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1.
Giorgia Scetta Jianzhu Ju Nathan Selles Patrick Heuillet Matteo Ciccotti Costantino Creton 《Journal of polymer science. Part A, Polymer chemistry》2021,59(8):685-696
We investigate the cyclic mechanical behavior in uniaxial tension of three different commercial thermoplastic polyurethane elastomers (TPU) often considered as a sustainable replacement for common filled elastomers. All TPU have similar hard segment contents and linear moduli but sensibly different large strain properties as shown by X-ray analysis. Despite these differences, we found a stiffening effect after conditioning in step cyclic loading which greatly differs from the common softening (also referred as Mullins effect) observed in chemically crosslinked filled rubbers. We propose that this self-reinforcement is related to the fragmentation of hard domains, naturally present in TPU, in smaller but more numerous sub-units that may act as new physical crosslinking points. The proposed stiffening mechanism is not dissimilar to the strain-induced crystallization observed in stretched natural rubber, but it presents a persistent nature. In particular, it may cause a local reinforcement where an inhomogeneous strain field is present, as is the case of a crack propagating in cyclic fatigue, providing a potential explanation for the well-known toughness and wear resistance of TPU. 相似文献
2.
Human Y‐chromosome SNP characterization by multiplex amplified product‐length polymorphism analysis 下载免费PDF全文
Laura Smeldy Jurado Medina Marina Muzzio Marisol Schwab María Leticia Bravi Costantino Guillermo Barreto Graciela Bailliet 《Electrophoresis》2014,35(17):2524-2527
We designed an allele‐specific amplification protocol to optimize Y‐chromosome SNP typing, which is an unavoidable step for defining the phylogenetic status of paternal lineages. It allows the simultaneous highly specific definition of up to six mutations in a single reaction by amplification fragment length polymorphism (AFLP) without the need of specialized equipment, at a considerably lower cost than that based on single‐base primer extension (SNaPshot?) technology or PCR‐RFLP systems, requiring as little as 0.5 ng DNA and compatible with the small fragments characteristic of low‐quality DNA. By designation of two primers recognizing the derived and ancestral state for each SNP, which can be differentiated by size by the addition of a noncomplementary nucleotide tail, we could define major Y clades E, F, K, R, Q, and subhaplogroups R1, R1a, R1b, R1b1b, R1b1c, J1, J2, G1, G2, I1, Q1a3, and Q1a3a1 through amplification fragments that ranged between 60 and 158bp. 相似文献
3.
Antonella Cristiano Alba Marcellan Bert J. Keestra Paul Steeman Costantino Creton 《Journal of Polymer Science.Polymer Physics》2011,49(5):355-367
Fracture properties of model elastomeric networks of polyurethane have been investigated with a double‐edge notch geometry. The networks were synthesized from monodisperse end‐functionalized polypropylene glycol precursors and a trifunctional isocyanate. All reagents were carefully purified and nearly defect‐free ideal networks were prepared at a stoichiometry very close to the theoretical one. Three networks were prepared: an unentangled network of short chains (Mn = 4 kg mol?1), an entangled network of longer chains (Mn = 8 kg mol?1) and a bimodal network with 8 kg mol?1 and 1 kg mol?1 chains. The presence of entanglements was found to increase significantly the toughness of the rubber, in particular at room temperature, relative to the bimodal networks and to the short chains network. Fracture experiments were carried out at different strain rates and temperatures and showed for all three networks a marked decrease in fracture toughness with increasing temperature and decreasing strain rate which mirrored reasonably well the rate and temperature dependence of tan δ, the dissipative factor. However the proportionality factor between tan δ, and GIC was very material dependent and the shift factors obtained for the master curves of the viscoelastic properties could not be used to build fracture energy master curves. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
4.
Minardi Giovannina Mura Emanuela Pistuddi Angelo M. Solinas Costantino Bacchi Alessia Pelizzi Corrado Pelizzi Giancarlo Chelucci Giorgio 《Transition Metal Chemistry》1999,24(4):481-485
Chelating properties of C2-symmetric chiral bipyridine ligands are discussed. In particular we report the syntheses of the cobalt(II), nickel(II), zinc(II) and copper(II) complexes of (4S,5S)-2,2-dimethyl-4,5-bis(2-pyridyl)-1,3-dioxolane. All compounds have been characterized by IR spectroscopy, and an X-ray diffraction analysis has been carried out on one of them: Co(L)(NO3)2. The ligand coordinates the cobalt atom by the two nitrogen donors N(1) and N(2). A seven-membered chelation ring is formed, presenting a remarkable non-crystallographic twofold pseudosymmetry around the axis connecting Co and the midpoint of the C(6)–C(7) bond. The metal also binds two monodentate nitrates, thus completing a distorted coordination tetrahedron. 相似文献
5.
Costantino Medori 《Bulletin des Sciences Mathématiques》2009,133(5):470-476
We study the moduli space of CR-projective complex foliated tori. We describe it in terms of isotropic subspaces of Grassmannians and we show that it is a normal complex analytic space. 相似文献
6.
Umberto Costantino Maria Antonietta Massucci Aldo La Ginestra Anna Maria Tarola Laura Zampa 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(2):147-162
The intercalation of imidazole and some organic species containing the imidazole ring, between the layers of crystalline zirconium phosphate has been investigated. Fourteen new, well-ordered intercalation compounds are obtained with the batch procedure at r.t. and/or 60°C. A mechanism of formation of the various compounds is proposed on the basis of the interaction between the guest molecules (with their dimensions and geometries) and the free PO3OH groups available between the layers of the host. The new phases have been characterized by TG and X-ray methods. 相似文献
7.
Francesco Costantino 《Geometriae Dedicata》2006,121(1):89-111
We provide sufficient conditions assuring that a suitably decorated 2-polyhedron can be thickened to a compact four-dimensional
Stein domain. We also study a class of flat polyhedra in 4-manifolds and find conditions assuring that they admit Stein, compact
neighborhoods. We base our calculations on Turaev’s shadows suitably “smoothed”; the conditions we find are purely algebraic
and combinatorial. Applying our results, we provide examples of hyperbolic 3-manifolds admitting “many” positive and negative
Stein fillable contact structures, and prove a four-dimensional analog of Oertel’s result on incompressibility of surfaces
carried by branched polyhedra.
相似文献
8.
Alessia Bacchi Giorgio Chelucci Manlio Grandino Giovannina Minardi Corrado Pelizzi Giancarlo Pelizzi Costantino Solinas 《Journal of chemical crystallography》1994,24(10):659-663
Cobalt(II), nickel(II), and copper(II) complexes of 2-[(2S)-2-pyrrolidinyllpyridine (L) have been synthesized and characterized. The crystal structure of the complex [Cu(L)2(NO3)]NO3 has been determined by X-ray diffraction. Crystals are monoclinic, space groupP2+, witha=10.766(3).b=7.525(2),c=13.447(4) Å. =104.64(2)°. and Z=2. The structure consists of [Cu(L)2(NO3)]+ cations and NO
3
t-
anions. The copper atom has a distorted trigonal bipyramidal coordination geometry with the two pyrrolidine nitrogens and one nitrate oxygen occupying the equatorial positions and the two pyridine nitrogens at the apices. The crystalline cohesion is ensured by a network of hydrogen bonds involving the pyrrolidine groups as donors and both coordinate and uncoordinate nitrates as acceptors. 相似文献
9.
Aqueous suspensions of delaminated zirconium phosphate have been recently obtained in our laboratory by a suitable intercalation-deintercalation of alkylamines. By filtering these suspensions thin and flexible sheets or pellicles of lamellar α-zirconium phosphate, with the most part of the layers oriented parallel to the pellicle surface, can be easily prepared. ac conductivity measurements have been carried out, in the temperature range 150–300°C, on pellets made of α-Zr(HPO4)2 pressed pellicles, oriented both parallel and perpendicular to the electric field. Independently of the pellet orientation, a slope variation was observed in the Arrhenius plot at about 220°C. As already found for the α-Zr(HPO4)2 powder, this is associated with a phase transition at this temperature, which causes a discontinuous change of the interlayer distance from 7.4 Å to 6.8 Å. The conductivity of samples oriented parallel to the electric field () is about two orders higher than the conductivity of the anhydrous microcrystalline powder, which, in turn, is higher than that of perpendicularly oriented samples (). 相似文献
10.
V. Vitagliano R. Sartorio A. Acampora L. Costantino S. Wurzburger 《European Polymer Journal》1973,9(9):909-918
The moving boundary technique has been used to measure independently the transference numbers of macroion and counterions in water solutions of sodium polyacrylate at 25° and in the concentration range 0·050-0·8 eq/l. The experimental results allow us to compute, without any arbitrary assumption, the fraction of counterions which contribute to the transport of current towards the cathode and which may be called the “fraction of free ions”. 相似文献