Spectrum and decays of hadronic atoms

We describe the spectra and decays of pi pi and pi K atoms within a non-relativistic effective field theory. The evaluations of the energy shifts and widths are performed at next-to-leading order in isospin symmetry breaking. The prediction for the lifetime of the pi K atom in its ground-state yields tau = (3.7 \pm 0.4) * 10^{-15} sec.Comment: To appear in the proceedings of MESON 2004: 8th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 4-8 June 2004. 7 page

Cooperative Dynamics in Unentangled Polymer Fluids

We present a Generalized Langevin Equation for the dynamics of interacting semiflexible polymer chains, undergoing slow cooperative dynamics. The calculated Gaussian intermolecular center-of-mass and monomer potentials, wich enter the GLE, are in quantitative agreement with computer simulation data. The experimentally observed, short-time subdiffusive regime of the polymer mean-square displacements, emerges here from the competition between the intramolecular and the intermolecular mean-force potentials.Comment: 9 pages, latex, 3 figure

Inter-molecular structure factors of macromolecules in solution: integral equation results

The inter-molecular structure of semidilute polymer solutions is studied theoretically. The low density limit of a generalized Ornstein-Zernicke integral equation approach to polymeric liquids is considered. Scaling laws for the dilute-to-semidilute crossover of random phase (RPA) like structure are derived for the inter-molecular structure factor on large distances when inter-molecular excluded volume is incorporated at the microscopic level. This leads to a non-linear equation for the excluded volume interaction parameter. For macromolecular size-mass scaling exponents, $\nu$, above a spatial-dimension dependent value, $\nu_c=2/d$, mean field like density scaling is recovered, but for $\nu<\nu_c$ the density scaling becomes non-trivial in agreement with field theoretic results and justifying phenomenological extensions of RPA. The structure of the polymer mesh in semidilute solutions is discussed in detail and comparisons with large scale Monte Carlo simulations are added. Finally a new possibility to determine the correction to scaling exponent $\omega_{12}$ is suggested.Comment: 11 pages, 5 figures; to be published in Phys. Rev. E (1999

The dynamical mass of the young cluster W3 in NGC 7252: Heavy-Weight globular cluster or ultra compact dwarf galaxy ?

We have determined the dynamical mass of the most luminous stellar cluster known to date, i.e. object W3 in the merger remnant galaxy NGC 7252. The dynamical mass is estimated from the velocity dispersion measured with the high-resolution spectrograph UVES on VLT. Our result is the astonishingly high velocity dispersion of sigma=45 +- 5 km/s. Combined with the large cluster size R_eff=17.5 +-1.8 pc, this translates into a dynamical virial mass for W3 of 8 +- 2 x 10^7 Msun. This mass is in excellent agreement with the value 7.2 x 10^7 Msun we previously estimated from the cluster luminosity M_V=-16.2 by means of stellar M/L ratios predicted by Simple Stellar Population models (with a Salpeter IMF) and confirms the heavy-weight nature of this object. This results points out that the NGC 7252-type of mergers are able to form stellar systems with masses up to ~ 10^8 Msun. We find that W3, when evolved to ~ 10 Gyr, lies far from the typical Milky Way globular clusters, but appears to be also separated from omegaCen in the Milky Way and G1 in M31, the most massive old stellar clusters of the Local Group, because it is too extended for a given mass, and from dwarf elliptical galaxies because it is much more compact for its mass. Instead the aged W3 is amazingly close to the compact objects named ultracompact dwarf galaxies (UCDGs) found in the Fornax cluster (Hilker et al. 1999; Drinkwater et al. 2000), and to a miniature version of the compact elliptical M32. These objects start populating a previously deserted region of the fundamental plane.Comment: 8 pages, 3 figures, A&A in pres

An integral equation approach to effective interactions between polymers in solution

We use the thread model for linear chains of interacting monomers, and the ``polymer reference interaction site model'' (PRISM) formalism to determine the monomer-monomer pair correlation function $h_{mm}(r)$ for dilute and semi-dilute polymer solutions, over a range of temperatures from very high (where the chains behave as self-avoiding walks) to below the $\theta$ temperature, where phase separation sets in. An inversion procedure, based on the HNC integral equation, is used to extract the effective pair potential between ``average'' monomers on different chains. An accurate relation between $h_{mm}(r)$, $h_{cc}(r)$ [the pair correlation function between the polymer centers of mass (c.m.)], and the intramolecular form factors is then used to determine $h_{cc}(r)$, and subsequently extract the effective c.m.-c.m. pair potential $v_{cc}(r)$ by a similar inversion procedure. $v_{cc}(r)$ depends on temperature and polymer concentration, and the predicted variations are in reasonable agreement with recent simulation data, except at very high temperatures, and below the $\theta$ temperature.Comment: 13 pages, 13 figures, revtex ; revised versio

USER'S GUIDE - GENERAL WEED MANAGEMENT MODEL VERSION 1.0 - DECEMBER 1994

Crop Production/Industries,

Computation in Physical Systems: A Normative Mapping Account

The relationship between abstract formal procedures and the activities of actual physical systems has proved to be surprisingly subtle and controversial, and there are a number of competing accounts of when a physical system can be properly said to implement a mathematical formalism and hence perform a computation. I defend an account wherein computational descriptions of physical systems are high-level normative interpretations motivated by our pragmatic concerns. Furthermore, the criteria of utility and success vary according to our diverse purposes and pragmatic goals. Hence there is no independent or uniform fact to the matter, and I advance the ‘anti-realist’ conclusion that computational descriptions of physical systems are not founded upon deep ontological distinctions, but rather upon interest-relative human conventions. Hence physical computation is a ‘conventional’ rather than a ‘natural’ kind