Homo heidelbergensis: The Tool to Our Success

Homo heidelbergensis, a physiological variant of the species Homo sapien, is an extinct species that existed in both Europe and parts of Asia from 700,000 years ago to roughly 300,000 years ago (carbon dating). This “subspecies” of Homo sapiens, as it is formally classified, is a direct ancestor of anatomically modern humans, and is understood to have many of the same physiological characteristics as those of anatomically modern humans while still expressing many of the same physiological attributes of Homo erectus, an earlier human ancestor. Since Homo heidelbergensis represents attributes of both species, it has therefore earned the classification as a subspecies of Homo sapiens and Homo erectus. Homo heidelbergensis, like anatomically modern humans, is the byproduct of millions of years of natural selection and genetic variation. It is understood through current scientific theory that roughly 200,000 years ago (carbon dating), archaic Homo sapiens and Homo erectus left Africa in pursuit of the small and large animal game that were migrating north into Europe and Asia. As they migrated north with their food source, the climates that these individuals faced were completely opposite to the environment that they were subjected to in Africa

Electron Spin Relaxation in a Transition-Metal Dichalcogenide Quantum Dot

We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer defined by electrostatic gating. Transition-metal dichalcogenides provide an interesting and promising arena for quantum dot nano-structures due to the combination of a band gap, spin-valley physics and strong spin-orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits states. We find that at low B-fields combined spin-valley Kramers qubits to be suitable, while at large magnetic fields pure spin or valley qubits can be envisioned. Then we present a discussion of the relaxation of a single electron spin mediated by electron-phonon interaction via various different relaxation channels. In the low B-field regime we consider the spin-valley Kramers qubits and include impurity mediated valley mixing which will arise in disordered quantum dots. Rashba spin-orbit admixture mechanisms allows for relaxation by in-plane phonons either via the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons give rise to relaxation. We find that the relaxation rates scale as $\propto B^6$ for both in-plane phonons coupling via deformation potential and the piezoelectric effect, while relaxation due to the direct spin-phonon coupling scales independant to B-field to lowest order but scales strongly on device mechanical tension. We will also discuss the relaxation mechanisms for pure spin or valley qubits formed in the large B-field regime.Comment: 10 pages, 4 figure

A Tight Binding Approach to Strain and Curvature in Monolayer Transition-Metal Dichalcogenides

We present a model of the electronic properties of monolayer transition-metal dichalcogenides based on a tight binding approach which includes the effects of strain and curvature of the crystal lattice. Mechanical deformations of the lattice offer a powerful route for tuning the electronic structure of the transition-metal dichalcogenides, as changes to bond lengths lead directly to corrections in the electronic Hamiltonian while curvature of the crystal lattice mixes the orbital structure of the electronic Bloch bands. We first present an effective low energy Hamiltonian describing the electronic properties near the K point in the Brillouin zone, then present the corrections to this Hamiltonian due to arbitrary mechanical deformations and curvature in a way which treats both effects on an equal footing. This analysis finds that local area variations of the lattice allow for tuning of the band gap and effective masses, while the application of uniaxial strain decreases the magnitude of the direct band gap at the K point. Additionally, strain induced bond length modifications create a fictitious gauge field with a coupling strength that is smaller than that seen in related materials like graphene. We also find that curvature of the lattice leads to the appearance of both an effective in-plane magnetic field which couples to spin degrees of freedom and a Rashba-like spin-orbit coupling due to broken mirror inversion symmetry.Comment: 16 pages, 2 figures, revised version v

The Republic of The Philippines: Epidemiology and Epigenetics

A brief, yet concise investigation was conducted on the Republic of the Philippines, with a keen interest in the epidemiology of the current urban areas of the nation (+150,000 inhabitants), as well as possible epigenetic change that may be induced from disease or environmental stressors upon these same groups of people. G6PD deficiency, a common disorder among persons in urban dwellings within the Republic of the Philippines (Hsia 1993) was found to have a strong correlation of incidence with members of other nations in localized proximity to the equator. Additionally, low birth weight in infants has been identified as a potential epigenetic cue in those of the emerging, current population (Kuzawa 2012).https://scholarscompass.vcu.edu/uresposters/1111/thumbnail.jp

Low-damping transmission of spin waves through YIG/Pt-based layered structures for spin-orbit-torque applications

We show that in YIG-Pt bi-layers, which are widely used in experiments on the spin transfer torque and spin Hall effects, the spin-wave amplitude significantly decreases in comparison to a single YIG film due to the excitation of microwave eddy currents in a Pt coat. By introducing a novel excitation geometry, where the Pt layer faces the ground plane of a microstrip line structure, we suppressed the excitation of the eddy currents in the Pt layer and, thus, achieved a large increase in the transmission of the Damon-Eshbach surface spin wave. At the same time, no visible influence of an external dc current applied to the Pt layer on the spin-wave amplitude in the YIG-Pt bi-layer was observed in our experiments with YIG films of micrometer thickness