47,126 research outputs found
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EASe : integrating search with learned episodes
Weak methods are insufficient to solve complex problems. Constrained weak methods, like hill-climbing, search too little of the problem space. Unconstrained weak methods, like breadth-first search, are intractable. Fortunately, through the integration of multiple weak methods more powerful problem solvers can be created. We demonstrate that augmenting a weak constrained search method with episodes provides a tractable method for solving a large class of problems. We demonstrate that these episodes can be generated using an unconstrained weak method while solving simple problems from a domain. We provide an analytical model of our approach and empirical results from the logic synthesis domain of VLSI design as well as the classic tile-sliding domain
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Automatic synthesis of analog layout : a survey
A review of recent research in the automatic synthesis of physical geometry for analog integrated circuits is presented. On introduction, an explanation of the difficulties involved in analog layout as opposed to digital layout is covered. Review of the literature then follows. Emphasis is placed on the exposition of general methods for addressing problems specific to analog layout, with the details of specific systems only being given when they surve to illustrate these methods well. The conclusion discusses problems remaining and offers a prediction as to how technology will evolve to solve them. It is argued that although progress has been and will continue to be made in the automation of analog IC layout, due to fundamental differences in the nature of analog IC design as opposed to digital design, it should not be expected that the level of automation of the former will reach that of the latter any time soon
Modeling the color evolution of luminous red galaxies - improvements with empirical stellar spectra
Predicting the colors of Luminous Red Galaxies (LRGs) in the Sloan Digital
Sky Survey (SDSS) has been a long-standing problem. The g,r,i colors of LRGs
are inconsistent with stellar population models over the redshift range
0.1<z<0.7. The g-r colors in the models are on average redder than the data
while the r-i colors in the models are bluer towards low redshift. Beyond
redshift 0.4, the predicted r-i color becomes instead too red, while the
predicted g-r agrees with the data. We provide a solution to this problem,
through a combination of new astrophysics and a fundamental change to the
stellar population modeling. We find that the use of the empirical library of
Pickles (1998) instead of theoretical spectra modifies the predicted colors
exactly in the way suggested by the data. The reason is a lower flux in the
empirical libraries, with respect to the theoretical ones, in the wavelength
range 5500-6500 AA. The discrepancy increases with decreasing effective
temperature independently of gravity. This result has general implications for
a variety of studies from globular clusters to high-redshift galaxies. The
astrophysical part of our solution regards the composition of the stellar
populations of these massive Luminous Red Galaxies. We find that on top of the
previous effect one needs to consider a model in which ~3% of the stellar mass
is in old metal-poor stars. Other solutions such as substantial blue Horizontal
Branch at high metallicity or young stellar populations can be ruled out by the
data. Our new model provides a better fit to the g-r and r-i colors of LRGs and
gives new insight into the formation histories of these most massive galaxies.
Our model will also improve the k- and evolutionary corrections for LRGs which
are critical for fully exploiting present and future galaxy surveys.Comment: Submitted to ApJ Letters. High resolution version available at
http://www.maraston.eu/Maraston_etal_2008.pd
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CHASSIS : a combined hardware selection and scheduling technique for performance driven synthesis
This report describes a new technique that combines the Hardware Scheduling and Component Selection phases for High Level Synthesis. Our technique simultaneously selects components from a given library while it schedules the operations into different control steps. The algorĂthm improves previous work in scheduling because component costs and performance are considered during the scheduling process, enlarging the design search space and resulting in better optimized desĂgns
OEXP Analysis Tools Workshop
This publication summarizes the software needs and available analysis tools presented at the OEXP Analysis Tools Workshop held at the NASA Langley Research Center, Hampton, Virginia on June 21 to 22, 1988. The objective of the workshop was to identify available spacecraft system (and subsystem) analysis and engineering design tools, and mission planning and analysis software that could be used for various NASA Office of Exploration (code Z) studies, specifically lunar and Mars missions
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