We present constraints on the origins of fast radio bursts (FRBs) using large cosmological simulations. We calculate contributions to FRB dispersion measures (DMs) from the Milky Way, from the Local ...Universe, from cosmological large-scale structure, and from potential FRB host galaxies, and then compare these simulations to the DMs of observed FRBs. We find that the Milky Way contribution has previously been underestimated by a factor of ∼2, and that the foreground-subtracted DMs are consistent with a cosmological origin, corresponding to a source population observable to a maximum redshift z ∼ 0.6–0.9. We consider models for the spatial distribution of FRBs in which they are randomly distributed in the Universe, track the star formation rate of their host galaxies, track total stellar mass, or require a central supermassive black hole. Current data do not discriminate between these possibilities, but the predicted DM distributions for different models will differ considerably once we begin detecting FRBs at higher DMs and higher redshifts. We additionally consider the distribution of FRB fluences, and show that the observations are consistent with FRBs being standard candles, each burst producing the same radiated isotropic energy. The data imply a constant isotropic burst energy of ∼7 × 1040 erg if FRBs are embedded in host galaxies, or ∼9 × 1040 erg if FRBs are randomly distributed. These energies are 10–100 times larger than had previously been inferred. Within the constraints of the available small sample of data, our analysis favours FRB mechanisms for which the isotropic radiated energy has a narrow distribution in excess of 1040 erg.
Somatic mutations have been identified in more than half of aldosterone-producing adenomas (APAs) through mutation hotspot sequencing. The underlying pathogenesis of inappropriate aldosterone ...synthesis in the remaining population is still unknown.
To investigate the prevalence and spectrum of somatic mutations in APAs using an aldosterone synthase (CYP11B2) immunohistochemistry (IHC)‒guided next-generation sequencing (NGS) approach.
Formalin-fixed paraffin-embedded adrenal tissue from white American patients with primary aldosteronism who underwent adrenalectomy at the University of Michigan was used. Genomic DNA was isolated from 75 APAs (identified by CYP11B2 IHC). NGS was performed to identify somatic mutations by sequencing the entire coding region of a panel of genes mutated in APAs.
Somatic mutations were identified in 66 of 75 APAs (88%). Of the APAs with somatic mutations, six were smaller than coexisting CYP11B2-negative adrenocortical adenomas. The most frequently mutated gene was KCNJ5 (43%), followed by CACNA1D (21%), ATP1A1 (17%), ATP2B3 (4%), and CTNNB1 (3%). In addition to identification of previously reported mutations, we identified five previously unreported mutations (two in KCNJ5, one in ATP1A1, one in ATP2B3, and one in CACNA1D genes). KCNJ5 mutations were more frequent in women (70% vs 24% in men).
Comprehensive NGS of CYP11B2-expressing adrenal tumors identified somatic mutations in aldosterone-driving genes in 88% of APAs, a higher rate than in previous studies using conventional approaches.
Attention mechanisms have led to many breakthroughs in sequential data modeling but have yet to be incorporated into any generative algorithms for molecular design. Here we explore the impact of ...adding self-attention layers to generative
-VAE models and show that those with attention are able to learn a complex "molecular grammar" while improving performance on downstream tasks such as accurately sampling from the latent space ("model memory") or exploring novel chemistries not present in the training data. There is a notable relationship between a model's architecture, the structure of its latent memory and its performance during inference. We demonstrate that there is an unavoidable tradeoff between model exploration and validity that is a function of the complexity of the latent memory. However, novel sampling schemes may be used that optimize this tradeoff. We anticipate that attention will play an important role in future molecular design algorithms that can make efficient use of the detailed molecular substructures learned by the transformer.
The utilization of methane, a potent greenhouse gas, is an important component of local and global carbon cycles that is characterized by tight linkages between methane-utilizing (methanotrophic) and ...nonmethanotrophic bacteria. It has been suggested that the methanotroph sustains these nonmethanotrophs by cross-feeding, because subsequent products of the methane oxidation pathway, such as methanol, represent alternative carbon sources. We established cocultures in a microcosm model system to determine the mechanism and substrate that underlay the observed cross-feeding in the environment. Lanthanum, a rare earth element, was applied because of its increasing importance in methylotrophy. We used co-occurring strains isolated from Lake Washington sediment that are involved in methane utilization: a methanotroph and two nonmethanotrophic methylotrophs. Gene-expression profiles and mutant analyses suggest that methanol is the dominant carbon and energy source the methanotroph provides to support growth of the nonmethanotrophs. However, in the presence of the nonmethanotroph, gene expression of the dominant methanol dehydrogenase (MDH) shifts from the lanthanide-dependent MDH (XoxF)-type, to the calcium-dependent MDH (MxaF)-type. Correspondingly, methanol is released into the medium only when the methanotroph expresses the MxaF-type MDH. These results suggest a cross-feeding mechanism in which the nonmethanotrophic partner induces a change in expression of methanotroph MDHs, resulting in release of methanol for its growth. This partner-induced change in gene expression that benefits the partner is a paradigm for microbial interactions that cannot be observed in studies of pure cultures, underscoring the importance of synthetic microbial community approaches to understand environmental microbiomes.
The inverse Evershed flow (IEF) is an inflow of material into the penumbra of sunspots in the solar chromosphere that occurs along dark, elongated super-penumbral fibrils extending from about the ...outer edge of the moat cell to the sunspot. The IEF channels exhibit brightenings in the penumbra, where the supersonic IEF descends to the photosphere causing shock fronts with localized heating. We used an 1 hr time series of spectroscopic observations of the chromospheric spectral lines of Ca ii IR at 854 nm and H at 656 nm taken with the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope to investigate the temporal evolution of IEF channels. Complementary information on the photospheric magnetic field was obtained from observations with the Facility Infrared Spectropolarimeter at 1083 nm and the Helioseismic and Magnetic Imager. We find that individual IEF channels are long-lived (10-60 minutes) and only show minor changes in position and flow speed during their lifetime. Initiation and termination of IEF channels takes several minutes. The IEF channels with line-of-sight velocities of about 10 km s−1 show no lasting impact from transient or oscillatory phenomena with maximal velocity amplitudes of only about 1 km s−1 that run along them. We could not detect any clear correlation of the location and evolution of IEF channels to local magnetic field properties in the photosphere in the penumbra or moving magnetic features in the sunspot moat. Our results support a picture of the IEF as a field-aligned siphon flow along arched loops. From our data we cannot determine if their evolution is controlled by events at the outer end in the moat or at the inner end in the penumbra.
We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we implement and test a vast ...majority of SPH improvement in the developer version of gadget-3. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity including high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modifications; however, when necessary we study the performance of individual code modules. We approximate hydrodynamical states more accurately and with significantly less noise than standard gadget-SPH. Furthermore, the new implementation promotes the mixing of entropy between different fluid phases, also within cosmological simulations. Finally, we study the performance of the hydrodynamical solver in the context of radiative galaxy formation and non-radiative galaxy cluster formation. We find galactic discs to be colder and more extended and galaxy clusters showing entropy cores instead of steadily declining entropy profiles. In summary, we demonstrate that our improved SPH implementation overcomes most of the undesirable limitations of standard gadget-SPH, thus becoming the core of an efficient code for large cosmological simulations.
Knowledge on nulear cluster physics has increased considerably since the pioneering discovery of12C+12C resonances half a century ago and nuclear clustering remains one of the most fruitful domains ...of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. The occurrence of "exotic" shapes and/or Bose-Einstein α condensates in light N=Z α-conjugate nuclei is investigated. Evolution of clustering from stability to the drip-lines examined with clustering aspects persisting in light neutron-rich nuclei is consistent with the extension of the"Ikeda-diagram" to non α-conjugate nuclei.
We determined the direction and strength of the photospheric and lower chromospheric magnetic field in the umbra and penumbra of a sunspot from inversions of spectropolarimetric observations of ...photospheric lines at 617 nm and 1565 nm and the chromospheric Ca ii IR line at 854 nm, respectively. We compare the magnetic field vector with the direction of 75 flow channels that harbor the chromospheric inverse Evershed effect (IEF) near their downflow points (DFPs) in the sunspot's penumbra. The azimuth and inclination of the IEF channels to the line of sight (LOS) were derived from spatial maps of the LOS velocity and line-core intensity of the Ca ii IR line and a thermal inversion of the Ca ii IR spectra to obtain temperature cubes. We find that the flow direction of the IEF near the DFPs is aligned with the photospheric magnetic field to within about 15°. The IEF flow fibrils make an angle of 30°-90° to the local vertical with an average value of about 65°. The average field strength at the DFPs is about 1.3 kG. Our findings suggest that the IEF in the lower chromosphere is a field-aligned siphon flow, where the larger field strength at the inner footpoints together with the lower temperature in the penumbra causes the necessary gas pressure difference relative to the outer footpoints in the hotter quiet Sun with lower magnetic field strength. The IEF connects to magnetic field lines that are not, like in the case of the regular Evershed flow, but which continue upward into the chromosphere, indicating an "uncombed" penumbral structure.
Context. Ellerman bombs (EBs) are enhanced emission in the wings of the Hα line in the solar spectrum. Aims. We study the structure of an EB in the photosphere and chromosphere. Methods. We analyze ...simultaneous observations of four chromospheric lines (Hα, Ca ii H, Ca ii IR 854 nm, and He i 1083 nm) as well as two photospheric lines (Fe i 630 and Si i 1082.7 nm) along with high-cadence 160 and 170 nm ultraviolet (UV) continuum filtergrams. Full Stokes data from the Helioseismic and Magnetic Imager (HMI) are used to trace the temporal evolution of the magnetic structure. Results. We identify the EB by excess emission in the wings of the Hα line, a brightening in the UV continuum, and large emission peaks in the core of the two Ca ii lines. The EB shows a blueshift in all chromospheric lines, while no shifts are observed in the photospheric lines. The blueshift in the chromospheric layer causes very asymmetric emission peaks in the Ca ii H line. The photospheric Si i spectral line shows a shallower line depth at the location of the EB. The UV continuum maps show that the EB was substantially brighter than its surroundings for about 30 min. The continuum contrast of the EB from 170 nm to 1080 nm shows a power-law dependency on the wavelength. The temperature enhancement amounts to 130 K in the low photosphere and 400 K at the temperature minimum level. This temperature excess is also seen in an LTE inversion of the Ca ii spectra. The total thermal and radiative energy content of the EB is about 1020 J and 1018 J in the photosphere and chromosphere, respectively. The HMI data hints at a photospheric magnetic flux cancellation as the driver of the EB. Conclusions. Ellerman bombs release the energy in a height range of several pressure scale heights around the temperature minimum such that they affect both the photosphere and the lower chromosphere.
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