Ion-induced kinetic electron emission from HOPG with different surface orientation

Total electron emission yields for impact of \chem{H^+}, \chem{{H_2}^+}, \chem{C^+}, \chem{N^+}, \chem{O^+} and \chem{Ar^+} ions (impact energy 2–10\un{keV}) on clean highly oriented pyrolytic graphite (HOPG) have been measured. An enhancement in the electron yield of more than a factor of 2 is found when comparing results for differently oriented HOPG surfaces (orientation of the graphite layers with respect to the surface). By analyzing these data we elucidate the influence of electron transport on kinetic electron emission and derive direction-dependent mean escape depths for low-energy electrons

fMRI of Emotion

Recent brain imaging work has expanded our understanding of the mechanisms of perceptual, cognitive, and motor functions in human subjects, but research into the cerebral control of emotional and motivational function is at a much earlier stage. Important concepts and theories of emotion are briefly introduced, as are research designs and multimodal approaches to answering the central questions in the field. We provide a detailed inspection of the methodological and technical challenges in assessing the cerebral correlates of emotional activation, perception, learning, memory, and emotional regulation behavior in healthy humans. fMRI is particularly challenging in structures such as the amygdala as it is affected by susceptibility-related signal loss, image distortion, physiological and motion artifacts, and colocalized Resting State Networks (RSNs). We review how these problems can be mitigated by using optimized echo-planar imaging (EPI) parameters, alternative MR sequences, and correction schemes. High-quality data can be acquired rapidly in these problematic regions with gradient-compensated multiecho EPI or high-resolution EPI with parallel imaging and optimum gradient directions, combined with distortion correction. Although neuroimaging studies of emotion encounter many difficulties regarding the limitations of measurement precision, research design, and strategies of validating neuropsychological emotion constructs, considerable improvement in data quality and sensitivity to subtle effects can be achieved. The methods outlined offer the prospect for fMRI studies of emotion to provide more sensitive, reliable, and representative models of measurement that systematically relate the dynamics of emotional regulation behavior with topographically distinct patterns of activity in the brain. This will provide additional information as an aid to assessment, categorization, and treatment of patients with emotional and personality disorders