Parabolic Plot Research Articles

Electromagnetic Weibel instability in spatial anisotropic electron–ion plasmas

The Weibel instability due to temperature anisotropy of electrons and ions in a plasma in the presence of cold and warm ions is reported. Numerical calculations of the normalized growth rate are carried out when the frequency of electromagnetic waves is greater than or less than the thermal velocity of electrons for typical existing plasma parameters. The normalized growth rate increases with an increasing normalized wave number, and after attaining maxima, it decreases due to thermal effects. Therefore, a parabolic plot is obtained for the growth rate. The threshold values of the growth rate depend on the anisotropy parameters. On increasing the value of the temperature anisotropy ratio of either plasma component, the observed growth rate increases. There is a considerable and contrasting effect of the presence of cold and warm ions on the growth rate of the Weibel instability in the plasma. The addition of cold ions stabilizes the instability and reduces the maximum growth rate values, while the addition of warm ions to the plasma increases the instability with a considerable decrease in the domain of instability. Our theoretical investigations of the effect of temperature anisotropy on the growth rate of the Weibel instability are in good agreement with the existing experimental results.

THE CONCEPT OF THE SHORT NOVEL (‘POVEST’) GENRE IN ANDREY PLATONOV’S CREATIVE WORK IN THE 1920S

Based on the material of the short novels (povest’) “The Ethereal Tract,” “Epiphany Locks,” “The City of Gradov,” “The Innermost Man,” “Yamskaya Sloboda,” the article presents the concept of the short novel (‘povest’) genre in the 1920s works by A. Platonov. The structural possibilities of this traditional genre of Russian literature allowed the writer to reflect the contemporary reality with all its tragic contradictions. The genre of the short novel (‘povest’) will have reached its peak by the 1930s, when the writer’s principal works were written (“The Pit,” “For the Future,” “Juvenile Sea,” “Bread and Reading,” “Jan”). Many of the techniques that the writer used in the short novels (‘povest’) of the 1920s were embodied in the works of Platonov later on. The article briefly presents the history of the study of the genre of the short novel (‘povest’) in Russian criticism and in modern research. Special attention is paid to the genre-forming factors and genre features of Platonov's short novel (‘povest’), among which one can distinguish: ideological and philosophical content (“volume of content”), type of narrative, plot-compositional structure, the concept of artistic time and space, the genre concept of man, the poetics of the finale. The authors refute the opinion of researchers, which states that Platonov's short novels (‘povest’) can be described in the language of a short story or a novella and that, in general, his short novels (‘povest’) can be called novelistic. The parabolic plot of the “departure-return”, the epic distance, the type of narration, as well as the genre concept of a person (“a person is a plot”) do not allow Platonov's short novel (‘povest’) to be reduced to a novella or grow into a novel. Platonov's short novel (‘povest’) has its own artistic concept, which is rooted in the traditional Russian short novel (‘povest’) genre, which is the “heir” of the Old Russian genre tradition, rather than the European novel. The short novel (‘povest’) of A. Platonov answered the demands of the time, and testified to the writer's understanding of its structural and substantive capabilities.

Experimental study on liquid fire behavior at different effective ceiling heights in a full-size simulated cargo compartment

When a fire occurs in an aircraft cargo compartment, the fire plume will rise from a different location, intermittently or continuously impact the ceiling, and form a ceiling jet flame at varying heights. Meanwhile, the low-pressure environment within the cargo compartment has a great influence on flame height and high-temperature zone, which could lead to the violent development of ceiling jet fire. Based on this discussion, a series of square oil pan fires were conducted in a full-size cargo compartment located in Kangding airport (altitude 4250 m, atmospheric pressure 61 kPa). Fire behaviors, such as burning rate, flame temperature, flame heights, and smoke gas temperature distribution beneath the ceiling, were measured and analyzed. The experimental results show that as the effective ceiling height decreases, the burning rate of 30 cm square pan fires grows, with a sharp change in the low-pressure environment (50 kPa), where flames impinges on the ceiling. For 20-cm square pan fires, the burning rate at 50 kPa has the same trend with 30 cm, at 75 kPa looks like a parabolic plot, and at 101 kPa shows a continuous dropping. The centerline flame temperature decreases slowly along the axis when the fire occurs at higher height above the floor. Considering the influence of ambient pressure, effective ceiling height, and oil pan size, an empirical correlation for the ceiling transverse smoke temperature distribution is proposed by modifying the current models.

Oxidation behaviour at 1123 K of AISI 304-Ni/Al-Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> multilayer system deposited by flame spray

The oxidation behaviour of alumina/titania (97/3, 87/13 and 60/40) ceramic coatings using a Ni-Al coupling layer was studied in a thermobalance. Both layers were deposited on an AISI 304 stainless steel base metal by the flame spray technique. The coated steel was heated from room temperature to 1,123 K at 40 K min –1 , oxidized in air for 50 h, and then cooled to room temperature at 40 K min –1 . The mass gain was mainly attributed to the oxidation of Ni-Al coupling layer. Kinetic laws, DW·S –1 (mg.mm –2 ) vs. time (hours) were close to a parabolic plot for each sample. Surface composition of ceramic top layer and the cross section of multilayer system were analysed using a wide range of experimental techniques including Scanning Electron Microscopy (SEM), equipped with a link energy dispersive X-Ray spectroscopy (EDX) and X-Ray diffraction (XRD) before and after the oxidation process. Coatings 97/3 and 87/13 presented a stable structure after flame spray deposition and they did not evolve with the oxidation process, while most of the 60/40 coating changed to a metastable structure after deposition and to a more stable structure after oxidation with high micro-cracks content. SEM and EDX microanalysis of the cross-sections showed that significant oxidation and a weak intergranular precipitation had been produced in the coupling layer and on the stainless steel base metal, respectively.

Short Term Oxidation of a Ti-46Al-8Nb Alloy at 700°C in Air

Thermogravimetry was used to study the oxidation behaviour of a lamellar Ti46Al8Nb alloy during holding at 700°C in synthetic air. A parabolic plot of the oxidation kinetics shows three different regimes over the total duration (50 h) of the tests corresponding to decreasing values of the parabolic rate constant. The oxide scale was characterized by glancing-angle X-Ray diffraction and transmission electron microscopy. The scale was found to be bi-layered with an outer part that consists of amorphous aluminium rich oxide whilst the inner layer is made of very small cristalites of titania distributed in the same amorphous oxide.

Distinction between Surface and Bulk Oxidation of Cu through N2O Decomposition

A Cu metal surface was evaluated by a novel technique combining temperature-programmed reduction (TPR) measurement with N2O oxidation. The technique consists of three steps: the usual TPR measurement, the oxidation of the Cu surface by N2O, and the subsequent TPR measurement. The surface Cu oxidized by N2O was determined as a ratio of the peak area of the second TPR profile to that of the first one. It was found that bulk oxidation gradually proceeds after surface oxidation even at 30°C. After the surface oxidation, the Cu2O produced by N2O oxidation varied with N2O exposure time (t) and had a linear correlation with t12 at temperatures below 100°C. The linear correlation in the parabolic plot proves that bulk oxidation proceeds through the diffusion process, and the Y-intercept corresponds to the surface oxidation. Both the dispersion and the Cu metal surface area of the sample were calculated from the intercept in the parabolic plot for the Cu2O produced by N2O oxidation. In addition, we found that a very large Cu metal surface area, as high as 32 m2 g−1cat, was created on a Cu–MgO catalyst through a citrate process using a molten mixture of copper nitrate, magnesium nitrate, and citric acid.

Corrosion of silicon nitride ceramics under hydrothermal conditions

Corrosion behaviour of Si3N4 ceramics containing Y2O3, Al2O3 and AIN as sintering aids was investigated under hydrothermal conditions at 200–300 ‡C and saturated vapour pressures of water for 1–10 days. Hydrothermal corrosion resulted in the dissolution of the Si3N4 matrix and the formation of a product layer consisting of the original grain-boundary phases and hydrated silica. The dissolution rate of Si3N4 ceramics decreased with decreasing crystallinity of the grain-boundary phase. The dissolution rate could be adequately described by a parabolic plot in the initial stage of the reaction. The apparent activation energies were 83.5–108 kJ mol−1, and the bending strength of the corroded samples decreased from ∼ 600 to 400 MPa in the initial stage of the reaction upto a weight loss of 0.004 g cm−2, and then was almost constant up to a weight loss of 0.012 g cm−2.

Effect of grain morphology in pressureless-sintered Si 3N 4z.sbnd;Y 2O 3/Al 2O 3 on leaching behavior under hydrothermal conditions

The purpose of this work is to study the effect of grain morphology in sintered Si3N4 on the leaching behavior under hydrothermal conditions. The pressureless-sintered Si3N4-Y2O3/Al2O3 specimens were produced using two kinds of commercial grade Si3N4 powders, i.e., prepared by the imide-decomposition method (specimen-A) and the silicon-nitridation method (specimen-B). Differences in microstructures were observed for sintered specimens from these Si3N4 starting powders, i.e., specimen-A resulted in a finer microstructure than specimen-B. Leaching test was carried out using an autoclave under the hydrothermal conditions at 300°C and 8.6MPa for 1-10 days. The two specimens showed the similar trend of weight loss in leaching test, but larger weight loss was measured in specimen-B in the whole leaching time. A parabolic plot of weight loss suggested that the leaching mechanism consisted of two stages. SEM observation revealed that the both leached layers consisted of porous layer at the first stage and flakes on it at the second stage. The porous layer for specimen-A was finer than that for specimen-B and the traces of machining grooves was still visible on both porous layers. The results of this experiment showed that the leaching weight loss of sintered Si3N4 under hydrothermal conditions and the microstructures of the leached layer depended remarkably on the microstructural grain morphology of the sintered body generated by the starting powders and also on its mechanical history by grinding.

Effect of Grain Morphology in Pressureless-Sintered Si<sub>3</sub>N<sub>4</sub>-Y<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> on Leaching Behavior under Hydrothermal Conditions

The purpose of this work is to study the effect of grain morphology in sintered Si3N4 on the leaching behavior under hydrothermal conditions. The pressureless-sintered Si3N4-Y2O3/Al2O3 specimens were produced using two kinds of commercial grade Si3N4 powders, i.e., prepared by the imide-decomposition method (specimen-A) and the silicon-nitridation method (specimen-B). Differences in microstructures were observed for sintered specimens from these Si3N4 starting powders, i.e., specimen-A resulted in a finer microstructure than specimen-B. Leaching test was carried out using an autoclave under the hydrothermal conditions at 300°C and 8.6MPa for 1-10 days. The two specimens showed the similar trend of weight loss in leaching test, but larger weight loss was measured in specimen-B in the whole leaching time. A parabolic plot of weight loss suggested that the leaching mechanism consisted of two stages. SEM observation revealed that the both leached layers consisted of porous layer at the first stage and flakes on it at the second stage. The porous layer for specimen-A was finer than that for specimen-B and the traces of machining grooves was still visible on both porous layers. The results of this experiment showed that the leaching weight loss of sintered Si3N4 under hydrothermal conditions and the microstructures of the leached layer depended remarkably on the microstructural grain morphology of the sintered body generated by the starting powders and also on its mechanical history by grinding.

Structure-acute toxicity relationship of dinitriles in mice.

Acute toxicity and metabolism of seven dinitriles in mice was studied in relation to the chemical structures. The oral LD50 for each nitrile was determined under different conditions for mice pretreated with either carbon tetrachloride (CCl4) or olive oil. All test nitriles were metabolized into cyanide in vivo and in vitro. The cyanide level was variable among the compounds (0.35-0.74 micrograms CN/g brain) at death in the brains of mice, the level for malono- and adiponitrile being comparable to that found in mice killed by dosing with potassium cyanide. After receiving each nitrile, the mean survival time of mice pretreated with CCl4 was prolonged and their brain cyanide level decreased when compared with the corresponding control. With malononitrile, the former did not significantly change and the latter decreased slightly. Brain cyanide levels of control mice at death showed a peak at the lower log P region, while those of CCl4-pretreated animals remained lower independently of log P, with the exception of malononitrile. Microsomal metabolism of nitriles to cyanide was greatly inhibited when microsomes were prepared from livers of mice pretreated with CCl4. The relationship between log (1/LD50-CCl4), LD50 in mice pretreated with CCl4, and log P fits a parabolic plot.

Studies on the mechanism of acute toxicity of nitriles in mice.

Acute toxicity and metabolism of 21 nitriles in mice were studied in relation to their chemical structures. All the test nitriles liberated cyanide ions both in vivo and in vitro, with the exception of benzonitrile , although the extent of liberation and the effect of carbon tetrachloride (CCl4) pretreatment on the mortality of animals differed among nitriles. From these results, test compounds were tentatively divided into three groups. In group 1 (13 compounds), acute toxicity was greatly reduced by CCl4 pretreatment, in group 2 (seven compounds), toxicity was not significantly changed or was somewhat enhanced, and in group 3, benzonitrile only, toxicity was clearly enhanced. The amount of cyanide was higher (0.68-0.80 microgram CN/g brain) at death in the brains of mice given group-1 compounds, the level being comparable to that found in mice killed by dosing with potassium cyanide. After oral doses of each nitrile, the time course for cyanide levels in the liver varied among the compounds. The difference between group-1 and -2 compounds lay in the dose-cyanide liberation relationship in liver, and in the kinetics for cyanide liberation in the hepatic microsomal enzyme system. Double-reciprocal plots of enzyme activity showed a linear relationship for nitriles of group 1 and a non-linear one for group 2. The relationship between log (1/LD50) and log P for the compounds in group 1 fitted a parabolic plot, while that for compounds in group 2 was linear.

Transient state in the selective oxidation of binary alloys with quasiparabolic kinetics: Solution for a fixed alloy-scale boundary

Analytical solutions for the concentration profile and the surface concentration of an oxidizable component during the selective oxidation of a binary alloy following pseudoparabolic kinetics are examined, assuming a fixed alloy-scale boundary. A solution similar to that already proposed for rate control by metal transfer across the metal-scale interface can be obtained also assuming diffusion control. In the case of formation of a metal-deficit scale growing mainly by cation diffusion it is shown that oxidation is controlled by the diffusion in the alloy. The rate law is found to be pseudoparabolic, although different from that usually found in practice, leading to negative intercepts in a parabolic plot. Positive intercepts cannot be obtained if the regression of the alloy interface during oxidation is disregarded.