Ion chamber measurements of transverse gamma knife beam profiles

A microchamber, PTW Pinpoint 31006, was used to measure transverse beam profiles for an Elekta Gamma Knife, Model B, and compared with profiles measured with film dosimetry. The microchamber sensitive volume has a diameter of 2 mm, which is smaller than the gamma knife beams, and a length of 5 mm. The chamber was mounted in a custom cassette in a spherical plastic phantom, supplied by Elekta, and oriented in a sagittal plane with the 2-mm dimension at right angles to the transverse plane. The phantom was manually moved across the beam, using the gamma knife x-coordinate trunnions, to measure the profiles. Profiles were also measured with V-film placed in a cassette mounted in the spherical plastic phantom. The films were scanned with a Scanditronix film scanner and converted to dose with a density to dose calibration curve. The results were superimposed for comparison. The beam width at the 50% intensity was measured from the film profiles to give the dimensions of the beams in the orthagonal planes. The ion chamber measurements are compared with the film results for the transverse, x profiles. Good agreement between the film and ion chamber transverse profiles is observed

Superimposition of beams to vary shot size in gamma knife stereotactic radiosurgery

The Leksell Gamma Knife [Elekta Corp] uses helmets as collimators to produce four standard beam sizes. The nominal beam diameters are 18, 14, 8, and 4 mm. During computer treatment planning for gamma knife stereotactic radiosurgery, the size of the treated volume may differ from the standard beam sizes. To maintain conformality of the isodose curves to the treated volume, beam sizes may be superimposed during computer treatment planning to produce beam diameters that are intermediate to the standard beams. A study of superimposed gamma knife beams was performed to confirm the accuracy of this method and to verify the accuracy of the GammaPlan treatment planning computer. Superimposed beams were simulated on the Elekta treatment planning computer, GammaPlan, version 4.12, and tested by film measurements of beam profiles for single helmet sizes and superimposed shots with various beam weightings. The weighting for each beam size is varied to attain the beam size diameter desired. The beams were defined at the 50% isodose line. The profiles of the superimposed beams were obtained and compared with the single helmet shots. The uniformity of the resulting beams was measured. The results show a linear relationship between beam size and beam weighting for the superimposed beams. The film measurements confirm the computer calculations

Aid and Poverty

SUMMARY The volume of aid received by the less developed countries, with some exceptions, is small in relation to the existing scale of poverty in those countries. Aid makes a significant but incremental contribution to available national resources. What aid can or cannot do for the poor has to be viewed and assessed within the context of overall national policies and priorities towards poverty elimination. In that context, it can be said that aid has made a smaller impact on poverty than one would expect. The reasons for this are varied and complex, and point to shortcomings in both donor and recipient policies. The aid experience, however, is by no means wholly negative. Particular forms of aid can make a positive contribution to a reduction in poverty, where national policies are directed towards the same objectives. More important for the future, perhaps, are the lessons that can be learnt from the aid experience about the do's and don'ts of aid policy. SOMMAIRE L'aide et la pauvreté Le volume de l'aide reçu par les pays moins développés, avec quelques exceptions, est petit en rapport avec la pauvreté dans ces pays. L'aide contribue substantiellement mais d'une manière incrémentale aux resources nationales disponibles de ces pays. Le potentiel de l'aide doit être évalué dans le contexte globale des politiques nationales et des priorités envers l'élimination de la pauvreté. Dans ce contexte, on peut dire que l'influence de l'aide sur la pauvreté a été plus petite de ce qu'on aurait prévu. Les raisons pour ceci sont diverses et complexes, et soulignent des défauts dans les politiques des donneurs, aussi bien que dans celles des pays recevants. Cependant, l'expérience de l'aide n'est d'aucune manière entièrement négative. Certaines formes d'aide peuvent réduire la pauvreté, lá où les politiques nationales sont formulées dans le même but. Plus important pour l'avenir, peut?être, sont les leçons de l'expérience de l'aide en ce qui concerne ce qu'on peut faire, et ce qu'on ne devrait pas faire en matière de politique de l'aide. RESUMEN Ayuda y Pobreza Con algunas excepciones, el volumen de la ayuda recibida por los países menos desarrollados es pequeño en relación a la escala de pobreza existente en esos países. La ayuda implica una contribución significativa y adicional a los recursos nacionales existentes. Lo que la ayuda puede y no puede hacer en favor de los pobres, debe considerarse y evaluarse en el contexto del conjunto de las políticas y prioridades nacionales de erradicación de la pobreza. En este contexto puede decirse que el impacto de la ayuda sobre la pobreza, es menor del que podría esperarse. Las razones son variadas y complejas y se refieren a deficiencias en las políticas de donantes y receptores. No obstante, la experiencia en ayuda está lejos de ser totalmente negativa. Determinadas formas de ayuda pueden realizar una contribución positiva en la reducción de la pobreza, en los casos en que las políticas nacionales están dirigidas a los mismos objetivos. Probablemente lo más importante para el futuro, son las lecciones que la experiencia en ayuda proporciona acerca de lo que debería y no debería involucrar la política de ayuda

An Investigation of Whether Vitamin E Preferentially Interacts with Polyunsaturated Lipids

poster abstractVitamin E (α-tocopherol) is a lipid-soluble antioxidant that has the role of protecting phospholipids from oxidation in membranes. A question that remains is how the low concentration of α-tocopherol found in whole cells can protect the relatively large concentration of polyunsaturated phospholipids found in membranes that are particularly vulnerable to oxidative attack. We hypothesize that α-tocopherol colocalizes with polyunsaturated phospholipids to optimize its role as an antioxidant. This project attempts to test this hypothesis by comparing the effect of α-tocopherol on the molecular organization of 1-palmitoyl-2-docosahexaenoyl-sn-glycerophosphatidylethanolamine (16:0-22:6PE, PDPE) and, as a monounsaturated control, 1-palmitoyl-2-oleoyl-sn-glycerophosphatidylethanolamine (16:0-18:1PE, POPE) in mixtures with sphingomyelin (SM). By solid-state 2H NMR spectroscopy, we directly observe order and phase behavior of POPE-d31 and PDPE-d31 (analogs of POPE and PDPE with a perdeuterated sn-1 chain) in the mixed membranes. In complementary X-ray diffraction and differential scanning calorimetry experiments we further probe phase behavior. The spectra observed for POPE-d31 in POPE/SM/α-tocopherol (2:2:1 mol) reveal that a transition from gel to liquid crystalline phase is no longer apparent. At higher temperatures there is a superposition of two spectral components that we ascribe to α-tocopherol promoting a transition from lamellar to inverted hexagonal (HII) phase. Analysis of depaked spectra shows that order is increased by about 8 % and that the amount of HII phase increases with temperature, ranging from 7 (31 °C) to 41 % (65 °C). In mixed membranes where POPE-d31 is replaced by PDPE-d31, we shall investigate whether there is a greater tendency for α-tocopherol to increase order and destabilize bilayer structure for the polyunsaturated phospholipid

Participatory and incremental development in an African local government accounting reform

Despite significant donor funding, government accounting reforms seeking transparent and effective management of public resources often fail or have limited success, especially in Africa, prompting questions about donors? implementation approach and calls for studies of successful reforms. This paper investigates a local government accounting reform in Benin supported by a German development agency ? perceived as successful due to the participatory, pragmatic and incremental approach reinforced by conditionalities in the face of neo-patrimonial leadership

Eureka and beyond: mining's impact on African urbanisation

This collection brings separate literatures on mining and urbanisation together at a time when both artisanal and large-scale mining are expanding in many African economies. While much has been written about contestation over land and mineral rights, the impact of mining on settlement, notably its catalytic and fluctuating effects on migration and urban growth, has been largely ignored. African nation-states’ urbanisation trends have shown considerable variation over the past half century. The current surge in ‘new’ mining countries and the slow-down in ‘old’ mining countries are generating some remarkable settlement patterns and welfare outcomes. Presently, the African continent is a laboratory of national mining experiences. This special issue on African mining and urbanisation encompasses a wide cross-section of country case studies: beginning with the historical experiences of mining in Southern Africa (South Africa, Zambia, Zimbabwe), followed by more recent mineralizing trends in comparatively new mineral-producing countries (Tanzania) and an established West African gold producer (Ghana), before turning to the influence of conflict minerals (Angola, the Democratic Republic of Congo and Sierra Leone)

World cities and peripheral development: The interplay of gateways and subordinate places in Argentina and Ghana’s upstream oil and gas sector

Serving as “gateways”, some world cities tie their wider hinterlands to global networks. The article revisits gateway–hinterland relations against the backdrop of assessments that lead to opposed conclusions on the benefits and shortcomings of integration into the world economy. Referring to the oil and gas sector in Argentina and Ghana, it answers the question of how gateways interact with subordinate places and also uncovers obstacles to peripheral development. The author finds that Accra and Buenos Aires concentrate corporate control. Argentina's capital serves as a gateway for knowledge generation and logistics too. Opportunities for peripheral development in both countries are considerable, albeit largely limited to generic services. Besides a certain concentration of business activities in the gateway cities, more important challenges to peripheral development are typical for small and medium enterprises (insufficient finance and management capabilities, unawareness of business opportunities, and the like). They include rent seeking and subcontracting. The latter leaves local companies in a particularly weak position vis‐à‐vis lead firms. The author argues that while integration into the world economy allows for peripheral development, the corresponding outcomes may not meet everyone's expectations. Related expectations must, therefore, be more down‐to‐earth than overly optimistic statements frequently made by politicians

Health-industry linkages for local health: reframing policies for African health system strengthening

The benefits of local production of pharmaceuticals in Africa for local access to medicines and to effective treatment remain contested. There is scepticism among health systems experts internationally that production of pharmaceuticals in sub-Saharan Africa (SSA) can provide competitive prices, quality and reliability of supply. Meanwhile low-income African populations continue to suffer poor access to a broad range of medicines, despite major international funding efforts. A current wave of pharmaceutical industry investment in SSA is associated with active African government promotion of pharmaceuticals as a key sector in industrialization strategies. We present evidence from interviews in 2013–15 and 2017 in East Africa that health system actors perceive these investments in local production as an opportunity to improve access to medicines and supplies. We then identify key policies that can ensure that local health systems benefit from the investments. We argue for a ‘local health’ policy perspective, framed by concepts of proximity and positionality, which works with local priorities and distinct policy time scales and identifies scope for incentive alignment to generate mutually beneficial health–industry linkages and strengthening of both sectors. We argue that this local health perspective represents a distinctive shift in policy framing: it is not necessarily in conflict with ‘global health’ frameworks but poses a challenge to some of its underlying assumptions