Effect of blend composition in BisEH-PFDTBT:PC70BM solar cells

The photovoltaic properties of bulk-heterojunction solar cells with an active layer made of an alternating fluorene copolymer, poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-2′-thienyl-2,1,3-benzothiadiazole)]}, and [6,6]-phenyl-C₇₁-butyric acid methylester are investigated by varying the blend composition and the incident light power intensity. An efficient donor-acceptor intermixing is reached with donor to acceptor weight ratios of at least 1:3, while at lower acceptor content charge trapping effects are evidenced by the light intensity dependent study. Reverse bias analysis demonstrates that a major limiting factor for the performance of the investigated solar cells is represented by the poor ability of the generation of free charge carriers, attributed to the low hole mobility in the polymer phase.     

Bridge Deck Patching Material Evaluation

Deck patching is a common practice used when bridge decks have local deterioration but do not yet warrant full replacement. Rapid setting patch materials provide a quick and economical way to patch deteriorated areas without significant lane closure time. While these materials set quickly and often achieve high early strength, their long-term performance in corrosive environments and under heavy traffic loads is sometimes poor. In addition, little guidance is provided in terms of standardized testing for these materials that addresses the key properties needed for long-term service life. This paper details a testing program that evaluates a number of deck patch materials and the development of a testing protocol for material evaluation.     

Early and late selection in unconscious information processing.

In four experiments, we investigated whether masked stimuli in priming experiments are subjected to early or to late selection. In Experiment 1, participants classified four target-pictures as being small or large. In line with early selection accounts, prime-pictures with a different perceptual appearance as the experienced targets did not elicit congruency effect. In Experiment 2, 40 targets all depicting animals were presented. Results were in line with late selections assumptions because novel animal primes but not novel primes from different semantic categories yielded congruency effects. In Experiment 3, the targets were chosen such that there is a second semantic feature that covaried with the required response. Here, novel primes picturing small animals did not influence target responses with regard to the instructed size classification, but with regard to their affiliation to the category animal. In Experiment 4, small and large pictures from two categories were presented. Category match did not influence priming, ruling out that feature overlap contaminated the former results. The results indicate that participants’ prestimulus expectations determine in which stage in the processing-stream masked stimuli are selected. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbon nanotubes/polydimethylsiloxanes systems for thermal management of miniaturized electronic components

The thermal performances of nanocomposite layers formed by Single-walled Carbon Nanotubes (SWCNT) dispersed in 2 different kind of polydimethyl-siloxane (PDMSO) matrices has been investigated by measuring the thermal resistance under conditions similar to the ones used for thermal management in microelectronics. A series of nanocomposite samples with thickness in the range 25 microm(-1) cm have been tested. The nanocomposites were prepared varying the amounts of nanotubes embedded in the matrix (from 0.1 to 5%w). In some cases also microsized graphites were mixed to the nanotube's fillers. For 25 micron thick layers, the thermal resistance of the neat silicone specimen can be reduced of 54% with the addition of 2%w carbon nanotubes. The variation of thermal conductivity as a function of the SWCNT's loading is reported and discussed. Furthermore the dispersion's effects of the nanotubes in the layers and the effects on the realization of a net-like system have been investigated.     

Carbon nanotube-based nanocarriers: the importance of keeping it clean

Nanotechnology-introduced materials have promising applications as nanocarriers for drugs, peptides, proteins and nucleic acids. Several studies showed that the geometry (shape and size) and chemical properties of nanoparticles affect the kinetics and pathways of cellular uptake and their intracellular trafficking and signaling. Accurate physico-chemical characterization of nanoparticles customarily precedes their use in cell biology and in vivo experiments. However, a fact that is easily overlooked is that nanomaterials decorated with organic matter or resuspended in aqueous buffers can be theoretically contaminated by fungal and bacterial microorganisms. While investigating the effects of extensively characterized PEGylated carbon nanotubes (PNTs) on T lymphocyte activation, we demonstrated bacterial contamination of PNTs, which correlated with low reproducibility and artifacts in cell signaling assays. Contamination and artifacts were easily eliminated by preparing the materials in sterile conditions. We propose that simple sterile preparation procedures should be adopted and sterility evaluation of nanoparticles should be customarily performed, prior to assessing nanoparticle intracellular internalization, trafficking and their effects on cells and entire organisms.     

Microstructure and mechanical properties of co-continuous metal/ceramic composites obtained from Reactive Metal Penetration of commercial aluminium alloys into cordierite

Co-continuous metal/ceramic composites were obtained by the Reactive Metal Penetration (RMP) method. With the aim of components cost reduction, commercial cordierite preforms and standard aluminium infiltrating alloys (1050, 2011 and 7075) were used in the process. Kinetics of the infiltration reaction, microstructure and mechanical properties of the composites were found to be influenced by both quantity and type of alloying elements. In particular, while Young’s modulus remains quite constant, a marked increase in microhardness is observed with 2011 and 7075 alloys, even if to the detriment of flexural strength.     

A multifractal analysis of fatigue crack growth and its application to concrete

As is well-known, strength of materials is influenced by the specimen or structure size. In particular, several experimental campaigns have shown a decrease of the material strength under static or fatigue loading with increasing structure size, and some theoretical arguments have been proposed to interpret such a phenomenon. As far as fatigue crack growth is concerned, limited information on size effect is available in the literature, particularly for so-called quasi-brittle materials like concrete. In the present paper, by exploiting concepts of fractal geometry, some definitions of fracture energy and stress intensity factor based on physical dimensions different from the classical ones are discussed. A multifractal size-dependent fatigue crack growth law (expressing crack growth rate against stress intensity factor range) is proposed and used to interpret relevant experimental data related to concrete.     

PPy doped PEG conducting polymer films synthesized on LiFePO4 particles

In this work, polyethyleneglycole (PEG) is introduced into polypyrrole (PPy) film coated on LiFePO₄ powder particles to promote the properties of cathode material for lithium-ion batteries. The enhancement of the electrochemical activity by the substitution of a carbon with electrochemically active polymer is investigated. Films of the PPy doped with the PEG were prepared by the chemical oxidative polymerization of pyrrole (Py) monomer. PEG has been added as an additive during polymerization process to improve mechanical and structural properties of the PPy in final PPy/PEG-LiFePO₄ cathode material. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge measurements were employed to characterize the electrochemical properties of PPy/PEG-LiFePO₄ material. The electrochemical performance of PPy-LiFePO₄ electrodes was greatly improved by introduction of PEG into the PPy films. Charge/discharge measurements confirmed the increase in capacity when applying PEG in PPy. The morphology and particle sizes of the prepared cathode powder material were investigated by scanning electron microscopy (SEM) and particle size analysis (PSA). Distribution of PPy and PPy/PEG films onto the LiFePO₄ particles surface was studied by time of flight secondary ion mass spectrometry (TOF-SIMS). In addition to polymeric coating layer on the surface of PPy-LiFePO₄ composite particles, some PPy unequally distributed between the particles was found. The median diameter value is 4.92 μm for PPy-LiFePO₄ sample. TOF-SIMS measurements and SEM images confirmed that thickness of polypyrrole coating on LiFePO₄ particles is about 100 nm.     

Sodium borohydride as an additive to enhance the performance of direct ethanol fuel cells

The effect of adding small quantities (0.1-1 wt.%) of sodium borohydride (NaBH₄) to the anolyte solution of direct ethanol fuel cells (DEFCs) with membrane-electrode assemblies constituted by nanosized Pd/C anode, Fe-Co cathode and anion-exchange membrane (Tokuyama A006) was investigated by means of various techniques. These include cyclic voltammetry, in situ FTIR spectroelectrochemistry, a study of the performance of monoplanar fuel cells and an analysis of the ethanol oxidation products. A comparison with fuel cells fed with aqueous solutions of ethanol proved unambiguously the existence of a promoting effect of NaBH₄ on the ethanol oxidation. Indeed, the potentiodynamic curves of the ethanol-NaBH₄ mixtures showed higher power and current densities, accompanied by a remarkable increase in the fuel consumption at comparable working time of the cell. A ¹³C and ¹¹B {¹H}NMR analysis of the cell exhausts and an in situ FTIR spectroelectrochemical study showed that ethanol is converted selectively to acetate while the oxidation product of NaBH₄ is sodium metaborate (NaBO₂). The enhancement of the overall cell performance has been explained in terms of the ability of NaBH₄ to reduce the PdO layer on the catalyst surface.     

Measurement method and results of ice adhesion force on the curved surface of a wind turbine blade

Experimental adhesion force measurements were conducted on accumulated ice on the leading edge of a scaled wind turbine blade in both glaze and rime icing regimes. An apparatus was first designed for specifically measuring the adhesion force of ice on a curved surface at climatic temperature where a vertical force was applied to the mounted structure in the test apparatus. Adhesion force measurements were measured and adhesion pressure calculated for plain and ice-mitigated test specimens. Results are presented for the increase in force of ice adhesion over a curved surface area in proportion to degree centigrade decrease in temperature.