3,100 research outputs found
Manipulating Underdetermination in Scientific Controversy: The Case of the Molecular Clock
Where there are cases of underdetermination in scientific controversies, such as the case of the molecular clock, scientists may direct the course and terms of dispute by playing off the multidimensional framework of theory evaluation. This is because assessment strategies themselves are underdetermined. Within the framework of assessment, there are a variety of trade-offs between different strategies as well as shifting emphases as specific strategies are given more or less weight in assessment situations. When a strategy is underdetermined, scientists can change the dynamics of a controversy by making assessments using different combinations of evaluation strategies and/or weighting whatever strategies are in play in different ways. Following an underdetermination strategy does not end or resolve a scientific dispute. Consequently, manipulating underdetermination is a feature of controversy dynamics and not controversy closure
Sewall Wright\u27s Adaptive Landscape: Philosophical Reflections on Heuristic Value
This volume brings together prominent historians of science, philosophers, ecologists, and evolutionary biologists, with the aim of discussing the state of the art of the Adaptive Landscape from several different perspectives
A Shifting Terrain: A Brief History of the Adaptive Landscape
This volume brings together prominent historians of science, philosophers, ecologists, and evolutionary biologists, with the aim of discussing the state of the art of the Adaptive Landscape from several different perspectives
Solvent mediated interactions between model colloids and interfaces: A microscopic approach
We determine the solvent mediated contribution to the effective potentials
for model colloidal or nano- particles dispersed in a binary solvent that
exhibits fluid-fluid phase separation. Using a simple density functional theory
we calculate the density profiles of both solvent species in the presence of
the `colloids', which are treated as external potentials, and determine the
solvent mediated (SM) potentials. Specifically, we calculate SM potentials
between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface,
and (iii) a colloid and a planar wall with an adsorbed wetting film. We
consider three different types of colloidal particles: colloid A which prefers
the bulk solvent phase rich in species 2, colloid C which prefers the solvent
phase rich in species 1, and `neutral' colloid B which has no strong preference
for either phase, i.e. the free energies to insert the colloid into either of
the coexisting bulk phases are almost equal. When a colloid which has a
preference for one of the two solvent phases is inserted into the disfavored
phase at statepoints close to coexistence a thick adsorbed `wetting' film of
the preferred phase may form around the colloids. The presence of the adsorbed
film has a profound influence on the form of the SM potentials.Comment: 17 Pages, 13 Figures. Accepted for publication in Journal of Chemical
Physic
Study of an Alternate Mechanism for the Origin of Fermion Generations
In usual extended technicolor (ETC) theories based on the group
, the quarks of charge 2/3 and -1/3 and the charged
leptons of all generations arise from ETC fermion multiplets transforming
according to the fundamental representation. Here we investigate a different
idea for the origin of SM fermion generations, in which quarks and charged
leptons of different generations arise from ETC fermions transforming according
to different representations of . Although this
mechanism would have the potential, {\it a priori}, to allow a reduction in the
value of relative to conventional ETC models, we show that, at least
in simple models, it is excluded by the fact that the technicolor sector is not
asymptotically free or by the appearance of fermions with exotic quantum
numbers which are not observed.Comment: 6 pages, late
Vitamin D Status and 5â Year Changes in Periodontal Disease Measures Among Postmenopausal Women: The Buffalo OsteoPerio Study
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141463/1/jper1321.pd
Optical systems integrated modeling
An integrated modeling capability that provides the tools by which entire optical systems and instruments can be simulated and optimized is a key technology development, applicable to all mission classes, especially astrophysics. Many of the future missions require optical systems that are physically much larger than anything flown before and yet must retain the characteristic sub-micron diffraction limited wavefront accuracy of their smaller precursors. It is no longer feasible to follow the path of 'cut and test' development; the sheer scale of these systems precludes many of the older techniques that rely upon ground evaluation of full size engineering units. The ability to accurately model (by computer) and optimize the entire flight system's integrated structural, thermal, and dynamic characteristics is essential. Two distinct integrated modeling capabilities are required. These are an initial design capability and a detailed design and optimization system. The content of an initial design package is shown. It would be a modular, workstation based code which allows preliminary integrated system analysis and trade studies to be carried out quickly by a single engineer or a small design team. A simple concept for a detailed design and optimization system is shown. This is a linkage of interface architecture that allows efficient interchange of information between existing large specialized optical, control, thermal, and structural design codes. The computing environment would be a network of large mainframe machines and its users would be project level design teams. More advanced concepts for detailed design systems would support interaction between modules and automated optimization of the entire system. Technology assessment and development plans for integrated package for initial design, interface development for detailed optimization, validation, and modeling research are presented
Double-Peaked Low-Ionization Emission Lines in Active Galactic Nuclei
We present a new sample of 116 double-peaked Balmer line Active Galactic
Nuclei (AGN) selected from the Sloan Digital Sky Survey. Double-peaked emission
lines are believed to originate in the accretion disks of AGN, a few hundred
gravitational radii (Rg) from the supermassive black hole. We investigate the
properties of the candidate disk emitters with respect to the full sample of
AGN over the same redshifts, focusing on optical, radio and X-ray flux, broad
line shapes and narrow line equivalent widths and line flux-ratios. We find
that the disk-emitters have medium luminosities (~10^44erg/s) and FWHM on
average six times broader than the AGN in the parent sample. The double-peaked
AGN are 1.6 times more likely to be radio-sources and are predominantly (76%)
radio quiet, with about 12% of the objects classified as LINERs. Statistical
comparison of the observed double-peaked line profiles with those produced by
axisymmetric and non-axisymmetric accretion disk models allows us to impose
constraints on accretion disk parameters. The observed Halpha line profiles are
consistent with accretion disks with inclinations smaller than 50 deg, surface
emissivity slopes of 1.0-2.5, outer radii larger than ~2000 Rg, inner radii
between 200-800Rg, and local turbulent broadening of 780-1800 km/s. The
comparison suggests that 60% of accretion disks require some form of asymmetry
(e.g., elliptical disks, warps, spiral shocks or hot spots).Comment: 60 pages, 19 figures, accepted for publication in AJ. For high
quality figures and full tables, please see
http://astro.princeton.edu/~iskra/disks.htm
Nonequilibrium spectral diffusion due to laser heating in stimulated photon echo spectroscopy of low temperature glasses
A quantitative theory is developed, which accounts for heating artifacts in
three-pulse photon echo (3PE) experiments. The heat diffusion equation is
solved and the average value of the temperature in the focal volume of the
laser is determined as a function of the 3PE waiting time. This temperature is
used in the framework of nonequilibrium spectral diffusion theory to calculate
the effective homogeneous linewidth of an ensemble of probe molecules embedded
in an amorphous host. The theory fits recently observed plateaus and bumps
without introducing a gap in the distribution function of flip rates of the
two-level systems or any other major modification of the standard tunneling
model.Comment: 10 pages, Revtex, 6 eps-figures, accepted for publication in Phys.
Rev.
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