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The fracture process zone related to the subcritical crack growth in a three point bend concrete specimen is investigated by interferometric methods. The specimen has an off-centered, single-edged precrack. The crack closing stress caused by the aggregate bridging is determined by the applied load and the crack opening models. The crack closing stress is increased when the zone subjected to aggregate interlocking.

On-line gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) was evaluated for use in stable isotope studies of human cholesterol metabolism. Calibration curves were constructed by analyzing underivatized and TMS-cholesterol over a range of 13C abundances from natural abundance to 0.05 mol of (3,4-13C)cholesterol per mole of unlabeled cholesterol (Delta 13C -24 to 270 per thousand). The calibration curves were highly linear (r squared = 0.99) with slopes of 0.98 and 0.88 for underivatized and TMS-cholesterol, respectively. Higher precision of 13C/12C ratio determination was obtained using TMS-cholesterol, with a detection limit (2 SD) of 0.3 per thousand or 0.004 mol% of (3,4-13C)cholesterol. By comparison standard GC/MS had a detection limit of 0.06 mol% for (3,4-13C)cholesterol. A 57-day study of cholesterol elimination was conducted in one human subject with oral administration of 50 mg of (3,4-13C)cholesterol. Peak enrichment was 9 per thousand above baseline (40 times the detection limit) and could be followed for 40-50 days. The results indicate that GC/C/IRMS provides 15-fold lower detection limits for (3,4-13C)cholesterol than GC/MS and is useful for human studies of cholesterol metabolism.

OBJECTIVE:: To test the hypothesis that the synthesis of intramyocellular triglycerides (imcTG) in skeletal muscle is increased in obese rats in which the content of imcTG is known to be abnormally high. ANIMALS:: Sprague-Dawley male lean and high-fat-induced obese rats were studied at the age of 4, 8 and 12 months after an overnight fast, awake. MEASUREMENTS:: [U-14C]glycerol was continuously infused intravenously for 2?h followed by muscle biopsies, and intracellular glycerol incorporation into imcTG was determined. imcTG content, intramyocellular free glycerol concentration and specific activity, systemic glycerol flux and plasma glycerol, free fatty acid (FFA) and glucose concentrations were also determined. RESULTS:: The rates of incorporation of intramyocellular glycerol into imcTG (nmol/g wet muscle/h) were markedly accelerated in obese rats compared to their lean littermates at all ages: 66±12 vs 12±2 (P=0.02) for gastrocnemius and 74±29 vs 31±7 (P=0.09) for soleus when 4 months old; 223±29 vs 58±27 (P=0.001) for gastrocnemius, 224±28 vs 70±21 (P=0.001) for soleus and 294±78 vs 49±22 (P=0.02) for tibialis anterior when 8 months old; and 25±4 vs 11±2 (P=0.01) for gastrocnemius and 22±8 vs 8.4±3 (P=0.04) for soleus when 12 months old. As expected, this was accompanied by a higher imcTG content in virtually all muscles at all ages tested. CONCLUSION:: The synthesis of imcTG in skeletal muscle is grossly increased in obese rats, which likely contributes to abnormal imcTG accumulation.International Journal of Obesity (2003) 27, 1014-1019. doi:10.1038/sj.ijo.0802380 [ABSTRACT FROM AUTHOR]

OBJECTIVE: To evaluate the feasibility of using deuterated water and isotope ratio mass spectrometry to measure de novo fatty acid synthesis in adipose tissue, and to compare this parameter in obese and lean women. SUBJECTS: Six lean and six obese premenopausal Caucasian women in the main study and three obese Pima Indians in a pilot study. MEASUREMENTS: Deuterated water was administered orally twice daily for 14 days to create stable deuterium enrichment in body water, during which series of blood samples were collected to measure body water deuterium enrichment and deuterium incorporation into plasma total Triacylglycerol (TG) fatty acids and total cholesterol. Subcutaneous fat at different sites were sampled at the beginning and the end of deuterium administration to measure deuterium incorporation into TG fatty acids. RESULTS: Fractional de novo synthesis rate of TG fatty acids in adipose tissue was 0.014 ± 0.005 and 0.014 ± 0.007% in lean and obese Caucasian women, corresponding to 2 ± 0.7 and 5.6 ± 3.2 g (P = 0.3) of fatty acids synthesized daily, respectively. Plasma TG fatty acids and cholesterol synthesis rates were comparable to those reported previously. A pilot study showed that de novo lipid synthesis in adipose tissue of obese Pima Indians was also quantitatively minor. CONCLUSION: Human adipose tissue, like the liver, does not make a major contribution to whole body lipogenesis under eucaloric conditions. A combination of deuterated water and isotope ratio mass spectrometry is a useful research tool for studying accumulation of de novo synthesized lipids in human adipose tissue. [ABSTRACT FROM AUTHOR]