On confluence versus strong confluence for one-rule trace-rewriting systems

Examples of one-rule trace-rewriting systems are given that are confluent but not strongly confluent. This contrasts with the situation for one-rule string-rewriting systems as well as with the situation for one-rule commutative string-rewriting systems.     

Head-to-head polymers: 33. Bromination of cis-1,4-polybutadiene to head-to-head poly(vinyl bromide)

Cis-1,4-polybutadiene (PB) in a 0.5% solution of a solvent mixture of dichloromethane and 1,2-dibromoethane or tetrahydrofuran was quantitatively brominated with elemental bromine at 0°C under careful exclusion of oxygen to head-to-head poly(vinyl bromide). Partially brominated PB has a structure of random or block sequences of butadiene units in the polymer depending on the bromination solvent but shows no stereospecificity in the CHBrCHBr-dyads. Partially brominated PB with block structure showed a microphase-separated morphology over a wide range of composition. Microphase separation is less pronounced for the more random structure of butadiene units. I.r and ¹³C n.m.r. spectroscopy of the partially brominated PB was used to follow the progress of the bromination.     

New developments in speciality polymers: polymeric stabilizers

Many new speciality polymers have been developed in the last few years. In this paper polymeric stabilizers (antioxidants, flame retardants and ultraviolet stabilizers) will be discussed. Polymeric antioxidants of the hindered-phenol type, copolymers of 2,6-ditertiarybutyl-4-vinyl(or isopropenyl)phenol with styrene, methyl methacrylate, or more importantly butadiene or isoprene have been prepared; hydrogenation of the latter copolymers gave copolymers of the two polymerizable phenolic antioxidants with ethylene or ethylene/propylene. The polymeric antioxidants have been blended with diene polymers and selected polyolefins and have improved the long-term oxidative stability of these polymers. Polymeric flame retardants have been prepared by copolymerizing styrene and/or acrylonitrile with acrylates and methacrylates of aliphatic bromine-containing alcohols or bromine-containing phenols. Polymers with polymer-bound flame retardants have a higher limiting oxygen index compared with the original polymer. A new class of polymerizable ultraviolet stabilizers has also been developed; these stabilizers are styryl, α-methylstyryl, acryloyl and methacryloyl derivatives of 2(2-hydroxyphenyl)2H-benzotriazoles. These monomers have been copolymerized with styrene, acrylates and methacrylates. 2(2-Hydroxyphenyl)2H-benzotriazoles substituted in the 4 position of the benzotriazole ring with hydroxyl, acetoxy or carboxyl groups suitable for incorporation into polyesters, polycarbonates, polyamides and epoxy resins have also been synthesized. All 2(2-hydroxyphenyl)2H-benzotriazole ultraviolet absorbers and the polymers into which they are incorporated have high light absorbency with γ_max between 330 and 350 nm and extinction coefficients in some cases as high as 4.5 × 10⁴ 1 mol^?1 cm^?1.     

The “burning ship” and its quasi-Julia sets

By manipulating the imaginary part of the complex-analytic quadratic equation, we obtain, by iteration, a set that we call the “burning ship” because of its appearance. It is an analogue to the Mandelbrot set (M-set). Its nonanalytic “quasi”-Julia sets yield surprizing graphical shapes.     

Proton exchange membranes by radiation grafting of styrene onto fep films. III. Structural investigation

Structural investigation on proton-exchange membranes, obtained by the radiation grafting of styrene onto FEP films and subsequent sulfonation, was carried out by differential scanning calorimetry. The membrane crystallinity was found to show a decreasing trend with increasing degree of grafting. The melting temperature of all the membranes also showed a slight decrease as compared to the ungrafted FEP. The results have been explained in terms of the cumulative effect of the decrease in the crystalline/amorphous ratio by the incorporation of amorphous polystyrene grafts and of disruption of spherulitic crystallites of the FEP component in the membranes. The glass transition temperature of the membranes with different water contents was also evaluated. A correlation of the glass transition temperature with the residual water in dried membranes was established. © 1994 John Wiley & Sons, Inc.     

Ein elektrisches Me\verfahren zur Integral- und Mittelwertbestimmung

Zusammenfassung Die beschriebene Me\anordnung gestattet, den Integralwert eines beliebigen. Kurvenverlaufes zu messen. Die für die jeweilige Ordinate der Kurven ma\gebenden Grö\en, z. B. Druck, Geschwindigkeit usw. werden vermittels eines verÄnderlichen Widerstandes in verhÄltnisgleiche Leitwerte umgesetzt. Der jeweilige Leitwert des Widerstandes ist bestimmend für die Geschwindigkeit der Teilentladung eines Kondensators. Die Summe der aufeinanderfolgenden Ladungs- bzw. Entladungsstö\e innerhalb einer gewissen Zeit gibt ein Ma\ für den Integralwert des Vorganges wÄhrend derselben Zeit. Die mittlere sekundliche Wechselzahl bestimmt den Mittelwert des Verlaufes. Die Anlegung einer zeitabhÄngigen Betriebsspannung an den Kondensatorkreis ermöglicht eine Kompensation des ursprünglich zeitbedingten Charakters der Ergebnisse und lÄ\t sonach auch die Integration zeitunabhÄngiger KurvenverlÄufe zu. Eine überlagung der resultierenden Frequenz bzw. Spannung mit anderen Einflu\grö\en bietet die Möglichkeit der Messung von VorgÄngen, die von mehreren Faktoren bestimmt sind.     

Increased expression of CD80, CD86 and CD70 on T cells from HIV-infected individuals upon activation in vitro: regulation by CD4+ T cells

T cells express CD28 and CD27 which transduce co-stimulatory signals after interaction with their ligands on antigen-presenting cells (APC). These ligands, CD80, CD86 and CD70, are also expressed to some extent on activated T cells. Here, we show that in human immunodeficiency virus (HIV)-infected individuals, CD28 and CD27 expression is decreased on CD8+ T cells. On the other hand, T cell stimulation in vitro induced high CD80, CD86 and CD70 expression on T cells from HIV-infected individuals. It appeared that an inverted CD4:CD8 T cell ratio could explain this enhanced expression of co-stimulatory ligands. Indeed, high expression levels of CD80, CD86 and CD70 were found on activated CD8+ T cells from HIV- individuals cultured in the absence of CD4+ T cells. Addition of CD4+ T cells prevented this up-regulation. However, in HIV-infected individuals, addition of excess autologous or healthy control CD4+ T cells did not completely counteract up-regulation of co-stimulatory ligand expression on CD8+ T cells. Thus, to some extent, CD8+ T cells in HIV-infected individuals appeared to be refractory to CD4+ T cell-mediated regulation of ligand expression in vitro. Activated T cells from HIV-infected individuals and activated CD8+ T cells from healthy controls were able to act as accessory cells in CD3-induced T cell proliferation, which was dependent on cell-cell contact. Thus, we showed that T cells from HIV-infected individuals express enhanced levels of co-stimulatory ligands upon activation, which provides them with accessory cell properties. Enhanced stimulatory potential of these nonprofessional APC may contribute to persistently high levels of immune activation in HIV infection related to disease progression.     

Functional polymers

Summary Polymeric antioxidants prepared from 2,6-di-tertiary-butyl-4-vinyl (4-lsopropenyl)phenol and butadiene or isoprene, and their hydrogenated products (6-8 mol % of phenolic AO in the polymer) were tested by oxygen uptake studies for their effectiveness as antioxidants for polyolefins and polydienes. The polymeric antioxidants seem to be slightly less effective in short-term protection against oxidation at 150° C as compared to low molecular weight antioxidants, but more effective in long-term protection of the polymer samples at a level of 0.1 weight percent.Part 43: P. Grosso, O. Vogl: J. Macromol. Sci. Chem., in pressNow Chemical Company, Midland, MI 48674, USATo whom all correspondence should be addressed: Herman F. Mark Professor of Polymer Science, Polytechnic Institute of New York, Brooklyn, NY 11201, USA     

The Swedish approach to research and development in fire protection

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The Swedish approach to research and development in fire protection