ZeTek Power recently introduced mass manufacturable and cost effective alkaline fuel cells on the market. Today's research is focused on further improvement both in terms of performance increase and cost reduction. This research is classically performed using small (4 cm2) experimental electrodes in the half-cell configuration. This allows the primary electrochemical losses in an anode or cathode to be determined independently. Additional performance losses occur when one integrates large electrodes into a module of 24 cells and in a stack comprised of many modules. By comparing the performance of half-cell experiments to that of modules, these losses can be distinguished and addressed. The information thus obtained, both for the small electrodes and in up-scaling is vital if one is to identify the key areas in which improvement is possible and where to focus future research. Furthermore, the identification of the losses in a module and system allows us to predict the final performance from half-cell measurements of a new laboratory scale experimental electrode. 相似文献
Dynamic mechanical and longitudinal sonic velocity measurements have been made on a series of semi-1-IPNs in which the network component is a polyurethane and the linear constituent a copolymer of methyl acrylate and ethyl acrylate. Dynamic mechanical analysis reveals phase separation. The shifting of the polyurethane glass transition in both the tan δ? and the E″–temperature plots indicates that some mixing occurs. The longitudinal sonic velocity results indicate that the polyurethane is present as a continuous phase in all the materials investigated. 相似文献
Considering the fact that faults may be revealed as undesired mutual effect of program predicates on each other, a new approach for localizing latent bugs, namely Hierarchy-Debug, is presented in this paper. To analyze the vertical effect of predicates on each other and on program termination status, the predicates are fitted into a logistic lasso model. To support scalability, a hierarchical clustering algorithm is applied to cluster the predicates according to their presence in different executions. Considering each cluster as a pseudo-predicate, a distinct lasso model is built for intermediate levels of the hierarchy. Then, we apply a majority voting technique to score the predicates according to their lasso coefficients at different levels of the hierarchy. The predicates with relatively higher scores are ranked as fault relevant predicates. To provide the context of failure, faulty sub-paths are identified as sequences of fault relevant predicates. The grouping effect of Hierarchy-Debug helps programmers to detect multiple bugs. Four case studies have been designed to evaluate the proposed approach on three well-known test suites, Space, Siemens, and Bash. The evaluations show that Hierarchy-Debug produces more precise results compared with prior fault localization techniques on the subject programs. 相似文献
The process of isothermal annealing of nodular monoclinic crystals of isotactic polypropylene (iPP) was analyzed by atomic force microscopy (AFM) and temperature-modulated differential scanning calorimetry (TMDSC). Initially nodular and mesomorphic domains were obtained by controlled melt-crystallization at high cooling rate. Subsequent heating triggers transition from mesomorphic to monoclinic structure, and melting of unstable nodules. Annealing allows re-crystallization, which is recognized by enlargement of domains from initially about 20 nm to about 35 and 55 nm after annealing at 393 and 433 K, respectively. Furthermore, the re-crystallization process is connected with a slight change of the aspect ratio of crystals. The isothermal re-crystallization of the liquid is superimposed by aggregation of crystals, to yield blocky, and string-like objects. The direct analysis of structure on isothermal annealing by AFM is for the first time compared with the isothermal decrease of the apparent specific heat capacity, or change of enthalpy, monitored by TMDSC. The apparent specific heat capacity decreases during annealing with an identical non-linear time dependence as the directly observed growth of the crystal size. Analysis of the annealing processes at different temperatures yields proportionality between the increase of the crystal size and the reduction of the apparent specific heat capacity. 相似文献
Multimedia Tools and Applications - In this paper, a novel chaos-based dynamic encryption scheme with a permutation-substitution structure is presented. The S-boxes and P-boxes of the scheme are... 相似文献
In this paper, a new fuzzy group decision-making methodology which determines and incorporates negotiation powers of decision makers is developed. The proposed method is based on a combination of interval type-2 fuzzy sets and a multi-criteria decision making (MCDM) model, namely TOPSIS. To examine the applicability of the proposed methodology, it is used for finding the best scenario of allocating water and reclaimed wastewater to domestic, agricultural, and industrial water sectors and restoring groundwater quantity and quality in the Varamin region located in Tehran metropolitan area in Iran. The results show that the selected scenario leads to an acceptable groundwater conservation level during a long-term planning horizon. Although the capital cost of this scenario is high, which leads to groundwater restoration during the 34-year planning horizon, it is determined as the best allocation scenario. This scenario also entails the second least pumping cost, due to less water allocation from the groundwater. To evaluate the results of the proposed methodology, they are compared with those obtained using some well-known interval type-2 decision-making approaches including arithmetic-based, TOPSIS-based, and likelihood-based comparison methods. The Spearman correlation coefficient shows that the obtained results generally concur with those of the other methods. It is also concluded that the proposed methodology gives more reasonable results by calculating and considering the negotiation powers of decision makers in an extended TOPSIS-based group decision-making model.
The effects of gum tragacanth obtained from two species of Astragalus Gossypinus (GT-G) and A. Parrowianus (GT-P) at two levels of 10% and 30% combined with cellulose nanofibers (CNF; 5%) on the physico-mechanical and structural properties of polyvinyl alcohol (PVA) nanocomposite film were investigated in this study. The water solubility and water vapor permeability of the films decreased with increasing the content of both gums, especially in the film containing 30% GT-P. The highest values of the tensile strength (39.3 MPa) and elongation at break (445%) belonged to the treatment containing 10% GT-P (90/10P/0). The FTIR and DSC analyses confirmed good interactions between GT and PVA in the 90/10P/0 treatment. SEM images indicated the dense structure of this film as the optimum treatment. Although the presence of CNF in the films containing GT-G improved some properties, especially the Young modulus, it impaired all the functional properties of nanocomposite GT-P film. 相似文献
Wound care has been a challenging subject for medical teams and researchers. Bacterial infections are one of the most serious complications in injured skins that often affect healing process. Antibacterial wound dressings can be used to facilitate wound healing process. The purpose of this study is to fabricate chitosan (Chito)/polyethylene glycol (PEG) antibacterial wound dressing doped with minocycline, and to evaluate the influence of composition ratio on the blending properties of the films. To improve the mechanical properties of these films, we examined various amounts of glycerol as a plasticizer. Moreover, we investigated morphological and mechanical aspects, water uptake, degradation, water vapor transmission and wettability properties of the films prepared with various ratios of Chito/PEG/Gly. Assessment of mechanical properties revealed that film containing 80:20 ratio Chito/PEG with 40 PHR Gly content exhibits the highest ultimate tensile strength and elongation at break (9.74 MPa and 45.73% respectively). Furthermore, results demonstrated that upon increasing PEG and Gly contents, degradability and hydrophilicity of the films increased whereas water uptake decreased. Water vapor transmission rate of the films was close to the range of 530–1200 g/m2d, indicating that the as formed films are possible candidates for dressing low exudate wounds or burns. Minocycline loaded films exhibited a biphasic drug release profile and it was more effective on gram-positive bacteria than on gram-negative bacteria. The polymeric film with the highest amount of loaded drug (2%) exhibited insignificant cytotoxicity (88%) against normal fibroblast cell line. 相似文献
Discrete linear quadratic control has been efciently applied to linear systems as an optimal control.However,a robotic system is highly nonlinear,heavily coupled and uncertain.To overcome the problem,the robotic system can be modeled as a linear discrete-time time-varying system in performing repetitive tasks.This modeling motivates us to develop an optimal repetitive control.The contribution of this paper is twofold.For the frst time,it presents discrete linear quadratic repetitive control for electrically driven robots using the mentioned model.The proposed control approach is based on the voltage control strategy.Second,uncertainty is efectively compensated by employing a robust time-delay controller.The uncertainty can include parametric uncertainty,unmodeled dynamics and external disturbances.To highlight its ability in overcoming the uncertainty,the dynamic equation of an articulated robot is introduced and used for the simulation,modeling and control purposes.Stability analysis verifes the proposed control approach and simulation results show its efectiveness. 相似文献
Realistic tire–pavement interface contact areas and stresses were incorporated into the Pavement Analysis using Nonlinear Damage Approach (PANDA) user interface (PUI). PANDA is a software library developed to simulate the complex thermo-viscoelastic–viscoplastic–viscodamage responses of the pavement to mechanical and environmental loads. The PUI is an interface generating a finite element representation of the pavement within PANDA. The application of realistic tire loading is necessary to calculate accurate pavement responses. The PUI incorporates a database of tire contact areas and stresses obtained from tire finite element simulations. The database includes tire interface characteristics with pavements for various applied loads, tire inflation pressures, vehicle speeds and scenarios of different rolling simulations. A parametric study was conducted to investigate the effect of simulations of tire contact stresses that match field measurements on viscoelastic and viscoplastic pavement responses. Pavement responses are greatly affected using realistic tire loading contact stresses and contact geometry as compared to simplified contact models. The impact on rutting and damage predictions cannot be ignored if reliable projections of pavement performance are to be made. This study confirms the importance of considering realistic three-dimensional contact stresses to design and analyse pavements. 相似文献