The evaluation of 4-hydroxy-3,5-di-tert-butylbenzyl alcohol as a combined antioxidant-tail-reducer for packed-column gas-liquid chromatography

Summary As an extension of previous work on the deactivation of diatomaceous supports by hydroxy compounds, 4-hydroxy-3,5-di-tert-butylbenzyl alcohol (HBBA) has been evaluated as a potential combined antioxidant tail-reducer. In contrast to diglycerol and the lower molecular weight polyoxyethylene glycols, HBBA is found to be an inefficient tail-reducer. The adsorption of HBBA from solution onto the surface of Phasesep P has been studied and possible explanations for the apparent lack of surface deactivation are offered. A reversed-phase high-performance liquid chromatographic assay for HBBA has been developed and used to monitor the adsorption of HBBA.     

Substituent effects on the chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane in the presence of disulfides and thiols

The chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane was investigated in the presence of four chain‐transfer agents: thiophenol (PhSH), thiobenzoic acid (BzSH), diphenyl disulfide (PhSSPh), and dibenzoyl disulfide (BzSSBz). The chain‐transfer constants for these compounds at 60 °C were 0.38 (PhSH), 0.76 (BzSH), 0.24 (PhSSPh), and 0.05 (BzSSBz). The variations in the thiol chain‐transfer constants could be explained in terms of the stability of the resulting radicals. The chain transfer to the disulfides, however, appeared to be determined by the electronic character of the disulfide bond, and this suggests that the transfer took place via an addition–fragmentation mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4421–4425, 2002     

Comparative Studies of Phase-Cycling Schemes for Multiple π-Pulse Sequences

Recently, a new phase cycling scheme was introduced by this laboratory for use in biological solid-state NMR experiments involving multiple π-pulses with characteristics that suggested it may enhance the sensitivity of these kind of experiments (Y. Li and J. N. S. Evans, 1995,Chem. Phys. Lett.241,79 and Erratum, 1995,ibid.246,527; Y. Li and J. N. S. Evans, 1996,J. Magn. Reson. B111,296). The new sequence followed the supercycled concept proposed a decade ago for heteronuclear decoupling experiments. In this paper, more detailed experiments demonstrate that the claim of enhanced sensitivity was unfounded, and in fact the supercycle proposed differs little from the established XY-8 and XY-16 based supercycles.     

纳米小球掩模技术

介绍一种纳米小球掩模技术.给出了这种掩模技术的原理和实验方法,分析了这种掩模中存在的各种缺陷及其原因和改进方法.并纠正了早期工作中对一些现象的误解.以这种掩模技术给出的各种金属小岛作为研究手段,提出了薄膜岛状生长研究的一种新的思路.     

A new proof of local C1,α regularity for solutions of certain degenerate elliptic p.d.e.

We prove C_loc^1,α estimates for solutions u?W^{1,p + 2} of the degenerate elliptic p.d.e. $\text{div}\text{(¦Du¦}{}^{\mathrm{p}}\text{Du) = 0}$ (p > 0).     

Itinerant oscillation with a cosine potential

The equations of motion of the planar itinerant librator are extended to involve a cosine potential rather than a harmonic form for interaction, and are solved numerically to produce the angular velocity autocorrelation function and its Fourier transform (real and imaginary parts). The behaviour of the cosine potential is matched with that of the harmonic potential through these functions and in general conforms more closely to the indication of zero-THz spectroscopy and computer simulation.     

Dissipators for symmetric quasi-free dynamical semigroups on the CAR algebra

Let L be a negative self-adjoint bounded operator on a Hilbert space $\text{H}$, and p a projection on $\text{H}$ with pLp trace class, and let {T_t: t ? 0} be the extension of {e^tL: t ? 0} to a strongly continuous semigroup of completely positive quasi-free unital maps of Fock type on the fermion algebra A$\text{H}$ built over $\text{H}$. Then it is shown that there exists a strongly continuous self-adjoint contraction semigroup {G_t: t ? 0} on the Hilbert space of the GNS decomposition of the quasi-free state gw_p such that in the representation of that state: T_t ? G_t(·)G_t, t ?0.     

The quantitative determination of FeS2 phases in coal by means of57Fe Mössbauer spectroscopy

A knowledge of the concentration of pyrite and marcasite in coals can provide important insight into the genesis of coal deposits. Determinations of the relative amounts of pyrite and marcasite by traditional methods of coal analysis are, however, beset with many difficulties. Using⁵⁷Fe Mössbauer spectroscopy and a mild chemical treatment with hydrofluoric acid, a technique has been devised for the quantitative determination of the relative concentrations of pyrite and marcasite in samples of whole coals or their low-temperature ashes. The sample preparation procedure is comparable to less accurate methods. Good qualitative agreement has been obtained between ore microscopic and Mössbauer spectroscopic techniques for a series of extensively investigated whole coal samples.     

The thermoconvective instability of plane poiseuille flow heated from below: A proposed benchmark solution for open boundary flows

The transient two-dimensional Navier-Stokes and energy equations have been solved numerically for flow in a horizontal channel heated from below in the Boussinesq limit. For the set of dimensionless parameters chosen, the flow consists of periodic transverse travelling waves resulting from a convective instability. The solution is proposed as a benchmark for the application of outflow boundary conditions (OBC) in time-dependent flows with strong buoyancy effects. Richardson extrapolation in both time and space is used in obtaining the solution. Field plots and profiles of velocity, temperature, vorticity and streamfunction at selected axial positions and times are also presented from the finest grid and smallest time step calculation. The calculations have been made on an extended domain so that the effects of OBC used in the present study would be negligible in the test region.     

The conductance of cyclic polyether-cation complexes

Precise conductance measurements are reported for sodium, potassium, and cesium salts in methanol and acetonitrile solutions containing cyclic polyethers dibenzo-18-crown-6 and dicyclohexyl-18-crown-6. Decreases in equivalent conductance caused by the addition of a cyclic polyether to solutions of constant ionic strength were analyzed by nonlinear least squares to give association constants and equivalent conductances of the cation-polyether complex. The selectivity observed for the complexing is a function not only of ionic size but also of solvent.