28,488 research outputs found
Energy functional for the three-level Lipkin model
We compute the energy functional of a three-level Lipkin model via a
Legrendre transform and compare exact numerical results with analytical
solutions obtained from the random phase approximation (RPA). Except for the
region of the phase transition, the RPA solutions perform very well. We also
study the case of three non-degenerate levels and again find that the RPA
solution agrees well with the exact numerical result. For this case, the
analytical results give us insight into the form of the energy functional in
the presence of symmetry-breaking one-body potentials.Comment: 6 pages, 5 figure
Three years of experience with the STELLA robotic observatory
Since May 2006, the two STELLA robotic telescopes at the Izana observatory in
Tenerife, Spain, delivered an almost uninterrupted stream of scientific data.
To achieve such a high level of autonomous operation, the replacement of all
troubleshooting skills of a regular observer in software was required. Care
must be taken on error handling issues and on robustness of the algorithms
used. In the current paper, we summarize the approaches we followed in the
STELLA observatory
Integrated control/structure optimization by multilevel decomposition
A method for integrated control/structure optimization by multilevel decomposition is presented. It is shown that several previously reported methods were actually partial decompositions wherein only the control was decomposed into a subsystem design. One of these partially decomposed problems was selected as a benchmark example for comparison. The system is fully decomposed into structural and control subsystem designs and an improved design is produced. Theory, implementation, and results for the method are presented and compared with the benchmark example
Two leaf beetles new to Florida (Coleoptera: Chrysomelidae)
Specimens recently submitted to the first author for identification turned out to represent two species of leaf beetles previously unknown from Florida, one of which is new to the eastern United States and the other new to the continental United States
An idiotypic cross-reaction between allotype a3 and allotype a negative rabbit antibodies to streptococcal carbohydrates
Two antibodies to Group C streptococcal carbohydrate isolated from an individual rabbit had similar relative binding affinities for a Group C immuno-adsorbent column. Their light chains were similar, if not identical, as were the constant regions of their heavy chains. Differences in the variable regions of the H chains of the two antibodies were detected by chemical analysis. The two antibodies had serologically identical idiotypic determinants although one antibody possessed the a3 allotype and the other had no detectable group a marker. The occurrence of such antibodies indicates the absence of obligatory associations between group a allotypes and idiotypic specificities, despite the fact that both determinants have antigenic components in the VH region of the H chain
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The Direct Costs and Benefits of US Electric Utility Divestitures
This paper studies the impact of divestiture on the efficiency and costs of electric utilities. The empirical literature shows that there exist economies of scope for electric utilities and that divestiture decreases distribution efficiency but increases generation efficiency. This paper is to bring together these different results. Our analysis covers distribution, transmission, and power sourcing. Our data is an unbalanced panel of about 138 US electric utilities for the years 1994 to 2006 over which we observe 30 divestitures between 1997 and 2003. First, we regress firmlevel efficiencies for distribution and power sourcing on various divestiture indicators. Second, we compare the weighted cost between divested and non-divested firms and calculate a net present value for the entire sample of divestitures. Last, we regress net benefits from divestiture on the distribution side on the net benefit for power sourcing to see whether individual firms successfully off-set any costs of divestiture. We find that divestiture reduces distribution efficiency but increases power sourcing efficiency. Both effects depend on the amount of own nuclear generation output but not fossil-fuel or hydro output. The net present value for all divestitures in our sample is $11.3 billion. It seems that relatively lower costs of power outweigh losses in economies of scope as well as other restructuring costs. However, lower costs of power might be the result of favourable contracts put in place at the time of divestiture. Our study complements traditional studies of economies of scope and shows that divestitures might well be worth it
On the Glauber model in a quantum representation
The Glauber model is reconsidered based on a quantum formulation of the
Master equation. Unlike the conventional approach the temperature and the Ising
energy are included from the beginning by introducing a Heisenberg-like picture
of the second quantized operators. This method enables us to get an exact
expression for the transition rate of a single flip-process
which is in accordance with the principle of detailed balance. The transition
rate differs significantly from the conventional one due to Glauber in the low
temperature regime. Here the behavior is controlled by the Ising energy and not
by the microscopic time scale.Comment: 8 page
AVIRIS foreoptics, fiber optics and on-board calibrator
The foreoptics, fiber optic system and calibration source of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) are described. The foreoptics, based on a modified Kennedy scanner, is coupled by optical fibers to the four spectrometers. The optical fibers allow convenient positioning of the spectrometers in the limited space and enable simple compensation of the scanner's thermal defocus (at the -23 C operating temp) by active control of the fiber focal plane position. A challenging requirement for the fiber optic system was the transmission to the spectral range 1.85 to 2.45 microns at .45 numerical aperture. This was solved with custom fluoride glass fibers from Verre Fluore. The onboard calibration source is also coupled to the spectrometers by the fibers and provides two radiometric levels and a reference spectrum to check the spectrometers' alignment. Results of the performance of the assembled subsystems are presented
Assessment of the environmental toxicity and carcinogenicity of tungsten-based shot.
The toxicity of elemental tungsten released from discharged shot was assessed against previous studies that established a 1% toxic threshold for soil organisms. Extremely heavy theoretical shot loadings of 69,000 shot/ha were used to generate estimated environmental concentrations (EEC) for two brands of tungsten-based shot containing 51% and 95% tungsten. The corresponding tungsten EEC values were 6.5–13.5 mg W/kg soil, far below the 1% toxic threshold. The same shot loading in water produced tungsten EEC values of 2.1–4.4 mg W/L, levels that are not toxic under experimental conditions. Pure tungsten has not been shown to exhibit carcinogenic properties when ingested or embedded in animal tissues, but nickel, with which it is often alloyed, has known carcinogenicity. Given the large number of waterfowl that carry shot embedded in their body, it is advisable to screen lead shot substitutes for their carcinogenic potential through intra-muscular implantation
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