Online Mapping and Perception Algorithms for Multi-robot Teams Operating in Urban Environments.

This thesis investigates some of the sensing and perception challenges faced by multi-robot teams equipped with LIDAR and camera sensors. Multi-robot teams are ideal for deployment in large, real-world environments due to their ability to parallelize exploration, reconnaissance or mapping tasks. However, such domains also impose additional requirements, including the need for a) online algorithms (to eliminate stopping and waiting for processing to finish before proceeding) and b) scalability (to handle data from many robots distributed over a large area). These general requirements give rise to specific algorithmic challenges, including 1) online maintenance of large, coherent maps covering the explored area, 2) online estimation of communication properties in the presence of buildings and other interfering structure, and 3) online fusion and segmentation of multiple sensors to aid in object detection. The contribution of this thesis is the introduction of novel approaches that leverage grid-maps and sparse multi-variate gaussian inference to augment the capability of multi-robot teams operating in urban, indoor-outdoor environments by improving the state of the art of map rasterization, signal strength prediction, colored point cloud segmentation, and reliable camera calibration. In particular, we introduce a map rasterization technique for large LIDAR-based occupancy grids that makes online updates possible when data is arriving from many robots at once. We also introduce new online techniques for robots to predict the signal strength to their teammates by combining LIDAR measurements with signal strength measurements from their radios. Processing fused LIDAR+camera point clouds is also important for many object-detection pipelines. We demonstrate a near linear-time online segmentation algorithm to this domain. However, maintaining the calibration of a fleet of 14 robots made this approach difficult to employ in practice. Therefore we introduced a robust and repeatable camera calibration process that grounds the camera model uncertainty in pixel error, allowing the system to guide novices and experts alike to reliably produce accurate calibrations.PhDComputer Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113516/1/jhstrom_1.pd

Fluoride solid lubricants for extreme temperatures and corrosive environments

Fluoride solid lubricants for extreme temperature and corrosive environment

Estrone and estradiol concentrations in human ovaries, testes, and adrenals during the first two years of life

To determine the origin of estrogens in infant blood, we measured estrone (E1) and estradiol (E2) in the gonads of 50 girls and 64 boys who died suddenly between birth and 2 yr of age as well as in the adrenals of 18 of these infant girls and 16 of the boys. In the adrenals, E1 [median, 2.8 ng/g (10.4 pmol/g); range, 1.1-4.8 ng/g (4.1- 17.8 pmol/g)] and E2 [median, 3.0 ng/g (10.9 pmol/g); range, 1.2-5.3 ng/g (4.4-19.5 pmol/g)] were found in similar concentrations and were independent of age and sex. In the gonads, E2 was the major estrogen, but the concentrations differed markedly between the sexes; E2 exceeded E1 almost 10-fold in the ovaries and 2-fold in the testes. On the average, the gonads of the infant girls had 5 times more E2 and 2 times more E1 than those of the boys. As in plasma, E2 concentrations were highest in the ovaries of 1- to 6-month-old girls [median, 10.5 ng/g (38.5 pmol/g); range, 1.1-55.1 ng/g (4.0-202.0 pmol/g)] and in testes of 1- to 3-month-old boys [median, 1.8 ng/g (6.6 pmol/g); range, 0.6- 6.4 ng/g (2.3-23.5 pmol/g)]. Ovarian E2 concentrations declined to less than 3.0 ng/g (11.0 pmol/g) by the end of the first year of life, and testicular E2 declined to less than 1.0 ng/g (3.7 pmol/g) after only 6 months of age. Gonadal estrogen concentrations paralleled changes in gonadal morphology. Ovarian weights varied in a pattern of rise and fall similar to that of ovarian E2 concentrations; the biggest ovaries contained multiple macroscopic cysts. Testicular E2 closely correlated with Leydig cell development and testicular testosterone concentrations. We infer, therefore, that the surge of plasma E2 in infant girls originates from ovarian follicles and that of boys from testicular Leydig cells, and that these both occur as a result of the postnatal surge in gonadotropin secretion. The basal plasma E1 and E2 pool, however, is derived from the adrenals and remains at a comparatively constant level in both sexe

A Side of Mercury Not Seen By Mariner 10

More than 60,000 images of Mercury were taken at ~29 deg elevation during two sunrises, at 820 nm, and through a 1.35 m diameter off-axis aperture on the SOAR telescope. The sharpest resolve 0.2" (140 km) and cover 190-300 deg longitude -- a swath unseen by the Mariner 10 spacecraft -- at complementary phase angles to previous ground-based optical imagery. Our view is comparable to that of the Moon through weak binoculars. Evident are the large crater Mozart shadowed on the terminator, fresh rayed craters, and other albedo features keyed to topography and radar reflectivity, including the putative huge ``Basin S'' on the limb. Classical bright feature Liguria resolves across the northwest boundary of the Caloris basin into a bright splotch centered on a sharp, 20 km diameter radar crater, and is the brightest feature within a prominent darker ``cap'' (Hermean feature Solitudo Phoenicis) that covers the northern hemisphere between longitudes 140-250 deg. The cap may result from space weathering that darkens via a magnetically enhanced flux of the solar wind, or that reddens low latitudes via high solar insolation.Comment: 7 pages, 4 PDF figures, pdfLaTeX, typos corrected, Fig. 2 modified slightly to add crater diameters not given in published versio

Rounding of Quartz and K-Feldspar Sand From Beach to Dune Settings Along the California and Oregon Coastlines: Implications for Ancient Sandstones

Sand samples were collected from seven different locations along the California and Oregon coastlines where beach sediments and eolian coastal dunes are in close proximity (\u3c 0.5 km) to each other. Beach sand was collected from the swash zone and dune sand was taken from the crests or lee faces of dunes. Loose sand was impregnated with epoxy and thin sections were cut. The slides were stained for K-feldspar. About 100 quartz and 100 K-feldspar sand grains were measured and scored for rounding from each environment and from each location (14 total slides). Roundness was scored according to the roundness scale of Powers (1953) and Folk (1955) on a scale of 0-6 to the nearest 0.5. All the slides were analyzed over a two-week time period by the same worker to try and minimize bias. In order to compare rounding of similar sized sand grains from the coupled environments a size sample of 1.0 standard deviations from each side of the mean (size) was selected from the dune sample and then compared with the same size/mineral population from the beach sample (where there is a much wider range of sand grain sizes). T tests were used to see if significant rounding occurred from the beach to the dune (2 tails, unequal variance, Microsoft Excel) in this size population for each mineral. It was found that long axes of most sand grains were in the 100-500 um range. Graphing grain size against rounding showed only a small increase of rounding (small positive slopes) regardless of mineral species. P values indicated the rounding in the same size populations of quartz grains does not change significantly over this short transport distance (0.21 mean change). K-feldspar on the other hand always showed a statistically significant change in rounding (0.66 mean change). It might be expected that further eolian transport of the sand would even show a more marked difference between the two minerals. From these results, one might cautiously conclude that even a small amount of eolian transport can result in significant rounding of the overall population of K-feldspar sand grains compared to quartz. One might expect much better-rounded K-feldspar sand compared to quartz sand when comparing the same grain size populations in ancient eolian deposits. Angular K-feldspar may be a good indicator of an aqueous deposit. More work is encouraged to see if these results are repeatable

The Significance of Angular K-feldspar Grains in Ancient Sandstones

In our studies of ancient sandstones, many of which are purported in the conventional literature to be eolian deposits, we frequently encountered angular K-feldspar sand grains. In particular, we encountered them while studying the Coconino Sandstone of Arizona, but we have found them in many other ancient sandstones as well. To gain some insights on the petrology of ancient “eolian” sandstones, we studied the petrology of a number small ergs in the western United States, beach and dune sands along the California and Oregon and reviewed the literature on the petrology of modern eolian and subaqueous deposits. In our literature review and from our own observations along the California and Oregon coastlines, we found that fluvial and shoreline processes are not sufficient to cause rounding of sand grains of any type, even after energetic and prolonged longshore transport and frequent tidal activity. Conversely, when sand grains are picked up by eolian processes and transported to coastal dunes, all species of mineral grains are quickly rounded, even over short distances. K-feldspar is rounded faster than quartz probably because it is softer and cleaves easier. We frequently encountered rounded K-feldspar grains in the small ergs we examined despite many of them being close in proximity to sources of angular K-feldspar sand grains. In larger ergs, all types of sand grains become quickly rounded and angular grains only occur if there are local fluvial or coastal sources for them. The frequent occurrence of angular K-feldspar grains that we found in ancient cross-bedded sandstones, purported to be made by eolian processes, causes us to question whether these deposits were made by eolian activities or not. The presence of angular K-feldspar may be one petrographic criterion for identifying ancient fluvial and marine deposits. The goal of this paper is to document the ubiquitous occurrence of angular K-feldspar grains in many supposed ancient cross-bedded sandstones. Coupled with other criteria, angular K-feldspar sand grains are a crucial piece of data that might be used to argue that these ancient sandstones were formed by aqueous rather than eolian processes

The Extraordinarily Rapid Expansion of the X-ray Remnant of Kepler's Supernova (SN1604)

Four individual high resolution X-ray images from ROSAT and the Einstein Observatory have been used to measure the expansion rate of the remnant of Kepler's supernova (SN 1604). Highly significant measurements of the expansion have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All measurements are consistent with a current expansion rate averaged over the entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when combined with the known age of the remnant, determines the expansion parameter m, defined as $R\propto t^m$, to be 0.93 (+/-0.06) (+0.07,-0.04). The error bars on these results include both statistical (first set of errors) and systematic (second set) uncertainty. According to this result the X-ray remnant is expanding at a rate that is remarkably close to free expansion and nearly twice as fast as the mean expansion rate of the radio remnant. The expansion rates as a function of radius and azimuthal angle are also presented based on two ROSAT images that were registered to an accuracy better than 0.5 arcseconds. Significant radial and azimuthal variations that appear to arise from the motion of individual X-ray knots are seen. The high expansion rate of the X-ray remnant appears to be inconsistent with currently accepted dynamical models for the evolution of Kepler's SNR.Comment: 14 pages, including 7 postscript figs, LaTeX, emulateapj. Accepted by Ap

The Significance of Micas in Ancient Cross-bedded Sandstones

In our study of thin sections of the cross-bedded Coconino Sandstone we encountered muscovite as a trace mineral in almost every thin section of the hundreds that we cut. As we began to study other similar cross-bedded sandstones like the Tensleep, Lyons and Hopeman the same pattern began to emerge. All of these sandstones have been conventionally interpreted as desert wind-blown deposits. A novel set of experiments were performed and recently published by some Cedarville University geology students and the lead author of this paper (Anderson et al., 2017). They found when muscovite-rich quartz sand was experimentally placed into a simulated eolian setting, muscovite only survived for a matter of days. When muscovite-rich quartz sand was experimentally placed into a simulated subaqueous setting it was still present after a year of constant agitation before the experiment was finally terminated. Even though this was a simple experiment and only a limited number of trials were performed it confirms field observations by the authors that mica is rare in modern eolian deposits (unless they are very near a granitic source) and its relative abundance in beach and marine sands. The implications are significant. Although more experiments could be performed, the experiments and observations suggest that mica is rapidly degraded in wind-blown environments and survives when transported by water. Evidently water cushions the grain-to-grain collisions and prevents rapid deterioration of the muscovite in subaqueous settings. This proposed paper will catalog and illustrate the large number of cross-bedded sandstones we have found that contain mica (mostly muscovite) as an accessory mineral. The dominant conventional view is that these sandstones are eolian, but the presence of muscovite based on experimental data and field observations suggests otherwise. The presence of muscovite in cross-bedded sandstones can be used as one of many criteria to argue for subaqueous deposition

Detection of Molecular Hydrogen Orbiting a "Naked" T Tauri Star

Astronomers have established that for a few million years newborn stars possess disks of orbiting gas and dust. Such disks, which are likely sites of planet formation, appear to disappear once these stars reach ages of 5-10 times 10^6 yr; yet, >= 10^7 yr is thought necessary for giant planet formation. If disks dissipate in less time than is needed for giant planet formation, such planets may be rare and those known around nearby stars would be anomalies. Herein, we report the discovery of H_2 gas orbiting a weak-lined T Tauri star heretofore presumed nearly devoid of circumstellar material. We estimate that a significant amount of H_2 persists in the gas phase, but only a tiny fraction of this mass emits in the near-infrared. We propose that this star possesses an evolved disk that has escaped detection thus far because much of the dust has coagulated into planetesimals. This discovery suggests that the theory that disks are largely absent around such stars should be reconsidered. The widespread presence of such disks would indicate that planetesimals can form quickly and giant planet formation can proceed to completion before the gas in circumstellar disks disperses.Comment: latex 12 pages, including 1 figur