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Chemical doping of organic semiconductors (i) increases conductivity, (ii) enables control of interface molecular level alignment, and (iii) facilitates carrier injection. Extensive work has therefore been done over the past decade to develop and characterize ever more powerful and efficient oxidant and reducing molecules. N-doping is particularly challenging, since it requires very low ionization energy donors to transfer electrons to the host matrix. Depending on the specific application, the donor oxidation potential must be as low as 2.5-3.0 eV, which is highly unstable against oxidation. We discuss here very recent results obtained with a new class of powerful air-stable organometallic reducing agents, usable both in vapor phase and in solution. The composition and structure of these compounds is discussed. Air-stability is demonstrated for periods of hours. We show effective n-doping of molecular films via co-evaporation and of polymer films via co-solution, and we suggest mechanisms that lead to the activation of the dopant. Fabrication of p-i-n homojunction diodes and other partially doped devices is reported.

A fundamental question in systems neuroscience is: What are the organization principles of human visual cortex? Visual cortex originates in primary visual cortex and extends through a hierarchy of early, intermediate, and high-level visual regions separated across two processing streams (dorsal and ventral). While much is known about the organization of early visual cortex, much less is known about the organization of high-level visual regions in the ventral stream, which are thought to be involved in visual recognition. Current theories suggest functional distinctions between early and high-level regions in the ventral processing stream: early and intermediate visual regions contain a systematic representation of the visual field across a series of multiple maps (Wandell and Winawer, 2011), whereas higher-level regions are thought to be specialized for processing specific types of stimuli such as objects, faces, body parts, words, and places (Kanwisher, 2010). Several alternative theories suggest other principles for the organization of the ventral stream, including expertise (Tarr and Gauthier, 2000), eccentricity biases (Malach et al., 2002), or distributed representations (Haxby et al., 2001; Kriegeskorte et al., 2008). Nevertheless, two notions are common to these theories. First, it is widely accepted that different rules underlie the functional organization of high-level and early visual cortex. Second, the profile of activations in high-level visual cortex is thought to be more variable across individuals compared to early visual cortex. Contrary to the prevailing view, we propose common organization principles throughout early and high-level visual cortex, where functional regions have consistent anatomical locations and preserved spatial relationships to neighboring regions as well as retinotopic maps. Employing these principles enables the first framework for consistent parcellation of high-level visual regions, which can also be applied to other sensory and nonsensory cortical systems.

We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs GRBs 090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor and Large Area Telescope (LAT) instruments on the Fermi satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases (1054 erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the relativistic energy budget of at least one of these events (GRB 090926A) exceeds the canonical value of 1051 erg by an order of magnitude. Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or a neutrino-driven collapsar, but remain compatible with theoretical expectations for magnetohydrodynamical collapsar models (e.g., the Blandford-Znajek mechanism). Our jet opening angles (θ) are similar to those found for pre-Fermi GRBs, but the large initial Lorentz factors (Γ0) inferred from the detection of GeV photons imply θΓ0 ≈ 70-90, values which are above those predicted in magnetohydrodynamic models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity progenitor stars. Future studies of Fermi-LAT afterglows at radio wavelengths with the order-of-magnitude improvement in sensitivity offered by the Extended Very Large Array should definitively establish the relativistic energy budgets of these events