Nonstandard Modeling of a Possible Blue Straggler Star, KIC 11145123

Nonstandard modeling of KIC 11145123, a possible blue straggler star, has been asteroseismically carried out based on a scheme to compute stellar models with the chemical compositions in their envelopes arbitrarily modified, mimicking the effects of some interactions with other stars through which blue straggler stars are thought to be born. We have constructed a nonstandard model of the star with the following parameters: M = 1.36 M ⊙, Y init = 0.26, Z init = 0.002, and f ovs = 0.027, where f ovs is the extent of overshooting described as an exponentially decaying diffusive process. The modification is down to the depth of r/R ∼ 0.6 and the extent ΔX, which is a difference in surface hydrogen abundance between the envelope-modified and unmodified models, is 0.06. The residuals between the model and the observed frequencies are comparable with those for the previous model computed assuming standard single-star evolution, suggesting that it is possible that the star was born with a relatively ordinary initial helium abundance of ∼0.26 compared with that of the previous models (∼0.30–0.40), then experienced some modification of the chemical compositions and gained helium in the envelope. Detailed analyses of the nonstandard model have implied that the elemental diffusion in the deep radiative region of the star might be much weaker than that assumed in current stellar evolutionary calculations; we need some extra mechanisms inside the star, rendering the star a much more intriguing target to be further investigated.

Out-of-sequence skeletal growth causing oscillatory zoning in arc olivines

Primitive olivines from the monogenetic cones Los Hornitos, Central-South Andes, preserve dendritic, skeletal, and polyhedral growth textures. Consecutive stages of textural maturation occur along compositional gradients where high Fo–Ni cores of polyhedral olivines (Fo92.5, Ni ~3500 ppm) contrast with the composition of dendritic olivines (Fo < 91.5, Ni < 3000 ppm), indicating sequential nucleation. Here we present a new growth model for oscillatory Fo–Ni olivine zoning that contrasts with the standard interpretation of continuous, sequential core-to-rim growth. Olivine grows rapidly via concentric addition of open-structured crystal frames, leaving behind compositional boundary layers that subsequently fill-in with Fo–Ni-depleted olivine, causing reversals. Elemental diffusion modeling reveals growth of individual crystal frames and eruption at the surface occurred over 3.5–40 days. Those timescales constrain magma ascent rates of 40–500 m/h (0.011 to 0.14 m/s) from the deep crust. Compared to ocean island basalts, where dendritic and skeletal olivines have been often described, magmas erupted at arc settings, experiencing storage and degassing, may lack such textures due to fundamentally different ascent histories.

Microstructure and Mechanical Properties of Vacuum Diffusion Bonded Ti2AlNb/Ti/TC4 Joint

In this paper, the Ti2AlNb alloy was bonded to TC4 alloy using the vacuum diffusion bonding method with a Ti interlayer. The interfacial microstructure of the Ti2AlNb/Ti/TC4 joint was characterized. The relationship between the bonding parameters and the microstructure and mechanical property of the joints was explored. Results indicated that the interdiffusion of Nb and Al elements between the interlayer and substrates promoted the formation of the lamellar α + β dual-phase structure in the joint. The bonding parameters determined the diffusion distance of Nb and Al elements, thus controlling the characteristics of the lamellar α + β dual-phase structure. When the Ti2AlNb alloy and TC4 alloy were bonded at 950 °C for 30 min under a pressure of 10 MPa, the elemental diffusion in the bonding couple was sufficient and the joint possessed the maximum shear strength of 549 MPa.

Effect of laser surfacing on the microstructure and mechanical properties of ultrasonic welded NiTi joints

In the present work, the effects of laser surfacing aiming at modify the surface roughness on NiTi sheets prior to the application of ultrasonic welding (USW) were investigated. Three different configurations joining original and laser surfaced specimens were performed: original/original (referred as O/O), original/treated (referred as O/T); treated/treated (referred as T/T). The influence of surface roughness on the interface formation, diffusion, and mechanical behavior was investigated. It is observed that when both bonding surfaces becomes rougher (T/T configuration), the joint strength is the highest, followed by both smooth bonding surfaces (O/O configuration), and the strength of the joint is the lowest when only one of the bonding surfaces was roughened (O/T configuration), which is related to the degree of plastic deformation at the joining interface. The main joining mechanism of NiTi to the Al interlayer was a metallic bond caused by shear plastic deformation and formation and growth of micro welds at the joining interfaces. Laser surfacing facilitates the metallic bonding, which is directly reflected in the change of the thickness of the Al interlayer after USW. This also helps to produce mechanical interlocking at the interface, although there is no significant difference in the elemental diffusion. Interfacial failure occurred in all joints tested under different surface contact conditions and exhibited ductile-like fracture characteristics.

Studies of Defect Structure in Epitaxial AlN/GaN Films Grown on (111) 3C-SiC

Several aspects such as the growth relation between the layers of the GaN/AlN/SiC heterostructure, the consistency of the interfaces, and elemental diffusion are achieved by High Resolution Transmission Electron Microscopy (HR-TEM). In addition, the dislocation densities together with the defect correlation lengths are investigated via High-Resolution X-ray Diffraction (HR-XRD) and the characteristic positron diffusion length is achieved by Doppler Broadening Spectroscopy (DBS). Moreover, a comparative analysis with our previous work (i.e., GaN/AlN/Si and GaN/AlN/Al2O3) has been carried out. Within the epitaxial GaN layer defined by the relationship (111) 3C-SiC || (0002) AlN || (0002) GaN, the total dislocation density has been assessed as being 1.47 × 1010 cm−2. Compared with previously investigated heterostructures (on Si and Al2O3 substrates), the obtained dislocation correlation lengths (Le = 171 nm and Ls =288 nm) and the mean distance between two dislocations (rd = 82 nm) are higher. This reveals an improved crystal quality of the GaN with SiC as a growth template. In addition, the DBS measurements upheld the aforementioned results with a higher effective positron diffusion length = 75 ± 20 nm for the GaN layer.

Insights into timescales of magmatic processes during the 2013-17 eruption at Volcán de Colima, Mexico

&lt;p&gt;Volc&amp;#225;n de Colima is an active stratovolcano in western Mexico. Its 2013-17 eruptive phase was characterised by transitions between effusive and explosive events. This persistent activity, comprising vulcanian explosions, pyroclastic flows, lava flows and ashfall present significant hazards to ~750,000 people near the volcano.&lt;/p&gt;&lt;p&gt;Tracing patterns of magma storage, recharge and mixing through volcanic systems is key to accurately interpreting monitoring data and understanding potential future hazards. However, at many volcanoes, including Colima, these patterns are poorly constrained and the link between monitoring data and magmatic processes is unclear. To better understand the magmatic plumbing system at Colima, mineral chemistry and textural studies were undertaken on representative 2013-17 samples to constrain different magmatic environments and mixing between them.&lt;/p&gt;&lt;p&gt;These samples contain plagioclase, orthopyroxene, clinopyroxene, Fe-Ti oxides, and rare resorbed olivine and amphibole, typical of Colima andesites. Pyroxene phenocrysts have varied core compositions (Mg#~69-88), zoning and textural patterns, reflecting crystallisation from melts within a heterogeneous magma mush. Whilst we interpret the bulk of the system to be relatively evolved, the presence of disequilibrium textures and high-Cr mafic bands and rims reflect periodic recharge of mafic melts and remobilisation of both evolved and mafic mush material prior to eruption.&lt;/p&gt;&lt;p&gt;The mineral chemistry and petrography indicate the presence of two broad magmatic environments crystallising these pyroxenes. An evolved end-member, crystallising Mg#69-75 pyroxene at between 980-1000&amp;#176;C, comprises the bulk of the system. By contrast, the mafic end-member crystallises high-Mg# pyroxene at a temperature typically between 1020-1080&amp;#176;C. Pressure estimates typically vary between 4-6 kbar or c. 12-20 km depth, in agreement with geophysical evidence suggesting a melt-rich mushy body at this depth.&lt;/p&gt;&lt;p&gt;Zoning patterns range from diffuse zoning in normal zoned pyroxenes to sharper core-rim boundaries in reverse zoned phenocrysts. We applied elemental diffusion modelling to constrain the timescales of pre-eruptive magmatic processes. The modelling indicates relative differences in residence times with long residence timescales typically of decades to centuries for diffuse, normally zoned phenocrysts versus shorter residence timescales of weeks to months in reverse-zoned phenocrysts.&lt;/p&gt;&lt;p&gt;Most notably, an increased frequency of reverse zoned pyroxenes was recorded in lavas erupted after an intense VEI 3 eruption in July 2015. Timescale estimates suggest a recharge and mixing event occurred at approximately this time and estimates from 2016 lavas indicate multiple injection events leading up to the eruption. This suggests that the July 2015 eruption may have been directly linked to this mafic injection.&lt;/p&gt;&lt;p&gt;Despite both eruptions being associated with mafic recharge, the difference in the style of activity between the explosive 2015 and effusive 2016 eruptions suggest other controls on activity. These may include the volume of magmatic recharge, the frequency of injections, ascent rate, or the supply of volatiles from the mafic magmas. Further refinement of the storage timescales and recharge events, and comparison of timescales to monitoring data, also will help clarify the effect of these processes on the eruption timing and style.&lt;/p&gt;

Effect of sodium doping on crystal growth and band matching of heterojunction in flexible CZTS solar cells

Treating kesterite layers with sodium has been proved to be an effective way to improve the photovoltaic performance of Cu2ZnSnS4 (CZTS) solar cells. However, elemental diffusion effects inside the film...