Dynamics of novel polybutadiene ionomers

The dynamics of novel ionomers based on a low‐molecular‐weight polybutadiene with zinc acrylate moieties were investigated as a function of the number of ionic bonds by using a combination of calorimetry, dielectric broadband spectroscopy and rheology. We find that the ionic bonds have profound effects on the mechanical properties, including the introduction of a sol–gel transition. However, all techniques consistently indicate that the segmental dynamics of the polymer chains remain largely unaffected, and only very small changes in the glass transition were observed. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1074–1079     

Transient Dipnictyl Analogues of Acrylamides,R−E=E′−CONR2, and a Related Diphosphadigalletane from Na[OCP] and (R2N)2ECl (E,E′=P,As, Ga)

The reaction of Na[OCP] with (R₂N)₂ECl (E=P or As; R=alkyl) granted direct access to transient amine-substituted diphospha- and arsaphospha-acrylamide analogues, (R₂N)E=P(CONR₂) 1 . Their facile formation allowed for a comprehensive reactivity study. Dimerization yielded the four-membered rings (R₂N)₂E₂P₂(CONR₂)₂, whereas in the presence of excess Na[OCP], a stepwise [2+2] cycloaddition occured, leading to the sodium salts of carboxotripnictides [(R₂N)EP₂CO(CONR₂)]⁻. These salts served as a reservoir of 1 , either by extrusion of Na[OCP] or by reaction with the appropriate (R₂N)₂ECl, giving the [4+2]-cycloaddition products (R₂N)EP(C₆H₁₀)(CONR₂) in the presence of 2,3-dimethylbutadiene. The formal conjugate addition product K[(tBuO)(R₂N)PP(CONR₂)] was obtained by reaction of Na[(R₂N)PP₂CO(CONR₂)] with tBuOK. In addition, a rare diphosphadigalletane with a ladder-type (R₂N)₂Ga₂P₂(CONR₂)₂ core was isolated from the reaction of Na[OCP] with (R₂N)₂GaCl (R=alkyl). The unprecedented pnictogenyl carboxamide compounds were thoroughly characterized, including single-crystal X-ray structure determinations, and mechanisms for their formation were investigated by DFT calculations.     

Triplet-State Position and Crystal-Field Tuning in Opto-Magnetic Lanthanide Complexes: Two Sides of the Same Coin

Lanthanide-complex-based luminescence thermometry and single-molecule magnetism are two effervescent fields of research, owing to the great promise they hold from an application standpoint. The high thermal sensitivity achievable, their contactless nature, along with sub-micrometric spatial resolution make these luminescent thermometers appealing for accurate temperature probing in miniaturised electronics. To that end, single-molecule magnets (SMMs) are expected to revolutionise the field of spintronics, thanks to the improvements made in terms of their working temperature—now surpassing that of liquid nitrogen—and manipulation of their spin state. Hence, the combination of such opto-magnetic properties in a single molecule is desirable in the aim of overcoming, among others, addressability issues. Yet, improvements must be made through design strategies for the realisation of the aforementioned goal. Moving forward from these considerations, we present a thorough investigation of the effect that changes in the ligand scaffold of a family of terbium complexes have on their performance as luminescent thermometers and SMMs. In particular, an increased number of electron-withdrawing groups yields modifications of the metal coordination environment and a lowering of the triplet state of the ligands. These effects are tightly intertwined, thus, resulting in concomitant variations of the SMM and the luminescence thermometry behaviour of the complexes. Supported by ab initio calculations, we can rationally interpret the observed trends and provide solid foundations for the development of opto-magnetic lanthanide complexes.     

A stochastic block model for interaction lengths

Advances in Data Analysis and Classification - We propose a new stochastic block model that focuses on the analysis of interaction lengths in dynamic networks. The model does not rely on a...     

Parallel transport and defects on nematic shells

Nematic shells are thin films of nematic liquid crystal deposited on the boundary of colloidal particles, where liquid crystal molecules may freely glide, while remaining tangent to the surface substrate. The surface nematic order is described here by an appropriate tensor field Q, which vanishes wherever a defect occurs in the molecular order. We show how the classical concept of parallel transport on a manifold introduced by Levi-Civita can be adapted to this setting to define the topological charge m of a defect. We arrive at a simple formula to compute m from a generic representation of Q. In a number of separate appendices, we revisit in a unified language several, apparently disparate applications of Levi-Civita’s parallel transport.     

Synthesis of Stephenson's six-bar linkages by an interactive technique

Summary An interactive approach to the computer aided synthesis of the planar Stephenson's six-bar linkages is reported. As known, in the applications, six-bar linkages may meet more sophisticated requirements than simpler mechanisms could allow.The design method consists in carefully selecting a suitable coupler point of a planar four-bar linkage: the coupler curve must fit the characteristics required by the law of motion of the follower. Knowledge of this curve supplies the needed directions to complete the six-bar linkage which is then automatically analysed.The analysis method and the computer program are fully explained. The program was implemented on a mini-computer: it needs essentially a video-display unit with grafic input-output capabilities.

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Sommario E' riportata una tecnica per il progetto degli esalateri articolati piani di Stephenson, basata sull'impiego interattivo dell'elaboratore elettronico. E'noto che gli esalateri articolati, rispetto a meccanismi più semplici, consentono di soddisfare a richieste più sofisticate in certe applicazioni.Il metodo di progetto proposto consiste nella ricerca di un opportuno punto di biella di un quadrilatero articolato piano, la cui traiettoria soddisfi a precise caratteristiche imposte dal movimento del cedente. Il meccanismo finale viene costruito a partire dal quadrilatero così ottenuto e viene analizzato automaticamente.Vengono illustrati il metodo di analisi e il programma di calcolo. Quest'ultimo è stato implementato per un minicomputer e richiede essenzialmente la disponibilità di un video grafico interattivo.

     

Numerical techniques for the evaluation of non-adiabatic interactions and the generation of quasi-diabatic potential energy surfaces using configuration interaction methods

CI techniques, based on nearly complete expansions over determinants for subsets of molecular orbitals and electrons, have been extended to evaluate, by finite differences, non-adiabatic interactions arising from the nuclear kinetic energy operator. A functional of the non-adiabatic interactions is defined and, from the minimum condition of the functional, a simple expression is obtained for the transformation matrix to the quasi-diabatic basis. Two different schemes for the minimization of the functional, with and without constraints to the form of the transformation matrix, have been compared. Simple tests are presented to verify the numerical accuracy of the non-adiabatic interactions and to compare the two schemes for the minimization of the functional.     

Transient behaviour of semilinear stochastic systems with random parameters

The transient solution of a class of nonautonomous, stochastic differential equations with given random initial conditions is studied. The considered evolution equation is characterized by the presence of a deterministic linear term and of a random nonlinear term whose parameters can be modeled by random processes of Rice noise type. Analytical approximated expressions for the first- and second-order moments and for the probability density of the solution process are derived and are applied to determine the statistical properties of a class of stochastic nonlinear oscillators.     

When the heart of a faithful torsion pair is a module category

An abelian category with arbitrary coproducts and a small projective generator is equivalent to a module category (Mitchell (1964) [17]). A tilting object in an abelian category is a natural generalization of a small projective generator. Moreover, any abelian category with a tilting object admits arbitrary coproducts (Colpi et al. (2007) [8]). It naturally arises the question when an abelian category with a tilting object is equivalent to a module category. By Colpi et al. (2007) [8], the problem simplifies in understanding when, given an associative ring R and a faithful torsion pair (X,Y) in the category of right R-modules, the heartH(X,Y)of the t-structure associated with (X,Y) is equivalent to a category of modules. In this paper, we give a complete answer to this question, proving necessary and sufficient conditions on (X,Y) for H(X,Y) to be equivalent to a module category. We analyze in detail the case when R is right artinian.