Measuring the Spin of GRS 1915+105 with Relativistic Disk Reflection

GRS 1915+105 harbors one of the most massive known stellar black holes in the Galaxy. In May 2007, we observed GRS 1915+105 for 117 ksec in the low/hard state using Suzaku. We collected and analyzed the data with the HXD/PIN and XIS cameras spanning the energy range from 2.3-55 keV. Fits to the spectra with simple models reveal strong disk reflection through an Fe K emission line and a Compton back-scattering hump. We report constraints on the spin parameter of the black hole in GRS 1915+105 using relativistic disk reflection models. The model for the soft X-ray spectrum (i.e. < 10 keV) suggests a/M = 0.56(2) and excludes zero spin at the 4 sigma level of confidence. The model for the full broadband spectrum suggests that the spin may be higher, a/M = 0.98(1) (1 sigma confidence), and again excludes zero spin at the 2 sigma level of confidence. We discuss these results in the context of other spin constraints and inner disk studies in GRS 1915+105.Comment: Accepted for publication in Ap

Tunneling edges at strong disorder

Scattering between edge states that bound one-dimensional domains of opposite potential or flux is studied, in the presence of strong potential or flux disorder. A mobility edge is found as a function of disorder and energy, and we have characterized the extended phase. "paper_FINAL.tex" 439 lines, 20366 characters In the presence of flux and/or potential disorder, the localization length scales exponentially with the width of the barrier. We discuss implications for the random-flux problem.Comment: RevTeX, 4 page

Role of Institutions of Higher Education in Community-Centric Risk Reduction

As relatively large organizations, often with substantial resources, institutions of higher education can partner with emergency management actors and schools to multiply education and outreach to help mitigate local hazards and improve general risk reduction. As an example, students in one university’s graduate course in emergency management collaborated with the American Red Cross and the local school district to implement disaster awareness training to children who then shared lessons with their households. The program indicates the potential for such initiatives to increase household resilience. Therefore, universities can partially fulfill their roles as stewards of place by actively partnering with local emergency management to support disaster education and response to improve the safety of people and places

Rewiring Neural Interactions by Micro-Stimulation

Plasticity is a crucial component of normal brain function and a critical mechanism for recovery from injury. In vitro, associative pairing of presynaptic spiking and stimulus-induced postsynaptic depolarization causes changes in the synaptic efficacy of the presynaptic neuron, when activated by extrinsic stimulation. In vivo, such paradigms can alter the responses of whole groups of neurons to stimulation. Here, we used in vivo spike-triggered stimulation to drive plastic changes in rat forelimb sensorimotor cortex, which we monitored using a statistical measure of functional connectivity inferred from the spiking statistics of the neurons during normal, spontaneous behavior. These induced plastic changes in inferred functional connectivity depended on the latency between trigger spike and stimulation, and appear to reflect a robust reorganization of the network. Such targeted connectivity changes might provide a tool for rerouting the flow of information through a network, with implications for both rehabilitation and brain–machine interface applications

Why are Orbital Currents Central to High Tc Theory?

We explain qualitatively why the staggered flux state plays a central role in the SU(2) formulation of the t-J model, which we use to model the pseudogap state in underdoped cuprates. This point of view is supported by studies of projected wavefunctions. In addition to staggered orbital current correlations, we present here for the first time results of correlations involving hole and spin chirality and show that the two are closely related. The staggered flux state allows us to construct cheap and fast vortices, which may hold the key to explaining the many anomalous properties of the normal state.Comment: 7 pages, 3 figures, be published in Solid State Communications as Proceedings of the Williamsburg HTSC Workshop, 200