257 research outputs found
Solid-State Excitation Laser for Laser-Ultrasonics
The inspection speed of laser-ultrasonics compared with conventional ultrasonic testing is limited by the pulse repetition rate of the excitation laser. The maximum pulse repetition rate reported up to now for CO2-lasers, which are presently used for nearly all systems, is in the range of 400 Hz. In this paper a new approach based on a diode-pumped solid-state laser is discussed, which is currently being developed. This new excitation laser is designed for a repetition rate of 1 kHz and will operate at a mid-IR wavelength of 3.3 m. The higher repeti-tion rate enables a higher inspection speed, whereas the mid-IR wavelength anticipates a better coupling efficiency. The total power for pumping the laser crystals is transported via flexible optical fibres to the compact laser head, thus allowing operation on a robot arm. The laser head consists of a master oscillator feeding several lines of power amplifiers and in-cludes nonlinear optical wavelength conversion by an optical parametric process. It is char-acterized by a modular construction which provides optimal conditions for operation at high average power as well as for easy maintenance. These features will enable building reliable, long-lived, rugged, smart laser ultrasonic systems in futur
First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments
In the tropics, deep convection is the major source of uncertainty in water vapor transport to the upper troposphere and into the stratosphere. Although accurate measurements in this region would be of first order importance to better understand the processes that govern stratospheric water vapor concentrations and trends in the context of a changing climate, they are sparse because of instrumental shortcomings and observational challenges. Therefore, the Falcon research aircraft of the Deutsches Zentrum fĂĽr Luft- und Raumfahrt (DLR) flew a zenith-viewing water vapor differential absorption lidar (DIAL) during the Tropical Convection, Cirrus and Nitrogen Oxides Experiment (TROCCINOX) in 2004 and 2005 in Brazil. The measurements were performed alternatively on three water vapor absorption lines of different strength around 940 nm. These are the first aircraft DIAL measurements in the tropical upper troposphere and in the mid-latitudes lower stratosphere. Sensitivity analyses reveal an accuracy of 5% between altitudes of 8 and 16 km. This is confirmed by intercomparisons with the Fast In-situ Stratospheric Hygrometer (FISH) and the Fluorescent Advanced Stratospheric Hygrometer (FLASH) onboard the Russian M-55 Geophysica research aircraft during five coordinated flights. The average relative differences between FISH and DIAL amount to −3%±8% and between FLASH and DIAL to −8%±14%, negative meaning DIAL is more humid. The average distance between the probed air masses was 129 km. The DIAL is found to have no altitude- or latitude-dependent bias. A comparison with the balloon ascent of a laser absorption spectrometer gives an average difference of 0%±19% at a distance of 75 km. Six tropical DIAL under-flights of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT reveal a mean difference of −8%±49% at an average distance of 315 km. While the comparison with MIPAS is somewhat less significant due to poorer comparison conditions, the agreement with the in-situ hygrometers provides evidence of the excellent quality of FISH, FLASH and DIAL. Most DIAL profiles exhibit a smooth exponential decrease of water vapor mixing ratio in the tropical upper troposphere to lower stratosphere transition. The hygropause with a minimum mixing ratio of 2.5 µmol/mol is found between 15 and 17 km. A high-resolution (2 km horizontal, 0.2 km vertical) DIAL cross section through the anvil outflow of tropical convection shows that the ambient humidity is increased by a factor of three across 100 km
First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments
eta-photoproduction in the resonance energy region
The production in the nucleon resonance energy region is studied
within the unitary coupled-channels effective Lagrangian approach of the
Giessen model. We demonstrate that the second peak recently observed in the
cross section of photoproduction on the neutron at =1.66 GeV
can be explained in terms of coupled-channel effects due to and
resonance excitations
Stable Generalized Finite Element Method (SGFEM)
The Generalized Finite Element Method (GFEM) is a Partition of Unity Method
(PUM), where the trial space of standard Finite Element Method (FEM) is
augmented with non-polynomial shape functions with compact support. These shape
functions, which are also known as the enrichments, mimic the local behavior of
the unknown solution of the underlying variational problem. GFEM has been
successfully used to solve a variety of problems with complicated features and
microstructure. However, the stiffness matrix of GFEM is badly conditioned
(much worse compared to the standard FEM) and there could be a severe loss of
accuracy in the computed solution of the associated linear system. In this
paper, we address this issue and propose a modification of the GFEM, referred
to as the Stable GFEM (SGFEM). We show that the conditioning of the stiffness
matrix of SGFEM is not worse than that of the standard FEM. Moreover, SGFEM is
very robust with respect to the parameters of the enrichments. We show these
features of SGFEM on several examples.Comment: 51 pages, 4 figure
SCIAMACHY validation by aircraft remote measurements: design, execution, and first results of the SCIA-VALUE mission
International audienceFor the first time three different remote sensing instruments ? a sub-millimeter radiometer, a differential optical absorption spectrometer in the UV-visible spectral range, and a lidar ? were deployed aboard DLR's meteorological research aircraft Falcon 20 to validate a large number of SCIAMACHY level 2 and off-line data products such as O3, NO2, N2O, BrO, OClO, H2O, aerosols, and clouds. Within two main validation campaigns of the SCIA-VALUE mission (SCIAMACHY VALidation and Utilization Experiment) extended latitudinal cross-sections stretching from polar regions to the tropics as well as longitudinal cross sections at polar latitudes at about 70° N and the equator have been generated. This contribution gives an overview over the campaigns performed and reports on the observation strategy for achieving the validation goals. We also emphasize the synergetic use of the novel set of aircraft instrumentation and the usefulness of this innovative suite of remote sensing instruments for satellite validation
Study of nucleon resonances with electromagnetic interactions
Recent developments in using electromagnetic meson production reactions to
study the structure of nucleon resonances are reviewed. Possible future works
are discussed.Comment: 25 pages, 19 figure
Evaluation of the polarization observables I^S and I^C in the reaction gamma p --> pi^0 eta p
We evaluate the polarization observables I^S and I^C for the reaction gamma p
--> pi^0 eta p, using a chiral unitary framework developed earlier. The I^S and
I^C observables have been recently measured for the first time by the
CBELSA/TAPS collaboration. The theoretical predictions of I^S and I^C, given
for altogether 18 angle dependent functions, are in good agreement with the
measurements. Also, the asymmetry dSigma/dcos(theta) evaluated here agrees with
the data. We show the importance of the Delta(1700)D33 resonance and its S-wave
decay into eta Delta(1232). The result can be considered as a further
confirmation of the dynamical nature of this resonance. At the highest
energies, deviations of the predictions from the data start to become
noticeable, which leaves room for additional processes and resonances such as a
Delta(1940)D33. We also point out how to further improve the calculation.Comment: Version accepted for publication by the European Physical Journal A,
9 pages, 7 figure
Photoproduction of mesons off nuclei
Recent results for the photoproduction of mesons off nuclei are reviewed.
These experiments have been performed for two major lines of research related
to the properties of the strong interaction. The investigation of nucleon
resonances requires light nuclei as targets for the extraction of the isospin
composition of the electromagnetic excitations. This is done with quasi-free
meson photoproduction off the bound neutron and supplemented with the
measurement of coherent photoproduction reactions, serving as spin and/or
isospin filters. Furthermore, photoproduction from light and heavy nuclei is a
very efficient tool for the study of the interactions of mesons with nuclear
matter and the in-medium properties of hadrons. Experiments are currently
rapidly developing due to the combination of high quality tagged (and
polarized) photon beams with state-of-the-art 4pi detectors and polarized
targets
Utilization of serology for the diagnosis of suspected Lyme borreliosis in Denmark: Survey of patients seen in general practice
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