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191 results on '"Bujkiewicz, S"'

7. Creation of solitons and vortices by Bragg reflection of Bose-Einstein condensates in an optical lattice

Author

Scott, R. G., Martin, A. M., Fromhold, T. M., Bujkiewicz, S., Sheard, F. W., and Leadbeater, M.

Subjects
Condensed Matter
Abstract

We study the dynamics of Bose-Einstein condensates in an optical lattice and harmonic trap. The condensates are set in motion by displacing the trap and initially follow simple semiclassical paths, shaped by the lowest energy band. Above a critical displacement, the condensate undergoes Bragg reflection. For high atom densities, the first Bragg reflection generates a train of solitons and vortices, which destabilize the condensate and trigger explosive expansion. At lower densities, soliton and vortex formation requires multiple Bragg reflections, and damps the center-of-mass motion., Comment: 5 pages including 5 figures (for higher resolution figures please email the authors)

Published
2002
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16. Chaotic electron diffusion through stochastic webs enhances current flow in superlattices

Author

Fromhold, T. M., Patane, A., Bujkiewicz, S., Wilkinson, P. B., Fowler, D., Sherwood, D., Stapleton, S. P., Krokhin, A. A., Eaves, L., Henini, M., Sankeshwar, N. S., and Sheard, F. W.

Subjects
Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Author(s): T. M. Fromhold (corresponding author) [1]; A. Patanè [1]; S. Bujkiewicz [1]; P. B. Wilkinson [1]; D. Fowler [1]; D. Sherwood [1]; S. P. Stapleton [1]; A. A. Krokhin [...]

Published
2004
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21. Chaotic Quantum Transport in Superlattices

Author

Fromhold, T. M., primary, Krokhin, A. A., additional, Belyaev, A. E., additional, Tench, C. R., additional, Bujkiewicz, S., additional, Wilkinson, P. B., additional, Sheard, F. W., additional, Eaves, L., additional, and Henini, M., additional

Published
2001
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23. Bayesian bivariate meta-analysis of correlated effects: Impact of the prior distributions on the between-study correlation, borrowing of strength, and joint inferences

Author

Burke, DL, Bujkiewicz, S, and Riley, RD

Subjects
Bayes, Models, Statistical, multiple outcomes, bivariate/multivariate meta-analysis, Bayes Theorem, Articles, Biostatistics, prior distributions, simulation study, Treatment Outcome, correlation, Data Interpretation, Statistical, Multivariate Analysis, Humans, Computer Simulation, RA
Abstract

Multivariate random-effects meta-analysis allows the joint synthesis of correlated results from multiple studies, for example, for multiple outcomes or multiple treatment groups. In a Bayesian univariate meta-analysis of one endpoint, the importance of specifying a sensible prior distribution for the between-study variance is well understood. However, in multivariate meta-analysis, there is little guidance about the choice of prior distributions for the variances or, crucially, the between-study correlation, ρB; for the latter, researchers often use a Uniform(-1,1) distribution assuming it is vague. In this paper, an extensive simulation study and a real illustrative example is used to examine the impact of various (realistically) vague prior distributions for ρB and the between-study variances within a Bayesian bivariate random-effects meta-analysis of two correlated treatment effects. A range of diverse scenarios are considered, including complete and missing data, to examine the impact of the prior distributions on posterior results (for treatment effect and between-study correlation), amount of borrowing of strength, and joint predictive distributions of treatment effectiveness in new studies. Two key recommendations are identified to improve the robustness of multivariate meta-analysis results. First, the routine use of a Uniform(-1,1) prior distribution for ρB should be avoided, if possible, as it is not necessarily vague. Instead, researchers should identify a sensible prior distribution, for example, by restricting values to be positive or negative as indicated by prior knowledge. Second, it remains critical to use sensible (e.g. empirically based) prior distributions for the between-study variances, as an inappropriate choice can adversely impact the posterior distribution for ρB, which may then adversely affect inferences such as joint predictive probabilities. These recommendations are especially important with a small number of studies and missing data.

Published
2016

32. The effectiveness of anti-TNF-alpha therapies when used sequentially in rheumatoid arthritis patients: a systematic review and meta-analysis

Author

Lloyd, S., Bujkiewicz, S., Wailoo, A.J., Sutton, A.J., and Scott, D.

Abstract

Objectives: To systematically review and meta-analyse evidence on the effectiveness of the TNF-a\ud inhibitors when used sequentially.\ud \ud Methods: Systematic review of comparative and single-arm observational studies. Data were synthesized\ud using random-effects meta-analysis. Treatment effects were estimated using four outcome measures from\ud the included studies: European League Against Rheumatism (EULAR) and ACR20 response rates and\ud mean improvement in disease activity score-28 (DAS-20) and HAQ. The effect of other factors was\ud explored via meta-regression and sub-group analyses.\ud \ud Results: Twenty studies comprising 2705 patients were included in the analysis. All studies were observational\ud and most had no control group. Therefore, our primary analysis considered patient changes from\ud baseline. The mean percentage of ACR20 responders was 60.8% (95% CI 53.8, 67.4), EULAR responders\ud 70.5% (95% CI 63.7, 76.6), mean overall improvement in DAS-28 scores was 1.53 (95% CI 1.25, 1.80) and\ud in HAQ scores was 0.25 (95% CI 0.11, 0.40). Four studies made comparisons with patients who received\ud TNF-a inhibitors for the first time. Response rates associated with sequential TNF-a inhibitor treatment\ud were lower than for first-time use.\ud \ud Conclusions: Sequential TNF-a inhibitor use is likely to lead to treatment benefit in terms of the signs and\ud symptoms of disease and physical function. There is also some evidence to suggest that the probability of\ud achieving a response is lower, and the average magnitude of response is lower than the first use. Further\ud evidence from randomized controlled trials is required to confirm and further quantify the role specific\ud anti-TNF-a agents have when used sequentially.

Published
2010

47. Etanercept, infliximab and adalimumab for the treatment of psoriatic arthritis: a systematic review and economic evaluation

Author

Rodgers, M, primary, Epstein, D, additional, Bojke, L, additional, Yang, H, additional, Craig, D, additional, Fonseca, T, additional, Myers, L, additional, Bruce, I, additional, Chalmers, R, additional, Bujkiewicz, S, additional, Lai, M, additional, Cooper, N, additional, Abrams, K, additional, Spiegelhalter, D, additional, Sutton, A, additional, Sculpher, M, additional, and Woolacott, N, additional

Published
2011
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48. Creation of solitons and vortices by Bragg reflection of Bose-Einstein condensates in an optical lattice

Author

Scott, RG, Martin, AM, Fromhold, TM, Bujkiewicz, S, Sheard, FW, Leadbeater, M, Scott, RG, Martin, AM, Fromhold, TM, Bujkiewicz, S, Sheard, FW, and Leadbeater, M

Abstract

We study the dynamics of Bose-Einstein condensates in an optical lattice and harmonic trap. The condensates are set in motion by displacing the trap and initially follow simple semiclassical paths, shaped by the lowest energy band. Above a critical displacement, the condensate undergoes Bragg reflection. For high atom densities, the first Bragg reflection generates a train of solitons and vortices, which destabilize the condensate and trigger explosive expansion. At lower densities, soliton and vortex formation requires multiple Bragg reflections, and damps the center-of-mass motion.

Published
2003

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