12,473 research outputs found
Signal-to-Noise Eigenmode Analysis of the Two-Year COBE Maps
To test a theory of cosmic microwave background fluctuations, it is natural
to expand an anisotropy map in an uncorrelated basis of linear combinations of
pixel amplitudes --- statistically-independent for both the noise and the
signal. These -eigenmodes are indispensible for rapid Bayesian analyses of
anisotropy experiments, applied here to the recently-released two-year COBE
{\it dmr} maps and the {\it firs} map. A 2-parameter model with an overall
band-power and a spectral tilt describes well inflation-based
theories. The band-powers for {\it all} the {\it dmr} + GHz
and {\it firs} 170 GHz maps agree, , and
are largely independent of tilt and degree of (sharp) -filtering. Further,
after optimal -filtering, the {\it dmr} maps reveal the same
tilt-independent large scale features and correlation function. The unfiltered
{\it dmr} + index is ; increasing the
-filtering gives a broad region at (1.0--1.2)0.5, a jump to
(1.4--1.6)0.5, then a drop to 0.8, the higher values clearly seen to be
driven by -power spectrum data points that do not fit single-tilt models.
These indices are nicely compatible with inflation values (0.8--1.2), but
not overwhelmingly so.Comment: submitted to Phys.Rev.Letters, 4 pages, uuencoded compressed
PostScript; also bdmr2.ps.Z, via anonymous ftp to ftp.cita.utoronto.ca, cd to
/pub/dick/yukawa; CITA-94-2
Arkansas Soybean Performance Tests 2018
Soybean variety and strain performance tests are conducted each year in Arkansas by the University of Arkansas System Division of Agriculture’s Arkansas Crop Variety Improvement Program. The tests provide information to companies developing varieties and/or marketing seed within the State, and aid the Arkansas Cooperative Extension Service in formulating variety recommendations for soybean producers
Constraining massive gravity with recent cosmological data
A covariant formulation of a theory with a massive graviton and no negative
energy state has been recently proposed as an alternative to the usual General
Relativity framework. For a spatially flat homogenous and isotropic universe,
the theory introduces modified Friedmann equations where the standard matter
term is supplemented by four effective fluids mimicking dust, cosmological
constant, quintessence and stiff matter, respectively. We test the viability of
this massive gravity formulation by contrasting its theoretical prediction to
the Hubble diagram as traced by Type Ia Supernovae (SNeIa) and Gamma Ray Bursts
(GRBs), the measurements from passively evolving galaxies, Baryon
Acoustic Oscillations (BAOs) from galaxy surveys and the distance priors from
the Cosmic Microwave Background Radiation (CMBR) anisotropy spectrum. It turns
out that the model is indeed able to very well fit this large dataset thus
offering a viable alternative to the usual dark energy framework. We finally
set stringent constraints on its parameters also narrowing down the allowed
range for the graviton mass.Comment: 10 pages, 1 figure, 2 tables, accepted for publication on Physical
Review
Holographic Dark Energy Characterized by the Total Comoving Horizon and Insights to Cosmological Constant and Coincidence Problem
The observed acceleration of the present universe is shown to be well
explained by the holographic dark energy characterized by the total comoving
horizon of the universe (HDE). It is of interest to notice that the very
large primordial part of the comoving horizon generated by the inflation of
early universe makes the HDE behave like a cosmological constant. As a
consequence, both the fine-tuning problem and the coincidence problem can
reasonably be understood with the inflationary universe and holographical
principle. We present a systematic analysis and obtain a consistent
cosmological constraint on the HDE model based on the recent cosmological
observations. It is found that the HDE model gives the best-fit result
() and the minimal
which is compatible with for the CDM model.Comment: 17 pages, 4 figures, two eqs. (26)(27) added for the consistent
approximate solution of dark energy in early universe, references added,
published version in PR
Gravitational Lensing Effect on the Two-point Correlation of Hotspots in the Cosmic Microwave Background
We investigate the weak gravitational lensing effect due to the large-scale
structure of the universe on two-point correlations of local maxima ({\em
hotspots}) in the 2D sky map of the cosmic microwave background (CMB)
anisotropy. According to the Gaussian random statistics as most inflationary
scenarios predict, the hotspots are discretely distributed with some {\em
characteristic} angular separations on the last scattering surface owing to
oscillations of the CMB angular power spectrum.
The weak lensing then causes pairs of hotspots which are separated with the
characteristic scale to be observed with various separations. We found that the
lensing fairly smoothes the oscillatory features of the two-point correlation
function of hotspots. This indicates that the hotspots correlations can be a
new statistical tool for measuring shape and normalization of the power
spectrum of matter fluctuations from the lensing signatures.Comment: 6 pages, 2 figures; replaced with published versio
A domain-specific design architecture for composite material design and aircraft part redesign
Advanced composites have been targeted as a 'leapfrog' technology that would provide a unique global competitive position for U.S. industry. Composites are unique in the requirements for an integrated approach to designing, manufacturing, and marketing of products developed utilizing the new materials of construction. Numerous studies extending across the entire economic spectrum of the United States from aerospace to military to durable goods have identified composites as a 'key' technology. In general there have been two approaches to composite construction: build models of a given composite materials, then determine characteristics of the material via numerical simulation and empirical testing; and experience-directed construction of fabrication plans for building composites with given properties. The first route sets a goal to capture basic understanding of a device (the composite) by use of a rigorous mathematical model; the second attempts to capture the expertise about the process of fabricating a composite (to date) at a surface level typically expressed in a rule based system. From an AI perspective, these two research lines are attacking distinctly different problems, and both tracks have current limitations. The mathematical modeling approach has yielded a wealth of data but a large number of simplifying assumptions are needed to make numerical simulation tractable. Likewise, although surface level expertise about how to build a particular composite may yield important results, recent trends in the KBS area are towards augmenting surface level problem solving with deeper level knowledge. Many of the relative advantages of composites, e.g., the strength:weight ratio, is most prominent when the entire component is designed as a unitary piece. The bottleneck in undertaking such unitary design lies in the difficulty of the re-design task. Designing the fabrication protocols for a complex-shaped, thick section composite are currently very difficult. It is in fact this difficulty that our research will address
Excavations at the Viking Barrow Cemetery at Heath Wood, Ingleby, Derbyshire
The cemetery at Heath Wood, Ingleby, Derbyshire, is the only known Scandinavian cremation cemetery in the British Isles. It comprises fifty-nine barrows, of which about one-third have been excavated on previous occasions, although earlier excavators concluded that some were empty cenotaph mounds. From 1998 to 2000 three barrows were examined. Our investigations have suggested that each of the barrows contained a burial, although not all contain evidence of a pyre. A full report of the 1998-2000 excavations is provided, alongside a summary of the earlier finds. The relationship of Heath Wood to the neighbouring site at Repton is examined, in order to understand its significance for the Scandinavian settlement of the Danelaw. It is concluded that Heath Wood may have been a war cemetery of the Viking Great Army of AD 873-8
Effects of high and low barometric pressures on susceptibility and resistance to infection Quarterly status report, 1 Apr. - 30 Jun. 1970
Effects of high and low barometric pressures on susceptibility and resistance to infectio
The scale of homogeneity in the Las Campanas Redshift Survey
We analyse the Las Campanas Redshift Survey using the integrated conditional
density (or density of neighbors) in volume-limited subsamples up to
unprecedented scales (200 Mpc/) in order to determine without ambiguity the
behavior of the density field. We find that the survey is well described by a
fractal up to 20-30 Mpc/, but flattens toward homogeneity at larger scales.
Although the data are still insufficient to establish with high significance
the expected homogeneous behavior, and therefore to rule out a fractal trend to
larger scales, a fit with a CDM-like spectrum with high normalization well
represents the data.Comment: 8 pages, 3 figures, accepted on Ap.J. Letter
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