Magnetic traveling-stripe-forcing: enhanced transport in the advent of the Rosensweig instability

A new kind of contactless pumping mechanism is realized in a layer of ferrofluid via a spatio-temporally modulated magnetic field. The resulting pressure gradient leads to a liquid ramp, which is measured by means of X-rays. The transport mechanism works best if a resonance of the surface waves with the driving is achieved. The behavior can be understood semi-quantitatively by considering the magnetically influenced dispersion relation of the fluid.Comment: 6 Pages, 8 Figure

Mutations and Allelic Loss of the NF2 Gene in Neurofibromatosis 2-Associated Skin Tumors

Schwannomas in the skin are frequently observed in neurofibromatosis 2 patients. In about one-quarter of the cases, skin tumors are the first clinical symptoms of this disease. Recognizing neurofibromatosis-2-related skin tumors is therefore important for early diagnosis of neurofibromatosis 2, especially in pediatric patients. In this study, we examined 40 skin tumors (36 schwannomas and four neurofibromas) from 20 neurofibromatosis 2 patients for NF2 mutations and allelic loss. NF2 mutations have been identified in blood from 15 (75%) of the 20 patients. We found NF2 mutations in five (13%) and NF2 allelic loss in 18 (45%) of the 40 analyzed tumors. Genetic alterations (allelic loss or mutation) were thus found in 50 (63%) out of the total of 80 examined alleles. In 17 (43%) tumors, alterations were found on both NF2 alleles. These results suggest that, as in the case of vestibular schwannomas and meningiomas, loss of functional NF2 gene product is also the critical event in the development of skin schwannomas. Identification of genetic alterations of the NF2 gene in skin tumors may help to identify neurofibromatosis-2-associated skin tumors, thus assisting in the diagnosis of neurofibromatosis 2 in ambiguous cases, and excluding neurofibromatosis 1 in unclear cases. We also report that the detection rate of constitutional mutations was higher in patients with skin tumors (65%) than in patients without skin tumors (40%)

Sulindac derivatives inhibit cell growth and induce apoptosis in primary cells from malignant peripheral nerve sheath tumors of NF1-patients

BACKGROUND: Malignant peripheral nerve sheath tumors (MPNSTs) are neoplasms leading to death in most cases. Patients with Neurofibromatosis type 1 have an increased risk of developing this malignancy. The metabolites of the inactive prodrug Sulindac, Sulindac Sulfide and Sulindac Sulfone (Exisulind) are new chemopreventive agents that show promising results in the treatment of different cancer types. In this study we examined the antineoplastic effect of these compounds on primary cells derived from two MPNSTs of Neurofibromatosis type 1 patients. RESULTS: Exisulind and Sulindac Sulfide showed a dramatic time- and dose-dependent growth inhibitory effect with IC50-values of 120 μM and 63 μM, respectively. The decrease in viability of the tested cells correlated with induction of apoptosis. Treatment with 500 μM Exisulind and 125 μM Sulindac Sulfide for a period of 2 days increased the rate of apoptosis 21-27-fold compared to untreated cells. Reduced expression of RAS-GTP and phosphorylated ERK1/2 was detected in treated MPNST cells. Moreover, elevated levels of phosphorylated SAPK/JNK were found after drug treatment, and low activation of cleaved caspase-3 was seen. CONCLUSIONS: Our results suggest that this class of compounds may be of therapeutic benefit for Neurofibromatosis type 1 patients with MPNST

Axially symmetric Hartree-Fock-Bogoliubov Calculations for Nuclei Near the Drip-Lines

Nuclei far from stability are studied by solving the Hartree-Fock-Bogoliubov (HFB) equations, which describe the self-consistent mean field theory with pairing interaction. Calculations for even-even nuclei are carried out on two-dimensional axially symmetric lattice, in coordinate space. The quasiparticle continuum wavefunctions are considered for energies up to 60 MeV. Nuclei near the drip lines have a strong coupling between weakly bound states and the particle continuum. This method gives a proper description of the ground state properties of such nuclei. High accuracy is achieved by representing the operators and wavefunctions using the technique of basis-splines. The detailed representation of the HFB equations in cylindrical coordinates is discussed. Calculations of observables for nuclei near the neutron drip line are presented to demonstrate the reliability of the method.Comment: 13 pages, 4 figures. Submitted to Physical Review C on 05/08/02. Revised on Dec/0

Shape Coexistence and the Effective Nucleon-Nucleon Interaction

The phenomenon of shape coexistence is discussed within the self-consistent Hartree-Fock method and the nuclear shell model. The occurrence of the coexisting configurations with different intrinsic shapes is traced back to the properties of the effective Hamiltonian.Comment: 40 pages (16 text, 24 figures). The file may also be retrieved at http://csep2.phy.ornl.gov/theory_group/people/dean/shape_coex/shapes.htm

Shell Corrections of Superheavy Nuclei in Self-Consistent Calculations

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.Comment: 14 pages REVTeX, 8 eps figures, submitted to Phys. Rev.

Shell structure of superheavy nuclei in self-consistent mean-field models

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.Comment: 22 pages REVTeX, 16 eps figures, accepted for publication in Phys. Rev.

Nuclear Skins and Halos in the Mean-Field Theory

Nuclei with large neutron-to-proton ratios have neutron skins, which manifest themselves in an excess of neutrons at distances greater than the radius of the proton distribution. In addition, some drip-line nuclei develop very extended halo structures. The neutron halo is a threshold effect; it appears when the valence neutrons occupy weakly bound orbits. In this study, nuclear skins and halos are analyzed within the self-consistent Skyrme-Hartree-Fock-Bogoliubov and relativistic Hartree-Bogoliubov theories for spherical shapes. It is demonstrated that skins, halos, and surface thickness can be analyzed in a model-independent way in terms of nucleonic density form factors. Such an analysis allows for defining a quantitative measure of the halo size. The systematic behavior of skins, halos, and surface thickness in even-even nuclei is discussed.Comment: 22 RevTeX pages, 22 EPS figures included, submitted to Physical Review

Atomic Parity Nonconservation: Electroweak Parameters and Nuclear Structure

There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the Standard Model at the level of one loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and non-relativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear structure effects may preclude using Pb isotope ratios to test the Standard Model at better than a one percent level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei.Comment: 44 pages, INT Preprint DOE/ER/40561-050-INT92-00-1