ABSTRACT We investigate the ultraharmonics response of a protoplanetary disk to an orbiting planet. We find that the multi-armed spiral structure can be excited by the higher-order forcing due to ...nonlinear mode-coupling. In particular, the preferential excitation of the gas response with a small azimuthal wavenumber is a direct consequence of mode-coupling among linear waves. The presence of multiple Fourier components in a planet's potential is a distinct feature compared to the previous studies in the context of spiral galaxies, which turns out to be crucial for the generation of ultraharmonics waves. This analysis may shed light on the understanding of some results regarding the spiral structures excited by a massive planet.
We investigate how planets interact with viscous accretion disks, in the limit that the disk is sufficiently low mass that the planet migrates more slowly than the disk material. In that case, the ...disk's surface density profile is determined by the disk being in viscous steady state (VSS) while overflowing the planet's orbit. We compute the VSS profiles with 2D hydrodynamical simulations, and show that disk material piles up behind the planet, with the planet effectively acting as a leaky dam. Previous 2D hydrodynamical simulations missed the pileup effect because of incorrect boundary conditions, while previous 1D models greatly overpredicted the pileup due to the neglect of nonlocal deposition. Our simulations quantify the magnitude of the pileup for a variety of planet masses and disk viscosities. We also calculate theoretically the magnitude of the pileup for moderately deep gaps, showing good agreement with simulations. For very deep gaps, current theory is inadequate, and we show why and what must be understood better. The pileup is important for two reasons. First, it is observable in directly imaged protoplanetary disks, and hence can be used to diagnose the mass of a planet that causes it or the viscosity within the disk. Second, it determines the planet's migration rate. Our simulations determine a new Type-II migration rate (valid for low-mass disks), and show how it connects continuously with the well-verified Type-I rate.
Accretion disks around stars, or other central massive bodies, can support long-lived, slowly precessing m = 1 disturbances in which the fluid motion is nearly Keplerian with non-zero eccentricity. ...We study such "slow modes" in disks that are subject to both pressure and self-gravity forces. We derive a second-order WKB dispersion relation that describes the dynamics quite accurately and show that the apparently complicated nature of the various modes can be understood in a simple way with the help of a graphical method. We also solve the linearized fluid equations numerically and show that the results agree with the theory. We find that when self-gravity is weak ( , where Q is Toomre's parameter and h is the disk aspect ratio), the modes are pressure-dominated. But when self-gravity is strong ( ), two kinds of gravity-dominated modes appear: one is an aligned elliptical pattern and the other is a one-armed spiral. In the context of protoplanetary disks, we suggest that if the radial eccentricity profile can be measured, it could be used to determine the total disk mass.
Accretion disks can be eccentric: they support m = 1 modes that are global and slowly precessing. But whether the modes remain trapped in the disk-and hence are long-lived-depends on conditions at ...the outer edge of the disk. Here we show that in disks with realistic boundaries, in which the surface density drops rapidly beyond a given radius, eccentric modes are trapped and hence can live for as long as the viscous time. We focus on pressure-only disks around a central mass, and show how this result can be understood with the help of a simple second-order WKB theory. We show that the longest-lived mode is the zero-node mode in which all of the disk's elliptical streamlines are aligned, and that this mode decays coherently on the viscous timescale of the disk. Hence, such a mode, once excited, could live as long as the lifetime of the disk. It may be responsible for asymmetries seen in recent images of protoplanetary disks.
The line width of ions has been observed to be systematically narrower than that of the coexisting neutrals in molecular clouds and been interpreted as the signature of the decoupling of the neutral ...turbulence from magnetic fields in partially ionized medium. As a sequel of Li & Houde, here we present further observational evidence that supports these earlier proposals with the velocity coordinate spectrum analysis. We recover the turbulent energy spectra of HCN and HCO+ (4 − 3) in a starless molecular cloud in NGC 6334 where magnetic fields play a dynamically important role. Our analysis showed that the neutral spectrum is consistent with Kolmogorov type ( k − 5 3 , where k is the wavenumber), while that of the ions is the same on the large scale, but steeper (∼k−2), for scales smaller than 0.404 pc. We carefully ruled out the possibilities that the spectrum difference can stem from the differences of ion and neutral optical depth and hyperfine structure.
ABSTRACT Excitation and propagation of waves in a thermally stratified disk with an arbitrary vertical temperature profile are studied. Previous analytical studies of three-dimensional waves had been ...focused on either isothermal or polytropic vertical disk structures. However, at the location in a protoplanetary disk where the dominant heating source is stellar irradiation, the temperature gradient may become positive in the vertical direction. We extend the analysis to study the effects of the vertical temperature structure on the waves that are excited at the Lindblad resonances. For a hotter disk atmosphere, the f-mode contributes less to the torque and remains confined near the midplane as it propagates away from the resonances. On the other hand, the excitation of the g-modes is stronger. As they propagate, they channel to the top of disk atmosphere and their group velocities decrease. The differences compared to previous studies may have implications in understanding the wave dynamics in a realistic disk structure.
The resource burden of healthcare disputes and medico-legal claims has been rising. A dispute resolution system operating at the hospital level could ameliorate this disturbing trend. This is a ...retrospective observational study on patient complaints and medico-legal cases received by the dispute resolution unit of an acute tertiary hospital from 2011 to 2015. We described the characteristics and analysed the resolution methodology and outcomes of all closed medico-legal cases. Patient complaints significantly increased at a compound annual growth rate (CAGR) of 4.2% (p<0.01), while medico-legal cases and ex-gratia payments for case settlements decreased at CAGRs of 4.8% (p<0.05) and 15.9% (p = 0.19), respectively. Out of 237 closed medico-legal cases, 88.6% were resolved without legal action, of which 78.1% were closed without any ex-gratia payments or waivers. Of the 11.4% of medico-legal cases that involved legal action, 66.7% were settled without ex-gratia payments or waivers. The primary resolution modes were the Patient Relations Service (PRS)'s engagement of the complainants and facilitation of written replies. No cases were brought to court. Cases were more likely resolved without legal action when there was engagement by the PRS (p = 0.009). These cases incurred a lower median settlement value than those with legal action. Our hospital-based dispute resolution system which addressed patients' core dissatisfactions and providers' perspectives, through a process of early engagement, open disclosure, and fair negotiations, was able to promote claims resolution before legal action was taken. This early dispute resolution strategy contained costs and maintained provider-patient relationships and complements system-level mediation and arbitration to reduce medico-legal litigation.
In this paper, we study the feathering substructures along spiral arms by considering the perturbational gas response to a spiral shock. Feathers are density fluctuations that jut out from the spiral ...arm to the interarm region at pitch angles given by the quantum numbers of the doubly periodic structure. In a localized asymptotic approximation, related to the shearing sheet except that the inhomogeneities occur in space rather than in time, we derive the linearized perturbation equations for a razor-thin disk with turbulent interstellar gas, frozen-in magnetic field, and gaseous self-gravity. Apart from the modal quantum numbers, the individual normal modes of the system depend on seven dimensionless quantities that characterize the underlying time-independent axisymmetric state plus its steady, nonlinear, two-armed spiral-shock response to a hypothesized background density wave supported by the disk stars of the galaxy. We show that some of these normal modes have positive growth rates. Their overdensity contours in the post-shock region are very reminiscent of observed feathering substructures in full magnetohydrodynamic simulations. The feathering substructures are parasitic instabilities intrinsic to the system; thus, their study not only provides potential diagnostics for important parameters that characterize the interstellar medium of external galaxies, but also yields a deeper understanding of the basic mechanism that drives the formation of the giant molecular clouds and the OB stars that outline observed grand-design spirals.
•Loss of function of TREM2 during systemic infection leads to an increased number of microglial cells in thalamus after inoculation.•Loss of function of TREM2 during systemic infection does not lead ...to increased expression of pro-inflammatory genes in the brain.•The role of TREM2 in the neuro-inflammatory response following systemic infection appears to be limited in our experiments.
Systemic infection is an important risk factor for delirium, associated with neurodegeneration and subsequent cognitive impairment in older people. Microglial cell response is a known key player in this process and we hypothesize that the triggering receptor expressed on myeloid cells 2 (TREM2) plays an important role in the regulation of this response.
8- to 10-week old male wild-type (WT) and TREM2 knock-out (Trem2-/-) mice were intraperitoneally inoculated with live Escherichia coli (E. coli) or saline. After inoculation, all mice were treated with ceftriaxone (an antimicrobial drug) at 12 and 24 h and were sacrificed after 2 and 3 days. Microglial response was determined by immunohistochemical staining with an ionized calcium-binding adaptor molecule 1 (Iba-1) antibody and flow cytometry. mRNA expression of pro- and anti-inflammatory mediators was measured to quantify the inflammatory response.
We observed increased Iba-1 positive cells number in thalamus of Trem2-/- mice at 3d after inoculation compared to WT mice (mean 120 cell/mm2 SD 8 vs 105 cell/mm2 SD 11; p = 0.03). Flow cytometry showed no differences in forward scatter or expression of CD11b, CD45 and CD14 between WT and Trem2-/- mice. The brain mRNA expression levels of tumor necrosis factor alpha (TNF-α) of Trem2-/- mice at 2d were higher compared to WT mice (p = 0.003). Higher mRNA expression of interleukin 1 beta (IL-1β), Iba-1, CD11b and mitogen-activated protein kinase 1 (MAPK-1) was found in brain of WT mice at 2d compared to Trem2-/- mice (respectively p = 0.02; p = 0.001; p = 0.03 and p = 0.02). In spleen there were no differences in inflammatory mediators, between WT and Trem2-/- mice.
Although the loss of function of TREM2 during systemic infection led to an increased number of activated microglia in the thalamus, we did not observe a consistent increase in expression of inflammatory genes in the brain. The role of TREM2 in the neuro-inflammatory response following systemic infection therefore appears to be limited.
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