The Protein Data Bank (PDB) is the central worldwide repository for three-dimensional (3D) structure data of biological macromolecules. The Research Collaboratory for Structural Bioinformatics (RCSB) has completely redesigned its resource for the distribution and query of 3D structure data. The re-engineered site is currently in public beta test at http://pdbbeta.rcsb.org. The new site expands the functionality of the existing site by providing structure data in greater detail and uniformity, improved query and enhanced analysis tools. A new key feature is the integration and searchability of data from over 20 other sources covering genomic, proteomic and disease relationships. The current capabilities of the re-engineered site, which will become the RCSB production site at http://www.pdb.org in late 2005, are described.
Abstract. The numerical realization of closed loop control for distributed parameter systems is still a significant challenge and in fact infeasible unless specific structural techniques are employed. In this paper we propose the combination of model reduction techniques based on proper orthogonal decomposition (POD) with the numerical treatment of the Hamilton-Jacobi-Bellman (HJB) equation for infinite horizon optimal control problems by a modification of an algorithm originated by Gonzales and 1. Introduction. In many applications the discretization of optimal control problems for time dependent partial differential equations, e.g., for the unsteady Navier-Stokes equations, require the solution of nonlinear systems with a large number of degrees of freedom. In particular, to compute closed loop controls in state feedback form we have to solve the HamiltonJacobi-Bellman (HJB) equation, which has been numerically infeasible for parabolic differential equations on a standard workstation equipment until today, if classical approximations like finite elements or finite differences are used. In this work model reduction is applied to reduce the number of unknowns significantly. The obtained low-dimensional models should guarantee a reasonable performance of the controlled plant while being computationally tractable. Proper orthogonal decomposition (POD) provides a method for deriving appropriate loworder models. It can be thought of as a Galerkin approximation in the spatial variable, built from functions corresponding to the solution of the physical system at prespecified time instances. These are called the snapshots. Due to possible linear dependence or almost linear dependence a singular value decomposition of the snapshots is carried out and the leading generalized eigenfunctions are chosen as a basis, referred to as the POD basis. Once a loworder model of the dynamical system is available, feedback synthesis based on approximate solutions to the stationary HJB equation becomes feasible.We demonstrate the feasibility of the proposed approach by means of an optimal boundary control problem for the Burgers equation. Open loop optimal control problems for the
This study describes the fabrication and biological evaluation of core-shell bilayered bioceramic microspheres with adjustable compositional distribution via a coaxial bilayer capillary system. Beyond the homogeneous hybrid composites, varying the diameter of capillary nozzles and the composition of the bioceramic slurries makes it easy to create bilayered β-tricalcium phosphate (CaP)/β-calcium silicate (CaSi) microspheres with controllable compositional distribution in the core or shell layer. Primary investigations in vitro revealed that biodegradation could be adjusted by compositional distribution or shell thickness and that poorly soluble CaP located on the shell layer of CaP or CaSi@CaP microspheres was particularly beneficial for mesenchymal stem cell adhesion and growth in the early stage, but the ion release from the CaP@CaSi exhibited a potent stimulating effect on alkaline phosphatase expression of the cells at longer times. When the bilayered microspheres (CaSi@CaP, CaP@CaSi) and the monolayered microspheres (CaP, CaSi) were implanted into the critical-sized femoral bone defect in rabbit models, significant differences in osteogenic capacity over time were measured at 6-18 weeks post implantation. The CaP microspheres showed the lowest biodegradation rate and slow new bone regeneration, whereas the CaSi@CaP showed a fast degradation of the CaSi core through the porous CaP shell so that a significant osteogenic response was observed at 12-18 weeks. The CaP@CaSi microspheres possessed excellent surface bioactivity and osteogenic activity, whereas the CaSi microspheres group exhibited a poor bone augmentation in the later stage due to extreme biodegradation. These findings demonstrated that the bioactive response in such core-shell-structured bioceramic systems could be adjusted by compositional distribution, and this strategy can be used to fabricate a variety of bioceramic microspheres with adjustable biodegradation rates and enhanced biological response for bone regeneration applications in medicine.
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