Determining the percentages of semi-conducting and metallic single-walled carbon nanotubes in bulk soot

A procedure is presented to determine the percentages of metallic and semi-conducting single-walled carbon nanotubes (SWCNTs) in as-produced soot synthesized by a cobalt/molybdenum-catalyzed chemical vapor deposition (CVD) process. The procedure involves the acquisition of UV–Vis–NIR absorption spectra of solvent-suspended soot samples, and the key aspect is the use of a physically-based subtraction of the π-plasmon absorbance from the overall absorbance to ensure that the percentage of semi-conducting SWCNTs is not overstated. The improvement in accuracy using the procedure is demonstrated using two lots of soot with different amounts of non-tubular carbon (NTC) contaminants. The semi-conducting SWCNT percentage of the soot containing low NTC levels was 82 ± 3%, and this mean was overestimated by 4% when the π-plasmon absorbance was not subtracted. The semi-conducting SWCNT percentage of the soot containing higher NTC levels was 76 ± 9%, and this mean was overestimated by 6% without subtraction of the π-plasmon absorbance.     

Evaluation of Disability Progression in Multiple Sclerosis via Magnetic-Resonance-Based Deep Learning Techniques

Short-term disability progression was predicted from a baseline evaluation in patients with multiple sclerosis (MS) using their three-dimensional T1-weighted (3DT1) magnetic resonance images (MRI). One-hundred-and-eighty-one subjects diagnosed with MS underwent 3T-MRI and were followed up for two to six years at two sites, with disability progression defined according to the expanded-disability-status-scale (EDSS) increment at the follow-up. The patients’ 3DT1 images were bias-corrected, brain-extracted, registered onto MNI space, and divided into slices along coronal, sagittal, and axial projections. Deep learning image classification models were applied on slices and devised as ResNet50 fine-tuned adaptations at first on a large independent dataset and secondly on the study sample. The final classifiers’ performance was evaluated via the area under the curve (AUC) of the false versus true positive diagram. Each model was also tested against its null model, obtained by reshuffling patients’ labels in the training set. Informative areas were found by intersecting slices corresponding to models fulfilling the disability progression prediction criteria. At follow-up, 34% of patients had disability progression. Five coronal and five sagittal slices had one classifier surviving the AUC evaluation and null test and predicted disability progression (AUC > 0.72 and AUC > 0.81, respectively). Likewise, fifteen combinations of classifiers and axial slices predicted disability progression in patients (AUC > 0.69). Informative areas were the frontal areas, mainly within the grey matter. Briefly, 3DT1 images may give hints on disability progression in MS patients, exploiting the information hidden in the MRI of specific areas of the brain.     

Differences in surface failure modes of soda lime silica glass under normal indentation versus tangential shear: A comparative study on Na+/K+-ion exchange effects

The effects of exchanging Na⁺ with K⁺ on the mechanical and mechanochemical properties of a soda lime silica (SLS) glass were investigated. It is known that replacing smaller modifier ions with bigger ions in the silicate glass network, at temperatures below the glass transition (T_g), produces a compressive stress in the subsurface region that enhances resistance to mechanical damages. This study found that when Na⁺ ions in SLS are exchanged with K⁺ ions at 400°C, the hardness, indentation fracture toughness, and crack initiation load of the surface are increased, which is consistent with the chemical strengthening effect. However, the resistance to mechanochemical wear in a near-saturation humidity condition (relative humidity RH = 90%) is deteriorated. When K⁺ ions are exchanged back with Na⁺ ions at 350°C, the wear resistance in high humidity conditions is recovered. These results indicate that the improvement of mechanical properties under indentation normal to the surface is irrelevant with the resistance to mechanochemical wear under tangential shear at the surface. Based on the analysis of the surface chemical composition, silicate network structure, and hydrogen-bonding interactions of hydrous species in the subsurface region, it is proposed that the leachable Na⁺ associated with non-bridging oxygen and subsurface hydrous species in the silicate network play more important roles in the mechanochemical wear of SLS at high RH.     

Chemical Durability of Silicon Oxycarbide Glasses

Silicon oxycarbide (SiOC) glasses with controlled amounts of Si—C bonds and free carbon have been produced via the pyrolysis of suitable preceramic networks. Their chemical durability in alkaline and hydrofluoric solutions has been studied and related to the network structure and microstructure of the glasses. SiOC glasses, because of the character of the Si—C bonds, exhibit greater chemical durability in both environments, compared with silica glass. Microphase separation into silicon carbide (SiC), silica (SiO₂), and carbon, which usually occurs in this system at pyrolysis temperatures of >1000°–1200°C, exerts great influence on the durability of these glasses. The chemical durability decreases as the amount of phase separation increases, because the silica/silicate species (without any carbon substituents) are interconnected and can be easily leached out, in comparison with the SiOC phase, which is resistant to attack by OH⁻ or F⁻ ions.     

The power of knowledge sharing

One commonly cited antidote for UK manufacturers against the effects of outsourcing is to innovate and increase the rate of technology transfer. Government policy supports this approach through the creation of knowledge economy - designed to promote the generation of high value-add knowledge, technology and associated skills. Attention is focused on the generation side of the knowledge economy, but without associated swift application, these policies are most likely to fail. This paper discusses the barriers which have to be broached by the UK manufacturing sector in order to gain the benefits of technology transfer.     

Maximizing accuracy in large data conversions

Data conversion looks easy to a lot of people. It's not-particularly if it's a large project. There are just too many ways things can go wrong. You can lose data or mess it up. And you can stall the conversion if you don't have enough computing resources. Project size really makes a difference. Some type of mapping tool can improve your chances for success because the data in the specification is the same data that drives the program that loads the target tables. Automation eliminated the mistakes that cause inconsistency. The tools and processes we developed on a large project worked well on a smaller project, but the reverse certainly would not have been true. A systematic process is required with some way to validate each step     

Analytical and numerical modeling of squeeze-film damping in perforated microstructures

The literature includes a variety of analytical and semi-analytical models to describe squeeze-film damping in MEMS perforated structures. Even if many of them have been validated by means of numerical simulations, nobody seems to have discussed about the accuracy of numerical approaches in this field. In the present paper, we apply both the main analytical models and a commercial finite element software, COMSOL Multiphysics, to solve a good number of squeeze-film problems. They refer to some cases, which were experimentally investigated during the past by different authors. The tested structures are rigid rectangular plates fabricated with different material, different perforation ratio (i.e., the ratio of the hole side to the holes pitch) and different number of perforations. We compare both the analytical and the numerical results with the available experimental data, in order to have an overview about their effectiveness. Numerical simulations offer in all the considered cases valuable agreement with experiments.     

Towards the use of the conformal-evaporated-film-by-rotation technique in fabricating microelectronic circuits and microsystems

We used the conformal-evaporated-film-by-rotation technique to deposit a conformal coating of chalcogenide glass on the external surface of a microsystem—specifically, the outermost surface of a microelectromechanical system comb resonator. We concluded that this technique could complement the multi-step, time-consuming and expensive traditional lithographic processes, resulting in a reduction of the number of steps needed for the fabrication of microsystems and nanosystems.     

Ultralow Dispersion Multicomponent Thin‐Film Chalcogenide Glass for Broadband Gradient‐Index Optics

A novel photothermal process to spatially modulate the concentration of sub‐wavelength, high‐index nanocrystals in a multicomponent Ge‐As‐Pb‐Se chalcogenide glass thin film resulting in an optically functional infrared grating is demonstrated. The process results in the formation of an optical nanocomposite possessing ultralow dispersion over unprecedented bandwidth. The spatially tailored index and dispersion modification enables creation of arbitrary refractive index gradients. Sub‐bandgap laser exposure generates a Pb‐rich amorphous phase transforming on heat treatment to high‐index crystal phases. Spatially varying nanocrystal density is controlled by laser dose and is correlated to index change, yielding local index modification to ≈+0.1 in the mid‐infrared.     

Corrosion of ISG fibers in alkaline solutions

The corrosion behavior of glass fibers synthesized from the International Simple Glass (ISG) reference ingot, an international High‐Level Waste (HLW) borosilicate glass standard, is reported. Bundles of glass fibers were submerged in 120 mL of four different solutions of initial pH values (pH_i) of 9.5, 10.5, 11.5, and 12.5 for static corrosion testing. While all the experiments reached a residual corrosion rate after ~50 days, which remained approximately constant for the duration of the pH_i 9.5‐11.5 experiments, the pH_i 12.5 experiment underwent a Stage II→III dissolution transition after 57 days. This transition was preceded by a decrease in the Al concentration in solution followed by an increase in B and Si concentration in the leachate. Zeolite NaP2 was observed to form on these fibers via scanning electron microscopy and X‐ray diffraction—the crystallinity of the fibers was estimated to be ~40%‐45% (relative to amorphous component) after the Stage II→III transition. Transmission electron microscopy cross‐sectional imaging of sampled fibers revealed several porous layers on the pH_i 9.5‐11.5 samples, and a more aggressive alteration mechanism in the pH_i 12.5 fibers. Potential markers that indicate a transition from Stage II→Stage III corrosion are shown to occur based on experimental observations.