Fuel efficient power management strategy for fuel cell hybrid powertrains

A real time control strategy for fuel cell hybrid vehicles is proposed. The objective is to reduce the hydrogen consumption by using an efficient power sharing strategy between the fuel cell system (FCS) and the energy buffer (EB). The energy buffer (battery or supercapacitor) is charge-sustained (no plug-in capabilities). The real time control strategy is derived from a non-causal optimization algorithm based on optimal control theory. The strategy is validated experimentally with a hardware-in-the-loop (HiL) test bench based on a 600 W fuel cell system.     

Parameter extraction of interdigital slow‐wave coplanar waveguide circuits using finite difference frequency domain algorithm

The slow wave effect can be obtained by a capacitively loaded structure with a symmetrical interdigital line connected on both sides of the coplanar waveguide (CPW) central line. The ferroelectric thin film with high dielectric constant can reduce the size of circuit and make it possible to realize tunable devices such as filter by applying voltage on it. Actually, this kind of slow wave structure is a periodic guided‐wave structure and can be analyzed by using classic finite difference frequency domain (FDFD) method for periodic guided‐wave structures. However, the very compact slow‐wave structures will usually result in simulation errors when the classic FDFD method is adopted, which will lead to a nonsymmetrical generalized eigenvalue problem. In this article, the shift‐and‐invert (SI) Arnoldi method is used to directly resolve this nonsymmetrical generalized eigenvalue problem. As a result, the accuracy of FDFD algorithm is improved. Especially for the large scale eigenvalue problem, SI method can also have a very fast speed of calculation. By means of its complex propagation constant obtained from simulation, one can extract circuit parameters of the interdigital capacitor. Consequently, one can analyze and design relevant resonators and filters in a quick and accurate manner, which are constructed with such interdigital slow wave structures. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

20-Gb/s integrated DBR laser-EA modulator by selective area growth for 1.55-/spl mu/m WDM applications

For the first time, selective area growth (SAG) has been used for the monolithic integration of a distributed Bragg reflector (DBR) laser with an electroabsorption (EA) modulator, designed for WDM communication systems at 1.55 /spl mu/m. A 16-GHz bandwidth combined with a 6-nm tuning range make this component compatible with multiwavelength 20-Gb/s transmission experiments.     

Confirming the pinking mechanism of PVC profiles in mild climatic conditions

Pinking of TiO₂‐pigmented PVC can be observed for profiles exposed to the mild environmental conditions of northern European countries. In a previous paper, the pinking phenomenon was accounted for at the molecular level by the formation of polyene sequences, which are not completely photooxidatively bleached in conditions of oxygen starvation. This causation has been confirmed by exposing to visible light in a SEPAP 12.24 apparatus profiles in which pinking was produced during 4 year‐weathering in N.W. France. The fast phototransformations in visible light of chloropolyenes in trans‐configurations leading to α‐chloropolyenes in cis‐configurations accounts for the conversion of pinking into limited graying. It appears that the first and more intense graying observed after the initial exposure to UV and visible light of profiles in the SEPAP 12.24 can be essentially attributed to the photoreduction products of lead stabilizers. Graying could be bleached through thermooxidation at 65°C, could not be converted into pinking, and has no environmental relevance.     

N2O and CH4 emissions from fertilized agricultural soils in southwest France

Emissions of nitrogen compounds from heavily fertilized and irrigated maize fields have been studied in the Southwest of France, over an annual cultivation cycle. Strong nitrous oxide emissions from denitrification were observed after application of nitrogen fertilizer. Flux intensity appears to be stimulated by rain or irrigation. Emission algorithms, taking into account both nitrogen input and soil water content were established on the basis of the experimental data set. They allowed us to estimate annual nitrogen loss in the form of nitrous oxide modulated by rainfall. Production of methane is observed at the level of the water table under anoxic conditions. Nevertheless, the net flux between soil and atmosphere is negative for most of the time. When methane is produced, fluxes were very low due to methane oxidation in the soil surface layer.     

Towards the prediction of pinking of PVC profiles in mild climatic conditions

Pinking of TiO₂‐pigmented PVC can be observed for profiles exposed to the mild environmental conditions of Northern European countries. In this paper, the pinking phenomenon is accounted for at the molecular level by the formation of polyene sequences which are not completely photooxidatively bleached under conditions of oxygen starvation. Photoreduction of TiO₂ to give Ti(III) species accounts for greying which cannot be converted into pinking under mild thermooxidative conditions (65°C). The polyenic sequences which account for an initial greying after brief exposure in the SEPAP 12.24 apparatus can be converted into shorter, modified polyene sequences which explain the pinking. From the basic understanding gained, a predictive test has been designed and validated by comparison with results obtained under natural exposure conditions.     

Effect of nitrogen fertiliser supply and winter cutting on morphological composition and herbage digestibility of a Dactylis glomerata L sward in spring

The aim of this study was to improve the prediction of sward digestibility in spring as affected by nitrogen supply and winter cutting, taking into account their effects on the leaf:stem ratio and the digestibility of the plant parts. Two nitrogen treatments (120 kg ha⁻¹ and nil) and two cutting regimes were studied over three growing seasons. Herbage digestibility measurements were made about 2 weeks before and after the heading stage. Nitrogen deficiency always decreased the proportion of stem in the herbage yield significantly, mainly because it reduced or delayed the number of tillers which reach the double‐ridge stage. The stem digestibility was higher when no nitrogen was supplied. We show that it decreased with increasing stem length, whatever the sampling date and the growing season. Morever, for a given stem length we noticed a positive effect of herbage nitrogen status, probably because the stem weight per unit length was lower when N was supplied. Green lamina digestibility decreased more slowly than that of stem, but at a different rate according to the growing season. At the whole herbage level, nitrogen supply always decreased the herbage digestibility, and sometimes cutting in winter increased it. These trends resulted mainly from the effect of nitrogen supply on the proportion of stem in the herbage and its digestibility. © 2000 Society of Chemical Industry     

Voltage and frequency dependent dielectric properties of BST-0.5 thin films on alumina substrates

Dielectric properties of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST-0.5) polycrystalline thin films, deposited on alumina substrates by means of reactive pulsed laser deposition (PLD), were measured at GHz frequencies using an interdigital capacitor (IDC). By applying a voltage up to 40 V between the two groups of fingers at room temperature, a high tunability of /spl sim/27% was achieved at 5 GHz. A relative dielectric constant of /spl sim/500 (consistent with the low-frequency IDC measurements) has been obtained using coplanar waveguides by means of the through-reflect-line (TRL) analysis combined with either a conformal mapping model or a full wave calculation. The BST loss tangent was estimated as /spl sim/0.05 in the range 3-16 GHz.     

Predictive energy management for hybrid vehicle

Hybrid vehicle control strategies are algorithms devoted to the energy management. At each sampling time they choose the powertrain operating point in order to minimize a criterion, usually the fuel consumption. In simulation, an optimization algorithm can be derived from the minimum principle. For real time control, a Model Predictive Control scheme can be used but it requires the prediction of the future driving conditions. Their time ordered prediction is very difficult. Moreover, if the optimal costate is constant, only the prediction of their distribution is sufficient and allows deriving a real time control strategy. Experimental results are provided to illustrate the benefits of this approach.