Scattering and Pairing in Cuprate Superconductors

The origin of the exceptionally strong superconductivity of cuprates remains a subject of debate after more than two decades of investigation. Here we follow a new lead: The onset temperature for superconductivity scales with the strength of the anomalous normal-state scattering that makes the resistivity linear in temperature. The same correlation between linear resistivity and Tc is found in organic superconductors, for which pairing is known to come from fluctuations of a nearby antiferromagnetic phase, and in pnictide superconductors, for which an antiferromagnetic scenario is also likely. In the cuprates, the question is whether the pseudogap phase plays the corresponding role, with its fluctuations responsible for pairing and scattering. We review recent studies that shed light on this phase - its boundary, its quantum critical point, and its broken symmetries. The emerging picture is that of a phase with spin-density-wave order and fluctuations, in broad analogy with organic, pnictide, and heavy-fermion superconductors.Comment: To appear in Volume 1 of the Annual Review of Condensed Matter Physic

Assessing urban water sustainability in South Africa – not just performance measurement

Urban water management – and the impacts that rapid population growth, industrialisation and climate change are having on it – is gaining increasing attention worldwide. In South Africa (SA), cities are under pressure to respond to not only the challenges of water availability and quality, but also to economic transformation and social division. New solutions for improving the sustainability of cities need to be found, including the development of tools to guide decision-makers. Several benchmarking initiatives have been implemented in the SA water sector – mostly in terms of performance measurement of specific water services for regulatory purposes – but none provide an integrated analysis to enable a deeper understanding of sustainability. The research described in this paper was thus focused on using a systems approach to create an understanding of, and measure the potential for, sustainability in a South African urban water context. This has been achieved through the development and evaluation of a composite index, the Sustainability Index for Integrated Urban Water Management (SIUWM). The first step involved compiling a vision of sustainability for the SA water sector, and expanding it into a sustainability framework to help identify suitable indicators for the assessment process, as well as those which link with existing measurement initiatives. Key performance indicator results from the Department of Water Affairs’ Regulatory Performance Management System (RPMS) and the Blue Drop / Green Drop schemes were used as partial input to the SIUWM, and scores were computed for the nine member cities of the South African Cities Network (SACN). The SIUWM links the results from the regulatory systems with a broader sustainability assessment process to provide a more detailed analysis which can be used to establish goals and inform strategic processes to leverage support for improved water services. In this way, the connections that link the different aspects of urban water management can be used to generate a greater awareness of the underlying issues by key decision makers and thus guide appropriate action.Keywords: urban water management; sustainability index; performance measuremen

Charging for stormwater in South Africa

The social, economic and environmental impacts of poor water quality on South Africa’s urban aquatic systems are increasingly being highlighted by the media. Improving the water quality in these systems will require catchment-wide strategies, including the monitoring and management of point and non-point source pollution collected in stormwater. Significant costs may be incurred; however, international experience suggests that these are outweighed by the benefits. Municipalities across South Africa charge their citizens for potable water and sewerage. Stormwater management, however, is generally funded through municipal rates. Competition with other pressing needs frequently results in the stormwater departments being significantly under-funded – at times only receiving a tenth of what is required for water quantity management. Internationally, an increasing number of cities have introduced a direct charge for stormwater management in order to secure the funding required to manage stormwater and its associated water pollution, and to serve as a disincentive to polluting practices on the part of landowners. In order to ensure adequate funding for stormwater management in South Africa, municipalities need to consider charging for stormwater management either based on an Equivalent Residential Unit (ERU) or Residential Equivalent Factor (REF), combined with an appropriate discount scheme for on-site stormwater management. Preliminary indicative rates have been calculated for municipalities across South Africa using the Damage Avoidance Cost (DAC) approach. The results indicate that the amount that municipalities could and should charge varies widely, from ZAR30 (2010) to ZAR110 (2010) per residential unit per month, depending on climatic zone and level of treatment.Keywords: stormwater management, damage avoidance cost, stormwater utilitie

Sustainable and equitable sanitation in informal settlements of Cape Town: a common vision?

Sustainability and equity are two desirable but ambiguous concepts often used to describe goals for sanitation services internationally and in South Africa. Both concepts are mentioned repeatedly in policy documents and government reports. There is, however, a gap between policy and implementation, and part of the problem lies in the challenge of reconciling the pressure to deliver immediate results with a long-term vision to strive towards sustainable and equitable sanitation services. Perspectives, priorities, and barriers to sustainability and equity in implementation, recognised amongst water and sanitation sector stakeholders in Cape Town, were analysed and compared with policy documents and municipal records. The research methods included a review of municipal and national sanitation policy documents and reports, and unstructured interviews with municipal officials, development NGO workers, sanitation consultants and entrepreneurs working in Cape Town municipality. In this paper, challenges to integrating sustainability and equity principles into various stages of sanitation service development are highlighted, and preliminary recommendations for addressing challenges are made, with an emphasis on stakeholder participation.Keywords: urban sanitation, sustainability, equity, South Afric

Mitigating the impact of swimming pools on domestic water demand

South Africa is a water-scarce country where the sustainable provision of water to its citizens is one of the most significant challenges faced. A recent study in Cape Town, South Africa, investigated the impact of residential swimming pools on household water demand and found that, on average, the presence of a swimming pool increased water demand by 8.85 kℓ/ month or 37.36%. Should cities in South Africa wish to develop in a water sensitive manner – where water is treated as a scarce resource with economic value in all its competing uses – it will be vital to understand the impact of swimming pools on residential water demand. Should there be a significant increase in water demand attributable to the presence of a swimming pool on a property, it would highlight the need to consider whether it is acceptable for properties to use municipal water to fill them or top them up – especially in water-scarce/stressed areas. This paper describes a study undertaken in the Liesbeek River catchment, Cape Town, to investigate the impact that swimming pools have on domestic water demand. The results support the contention that properties with swimming pools use significantly more water than those without. This study estimated the additional demand resulting from swimming pools at between 2.2–2.4 kℓ/month or 7–8% of total water demand. The data also indicate that the presence of a swimming pool correlates with a higher indoor demand. The study shows the need to reduce the impact of swimming pools. This could include: pool covers to reduce evaporation, the recycling of backwash water, the use of rainwater to top up swimming pools, water use surcharges and, finally, appropriate regulation and enforcement to prevent the use of municipal water in swimming pools – especially during droughts.Keywords: urban water management, swimming pools, water demand managemen

Application of a sustainability index for integrated urban water management in Southern African cities: Case study comparison – Maputo and Hermanus

Poor service provision in developing countries, and particularly the provision of water-related services, present serious challenges to urban development. It is estimated that 300 m. people in Africa do not have access to safe drinking water and 313 m. have limited access to adequate sanitation. The critical situation in the water sector continues to undermine strategies for poverty eradication and retards development. It is possible that the failure in service provision can in part be attributed to an inability by policy makers to address urban water management in a holistic  manner. In this study, a systems approach has been adopted to develop a composite index that could be used to assess the potential of a town or city to be sustainable. This index, the Sustainability Index for Integrated Urban Water Management (SIUWM) is composed of 5 components which disaggregate into 20 indicators and ultimately into 64 variables. Two Southern African urban centres, Hermanus and Maputo, were selected as initial case studies to test the applicability and validity of the index and to compare their sustainability index scores. Results of the SIUWM  application demonstrate that the index could highlight areas for  improvement and ultimately guide appropriate action and policy-making towards better service delivery and improved resource management

Global oral health inequalities: task group--periodontal disease.

Periodontal diseases constitute one of the major global oral health burdens, and periodontitis remains a major cause of tooth loss in adults worldwide. The World Health Organization recently reported that severe periodontitis exists in 5-20% of adult populations, and most children and adolescents exhibit signs of gingivitis. Likely reasons to account for these prevalent diseases include genetic, epigenetic, and environmental risk factors, as well as individual and socio-economic determinants. Currently, there are fundamental gaps in knowledge of such fundamental issues as the mechanisms of initiation and progression of periodontal diseases, which are undefined; inability to identify high-risk forms of gingivitis that progress to periodontitis; lack of evidence on how to prevent the diseases effectively; inability to detect disease activity and predict treatment efficacy; and limited information on the effects of integration of periodontal health as a part of the health care program designed to promote general health and prevent chronic diseases. In the present report, 12 basic, translational, and applied research areas have been proposed to address the issue of global periodontal health inequality. We believe that the oral health burden caused by periodontal diseases could be relieved significantly in the near future through an effective global collaboration.published_or_final_versio

Time-reversal symmetry breaking versus superstructure

One of the mysteries of modern condenced-matter physics is the nature of the pseudogap state of the superconducting cuprates. Kaminski et al.1 claimed to have observed signatures of time-reversal symmetry breaking in the pseudogap regime in underdoped Bi2Sr2CaCu2O8+d (Bi2212). Here we argue that the observed dichroism is due to the 5x1 superstructure replica of the electronic bands and therefore cannot be considered as evidence for the spontaneous time-reversal symmetry breaking in cuprates.Comment: 5 pages, pd

The performance of plant species in removing nutrients from stormwater in biofiltration systems in Cape Town

In 2009, the City of Cape Town (CoCT) adopted a stormwater policy which mandates that new and existing developments should reduce the concentration of phosphorus and suspended solids in stormwater runoff by 45% and 80%, respectively, but offered no explicit guidance about how these water quality targets might be achieved. This study aims to contribute to the limited knowledge that exists about the performance of local plant species to treat stormwater. A large nursery-based study was conducted to investigate the performance of 9 locally-occurring plant species to remove orthophosphate (PO4-3), ammonia (NH3) and nitrate (NO3-) found in urban stormwater. Synthetic stormwater was applied to each species as well as a control consisting only of soil (Malmesbury shale). The discharge was collected from a drainage pipe at the base of each of the 150 containers. The results show that all species (excluding Ficinia) reduced the average concentrations of PO4-3 by 81% and NH3 by 90%. By contrast, NO3- was reduced by an average of 69% (excluding by Elegia and Phragmites) with 8 of the 9 species removing significantly more than the control. The species that performed well for all three nutrients include Agapanthus and turf grasses, Stenotaphrum and Pennisetum. The results of the study highlight three important factors in the design of biofilters: that a substantial proportion of nutrients can be captured or absorbed by plants; that the soil medium is an important factor in the removal of PO4-3 and NH3; and that plant choice is essential in the removal of NO3-. Future research should test plant species in both the laboratory and field settings, and should include additional contaminants such as household detergents, heavy metals and bacteria

Strength of Correlations in electron and hole doped cuprates

High temperature superconductivity was achieved by introducing holes in a parent compound consisting of copper oxide layers separated by spacer layers. It is possible to dope some of the parent compounds with electrons, and their physical properties are bearing some similarities but also significant differences from the hole doped counterparts. Here, we use a recently developed first principles method, to study the electron doped cuprates and elucidate the deep physical reasons why their behavior is so different than the hole doped materials. We find that electron doped compounds are Slater insulators, e.g. a material where the insulating behavior is the result of the presence of magnetic long range order. This is in sharp contrast with the hole doped materials, where the parent compound is a Mott charge transfer insulator, namely a material which is insulating due to the strong electronic correlations but not due to the magnetic order.Comment: submitted to Nature Physic