Time frequency analysis in terahertz pulsed imaging

Recent advances in laser and electro-optical technologies have made the previously under-utilized terahertz frequency band of the electromagnetic spectrum accessible for practical imaging. Applications are emerging, notably in the biomedical domain. In this chapter the technique of terahertz pulsed imaging is introduced in some detail. The need for special computer vision methods, which arises from the use of pulses of radiation and the acquisition of a time series at each pixel, is described. The nature of the data is a challenge since we are interested not only in the frequency composition of the pulses, but also how these differ for different parts of the pulse. Conventional and short-time Fourier transforms and wavelets were used in preliminary experiments on the analysis of terahertz pulsed imaging data. Measurements of refractive index and absorption coefficient were compared, wavelet compression assessed and image classification by multidimensional clustering techniques demonstrated. It is shown that the timefrequency methods perform as well as conventional analysis for determining material properties. Wavelet compression gave results that were robust through compressions that used only 20% of the wavelet coefficients. It is concluded that the time-frequency methods hold great promise for optimizing the extraction of the spectroscopic information contained in each terahertz pulse, for the analysis of more complex signals comprising multiple pulses or from recently introduced acquisition techniques

Laser Based Mid-Infrared Spectroscopic Imaging – Exploring a Novel Method for Application in Cancer Diagnosis

A number of biomedical studies have shown that mid-infrared spectroscopic images can provide both morphological and biochemical information that can be used for the diagnosis of cancer. Whilst this technique has shown great potential it has yet to be employed by the medical profession. By replacing the conventional broadband thermal source employed in modern FTIR spectrometers with high-brightness, broadly tuneable laser based sources (QCLs and OPGs) we aim to solve one of the main obstacles to the transfer of this technology to the medical arena; namely poor signal to noise ratios at high spatial resolutions and short image acquisition times. In this thesis we take the first steps towards developing the optimum experimental configuration, the data processing algorithms and the spectroscopic image contrast and enhancement methods needed to utilise these high intensity laser based sources. We show that a QCL system is better suited to providing numerical absorbance values (biochemical information) than an OPG system primarily due to the QCL pulse stability. We also discuss practical protocols for the application of spectroscopic imaging to cancer diagnosis and present our spectroscopic imaging results from our laser based spectroscopic imaging experiments of oesophageal cancer tissue

Metal-Mold Reactions in CMSX-4 Single Crystal Superalloy Castings

Metal-mold reaction (MMR) layers are often found on the surface of as-cast CMSX-4 single-crystal alloy parts. These layers cannot be removed prior to solution heat treatment of cast parts because of the sensitivity of the single-crystal castings to recrystallization (RX) defect formation. Removal of the reaction layer after solution heat treatments is very costly, as the layer is very hard, and requires abrasive water jet and pressure (grit) blasting processes. To address this manufacturing concern, it was desirable to understand the mechanisms of reaction layer formation and hardening after solution heat treatment. With this understanding, we developed methods for minimizing the reaction layer formation, which will potentially bring a big cost saving for the CMSX-4 casting processes.In this work, we confirmed experimentally that silica (SiO2) reacts with Al, Hf, and Ti, facilitating surface oxidation and formation of a tenacious surface eutectic phase. To avoid this, elimination of the Si is desired. However, Si is present in many of the refractory and pattern materials used in the casting system, which can transfer into the alloy during the solidification process in both liquid and solid state. A two-path solution was investigated: 1) eliminate all Si sources, and 2) create surface diffusion barriers to prevent reaction of the SiO2 with the metal. Potential sources of silica/silicon in the casting system include: the CMSX-4 charge material (nominal Si content less than 400 ppm), thermocouple protection quartz tube (100% silica), crucible (4% silica), bushing (80% silica), funnel (if used-60% silica), ash in pattern waxes, mold release (silicone-based), binder for facecoating (includes nanoscale silica-4% in facecoat), and cores (when used-80% silica).For a diffusion barrier, an yttria slurry (short lifetime and high cost of fine yttria flour), was replaced with an yttria aerosol spray coating, applied directly to the wax pattern before normal zircon primary facecoating. This was followed by an yttria binder washing and soaking, applied on top of the spray coating shell after dewaxing for strengthening. This process showed good bonding in casting trials in an argon atmosphere Bridgman casting furnace. Optical microscopy, SEM/EDS, AES and XPS techniques were employed for characterization of MMR interfaces of both the CMSX-4 casting and the shell mold. These characterization methods revealed MMR layers with oxidation, Si and Hf rich features.In this study, the yttria spray (alone) slightly reduces the amount of MMR of CMSX-4, but when the yttria spray was combined with the binder wash, the reaction was further reduced

Discovering the cover: molecular imaging of Populus trichocarpa leaf surface by FT-IR spectroscopy and mass spectrometry techniques

All terrestrial plants are covered by cuticle and its most outer layer is called epicuticular waxes (EWs). This layer forms an actual leaf surface, therefore is a first line of defence against any environmental stress. Despite its crucial role in plant survival, for decades leaf surface was studied without required selectivity. In the present research, the leaf surface was investigated using selective sampling methods and molecular imaging tools: (1) MALDI-TOF-MS (matrix assisted laser/desorption ionization), (2) TOF-SIMS (time-of flight secondary ion) mass spectrometry imaging, (3) FT-IR (Fourier transform infrared) as well as (4) Raman spectroscopy imaging. These tools provide molecular specificity and spatially resolved information. The results were complemented with GC-MS, SEM (scanning electron microscopy), behavioral experiments and statistical analysis. The first sequenced tree, Populus trichocarpa, along with the leaf beetle Chrysomela populi were chosen as a model system. This system represents naturally occurring interaction between a specialist herbivore and its host plant. Following aspects were investigated: (1) Characterization of structure and chemical composition of leaf surface (2) Investigation of role of EW layer in the host recognition process (3) Analysis of wound-healing processes on the leaf surface in response to insect infestation (4) Distribution of leaf surface constituents with high resolution imaging techniques. Results allow to conclude, that: (1) Higly non polar aliphatic compounds detected on the leaf surface of P. trichocarpa play protective role rather than informative (2) EW layer lack compounds that would be necessary in the host recognition process (3) EWs are involved in early stage wound-healing process by their deposition on the injury area (4) Leaf surface compounds co-aggregate and form two distribution patterns, possibly transport of EW constituents depends on their chain length

Tubulin cofactors and Arl2 are cage-like chaperones that regulate the soluble αβ-tubulin pool for microtubule dynamics.

Microtubule dynamics and polarity stem from the polymerization of αβ-tubulin heterodimers. Five conserved tubulin cofactors/chaperones and the Arl2 GTPase regulate α- and β-tubulin assembly into heterodimers and maintain the soluble tubulin pool in the cytoplasm, but their physical mechanisms are unknown. Here, we reconstitute a core tubulin chaperone consisting of tubulin cofactors TBCD, TBCE, and Arl2, and reveal a cage-like structure for regulating αβ-tubulin. Biochemical assays and electron microscopy structures of multiple intermediates show the sequential binding of αβ-tubulin dimer followed by tubulin cofactor TBCC onto this chaperone, forming a ternary complex in which Arl2 GTP hydrolysis is activated to alter αβ-tubulin conformation. A GTP-state locked Arl2 mutant inhibits ternary complex dissociation in vitro and causes severe defects in microtubule dynamics in vivo. Our studies suggest a revised paradigm for tubulin cofactors and Arl2 functions as a catalytic chaperone that regulates soluble αβ-tubulin assembly and maintenance to support microtubule dynamics

Becoming-Other: Foucault, Deleuze, and the Political Nature of Thought

In this paper I employ the notion of the ‘thought of the outside’ as developed by Michel Foucault, in order to defend the philosophy of Gilles Deleuze against the criticisms of ‘elitism,’ ‘aristocratism,’ and ‘political indifference’—famously leveled by Alain Badiou and Peter Hallward. First, I argue that their charges of a theophanic conception of Being, which ground the broader political claims, derive from a misunderstanding of Deleuze’s notion of univocity, as well as a failure to recognize the significance of the concept of multiplicity in Deleuze’s thinking. From here, I go on to discuss Deleuze’s articulation of the ‘dogmatic image of thought,’ which, insofar as it takes ‘recognition’ as its model, can only ever think what is already solidified and sedimented as true, in light of existing structures and institutions of power. Then, I examine Deleuze’s reading of Foucault and the notion of the ‘thought of the outside,’ showing the ‘outside’ as the unthought that lies at the heart of thinking itself, as both its condition and its impossibility. Insofar as it is essential to thinking itself, finally, I argue that the passage of thought to the outside is not an absolute flight out of this world, as Hallward claims, but rather, a return of the different that constitutes the Self for Deleuze. Thinking is an ongoing movement of deterritorialization and reterritorialization, or as Foucault says, death and life. Thinking, as Deleuze understands it, is essentially creative; it reconfigures the virtual, thereby literally changing the world. Thinking is therefore, according to Deleuze, thoroughly political

Imaging fetal anatomy.

Due to advancements in ultrasound techniques, the focus of antenatal ultrasound screening is moving towards the first trimester of pregnancy. The early first trimester however remains in part, a 'black box', due to the size of the developing embryo and the limitations of contemporary scanning techniques. Therefore there is a need for images of early anatomical developmental to improve our understanding of this area. By using new imaging techniques, we can not only obtain better images to further our knowledge of early embryonic development, but clear images of embryonic and fetal development can also be used in training for e.g. sonographers and fetal surgeons, or to educate parents expecting a child with a fetal anomaly. The aim of this review is to provide an overview of the past, present and future techniques used to capture images of the developing human embryo and fetus and provide the reader newest insights in upcoming and promising imaging techniques. The reader is taken from the earliest drawings of da Vinci, along the advancements in the fields of in utero ultrasound and MR imaging techniques towards high-resolution ex utero imaging using Micro-CT and ultra-high field MRI. Finally, a future perspective is given about the use of artificial intelligence in ultrasound and new potential imaging techniques such as synchrotron radiation-based CT to increase our knowledge regarding human development