► We consider molecules with hindered internal rotation. ► We suggest a new model for taking into account hindered rotation in the refinement of their structural parameters. ► We show that the model ...provides close agreement with electron diffraction experiment.
Molecules with hindered internal rotation are considered. A new model for taking into account hindered rotation in the refinement of their structural parameters is suggested. The model provides close agreement with electron diffraction experiment.
This article describes a new Stata command, tsb, for performing a stratified two-stage nonparametric bootstrap resampling procedure for clustered data. Estimates for uncertainty around the point ...estimate, such as standard error and confidence intervals, are derived from the resultant bootstrap samples. A shrinkage estimator proposed for correcting possible overestimation due to second-stage sampling is implemented as default. Although this command is written with cost effectiveness analyses alongside cluster trials in mind, it is applicable to the analysis of continuous endpoints in cluster trials more generally. The use of this command is exemplified with a case study of a cost effectiveness analysis undertaken alongside a cluster randomized trial. We also report bootstrap confidence interval coverage by using data from a published simulation study.
Motivated by an ongoing study to develop a screening test able to identify patients with undiagnosed Sjögren's Syndrome in a symptomatic population, we propose methodology to combine multiple ...biomarkers and evaluate their performance in a two-stage group sequential design that proceeds as follows: biomarker data is collected from first stage samples; the biomarker panel is built and evaluated; if the panel meets pre-specified performance criteria the study continues to the second stage and the remaining samples are assayed. The design allows us to conserve valuable specimens in the case of inadequate biomarker panel performance. We propose a nonparametric conditional resampling algorithm that uses all the study data to provide unbiased estimates of the biomarker combination rule and the sensitivity of the panel corresponding to specificity of 1-t on the receiver operating characteristic curve (ROC). The Copas and Corbett (2002) correction, for bias resulting from using the same data to derive the combination rule and estimate the ROC, was also evaluated and an improved version was incorporated. An extensive simulation study was conducted to evaluate finite sample performance and propose guidelines for designing studies of this type. The methods were implemented in the National Cancer Institutes Early Detection Network Urinary PCA3 Evaluation Trial.
A critical problem in electron tomography is the deformation of the specimen due to radiation, or “shrinkage,” which interferes with image alignment and thereby limits resolution. Here, we describe a ...general strategy for refining preliminary reconstructions which allows the damage due to the shrinkage of plastic-embedded thin sectioned specimens (50–80
nm) to be corrected. The basic steps of the strategy involve: (a) the partition of the preliminary reconstruction into sub-volumes; (b) the extraction of corresponding sub-areas for each sub-volume from the micrographs of the tilt series; (c) the re-projection of each sub-volume according to the orientation parameters; and (d) the refinement of these parameters by correlating each sub-area to the corresponding computed projection. We tested the strategy by refining chemical synapses reconstructed from series imaged with conical, double and single tilt geometries. The results gathered with local refinement were evaluated by visually inspecting the structure of biological membranes in the maps. In an effort to quantify these improvements, we studied the refined maps using correlation criteria and mapped the corrections applied to the orientation parameters in each sub-volume of the reconstruction. Simulation experiments complemented the data gathered by correlation analysis. Based on these criteria, we concluded that local refinement significantly improves the overall quality of the reconstructions of chemical synapses calculated from series imaged with conical and double tilt geometries.
This article describes a new Stata command, tsb, for performing a stratified two-stage nonparametric bootstrap resampling procedure for clustered data. Estimates for uncertainty around the point ...estimate, such as standard error and confidence intervals, are derived from the resultant bootstrap samples. A shrinkage estimator proposed for correcting possible overestimation due to second-stage sampling is implemented as default. Although this command is written with cost effectiveness analyses alongside cluster trials in mind, it is applicable to the analysis of continuous endpoints in cluster trials more generally. The use of this command is exemplified with a case study of a cost effectiveness analysis undertaken alongside a cluster randomized trial. We also report bootstrap confidence interval coverage by using data from a published simulation study.
Aspherical plastic lenses for laser apparatus need submicron accuracy in the shape profile of injection molded parts. In the molding process, polymer changes from molten state to glassy state, and ...the cooling history of each point is different. These phenomena causes irregular shrinkage deformation. Usually, the mold shape is corrected overall using a constant shrinkage ratio. So it is difficult to develop highly shape accurate molded parts. In order to obtain better shape accuracy, shrinkage amounts must be computed exactly and the shape of mold must be corrected. Shrinkage amounts are computed from shape difference between the mold's shape and the shape of trial molded parts. The shapes of mold and molded parts are computed from regression of measuring data. This paper describes the shape regression algorithm, the correcting algorithm of mold, and the application of this method to aspherical lens's molds. Experiment shows that plastic lenses with a shape error of less than 0.3μm can be molded.
The surfaces of the organs of Sachs and Hunter of Electrophorus electricus L. were examined by scanning electron microscopy. Special attention was directed to morphological details of the electrocyte ...to provide a better understanding of its anterior and posterior faces. Some aspects of the microanatomy of these organs, which differ markedly from those of the main electric organ, provide new information on the structure as revealed previously by light and transmission electron microscopy. The relief, mainly expressed by papillae, is related to the actual membrane area, which is important for calculations of specific resistance and conductance. Information is also presented on the general organization of the tissue, in particular the distribution of the connective elements and external configuration of synaptic terminals. Shrinkage in preparation of tissue was evaluated and correction made whenever necessary. Correction factors for actual membrane area were calculated for anterior and posterior faces of electrocytes from both organs.
Extensive survey was made with a scanning electron microscope (SEM) of the surfaces of the main electric organ of Electrophorus electricus L. This study of the microanatomy of the electrocyte ...contributes to a better understanding of the relief of both anterior and posterior faces, showing peculiarities that could not be seen previously in sections either for light or for electron microscopy. The relief is evidently related to the actual membrane area, important for calculations of electrophysiological parameters. Also information on the general organization, specially the distribution of connective tissue and external configuration of synapses, is presented.
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