3,321 research outputs found
Towards building a team of intelligent robots
Topics addressed include: collision-free motion planning of multiple robot arms; two-dimensional object recognition; and pictorial databases (storage and sharing of the representations of three-dimensional objects)
Formation and evolution of clumpy tidal tails around globular clusters
We present some results of numerical simulations of a globular cluster
orbiting in the central region of a triaxial galaxy on a set of 'loop' orbits.
Tails start forming after about a quarter of the globular cluster orbital
period and develop, in most cases, along the cluster orbit, showing clumpy
substructures as observed, for example, in Palomar 5. If completely detectable,
clumps can contain about 7,000 solar masses each, i.e. about 10% of the cluster
mass at that epoch. The morphology of tails and clumps and the kinematical
properties of stars in the tails are studied and compared with available
observational data. Our finding is that the stellar velocity dispersion tends
to level off at large radii, in agreement to that found for M15 and Omega
Centauri.Comment: LaTeX 2e, uses AASTeX v5.x, 40 pages with 18 figures. Submitted to
The Astronomical Journa
The growth of galaxies in cosmological simulations of structure formation
We use hydrodynamic simulations to examine how the baryonic components of
galaxies are assembled, focusing on the relative importance of mergers and
smooth accretion in the formation of ~L_* systems. In our primary simulation,
which models a (50\hmpc)^3 comoving volume of a Lambda-dominated cold dark
matter universe, the space density of objects at our (64-particle) baryon mass
resolution threshold, M_c=5.4e10 M_sun, corresponds to that of observed
galaxies with L~L_*/4. Galaxies above this threshold gain most of their mass by
accretion rather than by mergers. At the redshift of peak mass growth, z~2,
accretion dominates over merging by about 4:1. The mean accretion rate per
galaxy declines from ~40 M_sun/yr at z=2 to ~10 M_sun/yr at z=0, while the
merging rate peaks later (z~1) and declines more slowly, so by z=0 the ratio is
about 2:1. We cannot distinguish truly smooth accretion from merging with
objects below our mass resolution threshold, but extrapolating our measured
mass spectrum of merging objects, dP/dM ~ M^a with a ~ -1, implies that
sub-resolution mergers would add relatively little mass. The global star
formation history in these simulations tracks the mass accretion rate rather
than the merger rate. At low redshift, destruction of galaxies by mergers is
approximately balanced by the growth of new systems, so the comoving space
density of resolved galaxies stays nearly constant despite significant mass
evolution at the galaxy-by-galaxy level. The predicted merger rate at z<~1
agrees with recent estimates from close pairs in the CFRS and CNOC2 redshift
surveys.Comment: Submitted to ApJ, 35 pp including 15 fig
Determining the galactic mass distribution using tidal streams from globular clusters
We discuss how to use tidal streams from globular clusters to measure the
mass distribution of the Milky Way. Recent proper motion determinations for
globular clusters from plate measurements and Hipparcos astrometry provide
several good candidates for Galactic mass determinations in the intermediate
halo, far above the Galactic disk, including Pal 5, NGC 4147, NGC 5024 (M53)
and NGC 5466; the remaining Hipparcos clusters provide candidates for
measurements several kpc above and below the disk. These clusters will help
determine the profile and shape of the inner halo. To aid this effort, we
present two methods of mass determination: one, a generalization of
rotation-curve mass measurements, which gives the mass and potential from
complete position-velocity observations for stream stars; and another using a
simple chi^2 estimator, which can be used when only projected positions and
radial velocities are known for stream stars. We illustrate the use of the
latter method using simulated tidal streams from Pal 5 and find that fairly
accurate mass determinations are possible even for relatively poor data sets.
Follow-up observations of clusters with proper motion determinations may reveal
tidal streams; obtaining radial velocity measurements would enable accurate
measurements of the mass distribution in the inner Galaxy.Comment: 21 pages, 6 figures, published in A
HEDGING CROP RISK WITH WEATHER INDEX AND INDIVIDUAL CROP INSURANCE
This paper provides a theoretical analysis for the optimal portfolio of weather index and individual crop insurance in farm level under mean-variance framework and stresses the impacts of risk aversion level, transaction cost, and basis risk. An empirical application of corn farms in Todd county of Kentucky is applied to.Risk and Uncertainty,
Collision-free motion of two robot arms in a common workspace
Collision-free motion of two robot arms in a common workspace is investigated. A collision-free motion is obtained by detecting collisions along the preplanned trajectories using a sphere model for the wrist of each robot and then modifying the paths and/or trajectories of one or both robots to avoid the collision. Detecting and avoiding collisions are based on the premise that: preplanned trajectories of the robots follow a straight line; collisions are restricted to between the wrists of the two robots (which corresponds to the upper three links of PUMA manipulators); and collisions never occur between the beginning points or end points on the straight line paths. The collision detection algorithm is described and some approaches to collision avoidance are discussed
AN EVALUATION OF AN ECONOMIC STRATEGY FOR PREVENTING WATER POLLUTION USING A PHOSPHORUS CONSISTENT TRANSPORTATION MODEL: A CASE OF BROILER LITTER MANAGEMENT
We calculated the profitability of using broiler litter as a source of plant nutrient using a phosphorus consistent litter application rule. We found that each ton of litter can be transferred cost effectively up to 164 miles from the production facilities. The minimum cost phosphorus consistent transportation model developed to meet the nutrient needs of 29 counties in North Alabama revealed that not all the litter can be utilized in the region. The total cost for nutrient supply increased when transportation of litter from heavily surplus counties were prioritized. The effect of chemical fertilizer price change minimally affected the total litter use.Environmental Economics and Policy,
Creative Design of a Device that not only Cleans the Teeth but also Anti-Germinates
In the past various methods have been found to clean the teeth but until recently not much importance has been given to the anti-germinating idea. After analyzing the causes of tooth decay the importance of anti-germinating has been found. Now there are various devices available to clean and anti-germinate the teeth but a system that combines both cleaning and anti-germinating has not been produced on a mass scale yet.
In this report we first study the history and evolution of cleaning the teeth. Then the various devices and chemicals used today to clean the teeth are analyzed. This is followed by the project analysis. Some designs that could provide a solution for the problem are found. Out of this the best design is found out considering factors like effort required, cost, efficiency, time. The various possible subsystems of the device are listed. The morphological analysis is then done. The most efficient and cost effective combination of subsystems is selected .This is the solution for the problem. The specification and size of the parts of the device is also given
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