Quasiparticle interaction in nuclear matter with chiral three-nucleon forces

We derive the effective interaction between two quasiparticles in symmetric nuclear matter resulting from the leading-order chiral three-nucleon force. We restrict our study to the L=0,1 Landau parameters of the central quasiparticle interaction computed to first order. We find that the three-nucleon force provides substantial repulsion in the isotropic spin- and isospin-independent component F_0 of the interaction. This repulsion acts to stabilize nuclear matter against isoscalar density oscillations, a feature which is absent in calculations employing low-momentum two-nucleon interactions only. We find a rather large uncertainty for the nuclear compression modulus due to a sensitive dependence on the low-energy constant c_3. The effective nucleon mass on the Fermi surface, as well as the nuclear symmetry energy, receive only small corrections from the leading-order chiral three-body force. Both the anomalous orbital g-factor and the Landau-Migdal parameter g'_{NN} (characterizing the spin-isospin response of nuclear matter) decrease with the addition of three-nucleon correlations. In fact, the anomalous orbital g-factor remains significantly smaller than its value extracted from experimental data, whereas g'_{NN} still compares well with empirical values. The inclusion of the three-nucleon force results in relatively small p-wave (L=1) components of the central quasiparticle interaction, thus suggesting an effective interaction of short range.Comment: 20 pages, 6 figure

The morality of attitudes toward nanotechnology: about God, techno-scientific progress, and interfering with nature

Using survey data, we examine public attitudes toward and awareness of nanotechnology in Germany (N = 750). First, it is shown that a majority of the people are still not familiar with nanotechnology. In addition, diffusion of information about nanotechnology thus far mostly seems to reach men and people with a relative higher educational background. Also, pro-science and technology views are positively related with nanotech familiarity. Results further show that a majority of the people have an indifferent, ambiguous, or non-attitude toward nanotechnology. Multinomial logit analyses further reveal that nanotech familiarity is positively related with people’s attitudes. In addition, it is shown that traditional religiosity is unrelated to attitudes and that individual religiosity is weakly related to nanotechnology attitudes. However, moral covariates other than religiosity seem of major importance. In particular, our results show that more negative views on technological and scientific progress as well as more holistic views about the relation between people and the environment increase the likelihood of having a negative attitude toward nanotechnology

On local linearization of control systems

We consider the problem of topological linearization of smooth (C infinity or real analytic) control systems, i.e. of their local equivalence to a linear controllable system via point-wise transformations on the state and the control (static feedback transformations) that are topological but not necessarily differentiable. We prove that local topological linearization implies local smooth linearization, at generic points. At arbitrary points, it implies local conjugation to a linear system via a homeomorphism that induces a smooth diffeomorphism on the state variables, and, except at "strongly" singular points, this homeomorphism can be chosen to be a smooth mapping (the inverse map needs not be smooth). Deciding whether the same is true at "strongly" singular points is tantamount to solve an intriguing open question in differential topology

Critical Enhancement of the In-medium Nucleon-Nucleon Cross Section at low Temperatures

The in-medium nucleon-nucleon cross section is calculated starting from the thermodynamic T-matrix at finite temperatures. The corresponding Bethe-Salpeter-equation is solved using a separable representation of the Paris nucleon-nucleon-potential. The energy-dependent in-medium N-N cross section at a given density shows a strong temperature dependence. Especially at low temperatures and low total momenta, the in-medium cross section is strongly modified by in-medium effects. In particular, with decreasing temperature an enhancement near the Fermi energy is observed. This enhancement can be discussed as a precursor of the superfluid phase transition in nuclear matter.Comment: 10 pages with 4 figures (available on request from the authors), MPG-VT-UR 34/94 accepted for publication in Phys. Rev.

A phenomenological equation of state for isospin asymmetric nuclear matter

A phenomenological momentum-independent (MID) model is constructed to describe the equation of state (EOS) for isospin asymmetric nuclear matter, especially the density dependence of the nuclear symmetry energy $E_{\text{\textrm{sym}}}(\rho)$. This model can reasonably describe the general properties of the EOS for symmetric nuclear matter and the symmetry energy predicted by both the sophisticated isospin and momentum dependent MDI model and the Skyrme-Hartree-Fock approach. We find that there exists a nicely linear correlation between $K_{\mathrm{sym}}$ and $L$ as well as between $J_{0}/K_{0}$ and $K_{0}$, where $L$ and $K_{\mathrm{sym}}$ represent, respectively, the slope and curvature parameters of the symmetry energy at the normal nuclear density $\rho_{0}$ while $K_{0}$ and $J_{0}$ are, respectively, the incompressibility and the third-order derivative parameter of symmetric nuclear matter at $\rho_{0}$. These correlations together with the empirical constraints on $K_{0}$, $L$ and $E_{\text{\textrm{sym}}}(\rho_{0})$ lead to an estimation of -477 MeV $\leq K_{\mathrm{sat,2}}\leq -241$ MeV for the second-order isospin asymmetry expansion coefficient for the incompressibility of asymmetric nuclear matter at the saturation point.Comment: 9 pages, 4 figures, contribution to Special Topic on Large-Scale Scientific Facilities (LSSF) in Science in China Series G: Physics, Mechanics & Astronom

Step-Indexed Normalization for a Language with General Recursion

The Trellys project has produced several designs for practical dependently typed languages. These languages are broken into two fragments-a_logical_fragment where every term normalizes and which is consistent when interpreted as a logic, and a_programmatic_fragment with general recursion and other convenient but unsound features. In this paper, we present a small example language in this style. Our design allows the programmer to explicitly mention and pass information between the two fragments. We show that this feature substantially complicates the metatheory and present a new technique, combining the traditional Girard-Tait method with step-indexed logical relations, which we use to show normalization for the logical fragment.Comment: In Proceedings MSFP 2012, arXiv:1202.240

The Meissl scheme for the geodetic ellipsoid

We present a variant of the Meissl scheme to relate surface spherical harmonic coefficients of the disturbing potential of the Earth's gravity field on the surface of the geodetic ellipsoid to surface spherical harmonic coefficients of its first- and second-order normal derivatives on the same or any other ellipsoid. It extends the original (spherical) Meissl scheme, which only holds for harmonic coefficients computed from geodetic data on a sphere. In our scheme, a vector of solid spherical harmonic coefficients of one quantity is transformed into spherical harmonic coefficients of another quantity by pre-multiplication with a transformation matrix. This matrix is diagonal for transformations between spheres, but block-diagonal for transformations involving the ellipsoid. The computation of the transformation matrix involves an inversion if the original coefficients are defined on the ellipsoid. This inversion can be performed accurately and efficiently (i.e., without regularisation) for transformation among different gravity field quantities on the same ellipsoid, due to diagonal dominance of the matrices. However, transformations from the ellipsoid to another surface can only be performed accurately and efficiently for coefficients up to degree and order 520 due to numerical instabilities in the inversion