A standard baseline scenario 2,3 that assumes no policy intervention to limit greenhouse-gas emissions has 10 TW (10 ؋ 10 12 watts) of carbon-emission-free power being produced by the year 2050, equivalent to the power provided by all today's energy sources combined. Here we employ a carbon-cycle/energy model to ¶ Present address: Boeing, Saal Beach, California 90740-7644, USA.

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The lateral force on a spinning baseball in a wind tunnel has been measured. The magnitude of the force is nearly independent of the orientation of the seams of the ball. The drag coefficient appears to be at most weakly dependent on Reynolds number and to be principally a function of the ratio of the rotational speed of the equator of the ball to the wind tunnel speed. This is to be compared to the work of Briggs, which implies a strong effect of Reynolds number on the drag coefficient.

A mathematical model for the unsteady fluid-dynamic response of the semicircular canals is developed. The endolymph is assumed to be an incompressible Newtonian fluid and the presence and effects of both the utricle and the cupula are specifically accounted for. A first approximate solution is obtained using a singular perturbation method. It is shown that the canal can be modelled as a heavily damped, second-order system which behaves as an angular-velocity meter. A comparison of the model response with experimental results is made; fairly good agreement is found.

The nature of the forces causing the erratic motion of a knuckleball has been investigated by measuring the lateral force on a baseball in a wind tunnel. We have identified two possible sources of a lateral force imbalance that can give rise to the observed erratic changes in the direction of a knuckleball as it moves through the air. One of these results because the nonsymmetrical location of the roughness elements (strings) gives rise to a nonsymmetrical lift (lateral) force. A very slowly spinning knuckleball will have imposed upon it a lateral force that changes as the positions of the strings change. A knuckleball whose spin is identically zero has a constant lateral force unless a portion of the strings is precisely at a location where boundary layer separation occurs. If this happens, the point of boundary layer separation switches alternatively from the front to the rear of the strings, shifting the wake from one position to another, and thereby giving rise to a second possible alternating force imbalance. A two-dimensional analysis of the trajectory of the baseball indicates that the measured force can cause a deflection of the baseball’s trajectory of more than a foot. An effective knuckleball should be thrown so that it rotates substantially less than once on its path to home plate.