Corrosion behaviour of steel in mortar with wood biomass ash

The present study investigates the influence of partial cement substitution with biomass ash on the corrosion behaviour of steel embedded in the mortar. To evaluate this influence, corrosion parameters of steel in mortar exposed to tap water and 3.5 wt% NaCl solution were monitored over a period of 50 days. The electrochemical cell consisted of a steel plate as a working electrode, covered with a layer of mortar that was exposed to the testing solution. Open-circuit potential and linear polarisation were used to monitor changes in corrosion behaviour, whereas electrical impedance spectroscopy was used to evaluate the conductivity of the matrix. Additional to corrosion parameters, the chloride migration coefficient was tested after 28 days. On the basis of the results, it was observed that mortars with biomass ash provide equal or better protection for embedded steel, compared with the reference mortar. Mortars that performed slightly better than the reference mortar and other mortars were prepared with ashes with a higher amount of pozzolanic oxides.     

The structure of adolescent peer networks.

Structural aspects of school-based peer networks of adolescents in 6th to 12th grade were mapped in 3 school systems. Female students were more connected to the peer network than were male students, and peer networks became more exclusive with increasing grade. The results also suggest that numeric minorities usually are less connected to school peer networks than the majority group. There was mixed evidence for hierarchical organization of the peer network. Best friends were highly embedded in friendship groups, but neither friendship group nor best friendship was highly embedded in social crowd. Adolescents name friends who are not in their friendship group and usually do not name everyone in the friendship group as a friend. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hybrid solar cells using PbS nanoparticles

Solution-processed bilayer heterojunction hybrid solar cells have been fabricated using size-quantized PbS nanoparticles and poly (3-hexylthiophene) (P3HT). PbS was used as an electron-transporting layer whereas P3HT was used for hole transport. A photovoltaic device consisting of PbS and P3HT exhibited 3% incident photon to current efficiencies (IPCE) under 550-nm monochromatic irradiation.     

Capacity limits of spectrum‐sharing systems over hyper‐fading channels

Cognitive radio (CR) with spectrum‐sharing feature is a promising technique to address the spectrum under‐utilization problem in dynamically changing environments. In this paper, the achievable capacity gain of spectrum‐sharing systems over dynamic fading environments is studied. To perform a general analysis, a theoretical fading model called hyper‐fading model that is suitable to the dynamic nature of CR channel is proposed. Closed‐form expressions of probability density function (PDF) and cumulative density function (CDF) of the signal‐to‐noise ratio (SNR) for secondary users (SUs) in spectrum‐sharing systems are derived. In addition, the capacity gains achievable with spectrum‐sharing systems in high and low power regions are obtained. The effects of different fading figures, average fading powers, interference temperatures, peak powers of secondary transmitters, and numbers of SUs on the achievable capacity are investigated. The analytical and simulation results show that the fading figure of the channel between SUs and primary base‐station (PBS), which describes the diversity of the channel, does not contribute significantly to the system performance gain. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficiency of non-linear lens distortion models in biomechanical analysis of human movement

Accurate camera calibration is required in applications, which involve quantitative measurements such as biomechanical analysis of the human movement. Some information concerning the measuring of human movement can be obtained by using uncalibrated cameras, however lens calibration is necessary when metric information is needed. When large field of view is required, wide-angle lenses are useful but they show significant non-linear distortion in the image. The aim of this study was to compare the accuracy of distortion models, which are used in biomechanical analysis of the human movement. A new calibration pattern was designed and the image of the calibration pattern was captured by using a wide-angle lens. The distorted image of the pattern was automatically processed to determine the dot centroids in the image. Lens distortion was modelled accounting for three sources of distortion: radial, decentring and thin prism distortions. These three effects result in seven distortion coefficients (k₁, k₂, k₃, p₁, p₂, s₁, and s₂) in vertical and horizontal directions. Marzan and Karara (1975) [9] suggested 12, 14 and 16 parameters along with the Direct Linear Transformations (DLT) methods that comprise radial and decentring distortion models. In this study thin prism distortion [6] was also included to observe its effect. These non-linear distortion functions were minimised by using three different numerical methods, which were Least Squares, Levenberg–Marquard (LM) and Gauss–Newton (GM). In conclusion, the lens distortion models typically improved the accuracy. Applying the Non-linear Least Squares Optimisation Method (LM) showed the highest accuracy among the distortion models. While the average and the maximum error in the distorted image were 3.394% and 10.994%, respectively, they decreased to 1.591% and 3.524% in the application of DLT 18 method.     

Highly efficient orange–red electroluminescence from a single layer MEH-PPV-POSS:CdS0.75Se0.25 hybrid PLED

In this study, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] end capped with polyhedral oligomeric silsesquioxanes (MEH-PPV-POSS): cadmium sulfide selenide quantum dots (CdS_0.75Se_0.25 QDs) nanocomposites based OLEDs were fabricated. By the addition of CdS_0.75Se_0.25 QDs into the polymer active layer, a considerable enhancement was observed in terms of hole and electron injection in devices. Additionally, the presence of QDs reduced the interchain interaction of polymer that resulted in narrower electroluminescence (EL) spectrum. The device structure of ITO/PEDOT: PSS/MEH-PPV-POSS: 25 wt% CdS_0.75Se_0.25/Ca (40 nm)/Al demonstrated the best performance with a brightness of 8672 cd/m² at 10 V, current efficiency of 2.5 cd/A at 8 V, and an EQE of 0.55% at 150 mA/cm².