Indentation plasticity and fracture in silicon

Measurements of the ductile-brittle transition temperature of heavily doped silicon were carried out using indentation techniques. Diamond pyramid hardness tests were performed on the (100) face of heavily doped N-type and P-type and intrinsic silicon single crystals. Tests were performed over the range 200 C to 850 C and loads of 100 to 500 g were used. Samples were subsequently etched to reveal dislocation rosettes produced by indentation. Intrinsic silicon underwent a ductile-brittle transition at 660 C, P-type at 645 C and N-type at 625 C. Hardness values varied from 1.1 GPa at 700 C to 11.7 GPa at 200 C. Significant effects of hardness on doping were present only at the highest temperatures. Lower loads generally produced higher hardness but load did not affect the Ductile-Brittle Transition Temperature (DBTT). Fracture toughness values ranged from 0.9 MPa m(1/2) at 200 C to 2.75 MPa m(1/2) near the DBTT. Doping did not affect the fracture toughness of silicon. P-type doping increased the size of dislocation rosettes observed after indentation, but N-type did not, in contradiction of the expected results. Results are discussed in terms of the effect of doping on the dislocation mobility in silicon

Challenging Cassandra: Household and Per Capita Household Income Distribution in the October Household Surveys 1995-1999, Income and Expenditure Surveys 1995 & 2000, and the Labour Force Survey 2000

This paper examines household income inequality in the South African October Household Survey datasets between 1995 and 1999, the Labour Force Survey 2000, and the Income and Expenditure Surveys 1995 and 2000. The paper reflects both on changing patterns of income inequality in South Africa, and on the quality and comparability of the data employed. We employ several measures of income inequality, employing nominal income and expenditure data from South Africa over the 1995-2000 period. Results prove sensitive to the choice of welfare measure. Furthermore, results from income data and expenditure data provide contrasting results. On self-reported income data, our findings are that inequality measures increased over the 1995 - 2000 time period. While we do not attach much credence to the evidence for reasons attaching to data quality, there is nevertheless evidence suggesting that the general increase in inequality for the African race group also hides a decrease in inequality for the bottom 1/3 of the income distribution, and (more unambiguously) a widening of inequality for the middle 1/3 of the income distribution for Africans. There is also some evidence of a narrowing inequality amongst rich households for the population as a whole. This suggests that there is at least some evidence consistent with a successful redistribution of income from richest to poorest households, though this has not yet reversed the high aggregate level of inequality in South Africa. Evidence from inequality measures based on expenditure data reverse the findings based on self-reported income. Where there is evidence of an increase in inequality, in most instances this proves to be statistically insignificant. On some measures African as well as total population inequality has declined significantly, and for a number of racial groups inequality has remained unchanged. The central conclusion of the paper is therefore that there is much contradictory evidence that emerges from household level data on income inequality - suggesting that the choice of data set is non-trivial in drawing inference on income inequality in South Africa

A Cognitive Framework to Secure Smart Cities

The advancement in technology has transformed Cyber Physical Systems and their interface with IoT into a more sophisticated and challenging paradigm. As a result, vulnerabilities and potential attacks manifest themselves considerably more than before, forcing researchers to rethink the conventional strategies that are currently in place to secure such physical systems. This manuscript studies the complex interweaving of sensor networks and physical systems and suggests a foundational innovation in the field. In sharp contrast with the existing IDS and IPS solutions, in this paper, a preventive and proactive method is employed to stay ahead of attacks by constantly monitoring network data patterns and identifying threats that are imminent. Here, by capitalizing on the significant progress in processing power (e.g. petascale computing) and storage capacity of computer systems, we propose a deep learning approach to predict and identify various security breaches that are about to occur. The learning process takes place by collecting a large number of files of different types and running tests on them to classify them as benign or malicious. The prediction model obtained as such can then be used to identify attacks. Our project articulates a new framework for interactions between physical systems and sensor networks, where malicious packets are repeatedly learned over time while the system continually operates with respect to imperfect security mechanisms

Configraphics:

This dissertation reports a PhD research on mathematical-computational models, methods, and techniques for analysis, synthesis, and evaluation of spatial configurations in architecture and urban design. Spatial configuration is a technical term that refers to the particular way in which a set of spaces are connected to one another as a network. Spatial configuration affects safety, security, and efficiency of functioning of complex buildings by facilitating certain patterns of movement and/or impeding other patterns. In cities and suburban built environments, spatial configuration affects accessibilities and influences travel behavioural patterns, e.g. choosing walking and cycling for short trips instead of travelling by cars. As such, spatial configuration effectively influences the social, economic, and environmental functioning of cities and complex buildings, by conducting human movement patterns. In this research, graph theory is used to mathematically model spatial configurations in order to provide intuitive ways of studying and designing spatial arrangements for architects and urban designers. The methods and tools presented in this dissertation are applicable in: arranging spatial layouts based on configuration graphs, e.g. by using bubble diagrams to ensure certain spatial requirements and qualities in complex buildings; and analysing the potential effects of decisions on the likely spatial performance of buildings and on mobility patterns in built environments for systematic comparison of designs or plans, e.g. as to their aptitude for pedestrians and cyclists. The dissertation reports two parallel tracks of work on architectural and urban configurations. The core concept of the architectural configuration track is the ‘bubble diagram’ and the core concept of the urban configuration track is the ‘easiest paths’ for walking and cycling. Walking and cycling have been chosen as the foci of this theme as they involve active physical, cognitive, and social encounter of people with built environments, all of which are influenced by spatial configuration. The methodologies presented in this dissertation have been implemented in design toolkits and made publicly available as freeware applications

Have Labour Market Outcomes Affected Household Structure in South Africa? A Descriptive Analysis of Households

This paper seeks to investigate how the demography of households relates to individual labour market outcomes. We comprehensively examine household size and structures in the October Household Surveys 1995, 1997, 1999 and the Labour Force Surveys September 2001 and 2002

Mad2l2 in primordial germ cell development and pluripotency

The development of primordial germ cells (PGCs) involves several waves of epigenetic reprogramming. A major step is the transition from the stably suppressive histone modification H3K9me2 to the more flexible, still repressive H3K27me3, while the cells are arrested in the G2 phase of their cell cycle. The significance and underlying molecular mechanism of these events were so far unknown. In this study, a role of the Mad2l2 (Mad2B, Rev7) gene product in development of PGCs was investigated. Mad2l2 is a HORMA domain protein, which is involved in proteinprotein interaction. Mad2l2 is essential for PGC, but not for somatic development. PGCs were specified normally in Mad2l2-/- embryos, but their chromatin did not proceed from the H3K9me2 to H3K27me3 state. Mad2l2-/- PGCs failed to arrest in the G2 phase, and were eliminated by apoptosis. Co-immunoprecipitation analysis showed that Mad2l2 could interact with the histone methyltransferases G9a and GLP, and thus lead to a downregulation of H3K9me2. It also interacts physically with Cdk1, which together with Cyclin B1 is the main driving force for mitotic entrance and progression. The inhibitory binding of Mad2l2 to Cdk1 could arrest the cell cycle in the G2 phase, and therefore allow the other histone methyltransferase, Ezh2, to upregulate H3K27me3. In conclusion, Mad2l2 is essential for epigenetic reprogramming in mouse PGCs. Mad2l2-/- ESC lines cultured in conventional condition (LIF/Serum) showed evidence for a spontaneous differentiation into epithelial-like cells with the molecular characteristics of primitive endoderm. They had a cell cycle similar to that of differentiated cells, failed to incorporate into chimeras, and deviated to primitive endoderm at the expense of pluripotency. They also manifested an epigenetic configuration distinct from normal ESCs, namely elevated H3K9me2 and H3K27me3 levels. Differentiating cells disappeared once the cultures were shifted to the chemically defined medium supplemented with two inhibitors of MEK and Wnt pathways (LIF/2i). Co-immunoprecipitation of Mad2l2 in ESCs followed by mass spectrometry identified CETN2 as its interacting partner. This interaction might be involved in regulation of Nanog expression and thus in sustaining self-renewal of ESCs. Altogether, these data point to essential role of Mad2l2 in pluripotent ESCs