1,082 research outputs found
Magnetic Seed Delivery Autodibble Planter
Apparatus for punch planting of seeds comprising a
slotted-rimmed wheel rotatably mounted on a frame
with an axis of rotation passing through the center of a
gear fixed to the frame. The wheel is equipped with a
plurality of drive gears which communicate with and
rotate around the fixed gear. On each drive gear is
pivotally mounted a magnetic-tipped punch. The rotation
of the wheel causes the punches to move in and out
of the slots in the wheel. The action of the punch produces
a small hole in the soil and embeds a coated seed
therein
Cultural and Genetic Approaches to Manage Aflatoxin Contamination: Recent Insights Provide Opportunities for Improved Control.
Aspergillus flavus is a morphologically complex species that can produce the group of polyketide derived carcinogenic and mutagenic secondary metabolites, aflatoxins, as well as other secondary metabolites such as cyclopiazonic acid and aflatrem. Aflatoxin causes aflatoxicosis when aflatoxins are ingested through contaminated food and feed. In addition, aflatoxin contamination is a major problem, from both an economic and health aspect, in developing countries, especially Asia and Africa, where cereals and peanuts are important food crops. Earlier measures for control of A. flavus infection and consequent aflatoxin contamination centered on creating unfavorable environments for the pathogen and destroying contaminated products. While development of atoxigenic (nonaflatoxin producing) strains of A. flavus as viable commercial biocontrol agents has marked a unique advance for control of aflatoxin contamination, particularly in Africa, new insights into the biology and sexuality of A. flavus are now providing opportunities to design improved atoxigenic strains for sustainable biological control of aflatoxin. Further, progress in the use of molecular technologies such as incorporation of antifungal genes in the host and host-induced gene silencing, is providing knowledge that could be harnessed to develop germplasm that is resistant to infection by A. flavus and aflatoxin contamination. This review summarizes the substantial progress that has been made to understand the biology of A. flavus and mitigate aflatoxin contamination with emphasis on maize. Concepts developed to date can provide a basis for future research efforts on the sustainable management of aflatoxin contamination
Structural Characterization of Rapid Thermal Oxidized Si\u3csub\u3e1−x−y\u3c/sub\u3eGe\u3csub\u3ex\u3c/sub\u3eC\u3csub\u3ey\u3c/sub\u3e Alloy Films Grown by Rapid Thermal Chemical Vapor Deposition
The structural properties of as-grown and rapid thermal oxidized Si1−x−yGexCy epitaxial layers have been examined using a combination of infrared, x-ray photoelectron, x-ray diffraction, secondary ion mass spectroscopy, and Raman spectroscopy techniques. Carbon incorporation into the Si1−x−yGexCy system can lead to compressive or tensile strain in the film. The structural properties of the oxidized Si1−x−yGexCy film depend on the type of strain (i.e., carbon concentration) of the as-prepared film. For compressive or fully compensated films, the oxidation process drastically reduces the carbon content so that the oxidized films closely resemble to Si1−xGex films. For tensile films, two broad regions, one with carbon content higher and the other lower than that required for full strain compensation, coexist in the oxidized films
Relativistic ponderomotive force, uphill acceleration, and transition to chaos
Starting from a covariant cycle-averaged Lagrangian the relativistic
oscillation center equation of motion of a point charge is deduced and
analytical formulae for the ponderomotive force in a travelling wave of
arbitrary strength are presented. It is further shown that the ponderomotive
forces for transverse and longitudinal waves are different; in the latter,
uphill acceleration can occur. In a standing wave there exists a threshold
intensity above which, owing to transition to chaos, the secular motion can no
longer be described by a regular ponderomotive force.
PACS number(s): 52.20.Dq,05.45.+b,52.35.Mw,52.60.+hComment: 8 pages, RevTeX, 3 figures in PostScript, see also
http://www.physik.th-darmstadt.de/tqe
On the Behavior of Hexane on Graphite at Near-Monolayer Densities
We present the results of molecular dynamics (MD) studies of hexane
physisorbed onto graphite for eight coverages in the range (in units of monolayers). At low temperatures the adsorbate molecules
form a uniaxially incommensurate herringbone (UI-HB) solid. At high coverages
the solid consists of adsorbate molecules that are primarily rolled on their
side perpen-dicular to the surface of the substrate. As the coverage is
decreased, the amount of molecular rolling diminishes until = 0.933
where it disappears (molecules become primarily parallel to the surface). If
the density is decreased enough, vacancies appear. As the temperature is
increased we observe a three-phase regime for (with an
orientationally ordered nematic mesophase), for lower coverages the system
melts directly to the disordered (and isotropic) liquid phase. The
solid-nematic transition temperature is very sensitive to coverage whereas the
melting temperature is quite insensitive to it, except for at low coverages
where increased in-plane space and ultimately vacancies soften the solid phase
and lower the melting temperature. Our results signal the importance of
molecular rolling and tilting (which result from an the competition between
molecule-molecule and molecule-substrate interactions) for the formation of the
intermediate phase, while the insensitivity of the system's melting temperature
to changing density is understood in terms of in-plane space occupation through
rolling. Comparisons and contrasts with experimental results are discussed
Cytokinin Action Is Coupled to Ethylene in Its Effects on the Inhibition of Root and Hypocotyl Elongation in Arabidopsis thaliana Seedlings
Small denominators, frequency operators, and Lie transforms for nearly integrable quantum spin systems
Based on the previously proposed notions of action operators and of quantum integrability, frequency operators are introduced in a fully quantum-mechanical setting. They are conceptually useful because another formulation can be given to unitary perturbation theory. When worked out for quantum spin systems, this variant is found to be formally equivalent to canonical perturbation theory applied to nearly integrable systems consisting of classical spins. In particular, it becomes possible to locate the quantum-mechanical operator-valued equivalent of the frequency denominators that may cause divergence of the classical perturbation series. The results that are established here link the concept of quantum-mechanical integrability to a technical question, namely, the behavior of specific perturbation series
NASA Radiation Protection Research for Exploration Missions
The HZETRN code was used in recent trade studies for renewed lunar exploration and currently used in engineering development of the next generation of space vehicles, habitats, and EVA equipment. A new version of the HZETRN code capable of simulating high charge and energy (HZE) ions, light-ions and neutrons with either laboratory or space boundary conditions with enhanced neutron and light-ion propagation is under development. Atomic and nuclear model requirements to support that development will be discussed. Such engineering design codes require establishing validation processes using laboratory ion beams and space flight measurements in realistic geometries. We discuss limitations of code validation due to the currently available data and recommend priorities for new data sets
Review of Nuclear Physics Experiments for Space Radiation
Human space flight requires protecting astronauts from the harmful effects of space radiation. The availability of measured nuclear cross section data needed for these studies is reviewed in the present paper. The energy range of interest for radiation protection is approximately 100 MeV/n to 10 GeV/n. The majority of data are for projectile fragmentation partial and total cross sections, including both charge changing and isotopic cross sections. The cross section data are organized into categories which include charge changing, elemental, isotopic for total, single and double differential with respect to momentum, energy and angle. Gaps in the data relevant to space radiation protection are discussed and recommendations for future experiments are made
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