Confinement-Higgs Phase Crossover as a Lattice Artifact in 1+1 Dimensions

We examine the phase structure of massive Yang-Mills theory in 1+1 dimensions. This theory is equivalent to a gauged principal chiral sigma model. It has been previously shown that the gauged theory has only a confined phase, and no Higgs phase in the continuum, and at infinite volume. There are no massive gluons, but only hadron-like bound states of sigma-model particles. The reason is that the gluon mass diverges, being proportional to the two-point correlation function of the renormalized field of the sigma model at $x=0$. We use exact large-$N$ results to show that after introducing a lattice regularization and typical values of the coupling constants used in Monte Carlo simulations, the gluon mass becomes finite, and even sometimes small. A smooth crossover into a Higgs phase can then appear. For small volumes and large $N$, we find an analytic expression for the gluon mass, which depends on the coupling constants and the volume. We argue that this Higgs phase is qualitatively similar to the one observed in lattice computations at $N=2$.Comment: Version accepted for publication in JHEP. Improved discussion of results, references adde

Hidden symmetries, instabilities, and current suppression in Brownian ratchets

The operation of Brownian motors is usually described in terms of out-of-equilibrium and symmetry-breaking settings, with the relevant spatiotemporal symmetries identified from the analysis of the equations of motion for the system at hand. When the appropriate conditions are satisfied, symmetry-related trajectories with opposite current are thought to balance each other, yielding suppression of transport. The direction of the current can be precisely controlled around these symmetry points by finely tuning the driving parameters. Here we demonstrate, by studying a prototypical Brownian ratchet system, the existence of {\it hidden} symmetries, which escape the identification by the standard symmetry analysis, and require different theoretical tools for their revelation. Furthermore, we show that system instabilities may lead to spontaneous symmetry breaking with unexpected generation of directed transport.Comment: To appear in Phys. Rev. Let

Using APL to build science tutors for the high school level

This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in APL Quote Quad, http://dx.doi.org/10.1145/327600.327644This paper describes the procedure used to build several courses on the sciences for the high school level. An APL2 program has been written that accepts problem models, including explanation models, and uses them to generate many different problems. Each course is provided with about one hundred problem models, from which the student is invited to solve many thousands of different actual problems. The unique features of APL2 have made it very simple to develop the program that supports the courses, which exists in both DOS and Windows versions

FDI, Foreign Affiliate Operations, and the Transfer Process: Macroeconomic Adjustment to FDI Inflows in the Case of Costa Rica

The theoretical and empirical literature on the macroeconomic effects of capital inflows posits that a net inflow of foreign capital leads to an equilibrium real exchange rate (RER) appreciation through an expansion in aggregate demand. But this literature fails to distinguish between the different types of flows, or their specific mechanisms of influence. This paper analyses the adjustment process to FDI inflows in the case of Costa Rica, and focuses on whether, to what extent and through what mechanisms such adjustment requires a RER appreciation. It argues that a study of the process of macroeconomic adjustment to a net inflow of FDI -the transfer process- should not be detached from an investigation into the trade and financial practices of the foreign-owned firms towards which FDI flows. A two-sector model is developed to capture the basic interactions between foreign investment, domestic investment and the RER. It shows that the sectoral allocation of FDI, the response of domestic investment to exogenous changes in the foreign capital stock, the input composition of foreign capital, and the financial practices of foreign investors, are crucial determinants of the long-run equilibrium RER. The paper also includes two empirical parts. The first one provides an overview of the general trends of aggregate FDI inflows into Costa Rica between 1970-99, and analyses some data on the trade and financial patterns of foreign affiliates operating in the country. The second undertakes an econometric examination of the impact of FDI on output, investment, exports, imports and the RER, using cointegration techniques. The study is based on annual data for the period 1970-99. It is found that FDI exerts a strong negative impact on the equilibrium RER.

Longitudinal Rescaling of Quantum Electrodynamics

We investigate quantum longitudinal rescaling of electrodynamics, transforming coordinates as $x^{0,3}\to\lambda x^{0,3}$ and $x^{1,2}\to x^{1,2}$, to one loop. We do this by an aspherical Wilsonian renormalization, which was applied earlier to pure Yang-Mills theory. We find the anomalous powers of $\lambda$ in the renormalized couplings. Our result is only valid for $\lambda \lesssim 1$, because perturbation theory breaks down for $\lambda \ll 1$.Comment: Version to appear in Phys. Rev.

Current reversals in a rocking ratchet: the frequency domain

Motivated by recent work [D. Cubero et al., Phys. Rev. E 82, 041116 (2010)], we examine the mechanisms which determine current reversals in rocking ratchets as observed by varying the frequency of the drive. We found that a class of these current reversals in the frequency domain are precisely determined by dissipation-induced symmetry breaking. Our experimental and theoretical work thus extends and generalizes the previously identified relationship between dynamical and symmetry-breaking mechanisms in the generation of current reversals

Automated soil hardness testing machine

This paper describes the design and performance of a mechatronic system for controlling a standard drop-hammer mechanism that is commonly used in performing outdoor soil or ground hardness tests. A low-cost microcontroller is used to control a hydraulic actuator to repeatedly lift and drop a standard free-falling weight that strikes a pipe (sampler) which is pushed deeper into the ground with each impact. The depth of the sampler pipe and position of the hydraulic cylinder are constantly monitored and the number of drops, soil penetration data and other variables are recorded in a database for future analysis. This device, known as the “EVH Trip Hammer”, allows the full automation and faster completion of what is typically a very labour-intensive and slow testing process that can involve human error and the risk of human injuries