Aberrant visual pathway development in albinism: from retina to cortex

Albinism refers to a group of genetic abnormalities in melanogenesis that are associated neuronal misrouting through the optic chiasm. Previous imaging studies have shown structural alterations at different points along the visual pathway of people with albinism (PWA) including foveal hypoplasia, optic nerve and chiasm size alterations and visual cortex reorganisation, but fail to provide a holistic in-vivo characterisation of the visual neurodevelopmental alterations from retina to visual cortex. We perform quantitative assessment of visual pathway structure and function in 23 PWA and 20 matched controls using optical coherence tomography (OCT), volumetric magnetic resonance imaging (MRI), diffusion tensor imaging and visual evoked potentials (VEP). PWA had a higher streamline decussation index (percentage of total tractography streamlines decussating at the chiasm) compared to controls (Z=-2.24, p=0.025), and streamline decussation index correlated weakly significantly with inter-hemispheric asymmetry measured using VEP (r=0.484, p=0.042). For PWA, a significant correlation was found between foveal development index and total number of streamlines (r=0.662, p less than 0.001). Optic nerve (p=0.001) and tract (p=0.010) width, and chiasm width (P less than 0.001), area (p=0.006) and volume (p=0.005), were significantly smaller in PWA compared to controls. Significant positive correlations were found between peri-papillary retinal nerve fibre layer thickness and optic nerve (r=0.642, p less than 0.001) and tract (r=0.663, p less than 0.001) width. Occipital pole cortical thickness was 6.88% higher (Z=-4.10, p less than 0.001) in PWA and was related to anterior visual pathway structures including foveal retinal pigment epithelium complex thickness (r=-0.579, p=0.005), optic disc (r=0.478, p=0.021) and rim areas (r=0.597, p=0.003). We were unable to demonstrate a significant relationship between OCT-derived foveal or optic nerve measures and MRI-derived chiasm size or streamline decussation index. Non-invasive imaging techniques demonstrate aberrant development throughout the visual pathways of PWA compared to controls. Our novel tractographic demonstration of altered chiasmatic decussation in PWA corresponds to VEP measured cortical asymmetry and is consistent with chiasmatic misrouting in albinism. We also demonstrate a significant relationship between retinal pigment epithelium and visual cortex thickness indicating that retinal pigmentation defects in albinism lead to downstream structural reorganisation of the visual cortex

A new recessively inherited disorder composed of foveal hypoplasia, optic nerve decussation defects and anterior segment dysgenesis maps to chromosome 16q23.3-24.1

PURPOSE: We have previously described two families with unique phenotypes involving foveal hypoplasia. The first family (F1) presented with foveal hypoplasia and anterior segment dysgenesis, and the second family (F2) presented with foveal hypoplasia and chiasmal misrouting in the absence of albinism. A genome-wide linkage search in family F1 identified a 6.5 Mb locus for this disorder on chromosome 16q23.2-24.1. The aim of this study was to determine if both families have the same disorder and to see if family F2 is also linked to the 16q locus. METHODS: Family members underwent routine clinical examination. Linkage was determined by genotyping microsatellite makers and calculating logarithm of the odds (LOD) scores. Locus refinement was undertaken with single nucleotide polymorphism (SNP) microarray analysis. RESULTS: The identification of chiasmal misrouting in family F1 and anterior segment abnormalities in family F2 suggested that the families have the same clinical phenotype. This was confirmed when linkage analysis showed that family F2 also mapped to the 16q locus. The single nucleotide polymorphism microarray analysis excluded a shared founder haplotype between the families and refined the locus to 3.1 Mb. CONCLUSIONS: We report a new recessively inherited syndrome consisting of foveal hypoplasia, optic nerve decussation defects and anterior segment dysgenesis, which we have abbreviated to FHONDA syndrome. The gene mutated in this disorder lies within a 3.1 Mb interval containing 33 genes on chromosome 16q23.3-24.1 (chr16:83639061 - 86716445, hg19)

High-frequency vector harmonic mode locking driven by acoustic resonances

A controllable passive harmonic mode locking (HML) in an erbium-doped fiber laser with a soliton pulse shaping using a single-wall carbon nanotube has been experimentally demonstrated. By increasing the pump power and adjusting the in-cavity polarization controller, we reached the 51st-order harmonic (902 MHz) having the output power of 37 mW. We attribute the observed high-frequency HML to the electrostriction effect caused by periodic pulses and leading to excitation of the radial and torsional-radial acoustic modes in the transverse section of the laser. The exited acoustic modes play the role of the bandpass filter, which stabilizes the high-frequency HML regime

Photonic Systems Based on Carbon Nanotubes: Photoluminescence Enhancement and Saturable Absorbers by Inkjet Printing and Integration on Fibre Tapers

The multifunctional properties of single-wall carbon nanotubes (SWNTs) created a robust platform for unprecedented innovations in a variety of applications in photonics, sensors, electronics, smart manufacturing and drug delivery. This thesis presents an experimental study of the author’s research using innovative approaches for the development of photonic systems based on SWNTs’ dispersions and composites, featuring enhanced and effective optical properties. The first set of experiments demonstrates a novel approach for the enhancement of SWNTs’ photoluminescent (PL) properties via complexation with organic dyes. One of the more significant findings to emerge from this investigation is the interaction of the indopentamethinedioxaborine dye (DOB-719) with SWNTs, which resulted in new optical features in the spectral range of the intrinsic excitation of the dye, providing clear evidence of the resonance energy transfer from DOB-719 to the SWNTs. The findings from this study allowed for the proposal of the mechanism of interaction between the SWNT and DOB-719, where the dye is attracted to the SWNT surface via π-π stacking with the hydrophobic part facing the aqueous medium by polar groups. The second set of experiments examined a limitation imposed by the use of SWNT-polymer composites for saturable absorber (SA) applications. The integration of this device in the fibre cavity resulted in modification of the composite properties under continuous high power laser irradiation, which limits the use of composites to generate ultrashort pulses with stable parameters for a long operation time (>10,000 hours). This stimulated the design of advanced approaches in this work as an alternative to the composite method. The first approach describes a method for the controllable integration of SWNT directly on the core of a fibre edge, using the inkjet printing technique. It is important to note that a direct correlation between the number of printed layers and properties of SA was determined, showing that a SA with 20,000 layers gives the best parameters. The obtained output power and pulse energy are higher than all earlier reported results on SA for erbium-doped fibre lasers using sandwiched SWNT- composites. The second approach is to coat the tapered fibre with a low refractive index SWNT-polymer composite. This method depends on lateral interaction with the evanescence field of the propagating pulse in the laser cavity. The study reports SAs devices with controllable saturation intensity, low losses and large saturable to non-saturable loss ratios

Exploring knowledge types and knowledge protection in organizations

Knowledge management has emerged as an area of enquiry for managing organizational knowledge. It is a key driver for organizational effectiveness and competitive advantage and an effective way to address economic problems including losses related to high turnovers and retiring workforce. It also has been considered an important weapon for maximizing the potential of knowledge for sustainable performance for public and private organizations. Knowledge is a critical resource for organizations, and the knowledge resources need to be properly recognized and used for achieving organizational goals. Knowledge has limited value if it is not shared within the organization. The aim of the chapter is to examine the relationship between knowledge types and knowledge protection. It will also identify several approaches (i.e. tools and programs) or mechanisms for protecting the knowledge from loss