6,140 research outputs found
Reversal of ferroelectric domains by ultrashort optical pulses
The response of a soft-phonon ferroelectric material subjected to a high-intensity optical pulse of duration much shorter than the period of the phonon is modeled using a classical, finite-temperature simulation. It is found that complete, permanent reversal of the orientation of the ferroelectric domains may occur even when the energy per atom imparted by the light pulse is much less than the average thermal energy. The result raises the possibility of using the effect to create optical switches or data storage media with switching times less than 10 psec
The Role of Reading Specialist in Developing IEP\u27s (Individual Education Programs)
Everywhere, supervisors, teachers and education specialists are busily engaged in inservice meetings and workshops in an effort to become familiar with writing, implementing and revising Individual Education Programs (IEP\u27s) for children eligible or enrolled in a Special Education Program. The provision in The Education For All Handicapped Children Act, Public Law 94-142, requiring an IEP for each handicapped child has caused a great deal of activity and development in the field of Special Education
Near-infrared spatially resolved spectroscopy of (136108) Haumea's multiple system
The transneptunian region of the solar system is populated by a wide variety
of icy bodies showing great diversity. The dwarf planet (136108) Haumea is
among the largest TNOs and displays a highly elongated shape and hosts two
moons, covered with crystalline water ice like Hamuea. Haumea is also the
largest member of the sole TNO family known to date. A catastrophic collision
is likely responsible for its unique characteristics. We report here on the
analysis of a new set of observations of Haumea obtained with SINFONI at the
ESO VLT. Combined with previous data, and using light-curve measurements in the
optical and far infrared, we carry out a rotationally resolved spectroscopic
study of the surface of Haumea. We describe the physical characteristics of the
crystalline water ice present on the surface of Haumea for both regions, in and
out of the Dark Red Spot (DRS), and analyze the differences obtained for each
individual spectrum. The presence of crystalline water ice is confirmed over
more than half of the surface of Haumea. Our measurements of the average
spectral slope confirm the redder characteristic of the spot region. Detailed
analysis of the crystalline water-ice absorption bands do not show significant
differences between the DRS and the remaining part of the surface. We also
present the results of applying Hapke modeling to our data set. The best
spectral fit is obtained with a mixture of crystalline water ice (grain sizes
smaller than 60 micron) with a few percent of amorphous carbon. Improvements to
the fit are obtained by adding ~10% of amorphous water ice. Additionally, we
used the IFU-reconstructed images to measure the relative astrometric position
of the largest satellite Hi`iaka and determine its orbital elements. An orbital
solution was computed with our genetic-based algorithm GENOID and our results
are in full agreement with recent results.Comment: Accepted for publication in A&
Stimulated-emission-induced enhancement of the decay rate of longitudinal optical phonons in IIIâV semiconductors
We explore the feasibility of reducing the lifetime of longitudinal optical phonons in InP by injecting coherent longitudinal acoustic modes of frequency given by the difference between those of the longitudinal and transverse optical phonons. Calculations show that a ten-fold reduction in the lifetime can be attained using a 40 mW acoustic source. The increase in the phonon decay should reduce the scattering rate of hot electrons in fast devices. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70344/2/APPLAB-80-16-2901-1.pd
Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media
Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal
the exis-tence of an unusually long-lived acoustic mode at ~ 0.6 THz, which
couples weakly to the environment by evading the sample boundaries. Classical
as well as quantum states that steer clear of surfaces are generally shown to
occur in the spectrum of periodic struc-tures, for most boundary conditions.
These surface-avoiding waves are associated with frequencies outside forbidden
gaps and wavevectors in the vicinity of the center and edge of the Brillouin
zone. Possible consequences for surface science and resonant cavity
ap-plications are discussed.Comment: 16 pages, 3 figure
Effect of Fibonacci Modulation On Superconductivity
We have studied finite-sized single band models with short range pairing
interactions between electrons in presence of diagonal Fibonacci modulation in
one dimension. Two models, namely the attractive Hubbard model and the
Penson-Kolb model, have been investigated at half-filling at zero temperature
by solving the Bogoliubov-de Gennes equations in real space within a mean field
approximation. The competition between ``disorder'' and the pairing interaction
leads to a suppression of superconductivity (of usual pairs with zero
centre-of-mass momenta) in the strong-coupling limit while an enhancement of
the pairing correlation is observed in the weak-coupling regime for both the
models. However, the dissimilarity of the pairing mechanisms in these two
models brings about notable difference in the results. The extent to which the
bond ordered wave and the -paired (of pairs with centre-of-mass momenta =
) phases of the Penson-Kolb model are affected by the disorder has also
been studied in the present calculation. Some finite size effects are also
identified.Comment: 14 pages, 13 figure
Three-dimensional advective--diffusive boundary layers in open channels with parallel and inclined walls
We study the steady laminar advective transport of a diffusive passive scalar
released at the base of narrow three-dimensional longitudinal open channels
with non-absorbing side walls and rectangular or truncated-wedge-shaped
cross-sections. The scalar field in the advective--diffusive boundary layer at
the base of the channels is fundamentally three-dimensional in the general
case, owing to a three-dimensional velocity field and differing boundary
conditions at the side walls. We utilise three-dimensional numerical
simulations and asymptotic analysis to understand how this inherent
three-dimensionality influences the advective-diffusive transport as described
by the normalised average flux, the Sherwood or Nusselt numbers for mass
or heat transfer, respectively. We show that is well approximated by an
appropriately formulated two-dimensional calculation, even when the boundary
layer structure is itself far from two-dimensional. This important result can
significantly simplify the modelling of many laminar advection--diffusion
scalar transfer problems: the cleaning or decontamination of confined channels,
or transport processes in chemical or biological microfluidic devices
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