MRC Laboratory of Molecular Biology
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Analog modulation by the flexoelectric effect in liquid crystals
No full textWe have solved the long-standing problems of stability and hysteresis, and we are able to obtain the homogeneous uniform lying helix structure in polymer-free cholesteric liquid crystals. This is instrumental for the present work to demonstrate the analog modulation at high speed and high precision. The device is configured for the transverse field switching wherein the substrate surface is flat. In addition to the response time of 10 ms at room temperature, we have obtained the R-squared and the adjusted R-squared as a measure of true sine wave for the sinusoidal responding transmissions from 1 Hz to 100 kHz that are all greater than 0.9993. In a Michelson interferometer, the phase shift at wavelength 633 nm after two passes has been measured to be equal to abou
Sound radiation from a semi-infinite lined duct
No full textIn this paper we consider the radiation properties of a pair of semi-infinite, parallel-plate ducts in which the inner duct is buried inside the outer duct. A Robin condition is applied to one of the inner walls (to represent an acoustic lining), while Neumann conditions are applied on all other surfaces. This leads to a matrix Wiener–Hopf problem, which requires the factorisation of a 3×3 matrix of a form which, to our knowledge, has not previously been considered in the literature and which is not directly amenable to standard pole-removal techniques. We derive the exact factorisation of this matrix here, and present results for the far-field scattered sound which show the effect of varying the properties of the wall lining
Tuning the composition and morphology of carbon nanotube-copper interface
No full textCarbon nanotube (CNT)-copper nanocomposites are promising materials for light-weight high-ampacity conductors. The key issue in hybridization of CNT and metal is creating a strong bonding between them. This requires proper modification of the CNT surface. However, experimental works on determining the effect of interfacial functionalization on the properties of the metal/CNT system is scarce. In this paper, the effect of CNT surface modification on the morphology, interfacial interactions, and electrical properties Cu/CNT hybrid system is investigated. For this purpose, CNTs with carboxyl, thiol, and nitrogen doped surface groups were used as substrate for growth of Cu particles via a facile electrochemical process. It is observed that not only the morphology but also the chemical state of the Cu deposits are affected by the surface functional group on CNT. Thiol group significantly enhances copper wettability towards CNT, facilitating a uniform deposition of copper, and impedes oxidation. Also, Cu/CNT thin films fabricated via vacuum filtration that contain thiol-activated CNTs shows four and seven times higher electrical conductivity compared with systems that contain carboxyl and N-doped surface groups, respectively
Evaluating the effectiveness of catchment-scale approaches in mitigating urban surface water flooding
No full textThe argument for natural flood management in the UK has strengthened in recent years with increasing awareness of the potential benefits gained from upstream interventions (especially improvements in water quality, public amenities and biodiversity). This study aims to develop an understanding of another potential benefit—interventions promoting free discharge at downstream urban drainage outfalls by moderating water levels in receiving watercourses. A novel, coupled model (linking dynamic TOPMODEL, HEC-RAS and Infoworks ICM) is calibrated for the Asker catchment in Dorset, England. This predominantly rural watershed drains to the town of Bridport, frequently submerging a surface drainage outfall in a nearby housing estate. Two forms of upstream, catchment-scale intervention (hillslope tree planting and in-channel large woody debris) are modelled to understand their impacts on the functioning of the drainage network during both the calibration period and a range of design storms. The results indicate that interventions have the greatest positive impact during frequent events. For example, during a storm with a 10% annual exceedance probability (AEP), upstream NFM could reduce outfall inundation by up to 3.75 h and remove any surcharging of flow within the drainage system in Bridport. In more severe storms, the results suggest interventions could slightly prolong the time the outfall was submerged. However, by slowing the wider catchment’s response during the 3.3% AEP storm, upstream interventions allow more water to escape the urban drainage system and reduce the maximum surface flooding extent within the housing estate by 35%. This article is part of the theme issue ‘Urban flood resilience’
Development and application of novel sodium silicate microcapsule-based self-healing oil well cement
No full textA majority of well integrity problems originate from cracks of oil well cement. To address the crack issues, bespoke sodium silicate microcapsules were used in this study for introducing autonomous crack healing ability to oil well cement under high-temperature service conditions at 80 °C. Two types of sodium silicate microcapsule, which differed in their polyurea shell properties, were first evaluated on their suitability for use under the high temperature of 80 °C in the wellbore. Both types of microcapsules showed good thermal stability and survivability during mixing. The microcapsules with a more rigid shell were chosen over microcapsule with a more rubbery shell for further tests on the self-healing efficiency since the former had much less negative effect on the oil well cement strength. It was found that oil well cement itself showed very little healing capability when cured at 80 °C, but the addition of the microcapsules significantly promoted its self-healing performance. After healing for 7 days at 80 °C, the microcapsule-containing cement pastes achieved crack depth reduction up to ∼58%, sorptivity coefficient reduction up to ∼76%, and flexural strength regain up to ∼27%. The microstructure analysis further confirmed the stability of microcapsules and their self-healing reactions upon cracking in the high temperature oil well cement system. These results provide a promising perspective for the development of self-healing microcapsule-based oil well cements
Buffer-Assisted Top-Seeded Infiltration and Growth for Fabricating Dense, Single-Grain (RE)-Ba-Cu-O Bulk Superconductors
No full text(RE)BCO, rare-earth based high temperature superconductors fabricated in the form of large, single grain bulk samples can trap comparatively large magnetic fields in relatively small sample volumes, unlike conventional permanent magnetic materials. Fabrication of (RE)BCO single grains has been achieved largely following the development of processing techniques based on melt growth (MG). In the present study, the recently developed alternative fabrication technique of infiltration and growth (IG) is discussed and its significance highlighted in the context of obtaining (RE)BCO bulk superconductors with dense microstructures. The necessity of employing a buffer layer in the IG methodology is elucidated. The path followed in solving the complex problem of controlling the amount of RE2BaCuO5 (RE-211) present in the microstructure of the end product to achieve enhanced and optimized flux pinning is described. A brief overview of the recently developed 2-step, buffer-assisted top-seeded infiltration and growth (BA-TSIG) fabrication technique, which enables successful fabrication of (RE)BCO bulks, is presented. Finally, two novel experiments based on the TSIG technique – fabrication of a bar-shaped YBCO sample (with size: 72 mm x 24 mm x 15 mm) and multi-seeding of YBCO (with two NdBCO seeds in 0°-0° configuration, with aligned a-b planes) – are described and further potential options for the fabrication of complex-shaped (RE)BCO bulk components for specific practical applications are outlined
Do government R&D subsidies stimulate collaboration initiatives in private firms?
No full textInput-driven policy is typically designed to support R&D and contribute to the enhancement of innovation competences in individual firms. However, it is not clear whether this ‘more is better’ approach has contributed to the establishment of a vibrant innovation ecosystem by stimulating firms’ inclination to collaborate. The current study investigates this question by analysing the data from 489 Korean innovative manufacturing firms using a propensity score matching analysis. As expected, the link to increased innovation collaborations was statistically significant between the recipients and R&D subsidies. The results show that R&D subsidies stimulate firms to choose partners more adventurously, by going outside the traditional value chains and regional boundaries. However, the impact of subsidies on innovation collaboration followed an inverted U-shaped curve: the impact in highly funded firms was smaller than that in firms that received a more modest amount. This finding suggests that government support encourages firms to work with a heterogeneous range of partners and to develop more diversified ecosystems. Our study suggests that different policy impacts, such as input and behavioural additionality, can occur simultaneously and even influence each other. Thus, there is a strong need for policy makers to develop more sophisticated policy tools for open innovation promotion
Oxidant-assisted direct-sulfidization of nickel foam toward a self-supported hierarchical Ni<inf>3</inf>S<inf>2</inf>@Ni electrode for asymmetric all-solid-state supercapacitors
No full textIn this work, we demonstrate, for the first time, a low-temperature direct-sulfidization of nickel foam (NF) assisted with oxidant K2S2O8 to fabricate a novel self-supported hierarchical porous Ni3S2@NF electrode for supercapacitors. The resultant Ni3S2@NF electrode exhibits a high specific capacitance of 2519.5 mF cm−2 at a current density of 1.0 mA cm−2, and a rate capability of 68.5% over a current density range of 1–20 mA cm−2. At the same time, the retention of areal specific capacitance amounts to ~100% of its initial capacitance at 20 mA cm−2 after 4000 consecutive charge−discharge cycles. Moreover, an asymmetric all-solid-state supercapacitor device Ni3S2@NF//activated carbon (AC)@NF has been assembled. Remarkably, this device can afford an energy density of 32.0 Wh kg−1 at a power density of 210.8 W kg−1 accompanied with excellent electrochemical cyclic stability. Such outstanding supercapacitive behavior of Ni3S2@NF can be credited to its unique porous interpenetrating architecture and the robust contact of Ni3S2 and NF, which can ensure rapid ion and electron transfers for redox reactions as well as tightly contacts among active component, substrate, and electrolyte. The direct-sulfidization of metals assisted with oxidants can offer a general, scalable, and viable protocol to fabricate high-performance electrochemical materials for energy-storage applications
Thermal-hydraulic design methodology and trade-off studies for a dual-salt breed-and-burn molten salt reactor
No full textA methodology is developed for thermal-hydraulic analysis and design of a breed-and-burn molten salt reactor (BBMSR). By using separate fuel and coolant molten salts, the BBMSR is proposed to overcome key materials limitations of traditional breed-and-burn and molten salt reactor designs. The BBMSR fuel concept includes an inner wall that divides the ascending and descending flows of naturally convecting fuel salt. A finite-difference model (FDM) is developed to iteratively solve for the temperature and velocity distributions in both sections of the concentric fuel. The FDM is used to perform parametric studies of the effect of fuel geometry and heat generation rate on the heat transfer performance of the fuel. The FDM is then integrated into a design search algorithm that identifies the operational limits for a given BBMSR fuel geometry, within a set of defined constraints. A range of thermal-hydraulic fuel design options are evaluated, and trade-off studies are performed to identify the most promising fuel design space for competitive power production and neutronic efficiency in the BBMSR
Structure Engineering of MoS<inf>2</inf> via Simultaneous Oxygen and Phosphorus Incorporation for Improved Hydrogen Evolution
No full textOxygen and phosphorus dual-doped MoS2 nanosheets (O,P-MoS2) with porous structure and continuous conductive network are fabricated using a one-pot NaH2PO2-assisted hydrothermal approach. By simply changing the precursor solution, the chemical composition and resulting structure can be effectively controlled to obtain desired properties toward the hydrogen evolution reaction (HER). Thanks to the beneficial structure and strong synergistic effects between the incorporated oxygen and phosphorus, the optimal O,P-MoS2 exhibit superior electrocatalytic performances compared with those of oxygen single-doped MoS2 nanosheets (O-MoS2). Specifically, a low HER onset overpotential of 150 mV with a small Tafel slope of 53 mV dec−1, excellent conductivity, and long-term durability are achieved by the structural engineering of MoS2 via O and P co-doping, making it an efficient HER electrocatalyst for water electrocatalysis. This work provides an alternative strategy to manipulate transition metal dichalcogenides as advanced materials for electrocatalytic and related energy applications