A Tale of Two Townships: Political Opportunity and Violent and Non-Violent Local Control in South Africa

A number of recent gains in social science have found that periods of violent civil disorder marked by chaos may actually exhibit an underlying order and a rationale on part of perpetrators in response to specific political conditions of the time. The conjecture is that violent control emerges as a grassroots effort to establish authority in areas experiencing a vacuum of central authority. Given those conditions, can these same theories of violence be applied to incidents of widespread non-violent control as well, where and when the political conditions are similar? Using a variety of accounts, from research conducted by human rights groups and media outlets and government data, this paper considers the actions of residents in two townships in South Africa during a twenty-day period of xenophobic violence in May 2008. While one township acted violently against its immigrant population, the other mobilized to protect its own immigrants. These actions are considered within a similar theoretical framework to demonstrate how both constituted an assertion of local control in the interests of residents during a time of political instability at the national level

CELL MECHANICS IN CARDIOVASCULAR DISEASE AND ELECTROSPUN SCAFFOLD FOR VASCULAR TISSUE ENGINEERING

Cardiovascular disease (CVD) is the leading cause of death worldwide. Atherosclerosis, one of the primary CVDs, is characterized as a chronic inflammatory disease. In the initial stages of atherosclerosis, there is a buildup of cholesterol and lipoproteins that triggers monocytes to enter the arterial wall and begin accumulating lipids. Vascular smooth muscle cells (VSMCs) begin to detach and migrate from the media toward the intima in a process known as phenotypic switching. Phenotypic switching transitions VSMCs from a contractile to synthetic phenotype and they gain the capacity for migration, proliferation, and secretion of extracellular matrix (ECM) proteins. Synthetic VSMCs experience a variety of microenvironments of differing stiffness and composition within the atherosclerotic plaque which elicit different biomechanical responses. The growth of atherosclerotic plaques can cause stenosis and reduced blood flow. One treatment for this is revascularization surgery using vascular grafts to bypass blockages. In this dissertation, we examine how VSMC biomechanics change in response to substrate stiffness and composition. Then we developed an electrospun polycaprolactone (PCL)-silk fibroin (SF) electrospun scaffold for use in vascular tissue engineering. In specific aim 1, the effect of substrate stiffness and collagen or fibronectin coatings on VSMC migration and cytoskeletal organization was analyzed. Protein coatings and substrate stiffness were found to synergistically regulate migration and cortical actin organization in the opposite manner. In specific aim 2, the differences in biomechanics of atherosclerotic ApoE-/- and wild type (WT) VSMCs was analyzed. ApoE-/- VSMCs were found to have lower adhesion forces but increased migration capacity, cytoskeletal alignment, and stiffness, with the latter two being enhanced by increasing substrate stiffness. In specific aim 3, an exploration into the use of electrospun PCL-SF scaffolds as vascular grafts was conducted. The addition of SF improved the mechanical properties of the graft, making them more similar to those of native arteries, as well as increasing the diameter of the nanofibers. Furthermore, the PCL-SF scaffolds supported the differentiation of mesenchymal stem cells into VSMC-like cells. Therefore, this dissertation provides further insights in the alteration of VSMC biomechanics during atherosclerosis and a promising material for the development a tissue engineered vascular graft

The temperature-dependence of carrier mobility is not a reliable indicator of the dominant scattering mechanism

The temperature dependence of experimental charge carrier mobility is commonly used as a predictor of the dominant carrier scattering mechanism in semiconductors, particularly in thermoelectric applications. In this work, we critically evaluate whether this practice is well founded. A review of 47 state-of-the-art mobility calculations reveals no correlation between the major scattering mechanism and the temperature trend of mobility. Instead, we demonstrate that the phonon frequencies are the prevailing driving forces behind the temperature dependence and can cause it to vary between $T^{-1}$ to $T^{-3}$ even for an idealised material. To demonstrate this, we calculate the mobility of 23,000 materials and review their temperature dependence, including separating the contributions from deformation, polar, and impurity scattering mechanisms. We conclusively demonstrate that a temperature dependence of $T^{-1.5}$ is not a reliable indicator of deformation potential scattering. Our work highlights the potential pitfalls of predicting the major scattering type based on the experimental mobility temperature trend alone

Automatic Configuration Recognition Methods in Modular Robots

Recognizing useful modular robot configurations composed of hundreds of modules is a significant challenge. Matching a new modular robot configuration to a library of known configurations is essential in identifying and applying control schemes. We present three different algorithms to address the problem of (a) matching and (b) mapping new robot configurations onto a library of known configurations. The first method solves the problem using graph isomorphisms and can identify configurations that share the same underlying graph structure, but have different port connections amongst the modules. The second approach compares graph spectra of configuration matrices to find a permutation matrix that maps a given configuration to a known one. The third algorithm exploits the unique structure of the problem for the particular robots used in our research to achieve impressive gains in performance and speed over existing techniques, especially for larger configurations. With these three algorithms, this paper presents novel solutions to the problem of configuration recognition and sheds light on theoretical and practical issues for long-term advances in this important area of modular robotics. Results and examples are provided to compare the performance of the three algorithms and discuss their relative advantages

The effect of off-diagonal density matrix in DFT+DMFT for Li2_2MnO3_3

Li$_2$MnO$_3$ has garnered much attention as one of the new-generation battery material, due to the high capacity and low cost. In the present work, we performed density functional theory (DFT)+$U$ and dynamical mean field theory (DMFT) calculations with continuous time quantum Monte Carlo impurity solver to study the electronic properties of Li$_2$MnO$_3$. Due to the nature of monoclinic $C2/m$ symmetry, the off-diagonal terms in the $d$-orbital block Hamiltonian (and $d$-orbital density matrix) are large, which results the large suppression of the energy gap due to the underestimation of the crystal-field splitting. We diagonalize the Mn $d$ block in the full $p-d$ Hamiltonian by applying unitary rotation matrix, and obtained an energy gap of 0.8 eV, although it is still smaller than the experimental gap of 2.1 eV even with the large $U$. In the $p$-$d$ model, a small double counting energy is essential to reduce the $p$-$d$ hybridization, thus to obtain the experimental gap. We show that the low-energy ($d$-only basis) model is efficient to study the electronic structure of Li$_2$MnO$_3$, since the Wannier basis is the hybridized state of Mn $d$ and O $p$ orbitals. These results suggest the correct way to investigate the low-symmetry materials using DFT+ DMFT method and to our knowledge, there is no systematic study of the effect of the off-diagonal terms so far. We also find that the antiferromagnetic ground state $\Gamma_{2u}$ is stable with $U \leq 2$ within DFT+$U$, which is much smaller than widely used $U$=5 eV.Comment: 8 pages, 8 figure