Relationship between acoustic emission and microcrack formation in single crystals of Hadfield steel

Abrasive wear is not favorable for Hadfield steel. The connection between the acoustic emission signal and th

Experimental Research Into Generation of Acoustic Emission Signals in the Process of Friction of Hadfield Steel Single Crystals

The results of experimental research into dry sliding friction of Hadfield steel single crystals involving registration of acoustic emission are presented in the paper. The images of friction surfaces of Hadfield steel single crystals and wear grooves of the counterbody surface made after completion of three serial experiments conducted under similar conditions and friction regimes are given. The relation of the acoustic emission waveform envelope to the changing friction factor is revealed. Amplitude-frequency characteristics of acoustic emission signal frames are determined on the base of Fast Fourier Transform and Short Time Fourier Transform during the run-in stage of tribounits and in the process of stable friction

The Interrelation Between Hardiness and Prognostic Potential of Students of Higher Education Institutions

The paper presents the results of an empirical study of specific features and the relationship between hardiness of students and prognostic potential of their personality. The methods of research comprised: theoretical analysis, empirical research (testing), qualitative analysis of the obtained data, mathematical and statistical data processing (SPSS Statistics, Excel). It has been found that students with a high level of prognostic potential development are distinguished by pronounced personality traits typical of hardy people. The authors have proved in the paper that the prognostic potential of students is a holistic system of personality resources, which is based on specific features of thinking and building a secondary image. There are criteria and development levels of the prognostic potential among students: an internal criterion (features of thinking and building secondary images) and an external criterion (the effectiveness of forecasting activities, the conformity of the stages of prognostic activity with the reference model). The prognostic potential is interconnected with personal and professional characteristics of students (features of the intellectual, communicative, emotional-volitional and motivation spheres). There are significant differences between students with different levels of development of prognostic potential according to the main personal and professional features. The correlation analysis of the data gave the following interrelations: there is a direct interrelationship between the level of development of prognostic potential and emotional stability of students; between the level of development of prognostic potential and such motives for studying at a university as professional and educational-cognitive motives; between the level of development of prognostic potential and the features of self-regulation. On the basis of the results of an empirical study, the authors designed a program for the prognostic potential development of students which includes active teaching methods, lectures, and trainings

Bacteriophage-Resistant Mutants in Yersinia pestis: Identification of Phage Receptors and Attenuation for Mice

Background: Bacteriophages specific for Yersinia pestis are routinely used for plague diagnostics and could be an alternative to antibiotics in case of drug-resistant plague. A major concern of bacteriophage therapy is the emergence of phageresistant mutants. The use of phage cocktails can overcome this problem but only if the phages exploit different receptors. Some phage-resistant mutants lose virulence and therefore should not complicate bacteriophage therapy. Methodology/Principal Findings: The purpose of this work was to identify Y. pestis phage receptors using site-directed mutagenesis and trans-complementation and to determine potential attenuation of phage-resistant mutants for mice. Six receptors for eight phages were found in different parts of the lipopolysaccharide (LPS) inner and outer core. The receptor for R phage was localized beyond the LPS core. Most spontaneous and defined phage-resistant mutants of Y. pestis were attenuated, showing increase in LD 50 and time to death. The loss of different LPS core biosynthesis enzymes resulted in the reduction of Y. pestis virulence and there was a correlation between the degree of core truncation and the impact on virulence. The yrbH and waaA mutants completely lost their virulence. Conclusions/Significance: We identified Y. pestis receptors for eight bacteriophages. Nine phages together use at least seven different Y. pestis receptors that makes some of them promising for formulation of plague therapeutic cocktails. Most phage-resistant Y. pestis mutants become attenuated and thus should not pose a serious problem for bacteriophag

Use of a combination of the RDC method and NOESY NMR spectroscopy to determine the structure of Alzheimer’s amyloid Aβ10–35 peptide in solution and in SDS micelles

The spatial structure of Alzheimer's amyloid A beta(10-35)-NH2 peptide in aqueous solution at pH 7.3 and in SDS micelles was investigated by use of a combination of the residual dipolar coupling method and two-dimensional NMR spectroscopy (TOCSY, NOESY). At pH 7.3 A beta(10-35)-NH2 adopts a compact random-coil conformation whereas in SDS micellar solutions two helical regions (residues 13-23 and 30-35) of A beta(10-35)-NH2 were observed. By use of experimental data, the structure of "peptide-micelle" complex was determined; it was found that A beta(10-35)-NH2 peptide binds to the micelle surface at two regions (residues 17-20 and 29-35)

Regio- and Stereoselective One-Pot Synthesis of New Heterocyclic Compounds with Two Selenium Atoms Based on 2-Bromomethyl-1,3-thiaselenole Using Phase Transfer Catalysis

To date, not a single representative of 2,3-dihydro-1,4-thiaselenin-2-yl selenides has been described in the literature. The reaction of 2-bromomethyl-1,3-thiaselenole with potassium selenocyanate at low temperature was accompanied by a rearrangement with ring expansion leading to six-membered 2,3-dihydro-1,4-thiaselenin-2-yl selenocyanate, which was used for the generation of sodium dihydro-1,4-thiaselenin-2-yl selenolate. The latter intermediate was involved in situ in the nucleophilic substitution and addition reactions under phase transfer catalysis conditions. The nucleophilic substitution reactions with alkyl halides gave alkyl, allyl and propargyl 2,3-dihydro-1,4-thiaselenin-2-yl selenides in 93–98% yields. The addition reactions of dihydro-1,4-thiaselenin-2-yl selenolate anion to alkyl acrylates, acrylonitrile and alkyl propiolates proceeded in a regio- and stereoselective fashion affording corresponding functionalized 2,3-dihydro-1,4-thiaselenin-2-yl selenides in 93–98% yields. Thus, the regio- and stereoselective one-pot synthesis of a novel family of 2,3-dihydro-1,4-thiaselenin-2-yl selenides has been developed based 2-bromomethyl-1,3-thiaselenole, potassium selenocyanate, alkyl halides and compound with activated double and triple bonds

Regioselective Synthesis of Novel Functionalized Dihydro-1,4-thiaselenin-2-ylsufanyl Derivatives under Phase Transfer Catalysis

The regioselective one-pot synthesis of novel functionalized 2,3-dihydro-1,4-thiaselenin-2-ylsufanyl derivatives in high yields based on 2-bromomethyl-1,3-thiaselenole and activated alkenes was developed under phase transfer catalysis conditions. The reactions proceed under mild conditions at room temperature in a regioselective manner with the addition of sodium dihydro-1,4-thiaselenin-2-ylthiolate exclusively at the terminal carbon atom of the double bond of vinyl methyl ketone, alkylacrylates, acrylamide, acrylonitrile, divinyl sulfone, and divinyl sulfoxide. The sodium dihydro-1,4-thiaselenin-2-ylthiolate was generated from 2-[amino(imino)methyl]sulfanyl-2,3-dihydro-1,4-thiaselenine hydrobromide. The latter compound was obtained by the reaction of 2-bromomethyl-1,3-thiaselenole with thiourea, which was accompanied by a rearrangement with ring expansion to the six-membered heterocycle. The obtained 2,3-dihydro-1,4-thiaselenin-2-ylsufanyl derivatives are a novel family of compounds with putative biological activity. The addition products of sodium dihydro-1,4-thiaselenin-2-ylthiolate at one double bond of divinyl sulfone and divinyl sulfoxide, containing vinylsulfonyl and vinylsulfinyl groups, are capable of further addition reactions. A possibility to obtain corresponding alcohol derivatives was shown in the reaction with vinyl methyl ketone

Acoustic emission characterization of sliding wear under condition of direct and inverse transformations in low-temperature degradation aged Y-TZP and Y-TZP-AL2O3

Abstract In this research, results of the investigation of the sliding friction and wear of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) and Y-TZP-Al2O3 samples preliminarily subjected to low-temperature degradation are reported. The investigation was carried out using a pin-on-disk tribometer with simultaneous recording of acoustic emission (AE) and vibration acceleration. The sliding wear process was found to be determined by dynamic direct and inverse Y-TZP transformations detected by monoclinic and tetragonal X-ray diffraction peak ratios. The AE signals generated under direct and inverse transformations can be used to characterize wear and friction mechanisms as well as direct and inversed sliding-induced phase transformations. The AE signal energy grows with the friction coefficient and the inverse transformation degree. Reduction of the AE signal energy indicates establishing the mild wear stage caused by effective stress-induced direct martensitic transformation. The AE signal median frequency increases in the case of lower friction. Numerical studies of wear subsurface fracture under conditions of stress-induced martensitic transformation were used to elucidate the role played by the phase transformation in Y-TZP and Y-TZP-Al2O3. Martensitic transformation in Y-TZP was described with use of the non-associated dilatant plasticity model. Simulation results particularly show that increase in the value of dilatancy coefficient from 0 to 0.2 is accompanied by 25%−30% reduce in characteristic length and penetration depth of sliding-induced subsurface cracks. As shown the AE may be an effective tool for in-situ monitoring the subsurface wear of materials experiencing both direct and inverse transformations