5,194 research outputs found
Ballistic Bunching of Photo-Injected Electron Bunches with Dielectric-Lined Waveguide
We describe a simple technique to passively bunch non-ultrarelativistics
(~MeV) electron bunches produced in conventional photoinjectors.
The scheme employs a dielectric-lined waveguide located downstream of the
electron source to impress an energy modulation on a picosecond bunch. The
energy modulation is then converted into a density modulation via ballistic
bunching. The method is shown to support the generation of sub-picosecond bunch
train with multi-kA peak currents. The relatively simple technique is expected
to find applications in compact, accelerator-based, light sources and advanced
beam-driven accelerator methods.Comment: 9 pages, 13 figure
Tailored electron bunches with smooth current profiles for enhanced transformer ratios in beam-driven acceleration
Collinear high-gradient beam-driven wakefield methods for
charged-particle acceleration could be critical to the realization of compact,
cost-efficient, accelerators, e.g., in support of TeV-scale lepton colliders or
multiple-user free-electron laser facilities. To make these options viable, the
high accelerating fields need to be complemented with large transformer ratios
, a parameter characterizing the efficiency of the energy transfer between
a wakefield-exciting "drive" bunch to an accelerated "witness" bunch. While
several potential current distributions have been discussed, their practical
realization appears challenging due to their often discontinuous nature. In
this paper we propose several alternative current profiles which are smooth
which also lead to enhanced transformer ratios. We especially explore a
laser-shaping method capable of generating one the suggested distributions
directly out of a photoinjector and discuss a linac concept that could possible
drive a dielectric accelerator
On the usefulness of the directional distance function in analyzing environmental policy on manure management
The purpose of this paper is to model the manure management policy implemented in the European Union, and more specifically the limit imposed on the spreading of organic nitrogen. A theoretical model is defined in such a way that a number of specificities concerning livestock production can be introduced.The theoretical framework is used to investigate how the land can be shared out optimally between the non-productive purpose of spreading manure in a manner compliant with the environmental regulation and the productive function of providing crops.Then,we define an empirical model derived from the previous theoretical model, using the directional distance function.It provides a framework for deriving shadow prices of pollutant, of productive and non productive use of land and of the constraint on organic manure involved by the European environmental regulation.Environmental Economics and Policy,
Difference of Convex Functions Programming Applied to Control with Expert Data
This paper reports applications of Difference of Convex functions (DC)
programming to Learning from Demonstrations (LfD) and Reinforcement Learning
(RL) with expert data. This is made possible because the norm of the Optimal
Bellman Residual (OBR), which is at the heart of many RL and LfD algorithms, is
DC. Improvement in performance is demonstrated on two specific algorithms,
namely Reward-regularized Classification for Apprenticeship Learning (RCAL) and
Reinforcement Learning with Expert Demonstrations (RLED), through experiments
on generic Markov Decision Processes (MDP), called Garnets
Magnetic-field-induced Stoner transition in a dilute quantum Hall system
In a recent paper [Phys.Rev.B.\textbf{84}, 161307 (2011)], experimental data
on spin splitting in the integer quantum Hall effect has been reported in a
high mobility dilute 2D electron gas with electron density as low as 0.2
10 cm . In this work, we show that an excellent
\emph{quantitative} description of these data can be obtained within the model
of the magnetic-field-induced Stoner transition in the quantum Hall regime.
This provides a powerful tool to probe the non-trivial density dependance of
electron-electron interactions in the dilute regime of the 2D electron gas
Is the Bellman residual a bad proxy?
This paper aims at theoretically and empirically comparing two standard
optimization criteria for Reinforcement Learning: i) maximization of the mean
value and ii) minimization of the Bellman residual. For that purpose, we place
ourselves in the framework of policy search algorithms, that are usually
designed to maximize the mean value, and derive a method that minimizes the
residual over policies. A theoretical analysis
shows how good this proxy is to policy optimization, and notably that it is
better than its value-based counterpart. We also propose experiments on
randomly generated generic Markov decision processes, specifically designed for
studying the influence of the involved concentrability coefficient. They show
that the Bellman residual is generally a bad proxy to policy optimization and
that directly maximizing the mean value is much better, despite the current
lack of deep theoretical analysis. This might seem obvious, as directly
addressing the problem of interest is usually better, but given the prevalence
of (projected) Bellman residual minimization in value-based reinforcement
learning, we believe that this question is worth to be considered.Comment: Final NIPS 2017 version (title, among other things, changed
Measuring the Effects of Alternative Support Policy Instruments on Beef Supply
The European Union beef market regulation is largely influenced by the Common Agricultural Policy (CAP). With the 1992 CAP reform, there was a partial shift by the EU from product price support to a more direct form of income support by way of direct payments. For beef there was a move to direct payments on intermediate products which was essentially a direct payment for the possession of various categories of animals and these were linked to a land resource base. The Agenda 2000 reform consists in a further price decrease associated with an increase in direct payments. The objective of this paper is to assess how the behaviour of beef producers is sensitive to changes in production prices and to changes in premiums. The analysis relies on an analytical framework which allows to take into account the dynamic feature of beef production and the subsidies provided by the Common Agricultural Policy. We studys how the beef supply response is modified when various exogenous variables like prices or premiums are changed. The application focuses on the dynamics of beef supply response in the French beef sector.beef supply, dynamic modelling, expectations, direct payments, Common Agricultural Policy, Agricultural and Food Policy, C61, Q12, Q18,
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