1,596 research outputs found
Signal detection in high dimension: The multispiked case
This paper deals with the local asymptotic structure, in the sense of Le
Cam's asymptotic theory of statistical experiments, of the signal detection
problem in high dimension. More precisely, we consider the problem of testing
the null hypothesis of sphericity of a high-dimensional covariance matrix
against an alternative of (unspecified) multiple symmetry-breaking directions
(\textit{multispiked} alternatives). Simple analytical expressions for the
asymptotic power envelope and the asymptotic powers of previously proposed
tests are derived. These asymptotic powers are shown to lie very substantially
below the envelope, at least for relatively small values of the number of
symmetry-breaking directions under the alternative. In contrast, the asymptotic
power of the likelihood ratio test based on the eigenvalues of the sample
covariance matrix is shown to be close to that envelope. These results extend
to the case of multispiked alternatives the findings of an earlier study
(Onatski, Moreira and Hallin, 2011) of the single-spiked case. The methods we
are using here, however, are entirely new, as the Laplace approximations
considered in the single-spiked context do not extend to the multispiked case
Representations of the -algebra and the loop representation in -dimensions
We consider the phase-space of Yang-Mills on a cylindrical space-time () and the associated algebra of gauge-invariant functions, the
-variables. We solve the Mandelstam identities both classically and
quantum-mechanically by considering the -variables as functions of the
eigenvalues of the holonomy and their associated momenta. It is shown that
there are two inequivalent representations of the quantum -algebra. Then we
compare this reduced phase space approach to Dirac quantization and find it to
give essentially equivalent results. We proceed to define a loop representation
in each of these two cases. One of these loop representations (for ) is
more or less equivalent to the usual loop representation.Comment: 15 pages, LaTeX, 1 postscript figure included, uses epsf.sty,
G\"oteborg ITP 93-3
Comparing international coverage of 9/11 : towards an interdisciplinary explanation of the construction of news
This article presents an interdisciplinary model attempting to explain how news is constructed by relying on the contributions of different fields of study: News Sociology, Political Communications, International Communications, International Relations. It is a first step towards developing a holistic theoretical approach to what shapes the news, which bridges current micro to macro approaches. More precisely the model explains news variation across different media organization and countries by focusing on the different way the sense of newsworthiness of journalists is affected by three main variables: national interest, national journalistic culture, and editorial policy of each media organization. The model is developed on the basis of an investigation into what shaped the media coverage of 9/11 in eight elite newspapers across the US, France, Italy and Pakistan
Of copulas, quantiles, ranks and spectra: An -approach to spectral analysis
In this paper, we present an alternative method for the spectral analysis of
a univariate, strictly stationary time series . We
define a "new" spectrum as the Fourier transform of the differences between
copulas of the pairs and the independence copula. This object
is called a copula spectral density kernel and allows to separate the marginal
and serial aspects of a time series. We show that this spectrum is closely
related to the concept of quantile regression. Like quantile regression, which
provides much more information about conditional distributions than classical
location-scale regression models, copula spectral density kernels are more
informative than traditional spectral densities obtained from classical
autocovariances. In particular, copula spectral density kernels, in their
population versions, provide (asymptotically provide, in their sample versions)
a complete description of the copulas of all pairs . Moreover,
they inherit the robustness properties of classical quantile regression, and do
not require any distributional assumptions such as the existence of finite
moments. In order to estimate the copula spectral density kernel, we introduce
rank-based Laplace periodograms which are calculated as bilinear forms of
weighted -projections of the ranks of the observed time series onto a
harmonic regression model. We establish the asymptotic distribution of those
periodograms, and the consistency of adequately smoothed versions. The
finite-sample properties of the new methodology, and its potential for
applications are briefly investigated by simulations and a short empirical
example.Comment: Published at http://dx.doi.org/10.3150/13-BEJ587 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
What makes for prize-winning television?
We investigate the determinants of success in four international television awards festivals between 1994 and 2012. We find that countries with larger markets and greater expenditure on public broadcasting tend to win more awards, but that the degree of concentration in the market for television and rates of penetration of pay-per-view television are unrelated to success. These findings are consistent with general industrial organisation literature on quality and market size, and with media policy literature on public service broadcasting acting as a force for quality. However, we also find that âhome countriesâ enjoy a strong advantage in these festivals, which is not consistent with festival success acting as a pure proxy for television quality
Comment on ``Evidence for Narrow Baryon Resonances in Inelastic pp Scattering''
Compton scattering data are sensitive to the existence of low-mass resonances
reported by Tatischeff et al. We show that such states, with their reported
properties, are excluded by previous Compton scattering experiments.Comment: One page, submitted to PR
Both apoptosis and necrosis occur early after intracerebral grafting of ventral mesencephalic tissue: a role for protease activation.
Neural transplantation is an experimental treatment for Parkinson's disease. Widespread clinical application of the grafting technique is hampered by a relatively poor survival (around 10%) of implanted embryonic dopamine neurones. Earlier animal studies have indicated that a large proportion of the grafted cells die during graft tissue preparation and within the first few days after intracerebral implantation. The present study was designed to reveal the prevalence of cell death in rat intrastriatal grafts at 90 min, 1, 3, 6 and 42 days after implantation. We examined apoptotic cell death using semi-thin and paraffin sections stained with methylene blue and an antibody against activated caspase 3, respectively. We identified abundant apoptotic cell death up to 3 days after transplantation. In addition, we studied calpain activation using an antibody specific for calpain-cleaved fodrin. We report a peak in calpain activity 90 min after grafting. Surprisingly, we did not observe any significant difference in the number of dopaminergic neurones over time. The present results imply that grafted cells may be victims of either an early necrotic or a later apoptotic cell death and that there is substantial cell death as early as 90 min after implantation
Semiparametrically Efficient Inference Based on Signs and Ranks for Median Restricted Models
Since the pioneering work of Koenker and Bassett (1978), econometric models involving median and quantile rather than the classical mean or conditional mean concepts have attracted much interest.Contrary to the traditional models where the noise is assumed to have mean zero, median-restricted models enjoy a rich group-invariance structure.In this paper, we exploit this invariance structure in order to obtain semiparametrically efficient inference procedures for these models.These procedures are based on residual signs and ranks, and therefore insensitive to possible misspecification of the underlying innovation density, yet semiparametrically efficient at correctly specified densities.This latter combination is a definite advantage of these procedures over classical quasi-likelihood methods.The techniques we propose can be applied, without additional technical difficulties, to both cross-sectional and time-series models.They do not require any explicit tangent space calculation nor any projections on these.
The uses and functions of ageing celebrity war reporters
This article starts from the premise that recognition of professional authority and celebrity status depends on the embodiment and performance of field-specific dispositional practices: thereâs no such thing as a natural, though we often talk about journalistic instinct as something someone simply has or doesnât have. Next, we have little control over how we are perceived by peers and publics, and what we think are active positioning or subjectifying practices are in fact, after Bourdieu, revelations of already-determined delegation. The upshot is that two journalists can arrive at diametrically opposed judgements on the basis of observation of the same actions of a colleague, and as individuals we are blithely hypocritical in forming (or reciting) evaluations of the professional identity of celebrities. Nowhere is this starker than in the discourse of age-appropriate behaviour, which this paper addresses using the examples of âstarâ war reporters John Simpson, Kate Adie and Martin Bell. A certain rough-around-the-edges irreverence is central to dispositional authenticity amongst war correspondents, and for ageing hacks this incorporates gendered attitudes to sex and alcohol as well as indifference to protocol. And yet perceived age-inappropriate sexual behaviour is also used to undermine professional integrity, and the paper ends by outlining the phenomenological context that makes possible this effortless switching between amoral and moralising recognition by peers and audiences alike
Deeply Virtual Compton Scattering
We study in QCD the physics of deeply-virtual Compton scattering (DVCS)---the
virtual Compton process in the large s and small t kinematic region. We show
that DVCS can probe a new type of off-forward parton distributions. We derive
an Altarelli-Parisi type of evolution equations for these distributions. We
also derive their sum rules in terms of nucleon form-factors of the twist-two
quark and gluon operators. In particular, we find that the second sum rule is
related to fractions of the nucleon spin carried separately by quarks and
gluons. We estimate the cross section for DVCS and compare it with the
accompanying Bethe-Heitler process at CEBAF and HERMES kinematics.Comment: 20 pages, 2 figures, replaced with the version to appear in Phys.
Rev.
- âŠ