Fast Compartment Model Calibration using Annealed and Transformed Variational Inference

Compartment models are widely used in climate science, epidemiology, and physics, among other disciplines. An important example of a compartment model is susceptible-infected-recovered (SIR) model, which can describe disease dynamics. Bayesian inference for SIR models is challenging because likelihood evaluation requires solving expensive ordinary differential equations. Although variational inference (VI) can be a fast alternative to the traditional Bayes approaches, VI has limited applicability due to boundary issues and local optima problems. To address these challenges, we propose flexible VI methods based on deep generative models that do not require parametric assumptions on the variational distribution. We embed a surjective transformation in our framework to avoid posterior truncation at the boundary. We provide theoretical conditions that guarantee the success of the algorithm. Furthermore, our temperature annealing scheme can avoid being trapped in local optima through a series of intermediate posteriors. We apply our method to variants of SIR models, illustrating that the proposed method can provide fast and accurate inference compared to its competitors

THREE ESSAYS ON ENVIRONMENTAL SHOCKS AND POLICY RESPONSE

Ph.D

The dual nature of constraints on foreign worker participation in sports and physical activity in South Korea during COVID-19

This study provides a different understanding of the constraints imposed by the pandemic and the official and unofficial restrictions that accompanied it. It is an empirical effort demonstrating that the pandemic's effects are not purely negative, but rather, also helped to produce positive and productive practices that draw upon both the inhibiting and enabling features of the constraints it triggered. Engaging with “productive power” in Foucault by considering constraints as practices that both inhibit and enable, the empirical goal of this paper is to explore how pandemic-related constraints on sports and physical activity prohibit foreign worker participation in sports and physical activity. It also examines how the constraints encourage them to pursue an active life in new and unique ways. To achieve this goal, the paper examines the South Korean context, particularly unskilled foreign workers with E-9 visas for non-professional employment in the fishing, farming, and manufacturing industries and their involvement in sports and physical activity during the COVID-19 pandemic. The findings address three “inhibitors” that specifically prevented foreign workers from getting actively involved, then demonstrate that explicit restrictions on sports and physical activity can be transformed into four “enablers” that encouraged foreign workers to participate. The conclusion offers critical reflections on Foucault's “ethical subject,” followed by the limitations and implications of the study

Structural changes of polyaniline/montmorillonite nanocomposites and their effects on physical properties

Polyaniline/montmorillonite (MMT) nanocomposites containing different PANI contents were prepared by the intercalation of aniline monomer into pristine MMT followed by the subsequent oxidative polymerization of the aniline in the interlayer spacings. The polyaniline/MMT nanocomposite structure intercalated with polyaniline (PANI) was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). From the full-width at half-maximum (FWHM) of the (001) reflection peaks in the XRD patterns, the PANI/MMT nanocomposite containing 12.3 wt% PANI (PMN12) was found to be in the most disordered state. The physical interaction between the intercalated PANI and the basal surfaces of MMT was monitored by FT-IR. The room-temperature conductivity (RT) varied from 9.1 × 10–9 to 1.5 × 100 S cm–1 depending on the PANI content in the nanocomposites. The temperature dependence of dc conductivity (dc(T)) of all the samples follows the quasi-1D variable range hopping (quasi-1D VRH) model (i.e., dc(T) exp [–(T0/T)1/2]). The charge transport behavior of this system was interpreted from the slopes (T0) of the dc curves and the highest T0 value was found for the PANI/MMT nanocomposite with 12.3 wt% PANI (PMN12). The FT-IR, dc(T) and RT results for the nanocomposites with varying content of PANI are consistently related to the structure of the PANI/MMT nanocomposites discussed in the XRD analysis. The structural argument was further supported by scanning electron microscopy (SEM) of all the samples. Thermogravimetric analysis (TGA) showed improved thermal stability for the intercalated nanocomposites in comparison with the pure PANI and a simple PANI/MMT mixture.We are very grateful for the financial support from the National Research Laboratory Fund from the Ministry of Science and Technology (MOST), the Korean Ministry of Education through the Brain Korea 21 Program, and the Research Institute of Advanced Materials (RIAM) at Seoul National University. We also thank Mrs Mee Jeong Kang for her kind SEM and TEM measurements

Selfrepairing SRAM for reducing parametric failures in nanoscaled memory

Abstract

How to Respond to the Fourth Industrial Revolution, or the Second Information Technology Revolution? Dynamic New Combinations between Technology, Market, and Society through Open Innovation

How can we respond to the Fourth Industrial Revolution in terms of technology?&rdqu

Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2

New phases of matter can be stabilized by a combination of diverging electronic density of states, strong interactions, and spin-orbit coupling. Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered a wealth of novel phases as a result of interaction-driven spin-valley flavour polarization. In this work, we explore correlated phases appearing due to the combined effect of spin-orbit coupling-enhanced valley polarization and large density of states below half filling ($\nu \lesssim 2$) of the moir\'e band in a TBG coupled to tungsten diselenide. We observe anomalous Hall effect, accompanied by a series of Lifshitz transitions, that are highly tunable with carrier density and magnetic field. Strikingly, the magnetization shows an abrupt sign change in the vicinity of half-filling, confirming its orbital nature. The coercive fields reported are about an order of magnitude higher than previous studies in graphene-based moir\'e systems, presumably aided by a Stoner instability favoured by the van Hove singularities in the malleable bands. While the Hall resistance is not quantized at zero magnetic fields, indicative of a ground state with partial valley polarization, perfect quantization and complete valley polarization are observed at finite fields. Our findings illustrate that singularities in the flat bands in the presence of spin-orbit coupling can stabilize ordered phases even at non-integer moir\'e band fillings.Comment: 17 pages, 15 figure

Autonomous task execution of a humanoid robot using a cognitive model

Abstract—These days, there are many studies on cognitive architectures, which are developed based on human cognitive models. Some other studies are focused on applying these cognitive architectures to the autonomous task execution of humanoid robots. In this paper, we have shown that a real world robot, Mahru-Z can execute a task autonomously in the Blocks World domain, using a cognitive architecture, ICARUS. For this project, diverse techniques such as system integration, human-like manipulation based on vision, environmental information update techniques etc are used. Successful completions of these tasks imply that we can expect similar results for the more diverse and complicated tasks as well. I

3D hierarchically porous magnetic molybdenum trioxide@gold nanospheres as a nanogap-enhanced Raman scattering biosensor for SARS-CoV-2

A multifunctional 3D magnetic molybdenum trioxide@gold nanosphere is deployed as a plug and play biosensor for SARS-CoV-2 spike proteins via ACE2-mediated immunocapture and magnetic-induced nanogap-enhanced Raman scattering (MINERS)