Model based design and test of cooling plates for an air-cooled polymer electrolyte fuel cell stack

Design of an effective cooling system in polymer electrolyte membrane fuel cells (PEMFCs) is vital for the heat management and overall performance of stacks. Depending on the stack size and application, either air or water-cooling can be used to extract excess heat and maintain the desired temperature distribution throughout the stack.A computational model previously assembled by the authors has been used to design cooling plates for a typical air-cooled stack configuration. The aim of these designs was to minimise temperature differences between cells, and dissipate heat from the stack. Three different cooling plate designs are analysed both computationally and experimentally within stacks containing electrically heated pads in place of active MEAs.Good agreement was achieved between the model and experiment, and results showed that implementing a cooling plate is an effective way to balance temperature variation within a stack and minimise thermal issues. It was found that the temperature variation may be minimised by implementing plates with wider cooling channels. As a result, more air may be forced through the channels with less resistance, which minimises the power required by the air blower, and hence the parasitic load on the system.     

Disjunctive merging: Quota and Gmin merging operators

When aggregating information from a group of agents, accepting the pieces of information shared by all agents is a natural requirement. In this paper, we investigate such a unanimity condition in the setting of propositional merging. We discuss two interpretations of the unanimity condition. We show that the first interpretation is captured by existing postulates for merging. But the second interpretation is not, and this leads to the introduction of a new disjunction postulate (Disj). It turns out that existing operators satisfying (Disj) do not perform well with respect to the standard criteria used to evaluate merging operators: logical properties, computational complexity and strategy-proofness. To fill this gap, we introduce two new families of propositional merging operators, quota operators and Gmin operators, which satisfy (Disj), and achieve interesting trade-offs with respect to the logical, computational, and strategy-proofness criteria.     

Development of Super‐CHO protein‐free medium based on a statistical design

Based on a Plackett–Burman (P‐B) experimental design, a chemically‐defined and protein‐free medium, named Super‐CHO protein‐free (SPF), was developed to support an autocrine Super‐CHO cell line, C2.8‐SPF, to grow as a single‐cell suspension culture with a growth rate and viable cell number profile comparable to that observed in a commercial medium containing undefined additives. The C2.8‐SPF was subsequently transfected with a metal‐inducible and amplifiable expression construct, pNK‐EH1, designed to produce a humanised anti‐CD48 monoclonal antibody, IgG1‐EH1 (EH1 MAb). This study demonstrated that while the statistical experimental design provided a simple method for medium optimisation of the host cell, the resulting formulation might not be optimal for derived cell lines and further modification (in this case, addition of iron, to ameliorate heavy metal toxicity) was required. Developments of Super‐CHO C2.8‐SPF autocrine cell line and protein‐free medium (SPF) described here provide a low‐cost and regulatory‐compliant recombinant protein expression platform, suitable for the manufacture of therapeutic recombinant proteins. Copyright © 2007 Society of Chemical Industry     

Abnormal grain growth in alumina-doped hafnia ceramics

Hafnia (HfO₂) ceramics containing 0.0, 5.0, and 10.0 vol% Al₂O₃, respectively, were sintered at 1600°C for various periods from 2–24 h. Abnormal grain growth was found to occur in the Al₂O₃-containing compositions. Hafnia containing 5.0 vol% Al₂O₃ exhibits an average grain size of almost double that of the Al₂O₃-free hafnia matrix, coupled with a much wider grain-size distribution. The material containing 10.0 vol% Al₂O₃ shows a smaller average grain size than the composition containing 5.0 vol% Al₂O₃. However, its average grain size is still larger than that of the Al₂O₃-free hafnia on sintering at 1600°C for more than 8 h. Microstructural characterization, carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive analysis facility (EDX), indicated that there existed a continuous segregant layer at the grain boundaries and grain junctions in the Al₂O₃-free hafnia. Hafnia exhibits a low solubility in the segregant layer phase which inhibits the growth of the hafnia grains. The Al₂O₃ particles act as a scavenger for the silicon-rich glassy phase, damaging the continuous nature of the boundary segregant layer and promoting grain growth in the Al₂O₃-doped hafnia ceramics. The microstructural development at the sintering temperature is an overall result of the concurrent scavenger effect and grain pinning by the Al₂O₃ particles.     

Recognizing the reversible nature of child-feeding decisions: breastfeeding, weaning, and relactation patterns in a shanty town community of Lima, Peru

Researchers have normally considered weaning to be a non-reversible event. To determine the validity of this assumption, we interviewed 36 mothers of toddlers who were living in a poor shanty town of Lima, Peru. Data from 32 women were complete and used in this analysis. Mothers described their beliefs, practices, and decisions about breastfeeding, weaning, and relactation (the reintroduction of breastfeeding after weaning). We recorded attempted weaning events if the mother reported (1) purposefully not breastfeeding with the intention to wean, or (2) carrying out an action that was believed to cause the child to stop breastfeeding. Using a constant comparative approach, references to child-feeding decisions were coded, categorized, and analyzed. All mothers breastfed for at least 12 months; the median duration of breastfeeding was 25 months. There were several different patterns of child-feeding. Thirteen women never attempted to wean their children or had weaned on the first attempt. The majority (n = 19) of women, however, attempted to wean their children - some as early as 3 months of age but relactated between less than 1 day and 3 months later. Factors that influenced feeding decisions were primarily related to maternal and child health, and maternal time commitments. Children were weaned when there was a perceived problem of maternal health or time commitments and child health was not at risk of deterioration. Mothers postponed weaning because of poor child health. The primary reason for relactation was a child's negative reaction to weaning (e.g., incessant crying or refusal to eat). Personalities of the mother and child were important determinants of feeding decisions. These results demonstrate that maternal and child factors jointly influence child-feeding decisions and that these decisions are easily reversed. As relactation is culturally acceptable, health practitioners should consider recommending relactation when children have been prematurely weaned and human milk would improve their nutritional and health status.     

Rural nurse practitioners: perceptions of ethical dilemmas

The purposes of this study were to identify ethical dilemmas encountered by rural nurse practitioners in primary practice and to identify constraints or enhancers that influenced ethical decision making. Nine nurse practitioners from Wyoming and Colorado responded to in-depth interviews. Six categories of ethical dilemmas and a list of constraints and enhancers were identified. One central concept, conflict between personal values and professional responsibility, emerged. Beneficence, nonmaleficence, justice, and patient autonomy, as core ethical principles, were related to this central conflict.     

A new FIR filterbank design algorithm using frequency scaling and modulation

Digital filterbanks, an important signal processing tool, are used in a radar signal processor to measure target range and/or velocity [4]. The windowed FFT is the most common radar filterbank. The FFT is a special case of modulated filterbank. Modulated filterbanks subdivide the frequency region by modulating a prototype baseband filter. This baseband filter usually satisfies certain frequency response constraints. Filterbanks used in radar applications are not concerned with reconstruction as are wavelet-based approaches [2], but rather with how well the filters subdivide the frequency region into a prescribed number of equal frequency regions. Wavelets use time decimation or frequency scaling to form filterbanks. This paper focuses on using a wavelet-like scaling approach along with modulation to design a digital filterbank. However, we are not concerned with reconstruction but with the subdivision of the frequency region into a prescribed number of equal segments. It will be shown that this new design algorithm has a frequency response performance comparable to existing techniques but with less computational effort. The performance measures considered are rejection of out of bands signals, uniformity of inband signal gain, and transition width from inband to stopband.     

A parametric shear damage evolution model for combined clamped and adhesively bonded interfaces

This paper presents the development of a damage model for shear decohesion analysis of combined clamped and adhesively bonded (hybrid) interfaces. The model takes into account the influence of normal pressure on the applied shear force vs. displacement response. Decohesion finite elements were used for the setup of the cohesive zone and a damage function was set to govern the degradation. Material constants for the damage evolution model were fitted based on experiments and computational results were validated against the test data. Considerable increase in the dissipated fracture energy was found for the cases involving high normal pressure.