bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tubular cationized pullulan hydrogels as local reservoirs for plasmid DNA
Authors: San Juan Aurélie , Ducrocq Grégory , Hlawaty Hanna , Bataille Isabelle , Guénin Erwann , Letourneur Didier , Feldman Laurent J. 
Published: June 2007

AbstractIn the present study, we measured the ability of various cationized pullulan tubular hydrogels to retain plasmid DNA, and tested the ability of retained plasmid DNA to transfect vascular smooth muscle cells (VSMCs). Cationized pullulans were obtained by grafting at different charge densities ethylamine (EA) or diethylaminoethylamine (DEAE) on the pullulan backbone. Polymers were characterized by elemental analysis, acid‐base titration, size exclusion chromatography, Fourier‐transform infrared spectroscopy, and proton nuclear magnetic resonance. The complexation of cationized pullulans in solution with plasmid DNA was evidenced by fluorescence quenching with PicoGreen. Cationized pullulans were then chemically crosslinked with phosphorus oxychloride to obtain tubular cationized pullulan hydrogels. Native pullulan tubes did not retain loaded plasmid DNA. In contrast, the ability of cationized pullulan tubes to retain plasmid DNA was dependent on both the amine content and the type of amine. The functional integrity of plasmid DNA in cationized pullulan tubes was demonstrated by in vitro transfection of VSMCs. Hence, cationized pullulan hydrogels can be designed as tubular structures with high affinity for plasmid DNA, which may provide new biomaterials to enhance the efficiency of local arterial gene transfer strategies. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
The response of osteoblast‐like cells towards collagen type I coating immobilized by p‐nitrophenylchloroformate to titanium
Authors: van den Dolder Juliette , Jansen John A. 
Published: June 2007

AbstractThe scaffold surface composition can be altered by the use of surface coatings. The use of thin coatings will give special surface properties, while the bulk properties of the scaffold are preserved. Collagen type I is known to play an important role during cell adhesion as well as osteoblast differentiation. A common way to coat surfaces is the adsorption method. An alternative way is the use of a protein immobilization method like p‐nitrophenyl chloroformate. In this study, we investigated the effect of a collagen type I coating and p‐nitrophenyl chloroformate as a protein immobilization method on osteoblast adhesion, proliferation, and differentiation. Titanium fiber meshes were treated with sodium hydroxide (NaOH), followed by p‐nitrophenyl chloroformate, and coated with collagen type I. Osteoblast‐like cells were seeded into the meshes and cultured for 24 days. The cell attachment, proliferation, and differentiation were measured by using Live and Dead assay, cell counting, DNA analysis, alkaline phosphatase activity assay, calcium content measurement, Real Time PCR (QPCR), and scanning electron microscopy (SEM). Results demonstrated that initially less cells were attached to the covalently bounded collagen meshes (NPC‐Col) compared with titanium as control (Ti) and adsorbed collagen meshes (ABS‐Col). Further, a decreased growth curve of cells cultured on the NPC‐Col meshes was observed in comparison with Ti and ABS‐Col meshes. The calcium measurements and SEM pictures revealed that all three surfaces showed differentiation of osteoblast‐like cells after 8–24 days. On the basis of our results, we conclude that initially less cells were attached to the NPC‐Col meshes and that they had a decreased proliferation rate. Further, we conclude that an adsorbed collagen type I coating stimulated the osteoblastic differentiation of rat bone marrow cells. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Antimicrobial polyethylene with controlled copper release
Authors: Zhang Wei , Zhang Yihe , Ji Junhui , Yan Qing , Huang Anping , Chu Paul K. 
Published: June 2007

AbstractGood antiinfection properties of medical polymers, especially those used in artificial organs, are crucial to the minimization of microbial attack in nosocomial treatments. However, medical polymers fabricated by conventional methods usually have unstable and short‐lived antimicrobial effects because of unsteady out‐diffusion of the antibacterial species from the organic matrix. Here, we introduce a dual plasma implantation process to enhance the properties. An inorganic antibacterial element, copper, is introduced into a medical polymer, polyethylene (PE), by means of copper plasma immersion ion implantation (PIII) and a subsequent nitrogen PIII process is used to regulate the release of the implanted Cu. X‐ray photoelectron spectroscopy and transmission electron microscopy reveal that a relatively large amount of copper of about 11% is implanted into PE to a depth of several hundred nanometers. Chemical analyses confirm that the implanted Cu does not bond with the polymer matrix. However, the N2 plasma treatment produces various functional bonds such as CN, and CN which exert appreciable influence on regulating the out‐diffusion rate of copper. The large amount of embedded Cu, coupled with controlled release of the element to the surface, gives rise to excellent and long‐lasting surface antibacterial properties of the plasma‐treated polymer. The capability of controlling the release and storing the antibacterial reagent in a buried layer leads to better antimicrobial polymeric materials for medicine. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007
Sensate scaffolds coupled to telemetry can monitor in vivo loading from within a joint over extended periods of time
Authors: Geffre Chris P. , Bliss Cody L. , Szivek John A. , DeYoung Donald W. , Ruth John T. , Margolis David S. 
Published: June 2007

AbstractPolymer scaffolds have been used as a tool to provide growth and integration of engineered tissue substrates to repair damaged tissues in many organ systems including articular cartilage. Previous work has shown that “sensate” scaffolds, with integrated strain gauges have the potential for use as both a delivery vehicle for engineered cartilage as well as a device that can measure real time, in vivo joint loading. The purpose of this study was to use an implanted subminiature telemetry system to collect in vivo joint loading measurements over an extended period following placement of a “sensate” scaffold. Measurements were collected from seven of nine sensors that were implanted into the stifles of three canines. The limb loading rates and load distribution through gait were dependent on stride time but did not vary with time post op. The peak loads were not dependent on stride time but significantly increased with time post op. This demonstrated that peak loading measured with “sensate” scaffolds can be used to monitor healing. The portability of the “sensate” scaffolds coupled to telemetry systems highlights the potential use of this system in a clinical research setting to gather important information to improve tissue engineering and rehabilitation regimens. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008
Induction of Id2 expression by cardiac transcription factors GATA4 and Nkx2.5
Authors: Lim Joong‐Yeon , Kim Won Ho , Kim Joon , Park Sang Ick 
Published: June 2007

AbstractInhibitor of differentiation/DNA binding (Id) proteins function as a regulator of helix‐loop‐helix proteins participating in cell lineage commitment and differentiation. Here, we observed a marked induction of Id2 during cardiomyocyte differentiation from P19CL6 murine embryonic teratocarcinoma stem cells, prompting us to investigate the upstream regulatory mechanism of Id2 induction. Computer analysis of Id2 promoter and subsequent electrophoretic mobility shift assay revealed several binding sites for GATA4 and Nkx2.5 within the Id2 promoter. By further deletion and mutation analysis of the respective binding site, we identified that two motifs located at −497/−502 and −264/−270 were functionally important for Id2 promoter activation by GATA4 and Nkx2.5, respectively. Overexpression of GATA4 and/or Nkx2.5 induced not only Id2 promoter activity but also Id2 protein expression. Additionally, Id proteins significantly inhibit the GATA4 and Nkx2.5‐dependent transcription, suggesting Id proteins may play a regulatory role in cardiogenesis. Collectively, our results demonstrate that GATA4 and Nkx2.5 could be one of the upstream regulators of Id2. J. Cell. Biochem. 103: 182–194, 2008. © 2007 Wiley‐Liss, Inc.
Liver regeneration
Authors: Michalopoulos George K. 
Published: June 2007

AbstractLiver regeneration after partial hepatectomy is a very complex and well‐orchestrated phenomenon. It is carried out by the participation of all mature liver cell types. The process is associated with signaling cascades involving growth factors, cytokines, matrix remodeling, and several feedbacks of stimulation and inhibition of growth related signals. Liver manages to restore any lost mass and adjust its size to that of the organism, while at the same time providing full support for body homeostasis during the entire regenerative process. In situations when hepatocytes or biliary cells are blocked from regeneration, these cell types can function as facultative stem cells for each other. J. Cell. Physiol. 213: 286–300, 2007. © 2007 Wiley‐Liss, Inc.
Circular‐arc digraphs: A characterization
Authors: Sen M. , Das S. , West Douglas B. 
Published: June 2007

AbstractGiven a family F of ordered pairs of sets {(Su,Tu): u ϵ V}, the intersection digraph of F is the digraph with vertices V defined by uv ϵ E(D) if Su ≠ Tv Ø. Interval digraphs are intersection digraphs of families in which every set is an interval, and were characterized in a previous paper by conditions on the adjacency matrix. In this paper, another such condition leads to an adjacency matrix characterization of circular‐arc digraphs, the intersection digraphs of families in which every set is an arc of a circle.
Domination in colored complete graphs
Authors: Erdös P. , Faudree R. , Gyárfás A. , Schelp R. H. 
Published: June 2007

AbstractWe prove the following conjecture of Erdös and Hajnal: For any fixed positive integer t and for any 2‐coloring of the edges of kn, there exists X ⊂ v(KN) such that |≦| and X monochromatically dominates all but at most n/2t vertices of Kn. In fact, X can be constructed by a fast greedy algorithm.
Regular graphs having the same path layer matrix
Authors: Dobrynin A. A. 
Published: June 2007

AbstractThe path layer matrix (or path degree sequence) of a graph G contains quantitative information about all paths in G. Elements (i,j) in this matrix is the number of simple paths in G having initial vertex v, and length j. For every r ≥ 3, pairs of nonisomorphic r‐regular graphs having the same path layer matrix are presented.
Hamilton cycles and closed trails in iterated line graphs
Authors: Catlin Paul A. , Janakiraman Iqbalunnisa T. N. , Srinivasan N. 
Published: June 2007

AbstractLet G be an undirected connected graph that is not a path. We define h(G) (respectively, s(G)) to be the least integer m such that the iterated line graph Lm(G) has a Hamiltonian cycle (respectively, a spanning closed trail). To obtain upper bounds on h(G) and s(G), we characterize the least integer m such that Lm(G) has a connected subgraph H, in which each edge of H is in a 3‐cycle and V(H) contains all vertices of degree not 2 in Lm(G). We characterize the graphs G such that h(G) — 1 (respectively, s(G)) is greater than the radius of G.
Bounds for the crossing number of the N‐cube
Authors: Madej Tom 
Published: June 2007

AbstractLet Qn denote the n‐dimensional hypercube. In this paper we derive upper and lower bounds for the crossing number v(Qn), i.e., the minimum number of edge‐crossings in any planar drawing of Qn. The upper bound is close to a result conjectured by Eggleton and Guy and the lower bound is a significant improvement over what was previously known. Let N = 2n be the number of vertices of Qn. We show that v(Qn) < 1/6N2. For the lower bound we prove that v(Qn) = Ω(N(lg N)c lg lg N), where c > 0 is a constant and lg is the logarithm base 2. The best lower bound using standard arguments is v(Qn) = Ω(N(lg N)2). The lower bound is obtained by constructing a large family of homeomorphs of a subcube with the property that no given pair of edges can appear in more than a constant number of the homeomorphs.
Improved lower bounds on k‐independence
Authors: Caro Yair , Tuza Zsolt 
Published: June 2007

AbstractA vertex set Y in a (hyper)graph is called k‐independent if in the sub(hyper)‐graph induced by Y every vertex is incident to less than k edges. We prove a lower bound for the maximum cardinality of a k‐independent set—in terms of degree sequences—which strengthens and generalizes several previously known results, including Turán's theorem.
Local extrema in genus‐stratified graphs
Authors: Gross Jonathan L. , Rieper Robert G. 
Published: June 2007

AbstractBeyond the obvious organization of all the orientable imbeddings of a graph according to the genus of the imbedding surface, there are several seemingly natural ways to ascribe proximity of imbeddings. One of these is to stipulate that two imbeddings are adjacent if one imbedding can be obtained from the other by moving one end of an edge in its rotation. If one associates “altitude” with genus, then one might hope to construct algorithms for minimum genus and maximum genus by descent and ascent, respectively. This investigation of the structure of the system of orientable graph imbeddings reveals that although there may occur arbitrarily deep traps among the local minima, there cannot exist any strict local maxima. These new discoveries seem consistent with a known contrast in the computational complexity of the maximum genus and minimum genus problems. That is, whereas Furst, Gross, and McGeoch have devised a polynomial‐time algorithm to find the maximum genus of an arbitrary graph, Thomassen has proved that the problem of finding the minimum genus is NP‐complete.
Bounding the number of embeddings of 5‐connected projective‐planar graphs
Authors: Kitakubo Shigeru 
Published: June 2007

AbstractA graph is said to be projective‐planar if it is nonplanar and is embeddable in a projective plane. In this paper we show that the numbers of projectiveplanar embeddings (up to equivalence) of all 5‐connected graphs have an upper bound c(⩽120).
The structure and maximum number of maximum independent sets in trees
Authors: Zito Jennifer 
Published: June 2007

AbstractA subset of vertices is a maximum independent set if no two of the vertices are joined by an edge and the subset has maximum cardinality. in this paper we answer a question posed by Herb Wilf. We show that the greatest number of maximum independent sets for a tree of n vertices ismagnified imageWe give the families of trees on which these maxima are achieved.Proving which trees are extremal depends upon the structure of maximum independent sets in trees. This structure is described in terms of adjacency rules between three types of vertices, those which are in all, no, or some maximum independent sets. We show that vertices that are in some but not all maximum independent sets of the tree are joined in pairs by the α‐critical edges (edges whose removal increases the size of a maximum independent set). The number of maximum independent sets is shown to depend on the structure within the tree of the α‐critical edges.
On the structure of unbreakable graphs
Authors: Olariu Stephan 
Published: June 2007

AbstractA nonempty set C of vertices is a star‐cutset in a graph G if G – C is disconnected and some vertex in C is adjacent to all the remaining vertices in C. Vašek Chvátal proposed to call a graph G unbreakable if neither G nor its complement G has a star‐cutset. A path with four vertices and three edges will be termed a P4. An edge uv of a graph G is called a wing, if for some vertices x, y, {u,v,x,y} induces a P4 in G. We define recursively the coercion class Cuv of a wing uv as follows:
uv ∈ Cuv, and
if xy ∈ Cuv and xy, x'y' are wings of a same P4 in G, then x'y' ∈ Cuv.
The purpose of this work is to present new results concerning unbreakable graphs, using the notion of coercion class. These results include a theorem asserting that every unbreakable graph contains at most two distinct coercion classes and a structure theorem for those unbreakable graphs that contain precisely two coercion classes. These results generalize several previously known results about unbreakable graphs.
Do 3n − 5 edges force a subdivision of K5?
Authors: Kézdy André E. , McGuinness Patrick J. 
Published: June 2007

AbstractA conjecture of Dirac states that every simple graph with n vertices and 3n − 5 edges must contain a subdivision of K5. We prove that a topologically minimal counterexample is 5‐connected, and that no minor‐minimal counterexample contains K4 – e. Consequently, Dirac's conjecture holds for all graphs that can be embedded in a surface with Euler characteristic at least − 2.
20‐relative neighborhood graphs are hamiltonian
Authors: Chang M. S. , Tang C. Y. , Lee R. C. T. 
Published: June 2007

AbstractFor any two points p and q in the Euclidean plane, define LUNpq = {v|v ∈ R2, dpv < dpq and dqv < dpq}, where duv is the Euclidean distance between two points u and v. Given a set of points V in the plane, let LUNpq(V) = V ∩ LUNpq. Toussaint defined the relative neighborhood graph of V, denoted by RNG(V) or simply RNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of RNG(V) if and only if LUNpq (V) = ϕ. The relative neighborhood graph has several applications in pattern recognition that have been studied by Toussaint. We shall generalize the idea of RNG to define the k‐relative neighborhood graph of V, denoted by kRNG(V) or simply kRNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of kRNG(V) if and only if | LUNpq(V) | < k, for some fixed positive number k. It can be shown that the number of edges of a kRNG is less than O(kn). Also, a kRNG can be constructed in O(kn2) time. Let Ec = {epq| p ∈ V and q ∈ V}. Then Gc = (V,Ec) is a complete graph. For any subset F of Ec, define the maximum distance of F as maxepq∈Fdpq. A Euclidean bottleneck Hamiltonian cycle is a Hamiltonian cycle in graph Gc whose maximum distance is the minimum among all Hamiltonian cycles in graph Gc. We shall prove that there exists a Euclidean bottleneck Hamiltonian cycle which is a subgraph of 20RNG(V). Hence, 20RNGs are Hamiltonian.
Vertex‐switching, isomorphism, and pseudosimilarity
Authors: Ellingham M. N. 
Published: June 2007

AbstractA vertex‐switching Gs of a graph G is obtained by deleting from G all edges of G with exactly one end in the set of vertices S, and then adding to G all edges of the complement of G with exactly one end in S. We characterize the situations in which Gs is isomorphic to G, a result with application to the vertex‐switching reconstruction problem. We use these results to construct pairs of vertex‐switching pseudosimilar vertices, nonsimilar vertices u and v in a graph G with G{u} isomorphic to G{v}. We show that every such pair can be constructed by our methods.
Some extremal results in cochromatic and dichromatic theory
Authors: Erdös Paul , Gimbel John , Kratsch Dieter 
Published: June 2007

AbstractFor a graph G, the cochromatic number of G, denoted z(G), is the least m for which there is a partition of the vertex set of G having order m. where each part induces a complete or empty graph.We show that if {Gn} is a family of graphs where Gn has o(n2 log2(n)) edges, then z(Gn) = o(n). We turn our attention to dichromatic numbers. Given a digraph D, the dichromatic number of D is the minimum number of parts the vertex set of D must be partitioned into so that each part induces an acyclic digraph. Given an (undirected) graph G, the dichromatic number of G, denoted d(G), is the maximum dichromatic number of all orientations of G. Let m be an integer; by d(m) we mean the minimum size of all graphs G where d(G) = m. We show that d(m) = θ(m2 ln2(m)).
On ramsey‐tuŕan numbers for 3‐graphs
Authors: Sidorenko A. F. 
Published: June 2007

AbstractFor every r‐graph G let π(G) be the minimal real number ϵ such that for every ϵ < 0 and n ϵ n0(λ, G) every R‐graph H with n vertices and more than (π + ϵ)(nr) edges contains a copy of G. The real number λ(G) is defined in the same way, adding the constraint that all independent sets of vertices in H have size 0(n). Erdös and Sós asked whether there exist r‐graphs G with π(G) < λ(G) < 0. Frankl and Rödl proved that there exist infinitely many such r‐graphs for every r ≦ 3. However, no example of an r‐graph with above property was known. We construct an example of such a 3‐graph with 7 vertices and 9 edges.
Projective‐planar graphs with even duals
Authors: Negami Seiya 
Published: June 2007

AbstractLet G be a connected graph which is projective‐planar but is not planar. It will be shown that G can be embedded in the projective plane so that it has only even faces if and only if either G is bipartite or its canonical bipartite covering is planar and that such an embedding is unique if G is 3‐connected.
Characterizing vertex‐transitive pq‐graphs with an imprimitive automorphism subgroup
Authors: Marušič Dragan , Scapellato Raffaele 
Published: June 2007

AbstractVertex‐transitive graphs with pq vertices, where p and q are primes, having an imprimitive subgroup of automorphisms, are characterized. © 1992 John Wiley & Sons, Inc.
A characterization of Hamiltonian prisms
Authors: Paulraja P. 
Published: June 2007

AbstractA characterization is established for a graph G to have a Hamilton cycle in G × K2, the prism over G. Moreover, it is shown that every 3‐connected graph has a 2‐connected spanning bipartite subgraph. Using this result, the existence of a Hamilton cycle in the prism over every 3‐connected cubic graph is established. Further, the existence of a Hamilton cycle in the prism over a cubic 2‐connected graph is also discussed. Earlier results in this direction are shown to be particular cases of the results obtained here. © 1993 John Wiley & Sons, Inc.
Constraints on the number of maximal independent sets in graphs
Authors: Liu Jiuqiang 
Published: June 2007

AbstractA maximal independent set of a graph G is an independent set that is not contained properly in any other independent set of G. Let i(G) denote the number of maximal independent sets of G. Here, we prove two conjectures, suggested by P. Erdös, that the maximum number of maximal independent sets among all graphs of order n in a family Φ is o(3n/3) if Φ is either a family of connected graphs such that the largest value of maximum degrees among all graphs of order n in Φ is o(n) or a family of graphs such that the approaches infinity as n → ∞.
Connectivity properties of locally semicomplete digraphs
Authors: Guo Yubao , Volkmann Lutz 
Published: June 2007

AbstractIt is shown that every k‐connected locally semicomplete digraph D with minimum outdegree at least 2k and minimum indegree at least 2k − 2 has at least m = max{2, k} vertices x1, x2, ⃛, xm such that D − xi is k‐connected for i = 1, 2, ⃛, m.
The w‐median of a connected strongly chordal graph
Authors: Lee Hai‐Yen , Chang Gerard J. 
Published: June 2007

AbstractSuppose G = (V, E) is a graph in which every vertex x has a non‐negative real number w(x) as its weight. The w‐distance sum of a vertex y is DG, w(y) = σx≅v d(y, x)w(x). The w‐median of G is the set of all vertices y with minimum w‐distance sum DG,w(y). This paper shows that the w‐median of a connected strongly chordal graph G is a clique when w(x) is positive for all vertices x in G.