135,959 research outputs found
Maximum likelihood method for fitting the Fundamental Plane of the 6dF Galaxy Survey
We have used over 10,000 early-type galaxies from the 6dF Galaxy Survey
(6dFGS) to construct the Fundamental Plane across the optical and near-infrared
passbands. We demonstrate that a maximum likelihood fit to a multivariate
Gaussian model for the distribution of galaxies in size, surface brightness and
velocity dispersion can properly account for selection effects, censoring and
observational errors, leading to precise and unbiased parameters for the
Fundamental Plane and its intrinsic scatter. This method allows an accurate and
robust determination of the dependencies of the Fundamental Plane on variations
in the stellar populations and environment of early-type galaxies.Comment: 3 pages, 1 figure, to appear in the proceedings of the IAU Symposium
262 "Stellar Populations: Planning for the Next Decade", Charlot and Bruzual
ed
Generalization of color by chickens: experimental observations and a Bayesian model
Sensory generalization influences animals' responses to novel stimuli. Because color forms a perceptual continuum, it is a good subject for studying generalization. Moreover, because different causes of variation in spectral signals, such as pigmentation, gloss, and illumination, have differing behavioral significance, it may be beneficial to have adaptable generalization. We report on generalization by poultry chicks following differential training to rewarded (T+) and unrewarded (T−) colors, in particular on the phenomenon of peak shift, which leads to subjects preferring stimuli displaced away from T−. The first three experiments test effects of learning either a fine or a coarse discrimination. In experiments 1 and 2, peak shift occurs, but contrary to some predictions, the shift is smaller after the animal learned a fine discrimination than after it learned a coarse discrimination. Experiment 3 finds a similar effect for generalization on a color axis orthogonal to that separating T+ from T−. Experiment 4 shows that generalization is rapidly modified by experience. These results imply that the scale of a “perceptual ruler” is set by experience. We show that the observations are consistent with generalization following principles of Bayesian inference, which forms a powerful framework for understanding this type of behavior
A numerical determination of the bow shock wave in transonic axisymmetric flow about blunt bodies
A numerical method was developed for calculating axisymmetric transonic (M greater than 1) flow about a blunt body; the bow shock wave location was investigated. A Rankine-Hugoniot jump was applied at the shock while relaxation on the isentropic equation of motion was used between shock and body. The shock wave is adjusted by a Newton type iteration scheme. Results are given for a sphere in the Mach number range 1.62 down to 1.02
An experimental investigation of the interior noise control effects of propeller synchrophasing
A simplified cylindrical model of an aircraft fuselage is used to investigate the mechanisms of interior noise suppression using synchrophasing techniques. This investigation allows isolation of important parameters to define the characteristics of synchrophasing. The optimum synchrophase angle for maximum noise reduction is found for several interior microphone positions with pure tone source excitation. Noise reductions of up to 30 dB are shown for some microphone positions, however, overall reductions are less. A computer algorithm is developed to decompose the cylinder vibration into modal components over a wide range of synchrophase angles. The circumferential modal response of the shell vibration is shown to govern the transmission of sound into the cylinder rather than localized transmission. As well as investigating synchrophasing, the interior sound field due to sources typical of propellers has been measured and discussed
Bubble statistics and coarsening dynamics for quasi-two dimensional foams with increasing liquid content
We report on the statistics of bubble size, topology, and shape and on their
role in the coarsening dynamics for foams consisting of bubbles compressed
between two parallel plates. The design of the sample cell permits control of
the liquid content, through a constant pressure condition set by the height of
the foam above a liquid reservoir. We find that in the scaling state, all
bubble distributions are independent not only of time but also of liquid
content. For coarsening, the average rate decreases with liquid content due to
the blocking of gas diffusion by Plateau borders inflated with liquid. By
observing the growth rate of individual bubbles, we find that von Neumann's law
becomes progressively violated with increasing wetness and with decreasing
bubble size. We successfully model this behavior by explicitly incorporating
the border blocking effect into the von Neumann argument. Two dimensionless
bubble shape parameters naturally arise, one of which is primarily responsible
for the violation of von Neumann's law for foams that are not perfectly dry
Coarsening of Two Dimensional Foam on a Dome
In this paper we report on bubble growth rates and on the statistics of
bubble topology for the coarsening of a dry foam contained in the narrow gap
between two hemispheres. By contrast with coarsening in flat space, where
six-sided bubbles neither grow nor shrink, we observe that six sided bubbles
grow with time at a rate that depends on their size. This result agrees with
the modification to von Neumann's law predicted by J.E. Avron and D. Levine.
For bubbles with a different number of sides, except possibly seven, there is
too much noise in the growth rate data to demonstrate a difference with
coarsening in flat space. In terms of the statistics of bubble topology, we
find fewer 3, 4, and 5 sided bubbles, and more 6 and greater sided bubbles, in
comparison with the stationary distribution for coarsening in flat space. We
also find good general agreement with the Aboav-Weaire law for the average
number of sides of the neighbors of an n-sided bubble
The (2√3×3)rect. phase of alkylthiolate self-assembled monolayers on Au(111): a symmetry-constrained structural solution
Low-energy electron-diffraction (LEED) patterns of the Au(111)(2√3×3)rect.-butylthiolate surface phase (a structure also seen in longer alkane chain thiolate self-assembled monolayers) show missing diffracted beams characteristic of glide symmetry, but do not show the larger set of missing beams found in surface x-ray diffraction (SXRD). The difference can be attributed to the greatly enhanced role of multiple scattering in LEED, but the combination of symmetry constraints placed on possible structural models by the observed SXRD and LEED beam extinctions greatly reduces the number of possible structural models. Only three such models are identified, one of which is clearly incompatible with other published experimental data. The relative merits of the remaining models, both involving Au adatom-thiolate moieties, are discussed in the light of the results of previous experimental studies
Benchmark ultra-cool dwarfs in widely separated binary systems
Ultra-cool dwarfs as wide companions to subgiants, giants, white dwarfs and
main sequence stars can be very good benchmark objects, for which we can infer
physical properties with minimal reference to theoretical models, through
association with the primary stars. We have searched for benchmark ultra-cool
dwarfs in widely separated binary systems using SDSS, UKIDSS, and 2MASS. We
then estimate spectral types using SDSS spectroscopy and multi-band colors,
place constraints on distance, and perform proper motions calculations for all
candidates which have sufficient epoch baseline coverage. Analysis of the
proper motion and distance constraints show that eight of our ultra-cool dwarfs
are members of widely separated binary systems. Another L3.5 dwarf, SDSS 0832,
is shown to be a companion to the bright K3 giant Eta Cancri. Such primaries
can provide age and metallicity constraints for any companion objects, yielding
excellent benchmark objects. This is the first wide ultra-cool dwarf + giant
binary system identified.Comment: 4 pages, 3 figures, conference, "New Technologies for Probing the
Diversity of Brown Dwarfs and Exoplanets", oral tal
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