Spectroscopic ellipsometry on thin films of conjugated polymers

This work presents results from spectroscopic ellipsometry measurements of thin films of conjugated polymers constructed by spin casting with rapid solvent evaporation. Accurate data for the optical functions of MEH-PPV, PF2/6am5, PPy and PmPy films are given for the first time in a broad spectral range. A uniaxial anisotropic character is present in these functions with the optical axis parallel to the surface normal. The amount of anisotropy is found to be fairly high even in polymer layers with less rigid rod molecule chains (PF2/6am5 and MEH-PPV) and very high for the highly 7r-stiff polymer PPy. The influence of an anisotropic and highly dispersive optical response on the efficiency of light emitting diodes made from PF2/6am4 is investigated. The out-coupling efficiency in such devices is found to be highly dependent on the emission wavelength. The results obtained are compared to the commonly used approximation n =const. = 2. The importance of a proper knowledge of the optical behavior of this material group when utilized in devices is shown by the significant difference between these methods. The ability of ellipsometry to monitor structural changes in conjugated polymers is demonstrated. The perfect rigid rod behavior of PPy and the loss of rigidity when forming a copolymer together with meta mPy is clearly visible in the ellipsometry data. The amount of anisotropy is dependent of the ratio of mPy and an isotropic respond is obtained for pure PmPy. Furthermore, the blue shifted absorption spectrum for higher ratios of PmPy validate breaks in the conjugation by the additional meta linkages in the chain

Null Subject Behavior in the Attrition of Brazilian Portuguese

The syntax of referential null subjects in Brazilian Portuguese (BP) is the topic of much recent work (Kato & Negrão 2000; Ferreira 2000, 2004; Martins & Nunes 2005, 2010; Modesto 2000; Rodrigues 2002, 2004). In light of the Interface Hypothesis (Tsimpli, Sorace 2006), uninterpretable features such as purely syntactical elements should not undergo attrition. This study tests whether this theory is valid in regard to the Null Subject behavior in the production of BP speakers under influence of L2 English. In order to do so, I conducted an experiment with monolingual BP speakers and bilingual (English/BP) speakers to establish a clear-cut comparison. The experiment consisted of an elicited production task and a grammaticality judgment task. The results of the data analysis show that BP speakers under influence of L2 English do seem to indicate attrition, thus encouraging further studies questioning the Interface Hypothesis

Bounded sets of Lagrange multipliers for vector optimization problems in infinite dimension

AbstractThe aim of this paper is to point out some sufficient constraint qualification conditions ensuring the boundedness of a set of Lagrange multipliers for vectorial optimization problems in infinite dimension. In some (smooth) cases these conditions turn out to be necessary for the existence of multipliers as well

Comparing anaphora resolution in early and late Brazilian Portuguese-European Portuguese bidialectal bilinguals

The present study examines anaphora resolution in two groups of speakers exposed to Brazilian and European Portuguese (BP and EP, respectively), considering the different null subject distribution in these languages. Our research question is whether late BP-EP bilinguals (age of EP onset: 29.1) and heritage BP speakers raised in Portugal (age of EP onset 5.6), tested in both dialects, will pattern like the native controls or display some effects of EP in their native BP or vice-versa. This is an interesting question in light of the Interface Hypothesis, which claims that external interfaces should be subject to general bilingualism effects irrespective of language pairing and age (Sorace, 2011). The results show that age has an effect, as the heritage speakers do not perform like the late learners, and that the high degree of typological proximity between the two languages rules out the possibility of late bidialectal acquisition

A steepest descent method for set optimization problems with set-valued mappings of finite cardinality

In this paper, we study a first-order solution method for a particular class of set optimization problems where the solution concept is given by the set approach. We consider the case in which the set-valued objective mapping is identified by a finite number of continuously differentiable selections. The corresponding set optimization problem is then equivalent to find optimistic solutions to vector optimization problems under uncertainty with a finite uncertainty set. We develop optimality conditions for these types of problems and introduce two concepts of critical points. Furthermore, we propose a descent method and provide a convergence result to points satisfying the optimality conditions previously derived. Some numerical examples illustrating the performance of the method are also discussed. This paper is a modified and polished version of Chapter 5 in the dissertation by Quintana (On set optimization with set relations: a scalarization approach to optimality conditions and algorithms, Martin-Luther-Universität Halle-Wittenberg, 2020)

Nonlinear Cone Separation Theorems in Real Topological Linear Spaces

The separation of two sets (or more specific of two cones) plays an important role in different fields of mathematics such as variational analysis, convex analysis, convex geometry, optimization. In the paper, we derive some new results for the separation of two not necessarily convex cones by a (convex) cone / conical surface in real (topological) linear spaces. We follow basically the separation approach by Kasimbeyli (2010, SIAM J. Optim. 20) based on augmented dual cones and normlinear separation functions. Classical separation theorems for convex sets will be the key tool for proving our main nonlinear cone separation theorems. Also in the setting of a real reflexive Banach space, we are able to extend the cone separation result derived by Kasimbeyli

On iterated minimization in nonconvex optimization

In dynamic programming and decomposition methods one often applies an iterated minimization procedure. The problem variables are partitioned into several blocks, say x and y. Treating y as a parameter, the first phase consists of minimization with respect to the variable x. In a second phase the minimization of the resulting optimal value function depending on y is considered. In this paper we treat this basic idea on a local level. It turns out that strong stability (in the sense of Kojima) in the first phase is a natural assumption. In order to show that the iterated local minima of the parametric problem lead to a local minimum for the whole problem, we use a generalized version of a positive definiteness criterion of Fujiwara-Han-Mangasarian