Radiation‐induced effects in gamma‐irradiated PLLA and PCL at ambient and dry ice temperatures

The effect of γ‐rays sterilization at ambient (23°C) and at dry ice temperatures (?78°C) on two biodegradable semicrystalline polyesters, namely poly(L ‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL), was studied. The radical processes generated by irradiation were investigated by electron paramagnetic resonance (EPR) spectroscopy, whereas postradiation changes were monitored for 5 months by scanning calorimetry, thermogravimetric analysis, and apparent viscosity measurements. It was confirmed that the radiation sterilization initiates degradation in both studied polymers, however, the effect is smaller in PCL than in PLLA, and that the range of changes might be limited by lowering temperature of the exposure to γ‐rays. Newly formed oxygen containing functional groups confirmed by EPR and thermogravimetric analysis methods are produced in the irradiated polyesters. In PCL, the process might give rise to thermally induced cross‐linking via oxygen containing intermolecular bridges. During storage, in both irradiated materials, morphology determined by differential scanning calorimetry is changing ‐ PCL ability toward crystallization decreases insignificantly, whereas in PLLA the tendency is opposite ‐ on irradiation a contribution of crystalline phase is growing considerably, from 18 and 19% to 41 and 31% for PLLA irradiated at 23°C and at ?78°C, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Properties of CO2 laser-welded butt joints of dissimilar magnesium alloys

The paper presents results of keyhole laser beam welding of dissimilar magnesium alloys that have been carried out with the CO₂ laser of maximum power of 2.5 kW. The workpieces of die-cast alloys AZ91 and AM50 with thicknesses of 4.5 mm have been butt-welded with helium used as a shielding gas. With the chosen flow rate of helium shielding and the focal position set on the metal surface the nearly parallel fusion zones boundaries were obtained. The analysis of microstructures of the joints, measurements of hardness distribution and the elemental distribution in the weld cross-sections permitted to find the changes due to heating in the fusion zones and recrystallization. The static tensile strength tests and the three point bending tests have allowed to determine the mechanical properties of the joints. The corrosion resistance tests performed by the electrochemical method on samples of as-cast materials and samples with the welds of similar and dissimilar alloys have not displayed the differences in the corrosion resistance. However, the microscopic observations of surfaces of welded samples have shown the influence of the joints on corrosion development.     

Cutting data correction in Inconel 718 turning

The paper presents research work concerning difficult-to-cut materials turning and chipbreakers reliability in local operating features. Inconel 718 alloy was used as a sample material and two different chipbreakers were tested. The aim of the research was to check the efficiency of chipbreakers in the area of applications recommended by tool manufacturers. As a result, the algorithm for cutting data selection and correction which combines experiments and simulation processes concerning chip breakage effectiveness was built. To estimate chip forms in tests, the visual system equipped with a high-speed camera was used. The cutting forces measuring system provided information for verification of simulation results. The simulation based on the FEM was applied to estimate chip groove filling. Distributions of temperature and stresses on the tool rake face in the function of distance from the cutting edge were calculated. The paper gives recommendations for cutting data correction to achieve acceptable chip forms.     

ENDER: a statistical framework for boosting decision rules

Induction of decision rules plays an important role in machine learning. The main advantage of decision rules is their simplicity and human-interpretable form. Moreover, they are capable of modeling complex interactions between attributes. In this paper, we thoroughly analyze a learning algorithm, called ENDER, which constructs an ensemble of decision rules. This algorithm is tailored for regression and binary classification problems. It uses the boosting approach for learning, which can be treated as generalization of sequential covering. Each new rule is fitted by focusing on examples which were the hardest to classify correctly by the rules already present in the ensemble. We consider different loss functions and minimization techniques often encountered in the boosting framework. The minimization techniques are used to derive impurity measures which control construction of single decision rules. Properties of four different impurity measures are analyzed with respect to the trade-off between misclassification (discrimination) and coverage (completeness) of the rule. Moreover, we consider regularization consisting of shrinking and sampling. Finally, we compare the ENDER algorithm with other well-known decision rule learners such as SLIPPER, LRI and RuleFit.     

Investigations on electrochemical α-methoxylation of selected dipeptides

Voltamperometric studies on the indirect electrochemical α-methoxylation of Boc-Pro-Gly-OMe and Boc-Val-Gly-OMe in MeOH in the presence of NaCl or NaBr as the mediator suggested that the first reaction step was a direct N-halogenation of the dipeptide by active chlorine or bromine adsorbed on the electrode surface. The kind of mediator (NaCl or NaBr), its concentration, the current density, and the applied electric charge had a significant influence on the reaction course. In the case of Boc-Pro-Gly-OMe, the use of sodium bromide was necessary to obtain a relatively high ratio of α-monomethoxylation to α,α-dimethoxylation. For Boc-Val-Gly-OMe, the selectivity for α-monomethoxylation was close to 100%, independently of the mediator. Optimisation of the selected electrolysis parameters allowed us to significantly improve the yield and selectivity of the α-methoxylation of Boc-Pro-Gly-OMe (Kardassis et al. Tetrahedron 54:3471, 1998) and to obtain good results in the α-methoxylation of Boc-Val-Gly-OMe.     

Society of self: The emergence of collective properties in self-structure.

Using cellular automata, the authors show how mutual influences among elements of self-relevant information give rise to dynamism, differentiation, and global evaluation in self-concept. The model assumes a press for integration that promotes internally generated dynamics and enables the self-structure to operate as a self-organizing dynamical system. When this press is set at high values, the self can resist inconsistent information and reestablish equilibrium after being perturbed by such information. A weak press for integration, on the other hand, impairs self-organization tendencies, making the system vulnerable to external information. Paradoxically, external information of a random nature may enhance the emergence of a stable self-structure in an initially disordered system. The simulation results suggest that important global properties of the self reflect the operation of integration processes that are generic in complex systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analyzing semiconductor devices using modulation spectroscopy

Improvements in the quality and yield of semiconductor devices will rely on characterization methods that are informative, nondestructive, convenient, easy to use, and inexpensive. Ideally, one would like to perform the characterization procedure at room temperature on entire wafers, possibly even before the structure is removed from the growth chamber. Because of their simplicity and proven ability, the contactless electro-modulation methods of photoreflectance and contactless electroreflectance are ideally suited for this purpose. Modulation spectroscopy has already been applied to examine such devices as heterojunction bipolar transistors, pseudomorphic high-electron-mobility transistors, quantum-well lasers, vertical cavity surface-emitting lasers, multiple-quantum-well infrared detectors, superlattice optical mirrors, resonant tunneling structures, solar cells, and metal-oxide-semiconductor configurations.     

Coupling monolayers for protection of microelectronic circuits

Two polymeric coatings, a silicone gel (Dow Corning 6646) and an epoxy resin (Dexter FP 4402), were glob-top coated onto representative microelectronic circuits, AT&T Triple Track Testers (TTTs), and subjected to the Pressure Cooker Test (PCT). Coupling monolayers were self- assembled on the TTTs prior to encapsulation to improve the moisture protection capabilities of the coatings. Leakage current measurements were made to evaluate the effect of applied monolayers on the moisture protection capability. The moisture protection capability was assessed in short-term and long-term leakage current measurements. MHDA (16-mercaptohexadecanoic acid) and APS (gamma-aminopropyltriethoxysilane) monolayers, in combination with silicone gel and epoxy resin respectively, exhibited very good moisture protection performance.     

High molecular arborescent polyoxyethylene with hydroxyl containing shell

Arborescent polyoxyethylene of high molar mass (2×10⁵ g/mol) and narrow molar mass distribution was synthesized in a three-stage process. In the first stage a triblock copolymer of ethylene oxide (central block, DP ca. 90) and 2,3-epoxypropanol-1 (short flanking blocks, DP ca. 5) was synthesized. The potassium alcoholate derived from this copolymer was used to initiate the polymerization of ethylene oxide and the subsequent addition of protected glycidol (1-etoxyethyl glycidyl ether). After deprotection the short polyglycidol blocks were used as branching units for the next generation. Repeated step by step process leads to the ‘pom-pom like’ branched polyoxyethylene macromolecules enriched with the reactive hydroxyl groups in the outer shell. The branched structure of the obtained polymers was evidenced by the size exclusion chromatography and NMR spectroscopy.