MRC Laboratory of Molecular Biology
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The in-plane elastic-plastic response of an incompressible, filled hexagonal honeycomb
No full textExact solutions are derived for the small-strain, in-plane, elasto-plastic response of a hexagonal honeycomb using slender beam theory; incompressibility of the honeycomb is enforced by filling its voids with an incompressible, inviscid fluid. The honeycomb has sides of equal length, but its inclined struts subtend an angle that can deviate from 120° with respect to the vertical side walls. The relative density is sufficiently small that the struts are slender and can be treated as Euler-Bernoulli beams. Exact solutions are obtained for the elastic moduli and macroscopic yield surface of the rigid, ideally plastic lattice under general in-plane loading: the solutions satisfy equilibrium, compatibility and the constitutive response of each elastic, ideally plastic beam. Prior to conducting an elastic analysis, and a rigid, ideally plastic analysis, initial insight is gained by exploring the vector space of inextensional collapse mechanisms of the pin-jointed, compressible version of the hexagonal truss. Two inextensional collapse mechanisms of the compressible honeycomb are identified from the null space of the kinematic matrix. The presence of an incompressible, inviscid fluid in the voids of the honeycomb locks-up one mechanism but the other mechanism survives and generates macroscopic shear strain. Consequently, the incompressible hexagonal honeycomb with rigid joints has a high shear compliance and a low shear strength, with values equal to that of the unfilled, compressible honeycomb. In contrast, macroscopic tensile straining of the incompressible honeycomb requires the stretching of bars in addition to bar-bending, and the tensile modulus and strength of the incompressible honeycomb are thereby elevated. Explicit analytical formulae are derived for the macroscopic tensile modulus and strength of the incompressible honeycomb
Mechanochromic, Structurally Colored, and Edible Hydrogels Prepared from Hydroxypropyl Cellulose and Gelatin
No full textHydroxypropyl cellulose (HPC) is an edible, cost-effective and widely used derivative of cellulose. Under lyotropic conditions in water, HPC forms a photonic, liquid crystalline mesophase with an exceptional mechanochromic response. However, due to insufficient physical cross-linking photonic HPC can flow freely as a viscous liquid, preventing the exploitation of this mechanochromic material in the absence of any external encapsulation or structural confinement. Here this challenge is addressed by mixing HPC and gelatin in water to form a self-supporting, viscoelastic, and edible supramolecular photonic hydrogel. It is demonstrated that the structural coloration, mechanochromism and non-Newtonian shear-thinning behavior of the lyotropic HPC solutions can all be retained into the gel state. Moreover, the rigidity of the HPC-gel provides a 69% shorter mechanochromic relaxation time back to its initial color when compared to the liquid HPC–water only system, broadening the dynamic color range of HPC by approximately 2.5× in response to a compressive pressure. Finally, the ability to formulate the HPC-gels in a scalable fashion from only water and “food-grade” constituents unlocks a wide range of potential applications, from response‑tunable mechanochromic materials and colorant-free food decoration, to short-term sensors in, for example, biodegradable “smart labels” for food packaging
Microstructure scaling in metal-insulator-transitions of atomic layer deposited VO<inf>2</inf> films
No full textThin films of VO2 are grown by atomic layer deposition onto low-cost amorphous substrates and compared to sputtered and pulsed laser deposited films on similar substrates. They were each analyzed in terms of the scaling with grain size of the resistivity change across the metal insulator transition, its thermal hysteresis and its full width at half maximum of the slopes. This finds a similar dependence and suggests that the cause is the sintering processes of these films during their deposition and annealing, which determine their microstructural properties
The variability of marine sediment erodibility with depth: Centimetric scale effects detected from portable erosion flume tests
No full textA portable erosion flume has been developed that is capable of estimating erosion threshold and erosion rate relationships for fine-grained specimens over the depth of a typical sample tube. This newly-designed apparatus is a recirculating flume capable of generating steady currents over the exposed section of the sample. In this paper, the erosion properties of two marine sediments have been determined and show a significant systematic variation with depth at centimetre scale that would have implications for the potential need for scour protection engineering. The tests showed that the critical erosion onset velocity doubled over the upper 200 mm of each sample, and the erosion rate fell by an order of magnitude. The increased erosion resistance with depth is consistent with the general trend of erodibility reducing with decreasing moisture content. Ignoring this depth effect when selecting design values of the erosion properties could lead to erroneous predictions of scour rate and extent around subsea structures, and unnecessary scour protection engineering costs
High-power laser-induced optical aberrations on beam director mirrors
No full textWe present a full-scale numerical study of thermally induced optical aberrations on the primary mirror of a beam director telescope. In particular, we investigate high-power laser-induced deformations, resulting monochromatic aberrations, and their effects on imaging and laser focusing performance of primary telescope mirrors in shared aperture beam director systems. As a practical example, we consider a system based on 6 × 4 kW single-mode high-power laser sources and a primary mirror having a 500 mm circular clear aperture. A detailed comparison of the monochromatic aberrations and their implications on the optical performance is provided for borosilicate and Zerodur® substrates having identical reflective coatings for potential laser beam director applications. Our analyses show that high-power lasers can be efficiently directed with negligible imaging degradation using athermal substrates (i.e., Zerodur®) with high reflective coatings (>99.9 %) for primary mirrors. On the other hand, substrates with a relatively higher coefficient of thermal expansion (i.e., borosilicate) can only be used effectively under a strictly controlled ambient temperature
Complex 3D microfluidic architectures formed by mechanically guided compressive buckling
No full textMicrofluidic technologies have wide-ranging applications in chemical analysis systems, drug delivery platforms, and artificial vascular networks. This latter area is particularly relevant to 3D cell cultures, engineered tissues, and artificial organs, where volumetric capabilities in fluid distribution are essential. Existing schemes for fabricating 3D microfluidic structures are constrained in realizing desired layout designs, producing physiologically relevant microvascular structures, and/or integrating active electronic/optoelectronic/microelectromechanical components for sensing and actuation. This paper presents a guided assembly approach that bypasses these limitations to yield complex 3D microvascular structures from 2D precursors that exploit the full sophistication of 2D fabrication methods. The capabilities extend to feature sizes <5 μm, in extended arrays and with various embedded sensors and actuators, across wide ranges of overall dimensions, in a parallel, high-throughput process. Examples include 3D microvascular networks with sophisticated layouts, deterministically designed and constructed to expand the geometries and operating features of artificial vascular networks
Effects of crystalline structure of IGZO thin films on the electrical and photo-stability of metal-oxide thin-film transistors
No full textIn this paper, we investigated the effects of crystalline structure of indium-gallium-zinc-oxide (IGZO) thin films on the electrical and photo-stability of metal-oxide thin-film transistors (TFTs). It was found that the TFTs with c-axis aligned crystalline (CAAC) IGZO channels exhibited enhanced stability under various combinations of electrical, temperature, and light-stressed conditions compared to those with amorphous (a) and nanocrystalline (nc) IGZO channels. From various electrical and spectroscopic studies, it is suggested that the low deep-level defects in CAAC-IGZO channels allowed high electrical performance and enhanced stability. Meanwhile, the a- and nc-IGZO TFTs showed relatively poor stability owing to the higher levels of deep-level defects in the channel layers. To explain the origin of the enhanced light-stability in CAAC-IGZO TFTs, we investigated the transient photo-response characteristics and it was found that the low activation energy for recombination and/or neutralization of photo-generated carriers was responsible for the enhanced stability
Monitoring on a shoestring: Low cost solutions for digital manufacturing
No full textDigital transformation can provide a competitive edge for many manufacturers, however many smaller companies may not have the capabilities needed to embrace this opportunity and may be left behind. This paper reports on an approach which is attempting to alleviate this by creating a low-cost pathway to help manufacturing small and medium sized enterprises (SMEs) engage with digitalisation. This paper focuses on industrial monitoring and explores the potential for developing simple monitoring systems that solve real operation challenges in SMEs using low-cost, off-the-shelf technologies. A blueprint for developing such systems is presented and then exemplified through a case study system. The paper concludes that low-cost monitoring can be feasible given the right application and operating environment
The feasibility of the PAM intervention to support treatment-adherence in people with hypertension in primary care: a randomised clinical controlled trial
No full textThe PAM intervention is a behavioural intervention to support adherence to anti-hypertensive medications and therefore to lower blood pressure. This feasibility trial recruited 101 nonadherent patients (54% male, mean age 65.8 years) with hypertension and high blood pressure from nine general practices in the UK. The trial had 15.5% uptake and 7.9% attrition rate. Patients were randomly allocated to two groups: the intervention group (n = 61) received the PAM intervention as an adjunct to usual care; the control group (n = 40) received usual care only. At 3 months, biochemically validated medication adherence was improved by 20% (95% CI 3-36%) in the intervention than control, and systolic blood pressure was reduced by 9.16 mmHg (95% CI 5.69-12.64) in intervention than control. Improvements in medication adherence and reductions in blood pressure suggested potential intervention effectiveness. For a subsample of patients, improvements in medication adherence and reductions in full lipid profile (cholesterol 1.39 mmol/mol 95% CI 0.64-1.40) and in glycated haemoglobin (3.08 mmol/mol, 95% CI 0.42-5.73) favoured the intervention. A larger trial will obtain rigorous evidence about the potential clinical effectiveness and cost-effectiveness of the intervention.Trial registration Trial date of first registration 28/01/2019. ISRCTN74504989. https://doi.org/10.1186/ISRCTN74504989
Microstructure scaling of metal-insulator transition properties of VO<inf>2</inf> films
No full textThe metallic to semiconducting resistivity ratios and the transition temperature sharpness of annealed atomic layer deposited VO2 films on amorphous silicon dioxide are found to depend on the grain size in a closely similar way to films from previous sputtered or pulse laser deposited work. This occurs because the dominance of grain growth and compaction processes leads to a common scaling of properties with the grain size. Density functional simulations find that V-V dimerizations allow grain boundaries to remain semiconducting but with a reduced bandgap, while others create metallic grain boundaries, reducing the resistivity ratio for smaller grains in both cases