2,343 research outputs found
Optimizing the G/T ratio of the DSS-13 34-meter beam-waveguide antenna
Calculations using Physical Optics computer software were done to optimize the gain-to-noise-temperature (G/T) ratio of Deep Space Station (DSS)-13, the Deep Space Network's (DSN's) 34-m beam-waveguide antenna, at X-band for operation with the ultra-low-noise amplifier maser system. A better G/T value was obtained by using a 24.2-dB far-field-gain smooth-wall dual-mode horn than by using the standard X-band 22.5-dB-gain corrugated horn
Casimir force calculations near the insulator-conductor transition in gold thin films
We present theoretical calculations of the Casimir force for Au thin films
near the insulator-conductor transition that has been observed experimentally.
The dielectric function of the Au thin films is described by the Drude-Smith
model. The parameters needed to model the dielectric function such as the
relaxation time, plasma frequency and the backscattering constant depend on the
thickness of the film. The Casimir force decreases as the film thickness
decreases until it reaches a minimum after which the force increases again. The
minimum of the force coincides with the critical film thickness where a
percolation conductor-insulator occurs.Comment: 5 figures, 1 tabl
X/X/Ka-band prime focus feed antenna for the Mars Observer beacon spacecraft
The results of an X/X/Ka-band feed design concept demonstration are presented. The purpose is to show the feasibility of adding a Ka-band beacon to the Mars Observer spacecraft. Scale model radiation patterns were made and analyzed
Van der Waals torque induced by external magnetic fields
We present a method for inducing and controlling van der Waals torques
between two parallel slabs using a constant magnetic field. The torque is
calculated using the Barash theory of dispersive torques. In III-IV
semiconductors such as , the effect of an external magnetic field is to
induce an optical anisotropy, in an otherwise isotropic material, that will in
turn induce a torque.
The calculations of the torque are done in the Voigt configuration, with the
magnetic field parallel to the surface of the slabs. As a case study we
consider a slab made of calcite and a second slab made of . In the
absence of magnetic field there is no torque. As the magnetic field increases,
the optical anisotropy of increases and the torque becomes different
from zero, increasing with the magnetic field. The resulting torque is of the
same order of magnitude as that calculated using permanent anisotropic
materials when the magnetic fields is close to 1 T.Comment: to appear in Journal of Applied Physic
Variations of the Lifshitz-van der Waals force between metals immersed in liquids
We present a theoretical calculation of the Lifshitz-van der Waals force
between two metallic slabs embedded in a fluid, taking into account the change
of the Drude parameters of the metals when in contact with liquids of different
index of refraction. For the three liquids considered in this work, water,
and the change in the Drude parameters of the metal imply a
difference of up to 15% in the determination of the force at short separations.
These variations in the force is bigger for liquids with a higher index of
refraction.Comment: 2 figures, 1 tabl
Reduction of the Casimir force using aerogels
By using silicon oxide based aerogels we show numerically that the Casimir
force can be reduced several orders of magnitude, making its effect negligible
in nanodevices. This decrease in the Casimir force is also present even when
the aerogels are deposited on metallic substrates. To calculate the Casimir
force we model the dielectric function of silicon oxide aerogels using an
effective medium dielectric function such as the Clausius-Mossotti
approximation. The results show that both the porosity of the aerogel and its
thickness can be use as control parameters to reduce the magnitude of the
Casimir force.Comment: to appear J. Appl. Phy
The Rise and Fall of Income Inequality in Mexico: 1989-2010
Inequality in Mexico rose between 1989 and 1994 and declined between 1994 and 2010. We examine the role of market forces (demand and supply of labour by skill), institutional factors (minimum wages and unionization rate), and public policy (cash transfers) in explaining changes in inequality. We apply the ‘re-centered influence function’ method to decompose changes in hourly wages into characteristics and returns. The main driver is changes in returns. Returns rose (1989-1994) due to institutional factors and labor demand. Returns declined (1994-2006) due to changes in supply and --to a lesser extent--in demand; institutional factors were not relevant. Government transfers contributed to the decline in inequality, especially after 2000.inequality, wages, disposable income, labor markets, Mexico
3D MHD simulation of polarized emission in SN 1006
We use three dimensional magnetohydrodynamic (MHD) simulations to model the
supernova remnant SN 1006. From our numerical results, we have carried out a
polarization study, obtaining synthetic maps of the polarized intensity, the
Stokes parameter , and the polar-referenced angle, which can be compared
with observational results. Synthetic maps were computed considering two
possible particle acceleration mechanisms: quasi-parallel and
quasi-perpendicular. The comparison of synthetic maps of the Stokes parameter
maps with observations proves to be a valuable tool to discern
unambiguously which mechanism is taking place in the remnant of SN 1006, giving
strong support to the quasi-parallel model.Comment: 6 pages, 4 figures, accepted by MNRA
- …