Surface dipoles and work functions of alkylthiolates and fluorinated alkylthiolates on Au(111)

We study the dipole formation at the surface formed by -CH(3) and -CF(3) terminated short-chain alkylthiolate monolayers on Au(111). In particular, we monitor the change in work function upon chemisorption using density functional theory calculations. We separate the surface dipole into two contributions, resulting from the gold-adsorbate interaction and the intrinsic dipole of the adsorbate layer, respectively. The two contributions turn out to be approximately additive. Adsorbate dipoles are defined by calculating dipole densities of free-standing molecular monolayers. The gold-adsorbate interaction is, to a good degree, determined by the Au-S bond only. This bond is nearly apolar and its contribution to the surface dipole is relatively small. The surface dipole of the self-assembled monolayer is then dominated by the intrinsic dipole of the thiolate molecules. Alkylthiolates increase the work function of Au(111), whereas fluorinated alkylthiolates decrease it.     

Functional Additive Mixed Models

We propose an extensive framework for additive regression models for correlated functional responses, allowing for multiple partially nested or crossed functional random effects with flexible correlation structures for, for example, spatial, temporal, or longitudinal functional data. Additionally, our framework includes linear and nonlinear effects of functional and scalar covariates that may vary smoothly over the index of the functional response. It accommodates densely or sparsely observed functional responses and predictors which may be observed with additional error and includes both spline-based and functional principal component-based terms. Estimation and inference in this framework is based on standard additive mixed models, allowing us to take advantage of established methods and robust, flexible algorithms. We provide easy-to-use open source software in the pffr() function for the R package refund. Simulations show that the proposed method recovers relevant effects reliably, handles small sample sizes well, and also scales to larger datasets. Applications with spatially and longitudinally observed functional data demonstrate the flexibility in modeling and interpretability of results of our approach.     

Functional Generalized Additive Models

We introduce the functional generalized additive model (FGAM), a novel regression model for association studies between a scalar response and a functional predictor. We model the link-transformed mean response as the integral with respect to t of F{X(t), t} where F( ·, ·) is an unknown regression function and X(t) is a functional covariate. Rather than having an additive model in a finite number of principal components as by Müller and Yao (2008 Müller, H.G., and Yao, F. (2008), “Functional Additive Models,” Journal of the American Statistical Association, 103, 1534–1544.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), our model incorporates the functional predictor directly and thus our model can be viewed as the natural functional extension of generalized additive models. We estimate F( ·, ·) using tensor-product B-splines with roughness penalties. A pointwise quantile transformation of the functional predictor is also considered to ensure each tensor-product B-spline has observed data on its support. The methods are evaluated using simulated data and their predictive performance is compared with other competing scalar-on-function regression alternatives. We illustrate the usefulness of our approach through an application to brain tractography, where X(t) is a signal from diffusion tensor imaging at position, t, along a tract in the brain. In one example, the response is disease-status (case or control) and in a second example, it is the score on a cognitive test. The FGAM is implemented in R in the refund package. There are additional supplementary materials available online.     

Stereospecific Synthesis and Photophysical Properties of Propeller-Shaped C90H48 PAH

Herein, we have synthesized an enantiomerically pure propeller-shaped PAH, C₉₀H₄₈, possessing three [7]helicene and three [5]helicene subunits. This compound can be obtained in gram quantities in a straightforward manner. The photophysical and chiroptical properties were investigated using UV/Vis absorption and emission, optical rotation and circular dichroism spectroscopy, supported by DFT calculations. The nonlinear optical properties were investigated by two-photon absorption measurements using linearly and circularly polarized light. The extremely twisted structure and packing of the homochiral compound were investigated by single-crystal X-ray diffraction analysis.     

ZnO lasing in complex systems with tetrapods

A ZnO structure in the form of a core–shell wire was grown with a modified vapour transport and condensation method. The wire consists of a dense core which may play the role of a waveguide and a shell formed mainly from tetrapod-type crystallites. The high optical quality of the produced ZnO material is confirmed by continuous wave photoluminescence (PL) analysis demonstrating that low- temperature PL is related to the recombination of bound excitons, while room-temperature PL is due to free excitons. Good quality of the crystal structure is demonstrated also by the Raman spectrum. The shell of the wire exhibits room-temperature laser action due to lasing modes in tetrapods under the excitation by nanosecond laser pulses. The nature of the lasing modes is discussed. A simplified model for one of the possible modes is suggested.     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

The Role of Information in Managing Interactions from a Multifractal Perspective

In the framework of the multifractal hydrodynamic model, the correlations informational entropy–cross-entropy manages attractive and repulsive interactions through a multifractal specific potential. The classical dynamics associated with them imply Hubble-type effects, Galilei-type effects, and dependences of interaction constants with multifractal degrees at various scale resolutions, while the insertion of the relativistic amendments in the same dynamics imply multifractal transformations of a generalized Lorentz-type, multifractal metrics invariant to these transformations, and an estimation of the dimension of the multifractal Universe. In such a context, some correspondences with standard cosmologies are analyzed. Since the same types of interactions can also be obtained as harmonics mapping between the usual space and the hyperbolic plane, two measures with uniform and non-uniform temporal flows become functional, temporal measures analogous with Milne’s temporal measures in a more general manner. This work furthers the analysis published recently by our group in “Towards Interactions through Information in a Multifractal Paradigm”.     

Maximum weight edge-constrained matchings

Practical questions arising from (for instance) biological applications can often be expressed as classical optimization problems with specific, new features. We are interested here in the version of the maximum weight matching problem (on a graph G) obtained by (1) defining a set F of pairs of incompatible edges of G and (2) asking that the matching contains at most one edge in each given pair. Such a matching is called an odd matching. The graph T(F)=(V_F,F), where V_F is the set of edges of G occurring in at least one pair of F, is called the trace-graph of G and F.We motivate the introduction of the maximum weight odd-matching (abbreviated as Odd-MWM) problem and study its complexity with respect to two parameters: the type of graph G and the graph class T to which T(F) belongs.Our contribution includes:

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A proof that Odd-MWM is NP-complete for 3-degree bipartite graphs when T(F) is a matching (i.e. when T is the class of 1-regular graphs), even if the weight function is constant.

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A proof that Odd-MWM is NP-complete (for 3-degree bipartite graphs as well as for any larger class) if and only if T is a class of graphs with unbounded induced matching. Otherwise, Odd-MWM is polynomial.

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A (Δ(T(F))+1)-approximate algorithm for Odd-MWM on general graphs. This algorithm becomes a χ(T(F))-approximate algorithm when the graph class T admits a polynomial algorithm for minimum vertex coloring.

     

Berge graphs with chordless cycles of bounded length

A graph is called weakly triangulated if it contains no chordless cycle on five or more vertices (also called hole) and no complement of such a cycle (also called antihole). Equivalently, we can define weakly triangulated graphs as antihole-free graphs whose induced cycles are isomorphic either to C₃ or to C₄. The perfection of weakly triangulated graphs was proved by Hayward [Hayward, J Combin Theory B. 39 (1985), 200–208] and generated intense studies to efficiently solve, for these graphs, the classical NP-complete problems that become polynomial on perfect graphs. If we replace, in the definition above, the C₄ by an arbitrary C_p (p even, at least equal to 6), we obtain new classes of graphs whose perfection is shown in this article. In fact, we prove a more general result: for any even integer p ≥ 6, the graphs whose cycles are isomorphic either to C₃ or to one of C_p, C_p+2, …, C_{2p 6} are perfect. © 1999 John Wiley & Sons, Inc. J Graph Theory 32: 73–79, 1999