1,221 research outputs found
Bistability and instability of dark-antidark solitons in the cubic-quintic nonlinear Schroedinger equation
We characterize the full family of soliton solutions sitting over a
background plane wave and ruled by the cubic-quintic nonlinear Schroedinger
equation in the regime where a quintic focusing term represents a saturation of
the cubic defocusing nonlinearity. We discuss existence and properties of
solitons in terms of catastrophe theory and fully characterize bistability and
instabilities of the dark-antidark pairs, revealing new mechanisms of decay of
antidark solitons.Comment: 8 pages, 10 figures, accepted in PR
Discrete breathers for understanding reconstructive mineral processes at low temperatures
Reconstructive transformations in layered silicates need a high tem- perature
in order to be observed. However, very recently, some systems have been found
where transformation can be studied at temperatures 600 C below the lowest
experimental results previously reported, including sol-gel methods. We explore
the possible relation with the existence of intrinsic localized modes, known as
discrete breathers. We construct a model for nonlinear vibrations within the
cation layer, obtain their parameters and calculate them numerically, obtaining
their energies. Their statistics shows that although there are far less
breathers than phonons, there are much more above the activation energy, being
therefore a good candidate to explain the reconstructive transformations at low
temperature.Comment: 27 pages, 11 figure
Optimal frequency conversion in the nonlinear stage of modulation instability
We investigate multi-wave mixing associated with the strongly pump depleted
regime of induced modulation instability (MI) in optical fibers. For a complete
transfer of pump power into the sideband modes, we theoretically and
experimentally demonstrate that it is necessary to use a much lower seeding
modulation frequency than the peak MI gain value. Our analysis shows that a
record 95 % of the input pump power is frequency converted into the comb of
sidebands, in good quantitative agreement with analytical predictions based on
the simplest exact breather solution of the nonlinear Schr\"odinger equation
Recognizing greenway network for quantifying students experience on campus-based universities : assessing the campus outdoor spaces at San Diego State University
This paper evaluates the potential of creating a green infrastructure â more specifically, an urban greenway â and its contribution the studentsâ campus experience, with emphasis on the outdoor university activities. To achieve best value for money â particularly in the current financial climate, with severe budget cuts constraining universities â justifying investments on campus outdoor spaces such as greenways, relies on a clear demonstration of their link to the overall success of the campus. Attempts of quantify the benefits from investments on such spaces are challenged by the scarcity of studies on the relationship between studentsâ experience and design (and related cost) of different types of campus landscape settings. This paper fills this gap by offering a thorough examination of a variety of extant campus developments and by measuring the performance of some selected open spaces against a âprice-tagâ mechanism. The case study of the San Diego State University has been chosen as core case study and supplemented by 16 sub-cases across California State. The assessment has been conducted through three steps. First, a site inventory of the physical characteristics and landscape features has been conducted, focusing on 7 typologies of campus outdoor spaces (COS). Second, four main use patterns (Individual-customized, Group-social, Programmed-scheduled, and Active experiences) have been assessed by calculating the intensity of use (function of the frequency and duration of use) for each of them. The data collected was based on syntax observation methods with photos and maps of COS as prompts. Third, a Campus-Experience-Score (C-E-C) has been calculated and normalized to the size and population of the university, matching it against the actual development costs of each COS setting. The C-E-C allows measuring the link between types and features of COS and related studentsâ experience. Findings were discussed and verified through six in-depth interviews with local and international academics and developers/practitioners. This paper offers valuable benchmark to designers and planners seeking to maximize the value for money of investments on COS such as greenways
Crossover dynamics of dispersive shocks in Bose-Einstein condensates characterized by two and three-body interactions
We show that the perturbative nonlinearity associated with three-atom
interactions, competing with standard two-body repulsive interactions, can
change dramatically the evolution of 1D dispersive shock waves in a
Bose-Einstein condensate. In particular, we prove the existence of a rich
crossover dynamics, ranging from the formation of multiple shocks regularized
by coexisting trains of dark and antidark matter waves, to 1D soliton collapse.
For a given scattering length, all these different regimes can be accessed by
varying the number of atoms in the condensate.Comment: 4 pages, 5 figure
Modulational instability in dispersion-kicked optical fibers
We study, both theoretically and experimentally, modulational instability in
optical fibers that have a longitudinal evolution of their dispersion in the
form of a Dirac delta comb. By means of Floquet theory, we obtain an exact
expression for the position of the gain bands, and we provide simple analytical
estimates of the gain and of the bandwidths of those sidebands. An experimental
validation of those results has been realized in several microstructured fibers
specifically manufactured for that purpose. The dispersion landscape of those
fibers is a comb of Gaussian pulses having widths much shorter than the period,
which therefore approximate the ideal Dirac comb. Experimental spontaneous MI
spectra recorded under quasi continuous wave excitation are in good agreement
with the theory and with numerical simulations based on the generalized
nonlinear Schr\"odinger equation
Heteroclinic structure of parametric resonance in the nonlinear Schr\"odinger equation
We show that the nonlinear stage of modulational instability induced by
parametric driving in the {\em defocusing} nonlinear Schr\"odinger equation can
be accurately described by combining mode truncation and averaging methods,
valid in the strong driving regime. The resulting integrable oscillator reveals
a complex hidden heteroclinic structure of the instability. A remarkable
consequence, validated by the numerical integration of the original model, is
the existence of breather solutions separating different Fermi-Pasta-Ulam
recurrent regimes. Our theory also shows that optimal parametric amplification
unexpectedly occurs outside the bandwidth of the resonance (or Arnold tongues)
arising from the linearised Floquet analysis
The Influence of Signaling Conspecific and Heterospecific Neighbors on Eavesdropper Pressure
The study of tradeoffs between the attraction of mates and the attraction of eavesdropping predators and parasites has generally focused on a single species of prey, signaling in isolation. In nature, however, animals often signal from mixed-species aggregations, where interactions with heterospecific group members may be an important mechanism modulating tradeoffs between sexual and natural selection, and thus driving signal evolution. Although studies have shown that conspecific signalers can influence eavesdropper pressure on mating signals, the effects of signaling heterospecifics on eavesdropper pressure, and on the balance between natural and sexual selection, are likely to be different. Here, we review the role of neighboring signalers in mediating changes in eavesdropper pressure, and present a simple model that explores how selection imposed by eavesdropping enemies varies as a function of a signaling aggregation\u27s species composition, the attractiveness of aggregation members to eavesdroppers, and the eavesdroppers\u27 preferences for different member types. This approach can be used to model mixed-species signaling aggregations, as well as same-species aggregations, including those with non-signaling individuals, such as satellites or females. We discuss the implications of our model for the evolution of signal structure, signaling behavior, mixed-species aggregations, and community dynamics
Matter X waves
We predict that an ultra-cold Bose gas in an optical lattice can give rise to
a new form of condensation, namely matter X waves. These are non-spreading 3D
wave-packets which reflect the symmetry of the Laplacian with a negative
effective mass along the lattice direction, and are allowed to exist in the
absence of any trapping potential even in the limit of non-interacting atoms.
This result has also strong implications for optical propagation in periodic
structuresComment: 5 pages, 2 figure
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