Modern turtle origins: the oldest known cryptodire.

The discovery of a turtle in the Early Jurassic(185 million years before present) Kayenta Formation of northeastern Arizona provides significant evidence about the origin of modern turtles. This new taxon possesses many of the primitive features expected in the hypothetical common ancestor of pleurodires and cryptodires, the two groups of modern turtles. It is identified as the oldest known cryptodire because of the presence of a distinctive cryptodiran jaw mechanism consisting of a trochlea over the otic chamber that redirects the line of action of the adductor muscle. Aquatic habits appear to have developed very early in turtle evolution. Kayentachelys extends the known record of cryptodires back at least 45 million years and documents a very early stage in the evolution of modern turtles.

Centrifuges for studying the effects of sustained acceleration on human physiology.

The operation, development, and use of high-performance centrifuges with high G-onset rates, similar to those found in modern fighter aircraft, are discussed. Their performance characteristics are examined, and the USAFSAM centrifuge at Brooks AFB in Texas is then described. Centrifuges for space research and large-radius track centrifuges are considered. The benefits of the latter are discussed.

Physiologic validation of a short-arm centrifuge for space application.

A short-arm centrifuge (SAC) of 5-6 ft (1.5-1.8 m) radius may be useful in space to measure tolerances to acceleration (G) and to stimulate the cardiovascular system, thereby reducing cardiovascular decompensation that occurs in weightlessness. Relaxed rapid (1G/s onset rate, ROR) and gradual (0.1 G/s onset rate, GOR) G tolerances were measured on seven men using a 5-ft (1.5 m) radius centrifuge and compared with their G tolerances obtained on the 20-ft (6.1 m) radius human-use centrifuge at the Armstrong Laboratory, Brooks AFB, TX. Since the subjects were required to flex their legs to assume a squatting position on the SAC, a similar position was used on the 20 ft (6.1 m) centrifuge called feet up (FU), and compared with normal-seated +Gz tolerances (controls). The subjects tolerated the SAC exposures without any problems. ROR and GOR tolerances were as follows: control, 3.6 G and 4.2 G; FU, 4.5 G and 5.6 G; and SAC, 4.6 G and 6.4 G. We concluded that a 5-ft radius centrifuge can be used to measure G tolerances. The increases in the SAC GOR tolerances over ROR tolerances indicate that the baroreceptors were stimulated by the G, and the SAC exposure would be useful in preventing cardiovascular decompensation in microgravity.

Unpredictability of fighter pilot G tolerance using anthropometric and physiologic variables.

Correlation and regression analyses were used to study relationships between centrifuge G tolerances of 1,434 fighter pilots during High-G Training (HGT) and anthropometric and physiologic variables. Multiple regression analyses yielded a four-variable model in which gradual onset run (GOR) relaxed-G tolerance was inversely correlated with height and directly correlated with age, weight, and diastolic blood pressure. Although the four-variable model was able to predict more of the variation in G tolerance than any single variable, neither method showed a correlation (r) of greater than 0.35 with GOR relaxed or straining G tolerance. No subject variable was significantly different between the pilot groups that did and did not experience G-induced loss of consciousness. We conclude that prediction of G tolerance during centrifuge HGT is unreliable using anthropometric and physiologic variables. The anti-G straining maneuver remains the major determinant of an individual's G tolerance.

A human-powered, small radius centrifuge for space application: a design study.

The necessity of preventing physiologic deconditioning of astronauts exposed to long duration space flights is well known. A method under consideration to prevent this deconditioning is the use of periodic exposure to artificial gravity which could be provided by a centrifuge. This paper presents a design study for a human-powered centrifuge which could be used aboard the NASA Space Shuttle with analyses which quantify many of the forces produced. Consideration is given to managing reaction forces to changes in centrifuge angular velocity, centrifuge imbalance effects, the effects of gyroscopic moment on spacecraft orientation changes, and torque and power requirements as a function of centrifuge performance parameters. A design concept for a "human powered" centrifuge which could provide both exercise and artificial gravity exposure is also considered.

Taking gravity into space.

NASA: The use of a personal centrifuge as a countermeasure to weightlessness during space flight is presented. The authors argue that it is more effective than exercise techniques now used. Recent research in intermittent gravity exposure is reviewed and future opportunities and requirements for research are examined.^ieng