Reversing type II migration: resonance trapping of a lighter giant protoplanet

We present a mechanism related to the migration of giant protoplanets embedded in a protoplanetary disc whereby a giant protoplanet is caught up, before having migrated all the way to the central star, by a lighter outer giant protoplanet. This outer protoplanet may get captured into the 2:3 resonance with the more massive one, in which case the gaps that the two planets open in the disc overlap. Two effects arise, namely a squared mass weighted torque imbalance and an increased mass flow through the overlapping gaps from the outer disc to the inner disc, which both play in favour of an outwards migration. Indeed under the conditions presented here, which describe the evolution of a pair of protoplanets respectively Jupiter and Saturn sized, the migration is reversed, while the planets semi-major axis ratio is constant and the eccentricities are confined to small values by the disc material. The long-term behaviour of the system is briefly discussed, and could account for the high eccentricities observed for the extrasolar planets with semi-major axis a>0.2 AU.Comment: 5 pages, 4 figures. Accepted for publication in MNRA

Characterization of Pump-Induced Acoustics in Space Launch System Main Propulsion System Liquid Hydrogen Feedline Using Airflow Test Data

High intensity acoustic edgetones located upstream of the RS-25 Low Pressure Fuel Turbo Pump (LPFTP) were previously observed during Space Launch System (STS) airflow testing of a model Main Propulsion System (MPS) liquid hydrogen (LH2) feedline mated to a modified LPFTP. MPS hardware has been adapted to mitigate the problematic edgetones as part of the Space Launch System (SLS) program. A follow-on airflow test campaign has subjected the adapted hardware to tests mimicking STS-era airflow conditions, and this manuscript describes acoustic environment identification and characterization born from the latest test results. Fluid dynamics responsible for driving discrete excitations were well reproduced using legacy hardware. The modified design was found insensitive to high intensity edgetone-like discretes over the bandwidth of interest to SLS MPS unsteady environments. Rather, the natural acoustics of the test article were observed to respond in a narrowband-random/mixed discrete manner to broadband noise thought generated by the flow field. The intensity of these responses were several orders of magnitude reduced from those driven by edgetones

On disc driven inward migration of resonantly coupled planets with application to the system around GJ876

We consider two protoplanets gravitationally interacting with each other and a protoplanetary disc. The two planets orbit interior to a tidally maintained disc cavity while the disc interaction indices inward migration. When the migration is slow enough, the more rapidly migrating outer protoplanet approaches and becomes locked in a 2:1 commensurability with the inner one. This is maintained in subsequent evolution. We study this evolution using a simple anaytic model, full hydrodynamic 2D simulations of the disc planet system and longer time N body integrations incorporating simple prescriptions for the effect of the disc on the planet orbits. The eccentricity of the protoplanets are found to be determined by the migration rate induced in the outer planet orbit by the external disc. We apply our results to the recently discovered resonant planets around GJ876. Simulation shows that a disc with parameters expected for protoplanetary discs causes trapping in the 2:1 commensurability when the planets orbit in an inner cavity and that eccentricities in the observed range may be obtained.Comment: 8 pages, 5 figures, submitted to A&A on 30/03/200

Oligarchic and giant impact growth of terrestrial planets in the presence of gas giant planet migration

We present the results of N--body simulations which examine the effect that gas giant planet migration has on the formation of terrestrial planets. The models incorporate a 0.5 Jupiter mass planet undergoing type II migration through an inner protoplanet--planetesimal disk, with gas drag included. Each model is initiated with the inner disk being at successively increased levels of maturity, so that it is undergoing either oligarchic or giant impact style growth as the gas giant migrates. In all cases, a large fraction of the disk mass survives the passage of the giant, either by accreting into massive terrestrial planets shepherded inward of the giant, or by being scattered into external orbits. Shepherding is favored in younger disks where there is strong dynamical friction from planetesimals and gas drag is more influential, whereas scattering dominates in more mature disks where dissipation is weaker. In each scenario, sufficient mass is scattered outward to provide for the eventual accretion of a set of terrestrial planets in external orbits, including within the system's habitable zone. An interesting result is the generation of massive, short period, terrestrial planets from compacted material pushed ahead of the giant. These planets are reminiscent of the short period Neptune mass planets discovered recently, suggesting that such `hot Neptunes' could form locally as a by-product of giant planet migration.Comment: 17 pages, 11 figures, to be published in A&A. Higher resolution pdf available at: http://www.users.globalnet.co.uk/~mfogg/3453fogg.pd

Modeling the resonant planetary system GJ876

The two planets about the star GJ 876 appear to have undergone extensive migration from their point of origin in the protoplanetary disk -- both because of their close proximity to the star (30 and 60 day orbital periods) and because of their occupying three stable orbital resonances at the 2:1 mean-motion commensurability. The resonances were most likely established by converging differential migration of the planets leading to capture into the resonances. A problem with this scenario is that continued migration of the system while it is trapped in the resonances leads to orbital eccentricities that rapidly exceed the observational upper limits of e_1 = 0.31 and e_2 = 0.05. As seen in forced 3-body simulations, lower eccentricities would persist during migration only for an applied eccentricity damping. Here we explore the evolution of the GJ 876 system using two-dimensional hydrodynamical simulations that include viscous heating and radiative effects. We find that a hydrodynamic evolution within the resonance, where only the outer planet interacts with the disk, always rapidly leads to large values of eccentricities that exceed those observed. Only if mass is removed from the disk on a time scale of the order of the migration time scale (before there has been extensive migration after capture), as might occur for photoevaporation in the late phases of planet formation, can we end up with eccentricities that are consistent with the observations.Comment: Paper accepted by A&A, 17 Pages, 17 Figure

The grinch who stole wisdom

Dr. Seuss is wise. How the Grinch Stole Christmas (Seuss, 1957) could serve as a parable for our time. It can also be seen as a roadmap for the development of contemplative wisdom. The abiding popularity of How the Grinch Stole Christmas additionally suggests that contemplative wisdom is more readily available to ordinary people, even children, than is normally thought. This matters because from the point of view of contemplatives in any of the world's philosophies or religions, people are confused about wisdom. The content of the nascent field of wisdom studies, they might say, is largely not wisdom at all but rather what it's like to live in a particular kind of prison cell, a well appointed cell perhaps, but not a place that makes possible either personal satisfaction or deep problem solving. I believe that what the contemplative traditions have to say is important; they offer a different orientation to what personal wisdom is, how to develop it, and how to use it in the world than is presently contained in either our popular culture or our sciences. In order to illustrate this I will examine, in some detail, one contemplative path within Buddhism. Buddhism is particularly useful in this respect because its practices are nontheistic and thus avoid many of the cultural landmines associated with the contemplative aspects of Western religions

From Loom to Machine: Tibetan Aprons and the Configuration of Place

In this paper I examine how objects become connected to place in complex and contradictory ways. Over the past ten to fi fteen years, rapid transformations in Chinese manufacturing and transportation networks have signifi cantly altered the production, marketing, and consumption of commodities made in the Tibet Autonomous Region and traded in Kalimpong, India, and Kathmandu, Nepal. In an attempt to connect the ethnographic study of material culture with more macrolevel processes of geoeconomic change, I begin the piece with an examination of the changing production, materials, and styles of a very specifi c commodity, the Tibetan women’s apron. I then explore traders’ narratives about the values of handmade, machine-made, wool, and synthetic commodities, arguing that we ought to look beyond dichotomies of ‘old’ versus ‘new’ or ‘authentic’ versus ‘inauthentic’ objects to show in detail how the attachment of commodities to representations of place fi gures importantly in the contemporary study both of globalization and uneven development. Finally, I suggest that Karl Marx’s notion of dead labor is useful in analyzing the recent move towards the revitalization of Tibetan wool for both the domestic Chinese industry and the global tourist industry

The development of endomycorrhizal root systems VIII. Effects of soil phosphorus and fungal colonization on the concentration of soluble carbohydrates in roots

Concentrations of phosphorus in shoot and soluble carbohydrates (fructose, glucose, sucrose and fructans) in root were measured in non-mycorrhizal and vesicular-arbuscular (VA) mycorrhizal (Glomus mosseae) leek plants (Allium porrum) raised at six concentrations of soil phosphate. In conditions when an increased concentration of soil phosphate reduced VA mycorrhizal infection, the concentrations of soluble carbohydrates in the root were at a maximum. Therefore the hypothesis that greater concentrations of soluble carbohydrates in roots favour VA mycorrhizal infection is discounted. There was a specific effect of VA mycorrhizas, in that infected roots contained a larger concentration of sucrose than did uninfected roots, in plants with similar phosphorus concentrations in dry matter of shoots. We conclude, first, that increased phosphorus supply from either phosphate addition to soil or VA mycorrhizal infection increases concentration of soluble carbohydrates in leek roots and, secondly, that the VA mycorrhizal root behaves as a particularly strong physiological sink when there is an excess concentration of sucrose in the host

A Review of Interventions to Reduce Mechanical Restraint and Seclusion among Adult Psychiatric Inpatients

Objective: This review examines nature and effectiveness of interventions to reduce the use of mechanical restraint and seclusion among adult psychiatric inpatients. Method: Electronic searches were conducted to locate post-1960 empirical studies of restraint and seclusion reduction in English. A total of 36 studies were identified, mostly from the USA. Analysis was conducted using a structured data extraction tool. Results: The majority of studies reported reduced levels or mechanical restraint and/or seclusion, but the standard of evidence was poor. There were no randomised trials. Most were retrospective studies of official records before and after the intervention was introduced, with varying follow-up periods. The interventions were diverse, but tended to include one or more of the following: new restraint and/or seclusion policies, staffing changes, staff training, review procedures and crisis management initiatives. The research was unable to address which of these elements was most effective. There was also evidence that some improved outcomes were achieved by substituting restraint or seclusion for each other or for alternatives forms of containment (medication in particular). Nurses’ attitudes, skills and approach to patient care were absent from the literature. Conclusions: Interventions probably can reduce the use of restraint and seclusion, but better designed research is required to demonstrate their effectiveness conclusively. More attention should also be paid to understanding how interventions work, particularly from the perspective of nursing staff. This is essential to the successful implementation of restraint and seclusion interventions across different psychiatric settings and treatment populations