Library

Notes: A technique for fitting mixture distributions to discrete and continuous instrument count data is presented. The use of the EM algorithm for performing maximum likelihood estimation is introduced and advantages over other methods are discussed. Equations are presented for fitting mixtures of Poisson distributions and mixtures of normal distributions. Examples of the fitting of these two types of mixture distribution are given, and it is shown how standard errors of the parameter estimates can be obtained from within the framework of the fitting process.

Notes: Ion beams with energies in the range 1–2 keV are used to sputter neutral Zr atoms from a polycrystalline surface. Laser induced fluorescence detection is used to obtain angular distributions of sputtered neutrals as a function of ion impact direction, ion mass, ion energy, and spin–orbit state of the exiting atoms. About 40% of the sputtered atoms are excited. Angular distributions depend weakly on ion mass and energy. The angular distributions are fitted well by a modified form of the Roosendaal and Saunders model of sputtering.

Notes: In the COMPASS-D tokamak three multiviewing diagnostic systems are combined by using the same collection optics. HeI line ratios from a helium thermal jet provide detailed edge Te(r) and ne(r) profiles. The spectrometer also provides the Dα profile. A Doppler spectrometer system provides Ti and Vθ profiles using HeII emission. The Te and ne profiles are used in extracting neutral densities from the Dα emissivities, and the radial electric field from the Doppler measurements. The behavior of Te(r), ne(r), 2nD(r), Er, and Vθ and their gradients can now be compared in detail to investigate the H-mode transition physics. © 2001 American Institute of Physics.

Notes: An apparatus utilizing laser-induced fluorescence (LIF) has been developed to measure high-resolution angular distributions of sputtered neutral atoms. LIF provides sensitive detection, a feature necessary to monitor the low atomic fluxes inherent to angularly resolved sputtering measurements in the static sputtering regime. The apparatus incorporates a detector assembly which rotates about the sample in an ultrahigh vacuum (UHV) chamber, allowing a large range of angular measurements at different ion beam incidence angles. Laser light is brought to the detector in the UHV chamber via a single optical fiber and fluorescence photons exit the chamber via a fiber bundle. The optical fiber and fiber bundle are mounted in a fixed orientation on the detector, maintaining constant alignment as the assembly rotates. Angular resolution in the polar plane containing the incident ion beam and the surface normal is better than 3°. Angular resolution in the direction perpendicular to the polar plane is governed by the Doppler shift and is 0.028° for 3.2 eV atoms. Overall detection efficiency is estimated to be 5×10−9 counts per sputtered atom and 2×10−3 counts per atom entering the detection volume. Initial experiments using polycrystalline Zr to characterize the device are described.

Notes: Objective To establish reference ranges for the levels of alpha-fetoprotein, albumin, prealbumin (transthyretin) alpha-1-antitrypsin, transferrin, ceruloplasmin and total protein in the plasma of normal human fetuses and newborn babies.Design Prospective study of individual normal cases to fulfil objectives.Setting Pathology laboratories of the University of Edinburgh and the biochemistry laboratories of the University of Keele.Subjects Twenty-two normal fetuses 13 to 22 weeks of gestation and 66 babies born between 24 and 41 weeks gestation.Results Albumin is the predominant plasma protein throughout gestation. The levels of alpha-fetoprotein and prealbumin fell significantly with increasing gestation, whereas the concentrations of the other proteins studied increased. The ratios of individual proteins to total protein demonstrated similar trends.Conclusions This study provides developmental profiles of normal human fetal plasma proteins to serve as possible reference data for abnormal fetuses. Declining levels of prealbumin (transthyretin) were unexpected and suggest a functional role for this protein in early pregnancy.

Notes: We describe a plasma-based dry etching procedure which permits selective etching of Si over Ge with a Si/Ge etch rate ratio of over 70 and negligible etching of the Ge underlayer. This is achieved in a SF6/H2/CF4 gas mixture by the formation of a thin ((approximately-equal-to)3 nm) involatile etch stop layer on the Ge surface which consists of Ge-sulfide and carbonaceous material.

Notes: The use of cement kilns for managing solid and hazardous wastes is facilitated by the high temperature, long gas retention periods, natural alkaline environment, minimum amount of waste produced and high thermal capacity. The main benefits include energy recovery, conservation of fossil fuels, reduction in cement production costs and the use of already existing facilities.The test burns conducted in cement kilns worldwide have demonstrated very high destruction efficiencies for most stable organic compounds, with toxic contaminants barely above the background levels.There are several cement plants in the US and Europe presently using solid and hazardous wastes as supplementary fuel. The application of this technology in Australia has been ignored in the past. An international conference (Kilnburn‘92) on the role of cement kilns in waste management was held recently in Australia and has enhanced the implementation of this technology in Australia.

Notes: This paper reviews the state of the field of the sub-disciplines within UK management research, based upon the submissions of 94 UK higher education institutions to the Business and Management Studies Panel in the UK's 2001 Research Assessment Exercise (RAE). It offers observations on the UK model of the assessment of quality in, and funding of, research conducted in publicly funded higher education institutions.

Notes: Objective To analyse biopsies of large loop excision of the transformation zone of the cervix; to identify factors associated with negative histology; and to develop predictive models in order to reduce the number of negative loop excisions.Design Retrospective analysis of patient notes and audit database.Setting Colposcopy clinic of a large district general hospital in North Staffordshire.Population Four hundred and fifty-two women who underwent a large loop excision of the transformation zone (LLETZ) procedure for suspected cervical intraepithelial neoplasia.Methods Women who underwent a LLETZ procedure were placed in two different groups, one positive for cervical intra epithelial neoplasia and the other negative for cervical intra epithelial neoplasia. Information was obtained on a number of clinical and colposcopic variables. Analysis was undertaken to determine if there were any differences between the two groups. These factors were then identified and three predictive models generated. Receiver-operator characteristic curves were used to assess and test these models.Main outcomes measures To identify factors associated with negative histology on a LLETZ specimen. To predict how to reduce the number of negative LLETZ specimens.Results Four hundred and fifty-two women underwent a LLETZ procedure, 88 were negative (19%) and 364 were positive (81%). In women who were treated at their first visit, 56/316 (18%) had negative histology. There were significant associations between negative histology in the LLETZ and negative or low grade cytological atypia, negative colposcopic findings and years of age 〉 50 in both bivariate analysis and stepwise logistic regression. In the predictive models, the sensitivity ranged between 72% and 80%, the specificity 59%–72%, and the area under the receiver-operator characteristic was 0.75–0.77. If we had used the predictor models and managed women with negative or low grade cervical atypia and negative colposcopy findings conservatively, we would have reduced the negative biopsy rate from 19% to 14%, but five cases of high grade disease and 25 cases of low grade disease would have been missed. If we had also included women aged 〉 50 years in this model, the negative biopsy rate would have dropped from 19% to 15%, with only one case of high grade disease and 11 cases of low grade disease missed. All these women would require continued cytological and colposcopic surveillance. Importantly, no cases of invasion would have been missed.Conclusion Using a predictive model can reduce the number of negative LLETZ specimens, but at the expense of continued cytological and colposcopic surveillance and cannot be recommended in normal practice. This raises the question whether current standards for negative histology in LLETZ specimens are set unrealistically high.