Universidad del Norte, Colombia

About: Universidad del Norte, Colombia is a education organization based out in Barranquilla, Colombia. It is known for research contribution in the topics: Population & Context (language use). The organization has 3562 authors who have published 4355 publications receiving 37861 citations. The organization is also known as: University of the North, Colombia & Uninorte.

Intrinsic Defects, Fluctuations of the Local Shape, and the Photo- Oxidation of Black Phosphorus

Abstract: Black phosphorus is a monatomic semiconducting layered material that degrades exothermically in the presence of light and ambient contaminants. Its degradation dynamics remain largely unknown. Even before degradation, local-probe studies indicate non-negligible local curvature—through a nonconstant height distribution—due to the unavoidable presence of intrinsic defects. We establish that these intrinsic defects are photo-oxidation sites because they lower the chemisorption barrier of ideal black phosphorus (>10 eV and out of visible-range light excitations) right into the visible and ultraviolet range (1.6 to 6.8 eV), thus enabling photoinduced oxidation and dissociation of oxygen dimers. A full characterization of the material’s shape and of its electronic properties at the early stages of the oxidation process is presented as well. This study thus provides fundamental insights into the degradation dynamics of this novel layered material.

Manipulating the Alpha Level Cannot Cure Significance Testing

Abstract: We argue that making accept/reject decisions on scientific hypotheses, including a recent call for changing the canonical alpha level from p = 0.05 to p = 0.005, is deleterious for the finding of new discoveries and the progress of science. Given that blanket and variable alpha levels both are problematic, it is sensible to dispense with significance testing altogether. There are alternatives that address study design and sample size much more directly than significance testing does; but none of the statistical tools should be taken as the new magic method giving clear-cut mechanical answers. Inference should not be based on single studies at all, but on cumulative evidence from multiple independent studies. When evaluating the strength of the evidence, we should consider, for example, auxiliary assumptions, the strength of the experimental design, and implications for applications. To boil all this down to a binary decision based on a p-value threshold of 0.05, 0.01, 0.005, or anything else, is not acceptable.

Prediction of preterm birth using the cervical consistency index

Abstract: Objectives To assess the diagnostic power of a new cervical consistency index (CCI) obtained using transvaginal sonography for the prediction of spontaneous preterm birth (PTB) and to establish reference ranges for this new variable. Methods Included in this prospective cross-sectional study were 1115 singleton pregnancies at 5–36 weeks of gestation. Anteroposterior cervical diameter was measured before (AP) and after (AP′) application of pressure on the cervix using the transvaginal probe. The index was calculated using the formula: CCI = ((AP′/AP) × 100). Cervical length was also measured. The outcomes evaluated were spontaneous PTB before 32, 34 and 37 weeks. Logistic regression and analysis of receiver–operating characteristics (ROC) curves were performed to evaluate the diagnostic power of CCI and cervical length (adjusted for gestational age). Intraclass correlation coefficients (ICCs) and Bland–Altman analysis were used to evaluate intra- and interobserver variability. Results In the 1031 women with follow-up, the rate of spontaneous PTB before 32 weeks was 0.87%, before 34 weeks was 2.13% and before 37 weeks was 7.76% (n = 80). There were 31 (3.01%) iatrogenic PTBs before 37 weeks. An inverse linear correlation between gestational age and CCI was observed, with regression equation: CCI (in %) = 89.8 − 1.35× (GA in weeks); r2 = 0.66, P < 0.001. Cervical length showed an inverse quadratic, though non-significant, relationship with gestational age: CL (in mm) = 31.084 − 0.0278× (GA in weeks)2 + 1.0772× (GA in weeks); r2 = 0.076, P < 0.14. The intra- and interobserver ICCs for CCI were 0.99 (95% CI, 0.988–0.994) and 0.98 (95% CI, 0.973–0.987), respectively. The area under the ROC curve for CCI in the prediction of spontaneous PTB before 32 weeks was 0.947, for spontaneous PTB before 34 weeks it was 0.943 and for spontaneous PTB before 37 weeks it was 0.907. For a 5% screen-positive rate, CCI had a sensitivity of 67%, 64% and 45% for prediction of spontaneous PTB before 32, 34 and 37 weeks, respectively, with equivalent values of 11%, 9% and 11% for cervical length. Conclusions CCI shows a clear inverse linear relationship with GA. Assessment of CCI is reproducible and is effective in the prediction of spontaneous PTB. This new variable appears to provide better prediction of spontaneous PTB than does cervical length. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.