Zeolites as catalysts in organic reactions. Claisen-Schmidt condensation of acetophenone with benzaldehyde

HY zeolites catalyze the crossed aldol condensation of acetophenone with benzaldehyde, in benzene at 80 °C, to give trans- and cis-chalcones. Together with these expected products, 3,3-diphenylpropiophenone is also produced. In the analogous basic condensation, using phase transfer catalysis, the Michael adduct was not detected, and besides chalcone a small percentage of the Cannizzaro reaction product was observed.     

A methodological approach to fully automated highly accelerated life tests

Microsystem Technologies - Highly accelerated life test (HALT) is a test methodology to evaluate reliability of mechanical and electromechanical devices. HALT is often used on devices that must be...     

Damage driven crack initiation and propagation in ductile metals using XFEM

Originally Continuum Damage Mechanics and Fracture Mechanics evolved separately. However, when it comes to ductile fracture, an unified approach is quite beneficial for an accurate modelling of this phenomenon. Ductile materials may undergo moderate to large plastic deformations and internal degradation phenomena which are well described by continuum theories. Nevertheless in the final stages of failure, a discontinuous methodology is essential to represent surface decohesion and macro-crack propagation. In this work, XFEM is combined with the Lemaitre ductile damage model in a way that crack initiation and propagation are governed by the evolution of damage. The model was built under a finite strain assumption and a non-local integral formulation is applied to avoid pathological mesh dependence. The efficiency of the proposed methodology is evaluated through various numerical examples.     

Fines characterization through the methylene blue and sand equivalent test: comparison with other experimental techniques and application of criteria to the aggregate quality assessment

In road construction the general term fines is used to describe particles passing the 0.063, 0.074 or 0.08 mm sieve. Some types of fines are considered to be relatively inert and have almost no effect on pavement performance, whilst the presence of even small amounts of others can significantly affect the stiffness and freezing–thawing behaviour of unbound and hydraulically bound layers. This paper presents the results of research on 12 Slovenian aggregates produced from limestone and dolomite bedrock, and naturally occurring river alluvium gravel. At each production site three different materials were sampled and tested: the actual aggregate for unbound base layers, the clayey soils, which presented the most potentially harmful component at the specific location, and the stony dust, which presented the finest size of crushed aggregate and is typically found as coatings on the crushed grains. Six different methods were used to identify the nature of the fines: X-ray diffractometry, carbonate content determination, methylene blue, sand equivalent, Enslin–Neff water absorption, Atterberg limits test, soil suction measurements and soil water characteristic curves. Based on the results, the relationship between the properties of the different fines was determined and included in draft Slovenian national criteria for sand equivalent and methylene blue values currently being trialed.     

Neural Net Based Hybrid Modeling of the Methanol Synthesis Process

A Hybrid modeling approach, combining an analytical model with a radial basis function neural network is introduced in this paper. The modeling procedure is combined with genetic algorithm based feature selection designed to select informative variables from the set of available measurements. By only using informative inputs, the model's generalization ability can be enhanced. The approach proposed is applied to modeling of the liquid–phase methanol synthesis. It is shown that a hybrid modeling approach exploiting available a priori knowledge and experimental data can considerably outperform a purely analytical approach.     

Effects of international collaboration and status of journal on impact of papers

This study examines the effect of international collaboration of Slovenian authors and the status of journals where papers are published (as determined by their impact factors) on the impact of papers as measured by the number of citations papers receive. Research programme groups working in Slovenia in the 2004–2008 period in the fields of physics, chemistry, biology, biotechnology, and medical science were used for analyses. The results of the analyses show that the effects of the two factors differ among the fields. We discuss possible reasons for this, including the possibility that differences are the result of Slovenia’s science policy.     

Mechanochemical reaction in the K2CO3–Nb2O5 system

We studied the mechanochemical synthesis of KNbO₃, starting from a powder mixture of K₂CO₃ and Nb₂O₅. The milling experiments were designed with different ball-impact energies in order to investigate the mechanochemical reactions. X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, Raman spectroscopy and transmission electron microscopy were used to characterize the samples. Based on the results, we propose a mechanism for the mechanochemical reaction between K₂CO₃ and Nb₂O₅. The first stage of the reaction is characterized by the formation of an amorphous carbonato complex, which decomposes after prolonged milling at higher ball-impact energy giving rise to the crystallization of KNbO₃ and other niobate phases with a molar ratio K/Nb < 1. The reaction course is discussed and compared with the Na₂CO₃–Nb₂O₅ system.     

Role of indocyanine green fluorescence videoangiography in evaluation of subretinal disease

BACKGROUND: Indocyanine green (ICG) is a sterile, water-soluble, tricarbocyanine dye that can be used in fundus angiography as an adjunct to sodium fluorescein. It has a peak spectral absorption of 805 nm in blood plasma or blood, as compared with fluorescein, which has a peak spectral absorption of 465 nm. Because the absorption and emission of ICG lies around 835 nm, transmission of energy by the retinal pigment epithelium (RPE) and serosanguinated material is more efficient in this region than in the region of visible light energy. ICG has the property of being approximately 98% bound to blood protein, disallowing extravasation of excessive dye in the highly fenestrated choroidal vasculature. METHODS: The characteristics of ICG are discussed, including administration and dosage, adverse reactions and use of infrared filters for fundus photography. In addition, two cases are presented to illustrate the clinical application of ICG for diagnosis and treatment of choroidal neovascular membranes. RESULTS: ICG videoangiography can be used to reveal subfoveal choroidal neovascular membranes not previously identified with fluorescein; angiograms can also be used to dramatically highlight retinal and choroidal changes. CONCLUSIONS: The use of ICG for fundus videoangiography provides a more accurate and complete evaluation in certain cases of subretinal and choroidal disease.