Oxidation Resistance of Thermal Barrier Coatings Based on Hollow Alumina Particles

Thermal barrier coatings were synthesized in a single step process from a slurry containing Al microspheres onto different Ni-based superalloys. Upon growth of the coating a top coat of hollow alumina spheres linked to an aluminium diffused coating through an alumina TGO formed. The isothermal and cyclic oxidation tests at different temperatures (900 till 1100 °C) up to 1000 h or 1500 cycles revealed progressive growth of different thermal oxides depending on the substrate composition. Faster degradation of the coatings occurred in the titanium-rich substrates (e.g. IN-738LC and PWA1483) compared to the titanium-poor ones (CM-247LC and René N5). By comparing with conventional low activity aluminide coatings, it appeared that the incorporation of alloying elements (notably Ti and Ta) to the diffused layers upon the high activity slurry coating process is responsible for such fastest degradation.     

Epithelial carcinogenesis in the mouse: correlating the genetics and the biology

Tumour formation relies on a complex combination of genetic and environmental factors. In particular, the contributions from inherited predisposition genes as well as carcinogens, for example from cigarettes or in the diet, are amongst the major contributors to tumorigenesis. Since the study of such processes in particularly difficult in human cancers, the availability of a well-defined model system is of obvious benefit. The mouse skin model of multistage carcinogenesis offers an excellent tool for the study of the target cells, the target genes and the biological events associated with neoplasia. In this system, tumorigenesis occurs in a series of defined stages, each of which is characterized by specific and reproducible alterations in genes such as H-ras, cyclin D1, p53 and p16INK4A. Additional changes occur in the production of, or response to, factors such as transforming growth factor beta (TGF beta). These genetic and biological alterations are mirrored in human tumours of epithelial origin. Hence, research into the general principles of tumour initiation, promotion and progression in the context of the mouse skin model is likely to prove valuable in the continual search for new methods for the diagnosis, prevention, and therapeutic treatment of human cancers.     

Charging of spacecraft materials simulated in a scanning electron microscope

The scanning electron microscope has been used to apply electric charge to spacecraft insulating materials, and to photograph the resulting patterns of charge distribution. Anomalies, possibly microscopic discharges, have been observed, usually associated with strong differential charging between adjacent regions of the same material. In thin materials, electron-beam penetration, temporarily induced conductivity and permanent subsurface damage have been identified.     

Dipole admittance for magnetoplasma diagnostics

A method is presented for calculating the admittance of a short thin dipole antenna in a cold collisional magnetoplasma. The theory is quasi-static, and the results are slightly more accurate than in previous analyses. Numerical calculations of admittance as a function of frequency are presented for several different orientations of the dipole with respect to the magnetic field. For any orientation the calculations show that the plasma frequency and the upper hybrid frequency can be readily identified.     

Effect of water soluble extract of nacre (Pinctada maxima) on alkaline phosphatase activity and Bcl-2 expression in primary cultured osteoblasts from neonatal rat calvaria

The nacre (mother of pearl) layer of the oyster Pinctada maxima shell can initiate bone formation by human osteoblasts in vivo and in vitro and is a new biomaterial that induces osteogenesis. This activity of nacre could be due to its water-soluble matrix. We examined the action of a water-soluble extract of nacre on the osteoblast phenotype of cells isolated from rat neonatal calvaria by measuring alkaline phosphatase (ALP) activity and by localization of the anti-apoptotic protein Bcl-2 by immunocytochemistry. ALP activity was increased 7% (p<0.001) by 100 g proteins/ml extract and 20% (p<0.001) by 50 g proteins/ml extract, but a low concentration of extract decreased the ALP activity by 8%. Cells treated with a high aspartic acid content fraction of the extract had increased ALP activity (23%, p<0.0001). Nacre extract and the fraction have no effect on the proliferation of mature osteoblasts. Immunoreactive Bcl-2 was overproduced in the cytoplasm and nuclei of osteoblasts at all stages of culture. Bcl-2 was found over the whole chromatin in quiescent and mitotic cells at the end of mitosis in the two nuclei in one cell, before cytodieresis. Bcl-2 was also found over chromosomes. Thus, nacre extract stimulates Bcl-2 production in osteoblasts, that is correlated with the cell cycle. Bcl-2 was also abundant in the nucleoli of extract-treated cells. Thus, the concentration and subcellular distribution of Bcl-2 in osteoblasts in primary cultures is influenced by nacre extract, and related to the cell cycle and the regulation of gene expression. Hence, knowledge of how water-soluble extracts of Pinctada maxima nacre act on osteoblasts in vitro may reveal the mechanisms involved in its action in vivo on bone cells and bone regeneration.     

A multiradius, reciprocal implementation of the thin-wire momentmethod

An implementation of the moment method, entitled the multiradius bridge-current (MBC) moment method, for electromagnetic analysis of multiradius thin-wire structures (including multiwire, multiradius junctions) is presented. It is extension of the authors' uniradius bridge-current reformulation (see ibid., vol.37, p.1224-34, Oct. 1989) of Richmond's uniradius thin-wire theory (1974). The method features an exactly symmetric mutual impedance matrix ensuring reciprocity between sources, it is unconstrained with respect to both the length ratio and the radius ratio of adjoining segments (provided that the wires are electrically thin), and it permits the self-consistent inclusion of coaxial cable sections in the configurations under analysis. The method is validated through comparison with transmission-line theory for a two-wire line and a coaxial cable, and through comparison with measurements on a sleeve monopole antenna and a log-periodic dipole antenna. The MBC moment method program is shown to surpass the Numerical Electromagnetics Code (NEC) in terms of reciprocity and convergence for both an AM broadcast tower detuning stub problem and a bent two-wire transmission-line problem     

Resonance phenomena of log-periodic antennas: characteristic-modeanalysis

The method of characteristic modes is implemented in the form of a general-purpose computer program based on an established moment-method program using piecewise sinusoids. Application of the method to the log-periodic dipole antenna (LPDA) yields characteristic modes that are insensitive to changes in moment-method segmentation and are revealing with regard to parasitic resonance phenomena. A study of the modes on the LPDAs shows that the asymmetry resonance is dominated by a mode that is not restricted to one cell, although the single-resonant-cell postulate remains a good first-order explanation. On the other hand, the symmetric termination resonance is shown to involve more than one mode. A numerical study of various antenna deformations shows that only length extensions cause strong asymmetry resonances. The E-plane array is analyzed, and the results are shown to compare favorably with experiment     

Cyclic and Isothermal Oxidation at 1,100 °C of a CVD Aluminised Directionally Solidified Ni Superalloy

CVD aluminide coatings deposited on a Directionally Solidified (DS) substrate were oxidized at 1,100 °C up to 240 h under isothermal and cyclic oxidation conditions to study the growth mechanisms of the oxide scales and the possible degradation of the coatings. The specimens were investigated using light and scanning electron (SEM) microscopy, energy-dispersive spectrometry (EDS) and X-Ray Diffraction (XRD). The results indicate that the coatings provide a much greater beneficial effect under isothermal conditions than upon cycling. The cycled specimens undergo oxide-scale spallation and increased roughening, which can derive from growth and thermal stresses as well as from the NiAl → Ni₃Al phase transformation associated with Al depletion. Under isothermal conditions, typical oxide scales formed with the appearance of some rumples. However, the origin of rumpling is uncertain from these experimental results.     

Transforming growth factor beta is essential for spindle cell conversion of mouse skin carcinoma in vivo: implications for tumor invasion

Transforming growth factor beta1 (TGF-beta1) regulates both cell growth and cellular plasticity and is therefore important in the molecular control of both the developmental and neoplastic processes. It has been suggested that TGF-beta1 may be a positive or negative regulator of tumorigenesis. Stimulation of tumorigenesis could be due to its action as an immunosuppressor or as an inducer of angiogenesis, or by its direct action on the cell in promoting cellular plasticity. In the current study, we provide evidence that TGF-beta1 can act directly on keratinocytes in vivo to induce the reversible epithelial-mesenchymal conversion of a malignant metastatic keratinocyte cell line. Two squamous clones from the cell line were shown to undergo a reversible conversion to a fibroblastoid phenotype after culture in 1 ng/ml TGF-beta1. The morphological conversion became apparent at 24 h post-TGF-beta treatment and was complete after another 24 h. The conversion was characterized by a rapid delocalization of E-cadherin within 6-12 h posttreatment, followed by down-regulation of E-cadherin levels by 72 h. These squamous clones spontaneously converted to a fibroblastoid phenotype after s.c. injection in nude mice. Importantly, four of four clones that had been stably transfected with a dominant negative TGF-beta type II receptor were unable to undergo this mesenchymal switch in vivo, despite the fact that all clones stably transfected with neomyocin resistance alone retained their spindle characteristics in vivo. This demonstrates that the epithelial-mesenchymal conversion event is mediated directly via the TGF-beta signaling pathway of the tumor cell per se, and that it is sufficient to significantly enhance tumorigenicity and the malignant and invasive characteristics of the tumor in vivo.     

Study of compressed log-periodic dipole antennas

The behavior of log-periodic dipole (LPD) antennas, which are compressed along the transmission-line axis, is studied both experimentally and theoretically. Compressed LPD antennas are found to be efficient, of low gain, and frequency independent. With compression, the radiation pattern approaches dipole-like behavior and the bandwidth increases slightly. It is also found that LPD antennas exhibit anomalous frequency-dependent behavior in narrow bands of frequencies (approx 1/8of a log period in width) when a reactive termination is used and when the scaling factortauis below about 0.92-0.93.