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The force produced by cat muscles over time with two stimuli separated by a short interval is approximately three times that produced by a twitch of cat muscles. This facilitation of force production by a second stimulus involves both increases in magnitude and duration of the contraction. Increased magnitude is relatively more important in the fast-twitch plantaris muscle, whereas increased duration is more important in the slow-twitch soleus muscle. The facilitation decays in an approximately exponential manner with the interval between stimuli, having a time constant between one and two times the twitch contraction time in different muscles. If a third stimulus is added, the greatest facilitation is seen at intervals longer than the twitch contraction time. The drug Dantrolene, which specifically reduces Ca +* release from the sarcoplasmic reticulum, eliminates the delayed peak in facilitation with three stimuli. Associated with the increases in force with one or more stimuli are increases in muscle stiffness, which can be measured with small, brief stretches and releases that do not alter the time-course of contraction. The stiffness of soleus muscle reaches a peak after the peak in force. The increasing stiffness of the muscle can considerably facilitate transmission of force generated internally, in addition to any facilitation arising from Ca++-release mechanisms.

The early autumn voyage of RV Sikuliaq to the southern Beaufort Sea in 2015 offered very favorable opportunities for observing the properties and thicknesses of frazil‐pancake ice types. The operational region was overlaid by a dense network of retrieved satellite imagery, including synthetic aperture radar (SAR) imagery from Sentinel‐1 and COSMO‐SkyMed (CSK). This enabled us to fully test and apply the SAR‐waves technique, first developed by Wadhams and Holt (1991), for deriving the thickness of frazil‐pancake icefields from changed wave dispersion. A line of subimages from a main SAR image (usually CSK) is analyzed running into the ice along the main wave direction. Each subimage is spectrally analyzed to yield a wave number spectrum, and the change in the shape of the spectrum between open water and ice, or between two thicknesses of ice, is interpreted in terms of the viscous equations governing wave propagation in frazil‐pancake ice. For each of the case studies considered here, there was good or acceptable agreement on thickness between the extensive in situ observations and the SAR‐wave calculation. In addition, the SAR‐wave analysis gave, parametrically, effective viscosities for the ice covering a consistent and narrow range of 0.03–0.05 m2 s−1.

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