Single-particle potential in a chiral approach to nuclear matter including short range NN-terms

We extend a recent chiral approach to nuclear matter of Lutz et al. [Phys. Lett. B474 (2000) 7] by calculating the underlying (complex-valued) single-particle potential U(p,k_f) + i W(p,k_f). The potential for a nucleon at the bottom of the Fermi-sea, U(0,k_{f0})= - 20.0 MeV, comes out as much too weakly attractive in this approach. Even more seriously, the total single-particle energy does not rise monotonically with the nucleon momentum p, implying a negative effective nucleon mass at the Fermi-surface. Also, the imaginary single-particle potential, W(0,k_{f0}) = 51.1 MeV, is too large. More realistic single-particle properties together with a good nuclear matter equation of state can be obtained if the short range contributions of non-pionic origin are treated in mean-field approximation (i.e. if they are not further iterated with 1pi-exchange). We also consider the equation of state of pure neutron matter $bar E_n(k_n)$ and the asymmetry energy A(k_f) in that approach. The downward bending of these quantities above nuclear matter saturation density seems to be a generic feature of perturbative chiral pion-nucleon dynamics.Comment: 12 pages, 7 figures, submitted to Physical Review

Possible strong symmetric hydrogen bonding in disodium trihydrogen bis(2,2'-oxydiacetate) nitrate

In the title compound, 2Na+·C8H11O10-·NO3-, the NaI atom is heptacoordinate with an approximately pentagonal-bipyramidal geometry. A possible strong symmetric hydrogen bond, with the H atom located at an inversion centre and an OO distance of 2.450 (2) Å, is observed in the crystal structure

Self-Employment in Germany: The Trend Has Been Increasing for Some Time

Entrepreneurial self-employment in Germany has undergone a strong upturn in the last 20 years. The number of self-employed people rose by 40 percent between 1991 and 2009. The reasons for this development are the catch-up processes in eastern Germany, structural change towards the service sector, and a strong willingness among the highly skilled, the unmarried and among foreigners to enter self-employment. Furthermore, the percentage of women becoming involved in start-ups increased substantially during the monitoring period. The decision to take up self-employment generally pays off: after three years, 38 percent of all entrepreneurs still being active in the market had a higher income, while only 17 percent had a lower income than in their former paid employment position.Entrepreneurship, self-employment, start-ups

Chiral approach to nuclear matter: Role of explicit short-range NN-terms

We extend a recent chiral approach to nuclear matter by including the most general (momentum-independent) NN-contact interaction. Iterating this two-parameter contact-vertex with itself and with one-pion exchange the emerging energy per particle exhausts all terms possible up-to-and-including fourth order in the small momentum expansion. The equation of state of pure neutron matter, $\bar E_n(k_n)$, can be reproduced very well up to quite high neutron densities of \rho_n=0.5\fmd by adjusting the strength of a repulsive $nn$-contact interaction. Binding and saturation of isospin-symmetric nuclear matter is a generic feature of our perturbative calculation. Fixing the maximum binding energy per particle to $-\bar E(k_{f0})= 15.3$MeV we find that any possible equilibrium density $\rho_0$ lies below \rho_0^{\rm max}=0.191\fmd. The additional constraint from the neutron matter equation of state leads however to a somewhat too low saturation density of \rho_0 =0.134 \fmd. We also investigate the effects of the NN-contact interaction on the complex single-particle potential $U(p,k_f)+i W(p,k_f)$. We find that the effective nucleon mass at the Fermi-surface is bounded from below by $M^*(k_{f0}) \geq 1.4 M$. This property keeps the critical temperature of the liquid-gas phase transition at somewhat too high values $T_c \geq 21$MeV. The downward bending of the asymmetry energy $A(k_f)$ above nuclear matter saturation density is a generic feature of the approximation to fourth order. Altogether, there is within this complete fourth-order calculation no "magic" set of adjustable short-range parameters with which one could reproduce simultaneously and accurately all semi-empirical properties of nuclear matter.Comment: 24 pages, 12 figures, accepted for publication in: Eur. Phys. J.

Effects of Selection for Halothane Resistance on Lipid Concentration and Composition in Drosophilia melanogaster

Drosophila melanogaster is increasingly used as a model system for anesthesia studies. Lipids may play a role in anesthetic resistance by sequestering the hydrophobic anesthetics from nervous tissue. Alternatively, changes in membrane lipid composition (phospholipids and/or cholesterols) may contribute to resistance through alteration of neurological membranes. This project studied the relationship of lipids to anesthetic resistance in a strain of Drosophilia melanogasier with a high level of halothane resistance produced by 13 generations of mass selection. The estimated dose of anesthetic needed to produce anesthesia in one-half of the flies tested (ED50( for this strain was 2.3 times that of the unselected control. Total lipids were extracted and the concentration of total lipids was determined. The average percent of total lipids +/- standard error found in D. melanogaster was 8.73% +/- 0.08 for the resistant strain and 7.57% +/- 0.03 for the control, a relative increase of 15.3%. After determining that the total lipid content was greater in the resistant population (p=0.0004), the fatty acids of the phospholipids were analyzed. The purpose of this study was to determine if alterations in fatty acids were associated with the increase in anesthetic resistance, as predicted by the fluidization hypothesis. Gas chromatography was used to analyze the percentage of saturated fatty acids in phospholipids. Both populations had the same mean normalized percent of saturated fatty acids. This result did not support the hypothesis that resistance was due to altered phospholipid fatty acids