Stability of the viscously spreading ring

We study analytically and numerically the stability of the pressure-less, viscously spreading accretion ring. We show that the ring is unstable to small non-axisymmetric perturbations. To perform the perturbation analysis of the ring we use a stretching transformation of the time coordinate. We find that to 1st order, one-armed spiral structures, and to 2nd order additionally two-armed spiral features may appear. Furthermore, we identify a dispersion relation determining the instability of the ring. The theoretical results are confirmed in several simulations, using two different numerical methods. These computations prove independently the existence of a secular spiral instability driven by viscosity, which evolves into persisting leading and trailing spiral waves. Our results settle the question whether the spiral structures found in earlier simulations of the spreading ring are numerical artifacts or genuine instabilities.Comment: 13 pages, 12 figures; A&A accepte

China’s foreign policy in Afghanistan

Examines China\u27s policy options in Afghanistan once the NATO-led mission there comes to an end in December 2014. Key findings Beijing is unlikely to make any meaningful security commitment to Afghanistan. Instead China will continue to enhance its diplomatic and economic engagement with the country. Beijing views economic engagement as its key contribution to stability in Afghanistan. The type of economic commitment will depend greatly on the security situation, the attitudes of Chinese companies, as well as requests from the Afghan government. Diplomatically, China will strengthen its contact with a range of political groups in Afghanistan including the Taliban, to prevent the country functioning as a haven for Uyghur militants and engage surrounding countries to increase regional cooperation

Circumstellar disks in binary star systems

In this paper we study the evolution of viscous and radiative circumstellar disks under the influence of a companion star. We focus on the eccentric {\gamma} Cephei and {\alpha} Centauri system as examples and compare the disk quantities such as disk eccentricity and precession rate to previous isothermal simulations. We perform two-dimensional hydrodynamical simulations of the binary star systems under the assumption of coplanarity of the disk, host star and binary companion. We use the grid-based, staggered mesh code FARGO with an additional energy equation to which we added radiative cooling based on opacity tables. The eccentric binary companion perturbs the disk around the primary star periodically. Upon passing periastron spirals arms are induced that wind from the outer disk towards the star. In isothermal simulations this results in disk eccentricities up to {\epsilon}_disk ~ 0.2, but in more realistic radiative models we obtain much smaller eccentricities of about {\epsilon}_disk ~ 0.04 - 0.06 with no real precession. Models with varying viscosity and disk mass indicate show that disks with less mass have lower temperatures and higher disk eccentricity. The rather large high disk eccentricities, as indicated in previous isothermal disk simulations, implied a more difficult planet formation in the {\gamma} Cephei system due to the enhanced collision velocities of planetesimals. We have shown that under more realistic conditions with radiative cooling the disk become less eccentric and thus planet formation may be made easier. However, we estimate that the viscosity in the disk has to very small, with {\alpha} \lesssim 0.001, because otherwise the disk's lifetime will be too short to allow planet formation to occur along the core instability scenario. We estimate that the periodic heating of the disk in eccentric binaries will be observable in the mid-IR regime.Comment: 12 pages, 15 figures, accepted for publication in A&

\u3cem\u3eFreedom from Religion Foundation v. Weber\u3c/em\u3e: Must Big Mountain Jesus Come Down from the Hillside?

Does the Freedom from Religion Foundation (“FFRF”) have standing to bring suit? Does the continued authorization of a privately owned statue of Jesus Christ on publicly owned land violate the Establishment Clause when the statue serves some secular purpose and is within the boundaries of a privately operated ski resort

\u3cem\u3ePaschen v. Paschen\u3c/em\u3e: When a Gift Is Not Just a Gift

The guiding principle of child support is “to meet the needs of the child according to the financial ability of the parents.” In Paschen v. Paschen, the Montana Supreme Court reviewed a divorce proceeding that presented a novel child support question: Should gifts factor into determination of maintenance and child support payments? Undermining the guiding principle of child support, a five-justice panel unanimously held gifts should not be a factor

Article V, Section 12 of the Montana Constitution: Restoring Meaning to a Forgotten Provision

The Montana Supreme Court does not—and should not—hesitate to refuse to “march lock-step” with the United States Supreme Court, “even where the state constitutional provision at issue is nearly identical to its federal counterpart.” However, in interpreting Montana’s constitutional restriction on special legislation, the Court has done the opposite, applying a federal constitutional test to a state constitutional provision with no federal counterpart. Article V, Section 12 of the Montana Constitution provides: Local and special legislation. The legislature shall not pass a special or local act when a general act is, or can be made, applicable. Section 12 can and should serve the Legislature and the people as a unique and meaningful protection of the democratic process. This paper explores and advocates for a return to the meaning of Montana’s constitutional restriction on special legislation

A Cost Benefit Study of Banning Leaf Burning in Cedar Falls, Iowa

This paper looks at the issue of leaf burning in the city of Cedar Falls, Iowa from an economic standpoint. It discusses the costs and benefits associated with leaf burning. A cost-benefit analysis was done over a 10 year period. The analysis suggests that a burning ban would be beneficial for Cedar Falls

\u3cem\u3eFreedom from Religion Foundation v. Weber\u3c/em\u3e: Must Big Mountain Jesus Come Down from the Hillside?

Does the Freedom from Religion Foundation (“FFRF”) have standing to bring suit? Does the continued authorization of a privately owned statue of Jesus Christ on publicly owned land violate the Establishment Clause when the statue serves some secular purpose and is within the boundaries of a privately operated ski resort