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672 results on '"Cousens, S"'

1. Enhanced laser-driven ion acceleration by superponderomotive electrons generated from near-critical-density plasma

Author

Bin, J. H., Yeung, M., Gong, Z., Wang, H. Y., Kreuzer, C., Zhou, M. L., Streeter, M. J. V., Foster, P. S., Cousens, S., Dromey, B., Meyer-ter-Vehn, J., Zepf, M., and Schreiber, J.

Subjects
Physics - Plasma Physics
Abstract

We report on the experimental studies of laser driven ion acceleration from double-layer target where a near-critical density target with a few-micron thickness is coated in front of a nanometer thin diamond-like carbon foil. A significant enhancement of proton maximum energies from 12 to ~30 MeV is observed when relativistic laser pulse impinge on the double-layer target under linear polarization. We attributed the enhanced acceleration to superponderomotive electrons that were simultaneously measured in the experiments with energies far beyond the free-electron ponderomotive limit. Our interpretation is supported by two-dimensional simulation results.

Published
2017
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2. Temporal structure of attosecond pulses from laser-driven coherent synchrotron emission

Author

Cousens, S., Reville, B., Dromey, B., and Zepf, M.

Subjects
Physics - Plasma Physics, Physics - Optics
Abstract

The microscopic dynamics of laser-driven coherent synchrotron emission transmitted through thin foils are investigated using particle-in-cell simulations. For normal incidence interactions, we identify the formation of two distinct electron nanobunches from which emission takes place each half-cycle of the driving laser pulse. These emissions are separated temporally by 130 attoseconds and are dominant in different frequency ranges, which is a direct consequence of the distinct characteristics of each electron nanobunch. This may be exploited through spectral filtering to isolate these emissions, generating electromagnetic pulses of duration ~70 as.

Published
2016
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3. Bright subcycle XUV pulse from a single dense relativistic electron sheet

Author

Ma, W. J., Bin, J. H., Wang, H. Y., Yeung, M., Kreuzer, C., Streeter, M., Foster, P. S., Cousens, S., Kiefer, D., Dromey, B., Yan, X. Q., Zepf, M., Meyer-ter-Vehn, J., and Schreiber, J.

Subjects
Physics - Plasma Physics, Physics - Optics
Abstract

Relativistic electrons are prodigious sources of photons. Beyond classical accelerators, ultra-intense laser interactions are of particular interest as they allow the coherent motion of relativistic electrons to be controlled and exploited as sources of radiation. Under extreme laser conditions theory predicts that isolated free relativistic electron sheets (FRES) can be produced and exploited for the production of a new class of radiation - unipolar extreme ultraviolet(XUV) pulses. However, the combination of extremely rapid rise-time and highest peak intensity in these simulations is still beyond current laser technology. We demonstrate a route to isolated FRES with existing lasers by exploiting relativistic transparency to produce an ultra-intense pulse with a steep rise time. When such an FRES interacts with a second, oblique target foil the electron sheet is rapidly accelerated ('kicked'). The radiation signature and simulations demonstrate that a single, nanometer thick FRES was produced. The experimental observations together with our theoretical modeling suggest the production of the first unipolar (half-cycle) pulse in the XUV - an achievement that has so far only been realized in the terahertz spectral domain., Comment: 10 pages, 3 figures

Published
2014
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4. Relativistic plasma optics enabled by near-critical density nanostructured material

Author

Bin, J. H., Ma, W. J., Wang, H. Y., Streeter, M. J. V., Kreuzer, C., Kiefer, D., Yeung, M., Cousens, S., Foster, P. S., Dromey, B., Yan, X. Q., Meyer-ter-Vehn, J., Zepf, M., and Schreiber, J.

Subjects
Physics - Plasma Physics, Physics - Accelerator Physics
Abstract

The nonlinear optical properties of a plasma due to the relativistic electron motion in an intense laser field are of fundamental importance for current research and the generation of brilliant laser-driven sources of particles and photons1-15. Yet, one of the most interesting regimes, where the frequency of the laser becomes resonant with the plasma, has remained experimentally hard to access. We overcome this limitation by utilizing ultrathin carbon nanotube foam16 (CNF) targets allowing the strong relativistic nonlinearities at near- critical density (NCD) to be exploited for the first time. We report on the experimental realization of relativistic plasma optics to spatio-temporally compress the laser pulse within a few micrometers of propagation, while maintaining about half its energy. We also apply the enhanced laser pulses to substantially improve the properties of an ion bunch accelerated from a secondary target. Our results provide first insights into the rich physics of NCD plasmas and the opportunities waiting to be harvested for applications., Comment: 11 pages+5 pages (supplementary information), 4 figures+ 2 figures (supplementary information)

Published
2014

6. Estimating the birth prevalence and pregnancy outcomes of congenital malformations worldwide

Author

Moorthie, Sowmiya, Blencowe, Hannah, Darlison, Matthew W., Lawn, Joy, Morris, Joan K., Modell, Bernadette, Congenital Disorders Expert Group, Bittles, A. H., Blencowe, H., Christianson, A., Cousens, S., Darlison, M. W., Gibbons, S., Hamamy, H., Khoshnood, B., Howson, C. P., Lawn, J., Mastroiacovo, P., Modell, B., Moorthie, S., Morris, J. K., Mossey, P. A., Neville, A. J., Petrou, M., Povey, S., Rankin, J., Schuler-Faccini, L., Wren, C., and Yunnis, K. A.

Published
2018
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8. The Epidemiology of Variant Creutzfeldt-Jakob Disease

Author

Smith, P. G., Cousens, S. N., d’Aignaux, J. N. Huillard, Ward, H. J. T., Will, R. G., Compans, R. W., editor, Cooper, M. D., editor, Honjo, T., editor, Koprowski, H., editor, Melchers, F., editor, Oldstone, M. B. A., editor, Olsnes, S., editor, Potter, M., editor, Vogt, P. K., editor, Wagner, H., editor, and Harris, David A., editor

Published
2004
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9. Research priorities to reduce the impact of COVID-19 in low- and middle-income countries

Author

Polasek, O, Wazny, K, Adeloye, D, Song, P, Chan, KY, Bojude, DA, Ali, S, Bastien, S, Becerra-Posada, F, Borrescio-Higa, F, Cheema, S, Cipta, DA, Cvjetkovic, S, Castro, LD, Ebenso, B, Femi-Ajao, O, Ganesan, B, Glasnovic, A, He, L, Heraud, JM, Igwesi-Chidobe, C, Iversen, PO, Jadoon, B, Karim, AJ, Khan, J, Biswas, RK, Lanza, G, Lee, SWH, Li, Y, Liang, L-L, Lowe, M, Islam, MM, Marusic, A, Mshelia, S, Manyara, AM, Htay, MNN, Parisi, M, Peprah, P, Sacks, E, Akinyemi, KO, Shahraki-Sanavi, F, Sharov, K, Rotarou, ES, Stankov, S, Supriyatiningsih, W, Chan, BTY, Tremblay, M, Tsimpida, D, Vento, S, Glasnovic, J, Wang, L, Wang, X, Ng, ZX, Zhang, J, Zhang, Y, Campbell, H, Chopra, M, Cousens, S, Krstic, G, Macdonald, C, Mansoori, P, Patel, S, Sheikh, A, Tomlinson, M, Tsai, AC, Yoshida, S, Rudan, I, Polasek, O, Wazny, K, Adeloye, D, Song, P, Chan, KY, Bojude, DA, Ali, S, Bastien, S, Becerra-Posada, F, Borrescio-Higa, F, Cheema, S, Cipta, DA, Cvjetkovic, S, Castro, LD, Ebenso, B, Femi-Ajao, O, Ganesan, B, Glasnovic, A, He, L, Heraud, JM, Igwesi-Chidobe, C, Iversen, PO, Jadoon, B, Karim, AJ, Khan, J, Biswas, RK, Lanza, G, Lee, SWH, Li, Y, Liang, L-L, Lowe, M, Islam, MM, Marusic, A, Mshelia, S, Manyara, AM, Htay, MNN, Parisi, M, Peprah, P, Sacks, E, Akinyemi, KO, Shahraki-Sanavi, F, Sharov, K, Rotarou, ES, Stankov, S, Supriyatiningsih, W, Chan, BTY, Tremblay, M, Tsimpida, D, Vento, S, Glasnovic, J, Wang, L, Wang, X, Ng, ZX, Zhang, J, Zhang, Y, Campbell, H, Chopra, M, Cousens, S, Krstic, G, Macdonald, C, Mansoori, P, Patel, S, Sheikh, A, Tomlinson, M, Tsai, AC, Yoshida, S, and Rudan, I

Abstract

BACKGROUND: The COVID-19 pandemic has caused disruptions to the functioning of societies and their health systems. Prior to the pandemic, health systems in low- and middle-income countries (LMIC) were particularly stretched and vulnerable. The International Society of Global Health (ISoGH) sought to systematically identify priorities for health research that would have the potential to reduce the impact of the COVID-19 pandemic in LMICs. METHODS: The Child Health and Nutrition Research Initiative (CHNRI) method was used to identify COVID-19-related research priorities. All ISoGH members were invited to participate. Seventy-nine experts in clinical, translational, and population research contributed 192 research questions for consideration. Fifty-two experts then scored those questions based on five pre-defined criteria that were selected for this exercise: 1) feasibility and answerability; 2) potential for burden reduction; 3) potential for a paradigm shift; 4) potential for translation and implementation; and 5) impact on equity. RESULTS: Among the top 10 research priorities, research questions related to vaccination were prominent: health care system access barriers to equitable uptake of COVID-19 vaccination (ranked 1st), determinants of vaccine hesitancy (4th), development and evaluation of effective interventions to decrease vaccine hesitancy (5th), and vaccination impacts on vulnerable population/s (6th). Health care delivery questions also ranked highly, including: effective strategies to manage COVID-19 globally and in LMICs (2nd) and integrating health care for COVID-19 with other essential health services in LMICs (3rd). Additionally, the assessment of COVID-19 patients' needs in rural areas of LMICs was ranked 7th, and studying the leading socioeconomic determinants and consequences of the COVID-19 pandemic in LMICs using multi-faceted approaches was ranked 8th. The remaining questions in the top 10 were: clarifying paediatric case-fatality rates (CFR) in

Published
2022

12. Polarization Gating in Relativistic Laser-Solid Interactions

Author

Yeung, M., primary, Dromey, B., additional, Cousens, S., additional, Coughlan, M., additional, Rykovanov, S., additional, Rödel, C., additional, Bierbach, J., additional, Kuschel, S., additional, Eckner, E., additional, Förster, M., additional, Paulus, G., additional, and Zepf, M., additional

Published
2015
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24. Distance to care, care seeking and child mortality in rural Burkina Faso: findings from a population‐based cross‐sectional survey

Author

Sarrassat, S., Meda, N., Badolo, H., Ouedraogo, M., Somé, H., and Cousens, S.

Subjects
Adult, Rural Population, neonatal mortality, mortalité néonatale, Health Services Accessibility, under‐five child mortality, Pregnancy, Burkina Faso, Infant Mortality, Humans, Maternal Health Services, Child, mortalité des moins de 5 ans, Maternal Welfare, Travel, Infant, Newborn, Infant, Prenatal Care, distance to care, care seeking, recherche de soins, Cross-Sectional Studies, Transportation of Patients, Socioeconomic Factors, Child, Preschool, Child Mortality, Original Article, Female, distance aux soins, Original Research Papers
Abstract

Objective Although distance has been identified as an important barrier to care, evidence for an effect of distance to care on child mortality is inconsistent. We investigated the association of distance to care with self‐reported care seeking behaviours, neonatal and post‐neonatal under‐five child mortality in rural areas of Burkina Faso. Methods We performed a cross‐sectional survey in 14 rural areas from November 2014 to March 2015. About 100 000 women were interviewed on their pregnancy history and about 5000 mothers were interviewed on their care seeking behaviours. Euclidean distances to the closest facility were calculated. Mixed‐effects logistic and Poisson regressions were used respectively to compute odds ratios for care seeking behaviours and rate ratios for child mortality during the 5 years prior to the survey. Results Thirty per cent of the children lived more than 7 km from a facility. After controlling for confounding factors, there was a strong evidence of a decreasing trend in care seeking with increasing distance to care (P ≤ 0.005). There was evidence for an increasing trend in early neonatal mortality with increasing distance to care (P = 0.028), but not for late neonatal mortality (P = 0.479) and post‐neonatal under‐five child mortality (P = 0.488). In their first week of life, neonates living 7 km or more from a facility had an 18% higher mortality rate than neonates living within 2 km of a facility (RR = 1.18; 95%CI 1.00, 1.39; P = 0.056). In the late neonatal period, despite the lack of evidence for an association of mortality with distance, it is noteworthy that rate ratios were consistent with a trend and similar to or larger than estimates in early neonatal mortality. In this period, neonates living 7 km or more from a facility had an 18% higher mortality rate than neonates living within 2 km of a facility (RR = 1.18; 95%CI 0.92, 1.52; P = 0.202). Thus, the lack of evidence may reflect lower power due to fewer deaths rather than a weaker association. Conclusion While better geographic access to care is strongly associated with increased care seeking in rural Burkina Faso, the impact on child mortality appears to be marginal. This suggests that, in addition to improving access to services, attention needs to be paid to quality of those services.

Published
2018

35. Aetiology of invasive bacterial infection and antimicrobial resistance in neonates in sub-Saharan Africa: a systematic review and meta-analysis in line with the STROBE-NI reporting guidelines

Author

Okomo, U, Akpalu, ENK, Le Doare, K, Roca, A, Cousens, S, Jarde, A, Sharland, M, Kampmann, B, and Lawn, JE

Abstract

BACKGROUND: Aetiological data for neonatal infections are essential to inform policies and programme strategies, but such data are scarce from sub-Saharan Africa. We therefore completed a systematic review and meta-analysis of available data from the African continent since 1980, with a focus on regional differences in aetiology and antimicrobial resistance (AMR) in the past decade (2008-18). METHODS: We included data for microbiologically confirmed invasive bacterial infection including meningitis and AMR among neonates in sub-Saharan Africa and assessed the quality of scientific reporting according to Strengthening the Reporting of Observational Studies in Epidemiology for Newborn Infection (STROBE-NI) checklist. We calculated pooled proportions for reported bacterial isolates and AMR. FINDINGS: We included 151 studies comprising data from 84 534 neonates from 26 countries, almost all of which were hospital-based. Of the 82 studies published between 2008 and 2018, insufficient details were reported regarding most STROBE-NI items. Regarding culture positive bacteraemia or sepsis, Staphylococcus aureus, Klebsiella spp, and Escherichia coli accounted for 25% (95% CI 21-29), 21% (16-27), and 10% (8-10) respectively. For meningitis, the predominant identified causes were group B streptococcus 25% (16-33), Streptococcus pneumoniae 17% (9-6), and S aureus 12% (3-25). Resistance to WHO recommended β-lactams was reported in 614 (68%) of 904 cases and resistance to aminoglycosides in 317 (27%) of 1176 cases. INTERPRETATION: Hospital-acquired neonatal infections and AMR are a major burden in Africa. More population-based neonatal infection studies and improved routine surveillance are needed to improve clinical care, plan health systems approaches, and address AMR. Future studies should be reported according to standardised reporting guidelines, such as STROBE-NI, to aid comparability and reduce research waste. FUNDING: Uduak Okomo was supported by a Medical Research Council PhD Studentship.

Published
2019

38. Transmissions to mice indicate that 'new variant' CJD is caused by the BSE agent

Author

Bruce, M.E., Will, R.G., Ironside, J.W., McConnell, I., Drummond, D., Suttie, A., McCardle, L., Chree, A., Hope, J., Birkett, C., Cousens, S., Fraser, H., and Bostock, C.J.

Subjects
Bovine spongiform encephalopathy -- Causes of, Creutzfeldt-Jakob disease -- Causes of, Prions -- Research, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

The strain of agent from cattle infected with bovine spongiform encephalopathy (BSE) gives a typical pattern of disease in mice that remains in place after experimental passage through several intermediate species. There is strong evidence that the same agent strain plays a role in both BSE and 'new variant' Creutzfeldt-Jakob disease (vCJD). It seems that the agent interacts with genetic factors in the host to control the timing and neuropathology of the disease with extreme precision. Transmissible spongiform encephalopathies carry some form of information that details strain-specific properties.

Published
1997

39. Visual field constriction as a cause of blindness or visual impairment

Author

Murdoch, I.E., Jones, B.R., Cousens, S., Liman, I., Babalola, O.E., Dauda, J., and Abiose, A.

Subjects
Vision disorders -- Diagnosis, Onchocerciasis -- Diagnosis, Visual fields -- Testing
Abstract

Reported are the results of a study of onchocerciasis in communities mesoendemic for savanna onchocerciasis in Kaduna State, northern Nigeria. The study involved 6831 individuals aged [equal to or greater than] 5 years who underwent an extensive screening examination for visual function including Friedmann field analysis. A total of 185 (2.7%) were bilaterally blind by acuity and an additional 28 (0.4%) were blind by visual field constriction. Also 118 (1.7%) individuals were visually impaired by acuity criteria. No criteria for visual impairment by field constriction have been established, and we therefore investigated three potential criteria. As a result, a further 60 (0.9%) individuals were identified with significant visual impairment due to field loss by the various definitions. Small islands of remaining peripheral field occurred in 50 individuals, while 40 individuals had marked reduction of binocular visual field below the horizontal meridian. Concentric visual field constriction to, Introduction In 1973 a WHO Study Group on the prevention of blindness proposed five categories of visual impairment that have since been widely adopted, permitting direct comparison of blindness and [...]

Published
1997

44. Structured observations of hygiene behaviours in Burkina Faso: validity, variability, and utility

Author

Curtis, V., Cousens, S., Mertens, T., Traore, E., Kanki, B., and Diallo, I.

Subjects
Health behavior -- Evaluation, Hygiene -- Evaluation, Burkina Faso -- Health aspects
Abstract

The use of observation techniques has been promoted for the study of hygiene practices; however, questions still remain about the validity and repeatability of such techniques. In this article we compare data on hygiene behaviours obtained from questionnaires with data obtained using a structured observation approach and examine the repeatability of structured observations of behaviours and spot observations of environmental conditions. Poor agreement between questionnaire responses and observations was found for child defecation and stool disposal practices ([Kappa] statistic: 0.25 and 0.28, respectively). There was evidence of over-reporting of "good" behaviours (P, Introduction In a review of studies of the health impact of water supply and sanitation programmes in developing countries, Cairncross concluded that health benefits stem from changes in hygiene behaviour [...]

Published
1993

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