An FPGA-based lock-in detection system to enable chemical species tomography using TDLAS

This paper presents the design, implementation and test of a compact, low-cost and fully digital signal recovery system for tunable diode laser absorption spectroscopy (TDLAS) in narrow line-width gas sensing applications. An FPGA-based digital lock-in amplifier (DLIA), in conjunction with TDLAS using the wavelength modulation spectroscopy (WMS) technique, is utilized to demodulate and extract first (1f) and second (2f) harmonic signals for a narrow CO2 feature in the spectrum region of 1997.2nm. The spectrum in this wavelength region shows suitably weak water absorption, enabling CO2 detection with high resolution. Gas-cell experiments were carried out using the DLIA and a conventional rack-mounted commercial lock-in amplifier. The comparison between the two systems shows good agreement, validating the feasibility of this approach and demonstrating the prospect for extension to a massively multichannel system to implement Chemical Species Tomography

A Fatal Case of Metastatic Pulmonary Calcification during the Puerperium

We present an unusual case of a fatal respiratory failure in a young woman developed two weeks after she gave birth at home. Circumstantial and clinical features of the case were strongly suggestive for a ‘classical’ septic origin of the respiratory symptoms. Autopsy, together with histopathological and immunohistochemical analyses allowed demonstrating a massive calcium redistribution consisting of an important osteolysis, especially from cranial bones and abnormal accumulation in lungs and other organs. Such physiopathology was driven by a primary hyperparathyroidism secondary to a parathyroid carcinoma as demonstrated by immunohistochemistry. This very rare case is furthermore characterised by a regular pregnancy course, ended with the birth of a healthy new-born. A complex interaction between pregnancy physiology and hyperparathyroidism might be hypothesised, determining the discrepancy between the relative long period of wellness and the tumultuous cascade occurred in the puerperium

The ‘ForensOMICS’ approach for postmortem interval estimation from human bone by integrating metabolomics, lipidomics, and proteomics

The combined use of multiple omics allows to study complex interrelated biological processes in their entirety. We applied a combination of metabolomics, lipidomics and proteomics to human bones to investigate their combined potential to estimate time elapsed since death (i.e., the postmortem interval [PMI]). This ‘ForensOMICS’ approach has the potential to improve accuracy and precision of PMI estimation of skeletonized human remains, thereby helping forensic investigators to establish the timeline of events surrounding death. Anterior midshaft tibial bone was collected from four female body donors before their placement at the Forensic Anthropology Research Facility owned by the Forensic Anthropological Center at Texas State (FACTS). Bone samples were again collected at selected PMIs (219-790-834-872days). Liquid chromatography mass spectrometry (LC-MS) was used to obtain untargeted metabolomic, lipidomic, and proteomic profiles from the pre- and post-placement bone samples. The three omics blocks were investigated independently by univariate and multivariate analyses, followed by Data Integration Analysis for Biomarker discovery using Latent variable approaches for Omics studies (DIABLO), to identify the reduced number of markers describing postmortem changes and discriminating the individuals based on their PMI. The resulting model showed that pre-placement metabolome, lipidome and proteome profiles were clearly distinguishable from post-placement ones. Metabolites in the pre-placement samples suggested an extinction of the energetic metabolism and a switch towards another source of fuelling (e.g., structural proteins). We were able to identify certain biomolecules with an excellent potential for PMI estimation, predominantly the biomolecules from the metabolomics block. Our findings suggest that, by targeting a combination of compounds with different postmortem stability, in the future we could be able to estimate both short PMIs, by using metabolites and lipids, and longer PMIs, by using proteins

A Custom, High-Channel-Count Data Acquisition System for Chemical Species Tomography of Aero-Jet Engine Exhaust Plumes

The fiber-laser imaging of gas turbine exhaust species project aims to provide a video-rate imaging (100 frames/s) diagnostic tool for application to the exhaust plumes of the largest civil aero-jet engines. This remit, enabled by chemical species tomography (CST) currently targeting carbon dioxide (CO 2 ), requires system design that facilitates expansion of multiple parameters. Scalability is needed in order to increase imaging speeds and spatial resolutions and extends the system toward other pertinent gases such as the oxides of nitrogen and sulfur and unburnt hydrocarbons. This paper presents a fully scalable, noninvasive instrument for installation in a commercial engine testing facility, technical challenges having been tackled iteratively through bespoke optical and mechanical design, and it specifically presents the high-speed data acquisition (DAQ) system required. Measurement of gas species concentration is implemented by tunable diode laser absorption with wavelength modulation spectroscopy (TDLAS-WMS) using a custom, high-speed 10-40-MS/s/channel 14-bit DAQ. For CO 2 tomography, the system uses six angular projections of 21 beams each. However, the presented DAQ has capacity for 192 fully parallel 10-Hz-3-MHz differential inputs, achieving a best-case signal-to-noise ratio (SNR) of 56.5 dB prior to filtering. A 12 Ethernet-connected digitization nodes based on field-programmable gate array technology with software control are distributed around a 7-m-diameter mounting “ring.” Hence, the high data rates of 8.96-Gb/s per printed circuit board and 107.52 Gb/s for the whole system can be reduced by using local digital lock-in amplifiers. We believe that this DAQ system is unique in both the TDLAS and CST literatures

Constrained models for optical absorption tomography

We consider the inverse problem of concentration imaging in optical absorption tomography with limited data sets. The measurement setup involves simultaneous acquisition of near infrared wavelength modulated spectroscopic measurements from a small number of pencil beams equally distributed among six projection angles surrounding the plume. We develop an approach for image reconstruction that involves constraining the value of the image to the conventional concentration bounds and a projection into low-dimensional subspaces to reduce the degrees of freedom in the inverse problem. Effectively, by reparameterising the forward model we impose simultaneously spatial smoothness and a choice between three types of inequality constraints, namely positivity, boundedness and logarithmic boundedness in a simple way that yields an unconstrained optimisation problem in a new set of surrogate parameters. Testing this numerical scheme with simulated and experimental phantom data indicates that the combination of affine inequality constraints and subspace projection leads to images that are qualitatively and quantitatively superior to unconstrained regularised reconstructions. This improvement is more profound in targeting concentration profiles of small spatial variation. We present images and convergence graphs from solving these inverse problems using Gauss-Newton's algorithm to demonstrate the performance and convergence of our method

Tomographic imaging of carbon dioxide in the exhaust plume of large commercial aero-engines

We report here the first implementation of chemically specific imaging in the exhaust plume of a gas turbine typical of those used for propulsion in commercial aircraft. The method used is chemical species tomography (CST) and the target species is CO2, absorbing in the near-infrared at 1999.4 nm. A total of 126 beams propagate transverse to the plume axis, along 7 m paths in a coplanar geometry, to probe a central region of diameter ≈1.5m. The CO2 absorption spectrum is measured using tunable diode laser spectroscopy with wavelength modulation, using the second harmonic to first harmonic (2f/1f) ratio method. The engine is operated over the full range of thrust, while data are recorded in a quasi-simultaneous mode at frame rates of 1.25 and 0.3125 Hz. Various data inversion methodologies are considered and presented for image reconstruction. At all thrust levels a persistent ring structure of high CO2 concentration is observed in the central region of the measurement plane, with a raised region in the middle of the plume assumed to be due to the engine’s boat tail. With its potential to target various exhaust species, the CST method outlined here offers a new approach to turbine combustion research, turbine engine development, and aviation fuel research and development

Towards chemical species tomography of carbon dioxide for aviation turbine emissions

This thesis sets out to examine the proposal that, by using tomography and gas sensing techniques to detect and image gas concentration in fast moving flows, engineers can improve the combustion diagnostics and emissions performance of gas turbines, enabling a better understanding of combustion and design optimisation of greener engines. The key factor is the combination of tomography with Tunable Diode Laser Absorption Spectroscopy (TDLAS) gas sensing technology, implemented simultaneously along many beams, to image the gas concentration distribution in the exhaust plume of a gas turbine, in a plane perpendicular to the plume flow direction. The target gas species is carbon dioxide, CO2, and the absorption feature chosen is at a wavelength of 1997.2 nm. The narrow spectral absorption properties of such small molecules present a considerable challenge for a multi-beam tomographic implementation. Moreover, the design, oriented to harsh and industrial environments, presents key challenges for the design of robust optics and electronics for the collection of reliable data. The development of a 126-beam tomography system required the investigation of recently developed TDLAS techniques and their compatibility with data acquisition (DAQ) system firmware strategies to be implemented by custom DAQ electronics. A novel FPGA-based single channel TDLAS CO2 detection system has been designed and built to demonstrate the feasibility for the replication of 126-channels in the full system. Further proof-of-concept experiments carried out at full scale have produced tomographic images of phantom CO2 distributions that demonstrate the utility of the CST technique

A Fatal Case of Metastatic Pulmonary Calcification during the Puerperium

We present an unusual case of a fatal respiratory failure in a young woman developed two weeks after she gave birth at home. Circumstantial and clinical features of the case were strongly suggestive for a ‘classical’ septic origin of the respiratory symptoms. Autopsy, together with histopathological and immunohistochemical analyses allowed demonstrating a massive calcium redistribution consisting of an important osteolysis, especially from cranial bones and abnormal accumulation in lungs and other organs. Such physiopathology was driven by a primary hyperparathyroidism secondary to a parathyroid carcinoma as demonstrated by immunohistochemistry. This very rare case is furthermore characterised by a regular pregnancy course, ended with the birth of a healthy new-born. A complex interaction between pregnancy physiology and hyperparathyroidism might be hypothesised, determining the discrepancy between the relative long period of wellness and the tumultuous cascade occurred in the puerperium