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Fracture studies in superalloysCrompton, Jeff S. January 1983 (has links)
This research is concerned with the effects of temperature and frequency on the fatigue crack propagation behaviour. The fatigue behaviour at elevated temperature has been reviewed with emphasis on the mechanisms of propagation proposed to explain the effects of temperature and frequency. The crack propagation characteristics of a single crystal superalloy have been investigated at various temperatures and frequencies. Determination of the fatigue crack propagation rates was combined with the measurement of crack tip plastic zone sizes and observation of the deformation behaviour. At elevated temperature, the fatigue crack propagation rates were determined to be dependent on the frequency of loading. At low and high crack growth rates increased crack propagation rates were associated with higher cycling frequencies. At intermediate crack growth rates, the highest propagation rates were associated with the lowest frequency. Selected area channelling pattern techniques were used to determine the plastic zone sizes and revealed that at high frequencies (>10Hz) the plastic zone sizes at elevated and ambient temperature are similar. With decreasing frequency at elevated temperature creep may lead to increased plastic zone sizes but may also affect the crack tip geometry thereby restricting further effects. At room temperature crack propagation is observed to occur by shear of the γ' precipitate on <110> {111} resulting in {111} crystallographic facets on the fracture surface. At elevated temperature (>6000 C) however, the crack growth mechanism changes and propagation takes place on {100}. Observations of the dislocation structure indicate that deformation is concentrated within the γ matrix. It is proposed that the observed crack propagation in the γ matrix on {100} arises by the constraints imposed by the surrounding γ' precipitate. A model is presented for the frequency dependence of the intermediate crack growth rate in terms of the observed strain gradients within the plastic zone and the achievement of a critical local fracture strain.
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762 |
A study on the acute and chronic effects of morphine on rat stomachs何美美, Ho, Mai-mai. January 1986 (has links)
published_or_final_version / Pharmacology / Doctoral / Doctor of Philosophy
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763 |
Modulation of the vascular system and the actions of lipoproteinsLeung, Wai-sum, Susan., 梁慧心. January 1999 (has links)
published_or_final_version / Pharmacology / Doctoral / Doctor of Philosophy
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764 |
Physiological responses of chlorococcum sp. to external stresses馬衍年, Ma, Yin-nin. January 2001 (has links)
published_or_final_version / Botany / Doctoral / Doctor of Philosophy
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765 |
Some effects of hypophsectomy on cold exposed rats裘大任, Chiu, Ta-jen, Daryl. January 1970 (has links)
published_or_final_version / Physiology / Master / Master of Science
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766 |
The effects of non-surgical periodontal treatment on gingival suppuration, bleeding on probing and pocket depths in male tobaccosmoking and non-smoking adults馮建裕, Fung, Kin Yue, Clive. January 1994 (has links)
published_or_final_version / Dentistry / Master / Master of Dental Surgery
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767 |
Auditory damage associated with solvent exposure: evidence from a cross-sectional studyFuente, Adrian. January 2008 (has links)
published_or_final_version / Speech and Hearing Sciences / Doctoral / Doctor of Philosophy
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768 |
Influence of various wavelengths of light on bone metabolism in enucleated ratsMcCarty, Ann Marie 07 January 1982 (has links)
The objective of this research was to indirectly determine the
existence of a possible retinal-endocrine pathway activated, or
Inhibited, by artificial fluorescent light as evidenced by it subsequent
effects on bone metabolism. Forty-eight male Long-Evans post-breeder
rats, half of which were bilaterally orbitally enucleated, were
used in this experiment. A 21-day pretreatment diet contained calcium
and phosphorus, each at a level of 0.2% of the diet, with no dietary
vitamin D. During the last seven days of this period the animals were
in complete darkness. For the 12-week experimental period, the diet
contained 0.6% calcium and 0.4% phosphorus, and oholecalciferol wets
administered the first day by intubation. During this time, four
groups of 12 animals each, half of which were bilaterally orbitally
enucleated, were exposed to either ultraviolet lights, cool green
lights, Vita-Lite (full spectrum) lamps, or kept in complete darkness
in specially constructed environmental boxes. On the first and last day
of the experimental period, the left femurs were x-rayed and blood was
sampled. The serum of the animals was analyzed for alkaline phosphatase,
total calcium and total phosphorus. Bone density was determined.
Femur ash was measured for total calcium and total phosphorus. Under
all lighting conditions, for both the sighted and enucleated rats, the
parameters measured in the serum declined. For serum alkaline phosphatase,
the sighted rats under the cool green lights had the least change;
the sighted in darkness had the greatest decline. The least change in
serum total calcium occurred for both the sighted and enucleated rats
under the cool green lights, whereas the greatest decline was for the
sighted rats under the Vita-Lite lamps and the enucleated under ultraviolet
lights. The sighted rats under the cool green lights had the
highest percent ash per gram of dry fat-free weight; the sighted under
the Vita-Lite lamps had the lowest. The highest ash calcium was in the
sighted rats under the cool green and the Vita-Lite lamps. By both
methods of bone density measurements, specific gravity and densitometry,
the sighted rats under the cool green lights had the greatest loss.
Overall there appeared to be more significant differences among the
sighted animals for the various lighting conditions than for the enucleated.
Also the enucleated rats had less extreme variations from the
mean than the sighted. The results of this study suggest that the light
mediated by the pbotoreceptors of the retina of the sighted rats produced
an effect on bone metabolism. / Graduation date: 1982
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769 |
Role of ammoniagenesis in the hypocalciuric effect of phosphorus in young menDing, Wei, 1967- 03 August 1995 (has links)
The present study sought to define a possible role of phosphorus-stimulated
ammoniagenesis, previously observed in vitro and in
experimental animals, in the hypocalciuric effect of phosphorus in young
men. It was hypothesized that titrating some of the hydrogen ions
destined for excretion with ammonia would be beneficial to kidney
calcium reabsorption because ammonium ion unlike hydrogen ion does
not increase urinary calcium loss. To test this hypothesis, seven young
men (22 - 31 years old and average weight of 70 kg) were fed a single
menu providing 800 mg phosphorus, 1200 mg calcium, 11.7 MJ (~ 2800
kcal) and 14.5 g nitrogen for 10 days. In a subsequent 10-day period,
dietary phosphorus was doubled to 1600 mg by the addition of cheddar
cheese and milk to the menu. Dietary nitrogen, calcium and vitamin D
were equalized for the two periods. Three 24-hour urine samples and a
fasting blood sample were collected at the end of each experimental
period. Comparison of period 2 with 1 showed urinary phosphorus
excretion + 82%, urinary calcium excretion - 38%, serum phosphorus
+ 6.2%, serum calcium - 3.8%, urinary sulfate and creatinine excretion
no change. Urinary ammonia nitrogen excretion increased in all seven
subjects with an average increase of 13%. Furthermore each individual
increase in ammonia nitrogen excretion was found to be directly
correlated with urinary phosphorus excretion (r = 0.76, P < 0.05).
Urinary urea nitrogen excretion was found to vary inversely with urinary
ammonia nitrogen excretion with an average decrease of 12% and
urinary total nitrogen excretion decreased 14% for the entire group.
Results obtained therefore offer a mechanism by which phosphorus
directly improves the non-parathyroid hormone portion of tubular
calcium reabsorption. The magnitude of the effects seen however suggest
that phosphorus-stimulated ammoniagenesis only plays a small role in
the mechanism of the hypocalciuric effect of phosphorus in young men. / Graduation date: 1996
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770 |
Extending shelf-life of fresh-cut pearsDong, Xiaoling 25 September 1998 (has links)
Different concentrations of various browning inhibitors and a firming agent were
evaluated to prevent browning and softening of Bartlett, Bosc and Anjou pear slices
during cold storage at 2-4°C. Browning inhibition effect of Semperfresh, Snow Fresh
and cysteine were compared with that of 4-hexylresorcinol (4-HR). The effect of
ripeness on color and texture changes as well as the influence of storage temperature on
texture and color retention was investigated. 4-HR residual content under different
treatment conditions and its sensory properties were analyzed. 4-HR was an effective
browning inhibitor at concentration as low as 0.005% when combined with 0.5% ascorbic
acid (AA). Cysteine (0.5%) with 0.5% ascorbic acid (AA) effectively inhibited Anjou
and Bosc pear slice browning for 25 days and its sensory properties merit further study.
A combination of 1.0% AA and 1.0% calcium lactate prevented Anjou pear slices from
discoloration, but also caused tissue leaking and softening. Semperfresh and Snow Fresh
did not maintain flesh color effectively. 1.0% calcium lactate maintained slice firmness
at an acceptable level for 30 days when the average firmness of whole pears at slicing
was 49, 38 and 43 Newton (N) for Bartlett, Bosc and Anjou respectively. A storage
temperature of 0°C significantly retained better texture than the control of 2-4°C. Slices with acceptable texture and color were achieved by treatment with a solution of 0.01% 4-HR, 0.5% AA, and 1.0% calcium lactate for 2 min, vacuum packaging, and storage at 2-4°C for 30 days for Bartlett and Bosc, and 15 days for Anjou.
4-HR residual content increased with increasing dipping times and concentrations,
with the latter being the major factor. The 4-HR residual decreased with storage time for
all the treatments. Sensory tests indicated that panelists detected the overall differences
between 0.01% 4-HR treated samples and the controls for both Bartlett and Anjou pears
(P<0.01). There were no significant differences in preference between treated sample
and control for Anjou pears. / Graduation date: 1999
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