A review of the introduced smooth-billed ani Crotophaga ani in Galápagos

The smooth-billed ani (Crotophaga ani) is a widespread introduced bird species in the biologically important archipelago of Galápagos. Many scientists and local people consider it to be a damaging invasive, and it is possible that it impacts native species and ecosystems via multiple mechanisms. However, evidence for this is largely anecdotal and research on smooth-billed anis in Galápagos is limited. Despite this, there have been repeated attempts to control or eradicate the population over the past few decades, all without long-term success. These attempts continue, but no official plan of action regarding this species currently exists.This review brings together all available information on smooth-billed anis in Galápagos. We use both published and unpublished research to answer the following questions:1.What is known about the history of the smooth-billed anis' introduction to Galápagos?2.What are the possible impacts of smooth-billed anis in Galápagos?3.What attempts have been undertaken to control or eradicate smooth-billed anis in Galápagos and what were their outcomes?In answering these questions, we highlight numerous knowledge gaps, in both the current understanding of the impacts of this introduced species and the effectiveness of potential control or eradication methods. We find an urgent need for further research before considered, resource-efficient decisions can be made regarding smooth-billed anis in Galápagos

Invariant Peano curves of expanding Thurston maps

We consider Thurston maps, i.e., branched covering maps $f\colon S^2\to S^2$ that are postcritically finite. In addition, we assume that $f$ is expanding in a suitable sense. It is shown that each sufficiently high iterate $F=f^n$ of $f$ is semi-conjugate to $z^d\colon S^1\to S^1$, where $d$ is equal to the degree of $F$. More precisely, for such an $F$ we construct a Peano curve $\gamma\colon S^1\to S^2$ (onto), such that $F\circ \gamma(z) = \gamma(z^d)$ (for all $z\in S^1$).Comment: 63 pages, 12 figure

The cyclo-synchrotron process and particle heating through the absorption of photons

We propose a new approximation for the cyclo-synchrotron emissivity of a single electron. In the second part of this work, we discuss a simple application for our approximation, and investigate the heating of electrons through the self-absorption process. Finally, we investigate the self-absorbed part of the spectrum produced by a power-law population of electrons. In comparison to earlier approximations, our formula provides a few significant advantages. Integration of the emissivity over the whole frequency range, starting from the proper minimal emitting frequency, gives the correct cooling rate for any energy particle. Further, the spectrum of the emission is well approximated over the whole frequency range, even for relatively low particle energies (beta << 0.1), where most of the power is emitted in the first harmonic. In order to test our continuous approximation, we compare it with a recently derived approximation of the first ten harmonics. Finally, our formula connects relatively smooth to the synchrotron emission at beta=0.9. We show that the self-absorption is a very efficient heating mechanism for low energy particles, independent of the shape of the particle distribution responsible for the self-absorbed synchrotron emission. We find that the energy gains for low energy particles are always higher than energy losses by cyclo-synchrotron emission. We show also that the spectral index of the self-absorbed part of the spectrum at very low frequencies differs significantly from the well known standard relation I(nu) ~ nu^(5/2).Comment: 9 pages, 4 figures, accepted for publication in A&

Durability and generalization of attribution-based feedback following failure: Effects on expectations and behavioral persistence

Objective: This experiment investigated, following perceived failure, the immediate, long-term (i.e., durability), and cross-situational (i.e., generalization) effects of attribution-based feedback on expectations and behavioral persistence. Design: We used a 3×2 (Group×Time) experimental design over seven weeks with attributions, expectations of success, and persistence as dependent measures. Method: 49 novice participants were randomly assigned to one of three treatment (attributional feedback) groups: (a) functional (i.e., controllable and unstable); (b) dysfunctional (i.e., uncontrollable and stable); or (c) no feedback. Testing involved three sessions, in which participants completed a total of five trials across two performance tasks (golf-putting and dart-throwing). In order to track whether the attributional manipulation conducted within the context of the golf-putting task in Session 2 would generalize to a new situation, participants performed a dart-throwing task in Session 3, and their scores were compared with those recorded at baseline (in Session 1). Results: Analysis of pre- and post-intervention measures of attributions, expectations, and persistence revealed that the functional attributional feedback led to more personally controllable attributions following failure in a golf-putting task, together with increases in success expectations and persistence. In contrast, dysfunctional attributional feedback led to more personally uncontrollable and stable attributions following failure, together with lower success expectations and reduced persistence. These effects extended beyond the intervention period, were present up to four weeks post intervention, and were maintained even when participants performed a different (i.e., dart-throwing) task. Conclusions: The findings demonstrate that attributional feedback effects are durable over time and generalize across situations

Prompt TeV neutrinos from dissipative photospheres of gamma-ray bursts

Recently, it was suggested that a photospheric component that results from the internal dissipation occurring in the optically thick inner parts of relativistic outflows may be present in the prompt $\gamma$/X-ray emission of gamma-ray bursts or X-ray flashes. We explore high-energy neutrino emission in this dissipative photosphere model, assuming that the composition of the outflow is baryon-dominated. We find that neutrino emission from proton-proton collision process forms an interesting signature in the neutrino spectra. Under favorable conditions for the shock dissipation site, these low-energy neutrinos could be detected by ${\rm km^3}$ detectors, such as Icecube. Higher energies (\ga10 TeV) neutrino emission from proton-proton collision and photo-pion production processes could be significantly suppressed for dissipation at relatively small radii, due to efficient Bethe-Heitler cooling of protons and/or radiative cooling of the secondary mesons in the photosphere radiation. As the dissipation shocks continue further out, high energy neutrinos from photo-pion production process becomes dominant.Comment: Accepted by ApJ Letters, some changes made following the referees' comments, conclusions unchanged. The paper was originally submitted to PRL on June 6 (2008); resubmitted to ApJL on Oct.1 (2008); accepted by ApJL on Dec. 9 (2008

GRBs on probation: testing the UHE CR paradigm with IceCube

Gamma ray burst (GRB) fireballs provide one of very few astrophysical environments where one can contemplate the acceleration of cosmic rays to energies that exceed 10^20 eV. The assumption that GRBs are the sources of the observed cosmic rays generates a calculable flux of neutrinos produced when the protons interact with fireball photons. With data taken during construction IceCube has already reached a sensitivity to observe neutrinos produced in temporal coincidence with individual GRBs provided that they are the sources of the observed extragalactic cosmic rays. We here point out that the GRB origin of cosmic rays is also challenged by the IceCube upper limit on a possible diffuse flux of cosmic neutrinos which should not be exceeded by the flux produced by all GRB over Hubble time. Our alternative approach has the advantage of directly relating the diffuse flux produced by all GRBs to measurements of the cosmic ray flux. It also generates both the neutrino flux produced by the sources and the associated cosmogenic neutrino flux in a synergetic way.Comment: 12 pages, 3 figures, matches version published in Astroparticle Physic

Nucleosome repositioning via loop formation

Active (catalysed) and passive (intrinsic) nucleosome repositioning is known to be a crucial event during the transcriptional activation of certain eucaryotic genes. Here we consider theoretically the intrinsic mechanism and study in detail the energetics and dynamics of DNA-loop-mediated nucleosome repositioning, as previously proposed by Schiessel et al. (H. Schiessel, J. Widom, R. F. Bruinsma, and W. M. Gelbart. 2001. {\it Phys. Rev. Lett.} 86:4414-4417). The surprising outcome of the present study is the inherent nonlocality of nucleosome motion within this model -- being a direct physical consequence of the loop mechanism. On long enough DNA templates the longer jumps dominate over the previously predicted local motion, a fact that contrasts simple diffusive mechanisms considered before. The possible experimental outcome resulting from the considered mechanism is predicted, discussed and compared to existing experimental findings

The Low Redshift Lyman Alpha Forest in Cold Dark Matter Cosmologies

We study the physical origin of the low-redshift Lyman alpha forest in hydrodynamic simulations of four CDM cosmologies. Our main conclusions are insensitive to the cosmological model but depend on our assumption that the UV background declines at low redshift. We find that the expansion of the universe drives rapid evolution of dN/dz (the number of absorbers per unit z) at z > 1.7, but that at lower redshift the fading of the UV background counters the influence of expansion, leading to slow evolution. At every redshift, weaker lines come primarily from moderate fluctuations of the diffuse, unshocked IGM, and stronger lines originate in shocked or radiatively cooled gas of higher overdensity. However, the neutral hydrogen column density associated with structures of fixed overdensity drops as the universe expands, so an absorber at z = 0 is dynamically analogous to an absorber with neutral hydrogen column density 10 to 50 times higher at z = 2-3. We find no clear distinction between lines arising in "galaxy halos" and lines arising in larger scale structures; however, galaxies tend to lie near the dense regions of the IGM that produce strong Lyman alpha lines. The simulations provide a unified physical picture that accounts for the most distinctive observed properties of the low redshift Lyman alpha forest: (1) a sharp transition in the evolution of dN/dz at z ~ 1.7, (2) stronger evolution for absorbers of higher equivalent width, (3) a correlation of increasing Lyman alpha equivalent width with decreasing galaxy impact parameter, and (4) a tendency for stronger lines to arise in close proximity to galaxies while weaker lines trace more diffuse large scale structure. (Abridged)Comment: 57 pages, 18 figures, submitted to Ap

Host Galaxies of Gamma-Ray Bursts and their Cosmological Evolution

We use numerical simulations of large scale structure formation to explore the cosmological properties of Gamma-Ray Burst (GRB) host galaxies. Among the different sub-populations found in the simulations, we identify the host galaxies as the most efficient star-forming objects, i.e. galaxies with high specific star formation rates. We find that the host candidates are low-mass, young galaxies with low to moderate star formation rate. These properties are consistent with those observed in GRB hosts, most of which are sub-luminous, blue galaxies. Assuming that host candidates are galaxies with high star formation rates would have given conclusions inconsistent with the observations. The specific star formation rate, given a galaxy mass, is shown to increase as the redshift increases. The low mass of the putative hosts makes them difficult to detect with present day telescopes and the probability density function of the specific star formation rate is predicted to change depending on whether or not these galaxies are observed.Comment: 11 pages, 10 figures. Accepted for publication in MNRA

Early afterglows from radially structured outflows and the application to X-ray shallow decays

In the fireball model, it is more physically realistic that gamma-ray burst (GRB) ejecta have a range of bulk Lorentz factors (assuming $M\propto \Gamma^{-s}$). The low Lorentz factor part of the ejecta will catch up with the high Lorentz factor part when the latter is decelerated by the surrounding medium to a comparable Lorentz factor. Such a process will develop a long-lasting weak reverse shock until the whole ejecta are shocked. Meanwhile, the forward shocked materials are gradually supplied with energy from the ejecta that are catching-up, and thus the temporal decay of the forward shock emission will be slower than that without an energy supply. However, the reverse shock may be strong. Here, we extend the standard reverse-forward shock model to the case of radially nonuniform ejecta. We show that this process can be classified into two cases: the thick shell case and the thin shell case. In the thin shell case, the reverse shock is weak and the temporal scaling law of the afterglow is the same as that in Sari & Mesz (2000). However, in the thick shell case, the reverse shock is strong and thus its emission dominates the afterglow in the high energy band. Our results also show slower decaying behavior of the afterglow due to the energy supply by low Lorentz factor materials, which may help the understanding of the plateau observed in the early optical and X-ray afterglows