Calori- and Resistometric Analyses of Ageing and Precipitation in Aluminum-Copper Alloys

Specific heat versus temperature curves have been obtained on polycrystalline and single crystal specimens of Al-4 wt% Cu alloys during reheating after various age-hardening treatments. The results have been analysed in comparison with those of the hardness tests, dilatometric and X-ray structural measurements of the previous workers ; the results are useful in providing further information on the low temperature ageing or the first stage of the ageing and its relation to the high temperature ageing. The reversion phenomena in the alloys aged at low temperatures are attributed to the dissolution of the G.P. zone. The effects of the ageing temperature and ageing time upon both the reversion temperature and the heat of reversion are examined from the heat absorption, and it is confirmed that the reversion temperature rises with ageing temperature. The incubation period for formation of the G.P. zone has been determined as a function of ageing temperature. The results represent a C-curve in good agreement with that determined by the X-ray study. An evidence has been obtained for the formation of the G.P. zone at 190℃ after the θ" and θ\u27 precipitations. The kinetics of precipitation processes at higher ageing temperatures reaching close to the solvus has been investigated by the electrical resistivity measurement. It has been recognized that there are two distinct, independent precipitation processes at temperatures higher than 200℃ with the apparent activation energies of 30.1 and 25.4 kcal/mol, respectively. These processes seem to correspond to the θ and θ\u27 precipitations, respectively

Age-Hardening of Aluminium-Gold Alloys

Ageing characteristics of aluminium-gold dilute alloy have been investigated by measuring the yield stress and the electrical resistivity. Two-stage yield stress-ageing time curves separated by a fiat plateau have been obtained during ageing at temperatures below 200℃. The first stage proceeds rapidly without any incubation period. During low-temperature ageing, the electrical resistivity increases at first and shows a rather steep maximum despite the small content of gold. The present results can be explained by the formation of G.P.-zones at low ageing temperatures

Femtosecond-laser-encoded distributed-feedback color center laser in lithium fluoride single crystals

金沢大学教育学部A distributed-feedback (DFB) color-center laser was fabricated by the holographic encoding method using an infrared femtosecond (fs) laser. Laser active color centers, waveguide structures and permanent gratings were written deep in lithium fluoride (LiF) crystals. It was shown that a refractive index change estimated from a guide propagation method was approximately +1% at a wavelength of 633 nm. The results show that the fabricated DFB laser structure oscillates at room temperature

Delta-like 4 is indispensable in thymic environment specific for T cell development

The thymic microenvironment is required for T cell development in vivo. However, in vitro studies have shown that when hematopoietic progenitors acquire Notch signaling via Delta-like (Dll)1 or Dll4, they differentiate into the T cell lineage in the absence of a thymic microenvironment. It is not clear, however, whether the thymus supports T cell development specifically by providing Notch signaling. To address this issue, we generated mice with a loxP-flanked allele of Dll4 and induced gene deletion specifically in thymic epithelial cells (TECs). In the thymus of mutant mice, the expression of Dll4 was abrogated on the epithelium, and the proportion of hematopoietic cells bearing the intracellular fragment of Notch1 (ICN1) was markedly decreased. Corresponding to this, CD4 CD8 double-positive or single-positive T cells were not detected in the thymus. Further analysis showed that the double-negative cell fraction was lacking T cell progenitors. The enforced expression of ICN1 in hematopoietic progenitors restored thymic T cell differentiation, even when the TECs were deficient in Dll4. These results indicate that the thymus-specific environment for determining T cell fate indispensably requires Dll4 expression to induce Notch signaling in the thymic immigrant cells

Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J=6-5 Line

We report on the results of a Submillimeter Array interferometric observation of the proto-planetary nebula CRL 618 in the 12CO J=6-5 line. With the new capability of SMA enabling us to use two receivers at a time, we also observed simultaneously in the 12CO J=2-1 and 13CO J=2-1 lines. The 12CO J=6-5 and 13CO J=2-1 lines were first interferometrically observed toward CRL 618. The flux of the high velocity component of the 12CO J=6-5 line is almost fully recovered, while roughly 80% of the flux of the low velocity component is resolved out. The low recovery rate suggests that the emission region of the low velocity component of the 12CO J=6-5 line is largely extended. Continuum emission is detected both at 230 and 690 GHz. The flux of the 690 GHz continuum emission seems to be partially resolved out, suggesting dust emission partly contaminates the 690 GHz continuum flux. The cavity structure, which has been confirmed in a previous observation in the 12CO J=2-1 line, is not clearly detected in the 12CO J=6-5 line, and only the south wall of the cavity is detected. This result suggests that the physical condition of the molecular envelope of CRL 618 is not exactly axial symmetric.Comment: 24 pages, 9 figures, 1 table, accepted for publication in AJ. Full resolution version available at http://www.asiaa.sinica.edu.tw/~junichi/paper