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Self-consistent mean field calculations with the SLy4 interaction and a density-dependent pairing force are presented for nuclei in the Nobelium mass region. Predicted quasi-particle spectra are compared with experiment for the heaviest known odd N and odd Z nuclei. Spectra and rotational bands are presented for nuclei around No252,4 for which experiments are either planned or already running., 13 pages LATEX, elsart style, 6 embedded eps figures

We use the Skyrme-Hartree-Fock method, allowing all symmetries to be broken, to calculate the time-reversal-violating nuclear Schiff moment (which induces atomic electric dipole moments) in the octupole-deformed nucleus 225Ra. Our calculation includes several effects neglected in earlier work, including self consistency and polarization of the core by the last nucleon. We confirm that the Schiff moment is large compared to those of reflection-symmetric nuclei, though ours is generally a few times smaller than recent estimates., Comment: Typos corrected, references added, minor changesin text. Version to appear in PRC. 10 pages, 4 figures

Starting from constrained Skyrme-mean-field calculations, the low-energy excitation spectrum of 16O is calculated by configuration mixing of particle-number and angular-momentum projected mean-field states in the framework of the Generator Coordinate Method. Without any adjustable parameters, this approach gives a very good description of those states and their transition moments that can be described with our restriction to axially and reflection-symmetric shapes. The structure of low-lying 0+ states is analyzed in terms of self-consistent 0p-0h, 2p-2h, and 4p-4h Hartree-Fock states., 15 pages LATEX, 6 figures, 3 tables, revision of sections 4 and 5

A recent paper [M. Rashdan, Phys. Rev. C 63, 044303 (2001)] introduces the new parameterization NL-RA1 of the relativistic mean-field model which is claimed to give a better description of nuclear properties than earlier ones. Using this model ^{298}114 is predicted to be a doubly-magic nucleus. As will be shown in this comment these findings are to be doubted as they are obtained with an unrealistic parameterization of the pairing interaction and neglecting ground-state deformation., 2 pages REVTEX, 3 figures, submitted to comment section of Phys. Rev. C. shortened and revised version

We present a microscopic analysis of the collective behaviour of the lead isotopes in the vicinity of Pb208. In this study, we rely on a coherent approach based on the Generator Coordinate Method including exact projection on N and Z numbers within a collective space generated by means of the constrained Hartree-Fock BCS method. With the same Hamiltonian used in HF+BCS calculations, we have performed a comprehensive study including monopole, quadrupole and octupole excitations as well as pairing vibrations. We find that, for the considered nuclei, the collective modes which modify the most the conclusions drawn from the mean-field theory are the octupole and pairing vibrations., 10 pages LATEX, 8 figures, submitted to EPJA

The quadrupole and hexadecapole coupling constants for {sup 127}I in LiI were determined from relativistic Dirac-Fock electronic structure and self-consistent nuclear structure calculations. While the calculated quadrupole coupling constant agrees with the experimental value, the predicted hexadecapole coupling constant ranges between +6 and +20 mHz, which is of opposite sign and about three orders of magnitude smaller than the value deduced from recent high resolution radio-frequency molecular beam measurements [J. Cederberg, D. Olson, A. Nelson, D. Laine, P. Zimmer, M. Welge, M. Feig, T. Ho''ft, and N. London, J. Chem. Phys. 110, 2431 (1999)].

We concentrate on the two most widely used mean-field models, Skyrme-Hartree-Fock and relativistic mean field. We discuss their performance in view of the extended range of experimental information in terms of a guided tour through selected examples of success, failures and subsequent improvement of the models drawn from comparison with key observables as isotopic shifts, trends of binding energies or single-particle spectra. Particular attention is paid to the extrapolative power with respect to superheavy elements (SHE). It turns out that the most important aspect is here the actual level sequence as implied by the given mean-field models. We will compare the performance of available parametrisations and discuss briefly possible improvements.

We investigate the effects of the spin-isospin channel of the Skyrme energy functional on predictions for Gamow-Teller distributions and superdeformed rotational bands. We use the generalized Skyrme interaction SkO' to describe even-even ground states and then analyze the effects of time-odd spin-isospin couplings, first term by term and then together via linear regression. Some terms affect the strength and energy of the Gamow-Teller resonance in finite nuclei without altering the Landau parameter g_0' that to leading order determines spin-isospin properties of nuclear matter. Though the existing data are not sufficient to uniquely determine all the spin-isospin couplings, we are able to fit them locally. Altering these coupling constants does not change the quality with which the Skyrme functional describes rotational bands., Comment: 21 pages REVTEX, 13 eps figures, submitted to Phys. Rev. C

By sequencing regions flanking the β-globin gene complex in mouse ( Hbbc ) and human ( HBBC ), we have shown that the β-globin gene cluster is surrounded by a larger cluster of olfactory receptor genes (ORGs). To facilitate sequence comparisons and to investigate the regulation of ORG expression, we have mapped 5′ sequences of mRNA from olfactory epithelium encoding β-globin-proximal ORGs. We have found that several of these genes contain multiple noncoding exons that can be alternatively spliced. Surprisingly, the only common motifs found in the promoters of these genes are a “TATA” box and a purine-rich motif. Sequence comparisons between human and mouse reveal that most of the conserved regions are confined to the coding regions and transcription units of the genes themselves, but a few blocks of conserved sequence also are found outside of ORG transcription units. The possible influence of β-globin regulatory sequences on ORG expression in olfactory epithelium was tested in mice containing a deletion of the endogenous β-globin locus control region, but no change in expression of the neighboring ORGs was detected. We evaluate the implications of these results for possible mechanisms of regulation of ORG transcription.

A comparison of calculated and experimental ${Q}_{\ensuremath{\alpha}}$ values of superheavy even-even nuclei and a few selected odd-$N$ nuclei is presented in the framework of the relativistic mean-field model with the parametrization NL-Z2. Blocking effects are found to be important for a proper description of ${Q}_{\ensuremath{\alpha}}$ of odd mass nuclei. The model gives a good overall description of the available experimental data. The mass and charge assignment of the recently measured decay chains from Dubna and Berkeley is in agreement with the predictions of the model. The analysis of the new data does not allow a final conclusion about the location of the expected island of spherical doubly magic superheavy nuclei.

Shell corrections to the nuclear binding energy as a measure of shell effects in superheavy nuclei are studied within the self-consistent Skyrme-Hartree-Fock and Relativistic Mean-Field theories. Due to the presence of low-lying proton continuum resulting in a free particle gas, special attention is paid to the treatment of single-particle level density. To cure the pathological behavior of shell correction around the particle threshold, the method based on the Green's function approach has been adopted. It is demonstrated that for the vast majority of Skyrme interactions commonly employed in nuclear structure calculations, the strongest shell stabilization appears for Z=124, and 126, and for N=184. On the other hand, in the relativistic approaches the strongest spherical shell effect appears systematically for Z=120 and N=172. This difference has probably its roots in the spin-orbit potential. We have also shown that, in contrast to shell corrections which are fairly independent on the force, macroscopic energies extracted from self-consistent calculations strongly depend on the actual force parametrisation used. That is, the A and Z dependence of mass surface when extrapolating to unknown superheavy nuclei is prone to significant theoretical uncertainties., 14 pages REVTeX, 8 eps figures, submitted to Phys. Rev. C

We study the extrapolation of nuclear shell structure to the region of superheavy nuclei in self-consistent mean-field models -- the Skyrme-Hartree-Fock approach and the relativistic mean-field model -- using a large number of parameterizations. Results obtained with the Folded-Yukawa potential are shown for comparison. We focus on differences in the isospin dependence of the spin-orbit interaction and the effective mass between the models and their influence on single-particle spectra. While all relativistic models give a reasonable description of spin-orbit splittings, all non-relativistic models show a wrong trend with mass number. The spin-orbit splitting of heavy nuclei might be overestimated by 40%-80%. Spherical doubly-magic superheavy nuclei are found at (Z=114,N=184), (Z=120,N=172) or (Z=126,N=184) depending on the parameterization. The Z=114 proton shell closure, which is related to a large spin-orbit splitting of proton 2f states, is predicted only by forces which by far overestimate the proton spin-orbit splitting in Pb208. The Z=120 and N=172 shell closures predicted by the relativistic models and some Skyrme interactions are found to be related to a central depression of the nuclear density distribution. This effect cannot appear in macroscopic-microscopic models which have a limited freedom for the density distribution only. In summary, our findings give a strong argument for (Z=120,N=172) to be the next spherical doubly-magic superheavy nucleus., 22 pages REVTeX, 16 eps figures, accepted for publication in Phys. Rev. C

The phenomenological adjustment of the nuclear pairing strength is usually performed with respect to the odd-even staggering of the binding energies. We find that the results strongly depend on the way in which the ground states of the odd nuclei are computed. A thorough calculation including all time-even and time-odd polarisation effects induced by the odd nucleon produces about 30% reduced odd-even staggering as compared to the standard spherical calculations in the relativistic mean-field model. The pairing strength must be enhanced by about 20% to compensate for that effect. The enhanced strength has dramatic consequences for the predicted deformation properties of the underlying mean-field models, possibly implying that new adjustments of their parameters become necessary as well., Comment: 5 pages REVTeX, 5 eps figures, accepted for publication in Phys. Lett. B

The use of homologous recombination to modify and thereby functionally analyze cis-regulatory DNA elements in mammalian cells has become an important approach in mammalian gene expression research. We have emphasized the necessity of designing a system that allows the removal of selectable markers used in targeting and facilitates the further modification of the region under study. To perform these tasks, we presently favor making an initial HR-mediated replacement of the entire element under study with an active positive selectable marker in combination with either an inactive second positive selectable marker or an active negative selectable marker. The plug and socket system, in which an inactive selectable marker is complemented by HR, is the most dependable and well-characterized option for making secondary modifications. However, the double-replacement system has certain advantages, and the recently developed RMCE approach, which allows replacement of a negative selectable marker by site-specific recombinase-mediated insertion without using a positive selectable marker, will likely prove very valuable in future experiments. Each of the systems, or combinations thereof, should be considered in light of the specifics of any given experiment to select the most appropriate option. Although the emphasis of this article has been the analysis of cis-acting regulatory elements involved in transcription, these same approaches can be used to analyze other regulatory elements (e.g., origins of replication) and to make multiple subtle mutations in polypeptides.

We discuss two widely used nuclear mean-field models, the relativistic mean-field model and the (nonrelativistic) Skyrme-Hartree-Fock model, and their capability to describe exotic nuclei with emphasis on neutron-rich tin isotopes and superheavy nuclei.

We investigate the structure of the potential energy surfaces of the superheavy nuclei 258Fm, 264Hs, (Z=112,N=166), (Z=114,N=184), and (Z=120,N=172) within the framework of self-consistent nuclear models, i.e. the Skyrme-Hartree-Fock approach and the relativistic mean-field model. We compare results obtained with one representative parametrisation of each model which is successful in describing superheavy nuclei. We find systematic changes as compared to the potential energy surfaces of heavy nuclei in the uranium region: there is no sufficiently stable fission isomer any more, the importance of triaxial configurations to lower the first barrier fades away, and asymmetric fission paths compete down to rather small deformation. Comparing the two models, it turns out that the relativistic mean-field model gives generally smaller fission barriers., Comment: 8 pages RevTeX, 6 figures

During the metamorphic reorganization of the insect central nervous system, the steroid hormone 20-hydroxyecdysone induces a wide spectrum of cellular responses including neuronal proliferation, maturation, cell death and the remodeling of larval neurons into their adult forms. In Drosophila, expression of specific ecdysone receptor (EcR) isoforms has been correlated with particular responses, suggesting that different EcR isoforms may govern distinct steroid-induced responses in these cells. We have used imprecise excision of a P element to create EcR deletion mutants that remove the EcR-B promoter and therefore should lack EcR-B1 and EcR-B2 expression but retain EcR-A expression. Most of these EcR-B mutant animals show defects in larval molting, arresting at the boundaries between the three larval stages, while a smaller percentage of EcR-B mutants survive into the early stages of metamorphosis. Remodeling of larval neurons at metamorphosis begins with the pruning back of larval-specific dendrites and occurs as these cells are expressing high levels of EcR-B1 and little EcR-A. This pruning response is blocked in the EcR-B mutants despite the fact that adult-specific neurons, which normally express only EcR-A, can progress in their development. These observations support the hypothesis that different EcR isoforms control cell-type-specific responses during remodeling of the nervous system at metamorphosis.

The shell structure of superheavy nuclei is investigated within various parametrizations of relativistic and nonrelativistic nuclear mean-field models. The heaviest known even-even nuclei are used as a benchmark to estimate the predictive value of the models. From that starting point, spherical and deformed shell closures in the superheavy region are searched.

We present test calculations of the quasiparticle random-phase approximation with Skyrme and delta-pairing forces. We examine the convergence of solutions in the isoscalar 0+ channel as we increase the number of single-quasiparticle states, and the separation of spurious states from physical excited states in the isoscalar 1− channel. Our calculation is fully self-consistent as it neglects no component of the interaction. We focus on Sn isotopes near the two-neutron drip line.

We investigate the pairing treatment with approximate particle number projection, known as the Lipkin-Nogami scheme, in connection with nuclear Hartree-Fock models. A prescription for the pairing strength is developed. It is based on the average gap method and employs a Thomas-Fermi model to estimate the average level density at the Fermi surface. The second-order variation of the Skyrme energy functional gives feedback to the self-consistent density and thus to the mean field. This effect turns out to be small but non-negligible. The Lipkin-Nogami scheme is compared with the conventional treatment of pairing based on the BCS approximation. The bulk observables, especially those which are related to surface properties, depend on the pairing scheme employed, with the differences most noticeable for light nuclei. Pronounced effects on deformation energy surfaces were found, leading to sizable differences in the deformation energies. {copyright} {ital 1996 The American Physical Society.}

The interphase cell nucleus is structurally and functionally compartmentalized, making the subnuclear position of genes an important determinant of their activity. During cellular differentiation, as tissue-specific expression programs unfold, dynamic reorganization of the nucleus positions sets of genes in active or repressive compartments. The nuclear periphery has emerged as an unusually complex compartment in this process. While it is marked by facultative heterochromatin and has been considered primarily as a repressive compartment, recent work suggests that active genes may also associate with the periphery. Moreover, the nuclear envelope is riddled with nuclear pore complexes, the gateways for molecular exchange between the cytoplasm and the nucleus, resulting in substantial traffic through this compartment. Using murine erythropoiesis as a model system, our recent three dimensional analysis of the positioning of the β-globin locus revealed that, when inactive in undifferentiated embryonic stem cells and erythroid progenitor cells, the locus is positioned predominantly at the nuclear periphery and appears to contact the lamina. This association is lost with progressing erythroid maturation, and the locus is repositioned towards the nuclear interior concomitant with increasing β-globin gene expression. Importantly, however, β-major globin expression begins at the nuclear periphery prior to relocalization, suggesting that associations of the locus at the periphery may shift from repressive to activating complexes. We are investigating the interactions of the β-globin locus with the nuclear periphery by two approaches: Using enhanced imaging permitted by Cryo-ImmunoFISH, we are analyzing the position of the locus relative to specific components of the nuclear lamina and nuclear pore complexes at distinct differentiation stages. In addition, we are probing the physical interactions of the locus with the periphery by biochemical means. To this end we are using ChIP-chip to identify lamina associated proteins binding the β-globin locus and to determine what sequence elements within the locus mediate these interactions. Ultimately these experiments will shed further light on mechanisms regulating β-globin gene expression during erythropoiesis and how stage-specific nuclear localization contributes to this process.

We have investigated the relationships among nuclear positioning, association with RNA polymerase II (PolII) and expression of the murine β-globin locus during erythroid differentiation, as well as the role of the locus control region (LCR) in these processes. Fetal liver cells from wildtype and LCR-deletion mouse strains were stained with a panel of antibodies, and flow cytometry was used to define and isolate cells from four stages of erythropoiesis spanning pro-erythroblasts (stage 1) to orthochromatic normoblasts and nucleated RBC (stage 4). DNA FISH analyses reveal that with increasing erythroid maturation the β-globin locus is less likely to be located in the nuclear periphery. Immuno-FISH demonstrates that PolII speckles initially are spread diffusely throughout the nucleus, with the exception of extreme periphery. With erythroid maturation the number of speckles decline and become more centrally located. Combined DNA FISH /PolII immuno-staining reveals an increase in co-localization of PolII and β-globin alleles during erythroid maturation. These results are consistent with a model in which the locus is more likely to be in the nuclear periphery and away from PolII foci prior to activation, and with maturation, the locus re-locates more centrally and associates with PolII speckles, leading to β-globin activation. To investigate this model, α and β-globin primary transcript FISH were performed and revealed that while β activation lags behind α, both start at stage 2 and increase with maturation. Notably, activation occurs prior to the increased localization of the locus away from the periphery during maturation, suggesting that localization of the locus away from the periphery may be secondary to the redistribution of PolII during erythroid maturation. Analysis of sorted erythroid cells from mice with a targeted deletion of the LCR reveals less co-localization of the β-globin locus and PolII speckles and loss of re-localization away from the periphery during maturation. Moreover, primary transcript FISH analysis of sorted cells from mice lacking the LCR and those carrying a combined deletion of HS 2 and 3 suggests that the LCR affects the likelihood that an allele is expressed, as well as the amount of transcript generated during periods of expression. Taken together our results suggest that the LCR plays a role in locating to, or stabilization of, interactions between the locus and PolII speckles, increasing the probability of β-globin expression, after which the LCR also affects the rate of transcription.

The activity of the β-globin locus is regulated by the locus control region (LCR) which in humans and mice is comprised of six DNaseI hypersensitive sites (HSs) located upstream of the β-like globin genes. Hispanic thalassemia, a naturally occurring deletion of the LCR plus 25kb upstream results in the failure to activate the β-globin locus at the levels of chromatin structure, transcription and replication. In order to examine how the HSs interact to regulate the endogenous β-globin locus, we have utilized homologous recombination for the mutational analysis of the endogenous murine β-globin LCR in embryonic stem cells, followed by the generation of mice. Previously we reported that deletion of the endogenous LCR by homologous recombination (ΔLCR) does not completely silence expression of the β-like genes, and has no measurable effect on nuclease sensitivity, promoter hypersensitive site formation or core histone hyperacetylation. Thus the LCR provides a necessary enhancer-like activity. In addition, while loss of the LCR leads to only a slight decrease in pre-initiation complex formation and Pol II binding to the promoter, there is a significant decrease in downstream polymerase and this correlates with a basal level of ser-5 phosphorylation of Pol II. To determine if the decrease in downstream Pol II observed along Δthe LCR allele is due to decreased release of polymerase from the promoter, or downstream polymerase pausing, KMnO4 in vivo foot-printing was done. Comparison of the 5′ end of WT and ΔLCR β-maj globin genes reveal similar patterns consistent with pol II pausing on both alleles, and suggesting that the LCR stimulates elongation by releasing promoter proximal paused polymerases. To further characterize LCR mediated activation and determine what characteristics vary with the level of transcription we have continued our analysis of mice with ΔLCR allele expressing at 1–4% of wild-type (WT), and mice with a deletion of HS 2 and 3 (Δ23) expressing at 30% of WT. The Δ23 allele was chosen as it demonstrates an intermediate transcriptional phenotype and is one of several double HS deletions that demonstrate that the LCR HSs contribute additively to globin gene transcription. To determine if histone modifications other than acetylation vary with LCR mutations and is associated with the level of transcription, the state of K4-tri and K79-di histone methylation was assayed along exon 3 of the β-maj gene of WT, Δ23 and ΔLCR alleles. While in some systems enrichment of methylation of K4 and K79 are associated with a permissive or activated state, we find increases in histone methylation with deletion of the LCR, and an intermediate degree of methylation with deletion of HS 2 and 3. Thus, surprisingly, increasing levels of transcription correlate with decreases in histone methylation. Finally, as enhancers increase the probability rather than the rate of expression we have analyzed WT, Δ23 and ΔLCR alleles with single allele transcription assays. RT-PCR reveals all Δ 23 and ΔLCR alleles express mRNA at 30 and 4% of WT respectively, consistent with bulk RNA analysis and suggesting that individual alleles are not permanently silenced. In contrast, primary transcript RNA FISH analysis demonstrates that the mutant alleles are less likely to be expressed, thus LCR HSs may affect the probability as well rate of transcription.

The Multi-Reference Energy Density Functional (MR-EDF) approach (also called configuration mixing or Generator Coordinate Method), that is commonly used to treat pairing in finite nuclei and project onto particle number, is re-analyzed. It is shown that, under certain conditions, the MR-EDF energy can be interpreted as a functional of the one-body density matrix of the projected state with good particle number. Based on this observation, we propose a new approach, called Symmetry-Conserving EDF (SC-EDF), where the breaking and restoration of symmetry are accounted for simultaneously. We show, that such an approach is free from pathologies recently observed in MR-EDF and can be used with a large flexibility on the density dependence of the functional., proceeding of the conference "Many body correlations from dilute to dense Nuclear systems", Paris, February 2011

We discuss the pairing gap, a measure for nuclear pairing correlations, in chains of spherical, semi-magic nuclei in the framework of self-consistent nuclear mean-field models. The equations for the conventional BCS model and the approximate projection-before-variation Lipkin-Nogami method are formulated in terms of local density functionals for the effective interaction. We calculate the Lipkin-Nogami corrections of both the mean-field energy and the pairing energy. Various definitions of the pairing gap are discussed as three-point, four-point and five-point mass-difference formulae, averaged matrix elements of the pairing potential, and single-quasiparticle energies. Experimental values for the pairing gap are compared with calculations employing both a delta pairing force and a density-dependent delta interaction in the BCS and Lipkin-Nogami model. Odd-mass nuclei are calculated in the spherical blocking approximation which neglects part of the the core polarization in the odd nucleus. We find that the five-point mass difference formula gives a very robust description of the odd-even staggering, other approximations for the gap may differ from that up to 30% for certain nuclei., 17 pages, 8 figures. Accepted for publication in EPJA

We present a formulation of the Hartree-Fock-Bogoliubov (HFB) equations which solves the problem directly in the basis of natural orbitals. This provides a very efficient scheme which is particularly suited for large scale calculations on coordinate-space grids., Comment: 5 pages RevTeX, (Postscript-file also available at http://www.th.physik.uni-frankfurt.de/~bender/nucl_struct_publications.html or at ftp://th.physik.uni-frankfurt.de/pub/bender ), accepted for publication in Z. Phys. A