Short-term changes in ocular biometry and refraction after discontinuation of long-term orthokeratology

OBJECTIVE: To assess refractive and biometric changes 1 week after discontinuation of lens wear in subjects who had been wearing orthokeratology (OK) contact lenses for 2 years. METHODS: Twenty-nine subjects aged 6 to 12 years and with myopia of -0.75 to -4.00 diopters (D) and astigmatism of ≤1.00 D participated in the study. Measurements of axial length and anterior chamber depth (Zeiss IOLMaster), corneal power and shape, and cycloplegic refraction were taken 1 week after discontinuation and compared with those at baseline and after 24 months of lens wear. RESULTS: A hyperopic shift was found at 24 months relative to baseline in spherical equivalent refractive error (+1.86±1.01 D), followed by a myopic shift at 1 week relative to 24 months (-1.93±0.92 D) (both P<0.001). Longer axial lengths were found at 24 months and 1 week in comparison to baseline (0.47±0.18 and 0.51±0.18 mm, respectively) (both P<0.001). The increase in axial length at 1 week relative to 24 months was statistically significant (0.04±0.06 mm; P=0.006). Anterior chamber depth did not change significantly over time (P=0.31). Significant differences were found between 24 months and 1 week relative to baseline and between 1-week and 24-month visits in mean corneal power (-1.68±0.80, -0.44±0.32, and 1.23±0.70 D, respectively) (all P≤0.001). Refractive change at 1 week in comparison to 24 months strongly correlated with changes in corneal power (r=-0.88; P<0.001) but not with axial length changes (r=-0.09; P=0.66). Corneal shape changed significantly between the baseline and 1-week visits (0.15±0.10 D; P<0.001). Corneal shape changed from a prolate to a more oblate corneal shape at the 24-month and 1-week visits in comparison to baseline (both P≤0.02) but did not change significantly between 24 months and 1 week (P=0.06). CONCLUSIONS: The effects of long-term OK on ocular biometry and refraction are still present after 1-week discontinuation of lens wear. Refractive change after discontinuation of long-term OK is primarily attributed to the recovery of corneal shape and not to an increase in the axial length.

Investigations of the spectral sensitivity of long period gratings fabricated in three-layered optical fiber

Long period gratings (LPGs) were written into a progressive three-layered (PTL) monomode optical fiber. The spectral sensitivity was experimentally measured with respect to temperature and the surrounding refractive index, and compared with theoretical predictions. The behavior of the devices suggests that this type of fiber may be useful as a means of reducing the sensitivity of LPGs to the surrounding medium and for simultaneous temperature and refractive index sensing.

A comparison of the sensing characteristics of long period gratings written in three different types of fiber

This paper compares the environmental sensing behaviour of long period gratings written in three fibers with different refractive index profiles: step, W and a progressive three layered fiber. The measurands considered are temperature, refractive index, axial strain and bending, and the spectral behaviour of individual attenuation bands were observed and, where possible, compared to theoretical predictions. Significant differences in the behaviour of the three fiber types were found. © 2003 Elsevier Inc. All rights reserved.

The interrogation and multiplexing of long period grating curvature sensors using a Bragg grating based, derivative spectroscopy technique

A long period grating is interrogated with a fibre Bragg grating using a derivative spectroscopy technique. A quasi-linear relationship between the output of the sensing scheme and the curvature experienced by the long period grating is demonstrated, with a sensitivity of 5.05 m and with an average curvature resolution of 2.9 × 10-2 m-1. In addition, the feasibility of multiplexing an in-line series of long period gratings with this interrogation scheme is demonstrated with two pairs of fibre Bragg gratings and long period gratings. With this arrangement the cross-talk error between channels was less than ± 2.4 × 10-3 m-1.

The spectral sensitivity of long period gratings fabricated in elliptical core D-shaped optical fibre

Long period gratings (LPGs) were written into a D-shaped optical fibre that has an elliptical core with a W-shaped refractive index profile and the first detailed investigation of such LPGs is presented. The LPGs’ attenuation bands were found to be sensitive to the polarisation of the interrogating light with a spectral separation of about 15 nm between the two orthogonal polarisation states. A finite element method was successfully used to model many of the behavioural features of the LPGs. In addition, two spectrally overlapping attenuation bands corresponding to orthogonal polarisation states were observed; modelling successfully reproduced this spectral feature. The spectral sensitivity of both orthogonal states was experimentally measured with respect to temperature and bending. These LPG devices produced blue and red wavelength shifts depending upon the orientation of the bend with measured maximum sensitivities of -3.56 and +6.51 nm m, suggesting that this type of fibre LPG may be useful as a shape/bend orientation sensor with reduced errors associated with polarisation dependence. The use of neighbouring bands to discriminate between temperature and bending was also demonstrated, leading to an overall curvature error of ±0.14 m-1 and an overall temperature error of ±0.3 °C with a maximum polarisation dependence error of ±8 × 10-2 m-1 for curvature and ±5 × 10-2 °C for temperature.

Bend sensing by measuring the resonance splitting of long-period fiber gratings

An application of long-period fiber gratings (fabricated in standard fiber) as bend sensors is reported. A simple model, taking account of the strain and compression in the fiber cladding, is used to calculate the splitting of the cladding modes and is found to be in excellent agreement with the experimental results. Over 80 nm resonance splitting was observed under a 5.6 m-1 bend curvature giving a bend sensitivity of 14.5 nm/(m-1), the best obtained data so far. © 2001 Elsevier Science B.V.

The spectral sensitivity of long period gratings fabricated in elliptical core D-shaped optical fiber

Long period gratings (LPGs) were written into a D-shaped optical fibre, which has an elliptical core with a W-shaped refractive index profile. The LPG's attenuation bands were found to be sensitive to the polarisation of the interrogating light with a spectral separation of about 15nm between the two orthogonal polarisation states. In addition, two spectrally overlapping attenuation bands corresponding to orthogonal polarisation states were observed; modelling successfully reproduced this spectral feature. The spectral sensitivity of both orthogonal states was experimentally measured with respect to temperature, surrounding refractive index, and directional bending. These LPG devices produced blue and red wavelength shifts of the stop-bands due to bending in different directions. The measured spectral sensitivities to curvatures, d?/dR , ranged from -3.56nm m to +6.51nm m. The results obtained with these LPGs suggest that this type of fibre may be useful as a shape/bend sensor. It was also demonstrated that the neighbouring bands could be used to discriminate between temperature and bending and that overlapping orthogonal polarisation attenuation bands can be used to minimise error associated with polarisation.

The sensing characteristics of long period gratings in three different types of fibre

In this paper, sensing characteristics of long period gratings in three different types of single mode optical fibre: a step-index fibre, a progressive three layered fibre and a suppressed-cladding fibre were investigated. It was found that variation in the refractive index profile and material constants of the fibre can produce a dramatic change in the spectral sensitivity for a particular measurand for a given long period grating attenuation band. © 2003 IEEE.

The Long-Term impact of Business Support? - Exploring the Role of Evaluation Timing using Micro Data

The original contribution of this work is threefold. Firstly, this thesis develops a critical perspective on current evaluation practice of business support, with focus on the timing of evaluation. The general time frame applied for business support policy evaluation is limited to one to two, seldom three years post intervention. This is despite calls for long-term impact studies by various authors, concerned about time lags before effects are fully realised. This desire for long-term evaluation opposes the requirements by policy-makers and funders, seeking quick results. Also, current ‘best practice’ frameworks do not refer to timing or its implications, and data availability affects the ability to undertake long-term evaluation. Secondly, this thesis provides methodological value for follow-up and similar studies by using data linking of scheme-beneficiary data with official performance datasets. Thus data availability problems are avoided through the use of secondary data. Thirdly, this thesis builds the evidence, through the application of a longitudinal impact study of small business support in England, covering seven years of post intervention data. This illustrates the variability of results for different evaluation periods, and the value in using multiple years of data for a robust understanding of support impact. For survival, impact of assistance is found to be immediate, but limited. Concerning growth, significant impact centres on a two to three year period post intervention for the linear selection and quantile regression models – positive for employment and turnover, negative for productivity. Attribution of impact may present a problem for subsequent periods. The results clearly support the argument for the use of longitudinal data and analysis, and a greater appreciation by evaluators of the factor time. This analysis recommends a time frame of four to five years post intervention for soft business support evaluation.

The long-term impact of business support? - Exploring the role of evaluation timing using micro data

The original contribution of this work is threefold. Firstly, this thesis develops a critical perspective on current evaluation practice of business support, with focus on the timing of evaluation. The general time frame applied for business support policy evaluation is limited to one to two, seldom three years post intervention. This is despite calls for long-term impact studies by various authors, concerned about time lags before effects are fully realised. This desire for long-term evaluation opposes the requirements by policy-makers and funders, seeking quick results. Also, current ‘best practice’ frameworks do not refer to timing or its implications, and data availability affects the ability to undertake long-term evaluation. Secondly, this thesis provides methodological value for follow-up and similar studies by using data linking of scheme-beneficiary data with official performance datasets. Thus data availability problems are avoided through the use of secondary data. Thirdly, this thesis builds the evidence, through the application of a longitudinal impact study of small business support in England, covering seven years of post intervention data. This illustrates the variability of results for different evaluation periods, and the value in using multiple years of data for a robust understanding of support impact. For survival, impact of assistance is found to be immediate, but limited. Concerning growth, significant impact centres on a two to three year period post intervention for the linear selection and quantile regression models – positive for employment and turnover, negative for productivity. Attribution of impact may present a problem for subsequent periods. The results clearly support the argument for the use of longitudinal data and analysis, and a greater appreciation by evaluators of the factor time. This analysis recommends a time frame of four to five years post intervention for soft business support evaluation.

Education 2.0: Exploring the challenges of Corvinus University in the long tail economy of global higher education

Our basic storyline is how the business and economics higher education landscape has changed with the introduction of the Bologna programs. We borrowed the fashionable long tail concept from e-business, and used it for modeling the new landscape of internationalization of universities. Internationalization, mobility, and the appearance of the internet generation at the gates of our universities in our opinion has brought us to a new e-era which, appropriately to our web analogies we might as well call Education 2.0.In our paper first we show the characteristics of the long tail model of the Bologna-based European higher education and potential messages for strategy making in this environment. We illustrate that benchmarking university strategies situated in the head of the long tail model will not always provide strategic guidance for universities sitting in the tail. For underlining some key concerns in the Hungarian niche, we used Corvinus University as a case study to illustrate some untapped challenges of the Hungarian Bologna reform. We explored three areas which are crucial elements of the “tail” strategy in our opinion: a) the influence of state regulation, b) social situations and impacts and c) internal university capabilities.

GRE as a predictor of graduate student success at a Hispanic serving institution of higher education

Accurately predicting the success of graduate students is an important aspect of determining which students should be admitted into graduate programs. The GRE is a pivotal factor to examine since it is one of the most widely used criteria for graduate school admission. Even though the GRE is advertised as an accurate tool for predicting first year graduate GPA, there is a lack of research on long term success factors such as time to degree and graduate rate (Luthy, 1996; Powers, 2004). Furthermore, since most studies have low minority sample sizes, the validity of the GRE may not be the same across all groups (ETS, 2008b; Kuncel, Hezlett, & Ones, 2001). Another gap in GRE studies is that few researchers analyze student characteristics, which may alter or moderate the prediction validity of the GRE. Thus, student characteristics such as degree of academic involvement, mentorship interactions, and other academic and social experiences have not been widely examined in this context. These gaps in the analysis of GRE validity are especially relevant given the high attrition rates within of some graduate programs (e.g., an estimated 68% of doctoral student never complete their programs in urban universities; Lovitts, 2001). A sequential mixed methods design was used to answer the research questions in two phases. The quantitative phase used student data files to analyze the relationship of two success variables (graduation rate and graduate GPA) to the GRE scores as well as other academic and demographic graduate student characteristics. The qualitative phase served to complement the first phase by describing a wider range of characteristics from the 11 graduate students who were interviewed. Both proximal and distal moderators influence student behaviors and success in graduate school. In the first phase of the study, the GRE was the distal facilitator under analysis. Findings suggested that both the GRE Quantitative and the GRE Verbal were predictors of success for master’s students, but the GRE Quantitative was not predictive of success for doctoral students. Other student characteristics such as demographic variables and disciplinary area were also predictors of success for the population of students studied. In the second phase of the study, it was inconclusive whether the GRE was predictive of graduate student success; though it did influence access to graduate programs. Furthermore, proximal moderators such as student involvement, faculty/peer interactions, motivational factors, and program structure were perceived to be facilitators and/or detractors for success.