Valley Splitting in Silicon from the Interference Pattern of Quantum Oscillations.

We determine the energy splitting of the conduction-band valleys in two-dimensional electrons confined in silicon metal oxide semiconductor Hall-bar transistors. These silicon metal oxide semiconductor Hall bars are made by advanced semiconductor manufacturing on 300 mm silicon wafers and support a two-dimensional electron gas of high quality with a maximum mobility of 17.6×10^{3} cm^{2}/Vs and minimum percolation density of 3.45×10^{10} cm^{-2}. Because of the low disorder, we observe beatings in the Shubnikov-de Haas oscillations that arise from the energy splitting of the two low-lying conduction band valleys. From the analysis of the oscillations beating patterns up to T=1.7 K, we estimate a maximum valley splitting of ΔE_{VS}=8.2 meV at a density of 6.8×10^{12} cm^{-2}. Furthermore, the valley splitting increases with density at a rate consistent with theoretical predictions for a near-ideal semiconductor-oxide interface.

Effects of retinoic acid on ascites cells of the TA3 mouse mammary carcinoma.

Retinoic acid caused a decrease in adhesiveness but no growth change in the allotransplantable TA3-Ha cell and no change in adhesiveness or growth in the strain specific TA3-St cell. The retinoic acid binding protein was detected in the TA3-Ha, but not the TA3-St, cell.

Physicochemical and morphological characterization of a new allotransplantable mammary carcinoma ascites subline, TA3-St/ticol/-A.

The TA3-St/ticol ascites cell (I), immunoselected from the strain-specific TA3-St mammary carcinoma ascites cell of the strain A mouse for decreased H-2a antibody-binding capacity, underwent a spontaneous transition in vivo to a new cell line, TA3-St/ticol/-A (II). Line II was more allotransplantable than was the parental line (line I), and its absorptive capacity for anti-H-2a antibody was manyfold less than line I. Disruption of line II cells by lyophilization did not increase the absorptive capacity, in contrast to its marked enhancement in the TA3-Ha ascites cell under similar conditions. An explanation for the enhanced allotransplantability of line II may be related to either a loss of H-2a antigens or altered macromolecular structures at the cell surface: sialic acid, consisting of 93% N-glycolylneuraminic acid for line II and 9% for line I; altered chemical structures of cell surface glycoproteins, particularly a high-molecular-weight glycoprotein present in much greater proportion in line II than in line I; a macromolecular complex released by a protease from line I, but not line II; and I being agglutinable by concanavalin A, but not line II. Electron microscopy showed line II to be more pleomorphic and less rounded than was line I. Under high-resolution electron microscopy, the cell surfaces of both allotransplantable cells, lines II and I, exhibited thin filamentous material, material not observed at the surface of the nonallotransplantable TA3-St ascites cell.

Cell surface characteristics of an allotransplantable TA3 ascites subline resulting from a process of immunoselection.

Comparison of the cell surface characteristics of the parental strain-specific TA3-St ascites cell (I) of the strain A mouse and the more allotransplantable TA3-St/ticol ascites cell (II), immunoselected for reduced absorption of anti-H-2a antibody from Cell I, revealed the following. Cell II, like Cell I, possessed no detectable epiglycanin at its surface, as neither cell absorbed more than 0.5% as much of the antiepiglycanin antibody as was absorbed by the epiglycanin-containing allotransplantable TA3-Ha ascites cell. Tritium-labeled glycoproteins, with polyacrylamide slab gel electrophoresis with sodium dodecyl sulfate and with isoelectric focusing of detergent-treated cells, exhibited marked quantitative differences, but qualitative differences were not established. Glycopeptides cleaved from each cell by proteolysis and fractionated by gel filtration gave similar elution profiles, and the column fractions possessed similar carbohydrate and amino acid compositions. Less sialic acid (170 micrograms/10(9) cells) was removed by neuraminidase from Cell II than from Cell I (270 micrograms/10(9) cells), and the compositions (9% N-glycolylneuraminic acid for Cell II and 20% for Cell I) were different. Transmission and scanning electron microscopy showed rough irregular folds and ridges on the surfaces of each cell, but Cell II appeared more pleomorphic and less rounded than did Cell I. High-resolution transmission electron microscopy showed filamentous material at the surface of Cell II, but not at the surface of Cell I.

Studies on the possible chemical, immunochemical and morphological differences at the cell surfaces of immunosensitive and immunoresistant, Moloney virus-induced, lymphoma cell-lines.

Comparison was made of several cell-surface parameters in the immunosensitive, Moloney virus-induced, mouse lymphoma, YAC, and its immunoresistant variant, YACIR. The characteristics of the two cell lines appeared to be similar by most of the criteria employed. The poly(acrylamide)-gel electrophoresis (with sodium dodecyl sulfate) patterns, after staining with Coomassie Brilliant Blue, of detergent-solubilized materials, appeared to be identical. After elution from a gel filtration column, no major differences were observed in the protein profiles of material cleaved from viable cells by proteolysis. Scanning and transmission electron microscopy revealed no major differences between the YAC and YACIR cells. The concentration of the lectins, Ricinus communis agglutinin, concanavalin A, wheat-germ agglutinin, and Solanum tuberosum (potato) agglutinin, required to agglutinate viable cells of the two lines were not significantly different. Neither cell was agglutinated by the lectins from Dolichos biflorus or Vicia graminea. Significant differences were, however, observed in the concentrations of lectin from Arachis hypogaea (peanut) needed to agglutinate the two cells. Although similar amounts (184-188 micrograms/10(9) cells) of sialic acid were released from viable cells by neuraminidase (V. cholerae), striking differences were observed in the composition of this material: 48% of N-glycolylneuraminic acid for YAC and 15% for YACIR. The remainder was N-acetylneuraminic acid for each cell line.