5,359 research outputs found
Numerical Simulations of Radiatively-Driven Dusty Winds
[abridged] Radiation pressure on dust grains may be an important mechanism in
driving winds in a wide variety of astrophysical systems. However, the
efficiency of the coupling between the radiation field and the dusty gas is
poorly understood in environments characterized by high optical depths. We
present a series of idealized numerical experiments, performed with the
radiation-hydrodynamic code ORION, in which we study the dynamics of such winds
and quantify their properties. We find that, after wind acceleration begins,
radiation Rayleigh-Taylor instability forces the gas into a configuration that
reduces the rate of momentum transfer from the radiation field to the gas by a
factor ~ 10 - 100 compared to an estimate based on the optical depth at the
base of the atmosphere; instead, the rate of momentum transfer from a driving
radiation field of luminosity L to the gas is roughly L/c multiplied by one
plus half the optical depth evaluated using the photospheric temperature, which
is far smaller than the optical depth one would obtain using the interior
temperature. When we apply our results to conditions appropriate to ULIRGs and
star clusters, we find that the asymptotic wind momentum flux from such objects
should not significantly exceed that carried by the direct radiation field,
L/c. This result constrains the expected mass loss rates from systems that
exceed the Eddington limit to be of order the so-called "single-scattering"
limit, and not significantly higher. We present an approximate fitting formula
for the rate of momentum transfer from radiation to dusty gas through which it
passes, which is suitable for implementation in sub-grid models of galaxy
formation. Finally, we provide a first map of the column density distribution
of gas in a radiatively-driven wind as a function of velocity, and velocity
dispersion.Comment: 19 pages, 17 figures, MNRAS in press; some additional discussion
compared to previous version, no changes in conclusion
Bloodied democracy: Duterte and the death of liberal reformism in the Philippines
Since assuming the presidency, Rodrigo R. Duterte has "stuck to his guns" in carrying out his campaign pledge to launch a violent anti-drug campaign. Duterte's presidency was preceded by six years of political stability and high growth under the relatively liberal and supposedly reformist administration of President Benigno "Noynoy" S. Aquino, III. What did voters find so appealing about Duterte given that drugs and criminality were not a major national concern until he launched his candidacy? Unlike previous populist politicians in the post-Marcos Philippines, Duterte's strongest support did not come from the poorest voters but rather from the elite and the middle class who most feared for their personal security. Although Aquino was widely perceived to be personally honest, his administration had become "systemically disjunctive" and vulnerable to replacement by violent illiberalism because its narrative of "good governance" had been undermined, its strategic allies were weakened, and liberal institutions discredited. Duterte is an illiberal populist who changed the prevailing political order into an illiberal one through a new law-and-order governing script, new key strategic groups (the communist left and the police), and the quick removal of remaining liberal constraints (particularly in Congress and the Supreme Court). Duterte constructed a strongman political model at the local level before "nationalising" it after his election as president
Introduction: the early Duterte presidency in the Philippines
After only a little over a half year in power, as of this writing, Rodrigo's R. Duterte presidency already represents a sea change in Philippine politics. Despite the personal popularity of Benigno "Noynoy" S. Aquino III (who had the highest opinion poll ratings among post-Marcos presidents), Duterte has quickly replaced a "liberal reformist" political order with its emphasis on civil liberties, if limited political participation, with an illiberal "law and order" regime
The Maximum Flux of Star-Forming Galaxies
The importance of radiation pressure feedback in galaxy formation has been
extensively debated over the last decade. The regime of greatest uncertainty is
in the most actively star-forming galaxies, where large dust columns can
potentially produce a dust-reprocessed infrared radiation field with enough
pressure to drive turbulence or eject material. Here we derive the conditions
under which a self-gravitating, mixed gas-star disc can remain hydrostatic
despite trapped radiation pressure. Consistently taking into account the
self-gravity of the medium, the star- and dust-to-gas ratios, and the effects
of turbulent motions not driven by radiation, we show that galaxies can achieve
a maximum Eddington-limited star formation rate per unit area
pc Myr,
corresponding to a critical flux of
kpc similar to previous estimates; higher fluxes eject mass in bulk,
halting further star formation. Conversely, we show that in galaxies below this
limit, our one-dimensional models imply simple vertical hydrostatic equilibrium
and that radiation pressure is ineffective at driving turbulence or ejecting
matter. Because the vast majority of star-forming galaxies lie below the
maximum limit for typical dust-to-gas ratios, we conclude that infrared
radiation pressure is likely unimportant for all but the most extreme systems
on galaxy-wide scales. Thus, while radiation pressure does not explain the
Kennicutt-Schmidt relation, it does impose an upper truncation on it. Our
predicted truncation is in good agreement with the highest observed gas and
star formation rate surface densities found both locally and at high redshift.Comment: Version accepted for publication in MNRAS. 12 pages, 8 figures. New
appendix on photon tirin
The applicability of self-regulation theories in sport : goal adjustment capacities, stress appraisals, coping and well-being among athletes
Objectives: We examined a model, informed by self-regulation theories, which included goal adjustment capacities, appraisals of challenge and threat, coping, and well-being. Design: Prospective. Methods: Two hundred and twelve athletes from the United Kingdom (n = 147) or Australia (n = 65), who played team (n = 135) or individual sports (n = 77), and competed at international (n = 7), national (n = 11), county (n = 67), club (n = 84), or beginner (n = 43) levels participated in this study. Participants completed measures of goal adjustment capacities and stress appraisals two days before competing. Athletes also completed questions on coping and well-being within three hours of their competition ending. Results: The way an athlete responds to an unattainable goal is associated with his or her well-being in the period leading up to and including the competition. Goal reengagement positively predicted well-being, whereas goal disengagement negatively predicted well-being. Further, goal reengagement was positively associated with challenge appraisals, which in turn was linked to task-oriented coping, and task-oriented coping positively associated with well-being. Conclusion: When highly-valued goals become unattainable, consultants could encourage athletes to seek out alternative approaches to achieve the same goal or help them develop a completely new goal
Sales Loss Determination in Food Contamination Incidents: An Application to Milk Bans in Hawaii
This article presents a procedure for estimating sales loss following a food contamination incident with application to the case of heptachlor contamination of fresh fluid milk in Oahu, Hawaii in 1982. A major finding is that media coverage following the incident had a significant impact on milk purchases and that negative coverage had a larger effect than positive coverage. This conclusion implies that public statements by producers or government to assure the public of safe food supplies may be ineffective in restoring consumer confidence following the discovery of a food safety problem. American Journal of Agricultural Economics, August, 1988.food contamination, food safety policy, milk demand, Food Consumption/Nutrition/Food Safety,
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Effective interaction between monolayers of block copolymer compatiblizer in a polymer blend
The stability of ternary blends of two immiscible homopolymers and a block copolymer compatiblizer depends crucially on the effective interaction between the copolymermonolayers that form between the unlike homopolymer domains. Here, the interaction is calculated for blends involving A and B homopolymers of equal size with ABABdiblock copolymers of symmetric composition using both self-consistent field theory (SCFT) and strong-segregation theory (SST). If the homopolymers are larger than the copolymer molecules, an attractive interaction is predicted which would destroy the blend. This conclusion coupled with considerations regarding the elastic properties of the monolayer suggests that the optimum size of the homopolymer molecules is about 80% that of the copolymer molecule. A detailed examination of the theory demonstrates that the attraction results from the configurational entropy loss of the homopolymer molecules trapped between the copolymermonolayers. We conclude by suggesting how the monolayers can be altered in order to suppress this attraction and thus improve compatiblization
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