Resolved shock structure of the Balmer-dominated filaments in Tycho's supernova remnant: Cosmic-ray precursor?

We report on the results from H{\alpha} imaging observations of the eastern limb of Tycho's supernova remnant (SN1572) using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. We resolve the detailed structure of the fast, collisionless shock wave into a delicate structure of nearly edge-on filaments. We find a gradual increase of H{\alpha} intensity just ahead of the shock front, which we interpret as emission from the thin (~1") shock precursor. We find that a significant amount of the H{\alpha} emission comes from the precursor and that this could affect the amount of temperature equilibration derived from the observed flux ratio of the broad and narrow H{\alpha} components. The observed H{\alpha} emission profiles are fit using simple precursor models, and we discuss the relevant parameters. We suggest that the precursor is likely due to cosmic rays and discuss the efficiency of cosmic-ray acceleration at this position.Comment: Prepared with emulateapj.sty (5 pages, 4 figures). Published in ApJL

An introduction to the UCSC Genome Browser

The Genome Browser at the University of California Santa Cruz provides a uniform graphical interface to sequences, features, and annotations of genomes across a wide spectrum of organisms, from yeast to humans. In particular, it covers seven nematode genomes: Caenorhabditis elegans, C. sp. 11, C. brenneri, C. briggsae, C. remanei, C. japonica, and Pristionchus pacificus and thus is particularly useful for multiple-genome comparative analysis. One can use the provided tools and visual aides to facilitate sequence feature detection and examination. This article provides a brief introduction for using the Genome Browser from the perspective of a C. elegans researcher. Interested users should read the official user guide and explore the site more deeply as there are many more features not mentioned here

American Greed: The Eleventh Circuit Analyzes Whether Booze, Babes, and Business Can Tightrope the Line Between Fraud and Deceit

South Beach, Miami, is renowned for its beautiful beaches, bikini-clad women, and incredible wealth. Such an environment is ripe for opportunistic businessmen who are anxious to make an easy buck. Enter Albert Takhalov, Isaac Feldman, and Stanislav Pavlenko (the “Defendants”), three Russian immigrants who built a business model aimed precisely at taking advantage of the unique opportunities that South Beach has to offer. By combining seductive women with tourism and alcohol, their profits quickly began to soar. There was only one problem. The crux of their plan involved misleading their patrons. While schemes to profit from unsuspecting customers are hardly a modern concept, at what point does merely deceiving a customer become “taking advantage” of him? And at what point can a legitimate business model morph into a fraudulent criminal enterprise? The gray area in the middle is where the law tends to get murky. This Note analyzes the facts and holdings of Takhalov and then delves into the history of statutes that prohibit employees from drinking and/or mingling with patrons, as well as the history of wire fraud. Next, it discusses the importance of not abusing the wire fraud statute so as to maintain a fine line between fraud and deceit. Lastly, this Note contends that the prosecution over-stepped its bounds by bringing charges pursuant to the wrong criminal statute and that the correct statute, under which the prosecution should have brought charges, needs to carry tougher penalties

A Hybrid Mechanism Forming a 2:1 Librating-Circulating Resonant Configuration in the Planetary System

A diversity of resonance configurations may be formed under different migration of two giant planets. And the researchers show that the HD 128311 and HD 73526 planetary systems are involved in a 2:1 mean motion resonance but not in apsidal corotation, because one of the resonance argument circulates over the dynamical evolution. In this paper, we investigate potential mechanisms to form the 2:1 librating-circulating resonance configuration. In the late stage of planetary formation, scattering or colliding among planetesimals and planetary embryos can frequently occur. Hence, in our model, we consider a planetary configuration of two giants together with few terrestrial planets. We find that both colliding or scattering events at very early stage of dynamical evolution can influence the configurations trapped into resonance. A planet-planet scattering of a moderate terrestrial planet, or multiple scattering of smaller planets in a crowded planetary system can change the resonant configuration. In addition, collision or merging can alter the masses and location of the giant planets, which also play an important role in shaping the resonant configuration during the dynamical evolution. In this sense, the librating-circulating resonance configuration is more likely to form by a hybrid mechanism of scattering and collision.Comment: 8 pages, 5 figures, 2 Tables, accepted for publication in MNRA

Group Size Effect on the Success of Wolves Hunting

Social foraging shows unexpected features such as the existence of a group size threshold to accomplish a successful hunt. Above this threshold, additional individuals do not increase the probability of capturing the prey. Recent direct observations of wolves in Yellowstone Park show that the group size threshold when hunting its most formidable prey, bison, is nearly three times greater than when hunting elk, a prey that is considerably less challenging to capture than bison. These observations provide empirical support to a computational particle model of group hunting which was previously shown to be effective in explaining why hunting success peaks at apparently small pack sizes when hunting elk. The model is based on considering two critical distances between wolves and prey: the minimal safe distance at which wolves stand from the prey, and the avoidance distance at which wolves move away from each other when they approach the prey. The minimal safe distance is longer when the prey is more dangerous to hunt. We show that the model explains effectively that the group size threshold is greater when the minimal safe distance is longer. Although both distances are longer when the prey is more dangerous, they contribute oppositely to the value of the group size threshold: the group size threshold is smaller when the avoidance distance is longer. This unexpected mechanism gives rise to a global increase of the group size threshold when considering bison with respect to elk, but other prey more dangerous than elk can lead to specific critical distances that can give rise to the same group size threshold. Our results show that the computational model can guide further research on group size effects, suggesting that more experimental observations should be obtained for other kind of prey as e.g. moose.Comment: 20 pages, 4 figures, 8 references. Other author's papers can be downloaded at http://www.denys-dutykh.com