Deep optical imaging of the field of PC1643+4631A&B, II: Estimating the colours and redshifts of faint galaxies

In an investigation of the cause of the cosmic microwave background decrement in the field of the z = 3.8 quasar pair PC1643+4631, we have carried out a study to photometrically estimate the redshifts of galaxies in deep multi-colour optical images of the field taken with the WHT. To examine the possibility that a massive cluster of galaxies lies in the field, we have attempted to recover simulated galaxies with intrinsic colours matching those of the model galaxies used in the photometric redshift estimation. We find that when such model galaxies are added to our images, there is considerable scatter of the recovered galaxy redshifts away from the model value; this scatter is larger than that expected from photometric errors and is the result of confusion, simply due to ground-based seeing, between objects in the field. We have also compared the likely efficiency of the photometric redshift technique against the colour criteria used to select z>3 galaxies via the strong colour signature of the Lyman-limit break. We find that these techniques may significantly underestimate the true surface density of z>3, due to confusion between the high-redshift galaxies and other objects near the line of sight. We argue that the actual surface density of z=3 galaxies may be as much as 6 times greater than that estimated by previous ground-based studies, and note that this conclusion is consistent with the surface density of high-redshift objects found in the HDF. Finally, we conclude that all ground-based deep field surveys are inevitably affected by confusion, and note that reducing the effective seeing in ground-based images will be of paramount importance in observing the distant universe.Comment: 18 pages, 60 figures, submitted to MNRAS, 2 large figure avaliable at ftp://ftp.mrao.cam.ac.uk:/pub/PC1643/paper2.figure50.eps and ftp://ftp.mrao.cam.ac.uk:/pub/PC1643/paper2.figure51.ep

Deep optical imaging of the field of PC1643+4631A&B, I: Spatial distributions and the counts of faint galaxies

We present deep optical images of the PC1643+4631 field obtained at the WHT. This field contains two quasars at redshifts z=3.79 & 3.83 and a cosmic microwave background (CMB) decrement detected with the Ryle Telescope. The images are in U,G,V,R and I filters, and are complete to 25th magnitude in R and G and to 25.5 in U. The isophotal galaxy counts are consistent with the results of Metcalde et al. (1996), Hogg et al. (1997), and others. We find an excess of robust high-redshift Ly-break galaxy candidates with 25.0<R<25.5 compared with the mean number found in the fields studied by Steidel et al. -we expect 7 but find 16 - but we do not find that the galaxies are concentrated in the direction of the CMB decrement. However, we are still not sure of the distance to the system causing the CMB decrement. We have also used our images to compare the commonly used object-finding algorithms of FOCAS and SExtractor: we find FOCAS the more efficient at detecting faint objects and the better at dealing with composite objects, whereas SExtractor's morphological classification is more reliable, especially for faint objects near the resolution limit. More generally, we have also compared the flux lost using isophotal apertures on a real image with that on a noise-only image: recovery of artificial galaxies from the noise-only image significantly overestimates the flux lost from the galaxies, and we find that the corrections made using this technique suffer a systematic error of some 0.4 magnitudes.Comment: 17 pages, 40 figures, submitted to MNRAS, 1 large figure avaliable at ftp://ftp.mrao.cam.ac.uk:/pub/PC1643/paper1.figure18.p

Europium as an inhibitor of Amyloid-β(1-42) induced membrane permeation

Soluble Amyloid-beta (Aβ) oligomers are a source of cytotoxicity in Alzheimer's disease (AD). The toxicity of Aβ oligomers may arise from their ability to interact with and disrupt cellular membranes mediated by GM1 ganglioside receptors within these membranes. Therefore, inhibition of Aβ–membrane interactions could provide a means of preventing the toxicity associated with Aβ. Here, using Surface Plasmon field-enhanced Fluorescence Spectroscopy, we determine that the lanthanide, Europium III chloride (Eu3+), strongly binds to GM1 ganglioside-containing membranes and prevents the interaction with Aβ42 leading to a loss of the peptides ability to cause membrane permeation. Here we discuss the molecular mechanism by which Eu3+ inhibits Aβ42-membrane interactions and this may lead to protection of membrane integrity against Aβ42 induced toxicity

Deep multicolour imaging of the field towards the quasar pair PC1643+463 A&amp;B

We present the first results of a deep imaging programme to identify the system responsible for the Cosmic Microwave Background decrement in the field towards the z = 3.8 quasar pair PC1643+4631 A&amp;B. Using the prime focus camera at the William Herschel Telescope we have carried out deep multicolour optical imaging to search for candidate cluster galaxies at extremely high redshift. Using UGR colour selection we find the surface density of z&gt; 3 Lyman-break galaxy candidates is at least as great as that found in the field of the z = 3.1 structure discovered by Steidel et al. (1998), and may be somewhat greater. 1

Minor psychiatric disorder in NHS Trust staff::Occupational and gender differences

BACKGROUND It is widely suggested that many National Health Service (NHS) workers experience high levels of minor psychiatric disorder. However, inadequacies of sampling and measurement in studies to date have not allowed this suggestion to be properly evaluated. METHOD The present study was designed to overcome these methodological weaknesses by using a sample of over 11,000 employees from 19 NHS trusts and a well-established measure of minor psychiatric disorder for which there are comparative data. RESULTS The findings show that 26.8% of the health service workers reported significant levels of minor psychiatric disorder, compared with 17.8% of people in the general population. Psychiatric morbidity was highest among managers, doctors, nurses and professions allied to medicine, with each of these groups recording higher rates than their professional counterparts outside the health service. It was lower among those in support occupations, such as administrative and ancillary staff. A feature of the findings was that female doctors and managers showed a much higher prevalence of minor psychiatric disorder than their male colleagues. CONCLUSION Studies are required to establish the organisational, occupational and individual determinants of minor psychiatric disorder among NHS employees