16,728 research outputs found
Pleomorphic adenoma of the nasal septum : a case report
Polypoid nasal lesions are commonly encountered in clinical practice and all should be examined histologically. The authors report a case of pleomorphic adenoma arising in the nasal septum in salivary-type tissue. The interest of this case is both in the relative rarity of the condition, and also in its being the first such report in local practice.peer-reviewe
Strong asymmetry for surface modes in nonlinear lattices with long-range coupling
We analyze the formation of localized surface modes on a nonlinear cubic
waveguide array in the presence of exponentially-decreasing long-range
interactions. We find that the long-range coupling induces a strong asymmetry
between the focusing and defocusing cases for the topology of the surface modes
and also for the minimum power needed to generate them. In particular, for the
defocusing case, there is an upper power threshold for exciting staggered
modes, which depends strongly on the long-range coupling strength. The power
threshold for dynamical excitation of surface modes increase (decrease) with
the strength of long-range coupling for the focusing (defocusing) cases. These
effects seem to be generic for discrete lattices with long-range interactions.Comment: 4 pages, 5 figures, submitted for publicatio
On the influence that the ground electrode diameter has in the propulsion efficiency of an asymmetric capacitor in nitrogen gas
In this work the propulsion force developed in an asymmetric capacitor will
be calculated for three different diameters of the ground electrode. The used
ion source is a small diameter wire, which generates a positive corona
discharge in nitrogen gas directed to the ground electrode. By applying the
fluid dynamic and electrostatic theories all hydrodynamic and electrostatic
forces that act on the considered geometries will be computed in an attempt to
provide a physical insight on the force mechanism that acts on the asymmetrical
capacitors, and also to understand how to increase the efficiency of
propulsion.Comment: 13 pages, 8 figures, Accepted for publication in "Physics of Plasmas
Aberrations in shift-invariant linear optical imaging systems using partially coherent fields
Here the role and influence of aberrations in optical imaging systems
employing partially coherent complex scalar fields is studied. Imaging systems
require aberrations to yield contrast in the output image. For linear
shift-invariant optical systems, we develop an expression for the output
cross-spectral density under the space-frequency formulation of statistically
stationary partially coherentfields. We also develop expressions for the output
cross{spectral density and associated spectral density for weak-phase,
weak-phase-amplitude, and single-material objects in one transverse spatial
dimension
Multidimensional solitons in a low-dimensional periodic potential
Using the variational approximation(VA) and direct simulations, we find
stable 2D and 3D solitons in the self-attractive Gross-Pitaevskii equation
(GPE) with a potential which is uniform in one direction () and periodic in
the others (but the quasi-1D potentials cannot stabilize 3D solitons). The
family of solitons includes single- and multi-peaked ones. The results apply to
Bose-Einstein condensates (BECs) in optical lattices (OLs), and to spatial or
spatiotemporal solitons in layered optical media. This is the first prediction
of {\em mobile} 2D and 3D solitons in BECs, as they keep mobility along .
Head-on collisions of in-phase solitons lead to their fusion into a collapsing
pulse. Solitons colliding in adjacent OL-induced channels may form a bound
state (BS), which then relaxes to a stable asymmetric form. An initially
unstable soliton splits into a three-soliton BS. Localized states in the
self-repulsive GPE with the low-dimensional OL are found too.Comment: 4 pages, 5 figure
Some Remarks about Variable Mass Systems
We comment about the general argument given to obtain the rocket equation as
it is exposed in standard textbooks. In our opinion, it can induce students to
a wrong answer when solving variable mass problems.Comment: 2 page
Nuclear Magnetohydrodynamic EMP, Solar Storms, and Substorms
In addition to a fast electromagnetic pulse (EMP), a high altitude nuclear
burst produces a relatively slow magnetohydrodynarnic EMP (MHD EMP), whose
effects are like those from solar storm geomagnetically induced currents (SS
GIC). The MHD EMP electric field E < 10^-1 V/m and lasts < 10^2 sec, whereas
for solar storms E > 10^-2 V/m and lasts >10^3 sec. Although the solar storm
electric field is lower than MHD EMP, the solar storm effects are generally
greater due to their much longer duration. Substorms produce much smaller
effects than SS GIC, but occur much more frequently. This paper describes the
physics of such geomagnetic disturbances and analyzes their effects.Comment: 29 pages, 14 figures, 5 table
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