31,185 research outputs found
Breakup coupling effects on near-barrier <sup>6</sup>Li, <sup>7</sup>Be and <sup>8</sup>B + <sup>58</sup>Ni elastic scattering compared
New data for near-barrier 6Li, 7Be and 8B + 58Ni elastic scattering enable a comparison of breakup coupling effects for these loosely-bound projectiles. Coupled Discretised Continuum Channels (CDCC) calculations suggest that the large total reaction cross sections for 8B + 58Ni are dominated by breakup at near-barrier energies, unlike 6Li and 7Be where breakup makes a small contribution. In spite of this, the CDCC calculations show a small coupling influence due to breakup for 8B, in contrast to the situation for 6Li and 7Be. An examination of the S matrices gives a clue to this counter-intuitive behaviour
Aphidophagous Coccinellids in Alfalfa, Small Grains, and Maize in Eastern South Dakota
In a 13-year study of aphidophagous coccinellids associated with alfalfa (Medicago sativa), maize (Zea mays), and small grain crops in eastern South Dakota, the following species were consistently associated with the crops: Hippodamia convergens, H. tredecimpunctata tibialis, H. parenthesis, Coleomegilla maculata lengi, Coccinella transversoguttata richardsoni, Cycloneda munda, and Adalia bipunctata. All species except A. bipunctata were associated with each of the three crops, while A. bipunctata occurred only in maize. Relative abundances of each species varied among crops and among years. Although only seven species were associated with the crops, additional species were captured on sticky traps stationed adjacent to sampled fields. The species diversity of immature coccinellids did not differ among crops but did differ among years. The diversity of adults differed among crops and years. The site from which samples were taken had no influence on the diversity of immatures or adults. Species relative abundances in alfalfa and small grains were more similar to each other than they were to relative abundances in maize
What measurable zero point fluctuations can(not) tell us about dark energy
We show that laboratory experiments cannot measure the absolute value of dark
energy. All known experiments rely on electromagnetic interactions. They are
thus insensitive to particles and fields that interact only weakly with
ordinary matter. In addition, Josephson junction experiments only measure
differences in vacuum energy similar to Casimir force measurements. Gravity,
however, couples to the absolute value. Finally we note that Casimir force
measurements have tested zero point fluctuations up to energies of ~10 eV, well
above the dark energy scale of ~0.01 eV. Hence, the proposed cut-off in the
fluctuation spectrum is ruled out experimentally.Comment: 4 page
A Descriptive Study of the Population Dynamics of Adult \u3ci\u3eDiabrotica Virgifera Virgifera\u3c/i\u3e (Coleoptera: Chrysomelidae) in Artificially Infested Corn Fields
The influence of corn plant phenology on the dynamics of adult western corn rootworm, Diabrotica virgifera virgifera, populations was studied during 1988 and 1989 in com fields artificially infested with eggs. Fifty percent of adult emergence from the soil occurred by day 194 in 1988 and day 203 in 1989. In both years, adult emergence was synchronized with corn flowering, eggs were recovered in soil samples approximately four days after reproductive females were first observed in the population, and oviposition was essentially complete about 25 days after it began. The number of reproductive female beetle-days accumulating per m2 was similar in both years. Approximately two times as many eggs were laid in 1988 (1239 eggs 1m2) as in 1989 (590 eggs 1m2). The difference in egg density may have been caused by differences among years in the temporal synchrony of reproductive beetles with flowering corn. Daily survival rates of adults were high while corn was flowering; exhibited a gradual decline during grain filling; and decreased rapidly during the grain drying stage
Proactive Algorithms for Job Shop Scheduling with Probabilistic Durations
Most classical scheduling formulations assume a fixed and known duration for
each activity. In this paper, we weaken this assumption, requiring instead that
each duration can be represented by an independent random variable with a known
mean and variance. The best solutions are ones which have a high probability of
achieving a good makespan. We first create a theoretical framework, formally
showing how Monte Carlo simulation can be combined with deterministic
scheduling algorithms to solve this problem. We propose an associated
deterministic scheduling problem whose solution is proved, under certain
conditions, to be a lower bound for the probabilistic problem. We then propose
and investigate a number of techniques for solving such problems based on
combinations of Monte Carlo simulation, solutions to the associated
deterministic problem, and either constraint programming or tabu search. Our
empirical results demonstrate that a combination of the use of the associated
deterministic problem and Monte Carlo simulation results in algorithms that
scale best both in terms of problem size and uncertainty. Further experiments
point to the correlation between the quality of the deterministic solution and
the quality of the probabilistic solution as a major factor responsible for
this success
Dark energy, chaotic fields, and fundamental constants
To explain the currently observed accelerated expansion of the universe, a
large number of different theoretical models are presently being discussed. In
one way or another, all of these contain `new physics', though at different
levels. The big question is how to select out of infinitely many possible
models the right one. Here we discuss a possibility that has so far been
somewhat neglected, namely that the new physics underlying dark energy arises
out of a gravitationally active amendment of the electroweak and strong sector
of the standard model. This amendment basically consists of a rapidly
fluctuating gravitationally active dynamics of vacuum fluctuations with a
cutoff of the order of the neutrino mass scale. We consider a concrete model
for this based on second-quantized self-interacting scalar fields, which evolve
in a chaotic way. It is shown that expectations with respect to the chaotic
dynamics yield statements on the observed numerical values of the electroweak
coupling constants with amazing precision, thus providing evidence for the
physical relevance of this model.Comment: 11 pages, 1 figure. Invited talk given at the 6th International
Symposium on Frontiers of Fundamental and Computational Physics, Udine, 2004.
To appear in the proceeding
Breakup coupling Effects on Near-Barrier 6Li, 7Be and 8B + 58Ni Elastic Scattering Compared
Submitted to Nucl. Phys. ANew data for near-barrier 6Li, 7Be and 8B + 58Ni elastic scattering enable a comparison of breakup coupling effects for these loosely-bound projectiles. Coupled Discretised Con- tinuum Channels (CDCC) calculations suggest that the large total reaction cross sections for 8B + 58Ni are dominated by breakup at near-barrier energies, unlike 6Li and 7Be where breakup makes a small contribution. In spite of this, the CDCC calculations show a small coupling influence due to breakup for 8B, in contrast to the situation for 6Li and 7Be. An examination of the S matrices gives a clue to this counter-intuitive behaviour
Cluster Model for Near-barrier Fusion Induced by Weakly Bound and Halo Nuclei
The influence on the fusion process of coupling transfer/breakup channels is
investigated for the medium weight Li+Co systems in the vicinity
of the Coulomb barrier. Coupling effects are discussed within a comparison of
predictions of the Continuum Discretized Coupled-Channels model. Applications
to He+Co induced by the borromean halo nucleus He are also
proposed.Comment: 5 pages, 3 figures, FINUSTAR2 Conference, Aghios Nikolaus, Crete,
Greece. 10-14 September 200
6Li direct breakup lifetimes
alpha-d coincidence data were studied for the 6Li + 59Co reaction at E(lab) =
29.6 MeV. By using a kinematic analysis, it was possible to identify which
process, leading to the same final state, has the major contribution for each
of the selected angular regions. Contributions of the 6Li sequential and direct
breakup to the incomplete fusion/transfer process were discussed by considering
the lifetimes obtained by using a semiclassical approach, for both breakup
components.Comment: 5 pages, 4 figures, Invited Talk (Parrallel Sessions) of A. Szanto de
Toledo, prepared for the Proccedings of the 10th International Conference on
Nucleus-Nucleus Collisions, August 16-21, 2009, Beijing, China; submitted to
Nucl. Phys. A (Proceedings of NN2009
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