No description available.

The central fatigue hypothesis proposes that an increase in central serotonergic (5-HT) activity is detrimental to exercise capacity. The negative effects of high ambient temperatures on exercise capacity are well recognised but are not readily explained in terms of the factors generally associated with the onset of fatigue during prolonged exercise (muscle glycogen depletion, hypohydration and hyperthermia). There is also some evidence to suggest that central 5-HT activity is modified by warm and cold exposure and that the responses of hormones that are considered to be peripheral indices of central 5-HT activity are exacerbated during the later stages of prolonged exercise in the heat but not in the cold. The primary purpose of the studies reported in this thesis was to examine the effects of peripheral or central manipulation of 5-HT activity on the ability to perform prolonged exercise in adverse environmental conditions. The responses of plasma prolactin (Prl) and cortisol were determined in all studies to provide a peripheral index of central 5-HT activity. Chapter 3, examined the effects of pre-cooling and pre-warming by warm and cool water immersion on the responses of Prl and cortisol during exercise in a warm environment. Chapter 4 considered the effect of limiting 5-HT pre-cursor availability by branched chain amino acid (BCAA) ingestion before and during exercise on ability to perform prolonged exercise in a warm environment. Chapter 5 examined the effect of selective 5-HT re-uptake transporter blockade by paroxetine on the time required to reach volitional fatigue in the warm and cool environments. Finally, Chapter 6 considered the effects of 5-HT2C receptor blockade on exercise performance and the thermal response during exercise in a warm environment. None of the studies reported in this thesis provided clear evidence to show that exercise capacity or performance in the heat is influenced by peripheral or central manipulation of central 5-HT activity.

Digitized by Kansas Correctional Industries

The railroad industry plays a pivotal role in commerce and greatly impacts America's economy. With this in mind, they cannot afford downtime or service interruptions due to bridge or member replacement. Corrosion of bridges causes millions of dollars each year for the railroad industry in terms of maintenance and inspection. Since a large number of these bridges are steel and their service life is typically governed by fatigue of welded details, it is important to determine the interactions of the corrosion and fatigue mechanisms. While there are differing opinions on the effects of corrosion on the fatigue life of welded steel attachments, the intent of this research is to experimentally investigate the relationship between fatigue and corrosion and determine whether this relationship is beneficial, neutral, or detrimental to the fatigue behavior of welded attachments. In order to investigate the effects of corrosion on the fatigue life of welded steel attachments, a testing methodology simulating the conditions a bridge could be expected to experience during its service life is established, executed and the results evaluated. Thirty-two specimens were subjected to cycles of corrosion and interval fatigue loading at varying corrosion times and fatigue cycles. These corrosion-fatigue specimens were then compared to the five control (non-corroded) control specimens and three pre-corroded specimens. The results show that the fatigue life of welded steel attachments is not decreased by the effects of corrosion until more than half of the cross section has been reduced. Specimens subjected to a 'pre-corrosion' period occurring in the absence of fatigue loading, then subjected to cyclic fatigue loading at a later time have drastically reduced fatigue lives.

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Thesis (Ph. D.)--Columbia University, 1918. / Vita. Published also as Columbia university contributions to philosophy and psychology, vol. XXVI, no. 2 (Archives of psychology, no. 41).

Thesis (Ph. D.)--Columbia University, 1914.

Thesis (Ph. D.)--Columbia University, 1927. / Vita. "Reprinted from Archives of psychology ... no. 90."

No description available.

No description available.