13,549 research outputs found
Three-Dimensional Navier-Stokes Simulation of Space Shuttle Main Propulsion 17-inch Disconnect Valves
A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle external tank/orbiter propellant feed line disconnect flapper valves with upstream elbows. The Navier-Stokes code, INS3D, is modified to handle interior obstacles and a simple turbulence model. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 million. The predicted hydrodynamical stability of the flappers correlates well with the measurements
Linear response to leadership, effective temperature and decision making in flocks
Large collections of autonomously moving agents, such as animals or
micro-organisms, are able to 'flock' coherently in space even in the absence of
a central control mechanism. While the direction of the flock resulting from
this critical behavior is random, this can be controlled by a small subset of
informed individuals acting as leaders of the group. In this article we use the
Vicsek model to investigate how flocks respond to leadership and make
decisions. Using a combination of numerical simulations and continuous modeling
we demonstrate that flocks display a linear response to leadership that can be
cast in the framework of the fluctuation-dissipation theorem, identifying an
'effective temperature' reflecting how promptly the flock reacts to the
initiative of the leaders. The linear response to leadership also holds in the
presence of two groups of informed individuals with competing interests,
indicating that the flock's behavioral decision is determined by both the
number of leaders and their degree of influence.Comment: 8 pages (incl. supplementary information), 8 figures, Supplementary
movies can be found at
http://wwwhome.lorentz.leidenuniv.nl/~giomi/sup_mat/20151108
On the structure of the scalar mesons and
We investigate the structure of the scalar mesons and
within realistic meson-exchange models of the and
interactions. Starting from a modified version of the J\"ulich model for
scattering we perform an analysis of the pole structure of the
resulting scattering amplitude and find, in contrast to existing models, a
somewhat large mass for the ( MeV,
MeV). It is shown that our model provides a description of
data comparable in quality with those of
alternative models. Furthermore, the formalism developed for the
system is consistently extended to the interaction leading to a
description of the as a dynamically generated threshold effect
(which is therefore neither a conventional state nor a
bound state). Exploring the corresponding pole position the
is found to be rather broad ( MeV,
MeV). The experimentally observed smaller width results from the influence of
the nearby threshold on this pole.Comment: 25 pages, 15 Postscript figure
Lattice realizations of unitary minimal modular invariant partition functions
The conformal spectra of the critical dilute A-D-E lattice models are studied
numerically. The results strongly indicate that, in branches 1 and 2, these
models provide realizations of the complete A-D-E classification of unitary
minimal modular invariant partition functions given by Cappelli, Itzykson and
Zuber. In branches 3 and 4 the results indicate that the modular invariant
partition functions factorize. Similar factorization results are also obtained
for two-colour lattice models.Comment: 18 pages, Latex, with minor corrections and clarification
Preliminary data on boulders at station 6, Apollo 17 landing site
A cluster of boulders at Station 6 (Apollo 17 landing site) consists of breccias derived from the North Massif. Three preliminary lithologic units were established, on the basis of photogeologic interpretations; all lithologies identified photogeologically were sampled. Breccia clasts and matrices studied petrographically and chemically fall into two groups by modal mineralogy: (1) low-K Fra Mauro or high basalt composition, consisting of 50-60% modal feldspar, approximately 45% orthopyroxene and 1-7% Fe-Ti oxide; (2) clasts consisting of highland basalt composition, consisting of 70% feldspar, 30% orthopyroxene and olivine and a trace of Fe-Ti oxide
Prospective Investigation of Pesticide Applicators' Health (PIPAH) study: a cohort study of professional pesticide users in Great Britain
PURPOSE: The purpose of the study is to monitor the exposure and health of workers in Great Britain who use pesticides as a part of their job, and to gain a better understanding of the relationship between long-term exposure to pesticides and health. PARTICIPANTS: Study participants are professional pesticide users who are certified in the safe use of pesticides or who were born before 1965 and apply pesticides under 'grandfather rights'. Overall response rate was 20%; participants are mostly male (98%) and the average age is 54 years, ranging from 17 to over 80 years. FINDINGS TO DATE: Participants have completed a baseline general questionnaire and three follow-up questionnaires on the use of pesticides. These data will enable investigations into the relationship between occupational pesticide exposure and health outcomes taking into account non-occupational confounding factors. FUTURE PLANS: There is no set end date for data collection. Recruitment into the cohort will continue, and for the foreseeable future there will be annual pesticide use questionnaires and five yearly follow-up general questionnaires.The intention is to validate the pesticide use questionnaire, and to develop a crop/job exposure matrix (C/JEM) which can be updated regularly. This C/JEM will be able to look at general categories of pesticide, such as insecticides, structurally related pesticides, such as organochlorines, or individual active ingredients. Data collected on use of personal protective equipment and method of application will provide information on how potential exposure to pesticide during application may have been modified. The study will be able to estimate changes in individual pesticide use over time, and to examine the associations between pesticide use and both baseline and long-term health outcomes.The cohort members will be linked to national databases for notification of hospital episode statistics, cancer incidence and mortality for follow-up of health outcomes
An experimental and analogue study of iron release from red sandstones
The Jurassic Entrada sandstone at Salt Wash Graben, Utah, USA, a red sandstone contains significant rock bleaching. The cause of the bleaching has been thought to be associated with the modern day CO2-rich fluids in the area which present on the surface by utalising the local fractures, some of which are filled with calcite and iron rich minerals (e.g. Jarosite). An experimental study was conducted to determine the cause of the bleaching. CO2 was found not to cause sandstone bleaching. However, the CO2 was found to mobilize significant amounts of iron from the fracture minerals suggesting that this is a possible source of the iron in the modern pore fluids
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