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| 2. |
- Ching, Tao-Chung, et al.
(författare)
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The JCMT BISTRO-2 Survey: Magnetic Fields of the Massive DR21 Filament
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 941:2
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Tidskriftsartikel (refereegranskat)abstract
- We present 850 mu m dust polarization observations of the massive DR21 filament from the B-fields In STar-forming Region Observations (BISTRO) survey, using the POL-2 polarimeter and the SCUBA-2 camera on the James Clerk Maxwell Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale ridge of the DR21 main filament. In the subfilaments, the magnetic fields are mainly parallel to the filamentary structures and smoothly connect to the magnetic fields of the main filament. We compare the POL-2 and Planck dust polarization observations to study the magnetic field structures of the DR21 filament on 0.1-10 pc scales. The magnetic fields revealed in the Planck data are well-aligned with those of the POL-2 data, indicating a smooth variation of magnetic fields from large to small scales. The plane-of-sky magnetic field strengths derived from angular dispersion functions of dust polarization are 0.6-1.0 mG in the DR21 filament and similar to 0.1 mG in the surrounding ambient gas. The mass-to-flux ratios are found to be magnetically supercritical in the filament and slightly subcritical to nearly critical in the ambient gas. The alignment between column density structures and magnetic fields changes from random alignment in the low-density ambient gas probed by Planck to mostly perpendicular in the high-density main filament probed by James Clerk Maxwell Telescope. The magnetic field structures of the DR21 filament are in agreement with MHD simulations of a strongly magnetized medium, suggesting that magnetic fields play an important role in shaping the DR21 main filament and subfilaments.
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| 3. |
- Kwon, Woojin, et al.
(författare)
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B-fields in Star-forming Region Observations (BISTRO): Magnetic Fields in the Filamentary Structures of Serpens Main
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 926:2
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Tidskriftsartikel (refereegranskat)abstract
- We present 850 mu m polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where NH2 < 0.93 x 10(22) cm(-2) (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at NH2 approximate to 4.6 x 10(22) NH2 approximate to 16 x 10(22) cm(-2), magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments (B-POS = 60-300 mu G)) using the Davis-Chandrasekhar-Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.
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| 4. |
- Lyo, A-Ran, et al.
(författare)
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The JCMT BISTRO Survey: An 850/450 mu m Polarization Study of NGC 2071IR in Orion B
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 918:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of simultaneous 450 mu m and 850 mu m polarization observations toward the massive star-forming region NGC 2071IR, a target of the BISTRO (B-fields in STar-forming Region Observations) Survey, using the POL-2 polarimeter and SCUBA-2 camera mounted on the James Clerk Maxwell Telescope. We find a pinched magnetic field morphology in the central dense core region, which could be due to a rotating toroidal disklike structure and a bipolar outflow originating from the central young stellar object IRS 3. Using the modified Davis-Chandrasekhar-Fermi method, we obtain a plane-of-sky magnetic field strength of 563 +/- 421 mu G in the central similar to 0.12 pc region from 850 mu m polarization data. The corresponding magnetic energy density of 2.04 x 10(-8) erg cm(-3) is comparable to the turbulent and gravitational energy densities in the region. We find that the magnetic field direction is very well aligned with the whole of the IRS 3 bipolar outflow structure. We find that the median value of polarization fractions is 3.0% at 450 mu m in the central 3 ' region, which is larger than the median value of 1.2% at 850 mu m. The trend could be due to the better alignment of warmer dust in the strong radiation environment. We also find that polarization fractions decrease with intensity at both wavelengths, with slopes, determined by fitting a Rician noise model of 0.59 +/- 0.03 at 450 mu m and 0.36 +/- 0.04 at 850 mu m, respectively. We think that the shallow slope at 850 mu m is due to grain alignment at the center being assisted by strong radiation from the central young stellar objects.
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| 5. |
- Ngoc, Nguyen Bich, et al.
(författare)
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Observations of Magnetic Fields Surrounding LkH alpha 101 Taken by the BISTRO Survey with JCMT-POL-2
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 908:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the first high spatial resolution measurement of magnetic fields surrounding LkH alpha 101, part of the Auriga-California molecular cloud. The observations were taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope within the framework of the B-fields In Star-forming Region Observations (BISTRO) survey. Observed polarization of thermal dust emission at 850 mu m is found to be mostly associated with the redshifted gas component of the cloud. The magnetic field displays a relatively complex morphology. Two variants of the Davis-Chandrasekhar-Fermi method, unsharp masking and structure function, are used to calculate the strength of magnetic fields in the plane of the sky, yielding a similar result of B-POS similar to 115 mu G. The mass-to-magnetic-flux ratio in critical value units, lambda similar to 0.3, is the smallest among the values obtained for other regions surveyed by POL-2. This implies that the LkH alpha 101 region is subcritical, and the magnetic field is strong enough to prevent gravitational collapse. The inferred delta B/B-0 similar to 0.3 implies that the large-scale component of the magnetic field dominates the turbulent one. The variation of the polarization fraction with total emission intensity can be fitted by a power law with an index of alpha = 0.82 0.03, which lies in the range previously reported for molecular clouds. We find that the polarization fraction decreases rapidly with proximity to the only early B star (LkH alpha 101) in the region. Magnetic field tangling and the joint effect of grain alignment and rotational disruption by radiative torques can potentially explain such a decreasing trend.
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| 6. |
- Chen, Shi-Peng, et al.
(författare)
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Guanidine-based protic ionic liquids as highly efficient intermolecular scissors for dissolving natural cellulose
- 2023
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Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 25:22, s. 9322-9334
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Tidskriftsartikel (refereegranskat)abstract
- The development of highly efficient and environmentally friendly solvents for dissolving cellulose, which is the most abundant natural polymer on Earth, remains a challenge, hindering its full utilization. Herein, a green protic ionic liquid, 1,1,3,3-tetramethylguanidinium methoxyacetate ([TMGH][MAA]), was found to exhibit attractive capacity to dissolve natural cellulose with an appropriate TMG/MAA molar ratio of 7 : 3 at 80 degrees C. The solubility of cotton linter and ultra-high molecular weight cotton fibers reached 13% (w/w) and 3% (w/w), respectively, surpassing that of most solvent systems currently used for the dissolution of cellulose. The experimental and simulation results verified that the excellent dissolution ability of [TMGH][MAA] for cellulose is mainly attributed to the destruction of the intrinsic hydrogen-bond networks in cellulose by the synergistic interactions of the [TMGH] cations and [MAA] anions with the hydroxyl groups in the cellulose chains, acting as highly efficient "intermolecular scissors". The superiority of this novel dissolution system was further demonstrated by the remarkable comprehensive properties of the regenerated cellulose film including satisfactory thermostability, high transparency, and excellent mechanical properties. Furthermore, the satisfactory recovery performance of this solvent highlights its significant feasibility for large-scale industrial manufacturing. The proposed [TMGH][MAA] in this study exhibits great potential as a next-generation processing solvent for dissolving, and thus processing cellulose, promoting the sustainable development of high-value-added cellulose materials.
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| 7. |
- Meng, Jingxiang, et al.
(författare)
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Adaptive Differentiation in Seedling Traits in a Hybrid Pine Species Complex, Pinus densata and Its Parental Species, on the Tibetan Plateau
- 2015
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- Evidence from molecular genetics demonstrates that Pinus densata is a natural homoploid hybrid originating from the parent species Pinus tabuliformis and Pinus yunnanensis, and ecological selection may have played a role in the speciation of Pinus densata. However, data on differentiation in adaptive traits in the species complex are scarce. In this study, we performed a common garden test on 16 seedling traits to examine the differences between Pinus densata and its parental species in a high altitude environment. We found that among the 16 analyzed traits, 15 were significantly different among the species. Pinus tabuliformis had much earlier bud set and a relatively higher bud set ratio but poorer seedling growth, and Pinus yunnanensis had opposite responses for the same traits. Pinus densata had the greatest fitness with higher viability and growth rates than the parents. The relatively high genetic contribution of seedling traits among populations suggested that within each species the evolutionary background is complex. The correlations between the seedling traits of a population within a species and the environmental factors indicated different impacts of the environment on species evolution. The winter temperature is among the most important climate factors that affected the fitness of the three pine species. Our investigation provides empirical evidence on adaptive differentiation among this pine species complex at seedling stages.
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| 8. |
- Zheng, Shao Fei, et al.
(författare)
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An inverse optimization of turbulent flow and heat transfer for a cooling passage with hierarchically arranged ribs in turbine blades
- 2024
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 220
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Tidskriftsartikel (refereegranskat)abstract
- Owing to the limited cold-air amount and pressure in supply systems, high-efficient heat transfer with low-level friction loss is highly desired for cooling units of a turbine blade. To exploit the potential improvement of hierarchically arranged ribs in cooling passages proposed previously, multi-parameter optimizations for rib arrangements are implemented by integrating the simplified conjugate-gradient algorithm with the turbulent flow and heat transfer model. Rib heights as design variables are optimized with various performance indices as objective functions at a fixed Re. The optimizations confirm that using the wall temperature difference and Nu as the objective function, respectively, a limited heat transfer improvement is achieved with a greatly increased friction loss. Taking the overall performance factor as the objective function, different optimal designs at different constraint conditions possess hierarchical characteristics. A significant friction loss reduction of 52.1%, 54.7%, and 54.8%, is achieved with a moderate heat transfer loss of 10.9%, 7.0%, and 2.3%. Despite different thermal and friction performances, their overall performances are consistent with a remarkable increase of 13.9%, 21.2%, and 27.3%. Finally, the optimization strategy coupling the multi-parameter optimization and hierarchical scheme is confirmed as effective for enhancing the thermohydraulic performance of convective heat transfer systems with perturbation elements.
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