MRC Laboratory of Molecular Biology
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Quantification of carbon particulates produced under open liquid pool and prevaporised flame conditions: Waste cooking oil biodiesel and diesel blends
No full textThe soot volume fraction (SVF) of waste cooking oil (WCO) biodiesel and blends was quantified and compared under the same total carbon flow rate via two experimental setups, namely prevaporised diffusion jet flames and pool flames using extinction calibrated laser induced-incandescence (LII). The spatial SVF distribution shows that for diesel-rich fuels, soot formation peaks near the flame and is convected downstream, whereas biodiesel flames show a more evenly distributed SVF at the flame center region. An increase in biodiesel fraction in diesel results in a reduced propensity for soot, as evident in both pool and vapour flames. Comparison of the radial profiles of SVF along the centerline shows broader SVF profiles for pool flames, reflecting the longer residence times for soot diffusion and growth compared to vapour flames, which reflected the lower mass flux for the pool burner. The total soot produced from pool flames was found to be higher than vapour flame by a factor of two for the same fuel mass consumption rate. WCO biodiesel exhibited the lowest total SVF value regardless of flame type owing to the combined effects of lack of aromatic compounds and fuel chemistry. The soot primary particle sizes produced by WCO biodiesel show lower mean diameter values by a factor of approximately 1.5 compared to diesel-produced soot. The pool flames produced carbon particulates of larger mean diameter by around 22% and 8% for diesel and WCO biodiesel, respectively, relative to the counterpart vapour flames, as a result of extended soot surface growth period
Control of Crystal Symmetry Breaking with Halogen-Substituted Benzylammonium in Layered Hybrid Metal-Halide Perovskites
No full textLayered hybrid metal-halide perovskites with non-centrosymmetric crystal structure are predicted to show spin-selective band splitting from Rashba effects. Thus, fabrication of metal-halide perovskites with defined crystal symmetry is desired to control the spin-splitting in their electronic states. Here, we report the influence of halogen para-substituents on the crystal structure of benzylammonium lead iodide perovskites (4-XC6H4CH2NH3)2PbI4 (X = H, F, Cl, Br). Using X-ray diffraction and second-harmonic generation, we study structure and symmetry of single-crystal and thin-film samples. We report that introduction of a halogen atom lowers the crystal symmetry such that the chlorine- and bromine-substituted structures are non-centrosymmetric. The differences can be attributed to the nature of the intermolecular interactions between the organic molecules. We calculate electronic band structures and find good control of Rashba splittings. Our results present a facile approach to tailor hybrid layered metal halide perovskites with potential for spintronic and nonlinear optical applications
A single-component photorheological fluid with light-responsive viscosity.
No full textViscoelastic fluids whose rheological properties are tunable with light have the potential to deliver significant impact in fields relying on a change in flow behavior, such as in-use tuning of combined efficient heat-transfer and drag-reduction agents, microfluidic flow and controlled encapsulation and release. However, simple, single-component systems must be developed to allow integration with these applications. Here, we report a single-component viscoelastic fluid, capable of a dramatic light-sensitive rheological response, from a neutral azobenzene photosurfactant, 4-hexyl-4'butyloxymonotetraethylene glycol (C6AzoOC4E4) in water. From cryo-transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and rheology measurements, we observe that the photosurfactant forms an entangled network of wormlike micelles in water, with a high viscosity (28 Pa s) and viscoelastic behaviour. UV irradiation of the surfactant solution creates a less dense micellar network, with some vesicle formation. As a result, the solution viscosity is reduced by four orders of magnitude (to 1.2 × 10-3 Pa s). This process is reversible and the high and low viscosity states can be cycled several times, through alternating UV and blue light irradiation
Simulation of mechanical stresses in reinforced REBaCuO disk bulks during pulsed-field magnetization
No full textWe have performed numerical simulations of the electromagnetic hoop stress, σθ, in a REBaCuO disk bulk reinforced by a metal ring during pulsed-field magnetization (PFM) using a solenoid coil, in which the superconducting characteristics of the bulk material were assumed to have realistic J c-B-T ones. The compressive and tensile σθ stresses were applied in the bulk during the ascending and descending stages of PFM, respectively. The time and position dependences of the mechanical stresses were estimated. The possibility of mechanical fracture due to these hoop stresses and the effect of the metal ring reinforcement were discussed
Hybrid band offset calculation for heterojunction interfaces between disparate semiconductors
No full textAccurate band offset calculations are challenging for heterojunction interfaces that consist of two very different host materials. For this, the key requirement is to have the correct bandgap of each material at the same time. A hybrid calculation scheme (HSE/-U scheme) is proposed to model the band offsets of such interfaces. Our HSE/-U method applies the hybrid functional for the whole interface supercell, but with an additional "reverse GGA+U" on the narrow gap semiconductor side, guaranteeing the correct bandgaps on both sides. Several supercell calculations of dielectric films including HfO2, ZrO2, Al2O3, TiO2, and GaN on an insulating phase VO2 are tested to verify it. All the studied oxides show the type-I band alignment with VO2, and the band edge line-up agrees well with the available experimental reports, supporting the reliability of the proposed hybrid calculation scheme
An assessment of the J-integral test for a metallic foam
No full textAn assessment is made of the J-integral test procedure for initial crack growth in an open-cell aluminium alloy foam by combining finite element (FE) simulations with experiment. It is found experimentally that a zone of randomly failed struts develops ahead of the primary crack tip, and is comparable in size to that of the plastic zone. Hence, a crack tip J-field is absent at the initiation of crack growth from the primary crack tip. This implies that the measured JIC value and the J versus crack extension Δa curve cannot be treated as material properties despite the fact that the specimen size meets the usual criteria for J validity. The toughness tests were performed on a single-edge notched bend specimen, and crack extension was measured by the direct current potential drop method, by digital image correlation and by X-ray computed tomography. The crack growth resistance of the foam is associated with two distinct zones of plastic dissipation: (i) a bulk plastic zone emanating from the crack tip (containing a cluster of randomly failed struts), and (ii) a crack bridging zone behind the advancing crack tip. The applicability of a cohesive zone model to predict the fracture response is explored for the observed case of large scale bridging. To do so, FE simulations are performed by replacing the discrete lattice of the open-cell metallic foam by a compressible, elastic-plastic hardening solid while the fracture process zone in the foam is represented by a cohesive zone, as characterised by a tensile traction versus separation law. A detailed comparison of the cohesive zone model with experimental observations reveals that it is possible to capture the load versus displacement response but not the details of the fracture process zone using a single set of process zone parameters
On the effect of pore-space properties and water saturation on explosive spalling of fire-loaded concrete
No full textIn this paper, the influence of concrete properties such as permeability and environmental conditions (water content) on the spalling behavior of concrete subjected to fire loading is investigated. For this purpose, a special fire-test setup is presented, allowing an improved reproduction of temperature histories observed, e.g., in tunnel fires. Moreover, the developed test setup enables a continuous monitoring of spalling, giving access to the spalling history and the final level of damage of concrete specimens. The obtained results, considering different water/cement-ratios and saturation degrees, are related to the required initial tensile strength determined by means of a numerical assessment tool. Finally, correlations between the identified parameters governing fire-spalling were established and allowed an evaluation of the spalling risk of concrete mixtures. These correlations revealed that – in contrast to requirements given in national and international standards – the combination of water content and permeability may serve as proper key and design parameter, defining the risk of spalling
Partitioning of sulfur between solid and liquid iron under Earth's core conditions: Constraints from atomistic simulations with machine learning potentials
No full textPartition coefficients of light elements between the solid and liquid iron phases are crucial for uncovering the state and dynamics of the Earth's core. As one of the major light element candidates, sulfur has attracted extensive interests for measuring its partitioning and phase behaviors over the last several decades, but the relevant experimental data under Earth's core conditions are still scarce. In this study, using a toolkit consisting of electronic structure theory, high-accuracy machine learning potentials and rigorous free energy calculations, we establish an efficient and extendible framework for predicting complex phase behaviors of iron alloys under extreme conditions. As a first application of this framework, we predict the partition coefficients of sulfur over wide range of temperatures and pressures (from 4000 K, 150 GPa to 6000 K, 330 GPa), which are demonstrated to be in good agreement with previous experiments and ab initio simulations. After a continuous increase below ∼250 GPa, the partition coefficient is found to be around 0.75 ± 0.07 at higher pressures and are essentially temperature-independent. Given these predictions, the partitioning of sulfur is confirmed to be insufficient to account for the observed density jump across the Earth's inner core boundary and its roles on the geodynamics of the Earth's core should be minor
Power Loss Characterization and Modeling for GaN-Based Hard-Switching Half-Bridges Considering Dynamic on-State Resistance
No full textIEEE Gallium Nitride enhancement-mode high electron mobility transistors (GaN E-HEMTs) can achieve high frequency and high efficiency due to its excellent switching performance compared with conventional Si transistors. Nevertheless, GaN HEMTs exhibit a more pronounced dynamic on-state resistance RDS(on) than silicon transistors. The variation of RDS(on) is caused by both the static RDS(on) due to junction temperature rise and the dynamic RDS(on) due to the electron trapping. Without a careful decoupling analysis, it is difficult to calculate and model the dynamic RDS(on) portion. This paper introduces a comprehensive approach of dynamic RDS(on) evaluation, comprising four techniques: 1) a clamping circuit for both the hard-switching (HS) device and synchronous rectification (SR) device; 2) a junction temperature monitoring technique; 3) control of both the pulse test and soak time; 4) continuous operation of device under test. Based on the dynamic RDS(on) test results, a new model of the RDS(on) variation is developed where two coefficients: kTj and kdR are defined to model the contribution of the heating effect and the impact of the trapping effect, respectively. The RDS(on) model is validated by the comparison between the calculated and measured junction temperatures of a 650 V/30 A GaN-based half-bridge. Furthermore, a detailed loss breakdown analysis is conducted for the GaN-based hard-switching half-bridge. Results show that the switching losses, Eon and Eoff are the dominant loss factors with high switching frequency. At last, the possible efficiency improvements are also discussed in detail