Minimal Flavor Violation with Axion-like Particles

We revisit the flavor-changing processes involving an axion-like particle (ALP) in the context of generic ALP effective lagrangian with a discussion of possible UV completions providing the origin of the relevant bare ALP couplings. We focus on the minimal scenario that ALP has flavor-conserving couplings at tree level, and the leading flavor-changing couplings arise from the loops involving the Yukawa couplings of the Standard Model fermions. We note that such radiatively generated flavor-changing ALP couplings can be easily suppressed in field theoretic ALP models with sensible UV completion. We discuss also the implication of our result for string theoretic ALP originating from higher-dimensional $p$-form gauge fields, for instance for ALP in large volume string compactification scenario.Comment: 41 pages, 3 figures; v3: a discussion on general extended Higgs sector added in sec. 2, version published in JHE

Nanoindentation of the a and c domains in a tetragonal BaTiO3 single crystal

Nanoindentation in conjunction with piezoresponse force microscopy was used to study domain switching and to measure the mechanical properties of individual ferroelectric domains in a tetragonal BaTiO3 single crystal. It was found that nanoindentation has induced local domain switching; the a and c domains of BaTiO3 have different elastic moduli but similar hardness. Nanoindentation modulus mapping on the a and c domains further confirmed such difference in elasticity. Finite element modeling was used to simulate the von Mises stress and plastic strain profiles of the indentations on both a and c domains, which introduces a much higher stress level than the critical value for domain nucleation

Nanostructured Organic Solar Cells: Toward High Efficiency, Large Scale and Versatility.

This dissertation is devoted to searching for solutions to realize low-cost, high efficiency and scalable organic solar cells (OSC), and their versatile application. For this purpose, my research has been focused on various nanostructures, which can be usable to maximize the performances of OSCs, and the effective fabrication processes to achieve those nanostructures. Furthermore novel device concepts based on those nanostructures have been introduced. First part of dissertation is about controlling the nanostructures in photoactive layers to develop more efficient OSC devices. A new process, named as ESSENCIAL, inducing superior bulk heterojunction (BHJ) morphology was developed. Compared with conventional annealing based-methods, the optimized BHJ morphology showing well-organized charge transporting pathways with high crystallinity was achieved. Moreover, by controlling the interface of the photoactive layer, further improvement of power conversion efficiency (PCE) was possible using BHJ structure. A new type of heterojunction nanostructure based on bilayer concept was also introduced. By maximizing interdiffusion of electron-donor and -acceptor, the optimized heterojunction morphology having internal quantum efficiency approaching about 100% was demonstrated. As another effort to realize the ideal interdigitated donor-acceptor structures, sub-20 nm scale nanopillars were prepared. Nanopillar and nanohole type nanoimprint lithography (NIL) molds were fabricated from a self-assembled block copolymer nanotemplate, and NIL-based nanopatterns are made in organic semiconductor. All these nanostructures could be realized by advanced processing that can be extended to high-speed manufacturing toward low-cost and high efficiency OSCs. Secondly, various nanostructures such as plasmonic nanostructures and light trapping structures were developed to enhance the absorption of light in OSC devices. NIL-based plasmonic nanostructures exhibit strong and tunable light extinction, and the enhanced electromagnetic field induces the increased photocurrent, leading to improved PCE. Moreover, by introducing periodic nanostructure at the metal electrode working as reflector in OSC, I could enhance the optical path length across a broad wavelength range of incident light. Lastly, the dual-function devices working as color filters and solar cells were demonstrated by applying photonic nanostructures to OSCs. This new conceptual device can recycle the wasted energy in color filter to generate the electricity for the revolutionary energy-saving e-media.Ph.D.Macromolecular Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91446/1/huijoon_3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91446/2/huijoon_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91446/3/huijoon_1.pd

Internal and external North Atlantic Sector variability in the Kiel Climate Model

The internal and external North Atlantic Sector variability is investigated by means of a multimillennial control run and forced experiments with the Kiel Climate Model (KCM). The internal variability is studied by analyzing the control run. The externally forced variability is investigated in a run with periodic millennial solar forcing and in greenhouse warming experiments with enhanced carbon dioxide concentrations. The surface air temperature (SAT) averaged over the Northern Hemisphere simulated in the control run displays enhanced variability relative to the red background at decadal, centennial, and millennial timescales. Special emphasis is given to the variability of the Meridional Overturning Circulation (MOC). The MOC plays an important role in the generation of internal climate modes. Furthermore, the MOC provides a strong negative feedback on the Northern Hemisphere SAT in both the solar and greenhouse warming experiments, thereby moderating the direct effects of the external forcing in the North Atlantic. The implications of the results for decadal predictability are discussed

The impact of sea surface temperature bias on equatorial Atlantic interannual variability in partially coupled model experiments

We examine the impact of sea surface temperature (SST) bias on inter-annual variability during boreal summer over the equatorial Atlantic using two suites of partially coupled model (PCM) experiments with and without surface heat flux correction. In the experiments, surface wind stress anomalies are specified from observations while the thermodynamic coupling between the atmospheric and oceanic components is still active as in the fully coupled model. The results show that the PCM can capture around 50% of the observed variability associated with the Atlantic Niño from 1958 to 2013, but only when the bias is substantially reduced using heat flux correction, with no skill otherwise. We further show that ocean dynamics explain a large part of the SST variability in the eastern equatorial Atlantic in both observations (50-60%) and the PCM experiments (50-70%) with heat flux correction, implying that the seasonal predictability potential may be higher than currently thought

Extension of the crRNA enhances Cpf1 gene editing in vitro and in vivo.

Engineering of the Cpf1 crRNA has the potential to enhance its gene editing efficiency and non-viral delivery to cells. Here, we demonstrate that extending the length of its crRNA at the 5 end can enhance the gene editing efficiency of Cpf1 both in cells and in vivo. Extending the 5 end of the crRNA enhances the gene editing efficiency of the Cpf1 RNP to induce non-homologous end-joining and homology-directed repair using electroporation in cells. Additionally, chemical modifications on the extended 5 end of the crRNA result in enhanced serum stability. Also, extending the 5 end of the crRNA by 59 nucleotides increases the delivery efficiency of Cpf1 RNP in cells and in vivo cationic delivery vehicles including polymer nanoparticle. Thus, 5 extension and chemical modification of the Cpf1 crRNA is an effective method for enhancing the gene editing efficiency of Cpf1 and its delivery in vivo