13,326 research outputs found
A comparison of the in vitro and in planta responses of Phytophthora cinnamomi isolates to phosphite
Research in plant pathology often relies on testing interactions between a fungicide and a pathogen in vitro and extrapolating from these results what may happen in planta. Likewise, results from glasshouse experiments are used to estimate what will happen if the fungicide is applied in the field. However, it is difficult to obtain conditions in vitro and in the glasshouse which reflect the conditions where the fungicide may eventually be used, in the field.
The aim of this paper is to compare results of the effect of phosphite on P. cinnamomi isolates in vitro and in planta
Physical space description of decorated quasicrystals
In this paper the systematic method of dealing with the arbitrary decorations
of quasicrystals is presented. The method is founded on the average unit cell
formalism and operates in the physical space only, where each decorating atom
manifests itself just by an additional component of the displacement density
function in the average unit cell. Such approach allows us to use almost all
classical crystallography algorithms for structure refining based on
experimental data and may meaningly decrease the number of parameters which
have to be fit. Further help for such analysis may be the use of proposed
recently average Patterson function, here applied to decorated sets. As an
example we present a description of a class of decorated quasicrystals based on
Sturmian sequence of two interatomic spacings: we calculate explicitly
structure factor, the shape of average Patterson function and give an algorithm
for pattern analysis.Comment: 17 pages, 5 figure
Langmuir Wave Generation Through A Neutrino Beam Instability
A standard version of a kinetic instability for the generation of Langmuir
waves by a beam of electrons is adapted to describe the analogous instability
due to a beam of neutrinos. The interaction between a Langmuir wave and a
neutrino is treated in the one-loop approximation to lowest order in an
expansion in in the standard electroweak model.
It is shown that this kinetic instability is far too weak to occur in a
suggested application to the reheating of the plasma behind a stalled shock in
a type II supernova (SN). This theory is also used to test the validity of a
previous analysis of a reactive neutrino beam instability and various
shortcomings of this theory are noted. In particular, it is noted that
relativistic plasma effects have a significant effect on the calculated growth
rates, and that any theoretical description of neutrino-plasma interactions
must be based directly on the electroweak theory. The basic scalings discussed
in this paper suggest that a more complete investigation of neutrino-plasma
processes should be undertaken to look for an efficient process capable of
driving the stalled shock of a type II SN.Comment: 23 pages, incl. 5 postscript figure
An improved calculation of the isospin-symmetry-breaking corrections to superallowed Fermi beta decay
We report new shell-model calculations of the isospin-symmetry-breaking
correction to superallowed nuclear beta decay. The most important improvement
is the inclusion of core orbitals, which are demonstrated to have a significant
impact on the mismatch in the radial wave functions of the parent and daughter
states. We determine which core orbitals are important to include from an
examination of measured spectroscopic factors in single-nucleon pick-up
reactions. We also examine the new radiative-correction calculation by Marciano
and Sirlin and, by a simple reorganization, show that it is possible to
preserve the conventional separation into a nucleus-independent inner radiative
term and a nucleus-dependent outer term. We tabulate new values for the three
theoretical corrections for twenty superallowed transitions, including the
thirteen well-studied cases. With these new correction terms the corrected Ft
values for the thirteen cases are statistically consistent with one another and
the anomalousness of the 46V result disappears. These new calculations lead to
a lower average Ft value and a higher value of Vud. The sum of squares of the
top-row elements of the CKM matrix now agrees exactly with unitarity.Comment: 15 pages, 2 postscript figures, revtex
A new analysis of 14O beta decay: branching ratios and CVC consistency
The ground-state Gamow-Teller transition in the decay of 14O is strongly
hindered and the electron spectrum deviates markedly from the allowed shape. A
reanalysis of the only available data on this spectrum changes the branching
ratio assigned to this transition by seven standard deviations: our new result
is (0.54 \pm 0.02)%. The Kurie plot data from two earlier publications are also
examined and a revision to their published branching ratios is recommended. The
required nuclear matrix elements are calculated with the shell model and, for
the first time, consistency is obtained between the M1 matrix element deduced
from the analog gamma transition in 14N and that deduced from the slope of the
shape-correction function in the beta transition, a requirement of the
conserved vector current hypothesis. This consistency is only obtained,
however, if renormalized rather than free-nucleon operators are used in the
shell-model calculations. In the mirror decay of 14C a similar situation
occurs. Consistency between the 14C lifetime, the slope of the shape-correction
function and the M1 matrix element from gamma decay can only be achieved with
renormalized operators in the shell-model calculation.Comment: 9 pages; revtex4; one figur
Survival Probability for Open Spherical Billiards
We study the survival probability for long times in an open spherical
billiard, extending previous work on the circular billiard. We provide details
of calculations regarding two billiard configurations, specifically a sphere
with a circular hole and a sphere with a square hole. The constant terms of the
long-term survival probability expansions have been derived analytically. Terms
that vanish in the long time limit are investigated analytically and
numerically, leading to connections with the Riemann hypothesis
A solenoidal electron spectrometer for a precision measurement of the neutron -asymmetry with ultracold neutrons
We describe an electron spectrometer designed for a precision measurement of
the neutron -asymmetry with spin-polarized ultracold neutrons. The
spectrometer consists of a 1.0-Tesla solenoidal field with two identical
multiwire proportional chamber and plastic scintillator electron detector
packages situated within 0.6-Tesla field-expansion regions. Select results from
performance studies of the spectrometer with calibration sources are reported.Comment: 30 pages, 19 figures, 1 table, submitted to NIM
Gravitational Microlensing Near Caustics I: Folds
We study the local behavior of gravitational lensing near fold catastrophes.
Using a generic form for the lensing map near a fold, we determine the
observable properties of the lensed images, focusing on the case when the
individual images are unresolved, i.e., microlensing. Allowing for images not
associated with the fold, we derive analytic expressions for the photometric
and astrometric behavior near a generic fold caustic. We show how this form
reduces to the more familiar linear caustic, which lenses a nearby source into
two images which have equal magnification, opposite parity, and are equidistant
from the critical curve. In this case, the simplicity and high degree of
symmetry allows for the derivation of semi-analytic expressions for the
photometric and astrometric deviations in the presence of finite sources with
arbitrary surface brightness profiles. We use our results to derive some basic
properties of astrometric microlensing near folds, in particular we predict for
finite sources with uniform and limb darkening profiles, the detailed shape of
the astrometric curve as the source crosses a fold. We find that the
astrometric effects of limb darkening will be difficult to detect with the
currently planned accuracy of the Space Interferometry Mission. We verify our
results by numerically calculating the expected astrometric shift for the
photometrically well-covered Galactic binary lensing event OGLE-1999-BUL-23,
finding excellent agreement with our analytic expressions. Our results can be
applied to any lensing system with fold caustics, including Galactic binary
lenses and quasar microlensing.Comment: 37 pages, 7 figures. Revised version includes an expanded discussion
of applications. Accepted to ApJ, to appear in the August 1, 2002 issue
(v574
- …