Early Visual Processing in Autism Spectrum Disorder as Assessed by Visual Evoked Potentials

Understanding early visual processing and the integrity of the visual pathways in Autism Spectrum Disorder (ASD) could help to develop a potential neuromarker. If these early stages of visual perception are compromised it could be impacting higher cognitive abilities that are necessary for social perception. For example, atypical visual behaviors such as poor eye gaze, difficulty with facial expression, and difficulty processing motion have been highly documented in social and nonsocial domains in ASD. These symptoms have been linked to abnormal sensory processing suggesting possible impairments in the magnocellular visual pathway (M-pathway). To assess early visual processing and the integrity of the visual pathways we used achromatic pattern-reversal along with a motion-onset and offset stimuli in children and adolescents with and without a diagnosis of ASD. Visual-evoked potentials (VEPs) were used to investigate early visual processing in adolescents with ASD compared to neurotypicals (NTs). For pattern-reversal, we used a black-and-white checkerboard with two different sizes (1° and 0.25°) and four different contrast levels (0.025 contrast, 0.05 contrast, 0.1 contrast, and 0.98 contrast). To study motion-onset and offset we used an expanding and contracting ‘dartboard.’ These stimuli were displayed to a total of seven male ASD and eight male NT subjects, ranging in age from 10-15 years old. VEPs were recorded on the scalp midline over the occipital (Oz) and parietal (Pz) cortices. For pattern-reversal, we examined the negative component N75, and the positive component P100. For motion-onset and motion-offset, we explored the positive component P100 and the negative component N135. VEPs responses were analyzed using measures of peak latency, peak amplitude, mean amplitude, and fractional area latency. Our results point to a disruption of the M-pathway where the ASD subjects often showed hyper-responsiveness to lower contrast stimuli presented at the largest check size. Individual waveforms in ASD subjects were variable, and may not be useful as a reliable early neuromarker. Some measures of the VEP seem to be related to symptom severity as assessed by the GARS-2, although these results never reached significance. For motion-onset, the ASD group presented larger amplitudes for the components P100 and N135 at electrode size Oz. Alterations to early visual processing in the ASD group suggest specific difficulties in the magnocellular system which could be causing a cascade of symptoms that impairs social communication. Although individual waveform variability limits the use of VEPs as a neuromarker, there is some potential relationship to symptom severity that deserves further study

Simple Model for Wet Granular Materials with Liquid Clusters

We propose a simple phenomenological model for wet granular media to take into account many particle interaction through liquid in the funicular state as well as two-body cohesive force by a liquid bridge in the pendular state. In the wet granular media with small liquid content, liquid forms a bridge at each contact point, which induces two-body cohesive force due to the surface tension. As the liquid content increases, some liquid bridges merge, and more than two grains interact through a single liquid cluster. In our model, the cohesive force acts between the grains connected by a liquid-gas interface. As the liquid content increases, the number of grains that interact through the liquid increases, but the liquid-gas interface may decrease when liquid clusters are formed. Due to this competition, our model shows that the shear stress has a maximum as a function of the liquid-content.Comment: 6 pages, 8 figures. Discussion is updated. Accepted for publication in EP

Net solar generation potential from urban rooftops in Los Angeles

Rooftops provide accessible locations for solar energy installations. While rooftop solar arrays can offset in-building electricity needs, they may also stress electric grid operations. Here we present an analysis of net electricity generation potential from distributed rooftop solar in Los Angeles. We integrate spatial and temporal data for property-level electricity demands, rooftop solar generation potential, and grid capacity constraints to estimate the potential for solar to meet on-site demands and supply net exports to the electric grid. In the study area with 1.2 million parcels, rooftop solar could meet 7200 Gigawatt Hours (GWh) of on-site building demands (~29% of demand). Overall potential net generation is negative, meaning buildings use more electricity than they can produce. Yet, cumulative net export potential from solar to grid circuits is 16,400 GWh. Current policies that regulate solar array interconnection to the grid result in unutilized solar power output of 1700 MW. Lower-income and at-risk communities in LA have greater potential for exporting net solar generation to the grid. This potential should be recognized through investments and policy innovations. The method demonstrates the need for considering time-dependent calculations of net solar potential and offers a template for distributed renewable energy planning in cities