525 research outputs found
Virulence of Russian Wheat Aphid, Diuraphis Noxia (Kurdjumov) (Homoptera: Aphididae) Populations in Kenya
The Russian wheat aphid (RWA) Diuraphis noxia (Kurdjumov) is a serious pest of wheat in Kenya. Development and use of RWA resistant wheat (Triticum aestivum L.) varieties, has been constrained by RWA populations evolving with differential virulence to given resistant host plants. To fully exploit host plant resistance (HPR) in management of RWA, local populations of RWA have to be evaluated for differential virulence and biotypes in order to develop and deploy cultivars that exhibit cross biotype resistance. A study was conducted at KARI-Njoro to characterize virulence of RWA populations from the endemic areas (Eldoret, Mau Narok, Njoro and Egerton) in Kenya. A factorial experiment in randomized complete block design replicated three times was set up to evaluate seedling resistance to RWA with variety and aphid collection source as main factors in the screen house. Five adult RWA aphids from each of the four collection locations were used to infest four host genotypes; PI624933-1 containing Dn4 gene, 2414-11-2 containing Dn7 gene, KRWA9 which contains an unknown Dn gene and a susceptible check, K.KWALE, for 28 days to determine virulence of the RWA aphids to seedlings of the four wheat genotypes in the greenhouse. Data was recorded on damage scores, plant height, plant height reduction, shoot biomass and biomass reduction of test plants 28 days after infestation. Results of an analysis of variance of these plant parameters show that Egerton population was more virulent than populations selected from other areas as it caused more damage on resistant lines. Keywords: Diuraphis noxia, biotype, virulence, RWA, Wheat.
Математична модель контактного з’єднання метало-пластмасових циліндричних оболонок
We consider alpha scale spaces, a parameterized class (alpha is an element of (0, 1]) of scale space representations beyond the well-established Gaussian scale space, which are generated by the alpha-th power of the minus Laplace operator on a bounded domain using the Neumann boundary condition. The Neumann boundary condition ensures that there is no grey-value flux through the boundary. Thereby no artificial grey-values from outside the image affect the evolution proces, which is the case for the alpha scale spaces on an unbounded domain. Moreover, the connection between the a scale spaces which is not trivial in the unbounded domain case, becomes straightforward: The generator of the Gaussian semigroup extends to a compact, self-adjoint operator on the Hilbert space L-2(Omega) and therefore it has a complete countable set of eigen functions. Taking the alpha-th power of the Gaussian generator simply boils down to taking the alpha-th power of the corresponding eigenvalues. Consequently, all alpha scale spaces have exactly the same eigen-modes and can be implemented simultaneously as scale dependent Fourier series. The only difference between them is the (relative) contribution of each eigen-mode to the evolution proces. By introducing the notion of (non-dimensional) relative scale in each a scale space, we are able to compare the various alpha scale spaces. The case alpha = 0.5, where the generator equals the square root of the minus Laplace operator leads to Poisson scale space, which is at least as interesting as Gaussian scale space and can be extended to a (Clifford) analytic scale space
A Search for Correlation of Ultra-High Energy Cosmic Rays with IRAS-PSCz and 2MASS-6dF Galaxies
We study the arrival directions of 69 ultra-high energy cosmic rays (UHECRs)
observed at the Pierre Auger Observatory (PAO) with energies exceeding 55 EeV.
We investigate whether the UHECRs exhibit the anisotropy signal expected if the
primary particles are protons that originate in galaxies in the local universe,
or in sources correlated with these galaxies. We cross-correlate the UHECR
arrival directions with the positions of IRAS-PSCz and 2MASS-6dF galaxies
taking into account particle energy losses during propagation. This is the
first time that the 6dF survey is used in a search for the sources of UHECRs
and the first time that the PSCz survey is used with the full 69 PAO events.
The observed cross-correlation signal is larger for the PAO UHECRs than for 94%
(98%) of realisations from an isotropic distribution when cross-correlated with
the PSCz (6dF). On the other hand the observed cross-correlation signal is
lower than that expected from 85% of realisations, had the UHECRs originated in
galaxies in either survey. The observed cross-correlation signal does exceed
that expected by 50% of the realisations if the UHECRs are randomly deflected
by intervening magnetic fields by 5 degrees or more. We propose a new method of
analysing the expected anisotropy signal, by dividing the predicted UHECR
source distribution into equal predicted flux radial shells, which can help
localise and constrain the properties of UHECR sources. We find that the 69 PAO
events are consistent with isotropy in the nearest of three shells we define,
whereas there is weak evidence for correlation with the predicted source
distribution in the two more distant shells in which the galaxy distribution is
less anisotropic.Comment: 23 pages, version published in JCA
Gamma-Ray Bursts: The Underlying Model
A pedagogical derivation is presented of the ``fireball'' model of gamma-ray
bursts, according to which the observable effects are due to the dissipation of
the kinetic energy of a relativistically expanding wind, a ``fireball.'' The
main open questions are emphasized, and key afterglow observations, that
provide support for this model, are briefly discussed. The relativistic outflow
is, most likely, driven by the accretion of a fraction of a solar mass onto a
newly born (few) solar mass black hole. The observed radiation is produced once
the plasma has expanded to a scale much larger than that of the underlying
``engine,'' and is therefore largely independent of the details of the
progenitor, whose gravitational collapse leads to fireball formation. Several
progenitor scenarios, and the prospects for discrimination among them using
future observations, are discussed. The production in gamma- ray burst
fireballs of high energy protons and neutrinos, and the implications of burst
neutrino detection by kilometer-scale telescopes under construction, are
briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture
Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure
Accuracy and Stability of Computing High-Order Derivatives of Analytic Functions by Cauchy Integrals
High-order derivatives of analytic functions are expressible as Cauchy
integrals over circular contours, which can very effectively be approximated,
e.g., by trapezoidal sums. Whereas analytically each radius r up to the radius
of convergence is equal, numerical stability strongly depends on r. We give a
comprehensive study of this effect; in particular we show that there is a
unique radius that minimizes the loss of accuracy caused by round-off errors.
For large classes of functions, though not for all, this radius actually gives
about full accuracy; a remarkable fact that we explain by the theory of Hardy
spaces, by the Wiman-Valiron and Levin-Pfluger theory of entire functions, and
by the saddle-point method of asymptotic analysis. Many examples and
non-trivial applications are discussed in detail.Comment: Version 4 has some references and a discussion of other quadrature
rules added; 57 pages, 7 figures, 6 tables; to appear in Found. Comput. Mat
Hadronic Mass Spectrum Analysis of D+ into K- pi+ mu+ nu Decay and Measurement of the K*(892)^0 Mass and Width
We present a Kpi mass spectrum analysis of the four-body semileptonic charm
decay D+ into K- pi+ mu+ nu in the range of 0.65 GeV < mKpi < 1.5 GeV. We
observe a non-resonant contribution of 5.30 +- 0.74 +0.99 -0.51 % with respect
to the total D+ into K- pi+ mu+ nu decay. For the K*(892)^0 resonance, we
obtain a mass of 895.41 +- 0.32 +0.35 -0.36 MeV, a width of 47.79 +- 0.86 +1.3
-1.1 MeV, and a Blatt-Weisskopf damping factor parameter of 3.96 +- 0.54 +0.72
-0.90 GeV^(-1). We also report 90 % CL upper limits of 4 % and 0.64 % for the
branching ratios of D+ into K*(1680)^0 mu+ nu with respect to D+ into K- pi+
mu+ nu and D+ into K*(1430)^0 mu+ nu with respect to D+ into K- pi+ mu+ nu,
respectively.Comment: 14 page
Study of the Cabibbo-suppressed decay modes D0-->Pi-pi+ and D0-->K-K+
Using data from the FOCUS (E831) experiment at Fermilab, we present a new
measurement for the branching ratios of the Cabibbo-suppressed decay modes
D0-->Pi-Pi+ and D0-->K-K+. We measured:
Gamma(D0-->K-K+)/Gamma(D0-->Pi-Pi+) = 2.81 +/- 0.10(stat) +/- 0.06(syst),
Gamma(D0-->K-K+)/Gamma(D0-->K-Pi+) = 0.0993 +/- 0.0014(stat) +/- 0.0014(syst),
and Gamma(D0-->Pi-Pi+)/Gamma(D0-->K-Pi+) = 0.0353 +/- 0.0012 (stat) +/-
0.0006(syst).
These values have been combined with other experimental data to extract the
ratios of isospin amplitudes and the phase shifts for the D-->KK and D-->PiPi
decay channels.Comment: 12 pages, 1 Figure, accepted for publication in Phys.Lett.
Gauge and Scheme Dependence of Mixing Matrix Renormalization
We revisit the issue of mixing matrix renormalization in theories that
include Dirac or Majorana fermions. We show how a gauge-variant on-shell
renormalized mixing matrix can be related to a manifestly gauge-independent one
within a generalized scheme of renormalization. This
scheme-dependent relation is a consequence of the fact that in any scheme of
renormalization, the gauge-dependent part of the mixing-matrix counterterm is
ultra-violet safe and has a pure dispersive form. Employing the unitarity
properties of the theory, we can successfully utilize the afore-mentioned
scheme-dependent relation to preserve basic global or local symmetries of the
bare Lagrangian through the entire process of renormalization. As an immediate
application of our study, we derive the gauge-independent renormalization-group
equations of mixing matrices in a minimal extension of the Standard Model with
isosinglet neutrinos.Comment: 31 pages, LaTeX, uses axodraw.st
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
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