Modeling the delamination process during shear premixing of nanoclay/thermoset polymer nanocomposites

As shear premixing is an important process for the dispersion of nanoclays in polymeric resins, this article studies the effect of temperature, duration, speed of premixing, and also the interlamellar spacing of clay platelets on the dispersion of organoclay in epoxy by using a high speed premixing technique which can generate high shear. The quality of dispersion and intercalation/exfoliation of organoclay in epoxy after premixing (before adding hardener) was analyzed by means of X‐ray diffraction (XRD) and rheological measurement. The dispersion and intercalation/exfoliation of organoclay in the epoxy nanocomposites (ENCs) after curing were characterized by TEM. The results illustrate that the intercalation/exfoliation of organoclay in epoxy at the premixing step is very much depending on the premixing parameters. This article also presents a model which takes into account the parameters such as the interlamellar spacing of clay platelets, the viscosity of the epoxy‐clay mixtures, and the velocity of the mixer to explain their effect on the dispersion of clay in epoxy resin. The study focuses on the flow of epoxy clay in the high shear mixer to describe a model for predicting the processing conditions necessary for achieving delamination of the clay layers. Experimental results on the dispersion of clay are also provided to validate the model. The model provides a guide for the premixing parameters necessary to separate the clay layers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Foliage Chemistry Influences Tree Choice and Landscape Use of a Gliding Marsupial Folivore

The chemical quality of forage may determine landscape use and habitat quality for some herbivorous species. However, studies that investigate the relationship between foliar chemistry and foraging choices in wild vertebrates are rare. Petauroides volans (the greater glider) is unique among Australian marsupial folivores because it glides. It also frequently consumes foliage from both major Eucalyptus subgenera, Eucalyptus (common name “monocalypt”) and Symphyomyrtus (common name “symphyomyrtle”), which differ markedly in their foliar chemistry. Such differences are thought to be a product of co-evolution that also led to guild-specific plant secondary metabolite (PSM) specialization among other marsupial eucalypt folivores. To explore whether foliar chemistry influences tree use, we analyzed foliage from eucalypt trees in which we observed P. volans during a radio tracking study and from eucalypt trees in which animals were never observed. We used a combination of chemical assays and near infrared spectrophotometry (NIRS) to determine concentrations of nitrogen (N), in vitro available nitrogen (AvailN), and in vitro digestible dry matter (DDM) from foliage sampled from the monocalypt and symphyomyrtle species, and total formylated phloroglucinol compounds (FPCs) and sideroxylonals (a class of FPCs) from the symphyomyrtle species (FPCs do not occur in monocalypts). Tree size and spatially-dependent, intraspecific variations in sideroxylonals and DDM concentrations in the symphyomyrtle foliage and of N, AvailN, and DDM in the monocalypt species were important indicators of tree use and habitat suitability for P. volans. The results i) demonstrate that guild-specific PSMs do not always lead to guild-specific foraging; ii) provide a compelling co-evolutionary case for the development of gliding in P. volans; and iii) have implications for the management and conservation of this and other folivorous species.     

Complexity-reduced Volterra series model for power amplifier digital predistortion

This paper expounds a complexity-reduced Volterra series model for radio frequency power amplifier (PA) behavioral modeling and digital predistortion (DPD). An analysis was conducted, which took into account the memory effect mechanisms of the PA. This led to a closed-form expression that relates the memoryless behavior of the PA to the finite impulse response feedback filter, which approximates the memory effects’ behavior. The analysis resulted in a complexity-reduced Volterra series model which allows for a substantial reduction in the requirements for digital signal processors and the time needed to construct and implement the DPD in a real-time environment. The proposed model was validated as a behavioral model and a DPD using two different PA architectures, employing two different transistor technologies, driven by both 20 MHz 1001 wideband code division multiple access and long term evolution signals. The results obtained demonstrate the excellent modeling and linearization capability of the complexity-reduced Volterra series model.     

An electronoptical study of the conversion coating formed on aluminium in a chromate/fluoride solution

The development of conversion coatings during the immersion of ‘bare’ aluminium, and aluminium covered by a barrier-type anodic film in a chromate/fluoride solution has been studied by transmission electron microscopy of stripped films and ultramicrotomed sections. The conversion coating produced on aluminium is always relatively uniform in thickness and grows at a rate that decreases rapidly with time. Fine randomly sited pathways through the coating apparently have an important role during film growth. During immersion of the barrier film non-uniform dissolution exposes the substrate metal and at sites where the metal is bared conversion coating formation occurs. Consequently, metal reaction and rapid conversion coating growth occur at these sites before all the adjacent barrier film is dissolved. This leads to a roughening of the surface.     

A study of the effects of inhibitive and aggressive ions on oxide-coated aluminium using secondary ion mass spectrometry

A Cameca Ion Analyser has been used to examine aluminium surfaces, supporting barrier-type anodic films ca. 720Å thick, after natural immersion for 1–25 h in 1M chloride and chromate/dichromate solutions of varying pH, and neutral 1M phosphate solution. In chloride solutions, chloride is present on the film surface, but not within the film material per se, within the limits of measurement. The degree of film thinning is governed by pH, being more pronounced in alkaline than acid solutions. In chromate/dichromate solutions, chromium uptake occurs by two distinct mechanisms. The first is associated with relatively rapid chromate/dichromate reduction to Cr₂O₃, probably hydrated, within flaws in the anodic film. The second is associated with a more gradual direct chromate/dichromate anion entry into the bulk material probably through the intercrystalline regions in the film, ultimately resulting in film thinning, even in neutral solutions. In phosphate solutions, phosphate anions penetrate and thin bulk anodic alumina in a similar manner to chromate/dichromate anions. The results are interpreted on the basis of the differing surface chemical properties of the various anions in relation to bulk alumina.     

Visual working memory for observed actions.

Human society depends on the ability to remember the actions of other individuals, which is information that must be stored in a temporary buffer to guide behavior after actions have been observed. To date, however, the storage capacity, contents, and architecture of working memory for observed actions are unknown. In this article, the author shows that it is possible to retain information about only 2-3 actions in visual working memory at once. However, it is also possible to retain 9 properties distributed across 3 actions almost as well as 3 properties distributed across 3 actions, showing that working memory stores integrated action representations rather than individual properties. Finally, the author shows that working memory for observed actions is independent from working memory for object and spatial information. These results provide evidence for a previously undocumented system in working memory for storing information about actions. Further, this system operates by the same storage principles as visual working memory for object information. Thus, working memory consists of a series of distinct yet computationally similar mechanisms for retaining different types of visual information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intrusion within a Simulated Water Distribution System due to Hydraulic Transients. I: Description of Test Rig and Chemical Tracer Method

A pilot-scale test rig was designed and constructed to simulate intrusion behavior associated with hydraulic transients initiated by sudden events such as rapid valve closure or uncontrolled change in on/off pump status (“pump trip”) in a water distribution system. After establishing steady state flow conditions, intrusion volumes were determined for 3.2 (1/8-in.) and 6.4 mm (1/4-in.) diam orifices overlaid with a column of water that provided 91 mm (3 ft) of external head. Average intrusion volumes associated with hydraulic transient events were determined by mass balance calculations using cesium as the tracer chemical. Average intrusion volumes were 11.4 and 71.2 mL for the two diameters, respectively. Given similar conditions in a water distribution system (i.e., an available pathway and favorable pressures), pathogens in the soil and water surrounding a water main potentially can intrude into the pipe during short-term pressure transient events.     

The management of infective gastroenteritis in adults. A consensus statement by an expert panel convened by the British Society for the Study of Infection

Rts1 is a large naturally occurring plasmid which has a kanamycin resistance gene and exhibits various temperature-sensitive phenotypes. A smaller derivative of plasmid, pOK, contains the Rts1 replicon and the kanamycin resistance gene of Rts1. This plasmid, pOK, is much more unstable than Rts1 at 42.5 degrees C. A DNA fragment, G3, 1590 nucleotides long from Rts1 DNA, stabilized pOK completely at 42.5 degrees C but only in the cis configuration. G3 did not change the copy number of pOK. The pOK derivative containing G3 was destabilized by the presence of a compatible plasmid containing G3. G3 has four inverted repeats, two 14-base direct repeats, and three ORFs. Smaller fragment of G3 also had a stabilization effect and these studies showed that the ORF does not play any role in stabilization.     

Causal attributions, sanctions, and normal mood variations.

Three experiments with a total of 288 undergraduates tested the causal-locus hypothesis (CLH), which asserts that persons making internal attributions for failure and external attributions for success experience more negative postoutcome moods than persons making the opposite attributions. Although outcomes consistently affected moods and attributions, attributions did not affect moods. Significant correlations consistent with the CLH were infrequently obtained. Another theory, the sanctioned-object hypothesis (SOH), was proposed for understanding how causal attributions lead to mood changes. The SOH asserts that the application of positive or negative sanctions to objects in the perceptual field is a central determinant of mood and that attributions affect mood when their content and salience activate sanctioning processes. Exp IV, with 96 undergraduates, evaluated the competing theories. Results support the SOH but not the CLH. Implications for understanding mood variations and the effects of moods on attributions and methodological alternatives are discussed. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)