Enhanced optical tweezing: from hydrodynamic micro-manipulation to optimised optical trapping

Optical tweezers, with their ability to trap particles at the focus of a laser beam and control their motion, have provided unparalleled insight into the inner workings of the micro-world of colloids, cells and biomolecules. However, not all materials yield to optical trapping, and living organisms can be damaged by direct light exposure. Many optical tweezing experiments are performed in aqueous environments. This offers a route to indirect particle manipulation via the surrounding fluid. We develop, study, and experimentally demonstrate an approach which, by employing optically controlled micro-rotors to induce flow currents in the surrounding fluid, exerts near field hydrodynamic control over freely diffusing particles, irrespective of their material. With our optically actuated hydrodynamic manipulation we were able to suppress the thermal motion of single sedimented micro-sized target particles of various materials in both translational and rotational degrees-of-freedom, translate individual particles over complex local trajectories or transport them over long distances across the holding sample cell, and exert control over multiple particles simultaneously. The biggest challenge in our hydrodynamic manipulation technique is the accuracy with which the optical tweezers can control the actuator motion. This boils down to optical trapping stiffness. We employ the generalised Wigner-Smith operators alongside an optimisation scheme to upgrade the optical trapping field from the standard Gaussian beam to a three-dimensionally stiffness-enhanced trap. Within simulations we demonstrate light fields with an order of magnitude stiffness enhancement in all three dimensions simultaneously. Such fields, as well as the techniques used to develop them, can find applications throughout the wide community of optical trapping and manipulation

Notes in Pure Mathematics & Mathematical Structures in Physics

These Notes deal with various areas of mathematics, and seek reciprocal combinations, explore mutual relations, ranging from abstract objects to problems in physics.Comment: Small improvements and addition

Integrated navigation and visualisation for skull base surgery

Skull base surgery involves the management of tumours located on the underside of the brain and the base of the skull. Skull base tumours are intricately associated with several critical neurovascular structures making surgery challenging and high risk. Vestibular schwannoma (VS) is a benign nerve sheath tumour arising from one of the vestibular nerves and is the commonest pathology encountered in skull base surgery. The goal of modern VS surgery is maximal tumour removal whilst preserving neurological function and maintaining quality of life but despite advanced neurosurgical techniques, facial nerve paralysis remains a potentially devastating complication of this surgery. This thesis describes the development and integration of various advanced navigation and visualisation techniques to increase the precision and accuracy of skull base surgery. A novel Diffusion Magnetic Resonance Imaging (dMRI) acquisition and processing protocol for imaging the facial nerve in patients with VS was developed to improve delineation of facial nerve preoperatively. An automated Artificial Intelligence (AI)-based framework was developed to segment VS from MRI scans. A user-friendly navigation system capable of integrating dMRI and tractography of the facial nerve, 3D tumour segmentation and intraoperative 3D ultrasound was developed and validated using an anatomically-realistic acoustic phantom model of a head including the skull, brain and VS. The optical properties of five types of human brain tumour (meningioma, pituitary adenoma, schwannoma, low- and high-grade glioma) and nine different types of healthy brain tissue were examined across a wavelength spectrum of 400 nm to 800 nm in order to inform the development of an Intraoperative Hypserpectral Imaging (iHSI) system. Finally, functional and technical requirements of an iHSI were established and a prototype system was developed and tested in a first-in-patient study

Advanced neuroimaging techniques to study the development of the cerebral cortex, subplate and thalamus in preterm infants at 3 Tesla

Preterm infants are at increased risk of neurodevelopmental delay, cognitive dysfunction, and behavioural disturbances. Recent studies of older preterm children with cognitive impairments implicate morphological and functional cortical abnormalities. However elucidation of the preterm cortical abnormalities has been challenging due to specific neonatal features. Using 3 Tesla neonatal MR images and Expectation Maximisation/Markov Random Field segmentation with incorporation of a novel knowledge based technique for removal of mislabelled partial volume voxels, neonatal 3D cortical extraction was possible from 25 to 48 weeks gestation. This enabled the study of the true cortical scaling exponent, cortical thickness, regional volumes and curvature measurements. It showed a relative excess of the cortical surface area for its volume which corresponded with a change in the intrinsic curvature and fissuration up to 36 weeks gestation, after which, the relative growth of the surface area and volume were proportional leading to dominant changes in the extrinsic curvature and cortical folding. Thus the curvature measurements showed an important mechanistic property of convolution. By term equivalent age, the cortex was thicker and there were changes in cortical curvature although there were no differences in the cortical surface area of preterm infants compared to term born controls. There were specific frontal and parietal deficits in the cortical volume. Diffusion MR showed that although the early cortical anisotropy diminished to noise levels by 35 weeks, the mean diffusivity reduced during the entire third trimester due to changes in the radial diffusivity. Regional variations in the mean diffusivity occurred during development with frontal abnormalities persisting at term equivalent age. Subplate and thalamic quantification showed important development features during the third trimester, however in the absence of overt lesions no associations with cortical measures were found. Thus this thesis provides interesting and novel insights into the macroscopic and microscopic development of the cortex.Imperial Users onl

Generalized averaged Gaussian quadrature and applications

A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal

MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications

Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described