A terminal Ni(III)-imide with diverse reactivity pathways

The synthesis and structure of the beta-diketiminato Ni(I) lutidine adducts [MexNN]Ni(2,4-lutidine) (x = 2 (2); x = 3 (3)) are described which serve as synthons to the "naked" 13-electron [MexNN]Ni fragments in reactions with N3Ad to give Ni-imido complexes. The singly bridged imide {[Me2NN]Ni}2(mu-NAd) (4) possesses short Ni-Ni (2.506(1) A) and Ni-N(imido) distances (1.732(4)-1.752(4) A). Steric modification of the beta-diketiminate ligand to include an additional methyl group in the N-aryl 4-position affords the Ni(III) terminal imide [Me3NN]Ni=NAd (8) isolated in 52% yield. The X-ray structure of terminal imide 8 reveals a contracted Ni-N(imido) bond distance (1.662(2) A) and an only somewhat bent imido linkage (Ni-N-C = 164.5(2) degrees ) consistent with a significant degree of multiple bond character. Frozen glass EPR studies of 5 indicate a rhombic environment in which one of the signals exhibits strong hyperfine coupling (A = 22 G) to the imido 14N (I = 1) nucleus. The terminal imide 5 undergoes complete imido group transfer to CO and CNBut to give AdNCO and AdNCNBut, respectively, as well as with PMe3 to afford AdN=PMe3. Exemplifying the radical character at the imido N atom, 5 adds to cobaltocene and abstracts a H atom from 1,4-cyclohexadiene to give the Ni(II)-amides [Me3NN]Ni-NAd(eta4-C5H5)CoCp (7) and [Me3NN]Ni-NHAd (8).     

Baric changes in refractive indices of K<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystals

The influence of uniaxial pressure applied along the principal crystallophysical directions on the dispersion and temperature dependences of the refractive indices n _i of K₂ZnCl₄ crystals has been investigated. The n _i values are found to be fairly sensitive to uniaxial pressure, whereas an uniaxial stress does not change the behavior of the dispersion and temperature dependences of n _i . The baric changes in n _i have been studied. The electronic polarizability α _i , refractions R, and parameters of UV oscillators (λ_0i , B _1i ) of mechanically deformed K₂ZnCl₄ crystals have been calculated. The contributions of UV and IR oscillators to n _i (λ) have been estimated for different temperatures, spectral regions, and stresses. A significant baric shift of the points of the paraelectric phase-incommensurate phase-commensurate phase transitions to different temperature ranges, depending on the direction of pressure application, is found; this shift is due to the effect of uniaxial stress on the K₂ZnCl₄ crystal structure.     

The Features of the Characteristics of Forced Whispering-Gallery Modes in an Ellipsoidal Dielectric Resonator with Small Eccentricity

We study experimentally the whispering-gallery modes excited in a dielectric ellipsoidal resonator by a lumped-parameter radiation source and through distributed coupling of a dielectric resonant structure with a dielectric waveguide. Peculiarities of the formation of mode fields and spectra for different mutual locations of the resonator and the exciting element are pointed out. The influence of the derivative of the ellipsoid-surface curvature on the behavior of the energy characteristics of forced modes is found.     

A progress report on simulating fermion field theories: QCD and beyond

Hybrid stochastic differential equations are introduced and applied to spin systems and lattice gauge theory with fermions. Accelerating the algorithm with Fast Fourier Transforms (FFT) is discussed. The status of dynamical fermion simulations is reviewed and evidence for asymptotic freedom and applications to thermodynamics, hierarchal mass scales, etc. are presented.     

Electron-positron annihilation and speculations on the renormalization group of strong interactions

Implications of recent measurements of the electron-positron annihilation cross section for other deep inelastic processes are discussed within the context of conventional field theory and conventional current algebra. Canonical scaling laws for deep inelastic electron and neutrino scattering are predicted to fail for $\text{Q}{}^2\text{? 15–25 GeV}{}^2$. Other easily measured consequences of a violation of scale invariance at short distances are discussed. Comments and speculations concerning the renormalization group of strong interactions are made.     

Chiral symmetry restoration in baryon rich environments

Chiral symmetry restoration in an environment rich in baryons is studied by computer simulation methods in SU(2) and SU(3) gauge theories in the quenched approximation. The basic theory of symmetry restoration as a function of chemical potential is illusstrated and the implementation of the ideas on a lattice is made explicit. A simple mean field model is presented to guide one's expectations. The second order conjugate-gradient iterative method and the pseudo-fermion Monte Carlo procedure are convergent methods of calculating the fermion propagator in an environment rich in baryons. Computer simulations of SU(3) gauge theory show an abrupt chiral symmetry restoring transition and the critical chemical potential and induced baryon density are estimated crudely. A smoother transition is observed for the color group SU(2).     

Twisted reduced chiral models at large N

We construct and study the twisted reduced SU(N)×SU(N) chiral model in two dimensions. The equivalence of the reduced model to the field theory is established by examining the Dyson-Schwinger equations and weak coupling perturbation expansion. We evaluate the internal energy and two-point correlation function by extensive Monte Carlo simulations for N=12, 24 and 36. We find a non-analyticity near the weak coupling edge of the crossover region in which the system flips back and forth between the “normal” state and one characterised by a strongly disordered correlation function.