3,077 research outputs found
Dynamic localization in Glauber-Fock lattices
Glauber-Fock lattices refer to a special class of semi-infinite tight-binding
lattices with inhomogeneous hopping rates which are found in certain simple
solid-state, quantum optics and quantum field theoretical models. Here it is
shown that dynamic localization, i.e. suppression of quantum diffusion and
periodic quantum self-imaging by an external sinusoidal force [D.H. Dunlap and
V.M. Kenkre, Phys. Rev. B {\bf 34}, 3625 (1986)], can be exactly realized in
Glauber-Fock lattices, in spite of inhomogeneity of hopping rates and lattice
truncation.Comment: 3 figure
PT-symmetric laser-absorber
In a recent work, Y.D. Chong et al. [Phys. Rev. Lett. {\bf 105}, 053901
(2010)] proposed the idea of a coherent perfect absorber (CPA) as the
time-reversed counterpart of a laser, in which a purely incoming radiation
pattern is completely absorbed by a lossy medium. The optical medium that
realizes CPA is obtained by reversing the gain with absorption, and thus it
generally differs from the lasing medium. Here it is shown that a laser with an
optical medium that satisfies the parity-time symmetry
condition for the dielectric
constant behaves simultaneously as a laser oscillator (i.e. it can emit
outgoing coherent waves) and as a CPA (i.e. it can fully absorb incoming
coherent waves with appropriate amplitudes and phases). Such a device can be
thus referred to as a -symmetric CPA-laser. The general
amplification/absorption features of the CPA-laser below lasing
threshold driven by two fields are determined.Comment: 5 pages; to be published in Phys. Rev. A (Rapid Communications
Spoken Thesaurus: Sorrow
The Hindi Thesaurus addresses such questions in a series of lively, unscripted Hindi-medium conversations about groups of words of related meaning. Concentrating on selected mainstream words and phrases, we help you to broaden your active vocabulary by encountering styles of language appropriate for everyday speech. The conversations are between Rupert Snell (Hindi teacher and perpetual Hindi learner) and Neha Ladha (mother-tongue speaker of Hindi). Glossaries for each podcast can be read online or downloaded in PDF format. (Length: 7:49)Asian Studie
Optical realization of relativistic non-Hermitian quantum mechanics
Light propagation in distributed feedback optical structures with gain/loss
regions is shown to provide an accessible laboratory tool to visualize in
optics the spectral properties of the one-dimensional Dirac equation with
non-Hermitian interactions. Spectral singularities and PT symmetry breaking of
the Dirac Hamiltonian are shown to correspond to simple observable physical
quantities and related to well-known physical phenomena like resonance
narrowing and laser oscillation.Comment: 4 page
Optical Zener-Bloch oscillations in binary waveguide arrays
Zener tunneling in a binary array of coupled optical waveguides with
transverse index gradient is shown to produce a sequence of regular or
irregular beam splitting and beam recombination events superimposed to Bloch
oscillations. These periodic or aperiodic Zener-Bloch oscillations provide a
clear and visualizable signature in an optical system of coherent multiband
dynamics encountered in solid-state or matter-wave system
Dirac Fields on Spacelike Hypersurfaces, Their Rest-Frame Description and Dirac Observables
Grassmann-valued Dirac fields together with the electromagnetic field (the
pseudoclassical basis of QED) are reformulated on spacelike hypersurfaces in
Minkowski spacetime and then restricted to Wigner hyperplanes to get their
description in the rest-frame Wigner-covariant instant form of dynamics. The
canonical reduction to the Wigner-covariant Coulomb gauge is done in the rest
frame. It is shown, on the basis of a geometric incosistency, that the
description of fermions is incomplete, because there is no bosonic carrier of
the spin structure describing the trajectory of the electric current in
Minkowski spacetime, as it was already emphasized in connection with the first
quantization of spinning particles in a previous paper.Comment: 44 pages, revte
Non-exponential decay via tunneling in tight-binding lattices and the optical Zeno effect
An exactly-solvable model for the decay of a metastable state coupled to a
semi-infinite tight-binding lattice, showing large deviations from exponential
decay in the strong coupling regime, is presented. An optical realization of
the lattice model, based on discrete diffraction in a semi-infinite array of
tunneling-coupled optical waveguides, is proposed to test non-exponential decay
and for the observation of an optical analog of the quantum Zeno effect
InSiDDe: A server for designing artificial disordered proteins
InSiDDe (In Silico Disorder Design) is a program for the in silico design of intrinsically disordered proteins of desired length and disorder probability. The latter is assessed using IUPred and spans values ranging from 0.55 to 0.95 with 0.05 increments. One to ten artificial sequences per query, each made of 50 to 200 residues, can be generated by InSiDDe. We describe the rationale used to set up InSiDDe and show that an artificial sequence of 100 residues with an IUPred score of 0.6 designed by InSiDDe could be recombinantly expressed in E. coli at high levels without degradation when fused to a natural molecular recognition element (MoRE). In addition, the artificial fusion protein exhibited the expected behavior in terms of binding modulation of the specific partner recognized by the MoRE. To the best of our knowledge, InSiDDe is the first publicly available software for the design of intrinsically disordered protein (IDP) sequences. InSiDDE is publicly available online
Scattering of accelerated wave packets
Wave-packet scattering from a stationary potential is significantly modified
when the wave-packet is subject to an external time-dependent force during the
interaction. In the semiclassical limit, wave--packet motion is simply
described by Newtonian equations and the external force can, for example,
cancel the potential force making a potential barrier transparent. Here we
consider wave-packet scattering from reflectionless potentials, where in
general the potential becomes reflective when probed by an accelerated
wave-packet. In the particular case of the recently-introduced class of complex
Kramers-Kronig potentials we show that a broad class of time dependent forces
can be applied without inducing any scattering, while there is a breakdown of
the reflectionless property when there is a broadband distribution of initial
particle momentum, involving both positive and negative components.Comment: 13 pages, 4 figures, to appear in Phys. Rev.
Church building beyond church architecture: evangelization and architecture / Construir iglesias más allá de la arquitectura religiosa: evangelización y arquitectura
En la historia de la cultura occidental, la Sagrada Escritura es una fuente arquetípica no sólo para el diseño de edificios de culto, sino también para la práctica de la construcción en general. El Antiguo Testamento ofrece un amplio repertorio de espacios y edificios que han nutrido el imaginario arquitectónico colectivo, tanto en el área del Mediterráneo como en la Europa continental.
Cuando consideramos el Nuevo Testamento, las referencias a las formas arquitectónicas se hacen mas evanescentes. Diversos pasajes evangélicos parecen sugerir que el cristianismo no tiene necesidad de espacios sagrados específicos. De hecho, en los momentos de reforma del pensamiento eclesiológico, estos pasajes se han utilizado para argumentar una concepción atópica del culto cristiano. La Buena Nueva parece anunciar no solo el fin del Templo de Jerusalén, sino también de toda arquitectura sagrada en favor de una arquitectura santa, hecha de cristianos santos, templos vivos de Dios.
El impulso para superar la arquitectura para el culto es corroborado por la visión escatológica en el último libro de la Escritura. El Apocalipsis considera la Nueva Jerusalén como un modelo integral, donde las mediaciones materiales para la relación con Dios ya no existirán. Toda la ciudad será el lugar de la Presencia Divina.
Sin embargo, sabemos que estas hipótesis, recurrentes en la historia del cristianismo y de la arquitectura, no han sido nunca expresamente utilizadas por ninguna comunidad organizada. El tema atraviesa el Renacimiento, con el auge del llamado culto interior, y retorna con fuerza tras el Concilio Vaticano II, que pone en el centro la formación de la asamblea celebrante, más que de la construcción de la casa de la asamblea.
Si el vínculo entre la arquitectura cristiana y Evangelio resulta tenue y no inmediato, algo parecido ocurre con la relación entre arquitectura y la actividad evangelizadora, que es el tema. -------- In the history of architectural culture, the Scripture is the archetypical source not only for designing worship buildings but also for the construction practice in general. The Old Testament offers a repertoire of spaces and buildings that has nurtured the architectural imaginary both in the area of the Mediterranean and in Europe.
When we consider the New Testament, the references to the architectural forms become more elusive. In fact, some episodes
have suggested that Christianity has no need for specific sacred spaces; that is to say, these passages have been used in support
of an atopic conception of the Christian cult. Not only had the Temple in Jerusalem to end, but also the sacred architecture
should give way to a saint architecture, made of saint Christians as living temples of God.
The impulse to surpass worship architecture is corroborated by the eschatological vision in the last book of the Scripture: the
apocalyptic vision of the New Jerusalem is considered in its entirety a model, but in the city of the end times the material mediations
of the relationship with God will no longer exist. The whole city will be the place of the Presence.
The hypothesis that material Christian temples are not necessary represents a recurrent aspiration in the history of Christianity
and in architecture, despite the fact that no organized community has ever tried to realize it. This topic is again at the center of
the debate over architecture in the post-conciliar epoch, which focuses on the construction of the celebrating assembly
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