948 research outputs found

    Toward a computational theory for motion understanding: The expert animators model

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    Artificial intelligence researchers claim to understand some aspect of human intelligence when their model is able to emulate it. In the context of computer graphics, the ability to go from motion representation to convincing animation should accordingly be treated not simply as a trick for computer graphics programmers but as important epistemological and methodological goal. In this paper we investigate a unifying model for animating a group of articulated bodies such as humans and robots in a three-dimensional environment. The proposed model is considered in the framework of knowledge representation and processing, with special reference to motion knowledge. The model is meant to help setting the basis for a computational theory for motion understanding applied to articulated bodies

    SyZyGy: A Straight Interferometric Spacecraft System for Gravity Wave Observations

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    We apply TDI, unfolding the general triangular configuration, to the special case of a linear array of three spacecraft. We show that such an array ("SyZyGy") has, compared with an equilateral triangle GW detector of the same scale, degraded (but non-zero) sensitivity at low-frequencies (f<<c/(arrany size)) but similar peak and high-frequency sensitivities to GWs. Sensitivity curves are presented for SyZyGys having various arm-lengths. A number of technical simplifications result from the linear configuration. These include only one faceted (e.g., cubical) proof mass per spacecraft, intra-spacecraft laser metrology needed only at the central spacecraft, placement in a single appropriate orbit can reduce Doppler drifts so that no laser beam modulation is required for ultra-stable oscillator noise calibration, and little or no time-dependent articulation of the telescopes to maintain pointing. Because SyZyGy's sensitivity falls off more sharply at low frequency than that of an equilateral triangular array, it may be more useful for GW observations in the band between those of ground-based interferometers (10-2000 Hz) and LISA (.1 mHz-.1 Hz). A SyZyGy with ~1 light- second scale could, for the same instrumental assumptions as LISA, make obseervations in this intermediate frequency GW band with 5 sigma sensitivity to sinusoidal waves of ~2.5 x 10^-23 in a year's integration.Comment: 13 pages, 6 figures; typos corrected, figure modified, references adde

    Lidar as a Shoreline Mapping Tool

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    Kodiak Brown Bears Surf the Salmon Red Wave: Direct Evidence from GPS Collared Individuals

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    One of the goals of Ecosystems Base Fisheries Management (EBFM) is recognizing and mitigating indirect effects of fisheries on trophic interactions. Most research on indirect effects has considered how the abundance of managed fishes influences trophic interactions with other species. However, recent work has shown that attributes besides abundance, such as life history variation, can strongly mediate species interactions.  For example, phenological variation within prey species may enhance foraging opportunities for mobile predators by increasing the duration over which predators can target vulnerable life stages of prey.  Here, we present direct evidence of individual brown bears (Ursus arctos middendorffi) exploiting variation in sockeye salmon spawning phenology by tracking salmon runs across a 2,800 km2 region of Kodiak Island.  Data from 40 GPS collared brown bears show bears visited multiple spawning sites in synchrony with the order of spawning phenology.  The average time spent feeding on salmon was 67 days, while the average duration of spawning for one population was only 40 days.  The number of sites used was correlated with the number of days a bear exploited salmon, suggesting phenological variation in the study area influenced bear access to salmon, a resource which strongly influences bear fitness.  These results suggest fisheries managers attempting to maximize harvest while minimizing impacts on brown bears should strive to protect the population diversity that underlies the phenological variation used by wildlife consumers.  These results underscore the need to understand how fisheries affect life history diversity in addition to abundance in order to minimize negative effects of fisheries management on non-target species, a goal of EBFM

    Using a Data-Driven Method of Accident Analysis: A Case Study of the Human Performance Reliability (HPR) Process

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    PresentationHuman error and its contribution to occupational accidents and incidents has received considerable research attention in recent years. However, more research is needed into the validity, practicality, and functionality of using data-driven accident/incident analysis methods to identify factors that contribute to incidents with the greatest frequency. This paper presents a case-study of one such method: Human Performance Reliability (HPR). Methods: The authors conducted approximately 30 HPR reviews to analyze incidents that occurred at a large refining company over a three year period. Through the HPR process, the authors identified the most common human errors, other contributing factors, and the controls (SOPs, processes, programs) that failed to prevent the accidents/incidents. Results: A Chi-Square Goodness-of-Fit test and post-hoc analysis of Standard Residuals on the human error frequencies revealed the most common human errors and contributing factors, while raw frequency counts showed the most commonly associated controls (see Tables 3-6). The Chi-Square statistic was X2 = 528.58, indicating that certain errors were contributing to incidents significantly more often than others. Discussion: Early evidence supports the notion that the HPR process is an effective tool for incident analysis and subsequent continuous improvement efforts in process safety

    Dam type and lake position characterize ice-marginal lake area change in Alaska and NW Canada between 1984 and 2019

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    Department of Geosciences, Warner College of Natural ResourcesIce-marginal lakes impact glacier mass balance, water resources, and ecosystem dynamics, and can produce catastrophic glacial lake outburst floods (GLOFs). Multitemporal inventories of ice-marginal lakes are a critical first step in understanding the drivers of historic change, predicting future lake evolution, and assessing GLOF hazards. Here, we use Landsat-era satellite imagery and supervised classification to semi-automatically delineate lake outlines for four ~5 year time periods between 1984 and 2019 in Alaska and northwest Canada. Overall, ice-marginal lakes in the region have grown in total number (+183 lakes, 38% increase) and area (+483 km2, 59% increase) between the time periods of 1984–1988 and 2016–2019, though 56% of inventoried lakes did not experience detectable change. Changes in lake numbers and area were notably unsteady and nonuniform. We demonstrate that lake area changes are connected to dam type (moraine, bedrock, ice, or supraglacial) and the spatial relationship to their source glacier (proglacial, detached, unconnected, ice, or supraglacial), with important differences in lake behavior between the sub-groups. In strong contrast to all other dam types, ice-dammed lakes decreased in number (–6, 9% decrease) and area (–51 km2, 40% decrease), while moraine-dammed lakes increased (+56, 26% and +479 km2, 87% for number and area, respectively), a faster rate than the average when considering all dam types together. Proglacial lakes experienced the largest area changes and rate of change out of any lake position throughout the period of study, and moraine-dammed lakes which experienced the largest increases are associated with clean-ice glaciers (<19% debris cover). By tracking individual lakes through time and categorizing lakes by dam type, subregion, and location, we are able to detect trends that would otherwise be obscured if these characteristics were not considered. This work highlights the importance of such lake characterization when performing ice-marginal lake inventories, and provides insight into the physical processes driving recent ice-marginal lake evolution

    Sex-Specific Modulation of Gene Expression Networks in Murine Hypothalamus

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    The hypothalamus contains nuclei and cell populations that are critical in reproduction and that differ significantly between the sexes in structure and function. To examine the molecular and genetic basis for these differences, we quantified gene expression in the hypothalamus of 39 pairs of adult male and female mice belonging to the BXD strains. This experimental design enabled us to define hypothalamic gene coexpression networks and provided robust estimates of absolute expression differences. As expected, sex has the strongest effect on the expression of genes on the X and Y chromosomes (e.g., Uty, Xist, Kdm6a). Transcripts associated with the endocrine system and neuropeptide signaling also differ significantly. Sex-differentiated transcripts often have well delimited expression within specific hypothalamic nuclei that have roles in reproduction. For instance, the estrogen receptor (Esr1) and neurokinin B (Tac2) genes have intense expression in the medial preoptic and arcuate nuclei and comparatively high expression in females. Despite the strong effect of sex on single transcripts, the global pattern of covariance among transcripts is well preserved, and consequently, males and females have well matched coexpression modules. However, there are sex-specific hub genes in functionally equivalent modules. For example, only in males is the Y-linked gene, Uty, a highly connected transcript in a network that regulates chromatin modification and gene transcription. In females, the X chromosome paralog, Kdm6a, takes the place of Uty in the same network. We also find significant effect of sex on genetic regulation and the same network in males and females can be associated with markedly different regulatory loci. With the exception of a few sex-specific modules, our analysis reveals a system in which sets of functionally related transcripts are organized into stable sex-independent networks that are controlled at a higher level by sex-specific modulators

    Reverse doming of the anterior mitral leaflet with severe aortic regurgitation

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    The normal anatomic relation of the anterior mitral leaflet to the left ventricular outflow tract suggests that significant aortic regurgitation should have a predictable hemodynamic effect on the motion and configuration of the leaflet, an effect that should be seen by two-dimensional echocardiography. Previous reports have identified an abnormality of mitral opening in the short-axis view that was quite specific but not sensitive. This study was undertaken to evaluate mitral valve motion and configuration in aortic insufficiency using two-dimensional echocardiography. A characteristic pattern of anterior leaflet motion was found in patients with moderately severe and severe aortic regurgitation. This pattern, termed “reverse doming,” was seen in the apical and long-axis views in 19 of 22 such patients. The previously described “diastolic indentation” in the short-axis view was found in 16 of these 22 patients. Only 2 of 16 patients with lesser degrees of insufficiency had reverse doming. The sign was not seen in normal subjects nor in 16 patients with cardiomyopathy. For each of the few false positive and false negative findings, there is a seemingly logical hemodynamic explanation.It is concluded that reverse doming of the anterior mitral leaflet appears to be a sensitive and specific sign for moderately severe and severe aortic regurgitation
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