Modelling mechanical percolation in graphene-reinforced elastomer nanocomposites

Graphene is considered an ideal filler for the production of multifunctional nanocomposites; as a result, considerable efforts have been focused on the evaluation and modeling of its reinforcement characteristics. In this work, we modelled successfully the mechanical percolation phenomenon, observed on a thermoplastic elastomer (TPE) reinforced by graphene nanoplatelets (GNPs), by designing a new set of equations for filler contents below and above the percolation threshold volume fraction (Vp). The proposed micromechanical model is based on a combination of the well-established shear-lag theory and the rule-of-mixtures and was introduced to analyse the different stages and mechanisms of mechanical reinforcement. It was found that when the GNPs content is below Vp, reinforcement originates from the inherent ability of individual GNPs flakes to transfer stress efficiently. Furthermore, at higher filler contents and above Vp, the nanocomposite materials displayed accelerated stiffening due to the reduction of the distance between adjacent flakes. The model derived herein, was consistent with the experimental data and the reasons why the superlative properties of graphene cannot be fully utilized in this type of composites, were discussed in depth.Comment: 29 pages, 12 figure

Prairie Crop Diversification

The Canadian prairies traditionally have been dominated by spring wheat production. Crop diversification is now being advocated to enhance farm-level risk management, ecological benefits, nutrient cycling, and pest and disease control, and to reduce the farm economy’s reliance on income from a single crop. There has always been interest in diversifying away from wheat, but until recently, economically feasible alternatives have been limited, and government policies may have constrained the shift to other crops. Knowing the impact of prices and policies on crop diversification is essential to understanding producer response and to determining strategies to enhance cropping diversity.Marketing,

Planning and assessing to improve campus--community engagement

Two methods for assessing the scholarship of engagement at the institutional level are presented: (a) the Comprehensive Assessment of the Scholarship of Engagement (CASE), a systematic method that compiles information about service learning and community engagement, identifies campus strengths, and prioritizes planning areas, and (b) an institutional portfolio that provides a rich data base of descriptive and evaluative information

Improved fidelity of triggered entangled photons from single quantum dots

We demonstrate the on-demand emission of polarisation-entangled photon pairs from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs planar microcavity. Improvements in the sample design blue shifts the wetting layer to reduce the contribution of background light in the measurements. Results presented show that >70% of the detected photon pairs are entangled. The high fidelity of the (|HxxHx>+|VxxVx>)/2^0.5 state that we determine is sufficient to satisfy numerous tests for entanglement. The improved quality of entanglement represents a significant step towards the realisation of a practical quantum dot source compatible with applications in quantum information.Comment: 9 pages. Paper is available free of charge at http://www.iop.org/EJ/abstract/1367-2630/8/2/029/, see also 'A semiconductor source of triggered entangled photon pairs', R. M. Stevenson et al., Nature 439, 179 (2006

Occurrence of steroid sex hormones in the Cache la Poudre River: and pathways for the removal in the environment

November 2009.Includes bibliographical references.Some chemicals have the apparent ability to disrupt normal endocrine system functions after exposure to concentrations so small that they are difficult to detect in the environment. In recent years, these so-called "endocrine disruptors" have become the subject of intensive scientific research. In wildlife, most of the evidence for endocrine disruption has come from studies on species living in, or closely associated with, aquatic environments. Reported effects of endocrine disruption include abnormal blood hormone levels, masculinization of females, feminization of males, altered sex ratios, intersexuality, and reduced fertility and fecundity. Among suspected endocrine disruptors, exogenous steroid sex hormones generally have the highest potencies for disrupting normal steroid sex hormone functions. In a national reconnaissance study conducted by the U.S. Geological Survey (USGS) from 1999 to 2000, steroid sex hormones were detected at varying concentrations and frequencies in water samples from 139 stream sites located in 30 states. Other studies have detected steroid sex hormones in surface waters throughout the world, including Colorado. Potential sources of steroid sex hormones in the environment include sewage treatment plants, septic systems, animal feeding operations, rangeland grazing, paper mills, aquaculture, and agricultural operations where manure and biosolids are applied as fertilizers. The objectives of this study were to investigate the presence of steroid sex hormones in northern Colorado's Cache la Poudre River, to determine the potential for steroid sex hormone biodegradation and photodegradation under natural conditions, and to characterize the mobility of selected steroid sex hormones in agricultural fields using a rainfall simulator. The study determined that steroid sex hormones are present in the Cache la Poudre River, at concentrations ranging from 0.6 ng L−1 (epitestosterone) to 22.6 ng L−1 (estrone). The study also determined that testosterone, progesterone, and 17β-estradiol can be degraded by manure-borne bacteria, and that testosterone degradation is faster under aerobic conditions and at higher temperatures (i.e., 37°C vs. 22°C), but little affected by changes in pH (from 6 to 7.5) or glucose amendments. In ultraviolet light λ > 340 nm, the study observed direct photodegradation of testosterone and progesterone, and indirect photodegradation of testosterone and 17β-estradiol in the presence of Elliot soil humic acid. On the other hand, in ultraviolet light λ > 310 nm, direct photodegradation of androstenedione was substantially faster than direct photodegradation of testosterone in ultraviolet light λ > 310 nm, and no indirect photodegradation observed. The study detected and identified three testosterone biodegradation products (dehydrotestosterone, androstenedione, and androstadienedione), and detected several products of testosterone and androstenedione photodegradation which appear to retain their steroid structure, and possibly their endocrine disrupting potential. Finally, the study generally observed that androgen runoff concentrations follow runoff rates and decrease after successive rainfall events, while runoff concentrations of other analytes (e.g., estrone) peak after the maximum runoff rate and first rainfall event. Sample and data analysis from the study are continuing, and comprehensive finding and recommendations are expected after the date of this report.Financed in part by the U.S. Department of the Interior, Geological Survey, through the Colorado Water Institute