Are digital natives a myth or reality? University students’ use of digital technologies

This study investigated the extent and nature of university students’ use of digital technologies for learning and socialising. The findings show that students use a limited range of mainly established technologies. Use of collaborative knowledge creation tools, virtual worlds, and social networking sites was low. ‘Digital natives’ and students of a technical discipline (Engineering) used more technology tools when compared to ‘digital immigrants’ and students of a non-technical discipline (Social Work). This relationship may be mediated by the finding that Engineering courses required more intensive and extensive access to technology than Social Work courses. However, the use of technology between these groups is only quantitatively rather than qualitatively different. The study did not find evidence to support popular claims that young people adopt radically different learning styles. Their attitudes to learning appear to be influenced by lecturers’ teaching approaches. Students appear to conform to traditional pedagogies, albeit with minor uses of tools delivering content. The outcomes suggest that although the calls for transformations in education may be legitimate it would be misleading to ground the arguments for such change in students’ shifting patterns of learning and technology use.     

Time‐domain hybrid formulations for wave simulations in three‐dimensional PML‐truncated heterogeneous media

We are concerned with the numerical simulation of wave motion in arbitrarily heterogeneous, elastic, perfectly‐matched‐layer‐(PML)‐truncated media. We extend in three dimensions a recently developed two‐dimensional formulation, by treating the PML via an unsplit‐field, but mixed‐field, displacement‐stress formulation, which is then coupled to a standard displacement‐only formulation for the interior domain, thus leading to a computationally cost‐efficient hybrid scheme. The hybrid treatment leads to, at most, third‐order in time semi‐discrete forms. The formulation is flexible enough to accommodate the standard PML, as well as the multi‐axial PML. We discuss several time‐marching schemes, which can be used à la carte, depending on the application: (a) an extended Newmark scheme for third‐order in time, either unsymmetric or fully symmetric semi‐discrete forms; (b) a standard implicit Newmark for the second‐order, unsymmetric semi‐discrete forms; and (c) an explicit Runge–Kutta scheme for a first‐order in time unsymmetric system. The latter is well‐suited for large‐scale problems on parallel architectures, while the second‐order treatment is particularly attractive for ready incorporation in existing codes written originally for finite domains. We compare the schemes and report numerical results demonstrating stability and efficacy of the proposed formulations. Copyright © 2014 John Wiley & Sons, Ltd.     

A method to determine resin flow during curing of composite laminates

An experimental method is presented to determine the amount of resin flow within a composite laminate during cure. The method is analogous to the use of radioactive tracers in other applications. Heavier elements such as chlorine and bromine, which may be naturally present in small amounts in epoxy resins are used to follow resin flow and mixing. The presence and the quantity of these “tags” is determined using wavelength dispersive X-ray analysis in a scanning electron microscope. With the resins in this study, it is shown that it is possible to measure volume fractions of resin with accuracies ranging from ±0.5 to ±3 volume %. By using brominated resin in only one layer of a laminate, the degree of flow and mixing can be followed accurately. The results suggest that there is considerable resin mixing as well as flow.     

Nanoethosomal formulation of gammaoryzanol for skin-aging protection and wrinkle improvement: a histopathological study

Background: Free radical scavengers and antioxidants, with the main focus on enhanced targeting to the skin layers, can provide protection against skin ageing.

Objective: The aim of the present study was to prepare nanoethosomal formulation of gammaoryzanol (GO), a water insoluble antioxidant, for its dermal delivery to prevent skin aging.

Methods: Nanoethosomal formulation was prepared by a modified ethanol injection method and characterized by using laser light scattering, scanning electronic microscope (SEM) and X-ray diffraction (XRD) techniques. The effects of formulation parameters on nanoparticle size, encapsulation efficiency percent (EE%) and loading capacity percent (LC%) were investigated. Antioxidant activity of GO-loaded formulation was investigated in vitro using normal African green monkey kidney fibroblast cells (Vero). The effect of control and GO-loaded nanoethosomal formulation on superoxide dismutase (SOD) and malondialdehyde (MDA) content of rat skin was also probed. Furthermore, the effect of GO-loaded nanoethosomes on skin wrinkle improvement was studied by dermoscopic and histological examination on healthy humans and UV-irradiated rats, respectively.

Results: The optimized nanoethosomal formulation showed promising characteristics including narrow size distribution 0.17?±?0.02, mean diameter of 98.9?±?0.05?nm, EE% of 97.12?±?3.62%, LC% of 13.87?±?1.36% and zeta potential value of –15.1?±?0.9?mV. The XRD results confirmed uniform drug dispersion in the nanoethosomes structure. In vitro and in vivo antioxidant studies confirmed the superior antioxidant effect of GO-loaded nanoethosomal formulation compared with control groups (blank nanoethosomes and GO suspension).

Conclusions: Nanoethosomes was a promising carrier for dermal delivery of GO and consequently had superior anti-aging effect.     

Use of a simple,inexpensive pressure sensor to measure hydrostatic resin pressure during processing of composite laminates

A simple and cheap method of measuring the resin pressure within a composite laminate during processing is presented. The method consists of using a small diameter, long needle filled with inert fluid and connected to an external pressure sensor, to measure the resin pressure at a point inside a composite laminate. This method can be used to investigate resin flow, laminate compaction, the control of voids, and in several composite material processing methods such as autoclave processing, hot press curing and resin transfer molding. The sensors are suitable for research and development or troubleshooting, but not for production. Sensor assemblies were developed and tested to show that their response is reproducible, linear and stable with temperature and time. Resin pressure profiles for two AS4/3501-6 laminates were generated and compared. The experimental results were also compared to the resin flow simulation of a general processing model for composites, COMPRO. It is shown that the resin profile in the laminate is influenced by the presence of the bleeder cloth and the vacuum bag pressure. A significant pressure drop corresponded to the point of minimum viscosity of the resin. Finally, the resin pressure was stabilized when the resin reached gelation.     

Numerical investigation of the ballistic efficiency of multi-ply fabric armours during the early stages of impact

The early impact behaviour of single and multi-ply Kevlar^® 129 fabric armour systems is investigated using an explicit finite element code, TEXIM, developed in-house. This numerical model is carefully validated using continuous temporal data obtained from an instrumented experimental setup. The model is then used to explore the loss in ballistic efficiency of woven fabric targets, as experienced early in the impact event, when either the number of layers in the panel or the yarn denier is increased.     

Computationally efficient pseudo-viscoelastic models for evaluation of residual stresses in thermoset polymer composites during cure

In this study of the constitutive modelling of thermoset polymers during cure, we compare what we call the “cure hardening instantaneously linear elastic (CHILE)” approach with the more computationally intensive viscoelastic approach. The CHILE approach is popular compared to the viscoelastic approach as the cost of material characterization, data reduction, finite element model development and implementation, and computer run time is significantly lower. However, CHILE models suffer from the fact that the justification for their validity is essentially anecdotal, rather than based on a clear linkage to viscoelastic theory; and in related manner, materials characterization is done at an intuitively low but essentially arbitrary frequency. In this work we show that there are approximations that allow the full viscoelastic approach to be simplified progressively, and that these approximations are appropriate for the typical cure cycle undergone by a thermoset polymer. We present the functions of time at which the elastic modulus of the polymer should be calibrated for these simplified ‘pseudo-viscoelastic’ models, and show that for the uniaxial loading of a fully constrained block of polymer undergoing a given cure cycle, the predicted residual stresses compare very well with those computed using the full viscoelastic model. For further simplification, at the price of slightly lower accuracy and generality, a constant time or frequency can be chosen to evaluate the modulus. In general, we show that the CHILE approach, when properly calibrated, is a valid and efficient pseudo-viscoelastic (PVE) model, and that there is a continuum of trade-off of investment versus accuracy as we go from a full viscoelastic approach to the simplest CHILE approach.     

A two‐dimensional flow model for the process simulation of complex shape composite laminates

A numerical flow‐compaction model is developed and implemented in a finite element code to simulate the multiple physical phenomena involved during the autoclave processing of fibre‐reinforced composite laminates. The model is based on the effective stress formulation coupled with a Darcian flow theory. A Galerkin approach is employed to discretize the weak form of the governing equations. The current formulation successfully describes the compaction behaviour of complex shape laminates caused by flow of the resin. A parametric study is performed to investigate the effect of the material properties on the compaction of angle‐shaped composite laminates. It is found that the fibre bed shear modulus significantly affects the compaction behaviour in the corner sections of curved laminates while the resin viscosity and fibre bed permeability affect the compaction rate of the laminate. Copyright © 1999 John Wiley & Sons, Ltd.     

Closed-form solution for process-induced stresses and deformation of a composite part cured on a solid tool: Part II – Curved geometries

In this study, closed-form expressions are developed that provide insight into the mechanisms that lead to the stress development in curved composite parts undergoing autoclave processing. Despite many assumptions that are made in the course of the analytical development, the closed-form predictions agree well with the more sophisticated finite element results. It is shown that stresses in a curved part develop mainly due to the thermo-chemical strain mismatch between the part and the tool in the tangential and radial directions. The unbalanced moment which causes the deformation due to the thermo-chemical strain mismatch in the tangential direction develops mostly at the early stages (heat-up) of the curing process when the part shear modulus is very low compared to its axial modulus. In contrast, the unbalanced moment due to the thermo-chemical strain mismatch in the radial direction develops mostly at the final stages (cool-down) of the cure cycle when the part shear modulus is relatively high.