Nonextensivity in the solar magnetic activity during the increasing phase of solar Cycle 23

In this paper we analyze the behavior of the daily Sunspot Number from the Sunspot Index Data Center (SIDC), the mean Magnetic Field strength from the National Solar Observatory/Kitt Peak (NSO/KP) and Total Solar Irradiance means from Virgo/SoHO, in the context of the $q$--Triplet which emerges within nonextensive statistical mechanics. Distributions for the mean solar Magnetic Field show two different behaviors, with a $q$--Gaussian for scales of 1 to 16 days and a Gaussian for scales longer than 32 days. The latter corresponds to an equilibrium state. Distributions for Total Solar Irradiance also show two different behaviors (approximately Gaussian) for scales of 128 days and longer, consistent with statistical equilibrium and $q$--Gaussian for scales $<$ 128 days. Distributions for the Sunspot Number show a $q$--Gaussian independent of timescales, consistent with a nonequilibrium state. The values obtained ("$q$--Triplet"$\equiv$$\{$$q$$_{stat}$,$q$$_{sen}$,$q$$_{rel}$$\}$) demonstrate that the Gaussian or $q$--Gaussian behavior of the aforementioned data depends significantly on timescales. These results point to strong multifractal behavior of the dataset analyzed, with the multifractal level decreasing from Sunspot Number to Total Solar Irradiance. In addition, we found a numerically satisfied dual relation between $q_{stat}$ and $q_{sen}$.Comment: 6 pages, 4 figure

Anisotropy and percolation threshold in a multifractal support

Recently a multifractal object, $Q_{mf}$, was proposed to study percolation properties in a multifractal support. The area and the number of neighbors of the blocks of $Q_{mf}$ show a non-trivial behavior. The value of the probability of occupation at the percolation threshold, $p_{c}$, is a function of $\rho$, a parameter of $Q_{mf}$ which is related to its anisotropy. We investigate the relation between $p_{c}$ and the average number of neighbors of the blocks as well as the anisotropy of $Q_{mf}$

A nonextensive insight to the stellar initial mass function

the present paper, we propose that the stellar initial mass distributions as known as IMF are best fitted by $q$-Weibulls that emerge within nonextensive statistical mechanics. As a result, we show that the Salpeter's slope of $\sim$2.35 is replaced when a $q$-Weibull distribution is used. Our results point out that the nonextensive entropic index $q$ represents a new approach for understanding the process of the star-forming and evolution of massive stars.Comment: 5 pages, 2 figures, Accepted to EP

Electromigration in thin tunnel junctions with ferromagnetic/nonmagnetic: nanoconstrictions, local heating, and direct and wind forces

Current Induced Resistance Switching (CIS) was recently observed in thin tunnel junctions with ferromagnetic (FM) electrodes \emph{i.e} FM/I/FM. This effect was attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier (I). Here we study how the CIS effect is influenced by a thin non-magnetic (NM) Ta layer, deposited just below the AlO$_x$ insulating barrier in tunnel junctions of the type FM/NM/I/FM (FM=CoFe). Enhanced resistance switching occurs with increasing maximum applied current (\Imax), until a plateau of constant CIS is reached for \Imax\sim65 mA (CIS$\sim$60%) and above. However, such high electrical currents also lead to a large ($\sim$9%) irreversible resistance decrease, indicating barrier degradation. Anomalous voltage-current characteristics with negative derivative were also observed near \pm\Imax and this effect is here attributed to heating in the tunnel junction. One observes that the current direction for which resistance switches in FM/NM/I/FM (clockwise) is opposite to that of FM/I/FM tunnel junctions (anti-clockwise). This effect will be discussed in terms of a competition between the electromigration contributions due to the so called direct and wind forces. It will be shown that the direct force is likely to dominate electromigration in the Ta (NM) layers, while the wind contribution likely dominates in the CoFe (FM) layers