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Simulating the Sorptive Removal of Dissolved Copper by Biocarrier Beads
Lee, M.,Wang, S. Springer Science + Business Media 2017 Environmental modeling & assessment Vol.22 No.1
<P>Biocarrier beads containing the dead biomass of Bacillus drentensis immobilized in polymer polysulfone were synthesized in order to remove heavy metals from wastewater. A series of batch experiments were carried out to identify the sorption mechanisms and the theoretical nature of the underlying processes. A mathematical model was developed to simulate the fate and transport of copper ions in a saturated fixed bed packed with biocarrier beads. Mass balance equations were established to represent the migration and distribution of metal ions in the biocarrier beads and the surrounding bulk liquid. Numerical experiments were performed using the proposed model for quantitative analysis of the temporal changes in the distribution of copper ions in and around the biocarrier beads in a fixed bed. The simulation results show that the biosorption of heavy metals by the biocarrier beads depends largely on surface adsorption. A sensitivity analysis was carried out on the major design parameters in a fixed bed. The effects of bed height, flow velocity, and influent concentration were examined by assessing a simulated breakthrough curve. The breakthrough time occurs earlier for a decreasing bed height and increasing flow velocity and influent Cu(II) concentration, whereas the slope at 50 % breakthrough becomes steeper as the flow velocity increases and the influent concentration decreases. The simulation results show that the proposed mathematical model can provide a quantitative analysis of the distribution of metal adsorbate in and around porous particulate adsorbents in a fixed bed and that it can be used as an effective predictive tool.</P>
Lee, M.,Bae, I.,Kwak, Y.,Moon, K. Elsevier 2012 Current Applied Physics Vol.12 No.suppl2
The surface morphology of Zn-Mg thin film prepared by vacuum evaporation PVD method has formed a structure of various shapes by diffusion of metal particles which is generated migration resulting from accelerated evaporation condition. The surface morphology became smaller as gas pressure increased. Consequently, the grain size decreased further on the low surface energy (101) plane than on the high surface energy (002) plane, which appeared in a vertical direction towards the metal surface due to the influence of residual gases in the vacuum chamber. Also, grain size became smaller with the increase of Mg contents by grain size miniature effect. The grain size of Zn-Mg thin films prepared by the PVD decreased as Mg content increased, and good corrosion resistance increased as well. Also, Zn-Mg thin films have been promoted not only film minuteness but also formation of passivation to corrosion course with the formative increase of intermetallic compound, i.e. MgZn<SUB>2</SUB>, Mg<SUB>2</SUB>Zn<SUB>11</SUB>.
Lee, M.,Kim, Y.,Ryu, J.H.,Kim, K.,Han, Y.M.,Lee, H. Elsevier BV 2016 ACTA BIOMATERIALIA Vol.32 No.-
For practical applications of human embryonic stem cells (hESCs) in regenerative medicine, hESCs should be cultured on a large scale, and at the same time their properties have to be maintained in a controllable manner. Here, we report a chemically defined, scalable culture platform involving co-immobilization of heparin-catechol (HepC) and collagen type-1 (Col) for the long-term maintenance (>18 passages) of hESCs in a feeder-free condition. This platform utilizes a wet-adhesive, mussel-inspired heparin-catechol conjugate as a key component. We hypothesized that the heparin's affinity toward a wide range of proteins, might support undifferentiated in vitro growth of hESC. In fact, on the HepC-coated substrate, most hESC clumps were adhered (~78% at passage 2 (P2)) and expressed pluripotency markers (Fig. 2). Although HepC alone wasn't able to support long-term maintenance of hESCs in a feeder-free system due to decrease in the adhesion rate of hESCs on HepC coating (~ 44% at P4) during the repeated passaging processes, we found that when collagen type I was co-immobilized in the process of HepC coating, the long-term maintenance (passage 18 or more) of hESCs could be achieved with 100% adhesion efficiency (Fig. 4). One remarkable observation is that hESCs on collagen type-I underwent spontaneous differentiation after P6 (Fig. 3), which implied co-immobilized HepC played a role to suppress differentiation of hESCs. This study suggests that unlike the previous studies using proteins, peptides, or synthetic polymers, a polysaccharide, heparin, can be used as a cost-effective component for chemically defined, feeder-free culture of hESC. Statement of Significance: Towards practical applications of human embryonic stem cells (hESCs) in regenerative medicine, hESCs should be cultured on a large scale, and their pluripotent property has to be maintained in a controllable manner. To address these issues, studies that develop chemically defined culture substrates have been explored to replace the widely used, complex, and undefined culture materials represented by Matrigel. Most reports have focused on utilizing proteins, peptides and/or synthetic polymers. However, there have not yet been studies on using polysaccharides as two-dimensional coating materials to potentially replace Matrigel coating. Here, we report that heparin is an effective polysaccharide for the feeder-free, two dimensional culture of hESCs. Our study implies that use of polysaccharides or a polysaccharide/ECM combination can be a new, alternative design principle for hESC culture systems.
General Expansiveness for Diffeomorphisms from the Robust and Generic Properties
Springer Science + Business Media 2016 Journal of dynamical and control systems Vol.22 No.3
<P>Let f:M -> M be a diffeomorphism on a closed smooth d(d a parts per thousand yen 2)-dimensional manifold. For each , if f belongs to C (1)-interior of the set of the n-expansive diffeomorphisms, then f satisfies quasi-Anosov. For C (1)-generic f, if f is n-expansive then f satisfies both Axiom A and the no-cycle condition.</P>
A function-based user authority delegation model
Lee, M.,Cho, N.D.,Gatton, T.M. North-Holland [etc ; Elsevier Science Ltd 2010 Information sciences Vol.180 No.5
User authority delegation is granting or withdrawing access to computer-based information by entities that own and/or control that information. These entities must consider who should be granted access to specific information in the organization and determine reasonable authority delegation. Role Based Access Control (RBAC) delegation management, where user access authority is granted for the minimum resources necessary for users to perform their tasks, is not suitable for the actual working environment of an organization. Currently, RBAC implementations cannot correctly model inheritance and rules for different delegations are in conflict. Further, these systems require that user roles, positions, and information access be continuously and accurately updated, resulting in a manual, error-prone access delegation system. This paper presents a proposal for a new authority delegation model, which allows users to identify their own function-based delegation requirements as the initial input to the RBAC process. The conditions for delegations are identified and functions to implement these delegations are defined. The criteria for basic authority delegation, authentication and constraints are quantified and formulated for evaluation. An analysis of the proposed model is presented showing that this approach both minimizes errors in delegating authority and is more suitable for authority delegation administration in real organizational applications.