7,893 research outputs found
The horizontal and vertical semi-diameters of the Sun observed at the Cape of Good Hope (1834 - 1887) and Paris (1837 - 1906): A report on work in progress
Cape and Paris meridian observations of the solar limbs which permit an estimate to be made of the solar semi-diameter were surveyed, sampled, and compared with Greenwich and U.S. Naval Observatory observations. Significant systematic errors were found in the Paris work and have been correlated with changes of instruments and observers. Results from the Cape series indicate that work should continue on the compilation of data from Cape observations of the Sun
Bounds on the entanglement of two-qutrit systems from fixed marginals
We discuss the problem of characterizing upper bounds on entanglement in a bipartite quantum system when only the reduced density matrices (marginals) are known. In particular, starting from the known two-qubit case, we propose a family of candidates for maximally entangled mixed states with respect to fixed marginals for two qutrits. These states are extremal in the convex set of two-qutrit states with fixed marginals. Moreover, it is shown that they are always quasidistillable. As a by-product we prove that any maximally correlated state that is quasidistillable must be pure. Our observations for two qutrits are supported by numerical analysis
Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy
The article describes an experimental method that allows to estimate the
inhomogeneous and homogeneous linewidths of the photoluminescence band of a
point defect in an amorphous solid. We performed low temperature time-resolved
luminescence measurements on two defects chosen as model systems for our
analysis: extrinsic Oxygen Deficient Centers (ODC(II)) in amorphous silica and
F+ 3 centers in crystalline Lithium Fluoride. Measurements evidence that only
defects embedded in the amorphous matrix feature a dependence of the radiative
decay lifetime on the emission energy and a time dependence of the first moment
of the emission band. A theoretical model is developed to link these properties
to the structural disorder typical of amorphous solids. Specifically, the
observations on ODC(II) are interpreted by introducing a gaussian statistical
distribution of the zero phonon line energy position. Comparison with the
results obtained on F+ 3 crystalline defects strongly confirms the validity of
the model. By analyzing experimental data within this frame, we obtain separate
estimations of the homogenous and inhomogeneous contributions to the measured
total linewidth of ODC(II), which results to be mostly inhomogeneous.Comment: 8 pages, 4 figure
Patterning molecular scale paramagnets at Au Surface: A root to Magneto-Molecular-Electronics
Few examples of the exploitation of molecular magnetic properties in
molecular electronics are known to date. Here we propose the realization of
Self assembled monolayers (SAM) of a particular stable organic radical. This
radical is meant to be used as a standard molecule on which to prove the
validity of a single spin reading procedure known as ESR-STM. We also discuss a
range of possible applications, further than ESR-STM, of magnetic monolayers of
simple purely organic magnetic molecule.Comment: This preprint is currently partially under revisio
Time-dependent Maxwell field operators and field energy density for an atom near a conducting wall
We consider the time evolution of the electric and magnetic field operators
for a two-level atom, interacting with the electromagnetic field, placed near
an infinite perfectly conducting wall. We solve iteratively the Heisenberg
equations for the field operators and obtain the electric and magnetic energy
density operators around the atom (valid for any initial state). Then we
explicitly evaluate them for an initial state with the atom in its bare ground
state and the field in the vacuum state. We show that the results can be
physically interpreted as the superposition of the fields propagating directly
from the atom and the fields reflected on the wall. Relativistic causality in
the field propagation is discussed. Finally we apply these results to the
calculation of the dynamical Casimir-Polder interaction energy in the far zone
between two atoms when a boundary condition such as a conducting wall is
present. Magnetic contributions to the interatomic Casimir-Polder interaction
in the presence of the wall are also considered. We show that, in the limit of
large times, the known results of the stationary case are recovered.Comment: 11 page
Performance Validation of Version 152.0 ANSER Control Laws for the F-18 HARV
The Actuated Nose Strakes for Enhanced Rolling (ANSER) Control Laws were modified as a result of Phase 3 F/A-18 High Alpha Research Vehicle (HARV) flight testing. The control law modifications for the next software release were designated version 152.0. The Ada implementation was tested in the Hardware-In-the-Loop (HIL) simulation and results were compared to those obtained with the NASA Langley batch Fortran implementation of the control laws which are considered the 'truth model.' This report documents the performance validation test results between these implementations for ANSER control law version 152.0
Performance validation of the ANSER control laws for the F-18 HARV
The ANSER control laws were implemented in Ada by NASA Dryden for flight test on the High Alpha Research Vehicle (HARV). The Ada implementation was tested in the hardware-in-the-loop (HIL) simulation, and results were compared to those obtained with the NASA Langley batch Fortran implementation of the control laws which are considered the 'truth model.' This report documents the performance validation test results between these implementations. This report contains the ANSER performance validation test plan, HIL versus batch time-history comparisons, simulation scripts used to generate checkcases, and detailed analysis of discrepancies discovered during testing
Using the HARV simulation aerodynamic model to determine forebody strake aerodynamic coefficients from flight data
The method described in this report is intended to present an overview of a process developed to extract the forebody aerodynamic increments from flight tests. The process to determine the aerodynamic increments (rolling pitching, and yawing moments, Cl, Cm, Cn, respectively) for the forebody strake controllers added to the F/A - 18 High Alpha Research Vehicle (HARV) aircraft was developed to validate the forebody strake aerodynamic model used in simulation
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