1,731 research outputs found
Tungsten nuclear rocket, phase II, part 1 Final report, Jan. 16 - Jun. 15, 1966
Critical experiments and nuclear analyses of tungsten water moderated nuclear rocket reacto
RAFCON: a Graphical Tool for Task Programming and Mission Control
There are many application fields for robotic systems including service
robotics, search and rescue missions, industry and space robotics. As the
scenarios in these areas grow more and more complex, there is a high demand for
powerful tools to efficiently program heterogeneous robotic systems. Therefore,
we created RAFCON, a graphical tool to develop robotic tasks and to be used for
mission control by remotely monitoring the execution of the tasks. To define
the tasks, we use state machines which support hierarchies and concurrency.
Together with a library concept, even complex scenarios can be handled
gracefully. RAFCON supports sophisticated debugging functionality and tightly
integrates error handling and recovery mechanisms. A GUI with a powerful state
machine editor makes intuitive, visual programming and fast prototyping
possible. We demonstrated the capabilities of our tool in the SpaceBotCamp
national robotic competition, in which our mobile robot solved all exploration
and assembly challenges fully autonomously. It is therefore also a promising
tool for various RoboCup leagues.Comment: 8 pages, 5 figure
Observation of simultaneous fast and slow light
We present a microresonator-based system capable of simultaneously producing
time-advanced and time-delayed pulses. The effect is based on the combination
of a sharp spectral feature with two orthogonally-polarized propagating
waveguide modes. We include an experimental proof-of-concept implementation
using a silica microsphere coupled to a tapered optical fiber and use a
time-domain picture to interpret the observed delays. We also discuss potential
applications for future all-optical networks.Comment: 6 pages, 5 figure
Thermalization via Heat Radiation of an Individual Object Thinner than the Thermal Wavelength
Modeling and investigating the thermalization of microscopic objects with
arbitrary shape from first principles is of fundamental interest and may lead
to technical applications. Here, we study, over a large temperature range, the
thermalization dynamics due to far-field heat radiation of an individual,
deterministically produced silica fiber with a predetermined shape and a
diameter smaller than the thermal wavelength. The temperature change of the
subwavelength-diameter fiber is determined through a measurement of its optical
path length in conjunction with an ab initio thermodynamic model of the fiber
structure. Our results show excellent agreement with a theoretical model that
considers heat radiation as a volumetric effect and takes the emitter shape and
size relative to the emission wavelength into account
Electromagnetic multipole theory for optical nanomaterials
Optical properties of natural or designed materials are determined by the
electromagnetic multipole moments that light can excite in the constituent
particles. In this work we present an approach to calculate the multipole
excitations in arbitrary arrays of nanoscatterers in a dielectric host medium.
We introduce a simple and illustrative multipole decomposition of the electric
currents excited in the scatterers and link this decomposition to the classical
multipole expansion of the scattered field. In particular, we find that
completely different multipoles can produce identical scattered fields. The
presented multipole theory can be used as a basis for the design and
characterization of optical nanomaterials
Divergence of Dipole Sums and the Nature of Non-Lorentzian Exponentially Narrow Resonances in One-Dimensional Periodic Arrays of Nanospheres
Origin and properties of non-Lorentzian spectral lines in linear chains of
nanospheres are discussed. The lines are shown to be super-exponentially narrow
with the characteristic width proportional to exp[-C(h/a)^3] where C is a
numerical constant, h the spacing between the nanospheres in the chain and a
the sphere radius. The fine structure of these spectral lines is also
investigated.Comment: 9 pages, 4 figure
Bound whispering gallery modes in circular arrays of dielectric spherical particles
Low-dimensional ordered arrays of optical elements can possess bound modes
having an extremely high quality factor. Typically, these arrays consist of
metal elements which have significantly high light absorption thus restricting
performance. In this paper we address the following question: can bound modes
be formed in dielectric systems where the absorption of light is negligible?
Our investigation of circular arrays of spherical particles shows that (1) high
quality modes in an array of 10 or more particles can be attained at least for
a refractive index , so optical materials like TiO or GaAs can
be used; (2) the most bound modes have nearly transverse polarization
perpendicular to the circular plane; (3) in a particularly interesting case of
TiO particles (rutile phase, ), the quality factor of the most
bound mode increases almost by an order of magnitude with the addition of 10
extra particles, while for particles made of GaAs the quality factor increases
by almost two orders of magnitude with the addition of ten extra particles. We
hope that this preliminary study will stimulate experimental investigations of
bound modes in low-dimensional arrays of dielectric particles.Comment: Submitted to Physical Review
Mie scattering by a charged dielectric particle
We study for a dielectric particle the effect of surplus electrons on the
anomalous scattering of light arising from the transverse optical phonon
resonance in the particle's dielectric constant. Excess electrons affect the
polarizability of the particle by their phonon-limited conductivity, either in
a surface layer (for negative electron affinity) or the conduction band (for
positive electron affinity). We demonstrate that surplus electrons shift an
extinction resonance in the infrared. This offers an optical way to measure the
charge of the particle and thus to use it in a plasma as a minimally invasive
electric probe.Comment: 5 pages, 5 figures, accepted manuscrip
Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles
We propose angle-resolved photoelectron spectroscopy of aerosol particles as
an alternative way to determine the electron mean free path of low energy
electrons in solid and liquid materials. The mean free path is obtained from
fits of simulated photoemission images to experimental ones over a broad range
of different aerosol particle sizes. The principal advantage of the aerosol
approach is twofold. Firstly, aerosol photoemission studies can be performed
for many different materials, including liquids. Secondly, the size-dependent
anisotropy of the photoelectrons can be exploited in addition to size-dependent
changes in their kinetic energy. These finite size effects depend in different
ways on the mean free path and thus provide more information on the mean free
path than corresponding liquid jet, thin film, or bulk data. The present
contribution is a proof of principle employing a simple model for the
photoemission of electrons and preliminary experimental data for potassium
chloride aerosol particles
Dynamical Theory of Artificial Optical Magnetism Produced by Rings of Plasmonic Nanoparticles
We present a detailed analytical theory for the plasmonic nanoring
configuration first proposed in [A. Alu, A. Salandrino, N. Engheta, Opt. Expr.
14, 1557 (2006)], which is shown to provide negative magnetic permeability and
negative index of refraction at infrared and optical frequencies. We show
analytically how the nanoring configuration may provide superior performance
when compared to some other solutions for optical negative index materials,
offering a more 'pure' magnetic response at these high frequencies, which is
necessary for lowering the effects of radiation losses and absorption.
Sensitivity to losses and the bandwidth of operation of this magnetic inclusion
are also investigated in details and compared with other available setups.Comment: 34 pages, 3 figure
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