8,961 research outputs found
Coulomb repulsion versus Hubbard repulsion in a disordered chain
We study the difference between on site Hubbard and long range Coulomb
repulsions for two interacting particles in a disordered chain. While Hubbard
repulsion can only yield weak critical chaos with intermediate spectral
statistics, Coulomb repulsion can drive the two particle system to quantum
chaos with Wigner-Dyson spectral statistics. For intermediate strengths U of
the two repulsions in one dimension, there is a crossover regime where
delocalization and spectral rigidity are maximum, whereas the limits of weak
and strong U are characterized by a stronger localization and uncorrelated
energy levels.Comment: 8 pages, 10 figure
Analysis and optimisation of the tuning of the twelfths for a clarinet resonator
Even if the tuning between the first and second register of a clarinet has
been optimized by instrument makers, the lowest twelfths remain slightly too
large (inharmonicity). In this article, we study the problem from two different
points of view. First, we systematically review various physical reasons why
this inharmonicity may take place, and the effect of different bore
perturbations inserted in cylindrical instruments. Applications to a real
clarinet resonator and comparisons with impedance measurements are then
presented. A commonly accepted idea is that the register hole is the dominant
cause for this inharmonicity: it is natural to expect that opening this hole
will raise the resonance frequencies of the instrument, except for the note for
which the hole is at the pressure node. We show that the real situation is
actually more complicated because other effects, such as open holes or bore
taper and bell, introduce resonance shifts that are comparable but with
opposite sign, so that a relatively good overall compensation takes place. The
origin of the observed inharmonicity in playing frequencies is therefore
different. In a second part, we use an elementary model of the clarinet in
order to isolate the effect of the register hole: a perfect cylindrical tube
without closed holes. Optimization techniques are then used to calculate an
optimum location for the register hole; the result turns out to be close to the
location chosen by clarinet makers. Finally, attempts are made numerically to
improve the situation by introducing small perturbations in the higher part of
the cylindrical resonator, but no satisfactory improvement is obtained.Comment: 28 June 2004 (submitted to Applied Acoustics
Equitable provision of long-term public goods: the role of negotiation mandates
In a one-period model, whether or not individual weights in the welfare function are based on initial endowments dictate who provides public goods. But with long-term public goods, banning wealth redistribution still allows for several equilibriums depending on Parties'willingness to acknowledge changes in negotiating powers over time, and on whether or not they care only for their own descendants. Adaptative and universal mandates lead to far more robust equilibrium. In all cases, a simple rule of thumb for allocating expenditures at first period emerges, independent of both the optimal level of public goods and the second-period distribution of expenditures.Montreal Protocol,Economic Theory&Research,Information Technology,Environmental Economics&Policies,General Technology,Montreal Protocol,Economic Theory&Research,Environmental Economics&Policies,Energy and Environment,Transport and Environment
Thirty-five years of long-run energy forecasting : lessons for climate change policy
This paper sheds light on an implicit dimension of the climate policy debate: the extent to which supply-side response (emission-reducing energy technologies) may substitute for the transformation of consumption behavior and thus help get around the political difficulties surrounding such behavioral transformation. The paper performs a meta-review of long-term energy forecasts since the end of the 1960s in order to put in perspective the controversies around technological optimism about the potential for cheap, large-scale, carbon-free energy production. This retrospective analysis encompasses 116 scenarios conducted over 36 years and analyzes their predictions for a) fossil fuels, b) nuclear energy, and c) renewable energy. The analysis demonstrates how the predicted relative shares of these three types of energy have evolved since 1970, for two cases: a) predicted shares in 2010, which shows how the initial outlooks for the 2000-2010 period have been revised as a function of observed trends; and b) predicted shares for t+30, which shows how these revisions have affected medium-term prospects. The analysis shows a decrease, since 1970, in technological optimism about switching away from fossil fuels; this decrease is unsurprisingly correlated with a decline in modelers’ beliefs in the suitability of nuclear energy. But, after a trend of increasing optimism, a declining trend also characterizes renewable energies in the 1980s and 1990s before a slight revival of technological optimism about renewables in the aftermath of Kyoto.Energy Production and Transportation,Energy and Environment,Environment and Energy Efficiency,Energy Demand,Climate Change Mitigation and Green House Gases
Idiosyncratic uncertainty, capacity utilization and the business cycle
In a stochastic dynamic general equilibrium framework, we introduce the concept of variable capacity utilization (as opposed to the concept of capital utilization). We consider an economy where imperfectly competitive firms use a putty-clay technology and decide on their productive capacity level under uncertainty. An idiosyncratic uncertainty about the exact position of the demand curve facedby each firm explains why sorne productive capacities may remain idle in the sequel and why individual capacity utilization rates differ across firms. The capacity underutilization at the aggregate level thus hides a diversity of microeconomic situations. The variability of the capacity utilization allows for a good description of sorne of the main stylized facts of the business cycle, propagates and magnifies aggregate technological shocks and generates endogenous persistence (Le., the output growth rate displays positive serial correlation)
Complex Eigenvalue Analysis for Structures with Viscoelastic Behavior
This document deals with a method for eigenvalue extraction for the analysis
of structures with viscoelastic materials. A generalized Maxwell model is used
to model linear viscoelasticity. Such kind of model necessitates a state-space
formulation to perform eigenvalue analysis with standard solvers. This
formulation is very close to ADF formulation. The use of several materials on
the same structure and during the same analysis may lead to a large number of
internal states. This article purpose is to identify simultaneously all the
viscoelastic materials and to constrain them to have the same time-constants.
As it is usually possible, the size of the state-space problem is therefore
widely reduced. Moreover, an accurate method for reducing mass and stiffness
operators is proposed; The enhancement of the modal basis allows to obtain good
results with large reduction. As the length of the paper is limited, only
theoretical development are presented in the present paper while numerical
results will be presented in the conference.Comment: ASME 2011 International Design Engineering Technical Conferences and
Computers and Information in Engineering Conference (IDETC/CIE2011),
Washington : France (2011
Tracer Dispersion in Rough Open Cracks
Tracer dispersion is studied in an open crack where the two rough crack faces have been translated with respect to each other. The different dispersion regimes encountered in rough-wall Hele-Shaw cell are first introduced, and the geometric dispersion regime in the case of self-affine crack surfaces is treated in detail through perturbation analysis. It is shown that a line of tracer is progressively wrinkled into a self-affine curve with an exponent equal to that of the crack surface.This leads to a global dispersion coefficient which depends on the distance from the tracer inlet, but which is still proportional to the mean advection velocity. Besides, the tracer front is subjected to a local dispersion (as could be revealed by point measurements or echo experiments) very different from the global one. The expression of this anomalous local dispersion coefficient is also obtained
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