Robert Cernik - Academia.edu (original) (raw)

Papers by Robert Cernik

General Data description: This is a hyperspectral (energy-resolved) ... more General Data description: This is a hyperspectral (energy-resolved) X-ray CT projection dataset of a lizard head sample, stained with an iodine contrast agent. It was acquired in a custom-built, laboratory micro-CT scanner with an energy-sensitive HEXITEC detector in the Henry Moseley X-ray Imaging Facility at The University of Manchester. The following data contains all the files necessary for reconstruction, after a hyperspectral scan was taken of a single, iodine-stained lizard head sample. The iodine contrast agent provided a spectral marker, measured by an energy-sensitive detector, which may be used for spatial mapping and segmentation of stained soft tissue regions. File descriptions: Contained are three MATLAB (.mat) data files, as well as a single text (.txt) file. Lizard_head_scan_parameters.txt provides the full sample and detector geometry of the scan acquisition. lizard_head_sinogram_full.mat contains the full 4D sinogram constructed following flatfield normalisation of the raw projection data. The 4D array contains the total number of energy channels acquired during scanning, followed by vertical and horizontal pixel number, and finally total projections angles acquired. The data provided is prior to application of any post-processing filters. Energy_axis.mat provides a direct conversion between the energy channels, and the energies (in keV) that they correspond to, following a calibration procedure prior to scanning. FF.mat contains the 4D flatfield data acquired when no sample was present. This data was used to normalise the projection datasets, as the sinogram was constructed.

General data description: This is a hyperspectral (energy-resolved) ... more General data description: This is a hyperspectral (energy-resolved) X-ray CT projection data set of a mineralised ore sample with small gold and galena deposits. It was acquired in a laboratory micro-CT scanner with an energy-sensitive HEXITEC detector in the Henry Moseley X-ray Imaging Facility at The University of Manchester. The data included contains all the relevant files required for reconstruction, following a hyperspectral scan of a mineralised ore sample. The sample contains a number of mineral phases, of varying concentration, distributed throughout. Some phases (including gold, and lead-based Galena) produce unique absorption edges, which act as spectral identifiers that can be measured by an energy-sensitive detector. File descriptions: The data set consists of one .txt file and three .mat (MATLAB) data files. Au_rock_scan_geometry.txt gives a breakdown of the full sample and detector geometry used when acquiring the raw projections. The number of horizontal detector pixels accounts for the fact that a set of 5 tiled scans of the sample were collected and later stitched together. Au_rock_sinogram_full.mat contains the full 4D sinogram constructed following flat-field normalisation of the raw projection data. The data matrix contains the total number of energy channels acquired during scanning, as well as the conventional elements of vertical/horizontal detector pixel number and total projection angles. commonX.mat provides a direct conversion between the energy channels, and the energies (in keV) that they correspond to, following a calibration procedure prior to scanning. FF.mat contains the 4D flatfield data acquired when no sample was present. This data was used to normalise the projection datasets, as the sinogram was constructed.

General Data description: This is a set of two hyperspectral (energy... more General Data description: This is a set of two hyperspectral (energy-resolved) X-ray CT projection datasets of a multi-phase phantom. It was acquired in a custom-built, laboratory micro-CT scanner with an energy-sensitive HEXITEC detector in the Henry Moseley X-ray Imaging Facility at The University of Manchester. The following data contains all the files necessary for reconstruction, following two hyperspectral scans of a metal, multi-phase phantom. The phantom consists of an external aluminium cylinder, with three holes, each filled with a different metal-based powder (CeO2, ZnO, Fe). Each powder provides a unique attenuation signal, with CeO2 in particular producing a distinct spectral marker which can be measured by an energy-sensitive detector. Two identical scans were acquired, with only the exposure time per projection changed. File descriptions: Contained is an image (.jpg) of the sample, along with five MATLAB (.mat) data files, as well as a single text (.txt) file. Where necessary, the files have been named to match the dataset they belong to, based on the different exposure times used for each dataset. Phantom_design_measurements.jpg contains a photograph of the physical phantom, combined with a diagram showing full sample measurements. Powder_phantom_scan_geometry.txt gives a breakdown of the full sample and detector geometry used when acquiring the raw projections for both scans. powder_phantom_30s_sinogram_full.mat contains the full 4D sinogram constructed following flatfield normalisation of the raw projection data, where an exposure time of 30 s was used for each projection. The 4D array contains the total number of energy channels acquired during scanning, followed by vertical and horizontal pixel number, and finally total projections angles acquired during scanning. powder_phantom_180s_sinogram_full.mat is the full 4D sinogram for the dataset, when exposure times of 180 s were used for each projection, following flatfield normalisation. A d [...]

Scientific Reports, 2021

Two sections of heat-treated (HT) and non-heat-treated (NHT) Cable-in-Conduit Conductor (CICC) of... more Two sections of heat-treated (HT) and non-heat-treated (NHT) Cable-in-Conduit Conductor (CICC) of a design similar to the ITER tokomak have been imaged using very high energy X-ray tomography at the ESRF beamline ID19. The sample images were collected at four temperatures down to 77 K. These results showed a greater degree of movement, bundle distortion and touching strands in the NHT sample. The HT sample showed non-linear movements with temperature especially close to 77 K; increasing non-circularity of the superconducting fibre bundles towards the periphery of the CICC, and touching bundles throughout the CICC. The images have highlighted where future design might improve potential weakness, in particular at the outer perimeters of the conductor and the individual sub-cable, ‘petal’ wraps.

ACS Applied Energy Materials, 2021

Developing a simple, safe and efficient route for the preparation of nanoparticulate ternary Chev... more Developing a simple, safe and efficient route for the preparation of nanoparticulate ternary Chevrel phases MxMo6S8 (CPs; where M = metal) is of great interest because of their applications in energy conversion and storage technologies. Currently, the wide use of these materials is restricted by the prolonged reaction time, the high energy demands required for their synthesis, the complexity of the preparation process and the ambiguity in the size of the resultant particles. Herein, we report a simple, efficient and controllable molecular precursor approach for the synthesis of nanoscale CP without the use of hydrogen gas as a reducing agent. A mixture of precursors based on molybdenum and copper dithiocarbamate complexes were subjected to thermolysis in the presence of finely divided molybdenum to furnish the copper CP, Cu2Mo6S8. The successful formation of the Cu2Mo6S8 CP is confirmed by X-ray diffraction analysis and Raman spectroscopy, while the surface chemistry of the material was examined by X-ray photoelectron spectroscopy photon depth profiling via tuneable synchrotron radiation. Microscopic characterisation results demonstrate that the synthesised material has a homogeneous structure at the nanoscale, in contrast to the microparticles obtained from conventional approaches previously reported. The prepared CP was assessed as an electrocatalyst for the hydrogen evolution reaction (HER) in acidic media. Due to its unique nanoscale texturing, the Cu-leached CP, Mo6S8, exhibits a highly promising electrocatalytic activity towards hydrogen evolution with an overpotential required to reach a current density of 10 mA cm-2 equal to 265 mV vs. RHE. The overpotential reduces to 232 mV upon mixing of the catalyst with 20% w/w of high conductivity carbon. It is expected that the proposed synthetic strategy, which represents a facile route to tailored CPs, can be extended to the preparation of versatile, easily tuneable CP Mo6S8-based electrode materials for applications in electrocatalysis.

Chemistry of Materials, 2020

Metal sulfide and metal oxide alloys of the form Mo 1−x W x S 2 and Mo 1−x W x O 3 (0 ≤ x ≤ 1) ar... more Metal sulfide and metal oxide alloys of the form Mo 1−x W x S 2 and Mo 1−x W x O 3 (0 ≤ x ≤ 1) are synthesized with varying nominal stoichiometries (x = 0, 0.25, 0.50, 0.75, and 1.0) by thermolysis of the molecular precursors MoL 4 and WS(S 2)L 2 (where L = S 2 CNEt 2) in tandem and in various ratios. Either transition-metal dichalcogenides or transition-metal oxides can be produced from the same pair of precursors by the choice of reaction conditions; metal sulfide alloys of the form Mo 1−x W x S 2 are produced in an argon atmosphere, while the corresponding metal oxide alloys Mo 1−x W x O 3 are produced in air, both under atmospheric pressure at 450°C and for only 1 h. Changes in Raman spectra and in powder X-ray diffraction patterns are observed across the series of alloys, which confirm that alloying is successful in the bulk materials. For the oxide materials, we show that the relatively complicated diffraction patterns are a result of differences in the tilt angle of MO 6 octahedra within three closely related unit cell types. Alloying of Mo and W in the products is characterized at the microscale and nanoscale by scanning electron microscopy−energy-dispersive X-ray spectroscopy (EDX) and scanning transmission electron microscopy−EDX spectroscopy, respectively.

SSRN Electronic Journal, 2020

Residual stress distributions as a function of depth in APS TBCs after different heat treatment t... more Residual stress distributions as a function of depth in APS TBCs after different heat treatment times have been measured by synchrotron XRD. Three types of residual stress distribution were observed. The first type was a low stress state from the as-received sample; the second type was a compressive stress state increasing from the surface to the interface with a discontinuous "jump feature" in the trend near the interface; the third type of residual stress distribution has two "jump" features in the trend, one was observed near the sample surface and the other near the interface. To understand the double "jump" features in the third kind of trend, the 3D microstructures of the measured samples were systematically measured X-ray μ-CT. Vertical cracks and edge cracks were observed. We have shown by image based modelling that the vertical cracks do not have a large effect on the residual stress distribution and that edge cracks are related to the "jump features" near the sample surface. The edge crack can be observed in all the measured samples with the third kind of the residual stress trend; and the measured samples with the second kind of the residual stress trend are crack free. The relationship between the middle and the through edge cracks and the residual stress distribution was also investigated by image based modelling. It was found that the middle crack can also cause a "jump feature" near the sample surface while the through edge crack seems to not have a large effect on the residual stress distribution. A semi-destructive method was developed to determine the existence and the position of horizontal cracks in the APS TBC samples based on the above findings.

Journal of Applied Crystallography, 2020

The residual strain distribution has been measured as a function of depth in both top coat and bo... more The residual strain distribution has been measured as a function of depth in both top coat and bond coat in as-received and heat-treated air plasma sprayed thermal barrier coating samples. High-energy synchrotron X-ray beams were used in transmission to produce full Debye–Scherrer rings whose non-circular aspect ratio gave the in-plane and out-of-plane strains far more efficiently than the sin2ψ method. The residual strain in the bond coat is found to be tensile and the strain in the β phase of the as-received sample was measured. The residual strains observed in the top coat were generally compressive (increasing towards the interface), with two kinds of nonlinear trend. These was a `jump' feature near the interface, and in some cases there was another `jump' feature near the surface. It is shown how these trend differences can be correlated to cracks in the coating.

Applied Surface Science, 2018

Measurement Science and Technology, 2016

We describe the implementation of a reliable, robust and flexible gain correction and energy cali... more We describe the implementation of a reliable, robust and flexible gain correction and energy calibration algorithm for pixelated spectroscopic X-ray detectors. This algorithm uses a data processing method known as correlation optimised warping which aligns shifted datasets by means of a segmental linear stretching and compression of the spectral data in order to best correlate with a reference spectrum. We found the algorithm to be very robust against low-count spectroscopy, and was reliable in a range of different spectroscopic applications. Analysis of the integrated spectrum over all pixels for a Cerium K-alpha X-ray emission (at 34.72 keV) yielded a peak width of 2.45 keV before alignment and 1.11 keV after alignment. This compares favourably with the best in class pixel peak width of 0.76 keV and the mean peak width for all pixels of 1.00 keV. We also found the algorithm to be more user friendly than other peak-search algorithms because there is less external input. A key advantage of this algorithm is that it requires no prior knowledge of the input spectral characteristics, shape or quality of the data. This therefore lends itself to being useful for in-line processing and potentially removes the need for a separate calibration standard (e.g. a radioactive source). This algorithm can be used for any system that simultaneously collects large numbers of spectral data-including multi-element detectors.

Acta Materialia, 2017

Residual stresses are considered to be the driving forces for the in-service failure of TBCs. The... more Residual stresses are considered to be the driving forces for the in-service failure of TBCs. The residual stress distribution through an APS TBC has been experimentally measured by high energy synchrotron X-ray diffraction (XRD) showing two distinct features. Firstly a discontinuity or 'jump' in the residual stress trend at a depth of approximately 100 μm from the interface. Secondly we observed a much larger stress gradient than that theoretically predicted. To understand these observations the measured residual stress was compared with analytical and finite element models based on the real 2D and 3D microstructure of the coating visualized by scanning electron microscopy (SEM) and high energy X-ray micro-computed tomography (μ-CT). The effect of the pores in the coating and the rumpled interface between the top coat and the bond coat on the residual stress distribution was studied by image based modelling. It was found that the pores did not have an obvious effect on the overall residual stress distribution. The rumpled interface however was primarily responsible for the jump in the trend. This feature was observed to be located at a depth of approximately 120 μm from the surface with an overall magnitude of approximately 200 MPa. The relaxation of the coating upon in-plane compression was investigated by mechanical testing coupled with DIC. These results are in good agreement with the much larger gradients in the measured residual stress distribution.

Data in brief, 2017

We carried out a residual stress distribution analysis in a APS TBC throughout the depth of the c... more We carried out a residual stress distribution analysis in a APS TBC throughout the depth of the coatings. The samples were heat treated at 1150 °C for 190 h and the data analysis used image based modelling based on the real 3D images measured by Computed Tomography (CT). The stress distribution in several 2D slices from the 3D model is included in this paper as well as the stress distribution along several paths shown on the slices. Our analysis can explain the occurrence of the "jump" features near the interface between the top coat and the bond coat. These features in the residual stress distribution trend were measured (as a function of depth) by high-energy synchrotron XRD (as shown in our related research article entitled 'Understanding the Residual Stress Distribution through the Thickness of Atmosphere Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) by high energy Synchrotron XRD; Digital Image Correlation (DIC) and Image Based Modelling') (Li et al., 2...

IEEE transactions on medical imaging, Sep 18, 2017

Contrast-enhanced digital mammography (CEDM) is an alternative to conventional X-ray mammography ... more Contrast-enhanced digital mammography (CEDM) is an alternative to conventional X-ray mammography for imaging dense breasts. However, conventional approaches to CEDM require a double exposure of the patient, implying higher dose and risk of incorrect image registration due to motion artifacts. A novel approach is presented, based on hyperspectral imaging, where a detector combining positional and high-resolution spectral information (in this case based on Cadmium Telluride) is used. This allows simultaneous acquisition of the two images required for CEDM. The approach was tested on a custom breast-equivalent phantom containing iodinated contrast agent (Niopam 150®). Two algorithms were used to obtain images of the contrast agent distribution: K-edge subtraction (KES), providing images of the distribution of the contrast agent with the background structures removed, and a dual-energy (DE) algorithm, providing an iodineequivalent image and a water-equivalent image. The high energy reso...

$Research paper thumbnail of A synchrotron X-ray diffraction deconvolution method for the measurement of residual stress in thermal barrier coatings as a function of depth$

Journal of Applied Crystallography, 2016

The average residual stress distribution as a function of depth in an air plasma-sprayed yttria s... more The average residual stress distribution as a function of depth in an air plasma-sprayed yttria stabilized zirconia top coat used in thermal barrier coating (TBC) systems was measured using synchrotron radiation X-ray diffraction in reflection geometry on station I15 at Diamond Light Source, UK, employing a series of incidence angles. The stress values were calculated from data deconvoluted from diffraction patterns collected at increasing depths. The stress was found to be compressive through the thickness of the TBC and a fluctuation in the trend of the stress profile was indicated in some samples. Typically this fluctuation was observed to increase from the surface to the middle of the coating, decrease a little and then increase again towards the interface. The stress at the interface region was observed to be around 300 MPa, which agrees well with the reported values. The trend of the observed residual stress was found to be related to the crack distribution in the samples, in ...

Physics World, 1992

Synchrotron radiation was first observed by physicists working on the GEC electron synchrotron at... more Synchrotron radiation was first observed by physicists working on the GEC electron synchrotron at Schenectady, New York, in 1947. Since then the building of synchrotron sources has accelerated and there are now about 70 synchrotrons in operation, or under construction, in Europe, the US, Japan and Asia. The largest of these, the Spring 8 machine being built in Tsukuba in Japan, will measure over 1400 m in circumference. So why has synchrotron radiation become so popular? Today there is intense competition for just a few hours of beamtime and scientists are prepared to travel across the world to use it. In the UK, industrial users are willing to pay almost £5000 for a day's synchrotron radiation and spent about £0.5m for synchrotron-related activities last year.

Polymer Testing, 2015

ABSTRACT Damage evolution in composites during a high velocity impact is difficult to observe. In... more ABSTRACT Damage evolution in composites during a high velocity impact is difficult to observe. In this work, quasi-static punch-shear (QS-PS) tests were conducted in an effort to determine damage that could develop during a penetrating impact event. Eight satin weave carbon/epoxy composite samples were fabricated and tested under different load levels. Load-displacement (P-δ) curves were obtained and type and extent of damage were identified in two/three dimensions using optical microscopy and X-ray computed tomography. Corresponding displacements at which the damage occurred were marked on the P-δ plots. A finite element analysis (FEA) was performed using the ABAQUS/Explicit commercial package with a progressive damage model to simulate experimental observations. It is found that the load pattern of the plate changes from local shearing to overall bending, which corresponds to the inflection stage of the P-δ curve. The final failure is caused by major delamination and fibre breakage due to shear and tensile stresses developed during the QS-PS tests. Keywords Composite materials; Damage mechanisms; Quasi-static punch-shear (QS-PS) test; Penetrating impact; X-ray computed tomography (X-CT); Finite element modelling (FEM)

Journal of the Chemical Society, Perkin Transactions 2, 1982

ABSTRACT The n.m.r. spectrum of the sodium salt (4; R = Na) was found to be temperature dependent... more ABSTRACT The n.m.r. spectrum of the sodium salt (4; R = Na) was found to be temperature dependent and this behaviour has been associated with a rapid degenerate rearrangement involving intramolecular hydride transfer from alkoxide to carbonyl. Dynamic 13C n.m.r. measurements gave a barrier of 13.7 (4 °C) kcal mol–1 for the rearrangement. A much slower competing process leading to the hemiacetal (5) was also found. The X-ray crystal structure of (4; R =p-nitrobenzoyl) has been determined and the ketonic carbonyl shows some pyramidalization.

$Research paper thumbnail of Tomographic energy dispersive X-ray diffraction apparatus comprising an array of detectors of associated collimators$

2008 IEEE Nuclear Science Symposium Conference Record, 2008

The X-ray performance of CdZnTe detectors with 300μm pixels was investigated. 2mm thick CdZnTe fr... more The X-ray performance of CdZnTe detectors with 300μm pixels was investigated. 2mm thick CdZnTe from eV Products Inc. was bump bonded to ERD2004 detector modules. Preliminary experiments with an eV Products detector at room temperature and −400V bias gave a FWHM of ...

$Research paper thumbnail of Simultaneous measurement of X-ray powder diffraction and ferroelectric polarisation data as a function of applied electric field at a range of frequencies$

Powder Diffraction, 2013

A variable frequency ferroelectric polarisation measurement system has been designed and built at... more A variable frequency ferroelectric polarisation measurement system has been designed and built at the UK's Diamond Light Source. The electric field induced phase transitions in Pb(Zr1−xTix)O3 (PZT) have been used to test the facility via in-situ measurements of electric polarisation and XRD. Stroboscopic and real time data collection methods on polycrystalline samples were employed as a function of frequency to determine the dynamic ferroelectric response. The system has been shown to deliver XRD patterns of good statistical quality measured over 40 points of a ferroelectric PE loop. The system is now available on station I11 as a user facility at the Diamond Light Source.