This paper presents the results of a simulation study regarding the energy consumption of a load-sensing excavator hydraulic system and discusses the possible energy savings by eliminating the directional control valves. The energy consumption of the excavator hydraulic system has been studied for typical working cycles. For this purpose a coupled multi-body dynamics and hydraulic system model was developed in the Matlab Simulink environment, including a precise measurement-based loss model of the variable displacement pump. Power transmission and dissipation was calculated for each component and subsystem, including pumps, motors, valves, cylinders, transmission lines, and others. The simulation results show the amount of dissipated energy, indicating the major loss sources during various operations. Furthermore, the potential recoverable energy in the cycle is calculated, highlighting the prospective advantages of equipping the existing machine with new pump-controlled actuator technology.
Diet specialization in the trophically polymorphic cichlid fish Herichthys minckleyi was examined using gut contents. Individual H. minckleyi were categorized as having molariform, papilliform or undetermined pharyngeal jaws. The presence of enlarged flattened pharyngeal jaw teeth was used to categorize H. minckleyi as molariform, and the possession of only small pencil-like pharyngeal teeth was used to classify fish as papilliform. Undetermined individuals (<50 mm standard length, L S ) were not assigned to one of the two larger morphotypes. Arthropods were found to be generally rare in H. minckleyi gut contents, but when present, they were most frequently recovered from undetermined individuals. The percentage of plant material consumed by undetermined H. minckleyi was not as great as papilliforms ingested on average, and snail crushing by undetermined H. minckleyi was not evident. A significantly greater mean percentage of plant detritus was recovered from papilliforms compared to molariforms. Snails were crushed by molariforms more frequently than by papilliforms. When only molariforms and papilliforms that had crushed snails were compared, a greater number of snails were crushed by molariforms. No relationship was found between molariform L S and the number of snails crushed, but greater molariform tooth number, adjusted for L S , was indicative of recent snail crushing. The maintenance of H. minckleyi pharyngeal jaw variation could be promoted by intraspecific diet differentiation.
In controlled N-nutrition experiments, differences in delta15N composition of leaves and roots are regularly found. In this paper we report results from a survey of nitrogen stable isotope signatures of leaves and roots of 16 plant species growing under natural conditions in a meadow and a forest understorey, which differed in nitrate and ammonium availability. Significant differences between leaf and root were observed. The range of delta15N [leaf-root] values was -0.97 to +0.86 per thousand, small compared to published values from controlled N-nutrition experiment, but almost as large as the range of leaf delta15N values (-1.04 to +1.08 per thousand). Forbs showed the largest differences between leaves and roots and showed a significant difference with respect to habitat. Grasses and legumes did not show significant differences in delta15N [leaf-root] between the two habitats. Care must be taken when using leaf delta15N values as representative for whole-plant 15N composition in these two habitats.
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