Some properties of mullite powders prepared by chemical vapour deposition

The sinterability of mullite (3Al₂O₃·2SiO₂) powder prepared by chemical vapour deposition was examined to improve the conditions for fabricating dense mullite ceramics. The starting powder contained not only mullite, but also a small amount of -Al₂O₃ (Al-Si spinel) and amorphous material. Although the compressed powder was fired at a temperature between 1550 and 1700 °C for 1, 3 and 5 h, the relative densities of the sintered compacts were limited to 90%: (i) due to the creation of pores/microcracks during the solid state reaction (1100–1350 °C), and (ii) due to restriction on the rearrangement of grains because the amount of liquid phase (1550–1700 °C) was insufficient. Calcination of the starting powder was effective for preparation of easily sinterable powder with homogeneous composition. When the compact formed by compressing the calcined powder at 1400 °C for 1 h was fired at 1650 °C for 3 h, the relative density was raised up to 97.2%; moreover, mullite was the only phase detected from the sintered compact. The sintered compact was composed of polyhedral grains with sizes of 1–2 m and elongated grains with long axes of 6 m.     

Effects of insertions and deletions in a beta-bulge region of Escherichia coli dihydrofolate reductase

The role of a beta-bulge in Escherichia coli dihydrofolate reductase (DHFR) has been explored by a series of insertion and deletion mutations. Insertion of a seven amino acid sequence from a structurally equivalent 'beta-blowout' sequence from human DHFR destabilizes E. coli DHFR by 3.6 kcal/mol and decreases catalytic efficiency (kcat/K(m)) 34- fold. Deletion of F137, delta 137, the looped out residue in the bulge, also destabilizes E. coli DHFR by 2.8 kcal/mol but only decreases catalytic efficiency threefold. Concurrent deletion of F137 and mutation of, V136 to proline to try and maintain the strand twist associated with the beta-bulge decreases protein stability by 3.4 kcal/mol and decreases catalytic efficiency 84-fold. These insertion/deletion mutations were also constructed in a D27S DHFR background. The D27S mutation has been described previously and proposed to remove the catalytic acid from the active site. The delta 137 mutation partially suppresses the effect of the D27S mutation as it decreases the K(m) for substrate, dihydrofolate, twofold. Non-additive effects are observed for the insertion/deletion mutations in wild-type versus D27S DHFR backgrounds, consistent with structural changes.      

Single and biphoton imaging and high dimensional quantum communication

Here, we present recent developments in the field of quantum imaging focusing on the high dimensionality aspects of single and biphoton imaging. We discuss some systems that have a ??quantum advantage?? over classical counterparts. We highlight some recent experiments in single-photon image discrimination, large alphabet quantum key distribution and image buffering.     

Enzymatic oxidative activity in sardine (Sardina pilchardus) and herring (Clupea harengus) during chilling and correlation with quality

 Enzymatic oxidative activity of two fatty fish species, sardine (Sardina pilchardus) and herring (Clupea harengus), was studied during chilled storage. Lipoxygenase enzyme activity was isolated and tested by measuring the hydroperoxides produced after induced oxidation of arachidonic and docosahexaenoic fatty acids. The most abundant degradation products of the hydroperoxides formed were 12- and 16-hydroxy acids which were detected by HPLC. Lipoxygenases were concentrated in the skin tissue of fish, and were active for up to 48 h of chilled storage. The pro-oxidative activity due to haem proteins continued for longer than that due to lipoxygenase. Trends of fluorescent formation resulting from interaction between oxidation products and biological amino constituents were compared with the pro-oxidative activities to establish correlations with quality loss during chilling. Received: 29 December 1998 / Revised version: 14 March 1999     

Long-wavelength stability of an unsupported multilayer liquid film falling under gravity

The long-wavelength stability of an unsupported multilayer liquid film falling under the effects of gravity and surface tension is investigated. By considering the Navier–Stokes equations for two fluid layers in the high-Reynolds-number and small-aspect-ratio limits the steady-state solutions are obtained. The stability criterion found by Lin (J Fluid Mech 104:111–118, 1981) for a one-layer fluid curtain is generalised to the two-layer case and the criterion for an n-layer curtain is established.     

Direct nn-Scattering Measurement With the Pulsed Reactor YAGUAR

Although crucial for resolving the issue of charge symmetry in the nuclear force, direct measurement of nn-scattering by colliding free neutrons has never been performed. At present the Russian pulsed reactor YAGUAR is the best neutron source for performing such a measurement. It has a through channel where the neutron moderator is installed. The neutrons are counted by a neutron detector located 12 m from the reactor. In preliminary experiments an instantaneous value of 1.1 × 10¹⁸/cm²s was obtained for the thermal neutron flux density. The experiment will be performed by the DIANNA Collaboration as International Science & Technology Center (ISTC) project No. 2286.     

In vitro antineoplastic activity of a novel lanthionine-containing peptide

It has been a long-term goal to discover peptides that can kill tumor cells while sparing normal tissues. Lan-7 is a novel, chemically stable peptide structurally related to somatostatin that contains a lanthionine bridge between the two cysteines in the peptide; TT-232 is a less stable analogue containing a disulfide bridge. The antitumor activity of Lan-7 was examined, relative to that of TT-232 and the clinically used analogue octreotide, against a panel of malignant human tumor cell lines and normal human hematopoietic precursors. Lan-7 was cytotoxic to all four tumor cell lines, with IC50 values ranging over a 2-fold range from 16 to 36 microM. The potency of Lan-7 was comparable to that of TT-232, and both of these agents were two to three times more potent than octreotide. At concentrations that were highly cytotoxic to tumor cells, Lan-7 produced no significant toxicity to normal human hematopoietic precursors. Lan-7 induced apoptosis in human ovarian carcinoma 2008 cells over the same concentration range at which it produced cytotoxicity, but it did so without activating G1, S, or G2 checkpoints, given that it produced no perturbation of cell cycle phase distribution. Cells engineered to overexpress P-glycoprotein were not more resistant to Lan-7 than isogeneic cells not expressing the mdr1 gene. These results make Lan-7 of interest as a potential cancer chemotherapeutic agent.