Nondestructive Characterization of Prepreg Ageing Using Nuclear Magnetic Resonance Techniques

Abstract

The ageing of prepregs of and fiber reinforced duroplastic polymers (glassfiber and carbonfiber reinforced polymers; GFRP and CFRP) during storage before manufacturing and during the manufacturing process at elevated temperatures is an essential technical problem. The resulting mechanical properties of cured components are strongly influenced by the ageing state of the prepregs. Nondestructive techniques up to now are unsufficient or time consuming. Nuclear magnetic resonance (NMR) techniques have been well known for 40 years and applied in analytical chemistry in order to characterize the microstructure and binding state of organic chemical compounds in fluid states. In medical diagnostics NMR-imaging is used for tissue characterization. Publications on solid state NMR-imaging are rare in technical literature because of the fact that the strong spin-spin-interaction in solids results in a broadening of the spectral lines, i.e., very short transversal relaxation times, T₂ (some μs), compared to fluids (up to some 100 ms). Therefore special electronics are needed in order to produce short pulses and to switch the gradient fields in short time periods.

The emphasis of the following contribution will be on the presentation of first results on the application of NMR techniques at prepegs in order to characterize the crosslink state after exposition at room and elevated (50°C) temperature. The results correlate with results of destructive tests and document the potential of NMR as a NDT tool. The experiments were performed with a MSL-400 Bruker NMR-spectrometer and micro-imaging system which works at 400 MHz (¹H resonance frequency at a magnetic field of 9.4 T).     

Refining the In-Parameter-Order Strategy for Constructing Covering Arrays

Covering arrays are structures for well-representing extremely large input spaces and are used to efficiently implement blackbox testing for software and hardware. This paper proposes refinements over the In-Parameter-Order strategy (for arbitrary t). When constructing homogeneous-alphabet covering arrays, these refinements reduce runtime in nearly all cases by a factor of more than 5 and in some cases by factors as large as 280. This trend is increasing with the number of columns in the covering array. Moreover, the resulting covering arrays are about 5 % smaller. Consequently, this new algorithm has constructed many covering arrays that are the smallest in the literature. A heuristic variant of the algorithm sometimes produces comparably sized covering arrays while running significantly faster.     

When do procedural fairness and outcome fairness interact to influence employees’ work attitudes and behaviors? The moderating effect of uncertainty.

Prior research has shown that procedural fairness interacts with outcome fairness to influence employees’ work attitudes (e.g., organizational commitment) and behaviors (e.g., job performance, organizational citizenship behavior), such that employees’ tendencies to respond more positively to higher procedural fairness are stronger when outcome fairness is relatively low. In the present studies, we posited that people’s uncertainty about their standing as organizational members would have a moderating influence on this interactive relationship between procedural fairness and outcome fairness, in that the interactive relationship was expected to be more pronounced when uncertainty was high. Using different operationalizations of uncertainty of standing (i.e., length of tenure as a proxy, along with self-reports and coworkers’ reports), we found support for this hypothesis in 4 field studies spanning 3 different countries. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of authority power in explaining procedural fairness effects.

Building on fairness heuristic theory, fairness theory, and trust development models, we argue that unfairly enacted procedures decrease followers' trust in the authority particularly when authorities have high power over their followers. Moreover, we expected trust to mediate procedural fairness effects on followers' attitudes (authorities' legitimacy and charisma attributed to authorities) and organizational citizenship behavior. Procedural fairness effects on these variables, as mediated by trust, should therefore also be stronger when authority power is high. The results of a single- and multisource field study and a laboratory experiment supported these predictions. These studies support the role of authority power as a theoretically and practically relevant moderator of procedural fairness effects and show that its effectiveness is explained through trust in authorities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cancer Stem Cells: Biological Functions and Therapeutically Targeting

Almost all tumors are composed of a heterogeneous cell population, making them difficult to treat. A small cancer stem cell population with a low proliferation rate and a high tumorigenic potential is thought to be responsible for cancer development, metastasis and resistance to therapy. Stem cells were reported to be involved in both normal development and carcinogenesis, some molecular mechanisms being common in both processes. No less controversial, stem cells are considered to be important in treatment of malignant diseases both as targets and drug carriers. The efforts to understand the role of different signalling in cancer stem cells requires in depth knowledge about the mechanisms that control their self-renewal, differentiation and malignant potential. The aim of this paper is to discuss insights into cancer stem cells historical background and to provide a brief review of the new therapeutic strategies for targeting cancer stem cells.     

Efficient Stacking on Protein Amide Fragments

The less polar π‐surface of protein amide groups is exposed in many receptor binding sites, either as part of the backbone or in Gln/Asn side chains. Using quantum chemical calculations and Protein Data Bank (PDB) searches on model systems, we investigate the energetics and geometric preferences for the stacking on amide groups of a large number of heteroarenes that are relevant to medicinal chemistry. From this study, we discern that the stacking energy of an aromatic ligand substituent can be improved by: 1) orienting the fragment dipole vector such that it is aligned in an antiparallel fashion with the dipole of the interacting protein amide group, 2) increasing its dipole moment, and 3) decreasing its π‐electron density. These guidelines should be helpful to more rationally exploit this interaction type in future structure‐based drug design.     

Sampling Archimedean copulas

The challenge of efficiently sampling exchangeable and nested Archimedean copulas is addressed. Specific focus is put on large dimensions, where methods involving generator derivatives are not applicable. Additionally, new conditions under which Archimedean copulas can be mixed to construct nested Archimedean copulas are presented. Moreover, for some Archimedean families, direct sampling algorithms are given. For other families, sampling algorithms based on numerical inversion of Laplace transforms are suggested. For this purpose, the Fixed Talbot, Gaver Stehfest, Gaver Wynn rho, and Laguerre series algorithm are compared in terms of precision and runtime. Examples are given, including both exchangeable and nested Archimedean copulas.     

Evaluation and optimization of a reusable hollow fiber ultrafilter as a first step in concentrating Cryptosporidium parvum oocysts from water.

Experiments with a small-scale hollow fiber ultrafiltration system (50,000 MWCO) was used to characterize the filtration process and identify conditions that optimize the recovery of Cryptosporidium parvum oocysts from 2 L samples of water. Seeded experiments were conducted using deionized water as well as four environmental water sources (tap, ground, Arkansas river, and Rio Grande river; 0-30.9NTU). Optimal and consistent recovery of spiked oocysts was observed (68-81%), when the membrane was sanitized with a 10% sodium dodecyl sulfate (SDS) solution and then blocked with 5% fetal bovine serum (FBS).