Towards an engineering model for curve squeal

Curve squeal is a strong tonal noise that may arise when a railway vehicle negotiates a curve. The wheel/rail contact model is the central part of prediction models, describing the frictional instability occurring in the contact during squeal. A previously developed time-domain squeal model considers the wheel and rail dynamics, and the wheel/rail contact is solved using Kalker’s nonlinear transient CONTACT algorithm with Coulomb friction. In this paper, contact models with different degree of simplification are compared to CONTACT within the previously developed squeal model in order to determine a suitable contact algorithm for an engineering curve squeal model. Kalker’s steady-state FASTSIM is evaluated, and, without further modification, shows unsatisfying results. An alternative transient single-point contact algorithm named SPOINT is formulated with the friction model derived from CONTACT. Comparing with the original model results, the SPOINT implementation results are promising and similar to results from CONTACT

Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions

The results from ten statistical multifragmentation models have been compared with each other using selected experimental observables. Even though details in any single observable may differ, the general trends among models are similar. Thus these models and similar ones are very good in providing important physics insights especially for general properties of the primary fragments and the multifragmentation process. Mean values and ratios of observables are also less sensitive to individual differences in the models. In addition to multifragmentation models, we have compared results from five commonly used evaporation codes. The fluctuations in isotope yield ratios are found to be a good indicator to evaluate the sequential decay implementation in the code. The systems and the observables studied here can be used as benchmarks for the development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume "Dynamics and Thermodynamics with Nuclear Degrees of Freedo

Precision Measurement of the Proton Flux in Primary Cosmic Rays from Rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station

A precise measurement of the proton flux in primary cosmic rays with rigidity (momentum/charge) from 1 GV to 1.8 TV is presented based on 300 million events. Knowledge of the rigidity dependence of the proton flux is important in understanding the origin, acceleration, and propagation of cosmic rays. We present the detailed variation with rigidity of the flux spectral index for the first time. The spectral index progressively hardens at high rigidities.</p

Incorporating dissipated impact into random vibration analyses through the modified hertzian contact model

The Hertzian contact model, which is usually used in analyzing the response of vibroimpact system with elastic contact, cannot deal with the dissipated contact problem in general. A modified Hertzian contact model that was developed through recent experiments, however, provides an opportunity to break this limitation. The random response of vibrating system with dissipated impact subjected to Gaussian white noise is investigated in this paper, and the dissipated impact is incorporated into random analysis through this modified model. The inelastic contact force can be separated into two parts: elastic restoring component and dissipative component. The restoring component is expressed as the gradient of the potential energy preserved in the system and the dissipative component is approximated by a damping force with energydependent damping coefficient through energy dissipation balance technique. The Ito stochastic differential equation with respect to the total energy of the system, which is a one-dimensional Markov process, is derived through the stochastic averaging of the energy envelope. The stationary probability density of system total energy, the joint probability density of system displacement and velocity, and the statistics of system response are analytically obtained from the associated Fokker-Planck-Kolmogorov equation. The agreement between the analytical results and Monte-Carlo simulations validates the effectiveness of the proposed technique. © 2013 American Society of Civil Engineers

Conducting perovskite LaNi0.6Co0.4O3 ceramics with glass additions

10.1007/s10832-006-9871-7Journal of Electroceramics164313-319JOEL