16,159 research outputs found
Fractional unit root tests allowing for a structural change in trend under both the null and alternative hypotheses
This paper considers testing procedures for the null hypothesis of a unit root process against the alternative of a fractional process, called a fractional unit root test. We extend the Lagrange Multiplier (LM) tests of Robinson (1994) and Tanaka (1999), which are locally best invariant and uniformly most powerful, to allow for a slope change in trend with or without a concurrent level shift under both the null and alternative hypotheses. We show that the limit distribution of the proposed LM tests is standard normal. Finite sample simulation experiments show that the tests have good size and power. As an empirical analysis, we apply the tests to the Consumer Price Indices of the G7 countries
Rattling and freezing in a 1-D transport model
We consider a heat conduction model introduced in \cite{Collet-Eckmann 2009}.
This is an open system in which particles exchange momentum with a row of
(fixed) scatterers. We assume simplified bath conditions throughout, and give a
qualitative description of the dynamics extrapolating from the case of a single
particle for which we have a fairly clear understanding. The main phenomenon
discussed is {\it freezing}, or the slowing down of particles with time. As
particle number is conserved, this means fewer collisions per unit time, and
less contact with the baths; in other words, the conductor becomes less
effective. Careful numerical documentation of freezing is provided, and a
theoretical explanation is proposed. Freezing being an extremely slow process,
however, the system behaves as though it is in a steady state for long
durations. Quantities such as energy and fluxes are studied, and are found to
have curious relationships with particle density
Kinetic decomposition for periodic homogenization problems
We develop an analytical tool which is adept for detecting shapes of
oscillatory functions, is useful in decomposing homogenization problems into
limit-problems for kinetic equations, and provides an efficient framework for
the validation of multi-scale asymptotic expansions. We apply it first to a
hyperbolic homogenization problem and transform it to a hyperbolic limit
problem for a kinetic equation. We establish conditions determining an
effective equation and counterexamples for the case that such conditions fail.
Second, when the kinetic decomposition is applied to the problem of enhanced
diffusion, it leads to a diffusive limit problem for a kinetic equation that in
turn yields the effective equation of enhanced diffusion
Dewetting of a solid monolayer
We report on the dewetting of a monolayer on a solid substrate, where mass
transport occurs via surface diffusion. For a wide range of parameters, a
labyrinthine pattern of bilayer islands is formed. An irreversible regime and a
thermodynamic regime are identified. In both regimes, the velocity of a
dewetting front, the wavelength of the bilayer island pattern, and the rate of
nucleation of dewetted zones are obtained. We also point out the existence of a
scaling behavior, which is analyzed by means of a geometrical model.Comment: to be published in PhysRevLet
Diffusion in a continuum model of self-propelled particles with alignment interaction
In this paper, we provide the corrections to the hydrodynamic
model derived by Degond and Motsch from a kinetic version of the model by
Vicsek & coauthors describing flocking biological agents. The parameter
stands for the ratio of the microscopic to the macroscopic scales.
The corrected model involves diffusion terms in both the mass and
velocity equations as well as terms which are quadratic functions of the first
order derivatives of the density and velocity. The derivation method is based
on the standard Chapman-Enskog theory, but is significantly more complex than
usual due to both the non-isotropy of the fluid and the lack of momentum
conservation
Atmospheric Calorimetry above 10 eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory
The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a
calorimeter to measure extensive air-showers created by particles of
astrophysical origin. Some of these particles carry joules of energy. At these
extreme energies, test beams are not available in the conventional sense. Yet
understanding the energy response of the observatory is important. For example,
the propagation distance of the highest energy cosmic-rays through the cosmic
microwave background radiation (CMBR) is predicted to be strong function of
energy. This paper will discuss recently reported results from the observatory
and the use of calibrated pulsed UV laser "test-beams" that simulate the
optical signatures of ultra-high energy cosmic rays. The status of the much
larger 200,000 km companion detector planned for the northern hemisphere
will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in
High Energy Physic
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