The Mossbauer Spectroscopy Studies of Cementite Precipitations during Continuous Heating from As-Quenched State of High Carbon Cr-Mn-Mo Steel

This work complements the knowledge concerning the kinetics of cementite precipitation during tempering. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The samples of investigated steel were austen- itized at the temperature of 900±C and quenched in oil. Then four of five samples were tempered. Tempering consisted of heating the samples up to chosen temperatures at the heating rate of 0.05±C/s and fast cooling after reaching desired temperature. This work presents the results of investigations performed carried out using the Mossbauer spectroscopy technique and their interpretation concerning cementite nucleation and growth during tempering. The values of hyperfine magnetic field on 57Fe atomic nuclei, determined for the third component of the Mossbauer spectrum as regards to its intensity, indicate that these are the components coming from ferro- magnetic carbides. Big differences in hyperfine magnetic fields coming from Fe atoms existing in the structure of carbides, measured on samples heated up to the temperatures of 80±C and 210±C, in comparison with values for 57Fe atoms precipitated from carbides during heating up to the temperaturę of 350±C and 470±C, allow to state that these are the carbides of different crystal structure. The influence of hardened steel heating temperature on cementite precipitation was determined. The Mossbauer spectroscopy was applied not only for magnetic hyperfine fileld studies, but also to analyze the values of quadrupole splitting and isomeric shift, which resulted in significant conclusions concerning the changes in cementite precipitations morphology, chemical composition and the level of stresses being present in this research

Structural and biochemical characterisation of the C-type lectin receptor DNGR 1 and its binding to F-actin

DNGR-1 is a C-type lectin receptor that has been implicated in the regulation of endocytic trafficking and cross-presentation of dead cell-associated antigens. Dendritic cells deficient in DNGR-1 are impaired in priming effector T-cell responses against cytopathic viruses and other dead cell-associated antigens. The ligand for DNGR-1 is the polymerized form of actin (F-actin) revealed in dead cells upon loss of membrane integrity. In this study we set out to determine biophysical, biochemical, and structural properties of DNGR-1 and its interaction with F-actin. First, we describe a conformational change that occurs in the neck region of the receptor in a pH- and ionic strength-dependent manner. Notably, the conformational change happens between conditions corresponding to the extracellular environment and the environment present in the vesicles of the endosomal pathway respectively, suggesting a possible role in the spatial regulation of the DNGR-1 function. Second, in collaboration with Keichii Namba and Takashi Fujii (RIKEN Quantitative Biology Center, Osaka, Japan) we used electron cryomicroscopy to solve the structure of DNGR-1 bound to F-actin at 7.7 Å resolution. Interestingly, DNGR-1 binds into the groove between actin protofilaments, making contacts with three actin subunits that are helically arranged in the F-actin structure. We identify the residues directly involved in the interaction, confirm their contribution to the binding and demonstrate the importance of avidity of the multivalent interaction between DNGR-1 and F-actin. Additionally, in collaboration with David Sancho and Salvador Iborra (Centro Nacional de Investigaciones Cardiovasculares, Madrid, Spain) we formally demonstrate that ligand recognition is prerequisite for the biological function of DNGR-1 in dendritic cells. Third, by using heterodimeric DNGR-1 proteins in which one half of the dimer is incapable of binding to ligand, we demonstrate that DNGR-1 can bind with both ligand binding domains to a single actin filament, suggesting an exceptional flexibility of the neck region, and demonstrating an absence of rigid dimerization interface between the ligand-binding domains. In summary, we provide a comprehensive description of the structural and biophysical properties of DNGR-1, offering novel insights into its function and shedding light into innate immune mechanisms involved in recognition of cell death

Energy Content of Colliding Plane Waves using Approximate Noether Symmetries

This paper is devoted to study the energy content of colliding plane waves using approximate Noether symmetries. For this purpose, we use approximate Lie symmetry method of Lagrangian for differential equations. We formulate the first-order perturbed Lagrangian for colliding plane electromagnetic and gravitational waves. It is shown that in both cases, there does not existComment: 18 pages, accepted for publication in Brazilian J Physic

Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Single-crystalline superalloy CMSX-4 is studied in the as-cast state and after heat treatment, with material being taken from turbine blade castings. The effect of the heat treatment on the defect structure of the root area near the selector/root connection is emphasized. Multiscale analysis is performed to correlate results obtained by X-ray topography and positron annihilation lifetime spectroscopy (PALS). Electron microscopy observations were also carried out to characterize the inhomogeneity in dendritic structure. The X-ray topography was used to compare defects of the misorientation nature, occurring in as-cast and treated states. The type and concentration of defects before and after heat treatment in different root areas were determined using the PALS method, which enables voids, mono-vacancies, and dislocations to be taken into account. In this way, differences in the concentration of defects caused by heat treatment are rationalized

The role of adsorbed ions during electrocatalysis in ionic liquids

The effects of electrode–adsorbate interactions on electrocatalysis at Pt in ionic liquids are described. The ionic liquids are diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], dimethylethylammonium trifluoromethanesulfonate, [dmea][TfO], and diethylmethylammonium bis(trifluoromethanesulfonyl)imide, [dema][Tf2N]. Electrochemical analysis indicates that a monolayer of hydrogen adsorbs onto Pt during potential cycling in [dema][[TfO] and [dmea][TfO]. In addition, a prepeak is observed at lower potentials than that of the main oxidation peak during CO oxidation in the [TfO]−-based liquids. In contrast, hydrogen does not adsorb onto Pt during potential cycling in [dema][Tf2N] and no prepeak is observed during CO oxidation. By displacing adsorbed ions on Pt surfaces with CO at a range of potentials, and measuring the charge passed during ion displacement, the potentials of zero total charge of Pt in [dema][TfO] and [dmea][TfO] were measured as 271 ± 9 and 289 ± 10 mV vs RHE, respectively. CO displacement experiments also indicate that the [Tf2N]− ion is bound to the Pt surface at potentials above −0.2 V and the implications of ion adsorption on electrocatalysis of the CO oxidation reaction and O2 reduction reaction in the protic ionic liquids are discussed

The cytoskeleton in cell-autonomous immunity: structural determinants of host defence

Host cells use antimicrobial proteins, pathogen-restrictive compartmentalization and cell death in their defence against intracellular pathogens. Recent work has revealed that four components of the cytoskeleton — actin, microtubules, intermediate filaments and septins, which are well known for their roles in cell division, shape and movement — have important functions in innate immunity and cellular self-defence. Investigations using cellular and animal models have shown that these cytoskeletal proteins are crucial for sensing bacteria and for mobilizing effector mechanisms to eliminate them. In this Review, we highlight the emerging roles of the cytoskeleton as a structural determinant of cell-autonomous host defence

The Mössbauer Spectroscopy Studies οf Cementite Precipitations during Continuous Heating from As-Quenched State of High Carbon Cr-Mn-Mo Steel

This work complements the knowledge concerning the kinetics of cementite precipitation during tempering. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The samples of investigated steel were austenitized at the temperature of 900°C and quenched in oil. Then four of five samples were tempered. Tempering consisted of heating the samples up to chosen temperatures at the heating rate of 0.05°C/s and fast cooling after reaching desired temperature. This work presents the results of investigations performed carried out using the Mössbauer spectroscopy technique and their interpretation concerning cementite nucleation and growth during tempering. The values of hyperfine magnetic field on $\text{}^{57}Fe$ atomic nuclei, determined for the third component of the Mössbauer spectrum as regards to its intensity, indicate that these are the components coming from ferromagnetic carbides. Big differences in hyperfine magnetic fields coming from Fe atoms existing in the structure of carbides, measured on samples heated up to the temperatures of 80°C and 210°C, in comparison with values for $\text{}^{57}Fe$ atoms precipitated from carbides during heating up to the temperature of 350°C and 470°C, allow to state that these are the carbides of different crystal structure. The influence of hardened steel heating temperature on cementite precipitation was determined. The Mössbauer spectroscopy was applied not only for magnetic hyperfine fileld studies, but also to analyze the values of quadrupole splitting and isomeric shift, which resulted in significant conclusions concerning the changes in cementite precipitations morphology, chemical composition and the level of stresses being present in this research

The Mössbauer Spectroscopy Studies of ϵ to Cementite Carbides Transformation during Isothermal Heating from As-Quenched State οf High Carbon Tool Steel

This work presents results of investigations using the Mössbauer spectroscopy technique and their interpretation concerning transformation of ϵ to cementite carbides during tempering in relation to the previously conducted dilatometric, microscopic and mechanical investigations. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The influence of the tempering time on nucleation and solubility of ϵ carbides, and on cementite nucleation and growth, was determined. The analysis of phase transformations during various periods of tempering using the Mössbauer spectroscopy technique made possible to reveal fine details connected with the processes

Structural Relaxation in Fe78Nb2B20Fe_{78}Nb_{2}B_{20} Amorphous Alloy Studied by Mössbauer Spectroscopy

It was shown that soft magnetic properties of $Fe_{78}Nb_{2}B_{20}$ amorphous alloy can be significantly improved by applying 1-h annealing at temperature 623 K (permeability increases even about 8 times). The Mössbauer Spectroscopy technique indicated that the optimized microstructure (corresponding to the maximum magnetic permeability) is free of iron nanograins and should be attributed to annealing out of free volume and a reduction of internal stresses i.e. to the relaxed amorphous phase