Search results for "polymers"

Stress-Strain Law for Confined Concrete with Hardening or Softening Behavior

2013

This paper provides a new general stress-strain law for concrete confined by steel, fiber reinforced polymer (FRP), or fiber reinforced cementitious matrix (FRCM), obtained by a suitable modification of the well-known Sargin’s curve for steel confined concrete. The proposed law is able to reproduce stress-strain curve of any shape, having both hardening or softening behavior, by using a single closed-form simple algebraic expression with constant coefficients. The coefficients are defined on the basis of the stress and the tangent modulus of the confined concrete in three characteristic points of the curve, thus being related to physical meaningful parameters. It will be shown that if the v…

1996

The uses of atomic force microscopy, scanning tunneling microscopy, electron spectroscopic imaging, electron energy loss spectroscopy and low voltage, high resolution scanning electron microscopy in polymer research are reviewed

Copper(II)–Thymine Coordination Polymer Nanoribbons as Potential Oligonucleotide Nanocarriers

2016

This is the peer reviewed version of the following article: Vegas, V. G., Lorca, R., Latorre, A., Hassanein, K., Gómez‐García, C. J., Castillo, O., ... & Amo‐Ochoa, P. (2017). Copper (II)–Thymine Coordination Polymer Nanoribbons as Potential Oligonucleotide Nanocarriers. Angewandte Chemie International Edition, 56(4), 987-991, which has been published in final form at https://doi.org/10.1002/anie.201609031. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions

Thermal-, pressure- and light-induced spin-crossover behviour in the two-dimensional Hofman-like coordination polymer [Fe(3-Clpy)2Pd(CN)4]

2013

The thermal spin-crossover behaviour, photoexcitation and subsequent relaxation, as well as the pressure-induced spincrossover behaviour at 298 K are discussed for the non-porous two-dimensional Hofmann-like coordination polymer [Fe(3-Clpy)(2)Pd(CN)(4)] (1). The title compound undergoes a two-step, cooperative thermal-induced SCO with critical temperatures T-c1(down arrow) = 159.6 K and T-c1(up arrow) = 164.5 K for the first step and T-c2(down arrow) = 141.4 K and T-c2(up arrow) = 148.4 K for the second step. Irradiation of the low-spin state with green light (514 nm) at 10 K induced the photoexcitation of around 60% of the iron(II) centres to the high-spin state (LIESST effect). The subseq…

Multidentate Tetrahydrofurfuryloxide Ligand in a Ziegler−Natta Catalyst Studied by Molecular Modeling

2008

The transition from a generation III Ziegler-Natta catalyst with a monodentate Lewis base to a more modem generation 1V/V system, containing a tetrahydrofuran derivative, the tetrahydrofurturyloxide C 4 H 7 O-CH 2 O - bidentate ligand (THFFO), was studied by means of molecular modeling and DFT calculations. This particular ligand was carefully chosen so that it remained in the titanium coordination sphere in the model active site. With such a constraint, the dual role of tetrahydrofurfuryloxide was identified: it was demonstrated how the presence of this ligand limits the number of isomeric active sites as well as enhances the selectivity of the species that can still exist. The results ind…

Amphiphilic poly(hydroxyethylaspartamide) derivative-based micelles as drug delivery systems for ferulic acid

2008

Self-assembling micelles, potentially useful as drug delivery systems for ferulic acid (FA), were obtained in aqueous media from amphiphilic alpha,beta-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) copolymers bearing at the polyamino acidic backbone both poly(ethyleneglycol) (2000 or 5000 Da) and hexadecylamine (C(16)) moieties, at a concentration of 7 x 10(- 3) and 4 x 10(- 3) g/l, respectively, with nanometre size and negative zeta potential. These micelles were able to entrap FA and to release it in a prolonged way in phosphate buffer solution at pH 7.4 and human plasma. These systems were also stable in storage conditions and have no cytotoxic effects on Caco-2, 16 HBE, HuDe and K562 cel…

Reliability Estimation of Optimal Viscoelastic Composite Shells in Critical-Time Calculations

2003

The problem of reliability estimation for optimal viscoelastic composite shells in critical-time calculations is considered. The weight minimization of a viscoelastic composite shell, with constraints on deflections at the critical time, leads to a system deforming unstably, whose deflections grow in time with an increasing rate. A method for estimating the reliability of such shells in calculating the critical time is discussed. This time is regarded as a random variable depending on many, roughly equivalent, factors. An analysis of the reliability is carried out for different values of coefficients of variation, occurring in practice.

Analysis of Early Host Responses for Asymptomatic Disease Detection and Management of Specialty Crops

2010

The rapid and unabated spread of vector-borne diseases within US specialty crops threatens our agriculture, our economy, and the livelihood of growers and farm workers. Early detection of vector-borne pathogens is an essential step for the accurate surveillance and management of vector-borne diseases of specialty crops. Currently, we lack the tools that would detect the infectious agent at early (primary) stages of infection with a high degree of sensitivity and specificity. In this paper, we outline a strategy for developing an integrated suite of platform technologies to enable rapid, early disease detection and diagnosis of huanglongbing (HLB), the most destructive citrus disease. The re…

Metallophilic interactions in polymeric group 11 thiols

2016

Three polymeric group 11 transition metal polymers featuring metallophilic interactions were obtained directly via self-assembly of metal ions and 4-pyridinethiol ligands. In the cationic [Cu2(S-pyH)4]n2+ with [ZnCl4]n2− counterion (1) and in the neutral [Ag(S-py) (S-pyH)]n (2) 4-pyridinethiol (S-pyH) and its deprotonated form (S-py) are coordinated through the sulfur atom. Both ligands are acting as bridging ligands linking the metal centers together. In the solid state, the gold(I) polymer [Au(S-pyH)2]Cl (3) consists of the repeating cationic [Au(S-pyH)2]+ units held together by aurophilic interactions. Compound 1 is a zig-zag chain, whereas the metal chains in the structures of 2 and 3 a…

Indication of an order-order-transition by a partial disordering in ABC-triblock copolymers

1996

Poly(ethylene-alt-propylene)-block-polyethylethylene-block-polystyrene (PEP-b-PEE-b-PS) triblock copolymers were synthesized by anionic polymerization and subsequent hydrogenation of poly-1,4-isoprene-block-poly-1,2-butadiene-block-polystyrene triblock copolymers (1,4PI-b-1,2PB-b-PS). Differential scanning calorimetry and dynamic mechanical spectroscopy reveal an order-order transition which is induced by the mixing of PEP and PEE above their respective order-disorder transition (ODT).