Dimensionality reduction beyond neural subspaces with slice tensor component analysis

Recent work has argued that large-scale neural recordings are often well described by patterns of coactivation across neurons. Yet the view that neural variability is constrained to a fixed, low-dimensional subspace may overlook higher-dimensional structure, including stereotyped neural sequences or slowly evolving latent spaces. Here we argue that task-relevant variability in neural data can also cofluctuate over trials or time, defining distinct ‘covariability classes’ that may co-occur within the same dataset. To demix these covariability classes, we develop sliceTCA (slice tensor component analysis), a new unsupervised dimensionality reduction method for neural data tensors. In three example datasets, including motor cortical activity during a classic reaching task in primates and recent multiregion recordings in mice, we show that sliceTCA can capture more task-relevant structure in neural data using fewer components than traditional methods. Overall, our theoretical framework extends the classic view of low-dimensional population activity by incorporating additional classes of latent variables capturing higher-dimensional structure

Fracture behaviour and damage characterisation in composite impact panels by laboratory X-ray computed tomography

<p>Presentation from Thermosets 2013, From Monomers to Components Conference in Berlin, Germany 16-18 September 2013.</p

Cold, Northern Winters: The Importance of Temperature to Overwinter Mortality of Age-0 White Crappies

Survival during the first winter of life can influence the recruitment of many fishes. We used field sampling and laboratory experiments to explore the mechanisms underlying first winter growth and survival of white crappie Pomoxis annularis, which exhibits variable recruitment. We sampled age-0 white crappies from four Ohio reservoirs before winter to evaluate whether large individuals had a greater energy density (kJ/g) than small ones and whether mean energy density differed among reservoirs. Energy density increased with fish size in all reservoirs, suggesting that small fish could die earlier if energy stores become limiting during winter. Mean energy density varied among reservoirs as well, suggesting that prewinter energy reserves could influence recruitment variability across reservoirs through their effects on winter starvation. Our laboratory experiment evaluated how fish size (small or large), feeding level (starved or fed), and winter severity (mild or severe) interact to influence the growth and survival of age-0 white crappies. The two winter severity treatments represented two extremes for Ohio winters (i.e., mild and severe). We calculated daily individual growth rates for all fish, energy density for a subset of fish, and percent survival across treatments. Winter severity strongly influenced survival: only 47% of all white crappies survived the severe winter, whereas 97% survived the mild winter. In the severe winter, neither size nor feeding level influenced mortality. Bomb calorimetry revealed energy density to be similar among fish that died and those that survived the severe winter, suggesting that energy depletion did not cause mortality. Rather, osmoregulatory failure may have occurred during exposure to temperatures colder than 4°C for at least 1 week. Thus, the availability of warm (≥4°C), oxygenated water during winter may be critical to the survival of age-0 white crappies. In the northern portion of their range, winter temperatures may account for some of the recruitment variability common to white crappie populations.This research was funded by Federal Aid in Sport Fish Restoration Project F-69-P, administered jointly by U.S. Fish and Wildlife Service and Ohio Department of Natural Resources, Division of Wildlife, and the Department of Evolution, Ecology, and Organismal Biology at the Ohio State University

Conversion of the Bayou Choctaw geological site characterization report to a three-dimensional model.

The geologic model implicit in the original site characterization report for the Bayou Choctaw Strategic Petroleum Reserve Site near Baton Rouge, Louisiana, has been converted to a numerical, computer-based three-dimensional model. The original site characterization model was successfully converted with minimal modifications and use of new information. The geometries of the salt diapir, selected adjacent sedimentary horizons, and a number of faults have been modeled. Models of a partial set of the several storage caverns that have been solution-mined within the salt mass are also included. Collectively, the converted model appears to be a relatively realistic representation of the geology of the Bayou Choctaw site as known from existing data. A small number of geometric inconsistencies and other problems inherent in 2-D vs. 3-D modeling have been noted. Most of the major inconsistencies involve faults inferred from drill hole data only. Modem computer software allows visualization of the resulting site model and its component submodels with a degree of detail and flexibility that was not possible with conventional, two-dimensional and paper-based geologic maps and cross sections. The enhanced visualizations may be of particular value in conveying geologic concepts involved in the Bayou Choctaw Strategic Petroleum Reserve site to a lay audience. A Microsoft WindowsTM PC-based viewer and user-manipulable model files illustrating selected features of the converted model are included in this report

Conversion of the Bryan Mound geological site characterization reports to a three-dimensional model.

The Bryan Mound salt dome, located near Freeport, Texas, is home to one of four underground crude oil-storage facilities managed by the U. S. Department of Energy Strategic Petroleum Reserve (SPR) Program. Sandia National Laboratories, as the geotechnical advisor to the SPR, conducts site-characterization investigations and other longer-term geotechnical and engineering studies in support of the program. This report describes the conversion of two-dimensional geologic interpretations of the Bryan Mound site into three-dimensional geologic models. The new models include the geometry of the salt dome, the surrounding sedimentary units, mapped faults, and the 20 oil-storage caverns at the site. This work provides an internally consistent geologic model of the Bryan Mound site that can be used in support of future work

Conversion of the Big Hill geological site characterization report to a three-dimensional model.

The Big Hill salt dome, located in southeastern Texas, is home to one of four underground oil-storage facilities managed by the U. S. Department of Energy Strategic Petroleum Reserve (SPR) Program. Sandia National Laboratories, as the geotechnical advisor to the SPR, conducts site-characterization investigations and other longer-term geotechnical and engineering studies in support of the program. This report describes the conversion of two-dimensional geologic interpretations of the Big Hill site into three-dimensional geologic models. The new models include the geometry of the salt dome, the surrounding sedimentary units, mapped faults, and the 14 oil storage caverns at the site. This work provides a realistic and internally consistent geologic model of the Big Hill site that can be used in support of future work

Conversion of the West Hackberry geological site characterization report to a three-dimensional model.

The West Hackberry salt dome, in southwestern Louisiana, is one of four underground oil-storage facilities managed by the U. S. Department of Energy Strategic Petroleum Reserve (SPR) Program. Sandia National Laboratories, as the geotechnical advisor to the SPR, conducts site-characterization investigations and other longer-term geotechnical and engineering studies in support of the program. This report describes the conversion of two-dimensional geologic interpretations of the West Hackberry site into three-dimensional geologic models. The new models include the geometry of the salt dome, the surrounding sedimentary layers, mapped faults, and a portion of the oil storage caverns at the site. This work provides a realistic and internally consistent geologic model of the West Hackberry site that can be used in support of future work