15,682 research outputs found
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
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