Comparisons of methods for multiple hypothesis testing in neuropsychological research.

Hypothesis testing with multiple outcomes requires adjustments to control Type I error inflation, which reduces power to detect significant differences. Maintaining the prechosen Type I error level is challenging when outcomes are correlated. This problem concerns many research areas, including neuropsychological research in which multiple, interrelated assessment measures are common. Standard p value adjustment methods include Bonferroni-, Sidak-, and resampling-class methods. In this report, the authors aimed to develop a multiple hypothesis testing strategy to maximize power while controlling Type I error. The authors conducted a sensitivity analysis, using a neuropsychological dataset, to offer a relative comparison of the methods and a simulation study to compare the robustness of the methods with respect to varying patterns and magnitudes of correlation between outcomes. The results lead them to recommend the Hochberg and Hommel methods (step-up modifications of the Bonferroni method) for mildly correlated outcomes and the step-down minP method (a resampling-based method) for highly correlated outcomes. The authors note caveats regarding the implementation of these methods using available software. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of graphene nanoplatelet incorporation and dispersion state on thermal,mechanical and electrical properties of biodegradable matrices

Graphene nanoplatelets (GNPs) were used as multifunctional nanofiller to enhance thermal and mechanical properties as well as electrical conductivity of two different biodegradable thermoplastics: poly lactide (PLA) and poly (butylene adipate-co-terephthalate) (PBAT). Morphological investigations showed different levels of GNP dispersion in the two matrices, and consequently physical properties of the two systems exhibited dissimilar behaviours with GNP incorporation. Crystallinity of PLA, determined from differential scanning calorimetry, was observed to increase markedly with addition of GNPs in contrast to the decrease in crystallinity of PBAT. Isothermal and non-isothermal thermogravimetric analyses also revealed a more significant delay in thermal decomposition of PLA upon addition of GNPs compared to that of PBAT. Furthermore, results showed that increasing GNP content of PLA and PBAT nanocomposites influenced their Young’s modulus and electrical conductivity in different ways. Modulus of PBAT increased continuously with increasing GNP loading while that of PLA reached a maximum at 9 wt% GNPs and then decreased. Moreover, despite the higher conductivity of pure PBAT compared to pure PLA, conductivity of PLA/GNP nanocomposites overtook that of PBAT/GNP nanocomposites above a certain GNP concentration. This demonstrated the determining effect of nanoplatelets dispersion state on the matrices properties.     

Analysis of air pollution during a severe smog episode of November 2012 and the Diwali Festival over Delhi,India

The hazardous combination of smoke and pollutant gases, smog, is harmful for health. The harmful smog episodes over London, the Meuse Valley, and Donora are some of the well-known pollution episodes formed due to the mixture of smoky fumes and adverse meteorological conditions. A severe smog episode was observed over Delhi, India, during November 2012, resulting in very low visibility and various respiratory problems. Very high values of pollutants (particulate matter, PM₁₀ as high as 989 µg m^?3, PM_2.5 as high as 585 µg m^?3, and nitrogen dioxide as high as 540 µg m^?3) were measured all over Delhi during the smog episode. In the study done, episodes of different nature and intensity are analysed based on remote-sensing data for 3 years (2010–2012): one of regional origin (the Delhi smog episode of 2012) and another of local origin (Diwali). Remote-sensing and in situ data have revealed an insight into the genesis and temporal and spatial variance during these episodes. Extensive use of satellite-derived parameters such as fire maps, the ultra violet aerosol index from the Aura satellite, and aerosol optical depth is made in the present study along with the output trajectories from the Hybrid Single-Particle Lagrangian-Integrated Trajectory model and in situ data. It is observed that during the smog episode all the aerosol optical depth, ultra violet aerosol index, PM_2.5, and PM₁₀ values surpassed those of the Diwali period (which in itself is a major dreaded annual air pollution event in the city) by a considerable amount at all stations across Delhi. The parameters used from the remote-sensing data and the ground-based observations at various stations across Delhi are very well in agreement with the intensity of smog episodes. The analysis clearly shows that regional pollution can have a greater contribution towards deteriorating air quality than local pollution under adverse meteorological conditions and is in agreement with other similar studies over Delhi.     

Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites

The first normal stress difference (N₁) behavior of polymer nanocomposites and liquid crystalline polymer (LCP) composites is a measure of elasticity and is affected by shear stress as a result of morphological alterations at the molecular and nanostructure levels. In this study, the steady shear rheological behaviors of polylactide (PLA) and nanographite platelet (NGP) bionanocomposites containing 1, 2, 3, and 5 wt% nanofiller were investigated. The shear rheological properties of glass fiber‐filled LCPs (filler aspect ratio > 100) were also examined. One of the objectives of this study was to obtain a correlation between N₁, filler contents, and shear stress/rate of the measurements. The results suggest that N₁ in PLA/NGP bionanocomposites is dependent on the level of filler loading as well as the shear rate beyond a critical value. For the LCP systems, N₁ is positive for the unfilled and negative for the glass fiber‐filled LCPs, respectively. A novel rectangular hyperbola model was successfully developed and utilized to fit the N₁ data of the neat PLA and PLA/NGP composites as well as the unfilled LCPs. The anomalous N₁ behavior of PLA/NGP and LCP composites was also thoroughly discussed in this study. POLYM. ENG. SCI., 54:1300–1312, 2014. © 2013 Society of Plastics Engineers     

An investigation of melt rheology and thermal stability of poly(lactic acid)/ poly(butylene succinate) nanocomposites

A systematic investigation of the rheological and thermal properties of nanocomposites prepared with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and organically modified layered silicate was carried out. PLA/PBS/Cloisite 30BX (organically modified MMT) clay nanocomposites were prepared by using simple melt extrusion process. Composition of PLA and PBS polymers were fixed at a ratio of 80 to 20 by wt % for all the nanocomposites. Rheological investigations showed that high clay (> 3 wt %) contents strongly improved the viscoelastic behavior of the nanocomposites. Percolation threshold region was attained between 3 and 5 wt % of clay loadings. With the addition of clay content for these nanocomposites, liquid‐like behavior of PLA/PBS blend gradually changed to solid‐like behavior as shown by dynamic rheology. Steady shear showed that shear viscosity for the nanocomposites decreased with increasing shear rates, exhibiting shear‐thinning non‐Newtonian behavior. At higher clay concentrations, pseudo‐plastic behavior was dominant, whereas pure blend showed almost Newtonian behavior. Thermogravimetric analysis revealed that both initial degradation temperature (at a 2% weight loss) and activation energy of thermal decomposition nanocomposite containing 3 wt % of C30BX were superior to those of other nanocomposites as well as to those of PLA/PBS blend. Nanocomposite having 1 wt % of C30BX did not achieve expected level of thermal stability due to the thermal instability of the surfactant present in the organoclay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Photo-stability of rhodamine-B/montmorillonite nanopigments in polypropylene matrix

A rhodamine-B based nanopigment was developed as a colorant for polypropylene products. The cationic dye rhodamine-B was intercalated into Na⁺-montmorillonite (Cloisite Na⁺) in an acidic medium. The dye-intercalated montmorillonite was centrifuged, dried and milled to prepare the nanopigment particles before mixing with polypropylene. X-ray diffraction studies on the intercalates showed an increase in the basal spacing, thus confirming intercalation of the dye molecules within the nanostructures of the interlayer spaces. Thermo-gravimetric investigations suggested improved thermal stability of the intercalated dye. UV-exposure tests on colored polypropylene/nanopigment composites showed a significant improvement in the photo-stability compared to the polypropylene/dye samples.     

Sample size and power calculations based on generalized linear mixed models with correlated binary outcomes

The generalized linear mixed model (GLIMMIX) provides a powerful technique to model correlated outcomes with different types of distributions. The model can now be easily implemented with SAS PROC GLIMMIX in version 9.1. For binary outcomes, linearization methods of penalized quasi-likelihood (PQL) or marginal quasi-likelihood (MQL) provide relatively accurate variance estimates for fixed effects. Using GLIMMIX based on these linearization methods, we derived formulas for power and sample size calculations for longitudinal designs with attrition over time. We found that the power and sample size estimates depend on the within-subject correlation and the size of random effects. In this article, we present tables of minimum sample sizes commonly used to test hypotheses for longitudinal studies. A simulation study was used to compare the results. We also provide a Web link to the SAS macro that we developed to compute power and sample sizes for correlated binary outcomes.     

Synthesis and Characterisation of Branched Poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (PET) were synthesised with a variety of molar masses and with a large range of degree of branching by introduction of mono-, tri-(glycerol) and tetra-functional (pentaerythritol) comonomers to dimethyl terephthalate and ethylene glycol. The monofunctional alcohols, dodecanol and benzyl alcohol, were used as terminating agents to minimise gelation. The effect of various reaction parameters, such as percentage glycerol or pentaerythritol and polymerisation time, on limiting viscosity number [η] and weight average molar mass (M_w) were investigated. The thermal behaviour of branched PET was studied by differential scanning calorimetry; all samples showed a characteristic double endothermic melting peak and the glass transition temperature was not observed. Some branched PETs were subjected to solid-state polymerisation to increase the molar mass of previously prepared branched polymers. The solid-state polymerisation technique showed that the process not only promoted the molar mass but, more importantly, it increased the crystallinity of the polymer. Overall, the solid-state reaction rate was governed by initial molar mass, crystallinity, reaction temperature and time. © of SCI.     

Dynamic rheology of branched poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (BPET) of varying molar mass have been synthesized with glycerol and pentaerythritol as branching comonomers, and their rheological behaviour has been measured. In this study, we describe the use of dynamic and steady shear measurements to examine the influence of the proportion and type of branching comonomers on the melt viscosity of BPET. Steady shear rheology has been used to measure the shear rate dependence on the apparent viscosity. Dynamic (oscillatory) measurements have been used to obtain the complex viscosity η* (ω) and the storage modulus G′ (ω) as a function of frequency. G′ (ω) represents the elastic component of the viscoelastic melt; this variable was measured as a function of frequency at various temperatures in the linear viscoelastic domain. Linear poly(ethylene terephthalate) (LPET) exhibited nearly Newtonian behaviour, while BPET became shear thinning at relatively low shear rates. The viscosity and elasticity increased with increase in molar mass and specific branching composition. This was attributed to increasing chain entanglements at higher molar mass and to increasing branching of the BPET. At higher shear rates or frequencies, the BPET show much greater shear thinning character than LPET and this is more pronounced with higher branching proportions. © 2000 Society of Chemical Industry