79 research outputs found
Molecular Characterization of the 16S rRNA Gene of Phytoplasmas Detected in Two Leafhopper Species Associated with Alfalfa Plants Infected with Witches' Broom in Oman
Two leafhopper species, Austroagallia avicula and Empoasca sp., were consistently found in alfalfa fields
infected with witches’ broom phytoplasma (OmanAlfWB) in the Al-Batinah, Dakhliya, North and South Sharqiya,
Muscat, and Al-Bureimi regions of the Sultanate of Oman. Phytoplasmas from both leafhoppers were detected by
specific polymerase chain reaction (PCR) amplification of the 16S rRNA gene and the spacer region in direct PCR
using P1/P7 primer pairs. Comparative RFLP profiles of the amplified rRNA gene and the spacer region from leafhopper
phytoplasmas and from 20 phytoplasma controls yielded patterns referable to phytoplasmas belonging to the peanut
witches’ broom group (16SrII group). In particular, extensive RFLP analyses with the endonucleases HpaII, Tru9I,
Tsp509I, and RsaI indicated that the phytoplasmas in A. avicula and Empoasca sp. were identical but showed some
differences from OmanAlfWB; however, RFLP patterns obtained with TaqI showed the OmanAlfWB and the
phytoplasmas from the two leafhoppers to be identical. Direct PCR products amplified from phytoplasma leafhopper
DNA using the P1/P7 primer pair were cloned and sequenced yielding 1758 bp and 1755 bp products from A. avicula
and Empoasca sp. respectively; the homology of these sequences with OmanAlfWB and papaya yellow crinkle
phytoplasmas was more than 98%. A phylogenetic tree based on the 16S rRNA gene and spacer region sequences
from 44 phytoplasmas revealed that the phytoplasmas from the leafhoppers clustered with OmanAlfWB, papaya
yellow crinkle, and gerbera phyllody phytoplasmas, all belonging to 16SrII group, but were distinct from lime witches’
broom phytoplasma, the most commonly found phytoplasma in the Sultanate of Oman
Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
We report a first measurement for ultra-high energy cosmic rays of the
correlation between the depth of shower maximum and the signal in the water
Cherenkov stations of air-showers registered simultaneously by the fluorescence
and the surface detectors of the Pierre Auger Observatory. Such a correlation
measurement is a unique feature of a hybrid air-shower observatory with
sensitivity to both the electromagnetic and muonic components. It allows an
accurate determination of the spread of primary masses in the cosmic-ray flux.
Up till now, constraints on the spread of primary masses have been dominated by
systematic uncertainties. The present correlation measurement is not affected
by systematics in the measurement of the depth of shower maximum or the signal
in the water Cherenkov stations. The analysis relies on general characteristics
of air showers and is thus robust also with respect to uncertainties in
hadronic event generators. The observed correlation in the energy range around
the `ankle' at differs significantly from
expectations for pure primary cosmic-ray compositions. A light composition made
up of proton and helium only is equally inconsistent with observations. The
data are explained well by a mixed composition including nuclei with mass . Scenarios such as the proton dip model, with almost pure compositions, are
thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray
flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report
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The energy spectrum of cosmic rays beyond the turn-down around 10^17 eV as measured with the surface detector of the Pierre Auger Observatory
We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays
Reconstruction of events recorded with the surface detector of the Pierre Auger Observatory
Cosmic rays arriving at Earth collide with the upper parts of the atmosphere, thereby inducing extensive air showers. When secondary particles from the cascade arrive at the ground, they are measured by surface detector arrays. We describe the methods applied to the measurements of the surface detector of the Pierre Auger Observatory to reconstruct events with zenith angles less than 60o using the timing and signal information recorded using the water-Cherenkov detector stations. In addition, we assess the accuracy of these methods in reconstructing the arrival directions of the primary cosmic ray particles and the sizes of the induced showers
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