66,158 research outputs found
Binding between two-component bosons in one dimension
We investigate the ground state of one-dimensional few-atom Bose-Bose
mixtures under harmonic confinement throughout the crossover from weak to
strong inter-species attraction. The calculations are based on the numerically
exact multi-configurational time-dependent Hartree method. For repulsive
components we detail the condition for the formation of a molecular
Tonks-Girardeau gas in the regime of intermediate inter-species interactions,
and the formation of a molecular condensate for stronger coupling. Beyond a
critical inter-species attraction, the system collapses to an overall bound
state. Different pathways emerge for unequal particle numbers and intra-species
interactions. In particular, for mixtures with one attractive component, this
species can be viewed as an effective potential dimple in the trap center for
the other, repulsive component.Comment: 10 pages, 10 figure
Cross Calibration of Imaging Air Cherenkov Telescopes with Fermi
An updated model for the synchrotron and inverse Compton emission from a
population of high energy electrons of the Crab Nebula is used to reproduce the
measured spectral energy distribution from radio to high energy gamma-rays. By
comparing the predicted inverse Compton component with recent Fermi
measurements of the nebula's emission, it is possible to determine the average
magnetic field in the nebula and to derive the underlying electron energy
distribution. The model calculation can then be used to cross calibrate the
Fermi observations with ground based air shower measurements. The resulting
energy calibration factors are derived and can be used for combining broad
energy measurements taken with Fermi in conjunction with ground based
measurements.Comment: 2009 Fermi Symposium, eConf Proceedings C091122, 5 pages, 5 figures,
3 table
Causes and Implications of the Food Price Surge
This paper analyzes the food price surge of 2005 to 2008 in order to better understand the factors causing higher and more volatile food prices during this period, to ascertain the relative importance and possible persistence of the different factors, and to suggest possible implications for future market behavior and policy reactions.Agricultural and Food Policy,
Time-dependent coupled-cluster method for atomic nuclei
We study time-dependent coupled-cluster theory in the framework of nuclear
physics. Based on Kvaal's bi-variational formulation of this method [S. Kvaal,
arXiv:1201.5548], we explicitly demonstrate that observables that commute with
the Hamiltonian are conserved under time evolution. We explore the role of the
energy and of the similarity-transformed Hamiltonian under real and imaginary
time evolution and relate the latter to similarity renormalization group
transformations. Proof-of-principle computations of He-4 and O-16 in small
model spaces, and computations of the Lipkin model illustrate the capabilities
of the method.Comment: 10 pages, 9 pdf figure
Simulation of Consensus Model of Deffuant et al on a Barabasi-Albert Network
In the consensus model with bounded confidence, studied by Deffuant et al.
(2000), two randomly selected people who differ not too much in their opinion
both shift their opinions towards each other. Now we restrict this exchange of
information to people connected by a scale-free network. As a result, the
number of different final opinions (when no complete consensus is formed) is
proportional to the number of people.Comment: 7 pages including 3 figs; Int.J.MOd.Phys.C 15, issue 2; programming
error correcte
Nonlinear force-free field modelling of solar coronal jets in theoretical configurations
Coronal jets occur frequently on the Sun, and may contribute significantly to the solar wind. With the suite of instruments available now, we can observe these phenomena in greater detail than ever before. Modeling and simulations can assist further in understanding the dynamic processes involved, but previous studies tend to consider only one mechanism (e.g. emergence or rotation) for the origin of the jet. In this study we model a series of idealised archetypal jet configurations and follow the evolution of the coronal magnetic field. This is a step towards understanding these idealised situations before considering their observational counterparts. Several simple situations are set up for the evolution of the photospheric magnetic field: a single parasitic polarity rotating or moving in a circular path; as well as opposite polarity pairs involved in flyby (shearing), cancellation or emergence; all in the presence of a uniform, open background magnetic field. The coronal magnetic field is evolved in time using a magnetofrictional relaxation method. While magnetofriction cannot accurately reproduce the dynamics of an eruptive phase, the structure of the coronal magnetic field, as well as the build up of electric currents and free magnetic energy are instructive. Certain configurations and motions produce a flux rope and allow the significant build up of free energy, reminiscent of the progenitors of so-called blowout jets, whereas other, simpler configurations are more comparable to the standard jet model. The next stage is a comparison with observed coronal jet structures and their corresponding photospheric evolution
Order-by-disorder in classical oscillator systems
We consider classical nonlinear oscillators on hexagonal lattices. When the
coupling between the elements is repulsive, we observe coexisting states, each
one with its own basin of attraction. These states differ by their degree of
synchronization and by patterns of phase-locked motion. When disorder is
introduced into the system by additive or multiplicative Gaussian noise, we
observe a non-monotonic dependence of the degree of order in the system as a
function of the noise intensity: intervals of noise intensity with low
synchronization between the oscillators alternate with intervals where more
oscillators are synchronized. In the latter case, noise induces a higher degree
of order in the sense of a larger number of nearly coinciding phases. This
order-by-disorder effect is reminiscent to the analogous phenomenon known from
spin systems. Surprisingly, this non-monotonic evolution of the degree of order
is found not only for a single interval of intermediate noise strength, but
repeatedly as a function of increasing noise intensity. We observe noise-driven
migration of oscillator phases in a rough potential landscape.Comment: 12 pages, 13 figures; comments are welcom
Fan Noise Prediction System Development: Source/Radiation Field Coupling and Workstation Conversion for the Acoustic Radiation Code
The Acoustic Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field acoustic radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan source noise generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the source and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the source and radiation fields is needed for accurate noise predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix
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