Theory of spin-polarized transport in ferromagnet-semiconductor structures: Unified description of ballistic and diffusive transport

A theory of spin-polarized electron transport in ferromagnet-semiconductor heterostructures, based on a unified semiclassical description of ballistic and diffusive transport in semiconductors, is outlined. The aim is to provide a framework for studying the interplay of spin relaxation and transport mechanism in spintronic devices. Transport inside the (nondegenerate) semiconductor is described in terms of a thermoballistic current, in which electrons move ballistically in the electric field arising from internal and external electrostatic potentials, and are thermalized at randomly distributed equilibration points. Spin relaxation is allowed to take place during the ballistic motion. For arbitrary potential profile and arbitrary values of the momentum and spin relaxation lengths, an integral equation for a spin transport function determining the spin polarization in the semiconductor is derived. For field-driven transport in a homogeneous semiconductor, the integral equation can be converted into a second-order differential equation that generalizes the spin drift-diffusion equation. The spin-polarization in ferromagnet semiconductor structures is obtained by matching the spin-resolved chemical potentials at the interfaces, with allowance for spin-selective interface resistances. Illustrative examples are considered.Comment: 11 pages, 4 figures; to appear in Materials Science and Engineering

Evaluating Behavioral Health Service Need for Sexual and Gender Minorities: A Community-Based Qualitative Study

The LGBTQ community experiences mental health challenges, such as anxiety, depression, and substance use disorders, at rates higher than heterosexual and cisgender counterparts. Given these disparities in mental health, it is crucial that the LGBTQ population has access to mental health services. However, LGBTQ individuals face barriers to accessing mental health care due to service affordability, availability, and/or lack of LGBT-inclusivity. A Place to Nourish your Health (APNH), formerly known as AIDS Project New Haven, has historically provided care to those in New Haven who live with HIV and AIDS. APNH is now seeking to re-define itself as an organization by expanding services to support those experiencing stigma related to gender identity, sexual orientation, addiction, and mental health. Thus, to aid APNH in their service expansion to stigmatized populations, we performed a qualitative community needs assessment in the greater New Haven area to inform where APNH’s priorities should lie in their expansion of services. Findings provided insight into the current mental health landscape of New Haven’s LGBTQ community and led to reccomendatios regarding APNH\u27s expanion of behavoral health services.https://elischolar.library.yale.edu/ysph_pbchrr/1024/thumbnail.jp

Equilibrium ion distribution in the presence of clearing electrodes and its influence on electron dynamics

Here we compute the ion distribution produced by an electron beam when ion-clearing electrodes are installed. This ion density is established as an equilibrium between gas ionization and ion clearing. The transverse ion distributions are shown to strongly peak in the beam's center, producing very nonlinear forces on the electron beam. We will analyze perturbations to the beam properties by these nonlinear fields. To obtain reasonable simulation speeds, we develop fast algorithms that take advantage of adiabatic invariants and scaling properties of Maxwell's equations and the Lorentz force. Our results are very relevant for high current Energy Recovery Linacs, where ions are produced relatively quickly, and where clearing gaps in the electron beam cannot easily be used for ion elimination. The examples in this paper therefore use parameters of the Cornell Energy Recovery Linac project. For simplicity we only consider the case of a circular electron beam of changing diameter. However, we parameterize this model to approximate non-round beams well. We find suitable places for clearing electrodes and compute the equilibrium ion density and its effect on electron-emittance growth and halo development. We find that it is not sufficient to place clearing electrodes only at the minimum of the electron beam potential where ions are accumulated

An ASP Approach for the Synthesis of CNOT Minimal Quantum Circuits

In the last year, physical working Quantum Computers have been built and made available for the end users. Such devices, working under the rules of Quantum Mechanics, can only apply a finite set of one/two qubit operations that form a universal set of gates. Single qubit gates are fault-tolerant, while the same cannot be said for two qubit gates. Hence, unitary matrices adopted in Quantum Algorithms must be synthesized in terms of this universal set of operations to obtain a quantum circuit. This synthesis procedure, however, is not constraint-free. In fact, we prefer circuits with minimum number of qubits and with minimum circuit depth. Clifford+T universal set is one of the most adopted in the literature for synthesis. In such set we have 3 single qubit gates and the CNOT, which is a two qubit gate. Many efforts have been directed to devise algorithms that synthesize general unitary matrices into Clifford+T circuits. These algorithms usually tend to optimize circuit depth or eventually the number of T gates. Since two qubit gates are not fault tolerant, in this work we propose an ASP based technique to minimize the number of CNOT gates inside a Clifford+T circuit. We start from a SAT encoding of the problem, and we translate it into an ASP model over a graph, by first working with a generic graph, and then by adopting the structure of a layered DAG. We provide experimental evidence of the scalability of our proposal