Magnetic resonance imaging (MRI) has become one of the premier non-invasive diagnostic tools, with around 60 million MRI scans applied each year. However, there is a risk of thermal injury due to radiofrequency (RF) induction heating of the tissue and implanted metallic device for the patients with the implanted metallic devices. Especially, MRI of the patients with implanted elongated devices such as pacemakers and deep brain stimulation systems is considered contraindicated. Many efforts, such as determining preferred MRI parameters, modifying magnetic field distribution, designing new structure and exploring new materials, have been made to reduce the induction heating. Improving the MRI-compatibility of implanted metallic devices by modifying the properties of the existing materials would be valuable. To evaluate the temperature rise due to RF induction heating on a metallic implant during MRI procedure, an electromagnetic model and thermal model are studied. The models consider the shape of RF magnetic pulses, interaction of RF pulses with metal plate, thermal conduction inside the metal and the convection at the interface between the metal and the surroundings. Transient temperature variation and effects of heat transfer coefficient, reflectivity and MRI settings on the temperature change are studied. Laser diffusion is applied to some titanium sheets for a preliminary study. An electromagnetic and thermal model is developed to choose the proper diffusant. Pt is the diffusant in this study. An electromagnetic model is also developed based on the principles of inverse problems to calculate the electromagnetic properties of the metals from the measured magnetic transmittance. iv This model is used to determine the reflectivity, dielectric constant and conductivity of treated and as-received Ti sheets. The treated Ti sheets show higher conductivity than the as-received Ti sheets, resulting higher reflectivity. A beam shaping lens system which is designed based on vector diffraction theory is used in laser diffusion. Designing beam shaping lens based on the vector diffraction theory offers improved irradiance profile and new applications such as polarized beam shaping because the polarization nature of laser beams is considered. Laser Pt diffusion are applied on the titanium and tantalum substrates using different laser beam polarizations. The concentration of Pt and oxygen in those substrates are measured using Energy Dispersive X-Ray Spectroscopy (EDS). The magnetic transmittance and conductivity of those substrates are measured as well. The effects of laser beam polarizations on Pt diffusion and the magnetic transmittance and conductivity of those substrates are studied. Treated Ti sheets show lower magnetic transmittance due to the increased conductivity from diffused Pt atoms. On the other hand, treated Ta sheets show higher magnetic transmittance due to reduced conductivity from oxidation. Linearly polarized light can enhance the Pt diffusion because of the excitation of local vibration mode of atoms. Laser Pt diffusion and thermo-treatment were applied on the Ta and MP35N wires. The Pt concentration in laser platinized Ta and MP35N wires was determined using EDS. The ultimate tensile strength, fatigue lives and lead tip heating in real MRI environment of those wires were measured. The lead tip hating of the platinized Ta wires is 42 % less than the as-received Ta wire. The diffused Pt increases the conductivity of Ta wires, resulting in more reflection of magnetic field. In the case of the platinized MP35N wire, the reduction in lead tip heating was only 1 °C v due to low concentration of Pt. The weaker ultimate tensile strength and shorter fatigue lives of laser-treated Ta and MP35N wires may attribute to the oxidation and heating treatment.

Context.The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of these fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines, and non-thermal radio/X-ray emission. Aims.To investigate the incidence of magnetic fields in O stars, we acquired 38 new spectropolarimetric observations with FORS 1 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Kueyen telescope of the VLT. Methods.Spectropolarimetric observations were obtained at different phases for a sample of 13 O stars. Ten stars were observed in the spectral range 348−589 nm, HD 36879 and HD 148937 were observed in the spectral region 325−621 nm, and HD 155806 was observed in both settings. To prove the feasibility of the FORS 1 spectropolarimetric mode for the measurements of magnetic fields in hot stars, we present in addition 12 FORS 1 observations of the mean longitudinal magnetic field in θ1 Ori C and compare them with measurements obtained with the MuSiCoS, ESPaDOnS, and Narval spectropolarimeters. Results.Most stars in our sample, which were observed on different nights, show a change of the magnetic field polarity, but a field at a significance level of 3σ was detected in only four stars, HD 36879, HD 148937, HD 152408, and HD 164794. The largest longitudinal magnetic field, Bz = −276 ± 88 G, was detected in the Of?p star HD 148937. We conclude that large-scale organized magnetic fields with polar field strengths larger than 1 kG are not widespread among O-type stars.

Controlled cell assembly is essential for fabricating in vitro models that mimic native tissue architecture. Conventional tissue engineering techniques are time-consuming and offer limited control over the spatial organization of cells within the assembled cell aggregates. We describe a label-free, scaffold-free, rapid cell manipulation technique to assemble cells into layered aggregates. Suspensions of cells in a culture medium with higher magnetic susceptibility are seeded into wells of a 96-well plate placed on a quartet magnet array. An FDA-approved paramagnetic agent is added to the regular cell culture medium to enhance the magnetic susceptibility. The inhomogeneous magnetic field and the susceptibility difference drive cells toward the lowest magnetic field region on the well surface. Two cell types are sequentially added to the wells to form layer-on-layer aggregates within 6 h. Next, the label-free technique is extended to develop a cell migration assay. Besides being time-consuming, the traditional scratch-based cell migration assay is not reproducible, whereas the alternate physical barrier-based method is expensive. Annular aggregates of human bronchial epithelial cells (HBEC3 KT) are formed within 3 h using a coaxially arranged ring-cylinder magnet array. The effects of the paramagnetic agent on cell viability, metabolism, and transcriptional profiles are investigated. The closures of the circular cell-free areas enclosed by HBEC3 KT are analyzed at different times in response to various signaling molecules and surface conditions. Further, we demonstrate the formation of the annular aggregates on human lung fibroblast-laden collagen hydrogel surfaces. The cell-free area closures on hydrogel surfaces in response to signaling molecules are analyzed. The high reproducibility and scalability of the label-free method make it amenable for preclinical research. / Thesis / Doctor of Philosophy (PhD) / Cell cultures are essential tools for studying cell functions under controlled conditions. A better understanding of cell behavior in tissues is required to develop effective treatments for diseases. The organized arrangement of cells in tissues controls tissue functions. The existing culture techniques are time-consuming and have limited control over the cellular arrangement. We describe a simple, rapid, and inexpensive bioprinting technique to arrange cells in layers, which resembles the cellular organization in tissues, such as the skin. The layered structures are formed in standard well plates within 6 h. Cell movement is an essential cell function in various biological processes, such as wound healing. Using the bioprinting method, we form ring-shaped cellular structures within 3 h to study cell movements in response to various signals. The ring structures enclose cell-free areas, which are populated over time as the cells move from the ring into the cell-free regions. The bioprinting method is easy to use and can rapidly form organized cellular structures for drug testing.

Методом точек помутнения изучены фазовые переходы систем ПС – метилацетат, ПВА – этанол, ПДМС – бутанон и ПММА – бутанол в магнитном поле и в его отсутствие. Построены фазовые диаграммы систем ПС (Mh = 2,0´105) – метилацетат, ПВА (Mη = 5,8´104) – этанол, ПДМС (Mη = 1,0x103) – бутанон и ПММА (Mh = 5,5´104) – бутанол. Установлено, что магнитное поле не влияет на температуру фазовых переходов растворов гибкоцепных аморфных полимеров. / Phase transitions of the PS – methyl acetate, PVAc – ethanol, PDMS – butanone, PMMA – butanol systems have been studied using the cloud-point method. Phase diagrams of these systems are constructed. It is shown that the magnetic field does not influence on the phase transition temperature of flexible chain amorphous polymer solutions.

Phase transitions of the gelatin – water and agaroza - water systems have been studied using the cloud-point method. Phase diagrams of these systems are constructed at different values of pH of medium. It is shown that pH of medium influences on the melting temperature of gelatin and agaroza gels. / Методом точек помутнения изучены фазовые переходы в системах желатин – вода и агароза – вода. Построены фазовые диаграммы систем при разных pH среды в магнитном поле и вне поля. Установлено, что pH среды влияет на температуру плавления гелей желатина и агарозы.

No description available.

No description available.

No description available.

<p>In this thesis, we investigate the properties of a model of an anti-phase modulated d-wave superconductor, particularly in the presence of a magnetic field. This so-called model of $\pi$-striped superconductor has been proposed to describe the decoupling between Cu-O planes in $1/8$ doped La$_{2-x}$Ba$_{x}$CuO$_{4}$. The d-wave superconducting order parameter in a $\pi$-striped superconductor oscillates spatially with period 8 and zero average value. Unlike a uniform d-wave superconductor, this model has non-zero density of states at zero energy and exhibits an extended Fermi surface. Within Bogoliubov-de Gennes theory, we study the mixed state of this model and compare it to the case of a uniform d-wave superconductor. We find a periodic structure of the low-energy density of states, with a period that is proportional to $B$, corresponding to Landau levels that are a coherent mixture of particles and holes. These results are also discussed in the context of experiments which observe quantum oscillations in the cuprates.</p> <p>Furthermore, within Bogoliubov-de Gennes theory, a semiclassical approximation is used to study quantum oscillations and to determine the Fermi surface area associated with these oscillations in this model. The Fermi surface is reconstructed via Andreev-Bragg scattering, and the semiclassical motion is along these Fermi surface sections as well as between them via magnetic breakdown. Oscillations periodic in 1/B are found in both the positions and widths of the lowest Landau levels. The area corresponding to these quantum oscillations for intermediate pairing interaction is similar to that reported for experimental measurements in the cuprates. A comparison is made of this theory to data for quantum oscillations in the specific heat measured by Riggs et al.</p> / Doctor of Philosophy (PhD)

Innovative methods to control the viscosity and turbulence in the flow of liquid suspension can be engineered by way of incorporating the concepts of electric and magnetic field into the rheology of complex fluids. Rheology of liquid Chocolate is a very crucial factor in determining the cost of manufacturing process as well as formulating varieties of end consumer products, for example, containing less fat. We have invented a method to lower the viscosity of liquid chocolate flow with the application of electric field. In the lab, we have found that viscosity of chocolate samples is reduced by 40~50% with our method. Thus, fat content in those samples can be reduced by 10% or more. Therefore, we expect to see much healthier and tastier chocolate product in the market once this technology gets implemented in commercial manufacturing. High viscosity and turbulence in blood flow greatly increase the risk of cardiac diseases. Hence, discovering new method to address turbulence suppression and viscosity reduction is critically important. In our study, we have found that in the in-vitro experiment, if blood is subjected to flow through a channel placed inside a strong magnetic field, its viscosity reduces by 10~20%. Based on these findings, a Megneto-Rheology (MR) therapeutic device has been developed to examine the effect on the blood pressure in human subjects. Preliminary clinical trials show that application of this MR therapy reduces blood pressure by 10% or more. In this thesis, above mentioned inventions for the flow of Blood and liquid Chocolate will be thoroughly discussed. / Physics / Accompanied by two .mpeg4 files.