Stabilization of metastable tetragonal zirconia nanocrystallites by surface modification

Metastable tetragonal zirconia nanocrystallites were studied in humid air and in water at room temperature (RT). A stabilizing effect of different surfactants on the tetragonal phase was observed. Furthermore, the phase stability of silanized metastable tetragonal zirconia nanocrystallites was tested by prolonged boiling in water. The samples were analyzed with X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Changes in the monoclinic volume fraction in the samples were calculated. A number of surfactants were screened for their ability to stabilize the tetragonal phase upon exposure to humidity. Only silanes and phosphate esters of these were able to stabilize the tetragonal phase in water. Even as small amounts of silanes as 0.25 silane molecule per nm² are able to stabilize the tetragonal phase in water at RT. Aminopropyl trimethoxy silane and γ-methacryloxypropyl trimethoxy silane were even capable of preventing phase transformation during boiling for 48 h in water.     

Synthesis and characterization of elastomeric polyurea foam

Polymeric foams are ubiquitous in impact mitigation for civilian and military applications; the performance in such loading scenarios can be elucidated through quasi-static and dynamic mechanical testing. The present study reports on the complex microstructure of newly synthesized polyurea foams exhibiting a hierarchical structure consisting of large perforated semi-closed spherical cells with a mean diameter of 370 ± 162 μm surrounded by smaller closed, spherical cells with size distribution of 69 ± 18 μm. The stress–strain curves were used to calculate the basic mechanical properties and to predict the dynamic behavior of the foams. Nonlinear regression and finite element analyses were used to calibrate the Ogden hyperfoam model to explicate the hyperelastic behavior. The performance of the polyurea foam was found to outperform a benchmark foam in nearly all the elastic and energy absorbing properties. For example, one variation of the newly synthesized foam stored nearly doubled the energy of the benchmark foam while being 12% lighter. Low-density polyurea foam was found to decelerate an incoming impact mass with a minimum G-level that was nearly one third lower than the higher density polyurea and benchmark foams. In all, the behavior of the foam is dependent on the parameters of the fabrication process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48839.     

A New Characterization of ACC0 and Probabilistic CC0

Barrington, Straubing & Thérien (1990) conjectured that the Boolean And function can not be computed by polynomial size constant depth circuits built from modular counting gates, i.e., by CC⁰ circuits. In this work we show that the And function can be computed by uniform probabilistic CC⁰ circuits that use only O(log n) random bits. This may be viewed as evidence contrary to the conjecture.     

Pre-incubation of chemically crosslinked hyaluronan-based hydrogels,loaded with BMP-2 and hydroxyapatite,and its effect on ectopic bone formation

The effects of pre-incubation of hyaluronan hydrogels, for different lengths of time after the initiation of chemical crosslinking and prior to injection, were explored both by investigating the in vitro BMP-2 release kinetics from the hydrogel and by studying the ectopic bone formation in rats. From the curing profile, obtained from rheological analysis, appropriate pre-incubation times (1 min, 5 h and 3 days) were selected, to prepare slightly, moderately and fully cured hydrogels. Comparable release profiles were observed for all three test groups in vitro. Furthermore, radiography, pQCT and histology of the explanted grafts showed cancellous bone formation in all groups after 5 weeks in vivo. However, longer pre-incubation times gave rise to an increase in bone volume, but a decrease in bone density. Moreover, the 5 h and the 3 days grafts appeared to be more ordered and resistant to deformation from the surrounding tissue than the 1 min grafts. The observed variations in mechanical and biological properties could potentially be used to adapt the treatment for a specific indication.     

Morphological differences in BMP-2-induced ectopic bone between solid and crushed hyaluronan hydrogel templates

The possibility to affect bone formation by using crushed versus solid hydrogels as carriers for bone morphogenetic protein 2 (BMP-2) was studied. Hydrogels, based on chemical crosslinking between hyaluronic acid and poly(vinyl alcohol) derivatives, were loaded with BMP-2 and hydroxyapatite. Crushed and solid forms of the gels were analyzed both in vitro via a release study using ¹²⁵I radioactive labeling of BMP-2, and in vivo in a subcutaneous ectopic bone model in rats. Dramatically different morphologies were observed for the ectopic bone formed in vivo in the two types of gels, even though virtually identical release profiles were observed in vitro. Solid hydrogels induced formation of a dense bone shell around non-degraded hydrogel, while crushed hydrogels demonstrated a uniform bone formation throughout the entire sample. These results suggest that by crushing the hydrogel, the construct’s three-dimensional network becomes disrupted. This could expose unreacted functional groups, making the fragment’s surfaces reactive and enable limited chemical fusion between the crushed hydrogel fragments, leading to similar in vitro release profiles. However, in vivo these interactions could be broken by enzymatic activity, creating a macroporous structure that allows easier cell infiltration, thus, facilitating bone formation.     

A longitudinal study of development and maintenance

ContextThe information systems we see around us today are at first sight very different from those that were developed 15 years ago and more. On the other hand, it seems that we are still struggling with many of the same problems, such as late projects and unfulfilled customer demands.ObjectiveThe paper presents finding relative to the distribution of work between maintenance and development tasks, comparing to the results reported earlier to assess the stability of important metrics within the area.MethodThis paper presents the main results of a survey-investigation performed in 2008 in 67 Norwegian organizations comparing the distribution of work to results from similar investigations performed in Norway in 1993, 1998, and 2003. Some comparisons to similar investigations performed in USA before this is also provided.ResultsThe amount of application portfolio upkeep (work made to keep up the functional coverage of the application system portfolio of the organization, including the development of replacement systems), is at the same level as reported in 1998 and 2003. The level of application maintenance is also on the same level as the similar investigations conducted in 2003 and 1998. There was a significant increase in both maintenance and application portfolio upkeep from 1993 to 1998, which could partly be attributed to be the extra maintenance and replacement-oriented work necessary to deal with the “year 2000 problem”, but this seemed to be reversed in 2003 and 2008. As for the 2003 investigation, the slow IT-market in general seemed to have influenced the results negatively seen from the point of view of application systems support efficiency in organization. No similar explanation can be used for the 2008 numbers.ConclusionBased on the last surveys it seems than a stable level of work distribution both on maintenance and application portfolio upkeep have been reached, although the underlying development technologies are still undergoing large changes. This is contrary to others claiming that the amount of maintenance is still increasing.     

125th Anniversary Review: Diacetyl and its control during brewery fermentation

Diacetyl is a butter‐tasting vicinal diketone produced as a by‐product of yeast valine metabolism during fermentation. Concentration is dependent on a number of factors including rate of formation of the precursor α‐acetolactate by yeast, spontaneous decarboxylation of this acetohydroxy acid to diacetyl and removal of diacetyl by yeast via the action of various reductase enzymes. Lowering concentrations of diacetyl in green beer represents an expensive and time‐consuming part of the brewing process and strategies to minimize diacetyl formation or hasten its reduction have potential for improving overall efficiency of the lager brewing system. Here we review the processes that determine diacetyl levels in green beer as well as the various ways in which diacetyl levels can be controlled. The amount of diacetyl produced during fermentation can be affected by modifying process conditions, wort composition or fermentation technique, or by yeast strain development through genetic engineering or adaptive evolution. The process of diacetyl reduction by yeast is not as well understood as the process of formation, but is dependent on factors such as physiological condition, cell membrane composition, temperature and pH. The process of diacetyl removal is typically rate‐limited by the reaction rate for the spontaneous decarboxylation of α‐acetolactate to diacetyl. Copyright © 2013 The Institute of Brewing & Distilling     

Symmetry As Geometry: Kuwait International Airport

Computer-aided design (CAD) software has often been associated with the limitations of Euclidean geometry. Kristoffer Josefsson , a mathematician and specialist geometer employed in the Specialist Modelling Group (SMG) at Foster + Partners, explains how the symmetry-encoded representation undertaken for Kuwait International Airport enabled the group to extend CAD tools for non-Euclidean use.     

Limitations of using Raman microscopy for the analysis of high-content-carbon-filled ethylene propylene diene monomer rubber

The effects of laser irradiation on changes to the surface chemistry and structure of a commercially available ethylene propylene diene monomer (EPDM) rubber sample after Raman microscopy analysis was investigated. The Raman measurements were carried out with different levels of laser power on the sample, ranging from 4.55 mW to 0.09 mW. The surface of the EPDM was analyzed before and after laser exposure using X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The techniques have surface probe depths of approximately < or = 10 nm and 1 microm, respectively. Both sets of analysis show that ingredients of the blended EPDM rubber "bloom" to the surface as a result of local heating that takes place due to the absorption of laser by carbon black during the Raman analysis. Scanning electron microscopy (SEM) analysis was also performed on the Raman analyzed areas to visually illustrate the effects created due to laser light exposure (i.e., burning marks). The change in surface chemistry also occurs in regions a few millimeters from the exposed sites, indicating that the effect is quite long range. However, this phenomenon has no major influence, as far as XPS or ATR-FTIR results disclose, on the backbone structure of the rubber sample. The results indicate that precautions should be taken when analyzing complex blended polymer samples using Raman spectroscopy.