Viscoelastic properties of epoxy-diamine networks

Eight epoxy–diamine networks have been formed, diamines with 2 to 12 methylene groups being used as curing agents. Dynamic mechanical tests revealed four transition regions in the dynamic loss modulus/temperature relationship. Two possible explanations for the relaxation of the glycidyl portion of the structure are proposed. One of the relaxations could be due to the breakdown of hydrogen bonds through the hydroxyl and ether groups. The second could be ascribed to the relaxation of the unbonded glycidyl groups or a second relaxation of the glycidyl groups after the breakdown of the hydrogen bonds.     

Transformation of sound-pressure level from the free field to the eardrum presented in numerical form

In an earlier work [E. A. G. Shaw, J. Acoust. Soc. Am. 56, 1848-1861 (1974)], self-consistent families of curves which best fitted the experimental data from 12 studies were presented to show the average sound-pressure transformation from the free field to the human eardrum in the horizontal plane. Tabulated values of azimuthal dependence at 15-deg intervals in azimuth and transformation to the eardrum at 0 degree azimuth are given at 43 selected frequencies between 0.2 and 12 kHz. These values are self-consistent within 0.1 dB.     

Phase-unwrapping algorithm in the presence of discontinuities using a system with crossed grating

A new phase-unwrapping algorithm for the phase map containing discontinuities by the use of a system with crossed grating is described in this paper. A crossed grating is projected onto the object in the usual way, the deformed grating image acquired is Fourier transformed and the frequency spectra for the individual gratings are separated. Using both phase distributions which have different sensitivities, the correct phase values in the presence of discontinuities, especially those caused by the object with height steps, can be obtained. This algorithm is fast and accurate. The results of the measurement of a three-dimensional object with height steps are presented.     

LSO-Ce fluorescence spectra and kinetics for UV,VUV and X-ray excitation

Abstract

LSO-Ce fluorescence emission and excitation spectra and decay kinetics have been measured for UV, VUV and X-ray excitation at RT and 80 K. The features of the fluorescence excitation spectra of two types of cerium centres in the region 3 to 6 eV are analysed in the assumption of competitative absorption between them. It is shown that the centres can have similar absorption bands. Forbidden energy bandgap for LSO is evaluated to be not less than 6.5 eV.     

Solid polymers doped with rare earth metal compounds. III. Formation and stability of macromolecular complexes comprising neodymium nitrate and dipivaloylmethane in poly(ethylene oxide)

The solubility, complexation, and morphology in the Nd(NO₃)₃-PEO and Nd(Dpm)₃-PEO systems were investigated using the FTIR, DSC, TGA, WAXD, and SAXS techniques. In both systems, dissolution was verified by the absence of features characteristic of the bulk-phase dopants detectable with WAXD and DSC, and complexation was evident from the FTIR spectral shifts involving the stretching motions of the EO unit. The extent of the Nd³⁺-EO interaction was found to be much stronger with Nd(NO₃)₃ than Nd(Dpm)₃. As a consequence, a T_g elevation from 222K in pure PEO to 335K at an EO/Nd³⁺ ratio (defined as n) of between 4.0 and 5.6 was observed in the Nd(NO₃)₃-PEO system. Moreover, completely dry and amorphous complexes were obtained at n ≥ 5.6, while residual moisture accompanying complexes at n ≤ 4 was found to persist upon prolonged vacuum drying. Being intrinsically hygroscopic at all doping levels, the Nd(NO₃)₃-PEO system was found to absorb moisture from the atmosphere resulting in wet amorphous complexes, although precipitation of Nd(NO₃)₃)·6H₂O was observed at n ≤ 4. It was proposed that moisture present in the Nd(NO₃)₃-PEO system be classified into two categories. One is tightly bound to Nd³⁺ to satisfy its coordination requirement, which was determined to be 11. The other is loosely bound, which is capable of being removed by heating and returning upon exposure to the atmosphere. It is the latter that can be readily quantified by the TGA technique and that lowers T_g via plasticization. In addition to the observed minor FTIR spectral shifts, a relatively weak Nd³⁺-EO interaction in the Nd(Dpm)₃-PEO system resulted in a lack of the T_g elevation for PEO, persistence of the crystalline portion of PEO at all doping levels, and the formation of new crystalline phases as revealed by the WAXD patterns and the DSC thermograms. The short-range order in PEO does not appear to be perturbed, but the SAXS data suggest that the long range-order is disrupted by the presence of Nd(Dpm)³ at an extremely low doping level (i.e., n ≥ 60). © 1994 John Wiley & Sons, Inc.     

Best accessible estimation: Convergence properties and limiting forms of the direct and reduced versions

Best accessible estimation is an iterative numerical procedure based on the stochastic extension concept that an integral equation of the first kind is improperly posed because it ignores background noise on the unknown function and measurement or computational error in the known function. Certain restrictions on the “reduced” version of the method, introduced originally to combat extreme noise levels, without resort to manipulation of very large matrices, have been removed. Alternate computational methods are presented, together with a basis for choosing between them according to the relative seriousness of different sources of error in a particular problem. It is shown that, in the absence of computational error, the iterative procedure would converge to the minimum-residue approximate solution of minimum norm, when appropriate ellipsoidal norms are employed which are defined by the noise and error processes present. There is no restriction on the form or correlation of these processes. Practical tests to detect cumulative numerical error and terminate iteration have been evaluated. An example, using actual experimental data, is given of the ability of the method to enhance the effective resolution of measurements. It is noteworthy that, when the equation to be solved represents inference of the input to a physical instrument from its measured output, then the iteration reveals most rapidly those sources to which the instrument responds most strongly and for the measurement of which it would most logically be employed. The concept of strength of response is sharpened by identification with the singular value belonging to a pair of basis functions for input and output, measured in terms of signal to noise ratio.     

Fourier-transform infrared study of coextrusion-drawn poly(ethylene terephthalate)

The effects of initial morphology and extrusion temperature on the orientational anisotropy and conformational changes on coextrusion drawing of poly(ethylene terephthalate) (PET) have been determined by Fourier-transform polarized infrared spectroscopy. The samples were drawn from both amorphous and semicrystalline (50%) PET at 50 and 90°C. A strong influence of coextrusion drawing temperature was observed for overall chain orientation evaluated from the dichroic ratio of the 795-cm^?1 band for the samples prepared from the amorphous state: this dependence was less prominent in samples drawn from the semicrystalline state. Under the same drawing conditions, the dichroic ratio for the 973-cm^?1 trans band for samples prepared from the amorphous state was higher than from the semicrystalline state. Furthermore, in all samples, the relative intensity of this band was almost proportional to the degree of crystallinity. In all samples, the gauche content, evaluated from the 896-cm^?1 band, decreased with increasing draw ratio. However, the dichroic ratio of this band was near unity regardless of draw ratio, initial morphology, or extrusion temperature. From these results it is considered that all gauche units in the amorphous phase are almost isotropic in the extrusion-drawn samples with overall orientation arising largely from the crystalline chains possessing totally the trans conformation (973 cm^?1) in its content. In order to evaluate the deformation mechanism of the coextrusion drawing method, the relationship between the bulk and film surface orientation is also reported.     

Local existence theorems with estimates for\bar \partial _b on weakly pseudo-convex CR manifolds

Partially supported by NSF grants DMS 89-01455 and DMS 91-01161