The influence of bridge groups nature in diepoxy compounds on kinetics of curing process by diamines and on physical and mechanical properties of forming polymers

Summary In the present work the initial monomer reactivity in curing reaction of epoxy compounds by aromatic diamines has been investigated. Also physical and mechanical properties of cured polumers of diglycidyl ethers 4,4-bisaromatic compounds with bridge groups have been examined.     

I.r. spectroscopy characterization of various types of structural irregularities in pyrolytic boron nitride

Samples of pyrolytic BN ceramics were produced by CVD from BCl₃-NH₃-N₂ mixtures at temperatures of 1300–2100°C, pressures 1–20 torr and varying partial pressures of the components. A theoretical analysis of the dependences of i.r. spectral band frequencies on interlayer distance and crystal block size is given. Five BN structure modifications have been found in BN ceramics from i.r. band shape analysis: hexagonal graphite-like, partially ordered, turbostratic, dense amorphous and highly dispersed amorphous, whose relative content strongly depends on the synthesis conditions.     

Evaluation of glass samples for forensic purposes — An application of likelihood ratios and an information-theoretical approach

This article presents an experimental study about the influence of the selection of an adequate database for evidence evaluation using chemical profiles. Evidence evaluation in the forensic sense can be seen as the comparison of two glass objects, one of known origin, denoted as control glass, and typically would be from the scene of a crime, and the other one of unknown origin, termed recovered glass, which might be found in association with a suspect. The aim is to obtain some estimate of the weight of evidence for the degree of support to any of the hypothesis in the case, typically these might be that the control and recovered glass come from the same source (θ_p), and control and recovered glass come from different sources (θ_d). A likelihood ratio is considered a suitable measure of the evidential weight for the competing propositions. The observations are of the elemental composition of glass, measured using a Scanning Electron Microscopy, coupled with an Energy Dispersive X-ray spectrometer technique. A number of glass objects have been analyzed and their chemical profiles form a database which represents several sources of variation. In this paper questions surrounding the choice of observations to make are addressed empirically by assessing the impact of building each model using a database different from the one using for comparison. The performance of each evidence evaluation method is assessed by classical methods such as Tippett plots, or more recent information-theoretical approaches such as empirical cross-entropy (ECE) plots.The results show that several of the compositional elements are very robust to the selection of the background database, namely; calcium, silicon and sodium observed in their oxide forms. We also show that the likelihood ratio computed with the combination of these variables show a remarkable discriminating power, and good calibration, allowing them to be employed for the calculation of the strength of evidence in forensic case work.     

Actor grammars

Actor systems are a model of massively parallel systems based on asynchronous message passing. This paper presents a formalism for a restricted version of actor systems in the framework of graph grammars. To this aim actor grammars are introduced, motivated, and illustrated by examples. Some of the basic properties pertinent to graph transformations in actor grammars are discussed.     

Primitivity is hereditary for 2-structures

It is proved that each primitive 2-structure on n elements (n3) contains a primitive substructure on either (n−1) or (n−2) elements.     

Bioactive Titanium Surfaces Enriched with Silver Nanoparticles Through an In Situ Reduction: Looking for a Balance Between Cytocompatibility and Antibacterial Activity

This research aims toward an antibacterial and osteoconductive Ti₆Al₄V surface by chemical etching–oxidation treatment and in situ reduction of silver nanoparticles. Starting from a previously developed process, already proved to enhance the osteoinductive ability of titanium, different parameters are changed to tailor the amount of silver and its distribution across the surface oxide layer thickness. The samples are characterized by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, release of silver, biofilm formation (Staphylococcus aureus), and cytocompatibility toward human osteoblasts progenitor cells. The total amount of silver in the surface oxide layer depends only on the concentration of the silver precursor. The time of the addition of the silver precursor, during the oxidation treatment, affects the oxide layer thickness, dimension, and distribution of the nanoparticles across the surface oxide: they are larger and accumulate on the outermost layer, if the addition occurs early. The maximum ion release occurs after 24 h and lasts up to 14 days; the later addition of silver precursors leads to sustaining the silver release for a longer time. The samples prepared with the higher concentration of the silver precursor are bactericide, but highly cytotoxic, whereas the other ones are bacteriostatic and moderately cytotoxic.