Forbidden Channels and SIMP Dark Matter

In this review, we focus on dark matter production from thermal freeze-out with forbidden channels and SIMP processes. We show that forbidden channels can be dominant to produce dark matter depending on the dark photon and / or dark Higgs mass compared to SIMP.Comment: 5 pages, Prepared for the proceedings of the 13th International Conference on Gravitation, 3-7 July 201

On thermal production of self-interacting dark matter

We consider thermal production mechanisms of self-interacting dark matter in models with gauged $Z_3$ symmetry. A complex scalar dark matter is stabilized by the $Z_3$, that is the remnant of a local dark $U(1)_d$. Light dark matter with large self-interaction can be produced from thermal freeze-out in the presence of SM-annihilation, SIMP and/or forbidden channels. We show that dark photon and/or dark Higgs should be relatively light for unitarity and then assist the thermal freeze-out. We identify the constraints on the parameter space of dark matter self-interaction and mass in cases that one or some of the channels are important in determining the relic density.Comment: 26 pages, 11 figures, Version to appear in Journal of High Energy Physic

Unitary inflaton as decaying dark matter

We consider the inflation model of a singlet scalar field (sigma field) with both quadratic and linear non-minimal couplings where unitarity is ensured up to the Planck scale. We assume that a $Z_2$ symmetry for the sigma field is respected by the scalar potential in Jordan frame but it is broken explicitly by the linear non-minimal coupling due to quantum gravity. We discuss the impacts of the linear non-minimal coupling on various dynamics from inflation to low energy, such as a sizable tensor-to-scalar ratio, a novel reheating process with quartic potential dominance, and suppressed physical parameters in the low energy, etc. In particular, the linear non-minimal coupling leads to the linear couplings of the sigma field to the Standard Model through the trace of the energy-momentum tensor in Einstein frame. Thus, regarding the sigma field as a decaying dark matter, we consider the non-thermal production mechanisms for dark matter from the decays of Higgs and inflaton condensate and show the parameter space that is compatible with the correct relic density and cosmological constraints.Comment: 36 pages, 7 figures, v2: minor corrections made and references added, v3: discussion on preheating added, accepted for Journal of High Energy Physics, v4: Lyman-alpha bound included and inflationary predictions refined for perturbative reheatin

A minimal flavored U(1)′U(1)' for BB-meson anomalies

We consider an anomaly-free $U(1)'$ model with favorable couplings to heavy flavors in the Standard Model(SM), as motivated by $B$-meson anomalies at LHCb. Taking the $U(1)'$ charge to be $Q'=y(L_\mu-L_\tau)+ x(B_3-L_3)$, we can explain the $B$-meson anomalies without invoking extra charged fermions or flavor violation beyond the SM. We show that there is a viable parameter space with a small $x$ that is compatible with other meson decays, tau lepton and neutrino experiments as well as the LHC dimuon searches. We briefly discuss the prospects of discovering the $Z'$ gauge boson at the LHC in the proposed model.Comment: 20 pages, 4 figures, v2: references and discussion on electroweak precision test added, v3: Version to appear in Physical Review

광전기화학전지를 위한 나노구조 전이금속 및 전이후금속 화합물 전극 연구

학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2015. 8. 성영은.Photoelectrochemical cells are electrochemical cells that generally comprise semiconductor photoelectrode, electrocatalytic counter electrode, and electrolyte. There are two types of photoelectrochemical cells according to the function of the electrolyte(i) photovoltaic cell with regenerative redox electrolyte and (ii) photosynthetic cell with sacrificial electrolye. Mesoscopic sensitized solar cells and photoelectrochemical water splitting cells are the typical examples of each kind, respectively. In this thesis, nanostructured electrodes composed of transition and post-transition metal compound for those cells were investigated. The main issues in the development of photoelectrodes, which are mainly metal oxide films, are improvements of light harvesting and charge collection. In contrast, replacement of high-cost and rare noble metal, typically platinum, with an economic and earth-abundant material has been the main objective of the research works on counter electrodes. Therefore, in this study, nanostructured metal oxides with intrinsically fast charge transport property and state-of-the-art nanomaterials with enlarged surface area were utilized as photoelectrodes. Also, nanostructured low-cost carbide and nitride materials with facile preparation methods were employed as electrocatalytic counter electrodes. Besides the discussions on quatitative improvements, in-depth physicochemical analyses for characterization of materials and photoelectrochemical cells were performed. After brief explanations of history, backgrounds, and previous research works on photoelectrochemical cells in chapter 1, in chapter 2 and 3, nanostructured metal oxide photoelectrodes with high carrier mobility are discussed. Mesoporous ZnO nanowire arrays with large surface area were synthesized by electrochemical anodization in a mild condition, and highly uniform SnO2 nanochannels were prepared by ultrasonic-assisted anodic oxidation. These nanostructured electrodes were employed as photoanode in quasi-solid dye-sensitized solar cells (DSCs), and fair energy conversion efficiencies were obtained, with further improvements by atomic layer deposition of TiO2 shells. In the next two chapters, strategies for efficient light harvesting by increased surface area were discussed. In chpater 4, TiO2 coated wrinkled silica nanoparticles were utilized as scattering centers in photoanode of DSCs. Superior performances to the DSCs with conventional sphere-shaped TiO2 scatterers were achieved due to the enlarged surface area, and futher observations on the relationship between spectral scattering properties and interwrinkle distances were made. In chapter 5, electrochemically anodized titanium and iron foams prepared by freeze-casting were used as photoanodes of DSCs and photoelectrochemical water splitting cells, respectively. By the anodic oxidation processes, one-dimensional TiO2 nanoatube arrays were formed on the titanium foam surface, and vertically aligned two-dimensional iron oxide nanoflakse were generated on the surface of the iron foam. These multidimensional structures had following three advantages(i) large surface area for light harvesting, (ii) low-dimensionally confined semiconductor structure for enhanced charge transport, and (iii) three-dimensionally extended current collector with very low resistnace. Based on these properties, large photocurrent densities were obtained in both DSCs and iron oxide based photoelectrochemical water splitting cells. In chapter 6, nanostructured tungsten carbide synthesized by electrochemical anodization followed by heat treatment in carbon monoxide atmosphere was used as a counter electrode for DSCs employing cobalt bipyridyl redox electrolyte. The transformation of oxide into carbide was successfully and completely done due to the amorphous nature of anodic oxide materials. Moreover, superior electrocatalytic activity and photovoltaic performances were oberseved, which were attributed to the well known platinum-like electronic structure and nanoporous morphology. In chapter 7 and 8, nanostructured nickel nitride and cobalt nitride were fabricated by reactive sputtering of nickel and cobalt in nitrogen atmosphere, respectively. By physicochemical charaterizations based on electron microscopy and X-ray analyses, the films were addressed to Ni2N and CoN with cauliflower-like morphologies. When these electrodes were used as counter electrodes of quantum dot-sensitized solar cells (QDSCs), both electrodes displayed superior performances to Pt. In addition, the energy conversion efficiency of DSC employing cobalt nitride counter electrode was comparable to that with platinum. Furthermore, in QDSCs, CoN exhibited higher stability than the state-of-the-art Cu2S counter. Photocurrent densities of QDSC with CoN counter electrode exceeded that with Cu2S within 20 min, though the initial performance was higher in QDSC employing Cu2S.Chapter 1. Introduction .............................................................1 1.1. General introduction to photoelectrochemical cells .........1 1.2. Mesoscopic sensitized solar cells .....................................7 1.3. Photoelectrochemical water splitting cells .....................17 1.4. References ......................................................................22 Chapter 2. Vertically aligned mesoporous anodic zinc oxide nanowire arrays as photoelectrode .........................................33 2.1. Introduction ....................................................................33 2.2. Experimental section ......................................................35 2.3. Results and discussion ....................................................37 2.4. Conclusions ....................................................................55 2.5. References ......................................................................56 Chapter 3. Highly uniform anodic tin oxide nanochannel arrays as photoelectrode ..........................................................60 3.1. Introduction ....................................................................60 3.2. Experimental section ......................................................63 3.3. Results and discussion ....................................................65 3.4. Conclusions ....................................................................86 3.5. References ......................................................................87 Chapter 4. Wrinkled silica/titania nanoparticles for light scattering in mesorporous TiO2 photoelectrode.....................92 4.1. Introduction ....................................................................92 4.2. Experimental section ......................................................94 4.3. Results and discussion ....................................................97 4.4. Conclusions ..................................................................119 4.5. References ....................................................................120 Chapter 5. Anodized metal foam with multidimensional and hierarchical structure as photoelectrode ..............................123 5.1. Introduction ..................................................................123 5.2. Experimental section ....................................................125 5.3. Results and discussion ..................................................128 5.4. Conclusions ..................................................................164 5.5. References ....................................................................165 Chapter 6. Electrochemically synthesized tungsten carbide as electrocatalytic counter electrode .........................................169 6.1. Introduction ..................................................................169 6.2. Experimental section ....................................................171 6.3. Results and discussion ..................................................173 6.4. Conclusions ..................................................................190 6.5. References ....................................................................192 Chapter 7. Reactively sputtered nanostructured nickel nitride as electrocatalytic counter electrode .....................................196 7.1. Introduction ..................................................................196 7.2. Experimental section ....................................................198 7.3. Results and discussion ..................................................201 7.4. Conclusions ..................................................................219 7.5. References ....................................................................221 Chapter 8. Vapor deposited nanostructured cobalt nitride as electrocatalytic counter electrode .........................................224 8.1. Introduction ..................................................................224 8.2. Experimental section ....................................................226 8.3. Results and discussion ..................................................229 8.4. Conclusions ..................................................................250 8.5. References ....................................................................251 Chapter 9. Conclusions ..........................................................257 9.1. Summary ......................................................................257 9.2. Perspectives ..................................................................260 9.3. References ....................................................................268 국문 초록 (Abstract in Korean) ..........................................273Docto

Malakoplakia of the Kidney Extending to the Descending Colon in a Patient with Secondary Adrenal Insufficiency: A Case Report

Malakoplakia is an uncommon but distinctive type of chronic granulomatous inflammation that occurs most commonly in the genitourinary tract, especially the urinary bladder. Most patients have associated conditions characterized by some degree of immunosuppression, as seen in solid-organ transplants, autoimmune diseases requiring steroid use, chemotherapy, chronic systemic diseases, alcohol abuse and poorly controlled diabetes. We report an unusual case of the renal malakoplakia that involved the perirenal space, extending to the descending colon in a 65-year-old Korean woman with secondary adrenal insufficiency and diabetes mellitus