Modelling of Thin Films Hardness Measured by a Spherical Indenter

In this theoretical contribution, we chose to use an indenter having a spherical geometrical form, which we used to model the surfaces mixture to separate the contributions of substrate and film in the composite covered material hardness. We have considered the coefficients α, β of the model as ratios of the projections of the imprints at the horizontal plans (disks surfaces). We prove that the film hardness of monolayer coating is dependent on the composite and substrate hardness, the geometrical form of the indenter, and the film thickness.В этой теоретической работе рассмотрен индентор сферической геометрической формы, который был использован для составления модели смешанных поверхностей, чтобы оценить вклады подложки и плёнки в твёрдость композитного материала покрытия. Коэффициенты модели α, β рассматриваются как отношения проекций отпечатков на горизонтальные плоскости (в виде дисков). Доказано, что твёрдость плёнки однослойного покрытия зависит от твёрдостей композитного покрытия и подложки, геометрической формы индентора и толщины плёнки.У цій теоретичній роботі розглянуто індентор сферичної геометричної форми, який було використано для складання моделю змішаних поверхонь, щоб оцінити внески підкладинки та плівки у твердість композитного матеріялу покриття. Коефіцієнти моделю α, β розглядаються як співвідношення проєкцій відбитків на горизонтальні площини (у вигляді дисків). Доведено, що твердість плівки одношарового покриття залежить від твердостей композитного покриття та підкладинки, геометричної форми індентора та товщини плівки

Tribological study of a bronze obtained by Sintering proceeds

Friction is a widely observed phenomenon requiring scientific capacity in the  tribological behavior of materials. Reliability specialists use language borrowed from the doctors, so they talk about teething, durations of life and death, it is true that the machines as living beings, are born, wear, get tired, suffer defaults and eventually die; That is to say, are reformed, but the comparison stops, because the machines have no nervous system or bloodstream, do not think and feel no pain. Factors that may affect the life, or the factors that affect wear are very numerous: surface characteristics, operating conditions of the lubricant, the atmosphere, and finally the time. In this work we present the effect of speed and load on the tribological characteristics of a Cu 8% Sn bronze pressure sintered self-lubricating mode for two lubricants with different viscosities.Keywords: sintering; powder metallurgy; tribology; lubrication; copper alloy

Measured Hardness by an Indenter Having Ellipsoidal Shape

Если при исследовании твердости в качестве индентора использовалось твердое тело эллипсоидальной формы, выражение для статической твердости рассматривалось как функция от глубины и радиусов отпечатка индентора. При этом применялась общая формула, связывающая статическую твердость с отношением нормальной силы, прилагаемой к индентору, к реальной площади его отпечатка. При получении конечной формулы для расчета твердости использовались геометрический и математический подходы.Якщо при дослідженні твердості за індентор слугувало тверде тіло еліпсоїдної форми, вираз для статичної твердості розглядався як функція від глибини і радіусів відбитка індентора. При цьому використовувалась загальна формула, що зв язувала статичну твердість із відношенням нормальної сили, прикладеної до індентора, до реальної площі його відбитка. При отриманні кінцевої формули для розрахунку твердості використовувались геометричний і механічний підходи

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg

© 2018, The Author(s). High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing

Molecular and functional variation in iPSC-derived sensory neurons

Induced pluripotent stem cells (iPSCs), and cells derived from them, have become key tools for modeling biological processes, particularly in cell types that are difficult to obtain from living donors. Here we present a map of regulatory variants in iPSC-derived neurons, based on 123 differentiations of iPSCs to a sensory neuronal fate. Gene expression was more variable across cultures than in primary dorsal root ganglion, particularly for genes related to nervous system development. Using single-cell RNA-sequencing, we found that the number of neuronal versus contaminating cells was influenced by iPSC culture conditions before differentiation. Despite high differentiation-induced variability, our allele-specific method detected thousands of quantitative trait loci (QTLs) that influenced gene expression, chromatin accessibility, and RNA splicing. On the basis of these detected QTLs, we estimate that recall-by-genotype studies that use iPSC-derived cells will require cells from at least 20-80 individuals to detect the effects of regulatory variants with moderately large effect sizes

Pharmacologically Reversible, Loss of Function Mutations in the tm2 and tm4 Inner Pore Helices of Trek-1 k2p Channels

A better understanding of the gating of TREK two pore domain potassium (K2P) channels and their activation by compounds such as the negatively charged activator, flufenamic acid (FFA) is critical in the search for more potent and selective activators of these channels. Currents through wild-type and mutated human K2P channels expressed in tsA201 cells were measured using whole-cell patch-clamp recordings in the presence and absence of FFA. Mutation of the TM2.6 residue of TREK-1 to a phenylalanine (G171F) and a similar mutation of TM4.6 (A286F) substantially reduced current through TREK-1 channels. In complementary experiments, replacing the natural F residues at the equivalent position in TRESK channels, significantly enhanced current. Known, gain of function mutations of TREK-1 (G137I, Y284A) recovered current through these mutated channels. This reduction in current could be also be reversed pharmacologically, by FFA. However, an appropriate length MTS (MethaneThioSulfonate) cross-linking reagent (MTS14) restricted the activation of TREK-1_A286C channels by repeated application of FFA. This suggests that the cross-linker stabilises the channel in a conformation which blunts FFA activation. Pharmacologically reversible mutations of TREK channels will help to clarify the importance of these channels in pathophysiological conditions such as pain and depression

Ultrafine grained plates of Al-Mg-Si alloy obtained by Incremental Equal Channel Angular Pressing : microstructure and mechanical properties

In this study, an Al-Mg-Si alloy was processed using via Incremental Equal Channel Angular Pressing (I-ECAP) in order to obtain homogenous, ultrafine grained plates with low anisotropy of the mechanical properties. This was the first attempt to process an Al-Mg-Si alloy using this technique. Samples in the form of 3 mm-thick square plates were subjected to I-ECAP with the 90˚ rotation around the axis normal to the surface of the plate between passes. Samples were investigated first in their initial state, then after a single pass of I-ECAP and finally after four such passes. Analyses of the microstructure and mechanical properties demonstrated that the I-ECAP method can be successfully applied in Al-Mg-Si alloys. The average grain size decreased from 15 - 19 µm in the initial state to below 1 µm after four I-ECAP passes. The fraction of high angle grain boundaries in the sample subjected to four I-ECAP passes lay within 53-57 % depending on the examined plane. The mechanism of grain refinement in Al-Mg-Si alloy was found to be distinctly different from that in pure aluminium with the grain rotation being more prominent than the grain subdivision, which was attributed to lower stacking fault energy and the reduced mobility of dislocations in the alloy. The ultimate tensile strength increased more than twice, whereas the yield strength - more than threefold. Additionally, the plates processed by I-ECAP exhibited low anisotropy of mechanical properties (in plane and across the thickness) in comparison to other SPD processing methods, which makes them attractive for further processing and applications