339 research outputs found
Long and Short GRB
We report evidence from the 3B Catalogue that short (T_90 < 10 s) and long
(T_90 > 10 s) GRB represent different populations and processes: Their spectral
behavior is qualitatively different, with short bursts harder in the BATSE
range, but chiefly long bursts detected at higher photon energies; \langle
V/V_max \rangle = 0.385 \pm 0.019 for short GRB but \langle V/V_max \rangle =
0.282 \pm 0.014 for long GRB, differing by 0.103 \pm 0.024. Long GRB may be the
consequence of accretion-induced collapse, but this mechanism fails for short
GRB, for which we suggest colliding neutron stars.Comment: 5 pp., latex, no figures, revised to work around bug in latex
compile
The Long and the Short of Gamma-Ray Bursts
We report evidence from the 3B Catalogue that long ( s) and
short ( s) gamma-ray bursts represent distinct source populations.
Their spatial distributions are significantly different, with long bursts
having but short bursts having
, differing by ,
significant at the level. Long and short bursts also differ
qualitatively in their spectral behavior, with short bursts harder in the BATSE
(50--300 KeV) band, but long bursts more likely to be detected at photon
energies > 1 MeV. This implies different spatial origin and physical processes
for long and short bursts. Long bursts may be explained by accretion-induced
collapse. Short bursts require another mechanism, for which we suggest neutron
star collisions. These are capable of producing neutrino bursts as short as a
few ms, consistent with the shortest observed time scales in GRB. We briefly
investigate the parameters of clusters in which neutron star collisons may
occur, and discuss the nuclear evolution of expelled and accelerated matter.Comment: 21 pp., AAS latex, 1 figure added as ps fil
Transcriptional profiling of phytoplasma infected plants treated with plasma activated water (PAW).
Background. Phytoplasmas are insect-transmitted plant pathogenic prokaryotes, associated with severe
diseases in agronomic important crops. Management of these diseases has mainly focused on insect vector
chemical control and on infected plant rouging. There is therefore a strong need for effective and friendly
control strategies for phytoplasma-associated diseases and the possibility to use plasma activated water
(PAW) as sustainable and effective method to them was therefore evaluated. PAW is produced by treating
distilled water with atmospheric pressure plasmas, inducing the production of reactive oxygen and nitrogen
species (RONS) and pH reduction. PAW has good potential for bacterial decontamination, degradation of
organic compounds and was shown to positively affect plant growth. Methods. Sterile deionized water (SDW)
was exposed to a nanosecond pulsed dielectric barrier discharge, operating in ambient air for 10 min
treatment with a peak voltage of 19 kV and a pulse repetition frequency of 1 kHz, which induced production of
nitrates, nitrites and peroxides, and a pH decrease. Phytoplasma infected and healthy periwinkles
micropropagated shoots were exposed to PAW for about 25 minutes and gene expression studies were then
performed. The theses used were: shoots treated with PAW, Fosetyl aluminum (as positive control) and SDW
(as negative control), with an exposition of about 25 minutes. Nine shoots for each thesis were then collected
at 6 different times after treatment and stored at -80\ub0C. Quantitative RT-PCR analyses were carried out to
determine the expression level of genes involved in the plant defense response. Parallel experiments were
carried out treating grapevine plants in vineyards previously tested for the phytoplasma presence. Treatments
were performed for three years injecting into the plant vascular tissues 10-20 ml of PAW or sterile distilled
water (as control) on each selected plant for a total of 60 plants (40 with phytoplasmas and 20 without
phytoplasmas). Results. Overexpression of selected genes involved in the phytoalexin metabolism was
detected in the periwinkles micropropagated shoots treated with PAW in comparison with the shoots treated
with Fosetyl-Al and distilled water. In the field trials, in a relevant number of cases, the PAW-treated
symptomatic plants showed reduction of symptoms, while the SDW-treated and untreated plants did not show
symptom reduction. No phytotoxicity was observed in the PAW treated grapevine and periwinkle plants.
Conclusion. The results obtained showed the capability of PAW to enhance plant defence mechanisms and,
as demonstrated in the field trials, confirmed its ability to improve the health status of the treated plant
Calculation of Elastic Green's Functions for Lattices with Cavities
In this Brief Report, we present an algorithm for calculating the elastic
Lattice Greens Function of a regular lattice, in which defects are created by
removing lattice points. The method is computationally efficient, since the
required matrix operations are on matrices that scale with the size of the
defect subspace, and not with the size of the full lattice. This method allows
the treatment of force fields with multi-atom interactions.Comment: 3 pages. RevTeX, using epsfig.sty. One figur
Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility
We present a systematic study of the effect of crack blunting on subsequent
crack propagation and dislocation emission. We show that the stress intensity
factor required to propagate the crack is increased as the crack is blunted by
up to thirteen atomic layers, but only by a relatively modest amount for a
crack with a sharp 60 corner. The effect of the blunting is far less
than would be expected from a smoothly blunted crack; the sharp corners
preserve the stress concentration, reducing the effect of the blunting.
However, for some material parameters blunting changes the preferred
deformation mode from brittle cleavage to dislocation emission. In such
materials, the absorption of preexisting dislocations by the crack tip can
cause the crack tip to be locally arrested, causing a significant increase in
the microscopic toughness of the crack tip. Continuum plasticity models have
shown that even a moderate increase in the microscopic toughness can lead to an
increase in the macroscopic fracture toughness of the material by several
orders of magnitude. We thus propose an atomic-scale mechanism at the crack
tip, that ultimately may lead to a high fracture toughness in some materials
where a sharp crack would seem to be able to propagate in a brittle manner.
Results for blunt cracks loaded in mode II are also presented.Comment: 12 pages, REVTeX using epsfig.sty. 13 PostScript figures. Final
version to appear in Phys. Rev. B. Main changes: Discussion slightly
shortened, one figure remove
Framing analysis, dramatism and terrorism coverage: politician and press responses to the Madrid airport bombing
The media and terrorism is an area that has attracted researchers’ attention in looking at the strategic dimensions of framing. This paper combines both Entman’s framing theory (and his ‘cascading activation’ model for analysis of framing contests) with a dramatistic approach to rhetoric (the Burkean concepts of the pentad and ratios) to see whether connections can be made that help provide a better understanding of the phenomenon of interactions between politicians’ words and media reactions to those words. Speeches given by the Spanish Prime Minister and the official opposition in reaction to a terrorist attack in Madrid are analysed. Our empirical analysis shows a highly fragmented capacity for cultural resonance, and a ‘two sided context’ with two very different interpretations of the situation. Our findings demonstrate that an appreciation of the dramatistic approach to rhetoric enhances our comprehension of people’s motives for adopting or rejecting the different frames used by leaders (politicians and the media) as they seek to frame issues for a range of purposes. They also suggest that combining approaches from the humanities and the social sciences by emphasizing motives as a key variable for the dynamics of framing contests might open up interesting avenues for research on framing as also on the relations between symbols and actions
Local density of states in the vortex lattice in a type II superconductor
Local density of states (LDOS) in the triangular vortex lattice is
investigated based on the quasi-classical Eilenberger theory. We consider the
case of an isotropic s-wave superconductor with the material parameter
appropriate to NbSe_2. At a weak magnetic field, the spatial variation of the
LDOS shows cylindrical structure around a vortex core. On the other hand, at a
high field where the core regions substantially overlap each other, the LDOS is
sixfold star-shaped structure due to the vortex lattice effect. The orientation
of the star coincides with the experimental data of the scanning tunneling
microscopy. That is, the ray of the star extends toward the nearest-neighbor
(next nearest-neighbor) vortex direction at higher (lower) energy.Comment: 10 pages, RevTex, 32 figure
The possible explanation of electric-field-doped C60 phenomenology in the framework of Eliashberg theory
In a recent paper (J.H. Schon, Ch. Kloc, R.C. Haddon and B. Batlogg, Nature
408 (2000) 549) a large increase in the superconducting critical temperature
was observed in C60 doped with holes by application of a high electric field.
We demonstrate that the measured Tc versus doping curves can be explained by
solving the (four) s-wave Eliashberg equations in the case of a finite,
non-half-filled energy band. In order to reproduce the experimental data, we
assume a Coulomb pseudopotential depending on the filling in a very simple and
plausible way. Reasonable values of the physical parameters involved are
obtained. The application of the same approach to new experimental data (J.H.
Schon, Ch. Kloc and B. Batlogg, Science 293 (2001) 2432) on electric
field-doped, lattice-expanded C60 single crystals (Tc=117 K in the hole-doped
case) gives equally good results and sets a theoretical limit to the linear
increase of Tc at the increase of the lattice spacing.Comment: latex2e, 6 pages, 7 figures, 1 table, revised versio
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