Synthesis,characterization, and enzymatic degradation of chitosan/PEG hydrogel films

Poly(ethyleneglycol) (PEG)/tartaric acid (TA)‐crosslinked chitosan hydrogel (CPT) films were prepared, and the formation of the PEG/TA‐crosslinked structure was confirmed by Fourier transformed infrared (FTIR), nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) measurements. The thermal properties of the crosslinked films were also determined with thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) analysis. The swelling properties of the films were investigated at different temperature and pH values. It was found that the swelling ratio increased with the decrease of pH value of the surrounding buffer solutions, amount of PEG, and with the increase of temperature. Swelling behavior of the PEG/TA‐crosslinked chitosan hydrogel films depended on pH and reversible with the temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Some properties of bacterial cellulose produced by new native strain Gluconacetobacter sp. A06O2 obtained from Turkish vinegar

The aim of the study was to isolate and identify an acetic acid bacterial strain having high cellulose yield and to investigate some physicochemical properties of bacterial cellulose (BC). Acetic acid bacteria were isolated by using 62 samples (vinegar, fruit, vegetable, and soil) from different region of Turkey. The cellulose production ability of 153 isolates was determined. A strain (A06O2) having high and stable cellulose yield was identified by biochemical tests and 16S rRNA gene sequencing and compared with type strain Gluconacetobacter xylinus NRRL B‐759. Based on the results, strain A06O2 was named at the genus level as Gluconacetobacter, however, species level identification could not be made. Celluloses from both strains were purified to investigate the physicochemical properties such as thermal properties, solubility in various solvents, elemental composition, tensile properties, and surface properties by FTIR and SEM. The results showed that the cellulose samples of two bacterial strains differed in the physicochemical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

An integrated reconfigurable control and self-organizing communication framework for community resilience microgrids

CRMs can effectively share distributed energy resources of multiple owners and enhance resilient electricity supply in communities during disruptions. However, in contrast to single-entity microgrids, CRMs present a unique structure and bring new challenges for operations and control, which can often be interrupted due to cascaded failures in interconnected electrical/communication components. An installation in Potsdam, New York, incorporates some control/communication solutions for resilient and economic operation of CRMs.     

Impact of visual performance management systems on the performance management practices of organisations

The purpose of this paper was to explore how visual strategy and performance management techniques impact performance measurement and management practices of organisations. A novel visual performance management approach is developed and implemented in qualitative case studies with seven manufacturing SMEs across Europe. The implementation cases demonstrate that visual management systems serve to support ongoing strategy development and implementation, facilitate performance measurement and review, enable people engagement, improve internal and external communication, enhance collaboration and integration, support the development of a continuous improvement culture and foster innovation. Additional explorative and longitudinal research is required to understand the long-term impact of such approaches in both small and larger organisations.     

Maghemite, γ-Fe2O3, nanoparticles preparation via carbon-templated solution combustion synthesis

High surface area maghemite, γ-Fe₂O₃, nanoparticles were prepared via carbon-templated solution combustion synthesis, which is a two-step approach. Step one involves the combustion synthesis of maghemite nanoparticles embedded in an amorphous carbon matrix, by using a fuel rich reaction mixture of triethylenetetramine and iron nitrate. Step two consists of residual carbon removal by treating the previously-obtained composite precursor with hydrogen peroxide, which releases the maghemite nanopowder. This approach avoids carbon removal by thermal treatment, thus preserving the nanometric size of maghemite nanoparticles (8–12?nm), yielding a high specific surface area of 191.9?m²/g. At the same time, the final maghemite nanoparticles presented a superparamagnetic behavior and a saturation magnetization of 26.2?emu/g, in relation to the small particle size.     

Comparison of chitosan apatite composites synthesized by different methods

This article presents some results concerning chitosan apatite composites obtained by two different methods. First method is based on phosphorylation, calcification and soaking in different calcium phosphate growth media (1.5 × SBF (simulated body fluid), Ca‐PTris (calcium phosphorous tris) and the second method is based on mixing of calcium deficient apatite powder with a chitosan solution. This research is focused on studying and understanding the effect of using different methods on Ca:P ratio of composites. The Ca:P ratio of composites formed in 1.5 × SBF are closer to that of bone when compared with the Ca:P ratio of composites formed in Ca‐PTris solution and Ca:P ratio of composites formed by mixing of calcium deficient apatite powder with a chitosan solution. The Ca:P ratio of the composite (1.75) immersed in 1.5 × SBF for 35 day is similar to the theoretical value of hydroxyapatite (1.67) and equal to the theoretical value of human bone (1.75). POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Structure of zirconium alloy oxides formed in pure water studied with synchrotron radiation and optical microscopy: relation to corrosion rate

A detailed study was undertaken of oxides formed in 360 °C water on four Zr-based alloys (Zircaloy-4, ZIRLO™,¹ Zr-2.5%Nb and Zr-2.5%Nb-0.5%Cu) in an effort to relate oxide structure to corrosion performance. Micro-beam X-ray diffraction was used along with transmitted light optical microscopy to obtain information about the structure of these oxides as a function of distance from the oxide-metal interface. Optical microscopy revealed a layered oxide structure in which the average layer thickness was inversely proportional to the post-transition corrosion rate. The detailed diffraction studies showed an oxide that contained both tetragonal and monoclinic ZrO₂, with a higher fraction of tetragonal oxide near the oxide-metal interface, in a region roughly corresponding to one oxide layer. Evidence was seen also of a cyclic variation of the tetragonal and monoclinic oxide across the oxide thickness with a period of the layer thickness. The results also indicate that the final grain size of the tetragonal phase is smaller than that of the monoclinic phase and the monoclinic grain size is smaller in Zircaloy-4 and ZIRLO than in the other two alloys. These results are discussed in terms of a model of oxide growth based on the periodic breakdown and reconstitution of a protective layer.     

Development and visualization of time-based building energy performance metrics

ABSTRACT

In the face of climate change, and as building codes and standards evolve to promote increased building energy efficiency and reduced carbon footprints, it is also important to ensure that buildings, especially housing, can withstand prolonged power outages during extended periods of both extreme cold and hot weather to provide habitable shelter passively. This paper examines an approach for visualizing the impact of robust passive measures in multi-unit residential buildings by examining the ‘weakest links in the chain’ – the suites most susceptible to underperforming – in three climatic zones: Toronto and Vancouver, Canada; and Adana, Turkey. Two time-based and thermal comfort-related metrics are explored: thermal autonomy, a measure of what fraction of the time a building can deliver comfort without supplemental active systems; and passive survivability (also termed thermal resilience), a measure of the length of time a building remains habitable following the onset of a prolonged power outage during a period of extended extreme weather. A visualization of the results of parametric building energy simulations helps guide the selection of passive architectural parameters at the early stages of design to promote enhanced environmental performance and resilience.     

The effects of nutritional habits on leucite-based ceramic repaired with nanohybrid composites

The purpose of the present in vitro study was to evaluate the effects of nutritional habits (various liquids) on the color change and early repair bond strength of a leucite-based ceramic repaired with different contents of nanohybrid composite resins currently used by the clinicians. Ninety-six IPS-Empress CAD ceramic samples were obtained with low-speed diamond saw. For all samples same repair method was performed. Samples were divided into groups according to four nanohybrid composite resins used as a repair material: Tetric-N-Ceram Bulk Fill, Filtek Z550, Clearfil-Majesty Esthetic, Bisco-Aelite Aesthetic Enamel (n?=?24). Composite resins were applied on ceramic surface and polymerized (40?sec). After waiting for 24?h, samples were divided into three subgroups according to liquid types: pomegranate-flavored mineral water, salad dressing, and distilled water (n?=?8). Before and after immersion the samples in the various liquids, color measurements were calculated (24?h). Then, shear bond strength was tested with an universal testing machine.For the statistical analyses two-way ANOVA, Tukey HSD, Spearman's correlation tests were used at a significance of p?≤?0.05. Nanohybrid composites, liquids (p?≤?0.001); correlation between nanohybrid composites and liquids (p?≤?0.006) had statistically significant impacts on the color change values. Nanohybrid composites (p?≤?0.017) and correlation between nanohybrid composites and liquids (p?≤?0.004) had statistically significant impacts on the shear bond strength values. There was not any statistically significant correlation between color change and shear bond strength (p?>?0.05). When a composite resin is selected as a repair material, nutritional habits of the patient should be taken into consideration. Although hydrophilic monomer type of a composite material is a more predominant factor associated with color change, filler weight has the same predominant effect on shear-bond strength.