Kohlenwasserstoffe

Ohne Zusammenfassung     

Massive lepton pair production as a test of models for particle production on nuclei

The nuclear-size dependence of massive lepton pair production on nuclei is found to provide a selective test of models describing hadron-nucleus interactions. In particular, a clear discrimination is possible between two types of models: the sequential multiple scattering models with energy degradation, and the “parallel” multiple scattering models with a long time scale involved. Both types of models are known to describe equally well the distributions of hadrons produced on nuclei. It is shown, however, that the observedA ¹-dependence of theD-Y process rules out the sequential scattering models as well as some oversimplified versions of the parallel multiple scattering models.     

Definability in the lattice of equational theories of semigroups

We study first-order definability in the latticeL of equational theories of semigroups. A large collection of individual theories and some interesting sets of theories are definable inL. As examples, ifT is either the equational theory of a finite semigroup or a finitely axiomatizable locally finite theory, then the set {T, T ^ϖ} is definable, whereT ^ϖ is the dual theory obtained by inverting the order of occurences of letters in the words. Moreover, the set of locally finite theories, the set of finitely axiomatizable theories, and the set of theories of finite semigroups are all definable. The research of both authors was supported by National Science Foundation Grant No. DMS-8302295     

Crystal and molecular structure of bis(aminomethylphosphonate)copper(II)

The crystal and molecular structure of bis(aminomethylphosphonate)-copper(II), C₂H₁₀N₂O₆P₂Cu, has been determined from MoK diffractometer data. The compound crystallizes in the monoclinic space groupP2₁/n witha =7.571(2),b = 4.943(1),c = 11.212(3) Å, = 105.84(2) °, andZ = 2. The structure was solved by the heavy-atom technique and refined by full-matrix least-squares methods toR = 0.041, using 1084 reflections for which ¦F _o¦ > 3.92 (¦F _o¦). In this complex, the Cu atom is square-planar coordinated by four O atoms from four phosphonic groups, and not by the amino group. The Cu-O bond lengths are 1.928(3) and 1.937(3) Å, and the phosphonic groups bridge adjacent Cu atoms in polymeric chains. The infrared spectrum of this complex is reported.     

The electronic structure of the oxygen double-bridged μμ′-dioxo-bis(oxodichloroaquo)dimolybdate (V)-ion by SCCC MO method

Results of SCCC MO calculations for the dimeric oxygen double-bridged [Mo₂O₄Cl₄(H₂O)₂]^2–ion are reported. On the basis of these results the previously reported spectra and magnetic properties may be explained. The strong direct molybdenum — molybdenum interaction in the Mo₂O ₄ ²⁺ core was proved to exist.

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Zusammenfassung Die Ergebnisse von SCCC MO-Rechnungen für das zweikernige Ion [Mo₂O₄Cl₄(H₂O)₂]^2– mit zweifacher Sauerstoffbrücke werden mitgeteilt. Danach können die früher angeführten magnetischen und spektralen Eigenschaften dieses Ions verstanden werden. Die Existenz starker unmittelbarer Molybdän-Molybdän Wechselwirkungen innerhalb des Mo₂O ₄ ²⁺ Kerns wird nachgewiesen.

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Résumé Résultats de calculs SCCCMO pour l'ion dimère Mo₂O₄Cl₄(H₂O) ₂ ^2– . Sur la base de ces résultats les propriétés spectrales et magnétiques précédemment obtenues peuvent être expliquées. L'existence d'une forte interaction directe molybdène-molybdène dans le coeur Mo₂O ₄ ²⁺ est clairement démontrée.

     

Electron spin resonance spectroscopy of copper(II) complexes with schiff bases as ligands

The ESR spectra of a series of Cu^II Schiff base complexes have been investigated in liquid and frozen solutions. The structures of these complexes are estimated on the basis of superhyperfine interactions and molecular orbital coefficients α² and β²₁ calculated from copper hyperfine parameters.     

Normal coordinate analysis of M2O7 systems with C2v symmetry (pyrophosphates and -arsenates) intramolecular forces in a urey-bradley-shimanouchi force field

The vibrational spectra of nickel and magnesium α-pyrophosphates and of potassium and sodium α-pyroarsenates were found. A normal coordinate analysis was carried out for both P₂O₇ and As₂O₇ molecular systems using the force field of the Urey-Bradley-Shimanouchi type and the C_2v symmetry model. On the basis of the results obtained the significant differences between the temperatures of the α/β phase transitions observed for Mg (68 °C) and Ni (565 °C) pyrophosphates have been explained.     

Design of an ultrasonic sensor for measuring distance and detecting obstacles

This paper introduces a novel method for designing the transducer of a highly directional ultrasonic range sensor for detecting obstacles in mobile robot applications. The transducer consists of wave generation, amplification, and radiation sections, and a countermass. The operating principle of this design is based on the parametric array method where the frequency difference between two ultrasonic waves is used to generate a highly directional low-frequency wave with a small aperture. The aim of this study was to design an optimal transducer to generate the two simultaneous longitudinal modes efficiently. We first derived an appropriate mathematical model by combining the continuum model of a bar and countermass with the compatibility condition between a piezoelectric actuator and a linear horn. Then we determined the optimal length of the aluminum horn and the piezoelectric actuator using a finite element method. The proposed sensor exhibited a half-power bandwidth of less than ±1.3° at 44.8 kHz, a much higher directivity than existing conventional ultrasonic range sensors.