Numerical study of the noninertial systems: applicationto train coupler systems

Car coupler forces have a significant effect on the longitudinal train dynamics and stability. Because the coupler inertia is relatively small in comparison with the car inertia; the high stiffness associated with the coupler components can lead to high frequencies that adversely impact the computational efficiency of train models. The objective of this investigation is to study the effect of the coupler inertia on the train dynamics and on the computational efficiency as measured by the simulation time. To this end, two different models are developed for the car couplers; one model, called the inertial coupler model, includes the effect of the coupler inertia, while in the other model, called the noninertial model, the effect of the coupler inertia is neglected. Both inertial and noninertial coupler models used in this investigation are assumed to have the same coupler kinematic degrees of freedom that capture geometric nonlinearities and allow for the relative translation of the draft gears and end of car cushioning (EOC) devices as well as the relative rotation of the coupler shank. In both models, the coupler kinematic equations are expressed in terms of the car body and coupler coordinates. Both the inertial and noninertial models used in this study lead to a system of differential and algebraic equations that are solved simultaneously in order to determine the coordinates of the cars and couplers. In the case of the inertial model, the coupler kinematics is described using the absolute Cartesian coordinates, and the algebraic equations describe the kinematic constraints imposed on the motion of the system. In this case of the inertial model, the constraint equations are satisfied at the position, velocity, and acceleration levels. In the case of the noninertial model, the equations of motion are developed using the relative joint coordinates, thereby eliminating systematically the algebraic equations that represent the kinematic constraints. A quasistatic force analysis is used to determine a set of coupler nonlinear force algebraic equations for a given car configuration. These nonlinear force algebraic equations are solved iteratively to determine the coupler noninertial coordinates which enter into the formulation of the equations of motion of the train cars. The results obtained in this study showed that the neglect of the coupler inertia eliminates high frequency oscillations that can negatively impact the computational efficiency. The effect of these high frequencies that are attributed to the coupler inertia on the simulation time is examined using frequency and eigenvalue analyses. While the neglect of the coupler inertia leads, as demonstrated in this investigation, to a much more efficient model, the results obtained using the inertial and noninertial coupler models show good agreement, demonstrating that the coupler inertia can be neglected without having an adverse effect on the accuracy of the solutio

Systematics of the Pacific monkey-faced bats (Chiroptera : Pteropodidae), with a new species of Pteraloplex and a new Fijian genus

Copyright © 2005 The Natural History MuseumThe fruit-bat genus Pteralopex comprises the monkey-faced bats, a group of six endangered species found only in old-growth forests on certain islands in the south-west Pacific (the Solomon Islands and Fiji). The taxonomy of the genus is reviewed in detail and updated accordingly. Two ‘cryptic’ biological species are shown to occur in sympatry on both Bougainville and Choiseul in the northern Solomon Islands (corresponding to Pteralopex anceps Andersen, 1909 and a previously undescribed species) and each is accordingly described and reviewed. A new genus (Mirimiri) is erected for the Fijian monkey-faced bat (formerly Pteralopex acrodonta), which differs greatly both morphologically and genetically from species of Pteralopex in the Solomon Islands. Ecomorphological differences between sympatric Pteralopex species are briefly reviewed, including potential differences in functional morphology and feeding ecology. Geographic patterns of occurrence and future survey priorities for monkey-faced bats are also discussed.Kristofer M. Helge

Notes on the lesser white-lined bat, Saccopteryx leptura (Schreber) (Chiroptera, Emballonuridae), from southeastern Brazil

Saccopteryx leptura (Schreber, 1774) is reported from two new localities in southeastern Brazil, both in Atlantic forest remains in the state of Rio de Janeiro. Analysisof food material showed that individuals from both localities had preyedon insects in the order Hymenoptera. Cheek contents were available from one specimen, and in this case identification of the food item (flying ants) achieved generic level (Pheidole Westwood, 1841). Aspects in the social behavior observed in a colony suggest that the same traits documented in Central American populations (small colonies, monogamic mating system, and retention of young for up to a year in the parental unit) may also characterize this species in the southern most part of its range. In both external and craniodental selected measurements, specimens from Rio de Janeiro were close to the upper limits of the ranges known for the species