10,486 research outputs found
Chemistry of the CO dimer at low temperatures
Researchers conducted a series of experiments on the chlorine-catalyzed photodecomposition of O sub 3 both in the gas and in inert solvents such as CF sub 4 and CO sub 2 in the temperature range about 190 to 225 K. The liquid medium was chosen in order to minimize possible surface loss of long-lived ClO dimer, and to aid in the stabilization of transient excited intermediates. The mechanism of dimer formation was as follows: (1) Cl sub 2 + hv yields Cl + Cl; (2) Cl + O sub 3 yields ClO + O sub 2; (3) ClO + ClO yields Cl sub 2 O sub 2. The experiments were done in cooled low temperature cells, with irradiation from an Osram high pressure mercury arc, filtered to remove radiation below 325 nm. Spectral analysis was by means of a Cary Model 2200 UV spectrometer. The principal objectives were: (1) to determine the lifetime of the dimer as a function of temperature; (2) to observe spectral changes in the mixtures which could be attributed to dimer or related products; and (3) to observe chemical or photochemical reactions of the dimer
Scaling of Information in Turbulence
We propose a new perspective on Turbulence using Information Theory. We
compute the entropy rate of a turbulent velocity signal and we particularly
focus on its dependence on the scale. We first report how the entropy rate is
able to describe the distribution of information amongst scales, and how one
can use it to isolate the injection, inertial and dissipative ranges, in
perfect agreement with the Batchelor model and with a fBM model. In a second
stage, we design a conditioning procedure in order to finely probe the
asymmetries in the statistics that are responsible for the energy cascade. Our
approach is very generic and can be applied to any multiscale complex system.Comment: in Europhysics Letters, 201
Reply to "Comment on `Quenches in quantum many-body systems: One-dimensional Bose-Hubbard model reexamined' ''
In his Comment [see preceding Comment, Phys. Rev. A 82, 037601 (2010)] on the
paper by Roux [Phys. Rev. A 79, 021608(R) (2009)], Rigol argued that the energy
distribution after a quench is not related to standard statistical ensembles
and cannot explain thermalization. The latter is proposed to stem from what he
calls the eigenstate thermalization hypothesis and which boils down to the fact
that simple observables are expected to be smooth functions of the energy. In
this Reply, we show that there is no contradiction or confusion between the
observations and discussions of Roux and the expected thermalization scenario
discussed by Rigol. In addition, we emphasize a few other important aspects, in
particular the definition of temperature and the equivalence of ensemble, which
are much more difficult to show numerically even though we believe they are
essential to the discussion of thermalization. These remarks could be of
interest to people interested in the interpretation of the data obtained on
finite-size systems.Comment: 3 page
Self-Similar Anisotropic Texture Analysis: the Hyperbolic Wavelet Transform Contribution
Textures in images can often be well modeled using self-similar processes
while they may at the same time display anisotropy. The present contribution
thus aims at studying jointly selfsimilarity and anisotropy by focusing on a
specific classical class of Gaussian anisotropic selfsimilar processes. It will
first be shown that accurate joint estimates of the anisotropy and
selfsimilarity parameters are performed by replacing the standard 2D-discrete
wavelet transform by the hyperbolic wavelet transform, which permits the use of
different dilation factors along the horizontal and vertical axis. Defining
anisotropy requires a reference direction that needs not a priori match the
horizontal and vertical axes according to which the images are digitized, this
discrepancy defines a rotation angle. Second, we show that this rotation angle
can be jointly estimated. Third, a non parametric bootstrap based procedure is
described, that provides confidence interval in addition to the estimates
themselves and enables to construct an isotropy test procedure, that can be
applied to a single texture image. Fourth, the robustness and versatility of
the proposed analysis is illustrated by being applied to a large variety of
different isotropic and anisotropic self-similar fields. As an illustration, we
show that a true anisotropy built-in self-similarity can be disentangled from
an isotropic self-similarity to which an anisotropic trend has been
superimposed
The Wide-field High-resolution Infrared TElescope (WHITE)
The Wide-field High-resolution Infrared TElescope (WHITE) will be dedicated
in the first years of its life to carrying out a few (well focused in terms of
science objectives and time) legacy surveys.
WHITE would have an angular resolution of ~0.3'' homogeneous over ~0.7 sq.
deg. in the wavelength range 1 - 5 um, which means that we will very
efficiently use all the available observational time during night time and day
time. Moreover, the deepest observations will be performed by summing up
shorter individual frames. We will have a temporal information that can be used
to study variable objects.
The three key science objectives of WHITE are : 1) A complete survey of the
Magellanic Clouds to make a complete census of young stellar objects in the
clouds and in the bridge and to study their star formation history and the link
with the Milky Way. The interaction of the two clouds with our Galaxy might the
closest example of a minor merging event that could be the main driver of
galaxy evolution in the last 5 Gyrs. 2) The building of the first sample of
dusty supernovae at z<1.2 in the near infrared range (1-5 um) to constrain the
equation of state from these obscured objects, study the formation of dust in
galaxies and build the first high resolution sample of high redshift galaxies
observed in their optical frame 3) A very wide weak lensing survey over that
would allow to estimate the equation of state in a way that would favourably
compete with space projects.Comment: Invited talk to the 2nd ARENA Conference : "The Astrophysical Science
Cases at Dome C" Potsdam 17-21 September, 200
An extremal model for amorphous media plasticity
An extremal model for the plasticity of amorphous materials is studied in a
simple two-dimensional anti-plane geometry. The steady-state is analyzed
through numerical simulations. Long-range spatial and temporal correlations in
local slip events are shown to develop, leading to non-trivial and highly
anisotropic scaling laws. In particular, the plastic strain is shown to
statistically concentrate over a region which tends to align perpendicular to
the displacement gradient. By construction, the model can be seen as giving
rise to a depinning transition, the threshold of which (i.e. the macroscopic
yield stress) also reveal scaling properties reflecting the localization of the
activity.Comment: 4 pages, 5 figure
Indirect Inference for Dynamic Panel Models
It is well-known that maximum likelihood (ML) estimation of the autoregressive parameter of a dynamic panel data model with .xed eects is inconsistent under .xed time series sample size (T) and large cross section sample size (N) asymptotics. The estimation bias is particularly relevant in practical applications when T is small and the autoregressive parameter is close to unity. The present paper proposes a general, computationally inexpensive method of bias reduction that is based on indirect inference (Gouriroux et al., 1993), shows unbiasedness and analyzes efficiency. The method is implemented in a simple linear dynamic panel model, but has wider applicability and can, for instance, be easily ex-tended to more complicated frameworks such as nonlinear models. Monte Carlo studies show that the proposed procedure achieves substantial bias reductions with only mild increases in variance, thereby substantially reducing root mean square errors. The method is compared with certain consistent estimators and bias-corrected ML estimators previously proposed in the literature and is shown to have superior .nite sample properties to GMM and the bias-corrected ML of Hahn and Kuersteiner (2002). Finite sample performance is compared with that of a recent estimator proposed by Han and Phillips (2005).Autoregression, Bias Reduction, Dynamic panel
- …