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We investigate the scaling properties of the primary flow modes and their sensitivity to aspect ratio in a liquid gallium (Prandtl number $Pr = 0.02$) convection system through combined laboratory experiments and numerical simulations. We survey cylindrical aspect ratios $1.4 \le \varGamma \le 3$ and Rayleigh numbers $10^{4} \lesssim Ra \lesssim 10^{6}$. In this range the flow is dominated by a large-scale circulation (LSC) subject to low-frequency oscillations. In line with previous studies, we show robust scaling of the Reynolds number $Re$ with $Ra$ and we confirm that the LSC flow is dominated by a jump-rope vortex (JRV) mode whose signature frequency is present in velocity and temperature measurements. We further show that both $Re$ and JRV frequency scaling trends are relatively insensitive to container geometry. The temperature and velocity spectra consistently show peaks at the JRV frequency, its harmonic and a secondary mode. The relative strength of these peaks changes and the presence of the secondary peak depend highly on aspect ratio, indicating that, despite having a minimal effect on typical velocities and frequencies, the aspect ratio has a significant effect on the underlying dynamics. Applying a bandpass filter at the secondary frequency to velocity measurements reveals that a clockwise twist in the upper half of the fluid layer coincides with a counterclockwise twist in the bottom half, indicating a torsional mode. For aspect ratio $\varGamma = 3$, the unified LSC structure breaks down into multiple rolls in both simulation and experiment.
To establish whether nasal bony landmarks on computed tomography could be utilised reliably in endoscopic approaches to the sphenopalatine foramen.
Methods:
A prospective analysis of 102 consecutive helical computed tomography scans of the paranasal sinuses was carried out by 2 senior ENT surgeons. Distances from the sphenopalatine foramen to endoscopically palpable bony landmarks were measured.
Results:
There were a total of 102 patients (45 females and 57 males), with a mean age of 62 years. The mean distance from the posterior fontanelle to the sphenopalatine foramen was 14.1 mm (standard deviation = 2.13). The average vertical distance of the sphenopalatine foramen opening from the bony attachment of the inferior turbinate was 14.13 mm. There were no statistically significant differences between any of these measurements (foramen width p-value = 0.714, distance from fontanelle p-value = 0.43 and distance from inferior turbinate p-value = 0.48).
Conclusion:
Determination of reliable bony landmarks is clinically useful in endoscopic surgery and can aid identification of the sphenopalatine foramen. The inferior turbinate concha and posterior fontanelle may be used as reliable computed tomography landmarks for endoscopic approaches to the sphenopalatine foramen.
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