30,445 research outputs found
Entomopathogenic nematodes for biological control of codling moth
Entomopathogenic nematodes are often found naturally infecting codling moth larvae. The
effect of an autumn treatment with S. feltiae on the fruit damage in the following summer
was evaluated by treating 4 different apple orchards in October 2004 and 2005 at
application rates of 3.75; 2 and 1.5 billion nematodes in 4000 l / ha. In three of the treated
orchards, one treated with 3.75x109 nematodes/ha the other two treated with 2e9
nematode/ha, reduction in fruit damage was around 50%. In the most heavily infested
orchard, which was treated with 1.5x109 nematode/ha only 33% reduction in fruit damage
was achieved. Compared to previous studies, this was the first assessing the effect on the
fruit damage in the summer following the treatment rather than assessing the mortality of
sentinel larvae fixed to the treated tree trunks
Analysis of integration error in the ODP-L program and the effect of selenopotential parameters on the solution vector
Analysis of integration error in lunar orbit trajectory program and effect of selenopotential parameters on solution vecto
Perfect Scalars on the Lattice
We perform renormalization group transformations to construct optimally local
perfect lattice actions for free scalar fields of any mass. Their couplings
decay exponentially. The spectrum is identical to the continuum spectrum, while
thermodynamic quantities have tiny lattice artifacts. To make such actions
applicable in simulations, we truncate the couplings to a unit hypercube and
observe that spectrum and thermodynamics are still drastically improved
compared to the standard lattice action. We show how preconditioning techniques
can be applied successfully to this type of action. We also consider a number
of variants of the perfect lattice action, such as the use of an anisotropic or
triangular lattice, and modifications of the renormalization group
transformations motivated by wavelets. Along the way we illuminate the
consistent treatment of gauge fields, and we find a new fermionic fixed point
action with attractive properties.Comment: 26 pages, 11 figure
Four-dimensional lattice results on the MSSM electroweak phase transition
We present the results of our large scale 4-dimensional (4d) lattice
simulations for the MSSM electroweak phase transition (EWPT). We carried out
infinite volume and continuum limit extrapolations and found a transition whose
strength agrees well with perturbation theory. We determined the properties of
the bubble wall that are important for a successful baryogenesis.Comment: 5 pages, 3figures. Talk presented at Johns Hopkins Workshop on
Nonperturbative Quantum Field Theory Methods and their Applications (19-21
August 2000.
Electroweak Phase Transition in the MSSM: 4-Dimensional Lattice Simulations
Recent lattice results have shown that there is no Standard Model (SM)
electroweak phase transition (EWPT) for Higgs boson masses above \approx 72
GeV, which is below the present experimental limit. According to perturbation
theory and 3-dimensional (3d) lattice simulations there could be an EWPT in the
Minimal Supersymmetric Standard Model (MSSM) that is strong enough for
baryogenesis up to m_h \approx 105 GeV. In this letter we present the results
of our large scale 4-dimensional (4d) lattice simulations for the MSSM EWPT. We
carried out infinite volume and continuum limits and found a transition whose
strength agrees well with perturbation theory, allowing MSSM electroweak
baryogenesis at least up to m_h = 103 \pm 4 GeV. We determined the properties
of the bubble wall that are important for a successful baryogenesis.Comment: 4 pages, 4 figures included; lightest Higgs mass bound relaxed
(abstract, fig. 3 changed), version to appear in Phys. Rev. Letter
Single-growth embedded epitaxy AlGaAs injection lasers with extremely low threshold currents
A new type of strip-geometry AlGaAs double-heterostructure laser with an embedded optical waveguide has been developed. The new structure is fabricated using a single step of epitaxial growth. Lasers with threshold currents as low as 9.5 mA (150 µm long) were obtained. These lasers exhibit operation in a single spatial and longitudinal mode, have differential quantum efficiencies exceeding 45%, and a characteristic temperature of 175° C. They emit more than 12 mW/facet of optical power without any kinks
Single contact tailored gain phased array of semiconductor lasers
We demonstrate a single contact tailored gain-guided array in which the gain profile across the array is made strongly asymmetric by varying the width of the contact stripes. A proton isolated array of six (GaAl)As lasers with 5-µm separations and widths varying linearly between 3 and 8 µm had a single lobed far field 2° wide, close to the diffraction limit for a single supermode. Fabrication of this device is simple, and suited to large-scale processing techniques. We also show that in such an asymmetric gain-guided array the fundamental mode is favored over higher order modes, and that higher order modes can have single lobed far-field patterns differing only slightly from that of the fundamental
The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk
We analyze high quality abundances data of solar neighborhood stars and show
that there are two distinct regimes of [alpha/Fe] versus age which we identify
as the epochs of the thick and thin disk formation. A tight correlation between
metallicity and [alpha/Fe] versus age is clearly identifiable on thick disk
stars, implying that this population formed from a well mixed ISM, over a time
scale of 4-5 Gyr. Thick disk stars vertical velocity dispersion correlate with
age, with the youngest objects having as small scale heights as those of thin
disk stars. A natural consequence of these two results is that a vertical
metallicity gradient is expected in this population. We suggest that the thick
disk set the initial conditions for the formation of the inner thin disk. This
provides also an explanation of the apparent coincidence between the step in
metallicity at 7-10 kpc in the thin disk and the confinment of the thick disk
at about R<10 kpc. We suggest that the outer thin disk developped outside the
influence of the thick disk, but also that the high alpha-enrichment of the
outer regions may originate from a primordial pollution by the gas expelled
from the thick disk. Local metal-poor thin disk stars, whose properties are
best explained by an origin in the outer disk, are shown to be as old as the
youngest thick disk (9-10 Gyr), implying that the outer thin disk started to
form while the thick disk formation was still on-going in the inner Galaxy. We
point out that, given the tight age-abundance relations in the thick disk, an
inside-out process would give rise to a radial gradient in abundances in this
population which is not observed. Finally, we argue that the data discussed
here leave little room for radial migration, either to have contaminated the
solar vicinity, or, to have redistributed stars in significant proportion
across the solar annulus.Comment: Accepted in A&A, Revised version with new figures and extended
discussio
Phase transitions, double-scaling limit, and topological strings
Topological strings on Calabi--Yau manifolds are known to undergo phase
transitions at small distances. We study this issue in the case of perturbative
topological strings on local Calabi--Yau threefolds given by a bundle over a
two-sphere. This theory can be regarded as a q--deformation of Hurwitz theory,
and it has a conjectural nonperturbative description in terms of q--deformed 2d
Yang--Mills theory. We solve the planar model and find a phase transition at
small radius in the universality class of 2d gravity. We give strong evidence
that there is a double--scaled theory at the critical point whose all genus
free energy is governed by the Painlev\'e I equation. We compare the critical
behavior of the perturbative theory to the critical behavior of its
nonperturbative description, which belongs to the universality class of 2d
supergravity. We also give evidence for a new open/closed duality relating
these Calabi--Yau backgrounds to open strings with framing.Comment: 49 pages, 3 eps figures; section added on non-perturbative proposal
and 2d gravity; minor typos correcte
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