Ji Hua Chen

Analysis of chaos in current-mode-controlled DC drive systems

In this paper, chaotic behavior in current-mode-controlled dc drive systems has been analyzed. The key is to derive an iterative map that describes the nonlinear system dynamics. Analytical modeling of fundamental and subharmonic oscillations as well as their stability analysis are presented. The results show that current-mode-controlled DC motor drive systems generally exhibit chaotic behavior. To avoid the occurrence of chaos, the stable ranges of various system parameters are determined. Both computer simulation and experimental measurement are given to verify the theoretical analysis.

Biomimetic remineralization of dentin

OBJECTIVES Remineralization of demineralized dentin is important for improving dentin bonding stability and controlling primary and secondary caries. Nevertheless, conventional dentin remineralization strategy is not suitable for remineralizing completely demineralized dentin within hybrid layers created by etch-and-rinse and moderately aggressive self-etch adhesive systems, or the superficial part of a caries-affected dentin lesion left behind after minimally invasive caries removal. Biomimetic remineralization represents a different approach to this problem by attempting to backfill the demineralized dentin collagen with liquid-like amorphous calcium phosphate nanoprecursor particles that are stabilized by biomimetic analogs of noncollagenous proteins. METHODS This paper reviewed the changing concepts in calcium phosphate mineralization of fibrillar collagen, including the recently discovered, non-classical particle-based crystallization concept, formation of polymer-induced liquid-precursors (PILP), experimental collagen models for mineralization, and the need for using phosphate-containing biomimetic analogs for biomimetic mineralization of collagen. Published work on the remineralization of resin-dentin bonds and artificial caries-like lesions by various research groups was then reviewed. Finally, the problems and progress associated with the translation of a scientifically sound concept into a clinically applicable approach are discussed. RESULTS AND SIGNIFICANCE The particle-based biomimetic remineralization strategy based on the PILP process demonstrates great potential in remineralizing faulty hybrid layers or caries-like dentin. Based on this concept, research in the development of more clinically feasible dentin remineralization strategy, such as incorporating poly(anionic) acid-stabilized amorphous calcium phosphate nanoprecursor-containing mesoporous silica nanofillers in dentin adhesives, may provide a promising strategy for increasing of the durability of resin-dentin bonding and remineralizing caries-affected dentin.

Experimental stabilization of chaos in a voltage-mode DC drive system

This paper first presents experimental evidence on the use of delayed self-controlling feedback to stabilize chaos in a practical voltage-mode DC drive system. Also, a new analytical approach to compute the domain of stabilization is proposed, based on a simple feedback loop, chaotic behavior can be successfully stabilized to fundamental or subharmonic operation using the same time delay.

Subharmonics and Chaos in Switched Reluctance Motor Drives

In this paper, the investigation of the nonlinear dynamics of an adjustable-speed switched reluctance motor (SRM) drive with voltage PWM regulation is carried out. Nonlinear iterative mappings based on both nonlinear and approximately linear flux linkage models are derived, hence the corresponding subharmonic and chaotic behaviors are analyzed. Although both flux linkage models can produce similar results, the nonlinear one offers the merit of accuracy but with the sacrifice of computational time. Moreover, the bifurcation diagrams show that the system generally exhibits a period-doubling route to chaos.

Infiltration of Silica Inside Fibrillar Collagen

Diatoms frustules are created under the control of biomolecules (silaffins, silacidins and long-chain polyamines) at close to physiologic conditions.[1–4] The mechanism of biosilica formation was traditionally based on the ability of zwitterionic water-soluble proteins to create macromolecular assemblies for silica polymerization.[5–7] Recent discoveries of water-insoluble collagen matrices within certain sponge biosilica spicules[8], chitin-based scaffolds in sponge and diatom biosilica formations[9,10], as well as cingulins within diatom girdle bands[4], revive the use of insoluble biomimetic organic templates for morphogenesis of non-porous silica structures. The use of fibrillar collagen as templates for biosilica synthesis was unsuccessful in the past as only extrafibrillar silica deposition was observed.[11,12] Intrafibrillar mineralization of collagen has important implications from a biophysical perspective.[13] Here, we report a collagen biosilicification scheme based on fusion of stabilized polysilicic acid into a fluidic precursor phase upon their infiltration into polyamine-enriched collagen. The latter serves as a template and catalyst for polymerization of the precursor phase into silica that faithfully reproduces the collagen tertiary architecture. Our findings provide a new concept in biosilica materials synthesis which does not require phosphate supplements.

Chaos in voltage-mode controlled DC drive systems

Remarkably complex behaviour, namely chaos, in voltage-mode controlled DC drive systems has been investigated. An iterative mapping that describes the nonlinear system dynamics in the continuous conduction mode is derived. It shows that different bifurcation diagrams can be obtained from different system parameters, and that the systems generally exhibit a period-doubling route to chaos. Analytical modelling of period-1 and hence the period-p orbits, as well as their stability analysis using the characteristic multipliers, is presented. Thus the stable ranges of various system parameters can be determined. The theoretical results are verified by using experimental measurement.

Collagen intrafibrillar mineralization as a result of the balance between osmotic equilibrium and electroneutrality

Mineralisation of fibrillar collagen with biomimetic process-directing agents has enabled scientists to gain insight into the potential mechanisms involved in intrafibrillar mineralisation. Here, by using polycation- and polyanion-directed intrafibrillar mineralisation, we challenge the popular paradigm that electrostatic attraction is solely responsible for polyelectrolyte-directed intrafibrillar mineralisation. Because there is no difference when a polycationic or a polyanionic electrolyte is used to direct collagen mineralisation, we argue that additional types of long-range non-electrostatic interactions are responsible for intrafibrillar mineralisation. Molecular dynamics simulations of collagen structures in the presence of extrafibrillar polyelectrolytes show that the outward movement of ions and intrafibrillar water through the collagen surface occurs irrespective of the charges of polyelectrolytes, resulting in the experimentally verifiable contraction of the collagen structures. The need to balance electroneutrality and osmotic equilibrium simultaneously to establish Gibbs-Donnan equilibrium in a polyelectrolyte-directed mineralisation system establishes a new model for collagen intrafibrillar mineralisation that supplements existing collagen mineralisation mechanisms.

Modeling, analysis, and experimentation of chaos in a switched reluctance drive system

In this brief, modeling, analysis, and experimentation of chaos in a switched reluctance (SR) drive system using voltage pulsewidth modulation are presented. Based on the proposed nonlinear flux linkage model of the SR drive system, the computation time to evaluate the Poincare/spl acute/ map and its Jacobian matrix can be significantly shortened. Moreover, stability analysis of the fundamental operation is conducted, enabling us to determine the stable parameter ranges and hence to avoid the occurrence of chaos. Both computer simulation and experimental measurement are given to verify the theoretical modeling and analysis.

Ability of new obturation materials to improve the seal of the root canal system: A review

New obturation biomaterials have been introduced over the past decade to improve the seal of the root canal system. However, it is not clear whether they have really produced a three-dimensional impervious seal that is important for reducing diseases associated with root canal treatment. A review of the literature was performed to identify models that have been employed for evaluating the seal of the root canal system. In vitro and in vivo models are not totally adept at quantifying the seal of root canals obturated with classic materials. Thus, one has to resort to clinical outcomes to examine whether there are real benefits associated with the use of recently introduced materials for obturating root canals. However, there is no simple answer because endodontic treatment outcomes are influenced by a host of other predictors that are more likely to take precedence over the influence of obturation materials. From the perspective of clinical performance, classic root filling materials have stood the test of time. Because many of the recently introduced materials are so new, there is not enough evidence yet to support their ability to improve clinical performance. This emphasizes the need to translate anecdotal information into clinically relevant research data on new biomaterials.

Intrafibrillar silicification of collagen scaffolds for sustained release of stem cell homing chemokine in hard tissue regeneration

Traditional bone regeneration strategies relied on supplementation of biomaterials constructs with stem or progenitor cells or growth factors. By contrast, cell homing strategies employ chemokines to mobilize stem or progenitor cells from host bone marrow and tissue niches to injured sites. Although silica‐based biomaterials exhibit osteogenic and angiogenic potentials, they lack cell homing capability. Stromal cell‐derived factor‐1 (SDF‐1) plays a pivotal role in mobilization and homing of stem cells to injured tissues. In this work, we demonstrated that 3‐dimensional collagen scaffolds infiltrated with intrafibrillar silica are biodegradable and highly biocompatible. They exhibit improved compressive stress‐strain responses and toughness over nonsilicified collagen scaffolds. They are osteoconductive and up‐regulate expressions of osteogenesis‐ and angiogenesis‐related genes more significantly than nonsilicified collagen scaffolds. In addition, these scaffolds reversibly bind SDF‐1α for sustained release of this chemokine, which exhibits in vitro cell homing characteristics. When implanted subcutaneously in an in vivo mouse model, SDF‐1α‐loaded silicified collagen scaffolds stimulate the formation of ectopic bone and blood capillaries within the scaffold and abrogate the need for cell seeding or supplementation of osteogenic and angiogenic growth factors. Intrafibrillar‐silicified collagen scaffolds with sustained SDF‐1α release represent a less costly and complex alternative to contemporary cell seeding approaches and provide new therapeutic options for in situ hard tissue regeneration.—Niu, L.‐N., Jiao, K., Qi, Y.‐P., Nikonov, S., Yiu, C. K. Y., Arola, D. D., Gong, S.‐Q., El‐Marakby, A., Carrilho, M. R. O., Hamrick, M. W., Hargreaves, K. M., Diogenes, A., Chen, J.‐H., Pashley, D. H., Tay, F. R. Intrafibrillar silicification of collagen scaffolds for sustained release of stem cell homing chemokine in hard tissue regeneration. FASEB J. 26, 4517–4529 (2012). www.fasebj.org