735 research outputs found
Making a “malherbario” as an input for the development of competencies for the “Weed control” course.
La falta de insumos para desarrollar el proceso de enseñanza- aprendizaje en la asignatura de Control de malezas, así como el contar con un solo texto guía desactualizado y ciertas restricciones para salidas de campo, motivaron la elaboración de material didáctico de apoyo con materia prima del sector. El proceso innovador se generó con la participación de los estudiantes para la construcción de un herbario propio, al cual se le denominó “malherbario”. Este sirvió para la consolidación de los contenidos y de la información teórica recibida en clase, a través del desarrollo de los tres saberes, y en especial del saber hacer. La acción educativa permitió la generación de competencias específicas que permiten al estudiante ser capaz de producir una respuesta propia que no había sido previamente memorizada.Lack of inputs to carry out the teaching-learning process in the Weed control course as well as having a single outdated guidebook and certain restrictions for field trips led to the creation of teaching support material using raw material of the surrounding areas. The innovative process was fostered with the participation of students for making their own herbarium, called “malherbario”. This served to strengthen the contents and the theoretical information received in class, through the development of three types of knowledge, in particular the know-how. The educational action allowed the development of specific competencies that enable students to be capable of producing their own response that had not been previously memorized
Matter--wave emission in optical lattices: Single particle and collective effects
We introduce a simple set--up corresponding to the matter-wave analogue of
impurity atoms embedded in an infinite photonic crystal and interacting with
the radiation field. Atoms in a given internal level are trapped in an optical
lattice, and play the role of the impurities. Atoms in an untrapped level play
the role of the radiation field. The interaction is mediated by means of lasers
that couple those levels. By tuning the lasers parameters, it is possible to
drive the system through different regimes, and observe phenomena like matter
wave superradiance, non-Markovian atom emission, and the appearance of bound
atomic states.Comment: 5 pages, 3 figure
Nonlinear vortex light beams supported and stabilized by dissipation
We describe nonlinear Bessel vortex beams as localized and stationary
solutions with embedded vorticity to the nonlinear Schr\"odinger equation with
a dissipative term that accounts for the multi-photon absorption processes
taking place at high enough powers in common optical media. In these beams,
power and orbital angular momentum are permanently transferred to matter in the
inner, nonlinear rings, at the same time that they are refueled by spiral
inward currents of energy and angular momentum coming from the outer linear
rings, acting as an intrinsic reservoir. Unlike vortex solitons and dissipative
vortex solitons, the existence of these vortex beams does not critically depend
on the precise form of the dispersive nonlinearities, as Kerr self-focusing or
self-defocusing, and do not require a balancing gain. They have been shown to
play a prominent role in "tubular" filamentation experiments with powerful,
vortex-carrying Bessel beams, where they act as attractors in the beam
propagation dynamics. Nonlinear Bessel vortex beams provide indeed a new
solution to the problem of the stable propagation of ring-shaped vortex light
beams in homogeneous self-focusing Kerr media. A stability analysis
demonstrates that there exist nonlinear Bessel vortex beams with single or
multiple vorticity that are stable against azimuthal breakup and collapse, and
that the mechanism that renders these vortexes stable is dissipation. The
stability properties of nonlinear Bessel vortex beams explain the experimental
observations in the tubular filamentation experiments.Comment: Chapter of boo
Microscopic theory for quantum mirages in quantum corrals
Scanning tunneling microscopy permits to image the Kondo resonance of a
single magnetic atom adsorbed on a metallic surface. When the magnetic impurity
is placed at the focus of an elliptical quantum corral, a Kondo resonance has
been recently observed both on top of the impurity and on top of the focus
where no magnetic impurity is present. This projection of the Kondo resonance
to a remote point on the surface is referred to as quantum mirage. We present a
quantum mechanical theory for the quantum mirage inside an ideal quantum corral
and predict that the mirage will occur in corrals with shapes other than
elliptical
Antiribosomal-P autoantibodies from psychiatric lupus target a novel neuronal surface protein causing calcium influx and apoptosis
The interesting observation was made 20 years ago that psychotic manifestations in patients with systemic lupus erythematosus are associated with the production of antiribosomal-P protein (anti-P) autoantibodies. Since then, the pathogenic role of anti-P antibodies has attracted considerable attention, giving rise to long-term controversies as evidence has either contradicted or confirmed their clinical association with lupus psychosis. Furthermore, a plausible mechanism supporting an anti-P–mediated neuronal dysfunction is still lacking. We show that anti-P antibodies recognize a new integral membrane protein of the neuronal cell surface. In the brain, this neuronal surface P antigen (NSPA) is preferentially distributed in areas involved in memory, cognition, and emotion. When added to brain cellular cultures, anti-P antibodies caused a rapid and sustained increase in calcium influx in neurons, resulting in apoptotic cell death. In contrast, astrocytes, which do not express NSPA, were not affected. Injection of anti-P antibodies into the brain of living rats also triggered neuronal death by apoptosis. These results demonstrate a neuropathogenic potential of anti-P antibodies and contribute a mechanistic basis for psychiatric lupus. They also provide a molecular target for future exploration of this and other psychiatric diseases
Extended parametric resonances in nonlinear Schrodinger systems
We study an example of exact parametric resonance in a extended system ruled
by nonlinear partial differential equations of nonlinear Schr\"odinger type. It
is also conjectured how related models not exactly solvable should behave in
the same way. The results have applicability in recent experiments in
Bose-Einstein condensation and to classical problems in Nonlinear Optics.Comment: 1 figur
Quantum Phases of Trapped Ions in an Optical Lattice
We propose loading trapped ions into microtraps formed by an optical lattice.
For harmonic microtraps, the Coulomb coupling of the spatial motions of
neighboring ions can be used to construct a broad class of effective
short-range Hamiltonians acting on an internal degree of freedom of the ions.
For large anharmonicities, on the other hand, the spatial motion of the ions
itself represents a spin-1/2 model with frustrated dipolar XY interactions. We
illustrate the latter setup with three systems: the linear chain, the zig-zag
ladder, and the triangular lattice. In the frustrated zig-zag ladder with
dipolar interactions we find chiral ordering beyond what was predicted
previously for a next-nearest-neighbor model. In the frustrated anisotropic
triangular lattice with nearest-neighbor interactions we find that the
transition from the one-dimensional gapless spin-liquid phase to the
two-dimensional spiraling ordered phase passes through a gapped spin-liquid
phase, similar to what has been predicted for the same model with Heisenberg
interactions. Further, a second gapped spin-liquid phase marks the transition
to the two-dimensional Neel-ordered phase.Comment: re-formatted; added discussion of feasibilit
One- and many-body effects on mirages in quantum corrals
Recent interesting experiments used scanning tunneling microscopy to study
systems involving Kondo impurities in quantum corrals assembled on Cu or noble
metal surfaces. The solution of the two-dimensional one-particle Schrodinger
equation in a hard wall corral without impurity is useful to predict the
conditions under which the Kondo effect can be projected to a remote location
(the quantum mirage). To model a soft circular corral, we solve this equation
under the potential W*delta(r-r0), where r is the distance to the center of the
corral and r0 its radius. We expand the Green's function of electron surface
states Gs0 for r<r0 as a discrete sum of contributions from single poles at
energies epsilon_i-I*delta_i. The imaginary part delta_i is the half-width of
the resonance produced by the soft confining potential, and turns out to be a
simple increasing function of epsilon_i. In presence of an impurity, we solve
the Anderson model at arbitrary temperatures using the resulting expression for
Gs0 and perturbation theory up to second order in the Coulomb repulsion U. We
calculate the resulting change in the differential conductance Delta dI/dV as a
function of voltage and space, in circular and elliptical corrals, for
different conditions, including those corresponding to recent experiments. The
main features are reproduced. The role of the direct hybridization between
impurity and bulk, the confinement potential, the size of the corral and
temperature on the intensity of the mirage are analyzed. We also calculate
spin-spin correlation functions.Comment: 13 pages, 12 figures, accepted for publication in Phys. Rev. B.
Calculations of spin correlations within an additional approximation adde
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