Fabrication of semi-conductive ceramics by combination of gelcasting and reduction sintering

In this study, we propose a new process to fabricate electrically semi-conductive alumina by the combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. Correspondingly, the rheological evaluation of aqueous slurry was conducted. The resulting fluidity exhibited that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPA·s at shear rate of 20 s⁻¹, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demolded, carefully dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical property. The sintered alumina body was characterized by electrical resistance, X-ray diffraction, and scanning electron microscopy. The results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistivity. The obtained lowest value was 3.6 × 10⁶ Ω-cm with 8.04 wt% monomer dosage and sintering at 1550°C with 2 h holding time. The resulting material is classified as semi-conductive, which is potential for electrostatic shielding applications. The effect of physical property and microstructure on electrical conductivity and the corresponding reaction mechanism were discussed in details.     

The Timing of Uncertainty and the Intensity of Policy

This article analyzes the trade-off between `caution' and `intensity' in the use of the control variable in a one-state one-control dynamic stochastic quadratic linear optimization problem with discount factor. It studies the effects that changes in uncertainty of the control parameter have on the optimal first period response of the control variable, showing that the trade-off between `caution' and `intensity' depends on the timing of the uncertainty. Given an increase in current uncertainty and an equal increase in future uncertainty, caution will always prevail over intensity. Moreover, the prevalence of caution will be enlarged as the increase in future uncertainty moves farther away into the future, while this prevalence will be reduced as the increase in future uncertainty expands into the future. Finally, for the infinite horizon case, caution is the optimal policy response.     

Prompt fission-neutron spectra in the reactions of 1.5-MeV neutrons with235U

Translated from Atomnaya énergiya, Vol. 69, No. 1, pp. 28–31, July, 1990.     

Polyelectrolyte screening effects on the dissolution of whey protein gels at high pH conditions

The literature reports an optimum NaOH concentration for the alkaline cleaning of whey deposits or gels; at NaOH concentrations higher than this optimum, cleaning proceeds much more slowly. Although this phenomenon is of great importance in the cleaning of dairy equipment, no conclusive physical explanation has yet been presented. In this study, we present strong evidence that the dissolution rate is affected by the equilibrium-swelling ratio in β-lactoglobulin (βLg) gels. The swelling ratio is greatly reduced in the presence of salts due to the polyelectrolyte screening effect of the cations. This has been observed in free-swelling βLg gels using gravimetrical analysis and in the uniaxial swelling of WPC gel deposits using fluid dynamic gauging. At high dissolution pH (>13.3), the high Na⁺ concentration reduces swelling in spite of the high surface charge of the protein. It is proposed that the reduction of the free volume inside the gel impedes the transport of the protein aggregates out of the NaOH penetration zone. We have also observed that the final dissolution rate of gels pre-soaked in 1 M NaOH or NaCl is similar, despite the difference in pH, and much lower than for untreated gels: the high Na⁺ concentration in the soaked gels hinders swelling, inhibiting the disentanglement of the protein clusters regardless of the high pH.     

Phylogenetic distribution of fungal mycosporines within the Pucciniomycotina (Basidiomycota)

The synthesis of the UV Absorbing compounds named mycosporines (MYCs) has been detected in a few basidiomycetous yeast groups. Conspicuous accumulation of mycosporine-glutaminol-glucoside (MGG) in yeasts requires photo-induction and its photoprotective function has been postulated. The distribution of the ability to produce MYCs appeared to be related to the yeast taxonomic affiliation. In view of the potential significance of MYCs in yeast taxonomy, we here studied the distribution of this trait among dimorphic basidiomycetes of the Pucciniomycotina. Of the 94 fungal species (377 strains and 33 genera) tested, almost half were MYC-positive and MGG was the main compound produced. MGG synthesis was observed for representatives of five of seven Pucciniomycotina classes, indicating that this trait is widely distributed in this group. MGG detection proved useful for the differentiation of species of the polyphyletic genera, such as Rhodotorula and Sporobolomyces, that are phylogenetically separated. MGG quantification and UV tolerance studies in Cystobasidiomycetes supported the idea that the habitat of origin of each strains is important in the level of MGG synthesis and that MYCs have a photoprotective function in yeasts. The taxonomic value of this trait in fungal systematics is discussed.     

Computational Economics: Help for the Underestimated Undergraduate

Our concern in this paper is that the capability of economics undergraduates is substantially underestimated in the design of the present college curriculum and that our students are insufficiently challenged and motivated. Students enter our classrooms with substantial previous knowledge about computers and computation and we are not taking full advantage of this opportunity. We suggest a set of examples from computational economics which are challenging enough to motivate students and simple enough that they can master them within a few hours. By encouraging the students to modify the models in directions of their own interest, avenues for creative endeavor are opened which deeply involve the students in their own education.     

Identification and characterization of a novel member of the fibroblast growth factor family

A new member of the fibroblast growth factor (FGF) family, FGF-13, has been molecularly cloned as a result of high throughput sequencing of a human ovarian cancer cell library. The open reading frame of the novel human gene (1419 bp) encodes for a protein of 216 a.a. with a molecular weight of 22 kDa. The FGF-13 sequence contains an amino-terminal hydrophobic region of 23 a.a. characteristic of a signal secretion sequence. FGF-13 is most homologous, 70% similarity at the amino acid level, to FGF-8. Northern hybridization analysis demonstrated prominent expression of FGF-13 in human foetal and adult brain, particularly in the cerebellum and cortex. In proliferation studies with BaF3 cells, FGF-13 preferentially activates cell clones expressing either FGF receptor variant, 3-IIIc or 4. The signal transduction pathways of FGF-13 and FGF-2 were compared in rat hippocampal astrocytes. The two FGFs induce an equivalent level of tyrosine phosphorylation of mitogen-activated protein kinase (MAPK) and c-raf activation. However, FGF-13 is more effective than FGF-2 in inducing the phosphorylation of phospholipase C-gamma (PLC-gamma). Treatment of neuronal cultures from rat embryonic cortex with FGF-13 increases the number of glutamic acid decarboxylase immunopositive neurons, the level of high-affinity gamma-aminobutyric acid (GABA) uptake, and choline acetyltransferase enzyme activity. The GABAergic neuronal response to FGF-13 treatment is rapid with a significant increase occurring within 72 h. We have identified a novel member of the FGF family that is expressed in the central nervous system (CNS) and increases the number as well as the level of phenotypic differentiation of cortical neurons in vitro.