2,486 research outputs found
A multiscale view on inverse statistics and gain/loss asymmetry in financial time series
Researchers have studied the first passage time of financial time series and
observed that the smallest time interval needed for a stock index to move a
given distance is typically shorter for negative than for positive price
movements. The same is not observed for the index constituents, the individual
stocks. We use the discrete wavelet transform to illustrate that this is a long
rather than short time scale phenomenon -- if enough low frequency content of
the price process is removed, the asymmetry disappears. We also propose a new
model, which explain the asymmetry by prolonged, correlated down movements of
individual stocks
Frequencies of some B blood group alleles in laying hens from a selection and crossbreeding experiment
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Median Statistics, H_0, and the Accelerating Universe
(Abridged) We develop median statistics that provide powerful alternatives to
chi-squared likelihood methods and require fewer assumptions about the data.
Applying median statistics to Huchra's compilation of nearly all estimates of
the Hubble constant, we find a median value H_0=67 km/s/Mpc. Median statistics
assume only that the measurements are independent and free of systematic
errors. This estimate is arguably the best summary of current knowledge because
it uses all available data and, unlike other estimates, makes no assumption
about the distribution of measurement errors. The 95% range of purely
statistical errors is +/- 2 km/s/Mpc. The statistical precision of this result
leads us to analyze the range of possible systematic errors in the median,
which we estimate to be roughly +/- 5 km/s/Mpc (95% limits), dominating over
the statistical errors. A Bayesian median statistics treatment of high-redshift
Type Ia supernovae (SNe Ia) apparent magnitude versus redshift data from Riess
et al. yields a posterior probability that the cosmological constant Lambda > 0
of 70 or 89%, depending on the prior information used. The posterior
probability of an open universe is about 47%. Analysis of the Perlmutter et al.
high-redshift SNe Ia data show the best-fit flat-Lambda model favored over the
best-fit Lambda = 0 open model by odds of 366:1; corresponding Riess et al.
odds are 3:1 (assuming prior odds of 1:1).Median statistics analyses of the SNe
Ia data do not rule out a time-variable Lambda model, and may even favor it
over a time-independent Lambda and a Lambda = 0 open model.Comment: Significant revisions include discussion of systematic errors in the
median of H_0. Accepted for publication in The Astrophysical Journal, v548,
February 20, 2001 issue. 47 pages incl. figures and table
Glucose-Dependent Insulinotropic Polypeptide May Enhance Fatty Acid Re-esterification in Subcutaneous Abdominal Adipose Tissue in Lean Humans
Frequencies of some B blood group alleles in laying hens from a selection and crossbreeding experiment
Metal Enrichment of the Intergalactic Medium in Cosmological Simulations
Observations have established that the diffuse intergalactic medium (IGM) at
z ~ 3 is enriched to ~0.1-1% solar metallicity and that the hot gas in large
clusters of galaxies (ICM) is enriched to 1/3-1/2 solar metallicity at z=0.
Metals in the IGM may have been removed from galaxies (in which they presumably
form) during dynamical encounters between galaxies, by ram-pressure stripping,
by supernova-driven winds, or as radiation-pressure driven dust efflux. This
study develops a method of investigating the chemical enrichment of the IGM and
of galaxies, using already completed cosmological simulations. To these
simulations, we add dust and (gaseous) metals, distributing the dust and metals
in the gas according to three simple parameterized prescriptions, one for each
enrichment mechanism. These prescriptions are formulated to capture the basic
ejection physics, and calibrated when possible with empirical data. Our results
indicate that dynamical removal of metals from >~ 3*10^8 solar mass galaxies
cannot account for the observed metallicity of low-column density Ly-alpha
absorbers, and that dynamical removal from >~ 3*10^10 solar mass galaxies
cannot account for the ICM metallicities. Dynamical removal also fails to
produce a strong enough mass-metallicity relation in galaxies. In contrast,
either wind or radiation-pressure ejection of metals from relatively large
galaxies can plausibly account for all three sets of observations (though it is
unclear whether metals can be distributed uniformly enough in the low-density
regions without overly disturbing the IGM, and whether clusters can be enriched
quite as much as observed). We investigate in detail how our results change
with variations in our assumed parameters, and how results for the different
ejection processes compare. (Abridged)Comment: Minor revision, 1 figure added addressing diffusion of metals after
their ejection. Accepted by ApJ. 31 EmulateApj Pages with 13 embedded
postscript figure
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