Solutions of the Strominger System via Stable Bundles on Calabi-Yau Threefolds

We prove that a given Calabi-Yau threefold with a stable holomorphic vector bundle can be perturbed to a solution of the Strominger system provided that the second Chern class of the vector bundle is equal to the second Chern class of the tangent bundle. If the Calabi-Yau threefold has strict SU(3) holonomy then the equations of motion derived from the heterotic string effective action are also satisfied by the solutions we obtain.     

A 1H NMR Study of the Kinetics of the Reaction of Diisocyanates with Ethlene Oxide-Dimethylsiloxane-Ethylene Oxide Block Copolymer

The reaction of pure 2–4 and 2–6 tolylene diisocyanate with an OH terminated ethylene oxide-dimethylsiloxane-ethylene oxide ABA block copolymer was carried out directly in a n.m.r. tube. The kinetic of the reaction was studied by ¹H nmr spectroscopy.     

A versatile A2 + B3 approach to hyperbranched polyacenaphthenequinones

A series of hyperbranched polyacenaphthenequinones has been prepared by superelectrophilic aromatic substitution of (substituted) acenaphthenequinone and 1,3,5‐tris‐(4‐phenoxybenzoyl)benzene via a facile A₂ + B₃ approach. Because of the strongly increased reactivity of the second A functionality, gelation was efficiently avoided during the polymerization. The structure of the resulting polymer was characterized by NMR spectroscopy and gel permeation chromatography. Further modification of the hyperbranched polyacenaphthenequinone was explored both on the acenaphthenequinone and aromatic moieties. Moreover, the polymer modified through sulfonation was investigated as a water‐soluble acid catalyst for the degradation of biomass resources. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2596‐2603     

Free energy and states of fractional-order hereditariness

Complex materials, often encountered in recent engineering and material sciences applications, show no complete separations between solid and fluid phases. This aspect is reflected in the continuous relaxation time spectra recorded in cyclic load tests. As a consequence the material free energy cannot be defined in a unique manner yielding a significative lack of knowledge of the maximum recoverable work that can extracted from the material. The non-uniqueness of the free energy function is removed in the paper for power-laws relaxation/creep function by using a recently proposed mechanical analogue to fractional-order hereditariness.     

A lower bound estimate of the critical load for compressible elastic solids

We determine lower bound estimates for the critical load for hyperelastic solids under monotonic dead load processes. By considering the Hadamard criterion of infinitesimal stability, we first determine a lower bound for the Hadamard stability functional; then, we develop a procedure for optimal lower bound estimates for the critical load. As examples, we apply our procedure to generalized Blatz-Ko solids under simple extension, simple compression and rectilinear shear, and compare our results with other proposals contained in the literature.     

Substituent Effects on 31P NMR Chemical Shifts and 1JP–Se of triarylselenophosphates

The effect of electron-withdrawing (EW) and electron-releasing (ER) substituents on the ³¹P NMR chemical shifts and the structural parameters of a series of tris-(p-X-aryl)selenophosphates is reported in this article. Similarly to O-aryl phosphates and O-aryl thiophosphates, EW groups attached to aromatic rings induce a shielding effect on the ³¹P NMR signal. After a detailed experimental and theoretical analysis, we confirmed that the selenium atom is the main part responsible for the charge density transfer toward phosphorus through a back-bonding effect. The obtained ¹J_P-Se values for the complete series agree with this observation.

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