Diurnal Atmospheric Variation in the Tropics and Surveying With the Aneroid.

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Interactive volume rendering of large datasets using the silicon graphics Onyx4 visualization system

technical reportMany recent approaches to interactive volume rendering have focused on leveraging the power of commodity graphics hardware. Though currently limited to relatively small datasets, these approaches have been overwhelmingly successful. As the size of volumetric datasets continues to grow at a rapid pace, the need for scalable systems capable of interactively visualizing large datasets has emerged. In an attempt to address this need, SGI, Inc. has introduced the Silicon Graphics Onyx4 family of visualization systems. We present the results of our preliminary investigation into the utility of an 8-pipe Onyx4 system for interactive volume rendering of large datasets. By rendering the image in parallel using an application called Rhesus, we find that the Onyx4 provides reasonable interactivity for datasets that consume as much as 512 MB of texture memory

Practical global illumination for interactive particle visualization

ManuscriptParticle-based simulation methods are used to model a wide range of complex phenomena and to solve time-dependent problems of various scales. Effective visualizations of the resulting state will communicate subtle changes in the three-dimensional structure, spatial organization, and qualitative trends within a simulation as it evolves. We present two algorithms targeting upcoming, highly parallel multicore desktop systems to enable interactive navigation and exploration of large particle datasets with global illumination effects. Monte Carlo path tracing and texture mapping are used to capture computationally expensive illumination effects such as soft shadows and diffuse interreflection. The first approach is based on precomputation of luminance textures and removes expensive illumination calculations from the interactive rendering pipeline. The second approach is based on dynamic luminance texture generation and decouples interactive rendering from the computation of global illumination effects. These algorithms provide visual cues that enhance the ability to perform analysis and feature detection tasks while interrogating the data at interactive rates. We explore the performance of these algorithms and demonstrate their effectiveness using several large datasets

Survey of the Itanium architecture from a programmer's perspective

Journal ArticleThe Itanium family of processors represents Intel;s foray into the world of Explicitly Parallel Instruction Computing and 64-bit system design. This survey contains an introduction to the Itanium architecture and instruction set, as well as some of the available implementations. Taking a programmer's perspective, we have attempted to distill the relevant information from a variety of sources, including the Intel Itanium architecture documentation

Waveform Design for Maximum Pass-Band Energy

One way to maximize the sensitivity of an ultrasonic inspection is by establishing the pulser output voltage waveform to provide the maximum possible fraction of its energy in the pass-band of the piezoelectric transducer. An analytical study is reported that is backed up with experimental verification. Two pulser constraints are analyzed in this study. The first constraint is to study the common and easily generated waveform shapes for which each waveform has unit energy and compare to the optimum waveform shape with unit energy that is determined analytically. The second constraint is to repeat the first analysis with waveforms having unit amplitude rather than unit energy. The analysis for the first constraint shows that the numerically intractable problem of summing a very large number of Fourier coefficients can be replaced by a mathematically equivalent evaluation of the pass-band energy which requires only the integration of smooth functions. This alternative formulation also leads to the result that the optimized waveform is the eigenfunction of a particular integral operator corresponding to the largest eigenvalue. The eigenvalue itself gives the maximum attainable passband energy. The optimized waveform is compared with sine waves, rectangular waves, trapezoidal waves, triangle waves and exponential spikes for 1/2, 1 and 3/2 cycle durations. The analysis for the second constraint shows that the unit amplitude is in the form of an inequality which is outside the realm of the classical calculus of variations. An exact characterization of the optimized waveform was not found but numerical integration techniques were employed to determine the pass-band energies for the waveforms considered under the first constraint. Finally, a breadboard pulser model is constructed and extensive comparisons of the various waveshapes, sensitivity studies, spectral distributions and experimental verification are made for each constraint

Muscle Activation During Landing Before and After Fatigue in Individuals With or Without Chronic Ankle Instability

Ankle instability is a common condition in physically active individuals. It often occurs during a jump landing or lateral motion, particularly when participants are fatigued

Observing object lifting errors modulates cortico-spinal excitability and improves object lifting performance.

PublishedJournal ArticleObserving the actions of others has been shown to modulate cortico-spinal excitability and affect behaviour. However, the sensorimotor consequences of observing errors are not well understood. Here, participants watched actors lift identically weighted large and small cubes which typically elicit expectation-based fingertip force errors. One group of participants observed the standard overestimation and underestimation-style errors that characterise early lifts with these cubes (Error video--EV). Another group watched the same actors performing the well-adapted error-free lifts that characterise later, well-practiced lifts with these cubes (No error video--NEV). We then examined actual object lifting performance in the subjects who watched the EV and NEV. Despite having similar cognitive expectations and perceptions of heaviness, the group that watched novice lifters making errors themselves made fewer overestimation-style errors than those who watched the expert lifts. To determine how the observation of errors alters cortico-spinal excitability, we measured motor evoked potentials in separate group of participants while they passively observed these EV and NEV. Here, we noted a novel size-based modulation of cortico-spinal excitability when observing the expert lifts, which was eradicated when watching errors. Together, these findings suggest that individuals' sensorimotor systems are sensitive to the subtle visual differences between observing novice and expert performance.G. Buckingham was supported with a Banting Postdoctoral Fellowship, awarded by the Natural Sciences and Engineering Council of Canada (NSERC

The human motor system alters its reaching movement plan for task-irrelevant, positional forces.

The minimum intervention principle and the uncontrolled manifold hypothesis state that our nervous system only responds to force perturbations and sensorimotor noise if they affect task success. This idea has been tested in muscle and joint coordinate frames and more recently using workspace redundancy (e.g., reaching to large targets). However, reaching studies typically involve spatial and or temporal constraints. Constrained reaches represent a small proportion of movements we perform daily and may limit the emergence of natural behavior. Using more relaxed constraints, we conducted two reaching experiments to test the hypothesis that humans respond to task-relevant forces and ignore task-irrelevant forces. We found that participants responded to both task-relevant and -irrelevant forces. Interestingly, participants experiencing a task-irrelevant force, which simply pushed them into a different area of a large target and had no bearing on task success, changed their movement trajectory prior to being perturbed. These movement trajectory changes did not counteract the task-irrelevant perturbations, as shown in previous research, but rather were made into new areas of the workspace. A possible explanation for this behavior change is that participants were engaging in active exploration. Our data have implications for current models and theories on the control of biological motion

Functional Plasticity in Somatosensory Cortex Supports Motor Learning by Observing.

An influential idea in neuroscience is that the sensory-motor system is activated when observing the actions of others [1, 2]. This idea has recently been extended to motor learning, in which observation results in sensory-motor plasticity and behavioral changes in both motor and somatosensory domains [3-9]. However, it is unclear how the brain maps visual information onto motor circuits for learning. Here we test the idea that the somatosensory system, and specifically primary somatosensory cortex (S1), plays a role in motor learning by observing. In experiment 1, we applied stimulation to the median nerve to occupy the somatosensory system with unrelated inputs while participants observed a tutor learning to reach in a force field. Stimulation disrupted motor learning by observing in a limb-specific manner. Stimulation delivered to the right arm (the same arm used by the tutor) disrupted learning, whereas left arm stimulation did not. This is consistent with the idea that a somatosensory representation of the observed effector must be available during observation for learning to occur. In experiment 2, we assessed S1 cortical processing before and after observation by measuring somatosensory evoked potentials (SEPs) associated with median nerve stimulation. SEP amplitudes increased only for participants who observed learning. Moreover, SEPs increased more for participants who exhibited greater motor learning following observation. Taken together, these findings support the idea that motor learning by observing relies on functional plasticity in S1. We propose that visual signals about the movements of others are mapped onto motor circuits for learning via the somatosensory system