ALBERT

Notes: Abstract Petrological and geochemical data on dredged samples from five submarine volcanos northwest of Samoa indicate that three of these volcanos belong to the Samoan volcanic province (Field, Lalla Rookh, and Combe banks), and two belong to separate magmatic zones (Wallis Islands and Alexa Bank). The Samoan volcanic province increases in age westward and both shield-building tholeiitic and alkalic lavas (Combe Bank) and strongly undersaturated (post-erosional?) melilitites or nephelinites and ankaramites (Field and Lalla Rookh banks) are present. The age progression and petrochemical character of these rocks is consistent with a fixed hotspot beneath eastern Samoa. Slightly askew from this trend is Alexa Bank where dredged lavas are ocean-island tholeiites; however, its radiometric age and compositional characteristics apparently preclude its association with Samoa by a fixed-hotspot model. Dredged volcanic rocks from near the Wallis Islands are geochemically, petrologically, and temporally different from Samoan volcanism, but are similar in these respects to Quaternary volcanism in Rotuma and Fiji and may be related to plate reorganization accompanying opening of the North Fiji Basin.

Notes: Abstract Clinopyroxene/melt and garnet/melt partition coefficients have been determined for Ti, Sr, Y, Zr, Nb, Hf, and rare earth elements from 19 doped experiments on 1921 Kilauea basalt. The experiments were carried out from 2.0 to 3.0 GPa and 1310° to 1470 °C. The purpose was to derive a set of partition coefficients for high-field-strength elements (HFSE) and rare earth elements (REE) in a systematic, linked set of experiments at P and T conditions relevant to basalt petrogenesis. These data are used in melting models to understand the development of negative HFSE anomalies observed in many abyssal peridotite clinopyroxenes. It is shown that melting can account for the observed trace element patterns in some residual peridotites, but that other processes may also be needed to account for most residual mantle compositions in mid-ocean ridge systems. It is also shown that REE are more strongly fractionated by garnet at these P-T conditions than previously thought.

Notes: Abstract The development of petrogenetic models of igneous processes in the mantle is dependent on a detailed knowledge of the diversity of magmas produced in the melting regime. These primary magmas, however, undergo significant mixing and fractionation during transport to the surface, destroying much of the evidence of their primary diversity. To circumvent this problem and to determine the diversity of melts produced in the mantle, we used melt inclusions hosted in primitive plagioclase phenocrysts from eight mid-ocean ridge basalts from the axial and West Valleys of the Endeavour Segment, Juan de Fuca Ridge. This area was selected for study because of the demonstrated close association of enriched (E-MORB) lavas and incompatible element enriched depleted (N-MORB) lavas. Rehomogenized melt inclusions from E-MORB, T-MORB, and N-MORB lavas have been analyzed by electron and ion microprobe for major and trace elements. The depleted and enriched lavas, as well as their melt inclusions, have very similar compatible element concentrations (major elements, Sr, Ni and Cr). Inclusion compositions are more primitive than, yet collinear with, the host lava suites. In contrast, the minor and trace element characteristics of melt inclusions from depleted and enriched lavas are different both in range and absolute concentration. N-MORB lavas contain both depleted and enriched melt inclusions, and therefore exhibit the largest compositional range (K2O: 0.01 to 0.4 oxide wt%, P2O5: 〈0.01 to 0.2 oxide wt%, LaN: 7 to 35, YbN: 1 to 13, and Ti/Zr: 〈100 to 1300). E-MORB lavas contain only enriched inclusions, and are therefore relatively homogeneous (K2O: 0.32 to 0.9 oxide wt %, P2O5: 0.02 to 0.35 oxide wt%, LaN: 11 to 60, YbN: 4 to 21, and Ti/Zr: ∼100). In addition, the most primitive E-32 inclusions are similar in composition to the most enriched inclusions from the depleted hosts. Major element data for melt inclusions from both N-MORB and E-MORB lavas suggest that the magmas lie on a low pressure cotectic, consistent with a petrogenesis including fractional crystallization. However, the minor and trace element compositions in melt inclusions vary independently of the major element composition implying an alternative history. When fractionation-corrected, inclusion compositions correlate with their host glass composition. Hence, the degree of enrichment of the lavas is a function of the composition of aggregated melts, not of processing in the upper mantle or lower crust. Based on this fact, the lava suites are not produced from a single parent magma, but from a suite of primary magmas. The chemistry of the melt inclusions from the enriched lavas is consistent with a derivation from variable percentages of partial melting within the spinel stability field by a process of open system (continuous or critical) melting assuming a depleted lherzolite source veined with clinopyroxenite. The low percentage melts are dominantly enriched melts of the clinopyroxenite. In contrast, the depleted lavas were created by melting of a harzburgite source, possibly fluxed with a fluid enriched in K, Ba and the LREE. Such a source was likely melted up to or past the point at which all of its clinopyroxene was consumed. This set of characteristics is consistent with a scenario by which diverse melts produced at different depths travel through the melting regime to the base of the crust without homogenizing en route. The homogeneous major element characteristics are created in the lower crust by fractional crystallization and reaction with lower crustal gabbros. Therefore, the degree of decoupling between major and trace element characteristics of the melt inclusions (and lavas) is dictated by the reaction rate of the melts with the materials in the conduit walls, as well as the residence times and flux rate, in the upper mantle and lower crust.

Notes: Abstract The dissolution rates of two lots of hydrocortisone (fine and coarse) were simulated using a computer program based on a Noyes–Whitney-type equation. Derivations of the equation were made to compare the accuracy of simulations using spherical and cylindrical particle geometry, with and without a time-dependent diffusion layer thickness. To approximate better the shape of the hydrocortisone particles, a shape factor was used to relate cylindrical length to radius. The most accurate simulations were obtained by assuming cylindrical geometry with and without a time-dependent diffusion layer thickness for the fine and coarse hydrocortisone, respectively. The program was also modified to simulate initial particle size distributions based on the log normal probability density function.

Notes: Abstract Purpose. To provide guidance in setting particle size specifications for poorly soluble drugs to minimize variability in absorption. Methods. A previously reported computer method was used to simulate the percent of dose absorbed as a function of solubility, absorption rate constant, dose, and particle size. Results. The simulated percent of dose absorbed was tabulated over a realistic range of solubilities, absorption rate constants, and doses using drug particle sizes that might be typically found in a dosage form. Conclusions. The greatest effect of particle size on absorption was simulated for low dose- low solubility drugs. In general, the sensitivity of absorption to particle size decreased with increasing dose or solubility. At a solubility of 1 mg/mL, particle size had practically no effect on the percent of dose absorbed over the range of doses simulated (1–250 mg).

Notes: Abstract The dynamics of electrostatic potential barriers at grain boundaries (GBs) in Nb-doped SrTiO3 bicrystals is investigated using a unique combination of bulk and in-situ TEM electrical measurements across isolated GBs, coupled with electron holography under in-situ applied bias. The Nb bulk-doped bicrystals exhibit a positive GB potential that suppresses reversibly under applied bias greater than the nonlinearity threshold in the current-voltage curve. This suppression is interpreted as break-down of the potential barrier to current transport. The results on Nb bulk-doped bicrystals have been compared to those in which Mn has been added as a grain boundary specific dopant. This acceptor doping of the grain boundary causes an appreciable increase in the grain boundary resistance and extension of the nonlinear regime. A preliminary account of static electron holography shows a relatively flat potential profile across the GB, indicating probable compensation of donor states at the GB core with Mn-acceptors. Interestingly, the phase profile under applied bias in this case exhibits a reversible “dip” at the GB which is interpreted as an activation of GB trap states due to Mn-acceptor dopants trapping extra electrons (the majority charge carriers) at the GB core, inducing a negative GB potential, and diminishing current transport until the threshold bias is exceeded. The synergistic combination of nanoscale TEM measurements coupled with traditional macroscopic electrical measurements is emphasized.