On the Design of Wide-Field X-ray Telescopes

X-ray telescopes having a relatively wide field-of-view and spatial resolution vs. polar off-axis angle curves much flatter than the parabolic dependence characteristic of Wolter I designs are of great interest for surveys of the X-ray sky and potentially for study of the Sun s X-ray emission. We discuss the various considerations affecting the design of such telescopes, including the possible use of polynomial mirror surface prescriptions, a method of optimizing the polynomial coefficients, scaling laws for mirror segment length vs. intersection radius, the loss of on-axis spatial resolution, and the positioning of focal plane detectors

Brain tissue properties differentiate between motor and limbic basal ganglia circuits

Despite advances in understanding basic organizational principles of the human basal ganglia, accurate in vivo assessment of their anatomical properties is essential to improve early diagnosis in disorders with corticosubcortical pathology and optimize target planning in deep brain stimulation. Main goal of this study was the detailed topological characterization of limbic, associative, and motor subdivisions of the subthalamic nucleus (STN) in relation to corresponding corticosubcortical circuits. To this aim, we used magnetic resonance imaging and investigated independently anatomical connectivity via white matter tracts next to brain tissue properties. On the basis of probabilistic diffusion tractography we identified STN subregions with predominantly motor, associative, and limbic connectivity. We then computed for each of the nonoverlapping STN subregions the covariance between local brain tissue properties and the rest of the brain using high-resolution maps of magnetization transfer (MT) saturation and longitudinal (R1) and transverse relaxation rate (R2*). The demonstrated spatial distribution pattern of covariance between brain tissue properties linked to myelin (R1 and MT) and iron (R2*) content clearly segregates between motor and limbic basal ganglia circuits. We interpret the demonstrated covariance pattern as evidence for shared tissue properties within a functional circuit, which is closely linked to its function. Our findings open new possibilities for investigation of changes in the established covariance pattern aiming at accurate diagnosis of basal ganglia disorders and prediction of treatment outcom

Eye Tracking Support for Visual Analytics Systems

Visual analytics (VA) research provides helpful solutions for interactive visual data analysis when exploring large and complex datasets. Due to recent advances in eye tracking technology, promising opportunities arise to extend these traditional VA approaches. Therefore, we discuss foundations for eye tracking support in VA systems. We first review and discuss the structure and range of typical VA systems. Based on a widely used VA model, we present five comprehensive examples that cover a wide range of usage scenarios. Then, we demonstrate that the VA model can be used to systematically explore how concrete VA systems could be extended with eye tracking, to create supportive and adaptive analytics systems. This allows us to identify general research and application opportunities, and classify them into research themes. In a call for action, we map the road for future research to broaden the use of eye tracking and advance visual analytics

Reliable 3D mapping of ocular dominance columns in humans using GE-EPI fMRI at 7 T

Since the discovery of the BOLD effect, detection of ocular dominance columns (ODCs) in primary visual cortex (V1) served as a benchmark for high-precision functional magnetic resonance imaging (fMRI) (Menon et al., 1997; Dechent and Frahm 2000; Cheng et al., 2001; Yacoub et al., 2007). Although gradient-echo (GE) echo-planar imaging (EPI) is often used at lower field strengths, the applicability for high-resolution fMRI at higher field strengths is still under debate because of its inherent sensitivity to large draining veins (Polimeni et al., 2010). To counteract the loss of specificity, it was recently suggested to only sample far away from the pial surface when using GE-EPI (Nasr et al., 2016; Polimeni et al., 2017). Here, we assessed whether differential ocular dominance responses can be resolved using GE-EPI with different isotropic resolutions (0.8 mm and 1.0 mm) and how the corresponding BOLD signal is distributed across the cortex

Closed-loop fMRI at the mesoscopic scale of columns and layers: Can we do it and why would we want to?

Technological advances in fMRI including ultra-high magnetic fields (≥ 7T) and acquisition methods that increase spatial specificity have paved the way for studies ofthe human cortex at the scale of layers and columns. This mesoscopic scale promises an improved mechanistic understanding of human cortical function so far only accessible to invasive animal neurophysiology. In recent years an increasing number of studies have applied such methods to better understand the cortical function in perception and cognition. This Future Perspective article asks whether closed-loop fMRI studies could equally benefit from these methods to achieve layer and columnar specificity. We outline potential applications and discuss the conceptual and concrete challenges, including data acquisition and volitional control of mesoscopic brain activity. We anticipate an important role of fMRI with mesoscopic resolution for closed-loop fMRI and neurofeedback, yielding new insights into brain function and potentially clinical applications

The Q^2-Dependence of Nuclear Transparency for Exclusive ρ0\rho^0 Production

Exclusive coherent and incoherent electroproduction of the $\rho^0$ meson from $^1$H and $^{14}$N targets has been studied at the HERMES experiment as a function of coherence length ($l_c$), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon ($-Q^2$). The ratio of $^{14}$N to $^1$H cross sections per nucleon, known as nuclear transparency, was found to increase (decrease) with increasing coherence length for coherent (incoherent) $\rho^0$ electroproduction. For fixed coherence length, a rise of nuclear transparency with $Q^2$ is observed for both coherent and incoherent $\rho^0$ production, which is in agreement with theoretical calculations of color transparency.Comment: 5 pages, 4 figure