Introducing a hybrid radiative transfer method for smoothed particle hydrodynamics     

Duncan Forgan  Ken Rice  Dimitris Stamatellos  Anthony Whitworth 《Monthly notices of the Royal Astronomical Society》2009,394(2):882-891

A new means of incorporating radiative transfer into smoothed particle hydrodynamics (SPH) is introduced, which builds on the success of two previous methods – the polytropic cooling approximation as devised by Stamatellos et al. and flux-limited diffusion. This hybrid method preserves the strengths of its individual components, while removing the need for atmosphere matching or other boundary conditions to marry optically thick and optically thin regions. The code uses a non-trivial equation of state to calculate temperatures and opacities of SPH particles, which captures the effects of H₂ dissociation, H⁰ ionization, He⁰ and He⁺ ionization, ice evaporation, dust sublimation, molecular absorption, bound-free and free–free transitions and electron scattering. The method is tested in several scenarios, including (i) the evolution of a  0.07 M_⊙  protoplanetary disc surrounding a  0.5 M_⊙  star; (ii) the collapse of a  1 M_⊙  protostellar cloud and (iii) the thermal relaxation of temperature fluctuations in a static homogeneous sphere.  相似文献   

Capelinhos 1957–1958, Faial, Azores: deposits formed by an emergent surtseyan eruption     

P. D. Cole  J. E. Guest  A. M. Duncan  J. -M. Pacheco 《Bulletin of Volcanology》2001,63(2-3):204-220

The 1957–1958 eruption of Capelinhos, Faial island, Azores, involved three periods of surtseyan, hydromagmatic activity: two in 1957 and one in 1958. Deposits from this eruption are exposed both in sea cliffs cut into the flanks of the tuff cone and more distally >1 km from the vent. Five lithofacies are identified: lithofacies I is composed of even thickness beds with laterally continuous internal stratigraphy and is interpreted to have been formed by fallout. Lithofacies II consists of beds with internally discontinuous lenses, and has sand-wave structures that increase in abundance toward the outer margins of the tuff cone. This lithofacies is interpreted as having been deposited from pyroclastic surges. Lithofacies III is composed of mantle-bedded deposits with laterally discontinuous internal stratigraphy. This lithofacies is interpreted to have been formed by hybrid processes where fallout of tephra occurred simultaneously with pyroclastic surges. In the outer flanks of the tuff cone, lithofacies III grades laterally into fallout beds of lithofacies I. Lithofacies IV consists of alternating beds of coarse ash aggregates and non-aggregated fine ash, and is particularly well developed in distal regions. Some of this facies was formed by fallout. Alternating beds also occur plastered against obstacles up to 2 km from the vent, indicating an origin from wet pyroclastic surges. The orientation of plastered tephra indicates that the surges were deflected by topography as they decelerated. The distinction between surge and fallout in distal regions is uncertain because wind-drifted fallout and decelerating surge clouds can generate similar deposits. Lithofacies V consists of scoria lapilli beds interpreted to be fallout from hawaiian-style fire-fountaining in the later stages of the eruption. Juvenile pyroclasts within hydromagmatic deposits are predominantly poorly vesicular (25–60% of clasts <30% vesicles). However, on both micro- and macroscopic scales, there is a wide range in clast vesicularity (up to 70% vesicles) indicating that, although fragmentation was predominantly hydromagmatic, vesiculation and magmatic-volatile-driven fragmentation operated simultaneously.  相似文献   

The creep of potash salt rocks from Saskatchewan     

E. J. Scott Duncan  Emery Z. Lajtai 《Geotechnical and Geological Engineering》1993,11(3):159-184

Summary The results of creep tests on the Esterhazy-and the Patience-Lake-types of potash salt rocks from Saskatchewan, Canada are presented. The investigations involved over 6 years of time-dependent experiments in uniaxial compression using potash from the Rocanville and the Lanigan mines of the Potash Corporation of Saskatchewan. A creep test at a given load would last from 2 to 8 months, with most tests conducted over a 4-month period.Since the yield stress of both types of potash lies between 9 and 11 MPa, there is very little creep below 11 MPa. Between 11 and 13 MPa, creep strain production increases sharply through plastic deformation. Above about 13 MPa, however, plastic creep is dominated by brittle creep caused by microcracking. As a result, the lateral and volume creep strain curves may then display the transient and the steady-state, or all three stages of creep, while the axial strain, which is not affected by microcracking, usually attenuates for the whole duration.Two different interpretations of the results are offered. Identifying the last (the fourth) month of testing with the steady-state model, the stress dependence of the steady-state rate has been established for both rock types. A unimodal rate model for the axial strain and a bimodal model for the lateral strain are suggested. The alternate interpretation proceeds on the assumption that under 13 MPa, both the axial and the lateral strain can be modelled through the power function formulation of transient strain.  相似文献