductors are calculated analytically by means of a critical state model based on a Josephson junction array description of this class of superconductors.

Propensity to spending of an average consumer over a brief period

Abstract Understanding consumption dynamics and its impact on the whole economy and welfare within the present economic crisis is not an easy task. Indeed the level of consumer demand for different goods varies with the prices, consumer incomes and demographic factors. Furthermore crisis may trigger different behaviors which result in distortions and amplification effects. In the present work we propose a simple model to quantitatively describe the time evolution over a brief period of the amount of money an average consumer decides to spend, depending on his/her available budget. A simple hydrodynamical analog of the model is discussed. Finally, perspectives of this work are briefly outlined.

Magnetic response of field-cooled type-I superconducting hollow cylinders

Abstract A type-I superconducting hollow cylinder may present positive field-cooled susceptibility in a very narrow applied field interval. This effect may be detected for ratios of the inner to outer radius of the cylinder greater than a limiting value α 0 =1/ 2 , below which the magnetic response is diamagnetic for all fields.

The effect of the behavior of an average consumer on the public debt dynamics

An important issue within the present economic crisis is understanding the dynamics of the public debt of a given country, and how the behavior of average consumers and tax payers in that country affects it. Starting from a model of the average consumer behavior introduced earlier by the authors, we propose a simple model to quantitatively address this issue. The model is then studied and analytically solved under some reasonable simplifying assumptions. In this way we obtain a condition under which the public debt steadily decreases.

A hydrodynamic model for cooperating solidary countries

Abstract The goal of international trade theories is to explain the exchange of goods and services between different countries, aiming to benefit from it. Albeit the idea is very simple and known since ancient history, smart policy and business strategies need to be implemented by each subject, resulting in a complex as well as not obvious interplay. In order to understand such a complexity, different theories have been developed since the sixteenth century and today new ideas still continue to enter the game. Among them, the so called classical theories are country-based and range from Absolute and Comparative Advantage theories by A. Smith and D. Ricardo to Factor Proportions theory by E. Heckscher and B. Ohlin. In this work we build a simple hydrodynamic model, able to reproduce the main conclusions of Comparative Advantage theory in its simplest setup, i.e. a two-country world with country A and country B exchanging two goods within a genuine exchange-based economy and a trade flow ruled only by market forces. The model is further generalized by introducing money in order to discuss its role in shaping trade patterns. Advantages and drawbacks of the model are also discussed together with perspectives for its improvement.

Current-phase relation of double-barrier Josephson junctions with a two-gap superconductor as intermediate electrode

The current-phase (I-ϕ) relation of a double-barrier Josephson junction with a two-gap superconductor as intermediate electrode is derived by means of a simplified version of Ohta’s model. As in conventional double-barrier Josephson junctions, a marked skewness in the I-ϕ curves is present. Moreover, as in heterotic Josephson devices, a reduction of the maximum Josephson current is predicted. An appropriate experiment to verify the rich behavior of this type of Josephson device is suggested.

Simplified Josephson junction arrays as models of granular superconductors

Abstract We describe the simplest Josephson junction array models that can be adopted in studying the diamagnetic properties of granular superconductors. We consider cylindrical superconducting granular samples in the presence of an axial external magnetic field H. The electrodynamic response of these systems can be analyzed by means of three-dimensional (3D) equivalent networks of Josephson junctions coupled through inductances. However, in the low field reversible regime a 2D Josephson junction array can be used. In order to study irreversible flux penetration in 3D systems, we give the equivalent network and qualitatively discuss the dynamics of flux penetration. We notice that, in analogy to 2D networks, First Irreversible Flux Penetration (FIFP) occurs when the value of the shielding current approaches the maximum Josephson current in the weakest external junction of the network.