428 research outputs found
Species of Bursaphelenchus Fuchs, 1937 (Nematoda: Parasitaphelenchidae) and other nematode genera associated with insects from Pinus pinaster in Portugal
Insects associated with maritime pine, Pinus pinaster, in Portugal were collected
and screened for the presence of Bursaphelenchus species. Nematodes were
identified using Internal Transcribed Spacers-Restriction Fragment Length
Polymorphism (ITS-RFLP) analysis of dauer juveniles and morphological
identification of adults that developed from dauer juveniles on fungal cultures
or on cultures in pine wood segments at 26 C. Several associations are
described: Bursaphelenchus teratospicularis and Bursaphelenchus sexdentati are
associated with Orthotomicus erosus; Bursaphelenchus tusciae, B. sexdentati and/or
Bursaphelenchus pinophilus with Hylurgus ligniperda and Bursaphelenchus hellenicus
with Tomicus piniperda, Ips sexdentatus and H. ligniperda. An unidentified
Bursaphelenchus species is vectored by Hylobius sp. The previously reported
association of Bursaphelenchus xylophilus with Monochamus galloprovincialis
was confirmed. The association of Bursaphelenchus leoni with Pityogenes sp. is
not definitively established and needs further studies for clarification.
Other nematode genera besides Bursaphelenchus were found to be associated
with the insects sampled, including two different species of Ektaphelenchus, Parasitorhabditis
sp., Parasitaphelenchus sp., Contortylenchus sp. and other unidentified
nematodes. The Ektaphelenchus species found in O. erosus is morphologically
similar to B. teratospicularis found in the same insect; adults of both the species
are found in cocoon-like structures under the elytra of the insects.
Introduction
Approximately one third of the nematodes belonging to
the order Aphelenchida Siddiqi, 1980 are associated with
insects (Poinar, 1983). These nematodes establish a variety
of associations with the insects, which may be
described as commensalism, e.g. phoresy (to the benefit
of the nematode but not affecting the insect), mutualism
(both the organisms benefit) or parasitism (nematodes
benefit at the expense of the insect) (Giblin-Davis,
2004).
Most Bursaphelenchus Fuchs, 1937 species are mycetophagous,
feeding on fungi in the galleries of bark beetles
and thu
Gravitational Waves From the End of Inflation: Computational Strategies
Parametric resonance or preheating is a plausible mechanism for bringing
about the transition between the inflationary phase and a hot, radiation
dominated universe. This epoch results in the rapid production of heavy
particles far from thermal equilibrium and could source a significant
stochastic background of gravitational radiation. Here, we present a numerical
algorithm for computing the contemporary power spectrum of gravity waves
generated in this post-inflationary phase transition for a large class of
scalar-field driven inflationary models. We explicitly calculate this spectrum
for both quartic and quadratic models of chaotic inflation, and low-scale
hybrid models. In particular, we consider hybrid models with an ``inverted''
potential. These models have a very short and intense period of resonance which
is qualitatively different from previous examples studied in this context, but
we find that they lead to a similar spectrum of gravitational radiation.Comment: 15 pages, 13 figure
Correlations Between Lag, Luminosity, and Duration in Gamma-ray Burst Pulses
We derive a new peak lag vs. peak luminosity relation in gamma-ray burst
(GRB) pulses. We demonstrate conclusively that GRB spectral lags are pulse
rather than burst properties and show how the lag vs. luminosity relation
determined from CCF measurements of burst properties is essentially just a
rough measure of this newly derived relation for individual pulses. We further
show that most GRB pulses have correlated properties: short-lag pulses have
shorter durations, are more luminous, and are harder within a burst than
long-lag pulses. We also uncover a new pulse duration vs. pulse peak luminosity
relation, and indicate that long-lag pulses often precede short-lag pulses.
Although most pulse behaviors are supportive of internal shocks (including
long-lag pulses), we identify some pulse shapes that could result from external
shocks.Comment: 14 pages, 4 figures, 1 table; accepted for publication in
Astrophysical Journal Letter
Quiescent Burst Evidence for Two Distinct GRB Emission Components
We have identified two quiescent GRBs (bursts having two or more
widely-separated distinct emission episodes) in which the post-quiescent
emission exhibits distinctly different characteristics than the pre-quiescent
emission. In these two cases (BATSE GRBs 960530 and 980125), the second
emission episode has a longer lag, a smoother morphology, and softer spectral
evolution than the first episode. Although the pre-quiescent emission satisfies
the standard internal shock paradigm, we demonstrate that the post-quiescent
emission is more consistent with external shocks. We infer that some observed
soft, faint, long-lag GRBs are external shocks in which the internal shock
signature is not observed. We further note that the peak luminosity ratio
between quiescent episodes is not in agreement with the ratio predicated by the
lag vs. peak luminosity relationship. We briefly discuss these observations in
terms of current collapsar jet models.Comment: 19 pages, 4 figures, 2 tables, accepted for publication in The
Astrophysical Journa
Evidence for an Early High-Energy Afterglow Observed with BATSE from GRB980923
In this Letter, we present the first evidence in the BATSE data for a prompt
high-energy (25-300 keV) afterglow component from a gamma-ray burst (GRB),
GRB980923. The event consists of rapid variabilty lasting ~40 s followed by a
smooth power law emission tail lasting ~400 s. An abrupt change in spectral
shape is found when the tail becomes noticeable. Our analysis reveals that the
spectral evolution in the tail of the burst mimics that of a cooling
synchrotron spectrum, similar to the spectral evolution of the low-energy
afterglows for GRBs. This evidence for a separate emission component is
consistent with the internal-external shock scenario in the relativistic
fireball picture. In particular, it illustrates that the external shocks can be
generated during the gamma-ray emission phase, as in the case of GRB990123.Comment: 4 pages, 4 figures, accepted for publication in Astrophysical Journal
Letter
Extended Power-Law Decays in BATSE Gamma-Ray Bursts: Signatures of External Shocks?
The connection between Gamma-Ray Bursts (GRBs) and their afterglows is currently not well understood. Afterglow models of synchrotron emission generated by external shocks in the GRB fireball model predict emission detectable in the gamma-ray regime (\gax 25 keV). In this paper, we present a temporal and spectral analysis of a subset of BATSE GRBs with smooth extended emission tails to search for signatures of the ``early high-energy afterglow'', i.e., afterglow emission that initially begins in the gamma-ray phase and subsequently evolves into X-Ray, uv, optical, and radio emission as the blast wave is decelerated by the ambient medium. From a sample of 40 GRBs we find that the temporal decays are best described with a power-law , rather than an exponential, with a mean index . Spectral analysis shows that of these events are consistent with fast-cooling synchrotron emission for an adiabatic blast wave; three of which are consistent with the blast wave evolution of a jet, with . This behavior suggests that, in some cases, the emission may originate from a narrow jet, possibly consisting of ``nuggets'' whose angular size are less than , where is the bulk Lorentz factor
Magnetic Monopole Dynamics in Spin Ice
One of the most remarkable examples of emergent quasi-particles, is that of
the "fractionalization" of magnetic dipoles in the low energy configurations of
materials known as "spin ice", into free and unconfined magnetic monopoles
interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45
(2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges
really does exist at low temperature in these materials and this discovery
provides a new perspective on otherwise largely inaccessible phenomenology. In
this paper, after a review of the different spin ice models, we present
detailed results describing the diffusive dynamics of monopole particles
starting both from the dipolar spin ice model and directly from a Coulomb gas
within the grand canonical ensemble. The diffusive quasi-particle dynamics of
real spin ice materials within "quantum tunneling" regime is modeled with
Metropolis dynamics, with the particles constrained to move along an underlying
network of oriented paths, which are classical analogues of the Dirac strings
connecting pairs of Dirac monopoles.Comment: 26 pages, 12 figure
A New Frequency-Luminosity Relation for Long GRBs?
We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts
(GRBs). We fitted the PDS with a simple power-law and extracted the exponent of
the power-law (alpha) and the noise-crossing threshold frequency (f_th). We
find that the distribution of the extracted alpha peaks around -1.4 and that of
f_th around 1 Hz. In addition, based on a sub-set of 58 bursts with known
redshifts, we show that the redshift-corrected threshold frequency is
positively correlated with the isotropic peak luminosity. The correlation
coefficient is 0.57 +/- 0.03.Comment: 9 pages, 17 figures, 1 table; Accepted for publication in MNRA
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