Nondestructive three-dimensional mapping of grain shape, crystallographic orientation, and grain boundary geometry by diffraction contrast tomography (DCT) provides opportunities for the study of the interaction between intergranular stress corrosion cracking and microstructure. A stress corrosion crack was grown through a volume of sensitized austenitic stainless steel mapped with DCT and observed in situ by synchrotron tomography. Several sensitization-resistant crack-bridging boundaries were identified, and although they have special geometric properties, they are not the twin variant boundaries usually maximized during grain boundary engineering.

Mn is an effective promoter for improving the activity and selectivity of Co-based Fischer-Tropsch synthesis (FTS) catalysts, but the mechanism by which this promoter functions is poorly understood. The work reported here was aimed at defining the manner in which Mn interacts with Co and how these interactions affect the activity and selectivity of Co. Detailed measurements are reported for the kinetics of FTS as a function of Mn/Co ratio, temperature, and reactant partial pressures. These data are described by a single, two-parameter rate expression. Mn-promotion was found to increase both the apparent rate constant for CO consumption and the CO adsorption constant. Further evidence for enhanced CO adsorption and dissociation was obtained from measurements of temperature-programmed desorption of CO and CO disproportionation rates, respectively. Quantitative analysis of elemental maps obtained by STEM-EDS revealed that the promoter accumulates preferentially on the surface of Co nanoparticles at low Mn loadings, resulting in a rapid onset of improvements in the product selectivity as the Mn loading increases. For catalysts prepared with loadings higher than Mn/Co = 0.1, the additional Mn accumulates in the form of nanometer-scale particles of MnO on the support. In situ IR spectra of adsorbed CO show that Mn promotion increases the abundance of adsorbed CO with weakened C-O bonds. It is proposed that the cleavage of the C-O bond is promoted through Lewis acid-base interactions between the Mn 2+ cations located at the edges of MnO islands covering the Co nanoparticles and the O atom of CO adsorbates adjacent to the MnO islands. The observed decrease in selectivity to CH4 and the increased selectivity to C5+ products with increasing Mn/Co ratio are attributed to a decrease in the ratio of adsorbed H to CO on the surface of the supported Co nanoparticles.

The fluorescent vital dye rhodamine 123 (Rh-123), which preferentially accumulates in mitochondrial membranes, can be used as a probe to indicate mitochondrial and hence cellular activity. In this study, mouse bone marrow hematopoietic stem cells were subdivided into Rh-123"', Rh123uued, and Rh-123hi populations. The Rh-1231 (resting) population was significantly enriched in cells with a higher proliferative potential compared to the Rh-123hI (activated) population. The resting population exhibited a 20-fold greater ability to differentiate into splenic colony-forming units (CFU-S) relative to the activated population, whereas the activated population contained about 4-fold more day 13 CFU-S on primary transfer relative to the resting population. The two populations produced morphologically distinct splenic colonies; however, the frequency and morphology of in vitro colonies were very similar. Only the resting population provided sufficient stem cells to transfer long-term hematopoietic repopulation to secondary recipient animals after lethal irradiation. On a single cell level, the resting and activated populations exhibited an equivalent ability to differentiate into lymphoid and myeloid progeny. These observations provide further insight into the heterogeneous nature of CFU-S and directly demonstrate that multipotent hematopoietic stem cells are heterogeneous with regard to their clonogenic capacities.

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In vitro infection of murine fetal liver cells with a retrovirus containing v-raf and v-myc oncogenes has produced continuous lines of immature erythroid cells that are leukemogenic. These cells synthesized a factor that stimulated their growth in vitro before autonomous variants emerged.Approximately 1000 high-affinity erythropoietin receptors could be detected per cell, and the hormone induced terminal differentiation in these cells. The lines were generated at an extremely low frequency (w1 in 107 cells), suggesting that the combination of rafand myc is insufficient to develop erythroid cell lines and that additional events are necessary for transformation.All murine erythroleukemia (MEL) Retroviruses harboring ras, src, and rafoncogenes can also stimulate erythroproliferation in vivo and in vitro (6-9). Infection of progenitor cells in vitro with the 3611 murine sarcoma (3611-MSV) virus, which has transduced the v-raf oncogene, results in the formation of erythroid colonies that hemoglobinize completely when exposed to erythropoietin (Epo) in vitro (9). In contrast, infection with the v-raf/v-myccontaining J2 virus produces poorly hemoglobinized colonies, which are approximately five times larger than v-raf colonies (9). The addition of v-myc to v-raf, therefore, results in enhanced proliferation of immature erythroid cells with a concomitant decrease in Epo-induced differentiation.As the J2 virus promotes proliferation of erythroid cells with reduced capacity to differentiate, we reasoned it might be possible to produce erythroid cell lines in vitro with this virus. To this end, fetal liver cells were infected with the J2 virus; then either plated in methylcellulose or maintained in liquid culture. We report here that erythroid cell lines can be generated in vitro. These cell lines develop at very low frequency and exhibit high-affinity Epo receptors, which are internalized and synthesize hemoglobin upon Epo stimulation. For up to 1 yr the cells produced a factor able to stimulate their own growth; then autonomous variants emerged that dominated the cultures.

SummaryMurine bone marrow Lin-, Ly6A/E + cells have been fractionated on the basis of rhodamine123 retention into Rh123 m~d/hi and Rh123 l~ subpopulations. These populations have different responses to hemopoietic growth factors with respect to in vitro colony formation. Cells from either fraction were not stimulated by only granulocyte-colony-stimulating factor (G-CSF), granulocyte/macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), interleukins 1 and 6 (IL-1 and -6), or leukemia inhibitory factor (LIF) alone. The Rh123 m~a/hi, but not the Rh1231~ fraction, contained calls that could be stimulated by either stem cell factor (SCF) or IL-3 alone. When combinations of growth factors were added, the Rh123 m~d/hi fraction produced more colonies, and responded to a wider range of factor combinations than the Rh123 l~ population. When tested in vivo, both populations contained no detectable day 8 colony-forming unit-spleen (CFU-S), and similar frequencies of day 13 CFU-S. When transplanted into lethally irradiated recipients (100 cells/recipient), significant numbers of donor ceils (67-73%) were found in the peripheral blood of Rh123 l~ recipients. Both myeloid and lymphoid cells were of donor origin. By comparison, the Rh123 reed/hi population produced recipients with 1-2% donor cells in peripheral blood, the majority of which were lymphoid.

Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO.

Cells from CBA fetal mouse liver formed pure or mixed erythroid colonies in semisolid agar culture after stimulation by medium conditioned by pokeweed mitogenstimulated mouse spleen cells. In general shape, the erythroid colonies resembled typical 7-day single or multiple (burst) colonies. However one-third to one-hal containe, in addition to erythroid cells, macrophages and neutrophils and, less commonly, megakaryocytes or eosinophils. Culture of micromanipulated single colony-forming cells showed these erythroid colonies to be clones. Colony-forming cells declined in frequency with advancing fetal age, but low numbers were detectable in adult bone marrow. Assays of spleen conditioned medium in polycythemic mice failed to detect erythropoietin; the cloning system may detect a fetal type of erythropoietinindependent, erythropoietic cell since few were detected in adult marrow.