Propagation of an electromagnetic wave in an absorbing anisotropic medium and infrared transmission of liquid crystals: comparison with experiments.

The theory of the absorbance of a semi-infinite medium characterized by a second-rank dielectric tensor for the entire electromagnetic spectrum, as given by Scaife and Vij [J. Chem. Phys. 122, 174901 (2005)], is extended to include molecules of prolate spheriodal shape with longitudinal and transverse polarizabilities and to cover the case of elliptically polarized incident radiation. The theory is applied to the infrared transmission experiments of biaxial liquid crystals. It is found that the formula for the dependence on frequency and on angle of polarization of the absorbance A(omega,theta)= -log(10)[10(A(omega,0)) cos(2) theta + (10(-A(omega,pi/2)) sin(2) theta)] is unaffected by the anisotropy of the molecules and by the elliptical polarization of the incident radiation. A small (+/-5%) discrepancy between theory and experiment has been found for bands with high absorbances. It is found that this discrepancy does not depend on birefringence of the sample but may depend on the precise method of absorbance measurement and on effects at the surface of the cell containing the liquid crystal under test.

Propagation of an electromagnetic wave in an absorbing anisotropic medium and infrared transmission spectroscopy of liquid crystals.

The theory of absorbance is developed for the entire electromagnetic spectrum of radiation in a semi-infinite anisotropic medium with a second rank dielectric tensor, the elements of which are complex and frequency dependent. The theory of the absorbance A(omega,theta) of an optically anisotropic liquid in an infrared (IR) test cell is then outlined and applied to IR transmission experiments. A formula for the dependence of A(omega,theta), on theta (theta being the angle between the electric vector and the principal optical axis) is derived from first principles. The formula, for radiation of angular frequency omega, viz, A(omega,theta)=-log(10)[10(-A(omega,0))cos(2)theta+10(-A(omega,pi2))sin(2)theta] is in agreement with that proposed by Jang, Park, Maclennan, Kim, and Clark [Ferroelectrics 180, 213 (1996) ] and confirms some of the work of Kocot, Wrzalik, and Vij [Liq. Cryst. 21, 147 (1996)]. The comments on this formula by Jang, Park, Kim, Glaser, and Clark [Phys. Rev. E 62, 5027 (2000)], and by Kocot et al. are discussed. The absorbance A(omega,0) and A(omega,pi2) have been expressed in terms of the optical properties of the material and the dimensions of the cell.

Socio-economic characteristics of adult frequent attenders in general practice: secondary analysis of data.

OBJECTIVE: This study was carried out to determine the effect of a range of socio-economic features on frequent attendance in general practice from a large database of general practice consultations using two definitions of frequent attendance. METHODS: Secondary analyses were carried out of data from the Fourth National Survey of Morbidity in General Practice covering 60 general practices in England and Wales. A total of 283 842 adult patients and their consultations between September 1991 and August 1992 were examined. The main outcome measure was the odds ratio of being a frequent attender (95% confidence intervals). RESULTS: Using a definition of 12+ consultations/year, men were less likely to be frequent attenders (OR 0.14, 95% CI 0.13-0.17); however, the difference between men and women lessens with age. Patients who were more likely to be frequent attenders included those who were divorced or widowed (1.41, 1.31-1.51); from social classes IIIM (1.23, 1.17-1.29) and IV/V (1.33, 1.26-1.41); South Asian people (1.38, 1.16-1.65); or unemployed (1.61, 1.46-1.77). Other factors signifying isolation or poverty were also linked to frequent attendance. Using the definition of '6+ consultations for minor problems' produced broadly similar results although the relative weight of the factors showed some differences. CONCLUSIONS: Socio-economic factors were important indicators of frequent attendance in general practice. Results were very similar using either definition, suggesting that both are valid for further work. Furthermore, frequent attendance is a complex process associated with many factors outside the control of the GP.

A comparison of the diagnostic utility of two image receptors for panoramic radiography.

OBJECTIVE: To compare the diagnostic utility of two screen-film systems for panoramic radiography, one based on green and the other on ultraviolet light. MATERIALS AND METHODS: Two hundred consecutive adult patients with teeth in all four quadrants requiring panoramic radiographs were randomly allocated to one of two groups. One group was imaged with OGA L (CEA AB, Strängnäs, Sweden) film using Lanex Regular (Eastman Kodak, Rochester, NY, USA) screens (the Lanex group). The other group was imaged using Ultra-Vision (Dupont UK Limited, Hertfordshire, UK) film and screens (the Ultra-vision group). Two different panoramic machines were used, a Planmeca (Planmeca OY, Helsinki, Finland) and Cranex (Soredex Orion Corporation, Helsinki, Finland). The radiographs were evaluated by two radiographers for overall quality and any faults recorded. Two dental radiologists evaluated the crestal and apical areas of every standing tooth on a 4-point scale. The likelihood of getting a high-quality image with the different films was modelled using logistic regression, adjusting for the radiologist and the area of the tooth being examined. Inter- and intra-examiner agreement was calculated using Kappa and weighted Kappa where appropriate. RESULTS: The radiographers recorded no significant differences in positioning errors between the two groups of film. However, the films produced on the Cranex were less likely to be recorded as excellent. The radiologists' interexaminer agreement for the lower molars and upper incisors was only moderate at best (kappa = 0.56). No significant differences were found between the likelihood of the two types of film providing a high-quality image. Crestal areas were more likely to be scored well than apical areas. CONCLUSION: There were no differences in ease of discerning apical and crestal areas between the two screen-film systems. There was only poor to moderate agreement between the two radiologists. Ultra-Vision can be recommended as an alternative to existing rare earth systems for panoramic radiography.

The effect of the 1996 'beef crisis' on depression and anxiety in farmers and non-farming controls.

This paper looks at the effect of the 1996 'BSE crisis' on the mental health of farmers from one semi-ural practice in North Yorkshire. In 1996, Hospital Anxiety and Depression (HAD) scales were sent to farmers and controls who had participated in a previous study in 1994. Comparative data for the two groups for the two years were obtained and analysed. The data showed that, despite fears raised as a result of the 'BSE crisis', the overall rates of depression and anxiety fell in both groups between 1994 and 1996, with the rates falling significantly more in the control group. However, the farmers were still more depressed and anxious than the controls, and those farmers that had been depressed or anxious in 1994 were more likely to be depressed or anxious in 1996. A longer period of time may be needed to determine the effect of the beef crisis on the mental health of farmers.

Survey of cervical cytology in general practice.

In a practice in an industrial area a cervical cytology service was offered to women, and in the years 1967-70 280 cervical smears were carried out. In 1971 all women born between 1 January 1920 and 31 December 1935 who had not had a cervical smear taken in the preceding four years were sent a letter explaining the service and inviting them to attend. Those who did not attend received a second letter and, if necessary, a visit by a nurse in an effort to persuade them to do so.Eventually 88.4% of the women in this age group who could be traced attended, and 16 abnormal cervical smears were reported. As a result of cone biopsy 12 women were found to have carcinoma in situ.