Implications of long tails in the distribution of mutant effects

Long-tailed distributions possess an in nite variance, yet a nite sample that is drawn from such a distribution has a nite variance. In this work we consider a model of a population subject to mutation, selection and drift. We investigate the implications of a long-tailed distribution of mutant allelic e¤ects on the distribution of genotypic e¤ects in a model with a continuum of allelic e¤ects. While the analysis is confined to asexual populations, it does also have implications for sexual populations. We obtain analytical results for a selectively neutral population as well as one subject to selection. We supplement these analytical results with numerical simulations, to take into account genetic drift. We nd that a long-tailed distribution of mutant e¤ects may a¤ect both the equilibrium and the evolutionary adaptive behaviour of a population

Efficiency of cosmic ray reflections from an ultrarelativistic shock wave

The process of cosmic ray acceleration up to energies in excess of $10^{20}$ eV at relativistic shock waves with large Lorentz factors, $\Gamma \gg 1$ requires $\sim \Gamma^2$ particle energy gains at single reflections from the shock (cf. Gallant & Achterberg 1999). In the present comment, applying numerical simulations we address an efficiency problem arising for such models. The actual efficiency of the acceleration process is expected to be substantially lower than the estimates of previous authors.Comment: 3 pages, 3 figures, accepted for publication in MNRAS (Letters

Angular size and emission time scales of relativistic fireballs

The detection of delayed X-ray, optical and radio emission, ``afterglow,'' associated with gamma-ray bursts (GRBs) is consistent with models, where the bursts are produced by relativistic expanding blast waves, driven by expanding fireballs at cosmological distances. In particular, the time scales over which radiation is observed at different wave bands agree with model predictions. It had recently been claimed that the commonly used relation between observation time t and blast wave radius r, t=r/2\gamma^{2}c where \gamma(r) is the fluid Lorentz factor, should be replaced with t=r/16\gamma^{2}c due to blast wave deceleration. Applying the suggested deceleration modification would make it difficult to reconcile observed time scales with model predictions. It would also imply an apparent source size which is too large to allow attributing observed radio variability to diffractive scintillation. We present a detailed analysis of the implications of the relativistic hydrodynamics of expanding blast waves to the observed afterglow. We find that modifications due to shock deceleration are small, therefore allowing for both the observed afterglow time scales and for diffractive scintillation. We show that at time t the fireball appears on the sky as a narrow ring of radius h=r/\gamma and width 0.1h, where r and t are related by t=r/2\gamma^{2}c.Comment: Submitted to ApJL (11 pages, LaTeX

TeV Neutrinos from Successful and Choked Gamma-Ray Bursts

Core collapse of massive stars resulting in a relativistic fireball jet which breaks through the stellar envelope is a widely discussed scenario for gamma-ray burst production. For very extended or slow rotating stars, the fireball may be unable to break through the envelope. Both penetrating and choked jets will produce, by photo-meson interactions of accelerated protons, a burst of neutrinos with energies in excess of 5 TeV while propagating in the envelope. The predicted flux, from both penetrating and chocked fireballs, should be easily detectable by planned cubic kilometer neutrino telescopes.Comment: Phys.Rev.Letters, in press, final version accepted 8/31/01 (orig. 3/17/01

Analysis of Performance of Dynamic Multicast Routing Algorithms

In this paper, three new dynamic multicast routing algorithms based on the greedy tree technique are proposed; Source Optimised Tree, Topology Based Tree and Minimum Diameter Tree. A simulation analysis is presented showing various performance aspects of the algorithms, in which a comparison is made with the greedy and core based tree techniques. The effects of the tree source location on dynamic membership change are also examined. The simulations demonstrate that the Source Optimised Tree algorithm achieves a significant improvement in terms of delay and link usage when compared to the Core Based Tree, and greedy algorithm

Stability of the Forward/Reverse Shock System Formed by the Impact of a Relativistic Fireball on an Ambient Medium

We analyze the stability of a relativistic double (forward/reverse) shock system which forms when the fireball of a Gamma-Ray Burst (GRB) impacts on the surrounding medium. We find this shock system to be stable to linear global perturbations for either a uniform or a wind (r^{-2}) density profile of the ambient medium. For the wind case, we calculate analytically the frequencies of the normal modes which could modulate the early short-term variability of GRB afterglows. We find that perturbations in the double shock system could induce oscillatory fluctuations in the observed flux on short (down to seconds) time scales during the early phase of an afterglow.Comment: ApJ, submitted, 26 pages, 5 figure

GeV Photons from Ultra High Energy Cosmic Rays accelerated in Gamma Ray Bursts

Gamma-ray bursts are produced by the dissipation of the kinetic energy of a highly relativistic fireball, via the formation of a collisionless shock. When this happens, Ultra High Energy Cosmic Rays up to 10^20 eV are produced. I show in this paper that these particles produce, via synchrotron emission as they cross the acceleration region, photons up to 300 GeV which carry away a small, ~0.01, but non-negligible fraction of the total burst energy. I show that, when the shock occurs with the interstellar medium, the optical depth to photon-photon scattering, which might cause energy degradation of the photons, is small. The burst thusly produced would be detected at Earth simultaneoulsy with the parent gamma-ray burst, although its duration may differ significantly from that of the lower energy photons. The expected fluences, ~10^{-5}-10^{-6} erg/cm^2 are well within the range of planned detectors. A new explanation for the exceptional burst GRB 940217 is discussed.Comment: Accepted for publication in The Physical Review Letters. 4 pages, RevTeX needed, no figure

The Federal Government\u27s Sovereign Immunity Under CERCLA and its Effects on the Hazardous Waste Cleanup of the District of Columbia\u27s Washington Navy Yard

The United States Supreme Court\u27s weakening of the waiver of federal sovereign immunity under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA or the Act ) is preventing federally contaminated sites such as the Washington Navy Yard from being fully remediated. In 1998, the United States Environmental Protection Agency (EPA) designated the Navy Yard- a property with a lengthy history of hazardous waste contamination- as a priority for cleanup pursuant to CERCLA. However, the hazardous waste currently contaminating the Navy Yard has not been remediated due to a lack of intra-governmental enforcement. This inaction leaves the people who live and work near the Navy Yard exposed to hazardous waste, which can have very severe health consequences

The Mortgage Banker-Industrial Loan Company: A New Exempt Lender

In 1973, to alleviate the plight of commercial real estate lenders caught between the rising costs of making loans and the limitations on interest and charges, the California Legislature enacted legislation which authorized the formation of the mortgage banker-industrial loan company, a new entity intended to fall within the class of exempt lenders created by article XX, section 22 of the California Constitution. The author discusses the nature and formation of the mortgage banker-industrial loan company and addresses provisions which allow the mortgage banker-industrial loan company to make assignments or transfers to nonexempt lenders. In this discussion he concludes that while such operations are generally authorized by the legislation, the courts will not allow the new institution to act as a mere conduit, circumventing the distinction between classes of exempt and nonexempt lenders. Finally, the author discusses he constitutionality of the mortgage banker-industrial loan company, marshalling arguments that the institution is a valid subclass of the constitutionality exempt industrial loan company, that public policy considerations support an affirmative finding of constitutionality, and that the creation of the institution does not violate equal protection of the law