One-pot two-step lipase-catalyzed synthesis of α,ω-thiophene-capped poly(ε-caprolactone) macromonomers and their use in electropolymerization

Macromonomers based on poly(ε-caprolactone) (PCL) with α,ω-thiophene functional end groups were prepared in bulk by enzymatic polymerization using immobilized Candida Antarctica lipase B (Novozym 435) as the catalyst. In the synthesis strategy, 3-thiophenemethanol was used to initiate the enzyme-assisted ring-opening polymerization of ε-caprolactone (ε-CL) to yield PCL with α-thiophene end group (initiation reaction, ThPCL) and then 3-thiopheneacetic acid was added to prepolymerized ε-CL to introduce ω-thiophene functionality in termination step (ThPCLTh). Macromonomers were characterized by ¹H and ¹³C NMR, FTIR, and GPC. Moreover, the obtained macromonomers were employed in electropolymerization experiments and copolymers with thiophene or pyrrole were synthesized through their end thiophene groups. These polymers were characterized by cyclic voltammetry (CV), FTIR, and scanning electron microscopy (SEM). Conductivity measurements were carried out by the four-probe technique.     

ESR studies of molecular motions at the interphase region of a blendlike polymeric material

The molecular motions of spin probes at the interphase region of poly(methyl methacrylate) particles sterically stabilized by polyisobutylene (PIB) were studied by ESR spectroscopy. The correlation times (τ) were measured by using the methods of Freed and Kivelson. Activation energies for different modes of motion were calculated at wide temperature range between ?140 and 140°C. Viscosities were estimated in methanol saturated PIB channels in the polymer particles. © 1994 John Wiley & Sons, Inc.     

Thermal and photochemical cationic polymerisations induced by AgPF6 in the presence of free radical initiators

Summary Cationic polymerisations of n-butylvinylether, tetrahydrofuran and a typical bis-epoxide are readily induced in the presence of AgPF⁶ by thermal and photochemically active sources of free radicals.     

In situ synthesized ceramic–polymer composites for bone tissue engineering: bioactivity and degradation studies

As an alternative to current bone grafting strategies, a poly-lactide-co-glycolide/calcium phosphate composite microsphere-based scaffold has been synthesized by the direct formation of calcium phosphate within forming microspheres. It was hypothesized that the synthesis of low crystalline calcium phosphate within forming microspheres would provide a site-specific delivery of calcium ions to enhance calcium phosphate reprecipitation onto the scaffold. Both polymeric and composite scaffolds were incubated in simulated body fluid (SBF) for 8 weeks, during which time polymer molecular weight, scaffold mass, calcium ion concentration of SBF, pH of SBF, and calcium phosphate reprecipitation was monitored. Results showed a 20% decrease in polymeric scaffold molecular weight compared to 11–14% decrease for composite scaffolds over 8 weeks. Composite scaffold mass and SBF pH decreased for the first 2 weeks but began increasing after 2 weeks and continued to do so up to 8 weeks, suggesting interplay between pH changes and calcium phosphate dissolution/reprecipitation. Free calcium ion concentration of SBF containing composite scaffolds increased 20–40% over control values within 4 h of incubation but then dropped as low as 40% below control values, suggesting an initial burst release of calcium ions followed by a reprecipitation onto the scaffold surface. Scanning electron micrographs confirm calcium phosphate reprecipitation on the scaffold surface after only 3 days of incubation. Results suggest the composite scaffold is capable of initiating calcium phosphate reprecipitation which may aid in bone/implant integration.     

Development of a decision support system for robot selection

With the availability of more different robot types and models along with their separate specifications, selecting the most appropriate robot is becoming more difficult and complicated for companies. Furthermore, a common set of robot selection criteria is not available for the decision makers. In this study, a two-phase robot selection decision support system, namely ROBSEL, is developed to help the decision makers in their robot selection decisions. In development of ROBSEL, an independent set of criteria is obtained first and arranged in the Fuzzy Analytical Hierarchy Process (FAHP) decision hierarchy. In the first elimination phase of the decision support system, the user obtains the feasible set of robots by providing limited values for the 15 requirements. ROBSEL, then, uses FAHP decision hierarchy to rank the feasible robots in the second phase. ROBSEL is illustrated and tested and several critical issues in its practical usage are explored in the paper. The applications of ROBSEL show that ROBSEL is a useful, practical and easy to use robot selection tool and improves robot selection decisions in the companies.     

Applied Genetic Algorithm for Solving Rich VRP

In this article, we present a study of the effectiveness of a genetic algorithm (GA) to solve a combinatorial problem, that is, a vehicle routing problem (VRP). We propose a new selection method, called “rank and select,” based on selection rate, and we compare it with roulette wheel selection. In this article, we use two types of crossover method and two types of mutation method. These are applied for comparing the best fitness at the end of a generation. The problem solved in this study is how to generate feasible route combinations for a rich VRP and meet all the requirements with an optimum solution. Initial test results show that the route produced by the GA was effectively used for solving rich VRP and especially for a large number of customers, depots, and vehicles. Fuel consumption by proposed routes was lower by about 20.38% compared to that of an existing route.     

A cost-sensitive decision tree approach for fraud detection

With the developments in the information technology, fraud is spreading all over the world, resulting in huge financial losses. Though fraud prevention mechanisms such as CHIP&PIN are developed for credit card systems, these mechanisms do not prevent the most common fraud types such as fraudulent credit card usages over virtual POS (Point Of Sale) terminals or mail orders so called online credit card fraud. As a result, fraud detection becomes the essential tool and probably the best way to stop such fraud types. In this study, a new cost-sensitive decision tree approach which minimizes the sum of misclassification costs while selecting the splitting attribute at each non-terminal node is developed and the performance of this approach is compared with the well-known traditional classification models on a real world credit card data set. In this approach, misclassification costs are taken as varying. The results show that this cost-sensitive decision tree algorithm outperforms the existing well-known methods on the given problem set with respect to the well-known performance metrics such as accuracy and true positive rate, but also a newly defined cost-sensitive metric specific to credit card fraud detection domain. Accordingly, financial losses due to fraudulent transactions can be decreased more by the implementation of this approach in fraud detection systems.     

Effect of different surface shapes formed by femtosecond laser on zirconia-resin cement shear bond strength

Objective: The purpose of this study was to evaluate the effect of different surface shapes formed by femtosecond (FS) laser on zirconia (Y-TZP)-resin cement shear bond strength (SBS). Background data: All ceramic restoration is used as an alternative to metal-ceramic restorations, due to its better aesthetics, strength, and toughness properties. However, bond strength of restoration to tooth and other materials is effective to long term success of the restoration, and to achieve it surface treatment is required on ceramic surface. Materials and methods: Forty square-shaped zirconia samples were prepared and assigned to four groups of 10. The details of the groups are as follows: Group A, square-shaped recessed surface; Group B, square-shaped projection surface; Group C, circular-shaped recessed surface; Group D, circular-shaped projection surface. The SBSs values were performed with a universal testing machine at a crosshead speed of 1 mm/min. The data were analyzed statistically using analysis of variance (ANOVA) and Tukey HSD multiple comparisons tests. Results: The one-way ANOVA results on SBSs of the zirconia material bonded with resin cement revealed significant differences among the groups (p < 0.05). The Tukey HSD test results revealed that Group B and D had significantly higher SBS values than other groups (p < 0.05), but there were no significant differences between each other (p > 0.05). Additionally, Group A and C had significantly lower values than other groups (p < 0.05). Conclusions: Different surface shapes formed by FS laser provided a significant increase in SBSs. The SBS values of projection surfaces of circular and square-shapes are greater than that of recessed surfaces of circular and square-shapes.     

A fast tool servo design for precision turning of shafts on conventional CNC lathes

A technique for precision turning of shafts on conventional CNC turning centers is presented. The shaft is semi-turned on a conventional CNC lathe. The precision finish turning operation is delivered by a piezoelectric based fast tool servo which is mounted on the same CNC lathe's turret. The precision tool tip motion is delivered by a proposed sliding mode controller which is robust to changes in the cutting process and hysteresis in the piezo actuator. Sliding mode controller is also quick to compensate the cutting force disturbances, and keeps the tool tip at the desired location within the displacement measurement sensor resolution (±0.1 μm). The fast tool servo system is packaged in a PC, and its effectiveness is demonstrated on a bearing location turning.