Radiation-induced modification of dielectric relaxation spectra of polyolefins: polyethylenes vs. polypropylene

The molecular relaxation behaviour of polyolefins exposed to high-energy radiation has been investigated by dielectric loss (tan δ) analysis. Therefore, low-density polyethylene, high-density polyethylene (HDPE), and isotactic polypropylene (iPP) were gamma-irradiated in air to various absorbed doses (up to 700 kGy). All relaxation zones (α, β, γ, and δ in the order of decreasing temperature), between 25 K and melting temperature, were studied. The radiation-induced changes observed in the dielectric relaxation spectra were related to the modifications in the structural and morphological parameters attributed to exposure of the polyolefins to radiation. Wide-angle X-ray diffraction, infrared spectroscopy, and gel measurements were used to determine the radiation-induced changes in the crystalline structure, oxidative degradation, and the degree of network formation, respectively. The present study reveals high dielectric and/or relaxation sensitivity of polyolefins to gamma radiation. Disappearance of some relaxations (such as β relaxation in HDPE and low temperature γ and δ relaxations in iPP) is clearly observed with irradiation. For the other relaxations, besides the large changes in the relaxation intensity, radiation also induces smaller/larger changes in the distribution of relaxation times, peak position, and activation energy.     

An Integrative Therapy Framework: Research and Practice.

Research in human development and studies on therapy process and outcome respectively address similar questions: How does change come about and what influences it? Very similar answers emerge from these two research domains. Both have much to offer to the contemporary endeavors for therapy integration. The comparisons of the findings combined with clinical experience provide a basis for an integrative framework for therapeutic practice that can be applied to any therapy model. The components of the framework are used to discuss differences and similarities among 3 major therapeutic models. Practice is seen as a starting point for integration, which ultimately happens at an individual level. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Wide view supertwisted nematic liquid-crystal light shutter

We present a novel concept of a wide viewing angle liquid-crystal display (LCD) light shutter, taking advantage of the highly symmetric 180 degrees -twisted liquid-crystal (LC) configuration and the light propagation starting with a single mode. In a specific case of the high voltage driven LCD light shutter, the resulting very high overall symmetry allows for the efficient angular compensation of the light attenuation in the optically closed state using just a simple, specifically tuned, negative-birefringent c-plate retarder. The latter can be adapted to compensate for the positive optical birefringence of the homeotropically aligned LC molecules as well as also for a great deal of the angular dependence of the crossed polarizers. We show that the additional partial compensation of the angular dependence of the crossed polarizers can be explained by a combined effect of the positive birefringence of the homeotropically aligned LC molecules, negative-birefringence c-plate retarder, and an in-plane residual positive birefringence (a-plate) of the boundary layers of the LC molecules.     

Learning in serious virtual worlds: Evaluation of learning effectiveness and appeal to students in the E-Junior project

The objective of this study is to present and to evaluate the E-Junior application: a serious virtual world (SVW) for teaching children natural science and ecology. E-Junior was designed according to pedagogical theories and curricular objectives to help children learn about the Mediterranean Sea and its environmental issues while playing. In this study, we present data about the E-Junior evaluation. A class in a serious virtual world (virtual group) was compared with a traditional type of class (traditional group) that contained identical learning objectives and contents but lacked a gaming aspect. Data collection consisted of quantitative and qualitative measures on a sample of 48 children. With regards to learning effectiveness, the results showed that the serious virtual world does not present statistically significant differences with the traditional type of class. However, students from the virtual group reported enjoying the class more, being more engaged, and having greater intentions to participate than students from the traditional group. The plausible explanation for this can be found in the qualitative data. The implications of these results and improvement proposals are also discussed in this work.     

Influence of Preparation Conditions of Alumina‐Based Refractory on the Morphological Parameters of Surface Defects

The surface defects on alumina‐based refractory arising from thermal shock were studied using image analysis and statistical tools. Alumina‐based refractory specimens were prepared by adding a different amount of fibers into their original composition and compacted on different pressures. Obtained specimens were subjected to thermal shock, and induced surface defects were characterized by their morphological parameters determined using the image analysis procedure. The influence of preparation conditions on the surface defects morphology was studied using principle component analysis. It was shown that morphological parameters of defects vary corresponding to the composition and preparation conditions of ceramic material.     

Calcium phosphate and calcium carbonate mineralization of bioinspired hydrogels based on β-chitin isolated from biomineral of the common cuttlefish (<Emphasis Type="Italic">Sepia officinalis</Emphasis>, L.)

Chitin, a bioactive, antibacterial and biodegradable polymer is commonly utilized by diverse marine organisms as the main scaffold material during biomineralization. Due to its properties, chitin is also of interest as a component of organo-inorganic composites for diverse biomedical applications. In this study, chitinous fibers isolated from the cuttlebone of the common cuttlefish (Sepia officinalis, L.) are characterized and evaluated for use as an integral part of mineralized hydrogels for biomedical applications. Since marine organisms use calcium carbonates (CaCO₃), while vertebrates use calcium phosphates (CaP) as the main inorganic hard tissue components, and both minerals are used in hard tissue engineering, they were compared to determine which composite is potentially a better biomaterial. Hydrogel mineralization was conducted by subsequent dipping into cationic and anionic reactant solutions, resulting in the formation of a CaCO₃ or CaP coating that penetrated into the hydrogel. Obtained composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), rheology, swelling tests and simple compression. The results indicate that β-chitin can be used for the preparation of moldable hydrogels that are easily mineralized. Mineralized hydrogels have higher elasticity than non-mineralized ones while swelling is better if the extent of mineralization is lower. Further optimization of the hydrogels composition could improve their stress response and Young’s modulus, where the current hydrogel with a higher extent of CaP mineralization excels in comparison to all other investigated composites.     

Microcellular open porous polyester membranes from thiol-ene polymerisations of high internal phase emulsions

A high internal phase emulsion templating procedure is applied for the preparation of membranes which exhibit an open porous morphology with interconnected macro pores and open porous surfaces. A doctor blading procedure is used to cast the high internal phase emulsion onto glass substrates. Continuous phase of the emulsions contain divinyladipate and pentaerythritol tetrakis(3-mercaptopropionate) which are photopolymerised using the thiol-ene click chemistry to yield polyester type polymer network. The resulting polymer morphology features primary pores as a result of emulsion’s droplet phase, with diameters between 7 and 14 µm and interconnecting pores as a result of polymerisation shrinkage, with diameters between 1.6 and 2.2 µm. The highly porous and interconnected morphology mirrors the precursor emulsion structure with a dense packing of internal (aqueous) phase droplets. Doctor blades with different slit dimensions are used for casting thus producing membranes with different thicknesses while in all cases typical polyHIPE morphology is observed. Mechanical tests show a dependence of tensile modulus and tensile strength on the membrane thickness and also on pore size distribution.     

Composite nanostructured hydroxyapatite/yttrium stabilized zirconia dental inserts – The processing and application as dentin substitutes

The objective of the study was to process nano-structured hydroxyapatite/yttrium-stabilized zirconia bioceramic and to investigate the possibilities of its application as dentin replacement in the form of dental inserts. The processing conditions were varied in order to optimize phase composition, microstructure, fracture toughness, hardness and shear bond strength (SBS) between the obtained composite inserts and restorative materials, following either the "total-etch" or ?self-etch“ clinical protocol. Composite nano-powder, obtained by mixing and homogenization of 80?wt% of stoichiometric hydroxyapatite (HAp) synthesized by modified precipitation method and 20?wt% of yttrium-stabilized ZrO₂ (YSZ) synthesized by plasma method, was isostatically pressed into cylinder-shaped green bodies. After dilatometric analysis, HAp/YSZ inserts were sintered in the temperature range from 1200?°C to 1300?°C. Hardness and fracture toughness of sintered inserts were ranged between 3.90?±?0.20 – 3.95?±?0.12?GPa and 1.82?±?0.04 – 1.88?±?0.03 MPam^1/2, respectively. Microstructural analysis of biphasic HAp/t-ZrO₂ inserts indicated two potential fracture mechanisms for fracture toughness increasing. Sintering temperature and different clinical protocols affected SBS between processed inserts and commercial dental restorative materials. Maximum SBS values of 10.50?±?4.94?MPa (mean±standard deviation) were reached in inserts sintered at 1300?°C, following the ?self-etch“ protocol of adhesive application. It could be concluded that resin-based composites could be strongly bonded to HAp/YSZ inserts, preferably with ?self-etch“ adhesive application. In addition, the values of fracture toughness and hardness of the obtained inserts indicated the possibility of their usage as dentin substitutes, which could be a good prerequisite for satisfactory mechanics of restored teeth.