bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fibroin/collagen hybrid hydrogels with crosslinking method: Preparation, properties, and cytocompatibility
Authors: Lv Qiang , Hu Kun , Feng QingLing , Cui Fuzhai 
Published: July 2007

AbstractSubstrate stiffness is an important physical factor in the response of many cell types. Although protein‐based hydrogels are widely used as cell‐culture substrates because of their resemblance to the natural extracellular matrix (ECM) and complex signaling, their rigidity should be further increased to facilitate the adhesion and growth of cells. In this study, fibroin/collagen hydrogels having suitable stiffness were prepared directly by adding 1‐ethyl‐3‐(3‐dimethylaminoprophy) carbodiimide hydrochloride (EDC) in fibroin/collagen solution to induce crosslinking. The storage moduli of these crosslinked hydrogels are above 3 kPa, and even exceed 10 kPa, having stronger mechanical strength than that of previously reported protein‐based hydrogels. Furthermore, the crosslinked hydrogels can maintain their configuration above 80oC, which proves their increased thermal stability. Although crosslinked, the hydrogels still maintain the mobility of fibroin molecules. The growth of vascular smooth muscle cells (VSMCs) in fibroin/collagen gels indicates that the crosslinking reaction has no negative influence on the biocompatibility of fibroin/collagen hydrogels. The fibroin/collagen hydrogels are more propitious to the growth of cells compared with fibroin/collagen scaffolds. Because of their inherent biocompatibility, excellent mechanical and thermal properties, and green preparation process, the fibroin/collagen hydrogels would become promising scaffolds for tissue engineering. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
The degradation profile of novel, bioresorbable PCL–TCP scaffolds: An in vitro and in vivo study
Authors: Yeo A. , Rai B. , Sju E. , Cheong J.J. , Teoh S.H. 
Published: July 2007

AbstractDegradation studies of scaffolds are important in bone tissue engineering. Previously, novel poly(ε‐caprolactone)–20% tricalcium phosphate (PCL–TCP) based scaffolds were developed and proven useful for bone regeneration. In this study in vitro degradation analyses were carried out with the PCL–TCP scaffolds immersed in standard culture medium for 24 weeks. In vivo degradation was performed with the scaffolds implanted in the abdomen of rats for the same period of time. Results demonstrated greater degradation of PCL–TCP scaffolds in vivo than in vitro. At 24 weeks, the increase of average porosity of the scaffolds in vivo was 29.2% compared to 2.65% in vitro. Gel permeation chromatography (GPC) analysis revealed a decrease of 29% and 20% respectively in the Mn and Mw values after 24 weeks in vitro. However, a significant decrease in Mn and Mw values (79.6% and 88.7% respectively) were recorded in vivo. The mechanical properties however, were relatively similar and closely match those of cancellous bone even at 24 weeks. The results showed that the scaffold can be used for dentoalveolar reconstruction and PCL–TCP scaffolds have shown to possess the potential to degrade within the desired time period of 5–6 months and favorable mechanical properties. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
Substitution effect on the geometry and electronic structure of the ferrocene
Authors: Zhang Guiling , Zhang Hui , Sun Miao , Liu Yanhong , Pang Xiaohong , Yu Xiaoyang , Liu Bo , Li Zesheng 
Published: July 2007

AbstractThe substitution effects on the geometry and the electronic structure of the ferrocene are systematically and comparatively studied using the density functional theory. It is found that NH2and OH substituents exert different influence on the geometry from CH3, SiH3, PH2, and SH substituents. The topological analysis shows that all the CC bonds ina–gare typical opened‐shell interactions while the FeC bonds are typical closed‐shell interactions. NBO analysis indicates that the cooperated interaction of d → π* and feedback π → d + 4s enhances the Fe‐ligand interaction. The energy partitioning analysis demonstrates that the substituents with the second row elements lead to stronger iron‐ligand interactions than those with the third row elements. The molecular electrostatic potential predicts that the electrophiles are expected to attack preferably the N, O, P, or S atoms in FerNH2, FerOH, FerPH2, and FerSH, and attack the ring C atoms in FerSiH3and FerCH3. In turn, the nucleophiles are supposed to interact predominantly by attacking the hydrogen atoms. The simulated theoretical excitation spectra show that the maximum absorption peaks are red‐shifted when the substituents going from second row elements to the third row elements. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007
Evaluation of different doses of UV irradiation to loach eggs for Genetic inactivation of the maternal genome
Authors: Fujimoto Takafumi , Sakao Suzu , Yamaha Etsuro , Arai Katsutoshi 
Published: July 2007

AbstractGenetic inactivation of the egg nucleus is an indispensable step in the production of androgenetic embryos in teleosts. However, few experimental studies have focused on determining the most effective means of achieving complete inactivation of the maternal genome. Here, we sought to identify the optimum conditions of ultraviolet (UV) irradiation for complete inactivation of the loach egg nucleus. Unfertilized eggs were UV irradiated from above with a dose in the range 0–200 mJ/cm2. Successful inactivation of the maternal genome was evaluated by the exclusive expression of a paternally inherited color phenotype. The presence or absence of putative maternal chromosome fragments was screened by flow cytometry of DNA content and by cytogenetic analysis. The majority of the larvae derived from irradiated eggs had an abnormal appearance. Haploid individuals were detected by measurement of DNA content flow cytometry and by chromosome counting in the groups that received more than 75 mJ/cm2 groups. Although the coefficient of variation of DNA content was apparently reduced in the 125–200 mJ/cm2 groups, chromosome fragments were still detected in all the groups from irradiated eggs. Inactivation of the egg nucleus was also histologically elucidated by the presence or absence of residual nuclear material in anuclear embryos that developed from UV‐irradiated eggs fertilized with UV‐irradiated sperm. Embryos that were completely or near‐completely anuclear were found in the 150 and 200 mJ/cm2 groups. We conclude that the optimum UV dose for complete genetic inactivation of the egg nucleus is more than 150 mJ/cm2. J. Exp. Zool. 307A:449–462, 2007. © 2007 Wiley‐Liss, Inc.
Characterization of the protein profile of donkey's milk whey fraction
Authors: Cunsolo Vincenzo , Saletti Rosaria , Muccilli Vera , Foti Salvatore 
Published: July 2007

AbstractCharacterization of the protein profile of the whey fraction from a milk sample taken from an individual donkey belonging to the ‘Ragusana’ species of the East of Sicily is reported. Direct RP‐HPLC/electrospray ionization (ESI)‐MS analysis of the whey fraction allowed the detection of some unknown components, together with the identification of already known whey proteins. Matrix‐assisted laser desorption/ionization (MALDI)‐TOF/MS and RP‐HPLC/ESI‐MS/MS analysis of the enzymatic digests of the unknown components resulted the identification and characterization of (1) two β‐casein fragments; (2) the sequence of donkey's serum albumin; and (3) the oxidized methionine forms of lysozyme B and α‐lactoalbumin. One of the two β‐casein fragments corresponds to the sequence Val176‐Arg189 of the horse's β‐casein. The second one corresponds the C‐terminal sequence Tyr199‐Val226 of the horse's β‐casein, with four amino acid substitutions (Q → R203, L/I → P206, F → L210 and P → A219). Both fragments, reasonably arising by endogenous proteases cleavage of the donkey's β‐casein, could be potential biologically active peptides. Direct mass spectrometric sequence characterization of the detected donkey's serum albumin reveals the presence of the amino acid substitution Val → Ile at position 497 with respect to the cDNA deduced sequence. The oxidized forms of lysozyme B and α‐lactoalbumin are selectively oxidized at methionine 79 and methionine 90, respectively. Copyright © 2007 John Wiley & Sons, Ltd.
Raman spectroscopic investigation of pure and ytterbium‐doped rare earth silicate crystals
Authors: Zheng Lihe , Zhao Guangjun , Yan Chengfeng , Xu Xiaodong , Su Liangbi , Dong Yongjun , Xu Jun 
Published: July 2007

AbstractRaman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y2SiO5 (YSO), Lu2SiO5 (LSO), (Lu0.5Y0.5)2SiO5 (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm−1 region assigned to the modes of SiO4 and oxygen vibrations. Multiple bands indicate the nonequivalence of the REO bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm−1 are an indication of impurities. The (SiO4)4− tetrahedra are characterized by bands near 200 cm−1 which show a separation of the components of ν4 and ν2, in the 500–700 cm−1 region which are attributed to the distorting bending vibration and in the 880–1000 cm−1 region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm−1 region of Re2SiO5 were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with SiO bending modes and REO stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd.
On the optimum flexure problem in structural mechanics
Authors: Carmichael D. G. , Clyde D. H. 
Published: July 2007

AbstractThe problem of optimal load transmission by flexure, and in particular the minimum moment volume problem in transversely loaded plane systems, is one of the few structural optimization problems admitting closed form solutions. The theory gives the minimum weight solutions for grillages, fibre‐reinforced plates, and space frames of preassigned depth. Characteristically, the route to the solution is through energy arguments or the calculus of variations. Early work also employed informal logical arguments, linear programming, and concave programming in the case of reinforced concrete slabs. More recently, concise function theoretic methods in Banach spaces have appeared. Initial investigations by the authors suggest that the optimum flexure problem can be handled straightforwardly by optimal control systems theory, a theory which offers the prospect of a consistent and systematic approach to design problems in general. New interpretations of, and insights into, the optimum flexure problem may be gained through optimal control theory.
Parallel digital penalty function constrained linear programming
Authors: Gibson J. A. , Gibbard R. W. 
Published: July 2007

AbstractSearch trajectories are determined with a research‐model, fully‐parallel, digital computer which has approximately the same speed capability as analogue computers and is constructed on similar design principles. Solution accuracy sensitivity to both algorithm and problem parameters is demonstrated. The advantages of speed and reliability of parallel digital circuits, in combination with the problem‐simplifying penalty function method, provides an improved optimization technique for applications in which speed rather than accuracy is the primary requirement.
The infinite‐order singular problem
Authors: Bortins R. , Boustany N. M. , Powers W. F. 
Published: July 2007

AbstractIn singular optimal control problems, the optimal control is determined by solving the algebraic equation which results by successively differentiating the switching function until the control appears explicitly. In certain classes of problems, the control never appears, and such problems are termed infinite‐order singular problems. It is shown that this class has many useful properties with respect to the theory and computation of optimal controls. In particular, it is shown that for the time‐invariant, singular, linear‐quadratic problem: (i) the singular order is infinity or less than or equal to the state dimension, (ii) infinite‐order problems can arise only from exact differential type cost functions, (iii) the range of the second‐variation operator (Hessian) is finite‐dimensional, (iv) the computational method converges strongly, and (v) conjugate direction methods converge in a finite number of steps. The latter property is especially useful in the generation of test problems for optimal control computation schemes.
Optimal maintenance policies under deterministic deterioration and stochastic failure
Authors: Feichtinger Gustav 
Published: July 2007

AbstractThompson1 considers a linear control model to ascertain the optimal preventive maintenance policy for production equipment and, simultaneously, its optimal sale date. He assumes age‐dependent deterministic continuous deterioration, production rate and linear efficiency of maintenance expenditures. In the present paper we first consider a linear maintenance model under a budget constraint. The impact of such a restriction is an earlier switch in the optimal bang‐bang policy. Then a non‐linear, non‐autonomous generalization of Thompson's model is analysed by the maximum principle. The optimal maintenance policy is shown to be downward sloping provided that in each time period the production rate is greater than the sum of interest and deterioration rate. The monotonicity of the optimal rate of preventive maintenance holds also under the additional possibility of random machine failure provided the production rate is greater than the sum of the rate of interest, the rate of deterioration and the rate of stochastic failure at each age. Moreover, it is shown that the higher the failure rate the smaller the optimal expenditures for preventive maintenance at any fixed age of the machine. In particular, the optimal maintenance rate at age t in a model without random failure is greater than those in any case including stochastic failure at the same age.
Aeroelastic optimization of orthotropic rectangular flat panels
Authors: Librescu L. , Beiner L. 
Published: July 2007

AbstractThe paper deals with a weight‐minimization problem of rectangular orthotropic flat panels placed in a high supersonic gas flow and subject to a flutter speed constraint. In‐plane compressive loads are taken into account. The problem is treated in the framework of the optimal control theory of distributed parameter systems. It is shown that the necessary optimality conditions are to be supplemented with a condition ensuring that the flutter speed of the optimal panel should coincide with the prescribed one. The general field equations governing the aeroelastic optimization problem are presented, and qualitative conclusions concerning the optimal thickness distribution are given. A few remarks on various methods for solving the field equations are also given.
The asymptotic ii‐test for singular periodic control problems with an application to the management of a class of ecosystems
Authors: Guardabassi G. , Scattolini R. 
Published: July 2007

AbstractA basic problem in optimal control theory is to identify circumstances under which a (non‐constant or proper) periodic control exists which is better than the optimal constant one. Considerable attention has therefore been devoted in the literature to the development of criteria to test for properness, i.e. to test whether the optimal constant operation of a given system can definitely be improved by (proper) cycling in the sense that the average return associated with the latter is greater than the obviously constant one associated with the former. One of the most powerful results in this direction is the so‐called II‐test. In this paper, a special form of the II‐test, valid for singular optimal periodic control problems, is presented (asymptotic II‐test), and an application to the periodic control of a class of multispecies ecosystems is discussed.
Singular perturbation analysis of the closed‐loop discrete optimal control problem
Authors: Naidu D. S. , Rao A. K. 
Published: July 2007

AbstractThe closed‐loop optimal control of a linear, time‐invariant, singularly perturbed discrete system is considered. The resulting matrix Riccati difference equation is formulated in the singularly perturbed structure. It is observed that the degeneration affects some of the final conditions of the Riccati equation. A singular perturbation method is developed to obtain approximate solutions in terms of an outer series and a final correction series. The outer series takes advantage of the order reduction associated with degeneration and the correction series takes care of the affected final conditions. Two examples are given to illustrate the proposed method.
Application of linear and dynamic programming to the optimization of the production of hydroelectric power
Authors: Ölçer S. , Harsa C. , Roch A. 
Published: July 2007

AbstractApplication of the methods of control theory to industrial problems demands a match of the necessary computational tools to the actual financial constraints. The development of suboptimal control algorithms allows performance gains that were limited in the past to installations with extensive computer facilities to be reached now by smaller ones. Advances in this domain lead naturally to a rational use of modern control tools based on mini‐ and microcomputers. Within this framework, we present a general method for the optimal control of electric power plants. The optimization problem is described and formulated as the optimal control of a multivariable state‐space model in which the state and control vectors are constrained by sets of equality or inequality relations. The solution is obtained in two steps with linear and dynamic programming methods; the results are expressed in the form of parametric algorithms which set up the working point of the turbine‐generator units so that the resulting profit represents a maximum. The application of the method to the optimization of the production of a Swiss electricity company illustrates the approach.
Instationary dolphin flight: The optimal energy exchange between a sailplane and vertical currents in the atmosphere
Authors: De Jong Jan L. 
Published: July 2007

AbstractSailplanes, when launched, need to extract energy from vertical motion of the air. The usual procedure is to circle and climb in vertical currents of limited spatial dimension (‘thermals’) under cumulus clouds and thereafter to exchange the gained height into distance by gliding out to the next cumulus cloud. While doing so, sailplane pilots will often encounter larger‐scale regions where the atmosphere moves in a vertical direction. Until recently the optimal strategy in such situations was assumed to be to fly slower through regions with upward moving air and faster through regions with downward moving air. Only a few years ago it was discovered both in theory, from energy considerations, as well as in practice, by contest pilots, that in some circumstances more energy could be extracted from the atmosphere when the loadfactor, i.e., the total aerodynamic lifting force on the wings divided by the weight, was varied. The research reported in this paper was set up to investigate this phenomenon. To that end a simple dynamic model is assumed for the sailplane, and the optimization problem is formulated as an optimal control problem with terminal constraints. This optimal control problem is solved numerically for a number of different widths and strengths of the vertical currents encountered. The computer program used for this purpose is a rather general continuous optimal control program based on the use of (conjugate) gradients in function space and a projection operation to account for the terminal constraints.
The optimal LQ regulator with cheap control for not strictly proper systems
Authors: Scherzinger B. M. , Davison E. J. 
Published: July 2007

AbstractThe LQ optimal regulator problem with cheap control is investigated for plants of the form x = Ax + Bu, y = Cx + Du, where D ± 0 makes the plant not strictly proper. It is found that perfect regulation of the output with closed‐loop stability is achieved if and only if the plant is detectable, is minimum phase and there exist independent inputs equal to or greater in number to the number of independent outputs.
The optimal times and levels of impulsive acquisition of automation
Authors: Gaimon Cheryl 
Published: July 2007

AbstractA dynamic optimization model is formulated to derive the optimal mix of output achieved manually and from automatic equipment. Therefore, the composition of the productive capacity is obtained for a firm over time. The actual times and levels at which automation should be acquired and the levels of change in manual output are determined over the planning horizon. Optimal policies are derived in order to minimize costs associated with deviation from the goal levels of total output, acquiring automation, changing the level of manual output, operating automation and operating manual equipment over time. Ordinary and impulsive optimal control theory techniques are applied to obtain solutions.
Synchronization of n non‐identical double‐integrated plants
Authors: Unbehauen H. , Vakilzadeh I. 
Published: July 2007

AbstractSynchronization of n non‐identical double‐integral plants with non‐identical output initial conditions will be studied. Achievement of two objectives will furnish us with our synchronization goal: (i) elimination of steady‐state errors between the n outputs and (ii) portraying each of the n identical steady‐state outputs as a double integral (dt2) of a common input x(t).
The non‐linear beam via optimal control with bounded state variables
Authors: Maurer H. , Mittelmann H. D. 
Published: July 2007

AbstractThe non‐linear beam with bounded deflection is considered as an optimal control problem with bounded state variables. The theory of necessary optimality conditions leads to boundary value problems with jump conditions which are solved by multiple‐shooting techniques. A branching analysis is performed which exhibits the different solution structures. In particular, the second bifurcation point is determined numerically. The bifurcation diagram reveals a hysteresis‐like behaviour and explains the jumping to a different state at this bifurcation point.
Multilevel learning control of an absorption column
Authors: Najim K. , Chtourou M. 
Published: July 2007

AbstractThis paper describes the modelling and learning control of a packed absorption column. The packed column is the most popular equipment used for process absorption. The absorption column is used to reduce the concentration of CO2 in a gas mixture to a desired value. A solution of diethanolamine (DEA) is used as the absorbent. The flow rate of the absorbent and the concentration of CO2 in the gas mixture are considered as control and controlled variables respectively. The process model has been developed from considerations of mass balances, transport phenomena and the chemical reaction in the liquid phase.A learning controller using a hierarchical structure of automata is used to achieve control of the column. The learning system is connected in a feedback manner with the column, which plays the role of the random medium where the learning system operates. Several simulation studies highlight the applicability of the learning control algorithm involved.