Annealed 1050-aluminum sheets were severely deformed at the strain magnitude of 2.32 through constrained groove pressing (CGP) process. Texture variations and mechanical properties were investigated ...during CGP and subsequent friction stir processing (FSP) with different volume fractions of SiC nanoparticles. The results revealed that the predominant texture component in the annealed aluminum was {001}〈100〉 cube texture. After CGP, deformed and shear texture components developed while the cube texture was partially remained. In the specimen undergone FSP without nanoparticles, {001}〈110〉 rotated cube and nearly {001}〈110〉 shear texture component C were mainly pronounced, which was indicative of shear deformation of material in the stir zone. Orientation distribution function analysis from the stir zone demonstrated variations in the texture development with the incorporation of SiC nanoparticles. An increase in the fraction of nanoparticles changed the grain orientation in such a way that the {001}〈110〉 shear texture component C gradually developed from the rotated cube texture. However, the overall texture intensity became weaker by increasing the fraction of SiC nanoparticles due to the activation of particle stimulated nucleation mechanism forming randomly oriented grains. The incorporation of SiC nanoparticles in the stir zone also enhanced the yield strength, Young's modulus, and hardness of the stir zone without considerable reduction in the elongation. In such situation, Orowan strengthening was suggested as a dominant mechanism involved.
Substorm‐type evolution of the Earth's magnetosphere is investigated by mining more than two decades (1995–2017) of spaceborne magnetometer data from multiple missions including the first two years ...(2016‐2017) of the Magnetospheric MultiScale mission. This investigation reveals interesting features of plasma evolution distinct from ideal magnetohydrodynamics (MHD) behavior: X‐lines, thin current sheets, and regions with the tailward gradient of the equatorial magnetic field Bz. X‐lines are found to form mainly beyond 20 RE, but for strong driving, with the solar wind electric field exceeding ∼5mV/m, they may come closer. For substorms with weaker driving, X‐lines may be preceded by redistribution of the magnetic flux in the tailward Bz gradient regions, similar to the magnetic flux release instability discovered earlier in PIC and MHD simulations as a precursor mechanism of the reconnection onset. Current sheets in the growth phase may be as thin as 0.2 RE, comparable to the thermal ions gyroradius, and at the same time, as long as 15 RE. Such an aspect ratio is inconsistent with the isotropic force balance for observed magnetic field configurations. These findings can help resolve kinetic mechanisms of substorm dipolarizations and adjust kinetic generalizations of global MHD models of the magnetosphere. They can also guide and complement microscale analysis of nonideal effects.
Plain Language Summary
The sun emits a steam of charged particles called the solar wind that flows past the Earth interacting with the planet's dipole magnetic field. This stretches the dipolar magnetic field away from the sun on the nightside of the planet storing energy in the stretched field. Once every few hours, this stretched configuration suddenly becomes more dipolar bringing particles and magnetic flux closer to the planet and powering aurora in the polar regions. During these processes, termed substorms, the gas of charged particles, protons, and electrons trapped by the dipole and known as plasma, behaves largely as a perfectly conducting fluid. However, only deviations from this ideal conducting plasma behavior can explain the substorm mechanisms. We mine two decades of spacecraft magnetometer data from multiple missions to form swarms of thousands of synthetic probes. They help reveal effects of nonideal plasma evolution during substorms, which cannot be captured by direct in situ observations because of their extreme paucity.
Key Points
X‐lines, including the 11 July 2017 reconnection event, are reconstructed at and beyond 20 RE, but for strong driving they can come closer
Current sheets in the growth phase may be as thin as 0.2 RE, and at the same time, as long as 15 RE, violating isotropic force balance
Bz humps form in the growth phase, and their reconfiguration may precede X‐line formation and substorm onset
Pulsating auroras (PsAs) are thought to be generated by precipitating electrons scattered by lower‐band chorus (LBC) waves near the magnetic equator. One‐to‐one correlation between the LBC intensity ...and the PsA intensity has been reported. Electrostatic electron cyclotron harmonic (ECH) waves can also scatter electrons. However, direct correlation between ECH and PsA has not been reported yet. In this study, using a coordinated Exploration of energization and Radiation in Geospace (Arase) satellite and ground‐based imager observation, we report that not only LBC but also ECH have correlation with PsA. We estimated the precipitating electron energy by assuming that the time lag when the cross‐correlation coefficient became the highest was travel time of electrons from the modulation region. We found that the estimated energies show reasonable values as the cyclotron resonance energy of each wave.
Plain Language Summary
Pulsating auroras (PsAs), which have quasiperiodic on‐off switching emission, are caused by the intermittent electron precipitation from the magnetosphere. Such electrons are precipitated by wave‐particle interactions. The candidate waves to interact with electrons are lower‐band chorus (LBC) and electrostatic electron cyclotron harmonic (ECH) waves. One‐to‐one correspondence between the LBC wave intensity and the PsA intensity has been reported by previous studies. However, the correlation between ECH and PsA has not been reported yet. In this study, using a coordinated Exploration of energization and Radiation in Geospace (Arase) satellite and ground‐based all‐sky imager observation, we report that not only LBC but also ECH waves have correlation with PsAs.
Key Points
The lower‐band chorus and electrostatic electron cyclotron harmonic wave intensities had correlation with the pulsating auroral intensity
Taking advantage of high sampling rate of the imager, we estimated the energy of precipitating electrons
The energy of precipitating electrons was reasonable compared with the cyclotron resonance energy of each wave
When subjected to low oxygen stress, plants accumulate alanine and γ-aminobutyric acid (GABA). To investigate the function of GABA metabolism under hypoxia and its contribution to alanine ...accumulation, we studied the genes that encode the two key enzymes of the GABA shunt, glutamate decarboxylase (GAD) and GABA transaminase (GABA-T). Among the five homologous GAD genes found in Arabidopsis thaliana, GAD1 expression was predominantly found in roots, while GAD2 expression was evident in all organs. Expression of the other three GAD genes was generally weak. In response to hypoxia, transcriptional induction was observed for GAD4 only. For GABA-T1, its expression was detected in all organs, but there was no significant transcriptional change under hypoxic conditions. Moreover, we have isolated and characterized Arabidopsis mutants defective in GAD1 and GABA-T1. In gad1 mutants, GAD activity was significantly reduced in roots but was not affected in shoots. In the gaba-t1 mutant, GABA-T activity was decreased to negligible levels in both shoots and roots. These mutants were phenotypically normal under normal growth conditions except for the reduced seed production of the pop2 mutants as described previously. However, metabolite analysis revealed significant changes in GABA content in gad1 and gaba-t1 mutants. The levels of alanine under hypoxic conditions were also affected in the roots of gad1 and gaba-t1 mutants. The partial inhibition of the hypoxia-induced alanine accumulation in roots of these mutants suggests that the GABA shunt is, in part, responsible for the alanine accumulation under hypoxia.
The near‐Earth plasma sheet becomes cold and dense under northward interplanetary magnetic field (IMF) condition, which suggests efficient solar wind plasma entry into the magnetosphere across the ...magnetopause for northward IMF and a possible contribution of ionospheric oxygen ion outflow. The cold and dense characteristics of the plasma sheet are more evident in the magnetotail flank regions that are the interface between cold solar wind plasma and hot magnetospheric plasma. Several physical mechanisms have been proposed to explain the solar wind plasma entry across the magnetopause and resultant formation of the cold‐dense plasma sheet (CDPS) in the tail flank regions. However, the transport path of the cold‐dense plasma inside the magnetotail has not been understood yet. Here, we present a case study of the CDPS in the dusk magnetotail by magnetospheric multiscale (MMS) spacecraft under strongly northward IMF and high‐density solar wind conditions. The ion distribution function consists of high‐ and low‐energy components, and the low‐energy one intermittently shows energy dispersion in the directions parallel and antiparallel to the local magnetic field. The time‐of‐flight analysis of the energy‐dispersed low‐energy ions suggests that these ions originate in the region farther down the tail, move along the magnetic field toward the ionosphere and then come back to the magnetotail by the mirror reflection. The pitch‐angle dispersion analysis gives consistent results on the traveling time and path length of the energy‐dispersed ions. Based on these observations, we discuss possible generation mechanisms of the energy‐dispersed structure of the low‐energy ions during the northward IMF.
Key Points
MMS observed the cold‐dense plasma sheet in the dusk magnetotail under strongly northward interplanetary magnetic field
Energy dispersions of field‐aligned and anti‐field‐aligned streaming low‐energy ions were identified
These ions were injected from tailside regions of the MMS location and moved along the magnetic field
While a substorm involves auroral poleward expansion after initial brightening, a pseudosubstorm (pseudobreakup) subsides without progressing to poleward expansion. To understand what makes this ...difference, we studied near‐Earth magnetotail conditions at a pseudosubstorm onset and the subsequent substorm onset, using multipoint Time History of Events and Macroscale Interactions during Substorms spacecraft data. In the present event, near‐Earth magnetic reconnection possibly occurred before initial brightening for both pseudosubstorm and substorm. In the near‐Earth magnetotail at X ∼− 10 RE, the ion β, ion pressure, and ion and total (ion plus magnetic) pressure gradient projection along two closely located spacecraft were smaller and magnetic field lines were less stretched around the pseudosubstorm initial brightening than around the substorm initial brightening. Dipolarization did not occur for the pseudosubstorm, whereas it began just before poleward expansion for the substorm. These observations suggest that conditions of the near‐Earth magnetotail possibly affect whether the initial action develops into a full‐fledged substorm.
Plain Language Summary
A pseudosubstorm, also called pseudobreakup, is an auroral phenomenon very similar to a substorm but essentially differs in absence of active auroral expansion. In this paper, we studied conditions of the magnetotail at the beginning of these auroral phenomena on the basis of spacecraft observations. This comparison is expected to give us some clues to understanding of substorm triggering and development mechanisms. We found that plasma and magnetic field conditions in the magnetotail differed between the two auroral phenomena. This finding implies that magnetotail conditions possibly affect auroral development.
Key Points
We compared near‐Earth magnetotail conditions at a pseudosubstorm onset and the subsequent substorm onset
The pressure gradient and ion beta in the near‐Earth magnetotail were smaller for the pseudosubstorm than for the substorm
We suggest that near‐Earth magnetotail conditions possibly affect whether the initial action develops into a full‐fledged substorm
Abstract Objective To assess 3- and 12-month angiographic restenosis rates and their clinical impact after infrapopliteal angioplasty. Design Prospective multicenter study. Materials and methods We ...analyzed 68 critical ischemic limbs (tissue loss: 58 limbs) from 63 consecutive patients due to isolated infrapopliteal lesions who underwent angioplasty alone. Primary endpoint was 3-month angiographic restenosis rate; secondary endpoints were 12-month angiographic restenosis rate, and 3- and 12-month rates of mortality, major amputation and reintervention. Three- and 12-month frequency of ambulatory status and of freedom from ischemic symptoms, and time to wound healing in the ischemic wound group, were compared between restenotic and non-restenotic groups. Angiographic restenosis predictors were assessed by multivariable analysis. Results 95% of cases had 3-month angiography; restenosis rate was 73%: 40% restenosis and 33% re-occlusion. Twelve-month follow-up angiography was conducted for the patients without 3-month angiographic restenosis, and restenosis rate at 12 months was 82%. Non-administration of cilostazol and statin, and chronic total occlusion were 3-month angiographic restenosis predictors. Three- and 12-month mortality was 5% and 12%, respectively. Despite no patients having undergone amputation, 15% had persistent ischemic symptoms, and 48% of limbs underwent reintervention within 12 months. During the same study period, ambulatory status and limbs with complete healing were more frequently observed in the non-restenosis group than in the restenosis group. In the tissue loss group, time to wound healing in the restenosis group was longer than in the non-restenosis group (127 days vs. 66 days, p = 0.02). Conclusion The extremely high angiographic restenosis rate after infrapopliteal angioplasty may adversely impact clinical status improvement.
Abnormal grain growth (AGG) phenomenon was observed during cryogenic friction stir processing (FSP) of a severely deformed 1050-aluminum. An ultrahigh cooling rate and a lower peak temperature ahead ...of the rotating tool along with the preliminarily stored strain within the base metal resulted in the AGG. This event was pronounced not only ahead of the FSP tool, but also in heat affected zone (HAZ). The abnormally grown grains were strain-free and they proceeded to grow beyond the high-angle grain boundaries evolved in the base metal. Also, the incident of AGG was simultaneous with the development of Cube and Goss texture components. The combined effects associated with the development of a dominant shear texture and the existence of strain-free grains in the base metal was found to be linked to the AGG. The base metal encompassed mainly deformed grains with the orientation close to the shear texture component B/B¯. However, other orientations such as θ-fiber texture were evident too. The observation of abnormally grown grains with orientations different from the dominant shear texture suggested the activation of texture-induced AGG. On the other hand, strain-induced grain boundary migration would be responsible for the AGG of a number of strain-free grains with orientations close to the dominant shear texture.
•Abnormal grain growth occurs around stir zone during cryogenic FSP of severely deformed aluminum.•Strong shear texture and remaining strain-free grains result in abnormal grain growth.•Abnormally grown grains either belong to shear textured volume or other orientations.•The Goss texture component develops as abnormal grain growth takes place.•Shear and deformation texture components become weaker as a result of recrystallization and abnormal grain growth.
The impacts of dopant nanoparticles, graphene nanosheets (GNSs) and cobalt decorated-graphene nanosheets (CoGNSs), were studied in relation to the wettability and rheological behavior in low-Ag ...lead-free SAC0307 (Sn–0.3Ag–0.7Cu) solder paste. The solidification range of the solders was evaluated using differential scanning calorimetry. Phase identification in the solder bulk and interface of the solder and copper substrate was carried out by X-ray diffraction and energy-dispersive X-ray spectroscopy. Spreading properties and reactive wetting behavior along with the rheological properties of the solders were also studied. Results showed that the addition of both nanoparticles did not considerably change the melting point of SAC0307 solder. During the reflow soldering, GNSs floated away and separated from the solder bulk because of their low density and inappropriate wetting by the molten tin because of the nonmetallic nature of GNSs. However, CoGNS nanoparticles resulted in better wettability and fluidity of the solder because of the modified density of CoGNS particles and better coherency of the metallic cobalt/tin interface as well as the increased active absorption surface on the copper substrate. The fluidity of solder including CoGNSs was significantly higher compared to the solder with GNSs in the solidification range. Additionally, CoGNSs played an important role in the interfacial reactions by forming the refined (Co,Cu)
6
Sn
5
compound with a flat morphology, which promoted reactive wetting.
The weld strength of thermoplastics with aluminium alloy, such as high density polyethylene and polypropylene sheets, is influenced by friction stir welding parameters. This paper focuses on the ...preliminary investigation of joining parameter at various levels as well as the mechanical properties of friction spot joining (FSJ) of aluminium alloy (A5052) to polyethylene terephthalate (PET). A number of FSJ experiments were carried out to obtain optimum mechanical properties by adjusting the plunge speed and plunge depth in the ranges of 5-40 mm min
−1
and 0·4-0·7 mm respectively, while spindle speed remains constant at 3000 rev min
−1
. The results indicated that A5052 and PET successfully joined with the aid of frictional heat energy originated from the friction spot welding process. The effect of plunge speed on the joined area and the effect of formation of bubbles at the interface of joints on the shear strength of joint are discussed.
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