Magnetic alignment study of rare-earth-containing liquid crystals

The liquid-crystalline rare-earth complexes of the type [Ln(LH)3(DOS)3]-where Ln is Tb, Dy, Ho, Er, Tm, or Yb; LH is the Schiff base N-octadecyl-4-tetradecyloxysalicylaldimine; and DOS is dodecylsulfate-exhibit a smectic A phase. Because of the presence of rare-earth ions with a large magnetic anisotropy, the smectic A phase of these liquid crystals can be easier aligned in an external magnetic field than smectic A phases of conventional liquid crystals. The magnetic anisotropy of the [Ln(LH)3(DOS)3] complexes was determined by measurement of the temperature-dependence of the magnetic susceptibility using a Faraday balance. The highest value for the magnetic anisotropy was found for the dysprosium(III) complex. The magnetic alignment of these liquid crystals was studied by time-resolved synchrotron small-angle X-ray scattering experiments. Depending on the sign of the magnetic anisotropy, the director of the liquid-crystalline molecules was aligned parallel or perpendicular to the magnetic field lines. A positive value of the magnetic anisotropy (and parallel alignment) was found for the thulium(III) and the ytterbium(III) complexes, whereas a negative value of the magnetic anisotropy (and perpendicular alignment) was observed for the terbium(III) and dysprosium(III) complexes.     

Broadband 10 Gb/s operation of graphene electro‐absorption modulator on silicon

High performance integrated optical modulators are highly desired for future optical interconnects. The ultra‐high bandwidth and broadband operation potentially offered by graphene based electro‐absorption modulators has attracted a lot of attention in the photonics community recently. In this work, we theoretically evaluate the true potential of such modulators and illustrate this with experimental results for a silicon integrated graphene optical electro‐absorption modulator capable of broadband 10 Gb/s modulation speed. The measured results agree very well with theoretical predictions. A low insertion loss of 3.8 dB at 1580 nm and a low drive voltage of 2.5 V combined with broadband and athermal operation were obtained for a 50 μm‐length hybrid graphene‐Si device. The peak modulation efficiency of the device is 1.5 dB/V. This robust device is challenging best‐in‐class Si (Ge) modulators for future chip‐level optical interconnects.     

Synthesis of the Natural Product Building Block 5‐(3‐Bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one and its Chiral Characterization by Using Chiroptical Spectroscopy

The absolute configuration of 5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, an intermediate in the synthesis of various natural products, is assigned by using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD). Experimental spectra were compared to density functional theory (DFT) calculations of the molecule with known configuration. These three techniques independently confirm that the absolute configuration is (S)‐5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, thus enabling us to assign the absolute configuration with high reliability. The reliability of the VCD analysis was assessed quantitatively by using the CompareVOA program. We found that, in cases in which the agreement between theory and experiment was very good, a value of 10 cm^?1 for the triangular weighting function gave a more‐realistic discriminative power between enantiomers than the default value of 20 cm^?1.     

Bayesian lasso binary quantile regression

In this paper, a Bayesian hierarchical model for variable selection and estimation in the context of binary quantile regression is proposed. Existing approaches to variable selection in a binary classification context are sensitive to outliers, heteroskedasticity or other anomalies of the latent response. The method proposed in this study overcomes these problems in an attractive and straightforward way. A Laplace likelihood and Laplace priors for the regression parameters are proposed and estimated with Bayesian Markov Chain Monte Carlo. The resulting model is equivalent to the frequentist lasso procedure. A conceptional result is that by doing so, the binary regression model is moved from a Gaussian to a full Laplacian framework without sacrificing much computational efficiency. In addition, an efficient Gibbs sampler to estimate the model parameters is proposed that is superior to the Metropolis algorithm that is used in previous studies on Bayesian binary quantile regression. Both the simulation studies and the real data analysis indicate that the proposed method performs well in comparison to the other methods. Moreover, as the base model is binary quantile regression, a much more detailed insight in the effects of the covariates is provided by the approach. An implementation of the lasso procedure for binary quantile regression models is available in the R-package bayesQR.     

Scheduling a non-professional indoor football league: a tabu search based approach

This paper deals with a real-life scheduling problem of a non-professional indoor football league. The goal is to develop a schedule for a time-relaxed, double round-robin tournament which avoids close successions of games involving the same team in a limited period of time. This scheduling problem is interesting, because games are not planned in rounds. Instead, each team provides time slots in which they can play a home game, and time slots in which they cannot play at all. We present an integer programming formulation and a heuristic based on tabu search. The core component of this algorithm consists of solving a transportation problem, which schedules (or reschedules) all home games of a team. Our heuristic generates schedules with a quality comparable to those found with IP solvers, however with considerably less computational effort. These schedules were approved by the league organizers, and used in practice for the seasons 2009–2010 till 2016–2017.

     

Precursor Design Strategies for the Low-Temperature Synthesis of Functional Oxides: It's All in the Chemistry

Solution-based (multi)metal oxide synthesis has been carried out employing a large diversity of precursor routes. The selection of an appropriate synthesis strategy is frequently dictated by the resulting material properties, although this choice should also be based on green chemistry principles, atom economy considerations and energy efficiency. In order to limit the required energy budget to convert the chemical precursor to the target oxide material, various approaches were recently reported. This Review summarizes some frequently encountered low-temperature routes, critically assessing their application window and advantages. More specifically, auto-combustion synthesis, UV-assisted decomposition routes, sol–gel network adjustments and precursor complex design concepts are discussed. It is expected that this toolbox of low-temperature strategies may assist further progress in the field, stimulating novel applications, such as flexible electronics or organic–oxide hybrid materials, which are very sensitive to the temperature requirements.     

Exact methods for combinatorial auctions

This is a summary of the author’s PhD thesis supervised by Frits Spieksma and defended on 20 December 2006 at the Katholieke Universiteit Leuven. The thesis is written in English and is available from the author’s website (http://www.econ.kuleuven.be/dries.goossens/public). This work deals with combinatorial auctions, i.e., auctions where bidders can bid on sets of items. We study two special cases, namely the total quantity discount auction and the matrix bid auction.      

Thickness dependence of the maximum DC Josephson current in superconducting proximity junctions

We investigated the maximum dc Josephson current I_M in NbNb_xO_yCu/Pb junctions as a function of normal layer thickness d_Cu. Theoretical calculations based on the McMillan proximity effect model are in good agreement with the experimental data. The monotonous decrease of RI_M (R is the normal tunneling resistance) indicates the absence of any oscillatory behaviour or anomaly in the pair amplitude F_Cu(d_Cu) of the Cu/Pb sandwich, in contradiction with theoretical prediction.     

The Red–Blue transportation problem

This paper considers the Red–Blue Transportation Problem (Red–Blue TP), a generalization of the transportation problem where supply nodes are partitioned into two sets and so-called exclusionary constraints are imposed. We encountered a special case of this problem in a hospital context, where patients need to be assigned to rooms. We establish the problem’s complexity, and we compare two integer programming formulations. Furthermore, a maximization variant of Red–Blue TP is presented, for which we propose a constant-factor approximation algorithm. We conclude with a computational study on the performance of the integer programming formulations and the approximation algorithms, by varying the problem size, the partitioning of the supply nodes, and the density of the problem.     

On the derivation of simple dynamic models of anaerobic digestion using macroscopic bioreaction schemes

In this study, the problem of developing simple dynamic models of an anaerobic digestion process is tackled using an identification procedure which proceeds in several consecutive steps. Starting from sets of experimental data describing the time evolution of several key component concentrations, i.e. biomass(es), substrates and products, the minimal number of macroscopic bioreactions required to represent the data at hand, as well as the parameters of the associated stoichiometry matrix, are determined using maximum likelihood principal component analysis. Then, the structure of the kinetic laws, together with their parameters, are identified using likelihood ratio tests to navigate through the branches of decision trees made of various kinetic structures. The effectiveness of the modelling procedure is illustrated with a simulated example of anaerobic digestion. As usual sensors only provide aggregate measurements of the component concentration, a deeper investigation of practical identifiability is achieved in relation with the influence of measurement errors.