628 research outputs found
Applications of ISES for vegetation and land use
Remote sensing relative to applications involving vegetation cover and land use is reviewed to consider the potential benefits to the Earth Observing System (Eos) of a proposed Information Sciences Experiment System (ISES). The ISES concept has been proposed as an onboard experiment and computational resource to support advanced experiments and demonstrations in the information and earth sciences. Embedded in the concept is potential for relieving the data glut problem, enhancing capabilities to meet real-time needs of data users and in-situ researchers, and introducing emerging technology to Eos as the technology matures. These potential benefits are examined in the context of state-of-the-art research activities in image/data processing and management
Numerical aperture limits on efficient ball lens coupling of laser diodes to single-mode fibers with defocus to balance spherical aberration
The potential capabilities and limitations of single ball lenses for coupling laser diode radiation to single-mode optical fibers have been analyzed; parameters important to optical communications were specifically considered. These parameters included coupling efficiency, effective numerical apertures, lens radius, lens refractive index, wavelength, magnification in imaging the laser diode on the fiber, and defocus to counterbalance spherical aberration of the lens. Limiting numerical apertures in object and image space were determined under the constraint that the lens perform to the Rayleigh criterion of 0.25-wavelength (Strehl ratio = 0.80). The spherical aberration-defocus balance to provide an optical path difference of 0.25 wavelength units was shown to define a constant coupling efficiency (i.e., 0.56). The relative numerical aperture capabilities of the ball lens were determined for a set of wavelengths and associated fiber-core diameters of particular interest for single-mode fiber-optic communication. The results support general continuing efforts in the optical fiber communications industry to improve coupling links within such systems with emphasis on manufacturing simplicity, system packaging flexibility, relaxation of assembly alignment tolerances, cost reduction of opto-electronic components and long term reliability and stability
The prismatic Sigma 3 (10-10) twin bounday in alpha-Al2O3 investigated by density functional theory and transmission electron microscopy
The microscopic structure of a prismatic twin
boundary in \aal2o3 is characterized theoretically by ab-initio
local-density-functional theory, and experimentally by spatial-resolution
electron energy-loss spectroscopy in a scanning transmission electron
microscope (STEM), measuring energy-loss near-edge structures (ELNES) of the
oxygen -ionization edge. Theoretically, two distinct microscopic variants
for this twin interface with low interface energies are derived and analysed.
Experimentally, it is demonstrated that the spatial and energetical resolutions
of present high-performance STEM instruments are insufficient to discriminate
the subtle differences of the two proposed interface variants. It is predicted
that for the currently developed next generation of analytical electron
microscopes the prismatic twin interface will provide a promising benchmark
case to demonstrate the achievement of ELNES with spatial resolution of
individual atom columns
"Free" Constituent Quarks and Dilepton Production in Heavy Ion Collisions
An approach is suggested, invoking vitally the notion of constituent massive
quarks (valons) which can survive and propagate rather than hadrons (except of
pions) within the hot and dense matter formed below the chiral transition
temperature in course of the heavy ion collisions at high energies. This
approach is shown to be quite good for description of the experimentally
observed excess in dilepton yield at masses 250 MeV < M < 700 MeV over the
prompt resonance decay mechanism (CERES cocktail) predictions. In certain
aspects, it looks to be even more successful, than the conventional approaches:
it seems to match the data somewhat better at dilepton masses before the
two-pion threshold and before the rho-meson peak as well as at higher dilepton
masses (beyond the phi-meson one). The approach implies no specific assumptions
on the equation of state (EOS) or peculiarities of phase transitions in the
expanding nuclear matter.Comment: 13 pages, 3 PNG figures. submitted to Sov. Nucl. Phy
In situ modification of nanostructure configuration through the manipulation of hydrogen bonded amphiphile self-association
Herein, we report the synthesis of a novel amphiphilic salt containing a number of hydrogen bond donating (HBD) and accepting (HBA) functionalities. This amphiphile has been shown to self-associate via hydrogen bond formation in a DMSO solution, confirmed through a combination of NMR, UV-Vis and dynamic light scattering and supported by X-ray diffraction studies. The combination of different HBD and HBA functionalities within the amphiphile structure gives rise to a variety of competitive, self-associative hydrogen bonding modes that result in the formation of ‘frustrated’ hydrogen bonded nanostructures. These nanostructures can be altered through the addition of competitive HBD arrays and/or HBA anionic guests. The addition of these competitive species modifies the type of self-associative hydrogen bonding modes present between the amphiphilic molecules, triggering the in situ formation of novel hydrogen bonded nanostructures
Lattice Distortions Around a Tl+ Impurity in NaI:Tl+ and CsI:Tl+ Scintillators. An Ab Initio Study Involving Large Active Clusters
Ab initio Perturbed Ion cluster-in-the-lattice calculations of the impurity
centers NaI:Tl+ and CsI:Tl+ are pressented. We study several active clusters of
increasing complexity and show that the lattice relaxation around the Tl+
impurity implies the concerted movement of several shells of neighbors. The
results also reveal the importance of considering a set of ions that can
respond to the geometrical displacements of the inner shells by adapting
selfconsistently their wave functions. Comparison with other calculations
involving comparatively small active clusters serves to assert the significance
of our conclusions. Contact with experiment is made by calculating absorption
energies. These are in excellent agreement with the experimental data for the
most realistic active clusters considered.Comment: 7 pages plus 6 postscript figures, LaTeX. Submmited to Phys, Rev.
Dielectron Cross Section Measurements in Nucleus-Nucleus Reactions at 1.0 A GeV
We present measured dielectron production cross sections for Ca+Ca, C+C,
He+Ca, and d+Ca reactions at 1.0 A GeV. Statistical uncertainties and
systematic effects are smaller than in previous DLS nucleus-nucleus data. For
pair mass < 0.35 GeV/c2 : 1) the Ca+Ca cross section is larger than the
previous DLS measurement and current model results, 2) the mass spectra suggest
large contributions from pi0 and eta Dalitz decays, and 3) dsigma/dM is
proportional to ApAt. For M > 0.5 GeV/c2 the Ca+Ca to C+C cross section ratio
is significantly larger than the ratio of ApAt values.Comment: Submitted to Physical Review Letters. Further analysis information
will be posted on our web pages -- http://macdls.lbl.gov Figure 1 has been
redrawn to make more legible. Text modified to support redrawn figur
The Sample Handling System for the Mars Icebreaker Life Mission: from Dirt to Data
The Mars icebreaker life mission will search for subsurface life on mars. It consists of three payload elements: a drill to retrieve soil samples from approx. 1 meter below the surface, a robotic sample handling system to deliver the sample from the drill to the instruments, and the instruments themselves. This paper will discuss the robotic sample handling system
Ab Initio Calculation of the Lattice Distortions induced by Substitutional Ag- and Cu- Impurities in Alkali Halide Crystals
An ab initio study of the doping of alkali halide crystals (AX: A = Li, Na,
K, Rb; X = F, Cl, Br, I) by ns2 anions (Ag- and Cu-) is presented. Large active
clusters with 179 ions embedded in the surrounding crystalline lattice are
considered in order to describe properly the lattice relaxation induced by the
introduction of substitutional impurities. In all the cases considered, the
lattice distortions imply the concerted movement of several shells of
neighbors. The shell displacements are smaller for the smaller anion Cu-, as
expected. The study of the family of rock-salt alkali halides (excepting CsF)
allows us to extract trends that might be useful at a predictive level in the
study of other impurity systems. Those trends are presented and discussed in
terms of simple geometric arguments.Comment: LaTeX file. 8 pages, 3 EPS pictures. New version contains
calculations of the energy of formation of the defects with model clusters of
different size
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