Optical coherence tomography confirmed resolution of macular edema in a diabetic patient after hemodialysis

Purpose: The authors report the first case, to their knowledge, of resolution of diffuse macular edema after hemodialysis, which has been confirmed by optical coherence tomography. Methods: A 53-year-old white woman with type 2 diabetes developed worsening macular edema and was examined in the ophthalmology clinic and scheduled for macular grid laser photocoagulation. The laser, however, was deferred for 4 weeks because she had also developed end-stage renal failure and required hemodialysis. Results: When she was reviewed in the ophthalmology clinic 4 weeks later for laser therapy, it was found that her macular edema had resolved, vision had improved, and laser was unnecessary. Review at 6 months showed that the macular edema remains resolved. Conclusion: Ophthalmologists should be aware that hemodialysis may reduce macular edema in such patients. Copyright © by Ophthalmic Communications Society Inc.

Fabrication and characterization of macroporous poly(ethylene glycol) hydrogels generated by several types of porogens

Polymer scaffolds play an important role in tissue engineering applications. Poly(ethylene glycol) based hydrogels have received a lot of attention in this field because of their high biocompatibility and ease of processing. However, in many cases they do not exhibit proper tissue invasion and nutrient transport because of their dense structure. In the present work, several approaches were developed and compared to each other to produce interconnected macroporous poly(ethylene glycol) hydrogels by including different types of porogens in the photocrosslinking reaction. The swelling capacity of the resulting hydrogels was analyzed and compared to non-porous hydrogel samples. Moreover, the obtained materials were characterized by means of mechanical properties and porosity using rheometry, scanning electron microscopy, and mercury intrusion porosimetry. Results showed that interconnected and uniform pores were obtained when a porogen template was used during hydrogel fabrication by photocrosslinking. On the other side, when the porogen particles were dispersed into the macromer solution before matrix photocrosslinking the interconnexion was negligible. The templates must be dissolved before the hydrogel's cell-seeding in vitro, while the dispersed porogen can be used in situ in the in vitro seeding tests. Copyright © 2013 Taylor & Francis Group, LLC.

Mean zonal flows generated by librations of a rotating spherical cavity

Longitudinal librations represent oscillations about the axis of a rotating axisymmetric fluid-filled cavity. An analytical theory is developed for the case of a spherical cavity in the limit when the libration frequency is small in comparison with the rotation rate, but large in comparison with the inverse of the spin-up time. It is shown that longitudinal librations create a steady zonal flow through the nonlinear advection in the Ekman layers. The theory can be applied to laboratory experiments as well as to solid planets and satellites with a liquid core. Copyright © Cambridge University Press 2010.

Bistability and hysteresis of dipolar dynamos generated by turbulent convection in rotating spherical shells

Bistability and hysteresis of magnetohydrodynamic dipolar dynamos generated by turbulent convection in rotating spherical fluid shells is demonstrated. Hysteresis appears as a transition between two distinct regimes of dipolar dynamos with rather different properties including a pronounced difference in the amplitude of the axisymmetric poloidal field component and in the form of the differential rotation. The bistability occurs from the onset of dynamo action up to about 9 times the critical value of the Rayleigh number for onset of convection and over a wide range of values of the ordinary and the magnetic Prandtl numbers including the value unity. Copyright © EPLA, 2009.

Browsing for information by highlighting automatically generated annotations:a user study and evaluation

The realization of the Semantic Web is constrained by a knowledge acquisition bottleneck, i.e. the problem of how to add RDF mark-up to the millions of ordinary web pages that already exist. Information Extraction (IE) has been proposed as a solution to the annotation bottleneck. In the task based evaluation reported here, we compared the performance of users without access to annotation, users working with annotations which had been produced from manually constructed knowledge bases, and users working with annotations augmented using IE. We looked at retrieval performance, overlap between retrieved items and the two sets of annotations, and usage of annotation options. Automatically generated annotations were found to add value to the browsing experience in the scenario investigated. Copyright 2005 ACM.

Thermochemical characterisation of various biomass feedstock and bio-oil generated by fast pyrolysis

The projected decline in fossil fuel availability, environmental concerns, and security of supply attract increased interest in renewable energy derived from biomass. Fast pyrolysis is a possible thermochemical conversion route for the production of bio-oil, with promising advantages. The purpose of the experiments reported in this thesis was to extend our understanding of the fast pyrolysis process for straw, perennial grasses and hardwoods, and the implications of selective pyrolysis, crop harvest and storage on the thermal decomposition products. To this end, characterisation and laboratory-scale fast pyrolysis were conducted on the available feedstocks, and their products were compared. The variation in light and medium volatile decomposition products was investigated at different pyrolysis temperatures and heating rates, and a comparison of fast and slow pyrolysis products was conducted. Feedstocks from different harvests, storage durations and locations were characterised and compared in terms of their fuel and chemical properties. A range of analytical (e.g. Py-GC-MS and TGA) and processing equipment (0.3 kg/h and 1.0 kg/h fast pyrolysis reactors and 0.15 kg slow pyrolysis reactor) was used. Findings show that the high bio-oil and char heating value, and low water content of willow short rotation coppice (SRC) make this crop attractive for fast pyrolysis processing compared to the other investigated feedstocks in this project. From the analytical sequential investigation of willow SRC, it was found that the volatile product distribution can be tailored to achieve a better final product, by a variation of the heating rate and temperature. Time of harvest was most influential on the fuel properties of miscanthus; overall the late harvest produced the best fuel properties (high HHV, low moisture content, high volatile content, low ash content), and storage of the feedstock reduced the moisture and acid content.

Three-dimensional calibration targets for optical coherence tomography

The recent expansion of clinical applications for optical coherence tomography (OCT) is driving the development of approaches for consistent image acquisition. There is a simultaneous need for time-stable, easy-to-use imaging targets for calibration and standardization of OCT devices. We present calibration targets consisting of three-dimensional structures etched into nanoparticle-embedded resin. Spherical iron oxide nanoparticles with a predominant particle diameter of 400 nm were homogeneously dispersed in a two part polyurethane resin and allowed to harden overnight. These samples were then etched using a precision micromachining femtosecond laser with a center wavelength of 1026 nm, 100kHz repetition rate and 450 fs pulse duration. A series of lines in depth were etched, varying the percentage of inscription energy and speed of the translation stage moving the target with respect to the laser. Samples were imaged with a dual wavelength spectral-domain OCT system and point-spread function of nanoparticles within the target was measured.

Nonlinearly generated advanced pulse waveforms for optical signal processing

Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses, and on the applications of advanced pulse waveforms in all-optical signal processing. Among other topics, we will discuss ultrahigh repetition-rate pulse sources, the generation of parabolic-shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion. © 2012 IEEE.

Extended-range, low coherence dual wavelength interferometry using a superfluorescent fibre source and chirped fibre Bragg gratings

We describe an all-fibre, passive scheme for making extended range interferometric measurements based on the dual wavelength technique. The coherence tuned interferometer network is illuminated with a single superfluorescent fibre source at 1.55 μm and the two wavelengths are synthesised at the output by means of chirped fibre Bragg gratings. We demonstrate an unambiguous sensing range of 270 μm, with a dynamic range of 2.7 × 105.

Third-order intermodulation products generated on transmission through nonlinear radio-on-fibre link

Two-tone intermodulation tests were simulated for an amplitude modulated radio-on-fibre link including fibre dispersion, nonlinearity and loss. The third-order intercept results are presented for varying fibre lengths and optical transmission powers.

Fibre Bragg grating sensor interrogation using an acousto-optic tunable filter and low-coherence interferometry

We describe how an acousto-optic tunable filter can be used to both demultiplex the signals from multiple fibre Bragg grating sensors and simultaneously provide wide bandwidth signal demodulation in a system using interferometric wavelength shift detection. In an experimental demonstration, the approach provided a noise limited strain resolution of 24.9 nε Hz -1/2 at 15 Hz. © 2007 IOP Publishing Ltd.

Coherence imaging by use of a Newton rings sampling function

We show that, with suitable optics in the arm of a Michelson interferometer, orthogonal galvo-scanning mirrors build a sampling function in the form of Newton rings when the two interferometer arms are matched. Using a low-coherence source, one can obtain transversal depth-resolved images. A fast display procedure using a storage oscilloscope was devised based on this method.

Influence of the generated power, measurement bandwidth, and noise level on intensity statistics of a quasi-CW Raman fiber laser

In the present paper we numerically study instrumental impact on statistical properties of quasi-CW Raman fiber laser using a simple model of multimode laser radiation. Effects, that have the most influence, are limited electrical bandwidth of measurement equipment and noise. To check this influence, we developed a simple model of the multimode quasi- CW generation with exponential statistics (i.e. uncorrelated modes). We found that the area near zero intensity in probability density function (PDF) is strongly affected by both factors, for example both lead to formation of a negative wing of intensity distribution. But far wing slope of PDF is not affected by noise and, for moderate mismatch between optical and electrical bandwidth, is only slightly affected by bandwidth limitation. The generation spectrum often becomes broader at higher power in experiments, so the spectral/electrical bandwidth mismatch factor increases over the power that can lead to artificial dependence of the PDF slope over the power. It was also found that both effects influence the ACF background level: noise impact decreases it, while limited bandwidth leads to its increase. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Advances in characterisation, calibration and data processing speed of optical coherence tomography systems

This thesis describes advances in the characterisation, calibration and data processing of optical coherence tomography (OCT) systems. Femtosecond (fs) laser inscription was used for producing OCT-phantoms. Transparent materials are generally inert to infra-red radiations, but with fs lasers material modification occurs via non-linear processes when the highly focused light source interacts with the materials. This modification is confined to the focal volume and is highly reproducible. In order to select the best inscription parameters, combination of different inscription parameters were tested, using three fs laser systems, with different operating properties, on a variety of materials. This facilitated the understanding of the key characteristics of the produced structures with the aim of producing viable OCT-phantoms. Finally, OCT-phantoms were successfully designed and fabricated in fused silica. The use of these phantoms to characterise many properties (resolution, distortion, sensitivity decay, scan linearity) of an OCT system was demonstrated. Quantitative methods were developed to support the characterisation of an OCT system collecting images from phantoms and also to improve the quality of the OCT images. Characterisation methods include the measurement of the spatially variant resolution (point spread function (PSF) and modulation transfer function (MTF)), sensitivity and distortion. Processing of OCT data is a computer intensive process. Standard central processing unit (CPU) based processing might take several minutes to a few hours to process acquired data, thus data processing is a significant bottleneck. An alternative choice is to use expensive hardware-based processing such as field programmable gate arrays (FPGAs). However, recently graphics processing unit (GPU) based data processing methods have been developed to minimize this data processing and rendering time. These processing techniques include standard-processing methods which includes a set of algorithms to process the raw data (interference) obtained by the detector and generate A-scans. The work presented here describes accelerated data processing and post processing techniques for OCT systems. The GPU based processing developed, during the PhD, was later implemented into a custom built Fourier domain optical coherence tomography (FD-OCT) system. This system currently processes and renders data in real time. Processing throughput of this system is currently limited by the camera capture rate. OCTphantoms have been heavily used for the qualitative characterization and adjustment/ fine tuning of the operating conditions of OCT system. Currently, investigations are under way to characterize OCT systems using our phantoms. The work presented in this thesis demonstrate several novel techniques of fabricating OCT-phantoms and accelerating OCT data processing using GPUs. In the process of developing phantoms and quantitative methods, a thorough understanding and practical knowledge of OCT and fs laser processing systems was developed. This understanding leads to several novel pieces of research that are not only relevant to OCT but have broader importance. For example, extensive understanding of the properties of fs inscribed structures will be useful in other photonic application such as making of phase mask, wave guides and microfluidic channels. Acceleration of data processing with GPUs is also useful in other fields.