1,381 research outputs found
Identification of stable resistance to <em>Phytophthora infestans</em> in potato genotypes evaluated in field experiments in Peru
Stabilizing Soybean Production in Northeast Texas with Early Planting of Early-Maturing Soybean Varieties.
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Dynamical percolation on general trees
H\"aggstr\"om, Peres, and Steif (1997) have introduced a dynamical version of
percolation on a graph . When is a tree they derived a necessary and
sufficient condition for percolation to exist at some time . In the case
that is a spherically symmetric tree, H\"aggstr\"om, Peres, and Steif
(1997) derived a necessary and sufficient condition for percolation to exist at
some time in a given target set . The main result of the present paper
is a necessary and sufficient condition for the existence of percolation, at
some time , in the case that the underlying tree is not necessary
spherically symmetric. This answers a question of Yuval Peres (personal
communication). We present also a formula for the Hausdorff dimension of the
set of exceptional times of percolation.Comment: 24 pages; to appear in Probability Theory and Related Field
Hydrodynamics of Spatially Ordered Superfluids
We derive the hydrodynamic equations for the supersolid and superhexatic
phases of a neutral two-dimensional Bose fluid. We find, assuming that the
normal part of the fluid is clamped to an underlying substrate, that both
phases can sustain third-sound modes and that in the supersolid phase there are
additional modes due to the superfluid motion of point defects (vacancies and
interstitials).Comment: 24 pages of ReVTeX and 7 uuencoded figures. Submitted for publication
in Phys. Rev.
Isospin Effects on Strangeness in Heavy-Ion Collisions
Kaon properties are studied within the framework of a fully covariant
transport approach. The kaon-nucleon potential is evaluated in two schemes, a
chiral perturbative approach and an effective One-Boson-Exchange model. Isospin
effects are explicitly accounted for in both models. The transport calculations
indicate a significant sensitivity of momentum distributions and total yields
of isospin states on the choice of the kaon-nucleon interaction.
Furthermore, isospin effects are rather moderate on absolute kaon yields, but
appear on strangeness ratios. This is an important issue in determining the
high density symmetry energy from studies of strangeness production in
heavy-ion collisions.Comment: 15 papes, 5 figures. Accepted for publication in Nuclear Physic
Photoconductance Quantization in a Single-Photon Detector
We have made a single-photon detector that relies on photoconductive gain in
a narrow electron channel in an AlGaAs/GaAs 2-dimensional electron gas. Given
that the electron channel is 1-dimensional, the photo-induced conductance has
plateaus at multiples of the quantum conductance 2e/h. Super-imposed on
these broad conductance plateaus are many sharp, small, conductance steps
associated with single-photon absorption events that produce individual
photo-carriers. This type of photoconductive detector could measure a single
photon, while safely storing and protecting the spin degree of freedom of its
photo-carrier. This function is valuable for a quantum repeater that would
allow very long distance teleportation of quantum information.Comment: 4 pages, 4 figure
Observations of Low Frequency Solar Radio Bursts from the Rosse Solar-Terrestrial Observatory
The Rosse Solar-Terrestrial Observatory (RSTO; www.rosseobservatory.ie) was
established at Birr Castle, Co. Offaly, Ireland (53 05'38.9", 7 55'12.7") in
2010 to study solar radio bursts and the response of the Earth's ionosphere and
geomagnetic field. To date, three Compound Astronomical Low-cost Low-frequency
Instrument for Spectroscopy and Transportable Observatory (CALLISTO)
spectrometers have been installed, with the capability of observing in the
frequency range 10-870 MHz. The receivers are fed simultaneously by biconical
and log-periodic antennas. Nominally, frequency spectra in the range 10-400 MHz
are obtained with 4 sweeps per second over 600 channels. Here, we describe the
RSTO solar radio spectrometer set-up, and present dynamic spectra of a sample
of Type II, III and IV radio bursts. In particular, we describe fine-scale
structure observed in Type II bursts, including band splitting and rapidly
varying herringbone features
Coherent Radio Pulses From GEANT Generated Electromagnetic Showers In Ice
Radio Cherenkov radiation is arguably the most efficient mechanism for
detecting showers from ultra-high energy particles of 1 PeV and above. Showers
occuring in Antarctic ice should be detectable at distances up to 1 km. We
report on electromagnetic shower development in ice using a GEANT Monte Carlo
simulation. We have studied energy deposition by shower particles and
determined shower parameters for several different media, finding agreement
with published results where available. We also report on radio pulse emission
from the charged particles in the shower, focusing on coherent emission at the
Cherenkov angle. Previous work has focused on frequencies in the 100 MHz to 1
GHz range. Surprisingly, we find that the coherence regime extends up to tens
of Ghz. This may have substantial impact on future radio-based neutrino
detection experiments as well as any test beam experiment which seeks to
measure coherent Cherenkov radiation from an electromagnetic shower. Our study
is particularly important for the RICE experiment at the South Pole.Comment: 44 pages, 29 figures. Minor changes made, reference added, accepted
for publication in Phys. Rev.
Radio Bursts Associated with Flare and Ejecta in the 13 July 2004 Event
We investigate coronal transients associated with a GOES M6.7 class flare and
a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the
flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were
observed. An EIT wave was detected later on. The main features in the radio
dynamic spectrum were a frequency-drifting continuum and two type II bursts.
Our analysis shows that if the first type II burst was formed in the low
corona, the burst heights and speed are close to the projected distances and
speed of the Moreton wave (a chromospheric shock wave signature). The
frequency-drifting radio continuum, starting above 1 GHz, was formed almost two
minutes prior to any shock features becoming visible, and a fast-expanding
piston (visible as the continuum) could have launched another shock wave. A
possible scenario is that a flare blast overtook the earlier transient, and
ignited the first type II burst. The second type II burst may have been formed
by the same shock, but only if the shock was propagating at a constant speed.
This interpretation also requires that the shock-producing regions were located
at different parts of the propagating structure, or that the shock was passing
through regions with highly different atmospheric densities. This complex
event, with a multitude of radio features and transients at other wavelengths,
presents evidence for both blast-wave-related and CME-related radio emissions.Comment: 14 pages, 6 figures; Solar Physics Topical Issue, in pres
The Muonium Atom as a Probe of Physics beyond the Standard Model
The observed interactions between particles are not fully explained in the
successful theoretical description of the standard model to date. Due to the
close confinement of the bound state muonium () can be used as
an ideal probe of quantum electrodynamics and weak interaction and also for a
search for additional interactions between leptons. Of special interest is the
lepton number violating process of sponteanous conversion of muonium to
antimuonium.Comment: 15 pages,6 figure
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