815 research outputs found
Recent developments in planet migration theory
Planetary migration is the process by which a forming planet undergoes a
drift of its semi-major axis caused by the tidal interaction with its parent
protoplanetary disc. One of the key quantities to assess the migration of
embedded planets is the tidal torque between the disc and planet, which has two
components: the Lindblad torque and the corotation torque. We review the latest
results on both torque components for planets on circular orbits, with a
special emphasis on the various processes that give rise to additional, large
components of the corotation torque, and those contributing to the saturation
of this torque. These additional components of the corotation torque could help
address the shortcomings that have recently been exposed by models of planet
population syntheses. We also review recent results concerning the migration of
giant planets that carve gaps in the disc (type II migration) and the migration
of sub-giant planets that open partial gaps in massive discs (type III
migration).Comment: 52 pages, 18 figures. Review article to be published in "Tidal
effects in Astronomy and Astrophysics", Lecture Notes in Physic
Global Solutions for Incompressible Viscoelastic Fluids
We prove the existence of both local and global smooth solutions to the
Cauchy problem in the whole space and the periodic problem in the n-dimensional
torus for the incompressible viscoelastic system of Oldroyd-B type in the case
of near equilibrium initial data. The results hold in both two and three
dimensional spaces. The results and methods presented in this paper are also
valid for a wide range of elastic complex fluids, such as magnetohydrodynamics,
liquid crystals and mixture problems.Comment: We prove the existence of global smooth solutions to the Cauchy
problem for the incompressible viscoelastic system of Oldroyd-B type in the
case of near equilibrium initial dat
A bayesian multilevel modeling approach for data query in wireless sensor networks
In power-limited Wireless Sensor Network (WSN), it is important to reduce the communication load in order to achieve energy savings. This paper applies a novel statistic method to estimate the parameters based on the realtime data measured by local sensors. Instead of transmitting large real-time data, we proposed to transmit the small amount of dynamic parameters by exploiting both temporal and spatial correlation within and between sensor clusters. The temporal correlation is built on the level-1 Bayesian model at each sensor to predict local readings. Each local sensor transmits their local parameters learned from historical measurement data to their cluster heads which account for the spatial correlation and summarize the regional parameters based on level-2 Bayesian model. Finally, the cluster heads transmit the regional parameters to the sink node. By utilizing this statistical method, the sink node can predict the sensor measurements within a specified period without directly communicating with local sensors. We show that this approach can dramatically reduce the amount of communication load in data query applications and achieve significant energy savings
Towards Controlling the Acceptance Factors for a Collaborative Platform in Engineering Design
International audienceThis paper might serve as a guide to take step towards a better acceptance of computer-based Knowledge management (KM) tools in institutional setting. At first time, it investigates a set of factors with different origins which are proved to have an effect on usage decision. Secondly, we set a list of candidate factor which are supposed to influence future users of a collaborative KM platform (Dimocode). At the end, we develop a methodology to take into account the selected factors and master their positive or negative impacts. The contents of this paper would be an appropriate framework in the way of Knowledge management systems (KMS) deployment
Radiative Corrections to One-Photon Decays of Hydrogenic Ions
Radiative corrections to the decay rate of n=2 states of hydrogenic ions are
calculated. The transitions considered are the M1 decay of the 2s state to the
ground state and the E1(M2) decays of the and states to
the ground state. The radiative corrections start in order , but the method used sums all orders of . The leading
correction for the E1 decays is calculated and compared
with the exact result. The extension of the calculational method to parity
nonconserving transitions in neutral atoms is discussed.Comment: 22 pages, 2 figure
Branch-and-lift algorithm for deterministic global optimization in nonlinear optimal control
This paper presents a branch-and-lift algorithm for solving optimal control problems with smooth nonlinear dynamics and potentially nonconvex objective and constraint functionals to guaranteed global optimality. This algorithm features a direct sequential method and builds upon a generic, spatial branch-and-bound algorithm. A new operation, called lifting, is introduced, which refines the control parameterization via a Gram-Schmidt orthogonalization process, while simultaneously eliminating control subregions that are either infeasible or that provably cannot contain any global optima. Conditions are given under which the image of the control parameterization error in the state space contracts exponentially as the parameterization order is increased, thereby making the lifting operation efficient. A computational technique based on ellipsoidal calculus is also developed that satisfies these conditions. The practical applicability of branch-and-lift is illustrated in a numerical example. © 2013 Springer Science+Business Media New York
The hypocretin neurotransmission system in myotonic dystrophy type 1
BACKGROUND: Patients with myotonic dystrophy type 1 (DM1) frequently have symptoms of excessive daytime sleepiness (EDS). Some patients with DM1 show sleep-onset REM, similar to that observed in narcolepsy. Narcolepsy is characterized by impaired hypocretin (Hcrt) neurotransmission. OBJECTIVE: To test for dysregulation of Hcrt neurotransmission in a prospective cohort of patients with DM1. METHODS: Hcrt levels in CSF were measured by radioimmunoassay. Sleep physiology was assessed by overnight polysomnography (PSG) and a multiple sleep latency test (MSLT). Splicing of Hcrt receptor 1 and 2 (HcrtR1 and HcrtR2) mRNA was examined in postmortem samples of temporal cortex. RESULTS: Seventeen of 38 patients with DM1 reported symptoms of EDS. Among patients with DM1 with EDS who underwent PSG/MSLT, 7 of 13 showed reduced sleep latency, sleep-onset REM, or both. However, CSF Hcrt levels in DM1 (mean 277 pg/mL, n = 38) were not different from controls (mean 277 pg/mL, n = 33). Also, splicing of HcrtR1 and HcrtR2 mRNA in patients with DM1 was similar to controls. CONCLUSIONS: Excessive daytime sleepiness and dysregulation of REM sleep occur frequently in patients with myotonic dystrophy type 1 (DM1). However, the pathophysiologic basis is distinct from narcolepsy, as patients with DM1 do not have a consistent defect of Hcrt release or receptor splicing
Anomalous diffusion and the first passage time problem
We study the distribution of first passage time (FPT) in Levy type of
anomalous diffusion. Using recently formulated fractional Fokker-Planck
equation we obtain three results. (1) We derive an explicit expression for the
FPT distribution in terms of Fox or H-functions when the diffusion has zero
drift. (2) For the nonzero drift case we obtain an analytical expression for
the Laplace transform of the FPT distribution. (3) We express the FPT
distribution in terms of a power series for the case of two absorbing barriers.
The known results for ordinary diffusion (Brownian motion) are obtained as
special cases of our more general results.Comment: 25 pages, 4 figure
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