Impact of the order of cavity elements in all-normal dispersion ring fiber lasers

Nonlinearity plays a critical role in the intra-cavity dynamics of high-pulse energy fiber lasers. Management of the intra-cavity nonlinear dynamics is the key to increase the output pulse energy in such laser systems. Here, we examine the impact of the order of the intra-cavity elements on the energy of generated pulses in the all-normal dispersion mode-locked ring fiber laser cavity. In mathematical terms, the nonlinear light dynamics in resonator makes operators corresponding to the action of laser elements (active and passive fiber, out-coupler, saturable absorber) non-commuting and the order of their appearance in a cavity important. For the simple design of all-normal dispersion ring fiber laser with varying cavity length, we found the order of the cavity elements, leading to maximum output pulse energy.

Effect of the Hofmeister anions upon the swelling of a self-assembled pH-responsive hydrogel

We report the effect of a range of monovalent sodium salts on the molecular equilibrium swelling of a simple synthetic microphase separated poly(methyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate)-block-poly(methyl methacrylate) (PMMA88-b-PDEA223-b-PMMA88) pH-responsive hydrogel. Sodium acetate, sodium chloride, sodium bromide, sodium iodide, sodium nitrate and sodium thiocyanate were selected for study at controlled ionic strength and pH; all salts are taken from the Hofmeister series (HS). The influence of the anions on the expansion of the hydrogel was found to follow the reverse order of the classical HS. The expansion ratio of the gel measured in solutions containing the simple sodium halide salts (NaCl, NaBr, and NaI) was found to be strongly related to parameters which describe the interaction of the ion with water; surface charge density, viscosity coefficient, and entropy of hydration. A global study which also included nonspherical ions (NaAce, NaNO3 and NaSCN) showed the strongest correlation with the viscosity coefficient. Our results are interpreted in terms of the Collins model,(1) where larger ions have more mobile water in the first hydration cage immediately surrounding the gel, therefore making them more adhesive to the surface of the stationary phase of the gel and ultimately reducing the level of expansion.

A structural investigation of the alkali metal site distribution within bioactive glass using neutron diffraction and multinuclear solid state NMR

The atomic-scale structure of Bioglass and the effect of substituting lithium for sodium within these glasses have been investigated using neutron diffraction and solid state magic angle spinning (MAS) NMR. Applying an effective isomorphic substitution difference function to the neutron diffraction data has enabled the Na-O and Li-O nearest-neighbour correlations to be isolated from the overlapping Ca-O, O-(P)-O and O-(Si)-O correlations. These results reveal that Na and Li behave in a similar manner within the glassy matrix and do not disrupt the short range order of the network former. Residual differences are attributed solely to the variation in ionic radius between the two species. Successful simplification of the 2 the difference method has enabled all the nearest neighbour correlations to be deconvolved. The diffraction data provides the first direct experimental evidence of split Na-O nearest-neighbour correlations in these melt quench bioactive glasses, and an analogous splitting of the Li-O correlations. The observed correlations are attributed to the metal ions bonded either to bridging or to non-bridging oxygen atoms. 23Na triple quantum MAS (3QMAS) NMR data corroborates the split Na-O correlations. The structural sites present will be intimately related to the release properties of the glass system in physiological fluids such as plasma and saliva, and hence to the bioactivity of the material. Detailed structural knowledge is therefore a prerequisite for optimizing material design.

Constructive updating/downdating of oblique projectors:a generalization of the Gram-Schmidt process

A generalization of the Gram-Schmidt procedure is achieved by providing equations for updating and downdating oblique projectors. The work is motivated by the problem of adaptive signal representation outside the orthogonal basis setting. The proposed techniques are shown to be relevant to the problem of discriminating signals produced by different phenomena when the order of the signal model needs to be adjusted. © 2007 IOP Publishing Ltd.

Femtosecond inscription of the first order Bragg gratings in pure fused silica

The fabrication of sub-micron periodic structures beyond diffraction limit is a major motivation for the present paper. We describe the fabrication of the periodic structure of 25 mm long with a pitch size of 260 nm which is less than a third of the wavelength used. This is the smallest reported period of the periodic structure inscribed by direct point-by-point method. A prototype of the add-drop filter, which utilizes such gratings, was demonstrated in one stage fabrication process of femtosecond inscription, in the bulk fused silica.

Femtosecond inscription of the first order Bragg gratings in pure fused silica

The fabrication of sub-micron periodic structures beyond diffraction limit is a major motivation for the present paper. We describe the fabrication of the periodic structure of 25 mm long with a pitch size of 260 nm which is less than a third of the wavelength used. This is the smallest reported period of the periodic structure inscribed by direct point-by-point method. A prototype of the add-drop filter, which utilizes such gratings, was demonstrated in one stage fabrication process of femtosecond inscription, in the bulk fused silica.

Higher-order factor structures and intercorrelations of the 16PF5 and FIRO-B

This study investigated the intercorrelations and the independent and combined factor structures of the Sixteen Personality Factor Questionnaire Fifth Edition (16PF5) and the Fundamental Interpersonal Orientation-Behaviour Scale (FIRO-B). Four thousand four hundred and fourteen U.S. participants completed these measures as part of executive assessments between 1994 and 2003. Exploratory factor analyses supported the five-factor higher-order structure of the 16PF5; however, the three-component structure for the FIRO-B was not supported. A six-factor structure was found to underlie the variance in the measures in combination. Five of these were close to the 16PF5 higher-order structure, but a sixth factor labelled Social Independence also emerged. This new factor consisted of the 16PF5 primaries of Liveliness and Social Boldness, and the FIRO-B Wanted Control scale.

A deficit in encoding the order of visual sequences in developmental dyslexia: a non -phonological deficit

The present thesis tested the hypothesis of Stanovich, Siegel, & Gottardo (1997) that surface dyslexia is the result of a milder phonological deficit than that seen in phonological dyslexia coupled with reduced reading experience. We found that a group of adults with surface dyslexia showed a phonological deficit that was commensurate with that shown by a group of adults with phonological dyslexia (matched for chronological age and verbal and non-verbal IQ) and normal reading experience. We also showed that surface dyslexia cannot be accounted for by a semantic impairment or a deficit in the verbal learning and recall of lexical-semantic information (such as meaningful words), as both dyslexic subgroups performed the same. This study has replicated the results of our published study that surface dyslexia is not the consequence of a mild retardation or reduced learning opportunities but a separate impairment linked to a deficit in written lexical learning, an ability needed to create novel lexical representations from a series of unrelated visual units, which is independent from the phonological deficit (Romani, Di Betta, Tsouknida & Olson, 2008). This thesis also provided evidence that a selective nonword reading deficit in developmental dyslexia persists beyond poor phonology. This was shown by finding a nonword reading deficit even in the presence of normal regularity effects in the dyslexics (when compared to both reading and spelling-age matched controls). A nonword reading deficit was also found in the surface dyslexics. Crucially, this deficit was as strong as in the phonological dyslexics despite better functioning of the sublexical route for the former. These results suggest that a nonword reading deficit cannot be solely explained by a phonological impairment. We, thus, suggested that nonword reading should also involve another ability relating to the processing of novel visual orthographic strings, which we called 'orthographic coding'. We then investigated the ability to process series of independent units within multi-element visual arrays and its relationship with reading and spelling problems. We identified a deficit in encoding the order of visual sequences (involving both linguistic and nonlinguistic information) which was significantly associated with word and nonword processing. More importantly, we revealed significant contributions to orthographic skills in both dyslexic and control individuals, even after age, performance IQ and phonological skills were controlled. These results suggest that spelling and reading do not only tap phonological skills but also order encoding skills.

Parabolic optical pulses under the action of the third-order dispersion

Recent developments in nonlinear optics reveal an interesting class of pulses with a parabolic intensity profile in the energy-containing core and a linear frequency chirp that can propagate in a fiber with normal group-velocity dispersion. Parabolic pulses propagate in a stable selfsimilar manner, holding certain relations (scaling) between pulse power, width, and chirp parameter. In the additional presence of linear amplification, they enjoy the remarkable property of representing a common asymptotic state (or attractor) for arbitrary initial conditions. Analytically, self-similar (SS) parabolic pulses can be found as asymptotic, approximate solutions of the nonlinear Schr¨odinger equation (NLSE) with gain in the semi-classical (largeamplitude/small-dispersion) limit. By analogy with the well-known stable dynamics of solitary waves - solitons, these SS parabolic pulses have come to be known as similaritons. In practical fiber systems, inherent third-order dispersion (TOD) in the fiber always introduces a certain degree of asymmetry in the structure of the propagating pulse, eventually leading to pulse break-up. To date, there is no analytic theory of parabolic pulses under the action of TOD. Here, we develop aWKB perturbation analysis that describes the effect of weak TOD on the parabolic pulse solution of the NLSE in a fiber gain medium. The induced perturbation in phase and amplitude can be found to any order. The theoretical model predicts with sufficient accuracy the pulse structural changes induced by TOD, which are observed through direct numerical NLSE simulations.

The throughput order of multicast traffics with physical-layer network coding in random wireless ad hoc networks

This paper attempts to address the effectiveness of physical-layer network coding (PNC) on the throughput improvement for multi-hop multicast in random wireless ad hoc networks (WAHNs). We prove that the per session throughput order with PNC is tightly bounded as T((nvmR (n))-1) if m = O(R-2 (n)), where n is the total number of nodes, R(n) is the communication range, and m is the number of destinations for each multicast session. We also show that per-session throughput order with PNC is tight bounded as T(n-1), when m = O(R-2(n)). The results of this paper imply that PNC cannot improve the throughput order of multicast in random WAHNs, which is different from the intuition that PNC may improve the throughput order as it allows simultaneous signal access and combination.

Hierarchy of governance institutions and the pecking order of privatisation

This article discusses property rights, corporate governance frameworks and privatisation outcomes in the Central–Eastern Europe and Central Asia (CEECA) region. We argue that while CEECA still suffers from deficient ‘higher order’ institutions, this is not attracting sufficient attention from international institutions like EBRD and the World Bank, which focus on ‘lower order’ indicators. We discuss factors that may alleviate the negative impact of the weakness in institutional environment and argue for the pecking order of privatisation, where equivalent privatisation is given a priority but speed is not compromised.

Imaging of the human fundus in the clinical setting:past present and future

The human fundus is a complex structure that can be easily visualized and the world of ophthalmology is going through a golden era of new and exciting fundus imaging techniques; recent advances in technology have allowed a significant improvement in the imaging modalities clinicians have available to formulate a diagnostic and treatment plan for the patient, but there is constant on-going work to improve current technology and create new ideas in order to gather as much information as possible from the human fundus. In this article we shall summarize the imaging techniques available in the standard medical retina clinic (i.e. not limited to the research lab) and delineate the technologies that we believe will have a significant impact on the way clinicians will assess retinal and choroidal pathology in the not too distant future.

Parabolic optical pulses under the action of the third-order dispersion

Recent developments in nonlinear optics reveal an interesting class of pulses with a parabolic intensity profile in the energy-containing core and a linear frequency chirp that can propagate in a fiber with normal group-velocity dispersion. Parabolic pulses propagate in a stable selfsimilar manner, holding certain relations (scaling) between pulse power, width, and chirp parameter. In the additional presence of linear amplification, they enjoy the remarkable property of representing a common asymptotic state (or attractor) for arbitrary initial conditions. Analytically, self-similar (SS) parabolic pulses can be found as asymptotic, approximate solutions of the nonlinear Schr¨odinger equation (NLSE) with gain in the semi-classical (largeamplitude/small-dispersion) limit. By analogy with the well-known stable dynamics of solitary waves - solitons, these SS parabolic pulses have come to be known as similaritons. In practical fiber systems, inherent third-order dispersion (TOD) in the fiber always introduces a certain degree of asymmetry in the structure of the propagating pulse, eventually leading to pulse break-up. To date, there is no analytic theory of parabolic pulses under the action of TOD. Here, we develop aWKB perturbation analysis that describes the effect of weak TOD on the parabolic pulse solution of the NLSE in a fiber gain medium. The induced perturbation in phase and amplitude can be found to any order. The theoretical model predicts with sufficient accuracy the pulse structural changes induced by TOD, which are observed through direct numerical NLSE simulations.

Foveation time measure in Congenital Nystagmus through second order approximation of the slow phases

Congenital Nystagmus (CN) is an ocular-motor disorder characterised by involuntary, conjugated ocular oscillations, and its pathogenesis is still unknown. The pathology is de fined as "congenital" from the onset time of its arise which could be at birth or in the first months of life. Visual acuity in CN subjects is often diminished due to nystagmus continuous oscillations, mainly on the horizontal plane, which disturb image fixation on the retina. However, during short periods in which eye velocity slows down while the target image is placed onto the fovea (called foveation intervals) the image of a given target can still be stable, allowing a subject to reach a higher visual acuity. In CN subjects, visual acuity is usually assessed both using typical measurement techniques (e.g. Landolt C test) and with eye movement recording in different gaze positions. The offline study of eye movement recordings allows physicians to analyse nystagmus main features such as waveform shape, amplitude and frequency and to compute estimated visual acuity predictors. This analytical functions estimates the best corrected visual acuity using foveation time and foveation position variability, hence a reliable estimation of this two parameters is a fundamental factor in assessing visual acuity. This work aims to enhance the foveation time estimation in CN eye movement recording, computing a second order approximation of the slow phase components of nystag-mus oscillations. About 19 infraredoculographic eye-movement recordings from 10 CN subjects were acquired and the visual acuity assessed with an acuity predictor was compared to the one measured in primary position. Results suggest that visual acuity measurements based on foveation time estimation obtained from interpolated data are closer to value obtained during Landolt C tests. © 2010 IEEE.