Formation of giant planets around stars with various masses

We examine the predictions of the core accretion - gas capture model concerning the efficiency of planet formation around stars with various masses. First, we follow the evolution of gas and solids from the moment when all solids are in the form of small grains to the stage when most of them are in the form of planetesimals. We show that the surface density of the planetesimal swarm tends to be higher around less massive stars. Then, we derive the minimum surface density of the planetesimal swarm required for the formation of a giant planet both in a numerical and in an approximate analytical approach. We combine these results by calculating a set of representative disk models characterized by different masses, sizes, and metallicities, and by estimating their capability of forming giant planets. Our results show that the set of protoplanetary disks capable of giant planet formation is larger for less massive stars. Provided that the distribution of initial disk parameters does not depend too strongly on the mass of the central star, we predict that the percentage of stars with giant planets should increase with decreasing stellar mass. Furthermore, we identify the radial redistribution of solids during the formation of planetesimal swarms as the key element in explaining these effects.Comment: Accepted for publication in A&A. 9 pages, 9 figure

Formation of giant planets in disks with different metallicities

We present the first results from simulations of processes leading to planet formation in protoplanetary disks with different metallicities. For a given metallicity, we construct a two-dimensional grid of disk models with different initial masses and radii ($M_0$, $R_0$). For each disk, we follow the evolution of gas and solids from an early evolutionary stage, when all solids are in the form of small dust grains, to the stage when most solids have condensed into planetesimals. Then, based on the core accretion - gas capture scenario, we estimate the planet-bearing capability of the environment defined by the final planetesimal swarm and the still evolving gaseous component of the disk. We define the probability of planet-formation, $P_p$, as the normalized fractional area in the ($M_0$, $\log R_0$) plane populated by disks that have formed planets inside 5 AU. With such a definition, and under the assumption that the population of planets discovered at $R$ $<$ 5 AU is not significantly contaminated by planets that have migrated from $R$ $>$ 5 AU, our results agree fairly well with the observed dependence between the probability that a star harbors a planet and the star's metal content. The agreement holds for the disk viscosity parameter $\alpha$ ranging from $10^{-3}$ to $10^{-2}$, and it becomes much poorer when the redistribution of solids relative to the gas is not allowed for during the evolution of model disks.Comment: Accepted for publication in A&A. 6 pages, 6 figure

The decay of wall-bounded MHD turbulence at low Rm

We present Direct Numerical Simulations of decaying Magnetohydrodynamic (MHD) turbulence at low magnetic Reynolds number. The domain considered is bounded by periodic boundary conditions in the two directions perpendicular to the magnetic field and by two plane Hartmann walls in the third direction. High magnetic fields (Hartmann number of up to 896) are considered thanks to a numerical method based on a spectral code using the eigenvectors of the dissipation operator. It is found that the decay proceeds through two phases: first, energy and integral lengthscales vary rapidly during a two-dimensionalisation phase extending over about one Hartmann friction time. During this phase, the evolution of the former appears significantly more impeded by the presence of walls than that of the latter. Once the large scales are close to quasi-two dimensional, the decay results from the competition of a two-dimensional dynamics driven by dissipation in the Hartmann boundary layers and the three-dimensional dynamics of smaller scales. In the later stages of the decay, three-dimensionality subsists under the form of barrel-shaped structures. A purely quasi-two dimensional decay dominated by friction in the Hartmann layers is not reached, because of residual dissipation in the bulk. However, this dissipation is not generated by the three-dimensionality that subsists, but by residual viscous friction due to horizontal velocity gradients. Also, the energy in the velocity component aligned with the magnetic field is found to be strongly suppressed, as is transport in this direction. This results reproduces the experimental findings of Kolesnikov & Tsinober (1974).Comment: submitted to JF

Average reference recording from the vagal nerve reveals an evoked indirect response

The vagal nerve conveys information from and to many organs, including the heart. The components of the compound action potentials (CAPs) recorded from the vagal nerve give information about the different fiber types present. In this paper, we show that with the average reference recording method an additional component can be measured. This component is missed when using a tripolar recording method. Recordings were made in anesthetized pigs. Results show that there is an indirect component in the CAP of the cervical vagal nerve. This component comes from the periphery most likely from the heart

Atrakcyjnosc polskich miast dla rozwoju outsourcingu i analiza korzysci dla regionu

W krajach zachodnich outsourcing od lat jest integralna czescia wielu biznesow, w Polsce zas coraz czesciej postrzegany jest jako efektywne narzedzie i czesc dlugofalowej strategii rozwoju. Mimo iz Polska stawia pierwsze kroki w tym obszarze, to coraz czesciej wymieniana jest wsrod panstw majacych wielkie szanse na zaistnienie jako jeden ze swiatowych liderow outsourcingu. Do atutow naszego kraju zaliczyc mozna bliskosc geograficzna i kulturowa do rynkow Europy Zachodniej, czlonkostwo w Unii Europejskiej, ciagly przyrost bezposrednich inwestycji zagranicznych oraz wykwalifikowane kadry posiadajace znajomosc roznych jezykow europejskich. Dzieki temu wiele polskich miast moze smialo konkurowac z europejskimi centrami biznesu. Najczesciej wymieniane miasta to Krakow, Warszawa, Wroclaw, lodz oraz Trojmiasto. Analizujac zjawisko outsourcingu w Polsce, nie mozna pominac jego oddzialywania na region, a takze na procesy spoleczne zwiazane np. z zamieszkaniem, ksztalceniem czy dojazdem do pracy. Wsrod najwazniejszych korzysci, jakie wyplywaja z lokowania firm outsourcingowych w naszym kraju, wymienic nalezy przyciaganie kolejnych inwestycji, dodatkowe wplywy do budzetu panstwa z tytulu podatkow, spadek bezrobocia, a takze pobudzanie roznego rodzaju inicjatyw spolecznych.rodzaje outsourcingu, centra outsourcingowe, rozwoj regionu

Radial Distribution of Planets. Predictions based on the Core Accretion Gas Capture Planet formation Model

We have investigated the problem of the distribution of both masses and orbital radii of planets resulting from the gas-accretion, gas-capture model. First we followed the evolution of gas and solids from the moment where all solids are in the form of small grains to the stage when most of them are in the form of planetesimals for a set of different initial masses and sizes of protoplanetary disks. Based on that we performed Monte Carlo calculations describing the formation of giant places at different locations. We included the effects of type II migration and growth of the mass of the planet after the gap opened. We discuss how these effects influence the final distribution of giant planets. We show that when the giant planets are not able to migrate or grow in mass after the gap opens, their distribution is mainly determined by the properties of the gaseous disk. However, with those two effects included, reproducing the parameters of the gaseous disks from the distribution of planets becomes difficult. We also checked the roles of both the material of which the solids consist and the mass of the central star. The main result is that, in disks around less massive stars, giant planets at the given location tend to be less massive. At the same time, the giant planets with the given mass tend to form closer to the less massive stars.Comment: Accepted for publication in A&A. 8 pages, 5 figures. Corrected typo

Models of the formation of the planets in the 47 UMa system

Formation of planets in the 47 UMa system is followed in an evolving protoplanetary disk composed of gas and solids. The evolution of the disk is calculated from an early stage, when all solids, assumed to be high-temperature silicates, are in the dust form, to the stage when most solids are locked in planetesimals. The simulation of planetary evolution starts with a solid embryo of ~1 Earth mass, and proceeds according to the core accretion -- gas capture model. Orbital parameters are kept constant, and it is assumed that the environment of each planet is not perturbed by the second planet. It is found that conditions suitable for both planets to form within several Myr are easily created, and maintained throughout the formation time, in disks with $\alpha \approx 0.01$. In such disks, a planet of 2.6 Jupiter masses (the minimum for the inner planet of the 47 UMa system) may be formed at 2.1 AU from the star in \~3 Myr, while a planet of 0.89 Jupiter masses (the minimum for the outer planet) may be formed at 3.95 AU from the star in about the same time. The formation of planets is possible as a result of a significant enhancement of the surface density of solids between 1.0 and 4.0 AU, which results from the evolution of a disk with an initially uniform gas-to-dust ratio of 167 and an initial radius of 40 AU.Comment: Accepted for publication in A&A. 10 pages, 10 figure