CHARACTERIZATION OF THE ATMOSPHERIC EFFECTS ON THE TRANSMISSION OF THERMAL RADIATION

Atmospheric scattering plays a crucial rule in degrading the performance of electro optical imaging systems operating in the visible and infra-red spectral bands, and hence limits the quality of the acquired images, either through reduction of contrast or increase of image blur. The exact nature of light scattering by atmospheric media is highly complex and depends on the types, orientations, sizes and distributions of particles constituting these media, as well as wavelengths, polarization states and directions of the propagating radiation. Here we follow the common approach for solving imaging and propagation problems by treating the propagating light through atmospheric media as composed of two main components: a direct (unscattered), and a scattered component. In this work we developed a detailed model of the effects of absorption and scattering by haze and fog atmospheric aerosols on the optical radiation propagating from the object plane to an imaging system, based on the classical theory of EM scattering. This detailed model is then used to compute the average point spread function (PSF) of an imaging system which properly accounts for the effects of the diffraction, scattering, and the appropriate optical power level of both the direct and the scattered radiation arriving at the pupil of the imaging system. Also, the calculated PSF, properly weighted for the energy contributions of the direct and scattered components is used, in combination with a radiometric model, to estimate the average number of the direct and scattered photons detected at the sensor plane, which are then used to calculate the image spectrum signal to- noise ratio (SNR) in the visible near infra-red (NIR) and mid infra-red (MIR) spectral wavelength bands. Reconstruction of images degraded by atmospheric scattering and measurement noise is then performed, up to the limit imposed by the noise effective cutoff spatial frequency of the image spectrum SNR. Key results of this research are as follows: A mathematical model based on Mie scattering theory for how scattering from aerosols affects the overall point spread function (PSF) of an imaging system was developed, coded in MATLAB, and demonstrated. This model along with radiometric theory was used to predict the limiting resolution of an imaging system as a function of the optics, scattering environment, and measurement noise. Finally, image reconstruction algorithms were developed and demonstrated which mitigate the effects of scattering-induced blurring to within the limits imposed by noise.

A comparative analysis of the characterization methods for submicron silicon waveguide propagation loss

An important parameter in integrated optical device is the propagation loss of the waveguide. Its characterization gives the information of the fabrication quality as well as the information of other passive devices on the chip as it is the basic building block of the passive devices. Although, over the last three decades many methods have been developed, there is not a single standard present yet. This paper presents a comparative analysis of the methods existing from the past as well as methods developed very recently in order to provide a complete picture of the pros and cons of different types of methods and from this comparison the best method is suggested according to the authors opinion. To support the claim, apart from the analytical comparison, this paper also presents a comparison performed with the experimental results between the suggested best method which is recently proposed by Massachusetts Institute of Technology (MIT) researchers based on undercoupled all-pass microring structure and the popular cut-back method.

SAFARI optical system architecture and design concept

SpicA FAR infrared Instrument, SAFARI, is one of the instruments planned for the SPICA mission. The SPICA mission is the next great leap forward in space-based far-infrared astronomy and will study the evolution of galaxies, stars and planetary systems. SPICA will utilize a deeply cooled 2.5m-class telescope, provided by European industry, to realize zodiacal background limited performance, and high spatial resolution. The instrument SAFARI is a cryogenic grating-based point source spectrometer working in the wavelength domain 34 to 230 μm, providing spectral resolving power from 300 to at least 2000. The instrument shall provide low and high resolution spectroscopy in four spectral bands. Low Resolution mode is the native instrument mode, while the high Resolution mode is achieved by means of a Martin-Pupplet interferometer. The optical system is all-reflective and consists of three main modules; an input optics module, followed by the Band and Mode Distributing Optics and the grating Modules. The instrument utilizes Nyquist sampled filled linear arrays of very sensitive TES detectors. The work presented in this paper describes the optical design architecture and design concept compatible with the current instrument performance and volume design drivers.

Exoplanet atmospheres Characterization Observatory payload short-wave infrared channel: EChO SWiR

EChO (Exoplanet atmospheres Characterization Observatory), a proposal for exoplanets exploration space mission, is considered the next step for planetary atmospheres characterization. It would be a dedicated observatory to uncover a large selected sample of planets spanning a wide range of masses (from gas giants to super-Earths) and orbital temperatures (from hot to habitable). All targets move around stars of spectral types F, G, K, and M. EChO would provide an unprecedented view of the atmospheres of planets in the solar neighbourhood. The consortium formed by various institutions of different countries proposed as ESA M3 an integrated spectrometer payload for EChO covering the wavelength interval 0.4 to 16 µm. This instrument is subdivided into 4 channels: a visible channel, which includes a fine guidance system (FGS) and a VIS spectrometer, a near infrared channel (SWiR), a middle infrared channel (MWiR), and a long wave infrared module (LWiR). In addition, it contains a common set of optics spectrally dividing the wavelength coverage and injecting the combined light of parent stars and their exoplanets into the different channels. The proposed payload meets all of the key performance requirements detailed in the ESA call for proposals as well as all scientific goals. EChO payload is based on different spectrometers covering the spectral range mentioned above. Among them, SWiR spectrometer would work from 2.45 microns to 5.45 microns. In this paper, the optical and mechanical designs of the SWiR channel instrument are reported on.

FABRICATION, CHARACTERIZATION, AND IRRADIATION OF AN AUSTENITIC OXIDE DISPERSION STRENGTHENED STEEL SUITED FOR NEXT GENERATION NUCLEAR APPLICATIONS

As nuclear energy systems become more advanced, the materials encompassing them need to perform at higher temperatures for longer periods of time. In this Master’s thesis we experiment with an oxide dispersion strengthened (ODS) austenitic steel that has been recently developed. ODS materials have a small concentration of nano oxide particles dispersed in their matrix, and typically have higher strength and better extreme temperature creep resistance characteristics than ordinary steels. However, no ODS materials have ever been installed in a commercial power reactor to date. Being a newer research material, there are many unanswered phenomena that need to be addressed regarding the performance under irradiation. Furthermore, due to the ODS material traditionally needing to follow a powder metallurgy fabrication route, there are many processing parameters that need to be optimized before achieving a nuclear grade material specification. In this Master’s thesis we explore the development of a novel ODS processing technology conducted in Beijing, China, to produce solutionized bulk ODS samples with ~97% theoretical density. This is done using relatively low temperatures and ultra high pressure (UHP) equipment, to compact the mechanically alloyed (MA) steel powder into bulk samples without any thermal phase change influence or oxide precipitation. By having solutionized bulk ODS samples, transmission electron microscopy (TEM) observation of nano oxide precipitation within the steel material can be studied by applying post heat treatments. These types of samples will be very useful to the science and engineering community, to answer questions regarding material powder compacting, oxide synthesis, and performance. Subsequent analysis performed at Queen’s University included X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometry (ICP-OES). Additional TEM in-situ 1MeV Kr2+ irradiation experiments coupled with energy dispersive X-ray (EDX) techniques, were also performed on large (200nm+) non-stoichiometric oxides embedded within the austenite steel grains, in an attempt to quantify the elemental compositional changes during high temperature (520oC) heavy ion irradiation.

The optical properties of metamaterials

This thesis studies the parametric investigation, polarisation dependence and characterization of fishnet structure at near infrared wavelengths. Detailed simulations are performed to understand the behaviour of the structure at near infrared and optical wavelengths. Simulations are performed to obtain negative refractive index of the fishnet structure formed from nanoimprint lithography (NIL) by taking into account the effect of substrate and polymethyl methacrylate (PMMA) beneath it. Two different structures have been designed and fabricated of varying dimensions using NIL and their resonant wavelength measured in the near infrared at 1.45 µm and 1.88 µm. Simulations suggest that a negative refractive index real part with the magnitude -0.24 is found at 1.53 µm and this decrease to a maximum magnitude of -0.57 at 1.9 µm. The PMMA and suppressed pillars are here responsible for the increasing material losses and limiting the value of negative refractive index. An analytical approach has been suggested to characterise fishnet structures at oblique incidence. The expressions for an absorbing medium are rewritten for an alternative definition of refractive index. The expressions are initially validated for a dielectric slab and a metal film. These results provide the possibility that this proposal may yield a general algorithm for obtaining the complex reflection and transmission coefficients for artificial structures. FDTD simulations have been extensively used in this thesis to understand the optical metamaterials and their characterization.

Characterization of the glaze and in-glaze pigments of the nineteenth-century relief tiles from the Pena National Palace, Sintra, Portugal

The glaze and in-glaze pigments of the historical nineteenth-century glazed tiles from the Pena National Palace (Sintra, Portugal) were characterized using a multi-analytical approach. Chemical composition and microstructural characterization were ascertained by µ-PIXE, µ-Raman, optical microscopy and VP-SEM–EDS. The manufacturing technique and colour palette in these tiles were found to be close to the ceramic pigments used in traditional majolica. The blue and purple colours derive from cobalt oxide and manganese oxide, respectively. A mixture of Pb–Sn–Sb yellow with cobalt oxide and iron oxide was used for green and dark yellow, respectively, while grey tonalities consist of a complex mixture of cobalt oxide, manganese oxide and Pb–Sn–Sb yellow in different proportions. Results obtained allowed the determination of the oxides and elements used in pigments as well as production techniques, resorting to traditional majolica manufacture, although the tiles were produced by the end of the nineteenth century.

Exploring New Material and Analytical Method for Characterization and Conservation of Artifacts

In this dissertation, we focus on developing new green bio-based gel systems and evaluating both the cleaning efficiency and the release of residues on the treated surface, different micro or no destructive techniques, such as optical microscopy, TGA, FTIR spectroscopy, HS-SPME and micro-Spatially Offset Raman spectroscopy (micro-SORS) were tested, proposing advanced analytical protocols. In the first part, a ternary PHB-DMC/BD gel system composed by biodiesel, dimethyl carbonate and poly-3 hydroxybutyrate was developed for cleaning of wax-based coatings applied on indoor bronze. The evaluation of the cleaning efficacy of the gel was carried out on a standard bronze sample which covered a layer of beeswax by restores of Opificio delle Pietre Dure in Florence, and a real case precious indoor bronze sculpture Pulpito della Passione attributed to Donatello. Results obtained by FTIR analysis showed an efficient removal of the wax coating. In the second part, two new kinds of combined gels based on electrospun tissues (PVA and nylon) and PHB-GVL gel were developed for removal of dammar varnish from painting. The electrospun tissue combined gels exhibited good mechanical property, and showed good efficient in cleaning over normal gel. In the third part, green deep eutectic solvent which consists urea and choline chloride was proposed to produce the rigid gel with agar for the removal of proteinaceous coating from oil painting. Rabbit glue and whole egg decorated oil painting mock-ups were selected for evaluating its cleaning efficiency, results obtained by ATR analysis showed the DES-agar gel has good cleaning performance. Furthermore, we proposed micro-SORS as a valuable alternative non-destructive method to explore the DES diffusion on painting mock-up. As a result, the micro-SORS was successful applied for monitoring the liquid diffusion behavior in painting sub-layer, providing a great and useful instrument for noninvasive residues detection in the conservation field.

Synthesis, characterization, and application of PHB-based gels for cultural heritage conservation

The aim of my master thesis is developing novel, greener approaches for the cleaning of artworks: such treatment consists in the removal of old varnish layers which tend to discolor or darken with time, thus allowing replacement with a new protecting coat. While protocols presently applied can be effective in the cleaning of the artworks, none of them take into account conservators’ health safety and environmental issues. Thus, using biomass-derived components, which are non-toxic and reusable and/or compostable might bring into the heritage conservation an additional awareness about safety and environmental claiming. The laboratory work for the thesis is a collaborative work between different groups. The biggest part of the work was at the Polymer group where gels were synthesized using Polyhydroxybutyrate (PHB) from sustainable resources and green solvents. The use of the gels might help to reduce the volatilization of solvents and contributes to the localization of the cleaning action. After the preparation of the gels, different characterization methods were used in order to estimate their properties and shelf-life. Finally, the work was completed on the application of the gels on sculpture, coated with undesired layers to be removed. Here, pre-mapping of the areas of interest was realized with different optical techniques, followed by the application of the gels for the cleaning and analyzing the effectiveness of cleaning.

Comprehensive characterization of snowfall in terms of microphysical features, quantitative precipitation estimation and scavenging properties by in situ and remote sensing observations at an Antarctic coastal site

Snow plays a crucial role in the Earth's hydrological cycle and energy budget, making its monitoring necessary. In this context, ground-based radars and in situ instruments are essential thanks to their spatial coverage, resolution, and temporal sampling. Deep understanding and reliable measurements of snow properties are crucial over Antarctica to assess potential future changes of the surface mass balance (SMB) and define the contribution of the Antarctic ice sheet on sea-level rise. However, despite its key role, Antarctic precipitation is poorly investigated due to the continent's inaccessibility and extreme environment. In this framework, this Thesis aims to contribute to filling this gap by in-depth characterization of Antarctic precipitation at the Mario Zucchelli station from different points of view: microphysical features, quantitative precipitation estimation (QPE), vertical structure of precipitation, and scavenging properties. For this purpose, a K-band vertically pointing radar collocated with a laser disdrometer and an optical particle counter (OPC) were used. The radar probed the lowest atmospheric layers with high vertical resolution, allowing the first trusted measurement at only 105 m height. Disdrometer and OPC provided information on the particle size distribution and aerosol concentrations. An innovative snow classification methodology was designed by comparing the radar reflectivity (Ze) and disdrometer-derived reflectivity by means of DDA simulations. Results of classification were exploited in QPE through appropriate Ze-snow rate relationships. The accuracy of the resulting QPE was benchmarked against a collocated weighing gauge. Vertical radar profiles were also investigated to highlight hydrometeors' sublimation and growth processes. Finally, OPC and disdrometer data allowed providing the first-ever estimates of scavenging properties of Antarctic snowfall. Results presented in this Thesis give rise to advances in knowledge of the characteristics of snowfall in Antarctica, contributing to a better assessment of the SMB of the Antarctic ice sheet, the major player in the global sea-level rise.

Development of thermochemiluminescence-based sensitive probes: synthesis, optimization, and characterization of c2- and c7-substituted acridine-containing 1,2-dioxetanes

After initial efforts in the late 1980s, the interest in thermochemiluminescence (TCL) as an effective detection technique has gradually faded due to some drawbacks, such as the high temperatures required to trigger the light emission and the relatively low intensities, which determined a poor sensitivity. Recent advances made with the adoption of variably functionalized 1,2-dioxetanes as innovative luminophores, have proved to be a promising approach for the development of reagentless and ultrasensitive detection methods exploitable in biosensors by using TCL compounds as labels, as either single molecules or included in modified nanoparticles. In this PhD Thesis, a novel class of N-substituted acridine-containing 1,2-dioxetanes was designed, synthesized, and characterized as universal TCL probes endowed with optimal emission-triggering temperatures and higher detectability particularly useful in bioanalytical assays. The different decorations introduced by the insertion of both electron donating (EDGs) and electron withdrawing groups (EWGs) at the 2- and 7-positions of acridine fluorophore was found to profoundly affect the photophysical properties and the activation parameters of the final 1,2-dioxetane products. Challenges in the synthesis of 1,2-dioxetanes were tackled with the recourse to continuous flow photochemistry to achieve the target parent compound in high yields, short reaction time, and easy scalability. Computational studies were also carried out to predict the olefins reactivity in the crucial photooxygenation reaction as well as the final products stability. The preliminary application of TCL prototype molecule has been performed in HaCaT cell lines showing the ability of these molecules to be detected in real biological samples and cell-based assays. Finally, attempts on the characterization of 1,2-dioxetanes in different environments (solid state, optical glue and nanosystems) and the development of bioconjugated TCL probes will be also presented and discussed.

Production and characterization of novel thermoplastic (nano)composite materials for additive manufacturing applications

The increasing environmental global regulations have directed scientific research towards more sustainable materials, even in the field of composite materials for additive manufacturing. In this context, the presented research is devoted to the development of thermoplastic composites for FDM application with a low environmental impact, focusing on the possibility to use wastes from different industrial processes as filler for the production of composite filaments for FDM 3D printing. In particular carbon fibers recycled by pyro-gasification process of CFRP scraps were used as reinforcing agent for PLA, a biobased polymeric matrix. Since the high value of CFs, the ability to re-use recycled CFs, replacing virgin ones, seems to be a promising option in terms of sustainability and circular economy. Moreover, wastes from different agricultural industries, i.e. wheat and rice production processes, were valorised and used as biofillers for the production of PLA-biocomposites. The integration of these agricultural wastes into PLA bioplastic allowed to obtain biocomposites with improved eco-sustainability, biodegradability, lightweight, and lower cost. Finally, the study of novel composites for FDM was extended towards elastomeric nanocomposite materials, in particular TPU reinforced with graphene. The research procedure of all projects involves the optimization of production methods of composite filaments with a particular attention on the possible degradation of polymeric matrices. Then, main thermal properties of 3D printed object are evaluated by TGA, DSC characterization. Additionally, specific heat capacity (CP) and Coefficient of Linear Thermal Expansion (CLTE) measurements are useful to estimate the attitude of composites for the prevention of typical FDM issues, i.e. shrinkage and warping. Finally, the mechanical properties of 3D printed composites and their anisotropy are investigated by tensile test using distinct kinds of specimens with different printing angles with respect to the testing direction.

Fluorogenic hyaluronan-based probe: characterization and use in advanced microscopy

Among all, the application of nanomaterials in biomedical research and most recently in the environmental one has opened the fields of nanomedicine and nanoremediation. Sensing methods based on fluorescence optical probe are generally requested for their selectivity, sensitivity. However, most imaging methods in literature rely on a fluorescent covalent labelling of the system. Therefore, the main aim of this project was to synthetise a biocompatible fluorogenic hyaluronan probe (HA) polymer functionalised with a rhomadine B (RB) moieties and study its behaviour as an optical probe with different materials with microscopy techniques. A derivatization of HA with RB (HA-RB) was successfully obtained providing a photophysical characterization showing a particular fluorescence mechanism of the probe. Firstly, we tested the interaction with different lab-grade micro and nanoplastics in water. Thanks to the peculiar photophysical behaviour of the probe nanoplastics can be detected with confocal microscopy and more interestingly their nature can be discriminated based on the fluorescence lifetime decay with FLIM microscopy. After, the interaction of a model plant derived metabolic enzyme GAPC1 undergoing oxidative-triggered aggregation was explored with the HA-RB. We highlighted the probe interaction with the protein even at early stage of the kinetic. Moreover, nanoparticle tracking analysis (NTA) experiment demonstrates that the probe is in fact able to interact with the small pre-aggregates in the early stage of the aggregation kinetic. Ultimately, we focused on the possibility to apply the probe in a super resolution microscopy technique, PALM, exploiting its aspecific interaction to characterize the surface topography of PTFE polydisperse microplastics. Optimal conditions were reached at high concentration of the probe (70 nM) where 0.5-5 nM is always advisable for this technique. Thanks to the polymeric nature and fluorescence mechanism of the probe, this technique was able to reveal features of PTFE surface under the diffraction limit (< 250 nm).

In-car sound linear simulation

In recent years, vehicle acoustics have gained significant importance in new car development: increasingly advanced infotainment systems for spatial audio and sound enhancement algorithms have become the norm in modern vehicles. In the past, car manufacturers had to build numerous prototypes to study the sound behaviour inside the car cabin or the effect of new algorithms under development. Nowadays, advanced simulation techniques can reduce development costs and time. In this work, after selecting the reference test vehicle, a modern luxury sedan equipped with a high-end sound system, two independent tools were developed: a simulation tool created in the Comsol Multiphysics environment and an auralization tool developed in the Cycling ‘74 MAX environment. The simulation tool can calculate the impulse response and acoustic spectrum at a specific position inside the cockpit. Its input data are the vehicle’s geometry, acoustic absorption parameters of materials, the acoustic characteristics and position of loudspeakers, and the type and position of virtual microphones (or microphone arrays). The simulation tool can also provide binaural impulse responses thanks to Head Related Transfer Functions (HRTFs) and an innovative algorithm able to compute the HRTF at any distance and angle from the head. Impulse responses from simulations or acoustic measurements inside the car cabin are processed and fed into the auralization tool, enabling real-time interaction by applying filters, changing the channels gain or displaying the acoustic spectrum. Since the acoustic simulation of a vehicle involves multiple topics, the focus of this work has not only been the development of two tools but also the study and application of new techniques for acoustic characterization of the materials that compose the cockpit and the loudspeaker simulation. Specifically, three different methods have been applied for material characterization through the use of a pressure-velocity probe, a Laser Doppler Vibrometer (LDV), and a microphone array.

Numerical Analysis and Redesign of a High Speed Linear Cascade Wind Tunnel for Aircraft Gas Turbine Engines Testing

Linear cascade testing serves a fundamental role in the research, development, and design of turbomachines as it is a simple yet very effective way to compute the performance of a generic blade geometry. These kinds of experiments are usually carried out in specialized wind tunnel facilities. This thesis deals with the numerical characterization and subsequent partial redesign of the S-1/C Continuous High Speed Wind Tunnel of the Von Karman Institute for Fluid Dynamics. The current facility is powered by a 13-stage axial compressor that is not powerful enough to balance the energy loss experienced when testing low turning airfoils. In order to address this issue a performance assessment of the wind tunnel was performed under several flow regimes via numerical simulations. After that, a redesign proposal aimed at reducing the pressure loss was investigated. This consists of a linear cascade of turning blades to be placed downstream of the test section and designed specifically for the type of linear cascade being tested. An automatic design procedure was created taking as input parameters those measured at the outlet of the cascade. The parametrization method employed Bézier curves to produce an airfoil geometry that could be imported into a CAD software so that a cascade could be designed. The proposal was simulated via CFD analysis and proved to be effective in reducing pressure losses up to 41%. The same tool developed in this thesis could be adopted to design similar apparatuses and could also be optimized and specialized for the design of turbomachines components.