Sound generation by a vortex ring collision

A collision between two vortex rings and its sound generation is studied numerically using the contour dynamics method. Results suggest that the radial acceleration and the rate of change of the axial acceleration of the vortex rings are the more important dynamic parameters for sound generation during the interaction. The former is important at or near the pass-through instant when the vortex rings are coplanar and are of unequal strength. The latter, being important in the sound generation during a head-on collision before the vortex ring cores are very close to each other, especially when the rings are thin, is also important in sound generation by an unequal strength vortex ring collision after the pass through when the vortex cores are separated by a distance so that the mutual induction strength does not result in significant change of the impulse of the stronger ring. ©1995 Acoustical Society of America.published_or_final_versio

Effects of a background axisymmetric potential flow on vortex ring pairing sound

Sound generated by the pairing of two coaxial vortex rings in the presence of a background axisymmetric potential flow was studied numerically. Results show that the background flow substantially affects the sound generation process in the beginning of the vortex ring interaction. They also suggest that the axial jerk and radial acceleration/deceleration of vortex rings are the major mechanisms through which pairing sound is produced. The effect of background flow mean shear rate on sound generation is also discussed and the results suggest that higher sound levels will be generated when the vortex rings are interacting within the region of high mean shear in a low speed laminar jet. ©1998 Acoustical Society of America.published_or_final_versio

Inviscid two dimensional vortex dynamics and a soliton expansion of the sinh-Poisson equation

The dynamics of inviscid, steady, two dimensional flows is examined for the case of a hyperbolic sine functional relation between the vorticity and the stream function. The 2-soliton solution of the sinh-Poisson equation with complex wavenumbers will reproduce the Mallier-Maslowe pattern, a row of counter-rotating vortices. A special 4-soliton solution is derived and the corresponding flow configuration is studied. By choosing special wavenumbers complex flows bounded by two rigid walls can result. A conjecture regarding the number of recirculation regions and the wavenumber of the soliton expansion is offered. The validity of the new solution is verified independently by direct differentiation with a computer algebra software. The circulation and the vorticity of these novel flow patterns are finite and are expressed in terms of well defined integrals. The questions of the linear stability and the nonlinear evolution of a finite amplitude disturbance of these steady vortices are left for future studies. © 1998 American Institute of Physics.published_or_final_versio

A double-track greedy channel routing algorithm

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A New Optimization Cost Model for VLSI Standard Cell Placement

In this paper, we propose a new optimization cost model for VLSI placement. It distinguishes itself from the traditional wire-length cost model by having direct impact on the quality of the detailed routing phase. We also extend the well-known simulated annealing standard cell placement algorithm by applying our new cost model. Experimental results show that we got 13% layout area reduction compared to traditional wire length model, 11% reduction to commercial tool.published_or_final_versio

Sound sources in the interactions of two inviscid two-dimensional vortex pairs

Author name used in this publication: S. K. Tang2000-2001 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Influence of age of mice on the susceptibility to murine schistosomiasis infection

Intensity of human schistosomiasis infection increases with age, a peak being attained at early puberty. Hormones could be involved in the age-related changes in susceptibility to schistosomiasis. Male BALB/c mice were infected with Schistosoma mansoni either before or after puberty and worm numbers, cellular immune responses, hormonal levels and pathology analysed. Pre-puberty infected mice had a significantly higher number of adult worms (

Adolescent Problem Gambling in Rural Ghana: Prevalence and Gender Differentiation

Abstract Problem gambling among young people is now a public health challenge in sub-Saharan Africa. However, the behaviour remains understudied, particularly, among rural-dwelling young people in countries within the subregion. We aimed to estimate the 12 months prevalence of problem gambling and to describe the overall and gender differences and commonalities in personal factors and social adversities associated with problem gambling among adolescents in rural Ghana. We conducted a cross-sectional survey involving a random sample of 1101 in-school adolescents aged 10–19 years in a rural district in Eastern Ghana; we used the DSM-IV-Multiple Response-Juvenile (DSM-IV-MR-J) questionnaire to assess problem gambling during the previous 12 months. Personal lifestyle and psychosocial variables were assessed using adopted items from the 2012 WHO–Global School-based Student Health Survey. Overall, three in 10 adolescents (3 in 10 females; 4 in 10 males) in rural Ghana reported problem gambling in the previous 12 months. Female adolescents who experienced problem gambling were more likely to report family-related social adversities, while adolescent male problem gambling was associated with school-related factors and interpersonal factors outside the family context. Regardless of gender, sexual abuse victimisation was associated with three times increase in the odds of experiencing problem gambling. Relative to the prevalence of gambling among adolescents in urban contexts in other countries within sub-Saharan Africa, the estimates of problem gambling among in-school rural adolescents in Ghana are higher. Although further studies are needed to understand the nuances of the behaviour, the evidence of this study underscores the need for general and targeted health promotion, intervention and prevention efforts to mitigate the family, school, and interpersonal social adversities associated with adolescent problem gambling in rural Ghana.</jats:p