Nuclear scissors with pairing and continuity equation

The coupled dynamics of the isovector and isoscalar giant quadrupole resonances and low-lying modes (including scissors) is studied with the help of the Wigner-function-moment method generalized to take into account pair correlations. Equations of motion for collective variables are derived on the basis of the time-dependent Hartree-Fock-Bogoliubov equations in the harmonic-oscillator model with quadrupole—quadrupole residual interaction and a Gaussian pairing force. Special care is taken of the continuity equation. The text was submitted by the authors in English.     

Chemical Raman enhancement of organic adsorbates on metal surfaces

Using first-principles theory and experiments, chemical contributions to surface-enhanced Raman spectroscopy for a well-studied organic molecule, benzene thiol, chemisorbed on planar Au(111) surfaces are explained and quantified. Density functional theory calculations of the static Raman tensor demonstrate a strong mode-dependent modification of benzene thiol Raman spectra by Au substrates. Raman active modes with the largest enhancements result from stronger contributions from Au to their electron-vibron coupling, as quantified through a deformation potential. A straightforward and general analysis is introduced to extract chemical enhancement from experiments for specific vibrational modes; measured values are in excellent agreement with our calculations.     

Approximate ground state of the Lipkin model hamiltonian in density-matrix formalism

A method for finding the ground state of a many-body system, which is consistent with the truncation scheme used in the time-dependent density-matrix formalism of Wang and Cassing, is presented and applied to the Lipkin model. It is found that the method gives better ground states than the Hartree-Fock approximation. However, they significantly differ from the exact ground states.     

A numerical comparison of three different approaches to the weak or intermediate coupling model for 2 particle — 1 hole states

The secular equation of the usual shell-model approach to 2 particle (p) — 1 hole (h) states is transcribed in such a way that it can be viewed as the simultaneous coupling of a hole to a (pp) vibrationand a particle to a particle-hole vibration. The resulting diagonalisation problem is built up by the subsolutions of the (ph) and (pp) TDA, i.e. no matrix elements of the bare two-body interaction enter the equations. We discuss the mathematical properties of the new equations and compare them to the usually applied formulation of the weak or intermediate coupling model. Finally we give a numerical study for the low-lying states of negative parity of O¹⁷.     

Evidence for reduced neutron pairing correlations in 165Yb

Three rotational sequences in ¹⁶⁵Yb have been extended to high spins by using the ¹³⁰Te(⁴⁰Ar, 5n) and ¹⁵⁰Nd(²⁰Ne, 5n) reactions. Evidence is presented for a reduction of the neutron pairing correlations at the highest rotational frequencies (hω > 0.40 MeV), but no quantitative measure of this reduction can be made. There appears to be a conflict with the expectations of simple CSM calculations.     

Surface behaviour of the pairing gap in a slab of nuclear matter

The surface behavior of the pairing gap previously studied for semi-infinite nuclear matter is analyzed in the slab geometry. The gap-shape function is calculated in two cases: a) pairing with the Gogny force in a hard-wall potential and b) pairing with the separable Paris interaction in a Saxon-Woods mean-field potential. It is shown that the surface features are preserved in the case of slab geometry, being almost independent of the width of the slab. It is also demonstrated that the surface enhancement is strengthened as the absolute value of chemical potential decreases which simulates the approach to the nucleon drip line.-1Received: 3 March 2003, Published online: 30 September 2003PACS: 21.30.-x Nuclear forces - 21.60.-n Nuclear structure models and methods - 21.65.+f Nuclear matter - 26.60.+c Nuclear matter aspects of neutron stars     

Condensate fragmentation in a new exactly solvable model for confined bosons

Based on Richardson's exact solution of the multilevel pairing model we derive a new class of exactly solvable models for the finite boson system. As an example we solve a particular Hamiltonian which displays a transition to a fragmented condensate for repulsive pairing interaction.     

A novel strategy for encapsulation and release of proteins: hydrogels and microgels with acid-labile acetal cross-linkers

A new acid-labile acetal cross-linker was synthesized and used to prepare protein-loaded hydrogels and microgels. This cross-linker undergoes an acid-catalyzed degradation with a half-life of 5.5 min at pH 5.0 and 24 h at pH 7.4. Protein-loaded hydrogels were synthesized with this cross-linker, and their release profiles were measured as a function of pH. Hydrogels made with the acetal cross-linker release their contents in a pH-dependent manner. The acetal cross-linker was also used to synthesize microgels with sizes between 1 and 10 mum, a range suitable for phagocytosis. The unique acid sensitivity of the acetal cross-linker should make it a useful synthetic intermediate in the design of acid-sensitive drug or gene delivery systems.