The resistance to hydrogen embrittlement (HE) of CrMnFeCoNi high-entropy alloy (HEA) at both room and cryogenic temperatures was examined through tensile experiments on specimens hydrogenated via ...cathodic electrochemical charging method. Two representative steels, i.e. 316L stainless steel (SS) and X80 pipeline steel (PS), were chosen for comparison due to their similar main constituent elements to CrMnFeCoNi HEA. Results show that the hydrogen pre-charged CrMnFeCoNi HEA has the smallest loss of ductility among the three materials at room temperature, while displays no reduction of elongation at 77 K, compared with the uncharged one. Fracture surfaces at both room and cryogenic temperatures of hydrogen pre-charged CrMnFeCoNi HEA are mainly composed of dimples, indicating ductile fractures, while brittle characteristics occur in pre-charged 316L SS and X80 PS. Typical deformation microstructure of the hydrogen pre-charged CrMnFeCoNi HEA at room temperature is tangled dislocations instead of highly dense dislocation walls (HDDWs) found in the pre-charged 316L SS. At 77 K, more deformation twins are formed in the both materials. Reasons for a higher resistance to HE of CrMnFeCoNi HEA at room temperature are attributed to the formation of less hydrogen trapping sites, thus a lower degree of hydrogen enrichment than 316L SS. While at 77 K, the atomic hydrogen is not able to promptly accumulate near these trapping sites due to its slow diffusion rate, which leads to strong HE resistance.
CHARMM: The biomolecular simulation program Brooks, B.R; Brooks, C.L. III; Mackerell, A.D. Jr ...
Journal of computational chemistry,
30 July 2009, Letnik:
30, Številka:
10
Journal Article
Recenzirano
Odprti dostop
CHARMM (Chemistry at HARvard Molecular Mechanics) is a highly versatile and widely used molecular simulation program. It has been developed over the last three decades with a primary focus on ...molecules of biological interest, including proteins, peptides, lipids, nucleic acids, carbohydrates, and small molecule ligands, as they occur in solution, crystals, and membrane environments. For the study of such systems, the program provides a large suite of computational tools that include numerous conformational and path sampling methods, free energy estimators, molecular minimization, dynamics, and analysis techniques, and model-building capabilities. The CHARMM program is applicable to problems involving a much broader class of many-particle systems. Calculations with CHARMM can be performed using a number of different energy functions and models, from mixed quantum mechanical-molecular mechanical force fields, to all-atom classical potential energy functions with explicit solvent and various boundary conditions, to implicit solvent and membrane models. The program has been ported to numerous platforms in both serial and parallel architectures. This article provides an overview of the program as it exists today with an emphasis on developments since the publication of the original CHARMM article in 1983.
Display omitted
► Significant grain refinement was achieved by severe plasticity burnishing (SPB). ► Strong basal textures were created concomitantly by SPB. ► Corrosion resistance of AZ31B processed ...by SPB was remarkably improved. ► Effects of texture become more critical than grain refinement when grain size was around 1μm. ► Residual stresses have less influence than texture and grain size.
Grain refinement and strong basal texture were produced on AZ31B Mg alloy surface concomitantly by a newly developed severe plastic deformation (SPD) process, severe plasticity burnishing (SPB). The remarkably improved corrosion resistance of AZ31 in NaCl solution after SPB was attributed mainly to dramatically reduced grain size and strongly basal-textured grain orientation. The residual stresses introduced by SPB were also found to influence the corrosion resistance to some extent. Compared with other SPD processes, SPB is fast, cost-effective, does not change material bulk properties and requires little changes to the industrial production process.
Abstract
Understanding the sources of lunar water is crucial for studying the history of lunar evolution, as well as the interaction of solar wind with the Moon and other airless bodies. Recent ...orbital spectral observations revealed that the solar wind is a significant exogenous driver of lunar surficial hydration. However, the solar wind is shielded over a period of 3–5 days per month as the Moon passes through the Earth’s magnetosphere, during which a significant loss of hydration is expected. Here we report the temporal and spatial distribution of polar surficial OH/H
2
O abundance, using Chandrayaan-1 Moon Mineralogy Mapper (
M
3
) data, which covers the regions inside/outside the Earth’s magnetosphere. The data shows that polar surficial OH/H
2
O abundance increases with latitude, and that the probability of polar surficial OH/H
2
O abundance remains at the same level when in the solar wind and in the magnetosphere by controlling latitude, composition, and lunar local time. This indicates that the OH/H
2
O abundance in the polar regions may be saturated, or supplemented from other possible sources, such as Earth wind (particles from the magnetosphere, distinct from the solar wind), which may compensate for thermal diffusion losses while the Moon lies within the Earth’s magnetosphere. This work provides some clues for studies of planet–moon systems, whereby the planetary wind serves as a bridge connecting the planet with its moons.
Recent studies have shown that the ambient plasma in the near-Earth magnetotail can be compressed by the arrival of a dipolarization front (DF). In this paper we study the variations in the ...characteristics of currents flowing in this compressed region ahead of the DF, particularly the changes in the cross-tail current, using observations from the THEMIS satellites. Since we do not know whether the changes in the cross-tail current lead to a field-aligned current formation or just form a current loop in the magnetosphere, we thus use redistribution to represent these changes of local current density. We found that (1) the redistribution of the cross-tail current is a common feature preceding DFs; (2) the redistribution of cross-tail current is caused by plasma pressure gradient ahead of the DF and (3) the resultant net current redistributed by a DF is an order of magnitude smaller than the typical total current associated with a moderate substorm current wedge (SCW). Moreover, our results also suggest that the redistributed current ahead of the DF is closed by currents on the DF itself, forming a closed current loop around peaks in plasma pressure, what is traditionally referred to as a banana current.
An ultrafine-grained surface layer was produced on Mg–Al–Zn alloy by a new severe plastic deformation process, cryogenic burnishing. The total burnishing-influenced zone was found to be over 3.4
mm ...thick. A large increase in hardness from 0.86 to 1.35
GPa was obtained near the topmost surface, where grains were refined from 12
μm down to 263
nm. The corrosion resistance was significantly enhanced, which may due to the combined effects of grain refinement and strong basal texture.
We investigate the plasma sheet pressure variations in the near‐Earth magnetotail (radius distance, R, from 7.5 RE to 12 RE and magnetic local time, MLT, from 18:00 to 06:00) during substorm growth ...phase with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. It is found that, during the substorm growth phase, about 39.4% (76/193) of the selected events display a phenomenon of equatorial plasma pressure (Peq) decrease. The occurrence rates of Peq decrease cases are higher in the dawn (04:00 to 06:00) and dusk (18:00 to 20:00) flanks (> 50%) than in the midnight region (20:00 to 04:00, < 40%). The mean values of the maximum percentages of Peq decrease during the substorm growth phases are larger in the dawn and dusk flanks (~ −20%) than in the midnight region (~ > −16%). The mean value of Peq increase percentages at the end of substorm growth phase is the highest (~ 40%) in the premidnight MLT bin (22:00 to 00:00) and is almost unchanged in the dawn and dusk flanks. Further investigations show that 13.0% of the events have more than 10% of Peq decrease at the end of substorm growth phase comparing to the value before the growth phase, and ~ 28.0% of the events have small changes (< 10%), and ~ 59.0% events have a more than 10% increase. This study also reveals the importance of electron pressure (Pe) in the variation of Peq in the substorm growth phase. The Pe variations often account for more than 50% of the Peq changes, and the ratios of Pe to ion pressure often display large variations (~ 50%). Among the investigated events, during the growth phase, an enhanced equatorial plasma convection flow is observed, which diverges in the midnight tail region and propagates azimuthally toward the dayside magnetosphere with velocity of ~ 20 km/s. It is proposed that the Peq decreases in the near‐Earth plasma sheet during the substorm growth phase may be due to the transport of closed magnetic flux toward the dayside magnetosphere driven by dayside magnetopause reconnection. Both solar wind and ionospheric conductivity effects may influence the distributions of occurrence rates for Peq decrease events and the Peq increase percentages in the investigated region.
Key Points
About 40% of the selected events in the near‐tail region display a phenomenon of equatorial plasma pressure decrease
An enhanced equatorial convection with speed of ~ 20 km/s is observed in our cases during the substorm growth phase
Statistical studies for the distributions of Peq properties and electron pressure variations are performed
We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in situ measurements of magnetic field, particles, and radio waves from ...the Juno Spacecraft in the outer magnetosphere, from ~ 80RJ to 60RJ during 17 to 22 March 2017. Two cycles of accumulation and release of magnetic flux, named magnetic loading/unloading, were identified during this period, which correlate well with electron energization and auroral intensifications. Magnetic reconnection events are identified during both the loading and unloading periods, indicating that reconnection and unloading are independent processes. These results show that the dynamics in the middle magnetosphere are coupled with auroral variability.
Key Points
Accumulation and release of magnetic flux in the middle Jovian magnetosphere modulate auroral intensifications
Magnetic reconnection process occurs independently of Jupiter's global loading and unloading of magnetic flux
We provide direct evidence that unloading of magnetic flux causes enhancements of auroral kilometric emissions
Flux transfer events (FTEs) are magnetic flux ropes formed at planetary magnetopauses (MPs). Although evidence suggests that FTEs form through time‐dependent magnetic reconnection, details of that ...process and 3D structure of the flux ropes remain largely unclear. This letter presents Double Star/TC‐1 data of an FTE occurred on 7 April 2004 which show that the FTE was separated by two X‐lines moving south‐dawnward. In particular, the electron energy‐pitch angle distribution implies that the FTE was composed of flux ropes of all four possible magnetic topologies, indicating that the field lines must have reconnected multiple times. This is an intrinsic property of FTEs formed by 3D multiple X‐line reconnection distinguished from quasi 2D FTE models. This knowledge of FTE magnetic topologies helps to improve our understanding of solar wind‐ magnetosphere coupling at the MP.
Key Points
In situ evidence that FTEs are in association with multiple sequential X‐line MR
Observation of four magnetic topologies in the FTE flux ropes
We report the in situ observation of a plasma vortex induced by a solar wind dynamic pressure enhancement in the nightside plasma sheet using multipoint measurements from Time History of Events and ...Macroscale Interactions during Substorms (THEMIS) satellites. The vortex has a scale of 5–10 Re and propagates several Re downtail, expanding while propagating. The features of the vortex are consistent with the prediction of the Sibeck (1990) model, and the vortex can penetrate deep (~8 Re) in the dawn‐dusk direction and couple to field line oscillations. Global magnetohydrodynamics simulations are carried out, and it is found that the simulation and observations are consistent with each other. Data from THEMIS ground magnetometer stations indicate a poleward propagating vortex in the ionosphere, with a rotational sense consistent with the existence of the vortex observed in the magnetotail.
Key Points
Solar wind pressure pulse‐driven vortex was observed in the magnetosphere
Simulation and ground magnetic field data confirm this tailward moving vortex
The vortex can penetrate deep inside the tail plasma sheet and couple to FLRs
PDF
