10,272 research outputs found
Modification of the MOOG spectral synthesis codes to account for Zeeman broadening of spectral lines
In an attempt to widen access to the study of magnetic fields in stellar
astronomy, I present MOOGStokes, a version of the MOOG one-dimensional LTE
radiative transfer code, overhauled to incorporate a Stokes vector treatment of
polarized radiation through a magnetic medium. MOOGStokes is a suite of three
complementary programs, which together can synthesize the disk-averaged
emergent spectrum of a star with a magnetic field. The first element (a
pre-processing script called CounterPoint) calculates for a given magnetic
field strength, wavelength shifts and polarizations for the components of
Zeeman sensitive lines. The second element (a MOOG driver called SynStokes
derived from the existing MOOG driver Synth) uses the list of Zeeman shifted
absorption lines together with the existing machinery of MOOG to synthesize the
emergent spectrum at numerous locations across the stellar disk, accounting for
stellar and magnetic field geometry. The third and final element (a
post-processing script called DiskoBall) calculates the disk-averaged spectrum
by weighting the individual emergent spectra by limb darkening and projected
area, and applying the effects of Doppler broadening. All together, the
MOOGStokes package allows users to synthesize emergent spectra of stars with
magnetic fields in a familiar computational framework. MOOGStokes produces
disk-averaged spectra for all Stokes vectors (I, Q, U, and V), normalized by
the continuum. MOOGStokes agrees well with the predictions of INVERS10 a
polarized radiative transfer code with a long history of use in the study of
stellar magnetic fields. In the non-magnetic limit, MOOGStokes also agrees with
the predictions of the scalar version of MOOG.Comment: 10 pages, 4 figures Accepted for publication by the Astronomical
Journal. Code and tutorial available at http://www.mpia.de/~dee
Truth, Inquiry and Democratic Authority in the Climate Debate
Recent attempts to legislate climate science out of existence raises the question of whether citizens are obliged to obey such laws. The authority of democratic law is rooted in both truth and popular consent, but neither is sufficient and they may conflict. These are reconciled in theory and, more importantly, in practice once we incorporate insights from the pragmatist theory of inquiry
Supergravitational Conformal Galileons
The worldvolume actions of 3+1 dimensional bosonic branes embedded in a
five-dimensional bulk space can lead to important effective field theories,
such as the DBI conformal Galileons, and may, when the Null Energy Condition is
violated, play an essential role in cosmological theories of the early
universe. These include Galileon Genesis and "bouncing" cosmology, where a
pre-Big Bang contracting phase bounces smoothly to the presently observed
expanding universe. Perhaps the most natural arena for such branes to arise is
within the context of superstring and -theory vacua. Here, not only are
branes required for the consistency of the theory, but, in many cases, the
exact spectrum of particle physics occurs at low energy. However, such theories
have the additional constraint that they must be supersymmetric. This
motivates us to compute the worldvolume actions of supersymmetric
three-branes, first in flat superspace and then to generalize them to
supergravitation. In this paper, for simplicity, we begin the process, not
within the context of a superstring vacuum but, rather, for the conformal
Galileons arising on a co-dimension one brane embedded in a maximally symmetric
bulk space. We proceed to supersymmetrize the associated
worldvolume theory and then generalize the results to supergravity,
opening the door to possible new cosmological scenarios.Comment: 39 pages, 1 figure. Version 4: Typos corrected, minor points on
notation clarifie
Russian Twitter disinformation campaigns reach across the American political spectrum
Evidence from an analysis of Twitter data reveals that Russian social media trolls exploited racial and political identities to infiltrate distinct groups of authentic users, playing on their group identities. The groups affected spanned the ideological spectrum, suggesting the importance of coordinated counter-responses from diverse coalitions of users
Numerical simulation of small bubble-big bubble-liquid three-phase flows
Numerical simulations of the small bubble-big bubble-liquid three phase heterogeneous flow\ud
in a square cross-sectioned bubble column were carried out with the commercial CFD\ud
package CFX-4.4 to explore the effect of superficial velocity and inlet dispersed phase\ud
fractions on the flow patterns. The approach of Krishna et al. (2000) was adopted in the\ud
Euler-Euler framework to numerically simulate the gas-liquid heterogeneous flow in bubble\ud
columns. On basis of an earlier study (Zhang et al. 2005), the extended multiphase k - ε\ud
turbulence model (Pfleger and Becker, 2001) was chosen to model the turbulent viscosity in\ud
the liquid phase and implicitly account for the bubble-induced turbulence. The obtained\ud
results suggest that, first of all, the extended multiphase k - ε turbulence model of Pfleger and\ud
Becker (2001) is capable of capturing the dynamics of the heterogeneous flow. With\ud
increasing superficial velocity, the dynamics of the flow, as well as the total gas hold-up\ud
increases. It is observed that with increasing inlet phase fraction of the big bubbles, the total\ud
gas holdup decreases while the dynamic nature of the flow increases, which indicates that the\ud
small bubble phase mainly determines the total gas holdup while the big bubble phase\ud
predominantly agitates the liquid
Detailed modeling of hydrodynamics mass transfer and chemical reactions in a bubble column using a discrete bubble model
A 3D discrete bubble model is adopted to investigate complex behavior involving hydrodynamics, mass transfer and chemical reactions in a gas¿liquid bubble column reactor. In this model a continuum description is adopted for the liquid phase and additionally each individual bubble is tracked in a Lagrangian framework, while accounting for bubble¿bubble and bubble¿wall interactions via an encounter model. The mass transfer rate is calculated for each individual bubble using a surface renewal model accounting for the instantaneous and local properties of the liquid phase in its vicinity. The distributions in space of chemical species residing in the liquid phase are computed from the coupled species balances considering the mass transfer from bubbles and reactions between the species. The model has been applied to simulate chemisorption of CO2 bubbles in NaOH solutions. Our results show that apart from hydrodynamics behavior, the model is able to predict the bubble size distribution as well as temporal and spatial variations of each chemical species involved
Comparison of PIV measurements and a discrete particle model in a rectangular 3D spout-fluid bed
Particle image velocimetry and a 3D hard sphere discrete particle model were applied to determine particle velocity profiles in the plane around a spout in a spoutfluid bed for various initial bed heights, spout and background fluidization velocities. Comparison between experimental and numerical results revealed that the particle velocities are underestimated by particle image velocimetry, which is probably caused by steep velocity gradients, and overestimated by the model, which is\ud
probably caused by the closure for fluid-particle drag
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