11,100 research outputs found
Dynamic autonomous intelligent control of an asteroid lander
One of the future flagship missions of the European Space Agency (ESA) is the asteroid sample return mission Marco-Polo. Although there have been a number of past missions to asteroids, a sample has never been successfully returned. The return of asteroid regolith to the Earth's surface introduces new technical challenges. This paper develops attitude control algorithms for the descent phase onto an asteroid in micro-gravity conditions and draws a comparison between the algorithms considered. Two studies are also performed regarding the Fault Detection Isolation and Recovery (FDIR) of the control laws considered. The potential of using Direct Adaptive Control (DAC) as a controller for the surface sampling process is also investigated. Use of a DAC controller incorporates increased levels of robustness by allowing realtime variation of control gains. This leads to better response to uncertainties encountered during missions
Potential relationship of epistemic games to group dynamics and learning orientations towards physics problem solving
Current investigations into pedagogical goals of introductory algebra-based
physics students at the University of Central Arkansas, by learning orientation
towards an in-class metacognitive group problem solving task, seek to determine
possible relationships with attitudinal shifts and course performance. Students
thus far have been untreated with known group-based learning pedagogies, so as
to establish trends of common group habits, and ultimately to properly inform
implementation of group-based pedagogies in reaction to these trends. However,
students' group dynamics and learning orientations prove difficult to map to
group-based measurements; an estimate of group learning orientation and
preferred working group dynamic is here explored as a potential means of
interpreting students' use of problem solving strategies. A means of "sampling"
audiovisual data in a live classroom of several simultaneous groups is also
presented as a way to estimate the frequency of chosen strategies to this end.Comment: 4 pages, 2 figures, 2 tables, conference proceeding
A new factorization property of the selfdecomposable probability measures
We prove that the convolution of a selfdecomposable distribution with its
background driving law is again selfdecomposable if and only if the background
driving law is s-selfdecomposable. We will refer to this as the factorization
property of a selfdecomposable distribution; let L^f denote the set of all
these distributions. The algebraic structure and various characterizations of
L^f are studied. Some examples are discussed, the most interesting one being
given by the Levy stochastic area integral. A nested family of subclasses
L^f_n, n\ge 0, (or a filtration) of the class L^f is given.Comment: Published at http://dx.doi.org/10.1214/009117904000000225 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Approaching Evaluation in Youth Community Informatics
In the Youth Community Informatics project, young people from disadvantaged communities use audio and video recording and editing tools, GPS/GIS, presentation software, graphics, and other digital technologies as the means for addressing community needs. They build community asset maps, document community history, develop exhibits in collaboration with libraries and museums, present cultural heritage, organize political action, operate community radio, create and maintain community technology centers, and express themselves through multiple media. These activities typically involve multiple partners and develop in unpredictable ways in response to community life. In order to understand what they mean in the lives of the youth and the community we need richer evaluation approaches.published or submitted for publicationis peer reviewe
Comment on "Correlation between Compact Radio Lout Quasars and Ultrahigh Energy Cosmic Rays"
In a recent paper, Farrar and Biermann argue that there is a strong
correlation between the direction of the five highest-energy cosmic-ray events
and compact, radio-loud quasars. This Comment shows that this analysis contains
several inconsistencies and errors so that the significance of any such
correlation is certainly greatly overestimated and perhaps nonexistent.Comment: 2 pages, REVTE
Movement patterns and athletic performance of leopards in the Okavango Delta
Although leopards are the most widespread of all the big cats and are known for their adaptability, they are elusive and little is known in detail about their movement and hunting energetics. We used high-resolution GPS/IMU (inertial measurement unit) collars to record position, activity and the first high-speed movement data on four male leopards in the Okavango Delta, an area with high habitat diversity and habitat fragmentation. Leopards in this study were generally active and conducted more runs during the night, with peaks in activity and number of runs in the morning and evening twilight. Runs were generally short (less than 100 m) and relatively slow (maximum speed 5.3 m s−1, mean of individual medians) compared to other large predators. Average daily travel distance was 11 km and maximum daily travel distance was 29 km. No direct correlation was found between average daily temperature and travel distance or between season and travel distance. Total daily energy requirements based on locomotor cost and basal metabolic rate varied little between individuals and over time. This study provides novel insights into movement patterns and athletic performance of leopards through quantitative high-resolution measurement of the locomotor, energetic, spatial and temporal movement characteristics. The results are unbiased by methodological and observational limitations characteristic of previous studies and demonstrate the utility of applying new technologies to field studies of elusive nocturnal species
Letter From J. Bertram Lippincott to Francis Mairs Huntington-Wilson, February 25, 1913
The document is a typed letter from J. B. Lippincott to the Assistant Secretary of State confirming his attendance at the upcoming anniversary meeting of the Philadelphia Society for Promoting Agriculture.https://digitalcommons.ursinus.edu/fmhw_other/1240/thumbnail.jp
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