The effect of (natural) polyols on the initial colour of heavy metal- and zinc-free poly(vinyl chloride)

The propensity of (natural) polyols dispersed in heavy metal- and zinc-free PVC sheets to improve the initial colour, e.g. the colour during the first minutes of exposure to high processing temperatures (short-term stability), has been investigated. It is shown using W(Lab) values that the initial colour improves upon addition of polyols containing primary hydroxyl groups. The polyols act as HCl scavengers, presumably via an acid-catalysed S_N2 substitution of the primary hydroxyl groups by chloride ions. In contrast, polyols with only secondary or tertiary hydroxyl groups accelerate the thermal degradation of PVC. Notwithstanding, the efficacy of the (natural) polyols containing primary hydroxyl groups will be reduced if the polyol is susceptible to competitive acid-catalysed intramolecular cyclodehydration reactions under the processing conditions. This is substantiated by a comparison of the behaviour of mannitol and 3,4-di-O-methyl-d-mannitol. The methylated derivative, which is less prone to undergo intramolecular cyclodehydration, improves the initial colour of heavy metal- and zinc-free PVC sheets more significantly than mannitol itself.     

Liquid crystalline properties of 4‐hexyloxybenzylidene‐4′‐alkyloxyanilines

The liquid‐crystalline polymorphism of the homologous series of 4‐hexyloxybenzylidene‐4′‐alkyloxyanilines is investigated. Basing on the polarization microscopy (POM, TOA), the DSC calorimetry and miscibility studies the following mesophases were detected: nematic, smectic A, smectic C and smectic I. The phase diagrams of the compounds of these series with 4‐hexyloxybenylidene‐4′‐pentylaniline (as the standard of mesophases) show induction of the smectic F mesophases. Their dependence on the alkyl chain length and mole fraction is shown.     

Liquid crystalline guanidinium phenylalkoxybenzoates: towards room temperature liquid crystals via bending of the mesogenic core and the use of triflate counter ions

A series of guanidinium salts 1(C _n ) _m –4(C _n ) _m ?X bearing phenyl alkoxybenzoate cores have been synthesised and their mesomorphic properties have been investigated by polarising optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction experiments (small-angle X-ray scattering and wide-angle X-ray scattering). While compounds 1(C₁₂)₁?X and 3(C₁₂)₁?X with one alkoxy chain showed smectic A (SmA) phases irrespective of the counter ion, compounds 1(C₁₂)₂?OTf and 3(C₁₂)₂?OTf with two alkoxy chains displayed SmA phases and the corresponding chlorides 1(C₁₂)₂?Cl and 3(C₁₂)₂?Cl displayed Col_h. Guanidinium salts 1(C _n )₃–4(C _n )₃?X with three alkoxy chains showed Col_h phases. Whereas the use of cyclic guanidinium head groups rather than acyclic ones had only a minor influence on the mesophase properties, melting points were significantly decreased by bent core units instead of linear core units. Replacement of chloride counterions by triflate lead to a further depression of the clearing points and shifted the mesophase towards room temperature.     

Accurate iteration-free mixed-stabilised formulation for laminar incompressible Navier–Stokes: Applications to fluid–structure interaction

Stabilised mixed velocity–pressure formulations are one of the widely-used finite element schemes for computing the numerical solutions of laminar incompressible Navier–Stokes. In these formulations, the Newton–Raphson scheme is employed to solve the nonlinearity in the convection term. One fundamental issue with this approach is the computational cost incurred in the Newton–Raphson iterations at every load/time step. In this paper, we present an iteration-free mixed finite element formulation for incompressible Navier–Stokes that preserves second-order temporal accuracy of the generalised-alpha and related schemes for both velocity and pressure fields. First, we demonstrate the second-order temporal accuracy using numerical convergence studies for an example with a manufactured solution. Later, we assess the accuracy and the computational benefits of the proposed scheme by studying the benchmark example of flow past a fixed circular cylinder. Towards showcasing the applicability of the proposed technique in a wider context, the inf–sup stable P2–P1 pair for the formulation without stabilisation is also considered. Finally, the resulting benefits of using the proposed scheme for fluid–structure interaction problems are illustrated using two benchmark examples in fluid-flexible structure interaction.     

Laser Stabilisation for the Measurement of Thermal Noise

In order to measure the thermal noise of a mirror suspended in a vacuum it is necessary for the length measurement error due to intensity and frequency noise of the probe laser to be reduced below the thermal noise level. Here we report on an experiment to reduce the frequency and intensity noise of a 40mW Nd:YAG laser for this purpose. The frequency is stabilised using the standard reflection locking technique. To stabilise the laser intensity a technique which uses the properties of an in loop light field has been developed. This technique is capable of suppressing the intensity noise below the shot noise limit without reducing the useful laser power. A servo based on this technique has been designed and tested. The experimental results indicate that the laser noise can be reduced to a level which will allow a displacement sensitivity of 1.5 × 10^-19m/ Hz for the detection of thermal noise in a frequency band of 10 to 500Hz.     

Self-avoiding walks in slits and slabs with interactive walls

Self-avoiding walk models of a polymer confined between two parallel attractive walls in two and three dimensions (slits and slabs, respectively) have recently had a revival of interest. They were first studied as simple models of steric stabilisation and sensitised flocculation in colloids. The revival has been catalysed by new exact solution techniques, that have allowed the solution of directed walk models in two dimensions in full generality, and by new Monte Carlo techniques that have allowed the simulation of the full parameter space in the three-dimensional slab model. Additionally, rigorous techniques applied to the slab problem have also yielded new results. The contributions to the study of this problem that have been recently added include a novel phase diagram for the “infinite-slab” (when the walls are a macroscopic distance apart but both walls may still “see” the polymer) the delineation of the repulsive and attractive regimes of the parameter space, and a conjectured scaling theory for the problem in general dimensions.     

Study of the high temperature reactions of a hindered aryl phosphite (Hostanox PAR 24) used as a processing stabiliser in polyolefins

The processing stabilising performance of various phosphorous antioxidants in polyolefins is affected significantly by their chemical composition. In order to explore the mechanism of stabilisation, the reactions of a hindered aryl phosphite [tris(2,4-di-tert-butylphenyl)phosphite (DTBPP), Hostanox PAR 24] were investigated at temperatures corresponding to polyethylene processing. The thermal and thermo-oxidative stability of the additive was determined by differential scanning calorimetric (DSC) and thermogravimetric methods. DTBPP was heat treated under argon and oxygen at 200 and 240 °C. The stabiliser was reacted at 200 °C with azobisisobutyronitrile (AIBN) in oxygen-free environment (carbon centred radicals) and under oxygen (peroxy radicals), with dicumyl peroxide (DCP) in oxygen atmosphere (oxy radicals), and with cumene hydroperoxide (CHP) under argon. The reaction products were identified by FT-IR, HPLC and HPLC-MS. The results revealed that besides the known reactions of hindered aryl phosphites, thermal decomposition and recombination reactions also take place above the melting point of the antioxidant. DTBPP does not react with molecular oxygen, but its decomposition is accelerated by oxygen and especially by radicals. Accordingly, the heat-stability of phosphorous stabilisers also has to be taken into account in their application, as it is one of the factors which influence the processing stabilisation of polyolefins.     

The effect of noise on the Chafee-Infante equation: A nonlinear case study

We investigate the effect of perturbing the Chafee-Infante scalar reaction diffusion equation, , by noise. While a single multiplicative Itô noise of sufficient intensity will stabilise the origin, its Stratonovich counterpart leaves the dimension of the attractor essentially unchanged. We then show that a collection of multiplicative Stratonovich terms can make the origin exponentially stable, while an additive noise of sufficient richness reduces the random attractor to a single point.

     

One and Two Photon Excitation of Radiofrequency Trapped Ca+

射频囚禁离子被广泛应用于量子信息和冷分子制备. 对于从单个离子到10^6个离子不等的样品,这些原子的内能和外能可以被控制到非常高的精度. 重点讨论了利用射频囚禁的Ca+来作为频率计量的标准方法.     

Small angle neutron scattering studies on non-aqueous dispersions of calcium carbonate. Part III. Concentrated dispersions

Small angle neutron scattering has been used to examine calcium carbonate dispersions in toluene over the w/w concentration range 5 to 40 %. The particles were stabilised by a combination of a surface active agent and a linear polymeric molecule. Analysis of the experimental data gave results for the structure factorS(Q) and the pair correlation functiong(r).Theoretical computations of the structure factor were made using a hard sphere model and the mean spherical approximation approach. These analyses indicated that the interaction was essentially soft at low volume fractions but became hard at the higher volume fractions.