2,906 research outputs found
Low-loss broadband antenna for efficient photon collection from a coherent spin in diamond
No full textWe report the creation of a low-loss broadband optical antenna giving highly directed output from a coherent single spin in the solid state. The device, a crystalline solid-state realization of a dielectric antenna, is engineered for individual nitrogen-vacancy electronic spins in diamond. We demonstrate a directionality close to 10. The photonic structure preserves the high spin coherence of single-crystal diamond ( T 2 ≳ 100 μ s). The single-photon count rate approaches a megahertz facilitating efficient spin readout. We thus demonstrate a key enabling technology for quantum applications such as high-sensitivity magnetometry and long-distance spin entanglement
Seedless, Etchless Deposition of Nanocrystalline Diamond Coatings for Performance Improvements of Micro End Mills using Carbon Ion Implantation
No full textThis study compares the cutting performance of (1) as-received uncoated, (2) acid etched plus seeded plus nanocrystalline diamond (NCD) coated, (3) carbon ion implanted (CII) plus NCD coated, and (4) only CII micro end mills
The inter-relationships between three proxies of health care need at the small area level: an urban/rural comparison
No full textStudy objective: To examine the relations between geographical variations in mortality, morbidity, and deprivation at the small area level in the south west of England and to assess whether these relations vary between urban and rural areas. Design: A geographically based cross sectional study using 1991 census data on premature limiting long term illness (LLTI) and socioeconomic characteristics, and 1991–1996 data on all cause premature mortality. The interrelations between the three widely used proxies of health care need are examined using correlation coefficients and scatterplots. The distribution of standardised LLTI residuals from a regression analysis on mortality are mapped and compared with the distribution of urban and rural areas. Multilevel Poisson modelling investigates whether customised deprivation profiles improve upon a generic deprivation index in explaining the spatial variation in morbidity and mortality after controlling for age and sex. These relations are examined separately for urban, fringe, and rural areas. Setting: Nine counties in the south west of England. Participants: Those aged between 0–64 who reported having a LLTI in the 1991 census, and those who died during 1991–1996 aged 0–74. Main results: Relations between both health outcomes and generic deprivation indices are stronger in urban than rural areas. The replacement of generic with customised indices is an improvement in all area types, especially for LLTI in rural areas. The relation between mortality and morbidity is stronger in urban than rural areas, with levels of LLTI appearing to be greater in rural areas than would be predicted from mortality rates. Despite the weak direct relations between mortality and morbidity, there are strong relations between the customised deprivation indices computed to predict these outcomes in all area types. Conclusions: The improvement of the customised deprivation indices over the generic indices, and the similarity between the mortality and morbidity customised indices within area types highlights the importance of modelling urban and rural areas separately. Stronger relations between mortality and morbidity have been revealed at the local authority level in previous research providing empirical evidence that the inadequacy of mortality as a proxy for morbidity becomes more marked at lower levels of aggregation, especially in rural areas. Higher levels of LLTI than expected in rural areas may reflect different perceptions or differing patterns of illness. The stronger relations between the three proxies in urban than rural areas suggests that the choice of indicator will have less impact in urban than rural areas and strengthens the argument to develop better measures of health care need in rural areas
Translating Patrick Kavanagh
No full textThe following concerns the translation I did of a selection of the poetry of Patrick Kavanagh into Spanish, the first translation of this important Irish poet into the Spanish language. It recounts the motives which impelled me to try this daunting task as well as the guidelines I followed, the help I received and the pitfalls I encountered and, hopefully, survived. It looks at some of the images and expressions used by the author and which need to be explained to students and it essays a comparison with the poetry of Antonio Machado, another much loved poet
Measuring industry-science links through inventor-author relations: A profiling method
No full textIn this pilot study we examine the performance of text-based profiling in recovering a set of validated inventor-author links. In a first step we match patents and publications solely based on their similarity in content. Next, we compare inventor and author names on the highest ranked matches for the occurrence of name matches. Finally, we compare these candidate matches with the names listed in a validated set of inventor-author names. Our text-based profile methodology performs significantly better than a random matching of patents and publications, suggesting that text-based profiling is a valuable complementary tool to the name searches used in previous studies.innovation; industry-science links; text-based profiling;
Design and Analysis of Advanced CVD Diamond Dielectric Structures
No full textCVD diamond has proven to be a viable material for creating electrical devices. This research focuses on the advanced development and characterization of CVD diamond dielectric films.
It is shown in this research that the single most important parameter in the development of diamond dielectric capacitors is electrical conductivity. Conductivity affects all electric mechanisms in a polycrystalline diamond film. Part of this research effort was devoted to analyzing the conduction mechanisms of CVD diamond films. The control and/or suppression of these conduction mechanisms determine the dielectric properties of CVD diamond.
This research also focused on the design and development of advanced capacitor structures using CVD diamond. Earlier published work on diamond dielectrics has been limited to basic characterization experiments with simple capacitive structures. Experiments proceeded in this research that produced multi-layer diamond capacitor designs and prototypes
Momentum and Heat Transport in MHD Turbulence in Presence of Stochastic Magnetic Fields
No full textTangled magnetic fields, often coexisting with an ordered mean field, have a major impact on turbulence and momentum transport in many plasmas, including those found in the solar tachocline and magnetic confinement devices. In this dissertation, we present research on the turbulent transport in presence of a stochastic magnetic field, and the discuss implications on the formation of astronomical objects and on the turbulence in edge plasma in fusion devices.The research is divided into three projects. First, we present a novel mean field theory of potential vorticity mixing in β -plane magnetohydrodynamic (MHD). Our results show that mean square stochastic fields strongly reduce Reynolds stress coherence. This decoherence of potential vorticity flux due to stochastic field scattering leads to suppression of momentum transport and zonal flow formation. We discuss a model of stochastic fields as a resisto-elastic network.In second project, we shows the breaking of the shear-eddy tilting feedback loop by stochastic fields is the key underlying physics mechanism. A simple calculation suggests that the breaking of the shear-eddy tilting feedback loop by stochastic fields is the key underlying physics mechanism. A dimensionless parameter that quantifies the increment in power threshold is identified and used to assess the impact of stochastic field on the L-H transition in fusion devices.Finally, we study the turbulent transport of parallel momentum and ion heat by the interaction of stochastic magnetic fields and turbulence in third project. Attention is focused on determining the kinetic stress and the compressive energy flux. A critical parameter is identified as the ratio of the turbulent scattering rate to the rate of parallel acoustic dispersion. For the parameter large, the kinetic stress takes the form of a viscous stress. For the parameter small, the quasilinear residual stress is recovered. In practice, the viscous stress is the relevant form, and the quasilinear limit is not observable. This is the principal prediction of this project
Characterization of Stress and Mosaicity in Homoepitaxial Diamond Films
No full textABSTRACTDiamond films were grown on (100) and (110) oriented natural diamond substrates by hot filament assisted chemical vapor deposition (HFCVD) to thicknesses of 7 to 100μm. Raman spectroscopy was used to measure tensile stresses of up to ∼2GPa for some of the (110) films. The development of stress was attributed to the incorporation of impurities (Re, Mo, and H). Impurity concentrations were greater at the interface than through the film thickness. Up to∼11% H and 50ppm Re were measured in the films with secondary ion mass spectrometry (SIMS). Homoepitaxial diamond films were further characterized using a seven crystal high resolution x-ray diffraction system. This new characterization tool allowed the separation of the effects of mosaicity from those of variation in lattice parameter.</jats:p
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Intrinsic plasma flows in straight magnetic fields: generation, frictionless saturation, and interaction
No full textWe develop a simple model for the generation and amplification of intrinsic axial flow in a linear device, Controlled Shear Decorrelation Experiment (CSDX). This model develops a novel dynamical symmetry breaking mechanism in drift wave turbulence, which does not require complex magnetic field structure, such as shear. Thus, the model is applicable to both tokamaks and linear devices. This mechanism is, essentially, a form of negative viscosity phenomenon. Negative compressibility ITG turbulence can also induce a negative viscosity increment. However, we show that no intrinsic axial flow can be generated by pure ITG turbulence in a straight magnetic field. When the flow gradient is steepened by any drive mechanism, the flow profile saturates at a level close to the value above which parallel shear flow instability (PSFI) becomes dominant over the ITG instability. This saturated flow gradient exceeds the PSFI linear threshold, and grows with as .The coupling of azimuthal and axial flows in CSDX--in absence of magnetic shear--is investigated.In particular, we focus on the apportionment of turbulence energy between azimuthal and axial flows, and how the azimuthal flow shear affects axial flow generation and saturation by drift wave turbulence.Detailed measurements of intrinsic axial flow parallel to the magnetic field are performed on CSDX, with no axial momentum input.The results present a direct demonstration that the broken spectral symmetry of drift wave turbulence causes the development of axial mean flows in cylindrical magnetized plasmas.Measurements suggest the axial flow is parasitic to the drift wave--zonal flow system.Besides, we show that consideration of wave--flow resonance resolves the long-standing problem of how zonal flows (ZFs) saturate in the limit of weak or zero frictional drag and also determines the ZF scale directly from analysis. We show that resonant vorticity mixing, which conserves potential enstrophy, enables ZF saturation in the absence of drag, and so is effective at regulating the Dimits up-shift regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect in an extended 0D predator--prey model of drift--ZF turbulence
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Topics in Mesoscopic Turbulent Transport
No full textThe interaction of turbulent microscales in a plasma can conspire to produce transport on mesoscopic or macroscopic scales, often with extremely important consequences for the system. In this dissertation, we present research on mesoscopic turbulent transport in plasmas relevant to fusion energy and astrophysics.The research is divided into three projects. First, we study drift-wave turbulence, a paradigm for gradient-driven turbulence in the tokamak, using a novel data-driven method. Deep learning is used to infer, from direct numerical simulation of the 2-D Hasegawa-Wakatani system, the dependencies of the turbulent fluxes which control the nonlinear dynamics on mesoscales, thus closing a simplified 1-D mean-field model. Using this approach, we show that the gradient of vorticity drives a nondiffusive particle flux. This nondiffusive flux, which we also recover analytically, modulates the profile in the presence of a quasiperiodic zonal flow. We also show that zonal flow formation is described by a Cahn-Hilliard-type model, both concurring with and expanding upon previous theoretical work. The self-propagation of turbulence, called ``turbulence spreading,'' can lead to turbulence invading linearly stable regions of a tokamak. In the second project, we introduce a new model for turbulence spreading based on turbulence bistability. This model takes the form a reaction-diffusion equation with cubic nonlinearity and nonlinear diffusion. We find that the bistable model remedies certain deficiencies of the popular, unistable Fisher model, for instance predicting far more robust penetration of turbulence into stable regions. We also find that the model exhibits a threshold for propagation of an initial seed of turbulence, which we liken to an avalanche. We analytically estimate this threshold using a simple physical argument.Finally, we study momentum transport in magnetohydrodynamic (MHD) turbulence on a -plane, which serves as a simple model for the solar tachocline. We show that the cross-helicity, which is conserved in pure MHD turbulence, builds up to a predictable level in this system. Using weak turbulence theory, we also show that the cross helicity spectrum is equivalent to the Els\"asser alignment spectrum, which determines momentum transport. We supplement and verify our results with direct numerical simulations
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