A comparative analysis of faunal remains from some roman and native sites in northern England

Not availabl

Learning From Early Attempts to Generalize Darwinian Principles to Social Evolution

Copyright University of Hertfordshire & author.Evolutionary psychology places the human psyche in the context of evolution, and addresses the Darwinian processes involved, particularly at the level of genetic evolution. A logically separate and potentially complementary argument is to consider the application of Darwinian principles not only to genes but also to social entities and processes. This idea of extending Darwinian principles was suggested by Darwin himself. Attempts to do this appeared as early as the 1870s and proliferated until the early twentieth century. But such ideas remained dormant in the social sciences from the 1920s until after the Second World War. Some lessons can be learned from this earlier period, particularly concerning the problem of specifying the social units of selection or replication

Bite Depth Penetration Patterns of Dairy Cows Foraging on Complex Swards

Sward height was the dominant cue used by dairy cattle to determine the depth of penetration on young vegetative swards. On more complex swards, bite depth penetration was controlled by variations in the depth of regrowth. Evidence showed that cattle grazed to the pseudostem:lamina interface, but sward height exerted a stronger effect on bite depth than pseudostem height. Modelling efforts to predict how the herbivore places bites in space in the vertical dimension across sward states are currently being restricted by the absence of detailed canopy structure descriptions. We argue that the contrast between strata is an important determinant of bite depth penetration through the conditioning effect on biting resistance, and that the “constant proportionality” concept of bite depth control should be treated with caution. Furthermore, we demonstrate that bite depth penetration is continuously being conditioned through information gained on a bite-by-bite basis, and that patch appraisal begins a new cycle at every patch

Isospin splitting of the nucleon mean field

The isospin splitting of the nucleon mean field is derived from the Brueckner theory extended to asymmetric nuclear matter. The Argonne V18 has been adopted as bare interaction in combination with a microscopic three body force. The isospin splitting of the effective mass is determined from the Brueckner-Hartree-Fock self-energy: It is linear acording to the Lane ansatz and such that $m^*_n > m^*_p$ for neutron-rich matter. The symmetry potential is also determined and a comparison is made with the predictions of the Dirac-Brueckner approach and the phenomenological interactions. The theoretical predictions are also compared with the empirical parametrizations of neutron and proton optical-model potentials based on the experimental nucleon-nucleus scattering and the phenomenological ones adopted in transport-model simulations of heavy-ion collisions. The direct contribution of the rearrangement term due to three-body forces to the single particle potential and symmetry potential is discussed.Comment: 8 pages, 10 figure

Global optical potential for nucleus-nucleus systems from 50 MeV/u to 400 MeV/u

We present a new global optical potential (GOP) for nucleus-nucleus systems, including neutron-rich and proton-rich isotopes, in the energy range of $50 \sim 400$ MeV/u. The GOP is derived from the microscopic folding model with the complex $G$-matrix interaction CEG07 and the global density presented by S{\~ a}o Paulo group. The folding model well accounts for realistic complex optical potentials of nucleus-nucleus systems and reproduces the existing elastic scattering data for stable heavy-ion projectiles at incident energies above 50 MeV/u. We then calculate the folding-model potentials (FMPs) for projectiles of even-even isotopes, $^{8-22}$C, $^{12-24}$O, $^{16-38}$Ne, $^{20-40}$Mg, $^{22-48}$Si, $^{26-52}$S, $^{30-62}$Ar, and $^{34-70}$Ca, scattered by stable target nuclei of $^{12}$C, $^{16}$O, $^{28}$Si, $^{40}$Ca $^{58}$Ni, $^{90}$Zr, $^{120}$Sn, and $^{208}$Pb at the incident energy of 50, 60, 70, 80, 100, 120, 140, 160, 180, 200, 250, 300, 350, and 400 MeV/u. The calculated FMP is represented, with a sufficient accuracy, by a linear combination of 10-range Gaussian functions. The expansion coefficients depend on the incident energy, the projectile and target mass numbers and the projectile atomic number, while the range parameters are taken to depend only on the projectile and target mass numbers. The adequate mass region of the present GOP by the global density is inspected in comparison with FMP by realistic density. The full set of the range parameters and the coefficients for all the projectile-target combinations at each incident energy are provided on a permanent open-access website together with a Fortran program for calculating the microscopic-basis GOP (MGOP) for a desired projectile nucleus by the spline interpolation over the incident energy and the target mass number.Comment: 25 pages, 13 figure

Influence of Vegetation Patch Characteristics on Discriminatory Grazing by Dairy Cows

Two studies involving the sequential grazing of sets of patches on a perennial ryegrass (Lolium perenne) sward were carried out to investigate the effects of patch characteristics on the selective behaviour of grazing cattle. Experiment 1 involved a range of combinations of sward height (8.9 - 19.6 cm) and bulk density (1.33 - 1.67 mg DM/cm3). Distribution of grazing activity (number of bites or residence time) was strongly and positively related to patch height, but additional effects of variation in bulk density were limited. In Experiment 2 patches were manipulated to offer contrasts in both height (13.4 and 21.8 cm) and maturity (leaf to stem ratio, 2.53 and 0.74). In this case animals concentrated grazing bites and time on the shorter, more leafy patches. Behaviour at a patch was not significantly affected by the characteristics of the preceding or the succeeding patch in either study. These results indicate that under short term observations decision rules are largely influenced by the factors influencing ease of ingestion of herbage

Nucleon-nucleon cross sections in neutron-rich matter and isospin transport in heavy-ion reactions at intermediate energies

Nucleon-nucleon (NN) cross sections are evaluated in neutron-rich matter using a scaling model according to nucleon effective masses. It is found that the in-medium NN cross sections are not only reduced but also have a different isospin dependence compared with the free-space ones. Because of the neutron-proton effective mass splitting the difference between nn and pp scattering cross sections increases with the increasing isospin asymmetry of the medium. Within the transport model IBUU04, the in-medium NN cross sections are found to influence significantly the isospin transport in heavy-ion reactions. With the in-medium NN cross sections, a symmetry energy of $E_{sym}(\rho)\approx 31.6(\rho /\rho_{0})^{0.69}$ was found most acceptable compared with both the MSU isospin diffusion data and the presently acceptable neutron-skin thickness in $^{208}$Pb. The isospin dependent part $K_{asy}(\rho _{0})$ of isobaric nuclear incompressibility was further narrowed down to $-500\pm 50$ MeV. The possibility of determining simultaneously the in-medium NN cross sections and the symmetry energy was also studied. The proton transverse flow, or even better the combined transverse flow of neutrons and protons, can be used as a probe of the in-medium NN cross sections without much hindrance from the uncertainties of the symmetry energy.Comment: 32 pages including 14 figures. Submitted to Phys. Rev.

Effects of isospin and momentum dependent interactions on thermal properties of asymmetric nuclear matter

Thermal properties of asymmetric nuclear matter are studied within a self-consistent thermal model using an isospin and momentum dependent interaction (MDI) constrained by the isospin diffusion data in heavy-ion collisions, a momentum-independent interaction (MID), and an isoscalar momentum-dependent interaction (eMDYI). In particular, we study the temperature dependence of the isospin-dependent bulk and single-particle properties, the mechanical and chemical instabilities, and liquid-gas phase transition in hot asymmetric nuclear matter. Our results indicate that the temperature dependence of the equation of state and the symmetry energy are not so sensitive to the momentum dependence of the interaction. The symmetry energy at fixed density is found to generally decrease with temperature and for the MDI interaction the decrement is essentially due to the potential part. It is further shown that only the low momentum part of the single-particle potential and the nucleon effective mass increases significantly with temperature for the momentum-dependent interactions. For the MDI interaction, the low momentum part of the symmetry potential is significantly reduced with increasing temperature. For the mechanical and chemical instabilities as well as the liquid-gas phase transition in hot asymmetric nuclear matter, our results indicate that the boundary of these instabilities and the phase-coexistence region generally shrink with increasing temperature and is sensitive to the density dependence of the symmetry energy and the isospin and momentum dependence of the nuclear interaction, especially at higher temperatures.Comment: 21 pages, 29 figure

Reconstructing the global topology of the universe from the cosmic microwave background

If the universe is multiply-connected and sufficiently small, then the last scattering surface wraps around the universe and intersects itself. Each circle of intersection appears as two distinct circles on the microwave sky. The present article shows how to use the matched circles to explicitly reconstruct the global topology of space.Comment: 6 pages, 2 figures, IOP format. To be published in the proceedings of the Cleveland Cosmology and Topology Workshop 17-19 Oct 1997. Submitted to Class. Quant. Gra

Isospin non-equilibrium in heavy-ion collisions at intermediate energies

We study the equilibration of isospin degree of freedom in intermediate energy heavy-ion collisions using an isospin-dependent BUU model. It is found that there exists a transition from the isospin equilibration at low energies to non-equilibration at high energies as the beam energy varies across the Fermi energy in central, asymmetric heavy-ion collisions. At beam energies around 55 MeV/nucleon, the composite system in thermal equilibrium but isospin non-equilibrium breaks up into two primary hot residues with N/Z ratios closely related to those of the target and projectile respectively. The decay of these forward-backward moving residues results in the strong isospin asymmetry in space and the dependence of the isotopic composition of fragments on the N/Z ratios of the target and projectile. These features are in good agreement with those found recently in experiments at NSCL/MSU and TAMU, implications of these findings are discussed.Comment: 9 pages, latex, + 3 figures available upon reques