Modelling of effects of ultrastructural morphology on the hygroelastic properties of wood fibres

Wood fibres constitute the structural framework of e.g. wood, paper, board and composites, where stiffness and dimensional stability are of importance. An analytical modelling approach has been used for prediction of hygroelastic response, and assessment of the stresses in thick-walled cylinder models of wood fibres. A wood fibre was idealised as a multilayered hollow cylinder made of orthotropic material with helical orientation. The hygroelastic response of the layered assembly due to axisymmetric loading and moisture content changes was obtained by solving the corresponding boundary value problem of elasticity. A simple solution scheme based on the state space approach and the transfer matrix method was employed. This was combined with an analytical ultrastructural homogenisation method, used to link hygroelastic properties of constituent wood polymers to properties of each layer. Predicted hygroelastic response captured experimentally measured behaviour. Fibres that were constrained not to twist showed a stiffer response than fibres allowed twisting under uniaxial loading. It was also shown that the ultrastructure, i.e. the microfibril angle, will control the hygroexpansion in the same way as it controls the compliance of the cell wall. Qualitative failure trends comparable with experimental observations could be established with stress analysis and a simple plane-stress failure criterion.     

Achieving traceability in large scale continuous integration and delivery deployment,usage and validation of the eiffel framework

The importance of traceability in software development has long been recognized, not only for reasons of legality and certification, but also to enable the development itself. At the same time, organizations are known to struggle to live up to traceability requirements, and there is an identified lack of studies on traceability practices in the industry, not least in the area of tooling and infrastructure. This paper presents, investigates and discusses Eiffel, an industry developed solution designed to provide real time traceability in continuous integration and delivery. The traceability needs of industry professionals are also investigated through interviews, providing context to that solution. It is then validated through further interviews, a comparison with previous traceability methods and a review of literature. It is found to address the identified traceability needs and found in some cases to reduce traceability data acquisition times from days to minutes, while at the same time alternatives offering comparable functionality are lacking. In this work, traceability is shown not only to be an important concern to engineers, but also regarded as a prerequisite to successful large scale continuous integration and delivery. At the same time, promising developments in technical infrastructure are documented and clear differences in traceability mindset between separate industry projects is revealed.     

Modulation of Viscoelasticity and HIV Transport as a Function of pH in a Reversibly Crosslinked Hydrogel

Materials that respond to physiological stimuli are important in developing advanced biomaterials for modern therapies. The reversibility of covalent crosslinks formed by phenylboronate (PBA) and salicylhydroxamate (SHA) has been exploited to provide a pH‐responsive gel for application to the vaginal tract. Dynamic rheology reveals that the gel frequency‐dependent viscoelastic properties are modulated by pH. At pH 4.8 the viscous component dominates throughout most of the frequency range. As the pH increases, the characteristic relaxation time continues to increase while the G′_Plateau levels off above pH 6. At pH 7.5, the elastic component dominates throughout the frequency sweep and is predominately independent of frequency. Particle tracking assesses the transport of both fluorescently labeled HIV‐1 and 100‐nm latex particles in the PBA–SHA crosslinked gel as a function of pH. At pH 4.8 the ensemble‐averaged mean squared displacement at lag times greater than three seconds reveals that transport of the HIV‐1 and 100‐nm particles becomes significantly impeded by the matrix, exhibiting diffusion coefficients less than 0.0002 µm² s^?1. This pH‐responsive gel thus displays properties that have the potential to significantly reduce the transport of HIV‐1 to susceptible tissues and thus prevent the first stage of male‐to‐female transmission of HIV‐1.     

Occupational burnout, tolerance for stress, and coping among nurses in rehabilitation units.

The relation of problem-solving confidence, perceived tolerance of stressors, and situation-specific coping efforts to occupational burnout was examined among 88 nurses in physical rehabilitation units. Participants completed measures of problem solving and burnout, and were administered a questionnaire that required them to list stressors encountered at work and their ability to tolerate this stressor. Participants were also asked to list their typical ways of coping with this stressor. Consistent with predictions, confidence in one's ability to handle problems and perceived tolerance were significantly predictive of lower burnout scores, regardless of time spent on the job. Of the coping variables, emotion-focused coping was significantly associated with higher burnout scores. Post-hoc analyses of self-reported coping activities indicated that some coping efforts (e.g., taking time off from work, confronting a supervisor) could be construed as symptoms of burnout, according to theoretical conceptualizations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developing control logic using aspect-oriented programming and sequence planning

A fundamental functionality of a Programmable Logic Controller (PLC) is to control and execute a set of operations. But a large part of the program code is more involved in supporting the user with concerns like alarm, HMI, communication, safety and manual control. Code related to these supporting concerns is often tangled with operation execution code, the core concerns, which makes it hard to reuse.This paper describes a method to reuse code and functionality when developing PLC programs and code libraries. The method proposes that core concerns are planned with a software tool called Sequence Planner, and the supporting concerns are integrated into the core concerns with a tool based on aspect-oriented programming.     

Influence of Molecular Weight on the Performance of Organic Solar Cells Based on a Fluorene Derivative

The performance of organic photovoltaic (OPV) bulk‐heterojunction blends comprising a liquid‐crystalline fluorene derivative and a small‐molecular fullerene is found to increase asymptotically with the degree of polymerization of the former. Similar to various thermodynamic transition temperatures as well as the light absorbance of the fluorene moiety, the photocurrent extracted from OPV devices is found to strongly vary with increasing oligomer size up to a number average molecular weight, M_n ≈ 10 kg mol^?1, but is rendered less chain‐length dependent for higher M_n as the fluorene derivative gradually adopts polymeric behavior.     

Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells

We describe a method to fill thin films of nanoporous TiO₂ with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO₂/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.     

Studies on mechanical properties of wood fiber reinforced cross-linked starch composites made from enzymatically degraded allylglycidyl ether-modified starch

In a previous work we introduced a new family of thermoset composites of softwood fiber and allylglycidyl ether modified potato starch (AGE-starch with a degree of substitution of 1.3 and 2.3) prepared by hot pressing. To improve the processability of AGE-starch with a DS = 1.3 (LDS-3) and to increase hygromechanical properties, the LDS-3 matrix has now been partially degraded by α-amylase at 45 °C (pH 6) for 0.5, 6 and 18 h. The study shows that already a 30 min enzymatic hydrolysis has a marked effect on the modified starch molecular weight and its thermal properties. The new composites with enzyme hydrolyzed AGE-starch, generically named D-LDS-3, showed good fiber dispersion and excellent interface between the fiber and matrix as studied by SEM. Premixes of D-LDS-3 matrix and fiber showed improved processability. The water vapor absorption was evaluated at 43.2% and 82.2% RH and the stiffness and strength properties were measured. The water uptake was shown to be reduced. The strength of neat matrix D-LDS-3-6 at ambient 68% RH reached 63 MPa and Young’s modulus 3200 MPa and with 40 wt.% wood fiber reinforcement impressive 128 MPa and 4500 MPa, respectively.     

Allyloxy-modified starch with low degree of substitution for fiber reinforced thermoset starch composites

In the present work dough moulding compound premixes of allyl glycidyl ether modified (AGE)-potato starch, (DS) = 0.2, has been prepared and tested for its fiber reinforced composite properties. The AGE-starch was hydrolyzed with α-amylase under neutral condition for 6 h at 45 °C for improved process ability. The grafting and hydrolytic scission was confirmed by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Homogeneous composite premixes of AGE-starch, wood fibers, various amount of glycerol and ethylene glycol dimethacrylate were successfully mixed with a Brabender-kneader at 55 °C and cured by compression molding at 150 °C using 2 wt% of dibenzoyl peroxide. Adding 5 wt% of glycerol did not reduce the ultimate strength of the composites; 10% glycerol reduced the strength from 60 MPa to 40 MPa, and 16% glycerol to 14 MPa. The results with 5 wt% glycerol are comparable with earlier achieved results. The water absorption rate increased with increased glycerol content and the mechanical strength of the composites was lost completely when the moisture uptake reached 15 wt%.     

Influence of molecular weight on strain‐gradient yielding in polystyrene

Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length‐scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano‐indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length‐scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver‐Pharr method. It was also shown that the length‐scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length‐scale parameter. The length‐scale parameter for strain‐gradient plasticity has a size of around 0.1 μm for polystyrene. Polym. Eng. Sci. 44:1987–1997, 2004. © 2004 Society of Plastics Engineers.