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  • 1
    Electronic Resource
    Electronic Resource
    Two- and three-body forces in the interaction of He atoms with Xe overlayers adsorbed on (0001) graphite (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6477-6493 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In order to address the problem of three-body interactions in gas–surface scattering, we considered the collision of a He atom with the (0001) surface of graphite coated by a monolayer of Xe. To eliminate the uncertainties connected with errors in the two-body He–Xe interaction, we determined the latter by crossed-beam differential collision cross-section measurements performed at two energies (67.2 and 22.35 meV). These scattering data together with room-temperature bulk diffusion data are then fitted with a Hartree–Fock–dispersion–type function to yield an interaction potential that explains most of the properties of this system within the experimental errors and represents an improvement on previously published He–Xe potentials. Helium diffraction measurements are then carried out from the Xe overlayer and the dependence of the specular intensity from the angle of incidence is carefully determined. Further, a He–surface potential is constructed by adding together the following terms: (1) the He–Xe pairwise sum, (2) the long-range He–(0001)C interaction, (3) the three-body contribution generated by the Axilrod–Teller–Muto term, (4) the so-called surface-mediated three-body interaction He–Xe–(0001)C first considered by A. D. McLachlan [Mol. Phys. 7, 381 (1964)], and finally (5) a small correction which is meant to take into account the nonstationary nature of the surface. Using this potential, well-converged close-coupling scattering calculations are carried out, and their results compared with the data. In general, good agreement is obtained. The agreement can, however, be improved by (a) an increase of about 30% in the contribution of three-body forces, (b) the lowering of the He–graphite long-range attraction coefficient by about 15%, or (c) a reduction of the two-body interaction well depth of 1.6% (the experimental error) together with any combination of the factors under (a) and (b) reduced by an adequate amount. Elimination of the contribution of the graphite surface by studying Xe multilayers is hindered by the uncertainties in the "thermal correction'' [point (5) above] which, due to the multilayer increased "softness,'' becomes an appreciable source of uncertainty.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457364
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  • 2
    Electronic Resource
    Electronic Resource
    The bright optical afterglow of the nearby γ-ray burst of 29 March 2003 (2003)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 423 (2003), S. 844-847 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Past studies of cosmological γ-ray bursts (GRBs) have been hampered by their extreme distances, resulting in faint afterglows. A nearby GRB could potentially shed much light on the origin of these events, but GRBs with a redshift z ≤ 0.2 have been estimated to occur only rarely, about ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01734
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  • 3
    Electronic Resource
    Electronic Resource
    Local linearization stability (1987)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 28 (1987), S. 1844-1847 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is shown that Einstein's equations are always linearization stable around any finite region of space-time. Let (Ω,g0ab ) be any region of space-time, admitting a compact Cauchy surface with nonempty smooth boundary, and with g0ab a sufficiently smooth solution of the vacuum Einstein equation. It is shown that for any solution g1ab of the linearized equation and any open region U⊆Ω, there exists a smooth one-parameter family gλab of solutions on U such that (gλab||λ=0 =g0ab ) ||U and ((d/dλ)gλab =g1ab )||U. By using a result of Choquet-Bruhat and York [The Cauchy Problem, General Relativity and Gravitation, edited by A. Held (Plenum, New York, 1980), Vol. 1] asserting the smoothness of the map that sends initial data into solutions of Einstein's evolution equations the proof of the above theorem is reduced to the proof of a similar theorem for Einstein's constraint equations. The proof of this latter theorem involves the use of the implicit function theorem in Hilbert spaces. This local result on linearization stability asserts, in contrast to the general global case, that linearization about any vacuum solution is locally physically meaningful.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527445
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic susceptibility in quasi one-dimensional Ba V O : chain segmentation versus the staggered field effect (2003)
    Springer
    The European physical journal 32 (2003), S. 43-47 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.10.Jm Quantized spin models – 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.) – 75.50.Ee Antiferromagnetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A pronounced Curie-like upturn of the magnetic susceptibility χ( T ) of the quasi one-dimensional spin chain compound Ba2V3O9 has been found recently [#!kaul:02!#]. Frequently this is taken as a signature for a staggered field mechanism due to the presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We calculate this contribution within a realistic structure of vanadium 3 d- and oxygen 2 p-orbitals and conclude that this mechanism is far too small to explain experimental results. We propose that the Curie term is rather due to a segmentation of spin chains caused by broken magnetic bonds which leads to uncompensated S = ½ spins of segments with odd numbers of spins. Using the finite-temperature Lanczos method we calculate their effective moment and show that ∼ 1% of broken magnetic bonds is sufficient to reproduce the anomalous low-T behavior of χ( T ) in Ba2V3O9.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2003-00072-0
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  • 5
    Electronic Resource
    Electronic Resource
    Measuring the chemical composition of cosmic rays at ∼ 1013–1015 eV by utilizing the solar and geomagnetic fields (1989)
    Springer
    Experimental astronomy 1 (1989), S. 21-34 
    Details
    ISSN: 1572-9508
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract According to a proposal of Lloyd-Evans (1985), the average charge of particles in the cosmic radiation near 1014eV can be determined by observing the effect of the solar magnetic field on the Sun's shadow in the angular distribution of energetic primary cosmic ray particles. This suggestion is shown to be realizable with a new type of EAS-array proposed for the purpose of high energy γ-ray astronomy. The same measurement provides information on the integrated strength of the solar magnetic field. As the array will be sensitive and provide good angular resolution down to a few times 1012eV, more detailed results on the primary composition near 1013eV can be obtained by investigating the shape of the shadow of the Moon as affected by the geomagnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414793
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  • 6
    Electronic Resource
    Electronic Resource
    Remarks on the determination of the kinetic parameter (2000)
    Springer
    Journal of materials science 19 (2000), S. 2183-2185 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006723413209
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  • 7
    Electronic Resource
    Electronic Resource
    Expertensysteme und Simulationsmodelle (1989)
    Springer
    OR spectrum 11 (1989), S. 191-195 
    Details
    ISSN: 1436-6304
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Summary The technique of designing and constructing simulation models is difficult and requires a lot of knowledge and experience. In general, users of simulation models don't have this expert knowledge. Up to now, it has not been possible to incorporate the expert knowledge necessary for the overall modelling within an expert system which would then in turn make the techniques accessible to the inexperienced user. In general, the close cooperation among experts in the fields of application and simulation techniques remains — for the time being — the only guarantee for successfully scrutinizing a model study. It is, however, possible to combine expert systems and simulation models when using carefully chosen, closely defined fields of application. It is here that an important area of interest and study lies. There are three conceivable alternatives: 1. To provide a simulation model with an intelligent environment which supports the user in constructing as well as evaluating the results made. 2. An expert system contains a simulation model as a possible component. If the expert system needs information that is not directly available, a simulation model is accessed which in turn sends the necessary data back to the expert system. 3. A simulation model contains an expert system as a component. In this case, the model has specific strategies at its disposal that are to be taken into consideration. If the model reaches a point where decisions have to be made, the simulation model turns to the expert system in order to receive information on relevant decisions. These relevant decisions are then used to determine the further course of the model. All three alternatives assume that the expert system as well as the simulation system have an open architecture. The open architecture is a prerequisite for the possibility of coupling the two. Up to now, this requirement has rarely been achieved.
    Notes: Zusammenfassung Der Entwurf und der Aufbau von Simulationsmodellen ist eine schwierige Technik, die sehr viel Wissen und Erfahrung voraussetzt. Die Anwender von Simulationsmodellen verfügen in der Regel über dieses Expertenwissen nicht. Bisher ist es nicht möglich, das für die Modellierung insgesamt erforderliche Expertenwissen in ein Expertensystem zu inkorporieren um es auf diese Weise dem in der Simulationstechnik unerfahrenen Anwender zugänglich zu machen. Im allgemeinen bleibt die enge Zusammenarbeit zwischen Fachleuten auf dem Anwendungsgebiet und der Simulationstechnik bis auf weiteres die einzige Garantie für eine erfolgreiche Modelluntersuchung. In ausgewählten, sehr engen abgegrenzten Anwendungsgebieten ist es jedoch möglich, Expertensysteme und Simulationsmodelle zu vereinen. Hier entwickelt sich ein bedeutendes Arbeits- und Aufgabenfeld. Es sind drei Alternativen vorstellbar: 1. Ein Simulationsmodell erhält eine intelligente Umgebung, die den Anwender beim Modellaufbau und bei der Ergebnisauswertung unterstützt. 2. Ein Expertensystem enthält als eine mögliche Komponente ein Simulationsmodell. Falls das Expertensystem Informationen benötigt, die nicht direkt verfügbar sind, wird ein Simulationsmodell angestoßen, das die erforderlichen Daten an das Expertensystem zurückliefert. 3. Ein Simulationsmodell enthält als Komponente ein Expertensystem. In diesem Fall enthält das Modell Strategien, die zu berücksichtigen sind. Falls das Modell an einen Punkt kommt, an dem Entscheidungen getroffen werden müssen, wendet sich das Simulationsmodell an das Expertensystem und läßt sich die maßgebenden, den weiteren Modellablauf bestimmenden Entscheidungen mitteilen. Alle drei Alternativen verlangen vom Expertensystem und dem Simulationssystem eine offene Architektur. Die offene Architektur ist Voraussetzung dafür, daß sich beide Systeme koppeln lassen. Diese Forderung ist bisher kaum erfüllt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01719913
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  • 8
    Electronic Resource
    Electronic Resource
    Vorbemerkungen der Herausgeber zum Themenheft „Simulation für betriebswirtschaftliche Entscheidungsprozesse“ (1989)
    Springer
    OR spectrum 11 (1989), S. 175-176 
    Details
    ISSN: 1436-6304
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01719908
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  • 9
    Electronic Resource
    Electronic Resource
    Zur Umsetzung von Bis(2-mercaptoethyl)phosphinen mit Organozinn-Verbindungen Molekülstruktur eines zinnhaltigen Sechzehnringes (1988)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 556 (1988), S. 161-169 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reaction of Bis(2-mercaptoethyl)phosphines with Organotin Compounds. Molecular Structure of a Tin Containing Sixteen-membered RingThe reaction of bis(2-mercaptoethyl)phosphine with di-t-butyltin dimethoxide yields mixture of oligomers of the type [t-Bu2Sn(SCH2CH2)2Pr]n (R = Me, Ph) from which the trans-configurated dimers (n = 2) have been isolated. By the reaction with sulphur and selenium, respectively, these dimers were transformed to the corresponding thioxo and selenoxo derivatives.The sixteen-membered ring trans-[t-Bu2Sn(SCH2CH2)2P(S)Ph]2 crystallizes in the space group P21/n with the unit cell dimensions a 1350.9, b 1310.2, c 1500.3 pm, β 96.36° and does not exhibit any intramolecular Sn—P interaction: The 1,5-diorgano-1-chloro-5-elementa-1-stanna(IV)-bicyclo-[3.3.01,5]octanes R(Cl)Sn(SCH2CH2)2E (6, R = Ph, E = PPh; 7, R = Ph, E = NMe) have been prepared from the corresponding sodium dithiolates and phenyltrichlorostannane. The transannulare Sn—P and Sn—N interactions in 6 and 7 are confirmed by 31P and 119Sn NMR investigations.
    Notes: Die Reaktion von Bis(2-mercaptoethyl)phosphinen mit Di-t-butylzinndimethoxid liefert Mischungen von Oligomeren des Typs [t-Bu2Sn(SCH2CH2)2PR]n (R = Me, Ph), von denen die trans-konfigurierten Dimere (n = 2) isoliert wurden. Durch Reaktion mit Schwefel bzw. Selen wurden diese in die entsprechenden Thio- bzw. Selenoderivate überführt. Der Sechzehnring trans-[t-Bu2Sn(SCH2CH2)2P(S)Ph]2 4 kristallisiert in der Raumgruppe P21/n mit den Gitterkonstanten a 1350,9, b 1310,2, c 1500,3 pm und β 96,36°, er enthält keine intramolekularen Sn—P.-Wechselwirkungen. Die 1,5-Diorgano-1-chloro-5-element-1-stanna(IV)-bicyclo[3.3.01,5]-octaneR(Cl)Sn(SCH2CH2)2E (6, R = Ph, E = PPh; 7, R = Ph, E = NMe) wurden aus den entsprechenden Natriumdithiolaten und Phenyltrichlorstannan erhalten. Die transannularen Sn—P- und Sn—N- Wechselwirkungen in 6 und 7 werden durch 31P- und 119Sn-NMR-Untersuchungen bestätigt.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19885560117
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  • 10
    Electronic Resource
    Electronic Resource
    Mg2IrB2-x, ein Magnesium-Iridiumborid mit W2CoB2 -verwandter Struktur (1986)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 543 (1986), S. 89-96 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Mg2IrB2-x, a Magnesium Iridium Boride with a Structure Related to the W2CoB2-TypeThe new compound Mg2IrB2-x with a small homogeneity range determined approximately as 0,2 ≤ x ≤ 0,35 crystallizes monoclinically in the space group C2/m, Z=4 (lattice constants see Inhaltsübersicht). The structure which was solved by single crystal X-ray and powder neutron diffraction methods is related to the W2CoB2-type and contains distorted Mg4Ir2-prisms. The boron atoms are partly disordered. They are situated either inside the prisms forming pairs or with very short Ir-B distances (199 pm) on an elongated prism edge formed by two iridium atoms.
    Notes: Die neue Verbindung Mg2IrB2-x mit einem schmalen Homogenitätsbereich, der näherungsweise zu 0,2 ≤ x ≤ 0,35 bestimmt wurde, kristallisiert monoklin in der Raumgruppe C2/m, Z = 4. Bei x = 0,35 betragen die Gitterkonstanten a = 858,0(1) pm, b = 484,6(1) pm, c = 683,6(1) pm, β = 115°43′(1). Die Struktur, die mit Röntgen-Einkristall- und Pulver-Neutronenbeugungsmethoden bestimmt wurde, leitet sich vom W2CoB2-Typ ab und enthält verzerrte Mg4Ir2-Prismen. Die Boratome sind zum Teil fehlgeordnet. Sie befinden sich entweder innerhalb der Prismen und bilden Paare, oder sie liegen auf einer aufgeweiteten, aus zwei Iridiumatomen bestehenden Prismenkante, wobei sehr kurze Ir-B-Abstände ausgebildet werden (199pm).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19865431211
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