Three-Port Bidirectional Converter for Hybrid Fuel Cell Systems

The implementation of a hybrid fuel cell/battery system is proposed to improve the slow transient response of a fuel cell stack. This system can be used for an autonomous device with quick load variations. A suitable three-port, galvanic isolated, bidirectional power converter is proposed to control the power flow. An energy management method for the proposed three-port circuit is analyzed and implemented. Measurements from a 500-W laboratory prototype are presented to demonstrate the validity of the approach     

An ecological approach to landscape planning using geographic information system technology

This paper describes two research programs that are aimed at developing ecologically-based landscape planning models. The first of these models was developed as part of a more comprehensive landscape planning research program at the University of Massachusetts. The second is an on-going program in forest land planning at the University of Vermont. In addition to an emphasis on ecological values, both projects make extensive use of computerized geographic information systems (GIS) for data storage, analysis and display. The emphasis has been to develop a synthesis of planning procedures, ecological theories and quantitative techniques. Both research efforts were guided by a three-part methodological framework adapted from the work of Eugene Odum. The Massachusetts work generated a two-part classification system. The first part of the classification uses the statistical technique of discriminant analysis to place land uses into five groups, each having similar ecological characteristics. The second part of the classification is based on the physical and environmental characteristics of a site. The biological and denudational potentials of a site are determined from soil characteristics and slope. A comparison of the two classification schemes was made to determine ecological compatibility. The procedures were applied to two communities in Western Massachusetts. The Vermont study was aimed at integrating ecological values into forest land management and planning processes. The research utilized soils and topographic information in the development of an ecologically based forest land suitability model. Forest site index and soil erosion potential were determined using data stored in a computerized geographic information system. Forest site index estimates were made by utilizing an existing, well documented soil-site index regression equation applicable to the Green Mountains of Vermont. Soil erosion potential estimates were made by combining a soil erodability factor (K) with slope. The site index and soil erosion estimates were combined to produce land suitability classes for resource protection, forest management, multiple-use and trade-off. The procedure was applied in the Mad River Valley in Central Vermont. Both the Massachusetts and the Vermont studies are seen as significant contributions toward the integration of ecological factors into processes for landscape planning and resource management.     

Mineral and trace element content of various vegetarian foodstuffs available in Belgium

 Atomic absorption spectrometry was used to determine mineral (Na, K, Ca and Mg) and trace element content (Zn, Fe, Cu and Si) of various vegetarian foodstuffs in Belgium. Thirty-five commercially available products were analysed after a wet-acid destruction in a closed-vessel destruction bomb. Various important sources of the minerals and trace elements were identified. Since data for vegetarian foods in Belgium are non-existent, the concentration values are compared with the scarce literature data and particularly with levels found in the same products available in The Netherlands. Received: 2 June 1998 / Revised version: 5 October 1998     

Asynchronous measurement and control: a case study on motor synchronization

The synchronization between two electrical motors (master and slave) is studied. To reduce the costs of the master–slave combination, the slave motor is mounted with a very low-resolution encoder (one pulse per revolution). Since the position measurements are asynchronous in time, standard control and analysis techniques are not applicable. Two methods are proposed to deal with these cheap, low-resolution encoders: the hybrid and the asynchronous control scheme. The presented controllers are successfully tested on a real industrial master-multi-slave system as is used for mailing machines.     

Properties of glass‐filled thermoplastic polyesters

The thermal, mechanical, and rheological properties of glass‐filled poly(propylene terephthalate) (GF PPT) were compared to glass‐filled poly(butylene terephthalate) (GF PBT). The impetus for this study was the recent commercial interest in PPT as a new glass‐reinforced thermoplastic for injection‐molding applications. This article represents the first systematic comparison of the properties of GF PPT and GF PBT in which differences in properties can be attributed solely to differences in the polyester matrices, that is, glass‐fiber size and composition, polymer melt viscosity, nucleant content and composition, polymerization catalyst composition and content, and processing conditions were kept constant. Under these controlled conditions, GF PPT showed marginally higher tensile and flexural properties and significantly lower impact strength compared to GF PBT. The crystallization behavior observed by cooling from the melt at a constant rate showed that GF PBT crystallized significantly faster than did GF PPT. Nucleation of GF PPT with either talc or sodium stearate increased the rate of crystallization, but not to the level of GF PBT. The slower crystallization rate of GF PPT was found to strongly affect thermomechanical properties of injection‐molded specimens. For example, increasing the polymer molecular weight and decreasing the mold temperature significantly increased the modulus drop associated with the glass transition. In contrast, the modulus–temperature response of GF PBT was just marginally influenced by the polymer molecular weight and was essentially independent of the mold temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 889–899, 1999