Assessment of Subsampling Schemes for Compressive Nano-FTIR Imaging

Nano-Fourier transform infrared (FTIR) imaging is a powerful scanning-based technique at nanometer spatial resolution that combines FTIR spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM). Recording large spatial areas using nano-FTIR is, however, limited, because its sequential data acquisition entails long measurement times. Compressed sensing and low-rank matrix reconstruction are mathematical techniques that can reduce the number of these measurements significantly by requiring only a small fraction of randomly chosen measurements. However, choosing this small set of measurements in a random fashion poses practical challenges for scanning procedures and does not save as much time as desired. We, therefore, consider different subsampling schemes of practical relevance that ensure rapid data acquisition, much faster than random subsampling, in combination with a low-rank matrix reconstruction procedure. It is demonstrated that the quality of the results for almost all subsampling schemes considered, namely, original Lissajous, triangle Lissajous, and random reflection subsampling, is similar to that achieved for random subsampling. This implies that nano-FTIR imaging can be significantly extended to also cover samples extended over large areas while maintaining its high spatial resolution

Imaging Sensors and Applications

In past decades, various sensor technologies have been used in all areas of our lives, thus improving our quality of life. In particular, imaging sensors have been widely applied in the development of various imaging approaches such as optical imaging, ultrasound imaging, X-ray imaging, and nuclear imaging, and contributed to achieve high sensitivity, miniaturization, and real-time imaging. These advanced image sensing technologies play an important role not only in the medical field but also in the industrial field. This Special Issue covers broad topics on imaging sensors and applications. The scope range of imaging sensors can be extended to novel imaging sensors and diverse imaging systems, including hardware and software advancements. Additionally, biomedical and nondestructive sensing applications are welcome

The role of chemistry and strut porosity and the influence of serum proteins in modulating cellular response to bone graft substitutes

The objective of this thesis was to investigate the role of hydroxyapatite and silicate-substituted hydroxyapatite synthetic bone graft substitute (SBG) material properties in modulating the processes of protein adsorption and desorption, and their combined role in the subsequent regulation of cell attachment, proliferation and differentiation on the surfaces of these materials in vitro. As a result of their purported role in promoting osteogenic behaviour in vivo the materials parameters selected for investigation were chemistry (stoichiometric hydroxyapatite (HA) versus 0.8wt% silicate-substituted hydroxyapatite (SA)) and strut porosity (20% versus 30% strut porosity). Cell attachment and response to different SBG was assessed to samples in the ‘as received’ condition as well as after a series of sequentially varied pre-treatments with solutions of phosphate buffered saline or cell culture media either unsupplemented or in combination with mixed serum proteins and/or Fibronectin (Fn). This enabled investigation of the effect of sample chemistry and strut porosity on mixed serum protein interactions and Fn adsorption under both competitive and non-competitive conditions, and the study of subsequent regulation of cell attachment and response as a consequence of pre-treatment. Results showed that serum protein interactions were key to modulation of cell response to chemistry, and there was evidence that for Fn this may be related to conformational changes in the adsorbed protein rather than its level of enrichment in the protein interlayer. In terms of the materials properties investigated strut porosity was found to be the most dominant factor in the regulation of cell response, where SBG with 30% strut porosity promoted human mesenchymal stem cell (hMSC) osteoblastic differentiation. Moreover hMSC response to SBG with 30% strut porosity seemed to be less sensitive to pre-treatment. In conclusion, the results of these experiments indicate that strut porosity more directly influences the cellular response to HA and SA BGS than chemistry in vitro. Moreover, the role that Fn and other serum proteins have in regulating this response is dependent on the physiological environment and BG

Material and Construction Optimization for Prevention of Premature Pavement Distress in PCC Pavements, Phase III Final Report, 2008

Mixture materials, mix design, and pavement construction are not isolated steps in the concrete paving process. Each affects the other in ways that determine overall pavement quality and long-term performance. However, equipment and procedures commonly used to test concrete materials and concrete pavements have not changed in decades, leaving gaps in our ability to understand and control the factors that determine concrete durability. The concrete paving community needs tests that will adequately characterize the materials, predict interactions, and monitor the properties of the concrete. The overall objectives of this study are (1) to evaluate conventional and new methods for testing concrete and concrete materials to prevent material and construction problems that could lead to premature concrete pavement distress and (2) to examine and refine a suite of tests that can accurately evaluate concrete pavement properties. The project included three phases. In Phase I, the research team contacted each of 16 participating states to gather information about concrete and concrete material tests. A preliminary suite of tests to ensure long-term pavement performance was developed. The tests were selected to provide useful and easy-to-interpret results that can be performed reasonably and routinely in terms of time, expertise, training, and cost. The tests examine concrete pavement properties in five focal areas critical to the long life and durability of concrete pavements: (1) workability, (2) strength development, (3) air system, (4) permeability, and (5) shrinkage. The tests were relevant at three stages in the concrete paving process: mix design, preconstruction verification, and construction quality control. In Phase II, the research team conducted field testing in each participating state to evaluate the preliminary suite of tests and demonstrate the testing technologies and procedures using local materials. A Mobile Concrete Research Lab was designed and equipped to facilitate the demonstrations. This report documents the results of the 16 state projects. Phase III refined and finalized lab and field tests based on state project test data. The results of the overall project are detailed herein. The final suite of tests is detailed in the accompanying testing guide

Review : Deep learning in electron microscopy

Deep learning is transforming most areas of science and technology, including electron microscopy. This review paper offers a practical perspective aimed at developers with limited familiarity. For context, we review popular applications of deep learning in electron microscopy. Following, we discuss hardware and software needed to get started with deep learning and interface with electron microscopes. We then review neural network components, popular architectures, and their optimization. Finally, we discuss future directions of deep learning in electron microscopy

Two dimensional angular domain optical imaging in biological tissues

Optical imaging is a modality that can detect optical contrast within a biological sample that is not detectable with other conventional imaging techniques. Optical trans-illumination images of tissue samples are degraded by optical scatter. Angular Domain Imaging (ADI) is an optical imaging technique that filters scattered photons based on the trajectory of the photons. Previous angular filters were limited to one dimensional arrays, greatly limiting the imaging capability of the system. We have developed a 2D Angular Filter Array (AFA) that is capable of acquiring two dimensional projection images of a sample. The AFA was constructed using rapid prototyping techniques. The contrast and the resolution of the AFA was evaluated. The results suggest that a 2D AFA can be used to acquire two dimensional projection images of a sample with a reduced acquisition time compared to a scanning 1D AFA

Novel sources of near- and mid-infrared femtosecond pulses for applications in gas sensing, pulse shaping and material processing

In this thesis the design, construction process and the performance of two femtosecond optical parametric oscillators and one second–harmonic generation femtosecond pulse shaper is described. One oscillator was applied to gas sensing while potential applications of other devices are outlined. ATi:sapphire oscillator was used to pump a periodically–poled lithium niobate– based optical parametric oscillator. This signal–resonant device was configured to produce broadband idler pulses tunable in the range of 2.7–3.4 μm. This wavelength coverage was matched to the ν3 optical absorption band of methane, and Fourier–transform spectroscopy of a CH4:N2 mixture was implemented by employing a mid–IR silica photonic bandgap fibre simultaneously as a gas cell and an optical waveguide. Methane sensing below a 1% concentration was demonstrated and the main limiting factors were identified and improvements suggested. Another optical parametric oscillator was demonstrated which was pumped by a commercial Yb:fibre master oscillator/power amplifier system and was based on a periodically–poled lithium niobate crystal. The signal was tunable between 1.42–1.57 μm and was intended as a source for a subsequent project for waveguide writing in silicon. The oscillator was a novel long–cavity device operating at 15 MHz. The 130 nJ pump pulse energies allowed for 21 nJ signal pulses at a pump power of 2 W. The performance of the oscillator was characterised via temporal and spectral measurements and the next steps of its development are outlined. Finally a pulse shaper based on second harmonic generation in a grating– engineered periodically–poled lithium niobate crystal was demonstrated. Pulses from a 1.53 μm femtosecond Er:fibre laser were compressed and then used as the input to the shaper. The performance of the shaper was tested by performing cross–correlation frequency–resolved optical gating measurements on the output second harmonic pulses and this confirmed the successful creation of multiple pulses and other tailored shapes including square and chirped pulses, agreeing well with theoretical calculations