(-)-isopinocampheol substituted mesogens: An investigation of the effect of bulky terminal groups in chiral smectic liquid crystals

in Ferroelectrics (2004), 311

A ferroelectric liquid crystal with an end-substituted (-)-isopinocampheol (IPC) group has been studied in isolation and in mixtures with the antiferroelectric compound EHPOCBC. The samples were studied ... [more ▼]

A ferroelectric liquid crystal with an end-substituted (-)-isopinocampheol (IPC) group has been studied in isolation and in mixtures with the antiferroelectric compound EHPOCBC. The samples were studied with respect to electroclinic coefficients, tilt angles, X-ray layer spacing, dielectric permittivity, spontaneous polarisation and relative birefringence under an applied field. In the pure isopinocampheol substituted compound, the SmA-SmC phase transition appears strongly first order and is associated with a significant increase in effective birefringence. The smectic layer spacing decreases below the transition approximately with the optical tilt. On increased EHPOCBC concentration the change in birefringence across the transition diminishes, until the point at which the mixture adopts an anticlinic SmC(A) phase, and the expected decrease in birefringence is observed. There is very little change in birefringence with field for the IPC compound, whilst EHPOCBC shows a marked increase with increasing field, for a few degrees above the phase transition. The results are analyzed with respect to two models. In one it is proposed that the bulky IPC group disorders the SmA phase by introducing undulations in the smectic layer. These undulations may disappear in the SmC phase due to an antiparallel arrangement of neighbouring molecules. In the other model the bent shape of the mesogen as a whole plays a crucial role in changing the optical properties at the SmA-SmC transition, due to the biased rotation around the molecular axis of inertia. [less ▲]

Isotope Cluster-Based Compound Matching in Gas Chromatography/ Mass Spectrometry for Non-Targeted Metabolomics

in Analytical Chemistry (2013), 85(8), 4030-4037

Gas chromatography coupled to mass spectrometry (GC/MS) has emerged as a powerful tool in metabolomics studies. A major bottleneck in current data analysis of GC/MS-based metabolomics studies is compound ... [more ▼]

Gas chromatography coupled to mass spectrometry (GC/MS) has emerged as a powerful tool in metabolomics studies. A major bottleneck in current data analysis of GC/MS-based metabolomics studies is compound matching and identification, as current methods generate high rates of false positive and false -negative identifications. This is especially true for data sets containing a high amount of noise. In this work, a novel spectral similarity measure based on the specific fragmentation patterns of electron impact mass spectra is proposed. An important aspect of these algorithmic methods is the handling of noisy data. The performance of the proposed method compared to the dot product, the current gold standard, was evaluated on a complex biological data set. The analysis results showed significant improvements of the proposed method in compound matching and chromatogram alignment compared to the dot product. [less ▲]

Isotopologue ratio normalization for non-targeted metabolomics

in Journal of Chromatography. A (2015), 1389

Robust quantification of analytes is a prerequisite for meaningful metabolomics experiments. In non-targeted metabolomics it is still hard to compare measurements across multiple batches or instruments ... [more ▼]

Robust quantification of analytes is a prerequisite for meaningful metabolomics experiments. In non-targeted metabolomics it is still hard to compare measurements across multiple batches or instruments. For targeted analyses isotope dilution mass spectrometry is used to provide a robust normalization reference. Here, we present an approach that allows for the automated semi-quantification of metabolites relative to a fully stable isotope-labeled metabolite extract. Unlike many previous approaches, we include both identified and unidentified compounds in the data analysis. The internal standards are detected in an automated manner using the non-targeted tracer fate detection algorithm. The ratios of the light and heavy form of these compounds serve as a robust measure to compare metabolite levels across different mass spectrometric platforms. As opposed to other methods which require high resolution mass spectrometers, our methodology works with low resolution mass spectrometers as commonly used in gas chromatography electron impact mass spectrometry (GC–EI-MS)-based metabolomics. We demonstrate the validity of our method by analyzing compound levels in different samples and show that it outperforms conventional normalization approaches in terms of intra- and inter-instrument reproducibility. We show that a labeled yeast metabolite extract can also serve as a reference for mammalian metabolite extracts where complete stable isotope labeling is hard to achieve. [less ▲]

The isotropic constant of random polytopes with vertices on convex surfaces

in Journal of Complexity (2019), 54

Isotropic-isotropic phase separation in mixtures of rods and spheres: Some aspects of Monte Carlo simulation in the grand canonical ensemble

in Computer Physics Communications (2008), 179(1-3), 13-16

The isotropic-nematic interface in colloidal suspensions

Presentation (2005)

The isotropic-nematic interface in suspensions of platelets

Scientific Conference (2006)

Isotropic-nematic transition and cholesteric phases of helical Yukawa rods

in Journal of Chemical Physics (2016), 145(194904),

We present a Monte Carlo simulation study of helical Yukawa rods as a model for chiral liquid crystal mesogens.To simulate the cholesteric phase, we introduce a newsimulation method that uses softwalls ... [more ▼]

We present a Monte Carlo simulation study of helical Yukawa rods as a model for chiral liquid crystal mesogens.To simulate the cholesteric phase, we introduce a newsimulation method that uses softwalls and self-determined boundary conditions. We observe that the isotropic-nematic phase transition is shifted to lower volume fractions with decreasing salt concentration as well as with increasing internal pitch of the rods. For particular sets of interaction parameters, the sense of the cholesteric pitch inverts, i.e., depending on concentration, mesogens of a given handedness can produce cholesteric phases of both chiral senses. [less ▲]

The issue of fuzzy concepts in test construction and possible remedies

in European Journal of Psychological Assessment (2015), 31(1), 1-4

Issue Reframing by Parties: The Effect of Issue Salience and Ownership

in Party Politics (2019), 25(4), 507-519

Issue reframing occurs when parties, while addressing an issue, shift the frame toward other policy domains. The literature has found that party issue framing affects how voters think about issues, yet ... [more ▼]

Issue reframing occurs when parties, while addressing an issue, shift the frame toward other policy domains. The literature has found that party issue framing affects how voters think about issues, yet scholars remain largely in the dark as to when and how parties frame issues. The study at hand theorizes and investigates when and how parties reframe issues in their external communication. Drawing on novel Belgian data about parties’ official stances regarding a large number of policy issues combined with their verbal argumentation of why they took this exact position, we test a new theory about the drivers and mechanisms of issue reframing. We find that parties reframe issues in terms of policy domains that are both salient to the general public and that are salient to the party itself—meaning that it has a history of devoting attention to the policy domain and “owns” it. [less ▲]