Nanoporous materials for optical applications

In this work, a new process of generating nanobubbles* in transparent polymers was developed. The azo-chemical initiators AIBN (Azobisisobutyronitrile) and ABVN (2,2’-Azobis(2,4-dimethylvaleronitrile)) were used as chemical blowing agents (CBA) that deliver nitrogen gas to form the bubbles. Specifically, the photo initiator Irgacure 819, which could be activated by a longer wavelength of UV (405 nm) than that of AIBN (345 nm), was added to the solution in order to minimize the decomposition of the azo chemicals during the first stage of sample preparation by UV-pre-curing. As a result, the CBAs remained unreacted, thus they could decompose and be used merely as a blowing agent. In addition, the post-foaming processes were conducted under the different foaming conditions to investigate critical factors affecting the nucleation and growth of bubbles. The results were discussed based on thermodynamics, mainly by conventional nucleation theory (CNT). Finally, stepwise optimization of those factors led to the generation of nanobubbles. This technique could be applicable to UV curable polymer systems in general. This novel approach was used to make prototype optical devices, such as security mark coating and light out-coupling in optical waveguide. This study also gives important information about the nucleation and growth of bubbles in meta-stable state of polymers, which could help to verify the background theories.In dieser Arbeit wurde ein neues Verfahren zur Herstellung von Nanobläschen in transparenten Polymeren entwickelt. Die azo-chemischen Initiatoren AIBN (Azobisisobutyronitril) und ABVN (2,2'-Azobis(2,4-Dimethylvaleronitril)) wurden als chemische Treibmittel (CBA) verwendet, die Stickstoff zur Bildung der Blasen abgeben. Der Photoinitiator Irgacure 819, der durch längeres UV-Licht (405 nm) als AIBN (345 nm) aktiviert werden kann, wurde zu der Lösung gegeben, um die Zersetzung der Azochemikalien während der ersten Stufe, der Probenvorbereitung durch UV-Vorhärtung, zu minimieren. Die nicht umgesetzten CBAs, zersetzten sich bei Erwärmung und fungierten als Treibmittel. Die Bedingungen der Aufschäumprozesse wurden variiert, um kritische Faktoren zu untersuchen, die Keimbildung und Wachstum von Blasen beeinflussen. Die Ergebnisse wurden auf der Grundlage der Thermodynamik im Kontext der konventionellen Keimbildungstheorie diskutiert. Die schrittweise Optimierung dieser Faktoren führte zur Erzeugung von Nanobläschen. Diese Technik könnte allgemein auf UV-härtbare Polymersysteme anwendbar sein. Dieser neuartige Ansatz wurde verwendet, um für optische Anwendungen Prototypen herzustellen, wie z.B. Beschichtung von Sicherheitsmarkierungen und Lichtauskopplung in optischen Wellenleitern. Diese Studie liefert auch wichtige Informationen zu Keimbildung und Wachstum von Blasen im metastabilen Zustand von Polymeren, die zur Verifizierung der Hintergrundtheorien beitragen könnten

Assessment of the Impacts of Various Grazing Management Strategies on Southern Minnesota Stream Channels

University of Minnesota M.S. thesis.May 2018. Major: Natural Resources Science and Management. Advisor: Joe Magner. 1 computer file (PDF); viii, 153 pages + 1 supplementary data file (Excel)Stream riparian corridors are inherent to many farms in southern Minnesota. They are complex and diverse ecosystems, provide transportation for drainage from agricultural fields, and contribute to the quality of the larger watershed to which they belong. However, much of the 3.5 million miles of rivers in the United States are impacted, with sedimentation and excess nutrients being the most significant causes of degradation. The agricultural areas of southern Minnesota commonly use stream corridors as pasture since they are generally unsuitable for crops and provide a natural source of water for livestock. Traditional methods of grazing livestock can cause reduced vegetative cover, compacted soils, water contamination, sedimentation, and eroded banks. Managing livestock by limiting the location and duration of their grazing has seen some success in reducing the impact compared to conventional grazing methods. My research aims to further determine the impacts various grazing management strategies have had on streams. Geomorphic data from four sites across three streams are analyzed to evaluate effects of current grazing strategies and changes in grazing strategies. Grassed and wooded areas are also compared, as grazing directly influences the vegetative communities. The results suggest that both managed and grazing exclusion sites showed healthier channels than conventional grazing sites did, and that grassed bank areas contribute more to channel stability than wooded bank areas. In certain situations, managed grazing has the potential to be more beneficial to stream channel health than the prohibition of grazing

NeBLa: Neural Beer-Lambert for 3D Reconstruction of Oral Structures from Panoramic Radiographs

Panoramic radiography (panoramic X-ray, PX) is a widely used imaging modality for dental examination. However, its applicability is limited as compared to 3D Cone-beam computed tomography (CBCT), because PX only provides 2D flattened images of the oral structure. In this paper, we propose a new framework which estimates 3D oral structure from real-world PX images. Since there are not many matching PX and CBCT data, we used simulated PX from CBCT for training, however, we used real-world panoramic radiographs at the inference time. We propose a new ray-sampling method to make simulated panoramic radiographs inspired by the principle of panoramic radiography along with the rendering function derived from the Beer-Lambert law. Our model consists of three parts: translation module, generation module, and refinement module. The translation module changes the real-world panoramic radiograph to the simulated training image style. The generation module makes the 3D structure from the input image without any prior information such as a dental arch. Our ray-based generation approach makes it possible to reverse the process of generating PX from oral structure in order to reconstruct CBCT data. Lastly, the refinement module enhances the quality of the 3D output. Results show that our approach works better for simulated and real-world images compared to other state-of-the-art methods.Comment: 10 pages, 4 figure

Non-Terrestrial Networks for UAVs: Base Station Service Provisioning Schemes with Antenna Tilt

By focusing on unmanned aerial vehicle (UAV) communications in non-terrestrial networks (NTNs), this paper provides a guideline on the appropriate base station (BS) service provisioning scheme with considering the antenna tilt angle of BS. Specifically, two service provisioning schemes are considered including the inclusive-service BS (IS-BS) scheme, which makes BSs serve both ground users (GUs) and aerial users (AUs) (i.e., UAVs) simultaneously, and the exclusive-service BS (ES-BS) scheme, which has BSs for GUs and BSs for AUs. By considering the antenna tilt angle-based channel gain, we derive the network outage probability for both IS-BS and ES-BS schemes, and show the existence of the optimal tilt angle that minimizes the network outage probability after analyzing the conflict impact of the antenna tilt angle. We also analyze the impact of various network parameters, including the ratio of GUs to total users and densities of total and interfering BSs, on the network outage probability. Finally, we analytically and numerically show in which environments each service provisioning scheme can be superior to the other one

3D Teeth Reconstruction from Panoramic Radiographs using Neural Implicit Functions

Panoramic radiography is a widely used imaging modality in dental practice and research. However, it only provides flattened 2D images, which limits the detailed assessment of dental structures. In this paper, we propose Occudent, a framework for 3D teeth reconstruction from panoramic radiographs using neural implicit functions, which, to the best of our knowledge, is the first work to do so. For a given point in 3D space, the implicit function estimates whether the point is occupied by a tooth, and thus implicitly determines the boundaries of 3D tooth shapes. Firstly, Occudent applies multi-label segmentation to the input panoramic radiograph. Next, tooth shape embeddings as well as tooth class embeddings are generated from the segmentation outputs, which are fed to the reconstruction network. A novel module called Conditional eXcitation (CX) is proposed in order to effectively incorporate the combined shape and class embeddings into the implicit function. The performance of Occudent is evaluated using both quantitative and qualitative measures. Importantly, Occudent is trained and validated with actual panoramic radiographs as input, distinct from recent works which used synthesized images. Experiments demonstrate the superiority of Occudent over state-of-the-art methods.Comment: 12 pages, 2 figures, accepted to International Conference on Medical Image Computing and Computer-Assisted Intervention MICCAI 202

R&D, Production Structure and Productivity Growth: A Comparison of the US, Japanese and Korean Manufacturing Sectors

We estimate and compare the production structures of the US, Japanese, and Korean total manufacturing sectors for the 1974-1990 period. We employ a translog variable cost function that includes such inputs as labor, materials, physical and R&D capital with the physical and R&D capital treated as quasi-fixed subject to adjustment costs. The paper provides estimates for markups, returns to scale, rates of return on physical and R&D capital, and technical change. The paper also identifies the sources of the growth of output, labor productivity, and total factor productivity. The results show that resource accumulation, not technical change, is the key factor in rapid output growth, and that the R&D capital and technical change have been major contributors of the TFP growth in the US and Japanese manufacturing but not in the Korean manufacturing sector.

R&D, Production Structure & Productivity Growth: A Comparison of US, Japanese & Korean Manufacturing Sectors

Factor demand, productivity, R&D expenditures, returns to scale