16,264 research outputs found
Quantum pumping in deformable quantum dots
The charge current pumped adiabatically through a deformable quantum dot is
studied within the Green's function approach. Differently from the
non-deformable case, the current shows an undefined parity with respect to the
pumping phase \phi. The unconventional current-phase relation, analyzed in the
weak pumping regime, is due to a dynamical phase shift \phi_D caused by the
elastic deformations of the central region (classical phonons). The role of the
quality factor Q of the oscillator, the effects induced by a mechanical
resonance and the implications for current experiments on molecular systems are
also discussed
ASSESSING THE FINANCIAL RISKS OF DIVERSIFIED COFFEE PRODUCTION SYSTEMS: AN ALTERNATIVE NONNORMAL CDF ESTIMATION APPROACH
Recently developed techniques are adapted and combined for the modeling and simulation of crop yields and prices that can be mutually correlated, exhibit heteroskedasticity or autocorrelation, and follow nonnormal probability density functions. The techniques are applied to the modeling and simulation of probability distribution functions for the returns of three tropical agroforestry systems for coffee production. The importance of using distribution functions that can more closely reflect the statistical behavior of yields and prices for risk analysis is discussed and illustrated.Risk and Uncertainty,
Transient and chaotic low-energy transfers in a system with bistable nonlinearity
The low-energy dynamics of a two-dof system composed of a grounded linear oscillator coupled to
a lightweight mass by means of a spring with both cubic nonlinear and negative linear components
is investigated. The mechanisms leading to intense energy exchanges between the linear oscillator,
excited by a low-energy impulse, and the nonlinear attachment are addressed. For lightly damped
systems, it is shown that two main mechanisms arise: Aperiodic alternating in-well and cross-well
oscillations of the nonlinear attachment, and secondary nonlinear beats occurring once the dynamics
evolves solely in-well. The description of the former dissipative phenomenon is provided in a
two-dimensional projection of the phase space, where transitions between in-well and cross-well
oscillations are associated with sequences of crossings across a pseudo-separatrix. Whereas the second
mechanism is described in terms of secondary limiting phase trajectories of the nonlinear
attachment under certain resonance conditions. The analytical treatment of the two aformentioned
low-energy transfer mechanisms relies on the reduction of the nonlinear dynamics and consequent
analysis of the reduced dynamics by asymptotic techniques. Direct numerical simulations fully
validate our analytical predictions
Time Evolution of Non-Lethal Infectious Diseases: A Semi-Continuous Approach
A model describing the dynamics related to the spreading of non-lethal
infectious diseases in a fixed-size population is proposed. The model consists
of a non-linear delay-differential equation describing the time evolution of
the increment in the number of infectious individuals and depends upon a
limited number of parameters. Predictions are in good qualitative agreement
with data on influenza.Comment: 21 page
Impurity effects on Fabry-Perot physics of ballistic carbon nanotubes
We present a theoretical model accounting for the anomalous Fabry-Perot
pattern observed in the ballistic conductance of a single-wall carbon
nanotubes. Using the scattering field theory, it is shown that the presence of
a limited number of impurities along the nanotube can be identified by a
measurement of the conductance and their position determined. Impurities can be
made active or silent depending on the interaction with the substrate via the
back-gate. The conceptual steps for designing a bio-molecules detector are
briefly discussed.Comment: 4 pages, 4 figure
N-body simulations with two-orders-of-magnitude higher performance using wavelets
Noise is a problem of major concern for N-body simulations of structure
formation in the early Universe, of galaxies and plasmas. Here for the first
time we use wavelets to remove noise from N-body simulations of disc galaxies,
and show that they become equivalent to simulations with two orders of
magnitude more particles. We expect a comparable improvement in performance for
cosmological and plasma simulations. Our wavelet code will be described in a
following paper, and will then be available on request.Comment: Mon. Not. R. Astron. Soc., in press. The interested reader is
strongly recommended to ignore the low-resolution Fig. 3 (and Fig. 4), and to
download the full-resolution paper (700 kb) from
http://www.oso.chalmers.se/~romeo/Paper_VI.ps.g
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