9,527 research outputs found
Hiroshi Machida −respected tephrochronologist, teacher, leader
Professor Emeritus Hiroshi Machida (Hiroshi hereafter) is the leading tephrochronologist of his generation in Japan. Perhaps more than any other geoscientist from Japan, Hiroshi carried the insights and advances of tephra studies and their application in palaeoenvironmental and archaeological applications, landscape processes, and volcanology and hazard analysis, to the outside world through a succession of papers and books written in English and through conference presentations. He has been the ‘international face’ of tephra studies in Japa
Review of Big Bang Nucleosynthesis and Primordial Abundances
Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei,
Deuterium, He3, He4 and Li7, during the first few minutes of the universe. This
review concentrates on recent improvements in the measurement of the primordial
(after BBN, and prior to modification) abundances of these nuclei. We mention
improvement in the standard theory, and the non-standard extensions which are
limited by the data. (abridged)Comment: 61 pages, to appear in Physica Script
Relative Flux Calibration of Keck HIRES Echelle Spectra
We describe a new method to calibrate the relative flux levels in spectra
from the HIRES echelle spectrograph on the Keck-I telescope. Standard data
reduction techniques that transfer the instrument response between HIRES
integrations leave errors in the flux of 5 - 10%, because the effective
response varies. The flux errors are most severe near the ends of each spectral
order, where there can be discontinuous jumps. The source of these errors is
uncertain, but may include changes in the vignetting connected to the optical
alignment. Our new flux calibration method uses a calibrated reference spectrum
of each target to calibrate individual HIRES integrations. We determine the
instrument response independently for each integration, and hence we avoid the
need to transfer the instrument response between HIRES integrations. The
procedure can be applied to any HIRES spectrum, or any other spectrum. While
the accuracy of the method depends upon many factors, we have been able to flux
calibrate a HIRES spectrum to 1% over scales of 200 A that include order joins.
We illustrate the method with spectra of Q1243+3047 towards which we have
measured the deuterium to hydrogen abundance ratio.Comment: 24 pages, 17 figures, submitted to PAS
Immediate versus water-storage performance of Class V flowable composite restoratives
Objectives
The aims of this investigation were to clarify the effects of 24 h water-storage and finishing time on mechanical properties and marginal adaptation to a Class V cavity of eight modern flowable resin-composites.
Methods
Eight flowable composites, plus two controls (one microfilled and one hybrid composite), were investigated with specimen sub-groups (n = 10) for each property measured. The principal series of experiments was conducted in model Class V cavities with interfacial polishing either immediately (3 min) after setting or after 24 h water-storage. After the finishing procedure, each tooth was sectioned in a buccolingual direction through the center of the restoration, and the presence or absence of marginal-gaps was measured (and then summed for each cavity) at 14 points (each 0.5 mm apart) along the cavity restoration interface (n = 10 per group; total points measured = 140). The shear bond-strengths to enamel and to dentin, and flexural strengths and moduli data were also measured at 3 min and after 24 h water-storage.
Results
For all flowable composites, polished immediately after setting, 14–30 summed gaps were observed (controls: 64 and 42). For specimens polished after 24 h, a significantly (p < 0.05) reduced number of 8–17 summed gaps occurred for only 3 flowable composites; whereas for 5 flowable composites there were non-significantly-different (p > 0.05) numbers (11–17) of summed gaps (controls: 28 and 22). After 24 h storage, shear bond-strengths to enamel and to dentin, flexural strengths and moduli increased highly significantly (p < 0.001) for all materials, except Silux Plus.
Significance
A post-cure interval of 24 h resulted in enhanced mechanical and adhesive properties of flowable dental composites. In a minority of cases there was also a reduced incidence of marginal-gap formation. However the latter effect may be partly attributed to 24 h delayed polishing, even though such a delay is not usual clinical practice.</p
Predicting QSO Continua in the Ly Alpha Forest
We present a method to make predictions with sets of correlated data values,
in this case QSO flux spectra. We predict the continuum in the Lyman-Alpha
forest of a QSO, from 1020 -- 1216 A, using the spectrum of that QSO from 1216
-- 1600 A . We find correlations between the unabsorbed flux in these two
wavelengths regions in the HST spectra of 50 QSOs. We use principal component
analysis (PCA) to summarize the variety of these spectra and we relate the
weights of the principal components for 1020 -- 1600 A to the weights for 1216
-- 1600 A, and we apply this relation to make predictions. We test the method
on the HST spectra, and we find an average absolute flux error of 9%, with a
range 3 -- 30%, where individual predictions are systematically too low or too
high. We mention several ways in which the predictions might be improved.Comment: 17 pages, 4 figures, submitted to Ap
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