Comments on "Angular Momentum Transport in Quasi-Keplerian Accretion Disks"

Subramanian, Pujari and Becker (2004) claim that the correct expression for the angular momentum transport in an accretion disc, which is proportional to dOmega/dR, can be derived on the basis of the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disc. We study their argument and show that their derivation contains several fundamental errors: 1) the biased choice of the desired formula from an infinite number of formulae; 2) the biased choice of parcel trajectories; and 3) confusion regarding the reference frames. Following 1) we could derive, for example, a (invalid) formula in which the angular momentum transport is proportional to dv_phi/dR, and from 2) we could even prove that the angular momentum transport is either inward or null. We present the correct approach to the problem of angular momentum transport in an accretion disc in terms of mean free path theory.Comment: 9 pages, 2 figures, to appear in Prog. Theor. Phys. Vol.113, No.6, 200

On Kinetic Theory Viscosity in a Rotating Gas

Clarke and Pringle (2004) derived a proper viscosity formula in a rotating gas by applying mean free path theory. We study their argument in detail and show that their result can be derived with a much simpler calculational procedure and physically clearer picture.Comment: 7 pages, 1 figure; Prog. Theor. Phys. Vol. 112, No.

A TVD Scheme using Roe's Flux and the Ambient Boundary Condition

Details of a second-order accurate TVD scheme using the Roe's Riemann solver is described for the three-dimensional Euler equation. The differential equations are discretized using a finite volume formulation. The ambient boundary condition proposed by us is also explained

The Osher Upwind Scheme and its Application to Cosmic Gas Dynamics

Details of the second order Osher scheme for the multi-dimensional Euler equation are presented. The adopted method to attain the second order of accuracy differs from the existing second order formulation by Osher. The present method is easy to be implemented and can be applied to other first order upwind schemes. Two types of numerical integration forms are coded. One is written in the integral form (cell method), and the other is the usual finite-difference form. Both forms work well and can capture strong shocks without any auxiliary artificial damping. The integration form strictly satisfies the flux conservation even on geometrical singular coordinate lines, which inevitably appear in three dimensional calculations with bodies embedded. Hydrodynamic calculations of the interaction between a stellar wind and an accretion flow are performed to demonstrate the ability of the present method

Reexamination of purely physical separation of the phase enriched in noble gases from the Allende meteorite

We have prepared a new sample of the "floating fraction" of the Allende meteorite and have analyzed the elemental and isotopic compositions of the noble gases to examine the properties of the separation technique. The "floating fraction" is the black fine material, which floats on the water during freeze-thaw disaggregation. The floating fraction separated in this study was enriched in noble gases, and its isotopic compositions were very similar to those of chemical residues. We thus confirmed that the physical separation is an effective method to obtain a noble-gas-rich fraction than the chemical treatment. The only major difference between our floating fraction and those previously prepared was that the former had small excesses in ^Ar and ^Xe which were supposed to be due to the contamination from small amounts of silicate like sodalite. There were some variations in the Xe-Q/Xe-HL ratios among floating fractions, suggesting that Q-and HL-components might be separable by a physical process

A laboratory experiment on the influence of aqueous alteration on noble gas compositions in the Allende meteorite

We have carried out a hydrothermal experiment on the Allende CV chondrite, in order to understand the observed noble gas loss from CM and CI chondrites, possibly caused by aqueous alteration on their parent bodies (L. B. Browning et al., Geochim. Cosmochim. Acta, 60,2621,1996; T. Nakamura et al., Geochim. Cosmochim. Acta, 63,257,1999). The Allende meteorite was disaggregated and kept with liquid water in a pressurized vessel under 15 atm of water vapor at 200℃ for a week. The abundances of helium, neon, argon, krypton and xenon in the samples have been measured by stepwise heating technique. The abundances of noble gases were decreased by 24% (He), 27% (Ne), 38% (Ar), 23% (Kr) and 34% (Xe) after the hydrothermal treatment, suggesting that the hot water treatment had contributed to reduce the concentrations of noble gases in Allende. This gas loss also affected the isotopic composition of xenon. For the 1200℃ fraction, the amount of ^Xe-HL was decreased from the sample by about 80% during the hot water treatment, while that of ^Xe-Q was decreased to a lesser extent (∿40%). This result seems to indicate that the carrier of Xe-HL is less resistant to the gas loss by the hot water alteration than phase Q for high temperature components. However, further studies are required as this trend becomes less obvious and rather similar if we take into consideration the xenon of 800℃ fraction

Alkali Elution Behavior of Steelmaking Slag Packed in an Open Channel Vessel in Seawater

The alkali elution behavior of steelmaking slag in seawater was kinetically investigated and simulated under continuous flow in an open channel vessel with packed bed of steelmaking slag. Two types of steelmaking slags, viz. decarburization slag and dephosphorization slag, were used in this study. The alkali elution rate of decarburization slag was larger than that of dephosphorization slag due to larger free CaO content. The pH value for dephosphorization slag was almost the same as the seawater pH value in 3–4 days, whereas that for decarburization slag was stabilized in 3 days although the pH value was slightly larger than that of seawater. The capacity coefficients of alkali elution for dephosphorization and decarburization slags decreased together in an exponential manner with time. Based on a regression equation on the mass transfer capacity coefficient change with time, the alkali elution behavior was simulated and the calculated results agreed well with the experimental ones. The temporal pH change was predicted by changing slag surface area and seawater flow rate as a parameter. According to the simulation results for dephosphorization slag, the seawater pH value did not reach a high level in the ocean area