SAS macros for point and interval estimation of area under the receiver operating characteristic curve for non-proportional and proportional hazards Weibull models

Aims and objectives  For prediction of risk of cardiovascular end points using survival models the proportional hazards assumption is often not met. Thus, non-proportional hazards models are more appropriate for developing risk prediction equations in such situations. However, computer program for evaluating the prediction performance of such models has been rarely addressed. We therefore developed SAS macro programs for evaluating the discriminative ability of a non-proportional hazards Weibull model developed by Anderson (1991) and that of a proportional hazards Weibull model using the area under receiver operating characteristic (ROC) curve.

Method  Two SAS macro programs for non-proportional hazards Weibull model using Proc NLIN and Proc NLP respectively and model validation using area under ROC curve (with its confidence limits) were written with SAS IML language. A similar SAS macro for proportional hazards Weibull model was also written.

Results  The computer program was applied to data on coronary heart disease incidence for a Framingham population cohort. The five risk factors considered were current smoking, age, blood pressure, cholesterol and obesity. The predictive ability of the non-proportional hazard Weibull model was slightly higher than that of its proportional hazard counterpart. An advantage of SAS Proc NLP in terms of the example provided here is that it provides significance level for the parameter estimates whereas Proc NLIN does not.

Conclusion  The program is very useful for evaluating the predictive performance of non-proportional and proportional hazards Weibull models.

Automated methods for the location of the boundaries of chromatographic peaks

Several simple techniques are presented for the identification of the boundaries of chromatographic peaks. These methods provide a significant reduction in the time needed to perform the rapid, automatic calculation of the central peak moments and to evaluate the quality of a separation while improving the accuracy of the measurements of column efficiencies. It was found that the identification of the peak boundaries as functions of the peak widths and the examination of the slope of the signal to noise versus time plot are viable alternatives to a manual determination.

Synthesis and characterization of surface-enhanced Raman-scattered gold nanoparticles

In this paper, we report a simple, rapid, and robust method to synthesize surface-enhanced Raman-scattered gold nanoparticles (GNPs) based on green chemistry. Vitis vinifera L. extract was used to synthesize noncytotoxic Raman-active GNPs. These GNPs were characterized by ultraviolet-visible spectroscopy, dynamic light-scattering, Fourier-transform infrared (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The characteristic surface plasmon-resonance band at ~528 nm is indicative of spherical particles, and this was confirmed by TEM. The N–H and C–O stretches in FTIR spectroscopy indicated the presence of protein molecules. The predominant XRD plane at (111) and (200) indicated the crystalline nature and purity of GNPs. GNPs were stable in the buffers used for biological studies, and exhibited no cytotoxicity in noncancerous MIO-M1 (Müller glial) and MDA-MB-453 (breast cancer) cell lines. The GNPs exhibited Raman spectral peaks at 570, 788, and 1,102 cm-1. These new GNPs have potential applications in cancer diagnosis, therapy, and ultrasensitive biomarker detection.

Plasma assisted finishing of cotton fabric with chitosan

Chitosan is a natural and non-toxic polymer which can be used as a multifunctional, e.g. antimicrobial or anti-wrinkle, agent on cotton fabrics. However, due to the lack of strong bonding forces between two polysaccharides, chitosan coating on cotton has poor durability. To provide efficient and irreversible chitosan adsorption on cotton substrate, it is required to build appropriate binding sites and to activate the substrate material properly. For this purpose, plasma treatment can be a promising method as it can activate the surface of the cotton fabric and improve the adsorption of chemicals in a completely harmless procedure. In this study, we investigated the effect of atmospheric pressure plasma treatment on adsorption of chitosan onto the cotton fabric. The purpose of the study was to investigate to which extent adsorption of chitosan on cotton can be improved by helium plasma treatment. Fibre surface and adsorption of chitosan were characterized by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared (FTIR) spectroscopy. Changes in hydrophobicity of fabric`s surface and fibre morphology were evaluated using contact angle method and scanning electron microscopy (SEM), respectively. The results from XPS showed an increase in the C=O bonds on cotton fabrics oxydised by helium plasma treatmnets, confirming the formation of aldehyde groups in cellulose. The characteristic absorbance band of chitosan, amide II (N-H bending vibration) showed an enlargement for all fabrics treated with helium and chitosan, as assesed by FTIR. The absorbance peaks of CH2 stretching vibrations, which confirm chitosan existence, were stronger for all treated fabrics compared to the untreated control. While the plasma only treated fabric surface was very hydrophilic, the surface became hydrophobic after chitosan coating.