Effect of ferromagnetic contacts on spin accumulation in an all-metallic lateral spin-valve system: Semiclassical spin drift-diffusion equations

We study the effect of the ferromagnetic (FM) contacts on the spin accumulation in the lateral spin valve system for the collinear magnetization configurations. When an additional FM electrode is introduced in the all-metallic lateral spin-valve system, we find that the transresistance can be fractionally suppressed or very weakly influenced depending on the position of the additional FM electrode, and relative magnitudes of contact resistance and the bulk resistance defined over the spin diffusion length. Nonlocal spin signals such as nonlocal voltage drop and leakage spin currents are independent of the magnetization orientation of the additional FM electrode. Even when the additional contact is nonmagnetic, nonlocal spin signals can be changed by the spin current leaking into the nonmagnetic electrode.Comment: 13 pages, 1 figure, revised versio

Association between polymorphisms of arachidonate 12-lipoxygenase (ALOX12) and schizophrenia in a Korean population

Arachidonic acid (AA), an essential polyunsaturated fatty acid, is one of the major components of neural membranes, which show an altered phospholipid composition in schizophrenia. Arachidonate 12-lipoxygenase (ALOX12), an important enzyme, metabolizes AA to 12-HPETE, which affects catecholamine synthesis. However, research has yet to show the genetic association between ALOX12 and schizophrenia. Therefore, we investigated single nucleotide polymorphisms (SNP) of the ALOX12 gene in schizophrenia, recruiting patients with schizophrenia (n = 289) and normal controls (n = 306) from a Korean population. We selected three SNPs (rs1126667, rs434473, and rs1042357) of the ALOX12 gene and genotyped them by direct sequencing. We reviewed the schizophrenic patients' medical records and assessed them clinically using the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Negative Symptoms (SANS), and the Operational Criteria Checklist (OPCRIT). Then we statistically analyzed the genetic associations between the SNPs and schizophrenia, finding a genetic association between both rs1126667 and rs1042357 and schizophrenia, in the recessive model (p = 0.015 and 0.015, respectively). We also found an association between rs434473 and negative symptoms, defined through a factor analysis of the OPCRIT data (p = 0.040). Consequently, we suggest that SNPs of the ALOX12 gene might be associated with schizophrenia and negative symptoms in this Korean population. These weak positives require additional study

Palladium Catalysts for Dehydrogenation of Ammonia Borane with Preferential B−H Activation

Cationic Pd(II) complexes catalyzed the dehydrogenation of ammonia borane in the most efficient manner with the release of 2.0 equiv of H_2 in less than 60 s at 25 °C. Most of the hydrogen atoms were obtained from the boron atom of the ammonia borane. The first step of the dehydrogenation reaction was elaborated using density functional theory calculations

Quantitative phase imaging: advances to 3D imaging and applications to neuroscience

This thesis provides a brief overview of quantitative phase imaging (QPI) methods along with applications and advances made on them. First, spatial light interference microscopy (SLIM) is introduced as a QPI method extensively used in this thesis. Using this setup, an application of QPI in neuroscience is demonstrated by studying the emergent formation of a neuronal network. Second, an expansion of this QPI method into a 3D quantitative imaging method, called white-light diffraction tomography (WDT), has been shown. Lastly, an initial result for another advance in SLIM is introduced by combining SLIM with a programmable illumination. In the first part of this work, the emergent self-organization of a neuronal network has been demonstrated using the SLIM system. The emergent self-organization of a neuronal network in a developing nervous system is the result of a remarkably orchestrated process involving a multitude of chemical, mechanical and electrical signals. Little is known about the dynamic behavior of a developing network (especially in a human model) primarily due to a lack of practical and non-invasive methods to measure and quantify the process. Using the SLIM system, several fundamental properties of neuronal networks have been measured non-invasively from the sub-cellular to the cell population level. This method quantifies network formation in human stem cell derived neurons and shows correlations between trends in the growth, transport, and spatial organization of such a system, by utilizing the quantitative phase data with novel analysis tools, including dispersion-relation phase spectroscopy (DPS). A deeper understanding of neuronal network formation has been provided by studying filopodia dynamics in neurons. By measuring the dry mass change over time and several other new metrics, it is shown that the filopodia dynamics successfully reflect the expected neurite outgrowth. In the second part, white-light diffraction tomography (WDT) is introduced as a new approach for imaging microscopic transparent objects such as live unlabeled cells in 3D. The approach extends diffraction tomography to white light illumination and imaging rather than scattering plane measurements. The experiments were performed using the SLIM system. The axial dimension of the object was reconstructed by scanning the focus through the object and acquiring a stack of phase-resolved images. The 3D structures of live, unlabeled red blood cells are imaged and compared with confocal and scanning electron microscopy images. The 350 nm transverse and 900 nm axial resolution achieved allows us to reveal sub-cellular structures at high resolution in E. coli cells and HT29 cells. Furthermore, a 4D imaging capability, with the fourth dimension being time, has also been demonstrated. The WDT theory is further extended to explain light scattering through thick tissue, which is not in the single scattering regime. The obtained inverse scattering solution for thick samples is then related to the time-reversal theory, and it is proven that there are strong constraints for time-reversal to work. By introducing a few specific examples, including scattering through a particle and scattering through a grating, the physics of light scattering and time-reversal theory is deeply understood. Lastly, an upgrade to the SLIM system with a programmable illumination source, a projector, has been demonstrated. By replacing the ring illumination of PC with a ring-shaped pattern projected onto the condenser plane, results comparable to those of the original SLIM were recovered. This new method minimized the halo artifact of the imaging system by minimizing the effect of spatial coherence caused by the thickness of the illumination. Further application of this technique into optogenetics is introduced and the initial results are presented