93,440 research outputs found
The Geoscience Laser Altimetry/Ranging System (GLARS)
The Geoscience Laser Altimetry Ranging System (GLARS) is a highly precise distance measurement system to be used for making extremely accurate geodetic observations from a space platform. It combines the attributes of a pointable laser ranging system making observations to cube corner retroreflectors placed on the ground with those of a nadir looking laser altimeter making height observations to ground, ice sheet, and oceanic surfaces. In the ranging mode, centimeter-level precise baseline and station coordinate determinations will be made on grids consisting of 100 to 200 targets separated by distances from a few tens of kilometers to about 1000 km. These measurements will be used for studies of seismic zone crustal deformations and tectonic plate motions. Ranging measurements will also be made to a coarser, but globally distributed array of retroreflectors for both precise geodetic and orbit determination applications. In the altimetric mode, relative height determinations will be obtained with approximately decimeter vertical precision and 70 to 100 meter horizontal resolution. The height data will be used to study surface topography and roughness, ice sheet and lava flow thickness, and ocean dynamics. Waveform digitization will provide a measure of the vertical extent of topography within each footprint. The planned Earth Observing System is an attractive candidate platform for GLARS since the GLAR data can be used both for direct analyses and for highly precise orbit determination needed in the reduction of data from other sensors on the multi-instrument platform. (1064, 532, and 355 nm)Nd:YAG laser meets the performance specifications for the system
Extrinsic models for the dielectric response of CaCu{3}Ti{4}O{12}
The large, temperature-independent, low-frequency dielectric constant
recently observed in single-crystal CaCu{3}Ti{4}O{12} is most plausibly
interpreted as arising from spatial inhomogenities of its local dielectric
response. Probable sources of inhomogeneity are the various domain boundaries
endemic in such materials: twin, Ca-ordering, and antiphase boundaries. The
material in and neighboring such boundaries can be insulating or conducting. We
construct a decision tree for the resulting six possible morphologies, and
derive or present expressions for the dielectric constant for models of each
morphology. We conclude that all six morphologies can yield dielectric behavior
consistent with observations and suggest further experiments to distinguish
among them.Comment: 9 pages, with 1 postscript figure embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/mc_ext/index.htm
Optimal Iris Fuzzy Sketches
Fuzzy sketches, introduced as a link between biometry and cryptography, are a
way of handling biometric data matching as an error correction issue. We focus
here on iris biometrics and look for the best error-correcting code in that
respect. We show that two-dimensional iterative min-sum decoding leads to
results near the theoretical limits. In particular, we experiment our
techniques on the Iris Challenge Evaluation (ICE) database and validate our
findings.Comment: 9 pages. Submitted to the IEEE Conference on Biometrics: Theory,
Applications and Systems, 2007 Washington D
Tree-level electron-photon interactions in graphene
Graphene's low-energy electronic excitations obey a 2+1 dimensional Dirac
Hamiltonian. After extending this Hamiltonian to include interactions with a
quantized electromagnetic field, we calculate the amplitude associated with the
simplest, tree-level Feynman diagram: the vertex connecting a photon with two
electrons. This amplitude leads to analytic expressions for the 3D angular
dependence of photon emission, the photon-mediated electron-hole recombination
rate, and corrections to graphene's opacity and dynamic
conductivity for situations away from thermal equilibrium, as
would occur in a graphene laser. We find that Ohmic dissipation in perfect
graphene can be attributed to spontaneous emission.Comment: 5 pages, 3 figure
Solar wind radiation damage effects in lunar material
The research on solar wind radiation damage and other effects in lunar samples which was conducted to understand the optical properties of lunar materials is reported. Papers presented include: solar radiation effects in lunar samples, albedo of the moon, radiation effects in lunar crystalline rocks, valence states of 3rd transition elements in Apollo 11 and 12 rocks, and trace ferric iron in lunar and meteoritic titanaugites
Improving the Functional Control of Aged Ferroelectrics using Insights from Atomistic Modelling
We provide a fundamental insight into the microscopic mechanisms of the
ageing processes. Using large scale molecular dynamics simulations of the
prototypical ferroelectric material PbTiO3, we demonstrate that the
experimentally observed ageing phenomena can be reproduced from intrinsic
interactions of defect-dipoles related to dopant-vacancy associates, even in
the absence of extrinsic effects. We show that variation of the dopant
concentration modifies the material's hysteretic response. We identify a
universal method to reduce loss and tune the electromechanical properties of
inexpensive ceramics for efficient technologies.Comment: 6 pages, 3 figure
Dressed States of a two component Bose-Einstein Condensate
A condensate with two internal states coupled by external electromagnetic
radiation, is described by coupled Gross Pitaevskii equations, whose
eigenstates are analogous to the dressed states of quantum optics. We solve for
these eigenstates numerically in the case of one spatial dimension, and explore
their properties as a function of system parameters. In contrast to the quantum
optical case, the condensate dressed states exhibit spatial behaviour which
depends on the system parameters, and can be manipulated by changing the cw
external field.Comment: 6 pages, including 6 figures. This paper was presented at ACOLS98,
and is submitted to a special issue of J. Opt.
RFID Key Establishment Against Active Adversaries
We present a method to strengthen a very low cost solution for key agreement
with a RFID device.
Starting from a work which exploits the inherent noise on the communication
link to establish a key by public discussion, we show how to protect this
agreement against active adversaries. For that purpose, we unravel integrity
-codes suggested by Cagalj et al.
No preliminary key distribution is required.Comment: This work was presented at the First IEEE Workshop on Information
Forensics and Security (WIFS'09) (update including minor remarks and
references to match the presented version
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