2,515 research outputs found
Solubility of strontium-substituted apatite by solid titration
Solid titration was used to explore the solubility isotherms of partially (Srx-HAp, x = 1, 5, 10, 40, 60 mol.%) and fully substituted strontium hydroxyapatite (Sr-HAp). Solubility increased with increasing strontium content. No phase other than strontium-substituted HAp, corresponding to the original titrant, was detected in the solid present at equilibrium; in particular, dicalcium hydrogen phosphate was not detected at low pH. The increase in solubility with strontium content is interpreted as a destabilization of the crystal structure by the larger strontium ion. Carbonated HAp was formed in simulated body fluid containing carbonate on seeding with Sr10-HAp, but the precipitate was strontium-substituted on seeding with Sr-HAp. Strontium-substituted HAp might be usable as a template for the growth of new bone, since nucleation appears to be facilitated. © 2008 Acta Materialia Inc.postprin
Solubility of strontium-substituted apatite by solid titration
Solid titration was used to explore the solubility isotherms of partially (Srx-HAp, x = 1, 5, 10, 40, 60 mol.%) and fully substituted strontium hydroxyapatite (Sr-HAp). Solubility increased with increasing strontium content. No phase other than strontium-substituted HAp, corresponding to the original titrant, was detected in the solid present at equilibrium; in particular, dicalcium hydrogen phosphate was not detected at low pH. The increase in solubility with strontium content is interpreted as a destabilization of the crystal structure by the larger strontium ion. Carbonated HAp was formed in simulated body fluid containing carbonate on seeding with Sr10-HAp, but the precipitate was strontium-substituted on seeding with Sr-HAp. Strontium-substituted HAp might be usable as a template for the growth of new bone, since nucleation appears to be facilitated. © 2008 Acta Materialia Inc.postprin
Asymptotic normality of the Parzen-Rosenblatt density estimator for strongly mixing random fields
We prove the asymptotic normality of the kernel density estimator (introduced
by Rosenblatt (1956) and Parzen (1962)) in the context of stationary strongly
mixing random fields. Our approach is based on the Lindeberg's method rather
than on Bernstein's small-block-large-block technique and coupling arguments
widely used in previous works on nonparametric estimation for spatial
processes. Our method allows us to consider only minimal conditions on the
bandwidth parameter and provides a simple criterion on the (non-uniform) strong
mixing coefficients which do not depend on the bandwith.Comment: 16 page
Validation of nonlinear PCA
Linear principal component analysis (PCA) can be extended to a nonlinear PCA
by using artificial neural networks. But the benefit of curved components
requires a careful control of the model complexity. Moreover, standard
techniques for model selection, including cross-validation and more generally
the use of an independent test set, fail when applied to nonlinear PCA because
of its inherent unsupervised characteristics. This paper presents a new
approach for validating the complexity of nonlinear PCA models by using the
error in missing data estimation as a criterion for model selection. It is
motivated by the idea that only the model of optimal complexity is able to
predict missing values with the highest accuracy. While standard test set
validation usually favours over-fitted nonlinear PCA models, the proposed model
validation approach correctly selects the optimal model complexity.Comment: 12 pages, 5 figure
From Nonspecific DNA–Protein Encounter Complexes to the Prediction of DNA–Protein Interactions
©2009 Gao, Skolnick. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.doi:10.1371/journal.pcbi.1000341DNA–protein interactions are involved in many essential biological activities. Because there is no simple mapping code between DNA base pairs and protein amino acids, the prediction of DNA–protein interactions is a challenging problem. Here, we present a novel computational approach for predicting DNA-binding protein residues and DNA–protein interaction modes without knowing its specific DNA target sequence. Given the structure of a DNA-binding protein, the method first generates an ensemble of complex structures obtained by rigid-body docking with a nonspecific canonical B-DNA. Representative models are subsequently selected through clustering and ranking by their DNA–protein interfacial energy. Analysis of these encounter complex models suggests that the recognition sites for specific DNA binding are usually favorable interaction sites for the nonspecific DNA probe and that nonspecific DNA–protein interaction modes exhibit some similarity to specific DNA–protein binding modes. Although the method requires as input the knowledge that the protein binds DNA, in benchmark tests, it achieves better performance in identifying DNA-binding sites than three previously established methods, which are based on sophisticated machine-learning techniques. We further apply our method to protein structures predicted through modeling and demonstrate that our method performs satisfactorily on protein models whose root-mean-square Ca deviation from native is up to 5 Å from their native structures. This study provides valuable structural insights into how a specific DNA-binding protein interacts with a nonspecific DNA sequence. The similarity between the specific DNA–protein interaction mode and nonspecific interaction modes may reflect an important sampling step in search of its specific DNA targets by a DNA-binding protein
Aspirin and extended-release dipyridamole versus clopidogrel for recurrent stroke
Background
Recurrent stroke is a frequent, disabling event after ischemic stroke. This study compared
the efficacy and safety of two antiplatelet regimens — aspirin plus extendedrelease
dipyridamole (ASA–ERDP) versus clopidogrel.
Methods
In this double-blind, 2-by-2 factorial trial, we randomly assigned patients to receive
25 mg of aspirin plus 200 mg of extended-release dipyridamole twice daily or to receive
75 mg of clopidogrel daily. The primary outcome was first recurrence of stroke.
The secondary outcome was a composite of stroke, myocardial infarction, or death
from vascular causes. Sequential statistical testing of noninferiority (margin of 1.075),
followed by superiority testing, was planned.
Results
A total of 20,332 patients were followed for a mean of 2.5 years. Recurrent stroke
occurred in 916 patients (9.0%) receiving ASA–ERDP and in 898 patients (8.8%) receiving
clopidogrel (hazard ratio, 1.01; 95% confidence interval [CI], 0.92 to 1.11). The
secondary outcome occurred in 1333 patients (13.1%) in each group (hazard ratio for
ASA–ERDP, 0.99; 95% CI, 0.92 to 1.07). There were more major hemorrhagic events
among ASA–ERDP recipients (419 [4.1%]) than among clopidogrel recipients (365
[3.6%]) (hazard ratio, 1.15; 95% CI, 1.00 to 1.32), including intracranial hemorrhage
(hazard ratio, 1.42; 95% CI, 1.11 to 1.83). The net risk of recurrent stroke or major
hemorrhagic event was similar in the two groups (1194 ASA–ERDP recipients [11.7%],
vs. 1156 clopidogrel recipients [11.4%]; hazard ratio, 1.03; 95% CI, 0.95 to 1.11).
Conclusions
The trial did not meet the predefined criteria for noninferiority but showed similar rates
of recurrent stroke with ASA–ERDP and with clopidogrel. There is no evidence that either
of the two treatments was superior to the other in the prevention of recurrent
stroke. (ClinicalTrials.gov number, NCT00153062.
Joint association of polymorphism of the FGFR4 gene and mutation TP53 gene with bladder cancer prognosis
The impact of the fibroblast growth factor receptor 4 (FGFR4) Gly388Arg polymorphism on bladder cancer is unknown. We found no clear correlations between the FGFR4 genotype and risk of bladder cancer or pathological parameters. Neither the polymorphism nor TP53 mutation status was an independent predictor of prognosis, but they might act jointly on the disease-specific survival of patients
Age is a predicting factor for the association between CagA positive Helicobacter pylori (Hp) infection and serum pepsinogen I:II ratio in a high gastric cancer risk region in China
published_or_final_versio
Testing in the incremental design and development of complex products
Testing is an important aspect of design and development which consumes significant time and resource in many companies. However, it has received less research attention than many other activities in product development, and especially, very few publications report empirical studies of engineering testing. Such studies are needed to establish the importance of testing and inform the development of pragmatic support methods. This paper combines insights from literature study with findings from three empirical studies of testing. The case studies concern incrementally developed complex products in the automotive domain. A description of testing practice as observed in these studies is provided, confirming that testing activities are used for multiple purposes depending on the context, and are intertwined with design from start to finish of the development process, not done after it as many models depict. Descriptive process models are developed to indicate some of the key insights, and opportunities for further research are suggested
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