854 research outputs found
Algae for controlled ecological life support system diet characterization of cyanobacteria 'spirulina' in batch cultures
Spirulina sp. is a bioregenerative photosynthetic and edible alga for space craft crews in a Closed Ecological Life Support System (CLESS). It was characterized for growth rate and biomass yield in batch cultures, under various environmental conditions. The cell characteristics were identified for one strain of Spirulina: S. maxima. Fast growth rate and high yield were obtained. The partitioning of the assimulatory products (proteins, carbohydrates, lipids) were manipulated by varying the environmental conditions. Experiments with Spirulina demonstrated that under stress conditions carbohydrate increased at the expense of protein. In other experiments, where the growth media were sufficient in nutrients and incubated under optimum growth conditions, the total proteins were increased up to almost 70 percent of the organic weight. In other words, the nutritional quality of the alga could be manipulated by growth conditions. These results support the feasibility of considering Spirulina as a subsystem in CELSS because of the ease with which its nutrient content can be manipulated
The Power Spectrum of the PSC Redshift Survey
We measure the redshift-space power spectrum P(k) for the recently completed
IRAS Point Source Catalogue (PSC) redshift survey, which contains 14500
galaxies over 84% of the sky with 60 micron flux >= 0.6 Jansky. Comparison with
simulations shows that our estimated errors on P(k) are realistic, and that
systematic errors due to the finite survey volume are small for wavenumbers k
>~ 0.03 h Mpc^-1. At large scales our power spectrum is intermediate between
those of the earlier QDOT and 1.2 Jansky surveys, but with considerably smaller
error bars; it falls slightly more steeply to smaller scales. We have fitted
families of CDM-like models using the Peacock-Dodds formula for non-linear
evolution; the results are somewhat sensitive to the assumed small-scale
velocity dispersion \sigma_V. Assuming a realistic \sigma_V \approx 300 km/s
yields a shape parameter \Gamma ~ 0.25 and normalisation b \sigma_8 ~ 0.75; if
\sigma_V is as high as 600 km/s then \Gamma = 0.5 is only marginally excluded.
There is little evidence for any `preferred scale' in the power spectrum or
non-Gaussian behaviour in the distribution of large-scale power.Comment: Latex, uses mn.sty, 14 pages including 11 Postscript figures.
Accepted by MNRA
Steps toward the power spectrum of matter. I.The mean spectrum of galaxies
We calculate the mean power spectrum of galaxies using published power
spectra of galaxies and clusters of galaxies. On small scales we use the power
spectrum derived from the 2-dimensional distribution of APM galaxies, on large
scales we use power spectra derived from 3-dimensional data for galaxy and
cluster samples. Spectra are reduced to real space and to the amplitude of the
power spectrum of APM galaxies. Available data indicate the presence of two
different populations in the nearby Universe. Clusters of galaxies sample a
relatively large region in the Universe where rich, medium and poor
superclusters are well represented. Their mean power spectrum has a spike on
scale 120 h^{-1}Mpc, followed by an approximate power-law spectrum of index n =
-1.9 towards small scales. The power spectrum found from LCRS and IRAS 1.2 Jy
surveys is flatter around the maximum, which may represent regions of the
Universe with medium-rich and poor superclusters.Comment: LaTex (sty files added), 35 pages, 5 PostScript figures and Table
with mean power spectrum embedded, Astrophysical Journal (accepted
Origin and evolution of halo bias in linear and non-linear regimes
We present results from a study of bias and its evolution for galaxy-size
halos in a large, high-resolution simulation of a LCDM model. We consider the
evolution of bias estimated using two-point correlation function (b_xi), power
spectrum (b_P), and a direct correlation of smoothed halo and matter
overdensity fields (b_d). We present accurate estimates of the evolution of the
matter power spectrum probed deep into the stable clustering regime
(k~[0.1-200]h/Mpc at z=0). The halo power spectrum evolves much slower than the
power spectrum of matter and has a different shape which indicates that the
bias is time- and scale-dependent. At z=0, the halo power spectrum is
anti-biased with respect to the matter power spectrum at wavenumbers
k~[0.15-30]h/Mpc, and provides an excellent match to the power spectrum of the
APM galaxies at all probed k. In particular, it nicely matches the inflection
observed in the APM power spectrum at k~0.15h/Mpc. We complement the power
spectrum analysis with a direct estimate of bias using smoothed halo and matter
overdensity fields and show that the evolution observed in the simulation in
linear and mildly non-linear regimes can be well described by the analytical
model of Mo & White (1996), if the distinction between formation redshift of
halos and observation epoch is introduced into the model. We present arguments
and evidence that at higher overdensities, the evolution of bias is
significantly affected by dynamical friction and tidal stripping operating on
the satellite halos in high-density regions of clusters and groups; we
attribute the strong anti-bias observed in the halo correlation function and
power spectrum to these effects. (Abridged)Comment: submitted to the Astrophys.Journal; 19 pages, 9 figures LaTeX (uses
emulateapj.sty
Double Inflation in Supergravity and the Large Scale Structure
The cosmological implication of a double inflation model with hybrid + new
inflations in supergravity is studied. The hybrid inflation drives an inflaton
for new inflation close to the origin through supergravity effects and new
inflation naturally occurs. If the total e-fold number of new inflation is
smaller than , both inflations produce cosmologically relevant density
fluctuations. Both cluster abundances and galaxy distributions provide strong
constraints on the parameters in the double inflation model assuming
standard cold dark matter scenario. The future satellite
experiments to measure the angular power spectrum of the cosmic microwave
background will make a precise determination of the model parameters possible.Comment: 19 pages (RevTeX file
Constraints on Galaxy Bias, Matter Density, and Primordial Non--Gausianity from the PSCz Galaxy Redshift Survey
We compute the bispectrum for the \IRAS PSCz catalog and find that the galaxy
distribution displays the characteristic signature of gravity. Assuming
Gaussian initial conditions, we obtain galaxy biasing parameters
and , with no sign of
scale-dependent bias for h/Mpc. These results impose stringent
constraints on non-Gaussian initial conditions. For dimensional scaling models
with statistics, we find N>49, which implies a constraint on
primordial skewness .Comment: 4 pages, 3 embedded figures, uses revtex style file, minor changes to
reflect published versio
Dyslexia and password usage:accessibility in authentication design
Governments and businesses are moving online with alacrity, driven by potential cost savings, changing consumer and citizen expectations, and the momentum towards general digital provision. Services are legally required to be inclusive and accessible. Now consider that almost every online service, where people have to identify themselves, requires a password. Passwords seem to be accessible, until one considers specific disabilities, one of which can lead to many challenges: dyslexia being a case in point. Dyslexia is associated with word processing and retention difficulties, and passwords are essentially words, phrases or alphanumeric combinations. We report on a literature review conducted to identify extant research into the impact of dyslexia on password usage, as well as any ameliorations that have been proposed. We discovered a relatively neglected field. We conclude with recommendations for future research into the needs of a large population of dyslexics who seem to struggle with passwords, in a world where avoiding passwords has become almost impossible. The main contribution of this paper is to highlight the difficulties dyslexics face with passwords, and to suggest some avenues for future research in this area
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