Control Of Structural Changes Research Articles

Heat Treatment of High Manganese Austenitic Steel: Structural and Mechanical Properties

Background: Technological progress is based on the development of different types of materials. Among the materials most solicited, we mention metals and alloys. The development of these materials has been initiated and resulted in a wide range of metallic materials, including austenitic manganese, constituting, until today, a center of interest for various research works given their wide use in the industry as well as the recent progress by observation and characterization instruments. Objective: The aim of the paper is to investigate the heat treatment conditions of high manganese austenitic steel and to determine their influence on the structure and mechanical properties. Methods: The samples were subjected to an austenitization treatment at five different temperatures: 980 °C, 1000 °C, 1020 °C, 1040 °C, and 1060 °C for 1 hour. The experimental techniques used are hardness, nanoindentation tests, optical microscopy and X-ray diffraction. Hardness and microhardness measurements were performed to determine the wear behavior of the studied steels. Result: The results indicated that the temperature affects the microstructure; by increasing the austenitizing temperature with pronounced growth of the austenite as well as the dissolution of carbides M7C3, the nano hardness and the modulus of elasticity decreases considerably. Conclusion: The heat treatment of materials modifying the microstructure is closely related to the mechanical behavior of the austenitic manganese steel. Therefore, the control of structural changes by heat treatment is essential to obtain the desired properties. The established heat treatment conditions of the obtained steel can be suitable for several industrial applications.

Моніторинг міграційної мобільності – інформаційно-аналітичне забезпечення емпірики впливу на людський потенціал

The information and analytical provision of migration mobility empiricism in Ukraine, the effectiveness of the implementation of the State policy of managing migration processes is not formed to the full extent, and the existing one is of poor quality; in addition, there is no methodological algorithm for the implementation of migration monitoring. The elimination of this shortcoming requires the development of a new model for monitoring migration mobility, which should be based on a three-level accounting of migration processes (national, regional and local), taking into account the peculiarities of the course of migration processes and the structural characteristics of both external and internal migration. The article is aimed at improvnig the system of monitoring migration mobility in the projection of socio-economic development of the State in order to build an information and analytical base of the empiricism of influence on human potential. The article proposes a model of systematic monitoring of migration mobility, its information-analytical and institutional-organizational provision is substantiated. Monitoring of migration mobility on the basis of a systematic approach allows to: implement three-level accounting of emigration, immigration flows, processes of acquisition and termination of citizenship, money transfers of migrants; cluster the country’s territories according to the criteria of differentiated socio-economic development and financial imbalances; guarantee flexible control of structural changes in migration processes based on the construction of migration profile and determination of the potential of territories. The implementation of monitoring of migration mobility will allow to simulate the intensity of external migration, taking into account changes in the level of socio-economic development, to determine the effectiveness of the implementation of the current policy of managing migration processes on the part of the State.

STRUCTURAL CHANGES IN STRUCTURAL STEELS DURING THERMAL CYCLING

Introduction: During experimental studies of structural steels responsible for the reliability of metal structures used, for example, in hoisting and transporting machinery, we established a correlation between the magnetic parameter Hp and characteristic changes in the metal microstructure during thermal cycling. It is shown that the Нр parameter depends on the initial structural state of steel, the amount and mass fraction of alloying elements, and the number of heating/cooling cycles. Methods: We found that an increase in the number of heating/cooling cycles and the amount of alloying elements, as well as preliminary cold plastic deformation with stage-by-stage control of structural changes using passive magnetic flux leakage testing results in a finer-grained structure, which was confirmed by metallographic analysis. Results: The paper considers specifics of structural changes in steels with different initial structures during thermal cycling. It is shown that the final grain size depends on the number of treatment cycles, the amount of alloying elements, and the initial microstructure. It is the fine-grain structure that improves the most important performance characteristics of steels: strength, cyclic strength, and cold brittleness.

Magnetic control of structural changes in structural steels during plastic deformation

The analysis and consideration of the influence of the main factors on the damage of welded metal structures during long-term operation. The relationship between the strength of the magnetic field of the Hр scattering and structural changes in structural steels that occur during cold plastic deformation to different degrees is established. It is shown that at small degrees of deformation, the change in the magnetic parameter Hр is large. As they increase, the HP value decreases and tends to the values of the Earth's magnetic field. The data of microstructural analysis of the metal of structural steels are in good agreement with the results of the passive ferrosonde method of control. A method for evaluating the effect of cold plastic deformation on the magnetic properties of metal in structural steels has been developed.

Systematic Control of Structural Changes in GeO2 Glass Induced by Femtosecond Laser Direct Writing

We report the structural changes inside germania glass induced by femtosecond laser pulses. Inspection by polarization microscopy and secondary electron microscopy indicate that the periodic nanostructures consist of oxygen defects such as ODCs (oxygen deficient centers) and NBOHCs (nonbridging oxygen hole centers) for laser pulse energy less than 0.2 μJ. However, the glass network was dissociated and O2 molecules were generated for laser pulse energy greater than 0.4 μJ. Two different structural changes, form‐birefringence and dissociation, were induced in GeO2 glass, depending on the laser pulse energy. The form‐birefringence exhibited by the nanogratings in GeO2 glass is larger than that in SiO2 glass for pulse energy less than 0.2 μJ, as the density of nanovoids enclosed by ODCs in GeO2 glass is higher than that in SiO2 glass. Arrhenius plots of the phase retardation caused by the nanogratings in GeO2 and SiO2 indicate that the oxygen defects are relaxed at a temperature 100°C above the glass‐transition temperature.

Connexin and fibrosis related microRNAs in complex fractionated atrial electrograms.

Connexin and fibrosis related microRNAs in complex fractionated atrial electrograms.

Impact of cationic surfactant on the self-assembly of sodium caseinate.

The impact of a cationic surfactant, dodecylammonium chloride (DDACl), on the self-assembly of sodium caseinate (SC) has been investigated by light scattering, zeta potential, and rheological measurements as well as by microscopy (transmission electron and confocal laser scanning microscopy). In SC dilute solutions concentration-dependent self-assembly proceeds through the formation of spherical associates and their aggregation into elongated structures composed of connected spheres. DDACl interacts with SC via its hydrophilic and hydrophobic groups, inducing changes in SC self-assembled structures. These changes strongly depend on the surfactant aggregation states (monomeric or micellar) as well as concentration ratio of both components, leading to the formation of soluble and insoluble complexes of nano- to microdimensions. DDACl monomers interact with SC self-assembled entities in a different way compared to their micelles. Surfactant monomers form soluble complexes (similar to surfactant mixed micelles) at lower SC concentration but insoluble gelatinous complexes at higher SC concentration. At surfactant micellar concentration soluble complexes with casein chains wrapped around surfactant micelles are formed. This study suggests that the use of proper cationic surfactant concentration will allow modification and control of structural changes of SC self-assembled entities.

Free-standing polymer nanoactuators, nanoshutters, and nanofilters

Our study demonstrates a facile approach for the synthesis of metal NP-embedded freestanding polyelectrolyte complexes (PECs) without sacrificial templates, which can be used as nanoactuators, nanoshutters, and nanofilters. The metal NP-PECs were prepared by mixing metal precursor-preadsorbed cation and anion PEs, using a nonstoichiometric ratio, followed by a controlled heat treatment. The metal NP-PECs showed reversible structural changes such as shrinking or swelling when they were exposed to various pH conditions. During the changes, they were also able to reversibly control the interparticle distance of the metal NPs embedded in the PECs, which has allowed the easy tuning of their catalytic and optical properties. By the reversible control of structural changes, the PECs can also be used as nanoshutters to reversibly control the flow of nanomaterials in the channels or pores. Furthermore, metal NP-embedded PECs, Au/Ag-PECs, were demonstrated to be useful as nanofilters for removing or transforming unwanted materials.

Light-Triggered Crystallization of a Molecular Host−Guest Complex

The control of structural changes in supramolecular assemblies is a key point in the development of molecular machines. The reversible photoisomerization of organic compounds such as azobenzene using light as an external input is especially suited because no waste products are generated. Based on our previous studies on the quantitative encapsulation of suitably sized bis-sulfonate guests by a self-assembled, metal-organic cage consisting of four rigid, bent bis-monodentate pyridyl ligands and two Pd(II) ions, we show here how the light-switchable guest cis-4,4'-azobenzene bis-sulfonate can be expelled from its 1:1 host-guest complex triggered by its photoisomerization to the trans-isomer. Using a highly soluble, PEGylated cage derivative, the full reversibility of this light-driven encapsulation/release process is demonstrated. In contrast, a sample of the less soluble, unsubstituted cages including 1 equiv of the cis-guest was shown to result in immediate crystallization upon photoisomerization of the guest. X-ray structure analysis confirmed the guest molecules having left the cavity of the host and on the contrary joining the cages into a polymeric material by binding to their Pd(II) centers from outside.

MiR-133 and miR-30 Regulate Connective Tissue Growth Factor

The myocardium of the failing heart undergoes a number of structural alterations, most notably hypertrophy of cardiac myocytes and an increase in extracellular matrix proteins, often seen as primary fibrosis. Connective tissue growth factor (CTGF) is a key molecule in the process of fibrosis and therefore seems an attractive therapeutic target. Regulation of CTGF expression at the promoter level has been studied extensively, but it is unknown how CTGF transcripts are regulated at the posttranscriptional level. Here we provide several lines of evidence to show that CTGF is importantly regulated by 2 major cardiac microRNAs (miRNAs), miR-133 and miR-30. First, the expression of both miRNAs was inversely related to the amount of CTGF in 2 rodent models of heart disease and in human pathological left ventricular hypertrophy. Second, in cultured cardiomyocytes and fibroblasts, knockdown of these miRNAs increased CTGF levels. Third, overexpression of miR-133 or miR-30c decreased CTGF levels, which was accompanied by decreased production of collagens. Fourth, we show that CTGF is a direct target of these miRNAs, because they directly interact with the 3' untranslated region of CTGF. Taken together, our results indicate that miR-133 and miR-30 importantly limit the production of CTGF. We also provide evidence that the decrease of these 2 miRNAs in pathological left ventricular hypertrophy allows CTGF levels to increase, which contributes to collagen synthesis. In conclusion, our results show that both miR-133 and miR-30 directly downregulate CTGF, a key profibrotic protein, and thereby establish an important role for these miRNAs in the control of structural changes in the extracellular matrix of the myocardium.

A Model of Optimal Control of Structural Changes in an Organizational System

An organizational system is considered, namely, an aggregate of certain elements that are hierarchically connected for fulfilling a collection of functions. It is assumed that the result of the work of the system depends on its structure. For a set of various structures (graphs of the organization), expenditures on the operation of the system and on the restructurization are defined. An optimal control of structural changes in a finite time interval involves the choice of the sequence of structural transformations that maximize the total profit. An optimal control enables balancing the expenditures for the operation (effectiveness) and for the restructurization (the stability to external actions).

Angiotensin converting enzyme inhibitors in angina and myocardial infarction. What role will they play in the 1990s?

Nearly 100 years ago, Tigerstedt and Bergman (1898) observed that renal extracts may increase blood pressure. In 1934, Goldblatt and associates described their animal model for renovascular hypertension. A series of studies showed thereafter that renin itself was ineffective, but that it liberated a plasma factor (angiotensin I) which needed to be converted into an active hormone (angiotensin II). Essential knowledge for a fuller understanding of the pathophysiology of the renin-angiotensin system came from the discovery of angiotensin II analogue receptor blockers and angiotensin converting enzyme (ACE) inhibitors. However, only the development of the orally active compounds captopril (Cushman et al. 1977) and enalapril (Patchett et al. 1980) allowed widespread exploitation of the system in clinical studies. Thus the 1970s had started with experimental analysis of the renin-angiotensin system and ended with clinical introduction of ACE inhibitors for the treatment of hypertension. It was puzzling, however, that ACE inhibitors were effective in lowering blood pressure in more than 50% of patients with low plasma renin activities. Increasing evidence was obtained showing that interference with the plasma renin-angiotensin system was not the only, and indeed perhaps not even the most important, mechanism of action of ACE inhibitors. Table I summarises other potential mechanisms of action. The effects may be related to the reninangiotensin-aldosterone system, bradykinin, or other hormones or mediators. The relative importance of the individual mechanisms remains unknown. However, research has increasingly focused on local tissue renin-angiotensin systems, and a cardiac renin-angiotensin system might participate in control of structural changes of the heart when failure is developing (Lindpainter & Ganten 1991). The observation that the renin-angiotensin system was activated in selected patients with heart failure (Dzau et al. 1981) initiated a new era of research. Vasodilators had been used successfully in acute therapy while long term studies revealed controversial results. Only the combination of hydralazine and isosorbide dinitrate reduced mortality in patients with severe chronic heart failure (Cohn et al. 1986). A follow-up study showed that the ACE inhibitor enalapril was slightly superior