Influence of information flow in the formation of economic cycles

A microscopic approach to macroeconomic features is intended. A model for macroeconomic behavior based on the Ausloos-Clippe-Pekalski model is built and investigated. The influence of a discrete time information transfer is investigated. The formation of economic cycles is observed as a function of the time of information delay. Three regions of delay time are recognized: short $t_d \in (2 IS, 4 IS)$ (IS - iteration steps) - the system evolves toward a unique stable equilibrium state, medium $t_d =5 IS$ or $t_d =6 IS$, the system undergoes oscillations: stable concentration cycles appear in the system. For long information flow delay times, $t_d \geq 7$, the systems may crash for most initial concentrations. However, even in the case of long delay time the crash time may be long enough to allow observation of the system evolution and to introduce an appropriate strategy in order to avoid the collapse of the e.g. company concentration. In the long time delay it is also possible to observe an "economy resonance" where despite a long delay time the system evolves for a long time or can even reach a stable state, which insures its existence.Comment: 18 pages,16 figures, to be published in Verhulst 200 Proceedings, M. Ausloos and M. Dirickx, Eds. (in press

From RE-211 to RE-123. How to control the final microstructure of superconducting single-domains

This paper reviews the usual techniques for producing YBCO-type single-domains and the microstructure of the as-obtained samples. The problems of seed dissolution and parasite nucleations are discussed in details. Formation of microstructural defects, such as pores and cracks, are examined. An important part of this review is devoted to the study of the influence of RE-211 particles [RE2BaCuO5 where RE denotes Y, Yb, Nd, Sm, Dy, Gd, Eu or a mixture of them. Generally Nd4Ba2Cu2O10 is preferred to Nd2BaCuO5] on the microstructure and properties of RE-Ba-Cu-O single-domains. Trapping/Pushing theory is described in order to explain the spatial distribution of RE-211 particles in the RE-123 [(RE)Ba2Cu3O7-d] monoliths. Formation of RE-211-free regions is discussed. Different ways to limit the RE-211 coarsening are reviewed. Microstructural defects in the RE-123 matrix caused by the RE-211 particles are presented. It is also shown that RE-211 particles play a significant role on the mechanical properties of single-domain samples. We finish this review by discussing the Infiltration and Growth process as a good technique to control the microstructure.Comment: review paper to be published in Supercond. Sci. Technol.; 19 figures; 137 references; 37 page

Anisotropic AC Behavior of Multifilamentary Bi-2223/Ag Tapes

In this communication, we report on the anisotropy of the superconducting properties of multifilamentary Bi-based tapes experimentally investigated by AC magnetic susceptibility measurements. The susceptibility $\chi= \chi' - j \chi''$ was measured using a commercial system and a couple of orthogonal pick-up coils. The $\chi''$ vs. temperature curves were shown to exhibit two peaks. The smaller of the peaks, occurring near T = 72K, was only visible for particular field directions and within a given frequency window. Such results point out the role played by the phase difference between the applied magnetic field and the internal magnetic field seen by the filaments.Comment: 4 pages (2 columns); 4 figure

Model of macroeconomic evolution in stable regionally dependent economic fields

We develop a model for the evolution of economic entities within a geographical type of framework. On a square symmetry lattice made of three (economic) regions, firms, described by a scalar fitness, are allowed to move, adapt, merge or create spin-offs under predetermined rules, in a space and time dependent economic environment. We only consider here one timely variation of the ''external economic field condition''. For the firm fitness evolution we take into account a constraint such that the disappearance of a firm modifies the fitness of nearest neighboring ones, as in Bak-Sneppen population fitness evolution model. The concentration of firms, the averaged fitness, the regional distribution of firms, and fitness for different time moments, the number of collapsed, merged and new firms as a function of time have been recorded and are discussed. Also the asymptotic values of the number of firms present in the three regions together with their average fitness, as well as the number of respective births and collapses in the three regions are examined. It appears that a sort of $critical$ selection pressure exists. A power law dependence, signature of self-critical organization is seen in the birth and collapse asymptotic values for a high selection pressure only. A lack of self-organization is also seen at region borders.Comment: 11 figures double columns on 7 page

Transverse voltage in high-Tc superconductors in zero magnetic fields

Longitudinal and transverse voltages have been measured in zero external magnetic fields. In close vicinity of the superconducting transition nonzero transverse voltage has been observed while far away from Tc, both above and below no such voltage has been detected. The value of the transverse resistivity depends on the value of the transport current. Several models have been discussed taking into account also the penetration of self field due to the applied transport current. It seems that observed results can be explained using the Kosterlitz-Thouless model as a result of an unpairing of vortex-antivortex pairs created below Tkt due to fluctuations. At Tkt free vortices and antivortices are created and can contribute to a dissipation of energy. Their movement should also be responsible for the observed nonzero transverse voltage.Comment: 3 pages in Latex, 3 figs.ep

Time dependent correlations in marine stratocumulus cloud base height records

The scaling ranges of time correlations in the cloud base height records of marine boundary layer stratocumulus are studied applying the Detrended Fluctuation Analysis statistical method. We have found that time dependent variations in the evolution of the $\alpha$ exponent reflect the diurnal dynamics of cloud base height fluctuations in the marine boundary layer. In general, a more stable structure of the boundary layer corresponds to a lower value of the $\alpha$ - indicator, i.e. larger anti-persistence, thus a set of fluctuations tending to induce a greater stability of the stratocumulus. In contrast, during periods of higher instability in the marine boundary, less anti-persistent (more persistent like) behavior of the system drags it out of equilibrium, corresponding to larger $\alpha$ values. From an analysis of the frequency spectrum, the stratocumulus base height evolution is found to be a non-stationary process with stationary increments. The occurrence of these statistics in cloud base height fluctuations suggests the usefulness of similar studies for the radiation transfer dynamics modeling.Comment: 12 pages, 6 figures; to appear in Int. J. Mod. Phys. C, Vol. 13, No. 2 (2002

Are Financial Crashes Predictable?

We critically review recent claims that financial crashes can be predicted using the idea of log-periodic oscillations or by other methods inspired by the physics of critical phenomena. In particular, the October 1997 `correction' does not appear to be the accumulation point of a geometric series of local minima.Comment: LaTeX, 5 pages + 1 postscript figur

Numerical simulation of the magnetization of high-temperature superconductors: 3D finite element method using a single time-step iteration

We make progress towards a 3D finite-element model for the magnetization of a high temperature superconductor (HTS): We suggest a method that takes into account demagnetisation effects and flux creep, while it neglects the effects associated with currents that are not perpendicular to the local magnetic induction. We consider samples that are subjected to a uniform magnetic field varying linearly with time. Their magnetization is calculated by means of a weak formulation in the magnetostatic approximation of the Maxwell equations (A-phi formulation). An implicit method is used for the temporal resolution (Backward Euler scheme) and is solved in the open source solver GetDP. Picard iterations are used to deal with the power law conductivity of HTS. The finite element formulation is validated for an HTS tube with large pinning strength through the comparison with results obtained with other well-established methods. We show that carrying the calculations with a single time-step (as opposed to many small time-steps) produce results with excellent accuracy in a drastically reduced simulation time. The numerical method is extended to the study of the trapped magnetization of cylinders that are drilled with different arrays of columnar holes arranged parallel to the cylinder axis