6,747,806 research outputs found
A computer program for grain-size data
The computer program presented here seeks to improve estimation of statistical parameters for grain-size data by use of interpolated values. Interpolation is made by fitting a series of overlapping parabolas to the data, and follows the method of Snyder (1961). The values are used in moment formulas to compute standard statistical measures. Skewness and kurtosis are reduced by the interpolation data, and extreme positive values of kurtosis tend to be greatly reduced. The program also picks major modes, the median, and sediment type .The United States Geological Survey under Contract USGS-14-08-0001-835
Ultra-compact radio sources: angular-size/redshift data
A compilation of angular-size/redshift data for ultra-compact radio sources is presented, which data derive from a 2.29 GHz VLBI survey undertaken by Preston et al. The sample has formed the basis of a number of investigations, which attempt to determine cosmological parameters from the angular-size/redshift diagram. Full details of the sample are not in the public domain, which omission is rectified here
Inference of historical population-size changes with allele-frequency data
With up to millions of nearly neutral polymorphisms now being routinely sampled in population-genomic surveys, it is possible to estimate the site-frequency spectrum of such sites with high precision. Each frequency class reflects a mixture of potentially unique demographic histories, which can be revealed using theory for the probability distributions of the starting and ending points of branch segments over all possible coalescence trees. Such distributions are completely independent of past population history, which only influences the segment lengths, providing the basis for estimating average population sizes separating tree-wide coalescence events. The history of population-size change experienced by a sample of polymorphisms can then be dissected in a model-flexible fashion, and extension of this theory allows estimation of the mean and full distribution of long-term effective population sizes and ages of alleles of specific frequencies. Here, we outline the basic theory underlying the conceptual approach, develop and test an efficient statistical procedure for parameter estimation, and apply this to multiple population-genomic datasets for the microcrustacean Daphnia pulex
Artifactual log-periodicity in finite size data: Relevance for earthquake aftershocks
The recently proposed discrete scale invariance and its associated
log-periodicity are an elaboration of the concept of scale invariance in which
the system is scale invariant only under powers of specific values of the
magnification factor. We report on the discovery of a novel mechanism for such
log-periodicity relying solely on the manipulation of data. This ``synthetic''
scenario for log-periodicity relies on two steps: (1) the fact that
approximately logarithmic sampling in time corresponds to uniform sampling in
the logarithm of time; and (2) a low-pass-filtering step, as occurs in
constructing cumulative functions, in maximum likelihood estimations, and in
de-trending, reddens the noise and, in a finite sample, creates a maximum in
the spectrum leading to a most probable frequency in the logarithm of time. We
explore in detail this mechanism and present extensive numerical simulations.
We use this insight to analyze the 27 best aftershock sequences studied by
Kisslinger and Jones [1991] to search for traces of genuine log-periodic
corrections to Omori's law, which states that the earthquake rate decays
approximately as the inverse of the time since the last main shock. The
observed log-periodicity is shown to almost entirely result from the
``synthetic scenario'' owing to the data analysis. From a statistical point of
view, resolving the issue of the possible existence of log-periodicity in
aftershocks will be very difficult as Omori's law describes a point process
with a uniform sampling in the logarithm of the time. By construction, strong
log-periodic fluctuations are thus created by this logarithmic sampling.Comment: LaTeX, JGR preprint with AGU++ v16.b and AGUTeX 5.0, use packages
graphicx, psfrag and latexsym, 41 eps figures, 26 pages. In press J. Geophys.
Re
- …