Absorbing state transitions in clean and disordered lattice models

Nonequilibrium systems can undergo continuous phase transitions between different steady states. These transitions are characterized by collective fluctuations over large distances and long times similar to the behavior of equilibrium critical points. They also can be divided into different universality classes according to their critical behavior. This dissertation considers two types of nonequilibrium transitions. First study concerns absorbing state transitions on a randomly diluted lattice. Second study deals with nonequilibrium models with several absorbing states. We investigate two specific nonequilibrium lattice models, i.e., the contact process and the generalized contact process by means of both theoretical and computational approaches. In section 1, we introduce the basic arguments and theories to support our investigations for both problems. In sections 2 and 3, we investigate nonequilibrium phase transitions of the contact process and the generalized contact process on a percolating lattice, focusing on the transition across the lattice percolation threshold. In this study, we show that the interplay between geometric criticality due to percolation and dynamical fluctuations of the nonequilibrium system leads to a new universality class. The critical point is characterized by ultra-slow activated dynamical scaling and accompanied by strong Griffiths singularities. We support our theory by extensive Monte-Carlo simulations. In sections 4 and 5, we investigate the generalized contact process on one and two-dimensional lattices. We treat the creation rate of active sites between inactive domains as an independent parameter. It turns out that this model has an unusual phase diagram with two different nonequilibrium phase transitions. The special point separating them shares some characteristics with a multicritical point. For one dimension, a small boundary rate takes the system from the directed percolation universality class to the parity-conserved class. For two dimensions, the critical behavior on the generic transition line is of mean-field type with logarithmic corrections suggesting that the two-dimensional generalized contact process is in the generalized voter universality class --Abstract, page iv

Generalized contact process with two symmetric absorbing states in two dimensions

We explore the two-dimensional generalized contact process with two absorbing states by means of large-scale Monte-Carlo simulations. In part of the phase diagram, an infinitesimal creation rate of active sites between inactive domains is sufficient to take the system from the inactive phase to the active phase. The system therefore displays two different nonequilibrium phase transitions. The critical behavior of the generic transition is compatible with the generalized voter (GV) universality class, implying that the symmetry-breaking and absorbing transitions coincide. In contrast, the transition at zero domain-boundary activation rate is not critical.Comment: 7 pages, 7 eps figures included, final version as publishe

Synergistic multi-doping effects on the Li7La3Zr2O12 solid electrolyte for fast lithium ion conduction.

Here, we investigate the doping effects on the lithium ion transport behavior in garnet Li7La3Zr2O12 (LLZO) from the combined experimental and theoretical approach. The concentration of Li ion vacancy generated by the inclusion of aliovalent dopants such as Al(3+) plays a key role in stabilizing the cubic LLZO. However, it is found that the site preference of Al in 24d position hinders the three dimensionally connected Li ion movement when heavily doped according to the structural refinement and the DFT calculations. In this report, we demonstrate that the multi-doping using additional Ta dopants into the Al-doped LLZO shifts the most energetically favorable sites of Al in the crystal structure from 24d to 96 h Li site, thereby providing more open space for Li ion transport. As a result of these synergistic effects, the multi-doped LLZO shows about three times higher ionic conductivity of 6.14 × 10(-4) S cm(-1) than that of the singly-doped LLZO with a much less efforts in stabilizing cubic phases in the synthetic condition

Phase Transitions of the Generalized Contact Process with Two Absorbing States

We investigate the generalized contact process with two absorbing states in one space dimension by means of large-scale Monte Carlo simulations. Treating the creation rate of active sites between inactive domains as an independent parameter leads to a rich phase diagram. In addition to the conventional active and inactive phases we find a parameter region where the simple contact process is inactive, but an infinitesimal creation rate at the boundary between inactive domains is sufficient to take the system into the active phase. Thus, the generalized contact process has two different phase transition lines. The point separating them shares some characteristics with a multicritical point. We also study in detail the critical behaviors of these transitions and their universality

Absorbing-state phase transitions on percolating lattices

We study nonequilibrium phase transitions of reaction-diffusion systems defined on randomly diluted lattices, focusing on the transition across the lattice percolation threshold. To develop a theory for this transition, we combine classical percolation theory with the properties of the supercritical nonequilibrium system on a finite-size cluster. In the case of the contact process, the interplay between geometric criticality due to percolation and dynamical fluctuations of the nonequilibrium system leads to a new universality class. The critical point is characterized by ultraslow activated dynamical scaling and accompanied by strong Griffiths singularities. To confirm the universality of this exotic scaling scenario we also study the generalized contact process with several (symmetric) absorbing states, and we support our theory by extensive Monte-Carlo simulations.Comment: 11 pages, 10 eps figures included, final version as publishe

Nonequilibrium phase transition on a randomly diluted lattice

We show that the interplay between geometric criticality and dynamical fluctuations leads to a novel universality class of the contact process on a randomly diluted lattice. The nonequilibrium phase transition across the percolation threshold of the lattice is characterized by unconventional activated (exponential) dynamical scaling and strong Griffiths effects. We calculate the critical behavior in two and three space dimensions, and we also relate our results to the recently found infinite-randomness fixed point in the disordered one-dimensional contact process.Comment: 4 pages, 1 eps figure, final version as publishe

Development of a hybrid magnetic resonance/computed tomography-compatible phantom for magnetic resonance guided radiotherapy

The purpose of the present study was to develop a hybrid magnetic resonance/computed tomography (MR/CT)-compatible phantom and tissue-equivalent materials for each MR and CT image. Therefore, the essential requirements necessary for the development of a hybrid MR/CT-compatible phantom were determined and the development process is described. A total of 12 different tissue-equivalent materials for each MR and CT image were developed from chemical components. The uniformity of each sample was calculated. The developed phantom was designed to use 14 plugs that contained various tissue-equivalent materials. Measurement using the developed phantom was performed using a 3.0-T scanner with 32 channels and a Somatom Sensation 64. The maximum percentage difference of the signal intensity (SI) value on MR images after adding K2CO3 was 3.31%. Additionally, the uniformity of each tissue was evaluated by calculating the percent image uniformity (%PIU) of the MR image, which was 82.18 ±1.87% with 83% acceptance, and the average circular-shaped regions of interest (ROIs) on CT images for all samples were within ±5 Hounsfield units (HU). Also, dosimetric evaluation was performed. The percentage differences of each tissue-equivalent sample for average dose ranged from -0.76 to 0.21%. A hybrid MR/CT-compatible phantom for MR and CT was investigated as the first trial in this field of radiation oncology and medical physics

In Vitro Chemosensitivity Using the Histoculture Drug Response Assay in Human Epithelial Ovarian Cancer

The choice of chemotherapeutic drugs to treat patients with epithelial ovarian cancer has not depended on individual patient characteristics. We have investigated the correlation between in vitro chemosensitivity, as determined by the histoculture drug response assay (HDRA), and clinical responses in epithelial ovarian cancer. Fresh tissue samples were obtained from 79 patients with epithelial ovarian cancer. The sensitivity of these samples to 11 chemotherapeutic agents was tested using the HDRA method according to established methods, and we analyzed the results retrospectively. HDRA showed that they were more chemosensitive to carboplatin, topotecan and belotecan, with inhibition rates of 49.2%, 44.7%, and 39.7%, respectively, than to cisplatin, the traditional drug of choice in epithelial ovarian cancer. Among the 37 patients with FIGO stage Ⅲ/Ⅳ serous adenocarcinoma who were receiving carboplatin combined with paclitaxel, those with carboplatin-sensitive samples on HDRA had a significantly longer median disease-free interval than patients with carboplatin- resistant samples (23.2 vs. 13.8 months, p＜0.05), but median overall survival did not differ significantly (60.4 vs. 37.3 months, p＝0.621). In conclusion, this study indicates that HDRA could provide useful information for designing individual treatment strategies in patients with epithelial ovarian cancer

Information Network Villages A community--focused digital divide reduction policy in rural Korea

This study examines South Korea's Information Network Village (INVIL) project as an exemplary policy of building sustainable communities through a digital divide policy implemented in small rural areas. INVIL project has three objectives: to close the digital gap between urban and rural areas, to create new sources of revenues from existing industries, and to build sustainable local communities. The conception was that rural digital divide can only be resolved by addressing deep rooted rural issues that influence the provision and adoption of ICT. While the INVIL programs may not remedy the gap in the short term, it provides a future vision to the communities. Due to this multi-layered and long term approach, the villages have been successful in narrowing the digital divide, not only in terms of access but also in effectively utilising broadband to enhance the local economy and building sustainable communities. This paper introduces the INVIL project, the plans and outcomes, as well as a qualitative evaluation of the process across a decade. Following a general description of the project, an in-depth case study of three successful INVILs is provided. The uniqueness of the program is that it emphasises investment in human capital rather than on infrastructure and includes a tailored vision of each local community. This motivates local residents to be active participants, which is the key to the success of the policy