17,961 research outputs found
Don\u27t Repeat a Word of This!
Can you write a composition of 100 words or more without repeating a single word? Without using even an a or an an or a the more than once
Resolvent Positive Linear Operators Exhibit the Reduction Phenomenon
The spectral bound, s(a A + b V), of a combination of a resolvent positive
linear operator A and an operator of multiplication V, was shown by Kato to be
convex in b \in R. This is shown here, through an elementary lemma, to imply
that s(a A + b V) is also convex in a > 0, and notably, \partial s(a A + b V) /
\partial a <= s(A) when it exists. Diffusions typically have s(A) <= 0, so that
for diffusions with spatially heterogeneous growth or decay rates, greater
mixing reduces growth. Models of the evolution of dispersal in particular have
found this result when A is a Laplacian or second-order elliptic operator, or a
nonlocal diffusion operator, implying selection for reduced dispersal. These
cases are shown here to be part of a single, broadly general, `reduction'
phenomenon.Comment: 7 pages, 53 citations. v.3: added citations, corrections in
introductory definitions. v.2: Revised abstract, more text, and details in
new proof of Lindqvist's inequalit
Newly identified lines in NeI isoelectronic sequences
Grazing-incidence spectrometer and low inductance spark source used to study lines of high degrees of ionization of Sc, Ti, and
A role for the developing lexicon in phonetic category acquisition
Infants segment words from fluent speech during the same period when they are learning phonetic categories, yet accounts of phonetic category acquisition typically ignore information about the words in which sounds appear. We use a Bayesian model to illustrate how feedback from segmented words might constrain phonetic category learning by providing information about which sounds occur together in words. Simulations demonstrate that word-level information can successfully disambiguate overlapping English vowel categories. Learning patterns in the model are shown to parallel human behavior from artificial language learning tasks. These findings point to a central role for the developing lexicon in phonetic category acquisition and provide a framework for incorporating top-down constraints into models of category learning
The Bull's-Eye Effect as a Probe of
We compare the statistical properties of structures normal and transverse to
the line of sight which appear in theoretical N-body simulations of structure
formation, and seem also to be present in observational data from redshift
surveys. We present a statistic which can quantify this effect in a
conceptually different way from standard analyses of distortions of the
power-spectrum or correlation function. From tests with --body experiments,
we argue that this statistic represents a new and potentially powerful
diagnostic of the cosmological density parameter, .Comment: Minor revisions; final version accepted for publication in ApJ
Letters. Latex, 16 pages, including 3 figures. Higher resolution versions of
figures, including supplementary figures not included in the manuscript, are
available at: ftp://kusmos.phsx.ukans.edu/preprints/melott/omeg
Lattice dynamics and reduced thermal conductivity of filled skutterudites
The great reduction in thermal conductivity of skutterudites upon filling the
``void'' sites with Rare Earth (RE) ions is key to their favorable
thermoelectric properties but remains to be understood. Using lattice dynamic
models based on first principles calculations, we address the most popular
microscopic mechanism, reduction via rattling ions. The model withstands
inelastic neutron scattering and specific heat measurements, and refutes
hypotheses of an anharmonic RE potential and of two distinct localized RE
vibrations of disparate frequencies. It does indicate a strong hybridization
between bare La vibrations and certain Sb-like phonon branches, suggesting
anharmonic scattering by harmonic RE motions as an important mechanism for
suppression of heat conductivity.Comment: modified version resubmitted to PRB. Results unchanged, text changed
substantiall
Recommended from our members
Retrieving Decadal Climate Change from Satellite Radiance Observations-A 100-year CO2 Doubling OSSE Demonstration.
Preparing for climate change depends on the observation and prediction of decadal trends of the environmental variables, which have a direct impact on the sustainability of resources affecting the quality of life on our planet. The NASA Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is proposed to provide climate quality benchmark spectral radiance observations for the purpose of determining the decadal trends of climate variables, and validating and improving the long-range climate model forecasts needed to prepare for the changing climate of the Earth. The CLARREO will serve as an in-orbit, absolute, radiometric standard for the cross-calibration of hyperspectral radiance spectra observed by the international system of polar operational satellite sounding sensors. Here, we demonstrate that the resulting accurately cross-calibrated polar satellite global infrared spectral radiance trends (e.g., from the Metop IASI instrument considered here) can be interpreted in terms of temperature and water vapor profile trends. This demonstration is performed using atmospheric state data generated for a 100-year period from 2000-2099, produced by a numerical climate model prediction that was forced by the doubling of the global average atmospheric CO2 over the 100-year period. The vertical profiles and spatial distribution of temperature decadal trends were successfully diagnosed by applying a linear regression profile retrieval algorithm to the simulated hyperspectral radiance spectra for the 100-year period. These results indicate that it is possible to detect decadal trends in atmospheric climate variables from high accuracy all-sky satellite infrared radiance spectra using the linear regression retrieval technique
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