Objectives: Older people commonly present with memory loss although on assessment are not found to have a full dementia complex. Previous studies have suggested however that people with subjective and objective cognitive loss are at higher risk of dementia. We aimed to determine from the literature the rate of conversion from mild cognitive impairment to dementia.Methods: Systematic review of MedLine, PsychLit and EmBase.Results: We identified 19 longitudinal studies published between 1991 and 2001 that addressed conversion of mild cognitive impairment to dementia. Overall the rate of conversion was 10% but with large differences between studies. The single biggest variable accounting for between study heterogeneity was source of subjects, with self-selected clinic attenders having the highest conversion rate. The most important factor accounting for heterogeneity within studies was cognitive testing, with poor performance predicting conversion with a high degree of accuracy.Conclusions: These data strongly support the notion that subjective and objective evidence of cognitive decline is not normal and predicts conversion to dementia. The more stringent the measures of both variables the better the prediction of conversion. Mild cognitive impairment, appropriately diagnosed, is a good measure with which to select subjects for disease modification studies.

We study the angular power spectra of polarized Galactic synchrotron in the range 10 < ∼ l ≤ 800, at several frequencies between 0.4 and 2.7 GHz and at several Galactic latitudes up to near the North Galactic Pole. Electric-and magnetic-parity polarization spectra are found to have slopes around α E,B = 1.4 − 1.5 in the Parkes and Effelsberg Galactic-Plane surveys, but strong local fluctuations of α E,B are found at |b| ≃ 10 • from the 1.4 GHz Effelsberg survey. The C P Il spectrum, which is insensitive to the polarization direction, is somewhat steeper, being α P I = 1.6 − 1.8 for the same surveys. The low-resolution multifrequency survey of Brouw and Spoelstra (1976) shows some flattening of the spectra below 1 GHz, more intense for C E,Bl than for C P Il . In no case we find evidence for really steep spectra. The extrapolation to the cosmological window shows that at 90 GHz the detection of E-mode harmonics in the cosmic background radiation should not be disturbed by synchrotron, even around l ≃ 10 for a reionization optical depth τ ri > ∼ 0.05.

Motivated by the relative lack of neutral hydrogen around Lyman‐break galaxies deduced from recent observations, we investigate the properties of the Lyα forest around high‐redshift galaxies. The study is based on improved numerical SPH simulations implementing, in addition to standard processes, a new scheme for multiphase and outflow physics description. Although on large scales our simulations reproduce a number of statistical properties of the intergalactic medium (because of the small filling factor of shock‐heated gas), they underpredict the Lyα optical depth decrease inside 1 Mpc h−1 of the galaxies by a factor of ≈15. We interpret this result as arising from the combined effect of infall occurring along the filaments, which prevents efficient halo gas clearing by the outflow, and the insufficient increase of (collisional) hydrogen ionization produced by the temperature increase inside the hot, outflow‐carved bubble. Unless either feedback is not properly modelled in cosmological simulations or an observational selection bias is present, we speculate that local photoionization could be a viable explanation to solve the puzzle.

We calculate the secondary anisotropies in the cosmic microwave background (CMB) produced by inhomogeneous reionization from simulations in which the effects of radiative and stellar feedback effects on galaxy formation have been included. This allows us to determine self-consistently the beginning z i < 30Y the duration dz < 20 and the (nonlinear) evolution of the reionization process for a critical density cold dark matter (CDM) model. In addition, from the simulated spatial distribution of ionized regions, we are able to calculate the evolution of the two-point ionization correlation function, C x , and obtain the power spectrum of the anisotropies, C`, in the range 5000 ,`, 10 6 X The power spectrum has a broad maximum around`< 30 000Y where it reaches the value 2 Â 10 212 X We also show that the ionization correlation function C x is not Gaussian, but at separation angles u & 10 24 rad it can be approximated by a modified Lorentzian shape; at larger separations an anticorrelation signal is predicted for both C x and C(u ). Detection of signals as above will be possible with future millimetre-wavelength interferometers like the Atacama Large Millimeter Array (ALMA), which appears as an optimum instrument to search for signatures of inhomogeneous reionization.

We study the effect of a prolonged epoch of reionization on the angular power spectrum of the cosmic microwave background. Typically reionization studies assume a sudden phase transition, with the intergalactic gas moving from a fully neutral to a fully ionized state at a fixed redshift. Such models are at odds, however, with detailed investigations of reionization, which favour a more extended transition. We have modified the code cmbfast to allow the treatment of more realistic reionization histories and applied it to data obtained from numerical simulations of reionization. We show that the prompt reionization assumed by cmbfast in its original form heavily contaminates any constraint derived on the reionization redshift. We find, however, that prompt reionization models give a reasonable estimate of the epoch at which the mean cosmic ionization fraction was ≈50 per cent, and provide a very good measure of the overall Thomson optical depth. The overall differences in the temperature (polarization) angular power spectra between prompt and extended models with equal optical depths are less than 1 per cent (10 per cent).