5632 research outputs found
Sort by
A Study of 90 GHz Dust Emissivity on Molecular Cloud and Filament Scales
No full textRecent observations from the MUSTANG2 instrument on the Green Bank Telescope have revealed evidence of enhanced long-wavelength emission in the dust spectral energy distribution (SED) in the Orion Molecular Cloud (OMC) 2/3 filament on 25″ (0.1 pc) scales. Here we present a measurement of the SED on larger spatial scales (map size 0.°5–3° or 3–20 pc), at somewhat lower resolution (120″, corresponding to 0.25 pc at 400 pc) using data from the Herschel satellite and Atacama Cosmology Telescope (ACT). We then extend the 120″-scale investigation to other regions covered in the Herschel Gould Belt Survey (HGBS), specifically the dense filaments in the southerly regions of Orion A, Orion B, and Serpens-S. Our data set in aggregate covers approximately 10 deg², with continuum photometry spanning from 160 μm to 3 mm. These OMC 2/3 data display excess emission at 3 mm, though less (10.9% excess) than what is seen at higher resolution. Strikingly, we find that the enhancement is present even more strongly in the other filaments we targeted, with an average excess of 42.4% and 30/46 slices showing an inconsistency with the modified blackbody to at least 4σ. Applying this analysis to the other targeted regions, we lay the groundwork for future high-resolution analyses. Additionally, we also consider a two-component dust model motivated by Planck results and an amorphous grain dust model. While both of these have been proposed to explain deviations in emission from a generic modified blackbody, we find that they have significant drawbacks, requiring many spectral points or lacking experimental data coverage
Computational graph completion
No full textWe introduce a framework for generating, organizing, and reasoning with computational knowledge. It is motivated by the observation that most problems in Computational Sciences and Engineering (CSE) can be described as that of completing (from data) a computational graph (or hypergraph) representing dependencies between functions and variables. In that setting nodes represent variables and edges (or hyperedges) represent functions (or functionals). Functions and variables may be known, unknown, or random. Data come in the form of observations of distinct values of a finite number of subsets of the variables of the graph (satisfying its functional dependencies). The underlying problem combines a regression problem (approximating unknown functions) with a matrix completion problem (recovering unobserved variables in the data). Replacing unknown functions by Gaussian processes and conditioning on observed data provides a simple but efficient approach to completing such graphs. Since the proposed framework is highly expressive, it has a vast potential application scope. Since the completion process can be automatized, as one solves √√2+√3 on a pocket calculator without thinking about it, one could, with the proposed framework, solve a complex CSE problem by drawing a diagram. Compared to traditional regression/kriging, the proposed framework can be used to recover unknown functions with much scarcer data by exploiting interdependencies between multiple functions and variables. The computational graph completion (CGC) problem addressed by the proposed framework could therefore also be interpreted as a generalization of that of solving linear systems of equations to that of approximating unknown variables and functions with noisy, incomplete, and nonlinear dependencies. Numerous examples illustrate the flexibility, scope, efficacy, and robustness of the CGC framework and show how it can be used as a pathway to identifying simple solutions to classical CSE problems. These examples include the seamless CGC representation of known methods (for solving/learning PDEs, surrogate/multiscale modeling, mode decomposition, deep learning) and the discovery of new ones (digital twin modeling, dimension reduction)
Gauge invariant propagators and states in quantum electrodynamics
No full textWe study combined matter/gauge field gauge invariant states in terms of data living on the boundary of gauge invariant path-integrals. To get concrete results, this is done for scalar and spinor QED, for both ‘time-slice’, and ‘causal diamond’ boundaries. We discuss both the standard case where the gauge field falls off to zero at the spatial boundaries, and the case of ‘large gauge transformations’, where it remains finite at these boundaries. The path-integral naturally generates a specific dressing factor for states living on time-slices, without fixing any gauge, and we identify a universal contribution which depends only on the nature of the boundaries. We also derive the analogous dressing for states defined on null infinity, showing both its Coulombic parts as well as soft-photon parts
Exploring the protist microbiome: The diversity of bacterial communities associated with Arcella spp. (Tubulina: Amoebozoa)
No full textResearch on protist-bacteria interactions is increasingly relevant as these associations are now known to play important roles in ecosystem and human health. Free-living amoebae are abundant in all environments and are frequent hosts for bacterial endosymbionts including pathogenic bacteria. However, to date, only a small fraction of these symbionts have been identified, while the structure and composition of the total symbiotic bacterial communities still remains largely unknown. Here, we use the testate amoeba Arcella spp. as model organisms to investigate the specificity and diversity of Arcella-associated microbial communities. High-throughput amplicon sequencing from the V4 region of the 16S rRNA gene revealed high diversity in the bacterial communities associated with the wild Arcella spp. To investigate the specificity of the associated bacterial community with greater precision, we investigated the bacterial communities of two lab-cultured Arcella species, A. hemispherica and A. intermedia, grown in two different media types. Our results suggest that Arcella-bacteria associations are species-specific, and that the associated bacterial community of lab-cultured Arcella spp. remains distinct from that of the surrounding media. Further, each host Arcella species could be distinguished based on its bacterial composition. Our findings provide insight into the understanding of eukaryotic-bacterial symbiosis
Reply to Oren et al., “New Phylum Names Harmonize Prokaryotic Nomenclature”
No full textWe thank Oren et al., 2022 (1) for providing the International Committee on Systematics of Prokaryotes (ICSP) Executive Board's response to the recent opinion piece “Harmonizing Prokaryotic Nomenclature: Fixing the Fuss over Phylum Name Flipping” (2).
Herein, we (a group of concerned microbiologists) offer several additional comments on the naming of prokaryotic phyla. Our concerns arise from the perception that the ICSP Executive Board is not directly addressing the plight of microbiologists around the world concerning the long-lasting confusion that the proposed phylum name changes will create throughout the scientific literature. Instead of selectively pointing out certain ICSP rules, we would have appreciated opening a door for a more inclusive discussion about the process of naming phyla. As previously stated (2), we are in favor of the International Code of Nomenclature of Prokaryotes (ICNP) rules for the recognition of the rank of “phylum” and the usage of “-ota” as the suffix for naming phyla. However, we feel that the drastic name changes of six phyla at the prefix level will create significant dissonance and confusion between the old and new names when considering past and future publications
R Coronae Borealis and dustless hydrogen-deficient carbon stars likely have different oxygen isotope ratios
No full textContext. R Coronae Borealis (RCB) and dustless Hydrogen-deficient Carbon (dLHdC) stars are believed to be remnants of low mass white dwarf mergers. These supergiant stars have peculiar hydrogen-deficient carbon-rich chemistries and stark overabundances of ¹⁸O. RCB stars undergo dust formation episodes resulting in large-amplitude photometric variations that are not seen in dLHdC stars. Recently, the sample of known dLHdC stars in the Milky Way has more than quintupled with the discovery of 27 new dLHdC stars.
Aims. It has been suggested that dLHdC stars have lower ¹⁶O/¹⁸O than RCB stars. We aim to compare the ¹⁶O/¹⁸O ratios for a large sample of dLHdC and RCB stars to examine this claim.
Methods. We present medium resolution (R ≈ 3000) near-infrared spectra of 20 newly discovered dLHdC stars. We also present medium resolution (R ≈ 3000 − 8000) K-band spectra for 49 RCB stars. Due to the several free parameters and assumptions in our fitting strategy, we provide wide range estimates on the ¹⁶O/¹⁸O ratios of seven dLHdC and 33 RCB stars that show ¹²C¹⁶O and ¹²C¹⁸O absorption bands, and present the largest sample of such 16O/18O wide-range values for dLHdC and RCB stars to date.
Results. We find that six of the seven dLHdC stars have ¹⁶O/¹⁸O 1. We also confirm that unlike RCB stars, dLHdC stars do not show strong blueshifted (> 200 km s⁻¹) He I 10 833 Å absorption, suggesting the absence of strong, dust-driven winds around them.
Conclusions. Although we only can place wide range estimates on the ¹⁶O/¹⁸O and these are more uncertain in cool RCBs, our medium resolution spectra suggest that most dLHdC stars have lower ¹⁶O/¹⁸O than most RCB stars. This confirms one of the first, long-suspected spectroscopic differences between RCB and dLHdC stars. The different oxygen isotope ratios rule out the existing picture that RCB stars represent an evolved stage of dLHdC stars. Instead, we suggest that whether the white dwarf merger remnant is a dLHdC or RCB star depends on the mass ratios, masses and compositions of the merging white dwarfs. Future high resolution spectroscopic observations will help confirm and more precisely quantify the difference between the oxygen isotope ratios of the two classes
A prebiotic diet modulates microglial states and motor deficits in α-synuclein overexpressing mice
No full textParkinson’s disease (PD) is a movement disorder characterized by neuroinflammation, α-synuclein pathology, and neurodegeneration. Most cases of PD are non-hereditary, suggesting a strong role for environmental factors, and it has been speculated that disease may originate in peripheral tissues such as the gastrointestinal (GI) tract before affecting the brain. The gut microbiome is altered in PD and may impact motor and GI symptoms as indicated by animal studies, although mechanisms of gut-brain interactions remain incompletely defined. Intestinal bacteria ferment dietary fibers into short-chain fatty acids, with fecal levels of these molecules differing between PD and healthy controls and in mouse models. Among other effects, dietary microbial metabolites can modulate activation of microglia, brain-resident immune cells implicated in PD. We therefore investigated whether a fiber-rich diet influences microglial function in α-synuclein overexpressing (ASO) mice, a preclinical model with PD-like symptoms and pathology. Feeding a prebiotic high-fiber diet attenuates motor deficits and reduces α-synuclein aggregation in the substantia nigra of mice. Concomitantly, the gut microbiome of ASO mice adopts a profile correlated with health upon prebiotic treatment, which also reduces microglial activation. Single-cell RNA-seq analysis of microglia from the substantia nigra and striatum uncovers increased pro-inflammatory signaling and reduced homeostatic responses in ASO mice compared to wild-type counterparts on standard diets. However, prebiotic feeding reverses pathogenic microglial states in ASO mice and promotes expansion of protective disease-associated macrophage (DAM) subsets of microglia. Notably, depletion of microglia using a CSF1R inhibitor eliminates the beneficial effects of prebiotics by restoring motor deficits to ASO mice despite feeding a prebiotic diet. These studies uncover a novel microglia-dependent interaction between diet and motor symptoms in mice, findings that may have implications for neuroinflammation and PD
Martian landscapes of fluvial ridges carved from ancient sedimentary basin fill
No full textLarge sedimentary basins contain archives of Earth history. It is unknown to what extent similar basins existed on Mars because there are few observations relating to the subsurface and it is difficult to identify buried deposits. Here, we used numerical simulations to show that landscapes of networks of topographic ridges that are abundant on the surface of Mars may represent erosional windows into thick, basin-filling river deposits that accumulated over long time spans. We used a numerical model to drive hillslope creep and differential erosion from the wind to simulate Mars-like exhumation processes acting on basin-filling fluvial strata, which we based on those buried in the Gulf of Mexico on Earth, as imaged using three-dimensional reflectance seismology. Simulations produced remarkably Martian landscapes in which the preferential erosion of mudstone relative to sandstone channel belts leads to the development of complex patterns of intersecting ridges. Our findings contrast to the existing view of ridged Martian landscapes as thin-skinned surface deposits preserving fluvial landscapes at a snapshot in time. Instead, the ridge cross-cutting patterns produced by the model reflect the exhumation of channel bodies at different stratigraphic levels, exposing basin strata accumulated over time scales of 500,000 years. Thus, we propose that fluvial ridges on Mars may expose an archive of long-lived aqueous processes
KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6
No full textWe present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲ z ≲ 3.6 in 202 H I-selected absorbers with 14.6 ≤ log N_HI 100) between absorbers separated by less than Δv < 500 km s−1 imply that the metals are poorly mixed in 14.6 ≤ log N_HI < 20 gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲ z ≲ 3.6. We find that the mean metallicity increases with N_HI, consistent with what is found in z < 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲ z ≲ 3.6 to z < 1, but the contribution of the 14.6 ≤ log N_HI < 19 absorbers to the total metal budget of the universe at z < 1 is a quarter of that at 2.2 ≲ z ≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] with N_HI, which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < − 2.4 at z ∼ 2–3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows
The HD 93963 A transiting system: A 1.04 d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS
No full textWe present the discovery of two small planets transiting HD 93963A (TOI-1797), a GOV star (M_* = 1.109 ± 0.043M_⊙, R_* = 1.043 ± 0.009 R_⊙) in a visual binary system. We combined TESS and CHEOPS space-borne photometry with MuSCAT 2 ground-based photometry, ‘Alopeke and PHARO high-resolution imaging, TRES and FIES reconnaissance spectroscopy, and SOPHIE radial velocity measurements. We validated and spectroscopically confirmed the outer transiting planet HD 93963 A c, a sub-Neptune with an orbital period of P_c ≈ 3.65 d that was reported to be a TESS object of interest (TOI) shortly after the release of Sector 22 data. HD 93963 A c has amass of M_c = 19.2 ± 4.1 M_⊕ and a radius of R_c = 3.228 ± 0.059 R_⊕, implying a mean density of ρ_c = 3.1 ± 0.7 g cm^(-3). The inner object, HD 93963 A b, is a validated 1.04 d ultra-short period (USP) transiting super-Earth that we discovered in the TESS light curve and that was not listed as a TOI, owing to the low significance of its signal (TESS signal-to-noise ratio ≈6.7, TESS + CHEOPS combined transit depth D_b = 141.5_(−8.3)^(+8.5) ppm). We intensively monitored the star with CHEOPS by performing nine transit observations to confirm the presence of the inner planet and validate the system. HD 93963 A b is the first small (R_b = 1.35 ± 0.042 R_⊕) USP planet discovered and validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is not significantly detected in our radial velocities (M_b = 7.8 ± 3.2 M_⊕). The two planets are on either side of the radius valley, implying that they could have undergone completely different evolution processes. We also discovered a linear trend in our Doppler measurements, suggesting the possible presence of a long-period outer planet. With a V-band magnitude of 9.2, HD 93963 A is among the brightest stars known to host a USP planet, making it one of the most favourable targets for precise mass measurement via Doppler spectroscopy and an important laboratory to test formation, evolution, and migration models of planetary systems hosting ultra-short period planets