Characterization of polyethylene with partially random chlorine substitution

A series of chlorine‐containing polymers were prepared by ring‐opening metathesis polymerization (ROMP) followed by hydrogenation. This synthesis route was chosen specifically so that chain microstructures would be obtained that resembled copolymers of ethylene and vinyl chloride. The chlorine content was varied by the copolymerization of 5‐chlorocyclooctene and cyclooctene. Differential scanning calorimetry, light microscopy, tapping‐mode atomic force microscopy, wide‐angle X‐ray diffraction (WAXD), and density were employed to characterize the polymers. The copolymers had certain restrictions on the length of the methylene sequence between substituted carbons, however, ROMP copolymerization introduced enough variation in the methylene sequence length that model copolymers with the equivalent of 14 mol % vinyl chloride or less closely resembled random copolymers of ethylene and vinyl chloride. These materials organized as spherulites and exhibited the orthorhombic crystal form. Constraints on the placement of chlorine atoms strongly affected the crystallization of polymers with more than the equivalent of 14 mol % vinyl chloride. More regular chlorine substitution along the polyethylene chain translated into better ordered crystal structures with sharp melting peaks. The granular morphology of these materials at ambient temperature was interpreted as fringed micellar crystals. The WAXD patterns provided definitive evidence that chains in the fringed micelle took the hexagonal crystal form. The lower density hexagonal form facilitated the crystallization of short ethylene sequences and accommodated chlorine atoms more easily than the orthorhombic form. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2062–2070, 2003     

Deformed states of neutron-deficient cerium and neodymium nuclei

High-spin levels in Ce and Nd isotopes excited by the reactions ^120,122Sn(¹⁶O, 3n) ^{133, 135}Ce and ^{122, 124}Te(¹⁶O, 3n)^{135, 137}Nd have been studied by in-beam γ-ray spectroscopic methods (prompt and delayed spectra, excitation functions, angular distributions and γ-γ coincidences). Bands built on the $\text{11}\text{2}{}^{\mathrm{?}}$ isomeric levels in ¹³⁵Ce and ¹³⁷Nd and on the $\text{9}\text{2}{}^{\mathrm{?}}$ground states in ¹³³Ce and ¹³⁵Nd have been found. A prolate deformation is required for these nuclei in order to explain the E2/M1 mixing ratios and the level ordering of these bands.     

An examination of the finite difference numerical approach to the solution of electrochemically-induced diffusive transport at stationary solid cylinder electrodes: Single sweep voltammetry of reversible systems

Extensive computational testing of a finite-element Galerkin/B-spline (GBS) numerical model of electrochemical transport recently developed in this laboratory yielded results which agreed with predictions for planar and spherical hydrodynamics but were in disagreement with M.M. Nicholson's explicit finite difference (CEFD) model for the important case of nernstian boundary conditions at stationary solid cylinder electrodes. This disparity prompted a detailed re-examination of both models. We shown in this note that the CEFD approach was imprecise in its formulation of the first-order space derivative and was incorrect in applying established criteria for computational stability. Our re-examination of the same problem using implicit (IFD) and modified explicit finite difference (EFD) methods gave stable solutions which agreed fairly closely with each other; the GBS model agreed with the IFD solution to within ±0.3%. We are thus obliged to conclude that attempts to use the original non-dimensionalized cylindrical CEFD model to calculate concentration profiles, surface fluxes, and current-voltage curves are destined to yield incorrect results except for large radii, fast potential scan rates, or both, in which cases transport occurs essentially by planar diffusion which this model adequately describes.     

Measurement of sound insulation with a sound level meter

The present technique for measuring the airborne sound insulation of walls and floors, involving measurements in 16 one-third octave bands, is tedious and expensive. The method provides more information than is needed for most purposes, and is more suited to research.Several investigators have proposed the measurement of the overall A-weighted sound level difference using a sound level meter, with a broad band source of white or pink noise. Consistent results have been obtained but their relation to accepted rating methods such as STC is rather empirical.The reference curves used for airborne sound insulation, i.e. STC and HPGW are very similar to the A weighting curve, and if the latter were adopted as the reference curve, there would be a firm theoretical basis for measurement with a sound level meter. Measurement of the difference between the linear sound level of a source of white noise, and the A weighted received level, would in practice be a test of the conformity to the A weighting curve of the transmission loss curve of the partition. Adverse deviations would show as a higher received level. Favourable deviations would have little effect.A study of practical walls and floors, taken from National Building Studies Research Paper 33, showed that there was good correlation between the sound level difference calculated as if it had been measured directly with a sound level meter, and a proposed rating method similar to ISO R717, but using the A weighting curve as the reference curve. Ninety-six per cent of results were within ±1 dB.The practical difficulties of achieving a reasonably flat transmitted spectrum, and of correcting for room absorption will reduce this precision, but bearing in mind the practical success of other short tests, the proposed test should provide a rapid test which is adequate for approval purposes.     

What can we learn from the finite temperature renormalization group?

The renormalization group for finite temperature quantum field theories is studied, in particular for λ?⁴. It is shown that the “high” temperature limit can only be discussed perturbatively ifT dependent renormalization schemes are implemented. Zero temperature renormalization schemes or renormalization at some fixed reference temperatureT _o are both inadequate as they imply perturbative expansions about fixed points of the renormalization group which are associated with a zero temperature system and a system at temperatureT _o respectively.T dependent schemes give rise to an expansion about the true fixed point of the system, the resulting renormalization group allows the entire crossover between high and low temperature behaviour to be investigated.     

Linear polarization and angular correlation of continuumγ-rays

The linear polarization and angular correlation of continuumγ-rays have been measured for the reactions¹²⁴Sn(⁴⁰Ar,xn)^164?x Er and¹¹⁰Pd(⁴⁰Ar,xn)^150?x Gd. From the angular correlation experiments we find that the dominant fractions of the radiation are stretched quadrupoles (50–80%) and stretched dipoles. The linear polarization results are compatible with mainlyM1 multipolarity for the dipole part of the continuum in the energy range between 0.5 and 1.6 MeV.     

Vibrational circular dichroism of matrix-isolated molecules

Vibrational circular dichroism (VCD) spectra are reported for (+), (?) and (±) α-pinene, and (?) ß-pinine, isolated in argon matrices at ≈ 18 K. These are the first observations of VCD of matrix-isolated molecules. Spectra are limited to the CH stretching region (2800–3100 cm^?1). In all cases, the VCD spectra are substantially more structured than the corresponding room-temperature spectra, as a result of much narrower linewidths. Further, VCD magnitudes are greater due to decreased cancellation of overlapping transitions with oppositely signed VCD. The largest anisotropy ratios observed are >5 × 10^?4 and are larger than any reported for room-temperature solutions of organic molecules. This technique will permit substantially more definitive evaluations of theoretical calculations of VCD.     

12th annual advanced photon source users meeting and workshops

The advantages of synchrotron infrared radiation for micro-spectroscopy have already been demonstrated and exploited in most of the synchrotron facilities. The development of a similar instrument at the ESRF was driven by a twofold motivation.     

A practical microbiochemical procedure for analysis of vitamin E in either solid or fluid tissues

The information presented above demonstrates the usefulness of the procedure to vitamin E research, and is also intended to encourage its application to the solution of other problems where information on the distribution of molecules that can be analyzed by mass spectrometry is important.