1,079 research outputs found
Salvador PIÉ-NINOT, Introducción a la Eclesiología, Ed. Verbo Divino, Estella 1995, 145 pp., 15 x 23. [RECENSIÓN]
Spontaneous Symmetry Breakdown in non-relativistic Quantum Mechanics
The advantages and disadvantages of some pedagogical non-relativistic
quantum-mechanical models, used to illustrate spontaneous symmetry breakdown,
are discussed. A simple quantum-mechanical toy model (a spinor on the line,
subject to a magnetostatic interaction) is presented, that exhibits the
spontaneous breakdown of an internal symmetry.Comment: 19 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1111.1213. Equations (30) and (31) have been corrected. Other minor
correction
Crystallization and melting of bacteria colonies and Brownian Bugs
Motivated by the existence of remarkably ordered cluster arrays of bacteria
colonies growing in Petri dishes and related problems, we study the spontaneous
emergence of clustering and patterns in a simple nonequilibrium system: the
individual-based interacting Brownian bug model. We map this discrete model
into a continuous Langevin equation which is the starting point for our
extensive numerical analyses. For the two-dimensional case we report on the
spontaneous generation of localized clusters of activity as well as a
melting/freezing transition from a disordered or isotropic phase to an ordered
one characterized by hexagonal patterns. We study in detail the analogies and
differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young
theory of equilibrium melting, as well as with another competing theory. For
that, we study translational and orientational correlations and perform a
careful defect analysis. We find a non standard one-stage, defect-mediated,
transition whose nature is only partially elucidated.Comment: 13 Figures. 14 pages. Submitted to Phys. Rev.
Tip charge dependence of three-dimensional AFM mapping of concentrated ionic solutions
A molecular scale understanding of the organization and structure of a liquid near a solid surface is
currently a major challenge in surface science. It has implications across different fields from
electrochemistry and energy storage to molecular biology. Three-dimensional AFM generates atomically
resolved maps of solid-liquid interfaces. The imaging mechanism behind those maps is under debate, in
particular, for concentrated ionic solutions. Theory predicts that the observed contrast should depend on the
tip’s charged state. Here, by using neutrally, negatively, and positively charged tips, we demonstrate that the
3D maps depend on the tip’s polarization. A neutral tip will explore the total particle density distribution
(water and ions) while a charged tip will reveal the charge density distribution. The experimental data
reproduce the key findings of the theor
On the mass of the neutron star in Cyg X-2
We present new high resolution spectroscopy of the low mass X-ray binary Cyg
X-2 which enables us to refine the orbital solution and rotational broadening
of the donor star. In contrast with Elebert et al (2009) we find a good
agreement with results reported in Casares et al. (1998). We measure
day, km s and km s. These values imply and
M (for ). Therefore, the
neutron star in Cyg X-2 can be more massive than canonical. We also find no
evidence for irradiation effects in our radial velocity curve which could
explain the discrepancy between Elebert et al's and our values.Comment: Accepted for publication in MNRA
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