Design and Optimization of a 3-D Plasmonic Huygens Metasurface for Highly-Efficient Flat Optics

For miniaturization of future USAF unmanned aerial and space systems to become feasible, accompanying sensor components of these systems must also be reduced in size, weight and power (SWaP). Metasurfaces can act as planar equivalents to bulk optics, and thus possess a high potential to meet these low-SWaP requirements. However, functional efficiencies of plasmonic metasurface architectures have been too low for practical application in the infrared (IR) regime. Huygens-like forward-scattering inclusions may provide a solution to this deficiency, but there is no academic consensus on an optimal plasmonic architecture for obtaining efficient phase control at high frequencies. This dissertation asks the question: what are the ideal topologies for generating Huygens-like metasurface building blocks across a full 2π phase space? Instead of employing any a priori assumption of fundamental scattering topologies, a genetic algorithm (GA) routine was developed to optimize a “blank slate” grid of binary voxels inside a 3D cavity, evolving the voxel bits until a near-globally optimal transmittance (T) was attained at a targeted phase. All resulting designs produced a normalized T≥80 across the entire 2π range, which is the highest metasurface efficiency reported to-date for a plasmonic solution in the IR regime

Research reports: 1987 NASA/ASEE Summer Faculty Fellowship Program

For the 23rd consecutive year, a NASA/ASEE Summer Faculty Fellowship Program was conducted at the Marshall Space Flight Center (MSFC). The program was conducted by the University of Alabama in Huntsville and MSFC during the period 1 June to 7 August 1987. Operated under the auspices of the American Society for Engineering Education, the MSFC program, as well as those at other NASA Centers, was sponsored by the Office of University Affairs, NASA Headquarters, Washington, D.C. The basic objectives of the program are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participant's institutions; and (4) to contribute to the research objectives of the NASA Centers. This document is a compilation of Fellow's reports on their research during the Summer of 1987

Direct Normal Irradiance and circumsolar radiation: modelling, measurement and impact on Concentrating Solar Power

In this work, the modelling and measurement of direct and circumsolar normal irradiance (DNI and CSNI, respectively) is studied, as well as their impact on the energy generation of concentrating solar power systems (CSP). To model DNI, two approaches are used: (i) developing a fast and simple model to estimate diffuse horizontal irradiance, and consequently, DNI; and (ii) assess the performance of three distinct state-of-the-art models with different degrees of complexity. Regarding the first approach, it was found that the developed model that considers the climate zone was able to outperform the models available in the literature. Regarding the second approach, it was found that the radiative transfer model libRadtran and the parametrization model SMARTS are the models that provide the best DNI predictions. In this way, libRadtran is used to generate a database of DNI and CSNI values. Then, a new CSNI model is developed to estimate CSNI for a half-opening angle of 2.5◦ that only requires solar radiation data as input. It was found that the proposed CSNI model outperforms the models available in the literature in almost all of the locations analysed. However, the half-opening angles of common CSP systems are lower than 2.5◦. Therefore, an upgrade of the CSNI model is developed that enables the determination of CSNI for a specific half-opening angle. The improved model is then able to predict the CSNI that reaches the CSP receiver and estimate the variation in the system’s intercept factor caused by CSNI variation. It was found that discarding CSNI could lead to up to a 7% difference between the measured DNI and the DNI that is captured by the CSP system. Furthermore, it was also found that higher rim angles are needed if the impact of CSNI variation is to be mitigated in parabolic trough concentrators; Resumo: Irradiância Direta Normal e radiação circunsolar: modelação, medição e impacto em Sistemas de Concentração Solar Neste trabalho, são estudadas a modelação e a medição da irradiância direta normal e circunsolar direta normal (DNI e CSNI, respetivamente), assim como o seu impacto na geração de energia em sistemas de concentração solar (CSP). São usadas duas abordagens para modelar a DNI: (i) desenvolvimento de um modelo simples e rápido para estimar a irradiância difusa horizontal e consequentemente a DNI; (ii) avaliar a performance de três modelos de última geração com diferentes graus de complexidade. Relativamente à primeira abordagem, verificou-se que o modelo desenvolvido e que considera a zona climática é capaz de superar os modelos disponíveis na literatura. Relativamente à segunda abordagem, verificou-se que os modelos de transferência radiativa libRadtran e de parametrização SMARTS são os que apresentam as melhores estimativas de DNI. Desta forma, o libRadtran é usado para gerar uma base de dados de valores de DNI e CSNI. De seguida, é desenvolvido um novo modelo para estimar a CSNI para um meio-ângulo de abertura de 2.5◦ que apenas necessita de dados de radiação solar. Verificou-se que o modelo desenvolvido supera os modelos disponíveis na literatura em quase todos os locais analisados. No entanto, o meio-ângulo de abertura de sistemas CSP comuns é inferior a 2.5◦. Por isso, foi desenvolvida uma atualização ao modelo que permite a determinação da CSNI para um meio-ângulo de abertura específico. O modelo atualizado é capaz de prever a CSNI que chega ao recetor do sistema CSP e estimar a variação do fator de interceção do sistema causada pela variação da CSNI. Verificou-se que descartar a CSNI pode levar a uma diferença de até 7% entre a DNI medida e a DNI que é intercetada pelo sistema CSP. Verificou-se ainda que para mitigar o impacto da variação da CSNI em concentradores cilindro-parabólicos é necessário ter rim angles maiores

Thirteenth International Laser Radar Conference

One hundred fifteen papers were presented in both oral and poster sessions. The topics of the conference sessions were: spaceborne lidar applications; extinction/visibility; differential absorption lidar; winds and tropospheric studies; middle atmosphere; clouds and multiple scattering; pollution studies; and new systems

Characterising the force balance between active pharmaceutical ingredients for inhalation and its impact on deposition

Interparticulate interactions play a significant role in determining the downstream behaviours of all pharmaceutical formulations and are therefore essential considerations when approaching formulation design. Inhalation product formulation in particular is inherently bound to an understanding of these forces. Delivery of drugs to the lower airways to treat conditions like asthma and COPD requires a particle size of below 5 micron. This implicitly demands micronization of the active pharmaceutical ingredients (APls) and this process renders many particles of large surface area with high surface energies and an auto-adhesive tendency. There is therefore a concurrent reduction in the flowability and dispersion properties of these systems. The interactive character predisposes agglomeration, flocculation or device retention and will compromise manufacture, stability, device function, and the aerosolization behavior of a formulation. Ultimately the ability of any aerosolized API to reach the deep airways is dependent upon adhesion force dynamics. As such, an appreciation of the forces of attraction and scale of particulate interactions within inhaler technology is critical if a successful drug delivery device is to be realized. The advancement of the atomic force microscope (AFM) as a force probing apparatus, has meant that it is now possible to measure the force of adhesion between two particles of interest. However these measurements could not easily be compared, because there is no simple means to account for differences in the contact regime (geometrics) between measurements. However, the development of the cohesive adhesive balance (CAB) approach by Begat, Morton, Stainforth and Price in 2004 has offered a means to negate this limitation. Using a colloidal probe microscopy (CPM) derived technique a particle of a selected material of interest (API, carrier molecule etc.) is attached to an AFM cantilever and ramped onto and off the surface of another material of interest (adhesion measurement), and to a surface of the same material as the tip (cohesion measurement). By graphically plotting the adhesive force values of a series of tips, as a function of the cohesive force values of the same tips, a representation of the relative particle interaction can be obtained. Quantitative information regarding the adhesive/cohesive nature of the interaction can then be extracted from the graph and a description of the interaction formulated that can be compared to other material combinations. The CAB work carried out to date has used recrystallized model substrates. These molecularly flat surfaces ensured there would be no difference between the contact geometry of a functionalised AFM probe and the adhesive and cohesive surfaces of the study respectively. In this fashion the only variable between the two measurements would be the chemical interactivity, and not the interactive surface area. However while using such methodology guarantees the validity of the approach, it is not necessarily a true representation of the materials 'in-situ' and requires more complex sample preparation and complex experimental design. For a variety of reasons this can be misleading in its own right. This thesis details the .investigation into the application of an adapted CAB approach in characterizing the force balance between APls for inhalation in their real state. In so doing, the aim was to see whether such a CAB would offer a quicker and simpler, yet relevant and informative assessment of a drug system force balance. It was hoped that said force balance could in turn be associated with a measurable impact upon the formulation performance of the characterised ingredients as measured 'in-vitro'. This interest was particularly directed at the lesser characterized pressurized metered dose inhaler (pMOI) systems. While these formulations are solvent based, it was of interest to identify whether a simple API to API challenge could infer a descriptive balance that could link to 'in-vitro' performance. Furthermore there was interest in evaluating the use of a range of surface specific imaging techniques to analyse the deposition dynamics of the combination formulations. It was hoped that by doing so, the localisation of the individual components within the binary deposits could again be associated back to the force balance of that system, and that an appreciation of the capability of the techniques involved would be gained. The work that follows therefore commences with the evaluation and description of the capacity for the CAB approach to be adapted to measure force relationships between real beclomethasone dipropionate (BOP) particles and pMDI component surfaces. From this assessment it was found that even with relatively smooth substrates, the combination of bulky functional particles and the inherent substrate roughness caused a critical failure in the CAB model. The parity between cohesive and adhesive geometries of contact was excessively stretched, leading to a loss of force normalisation which was reflected in uncorrelated CAB plots. As a consequence little could be confidently gleaned from the force data acquired, although there was the suggestion that the use of a fluorinated ethylene proplylene (FEP) coating reduced the adhesive interaction between the APls and the pMDI canister wall. This was then followed by an attempt to find a compromise between the model crystal substrates of a pure CAB process and the real particle morphologies that had caused the CAB model to fail. Using a compression process to form API powder compacts, in conjunction with small and discreet functional particles, a confident CAB was achieved for two combinations of APls selected on the basis of surface energy and physical stability analysis. Salbutamol sulphate was characterised with beclomethasone dipropionate, and salmeterol xinafoate with fluticasone propionate. Both combinations showed CAB plots with a sufficiently strong linear regression analysis to suggest a broad accuracy of force balance assessment. Both beta2-agonists showed cohesively dominated relationships with respect to the paired glucocortiocoids, while in reverse both glucocorticoids showed adhesively dominated relationships with the beta2-agonists. There was concern raised over the compression process of the powder discs, and its impact on the physicochemical state of the APls, with some thermodynamic evidence of polymorphic changes that required further work. The next chapter looks at the 'in-vitro' deposition performance of the two API combinations from a HFA134a pMDI system by analysis in an Andersen Cascade Impactor (ACI). The coformulation of salmeterol with fluticasone induced an improvement in the fine particle performance of fluticasone, with a concurrent decrease in the fine particle performance of salmeterol. This impact was hypothesised to be related to alterations in the structure and strength of particle-particle agglomerates. The impact on deposition performance of coformulating beclomethasone and salbutamol was unclear, as a critical unexplained loss of beclomethasone by total recovered mass was seen from all beclomethasone containing formulations. This instability of beclomethasone within the HFA134a system, precluded an accurate assessment of a direct impact on salbutamol deposition. The final chapter, compared a range of surface specific imaging techniques, including scanning electron microscopy (SEM), desorption electrospray ionization mass spectrometry (DESI), Raman spectrometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS) in assessing the extent and nature of 'in-vitro' co-deposition from the salmeterol and fluticasone pMDI formulations. It was apparent that the deposition of the two APls on ACI plates was not likely to be directly comparable assessment of the incidence of particle co-deposition 'in-vivo' due to the forced nature of nozzle directed impaction. However the combination of techniques employed produced a wealth of physical and chemical data that did suggest that the two APls showed extensive co-ordination 'in-vitro'. Raman spectroscopy was able to identify individual particle character and showed frequent salmeterol and fluticasone particle combinations, but suffered from exceptionally long run times and anomalies from photoreactive surface elements. The use of a multivariate approach to ToF-SIMs analysis defined the strong co-association of the two APls, although could not differentiate particle to particle deposition. Multivariate curve resolution (MeR) was used and produced distinct components that segregated ions from both APIS from the background plate but not from each other. SEM imaging was able to define the morphologies of the deposited particles, but was unable to differentiate the two. DES I imaging showed the presence of the two APls together within several drug spots, but could not be used to investigate individual drug spots, and the distribution within, due to inadequate spatial resolution and differences in desorption efficacy. While the co-association of the two APls was observed, the lack of a comparator in another combination of APls made the link between deposition performance and force balance purely descriptive. It was unclear as to whether the force balance of the system lends itself to a particular increase in co-deposition behaviour. However it was apparent that the analytical techniques employed all had respective strengths and weaknesses as mapping tools, and with further work with other formulations could be used to provide a tailored formulation screening process, if subsequent links to force balances could be made. To conclude, the work in this thesis details the successful process of adapting an AFM technique in characterising the broad force balance of combinations of APls. In so doing a force balance has been linked to the alteration in deposition behaviour of two APls when co-formulated in a HFA134 formulation. The subsequent co-deposition of the two APls was then analysed by a series of surface analytical techniques. This highlighted a general co-deposition trend, but the collective results were unable to definitively link to the force balance of the system. The information obtained forms the beginnings of what could be utilised as a fast and facile broad predictor of pMDI formulation performance, and an indication of appropriate analytical techniques for investigating particle association 'in-vitro'

Characterising the force balance between active pharmaceutical ingredients for inhalation and its impact on deposition

Interparticulate interactions play a significant role in determining the downstream behaviours of all pharmaceutical formulations and are therefore essential considerations when approaching formulation design. Inhalation product formulation in particular is inherently bound to an understanding of these forces. Delivery of drugs to the lower airways to treat conditions like asthma and COPD requires a particle size of below 5 micron. This implicitly demands micronization of the active pharmaceutical ingredients (APls) and this process renders many particles of large surface area with high surface energies and an auto-adhesive tendency. There is therefore a concurrent reduction in the flowability and dispersion properties of these systems. The interactive character predisposes agglomeration, flocculation or device retention and will compromise manufacture, stability, device function, and the aerosolization behavior of a formulation. Ultimately the ability of any aerosolized API to reach the deep airways is dependent upon adhesion force dynamics. As such, an appreciation of the forces of attraction and scale of particulate interactions within inhaler technology is critical if a successful drug delivery device is to be realized. The advancement of the atomic force microscope (AFM) as a force probing apparatus, has meant that it is now possible to measure the force of adhesion between two particles of interest. However these measurements could not easily be compared, because there is no simple means to account for differences in the contact regime (geometrics) between measurements. However, the development of the cohesive adhesive balance (CAB) approach by Begat, Morton, Stainforth and Price in 2004 has offered a means to negate this limitation. Using a colloidal probe microscopy (CPM) derived technique a particle of a selected material of interest (API, carrier molecule etc.) is attached to an AFM cantilever and ramped onto and off the surface of another material of interest (adhesion measurement), and to a surface of the same material as the tip (cohesion measurement). By graphically plotting the adhesive force values of a series of tips, as a function of the cohesive force values of the same tips, a representation of the relative particle interaction can be obtained. Quantitative information regarding the adhesive/cohesive nature of the interaction can then be extracted from the graph and a description of the interaction formulated that can be compared to other material combinations. The CAB work carried out to date has used recrystallized model substrates. These molecularly flat surfaces ensured there would be no difference between the contact geometry of a functionalised AFM probe and the adhesive and cohesive surfaces of the study respectively. In this fashion the only variable between the two measurements would be the chemical interactivity, and not the interactive surface area. However while using such methodology guarantees the validity of the approach, it is not necessarily a true representation of the materials 'in-situ' and requires more complex sample preparation and complex experimental design. For a variety of reasons this can be misleading in its own right. This thesis details the .investigation into the application of an adapted CAB approach in characterizing the force balance between APls for inhalation in their real state. In so doing, the aim was to see whether such a CAB would offer a quicker and simpler, yet relevant and informative assessment of a drug system force balance. It was hoped that said force balance could in turn be associated with a measurable impact upon the formulation performance of the characterised ingredients as measured 'in-vitro'. This interest was particularly directed at the lesser characterized pressurized metered dose inhaler (pMOI) systems. While these formulations are solvent based, it was of interest to identify whether a simple API to API challenge could infer a descriptive balance that could link to 'in-vitro' performance. Furthermore there was interest in evaluating the use of a range of surface specific imaging techniques to analyse the deposition dynamics of the combination formulations. It was hoped that by doing so, the localisation of the individual components within the binary deposits could again be associated back to the force balance of that system, and that an appreciation of the capability of the techniques involved would be gained. The work that follows therefore commences with the evaluation and description of the capacity for the CAB approach to be adapted to measure force relationships between real beclomethasone dipropionate (BOP) particles and pMDI component surfaces. From this assessment it was found that even with relatively smooth substrates, the combination of bulky functional particles and the inherent substrate roughness caused a critical failure in the CAB model. The parity between cohesive and adhesive geometries of contact was excessively stretched, leading to a loss of force normalisation which was reflected in uncorrelated CAB plots. As a consequence little could be confidently gleaned from the force data acquired, although there was the suggestion that the use of a fluorinated ethylene proplylene (FEP) coating reduced the adhesive interaction between the APls and the pMDI canister wall. This was then followed by an attempt to find a compromise between the model crystal substrates of a pure CAB process and the real particle morphologies that had caused the CAB model to fail. Using a compression process to form API powder compacts, in conjunction with small and discreet functional particles, a confident CAB was achieved for two combinations of APls selected on the basis of surface energy and physical stability analysis. Salbutamol sulphate was characterised with beclomethasone dipropionate, and salmeterol xinafoate with fluticasone propionate. Both combinations showed CAB plots with a sufficiently strong linear regression analysis to suggest a broad accuracy of force balance assessment. Both beta2-agonists showed cohesively dominated relationships with respect to the paired glucocortiocoids, while in reverse both glucocorticoids showed adhesively dominated relationships with the beta2-agonists. There was concern raised over the compression process of the powder discs, and its impact on the physicochemical state of the APls, with some thermodynamic evidence of polymorphic changes that required further work. The next chapter looks at the 'in-vitro' deposition performance of the two API combinations from a HFA134a pMDI system by analysis in an Andersen Cascade Impactor (ACI). The coformulation of salmeterol with fluticasone induced an improvement in the fine particle performance of fluticasone, with a concurrent decrease in the fine particle performance of salmeterol. This impact was hypothesised to be related to alterations in the structure and strength of particle-particle agglomerates. The impact on deposition performance of coformulating beclomethasone and salbutamol was unclear, as a critical unexplained loss of beclomethasone by total recovered mass was seen from all beclomethasone containing formulations. This instability of beclomethasone within the HFA134a system, precluded an accurate assessment of a direct impact on salbutamol deposition. The final chapter, compared a range of surface specific imaging techniques, including scanning electron microscopy (SEM), desorption electrospray ionization mass spectrometry (DESI), Raman spectrometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS) in assessing the extent and nature of 'in-vitro' co-deposition from the salmeterol and fluticasone pMDI formulations. It was apparent that the deposition of the two APls on ACI plates was not likely to be directly comparable assessment of the incidence of particle co-deposition 'in-vivo' due to the forced nature of nozzle directed impaction. However the combination of techniques employed produced a wealth of physical and chemical data that did suggest that the two APls showed extensive co-ordination 'in-vitro'. Raman spectroscopy was able to identify individual particle character and showed frequent salmeterol and fluticasone particle combinations, but suffered from exceptionally long run times and anomalies from photoreactive surface elements. The use of a multivariate approach to ToF-SIMs analysis defined the strong co-association of the two APls, although could not differentiate particle to particle deposition. Multivariate curve resolution (MeR) was used and produced distinct components that segregated ions from both APIS from the background plate but not from each other. SEM imaging was able to define the morphologies of the deposited particles, but was unable to differentiate the two. DES I imaging showed the presence of the two APls together within several drug spots, but could not be used to investigate individual drug spots, and the distribution within, due to inadequate spatial resolution and differences in desorption efficacy. While the co-association of the two APls was observed, the lack of a comparator in another combination of APls made the link between deposition performance and force balance purely descriptive. It was unclear as to whether the force balance of the system lends itself to a particular increase in co-deposition behaviour. However it was apparent that the analytical techniques employed all had respective strengths and weaknesses as mapping tools, and with further work with other formulations could be used to provide a tailored formulation screening process, if subsequent links to force balances could be made. To conclude, the work in this thesis details the successful process of adapting an AFM technique in characterising the broad force balance of combinations of APls. In so doing a force balance has been linked to the alteration in deposition behaviour of two APls when co-formulated in a HFA134 formulation. The subsequent co-deposition of the two APls was then analysed by a series of surface analytical techniques. This highlighted a general co-deposition trend, but the collective results were unable to definitively link to the force balance of the system. The information obtained forms the beginnings of what could be utilised as a fast and facile broad predictor of pMDI formulation performance, and an indication of appropriate analytical techniques for investigating particle association 'in-vitro'

Experimental investigation of flow boiling in silicon microchannel devices for electronics cooling

With the fast miniaturization of Very Large Scale Integration (VLSI) systems in the electronics industry, thermal management issues are becoming a serious challenge for sustaining the Moore’s law trend in the next years. Flow boiling in silicon microchannel evaporators has recently arisen as one of the best solutions for the thermal management of high heat flux electronic devices. Microscale flow boiling exhibits high heat transfer rates and reduced temperature gradients optimizing electronics operation. Silicon fabrication techniques enable the development of compact and highly integrated systems. However, the lack of a complete understanding of the physics processes involved and serious technical issues are currently delaying the introduction of silicon microchannel devices in consumable products. Following the great interest of the electronics industry, silicon microchannel devices have started to be considered also for the design of future particle detectors for High Energy Physics (HEP) experiments. This work presents new insights on the two-phase fluid dynamics and flow boiling heat transfer characteristics in silicon microchannel devices. The effect of surface wall roughness is also addressed with a dedicated test section featuring tailored microfabricated structures at the channel walls. The study of interconnected silicon micro-evaporators for the efficient thermal management of future silicon particle detectors at the Large Hadron Collider (LHC) is described. The thermal performance of the device are presented and discussed. The qualification of the complete fabrication processes based on standard microfabrication techniques and the solution of important technical challenges are addressed, paving the introduction of silicon microchannel devices in the design of future detector systems. The results obtained in this study have many potential applications in all the industrial sectors where high heat fluxes need to be efficiently managed with very compact systems

Proceedings of the First International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics

1st International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Kruger Park, 8-10 April 2002.This lecture is a principle-based review of a growing body of fundamental work stimulated by multiple opportunities to optimize geometric form (shape, structure, configuration, rhythm, topology, architecture, geography) in systems for heat and fluid flow. Currents flow against resistances, and by generating entropy (irreversibility) they force the system global performance to levels lower than the theoretical limit. The system design is destined to remain imperfect because of constraints (finite sizes, costs, times). Improvements can be achieved by properly balancing the resistances, i.e., by spreading the imperfections through the system. Optimal spreading means to endow the system with geometric form. The system construction springs out of the constrained maximization of global performance. This 'constructal' design principle is reviewed by highlighting applications from heat transfer engineering. Several examples illustrate the optimized internal structure of convection cooled packages of electronics. The origin of optimal geometric features lies in the global effort to use every volume element to the maximum, i.e., to pack the element not only with the most heat generating components, but also with the most flow, in such a way that every fluid packet is effectively engaged in cooling. In flows that connect a point to a volume or an area, the resulting structure is a tree with high conductivity branches and low-conductivity interstices.tm201