Theory and simulation of two-dimensional nematic and tetratic phases

Recent experiments and simulations have shown that two-dimensional systems can form tetratic phases with four-fold rotational symmetry, even if they are composed of particles with only two-fold symmetry. To understand this effect, we propose a model for the statistical mechanics of particles with almost four-fold symmetry, which is weakly broken down to two-fold. We introduce a coefficient $\kappa$ to characterize the symmetry breaking, and find that the tetratic phase can still exist even up to a substantial value of $\kappa$. Through a Landau expansion of the free energy, we calculate the mean-field phase diagram, which is similar to the result of a previous hard-particle excluded-volume model. To verify our mean-field calculation, we develop a Monte Carlo simulation of spins on a triangular lattice. The results of the simulation agree very well with the Landau theory.Comment: 7 pages, including 12 postscript figures, uses REVTeX

The Gender Pay Gap across Countries: A Human Capital Approach

The gender wage gap varies across countries. For example, among OECD nations women in Australia, Belgium, Italy and Sweden earn 80% as much as males, whereas in Austria, Canada and Japan women earn about 60%. Current studies examining cross-country differences focus on the impact of labor market institutions such as minimum wage laws and nationwide collective bargaining. However, these studies neglect labor market institutions that affect women'slifetime work behavior - a factor crucially important in gender wage gap studies that employ individual data. This paper explicitly concentrates on labor market institutions that are related to female lifetime work that affect the gender wage gap across countries. Using ISSP (International Social Survey Programme), LIS (Luxembourg Income Study) and OECD wage data for 35 countries covering 1970-2002, we show that the gender pay gap is positively associated with the fertilityrate (treated exogenously and endogenously with religion as the instrument), positively associated with the husbandwifeage gap at first marriage, and positively related to the top marginal tax rate, all factors which negatively affect women's lifetime labor force participation. In addition, we show that collective bargaining, as found in previous studies, is negatively associated with the gender pay gap.

Some new evidence on determinants of foreign direct investment in developing countries

The authors of this paper expand on earlier studies of the determinants of foreign direct investment (FDI) by empirically analyzing various factors - including political risk, business conditions, and macroeconomic variables - that influence direct investment flows to developing countries. They try to fill a gap in the literature by examining qualitative factors. Using a pooled model of developing countries, they test three groups of hypotheses on what influences direct investment. Tests of the first hypothesis indicate that a qualitative index of political risk is a significant determinant of FDI flows for countries that have historically attracted high FDI flows. For countries that have not attracted such flows, sociopolitical instability has a negative impact on investment flows. Tests of the second hypothesis show that a general qualitative index of business operation conditions is an important determinant of FDI in countries that receive high flows. This country group also shows a positive relationship between taxes on international transactions and FDI flows. Results from tests of the third hypothesis reveal that exports generally, especially manufacturing exports, are significant determinant of FDI flows for countries in which FDI is high. Finally, export orientation is the strongest variable for explaining why a country attracts FDI. This finding is in line with the secular trend toward increasing complementarity between trade and FDI.Labor Policies,Economic Theory&Research,Environmental Economics&Policies,Statistical&Mathematical Sciences,International Terrorism&Counterterrorism,Environmental Economics&Policies,Inequality,Statistical&Mathematical Sciences,Foreign Direct Investment,Economic Theory&Research

Capital flows to South Asian and ASEAN countries : trends, determinants, and policy implications

The authors compare the experiences of selected Asian countries in attracting different forms of external financing and examine how that financing has contributed to growth. They carry out the analysis for two subgroups - South Asian and ASEAN countries - with distinctly different dominant forms of capital flows. After reviewing recent trends in financial flows to individual countries, they perform a statistical analysis of the effects of foreign capital flows on the macroeconomic performance of developing countries in the region. They find that foreign direct investment has been a more significant positive factor than other types of resource flows in shaping the economic growth of ASEAN countries. Substantial increases in ODA flows are unlikely, and so is the resumption of significant bank lending, so policy makers in South Asia should pursue policies and nondistortionary incentive systems conducive to the infusion of foreign direct investment flows. The main findings are consistent with the Bank's emphasis on an increasingly important role for the private sector - and direct investment flows - in development. A focus on foreign direct investment is appropriate, given current constraints on external financing, particularly through traditional bank credits.Economic Theory&Research,Banks&Banking Reform,International Terrorism&Counterterrorism,Environmental Economics&Policies,Financial Intermediation

Proportional-Integral-Plus Control Strategy of an Intelligent Excavator

This article considers the application of Proportional-Integral-Plus (PIP) control to the Lancaster University Computerised Intelligent Excavator (LUCIE), which is being developed to dig foundation trenches on a building site. Previous work using LUCIE was based on the ubiquitous PI/PID control algorithm, tuned on-line, and implemented in a rather ad hoc manner. By contrast, the present research utilizes new hardware and advanced model-based control system design methods to improve the joint control and so provide smoother, more accurate movement of the excavator arm. In this article, a novel nonlinear simulation model of the system is developed for MATLAB/SIMULINK, allowing for straightforward refinement of the control algorithm and initial evaluation. The PIP controller is compared with a conventionally tuned PID algorithm, with the final designs implemented on-line for the control of dipper angle. The simulated responses and preliminary implementation results demonstrate the feasibility of the approach