9,352 research outputs found
A universally programmable Quantum Cellular Automaton
We discuss the role of classical control in the context of reversible quantum
cellular automata. Employing the structure theorem for quantum cellular
automata, we give a general construction scheme to turn an arbitrary cellular
automaton with external classical control into an autonomous one, thereby
proving the computational equivalence of these two models. We use this
technique to construct a universally programmable cellular automaton on a
one-dimensional lattice with single cell dimension 12.Comment: 4 pages, 4 figures, minor changes in introduction, fixed typos,
accepted for publication in Physical Review Letter
On the Effect of Cavitation on the Radial Forces and Hydrodynamic Stiffness of a Centrifugal Pump
The asymmetric flow within a volute exerts a radial force on a centrifugal impeller. The present paper presents experimental measurements of the radial forces on the impeller in the presence of cavitation
Glass transition and effective potential in the hypernetted chain approximation
We study the glassy transition for simple liquids in the hypernetted chain
(HNC) approximation by means of an effective potential recently introduced.
Integrating the HNC equations for hard spheres, we find a transition scenario
analogous to that of the long range disordered systems with ``one step replica
symmetry breaking''. Our result agree qualitatively with Monte Carlo
simulations of three dimensional hard spheres.Comment: 7 pages, 7 figures, Revtex fil
Rotordynamic Forces on Centrifugal Pump Impellers
The asymmetric flow around an impeller in a volute exerts a force upon the impeller. To study the rotordynamic force on an impeller which is vibrating around its machine axis of rotation, the impeller, mounted on a dynamometer, is made to whirl in a circular orbit within the volute. The measured force is expressed as the sum of a steady radial force and an unsteady force due to the eccentric motion of the impeller. These forces were measured in separate tests on a centrifugal pump with radically increased shroud clearance, a two-dimensional impeller, and an impeller with an inducer, the impeller of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Enginer). In each case, a destabilizing force was observed over a region of positive whirl
Fragile-glass behavior of a short range -spin model
In this paper we propose a short range generalization of the -spin
interaction spin-glass model. The model is well suited to test the idea that an
entropy collapse is at the bottom-line of the dynamical singularity encountered
in structural glasses. The model is studied in three dimensions through Monte
Carlo simulations, which put in evidence fragile glass behavior with stretched
exponential relaxation and super-Arrhenius behavior of the relaxation time. Our
data are in favor of a Vogel-Fulcher behavior of the relaxation time, related
to an entropy collapse at the Kauzmann temperature. We however encounter
difficulties analogous to those found in experimental systems when
extrapolating thermodynamical data at low temperatures. We study the spin glass
susceptibility investigating the behavior of the correlation length in the
system. We find that the the increase of the relaxation time is not accompanied
by any growth of the correlation length. We discuss the scaling properties of
off-equilibrium dynamics in the glassy regime, finding qualitative agreement
with the mean-field theory.Comment: 8 pages, LaTeX, 8 postscript figure
Relaxation processes and entropic traps in the Backgammon model
We examine the density-density correlation function in a model recently
proposed to study the effect of entropy barriers in glassy dynamics. We find
that the relaxation proceeds in two steps with a fast beta process followed by
alpha relaxation. The results are physically interpreted in the context of an
adiabatic approximation which allows to separate the two processes, and to
define an effective temperature in the off-equilibrium dynamics of the model.
We investigate the behavior of the response function associated to the density,
and find violations of the fluctuation dissipation theorem.Comment: 4 Pages including 3 Figures, Revte
Testing replica predictions in experiments
We review the predictions of the replica approach both for the statics and
for the off-equilibrium dynamics. We stress the importance of the
Cugliandolo-Kurchan off-equilibrium fluctuation-dissipation relation in
providing a bridge between the statics and the dynamics. We present numerical
evidence for the correctness of these relations. This approach allows an
experimental determination of the basic parameters of the replica theory.Comment: To appear in Chiarotti's Festschrift Volume (8 Pages, 3 figures
Evaluating uncertainty estimates in hydrologic models: borrowing measures from the forecast verification community
The hydrologic community is generally moving towards the use of probabilistic estimates of streamflow, primarily through the implementation of Ensemble Streamflow Prediction (ESP) systems, ensemble data assimilation methods, or multi-modeling platforms. However, evaluation of probabilistic outputs has not necessarily kept pace with ensemble generation. Much of the modeling community is still performing model evaluation using standard deterministic measures, such as error, correlation, or bias, typically applied to the ensemble mean or median. Probabilistic forecast verification methods have been well developed, particularly in the atmospheric sciences, yet few have been adopted for evaluating uncertainty estimates in hydrologic model simulations. In the current paper, we overview existing probabilistic forecast verification methods and apply the methods to evaluate and compare model ensembles produced from two different parameter uncertainty estimation methods: the Generalized Uncertainty Likelihood Estimator (GLUE), and the Shuffle Complex Evolution Metropolis (SCEM). Model ensembles are generated for the National Weather Service SACramento Soil Moisture Accounting (SAC-SMA) model for 12 forecast basins located in the Southeastern United States. We evaluate the model ensembles using relevant metrics in the following categories: distribution, correlation, accuracy, conditional statistics, and categorical statistics. We show that the presented probabilistic metrics are easily adapted to model simulation ensembles and provide a robust analysis of model performance associated with parameter uncertainty. Application of these methods requires no information in addition to what is already available as part of traditional model validation methodology and considers the entire ensemble or uncertainty range in the approach
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