Perceptual and eye movement responses elicited by linear acceleration following spaceflight.

Responses of four crewmembers were measured before and after a 9-d Spacelab Mission during inter-aural (y-axis) and longitudinal (z-axis) linear acceleration. During one test, eye movements were recorded with simultaneous sinusoidal acceleration and constant-velocity optokinetic stimulation. Postflight responses indicated changes in the horizontal sinusoidal response during the y-axis trials. In another test, subjects indicated direction of acceleration during a series of low acceleration steps. More incorrect direction indications were observed postflight, and the y-axis sensitivity increased while the z-axis sensitivity decreased for three subjects. In a third test, subjects used a joystick to null pseudo-random linear motion. Not one subject showed a significantly enhanced ability to null linear motion in the y-axis, while two subjects showed an enhanced ability during z-axis testing postflight. Oculomotor and perceptual responses to linear acceleration are modified by exposure to microgravity and become more variable postflight. The observed changes may be due to an altered interpretation of inertial cues in space that is inappropriate postflight.

A thermodynamic view of polymer degradation, and its application to extensive sonication of DNA.

A simple thermodynamic theory is developed, which predicts (in agreement with a wide variety of other theoretical approaches and experimental results) that for simple polymers the most probable Schulz distribution of fragments will be obtained in a polymer degradation process that is allowed to proceed to a dynamic equilibrium. When the same method is applied to a double-stranded polymer like DNA, however, it predicts that some narrowing of this distribution may occur in conjunction with a limited amount of base unpairing at the fragment termini. The compatibility of this prediction with the experimental results of long-time sonication of DNA is considered.