Spin-transfer switching and low-field precession in exchange-biased spin valve nano-pillars

Using a three-dimensional focused-ion beam lithography process we have fabricated nanopillar devices which show spin transfer torque switching at zero external magnetic fields. Under a small in-plane external bias field, a field-dependent peak in the differential resistance versus current is observed similar to that reported in asymmetrical nanopillar devices. This is interpreted as evidence for the low-field excitation of spin waves which in our case is attributed to a spin-scattering asymmetry enhanced by the IrMn exchange bias layer coupled to a relatively thin CoFe fixed layer.Comment: 11 pages, 4 figures. To appear in APL, April 200

Spin-orbit coupled j=1/2 iridium moments on the geometrically frustrated fcc lattice

Motivated by experiments on the double perovskites La2ZnIrO6 and La2MgIrO6, we study the magnetism of spin-orbit coupled j=1/2 iridium moments on the three-dimensional, geometrically frustrated, face-centered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear A-type antiferromagnetism, stripe order with moments along the [111]-direction, and incommensurate non-coplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures. We argue that existing thermodynamic data on these iridates underscores the presence of a dominant Kitaev exchange, and also suggest a resolution to the puzzle of why La2ZnIrO6 exhibits `weak' ferromagnetism, but La2MgIrO6 does not.Comment: 5 pages, 5 figs, significantly revised to address referee comments, to appear in PRB Rapid Com

In the Starlight : March

https://digitalcommons.library.umaine.edu/mmb-ps/1667/thumbnail.jp

State Regulation and Executive Function in Traumatic Brain Injury: EEG Correlates of Impairment and Intervention

Executive dysfunction is a common and persistent consequence of Traumatic Brain Injury (TBI) and has a significant detrimental impact on social, emotional, and occupational functioning. Abnormalities in EEG measures reflecting the energetic state of the brain are also common following TBI, and rehabilitation approaches such as cognitive and neurofeedback training aim to improve executive function (EF) by facilitating changes in brain state and function. However, the field is lacking a parsimonious and clinically applicable theory of the relationship between brain energetic state and cognition in TBI. The Cognitive Energetic Model (CEM; Sanders, 1983) may address this gap. The CEM provides an explanation of how two aspects of energetic state - arousal (baseline energetic state) and activation (mobilisation of arousal in response to processing demands) - interact with computational factors, effort, and evaluative processes to produce efficient cognitive performance. EEG measures of arousal (eyes-closed global alpha) and activation (changes in delta, theta, alpha, and beta bands between resting or task conditions) provide an empirical basis for investigating the applicability of this model to TBI sequelae and intervention. The aims of this thesis were: 1) to investigate the applicability of the CEM arousal and activation concepts to understanding energetic state abnormalities and their relationship to EF impairment in TBI; and 2) to investigate the effectiveness of a CEM-based neurocognitive training program for improving EF in TBI. Study 1 investigated EEG measures of arousal and activation recorded during eyes-closed and eyes-open resting conditions. Results showed intact arousal, but impaired activation for the TBI group, compared to healthy controls. The TBI group were characterised by reduced resting theta activation and a trend toward increased resting delta activation. Furthermore, enhanced resting delta and alpha activation and reduced resting theta activation were associated with impaired performance on a response inhibition task across groups. Together, the results suggested that it is not baseline resting state, but rather the ability to mobilise energetic state, that is impaired in TBI, and that this is associated with impaired EF

Making the Comeback from Combat: An Analysis of the Effectiveness of Occupational Therapy for Combat Veterans

Combat veterans have been found to experience difficulties with community reintegration after coming back from their deployments. Many of them experience physical and mental injuries from their deployment, such as mild traumatic brain injury, post-traumatic stress disorder, and amputations. Combat veterans not having effective treatment for these injuries can contribute to issues with community reintegration. These issues can consist of marital and financial problems, problems with alcohol or substance abuse, homelessness, and motor vehicle accidents. The Department of Veterans Affairs and the United States military have put forth efforts with improving community reintegration for combat veterans; one of those efforts is better utilizing the profession of occupational therapy. Occupational therapy provides a holistic approach to combat veterans with mild traumatic brain injuries, post-traumatic stress disorder, and amputations and has been shown to have several beneficial interventions when working with this population. The objective of this systematic review is to analyze the effectiveness of occupational therapy interventions on combat veterans experiencing difficulties with community reintegration