Nanoscale magnetometry through quantum control of nitrogen-vacancy centres in rotationally diffusing nanodiamonds

The confluence of quantum physics and biology is driving a new generation of quantum-based sensing and imaging technology capable of harnessing the power of quantum effects to provide tools to understand the fundamental processes of life. One of the most promising systems in this area is the nitrogen-vacancy centre in diamond - a natural spin qubit which remarkably has all the right attributes for nanoscale sensing in ambient biological conditions. Typically the nitrogen-vacancy qubits are fixed in tightly controlled/isolated experimental conditions. In this work quantum control principles of nitrogen-vacancy magnetometry are developed for a randomly diffusing diamond nanocrystal. We find that the accumulation of geometric phases, due to the rotation of the nanodiamond plays a crucial role in the application of a diffusing nanodiamond as a bio-label and magnetometer. Specifically, we show that a freely diffusing nanodiamond can offer real-time information about local magnetic fields and its own rotational behaviour, beyond continuous optically detected magnetic resonance monitoring, in parallel with operation as a fluorescent biomarker.Comment: 9 pages, with 5 figure

Hydrodynamic optimisation of an array of wave-power devices

Third generation wave-power devices are usually envisaged as being either a single large device or an array of smaller devices. The benefit of an array, compared to a single device, is that the individual components are relatively inexpensive to repair and replace; however issues arise due to interaction between the array members, which can lead to constructive or destructive interference of the wave-field, thus increasing or decreasing the power that can be absorbed. This thesis is concerned with the optimal formation and design of these arrays of wave-power devices from a hydrodynamic perspective. Previous literature has indicated that a deterministic optimisation of the array layout, which directly maximises the array performance, results in high sensitivity of the optimal performance to incoming wave parameters. This work considers a more robust optimisation, where the mean performance of the array is maximised. Determining the optimal array configuration is associated with numerical optimisation. Previous studies have shown that a balance must be struck between accurately modelling the devices of the array (including their interactions) and the requirement of establishing a reliable optimisation process. Thus, linear wave theory and the point absorber approximation are utilised within this work. Several array geometries are investigated, including linear and circular arrays, along with a general 2D optimisation without any imposed symmetry. Both constrained and unconstrained WEC motions are considered. Regular waves are assumed for the majority of this work, with a preliminary extension to irregular waves also investigated for elementary linear arrays. In general, it is shown that optimal unconstrained arrays tend to contain closely spaced groups of WECs, while constrained arrays are more spread out. A trade-off between peak performance and performance stability is identified for general WEC arrays, while linear arrays also exhibit a trade-off between stability to wavenumber variations and incident wave angle variations. Overall, it is shown that linear arrays perform poorly for some orientations, regardless of the array layout. Better constructive interaction can be achieved in beam seas for unconstrained motions, while head seas allow for the best interaction when WEC motions constraints are applied. As expected, better interaction can be achieved for more general array layouts, without a prescribed geometry

Urinary tract infections due to extended-spectrum beta-lactamase-producing Gram-negative bacteria: identification of risk factors and outcome predictors in an Australian tertiary referral hospital

Summary Extended-spectrum beta-lactamase-expressing Gram-negative bacilli (ESBL-GNB) now commonly cause community-acquired infections, including urinary tract infections (UTI), and represent a challenge for practitioners in choosing empirical antibiotics. The aim of this study was to describe the epidemiology and clinical characteristics of UTIs/bacteriuria due to ESBL-GNB in Australia. At a single-site tertiary referral hospital, 100 cases with UTIs/bacteriuria due to ESBL-GNB were matched to 100 cases where UTIs/bacteriuria were caused by organisms matching the ESBL bacterial species that had routine susceptibility to antibiotics. Potential risk factors for ESBL-GNB UTI/bacteriuria and differences in clinical outcomes were identified. Length of admission prior to positive sample (odds ratio (OR) 1.3, p=0.03, per week), exposure to antibiotics (OR 5.7, p<0.001), return from overseas travel (OR 6.5, p=0.002), and nursing home residency (OR 4.2, p=0.03) were identified as risk factors associated with ESBL-GNB UTI/bacteriuria in the multivariate analysis. In addition, ESBL-GNB-infected cases subsequently had a longer inpatient stay (median 6 vs. 2 days, p=0.002) and were admitted to the intensive care unit more frequently (28/100 vs. 8/100, p<0.001). Our results emphasize the need for culture of a mid-stream urine specimen prior to commencing antibacterials, especially in patients with the risk factors identified herein associated with ESBL-GNB UTI/bacteriuria