Motion robust acquisition and reconstruction of quantitative T2* maps in the developing brain

The goal of the research presented in this thesis was to develop methods for quantitative T2* mapping of the developing brain. Brain maturation in the early period of life involves complex structural and physiological changes caused by synaptogenesis, myelination and growth of cells. Molecular structures and biological processes give rise to varying levels of T2* relaxation time, which is an inherent contrast mechanism in magnetic resonance imaging. The knowledge of T2* relaxation times in the brain can thus help with evaluation of pathology by establishing its normative values in the key areas of the brain. T2* relaxation values are a valuable biomarker for myelin microstructure and iron concentration, as well as an important guide towards achievement of optimal fMRI contrast. However, fetal MR imaging is a significant step up from neonatal or adult MR imaging due to the complexity of the acquisition and reconstruction techniques that are required to provide high quality artifact-free images in the presence of maternal respiration and unpredictable fetal motion. The first contribution of this thesis, described in Chapter 4, presents a novel acquisition method for measurement of fetal brain T2* values. At the time of publication, this was the first study of fetal brain T2* values. Single shot multi-echo gradient echo EPI was proposed as a rapid method for measuring fetal T2* values by effectively freezing intra-slice motion. The study concluded that fetal T2* values are higher than those previously reported for pre-term neonates and decline with a consistent trend across gestational age. The data also suggested that longer than usual echo times or direct T2* measurement should be considered when performing fetal fMRI in order to reach optimal BOLD sensitivity. For the second contribution, described in Chapter 5, measurements were extended to a higher field strength of 3T and reported, for the first time, both for fetal and neonatal subjects at this field strength. The technical contribution of this work is a fully automatic segmentation framework that propagates brain tissue labels onto the acquired T2* maps without the need for manual intervention. The third contribution, described in Chapter 6, proposed a new method for performing 3D fetal brain reconstruction where the available data is sparse and is therefore limited in the use of current state of the art techniques for 3D brain reconstruction in the presence of motion. To enable a high resolution reconstruction, a generative adversarial network was trained to perform image to image translation between T2 weighted and T2* weighted data. Translated images could then be served as a prior for slice alignment and super resolution reconstruction of 3D brain image.Open Acces

Magnetic anisotropy in YbAlO3 studied by electron spin resonance

The magnetic anisotropy of the quantum-critical spin-chain system YbAlO$$_3$$is studied in detail in its paramagnetic phase by means of electron spin resonance. We find an uniaxial g factor anisotropy with $$g_\parallel =7.01$$and $$g_\perp = 0.47$$. The existence of two distinct magnetic Yb sites explains the resonance spectra well

Computational study of LnGaO3 (Ln=La+Gd) perovskites

Atomistic simulation techniques have been used to study the thermal properties of perovskite-type LnGaO3 (Ln = La-Gd). A set of interatomic potentials describing interatomic interactions in these compounds was developed and tested over a wide temperature range through utilizing free energyminimization.The predicted dielectric constants, thermal expansion coefficients, phonon density of states and its projections, heat capacity and entropy, elastic moduli, Gruneisen parameters, surface energies for main crystallographic directionsand Debye temperatures are in good agreement with the limited available experimental data. Perovskite-type LnGaO3 (Ln = La-Gd) compounds have been examined under conditions to which substrate materials are typically subjected. Only a narrow region in the phase diagram of LnGaO3 (Ln = La-Gd) and their solid solutions is recommended for use in substrate applications

Structural, magnetic, dielectric and mechanical properties of (Ba,Sr)MnO3_3 ceramics

Ceramic samples, produced by conventional sintering method in ambient air, 6H-SrMnO$_3$(6H-SMO), 15R-BaMnO$_3$(15R-BMO), 4H-Ba$_{0.5}$Sr$_{0.5}$MnO$_3$(4H-BSMO) were studied. In the XRD measurements for SMO the new anomalies of the lattice parameters at 600-800 K range and the increasing of thermal expansion coefficients with a clear maximum in a vicinity at 670 K were detected. The N$\acute{e}$el phase transition for BSMO was observed at $T_N$=250 K in magnetic measurements and its trace was detected in dielectric, FTIR, DSC, and DMA experiments. The enthalpy and entropy changes of the phase transition for BSMO at $T_N$ were determined as 17.5 J/mol and 70 mJ/K mol, respectively. The activation energy values and relaxation times characteristic for relaxation processes were determined from the Arrhenius law. Results of ab initio simulations showed that the contribution of the exchange correlation energy to the total energy is about 30%.Comment: 12 pages, 12 figure

Effect of cobalt doping on the dielectric response of B0.95Pb0.05TiO3B_{0.95}Pb_{0.05}TiO_3 ceramics

Dielectric response of Ba 0.95 Pb 0.05 TiO 3 ceramics doped with 0.1 and 1 wt.% of Co 2 O 3 , synthesized by conven- tional high-temperature method, wa s studied in wide temperature and frequency range. The temperature dependences of the real and the imaginary parts of dielectric permittivity of the ceramics were compared with those of BaTiO 3 and Ba 0.95 Pb 0.05 TiO 3. The addition of Co 3+ ions results in a broadening of dielectric anom- alies related to the transition to p araelectric cubic phase, and the structural transition between the tetragonal and the orthorhombic phases. At low temperatures (125 – 200 K) the dielectric absorp- tion of Co-doped Ba 0.95 Pb 0.05 TiO 3 ceramics was found to exhibit relaxor-like properties. The die lectric response has been found to contain the contributions characte ristic of fluctuations of the polar nanoregion boundaries and reorientations of the dipole moments between allowed directions in the nanoregions in the rhombohe- dral and the orthorhombic phases. The behavior speaks in favor of ordering of polar defects in the host lattice of Ba 0.95 Pb 0.05 TiO 3 in a form polar nanoregions

Antiferromagnetic ordering and dipolar interactions of YbAlO3_3

In this paper we report low-temperature magnetic properties of the rare-earth perovskite material YbAlO$_3$. Results of elastic and inelastic neutron scattering experiment, magnetization measurements along with the crystalline electrical field (CEF) calculations suggest that the ground state of Yb moments is a strongly anisotropic Kramers doublet, and the moments are confined in the $ab$-plane, pointing at an angle of $\varphi = \pm 23.5^{\circ}$ to the $a$-axis. With temperature decreasing below $T_{\rm N}=0.88$ K, Yb moments order into the coplanar, but non-collinear antiferromagnetic (AFM) structure $AxGy$, where the moments are pointed along their easy-axes. In addition, we highlight the importance of the dipole-dipole interaction, which selects the type of magnetic ordering and may be crucial for understanding magnetic properties of other rare-earth orthorhombic perovskites. Further analysis of the broad diffuse neutron scattering shows that one-dimensional interaction along the $c$-axis is dominant, and suggests YbAlO$_3$ as a new member of one dimensional quantum magnets.Comment: 8 pages, 6 figure

Multiple fermion scattering in the weakly coupled spin-chain compound YbAlO3

The Heisenberg antiferromagnetic spin-1/2 chain, originally introduced almost a century ago, is one of the best studied models in quantum mechanics due to its exact solution, but nevertheless it continues to present new discoveries. Its low-energy physics is described by the Tomonaga-Luttinger liquid of spinless fermions, similar to the conduction electrons in one-dimensional metals. In this work we investigate the Heisenberg spin-chain compound YbAlO3 and show that the weak interchain coupling causes Umklapp scattering between the left- and right-moving fermions and stabilizes an incommensurate spin-density wave order at q = 2kF under finite magnetic fields. These Umklapp processes open a route to multiple coherent scattering of fermions, which results in the formation of satellites at integer multiples of the incommensurate fundamental wavevector Q = nq. Our work provides surprising and profound insight into bandstructure control for emergent fermions in quantum materials, and shows how neutron diffraction can be applied to investigate the phenomenon of coherent multiple scattering in metals through the proxy of quantum magnetic systems

Multiple fermion scattering in the weakly coupled spin-chain compound YbAlO3

The Heisenberg antiferromagnetic spin-1/2 chain, originally introduced almost a century ago, is one of the best studied models in quantum mechanics due to its exact solution, but nevertheless it continues to present new discoveries. Its low-energy physics is described by the Tomonaga-Luttinger liquid of spinless fermions, similar to the conduction electrons in one-dimensional metals. In this work we investigate the Heisenberg spin-chain compound YbAlO3 and show that the weak interchain coupling causes Umklapp scattering between the left- and right-moving fermions and stabilizes an incommensurate spin-density wave order at q = 2kF under finite magnetic fields. These Umklapp processes open a route to multiple coherent scattering of fermions, which results in the formation of satellites at integer multiples of the incommensurate fundamental wavevector Q = nq. Our work provides surprising and profound insight into bandstructure control for emergent fermions in quantum materials, and shows how neutron diffraction can be applied to investigate the phenomenon of coherent multiple scattering in metals through the proxy of quantum magnetic systems

DAMPAK WISATAWAN ASING TERHADAP PERUBAHAN SOSIAL BUDAYA MASYARAKAT (STUDI PADA MASYARAKAT DI KEC. LHOKNGA KAB. ACEH BESAR)

ABSTRAKBerkembangnya pariwisata di tengah masyarakat membawa pengaruh terhadap kehidupan sosial budaya. Pariwisata selalu mempertemukan dua atau lebih kebudayaan yang akan menghasilkan berbagai proses perubahan seperti akulturasi, dominasi, asimilasi, adopsi, adaptasi dan sebagainya. Wisatawan mancanegara yang berkunjung ke Lhoknga telah membawa pengaruh terhadap masyarakat lokal di daerah sekitar objek wisata. Penelitian ini bertujuan untuk mengetahui dampak pariwisata terhadap perubahan sosial budaya masyarakat dan mengetahui bentuk perubahan sosial budaya yang terjadi pada masyarakat Lhoknga akibat perkembangan pariwisata di Mukim Lhoknga. Metodologi penelitian ini menggunakan pendekatan kualitatif dengan model studi deskriptif. Pengumpulan data dilakukan dengan wawancara mendalam dan observasi. Dari hasil penelitian menunjukkan bahwa terjadinya perubahan sosial budaya pada masyarakat lokal di Mukim Lhoknga, Kecamatan Lhoknga Kabupaten Aceh Besar. Namun perubahan yang dimaksud masih dikategorikan perubahan secara mikro, karena tidak membawa pengaruh yang mendalam pada kehidupan masyarakat lokal. Dampak pariwisata terhadap perubahan sosial budaya masyarakat dapat dipilah menjadi dua yaitu dampak positif dan dampak negatif. Dampak positifnya yaitu dengan adanya pariwisata telah membuka lapangan kerja baru bagi masyarakat lokal yang dapat meningkatkan pendapatan ekonomi, mampu menguasai bahasa asing, seperti bahasa Inggris, Jepang. Terbukanya akses bagi masyarakat lokal ke jaringan yang lebih luas, memperlihatkan keindahan alam dan budaya yang tak lepas dari rasa untuk meningkatkan persaudaraan dalam lingkungan nasional dan internasional Sedangkan dampak negatif yaitu, lunturnya budaya lokal (tradisional) akibat masuknya budaya luar (modern). Adapun bentuk-bentuk perubahan dapat dilihat dari dua segi yaitu perubahan segi sosial dan perubahan dari segi budaya. Bentuk perubahan dari segi sosial yaitu terjadinya perubahan struktur sosial masyarakat lokal dengan beralihnya sektor pekerjaan dari petani atau nelayan ke sektor industri, Meningkatnya keinginan untuk berpendidikan tinggi, sedangkan perubahan dari segi budaya yaitu terjadinya perkawinan dari dua unsur budaya yang berbeda, perubahan pada penggunaan bahasa, perubahan cara berpakaian dan perubahan perilaku dalam keluarga.Kata Kunci : Pariwisata, Wisatawan Asing, Perubahan Sosial, Perubahan Budaya.Banda Ace