Whether the stellar initial mass function (IMF) is universal or is instead sensitive to environmental conditions is of critical importance: The IMF influences most observable properties of stellar ...populations and thus galaxies, and detecting variations in the IMF could provide deep insights into the star formation process. This review critically examines reports of IMF variations, with a view toward whether other explanations are sufficient given the evidence. Studies of the field, young clusters and associations, and old globular clusters suggest that the vast majority were drawn from a universal system IMF: a power law of Salpeter index (... = 1.35) above a few solar masses, and a log normal or shallower power law (... ~ 0-0.25) for lower mass stars. The shape and universality of the substellar IMF is still under investigation. Observations of resolved stellar populations and the integrated properties of most galaxies are also consistent with a universal IMF, suggesting no gross variations over much of cosmic time. Indications of "nonstandard" IMFs in specific local and extragalactic environments clearly warrant further study. However, there is no clear evidence that the IMF varies strongly and systematically as a function of initial conditions after the first few generations of stars. (ProQuest: ... denotes formulae/symbols omitted.)
In no other field of astrophysics has the impact of new instrumentation been as substantial as in the domain of exoplanets. Before 1995 our knowledge of exoplanets was mainly based on philosophical ...and theoretical considerations. The years that followed have been marked, instead, by surprising discoveries made possible by high-precision instruments. Over the past decade, the availability of new techniques has moved the focus of research from the detection to the characterization of exoplanets. Next-generation facilities will produce even more complementary data that will lead to a comprehensive view of exoplanet characteristics and, by comparison with theoretical models, to a better understanding of planet formation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Aims.
We present a new estimate for the binary fraction (the fraction of stars with a single companion) for M dwarfs using a log-normal fit to the orbital separation distribution.
Methods.
We used ...point estimates of the binary fraction (binary fractions over specific separation and companion mass ratio ranges) from four M dwarf surveys sampling distinct orbital radii to fit a log-normal function to the orbital separation distribution. This model, alongside the companion mass ratio distribution given by Reggiani & Meyer (2013, A&A, 553, A124), is used to calculate the frequency of companions over the ranges of mass ratio (
q
) and orbital separation (
a
) over which the referenced surveys were collectively sensitive – 0.60 ≤
q
≤ 1.00 and 0.00 ≤
a
≤ 10 000 AU. This method was then extrapolated to calculate a binary fraction which encompasses the broader ranges of 0.10 ≤
q
≤ 1.00 and 0.00 ≤
a
< ∞ AU. Finally, the results of these calculations were compared to the binary fractions of other spectral types.
Results.
The binary fraction over the constrained regions of 0.60 ≤
q
≤ 1.00 and 0.00 ≤
a
≤ 10 000 AU was calculated to be 0.229 ± 0.028. This quantity was then extrapolated over the broader ranges of
q
(0.10−1.00) and a (0.00 − ∞ AU) and found to be 0.462
−0.052
+0.057
. We used a conversion factor to estimate the multiplicity fraction from the binary fraction and found the multiplicity fraction over the narrow region of 0.60 ≤
q
≤ 1.00 and 0.00 ≤
a
≤ 10 000 AU to be 0.270 ± 0.111. Lastly, we estimated the multiplicity fractions of FGK, and A stars using the same method (taken over 0.60 ≤
q
≤ 1.00 and 0.00 ≤
a
≤ 10 000 AU). We find that the multiplicity fractions of M, FGK, and A stars, when considered over common ranges of
q
and
a
, are more similar than generally assumed.
We present H- and K sub(s)-band polarized differential images of the Herbig Ae/Be star HD142527, revealing its optically thick outer disk and the nearly empty gap. The very small inner working angle ...(~0".1) and high-resolution achievable with an 8 m class telescope, together with a careful polarimetric calibration strategy, allow us to achieve images that surpass the quality of previous scattered-light images. Previously known substructures are resolved more clearly and new structures are seen. Specifically, we are able to resolve (1) half a dozen spiral structures in the disk, including previously known outer-disk spirals as well as new spiral arms and arcs close to the inner rim of the disk, (2) peculiar holes in the polarized surface brightness at position angles (P.A.'s) of ~0degrees and ~160degrees, (3) the inner rim on the eastern side of the disk, and (4) the gap between the outer and inner disk, ranging from the inner working angle of 0."1 out to between 0."7 and 1."0, which is nearly devoid of dust. We then use a Markov Chain Monte Carlo algorithm to determine several structural parameters of the disk, using very simple assumptions, including its inclination, eccentricity, and the scale height of the inner rim. We compare our results with previous work on this object and try to produce a consistent picture of the system and its transition disk.
Dynamical evolution of star-forming regions Parker, Richard J; Wright, Nicholas J; Goodwin, Simon P ...
Monthly notices of the Royal Astronomical Society,
02/2014, Letnik:
438, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We model the dynamical evolution of star-forming regions with a wide range of initial properties. We follow the evolution of the regions' substructure using the
-parameter, we search for dynamical ...mass segregation using the ΛMSR technique, and we also quantify the evolution of local density around stars as a function of mass using the ΣLDR method. The amount of dynamical mass segregation measured by ΛMSR is generally only significant for subvirial and virialized, substructured regions - which usually evolve to form bound clusters. The ΣLDR method shows that massive stars attain higher local densities than the median value in all regions, even those that are supervirial and evolve to form (unbound) associations. We also introduce the
plot, which describes the evolution of spatial structure as a function of mass-weighted local density in a star-forming region. Initially dense (>1000 stars pc−2), bound regions always have
1, \Sigma _{\rm LDR} > 2$>
after 5 Myr, whereas dense unbound regions always have
2$>
after 5 Myr. Less dense regions (<100 stars pc−2) do not usually exhibit ΣLDR > 2 values, and if relatively high local density around massive stars arises purely from dynamics, then the
plot can be used to estimate the initial density of a star-forming region.
The novel coronavirus pandemic continues to cause significant morbidity and mortality around the world. Diverse clinical presentations prompted numerous attempts to predict disease severity to ...improve care and patient outcomes. Equally important is understanding the mechanisms underlying such divergent disease outcomes. Multivariate modeling was used here to define the most distinctive features that separate COVID-19 from healthy controls and severe from moderate disease. Using discriminant analysis and binary logistic regression models we could distinguish between severe disease, moderate disease, and control with rates of correct classifications ranging from 71 to 100%. The distinction of severe and moderate disease was most reliant on the depletion of natural killer cells and activated class-switched memory B cells, increased frequency of neutrophils, and decreased expression of the activation marker HLA-DR on monocytes in patients with severe disease. An increased frequency of activated class-switched memory B cells and activated neutrophils was seen in moderate compared to severe disease and control. Our results suggest that natural killer cells, activated class-switched memory B cells, and activated neutrophils are important for protection against severe disease. We show that binary logistic regression was superior to discriminant analysis by attaining higher rates of correct classification based on immune profiles. We discuss the utility of these multivariate techniques in biomedical sciences, contrast their mathematical basis and limitations, and propose strategies to overcome such limitations.
Significance Mesoporous SnO ₂/TiO ₂ core/shell nanostructured electrodes derivatized with a surface-bound Ru(II) polypyridyl-based chromophore–catalyst assembly are used for water splitting into H ₂ ...and O ₂ with visible light in a dye-sensitized photoelectrosynthesis cell. Photocurrents with a small applied bias are among the highest reported. Stabilization of the assembly on the surface of the TiO ₂ shell by using atomic layer deposition to deposit overlayers of Al ₂O ₃ or TiO ₂ results in long-term water splitting even in a phosphate buffer at pH 7.
A hybrid strategy for solar water splitting is exploited here based on a dye-sensitized photoelectrosynthesis cell (DSPEC) with a mesoporous SnO ₂/TiO ₂ core/shell nanostructured electrode derivatized with a surface-bound Ru(II) polypyridyl-based chromophore–catalyst assembly. The assembly, (4,4’-(PO ₃H ₂) ₂bpy) ₂Ru(4-Mebpy-4’-bimpy)Ru(tpy)(OH ₂) ⁴⁺ (Ru ₐᴵᴵ-Ru bᴵᴵ-OH ₂ ⁴⁺, combines both a light absorber and a water oxidation catalyst in a single molecule. It was attached to the TiO ₂ shell by phosphonate-surface oxide binding. The oxide-bound assembly was further stabilized on the surface by atomic layer deposition (ALD) of either Al ₂O ₃ or TiO ₂ overlayers. Illumination of the resulting fluorine-doped tin oxide (FTO)|SnO ₂/TiO ₂|-Ru ₐᴵᴵ-Ru bᴵᴵ-OH ₂ ⁴⁺(Al ₂O ₃ or TiO ₂) photoanodes in photoelectrochemical cells with a Pt cathode and a small applied bias resulted in visible-light water splitting as shown by direct measurements of both evolved H ₂ and O ₂. The performance of the resulting DSPECs varies with shell thickness and the nature and extent of the oxide overlayer. Use of the SnO ₂/TiO ₂ core/shell compared with nano ITO/TiO ₂ with the same assembly results in photocurrent enhancements of ∼5. Systematic variations in shell thickness and ALD overlayer lead to photocurrent densities as high as 1.97 mA/cm ² with 445-nm, ∼90-mW/cm ² illumination in a phosphate buffer at pH 7.
Coronavirus disease 2019 (COVID-19) is currently a global pandemic, but human immune responses to the virus remain poorly understood. We used high-dimensional cytometry to analyze 125 COVID-19 ...patients and compare them with recovered and healthy individuals. Integrated analysis of ~200 immune and ~50 clinical features revealed activation of T cell and B cell subsets in a proportion of patients. A subgroup of patients had T cell activation characteristic of acute viral infection and plasmablast responses reaching >30% of circulating B cells. However, another subgroup had lymphocyte activation comparable with that in uninfected individuals. Stable versus dynamic immunological signatures were identified and linked to trajectories of disease severity change. Our analyses identified three immunotypes associated with poor clinical trajectories versus improving health. These immunotypes may have implications for the design of therapeutics and vaccines for COVID-19.
We present long-baseline Atacama Large Millimeter/submillimeter Array observations of the 870 m dust continuum emission and CO (3-2) from the protoplanetary disk around the Herbig Ae/Be star HD ...100546, which is one of the few systems claimed to have two young embedded planets. These observations achieve a resolution of 4 au (3.8 mas), an rms noise of 66 Jy beam−1, and reveal an asymmetric ring between ∼20 and 40 au with largely optically thin dust continuum emission. This ring is well fit by two concentric and overlapping Gaussian rings of different widths and a Vortex. In addition, an unresolved component is detected at a position consistent with the central star, which may trace the central inner disk (<2 au in radius). We report a lack of compact continuum emission at the positions of both claimed protoplanets. We use this result to constrain the circumplanetary disk (CPD) mass and size of 1.44 M⊕ and 0.44 au in the optically thin and thick regimes, respectively, for the case of the previously directly imaged protoplanet candidate at ∼55 au (HD 100546 b). We compare these empirical CPD constraints to previous numerical simulations. This suggests that HD 100546 b is inconsistent with several planet accretion models, while gas-starved models are also still compatible. We estimate the planetary mass as 1.65 MJ using the relation between planet, circumstellar, and circumplanetary masses derived from numerical simulations. Finally, the CO-integrated intensity map shows a possible spiral arm feature that could match the spiral features identified in near-infrared scattered light polarized emission, which suggests a real spiral feature in the disk surface that needs to be confirmed with further observations.
The diagnosis of unusual pathogens causing serious infections may be difficult. In this case report, next-generation sequencing was used in real time to diagnose a leptospirosis infection in the ...central nervous system, directing successful targeted antimicrobial therapy.
More than half the cases of meningoencephalitis remain undiagnosed, despite extensive clinical laboratory testing.
1
–
4
Because more than 100 different infectious agents can cause encephalitis, establishing a diagnosis with the use of cultures, serologic tests, and pathogen-specific PCR assays can be difficult. Unbiased next-generation sequencing has the potential to revolutionize our ability to discover emerging pathogens, especially newly identified viruses.
5
–
8
However, the usefulness of next-generation sequencing for the diagnosis of infectious diseases in a clinically relevant timeframe is largely unexplored.
9
We used unbiased next-generation sequencing to identify a treatable, albeit rare, bacterial cause of meningoencephalitis. In this case, the . . .
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