Key Kinematic Research Articles

Strings in the η Carinae Nebula: Hypersonic Radiative Cosmic Bullets

We present the results of a numerical study focusing on the propagation of a hypersonic bullet subject to radiative cooling. Our goal is to explore the feasibility of such a model for the formation of "strings" observed in the η Carinae Homunculus nebula. Our simulations were performed in cylindrical symmetry with the adaptive mesh refinement code AstroBEAR. The radiative cooling of the system was followed using the cooling curve described by Dalgarno and McCray. In this paper we discuss the evolution and overall morphology of the system as well as key kinematic properties. We find that radiative bullets can produce structures with properties similar to those of the η Carinae strings, i.e., high length-to-width ratios and Hubble-type flows in the form of a linear velocity increase from the base of the wake to the bullet head. These features, along with the appearance of periodic "ringlike" structures, may also make this model applicable to other astrophysical systems such as planetary nebulae, e.g., CRL 618 and NGC 6543, young stellar objects, etc.

Effect of angle of attack profiles in flapping foil propulsion

Propulsive performance of a harmonically heaving and pitching foil is degraded by a breakdown in the angle of attack profile, at high nondimensional frequencies. We build here upon the method employed by Read et al. (J. Fluid Structure 17 (2003) 163) to invert the key kinematic nonlinearity, and compare directly the performance obtained with four specific angle of attack profiles. These profiles are: (i) that due to simple harmonic motion in both heave and pitch motion, (ii) a square wave, (iii) a symmetric sawtooth wave, and (iv) a cosine function. The cosine angle of attack achieves a significant improvement over the other three cases, in the sense of high thrust values with reasonable efficiency. The highest thrust coefficients, however, are generally found in the sawtooth profile. Flow visualization confirms the partial or complete recovery of a reverse von Kármán wake by all three controlled profiles, concurrent with the enhanced force and efficiency at high frequencies.

Constraints on the kinetic, kinematic and spatiotemporal parameters of gait in Parkinson's disease

The characteristic slow, short stepped, shuffling walking pattern in Parkinson's disease (PD) results from a combination of constraints on locomotor control imposed by neurotransmitter imbalance. Previous research on the pathogenesis of gait disorders in PD has been confined to descriptions of changes in spatiotemporal parameters of the footstep pattern in response to antiparkinsonian medication and attentional strategies. By analysing the changes that occur in kinematics and kinetics with systematic manipulations of dopaminergic status and attention, a fuller understanding of the primary determinants of gait dysfunction in PD can be obtained. We illustrate this point with a case history on a 71 year old hypokinetic woman with PD who demonstrated normalisation of key kinematic and spatiotemporal variables of gait when provided with visual cues at peak-dose of the medication cycle, despite persistent abnormalities in gait kinetics. PsycINFO classification: 2330; 3297; 2520

Formulation of Mindlin-Engesser model for stiffened plate vibration

In this paper, a Mindlin-Engesser model is developed for the vibration analysis of moderately thick plates with arbitrarily oriented stiffeners. The theoretical derivation incorporates the Mindlin theory to account for the effects of transverse shear deformation and rotary inertia of plates, and the Engesser theory to account for the shear deformation of stiffeners with the inclusion of torsion effect. In the method of solution, the resulting energy functionals are minimized using the Ritz procedure with a set of admissible two-dimensional functions expressed in the form of simple polynomials. The key kinematic feature of these shape functions is that they are boundary oriented and no boundary losses are introduced as in discretization methods. With the aim of demonstrating the applicability and versatility of the method, numerical examples including plates of various shapes with arbitrarily oriented stiffeners are presented. Several findings and conclusions regarding the method have been highlighted and discussed.