2,427 research outputs found
A study of the deep structure of the energy landscape of glassy polystyrene: the exponential distribution of the energy-barriers revealed by high-field Electron Spin Resonance spectroscopy
The reorientation of one small paramagnetic molecule (spin probe) in glassy
polystyrene (PS) is studied by high-field Electron Spin Resonance spectroscopy
at two different Larmor frequencies (190 and 285 GHz). The exponential
distribution of the energy-barriers for the rotational motion of the spin probe
is unambigously evidenced at both 240K and 270K. The same shape for the
distribution of the energy-barriers of PS was evidenced by the master curves
provided by previous mechanical and light scattering studies. The breadth of
the energy-barriers distribution of the spin probe is in the range of the
estimates of the breadth of the PS energy-barriers distribution. The evidence
that the deep structure of the energy landscape of PS exhibits the exponential
shape of the energy-barriers distribution agrees with results from
extreme-value statistics and the trap model by Bouchaud and coworkers.Comment: Final version in press as Letter to the Editor on J.Phys.:Condensed
Matter. Changes in bol
Ocean ensemble forecasting. Part I: Ensemble Mediterranean winds from a Bayesian hierarchical model
A Bayesian hierarchical model (BHM) is developed to estimate surface vector
wind (SVW) fields and associated uncertainties over the Mediterranean Sea. The
BHM–SVW incorporates data-stage inputs from analyses and forecasts of the
European Centre for Medium-Range Weather Forecasts (ECMWF) and SVW
retrievals from the QuikSCAT data record. The process-model stage of the
BHM–SVW is based on a Rayleigh friction equation model for surface winds.
Dynamical interpretations of posterior distributions of the BHM–SVW parameters
are discussed. Ten realizations from the posterior distribution of the BHM–SVW
are used to force the data-assimilation step of an experimental ensemble ocean
forecast system for the Mediterranean Sea in order to create a set of ensemble
initial conditions. The sequential data-assimilation method of the Mediterranean
forecast system (MFS) is adapted to the ensemble implementation. Analyses
of sample ensemble initial conditions for a single data-assimilation period in
MFS are presented to demonstrate the multivariate impact of the BHM–SVW
ensemble generation methodology. Ensemble initial-condition spread is quantified
by computing standard deviations of ocean state variable fields over the ten ensemble
members. The methodological findings in this article are of two kinds. From the
perspective of statistical modelling, the process-model development is more closely
related tophysicalbalances than inpreviousworkwithmodels for the SVW.Fromthe
ocean forecast perspective, the generation of ocean ensemble initial conditions via
BHM is shown to be practical for operational implementation in an ensemble ocean
forecast system. Phenomenologically, ensemble spread generated via BHM–SVW
occurs on ocean mesoscale time- and space-scales, in close association with strong
synoptic-scale wind-forcing events. A companion article describes the impacts of
the BHM–SVW ensemble method on the ocean forecast in comparisons with more
traditional ensemble methods
Ocean ensemble forecasting. Part II: Mediterranean Forecast System response
This article analyzes the ocean forecast response to surface vector wind (SVW)
distributions generated by a Bayesian hierarchical model (BHM) developed in Part
I of this series. A new method for ocean ensemble forecasting (OEF), the socalled
BHM-SVW-OEF, is described. BHM-SVW realizations are used to produce
and force perturbations in the ocean state during 14 day analysis and 10 day
forecast cycles of the Mediterranean Forecast System (MFS). The BHM-SVW-OEF
ocean response spread is amplified at the mesoscales and in the pycnocline of
the eddy field. The new method is compared with an ensemble response forced
by European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble
prediction system (EEPS) surface winds, and with an ensemble forecast started from
perturbed initial conditions derived froman ad hoc thermocline intensified random
perturbation (TIRP) method. The EEPS-OEF shows spread on basin scales while the
TIRP-OEF response is mesoscale-intensified as in the BHM-SVW-OEF response.
TIRP-OEF perturbations fill more of the MFS domain, while the BHM-SVW-OEF
perturbations are more location-specific, concentrating ensemble spread at the sites
where the ocean-model response to uncertainty in the surface wind forcing is largest
Better Nonlinear Models from Noisy Data: Attractors with Maximum Likelihood
A new approach to nonlinear modelling is presented which, by incorporating
the global behaviour of the model, lifts shortcomings of both least squares and
total least squares parameter estimates. Although ubiquitous in practice, a
least squares approach is fundamentally flawed in that it assumes independent,
normally distributed (IND) forecast errors: nonlinear models will not yield IND
errors even if the noise is IND. A new cost function is obtained via the
maximum likelihood principle; superior results are illustrated both for small
data sets and infinitely long data streams.Comment: RevTex, 11 pages, 4 figure
A Support Group for Inpatient Abused Adolescents
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75359/1/j.1744-6171.1990.tb00438.x.pd
Ocean Ensemble Forecasting, Part II: Mediterranean Forecast System Response
This paper analyzes the ocean forecast response to surface vector wind (SVW) distributions
generated by a Bayesian Hierarchical Model (BHM) developed in Part I (Milliff et al., 2009).
A new method for Ocean Ensemble Forecasting (OEF), so-called BHM-SVW-OEF, is described.
BHM-SVW realizations are used to produce and force perturbations in the ocean
state during 14-day analysis and 10-day forecast cycles of the Mediterranean Forecast System
(MFS). The BHM-SVW-OEF ocean response spread is amplified at the mesoscales and
pycnocline of the eddy field. The new method is compared to an ensemble response forced by
ECMWF Ensemble Prediction System (EEPS) surface winds, and to an ensemble forecast
started from perturbed initial conditions derived from an ad hoc Thermocline Intensified
Random Perturbation (TIRP) method. The EEPS-OEF shows spread at the basin scales
while the TIRP-OEF response is mesoscale intensified as in the BHM-SVW-OEF response.
TIRP-OEF perturbations fill more of the MFS domain while the BHM-SVW-OEF perturbations
are more location-specific, concentrating ensemble spread at the sites where the ocean
model response to uncertainty in the surface wind forcing is largest. The BHM-SVW-OEF
method offers a practical and objective means for producing short-term forecast spread by
modeling surface atmospheric forcing uncertainties that have maximum impact at the ocean
mesoscales
A Single Dermatome Clinical Prediction Rule for Independent Walking 1 Year After Spinal Cord Injury
Objective: To derive and validate a simple, accurate CPR to predict future independent walking ability after SCI at the bedside that does not rely on motor scores and is predictive for those initially classified in the middle of the SCI severity spectrum. Design: Retrospective cohort study. Binary variables were derived, indicating degrees of sensation to evaluate predictive value of pinprick and light touch variables across dermatomes. The optimal single sensory modality and dermatome was used to derive our CPR, which was validated on an independent dataset. Setting: Analysis of SCI Model Systems dataset. Participants: Individuals with traumatic SCI. The data of 3679 participants (N=3679) were included with 623 participants comprising the derivation dataset and 3056 comprising the validation dataset. Interventions: Not applicable. Main Outcome Measures: Self-reported ability to walk both indoors and outdoors. Results: Pinprick testing at S1 over lateral heels, within 31 days of SCI, accurately identified future independent walkers 1 year after SCI. Normal pinprick in both lateral heels provided good prognosis, any pinprick sensation in either lateral heel provided fair prognosis, and no sensation provided poor prognosis. This CPR performed satisfactorily in the middle SCI severity subgroup. Conclusions: In this large multi-site study, we derived and validated a simple, accurate CPR using only pinprick sensory testing at lateral heels that predicts future independent walking after SCI
The Advanced LIGO Photon Calibrators
The two interferometers of the Laser Interferometry Gravitaional-wave
Observatory (LIGO) recently detected gravitational waves from the mergers of
binary black hole systems. Accurate calibration of the output of these
detectors was crucial for the observation of these events, and the extraction
of parameters of the sources. The principal tools used to calibrate the
responses of the second-generation (Advanced) LIGO detectors to gravitational
waves are systems based on radiation pressure and referred to as Photon
Calibrators. These systems, which were completely redesigned for Advanced LIGO,
include several significant upgrades that enable them to meet the calibration
requirements of second-generation gravitational wave detectors in the new era
of gravitational-wave astronomy. We report on the design, implementation, and
operation of these Advanced LIGO Photon Calibrators that are currently
providing fiducial displacements on the order of
m/ with accuracy and precision of better than 1 %.Comment: 14 pages, 19 figure
Business unusual: collective action against bribery in international business
Collective action initiatives in which governments and companies make anti-corruption commitments have proliferated in recent years. This apparently prosocial behavior defies the logic of collective action and, given that bribery often goes undetected and unpunished, is not easily explained by principal-agent theory. Club theory suggests that the answer lies in the institutional design of anti-corruption clubs: collective action can work as long as membership has high entry costs, members receive selective benefits, and compliance is adequately policed. This article contributes to the debate by examining how these conditions manifest in the case of anti-corruption clubs in the realm of international business, with particular focus on the international dimension of many initiatives. This vertical aspect of institutional design creates a richer, more complex set of reputational and material benefits for members, as well as allowing for more credible and consistent monitoring and enforcement
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