15,986 research outputs found
Conservative tolerance and confidence limits
Extension of exponential tolerance and confidence limits to class of distributions with monotone failure rat
Reliability growth during a development testing program
Binomial and trinomial mathematical models for reliability growth studies - statistical analysis of system failure
Tolerance and confidence limits for classes of distributions based on failure rate
Tolerance and confidence limits for classes of distributions based on failure rate
Tests for exponentiality against NBUE alternatives: a Monte Carlo comparison
Testing of various classes of life distributions has been addressed in the
literature for more than 45 years. In this paper, we consider the problem of
testing exponentiality (which essentially implies no ageing) against positive
ageing which is captured by the fairly large class of new better than used in
expectation (NBUE) distributions. These tests of exponentiality against NBUE
alternatives are discussed and compared. The empirical size of the tests is
obtained by simulations. Power comparisons for different popular alternatives
are done using Monte Carlo simulations. These comparisons are made for both
small and large sample sizes. The paper concludes with a discussion in which
suggestions are made regarding the choices of the test when a particular
alternative is suspected
Electrophoretic separation of human kidney cells at zero gravity
Electrophoretic isolation of cells results in a loss of resolution power caused by the sedimentation of the cells in the media. The results of an experiment to extract urokinase from human embryos during the Apollo Soyuz mission are presented and discussed
Early Dust Formation and a Massive Progenitor for SN 2011ja?
SN 2011ja was a bright (I = -18.3) Type II supernova occurring in the nearby
edge on spiral galaxy NGC 4945. Flat-topped and multi-peaked H-alpha and H-beta
spectral emission lines appear between 64 - 84 days post-explosion, indicating
interaction with a disc-like circumstellar medium inclined 30-45 degrees from
edge-on. After day 84 an increase in the H- and K-band flux along with heavy
attenuation of the red wing of the emission lines are strong indications of
early dust formation, likely located in the cool dense shell created between
the forward shock of the SN ejecta and the reverse shock created as the ejecta
plows into the existing CSM. Radiative transfer modeling reveals both ~1.5 x
10^-4 Msun of pre-existing dust located ~ 10^16.7 cm away and ~ 5 x 10^-5 Msun
of newly formed dust. Spectral observations after 1.5 years reveal the
possibility that the fading SN is located within a young (3-6 Myr) massive
stellar cluster, which when combined with tentative 56Ni mass estimates of 0.2
Msun may indicate a massive (> 25 Msun) progenitor for SN 2011ja.Comment: 13 pages, 8 figures, submitted to MNRAS awaiting final referee repor
Elemental boron doping behavior in silicon molecular beam epitaxy
Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2×1020 cm−3, to elucidate profile control and electrical activation over the growth temperature range 450–900 °C. Precipitation and surface segregation effects were observed at doping levels of 2×1020 cm−3 for growth temperatures above 600 °C. At growth temperatures below 600 °C, excellent profile control was achieved with complete electrical activation at concentrations of 2×1020 cm−3, corresponding to the optimal MBE growth conditions for a range of Si/SixGe1−x heterostructures
Temperature effects on the 15-85-micron spectra of olivines and pyroxenes
Far-infrared spectra of laboratory silicates are normally obtained at room
temperature even though the grains responsible for astronomical silicate
emission bands seen at wavelengths >20 micron are likely to be at temperatures
below ~150 K. In order to investigate the effect of temperature on silicate
spectra, we have obtained absorption spectra of powdered forsterite and
olivine, along with two orthoenstatites and diopside clinopyroxene, at 3.5+-0.5
K and at room temperature (295+-2K). To determine the changes in the spectra
the resolution must be increased from 1 to 0.25 cm^-1 at both temperatures
since a reduction in temperature reduces the phonon density, thereby reducing
the width of the infrared peaks. Several bands observed at 295 K split at 3.5
K. At 3.5 K the widths of isolated single bands in olivine, enstatites and
diopside are ~ 90% of their 295 K-widths. However, in forsterite the
3.5-K-widths of the 31-, 49- and 69-micron bands are, respectively, 90%, 45%
and 31% of their 295 K widths. Due to an increase in phonon energy as the
lattice contracts, 3.5-K-singlet peaks occur at shorter wavelengths than do the
corresponding 295-K peaks; the magnitude of the wavelength shift increases from
\~ 0-0.2 micron at 25 micron to ~0.9 micron at 80 micron. Changes in the
relative absorbances of spectral peaks are also observed. The temperature
dependence of lambda_pk and bandwidth shows promise as a means to deduce
characteristic temperatures of mineralogically distinct grain populations. In
addition, the observed changes in band strength with temperature will affect
estimates of grain masses and relative mineral abundances inferred using
room-temperature laboratory data.Comment: 11 pages, 7 figures including figures 3a and 3b. includes latex and
eps files. Accepted by MNRAS on 15th March 200
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