The standard core accretion model for planetesimal formation in protoplanetary discs (PPDs) is subject to a number of challenges. One is related to the vertical settling of dust to the disc mid-plane ...against turbulent stirring. This is particularly relevant in the presence of the vertical shear instability (VSI), a purely hydrodynamic instability applicable to the outer parts of PPDs, which drives moderate turbulence characterized by large-scale vertical motions. We investigate the evolution of dust and gas in the vicinity of local pressure enhancements (pressure bumps) in a PPD with turbulence sustained by the VSI. Our goal is to determine the morphology of dust concentrations and if dust can concentrate sufficiently to reach conditions that can trigger the streaming instability (SI). We performed a suite of global 2D axisymmetric and 3D simulations of dust and gas for a range of values for Σ
d
∕Σ
g
(ratio of dust-to-gas surface mass densities or metallicity), particle Stokes numbers,
τ
, and pressure bump amplitude,
A
. Dust feedback onto the gas is included. For the first time, we use global 3D simulations to demonstrate the collection of dust in long-lived vortices induced by the VSI. These vortices, which undergo a slow radial inward drift, are the dusty analogs of large long-lived vortices found in previous dust-free simulations of the VSI. Without a pressure bump and for solar metallicity
Z
≈ 0.01 and Stokes numbers
τ
~ 10
−2
, we find that such vortices can reach dust-to-gas density ratios slightly below unity in the discs’ mid-plane, while for
Z
≳ 0.05, long-lived vortices are largely absent. In the presence of a pressure bump, for
Z
≈ 0.01 and
τ
~ 10
−2
, a dusty vortex forms that reaches dust-to-gas ratios of a few times unity, such that the SI is expected to develop, before it eventually shears out into a turbulent dust ring. At intermediate metallicities,
Z
~ 0.03, this occurs for
τ
~ 5 × 10
−3
, but with a weaker and more short-lived vortex, while for larger
τ
, only a turbulent dust ring forms. For
Z
≳ 0.03, we find that the dust ring becomes increasingly axisymmetric for increasing
τ
and dust-to-gas ratios reach order unity for
τ
≳ 5 × 10
−3
. Furthermore, the vertical mass flow profile of the disc is strongly affected by dust for
Z
≳ 0.03, such that gas is transported inward near the mid-plane and outward at larger heights, which is the reversed situation compared to simulations with zero or small amounts of dust. We find viscous
α
-values to drop moderately as ~10
−3
–10
−4
for metallicities increasing as
Z
= 0–0.05. Our results suggest that the VSI can play an active role in the formation of planetesimals through the formation of vortices for plausible values of metallicity and particle size. Also, it may provide a natural explanation for the presence or absence of asymmetries of observed dust rings in PPDs, depending on the background metallicity.
The high carrier mobility of graphene has been exploited in field-effect transistors that operate at high frequencies. Transistors were fabricated on epitaxial graphene synthesized on the silicon ...face of a silicon carbide wafer, achieving a cutoff frequency of 100 gigahertz for a gate length of 240 nanometers. The high-frequency performance of these epitaxial graphene transistors exceeds that of state-of-the-art silicon transistors of the same gate length.
Superconductivity and charge density waves (CDWs) are competitive, yet coexisting, orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning ...their interaction on its natural length and time scale is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa
Cu
O
after the quench of superconductivity by an infrared laser pulse. We observe a nonthermal response of the CDW order characterized by a near doubling of the correlation length within ≈1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDWs manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations.
Translanguaging theories emphasize a fluid, dynamic view of language and differ from code-switching/mixing theories by de-centring the analytic focus from the language(s) being used in the ...interaction to the speakers who are making meaning and constructing original and complex discursive practices. Trans-semiotizing theories further broaden the focus to analyse language as entangled with many other semiotics (e.g. visuals, gestures, bodily movement) in meaning making. In this paper recent developments in trans/languaging and trans-semiotizing theories are discussed in conjunction with fine-grained classroom analyses to illustrate the key role played by trans/languaging and trans-semiotizing practices in the dialogic construal of content meaning in content-based education.
Conformational isomers (conformers) of molecules play a decisive role in biology and organic chemistry. However, experimental methods for investigating chemical reaction dynamics are typically not ...conformer-sensitive. We report on a gas-phase megaelectronvolt ultrafast electron diffraction investigation of α-phellandrene undergoing an electrocyclic ring-opening reaction. We directly imaged the evolution of a specific set of α-phellandrene conformers into the product isomer predicted by the Woodward-Hoffmann rules in real space and time. Our experimental results are in quantitative agreement with nonadiabatic quantum molecular dynamics simulations, which provide considerable detail of how conformation influences the time scale and quantum efficiency of photoinduced ring-opening reactions.
Nanodiamond (ND) has been proposed for various biomedical applications, including bioimaging, biosensing and drug delivery, owing to its physical‐chemical properties and biocompatibility. ...Particularly, ND has been demonstrated as fluorescence‐ and Raman‐detectable labels in many cellular models. Different surface functionalization methods have been developed, varying the ND's surface properties and rendering the possibility to attach biomolecules to provide interaction with biological targets. For this, toxicity is of major concern in animal models. Aside from cellular models, a cost‐effective animal test will greatly facilitate the development of applications. In this study, we use the rapid, sensitive and reproducible zebrafish embryo model for in vivo nanotoxicity test. We optimize the conditions for using this animal model and analyze the zebrafish embryonic development in the presence of ND. ND is observed in the embryo in vivo using laser confocal fluorescence microscopy and fluorescence lifetime imaging. Using the zebrafish model for a safety evaluation of ND‐based nanolabel is discussed.
The defects originated color centers of nanodiamond emit visible fluorescence upon laser illumination. With nanodiamond's low toxicity, it can be used as a biocompatible biolabel in the zebrafish model. When injected with nanodiamond, the green fluorescence from nanodiamond at the head of the larval zebrafish is brightly visible; and the nanodiamond can be traced in the zebrafish in vivo.
Electrocyclic reactions are characterized by the concerted formation and cleavage of both σ and π bonds through a cyclic structure. This structure is known as a pericyclic transition state for ...thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule α-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated π bonds. The σ bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.
ABSTRACT
We report on the determination of electron densities, and their impact on the outflow masses and rates, measured in the central few hundred parsecs of 11 local luminous active galaxies. We ...show that the peak of the integrated line emission in the active galactic nuclei (AGN) is significantly offset from the systemic velocity as traced by the stellar absorption features, indicating that the profiles are dominated by outflow. In contrast, matched inactive galaxies are characterized by a systemic peak and weaker outflow wing. We present three independent estimates of the electron density in these AGN, discussing the merits of the different methods. The electron density derived from the S ii doublet is significantly lower than that found with a method developed in the last decade using auroral and transauroral lines, as well as a recently introduced method based on the ionization parameter. The reason is that, for gas photoionized by an AGN, much of the S ii emission arises in an extended partially ionized zone where the implicit assumption that the electron density traces the hydrogen density is invalid. We propose ways to deal with this situation and we derive the associated outflow rates for ionized gas, which are in the range 0.001–0.5 M⊙ yr−1 for our AGN sample. We compare these outflow rates to the relation between $\dot{M}_{\rm out}$ and LAGN in the literature, and argue that it may need to be modified and rescaled towards lower mass outflow rates.
Background
Use of polysomnography (PSG) is the gold standard of diagnosis and measurement of treatment effectiveness for paediatric obstructive sleep apnoea (OSA). Although adenotonsillectomy (T&A) ...is effective in diminishing the apnoea–hypopnoea index (AHI), a meta‐analysis of postoperative changes for all other PSG parameters and outcome comparisons between obese and non‐obese children following T&A have never been conducted.
Objective of review
To comprehensively review polysomnographic findings after surgery for obese and non‐obese children with OSA.
Search strategy
Study protocol was registered on PROSPERO (CRD42013004737). Two authors independently searched databases including PubMed, MEDLINE, EMBASE and Cochrane Review from January 1997 to July 2014. The keywords used included the following: sleep apnea, OSA, sleep apnea syndromes, tonsillectomy, adenoidectomy, infant, child, adolescent, and Humans.
Evaluation method
A comprehensive systematic review and meta‐analysis for literature for OSA children treated by T&A with polysomnography data. Random‐effects model was applied to determine postoperative sleep parameter changes and the surgical success rate between obese and non‐obese groups. The quality of studies was assessed using the Newcastle–Ottawa Scale.
Results
In total, 51 studies with 3413 subjects were enrolled. After surgery, sleep architecture was altered by a significant decrease in sleep stage 1, and an increase in slow‐wave sleep and the rapid eye movement stage, and enhanced sleep efficiency. The mean difference between pre‐ and postoperative was a significant reduction of 12.4 event/h in AHI, along with a reduction of obstructive index, hypopnoea index, central index and arousal index. Mean and minimum oxygen saturation increased significantly after surgery. The overall success rate was 51% for postoperative AHI <1 (obese versus non‐obese versus combined, 34% versus 49% versus 56%), and 81% for AHI <5 (obese versus non‐obese versus combined, 61% versus 87% versus 84%). Meta‐regression analyses demonstrate that postoperative AHI was positively correlated with AHI and body mass index z score before surgery.
Conclusions
Meta‐analysis of current literature shows T&A offers prominent improvement in a variety of sleep parameters. Improvements in non‐obese children exceeded those for obese children. Postoperative residual OSA remained in roughly half of the children, especially those with severe disease and obesity, making additional treatment strategies and/or long‐term follow‐up highly desirable.
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