Migration and Final Location of Hot Super Earths in the Presence of Gas Giants

Based on the conventional sequential-accretion paradigm, we have proposed that, during the migration of first-born gas giants outside the orbits of planetary embryos, super Earth planets will form inside the 2:1 resonance location by sweeping of mean motion resonances (Zhou et al. 2005). In this paper, we study the subsequent evolution of a super Earth (m_1) under the effects of tidal dissipation and perturbation from a first-born gas giant (m_2) in an outside orbit. Secular perturbation and mean motion resonances (especially 2:1 and 5:2 resonances) between m_1 and m_2 excite the eccentricity of m_1, which causes the migration of m_1 and results in a hot super Earth. The calculated final location of the hot super Earth is independent of the tidal energy dissipation factor Q'. The study of migration history of a Hot Super Earth is useful to reveal its Q' value and to predict its final location in the presence of one or more hot gas giants. When this investigation is applied to the GJ876 system, it correctly reproduces the observed location of GJ876d around 0.02AU.Comment: 7 pages, 4 figure

Calculation of Turbulent Subsonic Diffuser Flows Using the NPARC Navier-Stokes Code

Axisymmetric subsonic diffuser flows were calculated with the NPARC Navier-Stokes code in order to determine the effects various code features have on the flow solutions. The code features examined in this work were turbulence models and boundary conditions. Four turbulence models available in NPARC were used: the Baldwin-Lomax algebraic model, the Baldwin-Barth one-equation model, and the Chien kappa-epsilon and Wilcox kappa-omega two-equation models. The three boundary conditions examined were the free boundary, the mass flux boundary and the subsonic outflow with variable static pressure. In addition to boundary condition type, the geometry downstream of the diffuser was varied to see if upstream influences were present. The NPARC results are compared with experimental data and recommendations are given for using NPARC to compute similar flows

Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles

We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. Firstly, aerosol photoemission studies can be performed for many different materials, including liquids. Secondly, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles

Determinants of Performance in Smallholder Farmer Groups in Uganda

The performance of farmer groups is critical for the success of the farmer-led Agricultural Extension approach currently used in Uganda. This study examines factors affecting performance of farmer groups accessing agricultural extension and advisory services from the National Agricultural Advisory Services in Eastern Uganda. The study collected data 200 members of 19 farmer groups in Eastern Uganda. Performance of farmer groups was the dependent variable, which was perceived to be influenced by individual members’ objectives, participation culture, power distance, structure of task, perceived equity, reward allocation and participation in group activities. Farmer group performance had a statistically significant positive relationship with power distance and perceived equity. Group participation culture and structure of tasks had a statistically negative relationship with group performance. Members tended to deflect group losses to factors beyond the seasonality of group activities, quality of farm inputs, and poor training delivered by advisory service providers. The advisory service providers and farmer group members need to use the political and social capital possessed by the local leadership, groups and community members for enhancing support and collective participation of the community in farmer groups. Since farmer groups are a sub-set of wider community, this empirical study brings into perspective the role of community culture in influencing performance of farmer groups in smallholder farming communities

RELAP5 model for advanced neutron source reactor thermal-hydraulic transients, three-element-core design

In order to utilize reduced enrichment fuel, the three-element-core design has been proposed. The proposed core configuration consists of inner, middle, and outer elements, with the middle element offset axially beneath the inner and outer elements, which are axially aligned. The three-element-core RELAP5 model assumes that the reactor hardware is changed only within the core region, so that the loop piping, heat exchangers, and pumps remain as assumed for the two-element-core configuration. However, the total flow rate through the core is greater and the pressure drop across the core is less so that the primary coolant pumps and heat exchangers are operating at a different point in their performance curves. This report describes the new RELAP5 input for the core components

In Vitro Multitissue Interface Model Supports Rapid Vasculogenesis and Mechanistic Study of Vascularization across Tissue Compartments

A significant challenge facing tissue engineers is the design and development of complex multitissue systems, including vascularized tissue-tissue interfaces. While conventional in vitro models focus on either vasculogenesis (de novo formation of blood vessels) or angiogenesis (vessels sprouting from existing vessels or endothelial monolayers), successful therapeutic vascularization strategies will likely rely on coordinated integration of both processes. To address this challenge, we developed a novel in vitro multitissue interface model in which human endothelial colony forming cell (ECFC)-encapsulated tissue spheres are embedded within a surrounding tissue microenvironment. This highly reproducible approach exploits biphilic surfaces (nanostructured surfaces with distinct superhydrophobic and hydrophilic regions) to (i) support tissue compartments with user-specified matrix composition and physical properties as well as cell type and density and (ii) introduce boundary conditions that prevent the cell-mediated tissue contraction routinely observed with conventional three-dimensional monodispersion cultures. This multitissue interface model was applied to test the hypothesis that independent control of cell-extracellular matrix (ECM) and cell-cell interactions would affect vascularization within the tissue sphere as well as across the tissue-tissue interface. We found that high-cell-density tissue spheres containing 5 × 10(6) ECFCs/mL exhibit rapid and robust vasculogenesis, forming highly interconnected, stable (as indicated by type IV collagen deposition) vessel networks within only 3 days. Addition of adipose-derived stromal cells (ASCs) in the surrounding tissue further enhanced vasculogenesis within the sphere as well as angiogenic vessel elongation across the tissue-tissue boundary, with both effects being dependent on the ASC density. Overall, results show that the ECFC density and ECFC-ASC crosstalk, in terms of paracrine and mechanophysical signaling, are critical determinants of vascularization within a given tissue compartment and across tissue interfaces. This new in vitro multitissue interface model and the associated mechanistic insights it yields provide guiding principles for the design and optimization of multitissue vascularization strategies for research and clinical applications

Description of TASHA: Thermal Analysis of Steady-State-Heat Transfer for the Advanced Neutron Source Reactor

This document describes the code used to perform Thermal Analysis of Steady-State-Heat-Transfer for the Advanced Neutron Source (ANS) Reactor (TASHA). More specifically, the code is designed for thermal analysis of the fuel elements. The new code reflects changes to the High Flux Isotope Reactor steady-state thermal-hydraulics code. These changes were aimed at both improving the code`s predictive ability and allowing statistical thermal-hydraulic uncertainty analysis to be performed. A significant portion of the changes were aimed at improving the correlation package in the code. This involved incorporating more recent correlations for both single-phase flow and two-phase flow thermal limits, including the addition of correlations to predict the phenomenon of flow excursion. Since the code was to be used in the design of the ANS, changes were made to allow the code to predict limiting powers for a variety of thermal limits, including critical heat flux, flow excursion, incipient boiling, oxide spallation, maximum centerline temperature, and surface temperature equal to the saturation temperature. Statistical uncertainty analysis also required several changes to the code itself as well as changes to the code input format. This report describes these changes in enough detail to allow the reader to interpret code results and also to understand where the changes were made in the code programming. This report is not intended to be a stand alone report for running the code, however, and should be used in concert with the two previous reports published on the original code. Sample input and output files are also included to help accomplish these goals. In addition, a section is included that describes requirements for a new, more modem code that the project planned to develop

Extrasolar planets and brown dwarfs around A-F type stars - VII. Theta Cygni radial velocity variations: planets or stellar phenomenon?

(abridged) In the frame of the search for extrasolar planets and brown dwarfs around early-type main-sequence stars, we present the results obtained on the early F-type star Theta Cygni. Elodie and Sophie at OHP were used to obtain the spectra. Our dedicated radial-velocity measurement method was used to monitor the star's radial velocities over five years. We also use complementary, high angular resolution and high-contrast images taken with PUEO at CFHT. We show that Theta Cygni radial velocities are quasi-periodically variable, with a ~150-day period. These variations are not due to the ~0.35-Msun stellar companion that we detected in imaging at more than 46 AU from the star. The absence of correlation between the bisector velocity span variations and the radial velocity variations for this 7 km/s vsini star, as well as other criteria indicate that the observed radial velocity variations are not due to stellar spots. The observed amplitude of the bisector velocity span variations also seems to rule out stellar pulsations. However, we observe a peak in the bisector velocity span periodogram at the same period as the one found in the radial velocity periodogram, which indicates a probable link between these radial velocity variations and the low amplitude lineshape variations which are of stellar origin. Long-period variations are not expected from this type of star to our knowledge. If a stellar origin (hence of new type) was to be confirmed for these long-period radial velocity variations, this would have several consequences on the search for planets around main-sequence stars, both in terms of observational strategy and data analysis. An alternative explanation for these variable radial velocities is the presence of at least one planet of a few Jupiter masses orbiting at less than 1 AU. (abridged)Comment: 9 pages, accepted in A

Advanced neutron source reactor conceptual safety analysis report, three-element-core design: Chapter 15, accident analysis

In order to utilize reduced enrichment fuel, the three-element-core design for the Advanced Neutron Source has been proposed. The proposed core configuration consists of inner, middle, and outer elements, with the middle element offset axially beneath the inner and outer elements, which are axially aligned. The three-element-core RELAP5 model assumes that the reactor hardware is changed only within the core region, so that the loop piping, heat exchangers, and pumps remain as assumed for the two-element-core configuration. To assess the impact of changes in the core region configuration and the thermal-hydraulic steady-state conditions, the safety analysis has been updated. This report gives the safety margins for the loss-of-off-site power and pressure-boundary fault accidents based on the RELAP5 results. AU margins are greater for the three-element-core simulations than those calculated for the two-element core