32 research outputs found
The role of quasi-momentum in the resonant dynamics of the atom-optics kicked rotor
We examine the effect of the initial atomic momentum distribution on the
dynamics of the atom-optical realisation of the quantum kicked rotor. The atoms
are kicked by a pulsed optical lattice, the periodicity of which implies that
quasi-momentum is conserved in the transport problem. We study and compare
experimentally and theoretically two resonant limits of the kicked rotor: in
the vicinity of the quantum resonances and in the semiclassical limit of
vanishing kicking period. It is found that for the same experimental
distribution of quasi-momenta, significant deviations from the kicked rotor
model are induced close to quantum resonance, while close to the classical
resonance (i.e. for small kicking period) the effect of the quasi-momentum
vanishes.Comment: 10 pages, 4 figures, to be published in J. Phys. A, Special Issue on
'Trends in Quantum Chaotic Scattering
Emergence of methicillin resistance predates the clinical use of antibiotics
The discovery of antibiotics more than 80 years ago has led to considerable improvements in human and animal health. Although antibiotic resistance in environmental bacteria is ancient, resistance in human pathogens is thought to be a modern phenomenon that is driven by the clinical use of antibiotics(1). Here we show that particular lineages of methicillin-resistant Staphylococcus aureus-a notorious human pathogen-appeared in European hedgehogs in the pre-antibiotic era. Subsequently, these lineages spread within the local hedgehog populations and between hedgehogs and secondary hosts, including livestock and humans. We also demonstrate that the hedgehog dermatophyte Trichophyton erinacei produces two beta-lactam antibiotics that provide a natural selective environment in which methicillin-resistant S. aureus isolates have an advantage over susceptible isolates. Together, these results suggest that methicillin resistance emerged in the pre-antibiotic era as a co-evolutionary adaptation of S. aureus to the colonization of dermatophyte-infected hedgehogs. The evolution of clinically relevant antibiotic-resistance genes in wild animals and the connectivity of natural, agricultural and human ecosystems demonstrate that the use of a One Health approach is critical for our understanding and management of antibiotic resistance, which is one of the biggest threats to global health, food security and development
Civil society leadership in the struggle for AIDS treatment in South Africa and Uganda
Includes abstract.Includes bibliographical references.This thesis is an attempt to theorise and operationalise empirically the notion of âcivil society leadershipâ in Sub-Saharan Africa. âAIDS leadership,â which is associated with the intergovernmental institutions charged with coordinating the global response to HIV/AIDS, is both under-theorised and highly context-specific. In this study I therefore opt for an inclusive framework that draws on a range of approaches, including the literature on âleadershipâ, institutions, social movements and the ânetworkâ perspective on civil society mobilisation. This framework is employed in rich and detailed empirical descriptions (âthick descriptionâ) of civil society mobilisation around AIDS, including contentious AIDS activism, in the key case studies of South Africa and Uganda. South Africa and Uganda are widely considered key examples of poor and good leadership (from national political leaders) respectively, while the Treatment Action Campaign (TAC) and The AIDS Support Organisation (TASO) are both seen as highly effective civil society movements. These descriptions emphasise âtransnational networks of influenceâ in which civil society leaders participated (and at times actively constructed) in order to mobilise both symbolic and material resources aimed at exerting influence at the transnational, national and local levels
Civil society and the state in Ugandaâs AIDS response
This paper investigates state-civil society relations in the Ugandan AIDS response through a critical exploration of the history of Ugandaâs âmulti-sectoralâ and âpartnershipâ approaches, particularly as it pertains to The AIDS Support Organisation (TASO). It finds that the Ugandan governmentâs reputation for successful prevention campaigns is not necessarily deserved, and that the effectiveness of civil society is limited by an authoritarian political culture. Despite these limitations, however, state-civil society partnership did contribute to the emergence of a relatively effective coalition for action against HIV/AIDS. Donors were essential in encouraging the emergence of this coalition, but have also inadvertently undermined the emergence of strong and independent civil society voices able to hold the Ugandan state accountable
Emergence of methicillin resistance predates the clinical use of antibiotics.
The discovery of antibiotics more than 80 years ago has led to considerable improvements in human and animal health. Although antibiotic resistance in environmental bacteria is ancient, resistance in human pathogens is thought to be a modern phenomenon that is driven by the clinical use of antibiotics1. Here we show that particular lineages of methicillin-resistant Staphylococcus aureus-a notorious human pathogen-appeared in European hedgehogs in the pre-antibiotic era. Subsequently, these lineages spread within the local hedgehog populations and between hedgehogs and secondary hosts, including livestock and humans. We also demonstrate that the hedgehog dermatophyte Trichophyton erinacei produces two ÎČ-lactam antibiotics that provide a natural selective environment in which methicillin-resistant S. aureus isolates have an advantage over susceptible isolates. Together, these results suggest that methicillin resistance emerged in the pre-antibiotic era as a co-evolutionary adaptation of S. aureus to the colonization of dermatophyte-infected hedgehogs. The evolution of clinically relevant antibiotic-resistance genes in wild animals and the connectivity of natural, agricultural and human ecosystems demonstrate that the use of a One Health approach is critical for our understanding and management of antibiotic resistance, which is one of the biggest threats to global health, food security and development
Bioactive volatiles from 'Geijera parviflora' Lindl. (Rutaceae): evidence for coumarin chemotypes
In the early 20th century, phytochemical studies focused on the leaves of 'Geijera parviflora' to solve the mystery of why grazing herbivores, such as sheep, foraged for some specimens, but not others. After an examination of the essential oils failed to highlight any pattern, phytochemists began examining larger compounds in the leaves and subsequently reported a variety of geographically variable coumarins that could explain this variability in sheep palatability. Today, the investigation continues, but with a view to relate coumarins to traditional medicinal uses employed by Aboriginal Australians. Phytochemical variability related to the sheep palatability of leaves may cast light on the traditional use of 'G. parviflora' for numbing the mouth to treat toothache and for general anaesthesia combating body aches and pains. In this preliminary study, several known and unknown coumarins (together with other chemical groups) have been separated and partially identified from dichloromethane extracts using GC-MS. This method clearly demonstrates a useful protocol for mapping geographical variability of coumarin chemotypes, but is limited to compounds no larger than 328 Daltons