The standard model of the thermal and chemical structure of cratons has been scrutinized in recent years as additional data have been collected. Recent seismological and petrological studies indicate that the notion of cratonic lithosphere as a thick thermal boundary layer with a very depleted and dehydrated composition may be too simplistic and does not fully explain all aspects of the seismological and petrological observations. We hypothesized that the cratonic lithosphere may be more complicated and designed an experiment to investigate its thermal, chemical, and mineralogical properties using a global database of fundamental mode Rayleigh surface waves. To test this hypothesis, the phase velocities of Rayleigh wave that travel paths primarily over cratons were selected. A 1-D global craton phase velocity profile was generated from these observations and compared to predicted phase-velocity curves using two different forward modeling techniques. With the first approach, profiles of shear velocity were generated based on educated guesses of upper mantle temperatures using geotherms. With the second approach, profiles of shear velocity were generated using random permutations about 1-D global model STW105. In total 5,625 geotherm and 80,000 random 1-D forward models were generated for comparison. Each shear velocity model was converted to phase velocity and compared to the observed range of cratonic phase velocities, defined as within one standard deviation of the mean. This method was able to constrain shear velocity in cratons relatively well though the 1-D profiles deviate at depths shallower than 100 km. Shear velocity is faster than PREM/STW105 to depths greater than 200 km with constantly increasing velocity with depth in the random model and a low velocity layer at 100-150 km.

Clinical ultrasound imaging techniques can be greatly improved by the use of ultrasound contrast agents (UCAs). While microbubbles (MBs) without shell are unstable and cannot be used for practical applications,a shell produced from biocompatible polyvinylalcohol (PVA) significantly improves chemical versatility and stability. The oscillation characteristics of a UCA are strongly dependent on concentration, applied pressure and viscoelastic parameters of the shell. Modifications in the shell as incorporation of antibodies or targeted molecules affect the bubble oscillation and resonance frequency of the MB suspension. In this presented work a tool for systematic characterization of UCAs is developed. Linear acoustic behaviour of PVA shelled MBs is examined. The acoustic driving pressure is kept below 100 kPa. The MB concentration is 1·10^{6} ml^{-1}. Attenuation and phase velocity profiles of ultrasound waves propagating through the UCA are measured using six narrow-band single crystal transducers that cover a frequency range between 1 and 15 MHz. The oscillation of a single bubble is modeled as a linear oscillator adapting HOFF’s model suitable for allshell thicknesses. The suspension is modeled through superposition of single bubbles. Knowing all parameters the resonance frequency of a MB suspension can be predicted. The model is fitted to experimental data to determine the viscoelastic shell parameters. The shell thickness is challenging to determine exactly and assumed to be either proportional to the outer shell radius or constant. Assuming a proportional shell thickness the calculated resulting shell parameters were shear modulus G_s = 14.5 MPa, shear viscosity η_s = 0.322 Pa·s and shell thickness d_s = 16 % of the outer radius. When instead assuming a constant shell thickness the determined parameters were in similar order of magnitude. Resonance frequency of the suspension was determined to 11.6 MHz. The developed tool can be used to characterize MBs with a modified shell independently of shell thickness and to predict resonance frequency of gas or air filled UCAs with known shell parameters.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18590号 / 工博第3951号 / 新制||工||1607(附属図書館) / 31490 / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 中部 主敬, 准教授 横峯 健彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Today, microbubbles are one of the most commonly used ultrasound contrast agents, since their high compressibility results in a strongly scattered signal. Despite this advantage, microbubbles experience limitations by the decreased stability and large diameter. The cellulose nanofiber (CNF) stabilized perfluoropentane (PFC5) droplets have the possibility of eliminating these drawbacks. In order to examine the droplet behavior and scattering ability when exposed to ultrasound, the acoustic response of the droplets is studied and compared with that of microbubbles (MBs). Therefore, this thesis aims to design an experimental set-up and a processing method to determine the phase velocity, bulk modulus and compressibility of the CNF-coated PFC5 droplets. The experimental study of the acoustic characterization uses pulse-echo spectroscopy with an aluminum reflector and seven flat transducers covering the frequency range 0.7 to 14.1 MHz. By using fast Fourier transform, while accounting for the 2πn ambiguity, the phase velocity profiles are obtained. The dispersions within this frequency spectrum are 1391-1487 m/s and 1387-1488 m/s for the concentrations 10 ∙ 106 and 50 ∙ 106 droplets/ml, respectively. These profiles display an increasing phase velocity with frequency and a slight increase in dispersion with concentration. These results agree with theory and studies examining the phase velocity of MBs. The bulk modulus presents values between 3-4 GPa, while the compressibility is 2.7 − 3.2 ∙ 10-10 𝑃𝑎-1 within the frequency range studied. Compared to water and certain MBs, both possessing a lower bulk modulus, the droplets are less compressible. To conclude, the droplets have similar phase velocity profiles with the same dependencies on frequency and concentration as MBs, resulting in similar behavior of these droplets when exposed to ultrasound. Hence, affecting the wave similarly to MBs in terms of spreading. The droplet are, however, not as compressible. This most likely affects their oscillation and they, hence, might not have equally beneficial scattering ability. This could reduce their utilization as contrast agents. Some of the potential error sources present during the laboratory work and the development of the post-processing code were not achieving perfect optimization of the transducer alignment, vaporization of the droplets resulting in reduced concentration, possible diffraction, not optimal processing of data and inadequate correction for 2πn ambiguity.

The current methodologies in body scanning diagnostic uses different simultaneous imaging modalities like Ultrasound (US), magnetic resonance imaging (MRI), single photon emission tomography (SPECT) and positron emission tomography (PET). The field requires combination of different modalities for effective use in clinical diagnostics. Such incorporation of different modalities has already been achieved. For example, PET-CT hybrid scanner is designed to acquire align functional and anatomical images and recently US-MRI scanner has successfully shown to improve diagnosis of prostate cancer. The non ionizing radiation hybrid US-MRI is of great interest in health care industry. Further these US and MRI modalities uses different contrast agents like micro-sized gas bubbles (MBs) encapsulated by surfactant for US and superparamagnetic nanoparticles for MRI imaging modalities to further enables new diagnostic opportunities and therapeutic applications. Recently in our 3MiCRON project, we have developed the multimodal contrast agent that could be supported for both US and MRI. This was achieved by coating the magnetic nanoparticles to the poly vinyl alcohol (PVA) surfactant shelled MBs. The nanoparticles in the shell effect the structure can alter the MBs performance as an ultrasound contrast agent. The present thesis is conducted to examine the acoustic and mechanical properties of such multimodal contrast agents. These multimodal contrast agents were prepared by coating the surface of PVA-shelled MBs by two following strategies: (1) The superparamagnetic iron oxide (Fe3O4) nano-particles (SPIONs) were chemically anchored to the surface of poly vinyl alcohol (PVA) shelled MBs namely MBs-chem and (2) in the second strategy the SPIONs were physical entrapped into the PVA shell while formation of PVA surface on the gas bubble were named as MBs-phys. To understand the scattering efficiency and viscoelastic properties of these modified agents, we investigated the backscattering power, attenuation coefficient and phase velocity measurements. Our acoustic experimental results indicate that both the modified MBs and non-modified plain PVA-shelled ultrasound contrast agents have the same echogenic response. The investigation of mechanical properties of modified MBs revealed that the attached SPIONs on the PVA shell has reduced the stiffness of MBs-chem shell, while, the SPIONs inside the shell has increased MBs-phys stiffness. As a result, MBs-chem exhibits soft shell behavior under ultrasound exposure than both MBs-phys. Finally, the images were obtained through the MRI investigations at the department of Radiology, Karolinksa Institute, has demonstrated that both MB types have enough magnetic susceptibility that further provides good detectability in vitro and in vivo. As an outlook, the modified magnetic gas bubbles, i.e. both MBs-chem and MBs-phys can be proposed as a potential contrast agent for both US and MR imaging and can be further utilized in potential therapeutic applications. / <p>QC 20131126</p>

This research deals with the second harmonic generation of Lamb waves in nonlinear elastic, homogeneous, isotropic plates. These waves find current applications in the field of ultrasonic, nondestructive testing and evaluation of materials. The second harmonic Lamb wave generation is investigated analytically in order to provide information on suitable excitation modes maximizing the second harmonic amplitude. Using an existing solution for the problem of second harmonic generation in wave guides, the solution is explained for the plate and examined as to the symmetry properties of the second harmonic wave, since published results are contradictory. It is shown that the cross-modal generation of a symmetric secondary mode by an antisymmetric primary mode is possible. Modes showing internal resonance, whose conditions are nonzero power flux from the primary wave and phase velocity matching, are shown to be most useful for measurements. In addition, group velocity matching is required. A material-independent analysis of the linear Lamb mode theory provides mode types satisfying all three requirements. Using the example of an aluminum plate, the found internally resonant modes are evaluated with regard to the rate of second harmonic generation and practical issues such as excitability and ease of measurement. Pros and cons of each mode type are presented.

Dans ce manuscrit, nous nous inéressons à l'étude du mouvement des vagues soumises uniquement à leur poids par le biais d'équations asymptotiques. Nous commençons par rappeler la dérivation des principaux modèles généralement utilisés (Boussinesq, Green-Naghdi,...). Nous introduisons également un nouveau modèle exprimé en amplitude-flux qui correspond à une variante des équations de Nwogu. Dans le second chapitre, nous démontrons un résultat d'existence en temps long pour ces nouvelles équations et nous étudions l'existence d'ondes solitaires pour les équations de Boussinesq. Ce travail permet notamment de calculer avec une grande précision ces solutions exactes. Le troisième chapitre détaille les différences non linéaires que l'on retrouve entre les différentes équations de Boussinesq (modèles en flux-amplitude comparés aux modèles en vitesse-amplitude). Enfin, les deux derniers chapitres introduisent un nouveau paradigme pour trouver des schémas numériques adaptés aux modèles asymptotiques. L'idée est d'appliquer une analyse asymptotique aux équations d'Euler discrétisées. Ce nouveau paradigme est appliqué aux équations de Peregrine, de Nwogu et de Green-Naghdi. Plusieurs cas tests sont proposés dans ces deux chapitres. / In this work, we are interested in the evolution of water waves under the gravity force using asymptotics models. We start by recalling the derivation of most used models (Boussinesq, Green-Naghdi,...) and we introduce a new model expressed amplitude-flux, which is an alternative version of the Nwogu equations. In the second chapter, we prove a long time existence result for the new model and we investigate the existence of solitary waves for the Boussinesq models. This work allow us to compute these solutions with a good precision. The third chapter highlights the nonlinear differences between the Boussinesq equations (amplitude-flux models versus amplitude-velocity models). Finally, the two last chapter introduce a new paradigm in order to find numerical schemes adapted to asymptotics models. The idea is to apply an asymptotic analysis to a discretized Euler system. This new paradigm is applied to Peregrine equations, Nwogu equations and Green-Naghdi equations. Test cases are presented in these two chapters

Autosomal dominant polycystic disease (ADPKD) is the most common hereditary renal disease and is characterized by renal cyst growth and enlargement. Hypertension occurs early when renal function is normal and is characterized by decreased renal blood flow. Accordingly, the measurement of blood flow in the renal arteries can be a valuable tool in evaluating disease progression. In studies performed in conjunction with this work, blood flow was measured through the renal arteries using magnetic resonance imaging (MRI). In order to validate these in vivo measurements, a vascular phantom was created using polyvinyl alcohol (PVA) and also scanned using MRI under controlled steady flow conditions. Ranges of vessel diameters and flow velocities were used to simulate actual flow in a normal and diseased population of adults and children. With the vessel diameters studied in this experiment, minimization of field of view and an increase in spatial resolution is important in obtaining accurate data. However, a significant difference does not exist between the results when using the 160 or 200 mm FOV. An increase in the number of phase encodings provides improved results, although an increase in image acquisition time is observed. Velocity-encoding in all three orthogonal directions does not improve image data. This method of using MRI to measure flow through a vessel is shown to be both accurate and reproducible, and the protocol providing the most correct results is prescribed. Breath-hold phase-velocity encoded MRI proves to be an accurate and reproducible technique in capturing flow and has the potential to be used for the purpose of observing hemodynamic changes in the renal arteries with the progression of ADPKD.

title: Surface Wave Analysis and Inversion Application to the Bohemian Massif author: Mgr. Petr Kolínský, DiS. author's e-mail address: kolinsky@irsm.cas.cz departments: Department of Geophysics Faculty of Mathematics and Physics Charles University Prague V Holešovičkách 2, Praha 8 - 180 00, Czech Republic and Department of Seismology Institute of Rock Structure and Mechanics, v.v.i. Academy of Sciences of the Czech Republic V Holešovičkách 41, Praha 8 - 182 09, Czech Republic supervisor: RNDr. Johana Brokešová, CSc. supervisor's e-mail address: johana.brokesova@mff.cuni.cz consultant: RNDr. Jiří Málek, PhD. consultant's e-mail address: malek@irsm.cas.cz keywords: surface waves, group velocity, phase velocity, frequency-time analysis, multiple filtering, tomography, inversion problems, Earth crust structure, Bohemian Massif An overview of surface wave analysis methods as well as of inversion techniques is given. Special attention is paid to the multiple filtering method for dispersion curve estimation, which is described by two different ways in detail. The isometric method is used for dispersion curve inversion and its description and tests are presented. Described methods are further used in applications. The applications show examples of surface wave analysis and inversion for 1D and 2D...

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