DEVELOPMENT AND STUDY OF ELECTRO-EROSION STRENGTHENING OF TOOL IN LIQUID NITROGEN

There the study objects are the mechanisms of forming process of defectless surface layer with the formation of wear-resistant phases on the nitride basis at the periodic action of cryogenic temperatures and of powerful heat sources, with result in the titanium sputtering. The mechanism of local formations of titanium nitride and of elimination of available microcracks without the clinging of titanium slivers on the treated surface has been detected and has been explored. It is showed that the gaseous nitrogen finds way into the microcrack during the erosion treatment process with the nitride post-formation under the action of plasma. The design procedure of displacement magnitude of strengthening zone against the cutting edge and been developed; it keeps the quality of grinding of tool. The quantity and the character of electrode wear with the development of recommendations for the bar shape have been explored. The electro-erosion strengthening process for the tools including for the medical instrument in the medium of liquid nitrogen has been designed and has been introduced. The bay for the strengthening of cutting tool has been madeAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Application of the method of phase portraits to the analysis of the kinetics of redistribution of metal ion concentrations in the polyelectrolyte hydrogel-multicomponent solution system

International audienceThe kinetics of redistribution of metal ion concentrations in a system based on a polyelectrolyte hydrogel and a multicomponent salt solution (CuSO 4 and Na 2SO 4) were experimentally examined and theoretically treated. Independently of the mixture composition, the hydrogel swelling-contraction behavior and the sorption-desorption of metal ions are determined by the reactivity of metal ions: the hydrogel sorbs copper ions from solution and collapses; as a result, sodium ions (counterions) are released into the solution. The presence of sodium ions in the mixture decreases the amount of absorbed copper ions and slows down their sorption rate. The method of phase portraits made it possible to obtain a phenomenological equation describing the kinetics of redistribution of metal ion concentrations in the hydrogel-solution system at each hydrogel swelling step (disappearance of dry phase, swelling, and collapse). Experimental data were treated using the frequency filtration technique, which is based on the numerical simulation of a low-pass filter used in radio engineering. With increasing filtration period, the difference between various hydrogel swelling steps is shown to vanish. Comparison of the phase portraits of various mixtures shows that an increase in the amount of any component in the mixture decreases the differences between swelling steps and, thus, substantially simplifies the theoretical description of the process kinetics

Adverse feedback sequences in exploited marine systems: Are deliberate interruptive actions warranted?

Several mechanisms for self-enhancing feedback instabilities in marine ecosystems are identified and briefly elaborated. It appears that adverse phases of operation may be abruptly triggered by explosive breakouts in abundance of one or more previously suppressed populations. Moreover, an evident capacity of marine organisms to accomplish extensive geographic habitat expansions may expand and perpetuate a breakout event. This set of conceptual elements provides a framework for interpretation of a sequence of events that has occurred in the Northern Benguela Current Large Marine Ecosystem (off south-western Africa). This history can illustrate how multiple feedback loops might interact with one another in unanticipated and quite malignant ways, leading not only to collapse of customary resource stocks but also to degradation of the ecosystem to such an extent that disruption of customary goods and services may go beyond fisheries alone to adversely affect other major global ecosystem concerns (e.g. proliferations of jellyfish and other slimy, stingy, toxic and/or noxious organisms, perhaps even climate change itself, etc.). The wisdom of management interventions designed to interrupt an adverse mode of feedback operation is pondered. Research pathways are proposed that may lead to improved insights needed: (i) to avoid potential 'triggers' that might set adverse phases of feedback loop operation into motion; and (ii) to diagnose and properly evaluate plausible actions to reverse adverse phases of feedback operation that might already have been set in motion. These pathways include the drawing of inferences from available 'quasi-experiments' produced either by short-term climatic variation or inadvertently in the course of biased exploitation practices, and inter-regional applications of the comparative method of science

First overview on trophic relationships of the invasive ctenophore Mnemiopsis leidyi in a Mediterranean coastal lagoon (Berre Lagoon, France): benthic–pelagic coupling evidenced by carbon and nitrogen stable isotope composition

The ctenophore Mnemiopsis leidyi, ranking among the 100 most damaging bioinvaders in the world, is a major predator of zooplankton, known to alter the biodiversity and functioning of the ecosystems in which it has been introduced. This first survey on the trophic relationships of M. leidyi in a Mediterranean lagoon (Berre, South of France) was performed through stable isotope analyses. Carbon and nitrogen isotope composition was used (1) to determine the types of prey ingested by this ctenophore and (2) the influence of individual size on its isotope composition, and (3) to make assumptions to explore its trophic relationships with the native jellyfish Aurelia sp.. The two gelatinous species ingested mainly (79% to 97% of the diet) planktonic prey (copepods, cirriped nauplii, gastropod larvae and cladocerans), but also preyed upon benthic organisms (mainly harpacticoid copepods and the amphipod Monocorophium insidiosum) in lower proportions (2.5% to 21%). Size-related changes in M. leidyi diet were evidenced with an increase in trophic level and benthic prey consumption in the larger individuals. These two gelatinous organisms probably play an important and underestimated role in the benthic–pelagic​ coupling in coastal lagoons by transferring benthic organic matter to the pelagic food webs