TOPICS ON FUNDAMENTALS OF PRECISION MACHINING

Precision machining is becoming increasingly important to meet the needs of technological progress as well as the social requirements of rapid industrialization. An overview on the quality of machined parts from a fundamental viewpoint of machining technology is presented in this article. The parameters that influence dimensional accuracy, surface finish, edge quality, surface integrity and chip control, and the relationship between the various types of chips and cutting forces are included.     

Effects of gastrin on the histamine-secretory and proliferative activity of cultured carcinoid cells derived from the stomach of the rodent Mastomys natalensis

In order to estimate the distribution of Salmonella including Salmonella enteritidis (SE) and SE-antibodies in commercial layer hen flocks in Hokkaido, the northern prefecture of Japan, a survey of spent layer hens was performed, from August 1996 to January 1997. From the three spent hen processing plants, samples of intestines and sera were collected from 740 birds presented for slaughter from 37 flocks of 22 layer hen farms. Intestines from each birds were cultured for Salmonella including Salmonella enteritidis. Serum from each bird was examined for SE-antibody with the enzyme-linked immunosorbent assay (ELISA). Salmonella (any serotype) and Salmonella enteritidis were isolated from 50 (6.8%) and three (0.4%) of 740 birds, respectively, and SE-antibody positive values were recorded from seven birds (0.9%). SE-antibody positive birds did not always indicate isolation of Salmonella enteritidis, however SE-antibody positive hens were demonstrated only from Salmonella enteritidis positive flocks. Salmonellae were isolated from the birds of ten layer hen farms, all of these hens were raised in houses without windows and with automatic feeders. No isolations of salmonella were made from birds raised in houses with windows. From the windowless houses, Salmonellae were isolated from 46 (21.8%) of 260 birds in houses with four to six cages piled up vertically, and from six (2.5%) of 240 samples from the houses with four to five cages piled in a slanting manner.     

Synthesis temperature of Ba4CuPt2O9 compounds and the influence of their addition on the orientation of the c-axes of fluorine-doped YBCO superconductors

An experimental study has been carried out to investigate the synergistic effect of Ba₄CuPt₂O₉ compounds on the critical current density of fluorine-doped YBCO superconductors. The Ba₄CuPt₂O₉ compounds were synthesized by a solid state reaction. It was found that the synthesis temperature of the Ba₄CuPt₂O₉ compounds was over 800°C, which was higher than that ever reported previously. In addition, the influence of Ba₄CuPt₂O₉ compounds on the critical current density of YBCO superconductors has been investigated using two types of Ba₄CuPt₂O₉ compounds: one is not heat-treated, i.e. source materials; and the other is heat-treated at 950°C. It was found that the former affected the orientation of the c-axes, but the latter did not have an influence on the orientation of the c-axes, but adversely affected the superconductivity of samples quenched at temperatures above 850°C.     

Evaluation of additive effects and homogeneity of the starting mixture on the nuclei-growth processes of barium titanate via a solid state route

In an attempt to obtain finest possible microparticles of BaTiO₃ (BT) with highest possible tetragonality via a solid state route, starting mixtures comprising BaCO₃ and TiO₂ were subjected to various pretreatments including addition of glycine and mechanical activation. Reaction processes were monitored by the changes in the weight, crystallinity, and morphology in detail. While mechanical activation with glycine significantly increased the rate of reaction and homogeneity of the particle size of the product, BT, simultaneous particle growth of BT was intolerably acute for micro-electronic devices. The fast particle coarsening was predominated by the coalescence of BT tiny particles formed around titania. A mixture with higher homogeneity was attained by using finer starting materials under wet mixing, avoiding significant mechanical stressing. Particle growth of BT was suppressed to ca. 100 nm to obtain fully crystallized BT particles without significant loss of tetragonality and, hence, close to meet our requirements for MLCCs.     

Preparation and properties of nano-amorphous organic and inorganic particles via chemical and mechanochemical routes

Nanomization and amorphization methods of solid particles via energy and ecology conscious routes are overviewed. Particular emphasis was laid on the treatment of molecular crystals. Importance of autogenous process was introduced in conjunction with charge transfer across the boundary between dissimilar species, either in liquid or solid states. While nano-amorphization of molecular crystals is attainable by co-grinding, it is by no means rational, particularly when we need intensive milling for a long time. We therefore demonstrated to reduce grinding time to give just a small amount of liquid. The process was also compared with a novel sol–gel process without any mechanical stressing. Absorption of solvent or water vapor in the presence of hydrophilic polymeric matrix to obtain nano-amorphous particles, an entirely new process, was briefly referred.     

A two-dimensional analysis of in-vessel buoyancy driven flows during a degraded core scenario

A transient two-dimensional thermal-hydraulic analysis of a full scale PWR uncovered degraded core heat up scenario based on the full Navier-Stokes equations was performed. The results show that the buoyancy forces produce significant two-dimensional circulations that induce strong mixing within the reactor pressure vessel. The results were also used to quantitatively assess the inadequacy of neglecting multidimensional dynamic effects in subchannel modeling of the in-vessel details of the reactor pressure vessel degraded core thermal-hydraulics.     

Size-dependent correction factors for absorption measurements using filter-based photometers: PSAP and COSMOS

Filter-based absorption photometers have been widely used to measure mass concentrations of black carbon (BC) by measurement of the absorption coefficient of BC. In these techniques, correction for the effect of multiple scattering by the filter medium is necessary, even if only BC particles are extracted by evaporating co-existing volatile compounds using a heated inlet. The correction depends on particle size, because it varies with the aerosol penetration depth into the filter. The size dependence has not, however, been taken into account in previous studies. For the first time, we quantify the particle size dependence of the sensitivities of two filter-based photometers, PSAP and COSMOS, using mono-disperse nigrosin particles, which were generated by the combination of a differential mobility analyzer and an aerosol particle mass analyzer. At diameters smaller than 200 nm, the absorption coefficients measured by PSAP and COSMOS were much larger than those calculated by Mie theory. The size-dependent correction factors for PSAP and COSMOS are determined by comparing the observed absorption coefficients at a flow rate of 0.7 standard liter per minute with those calculated by Mie theory. The correction factors to the mass absorption cross-section are also estimated for typical size distributions of ambient black carbon particles. The new factors reduce the mass absorption cross-sections measured by PSAP and COSMOS by 28–36% for typical ambient black carbon particles observed with an inlet heated to 400 °C.