171 research outputs found
The Zimbabwe external quality assessment scheme (ZEQAS) in clinical chemistry: results of the pilot programme
A pilot programme for assessing laboratory performance in clinical chemistry laboratories in Zimbabwe (ZEQAS) is described in this CAJM article.A pilot programme for assessing laboratory performance in clinical chemistry laboratories in Zimbabwe is described (ZEQAS). Twenty four laboratories providing patient care services participated. Eightlyphilised bovine sera were distributed over one year.
Consensus values and the spread of interlaboratory agreement were calculated for each of 12 analytes and compared with results previously obtained in a large mature national EQA scheme in the UK (UK NEQAS). For all analytes except phosphate, the mean consensus value obtained in ZEQAS was between 94 and 108 pc of the UK target, although the spread of results in ZEQAS was generally two to threefold greater for individual analytes than in UK NEQAS.
It is concluded that the ZEQAS consensus values for the analytes surveyed provide a valid target against which individual laboratory performance can be assessed. The wide spread of results from individual laboratories suggests there is considerable scope for improving inter-laboratory agreement. This is being addressed by the continuing programme, with increased interaction and production of local specimens
Eutectic colony formation: A phase field study
Eutectic two-phase cells, also known as eutectic colonies, are commonly
observed during the solidification of ternary alloys when the composition is
close to a binary eutectic valley. In analogy with the solidification cells
formed in dilute binary alloys, colony formation is triggered by a
morphological instability of a macroscopically planar eutectic solidification
front due to the rejection by both solid phases of a ternary impurity that
diffuses in the liquid. Here we develop a phase-field model of a binary
eutectic with a dilute ternary impurity and we investigate by dynamical
simulations both the initial linear regime of this instability, and the
subsequent highly nonlinear evolution of the interface that leads to fully
developed two-phase cells with a spacing much larger than the lamellar spacing.
We find a good overall agreement with our recent linear stability analysis [M.
Plapp and A. Karma, Phys. Rev. E 60, 6865 (1999)], which predicts a
destabilization of the front by long-wavelength modes that may be stationary or
oscillatory. A fine comparison, however, reveals that the assumption commonly
attributed to Cahn that lamella grow perpendicular to the envelope of the
solidification front is weakly violated in the phase-field simulations. We show
that, even though weak, this violation has an important quantitative effect on
the stability properties of the eutectic front. We also investigate the
dynamics of fully developed colonies and find that the large-scale envelope of
the composite eutectic front does not converge to a steady state, but exhibits
cell elimination and tip-splitting events up to the largest times simulated.Comment: 18 pages, 18 EPS figures, RevTeX twocolumn, submitted to Phys. Rev.
Inflation, cold dark matter, and the central density problem
A problem with high central densities in dark halos has arisen in the context
of LCDM cosmologies with scale-invariant initial power spectra. Although n=1 is
often justified by appealing to the inflation scenario, inflationary models
with mild deviations from scale-invariance are not uncommon and models with
significant running of the spectral index are plausible. Even mild deviations
from scale-invariance can be important because halo collapse times and
densities depend on the relative amount of small-scale power. We choose several
popular models of inflation and work out the ramifications for galaxy central
densities. For each model, we calculate its COBE-normalized power spectrum and
deduce the implied halo densities using a semi-analytic method calibrated
against N-body simulations. We compare our predictions to a sample of dark
matter-dominated galaxies using a non-parametric measure of the density. While
standard n=1, LCDM halos are overdense by a factor of 6, several of our example
inflation+CDM models predict halo densities well within the range preferred by
observations. We also show how the presence of massive (0.5 eV) neutrinos may
help to alleviate the central density problem even with n=1. We conclude that
galaxy central densities may not be as problematic for the CDM paradigm as is
sometimes assumed: rather than telling us something about the nature of the
dark matter, galaxy rotation curves may be telling us something about inflation
and/or neutrinos. An important test of this idea will be an eventual consensus
on the value of sigma_8, the rms overdensity on the scale 8 h^-1 Mpc. Our
successful models have values of sigma_8 approximately 0.75, which is within
the range of recent determinations. Finally, models with n>1 (or sigma_8 > 1)
are highly disfavored.Comment: 13 pages, 6 figures. Minor changes made to reflect referee's
Comments, error in Eq. (18) corrected, references updated and corrected,
conclusions unchanged. Version accepted for publication in Phys. Rev. D,
scheduled for 15 August 200
A rotação de cultura reduz a matocompetição e aumenta o teor de clorofila e a produtividade do arroz
Effect of compost-, sand-, or gypsum-amended waste foundry sands on turfgrass yield and nutrient content
To prevent the 7 to 11 million metric tons of waste foundry
sand (WFS) produced annually in the USA from entering
landfi lls, current research is focused on the reuse of WFSs as
soil amendments. Th e eff ects of diff erent WFS-containing
amendments on turfgrass growth and nutrient content were
tested by planting perennial ryegrass (Lolium perenne L.) and
tall fescue (Schedonorus phoenix (Scop.) Holub) in diff erent
blends containing WFS. Blends of WFS were created with
compost or acid-washed sand (AWS) at varying percent by
volume with WFS or by amendment with gypsum (9.6 g
gypsum kg–1 WFS). Measurements of soil strength, shoot and
root dry weight, plant surface coverage, and micronutrients (Al,
Fe, Mn, Cu, Zn, B, Na) and macronutrients (N, P, K, S, Ca,
Mg) were performed for each blend and compared with pure
WFS and with a commercial potting media control. Results
showed that strength was not a factor for any of the parameters
studied, but the K/Na base saturation ratio of WFS:compost
mixes was highly correlated with total shoot dry weight for
perennial ryegrass (r = 0.995) and tall fescue (r = 0.94). Th is was
further substantiated because total shoot dry weight was also
correlated with shoot K/Na concentration of perennial ryegrass
(r = 0.99) and tall fescue (r = 0.95). A compost blend containing
40% WFS was determined to be the optimal amendment for
the reuse of WFS because it incorporated the greatest possible
amount of WFS without major reduction in turfgrass growth
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