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Understanding the mechanical effects of smooth muscle cell (SMC) contraction on the initiation and the propagation of cardiovascular diseases such as aortic dissection is critical. Framed by elastic lamellar sheets in the lamellar unit, there are SMCs in the media with a distinct radial tilt, which indicates their contribution to the radial strength. However, the mechanical effects of this type of anisotropy have not been fully discussed. Therefore, in this study, we propose a constitutive framework that models the passive and active mechanics of the aorta, taking into account the dispersed nature of the aortic constituents by applying the discrete fibre dispersion method. We suggest an isoparametric approach by evaluating various numerical integration methods and introducing a non-uniform discretization of the unit hemisphere to increase its computational efficiency. Finally, the constitutive parameters are fitted to layer-specific experimental data and initial computational results are briefly presented. The radial tilt of SMCs is also analysed, which has a noticeable influence on the mechanical behaviour of the aorta. In the absence of sufficient experimental data, the results indicate that the active contribution of SMCs has a remarkable impact on the mechanics of the healthy aorta.

Detailed fibre architecture plays a crucial role in myocardial mechanics both passively and actively. Strong interest has been attracted over decades in mathematical modelling of fibrous tissue (arterial wall, myocardium, etc.) by taking into account realistic fibre structures, i.e. from perfectly aligned one family of fibres, to two families of fibres, and to dispersed fibres described by probability distribution functions. It is widely accepted that the fibres, i.e. collage, cannot bear the load when compressed, thus it is necessary to exclude compressed fibres when computing the stress in fibrous tissue. In this study, we have focused on mathematical modelling of fibre dispersion in myocardial mechanics, and studied how different fibre dispersions affect cardiac pump function. The fibre dispersion in myocardium is characterized by a non-rotationally symmetric distribution using a π -periodic Von Mises distribution based on recent experimental studies. In order to exclude compressed fibres for passive response, we adopted the discrete fibre dispersion model for approximating a continuous fibre distribution with finite fibre bundles, and then the general structural tensor was employed for describing dispersed active tension. We first studied the numerical accuracy of the integration of fibre contributions using the discrete fibre dispersion approach, then compared different mechanical responses in a uniaxially stretched myocardial sample with varied fibre dispersions. We finally studied the cardiac pump functions from diastole to systole in two heart models, a rabbit bi-ventricle model and a human left ventricle model. Our results show that the discrete fibre model is preferred for excluding compressed fibres because of its high computational efficiency. Both the diastolic filling and the systolic contraction will be affected by dispersed fibres depending on the in-plane and out-of-plane dispersion degrees, especially in systolic contraction. The in-plane dispersion seems affecting myocardial mechanics more than the out-of-plane dispersion. Despite different effects in the rabbit and human models caused by the fibre dispersion, large differences in pump function exist when fibres are highly dispersed at in-plane and out-of-plane. Our results highlight the necessity of using dispersed fibre models when modelling myocardial mechanics, especially when fibres are largely dispersed under pathological conditions, such as fibrosis.

There is a desire to overlay future optical access networks onto legacy passive optical networks (PONs) to provide increasingly advanced services by filling empty wavelength bands of legacy gigabit rate PONs. Nonlinear Raman crosstalk from new wavelengths onto legacy RF video services (1550–1560 nm band) and onto the legacy digital downstream at 1490 nm, however, can limit the number and the launch power of new wavelengths. As an example, straightforward physical-layer adjustments at the optical line terminal that increase the number of new, 10 Gbit/s channels launched in the 1575–1580 nm band by a factor of 16 without increasing the Raman penalty on the video signal are illustrated. A physical-layer (RF) filter modifies the on–off-keyed signal feeding each 10 Gbit/s transmitter, suppressing the RF Raman crosstalk on the video signal by 9 dB while incurring a power penalty on each 10 Gbit/s link of <0.5 (2.0) dB with (without) forward error correction. The previous Raman mitigation work used non-standard line-coding to shape the 10 Gbit/s electrical spectrum. In addition, polarisation-interleaving of new wavelengths lowers the worst-case RF DC crosstalk by ∼3 dB in fibres and it limits and stabilises DC crosstalk in low polarisation mode dispersion fibre links.

Collagen fibres within fibrous soft biological tissues such as artery walls, cartilage, myocardiums, corneas and heart valves are responsible for their anisotropic mechanical behaviour. It has recently been recognized that the dispersed orientation of these fibres has a significant effect on the mechanical response of the tissues. Modelling of the dispersed structure is important for the prediction of the stress and deformation characteristics in (patho)physiological tissues under various loading conditions. This paper provides a timely and critical review of the continuum modelling of fibre dispersion, specifically, the angular integration and the generalized structure tensor models. The models are used in representative numerical examples to fit sets of experimental data that have been obtained from mechanical tests and fibre structural information from second-harmonic imaging. In particular, patches of healthy and diseased aortic tissues are investigated, and it is shown that the predictions of the models fit very well with the data. It is straightforward to use the models described herein within a finite-element framework, which will enable more realistic (and clinically relevant) boundary-value problems to be solved. This also provides a basis for further developments of material models and points to the need for additional mechanical and microstructural data that can inform further advances in the material modelling.

The authors present numerical simulations of ultrashort pulse generation by a technique of linear spectral broadening in phase modulators and compression in dispersion compensating fibre, followed by a further stage of soliton compression in dispersion shifted fibre. This laser system is predicted to generate pulses of 140 fs duration with a peak power of 1.5 kW over a wide, user selectable repetition rate range while maintaining consistent characteristics of stability and pulse quality. The use of fibre compressors and commercially available modulators is expected to make the system setup compact and cost-effective.

The great potential of computational diffusion MRI (dMRI) relies on indirect inference of tissue microstructure and brain connections, since modelling and tractography frameworks map diffusion measurements to neuroanatomical features. This mapping however can be computationally highly expensive, particularly given the trend of increasing dataset sizes and the complexity in biophysical modelling. Limitations on computing resources can restrict data exploration and methodology development. A step forward is to take advantage of the computational power offered by recent parallel computing architectures, especially Graphics Processing Units (GPUs). GPUs are massive parallel processors that offer trillions of floating point operations per second, and have made possible the solution of computationally-intensive scientific problems that were intractable before. However, they are not inherently suited for all problems. Here, we present two different frameworks for accelerating dMRI computations using GPUs that cover the most typical dMRI applications: a framework for performing biophysical modelling and microstructure estimation, and a second framework for performing tractography and long-range connectivity estimation. The former provides a front-end and automatically generates a GPU executable file from a user-specified biophysical model, allowing accelerated non-linear model fitting in both deterministic and stochastic ways (Bayesian inference). The latter performs probabilistic tractography, can generate whole-brain connectomes and supports new functionality for imposing anatomical constraints, such as inherent consideration of surface meshes (GIFTI files) along with volumetric images. We validate the frameworks against well-established CPU-based implementations and we show that despite the very different challenges for parallelising these problems, a single GPU achieves better performance than 200 CPU cores thanks to our parallel designs. •The computational power offered by GPUs is used to accelerate the analysis of dMRI.•We present a generic and flexible parallel framework for microstructure modelling on GPUs.•And also a framework for performing probabilistic tractography and generating connectomes on GPUs.•A single GPU achieves better performance than 200 CPU cores with our frameworks.

In this paper, comprehensive analyses of triple-clad fibers are presented. The geometry of multiple-clad fibers has been considered as a four-layer cylindrical structure. The geometry consists of a core and three claddings. We have analyzed and compared different types of triple-clad refractive index profiles on the basis of dispersion, mode distribution and propagation constant. To enhance the optical characteristics of these three fibers, we have developed a combined formulation which is applicable for single-clad, double clad and triple-clad optical fibers. In optical fibers, two or more claddings are required for dispersion shifting, dispersion flattening and other specialized applications. Thus, an analysis of design dispersion-shifted, dispersion-flattened and dispersion-compensated fibers is presented. We have used a boundary match method for evaluating propagation wave vectors and guided modes.

This paper estimates transmission coefficient at the splice of single-mode dispersion shifted trapezoidal and dispersion flattened graded and step W fibers in presence as well as in absence of Kerr nonlinearity. We restrict our analysis for both angular and transverse offsets only since splices are highly tolerant in respect of longitudinal mismatch. Here, we apply method of iteration involving Chebyshev formalism in order to take care of Kerr nonlinearity. The concerned investigation requires very little computation. It has been shown that our results match excellently with the exact results both in absence as well as in presence of Kerr nonlinearity. Considering that prediction of exact results in presence of Kerr nonlinearity requires application of rigorous finite element technique, our formalism in this context can be treated as a simple alternative to the existing method. Thus, this user friendly method generates ample scope for many useful applications in the field of nonlinear photonics involving such kinds of fiber.

A new technique is presented for computing very useful propagation parameters like effective core area and effective index of refraction of mono-mode dispersion shifted and dispersion flattened fibers both in the presence and in the absence of Kerr nonlinearity. The technique involves application of accurate but simple expressions for modal fields developed by Chebyshev formalism. The study of the influence of Kerr nonlinearity on the aforementioned parameters, however, requires the application of the method of iteration. For the purpose of such investigation, in linear as well as nonlinear region, we take some typically used dispersion shifted and dispersion flattened fibers and we show that the results found by our simple formalism are in excellent agreement with those obtained by using complex finite element method. Further, the necessary evaluation by our simple method needs very less computations. Thus, our formalism generates ample opportunity for applications in many areas in the field of nonlinear optics.

The first experimental demonstration of a continuous-wave dual-pump fibre optical parametric amplifier operating near 1 µm is reported. A flat gain band of 23 dB spanning over 16 nm (4.5 THz) with <2 dB variation is reported. This fibre optical parametric amplifier is achieved with a dispersion stabilised microstructured optical fibre having a high figure of merit, i.e. high nonlinearity and low loss.