5,749 research outputs found
The Subcolonization and Buildup of \u3ci\u3eTetrastichus Julis,\u3c/i\u3e (Hymenoptera: Eulophidae) a Larval Parasitoid of the Cereal Leaf Beetle, (Coleoptera: Chrysomelidae) in the Lower Peninsula of Michigan
Following initial establishment of the parasitoid, Tetrastichus julis (Walker), at a carefully managed field nursery, releases of parasitized Oulema melanopus larvae were made by Michigan county agents at preselected sites throughout the lower peninsula during 1970-74. A follow-up recovery program during 1971-75 revealed continued dispersion and population increase for T. julis. An independent census verified the increasing rates of parasitism
Enhancement of the Curie temperature in GaMnAs/InGaMnAs superlattices
We report on an enhancement of the Curie temperature in GaMnAs/InGaMnAs
superlattices grown by low-temperature molecular beam epitaxy, which is due to
thin InGaMnAs or InGaAs films embedded into the GaMnAs layers. The pronounced
increase of the Curie temperature is strongly correlated to the In
concentration in the embedded layers. Curie temperatures up to 110 K are
observed in such structures compared to 60 K in GaMnAs single layers grown
under the same conditions. A further increase in T up to 130 K can be
achieved using post-growth annealing at temperatures near the growth
temperature. Pronounced thickness fringes in the high resolution X-ray
diffraction spectra indicate good crystalline quality and sharp interfaces in
the structures.Comment: 4 pages, 4 figures, submitted to Appl. Phys. Let
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An Assessment of the Impact of Uncertainty on Automatic Generation Control Systems
This paper proposes a framework to quantify the impact of uncertainty that arises from load variations, renewable-based generation, and noise in communication channels on the automatic generation control (AGC) system. To this end, we rely on a model of the power system that includes the synchronous generator dynamics, the network, and the AGC system dynamics, as well as the effect of various sources of uncertainty. Then, we develop a method to analytically propagate the uncertainty from the aforementioned sources to the system frequency and area control error (ACE), and obtain expressions that approximate their probability distribution functions. We make use of this framework to obtain probabilistic expressions for the frequency performance criteria developed by the North American Electric Reliability Corporation (NERC); such expressions may be used to determine the limiting values of uncertainty that the system may withstand. The proposed ideas are illustrated through the Western Electricity Coordination Council (WECC) 9-bus 3-machine system and a 140-bus 48-machine system
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Balancing Authority Area Coordination with Limited Exchange of Information
In this paper, we propose a coordination scheme between balancing authority (BA) areas in an interconnected power system that decreases the regulation amount needed as well as the associated costs. Our approach aims at mimicking the behavior of the automatic generation control (AGC) system in a scenario where the whole interconnected system is assumed to be operated by a single BA area. To this end, we modify the area control error (ACE), which is fed into the AGC system of each BA area, and determine the AGC allocation based on a distributed algorithm that identifies the least expensive generators, with the mismatch of the total regulation needed being the only information exchanged between BA areas. We demonstrate the proposed ideas with the 3-machine 9-bus Western Electricity Coordinating Council (WECC) system, and compare the performance of our method with other three existing coordination approaches
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Automatic Generation Control and its Implementation in Real Time
In power systems, the control mechanism responsible for maintaining the system frequency to the nominal value and the real power interchange between balancing authority areas to the scheduled values is referred to as automatic generation control (AGC). The purpose of this paper is to present a systematic way to determine, in real time, the power allocated to each generator participating in AGC by taking into account the cost and quality of the AGC service provided. To this end, we formulate the economic dispatch process and gain insights into the economic characteristics of the generating units. We value the quality of AGC service by taking into consideration the ramping constraints of the generating units. The proposed methodology is illustrated in the WECC system and is compared with other allocation methods
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Balancing Authority Area Model and its Application to the Design of Adaptive AGC Systems
In this paper, we develop a reduced-order model for synchronous generator dynamics via selective modal analysis. Then, we use this reduced-order model to formulate a balancing authority (BA) area dynamic model. Next, we use the BA area model to design an adaptive automatic generation control (AGC) scheme, with self-tuning gain, that decreases the amount of regulation needed and potentially reduces the associated costs. In particular, we use the BA area model to derive a relationship between the actual frequency response characteristic (AFRC) of the BA area, the area control error, the system frequency, and the total generation. We make use of this relationship to estimate the AFRC online, and set the frequency bias factor equal to the online estimation. As a result, the AGC system is driven by the exact number of MW needed to restore the system frequency and the real power interchange to the desired values. We demonstrate the proposed ideas with a single machine infinite bus, the 9-bus 3-machine Western Electricity Coordinating Council (WECC), and a 140-bus 48-machine systems
Single-nucleotide polymorphisms: analysis by mass spectrometry
Matrix-assisted laser desorption-ionization (MALDI) mass spectrometry has evolved as a powerful method for analyzing nucleic acids. Here we provide protocols for genotyping single-nucleotide polymorphisms (SNPs) by MALDI based on PCR and primer extension to generate allele-specific products. Furthermore, we present three different approaches for sample preparation of primer-extension products before MALDI analysis and discuss their potential areas of application. The first approach, the 'GOOD' assay, is a purification-free procedure that uses DNA-modification chemistry, including alkylation of phosphorothioate linkages in the extension primers. The other two approaches use either solid-phase extraction or microarray purification for the purification of primer-extension products. Depending on the reaction steps of the various approaches, the protocols take about 6–8 hours
Consistent Radiative Transfer Models including Time Dependent Energy Deposition for Type Ia Supernovae
Many aspects of the explosion mechanism of Type Ia supernovae (SN Ia) still
remain unclear -- causing uncertainties in the derived cosmological parameters.
Realistic models of the generation and transport of radiation in the ejecta are
required which link theoretical explosion models to observations. We aim to
construct theoretical spectra and light curves from consistent radiative
transfer models that allow to study the dependence of observable features on
the physical parameters of the explosion.Comment: To appear in "1604-2004: Supernovae as Cosmological Lighthouses",
Padua, June 16-19 2004, eds. Turatto et al., ASP conference Series. 2 page
Abundance stratification in Type Ia Supernovae - II: The rapidly declining, spectroscopically normal SN 2004eo
The variation of properties of Type Ia supernovae, the thermonuclear
explosions of Chandrasekhar-mass carbon-oxygen white dwarfs, is caused by
different nucleosynthetic outcomes of these explosions, which can be traced
from the distribution of abundances in the ejecta. The composition
stratification of the spectroscopically normal but rapidly declining SN2004eo
is studied performing spectrum synthesis of a time-series of spectra obtained
before and after maximum, and of one nebular spectrum obtained about eight
months later. Early-time spectra indicate that the outer ejecta are dominated
by oxygen and silicon, and contain other intermediate-mass elements (IME),
implying that the outer part of the star was subject only to partial burning.
In the inner part, nuclear statistical equilibrium (NSE) material dominates,
but the production of 56Ni was limited to ~0.43 \pm 0.05 Msun. An innermost
zone containing ~0.25 Msun of stable Fe-group material is also present. The
relatively small amount of NSE material synthesised by SN2004eo explains both
the dimness and the rapidly evolving light curve of this SN.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As
The effect of annealing at 250 C on the carrier depth profile, Mn
distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As
layers with thicknesses > 200 nm, grown by molecular-beam epitaxy at low
temperatures, is studied by a variety of analytical methods. The vertical
gradient in hole concentration, revealed by electrochemical capacitance-voltage
profiling, is shown to play a key role in the understanding of conductivity and
magnetization data. The gradient, basically already present in as-grown
samples, is strongly influenced by post-growth annealing. From secondary ion
mass spectroscopy it can be concluded that, at least in thick layers, the
change in carrier depth profile and thus in conductivity is not primarily due
to out-diffusion of Mn interstitials during annealing. Two alternative possible
models are discussed.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
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