MRC Laboratory of Molecular Biology
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Self-healing of cracks in mortars using novel PVA-coated pellets of different expansive agents
No full textThe potential for fine aggregates, a basic constituent of any mortar or concrete mix, has not been sufficiently exploited in developing self-healing systems. This paper investigates the self-healing capability of mortar mixes that contain polymeric coated pellets containing several potential self-healing agents. The pellets replaced 10% of the sand by weight in mortar mixtures and mortar prisms were pre-cracked up to 0.3 mm crack width at seven days. It was demonstrated through microscopy and ultrasonic observations that the addition of the coated pellets resulted in an improvement of the crack mouth and depth sealing by ~ 20–60% over and above the healing observed in the control samples. Water sorptivity and gas permeability tests confirmed the capability of the formed healing products through the use of the pellets in preventing the ingress of water, gas and/or deleterious liquids. In addition, the samples containing the pellets showed a considerable regain of flexural strength and stiffness after two rounds of water curing of the cracked samples. The significant contribution of pellets in forming the healing products in the crack volume was clear from the microstructural analyses conducted
Supporting multi-point fan design with dimension reduction
No full textMotivated by the idea of turbomachinery active subspace performance maps, this paper studies dimension reduction in turbomachinery 3D CFD simulations. First, we show that these subspaces exist across different blades-under the same parametrisation-largely independent of their Mach number or Reynolds number. This is demonstrated via a numerical study on three different blades. Then, in an attempt to reduce the computational cost of identifying a suitable dimension reducing subspace, we examine statistical sufficient dimension reduction methods, including sliced inverse regression, sliced average variance estimation, principal Hessian directions and contour regression. Unsatisfied by these results, we evaluate a new idea based on polynomial variable projection-a non-linear least-squares problem. Our results using polynomial variable projection clearly demonstrate that one can accurately identify dimension reducing subspaces for turbomachinery functionals at a fraction of the cost associated with prior methods. We apply these subspaces to the problem of comparing design configurations across different flight points on a working line of a fan blade. We demonstrate how designs that offer a healthy compromise between performance at cruise and sea-level conditions can be easily found by visually inspecting their subspaces
Experimental and numerical study on soot formation in laminar diffusion flames of biodiesels and methyl esters
No full textBiodiesel and blends with petroleum diesel are promising renewable alternative fuels for engines. In the present study, the soot concentration generated from four biodiesels, two pure methyl esters, and their blends with petroleum diesel are measured in a series of fully pre-vapourised co-flow diffusion flames. The experimental measurements are conducted using planar laser induced-incandescence (LII) and laser extinction optical methods. The results show that the maximum local soot volume fractions of neat biodiesels are 24.4% - 41.2% of pure diesel, whereas the mean soot volume fraction of neat biodiesel cases was measured as 11.3% - 21.3% of pure diesel. The addition of biodiesel to diesel not only reduces the number of inception particles, but also inhibits their surface growth. The discretised population balance modelling of a complete set of soot processes is employed to compute the 2D soot volume fraction and size distribution across the tested flames. The results show that the model also demonstrates a reduction of both soot volume fraction and primary particle size by adding biodiesel fuels. However, it is not possible to clearly determine which factors are responsible for the reduction from the comparison alone. Moreover, analysis of the discrepancies between numerical and experimental results for diesel and low-blending cases offers an insight for the refinement of soot formation modelling of combustion with large-molecule fuels
Singularities and Moments of Nonlinear Systems
No full textThe notions of eigenvalue, pole and moment at a pole of a continuous-time, nonlinear, time-invariant system are studied. Eigenvalues and poles are first characterized in terms of invariant subspaces. Tools from geometric control theory are used to define nonlinear enhancements of these notions and to study their relationship with the solution of certain partial differential equations, cascade decompositions and steady-state impulse responses. The theory is illustrated by means of worked-out examples and its significance is demonstrated by solving the model reduction problem by moment matching at poles for nonlinear systems
Active metamaterial polarization modulators for the Terahertz frequency range
No full textActive control of chirality in the terahertz frequency range is of great importance in many scientific areas, which include research into fundamental optical phenomena, investigation of novel materials, spectroscopy, imaging, wireless communications and chemistry. The lack of efficient, integrated and fast-reconfigurable polarization modulators has hindered, so far, the full exploitation of applications in all the aforementioned fields. Metamaterials are artificial resonant elements possessing unique remarkable properties such as high efficiency and miniaturization capability. The interplay of metallic metamaterial arrays with electrostatically tunable monolayer graphene has been demonstrated to be a valid approach for the realization of a novel class of THz devices. In this work, the realization of active chiral graphene/metamaterial modulator is presented. The versatility of this experimental approach allowed the device integration with broadband sources such as terahertz time domain spectrometers as well as with quantum cascade lasers. A continuous rotation of the polarization plane > 30° has been reported with a reconfiguration speed > 5 MHz. These results pave the way to the integration of fast terahertz polarization modulators in all the applications where these devices are in great demand
Simultaneous two-phase flame velocity measurement using laser-induced incandescence particle image velocimetry (LII-PIV)
No full textIn a previous study we demonstrated a novel two-phase PIV technique based on the laser-induced incandescence (LII) signal from black submicron tungsten carbide particles (WC), which achieved velocity measurement for both dispersed-form (large water droplet) and continuous-form (gas). Submicron WC particles are intentionally seeded into a two-phase flow, and heated by a light sheet generated by a doublepulsed PIV laser running at high energy. The 200 nm diameter, light absorbing WC particles are heated to several thousand degrees to emit strong incandescence signals, whilst the temperature rise in liquid droplets or large particles remains negligible. The small particles follow the gas phase flow, unlike the droplets which may have a di↵erent velocity. Droplets are detected via the Mie scatter signal at the same incident wavelength, whereas the LII signal from small WC particles is detected at a suitably di↵erent wavelength within the LII emission spectrum, thus allowing discrimination of velocities between phases. The LII-PIV technique had been implemented with a low-speed CCD PIV camera in non-reacting flows. In flames, the strong flame luminosity saturated the second frame due to the long exposure time as the characteristics of the device. To solve this problem, in the present study, we synchronized two high-speed CMOS cameras to a low speed laser. One records the LII signal and the other records the Mie scatter signal from 36.6 μm water droplets. The scattering from WC particles appears only as a weak background signal in the Mie image, which can be easily removed by applying a high-pass filter. Simultaneous velocity measurements for both gas and liquid phase are demonstrated in an air jet, a cold impinging flow, and finally in a Bunsen flame. The last two cases are repeated using the traditional two-phase PIV technique based on image segmentation so as to conduct a fair comparison of both techniques. We show that LII-PIV can achieve the same level of accuracy as the segmentation method in non-reacting flows, and can be applied to measure in flames with two-phase flows with less stringent requirements regarding seeding quality
Bistability and simultaneous mode actuation in electrostatically actuated initially curved coupled micro beams
No full textThe symmetric snap-through response of a bistable structure, composed from two beams, coupled via a rigid truss at their midpoint, is studied when subjected to a distributed electrostatic load. Both beams are double clamped and initially curved. The analysis is based on a reduced order (RO) model, resulting from Galerkin's decomposition. For the base functions, symmetric buckling modes are used for either beam. The results of the RO model are compared with results obtained via finite differences (FD) solutions, to validate the approximation to the original differential formulation, and a finite element (FE) model. Specifically, FE analysis was used as a reference under “mechanical” displacement-independent load, facilitating the usage of solutions extracted via FD for validation of the model under electrostatic, displacement-dependent, load. All solutions employed the usage of the arc-length “Riks” method to accommodate swerving equilibrium paths. To enable a broader approach, the two beams may have different initial elevations. The study indicates that a model with at least three degrees of freedom (DOF) is needed to depict an equilibrium path, for either load. For reliably quantitative equilibrium curves, a model with a minimum of five DOF was found to be necessary. The presented results also indicate that a double curved beam structure can attain actuation of several modes simultaneously, while demonstrating snap-through at reasonable voltages. In so doing, the model suggests that such a construct can be feasible for usage in various applications
Wirelessly controlled, bioresorbable drug delivery device with active valves that exploit electrochemically triggered crevice corrosion
No full textImplantable drug release platforms that offer wirelessly programmable control over pharmacokinetics have potential in advanced treatment protocols for hormone imbalances, malignant cancers, diabetic conditions, and others. We present a system with this type of functionality in which the constituent materials undergo complete bioresorption to eliminate device load from the patient after completing the final stage of the release process. Here, bioresorbable polyanhydride reservoirs store drugs in defined reservoirs without leakage until wirelessly triggered valve structures open to allow release. These valves operate through an electrochemical mechanism of geometrically accelerated corrosion induced by passage of electrical current from a wireless, bioresorbable power-harvesting unit. Evaluations in cell cultures demonstrate the efficacy of this technology for the treatment of cancerous tissues by release of the drug doxorubicin. Complete in vivo studies of platforms with multiple, independently controlled release events in live-animal models illustrate capabilities for control of blood glucose levels by timed delivery of insulin