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The Global ETD Search service is a free service for researchers
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Showing 161 to 165 of 165 (0.036 seconds)Spelling suggestions: "subject:"[een] POLARIMETRY"" "subject:"[enn] POLARIMETRY""
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Development and Optimization of an Integrated Faraday Modulator and Compensator Design for Continuous Polarimetric Glucose MonitoringClarke, Brandon William 22 August 2013 (has links)
No description available.
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| 162 |
Shape-temperature relationship of ice crystals in mixed-phase cloudsbased on observations with polarimetric cloud radar: Shape-temperature relationship of ice crystals in mixed-phase cloudsbased on observations with polarimetric cloud radarMyagkov, Alexander 04 January 2017 (has links)
This thesis is devoted to the experimental quantitative characterization of the shape and orientation distribution of ice particles in clouds. The characterization is based on measured and modeled elevation dependencies of the polarimetric parameters differential reflectivity and correlation coefficient. The polarimetric data is obtained using a newly developed 35-GHz cloud radar MIRA-35 with hybrid polarimetric configuration and scanning capabilities. The full procedure chain of the technical implementation and the realization of the setup of the hybrid-mode cloud radar for the shape determination are presented. This includes the description of phase adjustments in the transmitting paths, the introduction of the general data processing scheme, correction of the data for the differences of amplifications and electrical path lengths in the transmitting and receiving channels, the rotation of the polarization basis by 45°, the correction of antenna effects on polarimetric measurements, the determination of spectral polarimetric variables, and the formulation of a scheme to increase the signal-to-noise ratio. Modeling of the polarimetric variables is based on existing backscattering models assuming the spheroidal representation of cloud scatterers. The parameters retrieved from the model are polarizability ratio and degree of orientation, which can be assigned to certain particle orientations and shapes.
In the thesis the first quantitative estimations of ice particle shape at the top of liquid-topped clouds are presented. Analyzed ice particles were formed in the presence of supercooled water and in the temperature range from -20 °C to -3 °C. The estimation is based on polarizability ratios of ice particles measured by the MIRA-35 with hybrid polarimetric configuration, manufactured by METEK GmbH. For the study, 22 cases observed during the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign were used. Polarizability ratios retrieved for cloud layers with cloud-top temperatures of about -5, -8, -15, and -20 °C were 1.6, 0.9, 0.6, and 0.9, respectively. Such values correspond to prolate, quasi-isotropic, oblate, and quasi-isotropic particles, respectively. Data from a free-fall chamber were used for the comparison. A good agreement of detected shapes with well-known shape{temperature dependencies observed in laboratories was found.:1 Introduction
2 Formation and development of ice particles: Laboratory studies and remote observations
2.1 Heterogeneous ice formation in the atmosphere
2.2 Laboratory investigations of ice crystal development
2.3 Polarimetric radar observations of ice microphysics
2.3.1 Polarimetry in weather radar networks
2.3.2 Polarimetry in cloud radars
2.3.3 Polarization coupling
2.4 Aims and scientific questions
3 Effects of antenna patterns on cloud radar polarimetric measurements
3.1 Measurements of complex antenna patterns
3.1.1 Problem definition
3.1.2 Measurement description
3.1.3 Results of antenna pattern measurements
3.2 Correction of LDR measurements
3.3 Discrimination between insects and clouds
4 Cloud radar MIRA-35 with hybrid mode
4.1 Implementation and phase adjustment
4.2 Processing of the coherency matrix
4.3 Correction of the coherency matrix for differences of channels
4.4 The coherency matrix in the slanted basis
4.5 Correction for the antenna coupling
4.6 Spectral polarimetric variables
4.7 Sensitivity issue
5 Shape and orientation retrieval
5.1 Backscattering model
5.2 Retrieval technique
5.3 Case study
6 Shape-temperature relationship of pristine ice crystals
6.1 Instrumentation and data set
6.2 Examples of the shape retrieval
6.2.1 Case 1: 12 October 2014, 15:00-16:00 UTC
6.2.2 Case 2: 18 October 2014, 01:00-02:00 UTC
6.2.3 Case 3: 20 October 2014, 18:00-19:00 UTC
6.2.4 Case 4: 10 November 2014, 02:00-03:00 UTC
6.2.5 Case 5: 7 November 2014, 20:00-21:00 UTC
6.3 Comparison of shape with laboratory studies
6.4 Orientation of pristine ice crystals
7 Summary and outlook
Bibliography
List of Abbreviations
List of Symbols
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| 163 |
Etude des dynamiques moléculaires sondées par générations d'harmoniques d'ordres élevés / Studies of molecular dynamics probed by High Harmonic GenerationFerré, Amelie 03 October 2014 (has links)
Grâce à ses propriétés (cohérence, brillance, durée), le rayonnement XUV femtoseconde produit par génération d'harmoniques d'ordre élevé est utilisé comme un processus de sonde pour l'étude de dynamiques atomiques et moléculaires, avec une bonne résolution spatiale et temporelle (femtoseconde voire attoseconde). Ainsi, des dynamiques rotationnelles ont été résolues sur des petits systèmes moléculaires (N2, CO2). Les travaux de cette thèse ont consisté à étendre les méthodes de spectroscopie harmoniques et les appliquer à des systèmes moléculaires complexes d'intérêt femtochimique. Parmi elles, nous présenterons la génération d'harmoniques à deux sources, le réseau transitoire d'excitation ou encore la génération d'harmoniques à deux couleurs. Ces techniques nous ont permis de résoudre des dynamiques femtosecondes dans N2O4 et SF6. La HHG est aussi utilisée comme source de rayonnement XUV, en jouant le rôle d'impulsion pompe lors d'expériences de type pompe-sonde. Cette approche a été utilisée pour l'étude du dichroïsme circulaire de photoélectrons de molécules chirales ionisées par un champ XUV harmonique de polarisation quasi circulaire. Nous nous attarderons à détailler la découverte de cette nouvelle source XUV femtoseconde de polarisation quasi circulaire. / High harmonic generation (HHG) spectroscopy has proven to be a promisingtool (like probe in pump-probe experiments) in revealing the atomic and molecular dynamicswith the potential for subangstrom spatial resolution and subfemtosecond temporalresolution. Then, rotational dynamics have been resolved on small molecular systems (N2,CO2). This thesis looks to extending HHG spectroscopy methods to probe the structureand the dynamic of complex molecular systems. We will describe the two sources highharmonic generation, the transient grating of excitation and the two-color high harmonicgeneration. We enable to resolve the femtosecond nuclear dynamics in N2O4 and SF6. HHGis also used like a XUV radiation source, playing the role of pump pulse. This approach hasbeen used for the study of photoelectron circular dichroism. An XUV harmonic field witha quasi-circular polarization ionizes chiral molecules. In this manuscript, we will developthis new femtosecond XUV and quasi circular polarization radiation.
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| 164 |
Kleinskalige Magnetfelder der Sonne und ihr Einfluß auf Chromosphäre, Übergangszone und Korona / Small-Scale Solar Magnetic Fields and their Influence upon Chromosphere, Transition Region and CoronaWilken, Volker 28 June 2001 (has links)
No description available.
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| 165 |
Spektroskopie und Polarimetrie kleinskaliger magnetischer Strukturen der Sonnenoberfläche mit Methoden der Bildrekonstruktion / Spectroscopy and polarimetry of small-scale magnetic structures on the solar surface with image restoration techniquesKoschinsky, Markus 03 May 2001 (has links)
No description available.
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