18,977 research outputs found
Seam tracking performance of a Coaxial Weld Vision System and pulsed welding
This report describes a continuation of a series of tests on the Coaxial Weld Vision System at MSFC. The ability of the system to compensate for transients associated with pulsed current welding is analyzed. Using the standard image processing approach for root pass seam tracking, the system is also tested for the ability to track the toe of a previous weld bead, for tracking multiple pass weld joints. This Coaxial Weld Vision System was developed by the Ohio State University (OSU) Center for Welding Research and is a part of the Space Shuttle Main Engine Robotic Welding Development System at MSFC
Evolutionary consequences of behavioral diversity
Iterated games provide a framework to describe social interactions among
groups of individuals. Recent work stimulated by the discovery of
"zero-determinant" strategies has rapidly expanded our ability to analyze such
interactions. This body of work has primarily focused on games in which players
face a simple binary choice, to "cooperate" or "defect". Real individuals,
however, often exhibit behavioral diversity, varying their input to a social
interaction both qualitatively and quantitatively. Here we explore how access
to a greater diversity of behavioral choices impacts the evolution of social
dynamics in finite populations. We show that, in public goods games, some
two-choice strategies can nonetheless resist invasion by all possible
multi-choice invaders, even while engaging in relatively little punishment. We
also show that access to greater behavioral choice results in more "rugged "
fitness landscapes, with populations able to stabilize cooperation at multiple
levels of investment, such that choice facilitates cooperation when returns on
investments are low, but hinders cooperation when returns on investments are
high. Finally, we analyze iterated rock-paper-scissors games, whose
non-transitive payoff structure means unilateral control is difficult and
zero-determinant strategies do not exist in general. Despite this, we find that
a large portion of multi-choice strategies can invade and resist invasion by
strategies that lack behavioral diversity -- so that even well-mixed
populations will tend to evolve behavioral diversity.Comment: 26 pages, 4 figure
Entropy-expansiveness for partially hyperbolic diffeomorphisms
We show that diffeomorphisms with a dominated splitting of the form
, where is a nonhyperbolic central bundle that
splits in a dominated way into 1-dimensional subbundles, are entropy-expansive.
In particular, they have a principal symbolic extension and equilibrium states.Comment: 15 pages, 1 figur
Searches for Long-lived Particles at the Tevatron Collider
Several searches for long-lived particles have been performed using data from
p-pbar collisions from Run II at the Tevatron. In most cases, new analysis
techniques have been developed to carry out each search and/or estimate the
backgrounds. These searches expand the discovery potential of the CDF and D0
experiments to new physics that may have been missed by traditional search
techniques. This review discusses searches for (1) neutral, long-lived
particles decaying to muons, (2) massive, neutral, long-lived particles
decaying to a photon and missing energy, (3) stopped gluinos, and (4) charged
massive stable particles. It summarizes some of the theoretical and
experimental motivations for such searches.Comment: submitted to Mod. Phys. Lett.
Improving Reading Skills by Encouraging Children to Read: A Randomized Evaluation of the Sa Aklat Sisikat Reading Program in the Philippines
We evaluate a program that aims to improve children's reading skills by providing classes with age-appropriate reading material and incentivizing children to read through a 31 day read-a-thon. During the read-a-thon, the program significantly increases the propensity of children to read, causing 20 percent more children to have read a book in the last week at school and increasing the number of books read by 2.3 in the last week and 7.2 in the last month. These increases extend both after the end of the program and outside of school, although at lower rates. The program also increased studentsâ scores on a reading assessment, causing studentsâ scores to improve by 0.13 standard deviations immediately after the program. The effect persisted even after the program ended with an effect of 0.06 standard deviations three months later.education, reading, development
Young Stars with SALT
We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77
systems. All are low-proper-motion southern hemisphere objects and were
identified in a nearby star survey with a demonstrated sensitivity to young
stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph
(RSS) on the South African Large Telescope (SALT), we have determined radial
velocities, H-alpha, Lithium 6708\AA, and Potassium 7699\AA~equivalent widths
linked to age and activity, and spectral types for all our targets. Combined
with astrometric information from literature sources, we identify 44 young
stars. Eighteen are previously known members of moving groups within 100
parsecs of the Sun. Twelve are new members, including one member of the TW
Hydra moving group, one member of the 32 Orionis moving group, nine members of
Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We
also find fourteen young star systems that are not members of any known groups.
The remaining 33 star systems do not appear to be young. This appears to be
evidence of a new population of nearby young stars not related to the known
nearby young moving groups.Comment: 23 pages, 11 figures, 6 tables. Accepted to Ap
HOW MUCH VALUE IS THERE IN A PRODUCER BRANDED BRED HEIFER PROGRAM?
Agricultural producers are pursuing many methods by which to add value. Typically, some type of change in commodity form is used to add value. However, there exist methods by which added value occurs through intensive management practices, particularly in seedstock production. We investigated the brand premium to a producer-owned quality-based bred heifer program. Results indicated that producers garner in access of a $100/head premium, while potentially reducing future search/advertising costs through building brand loyalty.Livestock Production/Industries,
An investigation of the nature and reactivity of the carbonaceous species deposited on mordenite by reaction with methanol
An investigation of the nature of the carbonaceous species deposited upon mordenite by reaction with methanol has been undertaken. The nature of the species has been shown to be a strong function of both temperature and time on stream. Upon reaction at 300 degrees C a range of alkyl and aromatic species, consistent with the development of an active hydrocarbon pool, are evident and time on stream studies have shown that these are developed within 5 min. Upon reaction at 500 degrees C, a narrower range of hydrogen deficient aromatic species is evident. Thermal volatilisation analysis (TVA), not previously applied to the study of coked zeolites, is shown to be complementary to the more commonly applied C analysis, C-13 MAS NMR and TGA techniques
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