bluuebunny/crossref_metadata_2025 huggingface dataset:
A biodegradable polyurethane‐ascorbic acid scaffold for bone tissue engineering
Authors: Zhang Jianying , Doll Bruce A. , Beckman Eric J. , Hollinger Jeffrey O.
Published: October 2003

A novel, nontoxic, biodegradable, sponge‐like polyurethane scaffold was synthesized from lysine‐di‐isocyanate (LDI) and glycerol. Ascorbic acid (AA) was copolymerized with LDI‐glycerol. Our hypothesis was that the AA‐containing polymer foam would enhance the biological activity of the osteoblastic precursor cell (OPCs). The LDI‐glycerol‐AA matrix degraded in aqueous solution to the nontoxic products of lysine, glycerol, and AA. The degradation products did not significantly affect the solution pH. The physical properties of the polymer network supported the cell growth in vitro. Mouse OPCs attached to the polymer matrix and remained viable. OPCs produced multilayered confluent cultures, a characteristic typical of bone cells. Furthermore, AA release stimulated cell proliferation, type I collagen, and alkaline phosphatase synthesis. Cells grown on the LDI‐glycerol‐AA matrix also showed an enhancement of mRNA expression for pro‐α1 (I) collagen and transforming growth factor‐α1 after 1 week. Data were tested for significance with an analysis of variance model and multiple comparison test (Fisher's Protected Least Significant Difference) at p ≤ 0.05. The observations suggest that AA‐containing polyurethane may be useful in bone tissue engineering applications. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 389–400, 2003
Effective removal of alginate‐poly‐L‐lysine microcapsules from pancreatic islets by use of trypsin–EDTA
Authors: de Groot Martijn , Leuvenink Henri G. D. , Keizer Paula P. M. , Fekken Susan , Schuurs Theo A. , van Schilfgaarde Reinout
Published: October 2003

Although the transplantation of alginate‐poly‐L‐lysine‐alginate encapsulated islets of Langerhans usually is successful, graft survival is still limited. Molecular analysis by RT‐PCR of the encapsulated islets may provide insight into the mechanisms that affect islets during graft failure. However, RT‐PCR on encapsulated islets is not possible because the poly‐L‐lysine of the capsule interferes with both cDNA synthesis and PCR amplification. We applied a method that mechanically removes the microcapsules from the islets after a short trypsin–EDTA treatment (decapsulation), thereby enabling RT‐PCR analysis. The results of this study show that the decapsulation procedure does not affect islet vitality and has only minor effects on islet function and morphology. The decapsulation does not affect GAPDH, β‐actin, Bcl‐2, or Bax gene expression. This method is an improvement over the time‐consuming manual dissection of microcapsules because it allows for the rapid and relatively harmless removal of capsules on a larger scale. Decapsulation offers the possibility of applying RT‐PCR, as well as other methods, which cannot be performed on encapsulated islets. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 679–683, 2003
Biologically inspired synthesis of bone‐like composite: Self‐assembled collagen fibers/hydroxyapatite nanocrystals
Authors: Tampieri Anna , Celotti Giancarlo , Landi Elena , Sandri Monica , Roveri Norberto , Falini Giuseppe
Published: October 2003

Replacement of bone tissue by graft materials and products of tissue engineering having composition, structure, and biological features that mimic natural tissue is a goal to be pursued. A biomimetic synthesis was performed to prepare new bone‐like composites constituted of hydroxyapatite nanocrystals and self‐assembled type I collagen fibers. We used a biological inspired approach that proved that the biological systems stored and processed information at the molecular level. Two different methodologies were used: dispersion of synthetic hydroxyapatite in telopeptides free collagen molecules solution and direct nucleation of hydroxyapatite into reconstituted collagen fibers during their assembling. The different preparation techniques were experimented then the composites thoroughly characterized and compared. Composite obtained by direct nucleation showed an intimated interaction of the inorganic and proteic components, which modified the apatitic phase and made its composition, morphology and structure similar to the mineral component of natural bone. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 618–625, 2003
Synthesis of cytoadhesive poly(methylmethacrylate) for applications in targeted drug delivery
Authors: Tao Sarah L. , Lubeley Michael W. , Desai Tejal A.
Published: October 2003

The objective of this work was to incorporate cytoadhesive properties into poly(methylmethacrylate) (PMMA) for potential applications in highly localized tissue‐specific drug delivery. First, the PMMA was chemically modified by aminolysis to yield amine‐terminated surfaces. X‐ray photoelectron microscopy confirmed the presence of surface nitrogen entities, and the distribution of amine groups was found to be relatively uniform, as characterized by atomic force microscopy. The availability of these groups for attachment of biologically active molecules was characterized by fluorescence microscopy after immobilization of avidin‐FITC. To render the PMMA cytoadhesive, avidin molecules were conjugated to the amine‐terminated surfaces with a hydroxy‐succinimide‐catalyzed carbodiimide reagent and biotin‐labeled lectins (tomato, which binds selectively to Caco‐2 cells, and peanut, an unrelated lectin) subsequently were attached utilizing avidin‐biotin chemistry. Cytoadhesive activity was evaluated by characterizing the interactions between microfabricated PMMA particles and Caco‐2 monolayers. After 15‐, 30‐, 60‐, and 120‐min incubation periods, the tomato lectin‐conjugated PMMA showed a two to sixfold increase in Caco‐2 cell recognition over control particles. Furthermore, the stability of the cytoadhesive PMMA interactions appeared to be three to seven times greater than that of the control surfaces. These findings demonstrate the cytoadhesive properties of modified PMMA, making this novel bioactive polymer very promising for applications in targeted drug delivery. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 369–375, 2003
Development of a porous poly(L‐lactic acid)/hydroxyapatite/collagen scaffold as a BMP delivery system and its use in healing canine segmental bone defect
Authors: Hu Yunyu , Zhang Chao , Zhang Shuming , Xiong Zhuo , Xu Jianqiang
Published: October 2003

A hydroxyapatite/collagen (HAC) composite was produced to mimic the natural extracellular matrix of bone, with the collagen serving as a template for apatite formation. A three‐dimensional highly porous scaffold was developed by mixing HAC with poly(L‐lactic acid) (PLA) using a thermally induced phase separation technique. Naturally derived bovine bone morphogenetic protein (bBMP) was incorporated into the porous HAC‐PLA scaffolds, and the composite then was implanted in diaphyseal defects (2 cm in radius) of adult beagle dogs. Controls were implanted with scaffolds without BMP. The dogs were sacrificed at 6 months, at which time biocompatibility, biodegradability, and osteoinduction were evaluated by histologic and radiologic examination and by bone mineral density (BMD) measurements. All defects healed after treatment with BMP combined with HAC‐PLA, and BMD at the site of the defect was higher than the BMD of the intact radius. Fibrous union developed in the control group animals. Histologic observation indicated that the presence of BMP not only promoted osteogenesis but that it also accelerated degradation of the biomaterials. Optimized design parameters of a three‐dimensional porous biomaterial would give full scope to the role of BMP as an osteoinductive growth factor. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 591–598, 2003
On the fracture of human dentin: Is it stress‐ or strain‐controlled?
Authors: Nalla R. K. , Kinney J. H. , Ritchie R. O.
Published: October 2003

Despite substantial clinical interest in the fracture resistance of human dentin, there is little mechanistic information in archival literature that can be usefully used to model such fracture. In fact, although the fracture event in dentin, akin to other mineralized tissues like bone, is widely believed to be locally strain‐controlled, there has never been any scientific proof to support this belief. The present study seeks to address this issue through the use of a novel set of in vitro experiments in Hanks' balanced salt solution involving a double‐notched bend test geometry, which is designed to discern whether the critical failure events involved in the onset of fracture are locally stress‐ or strain‐controlled. Such experiments are further used to characterize the notion of “plasticity” in dentin and the interaction of cracks with the salient microstructural features. It is observed that fracture in dentin is indeed locally strain‐controlled and that the presence of dentinal tubules does not substantially affect this process of crack initiation and growth. The results presented are believed to be critical steps in the development of a micromechanical model for the fracture of human dentin that takes into consideration the influence of both the microstructure and the local failure mode. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 484–495, 2003
Oxygen radical production in neutrophils interacting with platelets and surface‐immobilized plasma proteins: Role of tyrosine phosphorylation
Authors: Nimeri Ghada , Majeed Meytham , Elwing Hans , Öhman Lena , Wetterö Jonas , Bengtsson Torbjörn
Published: October 2003

The interaction between neutrophil granulocytes and platelets is considered to play an important role in the inflammatory process induced by an implanted foreign material. However, the cellular mechanisms involved remain incompletely understood. We used a luminol‐dependent chemiluminescence (CL) technique to analyze the generation of reactive oxygen species (ROS) in human neutrophils interacting with different plasma protein‐coated surfaces in the presence or absence of unstimulated or stimulated platelets. The role of tyrosine phosphorylation in the regulation of NADPH oxidase activity was evaluated with quantitative fluorescence microscopy and the specific tyrosine kinase inhibitor genistein. We found that the ROS‐production is 2 to 3 times higher in neutrophils on immunoglobulin G (IgG)‐coated surfaces than in cells interacting with albumin‐ or fibrinogen‐coated surfaces. Incubation with superoxide dismutase and catalase revealed that about 45% of the ROS was released extracellularly on IgG surfaces whereas corresponding values were 90% and 85% in neutrophils interacting with albumin and fibrinogen, respectively. The presence of platelets markedly increased the extracellular generation of ROS, mainly in neutrophils interacting with IgG‐ or fibrinogen‐coated surfaces whereas the intracellular production was only modestly affected. Quantitative fluorescence microscopy of neutrophils stained with FITC‐conjugated anti‐phosphotyrosine antibodies showed a correlation between tyrosine phosphorylation, cell spreading, and ROS production. Platelets markedly amplified the anti‐phosphotyrosine staining on both fibrinogen‐ and IgG‐coated surfaces whereas the low level of tyrosine phosphorylation in neutrophils on albumin‐coated surfaces was not further elevated by platelets. Furthermore, the tyrosine kinase inhibitor genistein inhibited both extra‐ and intracellular ROS production in neutrophils regardless of the presence of platelets. We demonstrate that plasma protein coating and the presence of platelets are crucial for the inflammatory response of adhering neutrophils and that the oxidative response correlates with the extent of tyrosine phosphorylation of proteins in focal contacts. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 439–447, 2003
Biocompatibility of collagen membranes crosslinked with glutaraldehyde or diphenylphosphoryl azide: An in vitro study
Authors: Marinucci Lorella , Lilli Cinzia , Guerra Mario , Belcastro Salvatore , Becchetti Ennio , Stabellini Giordano , Calvi Edoardo M. , Locci Paola
Published: October 2003

Crosslinking of collagen biomaterials increases their resistance to degradation in vivo. Glutaraldehyde (GA) is normally used to crosslink collagen biomaterial, but is often cytotoxic. Diphenylphosphoryl azide (DPPA) has recently been proposed as reagent, but little is known about its effects on cell behavior. In this study, we determined which collagen membrane was the most biocompatible: Paroguide which is crosslinked with DPPA and contains chondroitin sulfate; Opocrin which is crosslinked with DPPA; Biomed Extend which is crosslinked with GA; and Bio‐Gide which is left untreated. Cell proliferation and extracellular matrix macromolecule deposition were evaluated in human fibroblasts cultured on the membranes. The GA‐crosslinked Biomed Extend membrane and the not‐crosslinked Bio‐Gide membrane reduced cell growth and collagen secretion compared with DPPA‐crosslinked biomembranes. When Paroguide and Opocrin were compared, better results were obtained with Paroguide. The greatest amount of transforming growth factor β1, a growth factor involved in extracellular matrix macromolecule accumulation and in tissue regeneration, was produced by cells cultured on Paroguide, with Opocrin second. Our data suggest that the DPPA method is more biocompatible than the GA for crosslinking collagen biomaterials and that membranes made of collagen plus chondroitin sulfate are better than membranes made of pure collagen. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 504–509, 2003
Modification of Ti6AL4V surfaces using collagen I, III, and fibronectin. II. Influence on osteoblast responses
Authors: Bierbaum Susanne , Hempel Ute , Geißler Ulrike , Hanke Thomas , Scharnweber Dieter , Wenzel Klaus‐Wolfgang , Worch Hartmut
Published: October 2003

Responses of osteoblastic cells are influenced by morphology and composition of the extracellular matrix, and this fact has been used to improve the biological acceptance of implants by modifying the surfaces with components of the extracellular matrix (ECM). In this study, the effect of the collagen types I and III on adhesion, proliferation, and differentiation was studied, using primary osteoblastic cells from rat calvariae. Differences in alkaline phosphatase activity (ALP) and collagen synthesis were observed between differently composed collagen coatings. An increase in collagen type III resulted in an increase in collagen synthesis and a concomitant decrease in ALP activity and Ca deposition. Initial adhesion mechanism of the cells depended on the substrate (titanium, collagen, fibronectin). © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 431–438, 2003
Nano‐fibrous scaffolding architecture selectively enhances protein adsorption contributing to cell attachment
Authors: Woo Kyung Mi , Chen Victor J. , Ma Peter X.
Published: October 2003

Tissue engineering aims at resolving problems such as donor shortage and immune rejection faced by transplantation. Scaffolds (artificial extracellular matrices) have critical roles in tissue engineering. Recently, we developed nano‐fibrous poly(L‐lactic acid) scaffolds under the hypothesis that synthetic nano‐fibrous scaffolding, mimicking the structure of natural collagen fibers, could create a more favorable microenvironment for cells. This is the first report that the nano‐fibrous architecture built in three‐dimensional scaffolds improved the features of protein adsorption, which mediates cell interactions with scaffolds. Scaffolds with nano‐fibrous pore walls adsorbed four times more serum proteins than scaffolds with solid pore walls. More interestingly, the nano‐fibrous architecture selectively enhanced protein adsorption including fibronectin and vitronectin, even though both scaffolds were made from the same poly(L‐lactic acid) material. Furthermore, nano‐fibrous scaffolds also allowed >1.7 times of osteoblastic cell attachment than scaffolds with solid pore walls. These results demonstrate that the biomimetic nano‐fibrous architecture serves as superior scaffolding for tissue engineering. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 531–537, 2003
Optimal heparin surface concentration and antithrombin binding capacity as evaluated with human non‐anticoagulated blood in vitro
Authors: Andersson Jonas , Sanchez Javier , Ekdahl Kristina Nilsson , Elgue Graciela , Nilsson Bo , Larsson Rolf
Published: October 2003

Contact between blood and a biomaterial surface takes place in many applications and is known to activate the coagulation and complement systems. Heparin surface coatings have been shown to reduce blood activation upon contact with artificial surfaces. To establish the optimal heparin surface concentration, blood was incubated in a tubing loop model at 37°C. The tubing was coated with different surface concentrations of heparin and rotated at three different velocities. We demonstrate that the blood compatibility of a surface with regard to coagulation, complement, and platelet activation can be improved by increasing the heparin surface concentration in the 6–12 pmol antithrombin/cm2 concentration interval. The binding of factor H is not influenced by the increased heparin surface concentration, suggesting that this factor is not the primary regulator of complement on heparin surfaces. In addition, the heparin coating has no effect on the complement activation that occurs on gas surfaces in extracorporeal circuits. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 458–466, 2003
Human bone marrow stromal cell and ligament fibroblast responses on RGD‐modified silk fibers
Authors: Chen Jingsong , Altman Gregory H. , Karageorgiou Vassilis , Horan Rebecca , Collette Adam , Volloch Vladimir , Colabro Tara , Kaplan David L.
Published: October 2003

Adhesion, spreading, proliferation, and collagen matrix production of human bone marrow stromal cells (BMSCs) on an RGD‐modified silk matrix was studied. Anterior cruciate ligament fibroblasts (ACLFs) were used as a control cell source. Scanning electron microscopy (SEM) and MTT analyses demonstrated that the modified silk matrices support improved BMSC and ACLF attachment and show higher cell density over 14 days in culture when compared with the non‐RGD‐modified matrices. Collagen type I transcript levels (at day 7) and content (at day 14) was significantly higher on the RGD‐modified substrate than on the nonmodified group. The ability of RGD‐coupled silk matrices to support BMSC attachment, which leads to higher cell density and collagen matrix production in vitro, combined with mechanical, fatigue, and biocompatibility properties of the silk protein matrix, suggest potential for use of this biomaterial for tissue engineering. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 559–570, 2003
Novel complexation hydrogels for oral peptide delivery: In vitro evaluation of their cytocompatibility and insulin‐transport enhancing effects using Caco‐2 cell monolayers
Authors: Ichikawa Hideki , Peppas Nicholas A.
Published: October 2003

Poly[methacrylic acid‐grafted‐poly(ethylene glycol)] [P(MAA‐g‐EG)] is a complexation hydrogel molecularly designed for oral peptide delivery. In this work, the cytotoxicity and insulin‐transport enhancing effect of P(MAA‐g‐EG) microparticles on intestinal epithelial cells were evaluated using Caco‐2 cell monolayers. A series of P(MAA‐g‐EG) microparticles with different polymer compositions were prepared by a photo‐initiated free radical solution polymerization and subsequent pulverization. The hydrogel microparticles were preswollen in either Ca2+‐containing (CM+) or Ca2+‐free medium (CM−; pH 7.4) and applied to the apical side of the Caco‐2 monolayers. No significant cytotoxic effects, as determined by a calorimetric assay with P(MAA‐g‐EG) microparticles preswollen in the CM+, were observed at doses ranging from 3 to 31 mg/cm2 of cell monolayer. Transepithelial electrical resistance (TEER) measurements showed that the P(MAA‐g‐EG) microparticles induced a Ca2+ concentration‐dependent lowering in TEER values. The reduction effect in CM− media was greater than that in CM+ media (17 ± 2% reduction in CM+ and 45 ± 3% reduction in CM−, respectively). Insulin transport in the presence of the preswollen P(MAA‐g‐EG) microparticles was also strongly depended on the Ca2+ concentration in the medium. The respective estimated permeability for insulin alone and the insulin with hydrogels in CM+ were 0.77 and 1.16 × 10−8 cm/s, whereas those in CM− were 1.18 and 24.78 × 10−8 cm/s. The results demonstrate that the P(MAA‐g‐EG) hydrogel microparticles could be used as a cytocompatible carrier possessing the transport‐enhancing effect of insulin on the intestinal epithelial cells. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 609–617, 2003
Fibronectin anchorage to polymer substrates controls the initial phase of endothelial cell adhesion
Authors: Pompe Tilo , Kobe Fritz , Salchert Katrin , Jørgensen Birgitte , Oswald Joachim , Werner Carsten
Published: October 2003

Early stages of the adhesion of human endothelial cells onto a set of smooth polymer films were analyzed to reveal the modulation of cell–matrix interactions by the physicochemical constraints of predeposited fibronectin (FN). Hydrophobic and hydrophilic polymer substrates, consisting of poly(octadecene‐alt‐maleic anhydride) and poly(propene‐alt‐maleic anhydride) films, were coated with similar amounts of FN at conditions of either covalent or noncovalent immobilization. The well‐defined substrates permit variation of the anchorage of FN at invariant topography, pliability, and molecular composition. Although all of the compared FN coatings were effective in stimulating attachment of endothelial cells, the initial formation of cell–matrix adhesions was found to be controlled by the type of interaction between predeposited FN and the underlying substrate. Covalent linkage and hydrophobic interactions of the predeposited FN with the polymer films interfered with the rapid generation of focal and fibrillar adhesions. It was demonstrated that this was caused by the fact that only weakly bound FN could become readily reorganized by the adherent cells. Upon prolonged culture periods at standard cell culture conditions, secretion and deposition of organized extracellular matrix by the attached cells was found to balance out the differences of the substrates. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 647–657, 2003
Extended delivery of the antimitotic agent colchicine from thermoresponsive N‐isopropylacrylamide‐based copolymer films to human vascular smooth muscle cells
Authors: Wilson S. J. , Gorelov A. V. , Rochev Y. A. , McGillicuddy F. , Dawson K. A. , Gallagher W. M. , Keenan A. K.
Published: October 2003

The aim of this study was to establish the capacity of thermoresponsive poly(N‐isopropylacrylamide) copolymer films to deliver bioactive concentrations of an antimitotic agent to human vascular smooth muscle cells (HASMC) over an extended period of time. Copolymer films were prepared using a 50:50 (w/w) ratio of N‐isopropylacrylamide (NiPAAm) monomer to the more hydrophobic N‐tert‐butylacrylamide (NtBAAm) and loaded with the antimitotic agent colchicine (0.1 μmol per film) at room temperature. Colchicine release from films was sustained over a 14‐day period. At 24 h postloading, the concentration of colchicine in the medium overlying films was 2.12 ± 0.16 μM; this fell to 0.20 ± 0.01 μM at 7 days and decreased further to 0.12 ± 0.01 μM after 14 days. Colchicine released from copolymer films inhibited proliferation when subsequently placed on HASMC: at 0.1 μM, released colchicine reduced proliferation to 18.5 ± 0.8% of control cells (p < 0.001, n = 9). The antiproliferative effect of released colchicine was comparable to that of native colchicine, as observed in separate experiments. Furthermore, colchicine released from 50:50 polymer films inhibited the proliferation of cells grown in the same environment as the copolymer. Inhibition of cell proliferation was not due to the release of cytotoxic particles from the copolymer because medium incubated with copolymer for 5 days and then applied to HASMC did not alter cell viability. In conclusion, this study demonstrates that 50:50 NiPAAm:NtBAAm copolymers can deliver bioactive concentrations of the antimitotic agent colchicine to human vascular cells over an extended period of time. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 667–673, 2003
Immunocamouflage: Prevention of transfusion‐induced graft‐versus‐host disease via polymer grafting of donor cells
Authors: Chen Audrey M. , Scott Mark D.
Published: October 2003

Graft‐versus‐host disease (GVHD) can occur following the transfer of allogeneic lymphocytes into immunosuppressed and, in rare cases, immunocompetent recipients. The initiation of GVHD requires the allorecognition of the recipient's disparate MHC molecules by the donor T lymphocytes (T cell). Currently, GVHD is controlled by cyclosporine administration—a potent, but toxic, T‐cell suppressing agent. To determine if the nontoxic grafting of methoxypoly(ethylene glycol) (mPEG) to immunologically foreign lymphocytes could prevent allorecognition and GVHD, in vitro and in vivo murine studies were performed. In vitro studies utilizing mixed lymphocyte reactions (MLRs) demonstrate that mPEG modification effectively prevented allorecognition and subsequent T‐cell proliferation. The loss of cellular proliferation was not due to mPEG cytotoxicity but rather to the inhibition of cell–cell interactions. Flow cytometric studies showed that T‐cell and antigen‐presenting cell adhesion molecules (CD2, CD11a), signaling (CD3ϵ, T‐cell receptor), and costimulatory molecules (CD28, CD80) were efficiently immunocamouflaged by mPEG derivatization. Interestingly, upon antigenic stimulation mPEG‐modified cells demonstrate enhanced apoptosis as evidenced by DNA laddering. In vivo studies using immunocompetent and immunosuppressed mice established that mPEG modification of donor lymphocytes effectively attenuated the in vivo proliferation of donor cells and the initiation of GVHD. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 626–636, 2003
The uniqueness theorem for complex‐valued neural networks and the redundancy of the parameters
Authors: Nitta Tohru
Published: October 2003

A complex neural network is obtained from an ordinary network by extending the (real‐valued) parameters, such as the weights and the thresholds, to complex values. Applications to problems involving complex numbers, such as communications systems, are expected. This paper presents the following uniqueness theorem. When a complex function is given, the three‐layered neural network that approximates the function is uniquely determined by a certain finite group, if it is irreducible. The above finite group specifies the redundancy of the parameters in the complex neural network, but has a structure which is different from that of the real‐valued neural network. The order of the finite group is examined, and it is shown that the redundancy of the complex‐valued neural network is an exponent multiple of the redundancy of the real‐valued neural network. Analysis of the redundancy is important in the theoretical investigation of the basic characteristics of complex‐valued neural networks, such as the local minimum property. A sufficient condition is derived for the given three‐layered complex‐valued neural network to be minimal. The above results are shown, in essence, by extending the approach of Sussmann for real‐valued neural networks. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 54–62, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10363
Event‐related potentials during a target discrimination task based on texture cue
Authors: Jung Jiuk , Kobayashi Tetsuo , Li Yuwen , Kuriki Shinya
Published: October 2003

In the current research, to elucidate cerebral processes having to do with target‐ground discrimination based on a texture cue in visual stimuli, the authors investigated the relationship between the target presentation area in the visual field and the reaction time required until discrimination. Also, they simultaneously measured the event‐related potentials (ERPs) during a target discrimination task at 63 locations on the scalp and then performed a spline Laplacian analysis to examine brain activities. The results clearly showed that a significant difference occurred in the reaction time depending on the area in which the target was presented. In addition, four distinct ERP components with different latencies accompanying execution of the discrimination task were observed. The spline Laplacian analysis of the ERPs indicated that the sources of the signals of these components were in the bilateral hemispheres of the frontal, parietal, and occipital lobes. Considering the reaction time, the frontal activity observed after the latency of about 270 ms may mainly be involved in the target recognition. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 34–43, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10397
A fast morphological filtering algorithm
Authors: Hagihara Yoshihiro , Kobatake Hidefumi
Published: October 2003

This paper proposes an algorithm for fast morphological filtering using structuring elements of arbitrary two‐dimensional shape. The conventional fast morphological filtering has the constraint that the structuring element should be decomposable. The proposed method solves this problem by adding the result for the area which becomes a new object of calculation as a result of the motion of the structuring element and deleting the result for the area which goes outside the object for calculation. The proposed method has the feature that the calculation result is retained for each area deleted simultaneously from the object of calculation, and then morphological filtering is realized. Compared to the conventional fast algorithm, the constraint is reduced in the sense that undecomposable structuring elements can be used, and the method can be applied to multivalued images. Furthermore, the processing speed is independent of the density resolution of the considered image. The computation complexity is O(4rs) for the case of a circular structuring element, for example, where r is the radius of the structuring element and s is the number of pixels in the original image. This paper presents an experiment for comparison between the proposed algorithm and the conventional algorithm. The experiment reveals that the proposed algorithm is approximately twice as fast as the conventional fast method. An experiment is also performed for ring‐shaped structuring elements, to which the conventional fast method is difficult to apply, and the result is compared to the conventional method without speed improvement. The results reveal that the processing time in the method without speed improvement increases when the number of pixels in the structuring element is increased, but it does not increase in the proposed method. Thus, the proposed method is more effective when the processing time required in the conventional method is long. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 23–33, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10438
Directory‐traverse‐cost‐based skew handling for parallel data access
Authors: Watanabe Akitsugu , Yokota Haruo
Published: October 2003

Techniques for load balancing by adjusting location of data are widely studied, because they are quite influential in improving the data‐access performance and the scalability of a parallel system. To make load balancing effective, distributed directory structures, methods for evaluating loads, and distributed control mechanism for handling skews are important. In this paper, we propose a distributed algorithm to evaluate loads precisely. It counts the loads of intermediate index nodes of a distributed directory, which were ignored in previous publications. We also propose a linear‐order distributed skew‐handling algorithm adopting the proposed load evaluation algorithm. We validate the effect of our load evaluation algorithm through simulations. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 13–22, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10445
A quick search method for multimedia signals using global pruning
Authors: Kimura Akisato , Kashino Kunio , Kurozumi Takayuki , Murase Hiroshi
Published: October 2003

The authors propose a new method for quickly searching for a specific audio or video signal to be detected within a long, stored audio or video stream to determine segments that contain signals that are nearly identical to the given signal. The Time‐series Active Search (TAS) method is one of the quick search methods that have been proposed previously. This signal searching technique based on histograms extracted from the signals had implemented quick searching by local pruning, that is, omitting comparisons of segments for which searching was unnecessary based on similarities in the vicinity of the matching window. In contrast, the proposed technique implements significantly quicker searching by introducing global pruning, which looks at the entire signal time‐series according to histogram classifications based on similarities of the entire signal to eliminate segments that need not be searched, in addition to local pruning. In this paper, the authors present a detailed discussion of the relationship between the degree of global pruning and the accuracy that is guaranteed. For example, the authors showed through experiments that when 128‐dimension histograms were classified to 1024 clusters, the proposed technique achieved a search speed approximately 9 times that of TAS while preserving the same degree of accuracy. The preprocessing calculation time increased by approximately 1% of the time for playing the signal. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(13): 47–58, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10472
Speaker change detection and speaker clustering using VQ distortion measure
Authors: Nakagawa Seiichi , Mori Kazumasa
Published: October 2003

This paper addresses the problem of the detection of speaker changes and clustering speakers when no information is available regarding speaker classes or even the total number of classes. This study provides preprocessing for a method which adapts speaker information based on incremental on‐line speaker clustering. We assume that no previous information on speakers is available (no speaker model, no training phase) and that people do not speak simultaneously. The aim is to apply speaker grouping information to speaker adaptation for speech recognition.

We use Vector Quantization (VQ) distortion as the criterion. A speaker model is created from successive utterances as a codebook by a VQ algorithm, and the VQ distortion is calculated between the model and an utterance.

The results of an experiment on speaker detection and speaker clustering are presented. The speaker change detection experiment was compared with results of the Generalized Likelihood Ratio (GLR) and Bayesian Information Criterion (BIC). By using GLR and BIC, we obtained F‐measures of 75.8 and 81.4, respectively. On the other hand, we obtained an F‐measure of 84.4 by the proposed method. Furthermore, by a combination of the method with an acoustic back‐off method, we obtained a measure of 93.1 and a classification rate of 97.7%. These results show the superiority of our proposed method. Finally, we demonstrate the validity of our proposed method by experiments on speech recognition using on‐line speaker adaptation. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(13): 25–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10488
Multi‐viewpoint gesture recognition by an integrated continuous state machine
Authors: Kawashima Hiroaki , Matsuyama Takashi
Published: October 2003

This paper proposes a system architecture for event recognition that dynamically integrates information from multiple sources (e.g., multimodal data from visual and auditory sensors). The proposed system consists of multiple event classifiers called Continuous State Machines (CSMs). Each CSM has a state transition rule in a continuous state space and classifies time‐varying patterns from a different single source. Since the rule is defined as an extension of Kalman filters (i.e., the next state is deduced from the trade‐off scheme between the input data and the model's prediction), CSMs support dynamic time warping and robustness against noise. We then introduce an interaction method among CSMs to classify events from multiple sources. A continuous state space (i.e., vector space) allows us to design interaction as minimization of an energy function. This interaction enables the system to dynamically suppress unreliable classifiers and improves system reliability and the accuracy of classifying events in dynamically changing situations (e.g., the object is temporary occluded from one of multiple cameras in a gesture recognition task). Experimental results on gesture recognition by two cameras show the effectiveness of our proposed system. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 1–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10507
Contribution of vestibular (otolith) and pursuit system to stabilizing vision during sinusoidal head movement
Authors: Hikita Shinichi , Kasai Takeshi
Published: October 2003

The purpose of this study was to investigate how the vestibular (otolith) system and the visual pursuit system contribute to stabilizing vision during head translation. Eye velocity when fixating a stationary target with sinusoidal head movement (visually enhanced LVOR, VLVOR) was compared to that of smooth pursuit (SP) with the same relative target velocity (20 to 180 deg/s) as in the case of VLVOR. The eye velocity during VLVOR was much higher than that during SP with increasing relative target velocity. The gain of the SP (eye velocity/target velocity) markedly decreased with increasing stimulus frequency (0.6 → 1.2 Hz) while the gain of the VLVOR decreased only slightly. The eye velocity during VLVOR depended on the target velocity, not on the velocity of head motion, and was not associated with the state of vergence. These findings suggest that the command signal of the VLVOR is generated mostly by the visual pursuit system, and that the signal from the otolith system modifies the command signal of the pursuit system to improve the target tracking performance. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(13): 13–24, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10513
Tracking of a moving object with occlusion by using an active vision system
Authors: Hada Takaya , Miyake Tetsuo
Published: October 2003

A person can keep an object which moves according to rules in roughly the center of their field of vision at all times. Even if the object is occluded during its movement, the person can continue to track it by estimating its later motion. In this paper, this kind of human system is taken into consideration for an automatic monitoring system, and such a system is constructed using an active vision system with a pan and tilt rotary mechanism. In order to automatically monitor a scene over a wide area at high resolution, the object to be monitored must be tracked while changing the pan and tilt using active vision. The tracking principle used in this system consists of detecting a moving object and estimating its motion. Detection is accomplished by using a background subtraction method which uses a background database, and motion estimation is handled by a Kalman filter. An experiment is performed on a person in a typical room environment, and it is confirmed that the person can be tracked by the proposed system even when occluded. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(13): 92–102, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1222
Introduction of linear constraints on the weight representation of multilayer networks for generalization and application to character recognition
Authors: Ishii Masaki , Kumazawa Itsuo
Published: October 2003

In the application of layered neural networks to practical problems, a high generalization power is required. This paper discusses a method of improving the generalization power of neural networks. The knowledge of the object to be learned is assumed to include the fact that the output function of the object to be learned remains invariant for a certain range of input pattern variation. An attempt is made to improve the generalization power by reflecting this invariant property in the weighting of the neural network. It is shown for the case in which the variation of the input pattern can be represented by a linear transformation that a sufficient condition for the neural network to have such invariance is that the linear dependency constraint is introduced into the weight expression. A learning process is proposed in which this kind of constraint for the weight expression is introduced into the evaluation function as an additional term. The proposed method can be considered as a generalization of the method in which deletion learning methods such as the weight decay method and the structural learning method are included as special cases. There has been discussion of the relation between the generalization power and the VC dimension. The improvement of the proposed method can be evaluated, by introducing a linear constraint into the weight expression, based on the reduction of the VC dimension. Lastly, results are presented for an experiment in which the proposed method is applied to the character recognition problem. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 83–91, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1224
An efficient scheme for accepting recursive method calls in object‐oriented concurrent programming
Authors: Yanagawa Kazuhisa , Sato Naohito , Osawa Noritaka , Yuba Toshitsugu
Published: October 2003

With object‐oriented concurrent programming languages that perform mutual exclusion at the level of objects, deadlock can easily occur due to recursive method calls. We propose a transparent mechanism to programmers called the Key/Lock method, which enables recursive method calls by eliminating recursion deadlock. The Key/Lock method assigns keys, which are uniquely associated with exclusive methods, to messages and especially accepts messages to which these keys are appended. This technique, which can reduce the overhead that accompanies message transmission and reception compared with conventional research techniques, is particularly effective when there are numerous thread branches. We incorporated the Key/Lock method in the concurrent programming language SR and performed performance evaluations to verify the effectiveness of this technique. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(14): 101–109, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1226
Cloning and characterisation of Myf5 and MyoD orthologues in Xenopus tropicalis
Authors: Fisher M.E. , Peck W. , Branney P.A. , Pownall M.E.
Published: October 2003

The myogenic regulatory genes MyoD and Myf5 are members of the bHLH transcription factor superfamily. These genes are expressed as an early response to mesoderm induction in the frog Xenopus laevis. This paper describes our work to determine the conservation of sequence, expression and function of the early myogenic genes in the closely related diploid species Xenopus tropicalis. To this end we have cloned and sequenced Xenopus tropicalis homologues of Myf5 and MyoD and found a high degree of conservation in the nucleotide and amino acid sequences of both genes. The expression of Myf5 and MyoD in Xenopus tropicalis was assayed by in situ hybridisation and the expression patterns were found to be similar to those described in Xenopus laevis. The bHLH myogenic regulatory factors are known to be able to auto‐ and cross‐activate expression of the myogenic genes. Interestingly, however, we found that while injection of mRNA coding for either Xenopus tropicalis myf5 (Xtmyf5) or Xenopus tropicalis myoD (XtmyoD) was capable of activating expression of the endogenous Xenopus laevis myoD (XmyoD) and cardiac actin genes, neither was capable of inducing expression from the endogenous Xenopus laevis (Xmyf5) gene.
Programmed cell death protein 4 (pdcd4): A novel target for antineoplastic therapy?
Authors: Lankat‐Buttgereit Brigitte , Göke Rüdiger
Published: October 2003

Pdcd4 is a novel gene first identified as a differentially expressed protein during apoptosis. In the meantime not only the impact of Pdcd4 in programmed cell death but also an implication in transformation suppression by inhibition of protein translation is discussed. These features implicate a potential value of Pdcd4 as a molecular target in cancer therapy. This review summarizes the current knowledge about expression, structure and function of Pdcd4.
Internodes can nearly double in length with gradual elongation of the adult rat sciatic nerve
Authors: Abe Ichiro , Ochiai Naoyuki , Ichimura Harumitsu , Tsujino Akihito , Sun Jia , Hara Yuki
Published: October 2003

Leg lengthening procedure is used increasingly to treat leg length discrepancy and some forms of dwarfism. We investigated adaptation in rat sciatic nerve to the gradual nerve elongation that occurs with leg lengthening. Indirect nerve elongation was produced by leg lengthening by a total of 15, 30, 45, or 70 mm at a rate of 1 mm/day. One day after leg lengthening completion, transverse semithin sections of sciatic nerve were prepared and examined; a teased‐fiber study also was performed. Elongation decreased axon diameter, but not significantly. In teased‐fiber preparations, internodal length was increased by 93%, and the longest internode measured 3000 μm after leg lengthening by 70 mm. Slopes of fiber diameter–internodal length regression lines increased with increasing elongation. Paranodal demyelination caused by nerve elongation worsened as elongation increased, stimulating remyelination (i.e., intercalation of a segment). Only 0.8% of axons showed degeneration in the group with 70 mm of elongation. We concluded that adult rat sciatic nerve can adapt itself to leg lengthening procedure with even doubling internodal length. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Observations concerning the quinol oxidation site of the cytochrome bc1 complex
Authors: Berry Edward A. , Huang Li-shar
Published: October 2003

A direct hydrogen bond between ubiquinone/quinol bound at the QO site and a cluster‐ligand histidine of the iron–sulfur protein (ISP) is described as a major determining factor explaining much experimental data on position of the ISP ectodomain, electron paramagnetic resonance (EPR) lineshape and midpoint potential of the iron–sulfur cluster, and the mechanism of the bifurcated electron transfer from ubiquinol to the high and low potential chains of the bc
1 complex.