We present new JVLA observations of the high-mass cluster-forming region W51A from 2 to 16 GHz with resolution θfwhm ≈ 0.3−0.5″. The data reveal a wealth of observational results: (1) Currently ...forming, very massive (proto-O) stars are traced by o - H2CO21,1−21,2 emission, suggesting that this line can be used efficiently as a massive protostar tracer; (2) there is a spatially distributed population of ≲mJy continuum sources, including hypercompact H ii regions and candidate colliding wind binaries, in and around the W51 proto-clusters; and (3) there are two clearly detected protoclusters, W51e and W51 IRS2, that are gas-rich but may have most of their mass in stars within their inner ≲0.05 pc. The majority of the bolometric luminosity in W51 most likely comes from a third population of OB stars between these clusters. The presence of a substantial population of exposed O-stars coincident with a population of still-forming massive stars, together with a direct measurement of the low mass loss rate via ionized gas outflow from W51 IRS2, implies that feedback is ineffective at halting star formation in massive protoclusters. Instead, feedback may shut off the large-scale accretion of diffuse gas onto the W51 protoclusters, implying that they are evolving toward a state of gas exhaustion rather than gas expulsion. Recent theoretical models predict gas exhaustion to be a necessary step in the formation of gravitationally bound stellar clusters, and our results provide an observational validation of this process.
Over several centuries, the Serer of the Siin region of Senegal developed a complex system of land tenure that resulted in a stable rural society, productive agriculture, and a well-managed ...ecosystem. Dennis Galvan tells the story of what happened when French colonial rulers, and later the government of the newly independent Senegal, imposed new systems of land tenure and cultivation on the Serer of Siin. Galvan's book is a painstaking and skillful autopsy of ruinous Western-style "rational" economic development policy forced upon a fragile, yet self-sustaining, society. It is also a disquieting demonstration of the general folly of such an approach and an attempt to articulate a better, more sensitive, and ultimately more productive model for change—a model Galvan calls "institutional syncretism."
We present a new catalog of TeV gamma-ray sources using 1523 days of data from the High-Altitude Water Cherenkov (HAWC) Observatory. The catalog represents the most sensitive survey of the northern ...gamma-ray sky at energies above several TeV, with three times the exposure compared to the previous HAWC catalog, 2HWC. We report 65 sources detected at ≥5 significance, along with the positions and spectral fits for each source. The catalog contains eight sources that have no counterpart in the 2HWC catalog, but are within 1° of previously detected TeV emitters, and 20 sources that are more than 1° away from any previously detected TeV source. Of these 20 new sources, 14 have a potential counterpart in the fourth Fermi Large Area Telescope catalog of gamma-ray sources. We also explore potential associations of 3HWC sources with pulsars in the Australia Telescope National Facility (ATNF) pulsar catalog and supernova remnants in the Galactic supernova remnant catalog.
Bismuth telluride thin films were grown by pulsed laser deposition by implementing a novel method that combines both Te and Bi plasmas resulting from the laser ablation of individual Bi and Te ...targets. Furthermore, the mean kinetic ion energy and density of the plasmas, as estimated by TOF curves obtained from Langmuir probe measurements, were used as control parameters for the deposition process. The obtained thin films exhibit a metallic mirror-like appearance and present good adhesion to the substrate. Morphology of the thin films was observed by SEM, yielding smooth surfaces where particulates were also observed (splashing). Chemical composition analysis obtained by EDS showed that apparently the films have a Te-rich composition (ratio of Te/Bi of 3); however, Te excess arises from the splashing as revealed by the structural characterization (XRD and Raman spectroscopy). The XRD pattern indicated that depositions have the rhombohedral (D3d5 (R3¯m)) structure of Bi2Te3. Likewise, Raman spectra exhibited the presence of signals that correspond to Eg2, A1u2 and A1g2(LO) vibrational modes of the same rhombohedral phase of Bi2Te3. Additionally, oxidation states, analyzed by XPS, resulted in signals associated to Bi3+ and Te2- that correspond to the Bi2Te3 compound. Finally, surface topology and thickness profiles were obtained from AFM measurements, confirming a combination of a smooth surface with particulates on top of it and a film thickness of 400 nm.
We present the first catalog of gamma-ray sources emitting above 56 and 100 TeV with data from the High Altitude Water Cherenkov Observatory, a wide field-of-view observatory capable of detecting ...gamma rays up to a few hundred TeV. Nine sources are observed above 56 TeV, all of which are likely galactic in origin. Three sources continue emitting past 100 TeV, making this the highest-energy gamma-ray source catalog to date. We report the integral flux of each of these objects. We also report spectra for three highest-energy sources and discuss the possibility that they are PeVatrons.
The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or ...via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations.
Amyloid beta-peptide (Abeta) is postulated to play a central role in the pathogenesis of Alzheimer's disease. We recently proposed a pathway of Abeta-induced toxicity that is APP dependent and ...involves the facilitation of APP complex formation by Abeta. The APP-dependent component requires cleavage of APP at position 664 in the cytoplasmic domain, presumably by caspases or caspase-like proteases, with release of a potentially cytotoxic C31 peptide. In this study we show that Abeta interacted directly and specifically with membrane-bound APP to facilitate APP homo-oligomerization. Using chimeric APP molecules, this interaction was shown to take place between Abeta and its homologous sequence on APP. Consistent with this finding, we demonstrated that Abeta also facilitated the oligomerization of beta-secretase cleaved APP C-terminal fragment (C99). We found that the YENPTY domain in the APP cytoplasmic tail and contained within C31 is critical for this cell death pathway. Deletion or alanine- scanning mutagenesis through this domain significantly attenuated cell death apparently without affecting either APP dimerization or cleavage at position 664. This indicated that sequences within C31 are required after its release from APP. As the YENPTY domain has been shown to interact with a number of cytosolic adaptor molecules, it is possible that the interaction of APP, especially dimeric forms of APP, with these molecules contribute to cell death.
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