RESUMEN
We study the nonequilibrium phase transition in the two-dimensional contact process on a randomly diluted lattice by means of large-scale Monte Carlo simulations for times up to 10;{10} and system sizes up to 8000x8000 sites. Our data provide strong evidence for the transition being controlled by an exotic infinite-randomness critical point with activated (exponential) dynamical scaling. We calculate the critical exponents of the transition and find them to be universal, i.e., independent of disorder strength. The Griffiths region between the clean and the dirty critical points exhibits power-law dynamical scaling with continuously varying exponents. We discuss the generality of our findings and relate them to a broader theory of rare region effects at phase transitions with quenched disorder. Our results are of importance beyond absorbing state transitions because, according to a strong-disorder renormalization group analysis, our transition belongs to the universality class of the two-dimensional random transverse-field Ising model.
RESUMEN
OBJECTIVE: An important but neglected consequence of the AIDS pandemic that continues across sub-Saharan Africa is the phenomenon of child-headed households (CHH). This study aims to describe the challenges to health and well-being for young people living in child-headed households. METHODS: A mixed-methods research approach linked common themes using qualitative and quantitative instruments to provide a broad picture of the location and challenges of CHH in Kabira, Kyotera and Kamuganja in the Rakai District of southern Uganda. Local knowledge was used to locate CHH. RESULTS: 163 children living in 40 CHH were traced: 42·5% of the household heads were double orphans caring for younger siblings, and 43% were also caring for chronically ill or disabled grandparents who were economically unproductive and largely dependent on the eldest child for survival. It was found that those heading households were more likely not to attend school than children living at home with a parent. Their immediate needs ranged from food and shelter to health-care and education. Fear was a major theme: 38% of those interviewed reported fear of 'violence'. Children as young as 13 were responsible for navigating through complex decision-making processes from everyday basic necessities to decisions on the health care of younger siblings and grandparents. CONCLUSION: Children and young people living in CHH are a largely invisible and highly vulnerable population. Clear, officially accepted definitions of CHH are a first step in recognising this vulnerable group for whom safeguards will be necessary as social work develops in lower- and middle-income countries (LMICs). The precise numbers of CHH are unknown and further examination of this undocumented group is needed.