A test of the nature of cosmic acceleration using galaxy redshift distortions.

Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this 'dark energy' corresponds to a 'cosmological constant', perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter beta = 0.70 +/- 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 +/- 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. The correct origin could be determined with a further factor-of-ten increase in the sampled volume at similar redshift.

A large population of galaxies 9 to 12 billion years back in the history of the Universe.

To understand the evolution of galaxies, we need to know as accurately as possible how many galaxies were present in the Universe at different epochs. Galaxies in the young Universe have hitherto mainly been identified using their expected optical colours, but this leaves open the possibility that a significant population remains undetected because their colours are the result of a complex mix of stars, gas, dust or active galactic nuclei. Here we report the results of a flux-limited I-band survey of galaxies at look-back times of 9 to 12 billion years. We find 970 galaxies with spectroscopic redshifts between 1.4 and 5. This population is 1.6 to 6.2 times larger than previous estimates, with the difference increasing towards brighter magnitudes. Strong ultraviolet continua (in the rest frame of the galaxies) indicate vigorous star formation rates of more than 10-100 solar masses per year. As a consequence, the cosmic star formation rate representing the volume-averaged production of stars is higher than previously measured at redshifts of 3 to 4.

Intervalo de referencia de homocisteína plasmática por inmunoanálisis de fluorescencia polarizada (IMx®) en niños / Plasma homocysteine reference interval by a fluorescence polarization immunoassay (Imx) in children

Elevadas concentraciones de homocisteína total en plasma son consideradas un factor de riesgo de enfermedad vascular aterotrombótica. Su determinación resulta de gran utilidad en el diagnóstico de la homocistinuria. El objetivo de este estudio es el establecimiento del intervalo de referencia por un procedimiento de inmunoanálisis de fluorescencia polarizada (IMx®, Abbott Laboratories) en una población de niños sanos. Se han seleccionado muestras de 178 niños (102 varones y 76 hembras) en edades comprendidas entre 3 meses y 15 años (x- ñ s = 7,45 ñ 4,30) divididos en tres grupos. El análisis de varianza demostró que existen diferencias significativas de la homocisteína plasmática en relación con la edad (p <0,001). No encontramos diferencias significativas entre sexos. Los niveles de homocisteína se asociaron positivamente con la creatinina (r = 0,55; p < 0,01).Los intervalos de referencia de la homocisteína plasmática para los tres grupos estudiados fueron: < 6 años = 2,17-7,11 µmol/L; 6-10 años=2,87-7,95 µmol/Ly 11-15 años=3,00-10,70 µmol/L. En conclusión: Se ha establecido el intervalo de referencia de la homocisteína plasmática en niños. Existe un aumento de la homocisteína con la edad, pero no existen diferencias significativas con respecto al sexo (AU)

Temperature dependent nonlinearity effects of a QED-200 detector in the visible.

The spectral response of the United Detector Technologies model QED-200 quantum efficiency detector, along with that of other photodiodes, has been measured for two different wavelengths in the visible. The QED shows a strong temperature dependent response at certain power levels. It is shown that the effect comes from an increase in internal quantum efficiency due to a supralinearity effect at power levels of ~1 mW.