Long‐Aliphatic‐Segment Polyamides: Salt Preparation and Subsequent Anhydrous Polymerization

Long‐aliphatic‐segment polyamides were prepared based on hexamethylenediamine and α,ω‐(CH₂)_x biosynthetic diacids (x = 10, 11, 12). The pertinent monomers (salts) were isolated as solids, thoroughly characterized for the first time, and then submitted to an anhydrous melt prepolymerization technique. The obtained prepolymers exhibited in the range of 5 100–11 800 g · mol^?1, and the molecular weight was further increased by up to 55% through solid‐state finishing. The suggested overall polyamidation cycle was conducted at short melt‐reaction times, so as to avoid any thermal degradation, and was proved efficient, indicating similar reactants polymerizability independently of the methylene content.

     

Effect of microwave heating on the migration of dioctyladipate and acetyltributylcitrate plasticizers from food-grade PVC and PVDC/PVC films into olive oil and water

Migration of dioctyladipate (DOA) and acetyltributylcitrate (ATBC) plasticizers from plasticized Polyvinylchloride (PVC) and polyvinylidene chloride (PVDC/PVC (Saran) films into both olive oil and distilled water during microwave heating has been studied. The plasticizer migrating into olive oil and water was determined using an indirect GC method after saponification of the ester-type plasticizer (DOA or ATBC) and subsequent collection of the alcohol component of the ester, namely: 2-ethyl-1-hexanol and 1-butanol, respectively. Migration was dependent on heating time, microwave power setting, the nature of the food simulant and the initial concentration of the plasticizer in the film. Migration of DOA into olive oil reached equilibrium after heating for 10 min at full power (604.6 mg DOA/1). Migration into distilled water was 74.1 mg/1 after 8 min of microwave cooking at full power. The amount of ATBC migrating into olive oil reached equilibrium after heating for 10 min at full power (73.9 mg ATBC/1). Migration into distilled water was 4.1 mg/1 after heating at full power for 8 min. Control samples containing olive oil gave DOA migration values which were significantly higher than the upper limit for global migration (60 mg/1) set by the European Community. It is proposed that PVC should not be used in direct contact with food in the microwave oven, while Saran may be used with caution in microwave heating and reheating applications, avoiding its direct contact with high fat foodstuffs.     

Minimum Moment Method for Resource Leveling Using Entropy Maximization

The minimum moment method for resource leveling is revisited and restated as an entropy-maximization problem. The minimum moment method assumes that the moment of the daily resource demands about the horizontal axis of a project’s resource histogram is a good measure of the resource utilization and that the optimal resource allocation exists when the total moment is at a minimum, thus when the resource histogram is of rectangular shape. The entropy-maximization method proposed in this paper makes use of the general theory of entropy and two of its principal properties (subadditivity and maximality) to revisit the minimum moment method for resource leveling. The entropy-maximization method presented allows for activity stretching and provides resource allocation solutions that show improvement over previous approaches. A case study is also presented that validates the results.     

Liquid phase growth of graphene on silicon carbide

We developed a novel method to produce graphene on silicon carbide (SiC) at a temperature as low as 1000 °C. The method is based on liquid phase growth (LPG) of graphene mediated by liquid gallium, which acts not only as a flux to store carbon dissolved from a surface of SiC when heated, but also as a catalyst to promote the formation of graphene on SiC when cooled. Our experimental results revealed that gallium-treated SiC substrates are coated with uniform and continuous graphene films. The LPG method is able to supply graphene films consisting of one to several hundreds of layers, depending on heating temperatures. Our approach can not only provide an alternative way to form graphene natively on SiC, but will also bring a technological breakthrough in industrial applications of graphene, e.g. the realization of graphene-on-insulator substrates.     

Serum and urine metal levels in patients with metal-on-metal surface arthroplasty

The resurgence of metal-on-metal articulating surfaces for hip arthroplasty has also heightened concerns about the degree and magnitude of metal particle generation and the accompanying increase in circulating metal ion concentrations. In this study, we measured the concentration of chromium in serum and urine and the concentration of cobalt in serum in twenty-five patients with modern metal-on-metal surface arthroplasty of the hip in a prospective manner. The results showed that the mean post-operative chromium in serum levels were 22-fold, 23-fold and 21-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The mean post-operative cobalt in serum levels were 8-fold, 7-fold and 6-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The mean post-operative chromium in urine levels were 9-fold, 10-fold and 14-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The values seen in this study with the current generation of surface arthroplasties are: (a) lower than those seen in an earlier generation of surface arthroplasties; (b) in the same range as those observed in association with metal-on-metal conventional total hip replacements, which typically have smaller head sizes; (c) higher than values observed in patients with conventional metal-on-polyethylene articulating couples.     

On a New Method for Iterative Calculation of Crack Trajectory

A new efficient iterative procedure to follow automatically crack trajectory is suggested. Parameters of the procedure and illustrative examples are given.     

Acquiring writing revision and self-regulatory skill through observation and emulation.

The influences of modeling and social feedback on the acquisition of writing revision were studied with 72 college students. Students watching a coping female model gradually improving her writing technique on a sentence-combining task were hypothesized to surpass students observing a mastery model perform the technique flawlessly on a writing-skill measure and an array of self-regulatory measures, such as self-satisfaction reactions, self-efficacy perceptions, and intrinsic interest in the task. Students observing a mastery model were expected, in turn, to surpass those learning without the benefit of modeling on these same measures. Support for both hypotheses was found. Social feedback during enactive performance assisted learners from all modeling groups in acquiring writing and self-regulatory skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)