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Dust from core-collapse supernovae (CCSNe), specifically Type IIP SNe, has been suggested to be a significant source of the dust observed in high-redshift galaxies. CCSNe eject large amounts of newly formed heavy elements, which can condense into dust grains in the cooling ejecta. However, infrared (IR) observations of typical CCSNe generally measure dust masses that are too small to account for the dust production needed at high redshifts. Type IIn SNe, classified by their dense circumstellar medium (CSM), are also known to exhibit strong IR emission from warm dust, but the dust origin and heating mechanism have generally remained unconstrained because of limited observational capabilities in the mid-IR. Here, we present a JWST/MIRI Medium Resolution Spectrograph (MRS) spectrum of the Type IIn SN 2005ip nearly 17 years post-explosion. The Type IIn SN 2005ip is one of the longest-lasting and most well-studied SNe observed to date. Combined with a Spitzer mid-IR spectrum of SN 2005ip obtained in 2008, this data set provides a rare 15-year baseline, allowing for a unique investigation of the evolution of dust. The JWST spectrum shows a new high-mass dust component ($\gtrsim0.08$ M$_{\odot}$) that is not present in the earlier Spitzer spectrum. Our analysis shows dust likely formed over the past 15 years in the cold, dense shell (CDS), between the forward and reverse shocks. There is also a smaller mass of carbonaceous dust ($\gtrsim0.005$ M$_{\odot}$) in the ejecta. These observations provide new insights into the role of SN dust production, particularly within the CDS, and its potential contribution to the rapid dust enrichment of the early Universe.
Es imposible seleccionar cinco libros de sociología sin dejar fuera importantes trabajos y desairar a muchos excelentes cientistas sociales, clásicos y contemporáneos, que merecen figurar en la mayoría de la lista de preferencias de cualquiera. Así que primero quisiera disculparme con los 95 autores que no tengo espacio para mencionar aquí....
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
No abstract is provided for this article.
Sketching and natural languages are effective communication media for interactive applications. We introduce Sketchforme, the first neural-network-based system that can generate sketches based on text descriptions specified by users. Sketchforme is capable of gaining high-level and low-level understanding of multi-object sketched scenes without being trained on sketched scene datasets annotated with text descriptions. The sketches composed by Sketchforme are expressive and realistic: we show in our user study that these sketches convey descriptions better than human-generated sketches in multiple cases, and 36.5% of those sketches are considered to be human-generated. We develop multiple interactive applications using these generated sketches, and show that Sketchforme can significantly improve language learning applications and support intelligent language-based sketching assistants.
Detailed mechanisms for the synthesis of p-xylene as well as the primary byproducts observed experimentally, 2,5-hexadione and 2,5-dimethyl-3-[(4-methyl-1,3-cyclohexadien-1-yl)methyl]furan, from ethylene and 2,5-dimethylfuran (DMF) mediated by H-BEA are obtained using an extended QM/MM model containing 208 tetrahedral atoms. The formation of p-xylene proceeds via Diels-Alder cycloaddition of ethylene and DMF, which is rate-limiting, followed by Brønsted acid-catalyzed dehydration. Secondary addition of DMF to the substrate following the Diels-Alder reaction leads to 2,5-dimethyl-3-[(4-methyl-1,3-cyclohexadien-1-yl)methyl]furan. The analysis of the free energies associated with the mechanisms suggests that the secondary addition can be eliminated by introducing n-heptane as an inert solvent to decrease the loading of DMF in the zeolite or by using a weak Brønsted acid site to facilitate the dehydration of the Diels-Alder product, for which the rate is determined by the deprotonation via the conjugate base of the active site. Water formed in the dehydration process can react directly with DMF to form 2,5-hexadione, thereby decreasing the yield of p-xylene. However, the free-energy barriers for the formation of 2,5-heaxdione compared to the Diels-Alder reaction indicate that DMF and 2,5-hexadione will be equilibrated. Therefore, the 2,5-hexadione yield can be minimized by operating at a high conversion of DMF.
The Tenderloin Senior Outreach Project (TSOP) is presented as a case study of effective community-based organizing among the isolated elderly in one of America's large “grey ghettos.” Based on the theoretical underpinnings of social support theory and Freire's “education for critical consciousness,” the Project has attempted to address the interrelated problems of poor health, social isolation and powerlessness endemic among the elderly in Single Room Occupancy hotels. The Project's metamorphosis is traced from a university-sponsored community development effort to a community-controlled organization focused on broad social action objectives. The transference of leadership from health education facilitators to indigenous elderly leaders within the hotels is examined, as are some of the strategies employed in increasing Project visibility, preventing burn-out, and facilitating replication in other areas.
The intramolecular addition of β-ketoesters to unactivated alkynes under neutral conditions and at room temperature is described. The method employs triphenylphosphinegold(I) cation as a catalyst for the formation of <i>exo</i>-methylenecycloalkanes. Both monocyclic and bicyclic cyclopentanes and cyclohexanes can be formed in excellent yields and with good diastereoselectivity.
