17,476 research outputs found
Modulation instability and solitary wave formation in two-component Bose-Einstein condensates
We investigate nonlinear dynamics induced by the modulation instability of a
two-component mixture in an atomic Bose-Einstein condensate. The nonlinear
dynamics is examined using numerical simulations of the time-dependent coupled
Gross-Pitaevskii equations. The unstable modulation grows from initially
miscible condensates into various types of vector solitary waves, depending on
the combinations of the sign of the coupling constants (intracomponent and
intercomponent). We discuss the detailed features of the modulation
instability, dynamics of solitary wave formation, and an analogy with the
collapsing dynamics in a single-component condensate with attractive
interactions.Comment: 15 pages, 10 figure
GRBs from unstable Poynting dominated outflows
Poynting flux driven outflows from magnetized rotators are a plausible
explanation for gamma-ray burst engines. We suggest a new possibility for how
such outflows might transfer energy into radiating particles. We argue that the
Poynting flux drives non-linearly unstable large amplitude electromagnetic
waves (LAEMW) which ``break'' at radii cm where the MHD
approximation becomes inapplicable. In the ``foaming'' (relativisticly
reconnecting) regions formed during the wave breaks the random electric fields
stochastically accelerate particles to ultrarelativistic energies which then
radiate in turbulent electromagnetic fields. The typical energy of the emitted
photons is a fraction of the fundamental Compton energy with plus additional boosting due to the bulk motion
of the medium. The emission properties are similar to synchrotron radiation,
with a typical cooling time sec. During the wave break, the
plasma is also bulk accelerated in the outward radial direction and at larger
radii can produce afterglows due to the interactions with external medium. The
near equipartition fields required by afterglow models maybe due to magnetic
field regeneration in the outflowing plasma (similarly to the field generation
by LAEMW of laser-plasma interactions) and mixing with the upstream plasma.Comment: 15 pages, 1 figur
Multicomputer communication system
A local area network is provided for a plurality of autonomous computers which operate at different rates and under different protocols coupled by network bus adapters to a global bus. A host computer (HC) divides a message file to be transmitted into blocks, each with a header that includes a data type identifier and a trailer. The associated network bus adapter (NBA) then divides the data into packets, each with a header to which a transport header and trailer is added with frame type code which specifies one of three modes of addressing in the transmission of data, namely a physical address mode for computer to computer transmission using two bytes for source and destination addresses, a logical address mode and a data type mode. In the logical address mode, one of the two addressing bytes contains a logical channel number (LCN) established between the transmitting and one or more receiving computers. In the data type mode, one of the addressing bytes contains a code identifying the type of data
Matter wave switching in Bose-Einstein condensates via intensity redistribution soliton interactions
Using time dependent nonlinear (s-wave scattering length) coupling between
the components of a weakly interacting two component Bose-Einstein condensate
(BEC), we show the possibility of matter wave switching (fraction of atoms
transfer) between the components via shape changing/intensity redistribution
(matter redistribution) soliton interactions. We investigate the exact
bright-bright N-soliton solution of an effective one-dimensional (1D) two
component BEC by suitably tailoring the trap potential, atomic scattering
length and atom gain or loss. In particular, we show that the effective 1D
coupled Gross-Pitaevskii (GP) equations with time dependent parameters can be
transformed into the well known completely integrable Manakov model described
by coupled nonlinear Schr\"odinger (CNLS) equations by effecting a change of
variables of the coordinates and the wave functions under certain conditions
related to the time dependent parameters. We obtain the one-soliton solution
and demonstrate the shape changing/matter redistribution interactions of two
and three soliton solutions for the time independent expulsive harmonic trap
potential, periodically modulated harmonic trap potential and kink-like
modulated harmonic trap potential. The standard elastic collision of solitons
occur only for a specific choice of soliton parameters.Comment: 11 pages, 14 figures, 1 tabl
Stationary scattering from a nonlinear network
Transmission through a complex network of nonlinear one-dimensional leads is
discussed by extending the stationary scattering theory on quantum graphs to
the nonlinear regime. We show that the existence of cycles inside the graph
leads to a large number of sharp resonances that dominate scattering. The
latter resonances are then shown to be extremely sensitive to the nonlinearity
and display multi-stability and hysteresis. This work provides a framework for
the study of light propagation in complex optical networks.Comment: 4 pages, 4 figure
Exploring Bicycle and Public Transit Use by Low-Income Latino Immigrants: A Mixed-Methods Study in the San Francisco Bay Area
Latin American immigrants will continue to make up a large share of transit ridership, bicycling and walking in the United States for the foreseeable future, but there is relatively little research about them. This mixed-methods study compares the travel patterns of low-income immigrants living in the San Francisco Bay Area with that of other groups and investigates the barriers and constraints faced by low-income immigrants when taking transit and bicycling. Much of the previous work on immigrant travel has relied on national surveys and qualitative analysis, which underrepresent disadvantaged population groups and slower modes of travel, or are unable to speak to broader patterns in the population. We conducted interviews with 14 low-income immigrants and a paper-based intercept survey of 2,078 adults. Interviewees revealed five major barriers that made public transit use difficult for them, including safety, transit fare affordability, discrimination, system legibility, and reliability. Although crime was the most prominent issue in interviews, the survey results suggest transit cost is the most pressing concern for low-income immigrants. Low-income immigrants were less likely than those with higher-incomes to have access to a motor vehicle, and were less likely than higher-income immigrants or the U.S.-born of any income to have access to a bicycle or bus pass. Finally, although most barriers to public transit use were the same regardless of nativity or household income, low-income immigrants were much less willing to take public transit when they had the option to drive and less willing to bicycle for any purpose. The prevalence of concerns about transit affordability, crime, and reliability suggest transit agencies should consider income-based fare reductions, coordinated crime prevention with local law enforcement, and improved scheduling
Propagation of temporal entanglement
The equations that govern the temporal evolution of two photons in the
Schr{\"o}dinger picture are derived, taking into account the effects of loss,
group-velocity dispersion, temporal phase modulation, linear coupling among
different optical modes, and four-wave mixing. Inspired by the formalism, we
propose the concept of quantum temporal imaging, which uses dispersive elements
and temporal phase modulators to manipulate the temporal correlation of two
entangled photons. We also present the exact solution of a two-photon vector
soliton, in order to demonstrate the ease of use and intuitiveness of the
proposed formulation.Comment: 8 pages, 4 figure
Consequences of self-consistency violations in Hartree-Fock random-phase approximation calculations of the nuclear breathing mode energy
We provide for the first time accurate assessments of the consequences of
violations of self-consistency in the Hartree-Fock based random phase
approximation (RPA) as commonly used to calculate the energy of the
nuclear breathing mode. Using several Skyrme interactions we find that the
self-consistency violated by ignoring the spin-orbit interaction in the RPA
calculation causes a spurious enhancement of the breathing mode energy for spin
unsaturated systems. Contrarily, neglecting the Coulomb interaction in the RPA
or performing the RPA calculations in the TJ scheme underestimates the
breathing mode energy. Surprisingly, our results for the Zr and
Pb nuclei for several Skyrme type effective nucleon-nucleon
interactions having a wide range of nuclear matter incompressibility ( MeV) and symmetry energy ( MeV) indicate that
the net uncertainty ( MeV) is comparable to the
experimental one.Comment: Revtex file (11 pages), Accepted for the publication in Phys. Rev.
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