Miscibility and specific interactions in polyacrylonitrile/ poly(p‐vinylphenol) blends

A rare miscible polyacrylonitrile (PAN) blend system is reported. PAN is miscible with poly(p‐vinylphenol) (PVPh) as shown by thermal and spectroscopic studies. A single glass transition temperature was found in each blend. Infrared spectroscopic studies showed that the hydroxyl band of PVPh and the cyano band of PAN shifted to lower frequencies upon blending, showing the existence of specific interactions between the two polymers. The involvement of cyano groups in specific interactions was further evidenced by the development of a high‐binding‐energy N1s peak in each blend from X‐ray photoelectron spectroscopic studies.     

A numerical study of the effect of free surface and water depth on the stability of wakes: use of GDQ formulation

The instability character of a wake in the presence of a free surface is examined by a recently developed GDQ (generalized differential quadrature) numerical method. It is shown that at low Froude number the wake near a free surface is convectively unstable, but when the Froude number is increased further it becomes absolutely unstable. The effect of water depth on the stability property of the wake flow is also investigated. It is found that the influence of water depth on the critical point of instability is limited to at most 20% variation in the complex frequency, while the change in temporal growth rate is also limited to about 20%. © 1997 John Wiley & Sons, Ltd.     

One-diregular subgraphs in semicomplete multipartite digraphs

The problem of finding necessary and sufficient conditions for a semicomplete multipartite digraph (SMD) to be Hamiltonian, seems to be both very interesting and difficult. Bang-Jensen, Gutin and Huang ( Discrete Math to appear) proved a sufficient condition for a SMD to be Hamiltonian. A strengthening of this condition, shown in this paper, allows us to prove the following three results. We prove that every k-strong SMD with at most k-vertices in each color class is Hamiltonian and every k-strong SMD has a cycle through any set of k vertices. These two statements were stated as conjectures by Volkmann (L. Volkmann, a talk at the second Krakw Conference of Graph Theory (1994)) and Bang-Jensen, Gutin, and Yeo (J. Bang-Jensen, G. Gutin, and A. Yeo, On k-strong and k-cyclic digraphs, submitted), respectively. We also prove that every diregular SMD is Hamiltonian, which was conjectured in a weaker form by Zhang (C.-Q. Zhang, Hamilton paths in multipartite oriented graphs, Ann Discrete Math. 41 (1989), 499–581). © 1997 John Wiley & Sons, Inc.     

Selective adhesion of intestinal epithelial cells on patterned films with amine functionalities formed by plasma enhanced chemical vapor deposition

Control of cell adhesion to surfaces is important to develop analytical tools in the areas of biomedical engineering. To control cell adhesiveness of the surface, we constructed a variety of plasma polymerized hexamethyldisiloxane (PPHMDSO) thin films deposited at the plasma power range of 10-100 W by plasma enhanced chemical vapor deposition (PECVD). The PPHMDSO film that was formed at 10 W was revealed to be resistant to cell adhesion. The resistance to cell adhesion is closely related to physicochemical properties of the film. Atomic force microscopic data show an increase in surface roughness from 0.52 nm to 0.74 nm with increasing plasma power. From Fourier transform infrared (FT-IR) absorption spectroscopy data, it was also determined that the methyl (-CH₃) peak intensity increases with increasing plasma power, whereas the hydroxyl (-OH) peak decreases. X-ray photoelectron spectroscopy data reveal an increase in C-O bonding with increasing plasma power. These results suggest that C-O bonding and hydroxyl (-OH) and methyl (-CH₃) functional groups play a critical part in cell adhesion. Furthermore, to enhance a diversity of film surface, we accumulated the patterned plasma polymerized ethylenediamine (PPEDA) thin film on the top of the PPHMDSO thin film. The PPEDA film is established to be strongly cell-adherent. This patterned two-layer film stacking method can be used to form the selectively limited cell-adhesive PPEDA spots over the adhesion-resistant surface.     

Small degree out‐branchings

Using a suitable orientation, we give a short proof of a strengthening of a result of Czumaj and Strothmann 4 : Every 2‐edge‐connected graph G contains a spanning tree T with the property that for every vertex v. As an analogue of this result in the directed case, we prove that every 2‐arc‐strong digraph D has an out‐branching B such that . A corollary of this is that every k‐arc‐strong digraph D has an out‐branching B such that , where . We conjecture that in this case would be the right (and best possible) answer. If true, this would again imply a strengthening of a result from 4 concerning spanning trees with small degrees in k‐connected graphs when k ≥ 2. We prove that for acyclic digraphs the existence of an out‐branching satisfying prescribed bounds on the out‐degrees of each vertex can be checked in polynomial time. A corollary of this is that the existence of arc‐disjoint branchings , , where the first is an out‐branching rooted at s and the second an in‐branching rooted at t, can be checked in polynomial time for the class of acyclic digraphs © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 297–307, 2003     

The intramolecular Baylis-Hillman reaction: easy preparation of versatile substrates, facile reactions, and synthetic applications

We have developed a general and highly efficient method for the preparation of diverse [small omega]-formyl-[small alpha],[small beta]-unsaturated carbonyl compounds and optimized the conditions for the intramolecular Baylis-Hillman reactions of these compounds to provide various biologically important polycyclic compounds.