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Semi-Stable Deformation Rings over Q_{p^f} in parallel Hodge--Tate Weights (0,1)
Get PDFDepartment of Mathematical SciencesLet p be an odd prime number. In this thesis, we compute the mod-p reduction of 2-dimensional semi-stable representations of G_{Q_{p^f}} for f>0 with parallel Hodge--Tate weights (0,1), by computing the Breuil modules corresponding to the mod-p reduction of the strongly divisible modules in the semi-stable representations we impose. We also use the parameterization of the strongly divisible modules we have found, to construct the semi-stable deformation rings in parallel Hodge--Tate weights (0,1).ope
Semi-Supervised Contrastive Learning for Anomaly Detection in Contaminated Data
Get PDFDepartment of Industrial EngineeringThis study was carried out at the refrigerator quality inspection station of LG Electronics to improve the performance to locate faulty products characterized by certain defects. The main challenge of this study is that (i) Difficulty of data labeling at the inspection station. (ii) Due to (i), real sensor data from an advanced manufacturing process might have been contaminated. To this end, we first apply the state-of-the-art (SOTA) self-supervised deep anomaly detection model, named Latent Outlier Exposure (NTL(with LOE)), which can consider contaminated scenarios. However, The NTL(with LOE) fails to utilize labeled anomaly. Here we propose Labeled anomaly-Informed Neural Transformations (NTL(with LOE+)), where labeled anomaly information can be considered.
The key idea is to modify the objective function of Latent Outlier Exposure (LOE), a joint loss function, such that NTL(with LOE) can utilize labeled anomaly. We validated the robustness of the proposed method for damage detection using simulation data and condition monitoring sensor data obtained from the real refrigerator inspection lanes.ope
Structural Changes of Telomere by DNA Damage Studied with CRISPR Imaging
Get PDFDepartment of Biomedical EngineeringThe telomere exists in a unique state protected by shelterin complexes at the ends of each chromosome to protect genetic information. Therefore, telomeres show different structural features from other genomic regions. The most widely used method for imaging the telomere is to use TRF1, one of the shelterin proteins. However, the existing TRF1 method for telomere detection has limitations such as differences due to changes in the expression level of TRF1, background signal of TRF1, and inability to apply to wild-type cells. Therefore, methods such as FISH, CRISPR transfection, and CASFISH were applied to telomere imaging to solve this problem by directly attaching fluorescence to the telomeric repeat sequence. The FISH experiment proceeded well with both the DNA probe and the PNA probe, and the imaging efficiency was also comparable. However, in the case of CRISPR transfection, the transfection efficiency in the mainly used U2-OS cell line was too low, making it difficult to use the CRISPR system that requires transfection of multiple plasmids. Therefore, another CRISPR system using image method, CASFISH was conducted. During CASFISH, there were problems such as instability of manual synthesized RNA and degradation by RNase in the cell, which has not been reproduced well since the original paper, but this was solved by purchasing RNA that had been chemically treated. As a result, we were able to succeed in telomere imaging through the CRISPR dCas9 system. Target specificity was confirmed by colocalizing with GFP tagged TRF1 which is transfected as plasmid, and it shows us better image quality than imaging through TRF1 in terms of signal brightness and background contrast ratio. As a result of CASFISH imaging, it was observed that the number and size of telomere foci significantly changed by DNA damage. This can be interpreted as the fact that, like the phenomenon of homologous recombination known as occurring in ALT, the distance to the telomeres of other chromosomes becomes closer, and the number of foci can increase due to DNA break.ope
Transition Metal Atomically Dispersed Catalysts for Electrochemical Chlorine Evolution Reaction
Get PDFDepartment of ChemistryChlorine evolution reaction (CER) is a crucial anodic reaction in the chlor???alkali process. Over the past few decades, the dimensionally stable anode (DSA), comprised of precious metal-based oxides, has been predominantly used as a CER catalyst. However, the DSA requires a large amount of precious metal and catalyzes oxygen evolution reaction as well, which invoke issues of cost and selectivity, respectively. In this work, we have developed a general synthetic strategy for atomically dispersed transition metal (TM??TM = Fe, Co, Ni, and Cu)-based CER catalysts. The synthesized atomically dispersed catalysts (ADCs) consist of isolated TM atoms on a polyaniline-doped carbon nanotube (TM1/aniCNT). Among the catalysts, the Ni1/aniCNT catalyst exhibited the best CER activity (10 mA cm???2 at 1.43 V in 0.1 M HClO4 and 1 M NaCl???) and reaction kinetics with the lowest Tafel slope. Ni1/aniCNT also showed superior catalytic activity to Ni nanoparticles on CNT. In addition, all TM1/aniCNTs showed over 90% selectivity in the same condition with chlor???alkali process (pH 2, 4.0 M NaCl). The Ni1/aniCNT catalyst with high atomic efficiency may help broaden the scope of CER catalysts.ope
User-Centered Design of Products for Acquisition of Procedural Knowledge : Case Study of Magnesticks
Get PDFDepartment of DesignAn understanding of product usage patterns is necessary for the formation of procedural knowledge in the instrumental product development process, which can be enhanced through the product design approach. This enhancement is demonstrated by a case study of Magnesticks, an instrumental product that helps people use chopsticks. A total of five user studies were conducted in turn through subjects ranging in age groups and experience. The presence or absence of the learner???s formed procedural knowledge for the instrumental product is found to induce conflicting results among the subjects, meaning that product-user experience can be confounded by procedural knowledge and enhanced by procedural knowledge. These findings shed light on how a user-centered design approach can be optimized for instrumental product development to maximize the acquisition of learners??? potential procedural knowledge.ope
A Universal Perovskite Nanocrystal Ink for High-Performance Optoelectronic Devices
No full textSemiconducting lead halide perovskite nanocrystals (PNCs) are regarded as promising candidates for next-generation optoelectronic devices due to their solution processability and outstanding optoelectronic properties. While the field of light-emitting diodes (LEDs) and photovoltaics (PVs), two prime examples of optoelectronic devices, has recently seen a multitude of efforts toward high-performance PNC-based devices, realizing both devices with high efficiencies and stabilities through a single PNC processing strategy has remained a challenge. In this work, diphenylpropylammonium (DPAI) surface ligands, found through a judicious ab-initio-based ligand search, are shown to provide a solution to this problem. The universal PNC ink with DPAI ligands presented here, prepared through a solution-phase ligand-exchange process, simultaneously allows single-step processed LED and PV devices with peak electroluminescence external quantum efficiency of 17.00% and power conversion efficiency of 14.92% (stabilized output 14.00%), respectively. It is revealed that a careful design of the aromatic rings such as in DPAI is the decisive factor in bestowing such high performances, ease of solution processing, and improved phase stability up to 120 days. This work illustrates the power of ligand design in producing PNC ink formulations for high-throughput production of optoelectronic devices; it also paves a path for "dual-mode" devices with both PV and LED functionalities
Engineering Catalysis within a Saturated In(III)-Based MOF Possessing Dynamic Ligand-Metal Bonding
No full textMetal-organic frameworks have developed into a formidable heterogeneous catalysis platform in recent years. It is well established that thermolysis of coordinated solvents from MOF nodes can render highly reactive, coordinatively unsaturated metal complexes which are stabilized via site isolation and serve as active sites in catalysis. Such approaches are limited to frameworks featuring solvated transition-metal complexes and must be stable toward the formation of "permanent" open metal sites. Herein, we exploit the hemilability of metal-carboxylate bonds to generate transient open metal sites in an In(III) MOF, pertinent to In-centered catalysis. The transient open metal sites catalyze the Strecker reaction over multiple cycles without loss of activity or crystallinity. We employ computational and spectroscopic methods to confirm the formation of open metal sites via transient dissociation of In(III)-carboxylate bonds. Furthermore, the amount of transient open metal sites within the material and thus the catalytic performance can be temperature-modulated
Crystallinity-modulated hollow CeO2-x nanorods as free radical scavengers for long-term photostability in organic photovoltaics
No full textHere we investigated the effects of CeO2-x nanostructures as free radical scavengers on the long-term photostability of an organic photovoltaic (OPV) structure. From powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and N-2 adsorption experiments, it was determined that the single-crystalline hollow CeO2-x nanorods were very effective as hydroxyl radical scavengers. This was attributed to their having more Ce3+ states and a wider surface area than other types of CeO2 nanostructures. Time-dependent UV-visible absorption spectra analyses also revealed that the improved scavenging of hydroxyl radicals in the OPV device was related to the better interfacial compatibility between the organic active and ZnO layers, resulting in improved OPV photostability
A Comparison Study of the Predictor-Corrector Quasi-static Method and CMFD-based Transient Fixed Source Problem for Transient Analysis
No full textDepartment of Nuclear EngineeringTransient analysis with a time-dependent transport equation delivers an accurate and consistent solution. Although, transport modeling with heterogeneous geometries of the reactor core increases computational expense in terms of memory and time. Numerous methods have been developed for heterogeneous geometric reactor core modeling. The predictor-corrector quasi-static method (PCQM) is a newly developed transient analysis technique that factorizes the angular neutron flux. At the same time, the time-dependent multigroup coarse-mesh finite difference (CMFD) method-based transient fixed source problem resolves the neutron diffusion equation. CMFD correction factors and cross#2;sections are updated from the transport solution. The reactor condition doesn???t change every time step is the crucial point for utilizing the CMFD-based transient fixed source problem (CTFSP). The angular neutron flux undergoes a factorized split to form the product of shape and amplitude functions. The method of characteristic/diamond difference (MOC/DD) method to the time-dependent neutron transport application provides the flux shape function. In contrast, the amplitude function is accomplished to resolve the exact point kinetics equations (EPKEs). The PCQM iteration scheme
couples the MOC/DD and the EPKEs level. On the other hand, MOC/DD method is applied to obtain the CMFD cell cross-sections and correction factors for the CTFSP. The 3D CMFD equation is solved to acquire the neutron flux, which reduces the computational cost and represents the problem solution. The transport solution is adjusted as soon as CTFSP completes the solution. A two-level CMFD technique is implemented to reduce the transient running time of the transport equation solution. Moreover, high-order polynomial interpolation is applied to the kinetics parameters utilized in EPKEs, to minimize the error when the reactivity insertion is nonlinear. The transport code, STREAM, used three thermal-hydraulic codes for Multiphysics coupling and
studied the core response after coupling feedback. The performance of the PCQM and the CTFSP were also examined without Multiphysics coupling. It is noted that both methods required approximately similar transient time without any feedback, whereas CTFSP resolved faster when Multiphysics coupling was applied. Finally, several numerical benchmarks are solved to justify the application of the procedures, proving that the methods maintain solution accuracy. The flux-volume weighted method is used for rod decusping to update the partially inserted control rod cell materials, which keeps the solution's stability. A smaller time step is needed to obtain accurate results, which increases the computational cost. The adaptive step control algorithm is robust in controlling the time step. This algorithm is based on regional cell errors and can accept or reject the solution. The performance and numerical accuracy of parallel computing, rod decusping, adaptive time step control, and thermal-hydraulic feedback were also presented. Obtained results are compared with other deterministic codes and experimental data. Lastly, performed a typical pressurized light-water reactor rod-ejection accident analysis to show the capability of large-scale PWR simulations, which was the goal of the work.clos
A Safety Analysis Code for Al-B4C Neutron Absorbers Used in Spent Nuclear Fuel Pool
No full textDepartment of Nuclear EngineeringAl-B4C metal matrix composite is a neutron absorber material that has been widely used in spent nuclear fuel pools to ensure subcriticality and related safety margins. The use of such a type of neutron absorber is expanding since the installation of high-density racks becomes a tentative solution to store more spent nuclear fuel assemblies minimizing additional spent fuel pool construction. The material integrity and neutron-absorbing performance of in-service Al-B4C neutron absorbers have commonly been monitored by characterizing the surveillance coupons.
Recent experimental studies on the Al-B4C surveillance coupons had revealed noticeable surface corrosion from several ???less than nine-year-used??? coupons, which was clearly unexpected since 40 years of service life was guaranteed for the absorber, however, based on separate gamma irradiation and corrosion tests. This premature corrosion was largely attributed to the accumulation of radiation damage and gaseous helium atoms from 10B(n, ??)7Li reactionsradiation-induced porous microstructure could have accelerated the corrosion of the non-clad absorber. The studies further revealed the presence of a significant amount of helium and hydrogen in the bubbles found near B4C particles in the absorber coupons using electron energy loss spectroscopy. This irradiation-induced porosification would likely propagate along the boundary between B4C particles and the aluminum matrix, which could lead to the detachment of the B4C particles and thus early depletion of 10B and subsequent increase of the criticality of the pool.
This material issue is in urgent need to address in order to certify the safe operation of spent nuclear fuel pools around the world. The spent nuclear fuel pool itself, however, can hardly be used for test purposes without an intentionally increased neutron flux for the test. To conduct further experimental studies on this material issue, in an accelerated manner without elevating public anxiety, ion-beam irradiation has to play a major role in the experimental emulation of the radiation damage and gas atom concentration in the absorber in time. Also, a dedicated computational code needs to be developed to plan such kind of irradiation test to be well matched with actual conditions inside the Al-B4C absorber installed in the spent nuclear fuel pool.
In accordance with the stand-out situation on the issues, this study developed a Safety Analysis code for NeuTron absorbers (SANTA) in spent nuclear fuel pool by integrating the existing codes (TRITON, ORIGEN, CSAS6, and modified SDTrimSP) with several newly developed modules. This code can provide essential experimental parameters required for the irradiation-assisted corrosion test of Al-B4C absorbers. It has a user-friendly framework, and whole sequences can be executed with a single integrated input without user intervention. Also, the code can efficiently account for the radiation damage aroused from 7Li ions and ??-particles emitted from 10B(n,??)7Li reactions. The spatial distribution of radiation damage and gaseous atom concentration is obtained in terms of displacement per atom (dpa) unit and helium concentration in atomic ppm (or atomic percent). This code could provide foundational inputs for the design of the ion-beam irradiation, the first half of the irradiation-assisted corrosion test of Al-B4C absorbers.
Example cases solved using SANTA code are included in this dissertation: radiation damage and helium concentration in a non-clad Al-B4C neutron absorber used in the high-density racks for 40 years were calculated and comparatively discussed with previously mentioned recent experimental studies. The calculated maximum radiation damage and helium concentration in the aluminum matrix of the neutron absorber surrounded by recently discharged spent fuel assemblies, 2.12??10-7 dpa and 4.31??10-3 appm, were relatively lower than experimental estimates in open literatures. The discrepancy between the code outputs and literature estimates could be attributed to hydrogen-assisted bubble formation and growth since the significant surface corrosion and the presence of hydrogen in the observed bubbles were apparently confirmed by the aforementioned experimental studies utilizing transmission electron microscopy and electron energy loss spectroscopy.
In search for the equivalent radiation damage and helium concentration achieved in the micrographs published in the recent experimental studies, therefore, to be experimentally emulated using ion-beam accelerators in follow-up experiments, the same type of Al-B4C surveillance coupons with the ones used in the experimental studies was simulated: two stand-alone sequences of SANTA, neutron flux and radiation damage calculations, were employed to estimate the total number of 10B(n, ??)7Li reactions that occurred in the absorber by referring to the measured 10B areal density and thickness reduction over the installed period in the spent fuel pool. For the maximum radiation damage and helium concentration in the aluminum matrix, the simulation yielded 1.95-3.63 dpa and 0.37-0.89 at% after 99 months of use, and 1.99-4.53 dpa and 0.38-1.13 at% after 40 years of use depending on the B4C particle diameter with slightly different corrosion conditions adopted for the simulation. To be noted, in actual cases, the local helium concentrations can be significantly higher than simulation results, especially near large size B4C particles, mainly due to high diffusivity of helium and its leakage through numerous irradiation-induced microcracks in B4C particles.
The simulation results suggest that if assuming neutron absorption is the only mode of 10B loss from the absorber the surveillance coupons should have been exposed under the neutron flux of over 1012 n/cm2-s on average to match the experimentally estimated 10B depletion. Such high neutron flux, however, greatly exceeds the experimentally measured neutron flux level in spent fuel pools, which is around 104-105 n/cm2-s. This mismatch between the SANTA simulation results and the generally known experimental value of spent fuel pool neutron flux could be partly due to the underestimation on corrosion-induced 10B areal density decrease. Absorber thickness measurement using calipers may have been associated with large errors since porous and low-density aluminum oxide layer covers the absorber surfacealso, the amount of detached B4C particles due to the pit corrosion had not been measured or considered for the estimation. Hence, the fraction of the neutron-induced 10B depletion could be relatively minor compared to irradiation-assisted corrosion-induced loss of 10B from the absorber coupon. Conclusively, and not so surprisingly, much small number of 10B(n, ??)7Li reactions had occurred in the coupons while such noticeable irradiation-induced microstructures had been developed.
Consistent underestimation on the radiation damage and helium concentration obtained from the SANTA example cases may indicate that there are some missing links between SANTA code and the spent fuel pool condition. Considering that the neutron emission rate is relatively well validated, two-fold possibility can be suggested: (1) the Monte Carlo transport program, CSAS6, used in SANTA may underrate the neutron flux near and within strong neutron absorber materials, perhaps due to its method of neutron tally. In this case, as the future work, a robust neutronics code, a more reliable one for strong neutron absorbers, may need to be developed and coupled into the framework of SANTA(2) chemical diffusion of helium and remnant hydrogen from surface corrosion plays a truly bigger role than the general expectation of forming irradiation-induced bubbles in the Al-B4C absorber. In this case, highly hydrided Al-B4C specimens need to be irradiated with a very low dose to confirm the lowest threshold dpa value to form an observable bubble structure with excessive gaseous atoms in the material.
SANTA is already one of a kind code that can partially simulate the irradiation-induced degradation of Al-B4C absorbers in spent nuclear fuel pools and it thus can provide essential parameters for proton and heavy-ion irradiation experiments on the material. However, a chemical diffusion module for hydrogen and helium needs to be developed to extend the code capability further to more thoroughly simulate the irradiation-assisted corrosion of Al-B4C neutron absorbers. The module was unable to be developed due to the absence of a physical model on the behavior of helium and hydrogen in the absorber. Admitting the missing parts, SANTA still could be a cornerstone for both simulation and experimental works at this moment, while waiting for more experimental works and modeling efforts to be done on the degradation of neutron absorber materials under various conditions, including spent nuclear fuel pool and dry cask storage.clos