Residual Expansion Research Articles

Effect of Residual Strain on the Electronic Structure of Alumina and Magnesia

The reflectance spectra of polycrystalline Al2O3 and singlecrystal MgO, with different surface treatments were measured using vacuum ultraviolet (VUV) spectroscopy to determine the effect of residual stresses and strains. The bulk stresses were estimated using the R‐line flourescence of trace Cr3+ in Al2O3. No grain‐size dependence was observed for the residual thermal expansion anisotropy stresses in polycrystalline Al2O3. The effects of mechanical‐polishing‐induced damage in Al2O3 shifted the band‐to‐band and exciton transitions to higher energies, compared with those of chemically polished Al2O3. There was little difference in peak positions between cleaved and chemically polished surfaces of MgO. However, mechanically polished MgO surfaces exhibited band‐to‐band and exciton‐peak shifts to higher energies. The VUV technique of determining the exciton‐peak and band‐gap shifts was used with knowledge of the band‐gap strain coefficient to estimate the magnitudes of residual surface stresses in the 1‐μm surface layer probed. The polishing‐damage‐induced residual surface stress is 2.2 GPa for Al2O3 and 1.1 GPa for MgO. These values are based on band‐gap strain coefficients of 700 meV/(lin% strain) derived for Al2O3 and 400 meV/(lin% strain) estimated for MgO.

Exfoliation of intercalated graphite

By X-ray diffraction, exfoliated graphite-Br 2 was found to exhibit the same in-plane superlattice ordering as intercalated graphite prior to exfoliation. This ordering persisted even after heating for 1 hr at 1700°C. By dilatometry, a single exfoliation event was found to consist of multiple expansion spurts, which occurred at ~ 150 and ~ 240°C for the first exfoliation, and ~ 100 and ~ 240°C for subsequent cycles. The amount of expansion was found to increase with decreasing intercalate activity during intercalation. With exfoliation cycles to higher temperatures or longer times, the amount of residual expansion after the collapse on cooling increased until no second exfoliation was observed or reheating. Due to intercalate desorption, the amount of expansion for concentrated samples increased with increasing sample width; desorbed samples showed little width dependence. Acoustic emission was observed before appreciable expansion during the first exfoliation cycle; it was not observed during the collapse or subsequent exfoliation cycles. A model of exfoliation involving intercalate islands is proposed.

Numerical Methods of Noise Reduction for Frequency Domain SEM

ABSTRACT This paper addresses the numerical problem of performing a pole residue expansion on noisy data. A method of combining dissimilar data sets to achieve an effective increase in signal-to-noise ratio is tested on computer generated data simulating scattering from a sphere and from a thin wire. The data is corrupted with white Gaussian noise and the algorithm is tested for signal-to-noise ratios ranging from -10 dB to 60 dB. An iterative version of the algorithm is also tested. Finally, the problem of filtering noise from relatively quiet data is discussed and a novel filtering algorithm is presented.

Fe-Cu 2元系混合圧粉体の焼結過程における異常膨張に及ぼす黒鉛添加の影響について

Using mixed powder compacts of Fe-8.0%Cu-C ternary system with different graphite contents, and Fe-Cu-1.0%C ternary system with different Cu contents, a study of the effect of graphite content on the elimination of the abnormal expansion during the heating process of the Fe-Cu binary mixed powder compacts was carried out mainly by the differential dilatometric method.The results obtained were as follows:(1) In the mixed powder compacts of the Fe-8.0%Cu-C ternary system with graphite contents up to 0.6%, the abnormal expansion persisted through out the sintering process in the γ region, although the amount of expansion was smaller than that of the Fe-8.0%Cu binary system.However, the specimens with the graphite content more than 0.8% showed a maximum expansion at a temperature slightly higher than 1090°C and then shrank at higher temperatures.(2) Dimensional change of the Fe-8.0%Cu-C ternary compacts subjected to isothermal sintering at 1150°C for 60 min decreased with increasing graphite content.For example, the residual expansion rate of the Fe-8.0%Cu binary system was 2.8%, while it was 1.05% for the specimen with 0.6%C and 0.05% for the specimen with 1.0%C, respectively. Furthermore, shrinkage was observed with the specimens containing more than 1.2%C.(3) The maximum expansion rate of the Fe-Cu-1.0%C ternary mixed powder compacts increased nearly in proportion to Cu content up to 6.0% but remained constant at higher Cu content.

On the role of the interstitial volume in the response of the rat to blood volume expansion.

Patterns of body fluid distribution and selected cardiovascular and renal responses were studied following vascular expansion in normal rats and in rats with altered interstitial fluid volume produced by dehydration, prehydration or hyperoncotic albumin infusion. In all four groups the patterns of the renal excretory response and the accompanying change in central venous pressure (CVP) were closely parallel and the disturbance in CVP was finally corrected in the presence of a considerable residual vascular expansion. During the diuresis and saluresis following iso-oncotic vascular expansion in prehydrated and dehydrated rats, both groups removed fluid chiefly from the interstitium; this fluid removal was attributable mainly to urinary excretion in prehydrated rats but mainly to redistribution into the cellsin dehydrated rats. In the latter series, preferential renal excretion of sodium over water was observed. Hyperoncotic vascular expansion led to a peak renal excretory response only 70% of that following iso-oncotic expansion. The excreted volume was accounted for by a similar depletion of interstitial fluid after the iso-oncotic load. These findings are consistent with the hypothesis that the renal response to volume expansion regulates some parameter which is more closely related to the mean central venous pressure than to the vascular volume. This regulation was associated with incomplete correction of the vascular expansion and absolute decrease in interstitial fluid volume compared to the initial size of that compartment. This provides support for a functionally important influence of the interstitial volume on venous compliance.

Frost action in cement paste

An earlier theory of frost action is further developed and its implications considered, particularly with regard to testing. Factors determining durability of paste, dimensions of sample, degree of saturation and rate of cooling are discussed. It is shown that cumulative residual expansion is a good indicator for testing frost resistance: samples can be evaluated after 10 to 15 freeze-thaw cycles. The results are discussed in relation to existing tests.

A Normal Mode Theory of an Underwater Acoustic Duct by Means of Green's Function

The resolvent Green's function technique is used to find the acoustic field due to a CW point source located in a laminar inhomogeneous medium. Results are in terms of a residue expansion (normal modes) and branch line integrals. This approach is then used to solve the wave equation for an underwater acoustic duct described by an Epstein layer. Only the residue expansion is evaluated. From the residue expansion, propagation loss is found as a function of range. Application to a realistic velocity‐depth profile indicates a pattern of beats resulting from a superposition of the normal modes. A general procedure is next described for obtaining exact solutions of the wave equation for a large variety of velocity‐depth profiles. This procedure may prove useful in developing future normal mode models.

THE INFLUENCE OF GRIND AND BURN ON THE CHARACTERISTICS OF SILICA BRICK1

Finer grinding improves the appearance of the brick and increases their strength somewhat but not in any marked degree, within the commercial limits of grinding. A grinding of from 15 to 20 minutes seems most desirable. The time of grinding does not affect the porosity appreciably. The firing temperature is the principal factor governing the final strength and also the permanent residual expansion. The maximum temperature cone 19, yielded the highest strength and the lowest expansion.