On Equivalent Expressions for the Faraday's Law of Induction

In this paper we give a rigorous proof of the equivalence of some different forms of Faraday's law of induction clarifying some misconceptions on the subject and emphasizing that many derivations of this law appearing in textbooks and papers are only valid under very special circumstances and not satisfactory under a mathematical point of view.Comment: Footnote 3 has been rewritte

A New Type of Cipher

We will define a new type of cipher that doesn't use neither an easy to calcualate and hard to invert matematical function like RSA nor a classical mono or polyalphabetic cipher

Creative Autonomy Through Salience and Multidominance in Interactive Music Systems: Evaluating an Implementation

Interactive music systems always exhibit some autonomy in the creative process. The capacity to generate novel material while retaining mutuality to the interaction is proposed here as the bare minimum for creative autonomy in such systems. Video Interactive VST Orchestra is a system incorporating an adaptive technique based both on the concept of salience as a means for retaining mutuality to the interplay and on multidominance in the adaptive generation process as a means for introducing novelty. We call this property reflexive multidominance. A case study providing evidence of such creative autonomy in VIVO is presented.Comment: 23 pages, 5 figures, 2 tables, 2 supplement material (audio/video links

A description of pseudo-bosons in terms of nilpotent Lie algebras

We show how the one-mode pseudo-bosonic ladder operators provide concrete examples of nilpotent Lie algebras of dimension five. It is the first time that an algebraic-geometric structure of this kind is observed in the context of pseudo-bosonic operators. Indeed we don't find the well known Heisenberg algebras, which are involved in several quantum dynamical systems, but different Lie algebras which may be decomposed in the sum of two abelian Lie algebras in a prescribed way. We introduce the notion of semidirect sum (of Lie algebras) for this scope and find that it describes very well the behaviour of pseudo-bosonic operators in many quantum models.Comment: In press in Journal of Geometry and Physic

Emptiness Formation Probability for the Anisotropic XY Spin Chain in a Magnetic Field

We study an asymptotic behavior of the probability of formation of a ferromagnetic string (referred to as EFP) of length "n" in a ground state of the one-dimensional anisotropic XY model in a transversal magnetic field as n goes to infinity. We find that it is exponential everywhere in the phase diagram of the XY model except at the critical lines where the spectrum is gapless. One of those lines corresponds to the isotropic XY model where EFP decays in a Gaussian way, as was shown in cond-mat/0106062. The other line is at the critical value of the magnetic field. There, we show that EFP is still exponential but acquires a non-trivial power-law prefactor with a universal exponent.Comment: 15 pages, 3 figures, elsart document clas

The corona of the dMe flare star AD Leo

We have studied the X-ray emission (both the quiescent component and the flares) of the dM3e star AD Leo, analyzing the Einstein IPC, ROSAT PSPC and ASCA SIS observations. Using a consistent method which explicitly considers sustained heating we have analyzed six flares with sufficient statistics, deriving constraints on the physical parameters of the flaring regions. In all cases the flaring loops are likely compact (L approx 0.3 R*), and confined to a rather narrow range of sizes, incompatible with the large (L >= R*) tenuous loops claimed by previous analyses of flares on AD Leo and other similar stars. The flaring loops appear to have a larger cross section (beta = r/L approx. 0.3) than customarily assumed (e.g. beta 0.1). All flares show evidence of significant heating during the decay phase. Although the derived peak pressures are high (up to P approx. 10^4 dyne/cm^2) with a peak temperature of approx. 50 MK, the magnetic fields required to confine such loops and to produce the observed flare luminosity are relatively modest (B approx. 1 to 2 kG) and fully compatible with the photospheric magnetic fields measured in several flare stars. If the narrow range of loop sizes obtained is extrapolated to the quiescent structures responsible for the active corona, the latter can be naturally scaled up from the solar case through a modest (a factor of 10) increase in pressure in otherwise solar-like active structures with a small surface filling factor (approx 5%). The quiescent component of the corona shows no evidence for abundance peculiarities with respect to the photosphere, and the quiescent coronal luminosity is remarkably constant (with variations of less than a factor of 2) across the almost 20 yr span of the observations discussed here.Comment: Accepted for publication in Astronomy & Astrophysisc

Eigenvalue estimates for submanifolds with locally bounded mean curvature

We give lower bounds for the first Dirichilet eigenvalues for domains in submanifolds with locally bounded mean curvatures. These bounds depend on the injectivity radius, sectional curvature (upperbound) of the ambient space and on the mean curvature of the submanifold. For submanifolds fo Hadamard manifolds these lower bounds depend only on the dimension and mean curvature of the submanifold.Comment: Paper writen in latex, 7 page

On the mean curvature of Nash isometric embeddings

J. Nash proved that the geometry of any Riemannian manifold M imposes no restrictions to be embedded isometrically into a (fixed) ball B_{\mathbb{R}^{N}}(1) of the Euclidean space R^N. However, the geometry of M appears, to some extent, imposing restrictions on the mean curvature vector of the embedding.Comment: A note of two page

An Extension of Barta's Theorem and Geometric Applications

We prove an extension of a theorem of Barta then we make few geometric applications. We extend Cheng's lower eigenvalue estimates of normal geodesic balls. We generalize Cheng-Li-Yau eigenvalue estimates of minimal submanifolds of the space forms. We prove an stability theorem for minimal hypersurfaces of the Euclidean space, giving a converse statement of a result of Schoen. Finally we prove a generalization of a result of Kazdan-Kramer about existence of solutions of certain quasi-linear elliptic equations.Comment: 23 pages. This paper is an improved version of our paper of the same Titled posted her

A software for learning Information Theory basics with emphasis on Entropy of Spanish

In this paper, a tutorial software to learn Information Theory basics in a practical way is reported. The software, called IT-tutor-UV, makes use of a modern existing Spanish corpus for the modeling of the source. Both the source and the channel coding are also included in this educational tool as part of the learning experience. Entropy values of the Spanish language obtained with the IT-tutor-UV are discussed and compared to others that were previously calculated under limited conditions