1,697 research outputs found
The Quantum Emergence of Chaos
The dynamical status of isolated quantum systems, partly due to the linearity
of the Schrodinger equation is unclear: Conventional measures fail to detect
chaos in such systems. However, when quantum systems are subjected to
observation -- as all experimental systems must be -- their dynamics is no
longer linear and, in the appropriate limit(s), the evolution of expectation
values, conditioned on the observations, closely approaches the behavior of
classical trajectories. Here we show, by analyzing a specific example, that
microscopic continuously observed quantum systems, even far from any classical
limit, can have a positive Lyapunov exponent, and thus be truly chaotic.Comment: 4 pages, 4 figure
Dragging a polymer chain into a nanotube and subsequent release
We present a scaling theory and Monte Carlo (MC) simulation results for a
flexible polymer chain slowly dragged by one end into a nanotube. We also
describe the situation when the completely confined chain is released and
gradually leaves the tube. MC simulations were performed for a self-avoiding
lattice model with a biased chain growth algorithm, the pruned-enriched
Rosenbluth method. The nanotube is a long channel opened at one end and its
diameter is much smaller than the size of the polymer coil in solution. We
analyze the following characteristics as functions of the chain end position
inside the tube: the free energy of confinement, the average end-to-end
distance, the average number of imprisoned monomers, and the average stretching
of the confined part of the chain for various values of and for the number
of monomers in the chain, . We show that when the chain end is dragged by a
certain critical distance into the tube, the polymer undergoes a
first-order phase transition whereby the remaining free tail is abruptly sucked
into the tube. This is accompanied by jumps in the average size, the number of
imprisoned segments, and in the average stretching parameter. The critical
distance scales as . The transition takes place when
approximately 3/4 of the chain units are dragged into the tube. The theory
presented is based on constructing the Landau free energy as a function of an
order parameter that provides a complete description of equilibrium and
metastable states. We argue that if the trapped chain is released with all
monomers allowed to fluctuate, the reverse process in which the chain leaves
the confinement occurs smoothly without any jumps. Finally, we apply the theory
to estimate the lifetime of confined DNA in metastable states in nanotubes.Comment: 13pages, 14figure
Espécies arbóreas nativas com potencial para recuperação de paisagens alteradas em Rondônia.
Com base na literatura sobre a ocorrência de espécies nativas da região amazônica e em listas de inventários realizados na porção ocidental da Amazônia, são apresentadas informações sobre a ecologia, silvicultura e plantio, com o objetivo de reunir informações sobre seis espécies arbóreas nativas da região amazônica com potencial para a recuperação de paisagens alteradas em Rondônia.bitstream/item/24814/1/doc128-especiesarboreas.pd
Manejo agroecológico de pastagens: experiências da fazendinha agro-ecológica km 47.
O objetivo deste trabalho foi avaliar o manejo agroecológico de pastagens consorciadas no pastejo de vacas leiteiras em sistema orgânico de produção. Foram avaliadas a disponibilidade de matéria seca (MS) e a composição química da pastagem pela produção de biomassa e teores de proteína bruta (PB), fibra em detergente neutro (FDN) e ácido (FDA), lignina, celulose e hemicelulose respectivamente. As experiencias foi realizado durante o período de 2006 à 2008 no Sistema Integrado de Produção Agroecológica (SIPA), convênio Embrapa/UFRRJ, localizado no município de Seropédica, Rio de Janeiro. O manejo agroecológico do consórcio com leguminosas constitui importante alternativa para se melhorar a qualidade nutricional da forragem em sistema orgânico de produção
Spin Dynamics of the LAGEOS Satellite in Support of a Measurement of the Earth's Gravitomagnetism
LAGEOS is an accurately-tracked, dense spherical satellite covered with 426
retroreflectors. The tracking accuracy is such as to yield a medium term (years
to decades) inertial reference frame determined via relatively inexpensive
observations. This frame is used as an adjunct to the more difficult and data
intensive VLBI absolute frame measurements. There is a substantial secular
precession of the satellite's line of nodes consistent with the classical,
Newtonian precession due to the non-sphericity of the earth. Ciufolini has
suggested the launch of an identical satellite (LAGEOS-3) into an orbit
supplementary to that of LAGEOS-1: LAGEOS-3 would then experience an equal and
opposite classical precession to that of LAGEOS-1. Besides providing a more
accurate real-time measurement of the earth's length of day and polar wobble,
this paired-satellite experiment would provide the first direct measurement of
the general relativistic frame-dragging effect. Of the five dominant error
sources in this experiment, the largest one involves surface forces on the
satellite, and their consequent impact on the orbital nodal precession. The
surface forces are a function of the spin dynamics of the satellite.
Consequently, we undertake here a theoretical effort to model the spin
ndynamics of LAGEOS. In this paper we present our preliminary results.Comment: 16 pages, RevTeX, LA-UR-94-1289. (Part I of II, postscript figures in
Part II
Promoción de la recuperación ambiental en propiedades de producción de leche de búfalo en la Amazonía Occidental Brasilera.
Chaos and Noise in a Truncated Toda Potential
Results are reported from a numerical investigation of orbits in a truncated
Toda potential which is perturbed by weak friction and noise. Two significant
conclusions are shown to emerge: (1) Despite other nontrivial behaviour,
configuration, velocity, and energy space moments associated with these
perturbations exhibit a simple scaling in the amplitude of the friction and
noise. (2) Even very weak friction and noise can induce an extrinsic diffusion
through cantori on a time scale much shorter than that associated with
intrinsic diffusion in the unperturbed system.Comment: 10 pages uuencoded PostScript (figures included), (A trivial
mathematical error leading to an erroneous conclusion is corrected
Continuous Quantum Measurement and the Emergence of Classical Chaos
We formulate the conditions under which the dynamics of a continuously
measured quantum system becomes indistinguishable from that of the
corresponding classical system. In particular, we demonstrate that even in a
classically chaotic system the quantum state vector conditioned by the
measurement remains localized and, under these conditions, follows a trajectory
characterized by the classical Lyapunov exponent.Comment: 5 pages, multicol revte
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