New liquid-crystalline heteroalicyclic compounds

Abstract

A wide variety of new sulphur-containing heteroalicyclic liquid-crystalline compounds have been synthesized. Special attention has thus been focussed on the influence of the heteroatoms on the mesomorphic behaviour. 2-Cyclohexyl substituted 1,3-dithianes and 1,3-oxathianes have been found to be superior to those with 2-phenyl substituents. The clearing temperatures of the 2-phenyl-1,3-dithianes depend on the electron donating or electron accepting properties of the substituents attached to the phenyl group. The mesophase stability of the 2-cyclohexyl substituted (hetero)alicycles increases in the order: 1,3-dioxane < 1,3-oxathiane < cyclohexane < 1,3-dithiane. This order is partly reversed for the cyclohexane annulated compounds: 1-oxa-3-thiadecalin < 1,3-dioxadecalin < decalin < 1,3-dithiadecalin. Selected values of the birefrigence and some melting enthalpies have been measured.     

Reversing the Brazil-nut effect: competition between percolation and condensation

We report on experiments on vertically shaken binary granular mixtures, which separate into their components due to the external excitation. This well-known phenomenon, where large particles rise to the top of the mixture, is called the Brazil-nut effect. Recent theoretical findings predict also a reverse Brazil-nut effect, where large particles sink to the bottom of the container. We choose spherical beads of various diameters and materials in order to observe the transition from Brazil-nut effect to its reverse form. The direction of demixing depends sensitively on the external excitation, so that it is possible to switch between both effects for a given mass density ratio.     

Conformational analysis—CXVII : Methyl ethyl disulfide. Molecular mechanics and molecular orbital calculations

The conformation of methyl ethyl disulfide was investigated by molecular mechanics calculations using a recently developed force field for sulfur-containing alkanes. The results indicate that in the gas phase the molecule exists predominantly in two conformations, both with the CSSC dihedral angle gauche (84°), and the SSCC dihedral angle either gauche (72°) or trans (179°), and the methyl protons staggered. Ab initio molecular orbital calculations using an STO-3G basis set were employed to corroborate that these two conformations are of roughly equal stability, and that the next most stable conformation (by 0.6 kcal/mole) has the SSCC dihedral angle gauche (295°) with the terminal methyls proximal. In contrast to earlier CNDO/2 (spd) predictions, the SSCC cis conformer is the least stable, and no sizable attractive S?HC nonbonded interactions are discerned. Reasons for this are traced to a failure of the CNDO/2 method, which is especially serious when d orbitals are included in the basis set (spd) and the rigid rotor approximation is used. The present results are found to be consistent with recent electron diffraction, IR, Raman spectroscopic and X-ray diffraction data. The conformation of diethyl disulfide was also investigated by molecular mechanics calculations, and again gauche and trans SSCC arrangements are predicted to be preferred.     

Multifactorial analysis of affinity-mass spectrometry data from serum protein samples: A strategy to distinguish patients with preeclampsia from matching control individuals

A multifactorial differential analysis of serum proteins using mass spectrometry distinguished samples from pregnant women with severe early-onset preeclampsia (n = 11) from those of control individuals with uneventful pregnancies (n = 13). Serum proteins were fractionated by either their affinities to reversed-phase material coated magnetic beads or by fractionated precipitation. The on-average most abundant ion signals were observed at m/z 9390, 9103, and 8886. The best differentiating ion signals between the two sample groups were found at m/z 13,715, 13,834, and 13,891. The normalized intensities of these ion signals were on-average lower in the preeclampsia group than in the control group. The six ion signal intensities enabled sorting of the individual spectra with high accuracy. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that a protein band migrating just above the 14 kDa marker band contained transthyretin (P02766; Mr (avg.): 13,761). Densitometric analysis of the transthyretin bands showed lower intensities in the preeclampsia samples with respect to those of the controls. Nephelometric analysis of the serum samples determined the mean concentration of transthyretin in the preeclampsia group were lower (0.16 mg/mL; range: 0.13 to 0.20; SD: 0.03) than that in the control group (0.19 mg/mL; range: 0.14 to 0.22; SD: 0.02), substantiating the role of transthyretin concentration differences in the comparison of the two groups. Altogether, our findings support the theory of preeclampsia being a heterogeneous disorder that might be sub-classified by a defined proteome signature in maternal blood using multifactorial analysis of affinity-fractionated serum samples.     

Multiple lot-sizing decisions in a two-stage production with an interrupted geometric yield and non-rigid demand

In a production system with random yield, it may be more cost effective to release lots multiple times towards fulfilling a customer order. Such a decision, called the multiple lot-sizing problem, has been investigated in various contexts. This paper proposes an efficient algorithm for solving a new multiple lot-sizing problem defined in the context of a two-stage production system with non-rigid demand when its process yields are governed by interrupted geometric distributions. We formulate this problem as a dynamic program (DP) and develop lemmas to solve it. However, solving such a DP may be computationally extensive, particularly for large-scale cases with a high yield. Therefore, this study proposes an efficient algorithm for resolving computational issues. This algorithm is designed to reduce the DP network into a much simpler algorithm by combining a group of DP branches into a single one. Extensive experiments were carried out. Results indicate that the proposed reduction algorithm is quite helpful for practitioners dealing with large-scale cases characterized by high-yield.     

The characteristics of gas/liquid flow in large risers at high pressures

Although most of the work reported on two-phase flows are limited to small pipe diameters, two-phase flow in large risers are increasingly being encountered in the petroleum and nuclear industries. In the present work, a wire mesh sensor was employed to obtain void fraction and bubble size distribution data and visualizations of steam/water flow in a large vertical pipe (194 mm in diameter) at 46 bar. For comparison purposes, measurements were made at similar phase velocities and physical properties to a dataset for nitrogen/naphtha flow in a similar-sized riser. There exist significant differences between both sets of data. Churn-turbulent flow is observed in the present work instead of slug flow, and this differs from the intermittent and semi-annular flow patterns reported for nitrogen/naphtha data. The mean void fraction of the nitrogen/naphtha data is higher than that of the present steam/water data due to the differences in purity in the liquid phases. Furthermore, core peak distributions are observed for the present work in contrast to the flatter profiles deduced for the nitrogen/naphtha using a power law relationship.     

Ferroelectricity driven by Y d0-ness with rehybridization in YMnO3

We investigated electronic structure of hexagonal multiferroic YMnO3 using the polarization dependent x-ray absorption spectroscopy (XAS) at O K and Mn L(2,3) edges. The spectra exhibit strong polarization dependence at both edges, reflecting anisotropic Mn 3d orbital occupation. Moreover, the O K edge spectra show that Y 4d states are strongly hybridized with O 2p ones, resulting in large anomalies in Born effective charges on off-centering Y and O ions. These results manifest that the Y d(0)-ness with rehybridization is the driving force for the ferroelectricity, and suggest a new approach to understand the multiferroicity in the hexagonal manganites.     

Topological Anderson insulator in three dimensions

We show that disorder, when sufficiently strong, can transform an ordinary metal with strong spin-orbit coupling into a strong topological "Anderson" insulator, a new topological phase of quantum matter in three dimensions characterized by disordered insulating bulk and topologically protected conducting surface states.