Effects of thermal treatment of nanostructured trititanates on their crystallographic and textural properties

Nanostructured titanates (TTNT) with general formula Na_xH_2−xTi₃O₇·nH₂O were synthesized by hydrothermally reacting different TiO₂ anatase (distinct crystal sizes) with NaOH at 120 °C followed by washing with water or diluted acid and drying of the precipitate. The resulting powders with different sodium contents were submitted to various calcination temperatures up to 800 °C and each calcined product was characterized as for its phase structure, composition, crystallite size and textural properties, namely BET surface area, mesopore volume and pore size distribution. Thermal transformations of TTNT samples were investigated by monitoring the modifications on crystallographic (X-ray diffraction) and textural (N₂ desorption isotherms) properties, revealing the influence of the type of starting anatase and sodium content over the stability of TTNT. Moreover, a detailed study on the reduction of the interlayer distance in TTNT samples upon thermal treatment allowed corroborating the formation of an intermediate nanostructured hexatitanate, just before phase transformation into the corresponding TiO₂ polymorphs and/or titanate crystals, depending on the sodium content and calcination temperature.     

A mechanistic study of enantiomeric separation with vancomycin and balhimycin as chiral selectors by capillary electrophoresis. Dimerization and enantioselectivity

The role of the sugar moiety of glycopeptide antibiotics in chiral recognition was investigated with capillary electrophoresis. Two glycopeptide antibiotics, vancomycin and balhimycin, were employed as models since they possess the same aglycon and almost identical sugar moieties, however, with different attachment sites to the aglycon. The observed enantioselectivity of balhimycin for dansylated alpha-amino acids is 2.6 times higher than that of vancomycin. Blocking of the sugar amino group of balhimycin by N-carbamoylation reaction with KOCN led to a significantly decreased enantioselectivity compared to vancomycin, which remained almost the same upon carbamoylation. These results suggest a major role of the amino sugar together with its site of attachment to the aglycon. A dimerization-based mechanism is proposed to explain this phenomenon due to the fact that the dimerization properties of glycopeptides are similarly related to their glycosylation patterns; e.g., the dimerization constant of balhimycin is 78 times higher than that of vancomycin. Furthermore, the dimerization of glycopeptides promotes their affinity to carboxyl-containing ligands via cooperativity effects between the dimerization and the formation of glycopeptide-ligand complexes. The higher dimer stability probably leads to a more favorable conformation for chiral recognition. Thus, it is concluded that a weakened dimerization of N-carbamoylated balhimycin results in a decreased enantioselectivity.     

An end-quality assessment system for electronically commutated motors based on evidential reasoning

Automatic end-quality assessment is a mean that helps reaching zero-fault products at the end of the manufacturing process. In this paper we present a system for assessing the quality of electronically commutated motors. The system consists of two major parts: feature extraction and overall quality assessment. The feature extraction part consists of signal processing algorithms tailored for mechanical fault detection. The quality assessment part, aimed for fault isolation and final quality decision, employs evidential reasoning for multi-attribute decision analysis. A prototype version of the system is validated on a test batch of 130 electronically commutated motors, demonstrating high diagnostic resolution and accuracy.     

Solving some overflow traffic models with changed serving intensities

This paper investigates specific systems with overflow traffic. A primary group with two Poisson traffics is considered whereupon the rejected calls from one traffic are directed to the alternative group with changed serving intensities. The generating function technique is used for analytical solving the model with secondary and ternary groups and the model that separately treated the channels in alternative groups. The obtained analytical solutions essentially reduce the constraints concerning the equation system size, convergence, and calculation time, which arise when numerically solving the steady-state system equations. For the case with single channels in the ternary group, explicit solutions for traffic parameters are obtained. Also, comparison with the model that has a unique serving intensity of overflow traffic is made.     

Impact of thicker cladding on the nuclear parameters of the NPP Krško fuel

To make fuel rods more resistant to grid-to-rod fretting or other cladding penetration failures, the cladding thickness could be increased or strengthened. Implementation of thicker fuel rod cladding was evaluated for the NPP Krško that uses 16 × 16 fuel design. Cladding thickness of the Westinghouse standard fuel design (STD) and optimized fuel design (OFA) is increased. The reactivity effect during the fuel burnup is determined. To obtain a complete realistic view of the fuel behaviour a typical, near equilibrium, 18-month fuel cycle is investigated. The most important nuclear core parameters such as critical boron concentrations, isothermal temperature coefficient and rod worth are determined and compared.     

Sub-micrometer-sized graphite as a conducting and catalytic counter electrode for dye-sensitized solar cells

Sub-micrometer-sized colloidal graphite (CG) was tested as a conducting electrode to replace transparent conducting oxide (TCO) electrodes and as a catalytic material to replace platinum (Pt) for I(3)(-) reduction in dye-sensitized solar cell (DSSC). CG paste was used to make a film via the doctor-blade process. The 9 μm thick CG film showed a lower resistivity (7 Ω/?) than the widely used fluorine-doped tin oxide TCO (8-15 Ω/?). The catalytic activity of this graphite film was measured and compared with the corresponding properties of Pt. Cyclic voltammetry and electrochemical impedance spectroscopy studies clearly showed a decrease in the charge transfer resistance with the increase in the thickness of the graphite layer from 3 to 9 μm. Under 1 sun illumination (100 mW cm(-2), AM 1.5), DSSCs with submicrometer-sized graphite as a catalyst on fluorine-doped tin oxide TCO showed an energy conversion efficiency greater than 6.0%, comparable to the conversion efficiency of Pt. DSSCs with a graphite counter electrode (CE) on TCO-free bare glass showed an energy conversion efficiency greater than 5.0%, which demonstrated that the graphite layer could be used both as a conducting layer and as a catalytic layer.     

A new anisotropic elasto-plastic model with degradation of elastic modulus for accurate springback simulations

Springback, a phenomenon that is governed by elastic strain recovery after the removal of forming loads, is of great concern in sheet metal forming. There is no doubt that in this regard, physically reliable numerical modelling of the forming process and predictions of springback obtained by respective computer simulations are crucial for controlling this problem. Unfortunately, by currently available approaches, springback still cannot be adequately predicted in general. In this paper, a new constitutive model is proposed which considers simultaneously sheet anisotropy, damage evolution and strain path-dependent stiffness degradation during sheet metal forming. For parameter identification of the built constitutive model, a particular experimental procedure is developed and an optimization procedure is employed to solve the inverse problem that arises. The proposed approach to constitutive modelling is validated in the end by a simulation of the springback in the formed HSS steel sheet. The simulation results, which prove to be in good agreement with the experimental ones, lead to the conclusion that accurate modelling only of anisotropic yielding is not enough to accurately predict the springback phenomenon; the constitutive model should also include the strain path-dependent change of the elastic moduli.     

Al2Mo3O12/polyethylene composites with reduced coefficient of thermal expansion

Recently, polymer composites reinforced with low fractions of thermomiotic nanoceramics have triggered a lot of research. The efforts have been focused on achieving considerable reduction of the coefficient of thermal expansion (CTE) of polymeric materials without deterioration of other physical properties. In this context, polyethylene (PE) composites reinforced with different loads of Al₂Mo₃O₁₂ nanofillers (0.5–4 mass %) were fabricated by micro-compounding. To enhance the interfacial interaction between the two components, chemical functionalization of Al₂Mo₃O₁₂ was performed with vinyltrimethoxysilane (VTMS) prior to micro-compounding. Infrared spectroscopy and thermogravimetry demonstrated the successful grafting of VTMS on the Al₂Mo₃O₁₂ surface. The composites showed strongly decreased CTEs, up to 46 % reduction for loadings of 4 mass % compared with neat PE, suggesting intimate filler–matrix interactions. The variation of CTEs of the composites in terms of the filler fraction was successfully described by Turner’s model allowing calculation of the bulk modulus of monoclinic Al₂Mo₃O₁₂ (13.6 ± 2.6 GPa), in agreement with the value obtained by an ultrasonic method. The thermal stability of the composites was improved, although the addition of functionalized fillers decreased the degree of crystallinity of the PE to a small extent. The Young’s modulus and yield strength of the composites increased from 6.6 to 19.1 % and 4.0–6.0 %, respectively, supporting the existence of strong filler–matrix interactions, contributing to an efficient load transfer. Finite element analysis of thermal stresses indicated absence of plastic deformation of the matrix or fracture of the nanofillers, for a 100 K temperature drop.     

Fuel with advanced burnable absorbers design for the IRIS reactor core: Combined Erbia and IFBA

IRIS is an advanced medium-size (1000 MW) PWR with integral primary system targeting deployment already around 2015–2017. Consistent with its aggressive development and deployment schedule, the “first IRIS” core design assumes current, licensed fuel technology, i.e., UO₂ fuel with less than 5% ²³⁵U enrichment. The core consists of 89 fuel assemblies employing the 17×17 Westinghouse Robust Fuel Assembly (RFA) design and Standard Fuel dimensions. The adopted design enables to meet all the objectives of the first IRIS core, including over 3-year cycle length with low soluble boron concentration, within the envelope of licensed, readily available fuel technology. Alternative fuel designs are investigated for the subsequent waves of IRIS reactors in pursuit of further improving the fuel utilization and/or extending the cycle length. In particular, an increase in the lattice pitch from the current 0.496 in. for the Standard Fuel to 0.523 in. is among the objectives of this study. The larger fuel pitch and increased moderator-to-fuel volume ratio that it entails fosters better neutron thermalization in an altogether under-moderated lattice thereby offering the potential for considerable increase of fuel utilization and cycle length, up to 5% in the two-batch fuel management scheme considered for IRIS. However, the improved moderation also favors higher values of the Moderator Temperature Coefficient, MTC, which must be properly counteracted to avoid undesired repercussions on the plant safety parameters or controllability during transient operations. This paper investigates counterbalancing the increase in the MTC caused by the enhanced moderation lattice by adopting a suitable choice of fuel burnable absorber (BA). In particular, a fuel design combining erbia, which benefits MTC due to its resonant behavior but leads to residual reactivity penalty, and IFBA, which maximizes cycle length, is pursued. In the proposed approach, IFBA provides the bulk of the hold-down, with no penalty on cycle length, while the amount of erbia is adjusted to obtain the desired margin in the core peaking power and MTC. Preliminary economic analysis proves that within the IRIS design envelope, the combined BA fuel together with the enhanced moderation lattice offer the potential for considerable fuel cycle cost savings when compared to the current core design based on the Westinghouse Standard 17×17 lattice with IFBA. Therefore a combined BA fuel with the enhanced moderation lattice is a promising option to consider for future developments of the IRIS core.