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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 20 (1979), S. 597-628 
    ISSN: 1572-9613
    Keywords: Stochastic models ; Markov processes ; master equation ; energy transfer ; exact solutions ; internal degrees of freedom ; Erdelyi expansions ; fractional operators
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe a new family of Markov processes, a prototype for which is in the statistics of a test molecule undergoing “random” energy transfer in collisional complexes with heat-bath particles. Master equations for several versions of this process are constructed and solved exactly under purely statistical prescriptions of the mechanism and degrees of freedom available. Their eigenfunctions, arising through a natural factorization of the transition kernels, prove to be classical polynomials of Laguerre and Jacobi type; the relaxation times are given by simple terminating series in the degree-of-freedom parameters. Moreover, the spectral representations of such kernels prove to be Erdelyi-type bilinear expansion in the respective eigenfunctions, giving these little-known formulas a previously unsuspected physical interpretation. A remarkable property of the solutions is that they are both exact and parametrized over the whole range of behavior from effective “Brownian motion” at one extreme to virtually purely random processes at the other. Autocorrelation functions for equilibrium fluctuations in the same ensembles are also obtained and shown to be strictly exponential. Applications of such “distributive processes” are discussed with reference to both the physics of energy transfer and possible alternative realizations, e.g., in operations research. Some related mathematical topics, notably the role of fractional integral-operators in the master equation, are pointed out.
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  • 2
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New, high-resolution 1.66 GHz MERLIN maps of Cep A2 and LkHα101 are presented and discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Company
    Nature biotechnology 4 (1986), S. 553-557 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] The size distribution and density of two types of protein inclusion bodies arising from the synthesis in E. coli of recombinant calf prochymosin and γ–interferon were examined. A combination of electrical sensing zone and centrifugal sedimentation techniques were used to characterize ...
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  • 4
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
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  • 5
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Isoelectric soya-protein precipitate densities were measured for mean particle sizes ranging from 3.4-65 μm by gradient centrifugation, centrifugation in water-immiscible solvents, tracerdilution, gravity sedimentation of isolated particles. Coulter counter volume determination, and a comparison of Coulter counter and centrifugal sedimentation size distributions. The immiscible system and tracer dilution methods were both found to be unreliable due to experimental uncertainties. The Coulter counter volume measurement indicated the existence of a density-size relationship with the aggregate density decreasing as the size increased. Comparison with sedimentation measurements showed that the Coulter counter measures 80% of the total aggregate volume for 6-μm particles. The relation between aggregate density (ρa, kg m -3) and size (d, μm) was measured for isoelectric soya protein and casein precipitated by ammonium sulfate, using a comparison of the Coulter counter size distribution and centrifugal sedimentation. The functions were described for soya by \documentclass{article}\pagestyle{empty}\begin{document}$$ \rho _a - 1004 = 246d^{ - 0.408} $$\end{document} and for casein by \documentclass{article}\pagestyle{empty}\begin{document}$$ \rho _a - 1136 = 31d^{ - 0.441} $$\end{document} The gradient centrifugation method measured the buoyant density of hydrated protein precipitate which was independent of size, and is consistent with an aggregate structure consisting of primary particles. However, the aggregate structure was not described for all sizes by the theoretical cubic packing of hard-sphere primary particles, nor by the successive random addition of primary particles. The density-size functions indicated up to a fivefold difference in Stokes settling velocities compared to those calculated assuming a constant density difference.
    Additional Material: 4 Ill.
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  • 6
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The acid precipitation of soya protein was studied in a continuous-flow tubular reactor under conditions of turbulent flow. Preliminary batchwise experiments of a semiquantitative nature were also carried out on a bench-scale reactor to better define the parameters affecting precipitate growth. The experiments indicated the dominant growth mechanism to be the aggregation of primary precipitate particles produced by the contacting of the protein and acid streams. The rate of particle growth was observed to rise with an increase in the protein concentration as well as with greater intensity of turbulence. The final mean particle size decreased with increased intensity of turbulence. A theoretical model was set up to simulate the growth of the precipitate particles.
    Additional Material: 14 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 36 (1990), S. 354-366 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A biochemical engineering framework for optimizing the design and operation of fractional protein precipitation has been developed. The method utilizes a fractionation diagram to represent the purification of a product protein relative to total contaminating protein. The purification factor for a single or double-cut fractional precipitation is obtained as the gradient of an appropriate operating tie-line. A computer algorithm has been devised to maximize the tie-line gradient for a given yield enabling a plot of optimum purification factor versus yield to be constructed. The recovery of the enzyme alcohol dehydrogenase from clarified bakers homogenate using saturated ammonium sulphate has been examined. Fractionation and purification versus yield diagrams were used to investigate the effects of such process parameters as pH, temperature, and initial total protein concentration on fractionation efficiency. The results are discussed in terms of the underlying solubility and mixing phenomena and the industrial application of fractional precipitation.
    Additional Material: 10 Ill.
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  • 8
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The use of a scroll decanter centrifuge for the removal and dewatering of affinity-flocculated yeast cell debris from a crude homogenate is described. Laboratory shear modulus measurements were used to compare the structure of flocculated and nonflocculated sediments and to indicate the dewatering conditions under which the sediment could be discharged from the centrifuge. The structure of the flocculated sediment was such that a dry beach could be used within the centrifuge while still being able to discharge the solids. The scroll decanter performance for recovery and dewatering of the flocculated homogenate was found to be independent of feed flow rate and differential scroll rate. Eighty-five percent of the solid material was recovered from the flocculated homogenate while the extent of sediment dewatering resulted in the loss of only 7% of the soluble protein in the sediment. The supernatant clarity matched that achieved by low-gravity laboratory centrifugation studies.
    Additional Material: 6 Ill.
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  • 9
    ISSN: 0006-3592
    Keywords: protein ; recovery ; purification ; crystallization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Bulk crystallization is emerging as a new industrial operation for protein recovery. Characterization of bulk protein crystallization is more complex than protein crystallization for structural study where single crystals are grown in flow cells. This is because both nucleation and crystal growth processes are taking place while the supersaturation falls. An algorithm is presented to characterize crystallization using the rates of the two kinetic processes, nucleation and growth. The values of these rates allow ready comparison of the crystallization process under different operating conditions. The crystallization, via adjustment to the isoelectric pH of a fungal lipase from clarified fermentation broth, is described for a batch stirred reactor. A maximum nucleation rate of five to six crystals formed per microliter of suspension per second and a high power dependency (≈11) on the degree of supersaturation were found. The suspended protein crystals were found to grow at a rate of up to 15-20 nm/s and also to exhibit a high power dependency (≈6) of growth rate on the degree of supersaturation. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 666-675, 1998
    Additional Material: 11 Ill.
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  • 10
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Laboratory and pilot-plant high-speed bead mills of 0.6 and 5 liter capacity and consisting of four and five impellers in series, respectively, were used to follow the batch and continuous disruption of bakers' yeast (Saccharomyces cerevisiae). The mills are not scaled equivalents. Throughputs ranging from 1 × 10-6m3/sec to 12 × 10-6m3/sec for the 0.6 liter mill and from 16 × 10-6m3/sec to 100 × 10-6m3/sec for the 5 liter mill were used for continuous disruption studies. Variables studied included the effect of impeller tip speed, temperature, and packed yeast concentration (ranging from 15 to75% by weight packed yeast). Disruption kinetics, as measured by the release of soluble protein, followed a first-order rate equation, the rate constant being a function of impeller tip speed and yeast concentration. For continuous disruption studies the bead mills behaved as a series of continuous stirred-tank reactors, each impeller forming a reactor. In the smaller mill a considerable degree of backflow between the reactors was evident. For certain mixing conditions the maximum amount of releasable protein was dependent on the impeller geometry, construction material, and also the concentration of packed yeast. The relative power efficiencies of the two mills are discussed along with possible criteria for scaling of bead mills.
    Additional Material: 18 Ill.
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