Non-standard techniques for the investigation of the visual field

The study investigated the potential applications and the limitations of non-standard techniques of visual field investigation utilizing automated perimetry. Normal subjects exhibited a greater sensitivity to kinetic stimuli than to static stimuli of identical size. The magnitude of physiological SKD was found to be largely independent of age, stimulus size, meridian and eccentricity. The absence of a dependency on stimulus size indicated that successive lateral spatial summation could not totally account for the underlying mechanism of physiological SKD. The visual field indices MD and LV exhibited a progressive deterioration during the time course of a conventional central visual field examination both for normal subjects and for ocular hypertensive patients. The fatigue effect was more pronounced in the latter stages and for the second eye tested. The confidence limits for the definition of abnormality should reflect the greater effect of fatigue on the second eye. A 330 cdm-2 yellow background was employed for blue-on-yellow perimetry. Instrument measurement range was preserved by positioning a concave mirror behind the stimulus bulb to increase the light output by 60% . The mean magnitude of SWS pathway isolation was approximately 1.4 log units relative to a 460nm stimulus filter. The absorption spectra of the ocular media exhibited an exponential increase with increase in age, whilst that of the macular pigment showed no systematic trend. The magnitude of ocular media absorption was demonstrated to reduce with increase in wavelength. Ocular media absorption was significantly greater in diabetic patients than in normal subjects. Five diabetic patients with either normal or borderline achromatic sensitivity exhibited an abnormal blue-on-yellow sensitivity; two of these patients showed no signs of retinopathy. A greater vulnerability of the SWS pathway to the diabetic disease process was hypothesized.

Enhanced Raman amplifier flatness with nonlinear broadening over non-standard transmission fibre

Nonlinear CW pump broadening over non-standard transmission fibre is used for the first time to achieve improved gain flatness in a single-pump broadband Raman amplifier. As an illustration of the benefits that can be obtained from this approach, a threefold increase in the bandwidth for 0.1 dB gain variation is reported when the broadened pump is used to produce 9.2 dB on-off gain over 25 km LEAF fibre. © 2005 Elsevier B.V. All rights reserved.

Non-verbal signalling in digital discourse:the case of letter repetition

This study focuses on the interactional functions of non-standard spelling, in particular letter repetition, used in text-based computer-mediated communication as a means of non-verbal signalling. The aim of this paper is to assess the current state of non-verbal cue research in computer-mediated discourse and demonstrate the need for a more comprehensive and methodologically rigorous exploration of written non-verbal signalling. The study proposes a contextual and usage-centered view of written paralanguage. Through illustrative, close linguistic analyses the study proves that previous approaches to non-standard spelling based on their relation to the spoken word might not account for the complexities of this CMC cue, and in order to further our understanding of their interactional functions it is more fruitful to describe the role they play during the contextualisation of the verbal messages. The interactional sociolinguistic approach taken in the analysis demonstrates the range of interactional functions letter repetition can achieve, including contribution to the inscription of socio-emotional information into writing, to the evoking of auditory cues or to a display of informality through using a relaxed writing style.

A regional analysis of contraction rate in written Standard American English

The goal of this study is to determine if various measures of contraction rate are regionally patterned in written Standard American English. In order to answer this question, this study employs a corpus-based approach to data collection and a statistical approach to data analysis. Based on a spatial autocorrelation analysis of the values of eleven measures of contraction across a 25 million word corpus of letters to the editor representing the language of 200 cities from across the contiguous United States, two primary regional patterns were identified: easterners tend to produce relatively few standard contractions (not contraction, verb contraction) compared to westerners, and northeasterners tend to produce relatively few non-standard contractions (to contraction, non-standard not contraction) compared to southeasterners. These findings demonstrate that regional linguistic variation exists in written Standard American English and that regional linguistic variation is more common than is generally assumed.

N'est-il de bon bec que de Paris?

Représentations littéraires de la langue non standard chez Arthur Masson (Wallonie), Fonson & Wicheler (Bruxelles) et Pagnol (Marseille)

Investigation of two-wave mixing in arbitrary oriented sillenite crystals

A generalized systematic description of the Two-Wave Mixing (TWM) process in sillenite crystals allowing for arbitrary orientation of the grating vector is presented. An analytical expression for the TWM gain is obtained for the special case of plane waves in a thin crystal (|g|d«1) with large optical activity (|g|/?«1, g is the coupling constant, ? the rotatory power, d the crystal thickness). Using a two-dimensional formulation the scope of the nonlinear equations describing TWM can be extended to finite beams in arbitrary geometries and to any crystal parameters. Two promising applications of this formulation are proposed. The polarization dependence of the TWM gain is used for the flattening of Gaussian beam profiles without expanding them. The dependence of the TWM gain on the interaction length is used for the determination of the crystal orientation. Experiments carried out on Bi12GeO20 crystals of a non-standard cut are in good agreement with the results of modelling.

The effects of metallurgical variables on the mechanical properties of high-chromium cast irons

The.use of high-chromium cast irons for abrasive wear resistance is restricted due to their poor fracture toughness properties. An.attempt was made to improve the fracture characteristics by altering the distribution, size and.shape of the eutectic carbide phase without sacrificing their excellent wear resistance. This was achieved by additions of molybdenum or tungsten followed by high temperature heat treatments. The absence of these alloying elements or replacement of them with vanadium or manganese did not show any significant effect and the continuous eutectic carbide morphology remained the same after application of high temperature heat treatments. The fracture characteristics of the alloys with these metallurgical variables were evaluated for both sharp-cracks and blunt notches. The results were used in conjunction with metallographic and fractographic observations to establish possible failure mechanisms. The fracture mechanism of the austenitic alloys was found to be controlled not only by the volume percent but was also greatly influenced by the size and distribution of the eutectic carbides. On the other hand, the fracture mechanism of martensitic alloys was independent of the eutectic carbide morphology. The uniformity of the secondary carbide precipitation during hardening heat treatments was shown to be a reason for consistant fracture toughness results being obtained with this series of alloys although their eutectic carbide morphologies were different. The collected data were applied to a model which incorporated the microstructural parameters and correlated them with the experimentally obtained valid stress intensity factors. The stress intensity coefficients of different short-bar fracture toughness test specimens were evaluated from analytical and experimental compliance studies. The.validity and applicability of this non-standard testing technique for determination of the fracture toughness of high-chromium cast irons were investigated. The results obtained correlated well with the valid results obtained from standard fracture toughness tests.

Investigation of chromatic function in the normal and abnormal eye

This study examined the use of non-standard parameters to investigate the visual field, with particular reference to the detection of glaucomatous visual field loss. Evaluation of the new perimetric strategy for threshold estimation - FASTPAC, demonstrated a reduction in the examination time of normals compared to the standard strategy. Despite an increased within-test variability the FASTPAC strategy produced a similar mean sensitivity to the standard strategy, reducing the effects of patient fatigue. The new technique of Blue-Yellow perimetry was compared to White-White perimetry for the detection of glaucomatous field loss in OHT and POAG. Using a database of normal subjects, confidence limits for normality were constructed to account for the increased between-subject variability with increase in age and eccentricity and for the greater variability of the Blue-Yellow field compared to the White-White field. Effects of individual ocular media absorption had little effect on Blue-Yellow field variability. Total and pattern probability analysis revealed five of 27 OHTs to exhibit Blue-Yellow focal abnormalities; two of these patients subsequently developed White-White loss. Twelve of the 24 POAGs revealed wider and/or deeper Blue-Yellow loss compared with the White-White field. Blue-Yellow perimetry showed good sensitivity and specificity characteristics, however, lack of perimetric experience and the presence of cataract influenced the Blue-Yellow visual field and may confound the interpretation of Blue-Yellow visual field loss. Visual field indices demonstrated a moderate relationship to the structural parameters of the optic nerve head using scanning laser tomography. No abnormalities in Blue-Yellow or Red-Green colour CS was apparent for the OHT patients. A greater vulnerability of the SWS pathway in glaucoma was demonstrated using Blue-Yellow perimetry however predicting which patients may benefit from B-Y perimetric examination is difficult. Furthermore, cataract and the extent of the field loss may limit the extent to which the integrity of the SWS channels can be selectively examined.

Statistical guidelines for clinical studies of human vision

Citation information: Armstrong RA, Davies LN, Dunne MCM & Gilmartin B. Statistical guidelines for clinical studies of human vision. Ophthalmic Physiol Opt 2011, 31, 123-136. doi: 10.1111/j.1475-1313.2010.00815.x ABSTRACT: Statistical analysis of data can be complex and different statisticians may disagree as to the correct approach leading to conflict between authors, editors, and reviewers. The objective of this article is to provide some statistical advice for contributors to optometric and ophthalmic journals, to provide advice specifically relevant to clinical studies of human vision, and to recommend statistical analyses that could be used in a variety of circumstances. In submitting an article, in which quantitative data are reported, authors should describe clearly the statistical procedures that they have used and to justify each stage of the analysis. This is especially important if more complex or 'non-standard' analyses have been carried out. The article begins with some general comments relating to data analysis concerning sample size and 'power', hypothesis testing, parametric and non-parametric variables, 'bootstrap methods', one and two-tail testing, and the Bonferroni correction. More specific advice is then given with reference to particular statistical procedures that can be used on a variety of types of data. Where relevant, examples of correct statistical practice are given with reference to recently published articles in the optometric and ophthalmic literature.

Suitability of dysphonia measurements for telemonitoring of Parkinson's disease

We present an assessment of the practical value of existing traditional and non-standard measures for discriminating healthy people from people with Parkinson's disease (PD) by detecting dysphonia. We introduce a new measure of dysphonia, Pitch Period Entropy (PPE), which is robust to many uncontrollable confounding effects including noisy acoustic environments and normal, healthy variations in voice frequency. We collected sustained phonations from 31 people, 23 with PD. We then selected 10 highly uncorrelated measures, and an exhaustive search of all possible combinations of these measures finds four that in combination lead to overall correct classification performance of 91.4%, using a kernel support vector machine. In conclusion, we find that non-standard methods in combination with traditional harmonics-to-noise ratios are best able to separate healthy from PD subjects. The selected non-standard methods are robust to many uncontrollable variations in acoustic environment and individual subjects, and are thus well-suited to telemonitoring applications.

The measurement and decomposition of economy-wide productivity growth:Assessing the accuracy and selecting between different approaches

Productivity at the macro level is a complex concept but also arguably the most appropriate measure of economic welfare. Currently, there is limited research available on the various approaches that can be used to measure it and especially on the relative accuracy of said approaches. This thesis has two main objectives: firstly, to detail some of the most common productivity measurement approaches and assess their accuracy under a number of conditions and secondly, to present an up-to-date application of productivity measurement and provide some guidance on selecting between sometimes conflicting productivity estimates. With regards to the first objective, the thesis provides a discussion on the issues specific to macro-level productivity measurement and on the strengths and weaknesses of the three main types of approaches available, namely index-number approaches (represented by Growth Accounting), non-parametric distance functions (DEA-based Malmquist indices) and parametric production functions (COLS- and SFA-based Malmquist indices). The accuracy of these approaches is assessed through simulation analysis, which provided some interesting findings. Probably the most important were that deterministic approaches are quite accurate even when the data is moderately noisy, that no approaches were accurate when noise was more extensive, that functional form misspecification has a severe negative effect in the accuracy of the parametric approaches and finally that increased volatility in inputs and prices from one period to the next adversely affects all approaches examined. The application was based on the EU KLEMS (2008) dataset and revealed that the different approaches do in fact result in different productivity change estimates, at least for some of the countries assessed. To assist researchers in selecting between conflicting estimates, a new, three step selection framework is proposed, based on findings of simulation analyses and established diagnostics/indicators. An application of this framework is also provided, based on the EU KLEMS dataset.

Investigation of two-wave mixing in arbitrary oriented sillenite crystals

A generalized systematic description of the Two-Wave Mixing (TWM) process in sillenite crystals allowing for arbitrary orientation of the grating vector is presented. An analytical expression for the TWM gain is obtained for the special case of plane waves in a thin crystal (|g|d«1) with large optical activity (|g|/?«1, g is the coupling constant, ? the rotatory power, d the crystal thickness). Using a two-dimensional formulation the scope of the nonlinear equations describing TWM can be extended to finite beams in arbitrary geometries and to any crystal parameters. Two promising applications of this formulation are proposed. The polarization dependence of the TWM gain is used for the flattening of Gaussian beam profiles without expanding them. The dependence of the TWM gain on the interaction length is used for the determination of the crystal orientation. Experiments carried out on Bi12GeO20 crystals of a non-standard cut are in good agreement with the results of modelling.

Enhanced Raman amplifier gain performance with HNLF broadening

Nonlinear CW pump broadening over non-standard transmission fiber is used for the first time to achieve superior gain variation performance in a single-pump broadband Raman amplifier. A threefold increase in the bandwidth for 0.1 dB gain variation is reported.

All-optical add-drop multiplexer for OFDM signals

We summarize our research work on the design and development of an add-drop multiplexer for spectrally overlapping OFDM signals. The standard node functions of sub-channel drop, extraction and insertion were obtained whilst the signals remained fully in the optical domain. Numerical simulations have been carried out to identify the main sources of degradation and to benchmark the architectural performance against critical design parameters, whereas the experimental demonstration of the scheme has been achieved for both single quadrature and dual quadrature signals. The reported scheme enables a fully flexible node compatible with future terabit per second super-channel transmission.

1220km propagation of 40Gbit/s single channel RZ data over dispersion managed standard (non-dispersion shifted) fibre

Error free propagation of a single polarisation optical time division multiplexed 40 Gbit/s dispersion managed pulsed data stream over dispersion (non-shifted) fibre. This distance is twice the previous record at this data rate.