133 research outputs found
Alpha Antihydrogen Experiment
ALPHA is an experiment at CERN, whose ultimate goal is to perform a precise
test of CPT symmetry with trapped antihydrogen atoms. After reviewing the
motivations, we discuss our recent progress toward the initial goal of stable
trapping of antihydrogen, with some emphasis on particle detection techniques.Comment: Invited talk presented at the Fifth Meeting on CPT and Lorentz
Symmetry, Bloomington, Indiana, June 28-July 2, 201
A novel antiproton radial diagnostic based on octupole induced ballistic loss
We report results from a novel diagnostic that probes the outer radial
profile of trapped antiproton clouds. The diagnostic allows us to determine the
profile by monitoring the time-history of antiproton losses that occur as an
octupole field in the antiproton confinement region is increased. We show
several examples of how this diagnostic helps us to understand the radial
dynamics of antiprotons in normal and nested Penning-Malmberg traps. Better
understanding of these dynamics may aid current attempts to trap antihydrogen
atoms
Compression of Antiproton Clouds for Antihydrogen Trapping
Control of the radial profile of trapped antiproton clouds is critical to
trapping antihydrogen. We report the first detailed measurements of the radial
manipulation of antiproton clouds, including areal density compressions by
factors as large as ten, by manipulating spatially overlapped electron plasmas.
We show detailed measurements of the near-axis antiproton radial profile and
its relation to that of the electron plasma
Antihydrogen formation dynamics in a multipolar neutral anti-atom trap
Antihydrogen production in a neutral atom trap formed by an octupole-based
magnetic field minimum is demonstrated using field-ionization of weakly bound
anti-atoms. Using our unique annihilation imaging detector, we correlate
antihydrogen detection by imaging and by field-ionization for the first time.
We further establish how field-ionization causes radial redistribution of the
antiprotons during antihydrogen formation and use this effect for the first
simultaneous measurements of strongly and weakly bound antihydrogen atoms.
Distinguishing between these provides critical information needed in the
process of optimizing for trappable antihydrogen. These observations are of
crucial importance to the ultimate goal of performing CPT tests involving
antihydrogen, which likely depends upon trapping the anti-atom
Search For Trapped Antihydrogen
We present the results of an experiment to search for trapped antihydrogen
atoms with the ALPHA antihydrogen trap at the CERN Antiproton Decelerator.
Sensitive diagnostics of the temperatures, sizes, and densities of the trapped
antiproton and positron plasmas have been developed, which in turn permitted
development of techniques to precisely and reproducibly control the initial
experimental parameters. The use of a position-sensitive annihilation vertex
detector, together with the capability of controllably quenching the
superconducting magnetic minimum trap, enabled us to carry out a
high-sensitivity and low-background search for trapped synthesised antihydrogen
atoms. We aim to identify the annihilations of antihydrogen atoms held for at
least 130 ms in the trap before being released over ~30 ms. After a three-week
experimental run in 2009 involving mixing of 10^7 antiprotons with 1.3 10^9
positrons to produce 6 10^5 antihydrogen atoms, we have identified six
antiproton annihilation events that are consistent with the release of trapped
antihydrogen. The cosmic ray background, estimated to contribute 0.14 counts,
is incompatible with this observation at a significance of 5.6 sigma. Extensive
simulations predict that an alternative source of annihilations, the escape of
mirror-trapped antiprotons, is highly unlikely, though this possibility has not
yet been ruled out experimentally.Comment: 12 pages, 7 figure
Particle Physics Aspects of Antihydrogen Studies with ALPHA at CERN
We discuss aspects of antihydrogen studies, that relate to particle physics
ideas and techniques, within the context of the ALPHA experiment at CERN's
Antiproton Decelerator facility. We review the fundamental physics motivations
for antihydrogen studies, and their potential physics reach. We argue that
initial spectroscopy measurements, once antihydrogen is trapped, could provide
competitive tests of CPT, possibly probing physics at the Planck Scale. We
discuss some of the particle detection techniques used in ALPHA. Preliminary
results from commissioning studies of a partial system of the ALPHA Si vertex
detector are presented, the results of which highlight the power of
annihilation vertex detection capability in antihydrogen studies.Comment: Invited talk at Pbar08 - Workshop on Cold Antimatter Plasmas and
Application to Fundamental Physics, Okinawa, Japan, 2008. 14 pages, 8 figure
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Inequitable childhood immunization uptake in Nigeria: a multilevel analysis of individual and contextual determinants
Background: Immunization coverage in many parts of Nigeria is far from optimal, and far from equitable.
Nigeria accounts for half of the deaths from Measles in Africa, the highest prevalence of circulating wild poliovirus in the world, and the country is among the ten countries in the world with vaccine coverage below 50 percent. Studies focusing on community-level determinants therefore have serious policy implications
Methods: Multilevel multivariable regression analysis was used on a nationally-representative sample of women aged 15-49 years from the 2003 Nigeria Demographic and Health Survey. Multilevel regression analysis was performed with children (level 1) nested within mothers (level 2), who were in turn nested within communities (level 3).
Results: Results show that the pattern of full immunization clusters within families and communities, and that socio-economic characteristics are important in explaining the differentials in full immunization among the children in the study. At the individual level, ethnicity, mothers' occupation, and mothers' household wealth were characteristics of the mothers associated with full immunization of the children. At the community level, the proportion of mothers that had hospital delivery was a determinant of full immunization status.
Conclusion: Significant community-level variation remaining after having controlled for child- and mother-level characteristics is indicative of a need for further research on community-levels factors, which would enable extensive tailoring of community-level interventions aimed at improving full immunization and other child health outcomes
Health care seeking behavior for diarrhea in children under 5 in rural Niger: results of a cross-sectional survey
Diarrhea remains the second leading cause of death in children under 5 years of age in sub-Saharan Africa. Health care seeking behavior for diarrhea varies by context and has important implications for developing appropriate care strategies and estimating burden of disease. The objective of this study was to determine the proportion of children under five with diarrhea who consulted at a health structure in order to identify the appropriate health care levels to set up surveillance of severe diarrheal diseases
Technical efficiency of peripheral health units in Pujehun district of Sierra Leone: a DEA application
BACKGROUND: The Data Envelopment Analysis (DEA) method has been fruitfully used in many countries in Asia, Europe and North America to shed light on the efficiency of health facilities and programmes. There is, however, a dearth of such studies in countries in sub-Saharan Africa. Since hospitals and health centres are important instruments in the efforts to scale up pro-poor cost-effective interventions aimed at achieving the United Nations Millennium Development Goals, decision-makers need to ensure that these health facilities provide efficient services. The objective of this study was to measure the technical efficiency (TE) and scale efficiency (SE) of a sample of public peripheral health units (PHUs) in Sierra Leone. METHODS: This study applied the Data Envelopment Analysis approach to investigate the TE and SE among a sample of 37 PHUs in Sierra Leone. RESULTS: Twenty-two (59%) of the 37 health units analysed were found to be technically inefficient, with an average score of 63% (standard deviation = 18%). On the other hand, 24 (65%) health units were found to be scale inefficient, with an average scale efficiency score of 72% (standard deviation = 17%). CONCLUSION: It is concluded that with the existing high levels of pure technical and scale inefficiency, scaling up of interventions to achieve both global and regional targets such as the MDG and Abuja health targets becomes far-fetched. In a country with per capita expenditure on health of about US$7, and with only 30% of its population having access to health services, it is demonstrated that efficiency savings can significantly augment the government's initiatives to cater for the unmet health care needs of the population. Therefore, we strongly recommend that Sierra Leone and all other countries in the Region should institutionalise health facility efficiency monitoring at the Ministry of Health headquarter (MoH/HQ) and at each health district headquarter
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