CLUSTER LEED - A VERY FAST METHOD FOR SURFACE-STRUCTURE DETERMINATION

A very fast method, cluster low-energy electron diffraction (LEED) is proposed for LEED I-V spectral analysis, in which three appproximations are introduced: the small-atom approximation, omission of the structure factors, and truncation of higher order ( > 2) scattering events. The method has been tested using a total of four sets of I-V spectra calculated by fully dynamic LEED for (i) the simple overlayer system, O on Ni{100}, and (ii) the reconstructed system, Cu on W{100}, and also one set of experimental data from W{100}-c(2 X 2)-Cu. In each case the correct structural parameters are recovered. It is suggested that for complex systems cluster LEED provides an efficient fast route to trial structures, which could be refined by automated tenser LEED.

Double ionization in R-matrix theory using a two-electron outer region

We have developed a two-electron outer region for use within R-matrix theory to describe double ionisation processes. The capability of this method is demonstrated for single-photon double ionisation of He in the photon energy region between 80 eV to 180 eV. The cross sections are in agreement with established data. The extended RMT method also provides information on higher-order processes, as demonstrated by the identification of signatures for sequential double ionisation processes involving an intermediate He⁺ state with n=2.

Effect of position of near addition in an asymmetric refractive multifocal intraocular lens on quality of vision

Purpose
To evaluate the impact of the position of an asymmetric multifocal near segment on visual quality.

Setting
Cathedral Eye Clinic, Belfast, United Kingdom.

Design
Retrospective comparative case series.

Methods
Data from consecutive patients who had bilateral implantation of the Lentis Mplus LS-312 multifocal intraocular lens were divided into 2 groups. One group received inferonasal near-segment placement and the other, superotemporal near-segment placement. A +3.00 diopter (D) reading addition (add) was used in all eyes. The main outcome measures included uncorrected distance visual acuity (UDVA), uncorrected near visual acuity (UNVA), contrast sensitivity, and quality of vision. Follow-up was 3 months.

Results
Patients ranged in age from 43 to 76 years. The inferonasal group comprised 80 eyes (40 patients) and the superotemporal group, 76 eyes (38 patients). The mean 3-month spherical equivalent was −0.11 D ± 0.49 (SD) in the inferonasal group and −0.18 ± 0.46 D in the superotemporal group. The mean postoperative UDVA was 0.14 ± 0.10 logMAR and 0.18 ± 0.15 logMAR, respectively. The mean monocular UNVA was 0.21 ± 0.14 logRAD and 0.24 ± 0.13 logRAD, respectively. No significant differences were observed in the higher-order aberrations, total Strehl ratio (point-spread function), or modulation transfer function between the groups. Dysphotopic symptoms measured with a validated quality-of-vision questionnaire were not significantly different between groups.

Conclusion
Positioning of the near add did not significantly affect objective or subjective visual function parameters.

Undergraduate Student perceptions of a Restorative Dentistry OSCE

Objectives: The Objective Structured Clinical Exam (OSCE) is a widely accepted assessment method in undergraduate dental education. It aims to test higher order skills, attitudes and aspects of professionalism which other summative assessments such as MCQs and other written examinations are less able to do. The aim of this study was to evaluate the perceptions of 4th year undergraduate dental students of an OSCE undertaken in the Conservation Department.
Methods: On completion of the OSCE examination 51 fourth year undergraduate students were asked to complete an anonymised questionnaire. The questionnaire was made 22 questions, and requiring the students to provide both open and closed responses.
Results: A lot of positive aspects to the OSCE were observed in responses, students felt that the OSCE was a meaningful way for assessing their clinical skills (85%), it reflected real life conditions (79%) and that it was a fair method of assessment (75%).
A number of negative aspects were also noted. Most students felt the OSCE was stressful (72%) and they felt nervous during the examination (77%). Of the undergraduates asked 42% did not feel confident doing the OSCE.
A number of students felt it would be helpful to have additional information given to them on the OSCE prior to the assessment process.
Conclusion: In general the students found the OSCE a fair, meaningful form of assessment which reflected real life clinical situations, providing them with an opportunity to show their clinical knowledge and practical skills. A number study cohort did not feel confident during the OSCE and felt nervous and stressed by the experience. The information gained from the reflective nature of the feedback questionnaire has proved invaluable in the design of subsequent diets of the OSCE examination.