9,535 research outputs found
Constraints on Dark Energy from Supernovae, Gamma Ray Bursts, Acoustic Oscillations, Nucleosynthesis and Large Scale Structure and the Hubble constant
The luminosity distance vs. redshift law is now measured using supernovae and
gamma ray bursts, and the angular size distance is measured at the surface of
last scattering by the CMB and at z = 0.35 by baryon acoustic oscillations. In
this paper this data is fit to models for the equation of state with w = -1, w
= const, and w(z) = w_0+w_a(1-a). The last model is poorly constrained by the
distance data, leading to unphysical solutions where the dark energy dominates
at early times unless the large scale structure and acoustic scale constraints
are modified to allow for early time dark energy effects. A flat LambdaCDM
model is consistent with all the data.Comment: 19 pages Latex with 8 Postscript figure files. A new reference and
constraint, w vs w' contour plots updated. Version accepted by the the Ap
Small business finance in two Chicago minority neighborhoods
The authors use survey data to measure the use of formal and informal sources of financing by owners of small businesses in two ethnic neighborhoods. The authors find substantial differences across ethnic groups in the amount of start-up funding obtained and in the use of trade credit.Small business ; Chicago (Ill.)
Observation of the dielectric-waveguide mode of light propagation in p-n junctions
Theoretical considerations of the propagation of electromagnetic energy near a p-n junction (1) show that the “sandwich” formed by having a depletion layer bounded by the p and n regions can act as a dielectric waveguide. (1,2
Using decision-tree classifier systems to extract knowledge from databases
One difficulty in applying artificial intelligence techniques to the solution of real world problems is that the development and maintenance of many AI systems, such as those used in diagnostics, require large amounts of human resources. At the same time, databases frequently exist which contain information about the process(es) of interest. Recently, efforts to reduce development and maintenance costs of AI systems have focused on using machine learning techniques to extract knowledge from existing databases. Research is described in the area of knowledge extraction using a class of machine learning techniques called decision-tree classifier systems. Results of this research suggest ways of performing knowledge extraction which may be applied in numerous situations. In addition, a measurement called the concept strength metric (CSM) is described which can be used to determine how well the resulting decision tree can differentiate between the concepts it has learned. The CSM can be used to determine whether or not additional knowledge needs to be extracted from the database. An experiment involving real world data is presented to illustrate the concepts described
Strategies for adding adaptive learning mechanisms to rule-based diagnostic expert systems
Rule-based diagnostic expert systems can be used to perform many of the diagnostic chores necessary in today's complex space systems. These expert systems typically take a set of symptoms as input and produce diagnostic advice as output. The primary objective of such expert systems is to provide accurate and comprehensive advice which can be used to help return the space system in question to nominal operation. The development and maintenance of diagnostic expert systems is time and labor intensive since the services of both knowledge engineer(s) and domain expert(s) are required. The use of adaptive learning mechanisms to increment evaluate and refine rules promises to reduce both time and labor costs associated with such systems. This paper describes the basic adaptive learning mechanisms of strengthening, weakening, generalization, discrimination, and discovery. Next basic strategies are discussed for adding these learning mechanisms to rule-based diagnostic expert systems. These strategies support the incremental evaluation and refinement of rules in the knowledge base by comparing the set of advice given by the expert system (A) with the correct diagnosis (C). Techniques are described for selecting those rules in the in the knowledge base which should participate in adaptive learning. The strategies presented may be used with a wide variety of learning algorithms. Further, these strategies are applicable to a large number of rule-based diagnostic expert systems. They may be used to provide either immediate or deferred updating of the knowledge base
How Filaments are Woven into the Cosmic Web
Observations indicate galaxies are distributed in a filament-dominated
web-like structure. Numerical experiments at high and low redshift of viable
structure formation theories also show filament-dominance. We present a simple
quantitative explanation of why this is so, showing that the final-state web is
actually present in embryonic form in the overdensity pattern of the initial
fluctuations, with nonlinear dynamics just sharpening the image. The web is
largely defined by the position and primordial tidal fields of rare events in
the medium, with the strongest filaments between nearby clusters whose tidal
tensors are nearly aligned. Applications of the cosmic web theory to
observations include probing cluster-cluster bridges by weak gravitational
lensing, X-rays, and the Sunyaev-Zeldovich effect and probing high redshift
galaxy-galaxy bridges by low column density Lyman alpha absorption lines.Comment: 9 pages, gzipped uuencoded postscript file, 4 figures in separate
files. The text + figures are also available from anonymous ftp site:
ftp://ftp.cita.utoronto.ca/ftp/cita/bond/bkp_natur
Abandoned Seabird Eggs as a Calcium Source for Terrestrial Gastropods
Birds’ use of terrestrial gastropods to supplement calcium for egg formation has been well documented, but the reverse, gastropods using avian eggshells as a calcium source, has not been recorded previously. We collected Arctic Tern, Sterna paradisaea, eggs, abandoned in July 2006, that were found to have many terrestrial gastropods on the surface, and it appeared as though the outer eggshell layers were removed. Using scanning electron microscopy, we compared “grazed” and “ungrazed” sections of the same shell with eggshells collected in 2005 that were not attended by snails. It appears as though the snails removed the outer eggshell layers, presumably to supplement their own shell growth
Industrial structural geology : principles, techniques and integration : an introduction
The authors wish to acknowledge the generous financial support provided in association with this volume to the Geological Society and the Petroleum Group by Badley Geoscience Ltd, BP, CGG Robertson, Dana Petroleum Ltd, Getech Group plc, Maersk Oil North Sea UK Ltd, Midland Valley Exploration Ltd, Rock Deformation Research (Schlumberger) and Borehole Image & Core Specialists (Wildcat Geoscience, Walker Geoscience and Prolog Geoscience). We would like to thank the fine team at the Geological Society’s Publishing House for the excellent support and encouragement that they have provided to the editors and authors of this Special Publication.Peer reviewedPublisher PD
Age problem in holographic dark energy
We study the age problem of the universe with the holographic DE model
introduced in [21], and test the model with some known old high redshift
objects (OHRO). The parameters of the model have been constrained using the
SNIa, CMB and BAO data set. We found that the age of the old quasar APM 08
279+5255 at z = 3.91 can be described by the model.Comment: 13 page
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