This paper investigates the air flow induced by a rigid circular disk or piston vibrating harmonically along its axis of symmetry in the immediate vicinity of a parallel surface. Previous attempts to characterize these so-called ‘squeeze-film’ systems largely relied on simplifications afforded by neglecting either fluid acceleration or viscous forces inside the thin enclosed gas layer. The present viscoacoustic analysis employs the asymptotic limit of small vibration amplitudes to investigate the flow by systematic reduction of the Navier–Stokes equations in two distinct flow regions, namely, the inner gaseous film where streamlines are nearly parallel to the confining walls and the near-edge region of non-slender flow that features gas exchange with the surrounding stagnant atmosphere. The flow in the gaseous film depends on the relevant Stokes number, defined as the ratio of the characteristic viscous time across the film to the characteristic oscillation time, and on a compressibility parameter, defined as the square of the ratio of the acoustic time for radial pressure equilibration to the oscillation time. A Strouhal number based on the local residence time emerges as an additional governing parameter for the near-edge region, which is incompressible at leading order. The method of matched asymptotic expansions is used to describe the solution in both regions, across which the time-averaged pressure exhibits comparable variations that give opposing contributions to the resulting time-averaged force experienced by the disk or piston. A diagram structured with the Stokes number and compressibility parameter as coordinates reveals that this steady squeeze-film force, typically repulsive for small values of the Stokes number, alternates to attraction across a critical separation contour in the parametric domain that exists for all Strouhal numbers. This analysis provides, for the first time, a unifying viscoacoustic theory of axisymmetric squeeze films, which yields a reduced parametric description for the time-averaged repulsion/attraction force that is potentially useful in applications including non-contact fluid bearings and robot locomotion.

This paper uses numerical and asymptotic methods to investigate the fluid dynamics underlying the anomalously large attractive forces that were recently observed in squeeze-film levitation systems driven by resonant vibrations of a flexible oscillator. Namely, in a recent experimental study, a thin plastic disk driven near one of its natural frequencies attractively levitated, for the first time, an object weighing several hundred grams. This behavior is in stark contrast with that of rigid-body systems, which produce attractive forces thousands of times weaker and only within a limited range of operating conditions. Flexural systems driven by standing-wave deformations of the oscillator are addressed in this paper in a unifying matched-asymptotic analysis that accounts for effects of fluid viscosity, inertia, and compressibility, as well as pressure variations beyond the outer boundary of the squeeze film. While the weak attractive forces produced by rigid-body systems are known to depend critically on the existence of a net pressure drop across this peripheral region, the present analysis reveals that the augmented attractive load capacity of resonant flexural systems is associated instead with spikes of underpressure near the nodes of the standing wave. Furthermore, the wavenumber, which represents the number of nodes in the waveform, is found to correlate strongly with the attractive load capacity as well as the range of frequencies and oscillator surface areas for which attractive forces can be produced.

Background: Breeds of animals differ with respect to anatomical, physiological and behavioural traits hence the study of inter-breed variation in pharmacokinetics becomes necessary. The aim of the current investigation was to determine the pharmacokinetics of enrofloxacin following intravenous bolus administration to assess the influence of breed on drug pharmacokinetics and availability. Methods: In the present study the pharmacokinetics of a common antimicrobial drug, enrofloxacin and its metabolite, ciprofloxacin was studied in adult, non-pregnant and dry Badri cows, wherein a commercial preparation of enrofloxacin (10% v/v) was administered at a dose rate of 7.5 mg/kg intravenously as a single dose. The plasma samples were collected at regular intervals and subjected to analysis by HPLC after appropriate processing. The results obtained were analysed using a software tool, “PK Solver” to obtain the pharmacokinetic parameters. Result: From the study, it was revealed that the Badri cattle showed a distribution half-life of 0.11 h, a volume of distribution of 7.63 L.kg-1, an elimination half-life of 4.27 h and an MRT of 5.93 h for enrofloxacin. Whereas, a maximum plasma concentration level of 0.12 µg.ml-1 was observed for ciprofloxacin in the current study. According to the results obtained in the pharmacokinetic study, an individualized dosage regimen containing a priming dose of 5 mg/kg and a maintenance dose of 4.5 mg/kg with an interval of 24 hours was suggested for the enrofloxacin in Badri cattle. The results of our current study when compared with the previously available literature on other cattle breeds suggested that the Badri cattle differed with respect to pharmacokinetic properties and further studies will be required to determine the conclusive reason for the differences.