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- Lunnan, R., et al.
(författare)
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Two New Calcium-rich Gap Transients in Group and Cluster Environments
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 836:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the Palomar Transient Factory discoveries and the photometric and spectroscopic observations of PTF11kmb and PTF12bho. We show that both transients have properties consistent with the class of calcium-rich gap transients, specifically lower peak luminosities and rapid evolution compared to ordinary supernovae, and a nebular spectrum dominated by [Ca II] emission. A striking feature of both transients is their host environments: PTF12bho is an intracluster transient in the Coma Cluster, while PTF11kmb is located in a loose galaxy group, at a physical offset similar to 150 kpc from the most likely host galaxy. Deep Subaru imaging of PTF12bho rules out an underlying host system to a limit of M-R > -8.0 mag, while Hubble Space Telescope imaging of PTF11kmb reveals a marginal counterpart that, if real, could be either a background galaxy or a globular cluster. We show that the offset distribution of Ca-rich gap transients is significantly more extreme than that seen for SNe Ia or even short-hard gamma-ray bursts (sGRBs). Thus, if the offsets are caused by a kick, they require higher kick velocities and/or longer merger times than sGRBs. We also show that almost all Ca-rich transients found to date are in group and cluster environments with elliptical host galaxies, indicating a very old progenitor population; the remote locations could partially be explained by these environments having the largest fraction of stars in the intragroup/intracluster light following galaxy-galaxy interactions.
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| 2. |
- Kwon, Soonhyoung, et al.
(författare)
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One-Pot Synthesis of CHA/ERI-Type Zeolite Intergrowth from a Single Multiselective Organic Structure-Directing Agent
- 2024
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Ingår i: ACS Applied Materials and Interfaces. - 1944-8244 .- 1944-8252. ; 16:12, s. 14661-14668
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Tidskriftsartikel (refereegranskat)abstract
- We report the one-pot synthesis of a chabazite (CHA)/erionite (ERI)-type zeolite intergrowth structure characterized by adjustable extents of intergrowth enrichment and Si/Al molar ratios. This method utilizes readily synthesizable 6-azaspiro[5.6]dodecan-6-ium as the exclusive organic structure-directing agent (OSDA) within a potassium-dominant environment. High-throughput simulations were used to accurately determine the templating energy and molecular shape, facilitating the selection of an optimally biselective OSDA from among thousands of prospective candidates. The coexistence of the crystal phases, forming a distinct structure comprising disk-like CHA regions bridged by ERI-rich pillars, was corroborated via rigorous powder X-ray diffraction and integrated differential-phase contrast scanning transmission electron microscopy (iDPC S/TEM) analyses. iDPC S/TEM imaging further revealed the presence of single offretite layers dispersed within the ERI phase. The ratio of crystal phases between CHA and ERI in this type of intergrowth could be varied systematically by changing both the OSDA/Si and K/Si ratios. Two intergrown zeolite samples with different Si/Al molar ratios were tested for the selective catalytic reduction (SCR) of NOx with NH3, showing competitive catalytic performance and hydrothermal stability compared to that of the industry-standard commercial NH3-SCR catalyst, Cu-SSZ-13, prevalent in automotive applications. Collectively, this work underscores the potential of our approach for the synthesis and optimization of adjustable intergrown zeolite structures, offering competitive alternatives for key industrial processes.
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| 3. |
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| 4. |
- Sugiyama, J., et al.
(författare)
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Desorption reaction in MgH 2 studied with in situ μ + SR
- 2019
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry. - 2398-4902. ; 3:4, s. 956-964
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the mechanism determining the desorption temperature (T d ) of hydrogen storage materials, we have measured positive muon spin rotation and relaxation (μ + SR) in MgH 2 over a wide temperature range including its T d . The pressure in the sample cell due to desorbed H 2 was measured in parallel with the μ + SR measurements under static conditions. Such in situ μ + SR measurements revealed that hydrogen starts to diffuse in MgH 2 well below T d . This indicates the important role of hydrogen diffusion in accelerating the desorption reaction by removing the reaction product, i.e. H 2 , from the reaction system.
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