Function of sulfur dioxide in the kinetic mechanism of oxidation of carbon

Retardation of the gasification reaction of carbon with oxygen by SO₂ was observed. Rates of oxidation were determined by thermal gravimetric analysis (TGA) of a nuclear graphite in the temperature range of 550–700°C, and of a coconut charcoal in the temperature range of 400–505°C. The oxidant gases were dry air containing 0–6% SO₂. Reduction of the rate by SO₂ varied with burn-off. Differential thermal analysis (DTA) was also applied to detect the retardation effect of SO₂. The technique of infrared internal reflection spectroscopy (IRS) was used to examine the surface species of reacted charcoal samples. Absorption bands were assigned to surface carbonyls, lactones, and a chemisorbed SO₂ in the form of sulfate. Chemisorption of SO₂ was attributed to cause the retardation of the oxidation reaction.     

Physical gelation of crystallizing metallocene and Ziegler-Natta ethylene-hexene copolymers

The effect of molecular architecture on the evolution of viscoelastic properties during crystallization was investigated using ethylene-hexene copolymers manufactured via metallocene (M-LLDPE) and Ziegler-Natta (ZN-LLDPE) processes. Differences in branching distribution were shown to have a drastic effect on the viscoelastic properties near the gel point. It is shown that the branching distribution rather than branch content is the determining parameter for the evolution of the rheological properties during isothermal and non-isothermal crystallization, and for the width of the solidification interval. We developed a partial melting technique for the preparation of stable critical gels of LLDPE whose viscoelastic properties correspond to the intermediate state between melt and solid. Local molecular conformation and crystallinity in these gels were characterized by Raman spectroscopy, which shows that the transition from melt-like to solid-like rheological behavior (physical gelation) in LLDPE occurs at a very low overall crystallinity of less than 5%.     

Mechanical analysis of hollow fiber membrane integrity in water reuse applications

In order to gain insight into membrane fiber failure (i.e., loss of integrity), properties of five hollow fiber membranes and four hollow fiber modules were evaluated. Specifically, membrane material, membrane symmetry, fiber modulus of elasticity, fiber diameter and thickness, module potting technique, module flow pattern (inside-out or outside-in), and coliform breakthrough were investigated. The approach combined evaluation of the above properties with mathematical modeling of structure-fluid interactions to comprehensively evaluate the properties most important for maintaining hollow fiber membrane integrity. Tensile strength testing revealed that the strongest fiber was an asymmetric polyacrylonitrile membrane fiber. The weakest fiber was a symmetric polyethylene membrane fiber. Pilot plant testing on the four membrane modules revealed that membrane symmetry may be a more important factor than potting technique for hollow fiber integrity. Results from the SEM and tensile testing were used as input to a finite element analysis model used to evaluate time-dependent structure-fluid interactions. It was found that additional stresses at the juncture of the potting material and the hollow fiber membranes exist. These stresses likely lead to the formation of fractures.     

Mechanical properties and structure of a nanoporous sodium borosilicate glass

The nanohardness (H) and microhardness (H _M) of sodium borosilicate glasses with and without nanopores were studied. From nanoindentation measurements, along with the hardness H, the Young’s modulus E was derived. While both H and H _M varied between ∼10 GPa and ∼7 GPa for the bulk glass, the values for nanoporous specimens were one order of magnitude lower at about 0.5 GPa. The Young’s moduli were found to be ∼82 GPa and ∼5 GPa for bulk and porous glasses, respectively. Cracks and pileups were observed, respectively, arising from microindents and nanoindents in the bulk glass, whereas none of them could be detected in the nanoporous material. The molecular structures of both glasses studied by X-ray diffraction are similar. The text was submitted by the authors in English.     

Ozonation of Humic Substances: Effects on Molecular Weight Distributions of Organic Carbon and Trihalomethane Formation Potential

Four different sources of humic substances were studied to determine the effects of ozonation on molecular weight-distributions, based on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP). Solutions of two soil-derived fulvic acids and a one soil-derived humic acid, as well as dissolved organic matter (DOM) associated with a natural water source were studied. Both gel permeation chromatography (GPC) and ultrafiltration (UF) were employed to define apparent molecular weight (AMW). Applied ozone doses ranged from 2.0 to 2.5 mg O₃/mg DOC. Overall samples of untreated and ozonated waters, as well as individual molecular weight fractions, were characterized according to DOC, UV absorbance, and THMFP. Ozonation resulted in a significant disappearance of higher AMW material with a corresponding increase in lower AMW material. Although little overall reduction in DOC concentration was observed, significant overall reductions in UV absorbance and THMFP levels were observed.     

Extended bisection method for parameter identification of the transient heat conduction equation for thermo-elastic deformations during drilling

A new interdisciplinary approach is discribed to identifying unknown parameters using an extended version of the known interval bisection method. This developed method is based on the use of finite elements for calibrating the simulation calculation. The resulting thermo-elastic deformations which occur in drilling processes with impaired cooling lubrication are to be used as correction values for tool positioning in the NC control. Based on the strong impact on workpiece temperature of machining, a simulation approach is presented for calculating the temperature fields and their thermo-elastic consequences. In addition, methods are presented to correct these effects. This paper particularly deals with the temperature fields of drilling operations. Special attention is paid to the technique employed for iterative numerical determination of the unknown heat flux η _w and heat transfer coefficient \(\bar {\gamma }\) values. Finally, the data obtained from experiments are compared with those achieved by numerical simulation in order to verify the efficiency of simulation and determination of parameters.     

On the mechanical performance of closed cell Al alloy foams

The mechanical properties of three different commercially available closed cell Al alloys all made by foam casting are examined. The objective is to assess the roles of cell morphology and of imperfections in governing the basic properties: stiffness, yield strength and fracture resistance. This assessment provides goals for manufacturing strategies that enable attainment of good mechanical performance with affordable process technologies. A prevalent role of curves and wiggles in the cell walls on stiffness and strength (anticipated by models) is affirmed by the present measurements. Systematically larger stiffnesses and yield strengths found in tension than in compression are consistent with a prominent role exerted by such imperfections. Moreover, foam casting is apparently capable of cell morphologies that impart properties approaching the best achievable values for an isotropic closed cell solid, devoid of imperfections. There are associated implications for performance and affordability. Fracture measurements indicate crack growth occurring along the cell walls by a mechanism analogous to the plastic tearing of thin sheets. The crack growth resistances are in the range of 1 kJm⁻². This mechanism infers a toughness that scales with the cell wall thickness and its yield strength.     

Ca15(CBN)6(C2)2O- a new cubic structure type containing CBN-anions together with acetylide and oxo anions

Ca₁₅(CBN)₆(C₂)₂O contains CBN⁴⁻ anions as well as C₂⁻ units and isolated O²⁻ anions. The compound is obtained by heating a stoichiometric mixture of CaO, C and BN with an excess of Ca in sealed niobium ampoules to 1270 K. It crystallizes in the space group Ia d with a = 1656.84(9) pm. Preparation, crystal structure, NMR and IR-spectroscopic properties are discussed.     

Filtering Multi‐Layer Shadow Maps for Accurate Soft Shadows

In this paper, we introduce a novel technique for pre‐filtering multi‐layer shadow maps. The occluders in the scene are stored as variable‐length lists of fragments for each texel. We show how this representation can be filtered by progressively merging these lists. In contrast to previous pre‐filtering techniques, our method better captures the distribution of depth values, resulting in a much higher shadow quality for overlapping occluders and occluders with different depths. The pre‐filtered maps are generated and evaluated directly on the GPU, and provide efficient queries for shadow tests with arbitrary filter sizes. Accurate soft shadows are rendered in real‐time even for complex scenes and difficult setups. Our results demonstrate that our pre‐filtered maps are general and particularly scalable.