5,065 research outputs found
Josephson Effects in a Bose-Einstein Condensate of Magnons
A phenomenological theory is developed, that accounts for the collective
dynamics of a Bose-Einstein condensate of magnons. In terms of such description
we discuss the nature of spontaneous macroscopic interference between magnon
clouds, highlighting the close relation between such effects and the well known
Josephson effects. Using those ideas we present a detailed calculation of the
Josephson oscillations between two magnon clouds, spatially separated in a
magnonic Josephson junction
Educational loans and attitudes towards risk
We explore the relationship between willingness to take financial risk and the probability of taking
out a loan for educational purposes as well as the influence of risk attitudes on the size of the loan using data
drawn from the U.S. Survey of Consumer Finances. The findings suggest a positive relationship between
individualsâ willingness to take financial risk and the probability of taking out a loan for educational purposes.
Similarly, individualsâ willingness to take financial risk appears to be an important determinant of the size of the
educational loan. The findings suggest that non-white individuals and individuals from less wealthy
backgrounds are less likely to finance education through loans which could potentially increase inequalities in
education and income if such individuals are deterred from investing in human capital
Cosmic Rays Induced Background Radiation on Board of Commercial Flights
The aim of this work is to determine the total integrated flux of cosmic
radiation which a commercial aircraft is exposed to along specific flight
trajectories. To study the radiation background during a flight and its
modulation by effects such as altitude, latitude, exposure time and transient
magnetospheric events, we perform simulations based on Magnetocosmics and
CORSIKA codes, the former designed to calculate the geomagnetic effects on
cosmic rays propagation and the latter allows us to simulate the development of
extended air showers in the atmosphere. In this first work, by considering the
total flux of cosmic rays from 5 GeV to 1 PeV, we obtained the expected
integrated flux of secondary particles on board of a commercial airplane during
the Bogot\'a-Buenos Aires trip by point-to-point numerical integration.Comment: 5 pages, 2 figures, Proceedings X SILAFAE Medellin-2014. To appear in
Nuclear Physics B - Proceedings Supplement
Spin wave vortex from the scattering on Bloch point solitons
The interaction of a spin wave with a stationary Bloch point is studied. The
topological non-trivial structure of the Bloch point manifests in the
propagation of spin waves endowing them with a gauge potential that resembles
the one associated with the interaction of a magnetic monopole and an electron.
By pursuing this analogy, we are led to the conclusion that the scattering of
spin waves and Bloch points is accompanied by the creation of a magnon vortex.
Interference between such a vortex and a plane wave leads to dislocations in
the interference pattern that can be measurable by means of magnon holography
Self-consistent calculation of particle-hole diagrams on the Matsubara frequency: FLEX approximation
We implement the numerical method of summing Green function diagrams on the
Matsubara frequency axis for the fluctuation exchange (FLEX) approximation. Our
method has previously been applied to the attractive Hubbard model for low
density. Here we apply our numerical algorithm to the Hubbard model close to
half filling (), and for , in order to study the
dynamics of one- and two-particle Green functions. For the values of the chosen
parameters we see the formation of three branches which we associate with the a
two-peak structure in the imaginary part of the self-energy. From the imaginary
part of the self-energy we conclude that our system is a Fermi liquid (for the
temperature investigated here), since Im
around the chemical potential. We have compared our fully self-consistent FLEX
solutions with a lower order approximation where the internal Green functions
are approximated by free Green functions. These two approches, i.e., the fully
selfconsistent and the non-selfconsistent ones give different results for the
parameters considered here. However, they have similar global results for small
densities.Comment: seven pages, nine figures as ps files. Accepted in Int. J. Modern
Phys. C (1997
Cosmological perturbations in coherent oscillating scalar field models
The fact that fast oscillating homogeneous scalar fields behave as perfect
fluids in average and their intrinsic isotropy have made these models very
fruitful in cosmology. In this work we will analyse the perturbations dynamics
in these theories assuming general power law potentials . At leading order in the wavenumber expansion, a simple
expression for the effective sound speed of perturbations is obtained
with the effective equation of
state. We also obtain the first order correction in
, when the wavenumber of the perturbations is
much smaller than the background oscillation frequency, .
For the standard massive case we have also analysed general anharmonic
contributions to the effective sound speed. These results are reached through a
perturbed version of the generalized virial theorem and also studying the exact
system both in the super-Hubble limit, deriving the natural ansatz for
; and for sub-Hubble modes, exploiting Floquet's theorem.Comment: 13 pages, 6 figures. Published on JHE
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