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Background Accumulation of multiple pockets of fluid at the fovea, as a complication of poor blood glucose control in diabetes, causes impairment of central vision. A new ability to demonstrate a pre-clinical phase of this maculopathy could be valuable, enabling diabetic individuals to be alerted to the need to improve their glycaemic control. This study aimed to use swept-source optical coherence tomography (SS-OCT) to measure foveal thickness and macular volume in diabetic individuals without cystoid macular oedema, and in non-diabetic individuals, and relate these measures to participants’ glycaemic control. Methods Centre point thickness (CPT) and total macular volume (TMV) were measured using SS-OCT (DRI OCT Triton™, Topcon, Tokyo, Japan). Participants’ glycosylated haemoglobin (HbA1c) level was also assessed (A1cNow®+ System, PTS Diagnostics, Indianapolis, IN, USA). The diabetic (n = 27) and non-diabetic (n = 27) groups were matched for age (p = 0.100) and sex (p = 0.414), and HbA1c level differed between diabetic and non-diabetic groups (p n = 7) and type 2 (n = 20) diabetic individuals who were matched for duration of diabetes (p = 0.617) and whose glycaemic control was similar (p = 0.814). Results Diabetic individuals had significantly higher CPT (t(37) = 3.859, p 1c level (β = 0.501, t(21) = 3.139, p = 0.005): there was a 19-μm increase in CPT for each 1% increase in HbA1c level. This relationship was not present in the non-diabetic group (β = − 0.068, t(23) = − 0.373, p = 0.712). Conclusions SS-OCT is the only way to measure macular thickness in vivo. Diabetic individuals en bloc had higher CPT compared with non-diabetic individuals. Moreover, in the diabetic group, HbA1c level significantly predicted CPT. Our results suggest that, in diabetes, sub-clinical thickening may occur at the fovea before cystoid macular oedema becomes clinically evident. This could provide diabetic individuals with an early warning of disease progression and motivate them to improve control of their diabetes, with a view to avoiding the need of intra-vitreal injections with their attendant risks.

Introduction Diabetes is a global issue that currently affects 425 million people worldwide. One observable microvascular complication of this condition is a change in the foveal avascular zone (FAZ). In this study, we used optical coherence tomography angiography (OCT-A) to investigate the effect of diabetes on the FAZ. Materials and methods Eleven diabetic and eleven non-diabetic participants took part in this study. Participants in both groups were matched for age (p = 0.217) and sex (p = 0.338), and had no history of ocular disease. Macular OCT-A scans of participants' right and left eyes were taken. Glycosylated haemoglobin (HbA1c ) and blood glucose levels were also measured. The FAZ area was manually segmented at the levels of the superficial capillary plexus (FAZSCP ) and deep capillary plexus (FAZDCP ). Results There was a strong relationship between the FAZ area of participants' right and left eyes (p ≤ 0.001) in both diabetic and non-diabetic groups. In the diabetic group, the FAZSCP (p = 0.047) and FAZDCP (p = 0.011) areas was significantly larger than in the non-diabetic group. Moreover, multiple linear regression analysis predicted a 0.07-mm2 increase in diabetic individuals' FAZSCP and FAZDCP areas for every 1% increase in their HbA1c level. Conclusions Our findings indicate that there is enlargement of the FAZ in diabetic individuals compared with non-diabetic individuals. In the diabetic group, this enlargement appears to be correlated with HbA1c level. OCT-A imaging could, therefore, be a useful tool to monitor the FAZ and identify potential early microvasculopathy in diabetes.

Topology optimization tools offer the potential to design novel aerospace structures that are subject to demanding strength and natural frequency requirements. However, algorithms for stress- and f...

Aims Diabetes mellitus affects about 6% of the world’s population, and the chronic complications of the disease may result in macro- and micro-vascular changes. The purpose of the current study was to shed light on visual cortical oxygenation in diabetic individuals. We then aimed to compare the haemodynamic response (HDR) to visual stimulation with glycaemic control, given the likelihood of diabetic individuals suffering from such macro- and micro-vascular insult. Methodology Thirty participants took part in this explorative study, fifteen of whom had diabetes and fifteen of whom were non-diabetic controls. The HDR, measured as concentrations of oxyhaemoglobin [HbO] and deoxyhaemoglobin [HbR], to visual stimulation was recorded over the primary visual cortex (V1) using a dual-channel oximeter. The stimulus comprised a pattern-reversal checkerboard presented in a block design. Participants’ mean glycated haemoglobin (HbA1c) level (± SD) was 7.2 ± 0.6% in the diabetic group and 5.5 ± 0.4% in the non-diabetic group. Raw haemodynamic data were normalised to baseline, and the last 15 s of data from each ‘stimulus on’ and ‘stimulus off’ condition were averaged over seven duty cycles for each participant. Results There were statistically significant differences in ∆[HbO] and ∆[HbR] to visual stimulation between diabetic and non-diabetic groups (p

Preliminary aircraft design studies use structural weight models that are calibrated with data from existing aircraft. Computing weights with these models is a fast procedure that provides reliable weight estimates when the candidate designs lie within the domain of the data used for calibration. However, this limitation is too restrictive when we wish to assess the relative benefits of new structural technologies and new aircraft configurations early in the design process. To address this limitation, we present a computationally efficient aerostructural design framework for initial aircraft design studies that uses a full finite-element model of key structural components to better assess the potential benefits of new technologies. We use a three-dimensional panel method to predict the aerodynamic forces and couple the lifting surface deflections to compute the deformed aerodynamic flying shape. To be used early in the design cycle, the aerostructural computations must be fast, robust, and allow for significant design flexibility. To address these requirements, we develop a geometry parametrization technique that enables large geometric modifications, we implement a parallel Newton---Krylov approach that is robust and computationally efficient to solve the aeroelastic system, and we develop an adjoint-based derivative evaluation method to compute the derivatives of functions of interest for design optimization. To demonstrate the capabilities of the framework, we present a design optimization of a large transport aircraft wing that includes a detailed structural design parametrization. The results demonstrate that the proposed framework can be used to make detailed structural design decisions to meet overall aircraft mission requirements.

Aeroelastic systems achieve the best performance when the aerodynamic shape and structural sizing are optimized concurrently, but such an optimization is challenging when high-fidelity aerodynamic and structural models are required. This paper addresses this challenge through several significant improvements. Fully coupled Newton–Krylov methods are presented for the solution of aerostructural systems and for the corresponding adjoint systems. The coupled adjoint method presented can compute gradients with respect to thousands of multidisciplinary design variables accurately and efficiently. This is enabled by several improvements in the computation of the multidisciplinary terms in the coupled adjoint. The parallel scalability of the methods is demonstrated for a full aircraft configuration using an Euler computational fluid dynamics model with more than 8×106 state variables and a detailed structural finite element model of the wing with more than 1×106 degrees of freedom. The coupled Newton–Krylov metho...

This paper presents a novel multidisciplinary framework for performing shape and topology optimization of a flexible wing structure. The topology optimization is integrated into a multidisciplinary algorithm in which both the aerodynamic shape and the structural topology are optimized concurrently using gradient-based optimization. The optimization results were compared with the results of a sequential procedure in which the aerodynamic shape was optimized separately and then used as a fixed design feature in a subsequent structural optimization. The results show that the concurrent approach offers a significant advantage, as this design achieved 42% less drag than the sequentially optimized wing.

In this paper we present a novel laminate parametrization technique for layered composite structures that can handle problems in which the ply angles are limited to a discrete set. In the proposed technique, the classical laminate stiffnesses are expressed as a linear combination of the discrete options and design-variable weights. An exact $\ell _{1}$ penalty function is employed to drive the solution toward discrete 0---1 designs. The proposed technique can be used as either an alternative or an enhancement to SIMP-type methods such as discrete material optimization (DMO). Unlike mixed-integer approaches, our laminate parametrization technique is well suited for gradient-based design optimization. The proposed laminate parametrization is demonstrated on the compliance design of laminated plates and the buckling design of a laminated stiffened panel. The results demonstrate that the approach is an effective alternative to DMO methods.

Next-generation additive manufacturing technologies will enable novel, low-weight, highperformance aircraft structures. Topology optimization techniques can be used to obtain unconventional internal aircraft wing structures that can be manufactured using additive methods which depart significantly from conventional rib-spar wing constructions. However, there are significant issues that must be overcome when applying traditional topology optimization techniques to the design of aerospace structures. These challenges include efficiently solving large-scale design problems, and applying buckling criteria within a topology optimization design formulation. In this paper, we seek to address these issues by applying a scalable topology optimization method to the undeformed Common Research Model (uCRM) wing with buckling constraints applied to the skins of the wingbox. The proposed approach uses a multigrid-preconditioned Krylov method to solve the large-scale finite element analysis problem, coupled with a parallel interior-point optimizer to solve the largescale constrained design optimization problem. This proposed method is applied to two different optimization problems: mass-constrained compliance minimization, and mass-constrained bucklingload maximization. In addition, we apply a segment-wise topology optimization design strategy to the uCRM wingbox.

The ability to discriminate minute deviations from circularity is dependent upon global summation mechanisms integrating information along entire contours. The aim of this study was to determine how the strength of global summation depends on various stimulus features. To determine if the strength of global summation differs between shapes, contour discrimination for various contour shapes, generated by applying a sinusoidal modulation to the radius of a circle (radial frequency – RF – patterns), was measured. Shapes differed in frequency (number of lobes RF3, RF5 and RF20) and amplitude (‘sharpness’ of the lobes ranged between 0 and 20× thresholds for detecting deviation from a circle). Low amplitudes test discrimination against a circle while high amplitudes measure sensitivity for highly non-circular shapes (e.g. five-pointed star-shapes). The ability to integrate information along contours was assessed by comparing the effect of applying radial deformations to the entire contour or to only fractions (various number of cycles). Results show that discrimination thresholds remain in the hyperacuity range for low amplitudes, but increase for higher amplitudes. Concerning signal integration, discrimination, expressed as a function of the amount of contour deformed, exhibits a shallow and a steep regime. Discrimination improves only slowly as more contour cycles are deformed until the point when the entire pattern is modulated, when sensitivity increases substantially. The initial shallow regime is well captured by probability summation. The increase in sensitivity when the entire pattern is modulated compared to a single cycle provides evidence for global pooling. The pattern of integration and the existence of global pooling is dependent on shape frequency. The two-part behavior is independent of shape amplitude but is only seen for low RFs (3 and 5). Data for RF20 follow the prediction of probability summation. We next investigated various stimulus characteristics and their effect on integration strength. Global pooling exceeding probability summation is evident for different pattern sizes, presentation times and for high as well as low absolute contrasts. Only if the contrasts of different fractions of a contour shape are individually scaled to match their respective visibilities is integration strength below the level of probability summation. This explains the lack of apparent global pooling in previous studies employing mixed contrasts. The marked increase in performance for discriminating completely modulated RF patterns argues in favor of highly specialized, global shape mechanisms that are seen over a wide range of stimulus configurations. The results indicate global, non-linear mechanisms, which respond most strongly when stimulated by the entire pattern and comparatively weakly when only stimulated by parts of it.

This paper presents a homogenization-based theory for three-dimensional anisotropic beams. The proposed beam theory uses a hierarchy of solutions to carefully-chosen beam problems that are referred to as the fundamental states. The stress and strain distribution in the beam is expressed as a linear combination of the fundamental state solutions and stress and strain residuals that capture the parts of the solution not accounted for by the fundamental states. This decomposition plays an important role in the homogenization process and provides a consistent method to reconstruct the stress and strain distribution in the beam in a post-processing calculation. A finite-element method is presented to calculate the fundamental state solutions. Results are presented demonstrating that the stress and strain reconstruction achieves accuracy comparable with full three-dimensional finite element computations, away from the ends of the beam. The computational cost of the proposed approach is three orders of magnitude less than the computational cost of full three-dimensional calculations for the cases presented here. For isotropic beams with symmetric cross-sections, the proposed theory takes the form of classical Timoshenko beam theory with Cowper’s shear correction factor and additional load-dependent corrections. The proposed approach provides an extension of Timoshenko’s beam theory that handles sections with anisotropic construction.

The next generation of civil transport aircraft will have larger wing spans and higher aspect ratios that enable greater aerodynamic efficiency and reduce fuel consumption relative to previous generations of aircraft. These larger wing spans lead to greater wing flexibility, making these designs more susceptible to adverse aeroelastic phenomena. Within the design process, dynamic aeroelastic constraints are frequently omitted from the preliminary design stage, leaving the possibility of costly late-stage design modifications to meet aeroelastic requirements. This paper addresses this issue by developing a method to incorporate flutter constraints within a gradient-based aeroelastic design optimization framework. We present the governing equations for the coupled aeroelastic system which forms the basis of a technique to evaluate the damping of the most-critical modes. We derive and implement an adjoint-based derivative evaluation technique to compute the gradient of the flutter constraint with respect to the design variables. The results demonstrate that the proposed technique is an effective approach for aeroelastic problems with large-scale structural models. The technique also shows promise for high-fidelity aerodynamic models that utilize computational fluid dynamics.

The goal of this paper is to develop techniques to enable the use of aeroelastic constraints within a high-fidelity design optimization framework. As a first-step towards this goal we have developed a fully-coupled aeroelastic analysis tool that includes a coupled structural and aerodynamic analysis as well as rigid-body degrees of freedom. This work departs from previous efforts in two important ways: first, we use solution techniques that are tailored for high-performance parallel computing; second, we implement a fully-coupled adjoint method using a coupled-Krylov approach for the evaluation of derivatives of time-dependent functions of interest. The coupled Newton‐Krylov approach enables us to perform simulations in the full structural space without modal reduction. The timedependent adjoint approach enables us to evaluate the gradient of functions of interest for cases with hundreds or thousands of design variables in a cost similar to the time-dependent simulation. In order to demonstrate our framework, we verify the gradient accuracy of some preliminary simulations of three transport aircraft wings with increasing span subject to gust loads.

In this paper we examine the design of metallic and composite aircraft wings in order to assess how the use of composites modifies the trade-off between structural weight and drag. In order to perform this assessment, we use a gradient-based aerostructural design optimization framework that combines a high-fidelity finite-element structural model that includes panel-level design variables with a medium fidelity aerodynamic panel method with profile and compressibility drag corrections. In order to examine the effect of the choice of the objective, we obtain a Pareto front of designs by minimizing a weighted combination of the mission fuel burn and take-off gross-weight of the aircraft over a multi-segment mission profile. The structural model includes both strength and buckling constraints and includes a detailed laminate parametrization that is used to obtain the optimal lamination stacking sequence and impose manufacturing requirements for composites including matrix-cracking and minimum ply-content constraints. We show that the composite wing designs are between 34% and 40% lighter than the equivalent metallic wings. Due to this large structural weight savings, the composite aircraft designs exhibit a fuel burn savings of between 5% and 8% and a take-off gross-weight savings of between 6% and 11%.

The purpose of this paper is to report a case of idiopathic isolated fovea plana showing asymmetry in the multifocal electroretinogram (mfERG). We carried out optical coherence tomography (OCT) imaging, macular pigment density measurement, genetic testing and electrophysiological testing with visual evoked potentials and mfERGs on a young, highly myopic female of Pakistani origin, who had good visual acuity and no nystagmus. OCT imaging revealed a complete absence of any foveal pit in either eye. Macular pigment density was normal and visual evoked potentials indicated normal chiasmal crossings, excluding albinism. Genetic testing revealed normal PAX6 coding data, excluding aniridia as a cause. mfERGs showed asymmetry consistent with off-centre fixation to the temporal side of the fovea in both eyes, but were otherwise normal. Lack of a foveal pit is a well-known finding in conditions such as oculocutaneous albinism and PAX6 gene-related aniridia. Isolated fovea plana is less common, and this case illustrates that the absence of a foveal pit does not necessarily result in a poor visual outcome. The finding of asymmetry in the mfERG in such a case is novel, and may indicate a functional adaptation to the structure of the fovea.

In this paper we present several significant improvements to both coupled solution methods and sensitivity analysis techniques for high-fidelity aerostructural systems. We consider the analysis of full aircraft configurations using Euler CFD models with more than 80 million state variables and structural finite-element models with more than 1 million degrees of freedom. A coupled Newton–Krylov solution method for the aerostructural system is presented that accelerates the convergence rate for highly flexible structures. A coupled adjoint technique is presented that can compute gradients with respect to thousands of design variables accurately and efficiently. The efficiency of the presented methods is assessed on a high performance parallel computing cluster for up to 544 processors. To demonstrate the effectiveness of the proposed approach and the developed framework, an aerostructural model based on the Common Research Model is optimized with respect to hundreds of variables representing the wing outer mold line and the structural sizing. Two separate problems are solved: one where fuel burn is minimized, and another where the maximum takeoff weight is minimized. Multi-point optimizations with 5 cruise conditions and 2 maneuver conditions are performed with a 2 million cell CFD mesh and 300 000 DOF structural mesh. The optima for problems with 476 design variables are obtained within 36 hours of wall time on 435 processors. The resulting optimal aircraft are discussed and analyze the aerostructural tradeoffs for each objective.

The focus of this paper is to introduce a proof-of-concept illustrating the integration of cost and performance as primary design drivers for structural design. Of particular interest to the aerospace industry is laminated structural design, therefore an example problem of a laminated plate structure is selected. This problem presents two primary challenges: linking cost in as general a way as possible to the design variables, and dealing with the many discrete design options available in a laminated plate. The first problem is addressed by using a theoretical cost model for advanced composite fabrication. The second problem is addressed by using a gradient based optimization algorithm and a Discrete Material Optimization (DMO) method, which is typically used in topology optimization of structures.

Studies of shape perception have typically focused on static shapes. Studies of motion perception have mainly investigated speed and direction. None have addressed performance for judging the shape of moving objects. We investigated this by determining the discrimination of geometric angles under various dynamic conditions (translation, rotation, and expansion). Angles were parts of imaginary triangles, defined by three vertex dots. Compared to static angles, results show no significant decline in the precision of angle judgments for any of the three motion types, up to speeds high enough to impair target visibility. Additional experiments provide evidence against a uniform mechanism underlying static and dynamic performance, which could rely on "snapshots" when processing moving angles. Rather, we find support for distinct mechanisms. Firstly, adding noise dots to the display affects rotating and expanding angles substantially more than those which are translating or static. Secondly, the ability to judge angles is unaffected when vertex dots are occluded for short periods. Given the dependence of dot trajectories on the overall triangle motion, the ability to precisely extrapolate the future position of a dot requires distinct computations for translating, expanding, and rotating shapes.

We have shown previously that the precision of angle judgments depends strongly on the global stimulus configuration: discrimination thresholds for angles that form part of isosceles triangles are up to 3 times lower than for those that form part of scalene triangles [Kennedy, G. J., Orbach, H. S., & Loffler, G. (2006). Effects of global shape on angle discrimination. VisionResearch, 46(8-9), 1530-1539]. Here, we investigated whether or not the perceived size of an angle (accuracy) is also affected by the overall shape of which it forms a part. Observers compared the relative sizes of angles contained in isosceles triangles with those of angles in scalene triangles and points of subjective equality were determined. For a reference angle of 60 degrees , angles embedded in isosceles triangles were judged to be on average 14 degrees larger than angles embedded in scalene triangles. This result is largely independent of the reference angle, triangle orientation and triangle size. Moreover, the effect is present whether or not triangles of different shapes enclose the same area, whether or not the side of the triangle opposite the angle is present and whether the triangle is outlined or defined by dots at its vertexes. In sum, our results provide evidence for a novel illusion where an angle embedded in an isosceles triangle is judged substantially larger than the same angle embedded in a scalene triangle. This finding demonstrates that mechanisms for computing angles are sensitive to the context within which angles are presented.

Humans manipulate objects chiefly within their lower visual field, a consequence of upright posture and the anatomical position of hands and arms.This study tested the hypothesis of enhanced sensitivity to a range of stimuli within the lower visual field. Following current models of hierarchical processing within the ventral steam, discrimination sensitivity was measured for orientation, curvature, shape (radial frequency patterns), and faces at various para-central locations (horizontal, vertical, and main diagonal meridians) and eccentricities (5° and 10°). Peripheral sensitivity was isotropic for orientation and curvature. By contrast, observers were significantly better at discriminating shapes throughout the lower visual field compared to elsewhere. For faces, however, peak sensitivity was found in the left visual field, corresponding to the right hemispheric localization of human face processing. Presenting head outlines without any internal features (e.g., eyes, mouth) recovered the lower visual field advantage found for simple shapes. A lower visual field preference for the shape of an object, which is absent for more localized information (orientation and curvature) but also for more complex objects (faces), is inconsistent with a strictly feed-forward model and poses a challenge for multistage models of object perception. The distinct lower visual field preference for contour shapes is, however, consistent with an asymmetry at intermediate stages of visual processing, which may play a key role in representing object characteristics that are particularly relevant to visually guided actions.

A method for flnding the optimal autoclave temperature history for reducing residual stresses in manufactured pre-impregnated thermosetting composites is presented. A coupled flnite element model which incorporates a thermo-chemical and incremental elastic analysis is used to predict the residual stress distribution at the edge of a thick composite beam. The optimal autoclave temperature is sought by formulating an objective function and an associated set of constraints. The objective is designed to maximize the failure load of the manufactured beam subjected to an axial force, while the constraints are imposed to ensure that the composite is uniformly cured and does not sustain temperature damage during the manufacturing process. A semi-analytic technique is presented for calculating the objective and constraint gradients. SNOPT, a powerful optimization program, is used to flnd the optimal temperature history. Typical results are presented and future lines of investigation are discussed.

A theory for laminated and sandwich beams is developed based on far-field stress and strain solutions called Fundamental State Solutions. Through-thickness stress and strain moments of the Fundamental Solutions are used to obtain homogenized axial, flexural and shear stiffness as well as a shear-strain moment correction. A sequence of beam models with similarity to the Timoshenko model are obtained. Excellent agreement is shown for all stress and strain components when compared to accurate two-dimensional finite element results.

Precortical vision is mediated by three opponent mechanisms that combine receptoral outputs to form a luminance channel (L + M) and two chromatic channels, red-green (L/M) and blue-yellow (S/L + M). Here we ask the extent to which these basic color opponent mechanisms interact in the phenomenon of crowding, where nearby targets interfere with the processing of a central test target. The task was to identify the orientation of a Gabor patch while an annular plaid surrounded the patch. The radius of the annulus was varied in order to produce different separations of the test and flanker. The chromatic content of the Gabor and the annulus could be varied independently along the (L + M), (L/M), and (S/L + M) cardinal axes. For all targets, when the target and flanker shared the same chromaticity, performance decreased with decreasing separation of the target and annulus, i.e., a typical crowding effect was seen. When the test and flanker isolated different chromatic mechanisms, very little crowding was observed, even at the minimum separation of test target and annulus. In addition to this, intermediate chromaticities were found to produce intermediate levels of crowding. Finally, crowding effects using "half-wave rectified" stimuli suggest a locus for crowding effects beyond the level of color opponent mechanisms.

Previous studies have been inconclusive as to whether angle discrimination performance can be predicted by the sensitivity of orientation discrimination mechanisms or by that of mechanisms specialised for angle coding. However, these studies have assumed that angle discrimination is independent of the shape of the object of which the angle is a part. This assumption was tested by measuring angle discrimination using angles that were parts of different triangular shapes. Angle discrimination thresholds were lowest when angles were presented in isosceles triangles (sides forming the angle were of identical length). Performance was significantly poorer when angles were presented in scalene triangles (sides of different lengths) and as much as three times worse when the sides forming the angle varied randomly in length between presentations. Comparing orientation discrimination for single lines with angle discrimination for different stimulus conditions (isosceles, scalene and random triangles) leads to conflicting conclusions as to the mechanisms underlying angle perception: line orientation sensitivity correctly predicts angle discrimination for random triangles, but underestimates angle acuity for isosceles triangles. The fact that performance in angle discrimination tasks is strongly dependant on the overall stimulus geometry implies that geometric angles are computed by mechanisms that are sensitive to global aspects of the stimulus.