A Numerical Model for Random Fibre Networks

Modelling a random fibre network representative of a real world material leads to a large sparse linear matrix system with a high condition number. Current off-lattice networks are not a realistic model for the mechanical properties of the large volume of random fibres seen in actual materials. In this paper, we present the numerical methods employed within our two-dimensional and three-dimensional models that improve the computational time limitations seen in existing off-lattice models. Specifically, we give a performance comparison of two-dimensional random fibre networks solved iteratively with different choices of preconditioner, followed by some initial results of our three-dimensional model

Equivalent random analysis of a buffered optical switch with general interarrival times

We propose an approximate analytic model of an optical switch with fibre delay lines and wavelength converters by employing Equivalent Random Theory. General arrival traffic is modelled by means of Gamma-distributed interarrival times. The analysis is formulated in terms of virtual traffic flows within the optical switch from which we derive expressions for burst blocking probability, fibre delay line occupancy and mean delay. Emphasis is on approximations that give good numerical efficiency so that the method can be useful for formulating dimensioning problems for large-scale networks. Numerical solution values from the proposed analysis method compare well with results from a discrete-event simulation of an optical burst switch

Computational Modelling of the Mechanical Properties of Elastic Fibre Networks

From everyday items such as paper, felt and nappies, to sophisticated biological structures such as mammalian cytoskeletons and the collagen of extracellular matrices, many materials are made up of complex disordered fibre networks with varying microstructures. It is often important to tune the mechanical properties of such networks for their specific application. The macroscopic network response to an applied load can be controlled by modifying the properties of component fibres at the microscopic level. A model relating the properties at these two scales is desirable for the design and fabrication of better materials. We developed a numerical code predicting the mechanical properties of 2D and 3D elastic fibre networks. Specifically, we find an efficient solution of the linear matrix system obtained from a large system of equations, representing a given random fibre network in mechanical equilibrium with an applied linear shear at the network boundary. This global system is assembled by considering the individual contributions of fibres modelled as cross-linked slender elastic rods, and then solved to obtain a prediction of the network displacement and total elastic energy for the applied shear. To study various network architectures, we also developed another code for network generation and visualisation. Using our software, we analysed the numerical performance of preconditioners for the iterative methods used to solve the linear system. This was applied to systems representing established 2D networks, and investigated the mechanical properties of layered 3D and fully 3D disordered systems. Our choices of preconditioners were motivated by exploiting the distinct block structure of our assembled matrix. Drawing from the application of needlepunched nonwoven fabrics, we designed a series of novel networks consisting of random 2D Mikado cross-linked layers. Applying our numerical model, we were able to explore the effects of material anisotropy on shear response, and provide a first analysis of how the macroscopic mechanics are driven by variations in microscopic properties. Evidence was also presented that our software can be used to model the mechanical properties of fully 3D random fibre networks under imposed macroscopic shear. This work can be used to direct future research, and offers the opportunity to model 3D fibrous materials using a geometry generated differently to many related works - in terms of both cross-linking procedure and cross-link type variability. The final outcome of this work is a reusable piece of software for modelling the mechanical properties of elastic fibre networks with various geometries under a macroscopically applied shear. Through use of numerical techniques and integration with the PETSc library [4], we solve the resulting systems of these networks effectively and within reasonable time scales, with the opportunity of additional optimisation if further work were to be carried out

Modeling cell movement in anisotropic and heterogeneous network tissues

Cell motion and interaction with the extracellular matrix is studied deriving a kinetic model and considering its diffusive limit. The model takes into account of chemotactic and haptotactic effects, and obtains friction as a result of the interactions between cells and between cells and the fibrous environment. The evolution depends on the fibre distribution, as cells preferentially move along the fibre direction and tend to cleave and remodel the extracellular matrix when their direction of motion is not aligned with the fibre direction. Simulations are performed to describe the behavior of ensemble of cells under the action of a chemotactic field and in presence of heterogeneous and anisotropic fibre networks

Strain-controlled criticality governs the nonlinear mechanics of fibre networks

Disordered fibrous networks are ubiquitous in nature as major structural components of living cells and tissues. The mechanical stability of networks generally depends on the degree of connectivity: only when the average number of connections between nodes exceeds the isostatic threshold are networks stable (Maxwell, J. C., Philosophical Magazine 27, 294 (1864)). Upon increasing the connectivity through this point, such networks undergo a mechanical phase transition from a floppy to a rigid phase. However, even sub-isostatic networks become rigid when subjected to sufficiently large deformations. To study this strain-controlled transition, we perform a combination of computational modeling of fibre networks and experiments on networks of type I collagen fibers, which are crucial for the integrity of biological tissues. We show theoretically that the development of rigidity is characterized by a strain-controlled continuous phase transition with signatures of criticality. Our experiments demonstrate mechanical properties consistent with our model, including the predicted critical exponents. We show that the nonlinear mechanics of collagen networks can be quantitatively captured by the predictions of scaling theory for the strain-controlled critical behavior over a wide range of network concentrations and strains up to failure of the material

A nanophotonic laser on a graph

Conventional nano-photonic schemes minimise multiple scattering to realise a miniaturised version of beam-splitters, interferometers and optical cavities for light propagation and lasing. Here instead, we introduce a nanophotonic network built from multiple paths and interference, to control and enhance light-matter interaction via light localisation. The network is built from a mesh of subwavelength waveguides, and can sustain localised modes and mirror-less light trapping stemming from interference over hundreds of nodes. With optical gain, these modes can easily lase, reaching $\sim$100 pm linewidths. We introduce a graph solution to the Maxwell's equation which describes light on the network, and predicts lasing action. In this framework, the network optical modes can be designed via the network connectivity and topology, and lasing can be tailored and enhanced by the network shape. Nanophotonic networks pave the way for new laser device architectures, which can be used for sensitive biosensing and on-chip optical information processing

Isu dan masalah sink hole terhadap penyelenggaraan jalan raya di Johor Bahru

Penyelenggaraan jalan adalah satu proses kerja-kerja yang terlibat bagi tujuan mengekalkan keadaan jalan seperti keadaan asalnya dari segi ciri-ciri geometri dan juga kekuatan strukurnya (Salleh, 2011). Selain itu, penyelenggaraan jalan merupakan kerja-kerja menjaga dan memperelokkan jalan dan bahagian-bahagian jalan yang telah siap dibina. Penyelenggaraan jalan juga melibatkan lain- lain struktur binaan yang terdapat pada jalan raya dan jalan yang mengalami kadar kerosakan yang bermula setelah siap dibina dan mula digunakan. Kerja-kerja penyelenggaraan dijalankan bagi mengawal kerosakan, menjamin jalan yang dibina boleh mencapai jangka hayat yang lama, menjaga jalan raya untuk kegunaan trafik dan memperbaiki perjalanan sistem trafik (JKR, 2009)

Transmission of natural scene images through a multimode fibre

The optical transport of images through a multimode fibre remains an outstanding challenge with applications ranging from optical communications to neuro-imaging. State of the art approaches either involve measurement and control of the full complex field transmitted through the fibre or, more recently, training of artificial neural networks that however, are typically limited to image classes belong to the same class as the training data set. Here we implement a method that statistically reconstructs the inverse transformation matrix for the fibre. We demonstrate imaging at high frame rates, high resolutions and in full colour of natural scenes, thus demonstrating general-purpose imaging capability. Real-time imaging over long fibre lengths opens alternative routes to exploitation for example for secure communication systems, novel remote imaging devices, quantum state control processing and endoscopy

BER and outage probability of DPSK subcarrier intensity modulated free space optics in fully developed speckle.

In this paper a differential phase shift keying (DPSK) subcarrier intensity modulated (SIM) free space optical (FSO) link is considered in negative exponential atmospheric turbulence environment. To mitigate the scintillation effect, the selection combining spatial diversity scheme (SelC) is employed at the receiver. Bit error rate (BER) and outage probability (Pout) analysis are presented with and without the SelC spatial diversity. It is shown that at a BER of 10-6, a maximum diversity gain 25 dB is predicted. And about 60 dBm signal power is required to achieve an outage probability of 10-6, based on a threshold BER of 10-4