Dynamics of domain walls in pattern formation under traveling-wave forcing

We study dynamics of domain walls in pattern forming systems that are externally forced by a moving space-periodic modulation close to 2:1 spatial resonance. The motion of the forcing induces nongradient dynamics, while the wave number mismatch breaks explicitly the chiral symmetry of the domain walls. The combination of both effects yields an imperfect nonequilibrium Ising-Bloch bifurcation, where all kinks (including the Ising-like one) drift. Kink velocities and interactions are studied within the generic amplitude equation. For nonzero mismatch, a transition to traveling bound kink-antikink pairs and chaotic wave trains occurs.

Bifurcations and chaos in single-roll natural convection with low Prandtl number

Convective flows of a small Prandtl number fluid contained in a two-dimensional cavity subject to a lateral thermal gradient are numerically studied by using different techniques. The aspect ratio (length to height) is kept at around 2. This value is found optimal to make the flow most unstable while keeping the basic single-roll structure. Two cases of thermal boundary conditions on the horizontal plates are considered: perfectly conducting and adiabatic. For increasing Rayleigh numbers we find a transition from steady flow to periodic oscillations through a supercritical Hopf bifurcation that maintains the centrosymmetry of the basic circulation. For a Rayleigh number of about ten times that of the Hopf bifurcation the system initiates a complex scenario of bifurcations. In the conductive case these include a quasiperiodic route to chaos. In the adiabatic one the dynamics is dominated by the interaction of two Neimark-Sacker bifurcations of the basic periodic solutions, leading to the stable coexistence of three incommensurate frequencies, and finally to chaos. In all cases, the complex time-dependent behavior does not break the basic, single-roll structure.

Application of fuzzy-rule-based postprocessing to correlation methods in pattern recognition

One of the most important problems in optical pattern recognition by correlation is the appearance of sidelobes in the correlation plane, which causes false alarms. We present a method that eliminate sidelobes of up to a given height if certain conditions are satisfied. The method can be applied to any generalized synthetic discriminant function filter and is capable of rejecting lateral peaks that are even higher than the central correlation. Satisfactory results were obtained in both computer simulations and optical implementation.

Design of surface forces apparatus for tribology studies combined with nonlinear optical spectroscopy

We describe the design, calibration, and performance of surface forces apparatus with the capability of illumination of the contact interface for spectroscopic investigation using optical techniques. The apparatus can be placed in the path of a Nd-YAG laser for studies of the linear response or the second harmonic and sum-frequency generation from a material confined between the two surfaces. In addition to the standard fringes of equal chromatic order technique, which we have digitized for accurate and fast analysis, the distance of separation can be measured with a fiber-optic interferometer during spectroscopic measurements (2 Å resolution and 10 ms response time). The sample approach is accomplished through application of a motor drive, piezoelectric actuator, or electromagnetic lever deflection for variable degrees of range, sensitivity, and response time. To demonstrate the operation of the instrument, the stepwise expulsion of discrete layers of octamethylcyclotetrasiloxane from the contact is shown. Lateral forces may also be studied by using piezoelectric bimorphs to induce and direct the motion of one surface.

Dynamics of turing patterns under spatiotemporal forcing

We study, both theoretically and experimentally, the dynamical response of Turing patterns to a spatiotemporal forcing in the form of a traveling-wave modulation of a control parameter. We show that from strictly spatial resonance, it is possible to induce new, generic dynamical behaviors, including temporally modulated traveling waves and localized traveling solitonlike solutions. The latter make contact with the soliton solutions of Coullet [Phys. Rev. Lett. 56, 724 (1986)] and generalize them. The stability diagram for the different propagating modes in the Lengyel-Epstein model is determined numerically. Direct observations of the predicted solutions in experiments carried out with light modulations in the photosensitive chlorine dioxide-iodine-malonic acid reaction are also reported.

Belleza escrita en femenino

La belleza femenina no es simplemente una cusetión estética, sino también política. Históricamente, la mujer ha sido el objeto pasivo de la mirada masculina, el objeto de sueño y de deseo de los hombres. Los cánones estéticos establecidos por pintores, escultures, fotógrafos, poetas -aunque variables según las épocas y la evolución de los gustos- llevaron siempre implícita una visión patriarcal del papel de la mujer en la sociedad y han conformado una imagen de la mujer que ésta ha asumido. Para la ensayista estadounidense Naomi Wolf, el "mito de la belleza" es un arma ideológica que frena el progreso de las mujeres, las aisla y genera hostilidad entre ellas mismas...

Belleza escrita en femenino

La belleza femenina no es simplemente una cusetión estética, sino también política. Históricamente, la mujer ha sido el objeto pasivo de la mirada masculina, el objeto de sueño y de deseo de los hombres. Los cánones estéticos establecidos por pintores, escultures, fotógrafos, poetas -aunque variables según las épocas y la evolución de los gustos- llevaron siempre implícita una visión patriarcal del papel de la mujer en la sociedad y han conformado una imagen de la mujer que ésta ha asumido. Para la ensayista estadounidense Naomi Wolf, el "mito de la belleza" es un arma ideológica que frena el progreso de las mujeres, las aisla y genera hostilidad entre ellas mismas...

Belleza escrita en femenino

La belleza femenina no es simplemente una cusetión estética, sino también política. Históricamente, la mujer ha sido el objeto pasivo de la mirada masculina, el objeto de sueño y de deseo de los hombres. Los cánones estéticos establecidos por pintores, escultures, fotógrafos, poetas -aunque variables según las épocas y la evolución de los gustos- llevaron siempre implícita una visión patriarcal del papel de la mujer en la sociedad y han conformado una imagen de la mujer que ésta ha asumido. Para la ensayista estadounidense Naomi Wolf, el "mito de la belleza" es un arma ideológica que frena el progreso de las mujeres, las aisla y genera hostilidad entre ellas mismas...

Protocol de viabilitat socioecològica del llop : àrea d'estudi de la Vall d'Alinyà

Aquest estudi analitza diferents variables ecològiques i socials amb l’objectiu de determinar la viabilitat de l’espècie Canis lupus en el territori que compren la Vall d’Alinyà, i definir unes pautes per extrapolar aquest tipus d’anàlisis a altres àrees d’estudi. El llop va desaparèixer de Catalunya a causa de la forta pressió antròpica exercida sobre l’espècie en el passat. En l’última dècada, s’han donat indicis d’una possible reaparició del súper depredador en el territori català. Com a mètode per a la cerca del llop s’ha experimentat amb l’ús de gossos de rastreig per a la cerca i diferenciació de rastres de llop, aquesta és una tècnica innovadora no utilitzada anteriorment per a aquest tipus d’objectiu. L’exploració de les inquietuds dels ramaders i caçadors de la zona, mostra una bona predisposició a la reaparició de l’animal. Malgrat no s’ha detectat llop amb els mètodes emprats, es demostra que li és viable d’establir-se a la zona.

Between Cratylism and Positivism: the Old Poem and What Alice Found There

En aquest article em referiré molt sumàriament a la fi lologia del dinou, mirant de relacionar-la amb tot el joc de paraules en Lewis Carrol, per tal d'establir-hi una trama correcta de (dis)continuïtats. El meu objectiu és considerar el Jabberwocky de Humpty Dumpty en el context de la feina i les descobertes de la moderna fi lologia. F. A. Wolf i J. Grimm condensen bona cosa dels experiments radicals i les troballes que tingueren lloc en aquells moments, que podríem contrastar amb les aventures textuals d'Alícia a l'altra banda de l'espill. Els llibres de l'altra banda necessiten intèrprets i cerquen la versió correcta, original, de la mateixa manera que la interpretació dels mots depèn d'un mètode fi able. Segurament Lewis Carroll com a jove fi lòleg era capaç de jugar bé amb aquelles troballes, entre un món que s'acabava i un altre que començava.

Percolation of spatially constrained Erdos-R enyi networks with degree correlations

Motivated by experiments on activity in neuronal cultures [J. Soriano, M. Rodr ́ıguez Mart́ınez, T. Tlusty, and E. Moses, Proc. Natl. Acad. Sci. 105, 13758 (2008)], we investigate the percolation transition and critical exponents of spatially embedded Erd̋os-Ŕenyi networks with degree correlations. In our model networks, nodes are randomly distributed in a two-dimensional spatial domain, and the connection probability depends on Euclidian link length by a power law as well as on the degrees of linked nodes. Generally, spatial constraints lead to higher percolation thresholds in the sense that more links are needed to achieve global connectivity. However, degree correlations favor or do not favor percolation depending on the connectivity rules. We employ two construction methods to introduce degree correlations. In the first one, nodes stay homogeneously distributed and are connected via a distance- and degree-dependent probability. We observe that assortativity in the resulting network leads to a decrease of the percolation threshold. In the second construction methods, nodes are first spatially segregated depending on their degree and afterwards connected with a distance-dependent probability. In this segregated model, we find a threshold increase that accompanies the rising assortativity. Additionally, when the network is constructed in a disassortative way, we observe that this property has little effect on the percolation transition.

Synthesis of highly focused fields with circular polarization at any transverse plane

We develop a method for generating focused vector beams with circular polarization at any transverse plane. Based on the Richards-Wolf vector model, we derive analytical expressions to describe the propagation of these set of beams near the focal area. Since the polarization and the amplitude of the input beam are not uniform, an interferometric system capable of generating spatially-variant polarized beams has to be used. In particular, this wavefront is manipulated by means of spatial light modulators displaying computer generated holograms and subsequently focused using a high numerical aperture objective lens. Experimental results using a NA=0.85 system are provided: irradiance and Stokes images of the focused field at different planes near the focal plane are presented and compared with those obtained by numerical simulation.