Computational modeling of intermediate temperature proton exchange membrane (PEM) fuel cells

A two-phase three-dimensional computational model of an intermediate temperature (120--190°C) proton exchange membrane (PEM) fuel cell is presented. This represents the first attempt to model PEM fuel cells employing intermediate temperature membranes, in this case, phosphoric acid doped polybenzimidazole (PBI). To date, mathematical modeling of PEM fuel cells has been restricted to low temperature operation, especially to those employing Nafion ® membranes; while research on PBI as an intermediate temperature membrane has been solely at the experimental level. This work is an advancement in the state of the art of both these fields of research. With a growing trend toward higher temperature operation of PEM fuel cells, mathematical modeling of such systems is necessary to help hasten the development of the technology and highlight areas where research should be focused.^ This mathematical model accounted for all the major transport and polarization processes occurring inside the fuel cell, including the two phase phenomenon of gas dissolution in the polymer electrolyte. Results were presented for polarization performance, flux distributions, concentration variations in both the gaseous and aqueous phases, and temperature variations for various heat management strategies. The model predictions matched well with published experimental data, and were self-consistent.^ The major finding of this research was that, due to the transport limitations imposed by the use of phosphoric acid as a doping agent, namely low solubility and diffusivity of dissolved gases and anion adsorption onto catalyst sites, the catalyst utilization is very low (∼1--2%). Significant cost savings were predicted with the use of advanced catalyst deposition techniques that would greatly reduce the eventual thickness of the catalyst layer, and subsequently improve catalyst utilization. The model also predicted that an increase in power output in the order of 50% is expected if alternative doping agents to phosphoric acid can be found, which afford better transport properties of dissolved gases, reduced anion adsorption onto catalyst sites, and which maintain stability and conductive properties at elevated temperatures.^

Impact of nutrition education on knowledge and eating patterns in HIV-infected individuals

Acquired Immune Deficiency Syndrome (AIDS) and impaired or threatened nutritional status seem to be closely related. It is now known that AIDS results in many nutritional disorders including anorexia, vomiting, protein-energy malnutrition (PEM), nutrient deficiencies, and gastrointestinal, renal, and hepatic dysfunction (1-7, 8). Reversibly, nutritional status may also have an impact on the development of AIDS among HIV-infected people. Not all individuals who have tested antibody positive for the Human Immunodeficiency Virus (HIV) have developed AIDS or have even shown clinical symptoms (9, 10). A poor nutritional status, especially PEM, has a depressing effect on immunity which may predispose an individual to infection (11). It has been proposed that a qualitatively or quantitatively deficient diet could be among the factors precipitating the transition from HIV-positive to AIDS (12, 13). The interrelationship between nutrition and AIDS reveals the importance of having a multidisciplinary health care team approach to treatment (11), including having a registered dietitian on the medical team. With regards to alimentation, the main responsibility of a dietitian is to inform the public concerning sound nutritional practices and encourage healthy food habits (14). In individuals with inadequate nutritional behavior, a positive, long-term change has been seen when nutrition education tailored to specific physiological and emotional needs was provided along with psychological support through counseling (14). This has been the case for patients with various illnesses and may also be true in AIDS patients as well. Nutritional education specifically tailored for each AIDS patient could benefit the patient by improving the quality of life and preventing or minimizing weight loss and malnutrition (15-17). Also, it may influence the progression of the disease by delaying the onset of the most severe symptoms and increasing the efficacy of medical treatment (18, 19). Several studies have contributed to a dietary rationale for nutritional intervention in HIV-infected and AIDS patients (2, 4, 20-25). Prospective, randomized clinical research in AIDS patients have not yet been published to support this dietary rationale; however, isolated case reports show its suitability (3). Furthermore, only nutrition intervention as applied by a medical team in an institution or hospital has been evaluated. Research is lacking concerning the evaluation of nutritional education of either non-institutionalized or hospitalized groups of persons who are managing their own food choice and intake. This study compares nutrition knowledge and food intakes in HIV-infected individuals prior to and following nutrition education. It was anticipated that education would increase the knowledge of nutritional care of AIDS patients and lead to better implementation of nutrition education programs.