Die Kopplung der Randelementmethode und der Methode der finiten Elemente zur Lösung dreidimensionaler elektromagnetischer Feldprobleme auf unendlichem Grundgebiet

Übersicht Will man elektromagnetische Probleme, die auf unendlichen Grundgebieten definiert sind, mit Hilfe der Methode der finiten Elemente lösen, so bereitet die Berücksichtigung der unendlichen Grundgebiete Schwierigkeiten. Um diese Schwierigkeiten zu überwinden, kann man beispielsweise zusätzlich infinite Elemente [1] oder sog. Ballooning-Elemente [2] verwenden. Eine andere Möglichkeit ist die Kopplung der Methode der finiten Elemente mit der Randelementmethode [4].In diesem Artikel wird die Berechnung elektrostatischer und magnetischer Felder im unendlichen Raum mit Hilfe einer solchen Hybridmethode vorgestellt. Die Probleme werden entweder mit dem skalaren elektrischen Potential oder mit dem magnetischen Vektorpotential A formuliert. Um die Leistungsfähigkeit des Hybridansatzes zu untersuchen, werden u. a. zwei Beispiele behandelt, und deren Ergebnisse werden mit den nach dem Biot-Savart'schen Gesetz gewonnenen Lösungen vergleichen.

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The coupling of the boundary element method and the finite element method for the solution of 3-dimensional electromagnetic problems on infinite domains

Contents If 3-dimensional electromagnetic problems are solved by finite elements, the computation of the fields for problems involving infinite space causes difficulties. To treat such problems either infinite elements [1] or so called ballooning elements [2] can be used. Another possibility is the coupling of finite elements and boundary elements.In this article the calculation of electrostatic and magnetostatic fields in infinite space is presented, utilizing coupled elements. The problems are formulated in terms of potentials. In the electrostatic case the scalar potential and in the magnetostatic case the vector potentialA is used. To investigate the capability of the coupled elements, among other things two examples have been calculated and compared to their solutions gained with the help of Biot-Savart's law.

     

Integrating External and Internal Clock Synchronization

We address the problem of how to integrate fault-tolerant external and internal clock synchronization. In this paper we propose a new external/internal clock synchronization algorithm which provides both external and internal clock synchronization for as long as a majority of the reference time servers (servers with access to reference time) stay correct. When half or more of the reference time servers are faulty, the algorithm degrades to a fault-tolerant internal clock synchronization algorithm. We prove that at least 2 F+1 reference time servers are necessary for achieving external clock synchronization when up to F reference time servers can suffer arbitrary failures, thus the proposed algorithm provides maximum fault-tolerance. In this paper we also derive lower bounds for the best maximum external deviation achievable in standard mode and the best drift rate achievable in degraded mode. Our algorithm is optimal with respect to these two bounds: (1) the maximum external deviation is optimal in standard mode, and (2) the drift rate of the clocks is optimal in standard and degraded mode.     

THE CHEMISTRY AND ANALYSIS OF LARGE PAHs

A large economic problem in petroleum processing, the plugging of catalytic hydrocracking units, led to a study of the production of large polycyclic aromatic hydrocarbons (PAHs) in this process. Through that work, many other studies of PAHs happened. These included the analysis of coal tar pitches, hydrothermal-vent bitumens, carbon black, Diesel particulate, and fullerene soots. Many new PAHs were synthesized or isolated during the course of these many studies.     

Fluorescence Emission Properties of Polycyclic Aromatic Compounds in Review

Fluorescence emission behavior of polycyclic aromatic hydrocarbons (PAHs), polycyclic aromatic nitrogen heterocycles (PANHs), polycyclic aromatic sulfur heterocycles (PASHs) and benzofluoranthenes dissolved in organic solvents of varying polarity is reviewed. Measured fluorescence properties are used to divide aromatic solutes into two categories, probe and nonprobe molecules, depending upon whether the molecule's emission intensity ratios vary systematically with solvent polarity. Seventeen polycyclic aromatic hydrocarbon solute probes are identified and possible probe character versus molecular structure correlations are examined. Also discussed are instrumental and chemical artifacts associated with accurate determination of fluorescence emission intensities.     

NO(2) photometer Based on Solid-State Light Sources

A sensitive NO(2) analyzer, that uses a commercial LED emitting near 450 nm, has been developed. The prototype can measure NO(2) concentrations as low as 1 part in 10(9) as defined by the Environmental Protection Agency. The response time of the system is 1 min. In addition, a demonstration of the use of external-cavity frequency-doubled diode laser radiation to accomplish similar measurements is reported. However, because of low nonlinear optical conversion efficiencies, comparable detection limits were not possible. Nonetheless, frequency-doubled diode-laser wavelengths have the potential to reach farther into the UV than LED technology, allowing the detection and measurement of numerous other gaseous species of interest.     

Surfactant effects of dopants on ordering in GaInP

The use of surfactants for control of specific aspects of the VPE growth process is beginning to be studied for both the elemental and III/V semiconductors. The objective is to change the characteristics of the material grown epitaxially by the addition of a surfactant during growth. Most reported surfactant effects for semiconductors relate to some detail of the morphology of the growing films. For ordered semiconductor alloys the effects can be much more dramatic, including major changes in the electrical and optical properties. Since the bandgap energy is dependent on the microscopic arrangement of the atoms in an alloy with a fixed composition, the change in order parameter induced by the surfactant translates into a marked change in the bandgap energy. This paper presents the results of a study of the effects of n-type (Te and Si), p-type (Zn), and isoelectronic (Sb) dopants on the ordering process in GaInP grown by OMVPE. All of the dopants studied were found to decrease or eliminate ordering; however, the mechanisms are quite different. The donor Te apparently affects the adatom attachment kinetics at steps on the (001) surface, a surfactant effect. On the other hand the donor Si was found to decrease the degree of order by an entirely different mechanism, attributed to an increase in the Ga and In diffusion coefficients in the bulk. It apparently does not involve the surface. Disordering due to the acceptor Zn was found to occur by the same mechanism. The isoelectronic impurity Sb is found to act as a surfactant and to decrease the order parameter by changing the surface reconstruction, eliminating the [110]-P dimers that provide the thermodynamic driving force for formation of the CuPt structure during growth.     

First occurrence of the mysid Hemimysis anomala in an inland lake in North America,Oneida Lake,NY

Hemimysis anomala (Crustacea, Mysidae) is a recent invader to North America that until now was reported only from the Laurentian Great Lakes and their immediate embayments, along with the St. Lawrence River. In August 2009, we identified Hemimysis in diets of white perch and yellow perch in Oneida Lake, NY. Night time vertical plankton net tows detected Hemimysis at four sites across the lake. Hemimysis in fish diets (5.5–8.6 mm) were larger than in net tows (2.2–7.0 mm) and reproduction is occurring as some females had brood sacs. This is the first documented introduction of Hemimysis to an inland lake in North America, outside the Great Lakes. Oneida Lake is located 53 river km upstream from Lake Ontario, the nearest known source of Hemimysis. No genetic differences were found between Hemimysis in Oneida Lake and Lake Ontario, indicating this is likely the source of introduction. Several large rapids, locks, and dams separate the two lakes, and as a result the most likely vector of introduction to Oneida Lake is pleasure boat or light commercial traffic via the canal system or overland transport. The presence of Hemimysis in Oneida Lake 3 years after it was first found in Lake Ontario suggests this species may spread rapidly throughout the basin. Despite an intensive monitoring program on Oneida Lake directed at fish, zooplankton, and limnology, Hemimysis was only detected in fish diets and night time zooplankton tows, indicating it may go undetected in lakes for some time using traditional daytime net tows.     

CHARACTERIZATION OF VANADIUM COMPOUNDS IN SELECTED CRUDES I. PORPHYRIN AND NON-PORPHYRIN SEPARATION

We have applied size-exclusion chromatography (SEC-HPLC) and reversed-phase chromatography (RP-HPLC), with element specific detection, [Inductively coupled and direct current plasma atomic emission spectroscopy (ICP and DCP)], to selected crude oils -- Boscan, Beta, Morichal, Arabian Heavy, and Maya -- and their separated fractions. By these procedures, we have further characterized both the V porphyrin and the V non-porphyrin compounds.

From the SEC-HPLC-ICP profiles of the heavy crude oils we found the V compounds generally have a bimodal distribution, with maxima at approx. 800 and 9000 polystyrene equivalent (PS) molecular weight (MW). Arabian Heavy, though, had relatively few of the small V compounds.

The crude oils were separated into porphyrin and non-porphyrin fractions by methanol extraction. From the SEC-HPLC-ICP profiles of the porphyrin fraction, we Identified and quantitated the maximum at approx. MW 800 (PS) as being V porphyrins. The remaining V compounds are non-porphyrin.