J. Dobeš

Boson mappings and four-particle correlations in algebraic neutron-proton pairing models

Neutron-proton pairing correlations are studied within the context of two solvable models, one based on the algebra SO(5) and the other on the algebra SO(8). Boson-mapping techniques are applied to these models and shown to provide a convenient methodological tool both for solving such problems and for gaining useful insight into general features of pairing. We first focus on the SO(5) model, which involves generalized T = 1 pairing. Neither boson meanfield methods nor fermion-pair approximations are able to describe in detail neutron-proton pairing in this model. The analysis suggests, however, that the boson Hamiltonian obtained from a mapping of the fermion Hamiltonian contains a pairing force between bosons, pointing to the importance of bosonboson (or equivalently four-fermion) correlations with isospin T = 0 and spin S = 0. These correlations are investigated by carrying out a second boson mapping. Closed forms for the fermion wave functions are given in terms of the fermion-pair operators. Similar techniques are applied – albeit in less detail – to the SO(8) model, involving a competition between T = 1 and T = 0 pairing. Conclusions similar to those of the SO(5) analysis are reached regarding the importance of four-particle correlations in systems involving neutron-proton pairing.

The finite depth of the nuclear potential well in the exciton model of preequilibrium decay

The density of states and the transition rates are derived for the equidistant spacing model with the limitation on the hole maximum energy. The previous results of Blann are generalized. The influence of the finite depth of nuclear potential well on the pre-equilibrium decay within the exciton model is investigated. The calculations of proton and deuteron spectra from the reaction120Sn+p are presented.

Two-component exciton model

The exciton model of nuclear reactions with the distinguishability of protons and neutrons explicitly included is discussed. The Pauli master equation and transition rates in this two-component formulation are given. Both the simple considerations and actual calculations show that the two-component model exhibits new features and modifies conclusions of the one-component formulation. The ratio of the proton to neutron preequilibrium emissions in proton induced reactions decreases twice to three times when compared with the usual one-component model.

Monodromy and excited-state quantum phase transitions in integrable systems: collective vibrations of nuclei

Quantum phase transitions affecting the structure of ground and excited states of integrable systems with the Mexican-hat type potential are shown to be related to a singular torus of classical orbits passing the point of unstable equilibrium. As a specific example, we consider nuclear collective vibrations described by the O(6)–U(5) transitional Hamiltonian of the interacting boson model. While all states with zero values of the O(5) invariant undergo a continuous phase transition when crossing the energy of unstable equilibrium, the other states evolve in an analytic way.

Thermodynamic analogy for quantum phase transitions at zero temperature

We propose a relationship between thermodynamic phase transitions and ground-state quantum phase transitions in systems with variable Hamiltonian parameters. It is based on a link between zeros of the canonical partition function at complex temperatures and branch points of a quantum Hamiltonian in the complex-extended parameter space. This approach is applied in the interacting boson model, where it is shown to properly distinguish the first- and second-order phase transitions.

A statistical derivation of the density of final states for the exciton model

Abstract A new method for the derivation of the density of final states in the nuclear equilibration process, based on the Darwin-Fowler method of statistical physics, is suggested. This method is generally valid for an arbitrary energy level scheme and includes the Pauli principle. When it is applied to the equidistant-spacing energy level scheme, the results are very close to those derived by Obložinský et al .

Gamma emission in the pre-equilibrium exciton model

Abstract The pre-equilibrium exciton model of nuclear reactions is extended to include gamma emission. Possible types of gamma transitions are considered for which densities of final accessible states are derived. The computed gamma spectra in the reaction (n, γ) with E n = 14.1 MeV on 93 Nb and 139 La are compared with experiment.

How to count nucleon pairs

Abstract Within the context of the isovector-pairing SO(5) model, three methods measuring numbers of different kinds of nucleon pairs are discussed. Though methods do not give the same results, the odd-even staggering in pair numbers in even-even and odd-odd N = Z nuclei and the reduction of the np-pair number with increasing Tz is observed in all three procedures.

HIC1 Tumor Suppressor Loss Potentiates TLR2/NF-κB Signaling and Promotes Tissue Damage-Associated Tumorigenesis.

Hypermethylated in cancer 1 (HIC1) represents a prototypic tumor suppressor gene frequently inactivated by DNA methylation in many types of solid tumors. The gene encodes a sequence-specific transcriptional repressor controlling expression of several genes involved in cell cycle or stress control. In this study, a Hic1 allele was conditionally deleted, using a Cre/loxP system, to identify genes influenced by the loss of Hic1. One of the transcripts upregulated upon Hic1 ablation is the toll-like receptor 2 (TLR2). Tlr2 expression levels increased in Hic1-deficient mouse embryonic fibroblasts (MEF) and cultured intestinal organoids or in human cells upon HIC1 knockdown. In addition, HIC1 associated with the TLR2 gene regulatory elements, as detected by chromatin immunoprecipitation, indicating that Tlr2 indeed represents a direct Hic1 target. The Tlr2 receptor senses “danger” signals of microbial or endogenous origin to trigger multiple signaling pathways, including NF-κB signaling. Interestingly, Hic1 deficiency promoted NF-κB pathway activity not only in cells stimulated with Tlr2 ligand, but also in cells treated with NF-κB activators that stimulate different surface receptors. In the intestine, Hic1 is mainly expressed in differentiated epithelial cells and its ablation leads to increased Tlr2 production. Finally, in a chemical-induced mouse model of carcinogenesis, Hic1 absence resulted in larger Tlr2-positive colonic tumors that showed increased proportion of proliferating cells. Implications: The tumor-suppressive function of Hic1 in colon is related to its inhibitory action on proproliferative signaling mediated by the Tlr2 receptor present on tumor cells. Mol Cancer Res; 13(7); 1139–48. ©2015 AACR.

IBA-2 analysis of M1 properties in the Pt and Os nuclei

Abstract The g -factors and E2/M1 mixing ratios in the Pt and Os nuclei are studied within the framework of IBA-2. The experimental data are reproduced using boson g -factors which are very different from the standard values suggested recently by Sambataro et al. The excitation of the 1 + collective state in the Pt isotopes would be difficult to measure experimentally if these unusual boson g -factors were applicable also to the transition 0 gs + → 1 + .