MRC Laboratory of Molecular Biology
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Linking Glass-Transition Behavior to Photophysical and Charge Transport Properties of High-Mobility Conjugated Polymers
No full textThe measurement of the mechanical properties of conjugated polymers can reveal highly relevant information linking optoelectronic properties to underlying microstructures and the knowledge of the glass transition temperature (Tg) is paramount for informing the choice of processing conditions and for interpreting the thermal stability of devices. In this work, we use dynamical mechanical analysis to determine the Tg of a range of state-of-the-art conjugated polymers with different degrees of crystallinity that are widely studied for applications in organic field-effect transistors. We compare our measured values for Tg to the theoretical value predicted by a recent work based on the concept of effective mobility ζ. The comparison shows that for conjugated polymers with a modest length of the monomer units, the Tg values agree well with theoretically predictions. However, for the near-amorphous, indacenodithiophene–benzothiadiazole family of polymers with more extended backbone units, values for Tg appear to be significantly higher, predicted by theory. However, values for Tg are correlated with the sub-bandgap optical absorption suggesting the possible role of the interchain short contacts within materials’ amorphous domains
Flexible Printed Circuit Board as Novel Electrodes for Acoustofluidic Devices
No full textSurface acoustic wave (SAW)-based acoustofluidics shows broad applications in biomedicine and chemistry. Conventional manufacturing process for SAW devices uses photolithography and metal deposition, thus requires accessing cleanroom facilities. This study presents an efficient and versatile technique based on a flexible printed circuit board (FPCB) for developing SAW acoustofluidic devices. By mechanically clamping interdigital electrodes (IDEs) made on the FPCB onto a piezoelectric substrate, SAWs can be effectively generated with an additional matching network. The SAW amplitudes were measured by a laser vibrometer, which increases with the applied input voltage. The FPCB-SAW device has been applied to actuate 10-μm microspheres to form strong streaming vortices inside a droplet, and to drive a sessile droplet for transportation on the substrate surface. The use of the FPCB rather than a rigid printed circuit board (PCB) can help cut down on the overall footprint of the device and save space. The low requirement in assembling the FPCB-SAW device can facilitate versatile acoustofluidic applications by providing fast prototyping devices
FullyPrinted Flexible Plasmonic Metafilms with Directional Color Dynamics
No full textPlasmonic metafilms have been widely utilized to generate vivid colors, but making them both active and flexible simultaneously remains a great challenge. Here flexible active plasmonic metafilms constructed by printing electrochromic nanoparticles onto ultrathin metal films (<15 nm) are presented, offering low-power electricallydriven color switching. In conjunction with commercially available printing techniques, such flexible devices can be patterned using lithography-free approaches, opening up potential for fullyprinted electrochromic devices. Directional optical effects and dynamics show perceived upward and downward colorations can differ, arising from the dissimilar plasmonic mode excitation between nanoparticles and ultrathin metal films
Moisture-induced cracking in a flexural bilayer with application to historical paintings
No full textCrack channelling in a brittle, flexural bilayer, composed of a coating adhering to a substrate of finite thickness, is addressed for the case of a uniform moisture content (or temperature) variation. The linear stress profile within the coating may lead to three different fracture mechanisms, which are a channelling crack with delamination absent, a channelling crack with delamination of finite length, and a channelling crack with delamination of unbounded extent. Failure mechanism maps illustrate the dependence of the active crack channelling mechanism, and the corresponding critical crack channelling stress, upon the stiffness mismatch between the layers and upon the ratio of interfacial toughness to coating toughness. Although the results are applicable to bilayers in a wide range of applications, the study focuses on the prediction of crack channelling in historical paintings. The significance of bending of the bilayer upon crack channelling is explored by comparing the fracture characteristics of the simply-supported, flexural bilayer with those of a rigidly supported bilayer that is constrained against bending. These two bilayer systems are representative of the different framing techniques commonly used for historical paintings, with the simply-supported bilayer reflecting a regular wooden panel that can bend freely, and the rigidly supported bilayer characterizing a wooden panel that does not bend as a result of cradle additions composed of several horizontal members and corresponding orthogonal cross-pieces. Independent of the type of framing technique applied, it is shown that crack channelling with delamination can be avoided in historical paintings when the delamination toughness exceeds the mode I toughness of the paint layer. Under these conditions paint flaking does not occur and the visual appearance of the painting is preserved. The failure maps constructed in this study provide a useful tool for museum conservators to identify acceptable indoor humidity and temperature variations such that historical paintings do not degrade by a combination of crack channelling and delamination
Asymptotic analysis of model selection criteria for general hidden Markov models
No full textThe paper obtains analytical results for the asymptotic properties of Model Selection Criteria – widely used in practice – for a general family of hidden Markov models (HMMs), thereby substantially extending the related theory beyond typical ‘i.i.d.-like’ model structures and filling in an important gap in the relevant literature. In particular, we look at the Bayesian and Akaike Information Criteria (BIC and AIC) and the model evidence. In the setting of nested classes of models, we prove that BIC and the evidence are strongly consistent for HMMs (under regularity conditions), whereas AIC is not weakly consistent. Numerical experiments support our theoretical results
Experimental investigation, using 3D digital image correlation, into the effect of component geometry on the wrinkling behaviour and the wrinkling mechanisms of a biaxial NCF during preforming
No full textThis study investigates the effect of component geometry on the wrinkling mechanisms of non-crimp fabrics (NCFs) during preforming. Using 3D digital image correlation, the wrinkling behaviour of a biaxial NCF formed over four benchmark geometries is characterised and related to the NCF's surface strains. It is shown that the effect of geometry on the severity of wrinkling is highly significant and that there are two possible wrinkling mechanisms (via shear lockup or via compression) for large wrinkles to occur, which are consistent across geometries. Importantly, an increase in local shear resistance (due to the stitches in this case) is shown to cause severe wrinkles in textile reinforcements at low shear angles due to lateral fabric compression. Additionally, tow wrinkling in NCFs is shown to correlate with local tow compression. Thus, it is not always valid to assume that fabrics are only likely to wrinkle during forming due to excessive shearing
Sub-millisecond switching of multi-level liquid crystal on silicon spatial light modulators for increased information bandwidth
No full textSub-millisecond response time with a refresh rate higher than 2000 frames per second (fps) and no degradation of the contrast ratio or diffraction efficiency is demonstrated in working liquid crystal on silicon (LCOS) spatial light modulators (SLMs) with 8-bit grey levels of amplitude and phase modulations. This makes possible to achieve an information bandwidth of about 190 Gb s-1 with a 4k LCOS operating at 10-bit phase modulation levels. The normalised contrast stays at almost the unit level for a frame rate up to 1700 fps and at higher than 0.9 for 2500 fps. The diffraction efficiency stays above -1.0 dB for a frame rate up to 2400 fps. Such a fast response allows us to eliminate image blurring in replaying a fast movie
Direct-write surface wettability modification for fluidic manufacturing processes
No full textEmerging applications for functionalized and smart glass surfaces have created a market pull effect for scalable digital manufacturing processes in the glass industry. Precise lateral and thickness control in additive fluid deposition processes such as inkjet printing, spray coating and drop casting rely on tuning surface wettability to match with the fluid properties. Typical industrial approaches to modifying surface wettability involve air plasma treatment and deposition of self-assembled monolayers. If patterned control of wettability is needed, these are normally followed by lithographic approaches. Here, we explore direct-write femtosecond laser patterning and shadow-masked plasma treatment as alternative approaches for rapid pattern modification of glass surface structure and surface chemistry to control wettability. We also show the use of these techniques for local removal of functional surface coatings. These capabilities can be combined to enable the digital patterning of contrasting regions of hydrophilicity-hydrophobicity on glass surfaces. We demonstrate surface confinement of liquid drops and capillary-driven spreading. The underlying mechanism of wettability control is determined through combining high-speed imaging of liquid flow with surface chemistry mapping. This research aims in the future to help enhance inkjet printed deposit adhesion, resolution and quality whilst eliminating artefacts such as the coffee ring effect
A 10 NANO-G/RT-HZ RESONANT MEMS ACCELEROMETER EMPLOYING ANTI-ALIASING CONTROL
No full textOptimization of the oscillator front-end for resonant sensors is critical to addressing key metrics such as noise floor and output stability. This paper reports a method to improve the noise floor of resonant MEMS accelerometers by avoiding aliasing of high-frequency seismic noise for long-period measurements. In particular, the optimization of a Phase Locked Loop (PLL) front-end is employed for continuous tracking of the output. A noise floor improvement of 13x is seen in comparison to the case with no anti-aliasing control. A custom PLL is designed to mitigate the impact of high-frequency noise enabling the realization of a resonant accelerometer sensor module with a noise floor of 10 ng/√Hz
Quantitative assessment of the impacts of BIM and lean on process and operations flow in construction projects
No full textPurpose: The study aims to test, measure and quantify the impacts of lean construction and BIM implementation on flow in construction projects. Design/methodology/approach: Detailed control data from a set of 18 high-rise residential construction projects executed between years 2011 and 2020 were analyzed using the construction flow index (CFI), a measure of workflow quality. Seven comparable projects with a diverse range of LPS, BIM, VDC and 5S implementation were selected to compare the impacts of these innovations on flow. Findings: Implementing BIM in the big room and applying the last planner system and other lean construction techniques increased the CFI from 4.31 to 8.12 (on a 10-point scale). Avoiding trades crossing one another's paths between tasks was the most significant aspect of improved flow. Moreover, the benefits of implementing lean practices with BIM or VDC were found to be measurably greater than when these approaches were implemented separately. Research limitations/implications: The primary limitation of the study is that the degree of confidence in the results is limited by the nature of the case study approach. Although 18 is a respectable number of case study projects, it cannot offer the degree of confidence that a broader, representative sample of projects could. Similarly, the case studies are all drawn from the same construction context (residential apartments) and the same geographic region, which necessarily limits confidence concerning the degree to which the findings can be generalized. Originality/value: The research is the first of its kind to quantitatively assess the impacts of BIM and lean construction on flow. Use of the CFI to quantify flow quality also highlights the potential value of CFI in providing project managers and planners a clear view of the smoothness or irregularity of flow and of differences between subcontractors' production rates