Search

We determined the heat capacities of four series of glasses and liquids of basaltic and basaltic andesite compositions from remelted volcanic rock samples and Fe-free synthetic analogues. The samples are low-alkali, Ca- and Mg-rich aluminosilicates with non-bridging oxygen to tetrahedrally-coordinated cation ratios (NBO/T) ranging between 0.33 and 0.67. Differential scanning calorimetry measurements were performed at atmospheric pressure between room temperature and ~ 100 K above the glass transition for hydrous samples and up to ~ 1800 K for dry samples. The water contents investigated range up to 5.34 wt.% (16.4 mol%). Water does not measurably affect the heat capacity of glasses. We derived a new value of the partial molar heat capacity of water in silicate glasses of C ¯ P , H 2 O glass = 82.804 + 10 − 3 T − 48.274 × 10 − 5 T − 2 (J/mol K) using our new data in combination with literature data on more and less polymerized compositions. The increase in heat capacity at the glass transition is of the order of ~ 30–40% and generally increases with increasing water content. The onset of the glass transition in hydrous samples occurs below the Dulong–Petit limit of 3R/g atom. The configurational heat capacity, i.e., the magnitude of the change in heat capacity observed at the glass transition, generally increases as polymerization decreases and as water content increases. We obtained a partial molar heat capacity of water in silicate liquids of basaltic composition of ~ 86 J/mol K. This value is comparable to the partial molar values for the major oxides which range from ~ 79 to 230 J/mol K. The partial molar heat capacity of water in silicate liquids appears to be compositionally-dependent, increasing as melt polymerization decreases. Such a dependence is certainly linked to the speciation and structural roles of water in complex silicate melts, however, a single value of ~ 93 J/mol K could reproduce the heat capacity of hydrous liquids of a wide range of NBO/T (0–1.51) at temperatures up to ~ 100 K above the glass transition and water contents of 0–3.76 wt.% with a root-mean square deviation of only 3.23 J/mol K.

Three silicate glasses were hydrated at high pressure and then heated at atmospheric pressure to exsolve the water into bubbles and create foams. The bubble size distribution in these foams was measured by x-ray microtomography on the GSECARS BM-13 beamline at the Advanced Photon Source. The bubble area distributions were measured in two dimensions using the image slices produced from the microtomography and the software ImageJ. The bubble volume distributions were measured from the three-dimensional tomographic images with the BLOB3D software. We found that careful analysis of the microtomography data in both two and three dimensions was necessary to avoid the physically unrealistic, experimental artifact of identifying and counting many small bubbles whose surfaces were not defined by a septum of glass. When this artifact was avoided the foams demonstrated power-law distributions of bubble sizes in both two and three dimensions. Conversion of the power-law exponents for bubble areas measured in two dimensions to exponents for bubble volumes usually agreed with the measured three dimensional volume exponents. Furthermore, the power-law distributions for bubble volumes typically agree with multiple theories of bubble growth, all of which yield an exponent of 1 for the cumulative bubble volume distribution. The measured bubble volume distributions with exponents near 0.3 can be explained by diffusive growth as proposed by other authors, but distributions with exponents near 1.4 remain to be explained and are the subject of continuing research on the effects of water concentration and melt viscosity on foaming behavior.

The effect of endurance swim training (3 hours per day, 5 days/week, for 10 weeks) on hepatic glucose production (HGP) in liver perfused in situ for 60 minutes with glucagon and insulin was studied in Sprague-Dawley rats. The experiments were performed in fed rats and in rats fasted for 24 hours, but with lactate (8 mmol/L) added to the perfusion medium. Liver glycogen content was significantly lower in fasted than fed rats (fasted untrained and trained: 14 +/- 4 and 11 +/- 3 micromol glycosyl U/g of liver wet weight (WW); fed untrained and trained: 205 +/- 11 and 231 +/- 11 micromol glycosyl U/g of liver WW; not significantly different in trained and untrained rats). Glucagon increased HGP in the 4 experimental groups, but the increases were more rapid and pronounced in trained than in untrained rats in both fed and fasted states. HGP values (area under the curve [AUC] in micromol/g of liver WW) were significantly higher in trained fed (112.1 +/- 7.1 v 85.9 +/- 12.2 in untrained rats) than in trained fasted rats (50.8 +/- 4.4 v 34.7 +/- 3.6 in untrained rats). When compared with untrained rats, the total amount of glucose released by the liver in response to glucagon in trained rats was approximately 30% higher in the fed state and approximately 45% larger in the fasted state. These results indicate that endurance training increases the response of both glycogenolysis and gluconeogenesis to glucagon.