Current methods for characterising mixing and flow in microchannels

This article reviews existing methods for the characterisation of mixing and flow in microchannels, micromixers and microreactors. In particular, it analyses the current experimental techniques and methods available for characterising mixing and the associated phenomena in single and multiphase flow. The review shows that the majority of the experimental techniques used for characterising mixing and two-phase flow in microchannels employ optical methods, which require optical access to the flow, or off-line measurements. Indeed visual measurements are very important for the fundamental understanding of the physics of these flows and the rapid advances in optical measurement techniques, like confocal scanning laser microscopy and high resolution stereo micro particle image velocimetry, are now making full field data retrieval possible. However, integration of microchannel devices in industrial processes will require on-line measurements for process control that do not necessarily rely on optical techniques. Developments are being made in the areas of non-intrusive sensors, magnetic resonance techniques, ultrasonic spectroscopy and on-line flow through measurement cells. The advances made in these areas will certainly be of increasing interest in the future as microchannels are more frequently employed in continuous flow equipment for industrial applications

Holistic improvement of image acquisition and reconstruction in fluorescence microscopy

Recent developments in microscopic imaging led to a better understanding of intra- and intercellular metabolic processes and, for example, to visualize structural properties of viral pathogens. In this thesis, the imaging process of widefield and confocal scanning microscopy techniques is treated holistically to highlight general strategies and maximise their information content. Poisson or shot noise is assumed to be the fundamental noise process for the given measurements. A stable focus position is a basic condition for e.g. long-term measurements in order to provide reliable information about potential changes inside the Field-of-view. While newer microscopy systems can be equipped with hardware autofocus, this is not yet the widespread standard. For image-based focus analysis, different metrics for ideal, noisy and aberrated, in case of spherical aberration and astigmatism, measurements are presented. A stable focus position is also relevant in the example of 2-photon confocal imaging and at the same time the situation is aggravated in the given example, the measurement of the retina in the living mouse. In addition to the natural drift of the focal position, which can be evaluated by means of previously introduced metrics, rhythmic heartbeat, respiration, unrhythmic muscle twitching and movement of the mouse kept in artificial sleep are added. A dejittering algorithm is presented for the measurement data obtained under these circumstances. Using the additional information about the sample distribution in ISM, a method for reconstructing 3D from 2D image data is presented in the form of thick slice unmixing. This method can further be used for suppression of light generated outside the focal layer of 3D data stacks and is compared to selective layer multi-view deconvolution. To reduce phototoxicity and save valuable measurement time for a 3D stack, the method of zLEAP is presented, by which omitted Z-planes are subsequently calculated and inserted

Instability, Intermixing and Electronic Structure at the Epitaxial LaAlO3/SrTiO3(001) Heterojunction

The question of stability against diffusional mixing at the prototypical LaAlO3/SrTiO3(001) interface is explored using a multi-faceted experimental and theoretical approach. We combine analytical methods with a range of sensitivities to elemental concentrations and spatial separations to investigate interfaces grown using on-axis pulsed laser deposition. We also employ computational modeling based on the density function theory as well as classical force fields to explore the energetic stability of a wide variety of intermixed atomic configurations relative to the idealized, atomically abrupt model. Statistical analysis of the calculated energies for the various configurations is used to elucidate the relative thermodynamic stability of intermixed and abrupt configurations. We find that on both experimental and theoretical fronts, the tendency toward intermixing is very strong. We have also measured and calculated key electronic properties such as the presence of electric fields and the value of the valence band discontinuity at the interface. We find no measurable electric field in either the LaAlO3 or SrTiO3, and that the valence band offset is near zero, partitioning the band discontinuity almost entirely to the conduction band edge. Moreover, we find that it is not possible to account for these electronic properties theoretically without including extensive intermixing in our physical model of the interface. The atomic configurations which give the greatest electrostatic stability are those that eliminate the interface dipole by intermixing, calling into question the conventional explanation for conductivity at this interface - electronic reconstruction. Rather, evidence is presented for La indiffusion and doping of the SrTiO3 below the interface as being the cause of the observed conductivity

Multi-exposure diffraction pattern fusion applied to enable wider-angle transmission Kikuchi diffraction with direct electron detectors

Diffraction pattern analysis can be used to reveal the crystalline structure of materials, and this information is used to nano- and micro-structure of advanced engineering materials that enable modern life. For nano-structured materials typically diffraction pattern analysis is performed in the transmission electron microscope (TEM) and TEM diffraction patterns typically have a limited angular range (less than a few degrees) due to the long camera length, and this requires analysis of multiple patterns to probe a unit cell. As a different approach, wide angle Kikuchi patterns can be captured using an on-axis detector in the scanning electron microscope (SEM) with a shorter camera length. These 'transmission Kikuchi diffraction' (TKD) patterns present a direct projection of the unit cell and can be routinely analyzed using EBSD-based methods and dynamical diffraction theory. In the present work, we enhance this analysis significantly and present a multi-exposure diffraction pattern fusion method that increases the dynamic range of the detected patterns captured with a Timepix3-based direct electron detector (DED). This method uses an easy-to-apply exposure fusion routine to collect data and extend the dynamic range, as well as normalize the intensity distribution within these very wide (>95{\deg}) angle patterns. The potential of this method is demonstrated with full diffraction sphere reprojection and highlight potential of the approach to rapidly probe the structure of nano-structured materials in the scanning electron microscope.Comment: as submitted, after one revisio

A novel optical microscope for imaging large embryos and tissue volumes with sub-cellular resolution throughout

Current optical microscope objectives of low magnification have low numerical aperture and therefore have too little depth resolution and discrimination to perform well in confocal and nonlinear microscopy. This is a serious limitation in important areas, including the phenotypic screening of human genes in transgenic mice by study of embryos undergoing advanced organogenesis. We have built an optical lens system for 3D imaging of objects up to 6 mm wide and 3 mm thick with depth resolution of only a few microns instead of the tens of microns currently attained, allowing sub-cellular detail to be resolved throughout the volume. We present this lens, called the Mesolens, with performance data and images from biological specimens including confocal images of whole fixed and intact fluorescently-stained 12.5-day old mouse embryos

Advanced Image Acquisition, Processing Techniques and Applications

"Advanced Image Acquisition, Processing Techniques and Applications" is the first book of a series that provides image processing principles and practical software implementation on a broad range of applications. The book integrates material from leading researchers on Applied Digital Image Acquisition and Processing. An important feature of the book is its emphasis on software tools and scientific computing in order to enhance results and arrive at problem solution

The development of a time-resolved confocal microscope for single molecule detection of luminescent polymers

This report details the construction and testing of a confocal microscope for use in single molecule fluorescence spectroscopy. With the prospect of making time-resolved lifetime and spectral measurements of π-conjugated polymers in the condensed phase, the system employs a pulsed 390nm, 65ps diode laser along with compact electronics for time-correlated single photon counting. Following optimisation the microscope records continuous photon arrival times with l00ps resolution, and fluorescence lifetime decays with 40ps resolution. Isolation of polymer chains has been investigated as a function of dilution by the dispersion of poly[9,9di(ethylhexyl)fluorene] (PF2/6) in a variety of host matrices. Films have been prepared by spin coating from toluene and the emission spectra, confocal lifetime and anisotropy have been investigated. Whilst the choice of host does not show any considerable influence on the spectral characteristics of the luminescent polymer, concentration and spin speed were observed to significantly influence the photophysical properties of the film. Spectral blue shifts in the emission band have been observed as the dilution of the luminescent polymer increases, reaching a maximum shift of 20nm in the most dilute samples. In line with the spectral shift, lifetime measurements show that the fluorescence decay becomes increasingly mono-exponential with dilution. In films exhibiting the maximum spectral blue shift, mono-exponential fluorescence decay was observed, for the oligomer oligo [9,9di(ethylhexyl)fluorene] (_N=20) (OF2/6) in zeonex the lifetime is found to be τ = 0.92ns. The dilution at which this occurs varies from 1x10(^-4) % w/w to 1x10(^-6) % w/w depending on spin speed and host matrix. Significantly longer that the lifetime of OF2/6 in solution, this is thought to be very close to the natural radiative lifetime of the polymer and is taken as a clear indication of chain isolation within the host matrix. Spectral blue shift and progression to mono-exponential fluorescence decay are explained in terms of the decline of low energy aggregate states and a reduction in non-radiative interchain energy transfer due to increased interchain separation. Confocal imaging using the specimen scanning technique has been developed using an electronically controlled x y piezo-stage. By optimising the optical set up the confocal image resolution is currently 0.369nm. The maximum theoretical confocal resolution at 390nm excitation is 0.268nm; the cause of this loss in resolution is thought to originate from slight non-uniformity in the excitation source

Micro-Nano Technologies for Cell Manipulation and Subcellular Monitoring

Rehabilitatio

Improvements in Digital Holographic Microscopy

The Ph.D. dissertation consists of developing a series of innovative computational methods for improving digital holographic microscopy (DHM). DHM systems are widely used in quantitative phase imaging for studying micrometer-size biological and non-biological samples. As any imaging technique, DHM systems have limitations that reduce their applicability. Current limitations in DHM systems are: i) the number of holograms (more than three holograms) required in slightly off-axis DHM systems to reconstruct the object phase information without applying complex computational algorithms; ii) the lack of an automatic and robust computation algorithm to compensate for the interference angle and reconstruct the object phase information without phase distortions in off-axis DHM systems operating in telecentric and image plane conditions; iii) the necessity of an automatic computational algorithm to simultaneously compensate for the interference angle and numerically focus out-of-focus holograms on reconstructing the object phase information without phase distortions in off-axis DHM systems operating in telecentric regime; iv) the deficiency of reconstructing phase images without phase distortions at video-rate speed in off-axis DHM operating in telecentric regime, and image plane conditions; v) the lack of an open-source library for any DHM optical configuration; and, finally, vi) the tradeoff between speckle contrast and spatial resolution existing in current computational strategies to reduce the speckle contrast. This Ph.D. dissertation is motivated to overcome or at least reduce the six limitations mentioned above. Each chapter of this dissertation presents and discusses a novel computational method from the theoretical and experimental point of view to address each of these limitations