MRC Laboratory of Molecular Biology
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Electronic structure of amorphous copper iodide: A p -type transparent semiconductor
No full textThe atomic and electronic structure of the p-type transparent amorphous semiconductor CuI is calculated by ab initio molecular dynamics. It is found to consist of a random tetrahedrally bonded network. The hole effective mass is found to be quite low, as in the crystal. The valence-band maximum (VBM) state has a mixed I(p)-Cu(t2g)-I(p) character, and its energy is relatively insensitive to disorder. An iodine excess creates holes that move the Fermi level into the valence band, but it does not pin the Fermi level above the VBM mobility edge. Thus the Fermi level can easily enter the valence band if p doped, similar to the behavior of electrons in In-Ga-Zn oxide semiconductors but opposite to that of electrons in a-Si:H. This suggests that amorphous CuI could make an effective p-type transparent semiconductor
Broad Bandwidth, Self-Powered Acoustic Sensor Created by Dynamic Near-Field Electrospinning of Suspended, Transparent Piezoelectric Nanofiber Mesh.
No full textFreely suspended nanofibers, such as spider silk, harnessing their small diameter (sub-micrometer) and spanning fiber morphology, behave as a nonresonating acoustic sensor. The associated sensing characteristics, departing from conventional resonant acoustic sensors, could be of tremendous interest for the development of high sensitivity, broadband audible sensors for applications in environmental monitoring, biomedical diagnostics, and internet-of-things. Herein, a low packing density, freely suspended nanofiber mesh with a piezoelectric active polymer is fabricated, demonstrating a self-powered acoustic sensing platform with broad sensitivity bandwidth covering 200-5000 Hz at hearing-safe sound pressure levels. Dynamic near-field electrospinning is developed to fabricate in situ poled poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofiber mesh (average fiber diameter ≈307 nm), exhibiting visible light transparency greater than 97%. With the ability to span the nanomesh across a suspension distance of 3 mm with minimized fiber stacking (≈18% fiber packing density), individual nanofibers can freely imitate the acoustic-driven fluctuation of airflow in a collective manner, where piezoelectricity is harvested at two-terminal electrodes for direct signal collection. Applications of the nanofiber mesh in music recording with good signal fidelity are demonstrated
Damage identification of brick masonry under cyclic loading based on acoustic emissions
No full textAgeing infrastructure, such as masonry railway bridges, suffers from structural deterioration due to fatigue loading. This paper presents an experimental study of brick masonry deterioration under gradually increasing cyclic loading with the aid of Acoustic Emission (AE) sensors. Two masonry beams were tested in the laboratory under similar stress conditions that masonry arches experience during train loading. An in-house AE monitoring system was developed for this study allowing both feature-based and waveform-based AE analysis. In the lab tests, different modes of damage were activated, such as tensile bond failure, brick and mortar crushing, diagonal shear failure and joint sliding. Feature-based AE analysis shows an increase in cracking rate before brittle failure events that is not necessarily accompanied by an increase in deformation rate. Statistical analysis reveals clear trends in AE results that correlate to different damage stages. The paper discusses how these findings can be leveraged to develop real-time structural alert systems that could provide early warning of damage before a significant increase in dynamic deformation occurs
First-Order Dynamic Modeling and Control of Soft Robots
No full textModeling of soft robots is typically performed at the static level or at a second-order fully dynamic level. Controllers developed upon these models have several advantages and disadvantages. Static controllers, based on the kinematic relations tend to be the easiest to develop, but by sacrificing accuracy, efficiency and the natural dynamics. Controllers developed using second-order dynamic models tend to be computationally expensive, but allow optimal control. Here we propose that the dynamic model of a soft robot can be reduced to first-order dynamical equation owing to their high damping and low inertial properties, as typically observed in nature, with minimal loss in accuracy. This paper investigates the validity of this assumption and the advantages it provides to the modeling and control of soft robots. Our results demonstrate that this model approximation is a powerful tool for developing closed-loop task-space dynamic controllers for soft robots by simplifying the planning and sensory feedback process with minimal effects on the controller accuracy
Influence of precursor dose and residence time on the growth rate and uniformity of vanadium dioxide thin films by atomic layer deposition
No full textThe growth of vanadium dioxide (VO2) thin films using tetrakis (ethyl-methyl) amino vanadium (TEMAV) and H2O by atomic layer deposition (ALD) has been investigated as a function of the exposure dose and residence time. A novel multiple pulse mode has been employed to mitigate the small deposition rate brought about by the low vapor pressure of TEMAV. Compared to the conventional ALD cycle with a single pulse of precursor, the use of multiple pulsing with very short pulse time allows lower consumption of precursor, but larger exposure dose and longer residence time on the growth surface, resulting in a higher growth rate for a low volatility precursor, while maintaining a good film uniformity across 4-in. wafers. The Raman analysis and the electrical resistivity modulation of the VO2 thin films show that the films synthesized by the multiple pulse mode is comparable to the films synthesized by the conventional single pulse mode
Integrating sustainable value thinking into technology forecasting: A configurable toolset for early stage technology assessment
No full textThere is an urgent need for technology development to make a sustainable or restorative contribution to the environment, with its inherent links to society and societal welfare. Forward-looking activities, such as firm level technology forecasting and technology intelligence, are increasingly important in providing positive impact that is complementary to policy level interventions. However, selecting and implementing appropriate approaches to conduct these activities and quantifying their value contribution is still difficult. This article seeks to demonstrate how technology opportunities may be explored more effectively by combining existing methods for assessing new technology and identifying sustainable value, in an approach for industry that is both configurable and practical while delivering tangible benefits. It details the two-year university-industry collaboration and testing of a configurable toolset, based on four templates used in a workshop setting. Results indicate that the toolset has successfully probed technological, environmental and social capabilities, promoted the selection and implementation of an appropriate approach and led to the quantification of value through the inclusive, transparent and documented assessment of technology opportunities and the tangible actions identified. In summary, the toolset supports company employees in realising a measure of prospective sensemaking, which is a key deliverable from forward-looking activities
Influence of liquid-gas interface dynamics in superhydrophobic surfaces for drag reduction
No full textDirect numerical simulation (DNS) is used to investigate liquid flow in turbulent channels with superhydrophobic surfaces. The effect of the gas bubbles trapped between surface protrusions is modeled as both a slip effect and, for the first time in literature, a deforming interface. The dynamics of the interface are modeled with a linearized boundary condition, derived from the equilibrium between the surface tension and the pressure jump across the interface. We study two- and three-dimensional patterned surfaces, analyzing the effect of the surface tension and the pattern geometry and alignment
DNS of inhomogeneous turbulence under rotation
No full textCopyright © ETC 2013 - 14th European Turbulence Conference.All rights reserved. Rotating turbulent flow is routinely encountered in geophysical environment, such as in cyclones and tornadoes. The number of investigations on inhomogeneous rotating turbulence is relatively sparse as compared to its homogeneous counterpart although they are more common in nature. The present study involves Direct Numerical Simulation (DNS) of a 'cloud' of turbulence with quiescent fluid on either side, under background rotation. The motivation behind the study is to understand the role of inertial waves in inhomogeneous rotating turbulence. In the results obtained, helicity - a quantity representative of the degree of entanglement of the vortices, is found to propagate in a way typical of inertial waves. The thickness of the growing cloud is found to scale linearly with time