Precise dipolar coupling constant distribution analysis in proton multiple-quantum NMR of elastomers

In this work we present an improved approach for the analysis of (1)H double-quantum nuclear magnetic resonance build-up data, mainly for the determination of residual dipolar coupling constants and distributions thereof in polymer gels and elastomers, yielding information on crosslink density and potential spatial inhomogeneities. We introduce a new generic build-up function, for use as component fitting function in linear superpositions, or as kernel function in fast Tikhonov regularization (ftikreg). As opposed to the previously used inverted Gaussian build-up function based on a second-moment approximation, this method yields faithful coupling constant distributions, as limitations on the fitting limit are now lifted. A robust method for the proper estimation of the error parameter used for the regularization is established, and the approach is demonstrated for different inhomogeneous elastomers with coupling constant distributions.     

An allenic Pauson-Khand approach to 6,12-guaianolides

Cyclocarbonylation of α-methylene butyrolactone-containing allene-ynes affords 6,12-guaianolide ring systems. Incorporation of the α-methylene butyrolactone early in a synthetic sequence is rare for reactivity reasons; however, this moiety proves to be beneficial to the allenic Pauson-Khand reaction. The three double bonds and the ketone in the resulting 5-7-5 ring system bear significant differences in their reactivity and are ideally positioned for synthetic application to 6,12-guaianolides and analogs.     

Central recirculation zone analysis in an unconfined tangential swirl burner with varying degrees of premixing

Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving the ability to produce low NOx systems coupled with wide stability limits. The common element is the swirl burner, which depends on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time dependent. The characteristics of the CRZ depend very strongly on the level of swirl (swirl number), burner configuration, type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success when compared to experimental results, the models still have difficulties at medium to high swirl levels, with complex geometries and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under varied combustion conditions with different geometries and some variation of swirl number in a generic swirl burner. CRZ behaviour has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than pure diffusive combustion.     

Searching for the Center on the Mathematics-Science Continuum

The history of mathematics and science integration in American schools can be illustrated through the use of a continuum which runs from math for math's sake at one end to science for science's sake at the other. True integration occurs at the center point. While published examples of integration focusing on process skills are common, those featuring integration of content are less often found. Two such lessons, developed around radioactive decay and efficiency in nature, are presented as examples of science and mathematics concepts taught in concert. Changes in preservice and in-service teacher training must occur if the potential for this type of integration is to be realized.     

Superfluorescence in the presence of inhomogeneousbroadening and relaxation

In this paper we show how inhomogeneous broadening produces dephasing, inhibits cooperative emission and thus reduces the intensity of the SF pulse. We also show how electronic relaxation or time-dependent hyperfine interactions can mollify the effect of inhomogeneous broadening so that SF can be recovered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transference numbers for anhydrous methanol solutions at 10 and 25°C

Transference numbers are reported for LiCl and NaCl in methanol at 25°C and for NaCl, KCl, and Bu₄NBr in methanol at 10°C. The potentiometric moving-boundary method as developed by Kay and Fratiello was employed to give a precision of about 0.05% and an accuracy of at least 0.1% as indicated by two independent determinations of the conductances of the Cl^– and Br^– ions. The data are extrapolated by the Fuoss-Onsager theory, and the magnitude of the electrophoretic effect is calculated as described by Kay and Dye. The agreement with this theory is quite good at both temperatures, although the å value required in the case of Bu₄NBr is considerably larger than that obtained from conductance data. This agreement contrasts with that obtained for ethanol and acetone solutions where the measured electrophoretic effect is considerably larger than the corresponding calculated values. The importance of this fact in the determination of ion-pair association constants is discussed.     

Synthesis and properties of metal clusters in polymeric matrices

A one-step plasma deposition process is described which allows the uniform dispersion of small metal clusters throughout a thin film polymer matrix. Plasma parameters and plasma gas phase diagnostics relevant to the control of film composition and structure are discussed. Chemical and structural analytical techniques such as I.R. absorption spectroscopy, E.S.C.A., Auger electron spectroscopy, X-ray fluorescence, X-ray and electron diffraction and microscopy are used to characterize the cluster containing films. Changes in cluster size and shape as a function of volume fraction and as a result of post deposition annealing are described. Optical and electrical properties are presented below and above the onset of percolation and are evaluated in terms of contemporary effective medium theories.     

Phase equilibria in the n-hexane + diethylamine system

Pressure-temperature-composition data for the binary system composed of n-hexane and diethylamine have been determined over a range of conditions extending into the critical region. Dew, bubble and critical points at six compositions are reported in this paper. Vapor pressures and liquid densities of pure diethylamine are also reported. Phase equilibria in this nonpolar+polar system have been correlated using the Peng-Robinson (PR) equation. The PR equation is shown to work well for this weakly associating system although it fails to reproduce the detailed behavior of the critical locus. A remarkable feature of this binary system is that the critical locus is also the locus of points of maximum temperature (maxcondentherm) and pressure (maxcondenbar). As a consequence, there is no retrograde region in the system. The critical locus also exhibits a minimum in temperature which is characteristic of azeotropic behavior in the critical region.