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11.
Vladimir L. Solozhenko ‡ Vladimir Z. Turkevich§ Georg Will† 《Journal of the American Ceramic Society》1996,79(10):2798-2800
Peculiarities of the formation of BN in a self-propagating reaction between LiBF4 and Li3 N have been studied under a wide range of p,T conditions within the region of thermodynamic stability of cBN. Boron nitride crystallized mainly in the form of highly ordered hBN (1700–2100 K), of mesographitic BN (2200–3000 K), or of turbostratic BN (>3000 K). Cubic boron nitride was obtained with a low yield (up to 14 vol%) as a result of precipitation from the metastable eutectic liquid in the BN-Li3 N system. These results give further evidence for an alternative metastable behavior in the BN phase formation under high pressures. 相似文献
12.
13.
Evidence for biotic control of Australian reservoir phytoplankton communities and the potential for applied biomanipulation 总被引:1,自引:0,他引:1
Vladimir Matveev 《Lakes & Reservoirs: Research and Management》1998,3(2):105-111
Although some concerns have been expressed with respect to the applicability of biomanipulation to Australian reservoirs and other inland waters, no major obstacles were found in this review. The previous doubts stimulated research, which has provided evidence for unexpected mechanisms of food web interactions, such as positive effects of small copepods on planktonic algae, higher than usual grazing potential of cladoceran communities, and direct positive effects of planktivores on phytoplankton. Further research into zooplankton-cyanobacteria interactions should indicate how widespread is the previously reported ability of some southern hemisphere crustaceans to benefit at a population level from feeding on cyanobacteria. Quantitative fisheries acoustics, which has not been widely used in biomanipulation trials before, is a promising new tool in the assessment of the biomass of planktivorous fish in the pelagic zone of reservoirs. 相似文献
14.
Low carbon steel was oxidized over the temperature range 1000‐1250°C in O2‐CO2‐H2O‐N2, O2‐H2O‐N2, and O2‐CO2‐N2 gas mixtures. Oxidation times were 12‐120 min. and the scales were 50‐2000 μm thick. The variations of these parameters were chosen to elucidate the phase composition of oxide scales under conditions similar to those of reheating furnaces in hot strip mills, using either thin slab casting or conventional casting and rolling technology. Two types of scales have been observed which are influenced by the furnace atmosphere, oxidation time, and temperature. The first type is a crystalline scale with an irregular outer surface, composed mostly of wustite (FeO), and a negligible amount of magnetite (Fe3O4). The second type is the classical three‐layer scale, composed of wustite (FeO), magnetite (Fe3O4), and hematite (Fe2O3). In general, the experiments showed that an increase in oxidation time decreased the percentage of wustite while the percentages of magnetite and hematite increased. A rise in oxygen concentration in the gas mixture increased the percentages of magnetite and hematite, confirming earlier experimental findings. In water vapour‐free atmospheres O2‐CO2‐N2, the oxide scales had a low percentage of wustite, and high percentage of magnetite and hematite. Carbon dioxide showed a small influence at 1100°C, and a negligible one at 1250°C. 相似文献
15.
Use has been made of potentiodynamic polarization curves, XRD, and scanning electron microscopy (SEM) in the electrolytic oxidation in 3% NaCl solution for specimens of nitrogen-deficient zirconium nitride (ZrN0.67, ZrN0.77, ZrN0.87, and ZrN0.97), as well as pure zirconium. In all cases, the anodic polarization curves have several stages which characterize during oxidation both active dissolution of ZrN x and Zr in the electrolyte as well as the formation of surface layers of ZrOCl2, ZrN x O y , and α‐ZrO2 of monoclinic form. The corrosion resistance of single-phase ZrN x specimens in 3% NaCl solution decreases in the sequence ZrN0.97 → ZrN0.87 → ZrN0.77, and the initial stages of interaction between the specimen surface and the electrolyte largely determine the subsequent behavior of specimens. It is found that ZrN x containing a large number of nitrogen atom vacancies, in particular ZrN0.77, is closer in corrosion behavior to metallic zirconium than it is to stoichiometric ZrN (the reduction in the corrosion resistance is undoubtedly due to the reduction in the ionic-covalent components of the bonds in ZrN x ). 相似文献
16.
Steven B. Kuzyk Alexander O. Pritchard Jocelyn Plouffe John L. Sorensen Vladimir Yurkov 《Journal of Great Lakes research》2021,47(3):715-724
Violet and purple bacterial pigmentations are uncommon when considering strict aerobes. Here we report discovery of two novel isolates, P102 and P117 from the freshwater Lake Winnipeg, each with violet to deep purple colony colouration. The relationship between pigment production and growth was investigated under different conditions, including a variety of carbon sources, pH, and temperatures. The violet compounds were purified using polar organic solvents, and then structurally characterized via mass spectrometry and nuclear magnetic resonance to be violacein and deoxyviolacein. Strain P117 produced higher concentrations of the darker pigment deoxyviolacein, which resulted in a deeper hue of violet than in cultures of P102. Strain P102, synthesized violacein maximally in liquid rich organic medium at pH 8 and 20 °C, and had 99.3% sequence similarity to the 16S rDNA from Janthinobacterium lividum. Strain P117, related to Massilia violaceinigra sharing 99.2% 16S rDNA sequence similarity, also produced violacein at similar optimal conditions, but developed higher concentrations of pigment at 15 °C. Culture-based methods found that violacein producers composed 0.001% or 0.023% CFU of environmental heterotrophic populations using BG-11 and potato-based media, respectively. Culture-independent high-throughput ribosomal 16S V4 sequencing of environmental DNA was used to detect Gram-negative species known for their production of violacein. Of all bacterial and archaeal sequences present during the fall in littoral waters and sediment of Lake Winnipeg, 5.5% and 6.3%, respectively, belonged to species that have similar pigment, demonstrating the scarcity of violacein producers in this aquatic freshwater system. 相似文献
17.
The Kohler slope of the linear magnetoresistance of potassium films measured in the Sondheimer geometry at 4.2 K depends on , the ratio of the film thickness to electron mean free path. The maximum value with a value of 0.1 occurs at =1. Calculations show that the slope decreases slowly from the maximum for smaller and larger values of . The slope is greater than 10–3 for between 0.035 and 100. The dependence of the Kohler slope on the residual resistance ratio of annealed samples measured by Taub et al. is attributed to the dependence. The results show that samples of centimeter thickness are required to reduce significantly the size-dependent Kohler slope, and the slope must be shown to be independent of the sample thickness for the study of intrinsic effects. 相似文献
18.
A probabilistic fire-protection siting model is described that places capacitated stations, engine companies, and truck companies in such a way that the population or calls covered by an engineand a truck with a joint reliability of at least is maximized. Probabilistic constraints are developed and numerical equivalents are found for the probability requirement for proximate server presence. The multiple co-location of servers at stations and the use of stations with a limited capacity are also investigated. Structures are utilized that preserve the integer properties when the model is solved by linear programming relaxation.An earlier version of this paper was presented at the 37th North American Meetings, Boston, November 1990. 相似文献
19.
This paper studies the behavior of motions of large-scale (LS) semistate systems (SSS) governed byP
i
(t)x
i
=M
i
(t,x
i
)x
i
+f
i
(t)+h
i
(t, x), i=1,2,...,s, =(x
1
T
x
2
T
x
s
T
)T, where matricesP
i
(t) are singular. Using Lyapunov's approach and the tools for LS system analysis, a variant of attractivity and ultimate boundedness of appropriate time-variable sets are investigated. The results are based on a specific choice of the aggregate functions. It is assumed that the reduction of equations to a normal form of lower order is inconvenient. The aggregation-decomposition approach used in this paper reduces the dimensionality of an aggregate matrix of the system to the number of its systems. Motion properties of LS systems are deduced from the properties of its isolated subsystems, the character of interconnections, and the conditions imposed on the system aggregate matrix. Sufficient algebraic conditions for the above-mentioned motion properties are developed. 相似文献
20.
Irina G. Bryndina Maria N. Shalagina Vladimir A. Protopopov Alexey V. Sekunov Andrey L. Zefirov Guzalia F. Zakirjanova Alexey M. Petrov 《International journal of molecular sciences》2021,22(5)
Muscle disuse and denervation leads to muscle atrophy, but underlying mechanisms can be different. Previously, we have found ceramide (Cer) accumulation and lipid raft disruption after acute hindlimb suspension (HS), a model of muscle disuse. Herein, using biochemical and fluorescent approaches the influence of unilateral denervation itself and in combination with short-term HS on membrane-related parameters of rat soleus muscle was studied. Denervation increased immunoexpression of sphingomyelinase and Cer in plasmalemmal regions, but decreased Cer content in the raft fraction and enhanced lipid raft integrity. Preliminary denervation suppressed (1) HS-induced Cer accumulation in plasmalemmal regions, shown for both nonraft and raft-fractions; (2) HS-mediated decrease in lipid raft integrity. Similar to denervation, inhibition of the sciatic nerve afferents with capsaicin itself increased Cer plasmalemmal immunoexpression, but attenuated the membrane-related effects of HS. Finally, both denervation and capsaicin treatment increased immunoexpression of proapoptotic protein Bax and inhibited HS-driven increase in antiapoptotic protein Bcl-2. Thus, denervation can increase lipid raft formation and attenuate HS-induced alterations probably due to decrease of Cer levels in the raft fraction. The effects of denervation could be at least partially caused by the loss of afferentation. The study points to the importance of motor and afferent inputs in control of Cer distribution and thereby stability of lipid rafts in the junctional and extrajunctional membranes of the muscle. 相似文献