Social organization of Platythyrea lamellosa (Roger) (Hymenoptera: Formicidae): I. Reproduction

Colonies of Platythyrea lamellosa contained 18-276 workers, but no queens were found. Dissected workers had five to nine ovarioles per ovary, the two ovaries of an individual often differing. In each of the colonies examined, only one worker was inseminated, and it was the only individual that laid diploid reproductive eggs. Virgin workers showed partial development of their ovaries and oocytes, but these appeared to regress with age, and they never laid eggs. Mating was not a prerequisite for reproductive dominance, since a single, young, virgin worker assumed the role of the mated worker when the latter was removed from its colony. Adult males are present in the population for most of the year, but are especially common during summer

Evaluation of the Environmental Impact of Milk Quotas

The aim of this study is to examine the environmental impacts of the different systems for allocation and transfer of milk quota under the Common Agricultural Policy (CAP) in individual Member States of the European Union (EU). In particular, it seeks to identify the ways in which differences in the implementation of milk quota regimes can impact on various sectoral and farm management trends and the environmental implications of these

The monopole mass in the three-dimensional Georgi-Glashow model

We study the three-dimensional Georgi-Glashow model to demonstrate how magnetic monopoles can be studied fully non-perturbatively in lattice Monte Carlo simulations, without any assumptions about the smoothness of the field configurations. We examine the apparent contradiction between the conjectured analytic connection of the `broken' and `symmetric' phases, and the interpretation of the mass (i.e., the free energy) of the fully quantised 't Hooft-Polyakov monopole as an order parameter to distinguish the phases. We use Monte Carlo simulations to measure the monopole free energy and its first derivative with respect to the scalar mass. On small volumes we compare this to semi-classical predictions for the monopole. On large volumes we show that the free energy is screened to zero, signalling the formation of a confining monopole condensate. This screening does not allow the monopole mass to be interpreted as an order parameter, resolving the paradox.Comment: 12 pages, 7 figures, uses revtex. Minor changes made to the text to match with the published version at http://link.aps.org/abstract/PRD/v65/e12500

Gribov Copies in the Maximally Abelian Gauge and Confinement

We fix $SU(2)$ lattice gauge fields to the Maximally Abelian gauge in both three and four dimensions. We extract the corresponding $U(1)$ fields and monopole current densities and calculate separately the confining string tensions arising from these $U(1)$ fields and monopole `condensates'. We generate multiple Gribov copies and study how the $U(1)$ fields and monopole distributions vary between these different copies. As expected, we find substantial variations in the number of monopoles, their locations and in the values of the $U(1)$ field strengths. The string tensions extracted from `extreme' Gribov copies also differ but this difference appears to be no more than about 20\%. We also directly compare the fields of different Gribov copies. We find that on the distance scales relevant to confinement the $U(1)$ and monopole fluxes that disorder Wilson loops are highly correlated between these different Gribov copies. All this suggests that while there is indeed a Gribov copy problem the resulting ambiguity is, in this gauge and for the study of confinement, of limited importance.Comment: 31 pages LaTeX plus 5 PostScript figures. Uses epsf.sty. Self-unpacking, uuencoded tar-compressed fil

Magnetic monopoles from gauge theory phase transitions

Thermal fluctuations of the gauge field lead to monopole formation at the grand unified phase transition in the early Universe, even if the transition is merely a smooth crossover. The dependence of the produced monopole density on various parameters is qualitatively different from theories with global symmetries, and the monopoles have a positive correlation at short distances. The number density of monopoles may be suppressed if the grand unified symmetry is only restored for a short time by, for instance, nonthermal symmetry restoration after preheating.Comment: 5 pages, updated to match the version published in PRD (http://link.aps.org/abstract/PRD/v68/e021301) on 11 July 200

Monopole clusters, center vortices, and confinement in a Z(2) gauge-Higgs system

We propose to use the different kinds of vacua of the gauge theories coupled to matter as a laboratory to test confinement ideas of pure Yang-Mills theories. In particular, the very poor overlap of the Wilson loop with the broken string states supports the 't Hooft and Mandelstam confinement criteria. However in the Z(2) gauge-Higgs model we use as a guide we find that the condensation of monopoles and center vortices is a necessary, but not sufficient condition for confinement.Comment: 13 pages, 6 figures, minor changes, version to be published on Phys. Rev.

Remarks on the multi-parameter reweighting method for the study of lattice QCD at non-zero temperature and density

We comment on the reweighting method for the study of finite density lattice QCD. We discuss the applicable parameter range of the reweighting method for models which have more than one simulation parameter. The applicability range is determined by the fluctuations of the modification factor of the Boltzmann weight. In some models having a first order phase transition, the fluctuations are minimized along the phase transition line if we assume that the pressure in the hot and the cold phase is balanced at the first order phase transition point. This suggests that the reweighting method with two parameters is applicable in a wide range for the purpose of tracing out the phase transition line in the parameter space. To confirm the usefulness of the reweighting method for 2 flavor QCD, the fluctuations of the reweighting factor are measured by numerical simulations for the cases of reweighting in the quark mass and chemical potential directions. The relation with the phase transition line is discussed. Moreover, the sign problem caused by the complex phase fluctuations is studied.Comment: 20 page, 6 figure

The QCD thermal phase transition in the presence of a small chemical potential

We propose a new method to investigate the thermal properties of QCD with a small quark chemical potential $\mu$. Derivatives of the phase transition point with respect to $\mu$ are computed at $\mu=0$ for 2 flavors of p-4 improved staggered fermions with $ma=0.1,0.2$ on a $16^3\times4$ lattice. The resulting Taylor expansion is well behaved for the small values of $\mu_{\rm q}/T_c\sim0.1$ relevant for RHIC phenomenology, and predicts a critical curve $T_c(\mu)$ in reasonable agreement with estimates obtained using exact reweighting. In addition, we contrast the case of isoscalar and isovector chemical potentials, quantify the effect of $\mu\not=0$ on the equation of state, and comment on the complex phase of the fermion determinant in QCD with $\mu\not=0$.Comment: 26 pages, 25 figures, minor modificatio