Conversion of transgranular to intergranular fracture in NiCr steels

The paper is focused on quantification of causes and characteristics that govern the intergranular fracture initiation and propagation of this fracture micromechanism in competition with cleavage one. A NiCr steel of commercial quality and the same steel with an increased content of impurity elements, Sn and Sb, have been used for this investigation. Step cooling annealing was applied in order to induce intergranular embrittlement and brittle fracture initiation in both steels. Standard bend and the pre-cracked Charpy type specimen geometries were both tested in three-point bending to determine the fracture toughness characteristics. Charpy V notch specimens tested statically in three-point bending supported by FEM calculation have been used for local fracture stress and other local parameters determination. Relation of cleavage fracture stress and critical stress for intergranular failure has been followed showing capability of this parameter for quantification of the transgranular/intergranular fracture conversion. In order to characterise the quantitative roughness differences in fracture surfaces fractal analysis was applied. A boundary level of fractal dimension has been determined to be 1.12 for the investigated steel; the fracture surface roughness with a higher value reflects high level of intergranular embrittlement and thus fracture toughness degradation.     

Deposition of Al nanoparticles and their nanocomposites using a gas aggregation cluster source

The study describes the preparation and properties of Al/Al _x O _y nanoparticles and their nanocomposites with hydrocarbon plasma polymer. The nanoparticles were deposited using a simple gas aggregation cluster source based on a planar magnetron. The influence of deposition parameters on size distribution was studied. It was found that Al nanoparticles may be deposited with mean diameter ranging from 30 to 60 nm by varying magnetron current from 0.4 to 0.2 A. Attention was also paid to the investigation of the charge of the nanoparticles. It is shown that a large portion of Al _x O _y nanoparticles leave the gas aggregation source as negatively charged. The nanoparticles were also embedded into the plasma polymer matrix by their simultaneous co-deposition with plasma-polymerized n-hexane. Morphology and chemical composition of such fabricated nanocomposites were determined. It was shown that Al _x O _y nanoparticles embedded into the polymeric matrix exhibit localized surface plasmon resonances in the deep ultraviolet region of the electromagnetic spectrum and the position of the plasmon peak is strongly correlated with nanoparticle size.     

Flow method for study of gas transport in polymers. Application to the study of oxygen,nitrogen, and carbon dioxide permeation through cellulose acetate membranes

Transient permeation of oxygen, nitrogen, and carbon dioxide through certain cellulose acetate (CA) dense membrances made from solutions in dioxane and dioxane-added ethanol were studied by the flow method. In order to explain the overshoots for transient permeation rates in the latter case, a new model is proposed. It postulates a time-dependence solubility coefficient, in the form of a series of exponential terms, which is combined in Fick's second law and solved. The model fits well the obtained permeation kinetics, leading to values of the diffusion, and permeation coefficients, and the structure change-related time. The overshoots are explained by the formation of unstable structure from dioxane-ethanol solvent mixtures, a memory effect of aggregated chains, which undergoes consolidation upon gas penetration. The stable state which results from the consolidation process is the same as that of membrances obtained from pure dioxane solutions. © 1994 John Wiley & Sons, Inc.     

Risk Factors Indoors and Prevalences of Childhood Respiratory Health in Four Countries in Western and Central Europe

Abstract The prevalence of respiratory symptoms and risk factors were gathered in four study centres in Western and Central Europe as part of an EU-funded multi-centre study addressing the use of small area methods in air pollution epidemiology (SAVI-AH). The study was carried out in Prague (CZ), Poznan (PL), Huddersfield (UK) and Amsterdam (NL). Prevalences of respiratory symptoms and risk factors between the centres were compared, and associations between risk factors and respiratory symptoms were calculated. Respiratory health was assessed by a self-administered questionnaire, distributed among parents or guardians of schoolchildren between the age of 7 and 11 years. Life-time wheezing and attacks of shortness of breath showed highest prevalences in Huddersfield (30% and 14%, respectively); usual cough showed highest prevalence in Poznan (27%). Differences in prevalence between the centres were found for the potential determinants “age” (due to different age ranges), “gas cooking” (highest in Amsterdam and Poznan), gas/coal heating (lowest in Central European centres), home dampness (highest in Western European centres), disturbance by traffic (highest in urban centres), maternal smoking (highest in Central European centres), family history (highest in Huddersfield) and education (highest in Huddersfield). The prevalence of pets in the home differed only slightly between the study centres. Of the potential deteminants studied, gender, family history of allergic diseases, dampness of the home and, to a lesser extent, passive smoking were important risk factors for life-time prevalence of respiratory symptoms in schoolchildren.     

Layered ceramic composites via control of electrophoretic deposition kinetics

The article summarises optimisation of electrophoretic deposition of alumina and zirconia from concentrated isopropanolic suspensions stabilised by monochloracetic acid. Method for in situ monitoring of deposited mass was developed and experimentally checked. Prediction of electrophoretic deposition kinetics was based on the voltage drop measurement and electrophoretic mobility estimation from experimental kinetics data. It was shown that voltage change during electrophoretic deposition did not affect relative density of the deposited layers in the laminates prepared. For this purpose a method of the relative density measurement using the microscopic measurement of relative shrinkage of individual layers was developed. Accuracy of the method was confirmed by comparison with shrinkage measurement using high temperature dilatometry. Adopting obtained results the alumina/zirconia laminate with precise control of layers thicknesses and final densities was prepared.     

On the determination of the stress-free temperature for alumina–zirconia multilayer structures

Internal residual stresses can enhance the fracture resistance and mechanical reliability of layered ceramics. The magnitude of the stresses depends on the elastic and thermal properties of the layers and the typically assumed reference (stress-free) temperature, below which internal stresses develop. A novel combined experimental and numerical simulation approach has been developed to determine the reference temperature and experimentally proved in alumina–zirconia ceramic laminates. Dilatometric data of monolithic phases are input for the numerical simulation and experimental data on the laminate properties are used for the stress-free temperature determination. In contrast to typical assumptions, reference temperature very near the sintering temperature (i.e. approx. T_ref≈1470 °C) was found, which should be considered for the estimation of internal (residual) stresses in alumina/zirconia-based layered ceramics.     

Rhenium Oxide Supported on Mesoporous Organised Alumina as a Catalyst for Metathesis of 1-Alkenes

Sulphate-promoted alkane combustion has been investigated over a series of Pt/Al₂O₃ catalysts using pre-sulphated alumina supports. Catalyst sulphation greatly enhanced ethane combustion over Pt/Al₂O₃, and also improved methane and propane light-off performance. Catalyst activity increased with Pt loading, however the magnitude of sulphate promotion was independent of Pt loading under oxidising conditions, but scaled with alkane chain length. Propane combustion activity was directly proportional to the surface coverage of aluminium sulphate sites; support-mediated alkane activation is the dominant process in sulphate promotion.     

Serum Metallothioneins in Childhood Tumours—A Potential Prognostic Marker

Metallothioneins (MT) are low molecular weight, cysteine-rich proteins maintaining metal ions homeostasis. They play a role in carcinogenesis and may also cause chemoresistance. The aim of the study was to explore the importance of MT serum levels in children suffering from malignant tumours. This prospective study involves examination of 865 samples from 172 patients with malignant tumours treated from 2008 to 2011 at University Hospital Motol. MT serum levels were determined using differential pulse voltammetry–Brdicka reaction. Mean MT level was 2.7 ± 0.5 μM. There was no statistically significant difference between MT levels in different tumours. We also did not find any correlation between MT levels and response to therapy or clinical stages. However, we found a positive correlation between MT levels and age (p = 0.009) and a negative correlation with absolute lymphocyte number (p = 0.001). The fact that patients who had early disease recurrence had lower MT levels during the treatment (complete remission 2.67 vs. recurring 2.34, p = 0.001) seems to be important for clinical practice. Accordingly we believe that there is benefit in further studies of serum MT levels in tumours.     

Remodelling of living bone induced by dynamic loading and drug delivery—Numerical modelling and clinical treatment

Remodelling is a dynamic process occurring during growth and it includes sensing of environmental changes, tissue resorbance, i.e. the removal of existing old bone, and formation of new tissue. The biomechanical remodelling process is relatively well formulated for bones and can be divided into three stages: (1) bone resorption based on the osteoclast activity, (2) bone deposition based on the osteoblast activity and (3) bone growth control established on RANK/RANKL/OPG pathway—RANKL/OPG balance. The main driving force of remodelling process is a dynamic loading (cyclic compression and expansion, e.g. walking or running), which strongly influences the rate of chemical reactions. The evolution from the homogeneous density distribution to the corticalis and cancellous bone formation is shown. An inevitable influence of a dynamic mechanical loading and osteoprotegerin (OPG) concentration is demonstrated. Deformations were calculated by commercial code ANSYS. The clinical experience indicates that the dynamic loading (above the threshold level 1500–2500 microstains/s), especially walking with a characteristic time approximately 1 s, influences the whole process of bone remodelling after a time period of approximately 3 months. The numerical simulation shows that the concentration of the new bone and the bone elastic constants substantially depend on history and intensity of the loading, drug delivery and nutrition.