18,224 research outputs found
Closed form solution of Lindblad master equations without gain
We present a closed form solution to the eigenvalue problem of a class of
master equations that describe open quantum system with loss and dephasing but
without gain. The method relies on the existence of a conserved number of
excitation in the Hamiltonian part and that none of the Lindblad operators
describe an excitation of the system. In the absence of dephasing Lindblad
operators, the eigensystem of the Liouville operator can be constructed from
the eigenvalues and eigenvectors of the effective non-Hermitian Hamiltonian
used in the quantum jump approach. Open versions of spin chains, the
Tavis-Cummings model and coupled Harmonic oscillators without gain can be
solved using this technique.Comment: 9 page
“La Primavera del Inmigrante”: Media and Voice in the Making of Chicago’s Immigrant Rights’ Movement, 2005-2006
Abstract:
As the most draconian legislative bill in modern immigration history, the Sensenbrenner Bill (H.R. 4437) aimed to criminalize the eleven million people living in this country without legal documents. What was intended to be the last nail on the “illegal alien” coffin instead generated a political blowback—it set in motion mass protests on a scale which had no parallel in American history. What began in Chicago on March 10, 2006 became contagious, spreading to the rest of the country at a speed that caught all by surprise. Millions participated in dozens of events in what came to be known as “la primavera del inmigrante.” This paper examines the relationship between media, especially Spanish-language radio, and voice (the mass mobilizations) in Chicago’s two earliest marches. On July 1, 2005 50,000 people marched to protest the Minuteman Project while the March 10 (2006) event was the first national mass action against the Sensenbrenner Bill. Using video, photographs, press clippings and field notes, I argue in this research project that the Spanish language media played a crucial role in both mobilizations, not only in promoting the events but also as main forum where people, mainly immigrants, waged their many concerns regarding all issues related to immigration. On the other hand, people (regardless of legal status) came out by the thousands because the Sensenbrenner Bill affected them in one way or another
Beyond Stemming and Lemmatization: Ultra-stemming to Improve Automatic Text Summarization
In Automatic Text Summarization, preprocessing is an important phase to
reduce the space of textual representation. Classically, stemming and
lemmatization have been widely used for normalizing words. However, even using
normalization on large texts, the curse of dimensionality can disturb the
performance of summarizers. This paper describes a new method for normalization
of words to further reduce the space of representation. We propose to reduce
each word to its initial letters, as a form of Ultra-stemming. The results show
that Ultra-stemming not only preserve the content of summaries produced by this
representation, but often the performances of the systems can be dramatically
improved. Summaries on trilingual corpora were evaluated automatically with
Fresa. Results confirm an increase in the performance, regardless of summarizer
system used.Comment: 22 pages, 12 figures, 9 table
Universal diagrams for te waves guided by thin films bounded by saturable nonlinear media
It is shown that universal V-b diagrams provide a powerful tool when analyzing the stationary waveguiding properties of the TE waves guided by a thin film bounded by a saturable nonlinear substrate or cladding. For a wide class of nonlinearities, the allowed and forbidden regions of these diagrams, for a stationary guided propagation to occur, display a universal pattern, the marginal loci separating different allowed regions from the forbidden ones being simple functions of only the asymmetry measure of the waveguide and the saturation value of the nonlinear permittivity. Relevant information for device design purposes is summarized on a few diagrams, so general waveguiding properties can be immediately read-off from them, and threshold power-independent values of the normalized thickness of the waveguide for a particular kind of guided wave to be allowed are obtained. Qualitative information concerning both the guided power and the stability of guided waves is also included in the diagrams.Peer ReviewedPostprint (published version
Chiral transport equation from the quantum Dirac Hamiltonian and the on-shell effective field theory
We derive the relativistic chiral transport equation for massless fermions
and antifermions by performing a semiclassical Foldy-Wouthuysen diagonalization
of the quantum Dirac Hamiltonian. The Berry connection naturally emerges in the
diagonalization process to modify the classical equations of motion of a
fermion in an electromagnetic field. We also see that the fermion and
antifermion dispersion relations are corrected at first order in the Planck
constant by the Berry curvature, as previously derived by Son and Yamamoto for
the particular case of vanishing temperature. Our approach does not require
knowledge of the state of the system, and thus it can also be applied at high
temperature. We provide support for our result by an alternative computation
using an effective field theory for fermions and antifermions: the on-shell
effective field theory. In this formalism, the off-shell fermionic modes are
integrated out to generate an effective Lagrangian for the quasi-on-shell
fermions/antifermions. The dispersion relation at leading order exactly matches
the result from the semiclassical diagonalization. From the transport equation,
we explicitly show how the axial and gauge anomalies are not modified at finite
temperature and density despite the incorporation of the new dispersion
relation into the distribution function.Comment: 9 pages, no figures. v2: Some comments and more details added, typos
fixed and reference list updated. Final version matching the published
articl
- …