An intensive study of stratospheric aerosols by means of a lidar (laser radar) was conducted at Aberystwyth (52.4°N, 4.1°W) during February and April 1983, when the optical depth due to aerosols associated with the El Chichon eruption was greatest. Very sharp vertical gradients in the aerosol backscatter profile (factors of 7 in 100 m) were found to accompany the onset and decay of a block in the tropospheric flow, and to be related to the proximity of the polar stratospheric vortex. Differential advection, identified as the process most likely to be responsible for such gradients, is suggested as a mechanism for the erosion of stratospheric vortices isolated from the pole by vigorous planetary wave activity. Statistical studies of the aerosol data reveal a time scale of 36-48 hours for temporal coherence above 17 km, corresponding to a length scale of about 300 km for the dominant irregularities in the cloud. Irregularities below 17 km were much smaller both in amplitude and scale. The observations of very sharp gradients in the aerosol cloud, facilitated by the excellent vertical resolution of the lidar technique (30 m), reveals interesting wave-like perturbations possibly caused by a gravity wave.
This article describes the conclusions of an expert panel that discussed four case studies; these were examples of patients typically encountered by nurses working in the community. The panel considered the nutritional and lifestyle advice that could be given by nurses relating to conditions such as irritable bowel syndrome (IBS), depression, chronic fatigue syndrome, vulnerability to common infections, elderly care, recurrent urinary tract infection, antibiotic use, and risk of type 2 diabetes. A general conclusion was the importance of motivational interviewing techniques in achieving full understanding of patients’ concerns and to determine the best health strategy. As well as specific guidance appropriate for each disorder, a range of information sources for both health professionals and patients are listed in the paper. The panel noted that, although general nutritional advice can be given by nurses working at GP surgeries and in the community, patients should always be referred to registered dietitians or nutritionists if significant dietary changes are considered.
Strains of Escherichia coli which belong to enteropathogenic serogroups usually fail to produce heat-labile or heat-stable enterotoxins. However, 1 of 34 strains of E. coli O44, 9 of 45 strains of E. coli O114, and 18 of 82 strains of E. coli O128 produced heat-labile or heat-stable enterotoxins. Most enterotoxigenic isolates were from tropical or developing countries; all three enterotoxigenic strains isolated in Britain were from patients returned from abroad. Enterotoxigenic strains were of many different flagellar types. Certain enterotoxigenic strains of E. coli O114 and O128 possessed colonization factor antigen I.
The effect of spatial separation on interactions between subsurface bacterial colonies was tested using a model system: the inhibition of Listeria monocytogenes by nisin-producing and nisin-non-producing Lactococcus lactis subsp. lactis. Separation distance was controlled by altering the number of inoculum organisms within the agar. Mean separation distance was calculated by determining the mean volume available to each cell at the start of the experiment. Inhibition was assessed by comparing the growth of L. monocytogenes in pure culture with its growth in the presence of Lac. lactis subsp. lactis. Increasing the distance between colonies resulted in an exponential decrease in inhibition. When L. monocytogenes and Lac. lactis subsp. lactis colonies were within 100 microns of each other, the increase in cell numbers per L. monocytogenes colony was only 0.6 c.f.u. (which indicated some cells had become non-viable). This was a log reduction of 3.5 compared to the pure culture control. A separation distance of 1000 microns resulted in a L. monocytogenes colony growth increment of 2.5 x 10(2) c.f.u. per colony, a log reduction of 3.0 compared to the control. Increasing the separation distance to 3000 microns resulted in a L. monocytogenes colony growth increment of 1.3 x 10(6) c.f.u. per colony, a log reduction of 0.9 compared to the control. The effects of nisin and acidity were investigated by using a nisin-non-producing strain of Lac. lactis subsp. lactis and by buffering the medium. Data were obtained for the effect of separation on inhibition, as well as competition between colonies of the same species. The inhibition was mathematically described in terms of a simplified 'territory' model of immobilized bacterial growth. There was a strong qualitative agreement between the mathematical model and the experimental data. It was concluded that the phenomenon of propinquity is of important consideration when modeling and predicting microbial growth within solid food systems.
The conditions controlling the vertical propagation of mountain waves in the troposphere and lower stratosphere have been examined using radar observations at 46.5 MHz of vertical-velocity perturbations at Aberystwyth (52.4°N, 4.1°W) and radiosonde observations from Aberporth, some 50 km to the south-west. Attention has been paid to the influence of the variation with height of the mean wind vector (U), the Brunt–Väisälä frequency and the Scorer parameter. Four case-studies show the absorption of mountain waves at heights where the mean wind component normal to the wave front vanishes; this corresponds to U = 0 if the wind direction does not change with increasing height, and to the wind vector being orthogonal to the wave vector if the wind rotates with increasing height. For two cases, enhanced turbulence is found in the upper few hundred metres of the mountain-wave field, directly below the height at which the waves disappear; for a third case, the enhancement extends over a broader range of heights, and for the fourth no clear identification of the enhancement is possible. The frequency power-spectra of the vertical-velocity oscillations show a ωn dependence, with n approaching −5/3 for regions of mountain-wave activity below the critical layers, and n = 0 for heights above the critical layers. Statistically, mountain waves generated by low-level easterly winds are often confined to tropospheric heights. An analysis of a large sample of radiosonde data indicates that critical-layer absorption associated with rotation of the background wind in addition to wave reflection and trapping, plays an important role in this confinement. The results are discussed in terms of the momentum flux associated with gravity waves, their turbulent breakdown near the critical layer, and the implications of the frequency spectra below and above such layers.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
 scale(5.56106)'%3e%3ccircle r='1'/%3e%3cg id='d'%3e%3cg id='c'%3e%3cpath id='b' d='M.195-.98 0-1.39l-.195.408' transform='rotate(11.25)'/%3e%3cuse xlink:href='%23b' transform='rotate(22.5)'/%3e%3cuse xlink:href='%23b' transform='rotate(45)'/%3e%3c/g%3e%3cuse xlink:href='%23c' transform='rotate(67.5)'/%3e%3c/g%3e%3cuse xlink:href='%23d' transform='scale(-1 1)'/%3e%3c/g%3e%3cg transform='translate(0 58.787) scale(8.1434)'%3e%3ccircle r='1'/%3e%3cg id='g'%3e%3cg id='f'%3e%3cpath id='e' d='M.259.966 0 1.576l-.259-.61'/%3e%3cuse xlink:href='%23e' transform='rotate(180)'/%3e%3c/g%3e%3cuse xlink:href='%23f' transform='rotate(90)'/%3e%3c/g%3e%3cuse xlink:href='%23g' transform='rotate(30)'/%3e%3cuse xlink:href='%23g' transform='rotate(60)'/%3e%3c/g%3e%3c/g%3e%3c/svg%3e)