1,418 research outputs found
A Class of Simple Distribution-free Rank-based Unit Root Tests (Revision of DP 2010-72)
We propose a class of distribution-free rank-based tests for the null hypothesis of a unit root. This class is indexed by the choice of a reference density g, which needs not coincide with the unknown actual innovation density f. The validity of these tests, in terms of exact finite sample size, is guaranteed, irrespective of the actual underlying density, by distribution-freeness. Those tests are locally and asymptotically optimal under a particular asymptotic scheme, for which we provide a complete analysis of asymptotic relative efficiencies. Rather than asymptotic optimality, however, we emphasize finitesample performances. Finite-sample performances of unit root tests, however, depend quite heavily on initial values. We therefore investigate those performances as a function of initial values. It appears that our rank-based tests significantly outperform the traditional Dickey-Fuller tests, as well as the more recent procedures proposed by Elliot, Rothenberg, and Stock (1996), Ng and Perron (2001), and Elliott and Mšuller (2006), for a broad range of initial values and for heavy-tailed innovation densities. As such, they provide a useful complement to existing techniques.Unit root;Dickey-Fuller test;Local Asymptotic Normality;Rank test
Estimating factor models for multivariate volatilities : an innovation expansion method
We introduce an innovation expansion method for estimation of factor models for conditional variance (volatility) of a multivariate time series. We estimate the factor loading space and the number of factors by a stepwise optimization algorithm on expanding the "white noise space". Simulation and a real data example are given for illustration
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
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.
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
Experimentally measured thermal masses of adsorption heat exchangers
The thermal masses of components influence the performance of many adsorption heat pump systems. However, typically when experimental adsorption systems are reported, data on thermal mass are missing or incomplete. This work provides original measurements of the thermal masses for experimental sorption heat exchanger hardware. Much of this hardware was previously reported in the literature, but without detailed thermal mass data. The data reported in this work are the first values reported in the literature to thoroughly account for all thermal masses, including heat transfer fluid. The impact of thermal mass on system performance is also discussed, with detailed calculation left for future work. The degree to which heat transfer fluid contributes to overall effective thermal mass is also discussed, with detailed calculation left for future work. This work provides a framework for future reporting of experimental thermal masses. The utilization of this framework will enrich the data available for model validation and provide a more thorough accounting of adsorption heat pumps
Loop Variables for compact two-dimensional quantum electrodynamics
Variables parametrized by closed and open curves are defined to reformulate
compact U(1) Quantum Electrodynamics in the circle with a massless fermion
field. It is found that the gauge invariant nature of these variables
accommodates into a regularization scheme for the Hamiltonian and current
operators that is specially well suited for the study of the compact case. The
zero mode energy spectrum, the value of the axial anomaly and the anomalous
commutators this model presents are hence determined in a manifestly gauge
invariant manner. Contrary to the non compact case, the zero mode spectrum is
not equally spaced and consequently the theory does not lead to the spectrum of
a free scalar boson. All the states are invariant under large gauge
transformations. In particular, that is the case for the vacuum, and
consequently the -dependence does not appear.Comment: 24 pages, 1 figure, to be published in Phys. Rev.
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.
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
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