57,492 research outputs found
The Distribution of Natural Enemies of the Corn Leaf Aphid (Homoptera: Aphdidae) on Field Corn
(excerpt)
The corn leaf aphid (CLA), Rhopalosiphum maidis (Fitch), is found on field corn in the midwest Cnited States each year. Except for infrequent and scattered outbreaks, CLA populations remain at low levels. Injury to corn occurs during tasseling (Snelling et aL 1941) and is caused by CLAs which are the progeny of colonizers that arrived 2-3 weeks earlier when the corn was in the whorl stage (Bryson 1934, Falter 1963)
Suggestions for Improved Benchmark Scenarios for Higgs-Boson Searches at LEP2
We suggest new benchmark scenarios for the Higgs-boson search at LEP2.
Keeping m_t and M_SUSY fixed, we improve on the definition of the maximal
mixing benchmark scenario defining precisely the values of all MSSM parameters
such that the new m_h^max benchmark scenario yields the parameters which
maximize the value of m_h for a given tan(beta). The corresponding scenario
with vanishing mixing in the scalar top sector is also considered. We propose a
further benchmark scenario with a relatively large value of |mu|, a moderate
value of M_SUSY, and moderate mixing parameters in the scalar top sector. While
the latter scenario yields m_h values that in principle allow to access the
complete M_A-tan(beta)-plane at LEP2, on the other hand it contains parameter
regions where the Higgs-boson detection can be difficult, because of a
suppression of the branching ratio of its decay into bottom quarks.Comment: 9 pages, no figures, Contribution to the Workshop on ``New
Theoretical Developments for Higgs Physics at LEP2'', CERN, October 199
The Exchange Gate in Solid State Spin Quantum Computation: The Applicability of the Heisenberg Model
Solid state quantum computing proposals rely on adiabatic operations of the
exchange gate among localized spins in nanostructures. We study corrections to
the Heisenberg interaction between lateral semiconductor quantum dots in an
external magnetic field. Using exact diagonalization we obtain the regime of
validity of the adiabatic approximation. We also find qualitative corrections
to the Heisenberg model at high magnetic fields and in looped arrays of spins.
Looped geometries of localized spins generate flux dependent, multi-spin terms
which go beyond the basic Heisenberg model.Comment: 13 pages, 8 figure
The Immunity of Polymer-Microemulsion Networks
The concept of network immunity, i.e., the robustness of the network
connectivity after a random deletion of edges or vertices, has been
investigated in biological or communication networks. We apply this concept to
a self-assembling, physical network of microemulsion droplets connected by
telechelic polymers, where more than one polymer can connect a pair of
droplets. The gel phase of this system has higher immunity if it is more likely
to survive (i.e., maintain a macroscopic, connected component) when some of the
polymers are randomly degraded. We consider the distribution of the
number of polymers between a pair of droplets, and show that gel immunity
decreases as the variance of increases. Repulsive interactions
between the polymers decrease the variance, while attractive interactions
increase the variance, and may result in a bimodal .Comment: Corrected typo
Chandra observations of the HII complex G5.89-0.39 and TeV gamma-ray source HESSJ1800-240B
We present the results of our investigation, using a Chandra X-ray
observation, into the stellar population of the massive star formation region
G5.89-0.39, and its potential connection to the coincident TeV gamma-ray source
HESSJ1800-240B. G5.89-0.39 comprises two separate HII regions G5.89-0.39A and
G5.89-0.39B (an ultra-compact HII region). We identified 159 individual X-ray
point sources in our observation using the source detection algorithm
\texttt{wavdetect}. 35 X-ray sources are associated with the HII complex
G5.89-0.39. The 35 X-ray sources represent an average unabsorbed luminosity
(0.3-10\,keV) of \,erg/s, typical of B7-B5 type stars. The
potential ionising source of G5.89-0.39B known as Feldt's star is possibly
identified in our observation with an unabsorbed X-ray luminosity suggestive of
a B7-B5 star. The stacked energy spectra of these sources is well-fitted with a
single thermal plasma APEC model with kT5\,keV, and column density
N\,cm (A). The residual
(source-subtracted) X-ray emission towards G5.89-0.39A and B is about 30\% and
25\% larger than their respective stacked source luminosities. Assuming this
residual emission is from unresolved stellar sources, the total
B-type-equivalent stellar content in G5.89-0.39A and B would be 75 stars,
consistent with an earlier estimate of the total stellar mass of hot stars in
G5.89-0.39. We have also looked at the variability of the 35 X-ray sources in
G5.89-0.39. Ten of these sources are flagged as being variable. Further studies
are needed to determine the exact causes of the variability, however the
variability could point towards pre-main sequence stars. Such a stellar
population could provide sufficient kinetic energy to account for a part of the
GeV to TeV gamma-ray emission in the source HESSJ1800-240B.Comment: 34 pages, 9 figure
Low-momentum Hyperon-Nucleon Interactions
We present a first exploratory study for hyperon-nucleon interactions using
renormalization group techniques. The effective two-body low-momentum potential
V_low-k is obtained by integrating out the high-momentum components from
realistic Nijmegen YN potentials. A T-matrix equivalence approach is employed,
so that the low-energy phase shifts are reproduced by V_low-k up to a momentum
scale Lambda ~ 500 MeV. Although the various bare Nijmegen models differ
somewhat from each other, the corresponding V_low-k interactions show
convergence in some channels, suggesting a possible unique YN interaction at
low momenta.Comment: 4 pages, 6 figure
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