Dipping low-velocity layer in the mid-lower mantle: evidence for geochemical heterogeneity

Data from western United States short-period seismic networks reveal a conversion from an S to a P wave within a low seismic velocity layer (greater than or equal to the 4 percent velocity difference compared to the surrounding mantle) in the mid-lower mantle (1400 to 1600 kilometers deep) east of the Mariana and Izu-Bonin subduction zones. The low-velocity layer (about 8 kilometers thick) dips 30 degrees to 40 degrees southward and is at least 500 kilometers by 300 kilometers. Its steep dip, large velocity contrast, and sharpness imply a chemical rather than a thermal origin. Ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low-velocity layer because of its broad thin extent.

Mechanism of Phreatic Eruptions at Aso Volcano Inferred from Near-Field Broadband Seismic Observations

Broadband seismometers deployed at Aso volcano in Japan have detected a hydrothermal reservoir 1 to 1.5 kilometers beneath the crater that is continually resonating with periods as long as 15 seconds. When phreatic eruptions are observed, broadband seismograms elucidate a dynamic interplay between the reservoir and discharging flow along the conduit: gradual pressurization and long-period (approximately20 seconds) pulsations of the reservoir during the 100 to 200 seconds before the initiation of the discharge, followed by gradual deflation of the reservoir concurrent with the discharging flow. The hydrothermal reservoir, where water and heat from the deeper magma chamber probably interact, appears to help control the surface activity at Aso volcano.

Viability of intraperitoneal free cancer cells in patients with gastric cancer.

The viability and morphologic changes of intraperitoneal free cancer cells in advanced gastric cancer patients were examined by Giemsa and enzymologic staining and by tritiated thymidine uptake. Although many free cancer cells in the pouch of Douglas showed moderate degeneration, viable, morphologically intact cells were noted, leading to the possibility of their implantation and proliferation in the peritoneum. Serosal cancer cells showed a high degree of viability. In patients undergoing gastric cancer surgery, the viability of free cancer cells was markedly decreased by a single intraoperative administration of 10 mg of mitomycin C (MMC) to the pouch of Douglas, suggesting that this may represent an effective means of preventing peritoneal dissemination.

Morphogenesis of peritoneal metastasis in human gastric cancer.

A comparative light microscopic and scanning electron microscopic study of the morphogenesis of peritoneal metastasis in 34 human gastric cancers was performed. Prior to adhesion of gastric cancer cells to the peritoneum, the mesothelial cells became hemispherical and exfoliated from the peritoneum, and gastric cancer cells adhered to the naked areas of the submesothelial connective tissue. A flat metastatic tumor was formed by cancer cell proliferation in the shallow region of the peritoneum. Subsequently, after the infiltration of cancer cells into the connective and adipose tissue, the formation of a large tumor mass was observed. There was a correlation between the surface and histological structure of the metastatic tumors. In poorly differentiated cancer, the cells were isolated while in differentiated cancer, they formed nodules with indistinguishable cell boundaries.

A scanning electron microscopic study on the peritoneal implantation of ascites hepatoma AH100B cells in rats.

The process and mechanism of peritoneal metastasis of tumor cells were studied experimentally by means of scanning or transmission electron microscopy, employing rat ascites hepatoma AH100B. Adhesion of tumor cells by microvilli and/or pseudopodia to the mesothelium was observed within 1 approximately 3 days after inoculation when there was no morphological changes of the mesothelial cells. Some changes of the mesothelial cells, such as irregularity, atrophy, and exfoliation, followed tumor cell adhesion 5 or 6 days after inoculation. It was noted that tumor cells adhered to the mesothelium first where no morphological changes were induced, and it is suggested that tumor cells infiltrate into the submesothelial tissue through mesothelial defects.

Intraperitoneal free cancer cells and their viability in gastric cancer.

Free cancer cells in the peritoneal cavity of 100 patients with gastric cancer were examined by means of Douglas lavage, and their viability was estimated by 3H-thymidine uptake with autoradiographical technic. Furthermore, the effect of mitomycin-C on the viability of free cancer cells in the peritoneal cavity was studied. The appearance of intraperitoneal free cancer cells was dependent on the degree of invasion of cancer to the gastric serosa; that is, free cancer cells were not found in cases without serosal invasion, but were found in 48% with serosal invasion. The viability of free cancer cells in the peritoneal cavity was relatively high, but could be suppressed remarkably by intraperitoneal administration of 10 mg of mitomycin-C.