5,053 research outputs found
The effect of within-crop habitat manipulations on the conservation biological control of aphids in field-grown lettuce
Within-crop habitat manipulations have the potential to increase the biological
control of pests in horticultural field crops. Wildflower strips have been shown to
increase the abundance of natural enemies, but there is little evidence to date of an
impact on pest populations. The aim of this study was to determine whether withincrop
wildflower strips can increase the natural regulation of pests in horticultural
field crops. Aphid numbers in plots of lettuce grown adjacent to wildflower strips
were compared with those in plots grown in the absence of wildflowers. The presence
of wildflower strips led to a decrease in aphid numbers on adjacent lettuce plants
during June and July, but had less impact in August and September. The decrease in
aphid numbers was greatest close to the wildflower strips and, the decrease in aphid
numbers declined with increasing distance from the wildflower strips, with little
effect at a distance of ten metres. The main natural enemies found in the crop were
those that dispersed aerially, which is consistent with data from previous studies on
cereal crops. Analysis and interpretation of natural enemy numbers was difficult due
to low recovery of natural enemies, and the numbers appeared to follow changes in
aphid abundance rather than being directly linked to the presence of wildflower
strips. Cutting the wildflower strips, to remove floral resources, had no impact on the
reduction in aphid numbers achieved during June and July, but decreased the effect
of the wildflower strips during August and September. The results suggest that
wildflower strips can lead to increased natural regulation of pest aphids in outdoor
lettuce crops, but more research is required to determine how this is mediated by
natural enemies and how the impact of wildflower strips on natural pest regulation
changes during the growing season
Explosive Event in MON-3 Oxidizer System Resulting from Pressure Transducer Failure
In 2003, a Druck(Registered Trademark) pressure transducer failed catastrophically in a test system circulating nitrogen tetroxide at NASA Johnson Space Center White Sands Test Facility. The cause of the explosion was not immediately obvious since the wetted areas of the pressure transducer were constructed of materials compatible with nitrogen tetroxide. Chemical analysis of the resulting residue and a materials analysis of the diaphragm and its weld zones were used to determine the chain of events that led to the catastrophic failure. Due to excessive dynamic pressure loading in the test system, the diaphragm in the pressure transducer suffered cyclic failure and allowed the silicon oil located behind the isolation diaphragm to mix with the nitrogen tetroxide. The reaction between these two chemicals formed a combination of 2,4-di and 2,4,6-trinitrophenol, which are shock sensitive explosives that caused the failure of the pressure transducer. Further research indicated numerous manufacturers offer similar pressure transducers with silicone oil separated from the test fluid by a thin stainless steel isolation diaphragm. Caution must be exercised when purchasing a pressure transducer for a particular system to avoid costly failures and test system contamination
The Importance Of Female Choice: Evolutionary Perspectives On Constraints, Expressions, And Variations
This chapter introduces the reader to some of the influential perspectives on female mate choice in human evolutionary biology, including parental investment theory. We then present two key theories in evolutionary psychology that have been applied to understand variations in women’s mating preferences and choices: sexual strategies theory and strategic pluralism theory. Although the importance of female choice has gained widespread acceptance in the biological sciences, the influence that female choice has on mating systems can be limited by many factors, such as control over mating decisions by parents and men’s control over women’s sexuality. Despite these constraints on female choice, women are able to exercise their mate preferences through extramarital affairs and influencing parental attempts to arrange marriages.https://digitalcommons.chapman.edu/psychology_books/1015/thumbnail.jp
VLSI implementation of an efficient method for the computation of line spectral frequencies
In speech coding applications using linear predictive techniques, the computation of line spectral frequencies (LSFs) from the predictor coefficients is an extremely computationally intensive task. The unique properties of the symmetric and antisymmetric polynomial roots limit the region which must be searched, however it is still necessary to perform a root-finding algorithm on a high-order polynomial.
Certain algorithms have been developed to reduce the complexity of the root finding exercise. One such algorithm, developed by Ramachandran and Kabal, takes advantage of certain properties of the symmetric and antisymmetric polynomials to map the upper portion of the unit circle onto the real interval [-1,1] by converting the polynomials into a Chebyshev polynomial series representation. Because Chebyshev polynomials may be evaluated efficiently using the Clenshaw recurrence formula, far fewer computations are necessary to search the linear region for zero crossings.
This work investigates the implementation of the Ramachandran-Kabal algorithm in a VLSI design suitable for integration into larger speech processing systems. An implementation exclusively in VHDL is developed. Simulation of the VHDL design is performed and the post-synthesis results evaluated
Direct readout meteorological satellite data processing with a low-cost, computer-linked system
September, 1974.Includes bibliographical references
Constraining the Nature of X-ray Cavities in Clusters and Galaxies
We present results from an extensive survey of 64 cavities in the X-ray halos
of clusters, groups and normal elliptical galaxies. We show that the evolution
of the size of the cavities as they rise in the X-ray atmosphere is
inconsistent with the standard model of adiabatic expansion of purely
hydrodynamic models. We also note that the majority of the observed bubbles
should have already been shredded apart by Rayleigh-Taylor and
Richtmyer-Meshkov instabilities if they were of purely hydrodynamic nature.
Instead we find that the data agrees much better with a model where the
cavities are magnetically dominated and inflated by a current-dominated
magneto-hydrodynamic jet model, recently developed by Li et al. (2006) and
Nakamura et al. (2006). We conduct complex Monte-Carlo simulations of the
cavity detection process including incompleteness effects to reproduce the
cavity sample's characteristics. We find that the current-dominated model
agrees within 1sigma, whereas the other models can be excluded at >5sigma
confidence. To bring hydrodynamic models into better agreement, cavities would
have to be continuously inflated. However, these assessments are dependent on
our correct understanding of the detectability of cavities in X-ray
atmospheres, and will await confirmation when automated cavity detection tools
become available in the future. Our results have considerable impact on the
energy budget associated with active galactic nucleus feedback.Comment: 21 pages, 12 figures, emulateapj, accepted for publication in ApJ,
responded to referee's comments and added a new model, conclusions unchange
Mitigating NPD And R&D Risks Via A Portfolio Effect In Country Choice
New Product Development as well as Research and Development projects tend to be inherently risky investments. Most MNC’s today have great latitude in choosing site and country locations to build or contract Research or Development projects. MNC R&D risks, corporate wide, can be moderated via a diversification of NPD/R&D projects across multiple cultures and countries. In fact there is some evidence that R&D global diversification can generate synergies. (Fast track projects that work around the clock via work being done in three locations each 8 hours off from the other.) Foreign R&D facilities can help serve as outposts to facilitate the entrance into strategic foreign markets. This paper attempts to develop decision methodologies for allocating NPD/R&D globally with the goal of both reducing risks and increasing global competitiveness
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