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The challenges of improving sintered MgO raw materials with special high temperature properties demand higher temperature calcination. In the process of dead burning of magnesite (DBM) in rotary kiln, the heat expenditures were found to be mainly due to dead burning of magnesite, loss through exhaust gases, loss through kiln shell by radiation & convection, clinker exit etc. The calcination process is highly energy intensive and involves various interdependent variable factors. An attempt was made to build a model and a screening design of experiment was performed with few process variables to identify the greatest effect of variables on the response quality. The design variables chosen were raw magnesite (RM) feed rate, kiln rotation (RPM), fuel consumption and burning zone temperature (BZT). The response variables were exit gas temperature and density of dead burnt magnesite (DBM). A fractional factorial design was used to keep the number of experimental runs to a minimum. ANOVA and normal plots were used to evaluate the effects of different variable factors on the sensory/response properties. The Experimental Design, ANNOVA, Response surface etc. given an insight of dead burning of magnesite in rotary kiln. This work had enabled us to correlate the BZT, RPM, RM feed with the exit gas temp and density of magnesite produced. The result opens up an avenue to look into the optimum region of operations within the ranges of variables considered in order to minimize the exhaust gas temp. and to maximize the density of the DBM produced.

Modeling and a screening design of experiment (DOE) was performed with the process variables to identify the greatest effect of variables on the response quality in the dead burning of magnesite refractory in a rotary kiln. Among various interdependent variable factors, the design variables chosen were raw magnesite (RM) feed rate, kiln rotation time i, e, seconds per rotation(SPM) and burning zone temperature (BZT). The response variables chosen were exit gas temperature and density of dead burnt magnesite(DBM). ANOVA and normal plots were used to evaluate the effects.This work had enabled to correlate the BZT, RPM, RM feed with the exit gas temp and density of magnesite produced. The result opens up an avenue to look into the optimum region of operations within the ranges of variables considered in order to conserve energy and to minimize the exhaust gas temperature and to maximize the density of the DBM produced.

The ceramic shell investment casting process has gained an important position in the family of precision casting techniques owing to the scientific advances in many of its aspects, such as binder solutions, refractory materials, pattern materials, and in the manufacturing process. In this endeavour an effort was made to investigate the effect of drying conditions on the performance of ceramic shell moulds. The binder used in this work was an acetone based polysilicic acid, which had been considered as an alternative to the conventionally used binders (namely, ethyl silicate, colloidal silica aquasols etc.). The effects of drying conditions were observed on ceramic wafers, prepared from the slurry, made of fused silica and the binder. The wafers were dried at different temperatures and relative humidity conditions. The effect of drying conditions was observed through the measurement of compressive strength of the ceramic shell wafers. The binder was also subjected to various drying conditions and t...

Phage D10, a Vibrio cholerae O-1 El Tor group X phage, is one of the five newly isolated phages used in the phage typing scheme developed for V. cholerae O-1 biotype El Tor and belongs to the Myoviridae family. From electron microscopic studies it is shown that phage D10 has a DNA genome of 32 +/- 0.2 kb. This is the first report where it has been shown by the construction of a partial denaturation map that this vibriophage genome is nonpermuted and has cohesive ends. The location of the ends of the DNA in the phage head has also been inferred.

The conventional phage typing scheme proposed by S. Basu and S. Mukerjee (Experientia 24:299-300, 1968) has been used routinely for identification of the strains at the Vibrio Phage Reference Laboratory since 1968. However, because of limitations of this scheme, a new phage typing scheme using five newly isolated phages was incorporated into the conventional scheme. A different definition of routine test dilution (almost confluent lysis) was found to be more useful than the one previously used (confluent lysis). The 1,000 strains tested could be clustered into 27 types with the five new phages. With the new scheme of 10 phages (5 new phages and 5 phages of Basu and Mukerjee), the 1,000 strains could be grouped into 146 types. The new phages were different from each other and also from those of Basu and Mukerjee, as revealed by lytic pattern, electron microscopy, restriction endonuclease digestion, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and antiphage antiserum studies. With the new typing scheme, 99.6% of the strains were typeable. Phage type 115 was the most common and includes 119 (11.9%) of the 1,000 strains tested. Next most common were phage types 142 (9.4%), 143 (7.0%), 104 and 116 (both 5.4%), 3 (5.3%), 5 (4.1%), 4 (3.9%), 24 (2.1%), and 100 (1.7%). The larger number of types would be useful for further classification of the strains for epidemiological purposes. This newly developed scheme is highly applicable to, and could be widely adopted for, phage typing of Vibrio cholerae O1 biotype El Tor strains.

Several cultures ofThiobacillus ferrooxidans were purified by isolation of single colonies and simple physiological and biochemical properties of the purified cultures, such as colony morphology, kinetics of ferrous ion oxidation, growth on elemental sulfur and thiosulfate, oxidation of ferrous ion by growing cells in the presence of organic compounds and metal ions, were examined. These properties may be used to characterize a range ofT. ferrooxidans isolates and for numerical taxonomy.

The cell-surface hydrophobicity of acidophilic heterotrophic bacteria originating from mines varied with the pH of the suspending medium and with the growth temperature. Adhesion of these bacterial cells on mineral particles depended upon the hydrophobic (or hydrophilic) nature of both the cells and the minerals. A strong correlation between these properties was usually observed at different pH values of the suspending medium. At a certain pH value, bacterial attachment depended upon the particle size of the minerals. Key words: hydrophobicity, acidophilic bacteria, Acidiphilium cryptum, Acidiphilium symbioticum, adhesion, manganese nodule, chalcopyrite, iron pyrite.

Addition of silver greatly accelerated the rate and extent of copper dissolution from chalcopyrite ores in the process of leaching with acidic ferric sulfate solution. The solubility of copper depended on silver- and ferric ion concentrations, pulp density, pH and temperature. The mineralogy of ores was probably the most important factor since the extent of copper extraction in the presence of Ag + from different samples varied under identical conditions. It was thought that the presence of other metal ions in the ores might have influenced extraction rates catalysed by silver. This was confirmed by pretreatment of ore particles with other metal ions, which exhibited either a positive or no effect on subsequent leaching of copper with solutions containing Ag + .

Developpement d'un liant pour les refractaires utilises dans les moules pour coulee de precision de superalliages

Prolonged exposure to carbon monoxide accelerates the development of atheroma in rabbits owing to intimal accretion of platelets and fibrin and intramural lipid accumulation (Wanstrup, Kjeldsen, and Astrup, 1967; Birnstingl, Hawkins, and McEwen, 1970). A group of 7 rabbits was exposed in a closed chamber to an atmosphere containing 400 p.p.m. CO for 6-14 hours on several occasions. Platelet stickiness was estimated by a modified Hellem's glass-bead method immediately after exposure and on the following day, for comparison with values in the resting period prior to exposure. There was a highly significant increase in platelet stickiness immediately after exposure to CO, followed the next day by a significant fall below the pre-exposure value. The increase in platelet stickiness after CO exposure may provide a link between tobacco smoking and peripheral vascular disease.

IN jute, the fibrils in the cell-wall are arranged in right-handed helices, that is, they show the Z twist of textile workers, and the drying-twist is counter-clockwise. In flax, with the fibrils in left-handed (or S) helices, the drying-twist is clockwise1. So far as we know, the following results are the first of their kind to be reported, and although they were obtained with bundles of jute fibre-strands, similar relationships must also hold for jute yarns. Tests were made in a room conditioned to about 75 per cent relative humidity, and the test-pieces were carefully sampled out.

WE have seen the comments1 of Sen and De on our note2. It seemed unnecessary to mention that the paired-variate method was used in each case in getting the standard error of the difference, the bundles used for each pair of tests (with S- and Z-twist) being obtained by dividing a sub-sample into two parts. If the results are examined in the light of this explanation, it will be seen that in the case of the breaking-load the difference between the S-twist and Z-twist results is highly significant for both samples.

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Networks of living neurons represent one of the most fascinating systems of biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behaviour of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behaviour is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. Spontaneous neuronal activity has recently shown features in common to other complex systems. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. These avalanches are characterized by a power law distribution for the size and duration, features found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behaviour. In this contribution we discuss a statistical mechanical model for the complex activity in a neuronal network. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. Then, we discuss the learning abilities of this neuronal network. Learning occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. The system is able to learn all the tested rules, in particular the exclusive OR (XOR) and a random rule with three inputs. The learning dynamics exhibits universal features as function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.