The effect of citric acid on the sintering of calcium phosphate bioceramics

Biphasic calcium phosphate particles were prepared using a rapid increase of the pH value by adding an amount of concentrated ammonia solution, into a well-mixed solution containing Ca(H₂PO₄)₂·H₂O and CaCl₂ with Ca/P = 1.667 molar ratio; with or without the presence of citric acid (CiA). The precipitation of Calcium Phosphates took place at 97 °C using high-speed dispersing equipment. The samples were characterized using XRD, FT-IR, BET and SEM techniques. The thermal behaviour was studied by TG, DTG and DTA techniques. The modified precipitation method leads to the formation of biphasic needle-like particles consisted of crystalline hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP). The presence of CiA in the initial solution leads to the formation of aggregated nonporous small spheroidal particles consisted of low crystallinity phases of HA and octacalcium phosphate (OCP). The later facilitates the sintering process. The calcined samples at 900 °C were consisted of calcium pyrophosphate (CPP) and TCP. α-TCP is formed in the presence of a large amount of calcium citrate complexes. The main sintering process took place at the temperature range between 750 and 1150 °C, which were strongly depended on the initial amount of the CiA in the precipitation process. These results indicated that the citrate presence in the initial solution have a strong influence on the nucleation and growth processes by complexation with calcium ions and incorporation into the solid structure during particle growth.     

Functional ceramic and nanocomposite fibers, cellular articles and microspheres via radiation curable colloidal dispersions

We present here new cellular ceramics, fibers and microspheres produced by novel and general microshaping techniques employing colloidal dispersions in solvent free radiation curable monomer mixtures. High loading, low viscosity dispersions of functional nanoparticles such as TiO₂ and α-Fe₂O₃ and colloidal Fe(C₂O₄)·2H₂O metal salt are achieved with comb-polyelectrolyte surfactants and/or mildly polar resins. TiO₂ dispersions are spun and solidified “on the fly” by UV radiation into continuous ceramic/polymer nanocomposite fibers with dimensions below 10 μm. Fe(C₂O₄)·2H₂O dispersions provide a UV curable alternative to α-Fe₂O₃ dispersions which can only be thermally cured. The Fe(C₂O₄)·2H₂O nanocomposites transform to α-Fe₂O₃ below 550 °C. Novel cellular Al₂O₃, TiO₂ and α-Fe₂O₃ articles with porosity >80% and precise replication of the pore-forming agents have also been produced from such dispersions. Al₂O₃ nanocomposite microspheres are produced by emulsification of the dispersions in an appropriate medium and UV curing.     

A COMPILATION OF THE D-OPTIMAL DESIGNS IN CHEMICAL KINETICS

This paper links the chemical kinetic models that obey the framework of nonlinear statistical models with optimal design theory. We provide the appropriate optimal designs for them, so that the involved parameters can be estimated as well as possible. Therefore, the D-optimality criterion is adopted, under the optimal design approach, for a number of models used in chemical kinetic applications. In the tables, the collected results are presented for 15 models.     

The three-stage ordered flow shop problem with flexible stage ordering

We consider a design problem involving a three-machine ordered flow shop with flexible stage ordering to determine, from a scheduling perspective, which layout (and which schedule) is the best. We conclude that the Small–Median–Large layout coupled with Shortest Processing Time (SPT) sequencing rule yield the best design with respect to both the maximum job completion time (makespan) and the total (average) job completion time criteria.     

The effect of modified atmosphere packaging on the microbiological,physical, chemical and sensory characteristics of broadtail squid (Illex coindetii)

The aim of this work was to evaluate the effect of various atmosphere compositions (20% CO₂/80% N₂ for modified atmosphere packaging (MAP) 1, 50% CO₂/50% N₂ for MAP 2, 70% CO₂/30% N₂ for MAP 3 and vacuum packaging) on the microbial (mesophiles, psychrophiles, Pseudomonas spp., Brochothrix thermosphacta and Enterobacteriaceae), physical, chemical [trimethylamine (TMA) and total volatile basic nitrogen (TVBN)] and sensorial characteristics of broadtail squid (Illex coindetii) stored for 10 days at 2 ± 1 °C. All microbial populations were severely restrained by MAP 3 with the exception of Enterobacteriaceae, which seemed to take advantage of the lack of competitive microflora and had enhanced microbial counts on MAP samples (P < 0.05). Colour attributes were better maintained on MAP‐stored samples. Drip loss was less on vacuum‐packaged squids. MAP 2 was the best atmosphere for the preservation of tissue consistency. TMA and TVBN formation was limited by high CO₂ atmospheres, even though both elevated in all studied conditions. Shelf life based on sensory characteristics was determined to be 10, 8, 6, 6 and 4 days for MAP 3, MAP 2, MAP 1, vacuum and control samples, respectively.     

Interaction mechanism of hydrogen storage materials with layer-by-layer applied protective polyelectrolyte coatings

Metal hydrides are promising compounds for the storage of hydrogen especially in the transport sector. Their high reactivity with moisture and difficult handling in ambient atmosphere prevents their easy application in tanks and thus the market penetration of this very promising and clean technology. In the present work we investigated the way to protect sodium borohydride with organic polyelectrolytes like polyethyleneimine (PEI) and dicarboxy terminated poly(acrylonitrile-co-butadiene-co-acrylic acid) (PABA) with emphasis on the interaction of those polyelectrolytes with the SBH. The polyelectrolytes protect SBH either by electrostatic adsorption or by reacting with it, depending on the reactive groups present in their structure. PABA undergoes only an electrostatic interaction with the SBH substrate. PEI on the other hand interacts chemically with the SBH substrate and forms complexes with groups on the SBH surface. Both polyelectrolytes can be applied in a layer-by-layer approach on the SBH in order to protect it. Regarding the best order of the layer application XPS results yield that the formation of the boron-amino-complexes between the PEI and the SBH is independent of the order in which the PABA and PEI layers are applied. However, the rearrangement of the SBH surface groups due to the application of the PEI films has been found to be considerably influenced by the order of application. The effect of a PEI film has been mostly compensated by the subsequent application of a PABA film, while the application of PEI had a much larger influence on the surface of a PABA coated SBH sample. Thus, the best order of the layer application with respect to the application according to XPS is to deposit the PEI layer at first and the PABA layer afterwards.     

Measuring instant emotions based on facial expressions during computer-based assessment

Emotions are very important during learning and assessment procedures. However, measuring emotions is a very demanding task. Several tools have been developed and used for this purpose. In this paper, the efficiency of the FaceReader during a computer-based assessment (CBA) was evaluated. Instant measurements of the FaceReader were compared with the researchers’ estimations regarding students’ emotions. The observations took place in a properly designed room in real time. Statistical analysis showed that there are some differences between FaceReader’s and researchers’ estimations regarding Disgusted and Angry emotions. Results showed that FaceReader is capable of measuring emotions with an efficacy of over 87% during a CBA and that it could be successfully integrated into a computer-aided learning system for the purpose of emotion recognition. Moreover, this study provides useful results for the emotional states of students during CBA and learning procedures. This is actually the first time that student’s instant emotions were measured during a CBA, based on their facial expressions. Results showed that most of the time students were experiencing Neutral, Angry, and Sad emotions. Furthermore, gender analysis highlights differences between genders’ instant emotions.     

Optimal Admission Control of Discrete Event Systems with Real-Time Constraints

The problem of optimally controlling the processing rate of tasks in Discrete Event Systems with hard real-time constraints has been addressed in prior work under the assumption that a feasible solution exists. Since this cannot generally be the case, we introduce in this paper an admission control scheme in which some tasks are removed with the objective of maximizing the number of remaining tasks which are all guaranteed feasibility. We derive several optimality properties based on which we develop a computationally efficient algorithm for solving this admission control problem under certain conditions. Moreover, when no future task information is available, we derive necessary and sufficient conditions under which idling is optimal and define a metric for evaluating when and how long it is optimal to idle. Numerical examples are included to illustrate our results.