3,054 research outputs found
Phase space description of the dynamics due to the coupled effect of the planetary oblateness and the solar radiation pressure perturbations
The aim of this work is to provide an analytical model to characterize the
equilibrium points and the phase space associated with the singly-averaged
dynamics caused by the planetary oblateness coupled with the solar radiation
pressure perturbations. A two-dimensional differential system is derived by
considering the classical theory, supported by the existence of an integral of
motion comprising semi-major axis, eccentricity and inclination. Under the
single resonance hypothesis, the analytical expressions for the equilibrium
points in the eccentricity-resonant angle space are provided, together with the
corresponding linear stability. The Hamiltonian formulation is also given. The
model is applied considering, as example, the Earth as major oblate body, and a
simple tool to visualize the structure of the phase space is presented.
Finally, some considerations on the possible use and development of the
proposed model are drawn
Quantum interference in nanometric devices: ballistic transport across arrays of T-shaped quantum wires
We propose that the recently realized T-shaped semiconductor quantum wires
(T-wires) could be exploited as three-terminal quantum interference devices.
T-wires are formed by intersecting two quantum wells (QWs). By use of a
scattering matrix approach and the Landauer-B\"uttiker theory, we calculate the
conductance for ballistic transport in the parent QWs and across the wire
region as a function of the injection energy. We show that different
conductance profiles can be selected by tailoring the widths of the QWs and/or
combining more wires on the scale of the Fermi wavelength. Finally, we discuss
the possibility of obtaining spin-dependent conductance of ballistic holes in
the same structures.Comment: To appear in the 09/15/97 issue of Appl. Phys. Lett. (9 pages in
REVTEX + 2 figures in postscript
Psycho-relational well-being in women with sexual pain: a preliminary study
Female sexual pain is a complex multi-factorial condition. Most of the research has focused on underlying biomedical factors. Although psychological and relational factors have been studied as possible correlates, data are still controversial. The aim of the present study was to investigate psychological and relational well-being in women who complain of sexual pain. The hypothesis was that sexual pain is associated with worse scores
The dynamical structure of the MEO region: long-term stability, chaos, and transport
It has long been suspected that the Global Navigation Satellite Systems exist
in a background of complex resonances and chaotic motion; yet, the precise
dynamical character of these phenomena remains elusive. Recent studies have
shown that the occurrence and nature of the resonances driving these dynamics
depend chiefly on the frequencies of nodal and apsidal precession and the rate
of regression of the Moon's nodes. Woven throughout the inclination and
eccentricity phase space is an exceedingly complicated web-like structure of
lunisolar secular resonances, which become particularly dense near the
inclinations of the navigation satellite orbits. A clear picture of the
physical significance of these resonances is of considerable practical interest
for the design of disposal strategies for the four constellations. Here we
present analytical and semi-analytical models that accurately reflect the true
nature of the resonant interactions, and trace the topological organization of
the manifolds on which the chaotic motions take place. We present an atlas of
FLI stability maps, showing the extent of the chaotic regions of the phase
space, computed through a hierarchy of more realistic, and more complicated,
models, and compare the chaotic zones in these charts with the analytical
estimation of the width of the chaotic layers from the heuristic Chirikov
resonance-overlap criterion. As the semi-major axis of the satellite is
receding, we observe a transition from stable Nekhoroshev-like structures at
three Earth radii, where regular orbits dominate, to a Chirikov regime where
resonances overlap at five Earth radii. From a numerical estimation of the
Lyapunov times, we find that many of the inclined, nearly circular orbits of
the navigation satellites are strongly chaotic and that their dynamics are
unpredictable on decadal timescales.Comment: Submitted to Celestial Mechanics and Dynamical Astronomy. Comments
are greatly appreciated. 28 pages, 15 figure
Strong exciton binding in quantum structures through remote dielectric confinement
We propose-a new type of hybrid systems formed by conventional semiconductor nanostructures with the addition of remote insulating layers,where the electron-hole interaction is enhanced by combining quantum and dielectric confinement over different length scales. Because of the polarization charges induced by the dielectric mismatch at the semicondcutor/insulator interfaces, we show that the exciton binding energy can be more than doubled. For conventional m-V quantum wires such remote dielectric confinement allows exciton binding at room temperature
A coupled rate-dependent/rate-independent system for adhesive contact in Kirchhoff-Love plates
We perform a dimension reduction analysis for a coupled
rate-dependent/rate-independent adhesive-contact model in the setting of
visco-elastodynamic plates. We work with a weak solvability notion inspired by
the theory of (purely) rate-independent processes, and accordingly term the
related solutions `Semistable Energetic'. For Semistable Energetic solutions,
the momentum balance holds in a variational sense, whereas the flow rule for
the adhesion parameter is replaced by a semi-stability condition coupled with
an energy-dissipation inequality. Prior to addressing the dimension reduction
analysis, we show that Semistable Energetic solutions to the three-dimensional
damped adhesive contact model converge, as the viscosity term tends to zero, to
three-dimensional Semistable Energetic solutions for the undamped corresponding
system. We then perform a dimension reduction analysis, both in the case of a
vanishing viscosity tensor (leading, in the limit, to an undamped model), and
in the complementary setting in which the damping is assumed to go to infinity
as the thickness of the plate tends to zero. In both regimes, the presence of
adhesive contact yields a nontrivial coupling of the in-plane and out-of-plane
contributions. In the undamped scenario we obtain in the limit an
energy-dissipation inequality and a semistability condition. In the damped
case, instead, we achieve convergence to an enhanced notion of solution,
fulfilling an energy-dissipation balance
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