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  • 1
    Electronic Resource
    Electronic Resource
    Modifications of weak localization contributions to magnetoresistance due to magnetic impurities in amorphous DyxY1−xNi alloys (invited) : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5813-5818 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-field magnetoresistance experiments performed on thick amorphous alloys offer a simple way to study three-dimensional (3D) weak localization of conduction electrons. After the precursor work of Fert et al. on nonmagnetic amorphous alloys, we found it interesting to study how these effects would disappear under substitutions of magnetic impurities (1% to 10% of Dy) in a nonmagnetic amorphous alloy (YNi). The experiments, performed between 1.5 to 50 K and in magnetic fields up to 20 T, showed (i) in YNi, characteristic features of the magnetoresistance due to weak localization under strong spin-orbit scattering and (ii) in DyxY1−xNi, a coexistence of weak localization effects with the classical contribution of spin alignment by the applied magnetic field, saturating at negative values. This last contribution dominates the behavior of Dy-richer samples whereas weak localization is clearly observed for x≤3%. In all the samples a dramatic increase of the initial magnetoresistance slope Δρ/ρH2 (where ρ=resistivity and H=applied field) is observed when magnetic impurity concentrations increase. We explain this increase of weak localization effects, in the framework of the available weak localization theory, by an enhancement of the Zeeman spin splitting due to interactions between localized (4f ) and delocalized (d, s) electronic states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350120
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  • 2
    Electronic Resource
    Electronic Resource
    Electrical resistivity and local magnetic order in random anisotropy amorphous ferromagnets : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6513-6515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In ferromagnetic systems with random anisotropy (RA), long-range magnetic order is destroyed and the correlation function of the magnetization exhibits an exponential form e−r/Rf, where the correlation length Rf corresponds to the size of Imry–Ma domains. Also, the law of approach to magnetic saturation follows a 1/(square root of)H law [ferromagnet with wandering axis (FWA) regime]. We have calculated the effect of magnetic correlations on the electrical resistivity and magnetoresistance of a RA ferromagnetic system at low temperatures. We find that in zero magnetic field RA introduces a positive contribution into the electrical resistivity, which increases with the anisotropy to exchange ratio, D/T. In the FWA regime the magnetoresistance has a logarithmic dependence on the magnetic field with a slope Δρ/(ρ ln H) inversely proportional to Rf. These features have been observed in an experimental study of the magnetoresistance at low temperatures (T≈4 K) of the amorphous series (DyxGd1−x)Ni in which the D/T ratio can be varied from near zero up to one from GdNi to DyNi. A quantitative analysis of the results enables the direct determination of the correlation length Rf and of the volume of structural correlations Ωc. We find that Rf varies from about 12 A(ring) in DyNi up to 300 A(ring) in (Dy0.1Gd0.9)Ni and Ωc is the same throughout the series (Ωc≈500 A(ring)3) in excellent agreement with the values determined from magnetic measurements on the approach to saturation. These results provide an independent confirmation of the exponential decay with distance and field dependence of magnetic correlations in random anisotropy systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356932
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  • 3
    Electronic Resource
    Electronic Resource
    Transport properties in amorphous Ux-T1−x films (T=Fe, Ni, Gd, Tb, and Yb) (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5453-5458 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe the competing magnetic, localization, and phonon effects on the transport properties of amorphous magnetic UxT1−x films, with T=Fe, Ni, Gd, Tb, and Yb. Amorphous UxFe1−x films change from collinear to random ferromagnetism as x increases, and the temperature dependence of the resistivity denotes the competing effects of spin-flip and non-spin-flip exchange scattering processes. The resistivity has a minimum at Tf rising sharply below this temperature. The sign of the magnetic resistivity and the magnetoresistance indicates 〈Si ⋅Sj 〉〉0, while the anisotropic magnetoresistance indicates a local exchange gap. Amorphous UxGd1−x and a-UxTb1−x are, respectively, spin glasses and random anisotropy dominated systems. The resistivity increases smoothly through Tf and has a slight upturn at low temperatures that we associate with weak localization. The magnetoresistance is negative in both systems and the anisotropic magnetoresistance is null, although the applied field induces anisotropic behavior in the Tb containing films (asperomagnets). All samples show quadratic and positive field dependence of magnetoresistance well inside the paramagnetic regime, and a linear regime below Tf. At low temperatures and in the a-UxGd1−x films, negative (H)1/2 and H2 regimes occur and are associated with weak localization processes dominated by the inelastic mean free path.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342346
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  • 4
    Electronic Resource
    Electronic Resource
    Studies of Baby Hamster Kidney Natural Cell Aggregation in Suspended Batch Cultures (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 745 (1994), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1994.tb44368.x
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  • 5
    Electronic Resource
    Electronic Resource
    High cell density reactor for the production ofLactobacillus plantarum (1991)
    Springer
    Journal of industrial microbiology and biotechnology 7 (1991), S. 63-69 
    Details
    ISSN: 1476-5535
    Keywords: Flocculation ; Fluidized bed reactor ; Lactobacillus plantarum ; Lactic starter culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The production of a flocculent strain ofLactobacillus plantarum was performed in a high cell density reactor: a fluidized bed reactor (FBR) with a settler and an external cell recirculation. Two variables were assessed, the recirculation rate (R) and the dilution rate (D). The effect of the latter is much more important than the effect of the former in ensuring a quick start up in the flocculation process. The cell volumetric productivities obtained with this system increase directly with dilution rate and recirculation rate. The values of cell volumetric productivities obtained are considerably higher than those obtained in continuous stirred tank reactors (CSTR) and much higher than in batch reactors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01575605
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  • 6
    Electronic Resource
    Electronic Resource
    Expression of recombinant antibody and secreted alkaline phosphatase in mammalian cells. Influence of cell line and culture system upon production kinetics (1994)
    Springer
    Applied microbiology and biotechnology 40 (1994), S. 851-856 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract. The growth and productivity of an Sp2/0 cell line, F3b10, expressing a recombinant antibody (rAb) and BHK21 cells expressing either the same rAb from the same plasmids (BHK.IgG) or secreted alkaline phosphatase (SEAP) (BHK.SEAP) were investigated. The F3b10 line was grown as a single cell suspension. The BHK lines were grown either as suspended natural aggregates or on Cytodex 3 microcarriers. The data for F3b10 showed that the cell-specific rAb production rate (QsrAb) increased in parallel with increases in the specific growth rate (μ). A similar result was obtained for suspended aggregate cultures of both recombinant BHK cell lines. In contrast, for microcarrier cultures of both BHK cell lines, Qsproduct increased as μ decreased. This report shows that the relationship between cell growth and Qsproduct for the cell lines and products studied is dependent upon the culture process. In systems where recombinant cells are growing as a single cell suspension or within a natural suspension aggregrate, Qsproduct increased with increases in μ. In such systems, the cells have a rounded morphology. When cells were grown on microcarriers, Qsproduct decreased as μ increased. Cells growing attached to a surface are flat and elongated. The observed differences in the relationship of Qsproduct to μ are correlated with changes in cell morphology. The relationship between Qsproduct and μ is also affected by the choice of cell line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530050079
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  • 7
    Electronic Resource
    Electronic Resource
    Changes in animal cell natural aggregates in suspended batch cultures (1994)
    Springer
    Applied microbiology and biotechnology 41 (1994), S. 203-209 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Some anchorage-dependent animal cells can form natural aggregates in stirred tanks. Baby hamster kidney (BHK) natural aggregates are described and characterized. Total cell concentration and viability could be obtained after aggregate mechanical dissociation, with negligible cell lysis and no change in cell membrane permeability. During a normal batch run, aggregates were formed immediately after inoculation, a few spherical aggregates increasing in size during the initial growth phase. At the end of the growth phase, an increase in aggregate concentration was observed, without a considerable increase in aggregate diameter. At the end of the batch run, 160 h after inoculation, aggregates disintegrated into smaller, non-spherical units, following a sharp viability decrease. Cell concentrations of 1.2⋅106 cells/ml were obtained, with 60% of the total cells being in aggregates; the cell concentration in aggregates achieved 5⋅108 cells/ml, with a porosity of 55%. Viability was consistently in the range 85–90%, both for aggregate and suspended cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530050131
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  • 8
    Electronic Resource
    Electronic Resource
    Changes in animal cell natural aggregates in suspended batch cultures (1994)
    Springer
    Applied microbiology and biotechnology 41 (1994), S. 203-209 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Some anchorage-dependent animal cells can form natural aggregates in stirred tanks. Baby hamster kidney (BHK) natural aggregates are described and characterized. Total cell concentration and viability could be obtained after aggregate mechanical aissociation, with negligible cell lysis and no change in cell membrane permeability. During a normal batch run, aggregates were formed immediately after inoculation, a few spherical aggregates increasing size during the initial growth phase. At the end of the growth phase, an increase in aggregate concentration was observed, without a considerable increase in aggregate diameter. At the end of the batch run, 160 h after inoculation, aggregates disintegrated into smaller, non-spherical units, following a sharp viability decrease. Cell concentrations of 1. 2 · 106 cells/ml were obtained, with 60% of the total cells being in aggregates; the cell concentration in aggregates achieved 5 · 108 cells/ml, with a porosity of 55%. Viability was consistently in the range 85–90%, both for aggregate and suspended cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00186960
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  • 9
    Electronic Resource
    Electronic Resource
    Cell-dislodging methods under serum-free conditions (1997)
    Springer
    Applied microbiology and biotechnology 47 (1997), S. 482-488 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In this work, a BHK21 clone producing a fusion protein consisting of a recombinant human IgG molecule with a cytokine tail, growing in a protein-free medium, was used to test several alternatives to avoid the use of serum for trypsin inactivation, currently used in cell dislodging. These included (1) trypsin inactivated with soybean trypsin inhibitor (STI); (2) cell dissociation solution instead of trypsin; (3) dispase instead of trypsin; (4) trypsin inactivated with fetal calf serum (positive control); (5) non-inactivated trypsin (negative control). Use of a centrifugation step was also tested for each alternative. Results indicate that the best method regarding cell growth, viability and adherent fraction is to use trypsin inactivated with STI followed by a centrifugation step. For all methods tested, the utilization of a centrifugation step always led to improved results. The optimal proportion for total trypsin inactivation is 1:1 trypsin (0.2% w/v) to STI (1 mg ml−1), equivalent to 2 mg trypsin to 1 mg STI. No toxic effect was observed for STI at the concentrations used. Long-term subculturing with this new, alternative dislodging method did not affect cell growth, viability and productivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530050960
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  • 10
    Electronic Resource
    Electronic Resource
    Metabolic responses to different glucose and glutamine levels in baby hamster kidney cell culture (1999)
    Springer
    Applied microbiology and biotechnology 51 (1999), S. 579-585 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In this work, a BHK21 clone producing a recombinant antibody/cytokine fusion protein was used to study the dependence of cell metabolism on the glucose and glutamine levels in the culture medium. Results obtained indicate that both glucose and glutamine consumptions show a Michaelis-Menten dependence on glucose and glutamine concentrations respectively. A similar dependence is also observed for lactate and ammonia productions. The estimated value of the Michaelis constant for the dependence of lactate production on glucose (K Glc Lac) was 1.4 ± 0.1 mM and for the dependence of ammonia production on glutamine (K Gln Amm) was 0.25 ± 0.11 mM and 0.10 ± 0.03 mM, at glucose concentrations of 0.28 mM and 5.6 mM respectively. At very low glucose concentrations, the glucose to lactate yield decreased markedly, showing a metabolic shift towards lower lactate production. This␣metabolic shift was also confirmed by the significant increase in the specific oxygen consumption rate also observed at low glucose concentrations. Although it was␣highly dependent on glucose concentration, the oxygen consumption also increased with the increase in␣glutamine concentration. At very low glutamine concentrations, the glutamine to ammonia yield increased, showing a more efficient glutamine metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530051435
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