Simulation and control of a stepping motor

Open-loop operatlon of the stepping motor exploits the inherent advantages of the machine. For near optimum operation: in this mode, however, an accurate system model is required to facilitate controller design. Such a model must be comprehensive and take account of the non-linearities inherent in the system. The result is a complex formulation which can be made manageable with a computational aid. A digital simulation of a hybrid type stepping motor and its associated drive circuit is proposed. The simulation is based upon a block diagram model which includes reasonable approximations to the major non-linearities. The simulation is shown to yield accurate performance predictions. The determination of the transfer functions is based upon the consideration of the physical processes involved rather than upon direct input-outout measurements. The effects of eddy currents, saturation, hysteresis, drive circuit characteristics and non-linear torque displacement characteristics are considered and methods of determining transfer functions, which take account of these effects, are offered. The static torque displacement characteristic is considered in detail and a model is proposed which predicts static torque for any combination of phase currents and shaft position. Methods of predicting the characteristic directly from machine geometry are investigated. Drive circuit design for high efficiency operation is considered and a model of a bipolar, bilevel circuit is proposed. The transfers between stator voltage and stator current and between stator current and air gap flux are complicated by the effects of eddy currents, saturation and hysteresis. Frequency response methods, combined with average inductance measurements, are shown to yield reasonable transfer functions. The modelling procedure and subsequent digital simulation is concluded to be a powerful method of non-linear analysis.

Out in psychology:lesbian, gay, bisexual, trans and queer perspectives

There has been a recent explosion of interest in Lesbian, Gay, Bisexual and Trans Perspective Psychology amongst students and academics, and this interest is predicted to continue to rise. Recent media debates on subjects such as same–sex marriage have fuelled interest in LGBTQ perspectives. This edited collection showcases the latest thinking in LGBTQ psychology. The book has 21 chapters covering subjects such as same sex parenting, outing, young LGBTQ people, sport, learning disabilities, lesbian and gay identities etc. The book has an international focus, with contributors from UK, US, Canada, Australia and New Zealand List of Contributors. Foreword by Jerry J. Bigner. 1. Introducing Out in Psychology (Victoria Clarke and Elizabeth Peel). 2. From lesbian and gay psychology to LGBTQ psychologies: A journey into the unknown (Victoria Clarke and Elizabeth Peel) 3. What comes after discourse analysis for LGBTQ psychology(Peter Hegarty). 4. Recognising race in LGBTQ psychology: Power, privilege and complicity (Damien W. Riggs). 5. Personality, individual differences and LGB psychology (Gareth Hagger Johnson). 6. Heteronormativity and the exclusion of bisexuality in psychology (Meg Barker). 7. A minority within a minority: Experiences of gay men with intellectual disabilities.(Christopher Bennett and Adrian Coyle). 8. Closet talk: The contemporary relevance of the closet in lesbian and gay interaction (Victoria Land and Celia Kitzinger) 9. Romance, rights, recognition, responsibilities and radicalism: Same-sex couples’ accounts of civil partnership and marriage (Victoria Clarke, Carole Burgoyne and Maree Burns). 10. The experience of social power in the lives of trans people (Clair Clifford and Jim Orford). 11. What do they look like and are they among us? Bisexuality, (dis.closure and (Maria Gurevich, Jo Bower, Cynthia M. Mathieson and Bramilee Dhayanandhan). 12. Heterosexism at work: Diversity training, discrimination law and the limits of liberal individualism (Rosie Harding and Elizabeth Peel). 13. Out on the ball fields: Lesbians in sport (Vikki Krane and Kerrie J. Kauer). 14. Homophobia, rights and community: Contemporary issues in the lives of LGB people in the UK (Sonja J. Ellis). 15. Striving for holistic success: How lesbians come out on top (Faith Rostad and Bonita C. Long). 16. On Passing: The Interactional Organization of Appearance Attributions in the Psychiatric Assessment of Transsexual Patients (Susan A. Speer and Richard Green). 17. Alcohol and gay men: Consumption, promotion and policy responses (Jeffrey Adams, Timothy McCreanor and Virginia Braun). 18. Towards a clinical-psychological approach to address the hetero sexual concerns of intersexed women (Lih-Mei Liao). 19. Educational psychology practice with LGB youth in schools: Individual and institutional interventions (Jeremy J. Monsen and Sydney Bailey). 20. Que(e)rying the meaning of lesbian health: Individual(izing and community discourses (Sara MacBride-Stewart). 21. Transsexualism: Diagnostic dilemmas, transgender politics and the future of transgender care (Katherine Johnson). Index.

The ratio of diffuse to mature beta/A4 deposits in Alzheimer's disease varies in cases with and without pronounced congophilic angiopathy

The density of diffuse, primitive, classic and compact beta/A4 deposits was estimated in the cortex and hippocampus in Alzheimer's disease (AD) cases with and without pronounced congophilic angiopathy (CA). The total density of beta/A4 deposits in a given brain region was similar in cases with and without CA. Significantly fewer diffuse deposits and more primitive/classic deposits were found in the cases with CA. The densities of the primitive, classic and compact deposits were positively correlated in the cases without CA. However, no correlations were observed between the density of the mature subtypes and the diffuse deposits in these cases. In the cases with CA, the density of the primitive deposits was positively correlated with the diffuse but not with the classic deposits. The data suggest that the mature beta/A4 deposits are derived from the diffuse deposits and that the presence of pronounced CA enhances their formation.

The influence of age on the pattern and flash visual evoked magnetic response (VEMR)

The visual evoked magnetic response (VEMR) was measured over the occipital cortex to pattern and flash stimuli in 86 normal subjects aged 15-86 years. The latency of the major positive component (outgoing magnetic field) to the pattern reversal stimulus (P100M) increased with age, particularly after 55 years, while the amplitude of the P100M decreased more gradually over the lifespan. By contrast, the latency of the major positive component to the flash stimulus (P2M) increased more slowly with age after about 50 years, while its amplitude may have decreased in only a proportion of the elderly subjects. The changes in the P100M with age may reflect senile changes in the eye and optic nerve, e.g. senile miosis, degenerative changes in the retina or geniculostriate deficits. The P2M may be more susceptible to senile changes in the visual cortex. The data suggest that the contrast channels of visual information processing deteriorate more rapidly with age than the luminance channels.

Visual evoked magnetic fields to flash and pattern in 100 normal subjects

The practicality of recording visual evoked magnetic fields in 100 subjects 15-87 yr of age using a single channel d.c. SQUID second order gradiometer in an unshielded environment was investigated. The pattern reversal response showed a major positive component between 90 and 120 msec (P100M) while the response to flash produced a major positive component between 90 and 140 msec (P2M). Latency norms of the P100M were more variable than the corresponding P100 and P2 visual evoked potentials. The latency of the P100M may show a steep increase with age in most subjects after about 55 yr whereas only a small trend of latency with age was detected for the flash P2M.

The reponse of lichen growth to transplantation to rock surfaces of different aspect

Thalli of four saxicolous lichens on slate rock fragments were transplanted from rock surafces to horizontal boards and then to south-east-facing and north-west-facing rock surfaces. The radial growth rate of Physcia orbicularis and Parmelia conspersa thalli declined after transplatation to north-west-facing rock surfaces and was unchanged after transplantation to south-east-facing rock surfaces cmpared with growth rates on the boards. The radial growth rate of P. glabratula ssp. fuliginosa thalli declined after transplantation to south-east-facing rock surfaces and was unchanged after transplantation to north-west-facing rock surfaces compared with grwoth rate on the boards. The radial growth rate of P. saxatilis thalli was similar on the horizontal boards, south-east-facing and north-west-facing rock surfaces. These results are dsicussed in relation to the aspect distribution of the four lichens in South Gwynedd, Wales.

A quantitative study of the neuropathology of 32 sporadic and familial cases of frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP)

To further characterize the neuropathology of the heterogeneous molecular disorder frontotemporal lobar degeneration (FTLD) with transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) proteinopathy (FTLD-TDP).

Bacteria and the eye

Bacteria are minute unicellular organisms present in abundance in air, water, soil and food and in association with the human body. The majority of bacteria are harmless to humans while a few are useful and have been exploited in, for example, the manufacture of dairy products. However, bacteria are also pathogenic and those include some of the most important human infections such as typhoid, syphilis and tuberculosis. A few bacteria are especially important to optometrists because they are associated with ocular disease, either by causing a primary eye infection or because there are ocular complications of a systemic bacterial infection.

Viruses and the eye

About 60% of human infections diseases are caused by viruses,including such important diseases as AIDS, polio, rabies and certain forms of cancer. A few groups of viruses are important to optometrists because they either cause a primary eye infection or a systemic viral infection with ocular complications.

AMD and smoking: an update

This article provides an update to a previous publication on this topic and includes the results of new epidemiological and physiological experiments which have implicated smoking as an important cause of AMD.

Distribution of A4 protein and neurofibrillary change in the hippocampus in Alzheimer's disease

The principal components of classical senile plaques (SP) in Alzheimer's disease (AD) appear to be A4/beta protein and paired helical filaments (PHF). A4 deposits may evolve into classical SP in brain regions vulnerable to the formation of PHF. We have investigated the diatribution of A4 deposits using an immunostain and the neurofibrillary change using the Gallyas stain in various regions of the hippocampus. This region is particularly affected in AD and also has relatively restricted inputs and outputs. In 6 patients we found a significant preponderance of A4 deposits in the adjacent parahippocampal gyrus (PHG) compared with all regions of the hippocampus. However, plaque-like clusters of PHF (Gallyas plaques) were more abundant in the subiculum while neurofibrillary tangles (NFT) were more abundant in the subiculum and region CA1 compared with the PHG and other hippocampal regions. Hence, A4 deposits appear to be concentrated in the region providing a major input into the hippocampus while the neurofibrillary changes are characteristic of the major output areas (subiculum and CA1). Hence, the data suggest that A4 formation and the neurofibrillary changes may occur in regions of the hippocampus that are connected anatomically.

The correlation between tests of visual function and perceived visual ability in central field loss patients

Purpose: To investigate the correlation between tests of visual function and perceived visual ability recorded with a 'quality-of-life' questionnaire for patients with central field loss. Method: 12 females and 7 males (mean age = 53.1 years; Range = 23 - 80 years) with subfoveal neovascular membranes underwent a comprehensive assessment of visual function. Tests included unaided distance vision, high and low contrast distance logMAR visual acuity (VA), Pelli-Robson contrast senstivity (at 1m), near logMAR word VA and text reading speed. All tests were done both monocularly and binocularly. The patients also completed a 28 point questionnaire separated into a 'core' section consisting of general questions about perceived visual function and a 'module' section with specific questions on reading function. Results: Step-wise multiple regression analysis was used to determine which visual function tests were correlated with the patients's perceived visual function and to rank them in order of importance. The visual function test that explains most of the variance in both 'core' score (66%0 and the 'module' score (68%) of the questionnaire is low contrast VA in the better eye (P<0.001 in both cases). Further, the module score also accounts for a significant proportion of the variance (P<0.01) of the distance logMAR VA in both the better and worse eye, and the near logMAR in both the better eye and binocularly. Conclusions: The best predictor of both perceived reading ability and of general perceived visual ability in this study is low contrast logMAR VA. The results highlight that distance VA is not the only relevant measure of visual fucntion in relation to a patients's perceived visual performance and should not be considered a determinant of surgical or management success.

Synthesis and characterisation of hydrogel polymers for medical applications

A fundamental if poorly understood problem that hydrogels display is the tendency of these contact lens materials to dehydrate, causing certain complications of the corneal epithelium. However, recent studies have indicated that the evaporation rate of water from different hydrogel lenses is the same and the severity of conditions such as corneal staining is controlled by the states of water in the material. A study was therefore undertaken which concluded that increased corneal desiccating staining occurred as the proportion of water existing in the bound state decreased. The possibility of using dehydrated hydrogels as packaging materials with desiccating properties has also been investigated. As hydrogels have a high affinity for water they have adequate ability to function as a moisture scavenger in an enclosed atmosphere. It was concluded that this ability is maximised by a high total water content and an increase in the proportion of this water existing in the bound state for the material when it is fully hydrated. N-vinyl pyrrolidone has a low reactivity in vinyl polymerisation reactions which results in polymers with local domains of the same chemical type which can lead to deposition. As contact lenses comprising of this monomer are susceptible to deposition, a monomer with a higher reactivity in vinyl polymerisations is acryloylmorpholine and its incorporation in favour of NVP is encouraged. Unfortunately a large proportion of high EWC hydrogels are mechanically weak and attempts to increase this property by increasing hydrophobicity or cross-linking results in a decrease in EWC. Monomers with the potential to carry a positive charge were incorporated into a high EWC, AMO-HEMA copolymer and the physical properties were investigated. Although EWC increased, mechanical properties decreased only slightly. Therefore simultaneous incorporation of a positively charged monomer and a negatively charged monomer was investigated. The resulting copolymers showed increased water content and increased initial modulus. A technique for measuring the coefficient of friction of contact lenses during lubrication has been developed.