Boson-fermion mapping and dynamical supersymmetry in fermion models
Abstract We show that a dynamical supersymmetry can appear in a purely fermionic system. This “supersymmetry without bosons” is constructed by application of a recently introduced boson-fermion Dyson mapping from a fermion space to a space comprised of collective bosons and ideal fermions. In some algebraic fermion models of nuclear structure, particular Hamiltonians may lead to collective spectra of even and odd nuclei that can be unified using the dynamical supersymmetry concept with Pauli correlations exactly taken into account.
Group theoretical aspects ofUB(6) ⊗UF(20) symmetry limits of IBFM related to theUB(5) andOB(6) limits of IBM
TheUB(6)⊗UF(20) Bose-Fermi dynamical symmetry of interacting boson-fermion model arises when the odd nucleon occupies single particle orbits withj=1/2, 3/2, 5/2, and 7/2. The subgroup structures ofUB(6)⊗UF(20) related to theUB(5) andOB(6) limits of sdIBM (UB(6)) are analysed. Broadly speaking,UB(6)⊗UF(20) admitsUBF(5)⊗UsF(4), SpinBF(5)⊗UkF(5) andUBF(5)⊗UsF(2) limits withUB(5) core and SpinBF(6),OBF(5)⊗UsF(4), SpinBF(6)⊗UkF(5) andOBF(6)⊗UsF(2) limits withOB(6) core respectively. For each of these seven symmetry limits, group chains, quantum numbers labelling the basis states, generators and Casimir operators for the various subgroups and energy formulas are given. Recoupling coefficients (reduced Wigner coefficients) for constructing wavefunctions of low-lying states are tabulated and these will allow (together with sdIBMUB(5) andOB(6) limit results) one to calculateB(E2)’s,B(M1)’s, one and two nucleon transfer strengths etc. in the seven symmetry limits. Experimental examples for theUB(6)⊗UF(20) symmetry limits are briefly discussed.
Time behavior of gas pressure and PD activity in insulation cavities under AC voltage
In the framework of developing defect-based life models (i.e. the life model of partial discharge-induced damage growth from a micro-void in polymer matrix), ageing tests were performed on PE layered specimens with artificial cavities under constant gas pressure and constant gas volume conditions, respectively. Time behavior of the discharge repetition rate and amplitude were recorded and compared under these two conditions. Results show that pressure variation has little influence on PD activities at constant gas volume. Under constant gas pressure, the evolution of gas volume has similar characteristic to the product of discharge amplitude and repetition rate.