Changes in large particle size distribution due to dry deposition processes

A dry deposition model is described that can simulate variations in the size-resolved mass size distribution of large ( diameter) atmospheric particles due to dry deposition processes. The model is unique because it is based on both gravitational and inertial effects in turbulent flow and includes deposition and suspension velocities for large, airborne particles. The model allows the integration of a large number of variables, covering a wide range of conditions (height of particle injection, meteorological conditions, and removal time). Changes in the size distributions that result from model simulations of deposition show the expected decrease in concentration with size since the deposition is greater for the larger particles. However, the size distribution does not decrease with size in a uniform manner as would be suggested by Stokes settling velocity due to the effect of inertial forces acting on the particles. Application of the model reveals a number of patterns, including the development of two peaks in the large particle mass size distribution, a persistent peak in the 1– size range, and a second peak in the 10– range that is strongly affected by meteorological conditions.     

Fatigue life simulation of multi-axial CFRP laminates considering material non-linearity

The objective of an on-going DFG research project is to investigate the effect of non-linear stress–strain curves (e.g. τ₁₂–γ₁₂) on the fatigue life simulation of carbon fiber reinforced polymer (CFRP) laminates under variable amplitude cyclic loading. Based on the critical element concept of Reifsnider and Stinchcomb appropriate models including a secant modulus iteration for the non-linear stress analysis, the evaluation of inter-fiber fracture effects applying a fracture plane criterion, and appropriate continuum mechanics based stiffness degradation algorithms to treat both inter-fiber cracking and ply delamination were implemented into an existing fatigue life prediction software. Using this software the fatigue life of a quasi-isotropic vinylester/urethane/carbon fiber composite laminate subjected to miniTWIST variable amplitude loading was analyzed and compared to experimental data.     

GENERALIZED CONJUGATE GRADIENT METHOD FOR THE EFFICIENT SOLUTION OF THREE-DIMENSIONAL FLUID FLOW PROBLEMS

A generalized conjugate gradient (CG) method was examined for use in the numerical calculation of recirculating turbulent three-dimensional fluid flows. The proposed algorithm was found to be a very efficient solution procedure in a large number of practical applications. Furthermore, the results obtained from two other CG-like solution methods that are entirely free of recursion clearly indicate the advantages of the recommended partly recursive method even for vector computers.     

The Universality of Higher-Order Attributed Tree Transducers

In this paper we present higher-order attributed tree transducers as a formal computational model for higher-order attribute grammars. The latter is a generalization of the classical concept of attribute grammars in the sense that during attribute evaluation, the input tree can be enlarged by inserting subtrees which were computed during attribute evaluation. We prove the universality of this formalism by showing that the class of functions described by higher-order attributed tree transducers coincides with the class of (partial) recursive tree functions. Received May 12, 1999. Online publication December 5, 2000.     

Measurements of the equivalent dose in aircraft with TLDS

For measurements of the equivalent dose of the mixed radiation fields in aircraft many different measuring devices are usually necessary for consideration of the different components of the radiation field. The possibility is discussed of using thermoluminescence dosemeters (TLDS) for determination of absorbed dose and average LET of this complex radiation field in aircraft. The HTR method, developed for determination of the equivalent dose in spacecraft, enables the measurement of the average LET in addition to the absorbed dose. Furthermore, a rem counter based on TLDs and a modified pair method (TLD-600, TLD-700) was used for determination of the absorbed dose due to the neutron component. Using small TLD crystals it is possible to obtain the depth distribution of absorbed dose and average LET by exposing TLDs in Bonner spheres with different diameters. The results indicate that the standards for determination of the effective dose may not be applicable in these mixed radiation fields in aircraft.     

Einfluss und Bedeutung chemischer Entmischungen auf mechanische Eigenschaften thixogeformter Bauteile

Chemical Segregation Effect on Mechanical Properties of Thioxo Formed Components Thixoforming is a near net shape forming process of semi solid billets with a stiffness, which is comparable to “butter”. Advantages of conventional forming and casting processes can be combined due to this modern forming process technology. The objective of this investigation is to identify the effect of local chemical segregation regarding the microstructure and mechanical properties in various parts of a component. Different components and component regions – with diverse cross‐sections and flow lengths – have been tested. Tensile, charpy and fatigue tests are completed by metallography and local chemical analysis. The investigation was focused on AlSi7Mg0.3 and AlSi6Cu3 aluminium casting alloys. It can be confirmed, that chemical composition of the raw material and segregation are important effects on mechanical properties of components. Chemical segregation can be caused by abrupt changes in cross‐section. The inhomogeneity verified by chemical analysis and metallography are important effects on mechanical properties of Thixoforming components. In future the counteract between metal structure and processing steps regarding mechanical properties of components must be examined more intensively. The aim is to create a fundamental understanding of the relationship between the structure, chemical composition, homogeneity and characteristics of aluminium materials.     

Sickle cell disease pain in children and adolescents: change in pain frequency and coping strategies over time

Examined 9-month follow-up data obtained from children and adolescents with sickle cell disease (SCD) and their parents participating in a longitudinal study of pain coping strategies. Of 87 subjects completing the baseline assessment of pain coping strategies, 70 (80%) of their parents completed a structured pain interview assessing their child's health care use and activity reduction during painful episodes over the follow-up period. Regression analyses controlling for age and pain frequency revealed that baseline Coping Attempts were associated with higher levels of school, household, and social activity during painful episodes. Baseline Passive Adherence was associated with more frequent health care contacts during the subsequent 9 months. Increases in Negative Thinking over time were associated with further increases in health care contacts during the follow-up period. Comparing pain coping strategies assessed at baseline to pain coping strategies measured at follow-up revealed that pain coping strategies were relatively stable over time for younger children but changed more for adolescents.     

In-line catalytic purification of carbon dioxide used in analytical-scale supercritical fluid extraction

Supercritical fluid extraction analyses are often compromised by trace impurities present in the solvent carbon dioxide. These impurities, commonly used as lubricants in the specialty gas industry, can produce significant background levels, increasing limits of detection and quantification. This problem is especially severe when electron capture detection (ECD) is used for trace concentrations of analytes (e.g., polychlorinated biphenyls and chlorinated pesticides). In this study, an in-line catalyst-based purification system was successfully employed to remove ECD-responsive contaminants from CO2. Low-purity (98%) "Bone Dry" CO2 was purified to levels cleaner than a very-high-purity grade of CO2 specified at less than 10 ppt ECD-responsive contaminants. Purification was successfully applied to extremely sensitive on-column experiments as well as higher flow rate off-line experiments. In addition to lowering limits of detection and quantification, significant cost savings can be realized by purifying inexpensive, low-purity CO2 instead of relying on much more expensive, prepurified CO2.