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Aggregation Step (aggregation + step)

Distribution by Scientific Domains

Life Sciences	66%

Selected Abstracts

Investigations of the Morphogenesis of Filamentous Microorganisms,

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2006
S. Kelly
Abstract Several biotechnological production processes are based on the cultivation of filamentous microorganisms like the fungus Aspergillus niger. The morphological development plays an important role for transport phenomena and the related productivity. The description of filamentous morphogenesis of A. niger as a model organism, given here, is structured in three morphological growth processes, a very fast conidial aggregation, followed by a second slower aggregation step promoted by germination and hyphal tip growth, and the growth of pellets as the last process. [source]

A Combined Cluster and Interaction Model: The Hierarchical Assignment Problem

GEOGRAPHICAL ANALYSIS, Issue 3 2005
Mark W. Horner
This article presents a new spatial modeling approach that deals with interactions between individual geographic entities. The developed model represents a generalization of the transportation problem and the classical assignment problem and is termed the hierarchical assignment problem (HAP). The HAP optimizes the spatial flow pattern between individual origin and destination locations, given that some grouping, or aggregation of individual origins and destinations is permitted to occur. The level of aggregation is user specified, and the aggregation step is endogenous to the model itself. This allows for the direct accounting of aggregation costs in pursuit of optimal problem solutions. The HAP is formulated and solved with several sample data sets using commercial optimization software. Trials illustrate how HAP solutions respond to changes in levels of aggregation, as well as reveal the diverse network designs and allocation schemes obtainable with the HAP. Connections between the HAP and the literature on the p-median problem, cluster analysis, and hub-and-spoke networks are discussed and suggestions for future research are made. [source]

Population balance modeling of the conidial aggregation of Aspergillus niger

BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2008
P.-J. Lin
Abstract Numerous biotechnological production processes are based on the submerse cultivation of filamentous fungi. Process design, however, is often hampered by the complex growth pattern of these organisms. In the morphologic development of coagulating filamentous fungi, like Aspergillus niger, conidial aggregation is the first step of filamentous morphogenesis. For a proper description of this phenomenon it is necessary to characterize conidial populations. Kinetic studies performed with an in-line particle size analyzer suggested that two distinct aggregation steps have to be considered. The first step of conidial aggregation starts immediately after inoculation. Both the rate constants of formation and disintegration of aggregates have been determined by measuring the concentration of conidia at the beginning of the cultivation and the concentration of particles at steady state during the first hours of cultivation. In contrast to the first aggregation step, where the collision of conidia is presumed to be responsible for the process, the second aggregation step is thought to be initiated by germination of conidia. Growing hyphae provide additional surface for the attachment of non- germinated conidia, which leads to a strong decrease in particle concentration. The specific hyphal length growth rate and the ratio of particle concentration to the growing adhesion hyphal surface are decisive matters of the second aggregation step. Both aggregation steps can be described by population dynamics and simulated using the program package PARSIVAL (PARticle SIze eVALution) for the treatment of general particle population balances. Biotechnol. Bioeng. 2008;99: 341,350. © 2007 Wiley Periodicals, Inc. [source]

Primary Steps of pH-Dependent Insulin Aggregation Kinetics are Governed by Conformational Flexibility

CHEMBIOCHEM, Issue 11 2009
Jürgen Haas Dr.
Abstract Insulin aggregation critically depends on pH. The underlying energetic and structural determinants are, however, unknown. Here, we measure the kinetics of the primary aggregation steps of the insulin monomer in vitro and relate it to its conformational flexibility. To assess these primary steps the monomer concentration was monitored by mass spectrometry at various pH values and aggregation products were imaged by atomic force microscopy. Lowering the pH from 3 to 1.6 markedly accelerated the observed aggregation kinetics. The influence of pH on the monomer structure and dynamics in solution was studied by molecular dynamics simulations, with the protonation states of the titrable groups obtained from electrostatic calculations. Reduced flexibility was observed for low pH values, mainly in the C terminus and in the helix of the B chain; these corresponded to an estimated entropy loss of 150 J,mol,1,K,1. The striking correlation between entropy loss and pH value is consistent with the observed kinetic traces. In analogy to the well-known , value analysis, this result allows the extraction of structural information about the rate determining transition state of the primary aggregation steps. In particular, we suggest that the residues in the helix of the B chain are involved in this transition state. [source]