Trapping of giant-planet cores - I. Vortex aided trapping at the outer dead zone edge

In this paper the migration of a 10 Earth-mass planetary core is investigated at the outer boundary of the dead zone of a protoplanetary disc by means of 2D hydrodynamic simulations done with the graphics processor unit version of the FARGO code. In the dead zone, the effective viscosity is greatly reduced due to the disc self-shielding against stellar UV radiation, X-rays from the stellar magnetosphere and interstellar cosmic rays. As a consequence, mass accumulation occurs near the outer dead zone edge, which is assumed to trap planetary cores enhancing the efficiency of the core-accretion scenario to form giant planets. Contrary to the perfect trapping of planetary cores in 1D models, our 2D numerical simulations show that the trapping effect is greatly dependent on the width of the region where viscosity reduction is taking place. Planet trapping happens exclusively if the viscosity reduction is sharp enough to allow the development of large-scale vortices due to the Rossby wave instability. The trapping is only temporarily, and its duration is inversely proportional to the width of the viscosity transition. However, if the Rossby wave instability is not excited, a ring-like axisymmetric density jump forms, which cannot trap the 10 Earth-mass planetary cores. We revealed that the stellar torque exerted on the planet plays an important role in the migration history as the barycentre of the system significantly shifts away from the star due to highly non-axisymmetric density distribution of the disc. Our results still support the idea of planet formation at density/pressure maximum, since the migration of cores is considerably slowed down enabling them further growth and runaway gas accretion in the vicinity of an overdense region.Comment: 23 pages, 31 figures, accepted for publication in MNRA

Algorithms for Rapidly Dispersing Robot Swarms in Unknown Environments

We develop and analyze algorithms for dispersing a swarm of primitive robots in an unknown environment, R. The primary objective is to minimize the makespan, that is, the time to fill the entire region. An environment is composed of pixels that form a connected subset of the integer grid. There is at most one robot per pixel and robots move horizontally or vertically at unit speed. Robots enter R by means of k>=1 door pixels Robots are primitive finite automata, only having local communication, local sensors, and a constant-sized memory. We first give algorithms for the single-door case (i.e., k=1), analyzing the algorithms both theoretically and experimentally. We prove that our algorithms have optimal makespan 2A-1, where A is the area of R. We next give an algorithm for the multi-door case (k>1), based on a wall-following version of the leader-follower strategy. We prove that our strategy is O(log(k+1))-competitive, and that this bound is tight for our strategy and other related strategies.Comment: 17 pages, 4 figures, Latex, to appear in Workshop on Algorithmic Foundations of Robotics, 200

Experimental Testbeds for ECOSEL: A Market Framework for Private Provision of Forest Ecosystem Services

We attempt to design a market framework (which we call ECOSEL) for private provision of forest ecosystem services. ECOSEL is a non-regulatory framework that uses a voluntary public good provision mechanism (in a form of an auction) in conjunction with a multiobjective optimization algorithm to create a market for forest ecosystem services. It is expected to be attractive to the demand side of the ecosystem service market since only Pareto-efficient bundles of services are offered for auction, and it is expected to be attractive to the supply side as well by creating a source of non-timber income for forest landowners. ECOSEL is capable of flexible response to demand for other relevant dimensions of forest-related environmental amenities such as biodiversity, viewshed or recreational services. Following Roth’s (2002) advice on behavior of economists as “market engineers”, we use both experimental economics to improve the design of the ecosystem services market. Concurrently, we provide experimental evidence on the efficiency and revenue-generating properties of a multi-good subscription game of incomplete information.Environmental Economics and Policy, Marketing,

Topology with Dynamical Overlap Fermions

We perform dynamical QCD simulations with $n_f=2$ overlap fermions by hybrid Monte-Carlo method on $6^4$ to $8^3\times 16$ lattices. We study the problem of topological sector changing. A new method is proposed which works without topological sector changes. We use this new method to determine the topological susceptibility at various quark masses.Comment: 15 pages, 3 figure

Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration

Problems related to the design and control of a mobile planetary vehicle to implement a systematic plan for the exploration of Mars are reported. Problem areas include: vehicle configuration, control, dynamics, systems and propulsion; systems analysis, terrain modeling and path selection; and chemical analysis of specimens. These tasks are summarized: vehicle model design, mathematical model of vehicle dynamics, experimental vehicle dynamics, obstacle negotiation, electrochemical controls, remote control, collapsibility and deployment, construction of a wheel tester, wheel analysis, payload design, system design optimization, effect of design assumptions, accessory optimal design, on-board computer subsystem, laser range measurement, discrete obstacle detection, obstacle detection systems, terrain modeling, path selection system simulation and evaluation, gas chromatograph/mass spectrometer system concepts, and chromatograph model evaluation and improvement

Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration

Problems related to an unmanned exploration of the planet Mars by means of an autonomous roving planetary vehicle are investigated. These problems include: design, construction and evaluation of the vehicle itself and its control and operating systems. More specifically, vehicle configuration, dynamics, control, propulsion, hazard detection systems, terrain sensing and modelling, obstacle detection concepts, path selection, decision-making systems, and chemical analyses of samples are studied. Emphasis is placed on development of a vehicle capable of gathering specimens and data for an Augmented Viking Mission or to provide the basis for a Sample Return Mission

Spinal release of tumour necrosis factor activates c-Jun N-terminal kinase and mediates inflammation-induced hypersensitivity.

BackgroundMounting evidence points to individual contributions of tumour necrosis factor-alpha (TNF) and the c-Jun N-terminal kinase (JNK) pathway to the induction and maintenance of various pain states. Here we explore the role of spinal TNF and JNK in carrageenan-induced hypersensitivity. As links between TNF and JNK have been demonstrated in vitro, we investigated if TNF regulates spinal JNK activity in vivo.MethodsTNF levels in lumbar cerebrospinal fluid (CSF) were measured by enzyme-linked immunosorbent assay, spinal TNF gene expression by real-time polymerase chain reaction and TNF protein expression, JNK and c-Jun phosphorylation by western blotting. The role of spinal TNF and JNK in inflammation-induced mechanical and thermal hypersensitivity was assessed by injecting the TNF inhibitor etanercept and the JNK inhibitors SP600125 and JIP-1 intrathecally (i.t.). TNF-mediated regulation of JNK activity was examined by assessing the effect of i.t. etanercept on inflammation-induced spinal JNK activity.ResultsTNF levels were increased in CSF and spinal cord following carrageenan-induced inflammation. While JNK phosphorylation followed the same temporal pattern as TNF, c-jun was only activated at later time points. Intrathecal injection of TNF and JNK inhibitors attenuated carrageenan-induced mechanical and thermal hypersensitivity. TNF stimulation induced JNK phosphorylation in cultured spinal astrocytes and blocking the spinal actions of TNF in vivo by i.t. injection of etanercept reduced inflammation-induced spinal JNK activity.ConclusionsHere we show that spinal JNK activity is dependent on TNF and that both TNF and the JNK signalling pathways modulate pain-like behaviour induced by peripheral inflammation