Viscous diffusion and photoevaporation of stellar disks

The evolution of a stellar disk under the influence of viscous evolution, photoevaporation from the central source, and photoevaporation by external stars is studied. We take the typical parameters of TTSs and the Trapezium Cluster conditions. The photoionizing flux from the central source is assumed to arise both from the quiescent star and accretion shocks at the base of stellar magnetospheric columns, along which material from the disk accretes. The accretion flux is calculated self-consistently from the accretion mass loss rate. We find that the disk cannot be entirely removed using only viscous evolution and photoionization from the disk-star accretion shock. However, when FUV photoevaporation by external massive stars is included the disk is removed in 10^6 -10^7yr; and when EUV photoevaporation by external massive stars is included the disk is removed in 10^5 - 10^6yr. An intriguing feature of photoevaporation by the central star is the formation of a gap in the disk at late stages of the disk evolution. As the gap starts forming, viscous spreading and photoevaporation work in resonance. There is no gap formation for disks nearby external massive stars because the outer annuli are quickly removed by the dominant EUV flux. On the other hand, at larger, more typical distances (d>>0.03pc) from the external stars the flux is FUV dominated. As a consequence, the disk is efficiently evaporated at two different locations; forming a gap during the last stages of the disk evolution.Comment: 27 pages, 11 figures, accepted for publication in Ap

Impacts of Dreissena polymorpha on vertical mobility of Campeloma decisum, and susceptibility on shell morphology

Natural History & EvolutionDreissena polymorpha, zebra mussel is an invasive species that alter aquatic ecosystem and can indirectly cause extinction in native invertebrate populations. As a result, they cause a lot of ecological and economic damage to the environment. The mussels recently appeared in Douglas Lake, MI. Campeloma decisum, a snail that is native to the lake, is getting colonized very rapidly. The purpose of this study was to figure out whether some snail characteristics make them susceptible to zebra mussels and to re-examine zebra mussel s influence over Campeloma mobility. Two random samples of Campeloma were collected on different days at the same site. The statistical analysis failed to yield the same result in two groups, and restriction on Campeloma movement by zebra mussels is clearly visualized; however it still remained unclear whether the shell morphology determines alteration of burrowing depth or the presence of zebra mussels do.http://deepblue.lib.umich.edu/bitstream/2027.42/57491/1/Lee_Bell_2007.pd

The JCMT Transient Survey: An Extraordinary Submillimetre Flare in the T Tauri Binary System JW 566

The binary T Tauri system JW 566 in the Orion Molecular Cloud underwent an energetic, short-lived flare observed at submillimetre wavelengths by the SCUBA-2 instrument on 26 November 2016 (UT). The emission faded by nearly 50% during the 31 minute integration. The simultaneous source fluxes averaged over the observation are 500 +/- 107 mJy/beam at 450 microns and 466 +/- 47 mJy/beam at 850 microns. The 850 micron flux corresponds to a radio luminosity of $L_{\nu}=8\times10^{19}$ erg/s/Hz, approximately one order of magnitude brighter (in terms of $\nu L_{\nu}$) than that of a flare of the young star GMR-A, detected in Orion in 2003 at 3mm. The event may be the most luminous known flare associated with a young stellar object and is also the first coronal flare discovered at sub-mm wavelengths. The spectral index between 450 microns and 850 microns of $\alpha = 0.11$ is broadly consistent with non-thermal emission. The brightness temperature was in excess of $6\times10^{4}$ K. We interpret this event to be a magnetic reconnection that energised charged particles to emit gyrosynchrotron/synchrotron radiation.Comment: Accepted in ApJ. 16 pages (single column), 6 figure

The JCMT Transient Survey: An Extraordinary Submillimeter Flare in the T Tauri Binary System JW 566

© 2019 The American Astronomical Society. All rights reserved.The binary T Tauri system JW 566 in the Orion Molecular Cloud underwent an energetic, short-lived flare observed at submillimetre wavelengths by the SCUBA-2 instrument on 26 November 2016 (UT). The emission faded by nearly 50% during the 31 minute integration. The simultaneous source fluxes averaged over the observation are 500 +/- 107 mJy/beam at 450 microns and 466 +/- 47 mJy/beam at 850 microns. The 850 micron flux corresponds to a radio luminosity of $L_{\nu}=8\times10^{19}$ erg/s/Hz, approximately one order of magnitude brighter (in terms of $\nu L_{\nu}$) than that of a flare of the young star GMR-A, detected in Orion in 2003 at 3mm. The event may be the most luminous known flare associated with a young stellar object and is also the first coronal flare discovered at sub-mm wavelengths. The spectral index between 450 microns and 850 microns of $\alpha = 0.11$ is broadly consistent with non-thermal emission. The brightness temperature was in excess of $6\times10^{4}$ K. We interpret this event to be a magnetic reconnection that energised charged particles to emit gyrosynchrotron/synchrotron radiation.Peer reviewedFinal Published versio

Observatory/data centre partnerships and the VO-centric archive: The JCMT Science Archive experience

We present, as a case study, a description of the partnership between an observatory (JCMT) and a data centre (CADC) that led to the development of the JCMT Science Archive (JSA). The JSA is a successful example of a service designed to use Virtual Observatory (VO) technologies from the start. We describe the motivation, process and lessons learned from this approach.Comment: Accepted for publication in the second Astronomy & Computing Special Issue on the Virtual Observatory; 10 pages, 5 figure

Antitrust and Competition Law Update: U.S. v. Visa: Government Wins Major Rule of Reason Case

On September 17, 2003, the Second Circuit issued an important decision in U.S. v. Visa U.S.A., Inc., 2003 WL 22138519 (2d Cir. Sept. 17, 2003). The court affirmed a district court ruling invalidating Visa and Mastercard rules that prohibit member banks from issuing American Express or Discover.1 The district court had found that these ìexclusionary rulesî substantially harmed competition and failed scrutiny under a rule of reason analysis. Visa is noteworthy both because it is a (relatively rare) government win in a major rule of reason case ó with the Second Circuit affirming the trial courtís rigorous inquiry into the rulesí anticompetitive effects and proffered procompetive justification ó and because it may bring pressure for substantial structural changes in the card industry

Verizon Communications Inc. v. Law Offices of Curtis V. Trinko, LLP:

Last week, the U.S. Supreme Court issued an important opinion concerning Section 2 of the Sherman Act, which prohibits monopolization and attempted monopolization. The opinion, written by Justice Scalia, limits the circumstances under which antitrust law will compel companies to assist their rivals

Antitrust and Competition Law Update: Busy Times for U.S. Antitrust Enforcement

The last several weeks have seen a flurry of important developments in antitrust enforcement, with major decisions in one merger and one joint venture case, an important Federal Trade Commission policy statement about disgorgement and restitution remedies, and an announced FTC challenge to a consummated merger. Each of these developments is significant standing alone; collectively, they reflect extremely active Justice Department and FTC antitrust enforcement programs, with the agencies at times adopting more aggressive positions than some might have expected from a Republican administration

The Summary Judgment Standard and Pleading Requirements for Conspiracy Claims Relying on the Doctrine of Conscious Parallelism

Last spring there was growing concern in the wake of the Seventh Circuit’s decision in In re High Fruc-tose Corn Syrup1 that the courts might be adopting a more receptive attitude toward antitrust claims based on allegations of consciously parallel pricing and other behavior in highly concentrated industries. Three decisions in the last few months suggest that High Fructose Corn Syrup may remain an aberration and that most courts remain deeply skeptical of claims that seek to infer agreement from consciously parallel conduct without any hard evidence of conspiracy. Two of these three decisions, Williamson Oil Co., Inc. v. Phillip Morris2 and Hall v. United Air Lines, Inc.3 involved consciously parallel pricing behavior and arose on mo-tions for summary judgment. Both decisions applied the well established analytical framework under which a plaintiff, to survive a defendant’s motion for summary judgment, must offer evidence of so-called plus factors, that is, of facts, in addition to the consciously parallel behavior itself, that support an inference of unlawful conspiracy. The third decision, Twombly v. Bell Atlantic Corp.,4 applies this analytical framework to allegations of agreement arising from consciously parallel conduct to dismiss the case on the pleadings. The case is of additional interest because it is one of the few conscious parallelism cases involving an al-leged market allocation agreement, rather than alleged price fixing

United States v. AMR Corp.: Non-Traditional Cost Measures and Expanding Predatory Pricing Exposure

Historically, industries with low average variable costs (AVC) have been as a practical matter largely immune from predatory pricing claims. The reason is simple. Predatory pricing claims require the plaintiff to establish, among other things, that the defendant priced below an appropriate measure of cost. Because marginal costs are notoriously difficult to measure, courts have commonly compared the defendant’s prices to AVC (total costs that vary with output/units of output). Consequently, in industries where average variable costs are very low, plaintiffs are unlikely to be able to prove that defendants have priced below AVC, even when defendants have drastically slashed prices. Airlines are a classic example of such an industry