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Search Results: 1 - 10 of 300353 matches for " Donald J. Goodwin "
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Within-Subject Interlaboratory Variability of QuantiFERON-TB Gold In-Tube Tests
William C. Whitworth, Lanette R. Hamilton, Donald J. Goodwin, Carlos Barrera, Kevin B. West, Laura Racster, Laura J. Daniels, Stella O. Chuke, Brandon H. Campbell, Jamaria Bohanon, Atheer T. Jaffar, Wanzer Drane, David Maserang, Gerald H. Mazurek
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0043790
Abstract: Background The QuantiFERON?-TB Gold In-Tube test (QFT-GIT) is a viable alternative to the tuberculin skin test (TST) for detecting Mycobacterium tuberculosis infection. However, within-subject variability may limit test utility. To assess variability, we compared results from the same subjects when QFT-GIT enzyme-linked immunosorbent assays (ELISAs) were performed in different laboratories. Methods Subjects were recruited at two sites and blood was tested in three labs. Two labs used the same type of automated ELISA workstation, 8-point calibration curves, and electronic data transfer. The third lab used a different automated ELISA workstation, 4-point calibration curves, and manual data entry. Variability was assessed by interpretation agreement and comparison of interferon-γ (IFN-γ) measurements. Data for subjects with discordant interpretations or discrepancies in TB Response >0.05 IU/mL were verified or corrected, and variability was reassessed using a reconciled dataset. Results Ninety-seven subjects had results from three labs. Eleven (11.3%) had discordant interpretations and 72 (74.2%) had discrepancies >0.05 IU/mL using unreconciled results. After correction of manual data entry errors for 9 subjects, and exclusion of 6 subjects due to methodological errors, 7 (7.7%) subjects were discordant. Of these, 6 (85.7%) had all TB Responses within 0.25 IU/mL of the manufacturer's recommended cutoff. Non-uniform error of measurement was observed, with greater variation in higher IFN-γ measurements. Within-subject standard deviation for TB Response was as high as 0.16 IU/mL, and limits of agreement ranged from ?0.46 to 0.43 IU/mL for subjects with mean TB Response within 0.25 IU/mL of the cutoff. Conclusion Greater interlaboratory variability was associated with manual data entry and higher IFN-γ measurements. Manual data entry should be avoided. Because variability in measuring TB Response may affect interpretation, especially near the cutoff, consideration should be given to developing a range of values near the cutoff to be interpreted as “borderline,” rather than negative or positive.
Variability of the QuantiFERON?-TB Gold In-Tube Test Using Automated and Manual Methods
William C. Whitworth, Donald J. Goodwin, Laura Racster, Kevin B. West, Stella O. Chuke, Laura J. Daniels, Brandon H. Campbell, Jamaria Bohanon, Atheer T. Jaffar, Wanzer Drane, Paul A. Sjoberg, Gerald H. Mazurek
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086721
Abstract: Background The QuantiFERON?-TB Gold In-Tube test (QFT-GIT) detects Mycobacterium tuberculosis (Mtb) infection by measuring release of interferon gamma (IFN-γ) when T-cells (in heparinized whole blood) are stimulated with specific Mtb antigens. The amount of IFN-γ is determined by enzyme-linked immunosorbent assay (ELISA). Automation of the ELISA method may reduce variability. To assess the impact of ELISA automation, we compared QFT-GIT results and variability when ELISAs were performed manually and with automation. Methods Blood was collected into two sets of QFT-GIT tubes and processed at the same time. For each set, IFN-γ was measured in automated and manual ELISAs. Variability in interpretations and IFN-γ measurements was assessed between automated (A1 vs. A2) and manual (M1 vs. M2) ELISAs. Variability in IFN-γ measurements was also assessed on separate groups stratified by the mean of the four ELISAs. Results Subjects (N = 146) had two automated and two manual ELISAs completed. Overall, interpretations were discordant for 16 (11%) subjects. Excluding one subject with indeterminate results, 7 (4.8%) subjects had discordant automated interpretations and 10 (6.9%) subjects had discordant manual interpretations (p = 0.17). Quantitative variability was not uniform; within-subject variability was greater with higher IFN-γ measurements and with manual ELISAs. For subjects with mean TB Responses ±0.25 IU/mL of the 0.35 IU/mL cutoff, the within-subject standard deviation for two manual tests was 0.27 (CI95 = 0.22–0.37) IU/mL vs. 0.09 (CI95 = 0.07–0.12) IU/mL for two automated tests. Conclusion QFT-GIT ELISA automation may reduce variability near the test cutoff. Methodological differences should be considered when interpreting and using IFN-γ release assays (IGRAs).
A Model of the Universe that Can Explain Dark Matter, Dark Energy, and the Fourth Space Dimension  [PDF]
Donald J. Koterwas
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.710112
Abstract: This paper explains how a model of the universe can be constructed by incorporating time and space into geometry in a unique way to produce a 4-space dimension/1-time dimension model. The model can then show how dark matter can be the gravity that is produced by real matter that exists throughout our entire universe. The model can also show how dark energy is not an increase in energy that is causing the accelerated expansion of the universe, but is an accelerating decrease in matter throughout the universe as the stars and galaxies in the universe continue to convert matter into energy during their life cycles. And then the model can show how a fourth space dimension must exist in our universe to locate a point in space.
The role of cluster evolution in disrupting planetary systems and disks: the Kozai mechanism
Richard J. Parker,Simon P. Goodwin
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15037.x
Abstract: We examine the effects of dynamical evolution in clusters on planetary systems or protoplanetary disks orbiting the components of binary stars. In particular, we look for evidence that the companions of host stars of planetary systems or disks could have their inclination angles raised from zero to between the threshold angles (39.23 degrees and 140.77 degrees) that can induce the Kozai mechanism. We find that up to 20 per cent of binary systems have their inclination angles increased to within the threshold range. Given that half of all extrasolar planets could be in binary systems, we suggest that up to 10 per cent of extrasolar planets could be affected by this mechanism.
The same, but different: Stochasticity in binary destruction
Richard J. Parker,Simon P. Goodwin
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21190.x
Abstract: Observations of binaries in clusters tend to be of visual binaries with separations of 10s - 100s au. Such binaries are 'intermediates' and their destruction or survival depends on the exact details of their individual dynamical history. We investigate the stochasticity of the destruction of such binaries and the differences between the initial and processed populations using N-body simulations. We concentrate on Orion Nebula Cluster-like clusters, where the observed binary separation distribution ranges from 62 - 620 au. We find that, starting from the same initial binary population in statistically identical clusters, the number of intermediate binaries that are destroyed after 1 Myr can vary by a factor of >2, and that the resulting separation distributions can be statistically completely different in initially substructured clusters. We also find that the mass ratio distributions are altered (destroying more low mass ratio systems), but not as significantly as the binary fractions or separation distributions. We conclude that finding very different intermediate (visual) binary populations in different clusters does not provide conclusive evidence that the initial populations were different.
PASCal: A principal-axis strain calculator for thermal expansion and compressibility determination
Matthew J. Cliffe,Andrew L. Goodwin
Physics , 2012, DOI: 10.1107/S0021889812043026
Abstract: We describe a web-based tool (PASCal; Principal Axis Strain Calculator) aimed at simplifying the determination of principal coefficients of thermal expansion and compressibilities from variable-temperature and variable-pressure lattice parameter data. In a series of three case studies, we use PASCal to re-analyse previously-published lattice parameter data and show that additional scientific insight is obtainable in each case. First, the two-dimensional metal-organic framework Cu-SIP-3 is found to exhibit the strongest area-negative thermal expansion (NTE) effect yet observed; second, the widely-used explosive HMX exhibits much stronger mechanical anisotropy than had previously been anticipated, including uniaxial NTE driven by thermal changes in molecular conformation; and, third, the high-pressure form of the mineral malayaite is shown to exhibit a strong negative linear compressibility (NLC) effect that arises from correlated tilting of SnO6 and SiO4 coordination polyhedra.
Nanostructure determination from the pair distribution function: A parametric study of the INVERT approach
Matthew J. Cliffe,Andrew L. Goodwin
Physics , 2013, DOI: 10.1088/0953-8984/25/45/454218
Abstract: We present a detailed study of the mechanism by which the INVERT method [Phys. Rev. Lett. 104, 125501] guides structure refinement of disordered materials. We present a number of different possible implementations of the central algorithm and explore the question of algorithm weighting. Our analysis includes quantification of the relative contributions of variance and fit-to-data terms during structure refinement, which leads us to study the roles of density fluctuations and configurational jamming in the RMC fitting process. We present a parametric study of the pair distribution function solution space for C60, a-Si and a-SiO2, which serves to highlight the difficulties faced in developing a transferable weighting scheme.
Comparisons between different techniques for measuring mass segregation
Richard J. Parker,Simon P. Goodwin
Physics , 2015, DOI: 10.1093/mnras/stv539
Abstract: We examine the performance of four different methods which are used to measure mass segregation in star-forming regions: the radial variation of the mass function $\mathcal{M}_{\rm MF}$; the minimum spanning tree-based $\Lambda_{\rm MSR}$ method; the local surface density $\Sigma_{\rm LDR}$ method; and the $\Omega_{\rm GSR}$ technique, which isolates groups of stars and determines whether the most massive star in each group is more centrally concentrated than the average star. All four methods have been proposed in the literature as techniques for quantifying mass segregation, yet they routinely produce contradictory results as they do not all measure the same thing. We apply each method to synthetic star-forming regions to determine when and why they have shortcomings. When a star-forming region is smooth and centrally concentrated, all four methods correctly identify mass segregation when it is present. However, if the region is spatially substructured, the $\Omega_{\rm GSR}$ method fails because it arbitrarily defines groups in the hierarchical distribution, and usually discards positional information for many of the most massive stars in the region. We also show that the $\Lambda_{\rm MSR}$ and $\Sigma_{\rm LDR}$ methods can sometimes produce apparently contradictory results, because they use different definitions of mass segregation. We conclude that only $\Lambda_{\rm MSR}$ measures mass segregation in the classical sense (without the need for defining the centre of the region), although $\Sigma_{\rm LDR}$ does place limits on the amount of previous dynamical evolution in a star-forming region.
The dynamical evolution of very-low mass binaries in open clusters
Richard J. Parker,Simon P. Goodwin
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17722.x
Abstract: Very low-mass binaries (VLMBs), with system masses <0.2 Msun appear to have very different properties to stellar binaries. This has led to the suggestion that VLMBs form a distinct and different population. As most stars are born in clusters, dynamical evolution can significantly alter any initial binary population, preferentially destroying wide binaries. In this paper we examine the dynamical evolution of initially different VLMB distributions in clusters to investigate how different the initial and final distributions can be. We find that the majority of the observed VLMB systems, which have separations <20 au, cannot be destroyed in even the densest clusters. Therefore, the distribution of VLMBs with separations <20 au now must have been the birth population (although we note that the observations of this population may be very incomplete). Most VLMBs with separations >100 au can be destroyed in high-density clusters, but are mainly unaffected in low-density clusters. Therefore, the initial VLMB population must contain many more binaries with these separations than now, or such systems must be made by capture during cluster dissolution. M-dwarf binaries are processed in the same way as VLMBs and so the difference in the current field populations either points to fundamentally different birth populations, or significant observational incompleteness in one or both samples.
Quantification of local geometry and local symmetry in models of disordered materials
Matthew J. Cliffe,Andrew L. Goodwin
Physics , 2012, DOI: 10.1002/pssb.201248553
Abstract: We suggest two metrics for assessing the quality of atomistic configurations of disordered materials, both of which are based on quantifying the orientational distribution of neighbours around each atom in the configuration. The first metric is that of geometric invariance: i.e., the extent to which the neighbour arrangements are as similar as possible for different atoms, allowing for variations in frame of reference. The second metric concerns the degree of local symmetry. We propose that for a set of configurations with equivalent pair correlations, ranking highly those configurations with low geometric invariance but with high local symmetry selects for structural simplicity in a way that does not rely on formal group theoretical language (and hence long-range periodic order). We show that these metrics rank a range of SiO2 and a-Si configurations in an intuitive manner, and are also significantly more sensitive to unphysical features of those configurations in a way that metrics based on pair correlations are not. We also report that implementation of the metrics within a reverse Monte Carlo algorithm gives rise to an energy landscape that is too coarse (at least in this initial implementation) for amorphous structure "solution".
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