786 research outputs found
Disordered free fermions and the Cardy Ostlund fixed line at low temperature
Using functional RG, we reexamine the glass phase of the 2D random-field Sine
Gordon model. It is described by a line of fixed points (FP) with a
super-roughening amplitude as
temperature is varied. A speculation is that this line is identical to the
one found in disordered free-fermion models via exact results from ``nearly
conformal'' field theory. This however predicts , contradicting
numerics. We point out that this result may be related to failure of
dimensional reduction, and that a functional RG method incorporating higher
harmonics and non-analytic operators predicts a non-zero which
compares reasonably with numerics.Comment: 8 pages, 3 figures, only material adde
Analyzing the Anticipation of Treatments Using Data on Notification Dates
When treatments may occur at different points in time, most evaluation methods assume – implicitly or explicitly – that all the information used by subjects about the occurrence of a future treatment is available to the researcher. This is often called the “no anticipation” assumption. In reality, subjects may receive private signals about the date when a treatment may start. We provide a methodological and empirical analysis of this issue in a setting where the outcome of interest as well as the moment of information arrival (notification) and the start of the treatment can all be characterized by duration variables. Building on the "Timing of Events" approach, we show that the causal effects of notification and of the treatment on the outcome are identified. We estimate the model on an administrative data set of unemployed workers in France which provides the date when job seekers receive information from caseworkers about their future treatment status. We find that notification has a significant and positive effect on unemployment duration. This result violates the standard "no anticipation" assumption and rules out a "threat effect" of training programs in France.evaluation of labor market programs, training, duration model, timing of events, anticipation
Active Labor Market Policy Effects in a Dynamic Setting
This paper implements a method to identify and estimate treatment effects in a dynamic setting where treatments may occur at any point in time. By relating the standard matching approach to the timing-of-events approach, it demonstrates that effects of the treatment on the treated at a given date can be identified even though non-treated may be treated later in time. The approach builds on a "no anticipation" assumption and the assumption of conditional independence between the duration until treatment and the counterfactual durations until exit. To illustrate the approach, the paper studies the effect of training for unemployed workers in France, using a rich register data set. Training has little impact on unemployment duration. The contamination of the standard matching estimator due to later entries into treatment is large if the treatment probability is high.treatment, program participation, unemployment duration, matching, training, propensity score, contamination bias
Active labor market policy effects in a dynamic setting
This paper implements a method to identify and estimate treatment effects in a dynamic setting where treatments may occur at any point in time. By relating the standard matching approach to the timing-of-events approach, it demonstrates that effects of the treatment on the treated at a given date can be identified even though non-treated may be treated later in time. The approach builds on a "no anticipation" assumption and the assumption of conditional independence between the duration until treatment and the counterfactual durations until exit. To illustrate the approach, the paper studies the effect of training for unemployed workers in France, using a rich register data set. Training has little impact on unemployment duration. The contamination of the standard matching estimator due to later entries into treatment is large if the treatment probability is high.Treatment; program participation; unemployment duration; training; propensity score; matching; contamination bias
Super-Rough Glassy Phase of the Random Field XY Model in Two Dimensions
We study both analytically, using the renormalization group (RG) to two loop
order, and numerically, using an exact polynomial algorithm, the
disorder-induced glass phase of the two-dimensional XY model with quenched
random symmetry-breaking fields and without vortices. In the super-rough glassy
phase, i.e. below the critical temperature , the disorder and thermally
averaged correlation function of the phase field , behaves, for , as where and is a microscopic length scale. We
derive the RG equations up to cubic order in and predict
the universal amplitude . The
universality of results from nontrivial cancellations between
nonuniversal constants of RG equations. Using an exact polynomial algorithm on
an equivalent dimer version of the model we compute numerically and
obtain a remarkable agreement with our analytical prediction, up to .Comment: 5 pages, 3 figure
Operational loads on a tidal turbine due to environmental conditions
Accurate assessment of the fatigue life of tidal stream turbines and components requires prediction of the unsteady loading of turbine components over a wide range of frequencies. This study focuses on the influence of ambient turbulence, velocity shear and the approach taken to model wave kinematics, on the variation of thrust load imposed on the rotor shaft and supporting tower. Load cycles are assessed based on sea-state occurrence data taken over a five month period for a case study site. The influence of each environmental parameter on component loading is evaluated and the impact on material design parameters assessed. Alternative approaches are considered for modelling turbulent loading and wave loading. The frequency variation of loads due to turbulence are scaled from experimental data from trials of a three-bladed horizontal axis turbine of 1.2 m diameter on a bed-mounted supporting structure. Frequency dependent wave loading is estimated by a relative form of the drag term of the widely used equation of Morison et al. (1950), with the depth decay of kinematics modelled by linear wave theory. Over the five month interval considered a ten year design life can be obtained with a lower design load by accounting for variation of turbulence intensity that occurs during each tidal cycle. This is expected to vary further with the approach taken to model the onset turbulence. A component can also be designed for lower loads over the same time period if irregular waves are modelled instead of regular
New implementation of stability-based transition model by means of transport equations
International audienceA new natural laminar-turbulent transition model compatible with Computation Fluid Dynamics is presented. This model accounts for longitudinal transition mechanisms (i.e. Tollmien-Schlichting induced transition) thanks to systematic stability computation on similar boundary profiles from Mach zero to four both on adiabatic and isothermal wall. The model embeds as well the so-called “C1-criterion” for transverse transition mechanisms (i.e. cross-flow wavesinduced transition). The transition model is written under transport equations formalism and has been implemented in the solver elsA (ONERA-Airbus-Safran property). Comparisons are performed on two-dimensional and three-dimensional configurations against transition database approach
Number statistics for -ensembles of random matrices: applications to trapped fermions at zero temperature
Let be the probability that a
-ensemble of random matrices with confining potential
has eigenvalues inside an interval of the real
line. We introduce a general formalism, based on the Coulomb gas technique and
the resolvent method, to compute analytically for large . We show that this probability scales for large
as , where is the Dyson index of the
ensemble. The rate function , independent of ,
is computed in terms of single integrals that can be easily evaluated
numerically. The general formalism is then applied to the classical
-Gaussian (), -Wishart () and
-Cauchy () ensembles. Expanding the rate function
around its minimum, we find that generically the number variance exhibits a non-monotonic behavior as a function of the size
of the interval, with a maximum that can be precisely characterized. These
analytical results, corroborated by numerical simulations, provide the full
counting statistics of many systems where random matrix models apply. In
particular, we present results for the full counting statistics of zero
temperature one-dimensional spinless fermions in a harmonic trap.Comment: 34 pages, 19 figure
Maximum relative height of one-dimensional interfaces : from Rayleigh to Airy distribution
We introduce an alternative definition of the relative height h^\kappa(x) of
a one-dimensional fluctuating interface indexed by a continuously varying real
paramater 0 \leq \kappa \leq 1. It interpolates between the height relative to
the initial value (i.e. in x=0) when \kappa = 0 and the height relative to the
spatially averaged height for \kappa = 1. We compute exactly the distribution
P^\kappa(h_m,L) of the maximum h_m of these relative heights for systems of
finite size L and periodic boundary conditions. One finds that it takes the
scaling form P^\kappa(h_m,L) = L^{-1/2} f^\kappa (h_m L^{-1/2}) where the
scaling function f^\kappa(x) interpolates between the Rayleigh distribution for
\kappa=0 and the Airy distribution for \kappa=1, the latter being the
probability distribution of the area under a Brownian excursion over the unit
interval. For arbitrary \kappa, one finds that it is related to, albeit
different from, the distribution of the area restricted to the interval [0,
\kappa] under a Brownian excursion over the unit interval.Comment: 25 pages, 4 figure
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