On the evaluation of the quantum corrections to periodic TDHF orbits

The evaluation of the leading order quantum correction to periodic mean-fields within the path integral approach is reinvestigated. The corresponding gaussian functional integral is well defined only after restoring the time-translation invariance broken by the time-dependent meanfield approximation. The particular structure of the action function permits one to restore the invariance in two different ways, that seem to exhibit an ambiguity in the evaluation of the leading order quantum correction. We prove, however, that both ways of restoring the time-translation invariance yield the same result, showing that the leading order quantum correction is uniquely defined within the path integral approach.     

Ein einfacher Beweis des Kohärenzsatzes von Grauert

Ohne Zusammenfassung     

Absence of Knight-shift in the metallic state of polyacetylene

NMR spectra on ¹³C of polyacetylene have been recorded using the magic angle spinning technique. Despite the high metallic conductivity of AsF₅-doped samples in the doping range from 1–7 %, no Knight-shift can be detected. Only for concentrations above 7 %, far beyond the insulator-metal transition, a Knight-shift of about 30 ppm and strong line broadening is observed. This absence of the Knight-shift below the critical concentration of 7 % is in good agreement with the previously reported lack of Pauli-paramagnetism and hence confirms the existence of a novel mechanism of electrical conductivity with spinless charge carriers in the doping range from 1 to 7 %.     

Preparation,molecular structure and electronic structure of the rhombic,six-coordinate niobium(IV) complex NbCl2(ButC(O)CHC(O)But)2

The compound trans-NbCl₂(dpm)₂, Hdpm = 2,2,6,6-tetramethylheptane-3,5-dione, has been prepared and the molecular structure determined in each of two crystalline polymorphs by X-ray diffraction. The visible spectrum and the EPR spectrum have been measured and a Fenske—Hall calculation performed. The combined results give a reasonable and internally consistent picture of the electronic structure of the molecule. The HOMO is a b_3g-orbital (predominantly d_yz), while the two lowest-lying unoccupied orbitals (ca 16,000 cm^?1 higher) are b_2g(sim; d_xz) and a_g(sim; d_x²_?y²) orbitals, all in the D_2h-symmetry. The b_3g → b_2g and b_3g → a_g transitions are observed at 588.4 and 626.7 nm. The EPR spectrum in solution is a decet; the measured value of <g > is 1.930 and <A_iso > is 149 G. For the crystalline polymorph 1 the crystal data are: orthorhombic (P2₁2₁2₁), a = 13.649(3) Å, b = 18.166(4) Å, c = 11.425(4) Å, V = 2833(2) ų and Z = 4. Polymorph 2 is monoclinic (P2₁/n) with a = 12.288(5) Å, b = 9.226(4) Å, c = 12.545(4) Å, β = 94.24(3)°, V = 1418(2) ų and Z = 2. The molecule in 2 is centrosymmetric with virtual D_2h-symmetry. In 1 there are distortions in the chelate plane postulated to be due to packing forces. The two forms have comparable averaged values of interatomic dimensions.     

The structures of lithium-inserted metal oxides: LiReO3 and Li2ReO3

The crystal structures of LiReO₃ and Li₂ReO₃, obtained by Li insertion into ReO₃, were determined by neutron diffraction powder profile analysis. For both phases, the ReO₃ host lattice, made exclusively of corner-shared octahedra, was altered significantly on Li insertion without breaking bonds. The original 12-coordinated perovskite-like cavity was changed into two octahedral sites, which are occupied by the lithium ions.     

Self-induced parametric amplification of high-order harmonics

A theoretical analysis of self-induced parametric amplification of high-order harmonics is given. This mechanism permits the elimination of limitations on the harmonic-generation efficiency that are imposed by absorption.     

Simulation of attitude motions of torque-free,deformable spacecraft

Equations of motion are derived for torque-free, elastic, dissipative systems possessing a finite number of degrees of freedom. The equations are linearized about a particular solution in the variables describing the “internal” configuration of the system, and then SAM, a computer program based on these equations, is described. The program permits the user to obtain information about motions of a given system without writing any computer code. The paper concludes with an illustrative example involving a comparison of results obtained, on the one hand, by solving the exact equations of motion and, on the other hand, by using SAM to explore the behavior of a satellite containing a passive nutation damper. The example shows rather vividly both that relatively small deformational motions can give rise to large attitude motions and that SAM can describe these motions satisfactorily.