Cough airflow dynamics have been previously studied using a variety of experimental methods. In this study, real-time, non-invasive shadowgraph imaging was applied to obtain additional analyses of cough airflows produced by healthy volunteers. Twenty healthy volunteers (10 women, mean age 32.2±12.9 years; 10 men, mean age 25.3±2.5 years) were asked to cough freely, then into their sleeves (as per current US CDC recommendations) in this study to analyze cough airflow dynamics. For the 10 females (cases 1–10), their maximum detectable cough propagation distances ranged from 0.16–0.55 m, with maximum derived velocities of 2.2–5.0 m/s, and their maximum detectable 2-D projected areas ranged from 0.010–0.11 m2, with maximum derived expansion rates of 0.15–0.55 m2/s. For the 10 males (cases 11–20), their maximum detectable cough propagation distances ranged from 0.31–0.64 m, with maximum derived velocities of 3.2–14 m/s, and their maximum detectable 2-D projected areas ranged from 0.04–0.14 m2, with maximum derived expansion rates of 0.25–1.4 m2/s.These peak velocities were measured when the visibility of the exhaled airflows was optimal and compare favorably with those reported previously using other methods, and may be seen as a validation of these previous approaches in a more natural setting. However, the propagation distances can only represent a lower limit due to the inability of the shadowgraph method to visualize these cough airflows once their temperature cools to that of the ambient air, which is an important limitation of this methodology.The qualitative high-speed video footage of these volunteers coughing into their sleeves demonstrates that although this method rarely completely blocks the cough airflow, it decelerates, splits and redirects the airflow, eventually reducing its propagation. The effectiveness of this intervention depends on optimum positioning of the arm over the nose and mouth during coughing, though unsightly stains on sleeves may make it unacceptable to some.

A long series of Southend sea-level observations, extending over a period of 51 years , is analysed using the harmonic method of tidal analysis. The harmonic method of tidal analysis and prediction works on the assumption that the relationship of nodal terms with their respective principal terms in the physical tide is the same as in the equilibrium tide. It is concluded that although this assumption is very useful in accounting for those terms which are not separable from a given length of observations it is not always fully valid. As a result a systematic error is introduced in tidal analysis and prediction.It is observed that small secular trends are present in amplitudes and phase lags of some principal tidal constituents. In the diurnal band, amplitudes of O1 and K 1 are almost constant, but the phase lag of K , is increasing and the phase lag of 0' is decreasing. In the semi-diurnal band, amplitudes of M 2 , S2 and K 2 are increasing, while the phase lag of M z is decreasing and the phase lag of K 2 is increasing. The influence of these secular trends in amplitudes is to increase the tidal range and extreme levels. This is confirmed by increases in the range of tide in the last one and a half centuries. Statistically, no significance can be attached to trends in phase lags because standard errors are large.A comparison of old records with tides synthesized by modern constituents for London Bridge suggests that the phase of the tide was almost stable there from 1683 to 1835; then a large change occurred after 1835. Similar changes are noted in the tidal range. The nature of these changes indicates that they are partly due to increased input at Southend resulting from secular trends in tidal harmonics and partly due to man-made alterations: embankment, bank raising and deepening of the estuary.

Long-period tidal records from eight ports on the west coast of Great Britain are analysed, using both the harmonic method and the response function. Time series up to 9.5 yr were used so that fine structure of certain regions of high energy in the tidal residual spectrum may be examined. This also assisted in accurate separation of tides from surges. According to the currently accepted formulation of MI, its composition is not compatible with its actual composition in the real tide and, as such, has no useful purpose to serve in computation of predictions. Constituents Sa, Ssa, MA, and MB, are adversly affected by weather and long records are essential for their accurate separation. It has been observed that annual perturbations of Sz, similar to those confirmed in recent years for M2, also exist but these are not readily recognisable because their speeds are the same as those of constituents T, and R,. These perturbations, being highly sensitive to meteorological forces, are mainly responsible for cusps or humps in the vicinity of major tidal constituents in tidal residual spectra. The relationship of radiational and gravitational tides is found to be in very good agreement with theoretical results. In summer months non-predictable variance reduces to about half of the annual variance, reflecting the regional weather conditions of summer and winter.

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