1,489 research outputs found
Obtaining Breathers in Nonlinear Hamiltonian Lattices
We present a numerical method for obtaining high-accuracy numerical solutions
of spatially localized time-periodic excitations on a nonlinear Hamiltonian
lattice. We compare these results with analytical considerations of the spatial
decay. We show that nonlinear contributions have to be considered, and obtain
very good agreement between the latter and the numerical results. We discuss
further applications of the method and results.Comment: 21 pages (LaTeX), 8 figures in ps-files, tar-compressed uuencoded
file, Physical Review E, in pres
Quantum localized modes in capacitively coupled Josephson junctions
We consider the quantum dynamics of excitations in a system of two
capacitively coupled Josephson junctions. Quantum breather states are found in
the middle of the energy spectrum of the confined nonescaping states of the
system. They are characterized by a strong excitation of one junction. These
states perform slow tunneling motion from one junction to the other, while
keeping their coherent nature. The tunneling time sensitively depends on the
initial excitation energy. By using an external bias as a control parameter,
the tunneling time can be varied with respect to the escape time and the
experimentally limited coherence time. Thus one can control the flow of quantum
excitations between the two junctions.Comment: 5 pages, 3 figures. Improved version, title was slightly changed.
Accepted in Europhysics Letters (http://www.iop.org/EJ/journal/EPL
Quantum breathers in capacitively coupled Josephson junctions: Correlations, number conservation, and entanglement
We consider the classical and quantum dynamics of excitations in a system of
two capacitively coupled Josephson junctions. In the classical case the
equations of motion admit discrete breather solutions, which are time periodic
and localized predominantly on one of the junctions. In the quantum case
breather states are found in the central part of the energy spectrum of the
confined nonescaping states of the system. We perform a systematic analysis of
their tunneling frequency, site correlations, fluctuations of the number of
quanta, and entanglement. Quantum breather states show strong site correlation
of quanta and are characterized by a strong excitation of quanta on one
junction which perform slow coherent tunneling motion from one junction to the
other. They suppress fluctuations of the total number of excited quanta.
Quantum breather states are the least entangled states among the group of
eigenstates in the same range of the energy spectrum. We describe how quantum
breather excitations could be experimentally observed by employing the already
developed techniques for quantum information processing using Josephson
junctions.Comment: 10 pages, 9 figures. Improved version with further discussions.
Accepted in Physical Review
Breathers on lattices with long range interaction
We analyze the properties of breathers (time periodic spatially localized
solutions) on chains in the presence of algebraically decaying interactions
. We find that the spatial decay of a breather shows a crossover from
exponential (short distances) to algebraic (large distances) decay. We
calculate the crossover distance as a function of and the energy of the
breather. Next we show that the results on energy thresholds obtained for short
range interactions remain valid for and that for (anomalous
dispersion at the band edge) nonzero thresholds occur for cases where the short
range interaction system would yield zero threshold values.Comment: 4 pages, 2 figures, PRB Rapid Comm. October 199
Acoustic breathers in two-dimensional lattices
The existence of breathers (time-periodic and spatially localized lattice
vibrations) is well established for i) systems without acoustic phonon branches
and ii) systems with acoustic phonons, but also with additional symmetries
preventing the occurence of strains (dc terms) in the breather solution. The
case of coexistence of strains and acoustic phonon branches is solved (for
simple models) only for one-dimensional lattices.
We calculate breather solutions for a two-dimensional lattice with one
acoustic phonon branch. We start from the easy-to-handle case of a system with
homogeneous (anharmonic) interaction potentials. We then easily continue the
zero-strain breather solution into the model sector with additional quadratic
and cubic potential terms with the help of a generalized Newton method. The
lattice size is . The breather continues to exist, but is dressed
with a strain field. In contrast to the ac breather components, which decay
exponentially in space, the strain field (which has dipole symmetry) should
decay like . On our rather small lattice we find an exponent
Quantum q-breathers in a finite Bose-Hubbard chain: The case of two interacting bosons
We study the spectrum and eigenstates of the quantum discrete Bose-Hubbard
Hamiltonian in a finite one-dimensional lattice containing two bosons. The
interaction between the bosons leads to an algebraic localization of the
modified extended states in the normal mode space of the noninteracting system.
Weight functions of the eigenstates in the space of normal modes are computed
by using numerical diagonalization and perturbation theory. We find that
staggered states do not compactify in the dilute limit for large chains.Comment: 7 pages, 7 figures. Minor changes and additional comments. Acepted in
Physical Review
On the interactions between land and water use in Brazilian rainfed agriculture
In the coming decades, one of humankind’s main challenges will be to guarantee food supply for a growing population while managing ever more scarce resources, and safeguarding the availability of water and land for natural ecosystems. Brazil is a country with abundance of water and land resources, and has recently become one of the world’s main exporters of agricultural commodities. The Brazilian agricultural sector recently went through unprecedented intensification and extensification processes, which include the expansion of cropland and pasture areas into vulnerable ecosystems. This PhD thesis advances the research field on water and land resources assessment by investigating the following processes: i) changes in green water use by major rainfed crops in Brazil during recent decades ii) potential improvements of land and green water productivity for Brazilian rainfed crops, with and without implementation of supplemental irrigation, iii) influences of intensification and expansion of soybean production in Brazil on green water use, and iv) impacts of double-cropping on water use intensity. The process-based biogeophysical crop model EPIC was chosen and applied to simulate water use and crop growth for Brazilian rainfed crops, under diverse management conditions. In Chapter 2, I simulated yields, water use and water productivity for soybeans, maize, cotton and wheat under different scenarios of agricultural management, for rainfed and irrigated conditions. Chapter 3 focuses on soybean and maize, and analyzes water use for the production of these crops under single and double-cropping conditions. The results show an increase in green water use for the production of maize, cotton, soybeans and wheat from 145 to 263 km3 per year between 1990 and 2013. This increase is in large part due to the expansion of harvested area for soybean production. The analysis of management scenarios shows that improving nutrient management has a larger potential to improve land and water productivity compared to supplemental irrigation. Furthermore, supplemental irrigation would lead to a reduction in water productivity despite marginal improvements in land productivity. The analysis of double-cropping practices for soybean and maize production systems finds a greater water appropriation of these systems avoiding cropland expansion and improving overall water productivity. This thesis improves the understanding of current and future use of land and water, the role of intensification and expansion processes, and interactions between land and water use. The results lead to the main conclusion that harvested area expansion has been a major driving force in the increase of green water appropriation in Brazil in the last decades, but that different intensification processes have led to a more productive use of water and land over time. More importantly, the growth of double-cropping has allowed a decoupling between the appropriation of water and land, allowing a great increase of agricultural water use without further expansion of cropland
Slow Relaxation and Phase Space Properties of a Conservative System with Many Degrees of Freedom
We study the one-dimensional discrete model. We compare two
equilibrium properties by use of molecular dynamics simulations: the Lyapunov
spectrum and the time dependence of local correlation functions. Both
properties imply the existence of a dynamical crossover of the system at the
same temperature. This correlation holds for two rather different regimes of
the system - the displacive and intermediate coupling regimes. Our results
imply a deep connection between slowing down of relaxations and phase space
properties of complex systems.Comment: 14 pages, LaTeX, 10 Figures available upon request (SF), Phys. Rev.
E, accepted for publicatio
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