The propagation of pressure in a gelled waxy oil pipeline as studied by particle imaging velocimetry

Paraffinic crude oils in pipelines may form waxy gels during flow shutdowns. These gels can be dislodged by applying pressure if the wall shear stress, proportional to the local pressure gradient, exceeds the gel yield stress. The simplest models assume that the axial pressure profile becomes linear immediately after a jump in upstream pressure, but this fails to account for gel time‐dependent rheology or the effect of gel voids on pressure wave propagation. To investigate the former factor, pressure profile and particle imaging velocimetry (PIV) measurements were performed on a model oil gelled under pressure to reduce void formation. After a jump in upstream pressure to a value insufficient to restart flow, the axial pressure profile becomes linear in a two‐step process, with an immediate small rise in downstream pressure followed by a time‐delayed jump. The local downstream gel deformation measured by PIV exhibits similar two‐step time dependence. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

“Tropicalisation” of Feed-in Tariffs: A custom-made support scheme for hybrid PV/diesel systems in isolated regions

The interest and actions towards introducing renewables for off-grid regions has increased due to their ostensible cost-effectiveness, eco-friendliness and quality services provided. Nevertheless, in many isolated areas diesel generators appear as a common option, confirming that there is a need for financial support mechanisms that aid the introduction of renewables due to their higher initial investment costs.This paper proposes a so-called ‘tropicalisation’ of the Feed-in Tariff scheme to promote the introduction of hybrid systems in isolated communities based on the idea of awarding for each kWh produced by renewable energies a premium value during a guaranteed period of time. The proposed Renewable Energy Premium Tariff (RPT) scheme is an alternative mechanism to the usual initial investment donation for off-grid energy development projects by recognising the production of renewable electricity and opting for a long-term sustainability of the projects. Ecuador presents ideal conditions to study the introduction of such a ‘tropicalised’ scheme since a Feed-in Law including off-grid projects was established in 2002 and since there are governmental and local efforts for the introduction of renewable hybrids in isolated regions.Modelling of the introduction of photovoltaics (PVs) into diesel systems for several mini-grids located in isolated regions of Ecuador has been performed, and included a detailed financial analysis for optimisation of RPT values and a comparison with existing stand-alone diesel systems. The results show the cost-effectiveness of PV/diesel hybrids over diesel gensets, taking into account present and future diesel prices. To obtain long-term sustainability of the project, the RPT values are set at 0.70–1.20$ kWh covering the operability of the whole system for 20 years, where the renewable fraction should have the largest share in the hybrid system. The proposed mechanism is expected to aid the introduction of renewable technologies to bring solutions and sustainable energy options to final users of off-grid isolated regions.     

Specificity studies of bacillus 1,3-1,4-beta-glucanases and application to glycosynthase-catalyzed transglycosylation

Bacillus 1,3-1,4-beta-glucanases hydrolyze 1,3-1,4-beta-gluco-oligosaccharides with a retaining mechanism. The binding-site cleft of these endoglycosidases is composed of six subsites (-4 to +2) of which subsite -3 makes the largest contribution to transition state stabilization. The specificity of this subsite is here analyzed for both glycosidase and glycosynthase activities in the wild-type and the nucleophile-less E134A mutant Bacillus licheniformis enzymes. A D-galactosyl residue on the nonreducing end of a trisaccharide substrate is accepted by the enzyme and binds at subsite -3 in the productive enzyme-substrate complex. The wild-type enzyme catalyzes the hydrolysis of the substrate Glcbeta4Glcbeta3GlcbetaMU (Glc=glucosyl, MU=4-methylumbelliferyl) with a k(cat)/K(M) value only 1.3-fold higher than for the Galbeta4Glcbeta3GlcbetaMU (Gal=galactosyl) substrate. The corresponding alpha-fluorides act as good donors for the glycosynthase condensation reaction with mono- and disaccharide acceptors catalyzed by the E134A mutant. Whereas self-condensation and elongation products are also obtained as minor compounds with the Glcbeta4Glcbeta3GlcalphaF donor, nearly quantitative yields of single condensation products are obtained with the Galbeta4Glcbeta3GlcalphaF donor, in which the axial configuration of the 4-OH group on the nonreducing end prevents self-condensation and elongation reactions.     

Channel access and interference issues in multi-code DS-CDMA wireless packet (ATM) networks

Multi-Code Direct-Sequence Code-Division-Multiple-Access (MC-CDMA) has been proposed as a flexible multiple access scheme for wireless packet networks that support a large variety of mobiles with different and even time-varying rates. Using MC-CDMA, traffic streams with significantly different transmission rates can be easily integrated into a unified architecture, with all the transmissions occupying the same bandwidth and having the same spread spectrum processing gain. In this paper, we address medium-access and interference issues in MC-CDMA wireless packet networks. For medium access, we propose and study Multi-Code CDMA (MC-CDMA) with Distributed-Queueing Request Update Multiple Access (DQRUMA) to form a unified bandwidth-on-demand fair-sharing platform for multi-rate wireless services. DQRUMA is an efficient demand-assignment multiple access protocol for wireless access and scheduling. Pseudo-Noise (PN) codes (primary codes) and optimal power levels are allocated to the mobiles on a slot-by-slot basis, and a Maximum Capacity Power Allocation (MCPA) criterion exploits the sub-code concatenation property of the MC-CDMA transmission. Simulation results show that the system provides close to ideal-access performance for multi-rate mobiles, both with homogeneous traffic characteristics and with a mix of heterogeneous traffic characteristics. Finally, we analyze the effects of MC-CDMA intercell interference on the reverse link (i.e., mobile to cell site) and investigate interference reduction by using the Maximum Capacity Power Allocation (MCPA) criterion. Our results show significant reduction in reverse-link MC-CDMA intercell interference is possible using the MCPA criterion.     

Longitudinal evidence that psychopathy scores in early adolescence predict adult psychopathy.

This study examined the relation between psychopathy assessed at age 13 by using the mother-reported Childhood Psychopathy Scale (D. R. Lynam, 1997) and psychopathy assessed at age 24 by using the interviewer-rated Psychopathy Checklist: Screening Version (PCL:SV; S. D. Hart, D. N. Cox, & R. D. Hare, 1995). Data from over 250 participants of the middle sample of the Pittsburgh Youth Study were used to examine this relation; approximately 9% of the sample met criteria for a possible PCL:SV diagnosis. Despite the long time lag, different sources, and different methods, psychopathy from early adolescence into young adulthood was moderately stable (r=.31). The relation was present for the PCL:SV total and facet scores, was not moderated by initial risk status or initial psychopathy level, and held even after controlling for other age 13 variables. Diagnostic stability was somewhat lower. Both specificity and negative predictive power were good, and sensitivity was adequate, but positive predictive power was poor. This constitutes the first demonstration of the relative stability of psychopathy from adolescence into adulthood and provides evidence for the incremental utility of the adolescent psychopathy construct. Implications and future directions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of very long aging on the relaxation behavior of flame‐retardant printed circuit board epoxy composites under mechatronic conditions

Very long aging times, up to 15,100 h (629 days) at 110°C, were achieved on flame‐retardant printed circuit board laminates commonly used in automotive design. This composite was fabricated from glass fibers embedded in an epoxy resin. Aging was performed in an oven under an air atmosphere at a temperature lower than the glass‐transition temperature. Temperature‐modulated differential scanning calorimetric analysis was used to investigate the influence of such aging on the glass‐transition phenomena. A new amorphous phase appeared during aging. By extending the analysis to samples collected at different thicknesses, we demonstrated the existence of a time‐dependent gradient of the properties. A skin–core structure was evidenced, and this slowed down oxidation and allowed physical aging to occur in the bulk sample. An exponential law described the variations of the glass‐transition of the new external compound. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 786‐792, 2013     

Characterization of stabilized porous magnetite core–shell nanogel composites based on crosslinked acrylamide/sodium acrylate copolymers

Stabilized and dispersed superparamagnetic porous nanogels based on sodium acrylate (AA‐Na) and acrylamide (AM) in a surfactant‐free aqueous system were synthesized via solution polymerization at room temperature. The formation of magnetite nanoparticles was confirmed and their properties characterized using Fourier transform infrared spectroscopy. Extensive characterization of the magnetic polymer particles using transmission electron microscopy (TEM), dynamic light scattering and zeta potential measurements revealed that Fe₃O₄ nanoparticles were incorporated into the shells of poly(AM/AA‐Na). The average particle size was 5–8 nm as determined from TEM. AM/AA‐Na nanoparticles with a diameter of about 11 nm were effectively assembled onto the negatively charged surface of the as‐synthesized Fe₃O₄ nanoparticles via electrostatic interaction. Crosslinked magnetite nanocomposites were prepared by in situ development of surface‐modified magnetite nanoparticles in an AM/AA‐Na hydrogel. Scanning electron microscopy was used to study the surface morphology of the prepared composites. The morphology, phase composition and crystallinity of the prepared nanocomposites were characterized. Atomic force microscopy and argon adsorption–desorption measurements of Fe₃O₄.AM/AA indicated that the architecture of the polymer network can be a hollow porous sphere or a solid phase, depending on the AA‐Na content. © 2013 Society of Chemical Industry     

Serious conduct problems in the children of adolescent mothers: Disentangling confounded correlations.

Early motherhood (r?=?.33) with the number of Diagnostic and Statistical Manual of Mental Disorders (DSM-III) symptoms of conduct disorder in a sample of 253 boys (aged 6–13 yrs) who had been referred to outpatient clinics. The following models were compared using path analysis: (1) Teenage motherhood, parental antisocial personality, and socioeconomic status (SES) each contribute uniquely to the prediction of childhood conduct problems; (2) teenage motherhood mediates the association of SES and parental antisocial personality with child conduct problems; and (3) teenage motherhood is spuriously related with child conduct problems because of common associations with SES and parental antisocial personality. Model (3) best fit the data. Similar results were obtained whether maternal age at the birth of the firstborn child or the proband child was used to define maternal age and when teenage motherhood was defined as giving birth at