5,341 research outputs found
Tunneling effects on impurity spectral function in coupled asymmetric quantum wires
The impurity spectral function is studied in coupled double quantum wires at
finite temperatures. Simple anisotropy in the confinement direction of the
wires leads to finite non-diagonal elements of the impurity spectral function
matrix. These non-diagonal elements are responsible for tunneling effects and
result in pronounced extra peak in the impurity spectral function up to
temperatures as high as 20 K.Comment: Accepted in Phys. Rev.
Paradoxical popups: Why are they hard to catch?
Even professional baseball players occasionally find it difficult to
gracefully approach seemingly routine pop-ups. This paper describes a set of
towering pop-ups with trajectories that exhibit cusps and loops near the apex.
For a normal fly ball, the horizontal velocity is continuously decreasing due
to drag caused by air resistance. But for pop-ups, the Magnus force (the force
due to the ball spinning in a moving airflow) is larger than the drag force. In
these cases the horizontal velocity decreases in the beginning, like a normal
fly ball, but after the apex, the Magnus force accelerates the horizontal
motion. We refer to this class of pop-ups as paradoxical because they appear to
misinform the typically robust optical control strategies used by fielders and
lead to systematic vacillation in running paths, especially when a trajectory
terminates near the fielder. In short, some of the dancing around when
infielders pursue pop-ups can be well explained as a combination of bizarre
trajectories and misguidance by the normally reliable optical control strategy,
rather than apparent fielder error. Former major league infielders confirm that
our model agrees with their experiences.Comment: 28 pages, 10 figures, sumitted to American Journal of Physic
Carrier relaxation due to electron-electron interaction in coupled double quantum well structures
We calculate the electron-electron interaction induced energy-dependent
inelastic carrier relaxation rate in doped semiconductor coupled double quantum
well nanostructures within the two subband approximation at zero temperature.
In particular, we calculate, using many-body theory, the imaginary part of the
full self-energy matrix by expanding in the dynamically RPA screened Coulomb
interaction, obtaining the intrasubband and intersubband electron relaxation
rates in the ground and excited subbands as a function of electron energy. We
separate out the single particle and the collective excitation contributions,
and comment on the effects of structural asymmetry in the quantum well on the
relaxation rate. Effects of dynamical screening and Fermi statistics are
automatically included in our many body formalism rather than being
incorporated in an ad-hoc manner as one must do in the Boltzman theory.Comment: 26 pages, 5 figure
Study of the impact of the discharges of the Vila-Viçosa small hydroelectric development (Portugal) on the water quality and on the fish communities of the Ardena river
A study of the Vila-Viçosa small hydroelectric development, situated on the Ardena river (hydrographical basin of the river Douro, Portugal) was carried out for one year, with the purpose of evaluating the existence of differences in the fish communities found downstream and upstream of the development. A characterization of the system was made, bearing in mind morphological, hydrological and physical and chemical characteristics and studying the structure and dynamics of the fish communities. With the collected data on physical and chemical parameters a study of its space-time variation was made. Moreover, with the data relative to the fish communities a study of the space-time variation of some parameters was carried out. After the analysis of the data, it is possible to conclude that the Ardena river is a lotic system with water of good quality and that the functioning of the hydroelectric plant does not produce variations of the values of the parameters measured. The results obtained for the space-time variation of the fish community reveal some alterations in its distribution.Durante un año se ha estudiado la minicentral hidroeléctrica de Vila Viçosa en el río Ardena (cuenca del Duero, Portugal), con el objetivo de evaluar la existencia de diferencias en las comunidades de peces situadas abajo y arriba de la minicentral hidroeléctrica, caracterizando el sistema desde el punto de vista morfológico, hidrológico y físico-químico y estudiando la estructura y dinámica de las comunidades de peces. Con los datos relativos a los parámetros físico-químicos y los peces se ha hecho el estudio de la variación espacio-temporal. Además con los datos de los peces se ha estudiado la variación espacial y temporal de algunos parámetros. Después de analizados los datos, se puede decir que el río Ardena es un sistema lotico con agua de buena calidad y que el funcionamiento de la minicentral no provoca alteraciones de los valores encontrados. Los resultados de la variación espacial y temporal de la comunidad de peces reflejan alteraciones en su distribución
Out-of-phase oscillation between superfluid and thermal components for a trapped Bose condensate under oscillatory excitation
The vortex nucleation and the emergence of quantum turbulence induced by
oscillating magnetic fields, introduced by Henn E A L, et al. 2009 (Phys. Rev.
A 79, 043619) and Henn E A L, et al. 2009 (Phys. Rev. Lett. 103, 045301), left
a few open questions concerning the basic mechanisms causing those interesting
phenomena. Here, we report the experimental observation of the slosh dynamics
of a magnetically trapped Rb Bose-Einstein condensate (BEC) under the
influence of a time-varying magnetic field. We observed a clear relative
displacement in between the condensed and the thermal fraction center-of-mass.
We have identified this relative counter move as an out-of-phase oscillation
mode, which is able to produce ripples on the condensed/thermal fractions
interface. The out-of-phase mode can be included as a possible mechanism
involved in the vortex nucleation and further evolution when excited by time
dependent magnetic fields.Comment: 5 pages, 5 figures, 25 reference
Static quantities of the W boson in the SU_L(3) X U_X(1) model with right-handed neutrinos
The static electromagnetic properties of the boson, and
, are calculated in the SU_L(3)} \times U_X(1) model with
right-handed neutrinos. The new contributions from this model arise from the
gauge and scalar sectors. In the gauge sector there is a new contribution from
a complex neutral gauge boson and a singly-charged gauge boson .
The mass of these gauge bosons, called bileptons, is expected to be in the
range of a few hundreds of GeV according to the current bounds from
experimental data. If the bilepton masses are of the order of 200 GeV, the size
of their contribution is similar to that obtained in other weakly coupled
theories. However the contributions to both and are
negligible for very heavy or degenerate bileptons. As for the scalar sector, an
scenario is examined in which the contribution to the form factors is
identical to that of a two-Higgs-doublet model. It is found that this sector
would not give large corrections to and .Comment: New material included. Final version to apppear in Physical Review
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