Renormalized interactions with a realistic single particle basis

Neutron-rich isotopes in the sdpf space with Z < 15 require modifications to derived effective interactions to agree with experimental data away from stability. A quantitative justification is given for these modifications due to the weakly bound nature of model space orbits via a procedure using realistic radial wavefunctions and realistic NN interactions. The long tail of the radial wavefunction for loosely bound single particle orbits causes a reduction in the size of matrix elements involving those orbits, most notably for pairing matrix elements, resulting in a more condensed level spacing in shell model calculations. Example calculations are shown for 36Si and 38Si.Comment: 6 page

Quenching of spectroscopic factors for proton removal in oxygen isotopes

We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes $^{14,16,22,24,28}$O with the chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds.Comment: 3 figure

Simulated Dark-Matter Halos as a Test of Nonextensive Statistical Mechanics

In the framework of nonextensive statistical mechanics, the equilibrium structures of astrophysical self-gravitating systems are stellar polytropes, parameterized by the polytropic index n. By careful comparison to the structures of simulated dark-matter halos we find that the density profiles, as well as other fundamental properties, of stellar polytropes are inconsistent with simulations for any value of n. This result suggests the need to reconsider the applicability of nonextensive statistical mechanics (in its simplest form) to equilibrium self-gravitating systems.Comment: Accepted for publication in Physical Review

Ab-initio computation of neutron-rich oxygen isotopes

We compute the binding energy of neutron-rich oxygen isotopes and employ the coupled-cluster method and chiral nucleon-nucleon interactions at next-to-next-to-next-to-leading order with two different cutoffs. We obtain rather well-converged results in model spaces consisting of up to 21 oscillator shells. For interactions with a momentum cutoff of 500 MeV, we find that 28O is stable with respect to 24O, while calculations with a momentum cutoff of 600 MeV result in a slightly unbound 28O. The theoretical error estimates due to the omission of the three-nucleon forces and the truncation of excitations beyond three-particle-three-hole clusters indicate that the stability of 28O cannot be ruled out from ab-initio calculations, and that three-nucleon forces and continuum effects play the dominant role in deciding this question.Comment: 5 pages + eps, 3 figure

The galaxies in the field of the nearby GRB980425/SN1998bw

We present spectroscopic observations of ESO 184-G82, the host galaxy of GRB980425/SN1998bw, and six galaxies in its field. A host redshift of z=0.0087+/-0.0006 is derived, consistent with that measured by Tinney et al. (1998). Redshifts are obtained for the six surrounding galaxies observed. Three of these galaxies lie within 11 Mpc of each other, confirming the suggestion that some of these galaxies form a group. However, all of the field galaxies observed lie at significantly greater distances than ESO 184-G82 and are therefore not associated with it. The host galaxy of GRB980425/SN1998bw thus appears to be an isolated dwarf galaxy and interactions with other galaxies do not seem to be responsible for its star formation.Comment: 5 pages, 2 figures, accepted for publication in A&

The Redshift Distribution of the TOUGH Survey

We present the redshift results from a Very Large Telescope program aimed at optimizing the legacy value of the Swift mission: to characterize a homogeneous, X-ray selected, sample of 69 GRB host galaxies. 19 new redshifts have been secured, resulting in a 83% (57/69) redshift completion, making the survey the most comprehensive in terms of redshift completeness of any sample to the full Swift depth, available to date. We present the cumulative redshift distribution and derive a conservative, yet small, associated uncertainty. We constrain the fraction of Swift GRBs at high redshift to a maximum of 10% (5%) for z > 6 (z > 7). The mean redshift of the host sample is assessed to be > 2.2. Using this more complete sample, we confirm previous findings that the GRB rate at high redshift (z > 3) appears to be in excess of predictions based on assumptions that it should follow conventional determinations of the star formation history of the universe, combined with an estimate of its likely metallicity dependence. This suggests that either star formation at high redshifts has been significantly underestimated, for example due to a dominant contribution from faint, undetected galaxies, or that GRB production is enhanced in the conditions of early star formation, beyond those usually ascribed to lower metallicity.Comment: 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 34 in eConf Proceedings C130414

MLL/GAS7 fusion in a pediatric case of t(11;17)(q23;p13)-positive precursor B-cell acute lymphoblastic leukemia

AML/GAS7, resulting from t(11;17)(q23;p13), has been reported in one case of treatment-related acute myeloid leukemia (AML). We present a de novo case of t(11;17)-positive pediatric acute lymphoblastic leukemia. Fluorescent in situ hybridization and reverse transcriptase polymerase chain reaction analyses revealed an MLL/GAS7 chimera identical to the one previously described in AML. The molecular genetic features of MLL/GAS7 and the clinical impact of t(11;17) are discussed