4,064 research outputs found
A survey of load methodologies for shuttle orbiter payloads
Loads methods currently being used to design shuttle orbiter payloads are summarized. Methods used for the design of payloads launched by expendable launch vehicles are described in historical perspective. Experiences gained from expendable launch vehicle payloads are used to develop methodologies for the space shuttle orbiter payloads. The objectives for the development of a new methodology for the shuttle payloads are to reduce the cost and schedule for the payload load analysis by decoupling the payload analysis from the launch vehicle to the maximum extent possible. Methods are described for payload member load estimation or obtaining upper bounds for dynamic loads, as well as load prediction or calculating actual transient member load time histories
Nondestructive Evaluation of Bulk Stresses in Aluminum and Copper
The effect of applied stress on the temperature dependence of the longitudinal ultrasonic velocity has been investigated in commercial aluminum and copper. Velocities of 10 MHz longitudinal waves as a function of temperature were measured on ten specimens of these metals while they were subjected to external compressive stresses. In all measurements, the velocity increased linearly as the temperature was lowered in the temperature range between 280 and 200 K. Furthermore, the slope of this linear relationship was found to decrease linearly as the amount of applied compressive stress was increased within the elastic limit of the specimen under investigation. The maximum decrease in the temperature dependence of aluminum and copper were respectively 23% which occurred at a stress of 96 MPa, and 6% which occurred at 180 MPa. The linear relationship between the temperature dependence of the ultrasonic velocity and the applied stress was then used to determine the change as a function of distance of the tangential compon.ent of the stresses developed when an aluminum rod was shrunk fit into a slightly smaller hole drilled in an aluminum disc. Excellent agreement was obtained between the computed stress distribution, and that measured using the temperature dependence method
Technique for validating remote sensing products of water quality
Remote sensing of water quality is initiated as an additional part of the on going activities of the EAGLE2006 project.
Within this context intensive in-situ and airborne measurements campaigns were carried out over the Wolderwijd and
Veluwemeer natural waters. However, in-situ measurements and image acquisitions were not simultaneous. This poses
some constraints on validating air/space-borne remote sensing products of water quality. Nevertheless, the detailed insitu
measurements and hydro-optical model simulations provide a bench mark for validating remote sensing products.
That is realized through developing a stochastic technique to quantify the uncertainties on the retrieved aquatic inherent
optical properties (IOP).
The output of the proposed technique is applied to validate remote sensing products of water quality. In this processing
phase, simulations of the radiative transfer in the coupled atmosphere-water system are performed to generate spectra
at-sensor-level. The upper and the lower boundaries of perturbations, around each recorded spectrum, are then modelled
as function of residuals between simulated and measured spectra. The perturbations are parameterized as a function of
model approximations/inversion, sensor-noise and atmospheric residual signal. All error sources are treated as being of
stochastic nature. Three scenarios are considered: spectrally correlated (i.e. wavelength dependent) perturbations,
spectrally uncorrelated perturbations and a mixed scenario of the previous two with equal probability of occurrence.
Uncertainties on the retrieved IOP are quantified with the relative contribution of each perturbation component to the
total error budget of the IOP.
This technique can be used to validate earth observation products of water quality in remote areas where few or no in–
situ measurements are available
Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure
We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250°C). Using extended x-rayabsorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations ≤0.05 at.%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations.We acknowledge the support from the Research Foundation
Flanders, the epi-team from imec, the KU Leuven
GOA 09/06 project, the IUAP program P6/42 and the Australian
Research Council. S.C. acknowledges support from
OCAS NV by an OCAS-endowed chair at Ghent University
Photoinduced Fluorescence from the Perylene Cation Isolated in Ne and Ar Matrices
The fluorescence and fluorescence excitation spectra of the perylene cation isolated in neon and argon matrices are reported. This is the first report of the fluorescence spectrum of a polycyclic aromatic hydrocarbon ion in any phase
The 2.5-5.0 micron spectra of Io: Evidence for H2S and H2O frozen in SO2
The techniques of low temperature spectroscopy are applied to identify the constituents of the ices covering the surface of Io, a satellite of Jupiter. Infrared spectra of Io in the 4000-2000 cm exp -1 region, including new observational data, are analyzed using laboratory studies of plausible surface ices
Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure
Visible photodissociation spectroscopy of PAH cations and derivatives in the PIRENEA experiment
The electronic spectra of gas-phase cationic polycyclic aromatic hydrocarbons
(PAHs), trapped in the Fourier Transform Ion Cyclotron Resonance cell of the
PIRENEA experiment, have been measured by multiphoton dissociation spectroscopy
in the 430-480 nm spectral range using the radiation of a mid-band optical
parametric oscillator laser. We present here the spectra recorded for different
species of increasing size, namely the pyrene cation (C16H10+), the
1-methylpyrene cation (CH3-C16H9+), the coronene cation (C24H12+), and its
dehydrogenated derivative C24H10+. The experimental results are interpreted
with the help of time-dependent density functional theory calculations and
analysed using spectral information on the same species obtained from matrix
isolation spectroscopy data. A kinetic Monte Carlo code has also been used, in
the case of pyrene and coronene cations, to estimate the absorption
cross-sections of the measured electronic transitions. Gas-phase spectra of
highly reactive species such as dehydrogenated PAH cations are reported for the
first time
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