Linear viscoelastic and morphological description of multiphase systems affected by processing parameters

Influence of processing methods, in terms of comparing compression and injection moldings, on the rheological behavior of polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) blends and PC/ABS/glass fibers composites is presented. Blend compositions and fiber content are considered as material variables. For blends, the effect of the processing route on the viscoelastic functions is evident only for low shearing frequencies. Injection molding created morphology with cocontinuous character, while compression molded blends have “relaxed” structure, where dispersed phase domains are several times larger than in injection molded ones. The glass fiber reinforcement led to the significant differences in viscoelastic properties of composites processed by injection and compression molding. Injected composites have both moduli always higher than compression molded. Also, fiber lengths are reduced more for compressing molding. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dewetted Bridgman crystal growth: practical stability over a bounded time period in a forced regime

The concept of practical stability is applied to the case of dewetted Bridgman crystal growth on Earth, in a simplified configuration. Taking into account both heat transfer and capillarity, it is formally demonstrated that the process is stable in case of convex menisci, provided that pressure fluctuations remain in a range which can be computed. The theoretical concepts are illustrated by examples involving InSb and GaSb crystal growth. It is concluded that practical stability gives valuable knowledge of the dynamics of the studied technique and could be usefully applied to other crystal-growth processes, especially those involving capillary shaping.     

An attempt to identify the presence of polytype stacking faults in hBN powders by means of X-ray diffraction

X-ray diffraction techniques have been used to characterize the three-dimensional order and the crystallite size for 17 hBN powders intended to be used as precursors in the cBN synthesis. Six hBN powders (group A) were obtained by the amidic method (borax + urea) purposely for this research and the remaining 11 hBN powders (group B) were commercial products of recognized companies. Attempts have been made to establish linear correlations between the X-ray revealed parameters of the hBN powders. An explanation sustained on experimental basis is proposed for the different linear correlation between the graphitizing index G.I. and order parameter p₃ in the two groups, that points to the existence of polytype stacking faults in hBN depending on the way of fabrication.     

The Influence of Rh Addition on the Catalytic Activity of Cubic Pt Nanocrystals Supported on Alumina for NO/CH4 Reaction

The effect of the Rh addition to the well defined cubic (≈70%) Pt nanocrystals of around 13 nm supported on alumina was investigated for NO/CH₄ reaction. The impact of size and shape of Pt nanoparticles on the catalytic activity were also analyzed by comparing the results with a conventionally prepared catalyst.     

Using system dynamics to evaluate control strategies for mosquito-borne diseases spread by human travel

The aim of this paper is to evaluate the effectiveness of control strategies for diseases transmitted by the Aedes albopictus mosquito (the “Asian tiger”) and spread by human travel. This mosquito, which has become established in southern Europe in recent years, is a vector for many diseases. For example, an outbreak of chikungunya, hitherto regarded as a tropical disease, occurred in Italy in 2007. The initial case was a person who had acquired the disease overseas. Mosquito-borne infections can only be spread over large distances by human travel, as the flight range of mosquitos is very limited. A system dynamics model has been developed which describes the mosquito life-cycle, the natural history of mosquito-borne disease in humans and mosquitos, and human behaviour including travel. Potential disease control strategies include chemical treatments to destroy either larvae or adult mosquitos, campaigns to influence human behaviour, or quarantine of infectious people. In this paper, which is based on the Italian chikungunya outbreak, this model is used to study and compare the effect of different control strategies, where the various actions are combined in different ways and implemented for different time periods.     

A new parameter for modelling three-dimensional damage evolution validated by synchrotron tomography

Novel methods of correlating damage evolution measurement techniques are explored to produce improved constitutive equations that better account for the effect of initial inclusion distributions on damage softening behaviour. Based on ex situ, high resolution, synchrotron tomographic quantification of the three-dimensional interactions of damage formed during hot deformation of free cutting steel, a new parameter to account for the effect of inclusions on damage is proposed. Uniaxial tensile samples deformed at 1100 °C and a strain rate of 0.1 s^?1 were interrupted at various strains prior to failure. Ex situ synchrotron X-ray computed tomography (sCT) was then used to quantify the growth of damage in the hot deformation of a leaded free cutting steel. Void growth is related to nucleated microvoids at inclusions. The number and volume fraction of voids were calculated for each tensile sample, allowing quantification of the evolving ductile damage via the measured increase in average void diameter after each strain increment. The equivalent diameter, spacing and volume fraction of inclusions were measured at the different interrupt strains. The local strain and stress state, evaluated using the finite element method at the microscale, were related to the local void populations. There was evidence that after necking the damage localized due to clustered inclusions. Damage localization was confirmed with a three-dimensional micromechanics model of 100 inclusions, whose distribution was taken directly from the sCT results, and a novel approach to extract the damage fraction is presented. A new parameter was introduced to account for inclusion size, spacing and clustering, which was validated against the sCT results.     

Investigation of FE model size definition for surface coating application

An efficient prediction mechanical performance of coating structures has been a constant concern since the dawn of surface engineering. However, predictive models presented by initial research are normally based on traditional solid mechanics, and thus cannot predict coating performance accurately. Also, the high computational costs that originate from the exclusive structure of surface coating systems (a big difference in the order of coating and substrate) are not well addressed by these models. To fill the needs for accurate prediction and low computational costs, a multi-axial continuum damage mechanics (CDM)-based constitutive model is introduced for the investigation of the load bearing capacity and fracture properties of coatings. Material parameters within the proposed constitutive model are determined for a typical coating (TiN) and substrate (Cu) system. An efficient numerical subroutine is developed to implement the determined constitutive model into the commercial FE solver, ABAQUS, through the user-defined subroutine, VUMAT. By changing the geometrical sizes of FE models, a series of computations are carried out to investigate (1) loading features, (2) stress distributions, and (3) failure features of the coating system. The results show that there is a critical displacement corresponding to each FE model size, and only if the applied normal loading displacement is smaller than the critical displacement, a reasonable prediction can be achieved. Finally, a 3D map of the critical displacement is generated to provide guidance for users to determine an FE model with suitable geometrical size for surface coating simulations. This paper presents an effective modelling approach for the prediction of mechanical performance of surface coatings.     

A possible molecular basis for the effect of gastric anti-ulcerogenic drugs

The exact mechanism of action of the anti-ulcerogenic drugs is still under debate. According to the literature, under normal conditions the cAMP:cGMP ratio in the rat gastric mucosa is approximately 8:10. Following prostacyclin administration, this ratio transiently decreases but later shows a strong elevation, indicating profound changes in the intracellular cyclic nucleotide balance. There is evidence that this elevation or 'shift' in the cAMP:cGMP ratio is linked, on a cellular or molecular level, to the anti-ulcerogenic, cytoprotective processes in the stomach. Cimetidine and ranitidine (widely used H2 receptor-blocking drugs) administered at doses that are too low to interfere with gastric acid secretion, cause an elevation in the cAMP:cGMP ratio, an effect that is also observed with other prostaglandin derivatives and anti-ulcerogenic drugs. In this article, Gabor A. Balint discusses these data and how the elevation of the gastric mucosal cAMP:cGMP ratio is a useful molecular marker that could provide insights into the effects of anti-ulcerogenic drugs.     

Structural Stability of Simplified Dynamical System Governing Motion of ALFLEX Reentry Vehicle

It is shown that the simplified system of differential equations that governs the motion of the automatic-landing flight-experiment (ALFLEX) reentry vehicle is neither structurally stable, nor topologically equivalent to the general dynamical system governing the same motion. Hence, the general and the simplified mathematical models of ALFLEX give different images of the same reality.     

An Insight into the Role of Non-Porphyrinoid Photosensitizers for Skin Wound Healing

The concept behind photodynamic therapy (PDT) is being successfully applied in different biomedical contexts such as cancer diseases, inactivation of microorganisms and, more recently, to improve wound healing and tissue regeneration. The effectiveness of PDT in skin treatments is associated with the role of reactive oxygen species (ROS) produced by a photosensitizer (PS), which acts as a “double agent”. The release of ROS must be high enough to prevent microbial growth and, simultaneously, to accelerate the immune system response by recruiting important regenerative agents to the wound site. The growing interest in this subject is reflected by the increasing number of studies concerning the optimization of relevant experimental parameters for wound healing via PDT, namely, light features, the structure and concentration of the PS, and the wound type and location. Considering the importance of developing PSs with suitable features for this emergent topic concerning skin wound healing, in this review, a special focus on the achievements attained for each PS class, namely, of the non-porphyrinoid type, is given.