B2 Region Research Articles

C3H8O2 Isomers: Insights into Potential Interstellar Species.

2-Methoxyethanol, with a formula C3H8O2, was recently identified in the massive protocluster NGC 6334I. However, its structural isomers, 1,2-propanediol and 1,3-propanediol, remain undetected despite extensive searches in the Sgr B2 region. In this study, we explored the potential energy surface of the C3H8O2 system using CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ calculations, identifying 11 species, with the geminal diols 2,2-propanediol and 1,1-propanediol as the most stable forms. We examined the gas-phase decomposition barrier of these geminal diols and found that 1,1-propanediol is thermodynamically stable at low temperatures (10-150 K). C3H8O2 isomers with energies below 30 kcal/mol are relevant to the ISM, as they have been identified or tentatively detected in irradiation experiments of ice analogs of CO, H2O, and CH3OH.

Aqueous humour protein dysregulation in Asian eyes with primary open angle glaucoma

The pathophysiology of Primary Open Angle Glaucoma (POAG) remains poorly understood. Through proteomic analysis of aqueous humour (AH) from POAG patients, we aim to identify changes in protein composition of these samples compared to control samples.High resolution mass spectrometry-based TMT6plex quantitative proteomics analysis is performed on AH samples collected from POAG patients, and compared against a control group of patients with cataracts. Data are available via ProteomeXchange with identifier PXD033153.1589 proteins were quantified from the aqueous samples using Proteome Discoverer version 2.2 software. Among these proteins, 210 were identified as unique master proteins. The proteins which were up or down-regulated by ±3 fold-change were considered significant. Human neuroblastoma full-length cDNA clone CS0DD006YL02 was significantly upregulated in patients with severe POAG on >2 medications, while actin, cytoplasmic 1, V2-7 protein (fragment), immunoglobulin-like polypeptide 1 and phosphatidylethanolamine-binding protein 4 were only present in these patients with severe POAG on >2 medications.Beta-crystallin B1 and B2, Gamma-crystallin C, D and S were significantly downregulated in the severe POAG ≤2 glaucoma medications group.Beta-crystallin B2, Gamma-crystallin D and GCT-A9 light chain variable region (fragment) were significantly downregulated in the non-severe POAG group.Actin, cytoplasmic 1 was significantly upregulated in subjects with severe POAG who required more than 2 glaucoma medications. Crystallins (Beta-crystallin B1 and B2, Gamma-crystallin C, D and S) were significantly downregulated in subjects with severe POAG who required less than 2 glaucoma medications.

Differences in monophenolic content and composition of persimmon fruit slices from different regions under fresh and microwave drying

The browning of moon persimmons during the drying process was primarily caused by the oxidation of phenolic compounds. Additionally, microwave drying led to uneven browning of the fruit slices. This study aimed to evaluate effect of microwave drying on the content of 19 monophenolic compounds in moon persimmon fruit slices from six different regions (A1, A2, B1, B2, C1 and C2). The analysis was conducted using ultra-performance liquid chromatography with high-resolution mass spectrometry. The findings indicated that the three primary monophenols with the highest concentrations in fresh moon persimmon fruit slices were gallic acid, phenylalanine and catechin; these concentrations ranged from 0.554 to 6.797 mg/100 g. The distribution of monophenol species was higher in the outer edge region of the fruit slices, with 14 monophenols detected in the C2 region. Microwave drying increased gallic acid content and decreased other monophenol content. Monophenolic compounds under microwave drying underwent autoxidation and also transformed into each other. The B2 region of the fruit slices displayed the earliest occurrence of browning and exhibited the most significant changes in both rate and magnitude of phenolic content. The colour deterioration of moon persimmon fruit slices during microwave drying is related to the change in phenol content, which may be caused by the phenol autoxidation reaction.

Alloying behavior of W and Mo in the as-cast dual-phase FeNiCrAl multi-component alloys

The W and Mo are in the same groups of periodic table and are usually used as solid solution elements. In this investigation, the minor alloying behaviors of W and Mo in Fe37Ni36Al17Cr10 alloy were explored. The addition does not change the casting microstructure greatly, with dendrite region of FCC + B2 and inter-dendrite region of FCC phase. For tensile properties at ambient temperature, as-cast Fe36Ni36Al17Cr10Mo1 alloy exhibited higher yield strength and fracture strength compared with Fe37Ni36Al17Cr10 alloy. Then, dual-phase alloys with Mo content of 2 and 3 at% were further designed and carefully studied. It is found that a nano-scale structure occurred in as-cast Fe35Ni36Al17Cr10Mo2 alloy, where a large number of spherical BCC precipitates are distributed in the dendrite region of B2 phase. Meanwhile a mixture of irregular B2 phase and FCC phase is contributed to the inter-dendrite area. The Fe35Ni36Al17Cr10Mo2 alloy exhibited the most excellent and comprehensive mechanical properties due to the fine structure and its high work hardening ability. The yield strength, ultimate tensile strength and fracture elongation of as-cast Fe35Ni36Al17Cr10Mo2 alloy are 863 ± 20 MPa, 1285 ± 17 MPa and 16.0 ± 1.0 %, respectively, which is higher than the most of reported dual-phase as-cast FeNiCrAl multi-component alloys.

Study on the evolution of phase relations in the Ti–Al–Nb/Cr systems at 0–50 at.% Al region

β-Solidifying γ-TiAl based alloys have gained scientific attention and showed potential applications as structure materials. When adding the β-stabilizing elements (e.g., Nb and Cr), ordered B2 and ωo phases are often formed during the production process of the TiAl based alloys. The information about the evolution of these phases as the temperature changes is necessary and important for design and preparation of desired TiAl based alloys with excellent properties. In this work, phase relationships and evolvement of Ti–Al–Nb/Cr systems have been investigated in the service temperature ranging from 950 to 700 °C. In the Ti–Al–Nb ternary system, B2 phase will directly transform into ωo phase at the temperature range of 913.6–921.1 °C, which results in an increase of the microhardness (i.e. 460 HV to 530 HV). At 700 °C, ωo phase has the composition of 15.8–20.4 at.% Nb, 29.8–33.3 at.% Al, and 46.3–54.4 at.% Ti. Equilibrium composition of ωo is defined as Ti3Al2Nb. The ternary compound O_Ti2AlNb has been found to be formed via β(Ti)+Ti3Al + Nb2Al→O at 981.5 ± 6.5 °C. As for the Ti–Al–Cr ternary system, when temperature decreases from 950 to 900 °C, the center section of the β(Ti) phase region shrinks and separates, resulting in the formation of independent B2 phase region. The island-like B2 region can remain stable at 700 °C. According to the evolution of phase relationship, one solid transition reaction Ti3Al + C14→B2+C15 at 900–800 °C has been deduced to occur in the Ti–Al–Cr ternary system. Present work provides an important guide for fabricating Ti–Al–Nb/Cr alloys with different ratio and distribution of plastic/brittle phases.

Nano-mechanical properties and onset of plasticity in Fe–Mn–Al–Ni–C duplex lightweight steel processed by high temperature compression

In the present study, nano-indentation tests have been performed on the Fe–Mn–Al–Ni–C duplex lightweight steel following hot compression at 1223 K and 1423 K at a strain rate of 0.1 s−1. The nano-hardness values of various composite regions are determined and correlated with the complex deformed microstructural features, strain gradient, elemental partitioning, intergranular/intragranular precipitates and lattice distortion effect. The estimated elastic modulus value of FCC and BCC matrix regions in the studied steel is relatively higher than those reported for other conventional duplex steels, highlighting the contribution of intragranular B2 and к-carbide precipitates on the overall elastic modulus. Additionally, the deformation behavior of the matrix regions reveals that the onset of plasticity is governed by both homogeneous dislocation nucleation mechanism and multiplication of pre-existing dislocations under the indenter tip. The BCC + B2 region exhibits higher maximum shear stress (τmax) value as compared to the FCC + к-carbide region, indicating that the plastic deformation would first initiate in the latter region. This is related to the pre-existing high strain gradient in the soft FCC + к-carbide region that would facilitate the onset of plasticity more easily as compared to the BCC + B2 region during indentation. Moreover, it is observed that the elasto-plastic regime of the indentation loading curve exhibits random pop-in events associated with the resistance generated by the various intragranular precipitates in the FCC and BCC matrix regions, against the dislocation motion during nano-indentation test.

New Ammonia Masers in the High-mass Star-forming Region Sgr B2(N)

Abstract We report a systemic search for nonmetastable NH3 masers toward a high-mass star-forming region Sgr B2(N) using the Shanghai 65 m Tianma radio telescope with its Ku-band (12–18 GHz) and K-band (18–26.5 GHz) receivers. A total of 18 maser emission transitions were detected, and eight of these are newly identified NH3 maser transitions in interstellar space. Most (five) of the new maser transitions were found from the Ku-band observations which were absent from previous searches. Rotation diagram analysis for the 18 quasi-thermal transitions derived a high gas kinematic temperature (∼400 K) and an extremely high H2 column density (∼5 × 1025 cm−2). Such conditions suggest that the NH3 masers are likely pumped by vibrational excitation. Compared with quiet maser activity observed more than 20 yr ago, NH3 masers may be bursting in our observation time when the gas kinematic temperature might increase from ∼150 to ∼400 K. As extreme conditions (either high gas kinematic temperature and/or high gas column density) are required to excite nonmetastable NH3 masers, it can be argued that the detected NH3 maser outburst may be linked to a more intensive accretion-burst event from an high-mass young stellar object in the Sgr B2(N) region.

A Mean Density of 112 M⊙ pc−3 for Central Molecular Zone Clumps—Evidences for Shear-enabled Pressure Equilibrium in the Galactic Center

Abstract We carry out a systematic study of the density structure of gas in the Central Molecular Zone (CMZ) in the Galactic center by extracting clumps from the APEX Telescope Large Area Survey of the Galaxy survey at 870 μm. We find that the clumps follow a scaling of m = ρ 0 r 3, which corresponds to a characteristic density of (ρ 0 = 112 M ⊙ pc−3) with a variation of ≈0.5 dex, where we assumed a gas-to-dust mass ratio of 100. This characteristic density can be interpreted as the result of thermal pressure equilibrium between the molecular gas and the warm ambient interstellar medium. Such an equilibrium can plausibly be established since shear has approximately the same strength as self-gravity. Our findings may explain the fact that star formation in the CMZ is highly inefficient compared to the rest of the Milky Way disk. We also identify a population of clumps whose densities are two orders of magnitudes higher in the vicinity of the Sgr B2 region, which we propose are produced by collisions between the clumps of lower densities. For these collisions to occur, processes such as compressive tides probably have created the appropriate condition by assembling the clumps together.

Tracing shock type with chemical diagnostics

Aims.The physical structure of a shock wave may take a form unique to its shock type, implying that the chemistry of each shock type is unique as well. We aim to investigate the different chemistries of J-type and C-type shocks in order to identify unique molecular tracers of both shock types. We apply these diagnostics to the protostellar outflow L1157 to establish whether the B2 clump could host shocks exhibiting type-specific behaviour. Of particular interest is the L1157-B2 clump, which has been shown to exhibit bright emission in S-bearing species and HNCO.Methods.We simulate, using a parameterised approach, a planar, steady-state J-type shock wave using UCLCHEM. We compute a grid of models using both C-type and J-type shock models to determine the chemical abundance of shock-tracing species as a function of distance through the shock and apply it to the L1157 outflow. We focus on known shock-tracing molecules such as H2O, HCN, and CH3OH.Results.We find that a range of molecules including H2O and HCN have unique behaviour specific to a J-type shock, but that such differences in behaviour are only evident at lowvsand lownH. We find that CH3OH is enhanced by shocks and is a reliable probe of the pre-shock gas density. However, we find no difference between its gas-phase abundance in C-type and J-type shocks. Finally, from our application to L1157, we find that the fractional abundances within the B2 region are consistent with both C-type and J-type shock emission.

Hot Workability of a Spark Plasma Sintered Intermetallic Iron Aluminide Alloy Above and Below the Order-disorder Transition Temperature

The Fe-25Al-1.5Ta alloy has proved to be qualified for structural applications at and above 600°C due to a superior creep resistance to its binary counterpart. The creep resistance of the Fe-25Al-1.5Ta alloy at 650°C surpasses that of the P92 martensitic-ferritic steel, which is one of the most developed creep resistant alloys for steam turbine applications. From the viewpoint of cost-effectiveness in real-scale forgings, it is important to safely deform the material at as low as possible temperatures. Based on Thermo-Calc computations, the Fe-25Al-1.5Ta alloy shows a B2-to-A2 order-disorder transition at around 860ºC. This paper investigates the hot compression behavior and microstructural evolution of a Fe-25Al-1.5Ta alloy deformed in the disordered A2 (900-1100ºC) and ordered B2 (800-850ºC) regimes. Effects of ordering on plastic deformation, energy dissipation efficiency and instability parameters are identified using the concept of processing maps, and the underlying deformation mechanisms are characterized using scanning electron microscopy and electron back-scattered diffraction. The samples deformed in the A2 disorder region showed no flow instability for the deformation conditions tested, while the specimens deformed in the ordered B2 region revealed a region of flow instability located at 900ºC/1s-1. The observed flow instability region manifests itself in a longitudinal surface crack formed in the samples deformed at 900ºC/1s-1. The change of activation energy of hot deformation and efficiency of energy dissipation are discussed based on the ordering effect and movement of super-dislocations in the B2 regime. The current study identifies processing parameters to safely deform the Fe-25Al-1.5Ta alloy at lower temperatures of 800ºC and at strain rates below 1s-1.

The physical and chemical structure of Sagittarius B2

Context. The giant molecular cloud Sagittarius B2 (hereafter Sgr B2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of Sgr B2, we encounter the Sgr B2(DS) region, which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended H II region. Hints of non-thermal emission have been found in the H II region associated with Sgr B2(DS). Aims. We seek to characterize the spatial structure and the spectral energy distribution of the radio continuum emission in Sgr B2(DS). We aim to disentangle the contribution from the thermal and non-thermal radiation, as well as to study the origin of the non-thermal radiation. Methods. We used the Very Large Array in its CnB and D configurations, and in the frequency bands C (4–8 GHz) and X (8–12 GHz) to observe the whole Sgr B2 complex. Continuum and radio recombination line maps are obtained. Results. We detect radio continuum emission in Sgr B2(DS) in a bubble-shaped structure. From 4 to 12 GHz, we derive a spectral index between − 1.2 and − 0.4, indicating the presence of non-thermal emission. We decomposed the contribution from thermal and non-thermal emission, and find that the thermal component is clumpy and more concentrated, while the non-thermal component is more extended and diffuse. The radio recombination lines in the region are found to be not in local thermodynamic equilibrium but stimulated by the non-thermal emission. Conclusions. Sgr B2(DS) shows a mixture of thermal and non-thermal emission at radio wavelengths. The thermal free–free emission is likely tracing an H II region ionized by an O 7 star, while the non-thermal emission can be generated by relativistic electrons created through first-order Fermi acceleration. We have developed a simple model of the Sgr B2(DS) region and found that first-order Fermi acceleration can reproduce the observed flux density and spectral index.

ALMA Observations of the ρ Ophiuchus B2 Region. I. Molecular Outflows and Their Driving Sources

Abstract We present the results of ALMA mosaic observations of dust continuum and 12CO (J = 2−1), 13CO (J = 2−1), and C18O (J = 2−1) molecular lines toward the ρ Ophiuchus B2 region. The 1.3 mm dust continuum image made from the combined 12 and 7 m array data reveals not only the dense cores identified by past single-dish observations but also their detailed internal substructures. The 12CO (J = 2−1) images show very complex structures of protostellar outflows. They suggest that the gigantic outflow lobes in Oph B2 are presumably driven at least by two protostars, EL 32 and EL 33. We do not detect clear high-velocity components associated with the Class I protostar SST c2d J162730.9−242733 and the flat-spectrum object SST c2d J162721.8−242727. In addition, we find interesting striations with 15″ (≈2000 au) separations in both the 12CO and 13CO channel maps. The CO striations appear to be roughly parallel to the magnetic field direction, and we speculate that the directions of the striations may follow the magnetic field in the envelope of Oph B2.

Continuous cooling transformation (CCT) behavior of a high Nb-containing TiAl alloy

The continuous-cooling-transformation (CCT) diagram is significant to the microstructural design and the control of mechanical properties. The CCT behavior of a high Nb-containing TiAl alloy was experimentally investigated in the present study. Samples with the nominal composition of Ti-45Al-8.5Nb-(W, B, Y) (at.%) were isothermally held at 1500 °C (in the single β phase field) and subsequently cooled at different cooling rates. Based on the samples quenched from high temperatures, the microstructures during continuous cooling was characterized and the CCT diagram was established and evaluated. With the increase of cooling rate (5, 20, 100, 700 K/min), the phase transformation presented a lagging behavior comparing with the equilibrium phase diagram. Meanwhile, the decomposition of high-temperature β/B2 phase was incomplete at large cooling rate, indicating that a fully lamellar (FL) microstructure alloy can be obtained only below a critical cooling rate. Further, the discontinuously coarsened γ phase, the crystalline orientations of precipitated block γ and ω particles in B2 region were characterized and the phase transformation mechanisms were discussed.

Dual structure O + B2 for enhancement of hardness in furnace-cooled Ti2AlNb-based alloys by powder metallurgy

Powder metallurgic Ti2AlNb alloys were sintered at 900°C, 990°C, 1060°C, and 1100°C (i.e. in the O+B2, α2+B2+O, α2+B2, and B2 phase region, respectively) for 12h, followed by water quenching and furnace cooling. Quenching was employed to reserve the high-temperature phase and microstructure, and furnace cooling aimed to regulate the room-temperature microstructure for the enhancement of hardness. Widmanstatten B2+O structure, which contributes to the properties, was induced from B2 crystals by sintering, unless the alloy was treated in the α2+B2 phase region. With the elevation of the sintering temperature, the content of α2 phase became lower in the furnace-cooled alloys, and the hardness was improved accordingly. The highest hardness performance, 389±23HV, was obtained in the alloy solution treated in the single B2 region, and the alloy was comprised of complete O+B2 Widmanstatten structure.

Effects of Solution Treatment on the Microstructure and Mechanical Properties of Ti–22Al–25Nb Alloys

The effects of solution treatment on the microstructure and mechanical properties of Ti‐22Al‐25Nb alloy are investigated. Numerous equiaxed α2 particles distribute in a B2 matrix after solution treatment in the α2 + B2 region. The growth rate of the B2 grain increases with solution temperature and decreases with increasing holding time. When the solution temperature is lower than B2‐transus, it is seen that both the strength and ductility decrease with increasing solution temperature and holding time. After being solution‐treated at a super‐transus temperature, the alloy with a fully B2 microstructure shows an ultralow elongation (∼5%) and a typical brittle fracture characteristic.

The Effect of Pressure Stress on the Evolution of B2(ω) Phase in High Nb Containing TiAl Alloy

The thermal stability of the B2(ω) phase in high Nb containing TiAl alloy has attracted intense attention in recent years. This study focuses on the phase transformation between B2 and ω phases under the influence of thermal pressure stress in the Ti–45Al–8.5Nb–(W, B, Y) alloy. A large number of ω phases with the volume fraction of 42.3% exist within the B2 region in as‐cast alloys. The as‐cast samples were subjected to thermo‐compressive loading at 850 and 900 °C under the stresses of 300 and 500 MPa. Results show that the transformation of B2 → ω occurs at 850 °C, which can be promoted under a pressure stress. Further, the ω particles dissolved into the B2 matrix at 900 °C, and this transformation is suppressed by the role of thermal pressure. The mechanisms of the phase transformations mentioned above were discussed.

Evolution of B2(ω) region in high-Nb containing TiAl alloy in intermediate temperature range

The thermal stability of the B2(ω) region within an intermediate temperature range in a Ti-45Al-8.5Nb-(W, B, Y) (at.%) alloy was investigated. First, the “pure B2 region” without the ω phase was obtained after 1100 °C/1 h followed by water quenching. Then, the samples were heat treated at 700 °C, 800 °C and 850 °C for 1 h and 96 h respectively. The results show that B2 decomposes into four types of ωo variants and γ phase at 700 °C; but only one ωo variant would remain as the ageing time increased. The size of the ωo particles obviously increases with the increase of heating temperature and treating time. It is also found that the phase transformation of B2 → γ occurred at 800 °C and the γ phase prefers to nucleate at B2 region boundaries. γp would further coarsen to micron size after 96 h. In contrast, no γ phase in the B2 matrix is observed when the annealing temperature increases to 850 °C, which could be attributed to the influence of W element on the formation of γ phase in B2 phase. Phase transformation mechanisms in the B2(ω) region, involving B2 → ωo and B2 → γ, were discussed.

Experimental investigation of phase equilibria in the Ru–Fe–Al system at 1473 K

The low-Al part of the ternary Ru–Fe–Al phase diagram at 1473 K is established in this work. Due to the very promising properties of B2 ruthenium aluminide, the investigation of the B2 region of this system is of special interest. The experimental work includes diffusion methods, as well as quenching of annealed single-phase and two-phase alloys. The results of the different methods are in good agreement. Optical and scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction are used to investigate the samples. It is shown in this work that a three-component B2 phase exists over a wide composition range.

Synthesis of Fe-Al-Ti Based Intermetallics with the Use of Laser Engineered Net Shaping (LENS)

The Laser Engineered Net Shaping (LENS) technique was combined with direct synthesis to fabricate L21-ordered Fe-Al-Ti based intermetallic alloys. It was found that ternary Fe-Al-Ti alloys can be synthesized using the LENS technique from a feedstock composed of a pre-alloyed Fe-Al powder and elemental Ti powder. The obtained average compositions of the ternary alloys after the laser deposition and subsequent annealing were quite close to the nominal compositions, but the distributions of the elements in the annealed samples recorded over a large area were inhomogeneous. No traces of pure Ti were observed in the deposited alloys. Macroscopic cracking and porosity were observed in all investigated alloys. The amount of porosity in the samples was less than 1.2 vol. %. It seems that the porosity originates from the porous pre-alloyed Fe-Al powders. Single-phase (L21), two-phase (L21-C14) and multiphase (L21-A2-C14) Fe-Al-Ti intermetallic alloys were obtained from the direct laser synthesis and annealing process. The most prominent feature of the ternary Fe-Al-Ti intermetallics synthesized by the LENS method is their fine-grained structure. The grain size is in the range of 3–5 μm, indicating grain refinement effect through the highly rapid cooling of the LENS process. The Fe-Al-Ti alloys synthesized by LENS and annealed at 1000 °C in the single-phase B2 region were prone to an essential grain growth. In contrast, the alloys annealed at 1000 °C in the two-phase L21-C14 region exhibited almost constant grain size values after the high-temperature annealing.

CO and its Isotopomers Observation towards Sgr B2

We present our observations toward Sgr B2 region in J = 1−0 lines of 12CO, 13CO, C18O and C17O using 13.7-m Delingha millimeter telescope with newly installed 9-beam SIS superconducting receiver. From the integrated line intensity, we derive the abundance ratio of C18O/C17O with a mean value of 3.11 ± 0.10, which is consistent with the previous results.