79 research outputs found
Quantum Corrections to the Energy Density of a Homogeneous Bose Gas
Quantum corrections to the properties of a homogeneous interacting Bose gas
at zero temperature can be calculated as a low-density expansion in powers of
, where is the number density and is the S-wave
scattering length. We calculate the ground state energy density to second order
in . The coefficient of the correction has a
logarithmic term that was calculated in 1959. We present the first calculation
of the constant under the logarithm. The constant depends not only on , but
also on an extra parameter that describes the low energy scattering of
the bosons. In the case of alkali atoms, we argue that the second order quantum
correction is dominated by the logarithmic term, where the argument of the
logarithm is , and is the length scale set by the van
der Waals potential.Comment: 29 pages + 6 figures; section 5.3 rewritte
Effective field theory approach to N=4 supersymmetric Yang-Mills at finite temperature
We study the perturbation expansion of the free energy of N=4 supersymmetric
SU(N) Yang-Mills at finite temperature in powers of 't Hooft's coupling g^2 N
in the large N limit. Infrared divergences are controlled by constructing a
hierarchy of two 3 dimensional effective field theories. This procedure is
applied to the calculation of the free energy to order (g^2 N)^(3/2), but it
can be extended to higher order corrections.Comment: LaTeX, 10 pages, 1 figure, uses eps
Perturbative QCD at High Temperature
Recent developments of perturbation theory at finite temperature based on
effective field theory methods are reviewed. These methods allow the
contributions from the different scales to be separated and the perturbative
series to be reorganized. The construction of the effective field theory is
shown in detail for phi^4 theory and QCD. It is applied to the evaluation of
the free energy of QCD at order g^5 and the calculation of the g^6 term is
outlined. Implications for the application of perturbative QCD to the
quark-gluon plasma are also discussed.Comment: LaTeX, 27 pages, 15 figures. Final versio
A propĂłsito de Ezequiel Adamovsky, Historia de las clases populares en la Argentina. Desde 1880 hasta 2003, Tomo II, Buenos Aires, Sudamericana, 492 pp.
A propĂłsito de Ezequiel Adamovsky, Historia de las clases populares en la Argentina. Desde 1880 hasta 2003, Tomo II, Buenos Aires, Sudamericana, 492 pp
Evaluating Sums over the Matsubara Frequencies
Perturbative calculations in field theory at finite temperature involve sums
over the Matsubara frequencies. Besides the usual difficulties that appear in
perturbative computations, these sums give rise to some new obstacles that are
carefully analized here. I present a fast and realible recipe to work out sums
over the Matsubara frequencies. As this algorithm leads to deal with very
cumbersome algebraic expressions, it has been written for computers by using
the symbolic manipulation program Mathematica. It is also shown this algorithm
to be self-consistent when it is applied to more than one loop computations.Comment: 10 page
Managing 2.0 newsrooms: insight stories of spontaneous innovation and improvisation
Nowadays audiences love live communication (Deuze, 2011), the possibility of reaching news in real time, receiving contents without the effort of having to search for them. The concept ânews nowâ (Sheller, 2014) is an audience imperative.
Previous research show that media have developed in the last decade a great dependence on social networks (Singer et alt, 2011). Source of new audiences, social media are also a space for the verification and localization of new contents. Sometimes these functions has forced to alter editorial models to host viral topics, necessary to try to overcome the crisis of attention particularly concerning in the context of the young people (Boczkowski and Mitchelstein, 2016). Digital media estimate that one third of their visits come from Facebook (Somaya, 2014), a figure that forces them to create specific strategies that ensure the reputation and growth of the company in the 2.0 sphere because the atomization of content causes fragmented and decontextualized audiences to consume individual news. Recently, Emily Bell (2018) confirmed also that Facebook is reshaping newsrooms.
From the point of view of the audience, the number of users of Facebook or Twitter in Spain is not reached by any mass media. This context generates a strange symbiosis, which combines the need and the competition that we consider relevant to analyze. One of the routines which come from this relationship has been the integration of soft news on the front page of online media. This practice has also affected media credibility.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Renormalization Effects in a Dilute Bose Gas
The low-density expansion for a homogeneous interacting Bose gas at zero
temperature can be formulated as an expansion in powers of ,
where is the number density and is the S-wave scattering length.
Logarithms of appear in the coefficients of the expansion. We show
that these logarithms are determined by the renormalization properties of the
effective field theory that describes the scattering of atoms at zero density.
The leading logarithm is determined by the renormalization of the pointlike scattering amplitude.Comment: 10 pages, 1 postscript figure, LaTe
A Hybrid Parameterization Technique for Speaker Identification
Classical parameterization techniques for Speaker Identification use the codification of the power spectral density of raw speech, not discriminating between articulatory features produced by vocal tract dynamics (acoustic-phonetics) from glottal source biometry. Through the present paper a study is conducted to separate voicing fragments of speech into vocal and glottal components, dominated respectively by the vocal tract transfer function estimated adaptively to track the acoustic-phonetic sequence of the message, and by the glottal characteristics of the speaker and the phonation gesture. The separation methodology is based in Joint Process Estimation under the un-correlation hypothesis between vocal and glottal spectral distributions. Its application on voiced speech is presented in the time and frequency domains. The parameterization methodology is also described. Speaker Identification experiments conducted on 245 speakers are shown comparing different parameterization strategies. The results confirm the better performance of decoupled parameterization compared against approaches based on plain speech parameterization
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