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Caitlin M Hudac1, Srinivas Kota1, James L Nedrow2, Dennis L Molfese1,31Department of Psychology, University of Nebraska-Lincoln, 2Oculi Vision Rehabilitation, 3Center for Brain, Biology, and Behavior, University of Nebraska-Lincoln, Lincoln, NEAbstract: Mild to severe traumatic brain injuries have lasting effects on everyday functioning. Issues relating to sensory problems are often overlooked or not addressed until well after the onset of the injury. In particular, vision problems related to ambient vision and the magnocellular pathway often result in posttrauma vision syndrome or visual midline shift syndrome. Symptoms from these syndromes are not restricted to the visual domain. Patients commonly experience proprioceptive, kinesthetic, vestibular, cognitive, and language problems. Neurooptometric rehabilitation often entails the use of corrective lenses, prisms, and binasal occlusion to accommodate the unstable magnocellular system. However, little is known regarding the neural mechanisms engaged during neurooptometric rehabilitation, nor how these mechanisms impact other domains. Event-related potentials from noninvasive electrophysiological recordings can be used to assess rehabilitation progress in patients. In this case report, high-density visual event-related potentials were recorded from one patient with posttrauma vision syndrome and secondary visual midline shift syndrome during a pattern reversal task, both with and without prisms. Results indicate that two factors occurring during the end portion of the P148 component (168–256 milliseconds poststimulus onset) map onto two separate neural systems that were engaged with and without neurooptometric rehabilitation. Without prisms, neural sources within somatosensory, language, and executive brain regions engage inefficient magnocellular system processing. However, when corrective prisms were worn, primary visual areas were appropriately engaged. The impact of using early neurooptometric rehabilitation for posttrauma vision syndrome, visual midline shift syndrome, and other similar subtle vision disorders to support neural reorganization is discussed.Keywords: traumatic brain injury, posttrauma vision syndrome, visual midline shift syndrome, visual event-related potentials, source localization, neural reorganization

The coefficients of thermal expansion (CTE) of the ternary borides, MoAlB, Cr2AlB2, Mn2AlB2, and Fe2AlB2, and the binary boride, CrB, were calculated from in situ high-temperature powder X-ray diffraction patterns. The order—from low to high—of the average linear thermal expansions was MoAlB (7.3 × 10−6 K−1), CrB (8.6 × 10−6 K−1), Fe2AlB2 (10.3 × 10−6 K−1), Cr2AlB2 (10.5 × 10−6 K−1), and Mn2AlB2 (14.0 × 10−6 K−1). Despite their structural and chemical similarities, the CTE anisotropies of these phases were different and could be grouped into two groups. In the first group, MoAlB and Fe2AlB2, the highest CTE values were along the stacking direction and the lowest were parallel to the B–B chains. In the second group, Cr2AlB2, Mn2AlB2, and CrB, the lowest CTE was along the stacking direction and the highest was normal to the chains. The thermal expansions parallel to the B–B chains were significantly lower (32% to 103%) than those perpendicular to the chains in all the ternaries except for MoAlB. In general, the relative CTEs parallel to the B–B chains in both the M2AlB2 ternaries and corresponding binary monoborides suggest that strong covalent character of the B–B bonds are at least partially responsible for the large thermal expansion anisotropies observed. [ABSTRACT FROM AUTHOR]

The coefficients of thermal expansion (CTE) of the ternary borides, MoAlB, Cr2AlB2, Mn2AlB2, and Fe2AlB2, and the binary boride, CrB, were calculated from in situ high-temperature powder X-ray diffraction patterns. The order—from low to high—of the average linear thermal expansions was MoAlB (7.3 × 10−6 K−1), CrB (8.6 × 10−6 K−1), Fe2AlB2 (10.3 × 10−6 K−1), Cr2AlB2 (10.5 × 10−6 K−1), and Mn2AlB2 (14.0 × 10−6 K−1). Despite their structural and chemical similarities, the CTE anisotropies of these phases were different and could be grouped into two groups. In the first group, MoAlB and Fe2AlB2, the highest CTE values were along the stacking direction and the lowest were parallel to the B–B chains. In the second group, Cr2AlB2, Mn2AlB2, and CrB, the lowest CTE was along the stacking direction and the highest was normal to the chains. The thermal expansions parallel to the B–B chains were significantly lower (32% to 103%) than those perpendicular to the chains in all the ternaries except for MoAlB. In general, the relative CTEs parallel to the B–B chains in both the M2AlB2 ternaries and corresponding binary monoborides suggest that strong covalent character of the B–B bonds are at least partially responsible for the large thermal expansion anisotropies observed. [ABSTRACT FROM AUTHOR]

Visual stimuli without sharp edges fade gradually under visual fixation. This phenomenon is known as Troxler fading or fading illusion. Traditionally, this fading is explained by a hypothesis that physical stimulus is cancelled by a negative image generated in the visual pathway, because the negative image is perceived momentarily when the physical stimulus is removed suddenly. One prediction that may be tested neurophysiologically is that, in the faded or adapted state, visual neurons actually respond to a blank screen, as if they actually ‘see’ the negative image. To examine this prediction in cat V1, we measured the contrast response function of single neurons by presenting flashed grating stimuli of various contrasts (7 contrasts in straddle, ±25%, range and pedestal, within 0–50%, range; negative values for phase reversal) in a rapid succession. Data were analyzed using reverse correlation. The orientation and spatial frequency of gratings were fixed at the optimal value of each cell. We found that V1 neurons showed a shift of contrast response function during pedestal conditions to respond to a blank screen (i.e., 0% contrast stimulus). The amount of shift was consistent with the arithmetic mean of contrasts in each experimental condition. These results support the hypothesis that a negative image is generated during visual fading, and it behaves as if it were a real stimulus. Additionally, we examined phase retardation using periodic stimuli to investigate the temporal transition of contrast response functions. The time constant of phase retardation was comparable to that we observed perceptually.

Altered sensory experience in early life often leads to remarkable adaptations in humans and animals. Consistent with this, previous studies have reported that restricting visual inputs in young animals can make drastic long-lasting changes in the early sensory areas of their brains. Typically, the majority of sensory neurons are allocated to stimulus features to which the animals were exposed. However, if that is the only change, it will make the sensory encoding highly redundant with many neurons signaling the same features. Are there additional changes, heretofore unnoticed, to functional properties of single neurons in such adaptation processes? Here we show that stimulus selectivities like the sharpness of tuning of single neurons in the primary visual cortex are modified to match a particular environment that has a restricted range of orientations. Specifically, we found in orientation-restricted animals that neurons tuned to an experienced orientation show sharper orientation tuning than neurons in normal animals, whereas the opposite was true for neurons tuned to non-experienced orientations. The sharpened tuning appears to be due to elongated receptive fields. Additionally, quality of signals such as the signal-to-noise ratio can be improved by averaging the activities of a population of neurons unless the same noise source is shared. Correlation of noise shared across neurons in the orientation-restricted animals was comparable to that in normal animals, confirming the potential for such improvements. Our results demonstrate that restricted sensory experiences can sculpt the supranormal functions of neurons tailored for a particular environment.

This paper introduces the benefits of exploiting elasticity in the engineering design of surgical tools, in general, and of minimally invasive procedures, in particular. Compliant mechanisms are jointless mechanisms that rely on elastic deformation to transmit forces and motion. The lack of traditional joints in these single-piece flexible structures offers many benefits, including the absence of wear debris, pinch points, crevices, and lubrication. Such systems are particularly amenable to embedded sensing for haptic feedback and embedded actuation with active-material actuators. The paper provides an overview of design synthesis methods developed at the Compliant Systems Design Laboratory and focuses specifically on surgical applications. Compliant systems have potential to integrate well within the constraints of laparoscopic procedures and telerobotic surgery. A load-path representation is used within a genetic algorithm to solve two gripper example problems. In addition, the paper illustrates the design and construction of an organ (kidney) manipulator for use in minimally invasive procedures. [DOI: 10.1115/1.2056561]

This study estimates the potential source regions contributing to PM2.5 in the capital city of Thimphu, Bhutan, during the years 2018–2020 using the ground-based data, followed by the HYSPLIT back trajectory analysis. The average PM2.5 concentration in the entire study period was 32.47 µg/m3 which is three times of the World Health Organization recommended limit of 10 µg/m3. Less than half of the days in pre-monsoon (43.47%) and post-monsoon (46.41%), and no days in winter were within the 24-h average WHO guideline of 25 μg/m3. During the COVID-19 lockdown imposed from August 11 to September 21 in Bhutan, only a marginal reduction of 4% in the PM2.5 concentrations was observed, indicating that nonlocal emissions dominate the PM2.5 concentrations in Thimphu, Bhutan. Most back trajectories in the analysis period were allocated to south or south-west sector. India was the major contributor (~ 44%), followed by Bangladesh (~ 19%), Bhutan itself (~ 19%) and China (~ 16%). This study confirms that there are significant contributions from transboundary sources to PM2.5 concentrations in Thimphu, Bhutan, and the elevated PM2.5 concentrations need to be tackled with appropriate action plans and interventions. [ABSTRACT FROM AUTHOR]

Compliant four-bar mechanisms treated in previous works consisted of at least one rigid moving link, and such mechanisms synthesized for motion generation tasks have always comprised a rigid coupler link, bearing with the conventional definition of motion generation for rigid-link mechanisms. This paper introduces a new task called compliant-segment motion generation where the coupler is a flexible segment and requires a prescribed shape change along with a rigid-body motion. The paper presents a systematic procedure for synthesis of single-loop compliant mechanisms with no moving rigid-links for compliant-segment motion generation task. Such compliant mechanisms have potential applications in adaptive structures. The synthesis method presented involves an atypical inverse elastica problem that is not reported in the literature. This inverse problem is solved by extending the loop-closure equation used in the synthesis of rigid-links to the flexible segments, and then combining it with elastic equilibrium equation in an optimization scheme. The method is illustrated by a numerical example.

Compliant mechanisms are jointless mechanical devices that take advantage of elastic deformation to achieve a force or motion transformation. An important step toward automated design of compliant mechanisms has been the development of topology optimization techniques. The next logical step is to incorporate size and shape optimization to perform dimensional synthesis of the mechanism while simultaneously considering practical design specifications such as kinematic and stress constraints. An improved objective formulation based on maximizing the energy throughput of a linear static compliant mechanism is developed considering specific force and displacement operational requirements. Parametric finite element beam models are used to perform the size and shape optimization. This technique allows stress constraints to limit the maximum stress in the mechanism. In addition, constraints which restrict the kinematics of the mechanism are successfully applied to the optimization problem. Resulting optimized mechanisms exhibit efficient mechanical transmission and meet kinematic and stress requirements. Several examples are given to demonstrate the effectiveness of the optimization procedure.