Dirac-Brueckner Hartree-Fock Approach: from Infinite Matter to Effective Lagrangians for Finite Systems

One of the open problems in nuclear structure is how to predict properties of finite nuclei from the knowledge of a bare nucleon-nucleon interaction of the meson-exchange type. We point out that a promising starting point consists in Dirac-Brueckner-Hartree-Fock (DBHF) calculations us- ing realistic nucleon-nucleon interactions like the Bonn potentials, which are able to reproduce satisfactorily the properties of symmetric nuclear matter without the need for 3-body forces, as is necessary in non-relativistic BHF calculations. However, the DBHF formalism is still too com- plicated to be used directly for finite nuclei. We argue that a possible route is to define effective Lagrangians with density-dependent nucleon-meson coupling vertices, which can be used in the Relativistic Hartree (or Relativistic Mean Field (RMF)) or preferrably in the Relativistic Hartree- Fock (RHF) approach. The density-dependence is matched to the nuclear matter DBHF results. We review the present status of nuclear matter DBHF calculations and discuss the various schemes to construct the self-energy, which lead to differences in the predictions. We also discuss how effective Lagrangians have been constructed and are used in actual calculations. We point out that completely consistent calculations in this scheme still have to be performed.Comment: 16 pages, to be published in Journal of Physics G: Nuclear and Particle Physics, special issue

Clinical Experience with the PillCam Patency Capsule prior to Video Capsule Endoscopy: A Real-World Experience

Background. In patients with known or suspected risk factors for gastrointestinal stenosis, the PillCam patency capsule (PC) is given before a video capsule endoscopy (VCE) in order to minimize the risk of capsule retention (CR). CR is considered unlikely upon excretion of the PC within 30 hours, excretion in an undamaged state after 30 hours, or radiological projection to the colon. Methods. We performed a retrospective analysis of 38 patients with risk factors for CR, who received a PC from 02/2013 to 04/2015 at Klinikum Augsburg. Results. Sixteen of our 38 patients observed a natural excretion after a mean time of 34 hours past ingestion. However, only 8 patients observed excretion within 30 hours, as recommended by the company. In 20 patients passage of the PC into the colon was shown via RFID-scan or radiological imaging (after 33 and 45 hours, resp.). Only 2 patients showed a pathologic PC result. In consequence, 32 patients received the VCE; no CR was observed. Conclusion. Our data indicates that a VCE could safely be performed even if the PC excretion time is longer than 30 hours and the excreted PC was not screened for damage

Auxiliary potential in no-core shell-model calculations

The Lee-Suzuki iteration method is used to include the folded diagrams in the calculation of the two-body effective interaction $v^{(2)}_{\rm eff}$ between two nucleons in a no-core model space. This effective interaction still depends upon the choice of single-particle basis utilized in the shell-model calculation. Using a harmonic-oscillator single-particle basis and the Reid-soft-core {\it NN} potential, we find that $v^{(2)}_{\rm eff}$ overbinds ^4\mbox{He} in 0, 2, and $4\hbar\Omega$ model spaces. As the size of the model space increases, the amount of overbinding decreases significantly. This problem of overbinding in small model spaces is due to neglecting effective three- and four-body forces. Contributions of effective many-body forces are suppressed by using the Brueckner-Hartree-Fock single-particle Hamiltonian.Comment: 14 text pages and 4 figures (in postscript, available upon request). AZ-PH-TH/94-2

Ground State Energy of the Low Density Bose Gas

Now that the properties of low temperature Bose gases at low density, $\rho$, can be examined experimentally it is appropriate to revisit some of the formulas deduced by many authors 4-5 decades ago. One of these is that the leading term in the energy/particle is $2\pi \hbar^2 \rho a/m$, where $a$ is the scattering length. Owing to the delicate and peculiar nature of bosonic correlations, four decades of research have failed to establish this plausible formula rigorously. The only known lower bound for the energy was found by Dyson in 1957, but it was 14 times too small. The correct bound is proved here.Comment: 4 pages, Revtex, reference 12 change

Nonuniversal Effects in the Homogeneous Bose Gas

Effective field theory predicts that the leading nonuniversal effects in the homogeneous Bose gas arise from the effective range for S-wave scattering and from an effective three-body contact interaction. We calculate the leading nonuniversal contributions to the energy density and condensate fraction and compare the predictions with results from diffusion Monte Carlo calculations by Giorgini, Boronat, and Casulleras. We give a crude determination of the strength of the three-body contact interaction for various model potentials. Accurate determinations could be obtained from diffusion Monte Carlo calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te

Clinical Study Clinical Experience with the PillCam Patency Capsule prior to Video Capsule Endoscopy: A Real-World Experience

Background. In patients with known or suspected risk factors for gastrointestinal stenosis, the PillCam patency capsule (PC) is given before a video capsule endoscopy (VCE) in order to minimize the risk of capsule retention (CR). CR is considered unlikely upon excretion of the PC within 30 hours, excretion in an undamaged state after 30 hours, or radiological projection to the colon. Methods. We performed a retrospective analysis of 38 patients with risk factors for CR, who received a PC from 02/2013 to 04/2015 at Klinikum Augsburg. Results. Sixteen of our 38 patients observed a natural excretion after a mean time of 34 hours past ingestion. However, only 8 patients observed excretion within 30 hours, as recommended by the company. In 20 patients passage of the PC into the colon was shown via RFID-scan or radiological imaging (after 33 and 45 hours, resp.). Only 2 patients showed a pathologic PC result. In consequence, 32 patients received the VCE; no CR was observed. Conclusion. Our data indicates that a VCE could safely be performed even if the PC excretion time is longer than 30 hours and the excreted PC was not screened for damage

Correspondence between solar fine-scale structures in the corona, transition region, and lower atmosphere from collaborative observations

The Soft X-Ray Imaging Payload and the High Resolution Telescope and Spectrograph (HRTS) instrument were launched from White Sands on 11 December 1987 in coordinated sounding rocket flights to investigate the correspondence of coronal and transition region structures, especially the relationship between X-ray bright points (XBPs) and transition region small spatial scale energetic events. The coaligned data from X-ray images are presented along with maps of sites of transition region energetic events observed in C IV (100,000 K), HRTS 1600 A spectroheliograms of the T sub min region and ground based magnetogram and He I 10830 A images

Fermi systems with long scattering lengths

Ground state energies and superfluid gaps are calculated for degenerate Fermi systems interacting via long attractive scattering lengths such as cold atomic gases, neutron and nuclear matter. In the intermediate region of densities, where the interparticle spacing $(\sim 1/k_F)$ is longer than the range of the interaction but shorter than the scattering length, the superfluid gaps and the energy per particle are found to be proportional to the Fermi energy and thus differs from the dilute and high density limits. The attractive potential increase linearly with the spin-isospin or hyperspin statistical factor such that, e.g., symmetric nuclear matter undergoes spinodal decomposition and collapses whereas neutron matter and Fermionic atomic gases with two hyperspin states are mechanically stable in the intermediate density region. The regions of spinodal instabilities in the resulting phase diagram are reduced and do not prevent a superfluid transition.Comment: extended and revised version, 7 pages including new phase diagra

Towards a fully self-consistent spectral function of the nucleon in nuclear matter

We present a calculation of nuclear matter which goes beyond the usual quasi-particle approximation in that it includes part of the off-shell dependence of the self-energy in the self-consistent solution of the single-particle spectrum. The spectral function is separated in contributions for energies above and below the chemical potential. For holes we approximate the spectral function for energies below the chemical potential by a $\delta$-function at the quasi-particle peak and retain the standard form for energies above the chemical potential. For particles a similar procedure is followed. The approximated spectral function is consistently used at all levels of the calculation. Results for a model calculation are presented, the main conclusion is that although several observables are affected by the inclusion of the continuum contributions the physical consistency of the model does not improve with the improved self-consistency of the solution method. This in contrast to expectations based on the crucial role of self-consistency in the proofs of conservation laws.Comment: 26 pages Revtex with 4 figures, submitted to Phys. Rev.

Analytical and numerical study of hardcore bosons in two dimensions

We study various properties of bosons in two dimensions interacting only via onsite hardcore repulsion. In particular, we use the lattice spin-wave approximation to calculate the ground state energy, the density, the condensate density and the superfluid density in terms of the chemical potential. We also calculate the excitation spectrum, $\omega({\bf k})$. In addition, we performed high precision numerical simulations using the stochastic series expansion algorithm. We find that the spin-wave results describe extremely well the numerical results over the {\it whole} density range $0\leq \rho \leq 1$. We also compare the lattice spin-wave results with continuum results obtained by summing the ladder diagrams at low density. We find that for $\rho \leq 0.1$ there is good agreement, and that the difference between the two methods vanishes as $\rho^2$ for $\rho \to 0$. This offers the possibility of obtaining precise continuum results by taking the continuum limit of the spin-wave results for all densities. Finaly, we studied numerically the finite temperature phase transition for the entire density range and compared with low density predictions.Comment: 10 pages, 8 figures include