145 research outputs found
Random geometric graphs with general connection functions
No full textSpatially Embedded Networks is an EPSRC funded project, EP/N002458/1, linked to a project in Oxford EP/N002350/1. It involves exploring mathematical and network properties random graphs in which the nodes are located in space, with application to wireless communications. These data files are for Figs 4-6 of the paper "Random geometric graphs with general connection functions" C. P. Dettmann and O. Georgiou
Distributed Synchronization on Weakly Connected Networks
No full textDistributed synchronization for wireless networks is based on the mutual exchange of the same chirp-signature by nodes. Collisions of these signatures drive the system toward time and (carrier) frequency synchronization using distributed consensus algorithms. This letter investigates the convergence and the asymptotic distortion properties on noisy networks when neighboring clusters of nodes are weakly connected to each other only through a subset of nodes and bridging links. These heavily connected clusters act as macroagents, and the consensus properties of the ensemble depend on the number of bridge links between them. The convergence rate and mean square synchronization deviation are derived as functions of the number of bridge links for different examples of weakly connected noisy networks via the analytic calculation of Laplacian spectra. Our approach facilitates the study of network topology optimization for distributed synchronization
Transdermal delivery of insulin across human skin in vitro with 3D printed hollow microneedles
No full textIn the current study hollow microneedles (HMNs) were fabricated by means of vat polymerization method for the transdermal delivery of insulin. Two geometries of HMNs were designed in a Computer Aided Design (CAD) software namely, curved pyramid and syringe-like and fabricated with Liquid Crystal Display (LCD) method. Dimensions were determined and quality features were imaged with scanning electron microscopy (SEM). Volumetric characterization of HMNs and microchannels was performed by microfocus computed tomography (μCT) whereas mechanical characterization and skin penetration tests of the two geometries were carried out both experimentally and by Finite Element Analysis (FEA) simulation. Diffusion studies of insulin across full thickness human skin were performed in vitro using Franz diffusion cells. Insulin samples were analyzed with liquid chromatography-mass spectrometry (LC-MS). The results show that the transport might be affected by the shape of the microneedles
Isolation statistics in temporal spatial networks
No full textThe reliability and robustness of infrastructure networks are important problemsrequiring network models with nodes at fixed locations and links that break and reform with time. These temporal spatial networks are however difficult to analyse and understand due to the coexistence of short and long range links and inherent temporal correlations. We provide a mathematically tractable framework to analytically study the isolation statistics responsible for disconnecting spatial networks. Small-world effects and temporal correlations are also incorporatedin our framework as we investigate the distribution of the time needed for information packets to be able to reach the whole network
Transmission and reflection in the stadium billiard: Time-dependent asymmetric transport
No full textThe survival probability of the open stadium billiard with one hole on its boundary is well known to decay asymptotically as a power law. We investigate the transmission and reflection survival probabilities for the case of two holes placed asymmetrically. Classically, these distributions are shown to lose their algebraic decay tails depending on the choice of injecting hole, therefore exhibiting asymmetric transport. The mechanism behind this is explained while exact expressions are given and confirmed numerically. We propose a model for experimental observation of this effect using semiconductor nanostructures and comment on the relevant quantum time scales.</p
Sunflower hard disk graphs
No full textThe random geometric graph consists of a random point set with links between points with mutual distance below a fixed threshold. Here, we use the same geometric connection rule (“hard disk graph”) but for a deterministic point set, the sunflower spiral. At large distances, the local structure is asymptotically a lattice where for each lattice vector, there is another of length a factor√5 greater, and the angle between these varies log-periodically with distance from the origin. Graph properties including node degrees, stretch factor, clique and chromatic numbers are considered, as well as link formation, connectivity and planarity transitions. Properties depend on a combination of the central region and the perturbed distant lattices, in a rich and varied manner
Quantifying intermittency in the open drivebelt billiard
No full textA "drivebelt" stadium billiard with boundary consisting of circular arcs of differing radius connected by their common tangents shares many properties with the conventional "straight" stadium, including hyperbolicity and mixing, as well as intermittency due to marginally unstable periodic orbits (MUPOs). Interestingly, the roles of the straight and curved sides are reversed. Here, we discuss intermittent properties of the chaotic trajectories from the point of view of escape through a hole in the billiard, giving the exact leading order coefficient lim(t) (,infinity) tP(t) of the survival probability P(t) which is algebraic for fixed hole size. However, in the natural scaling limit of small hole size inversely proportional to time, the decay remains exponential. The big distinction between the straight and drivebelt stadia is that in the drivebelt case, there are multiple families of MUPOs leading to qualitatively new effects. A further difference is that most marginal periodic orbits in this system are oblique to the boundary, thus permitting applications that utilise total internal reflection such as microlasers. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3685522]</p
Solar tracking of perovskite-silicon tandem PV modules under real-world conditions
No full textIncreasing the energy yield per unit area of Photovoltaic (PV) modules is one of the main challenges the PV technology is currently facing. In search of ways to address this issue, solar tracking systems are a favorable solution, which according to literature can enhance the energy yield by up to 45%. Another way is to opt for high-efficiency solar cells. Tandem cells have emerged as a promising technology, achieving efficiencies of over 30%. The integration of these tandem cells with sun-tracking techniques suggests high-performing solar modules. The present work develops a solar tracking model to simulate the performance of tracking PV systems equipped with tandem modules. The model will be incorporated into the PVMD toolbox, a PV modeling software developed within the PVMD group. This software can predict the energy yield of PV systems using self-consistent models for each aspect of the energy conversion.The current version of the toolbox makes it impractical to include solar tracking due to the time-consuming nature of ray tracing used to compute the irradiance. Ray tracing generates sensitivity values that illustrate how sensitive is the module to incoming irradiance from any direction in the skydome. Initially, this work focuses on substituting ray tracing with an alternative faster approach to express sensitivity based on view factors. The view factor and ray tracing method are compared with respect to computational time and extent of agreement. It was found that the view factor can significantly reduce the computational time from over 12 minutes, as required in ray tracing, to a few milliseconds for a single module orientation. Additionally, the view factor method generates sensitivity values closely matching those from ray tracing. For instance, a mean RMSE of 1.2% between the two methods is achieved, for an albedo of 0.2 and module tilt of 30 degrees. Sun tracking aims to locate the module orientation that maximizes the in-plane irradiance. Directly calculating the irradiance for every orientation to identify the optimal, is not a viable option, as it requires substantialtime. Thus, sun tracking was expressed as an optimization problem and algorithms were employed to address it. Based on the prevailing sky conditions three optimization case studies were defined on an hourly basis: sunny, cloudy, and intermediate hours. Multiple algorithms were compared across the three cases with selected criteria the convergence to the optimum and runtime. Matlab’s surrogate solver and an author-developed algorithm were selected, as a satisfying solution, compromising those two criteria.Finally, energy yield simulations were performed on perovskite-silicon tandem modules mounted on a dual-axis tracking system. Four locations were selected, representing different real-world conditions: Stockholm, Athens, Bombay and Bogota. Results show the module’s tilt dynamic adaptability to sky conditions: increas- ing nearly to the sun’s zenith when direct light dominates, and lowering when diffuse light is prevalent. Furthermore, the seasonal fluctuations of the energy gain of tracking systems are explored, with locations further from the equator such as Stockholm exhibiting the highest variability of 19% in winter to 36.9% in summer. In addition, the annual energy gained among the locations was found to span between 24.8% (Bogota) and 34.1% (Bombay). An important finding is the direct proportionality in gains from absorbed irradiance to DC and AC yields, illustrating a 1:1:1 ratio. Then, the effect of tracking technology on mismatch losses of tandem modules was examined. Results indicated that tracking has little impact on both the current and power mismatch. For example, the power mismatch losses slightly increased from 1.10-1.46% in static PV systems to 1.29-1.77% for tracking topologies in the locations examined. Moreover, the tandem’s annual energy gain is compared to silicon heterojunction modules. The analysis showed similar gains across locations for both cell technologies.Electrical Engineering | Sustainable Energy Technolog
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