Kinetics of cell proliferation and polyamine synthesis during Ehrlich ascites tumor growth

The kinetics of cell proliferation and polyamine synthesis during Ehrlich ascites tumor growth were studied. The steady deceleration of the specific growth rate with increasing tumor mass that was observed was attributable to a prolongation of the cell cycle, particularly of the S and G2 phases. The cell cycle time (Tc) was 43.3 hr (TG1 equals 10.8, TS equals 26.8, and TG2 equals 5.7 hr) on the seventh day of growth and 76.0 hr (TG1 equals 14.0, TS equals 52.0, and TG2 equals 10.0 hr) on the tenth day of growth. The growth fraction showed a decrease from 0.77 to 0.60 during the 7- to 10-day tumor growth interval. The cell death rate remained low and essentially unchanged during this period. A high correlation was found between polyamine synthesis (ornithine decarboxylase activity) and the specific growth rate; the correlation coefficient was 0.985. There was also a high positive correlation between the cellular polyamine (spermidine and spermine) and nucleic acid content (spermidine: DNA equals 0.916, spermine: DNA equals 0.947, spermidine:RNA equals 0.907, and spermine: RNA equals 0.881). These observations suggest that there may be a functional coupling between polyamines and nucleic acids, and they support the hypothesis that polyamines play an important role in DNA replication and cell division.     

EVALUATION OF A METHOD FOR MEASURING MIXING TIME USING NUMERICAL SIMULATION AND EXPERIMENTAL DATA

A method for measuring mixing performance in large-scale vessels is investigated. The method is evaluated experimentally in a pilotscale reactor and by using a model based on the three-dimensional calculation of the flow field. The method is based on injection of a tracer and measuring the concentration with several detectors at different locations. The mixing performance is measured as the decay rate of the difference between the concentration at the detectors and the final concentration.

The model predicts a strong dependence on injection point. The assumption of a first-order decay rate of the concentration deviation is more appropriate for some injection points.     

Optimal Power Flow of Multiple Energy Carriers

This paper presents an approach for combined optimization of coupled power flows of different energy infrastructures such as electricity, gas, and district heating systems. A steady state power flow model is presented that includes conversion and transmission of an arbitrary number of energy carriers. The couplings between the different infrastructures are explicitly taken into account based on the new concept of energy hubs. With this model, combined economic dispatch and optimal power flow problems are stated covering transmission and conversion of energy. A general optimality condition for optimal dispatch of multiple energy carriers is derived, and the approach is compared with the standard method used for electrical power systems. Finally, the developed tools are demonstrated in examples     

The beta-gal interferon assay: a new, precise and sensitive method

Cells of a human glioblastoma line were stably transfected with a glial fibrillary acidic protein (GFAP) promoter sequence/lacZ reporter gene. Following this modification, they produced Escherichia coli beta-galactosidase constitutively in amounts that could be measured through their conversion of an added fluorophore into a product readily estimated by fluorimetry. Human interferons (IFN) selectively and in a dose-dependent manner reduce the formation of beta-galactosidase in this system. We have used it as the basis for a novel assay that is sensitive (4-40 pg/ml), precise, completed in 30 h, and applicable to both type I and type II human IFNs. Statistical analysis showed interassay relative standard deviations ranging from 5% to 11%, and most individual assays revealed potencies with limits of error within 85%-115%. Neither partially trypsin-digested IFN nor the other cytokines and mitogens we tested reacted in this system, except for tumor necrosis factor-alpha (TNF-alpha). The high selectivity was further shown by the loss of response to IFN in the presence of the appropriate specific anti-IFN or anti-IFN-gamma receptor antibodies.