Diffusion of spins in a strongly spatially varying local magnetic field

Mathematical and Physical Sciences: 1st Place (The Ohio State University Denman Undergraduate Research Forum)In recent years, the field of spintronics has gained immense interest in the research community. In conventional computing, data is encoded by turning electrical signals on and off; with spintronics, data is encoded with electron spin, allowing for new electronic devices that can move more data at reduced voltages. To further this field, an understanding of spin behavior at the local level is necessary. In my group, magnetic force detection experiments are being used to understand these local phenomena. In these experiments, a micro-magnetic probe couples to the spins generated in a gallium arsenide sample. The sample in these experiments is a 2 micron thick n-GaAs (3e16 cm-3 Si doped) epitaxial membrane. Spins were injected into the membrane over a 10 micron region using standard optical pumping techniques. My presentation focuses on numerical analysis of the spin diffusion equation to better understand the effects of the local magnetic field generated by the probe tip. These simulations provide spatial maps of spin polarization. They also provide information concerning the procession of the spins about an external transverse magnetic field. These were simulated for the conditions experienced by the sample in the experiment. A key result is that the presence of localized, strongly inhomogeneous magnetic fields leads to spatial features in the spin distribution smaller than the injection spot size. These changes in the spatial maps and spin precession due to an external magnetic field as a function of the magnetic tip position can help obtain information regarding spin diffusion, precession, and relaxation with enhanced spatial resolution. The strong field gradients produced by local spin features can also increase the signal in magnetic force microscopy of the sample.OSU ENCOMMCEMNSFDOE Office of ScienceAcademic Major: Electrical and Computer Engineerin

Voltage driven, local, and efficient excitation of nitrogen-vacancy centers in diamond

Magnetic sensing technology has found widespread application in industries as diverse as transportation, medicine, and resource exploration. Such use cases often require highly sensitive instruments to measure the extremely small magnetic fields involved, relying on difficult to integrate Superconducting Quantum Interference Device (SQUID) and Spin-Exchange Relaxation Free (SERF) magnetometers. A potential alternative, nitrogen vacancy (NV) centers in diamond, has shown great potential as a high sensitivity and high resolution magnetic sensor capable of operating in an unshielded, room-temperature environment. Transitioning NV center based sensors into practical devices, however, is impeded by the need for high power RF excitation to manipulate them. Here we report an advance that combines two different physical phenomena to enable a highly efficient excitation of the NV centers: magnetoelastic drive of ferromagnetic resonance (FMR) and NV-magnon coupling. Our work demonstrates a new pathway to combine acoustics and magnonics that enables highly energy efficient and local excitation of NV centers without the need for any external RF excitation, and thus could lead to completely integrated, on-chip, atomic sensors.Comment: Fixed an issue with the display of figure

Universal geometrical factor of protein conformations as a consequence of energy minimization

The biological activity and functional specificity of proteins depend on their native three-dimensional structures determined by inter- and intra-molecular interactions. In this paper, we investigate the geometrical factor of protein conformation as a consequence of energy minimization in protein folding. Folding simulations of 10 polypeptides with chain length ranging from 183 to 548 residues manifest that the dimensionless ratio (V/(A)) of the van der Waals volume V to the surface area A and average atomic radius of the folded structures, calculated with atomic radii setting used in SMMP [Eisenmenger F., et. al., Comput. Phys. Commun., 138 (2001) 192], approach 0.49 quickly during the course of energy minimization. A large scale analysis of protein structures show that the ratio for real and well-designed proteins is universal and equal to 0.491\pm0.005. The fractional composition of hydrophobic and hydrophilic residues does not affect the ratio substantially. The ratio also holds for intrinsically disordered proteins, while it ceases to be universal for polypeptides with bad folding properties.Comment: 6 pages, 1 table, 4 figure

A Descriptive Analysis of Porcupine Scavenging in an Experimental Forensic Context

Addressing the impact of scavengers is essential for a complete analysis of many forensic sites. Despite considerable research on canids and rodents on a broad taphonomic scale (Haglund 1992; Haglund et al. 1989; Haynes 1983), the North American porcupine (Erethizon dorsatum) has not been studied for its impact in forensic contexts. In order to address this research gap, I will explore the role of the porcupine in scavenging bone based on data collected during a recent experimental taphonomic study (Sorg 2013). Funded by the National Institute of Justice, this study included data from motion- and heat-sensitive cameras focused on domesticated pig (Sus scrofa) cadavers exposed in the western Maine woods between 2010 and 2012. Using the photographic and videographic evidence of scavenger visitations at two of these sites, I will examine the behavior of the North American porcupine each time an animal of that species visited the remains. I will compare their observed behavior to the literature regarding porcupine behavior and the behavior of other scavengers, including rodents and canids. Finally, I will compare porcupine dental morphology to the tooth-marks left on the remains to address the possibility of identifying porcupine-scavenged remains in forensic contexts

Análise comparativa de métodos de otimização topológica em elasticidade 2D e 3D

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânic

A novel transport mechanism for MOMP in Chlamydophila pneumoniae and its putative role in immune-therapy

Major outer membrane proteins (MOMPs) of Gram negative bacteria are one of the most intensively studied membrane proteins. MOMPs are essential for maintaining the structural integrity of bacterial outer membranes and in adaptation of parasites to their hosts. There is evidence to suggest a role for purified MOMP from Chlamydophila pneumoniae and corresponding MOMP-derived peptides in immune-modulation, leading to a reduced atherosclerotic phenotype in apoE−/− mice via a characteristic dampening of MHC class II activity. The work reported herein tests this hypothesis by employing a combination of homology modelling and docking to examine the detailed molecular interactions that may be responsible. A three-dimensional homology model of the C. pneumoniae MOMP was constructed based on the 14 transmembrane β-barrel crystal structure of the fatty acid transporter from Escherichia coli, which provides a plausible transport mechanism for MOMP. Ligand docking experiments were used to provide details of the possible molecular interactions driving the binding of MOMP-derived peptides to MHC class II alleles known to be strongly associated with inflammation. The docking experiments were corroborated by predictions from conventional immuno-informatic algorithms. This work supports further the use of MOMP in C. pneumoniae as a possible vaccine target and the role of MOMP-derived peptides as vaccine candidates for immune-therapy in chronic inflammation that can result in cardiovascular events