Analytic calculation of the 1-loop effective action for the O(N+1)-symmetric 2-dimensional nonlinear sigma-model

Polyakov's calculation of the effective action for the 2d nonlinear sigma-Model is generalized by purely analytic means to include contributions which are not UV-divergent and which depend on the choice of block spin. An analytic approximation to the background field which determines the classical perfect action is given, and approximations to the 1-loop correction are found. The results should be useful for numerical simulations.Comment: 38 p, 1 figur

1-Loop improved lattice action for the nonlinear sigma-model

In this paper we show the Wilson effective action for the 2-dimensional O(N+1)-symmetric lattice nonlinear sigma-model computed in the 1-loop approximation for the nonlinear choice of blockspin $\Phi(x)$, \Phi(x)= \Cav\phi(x)/{|\Cav\phi(x)|},where \Cav is averaging of the fundamental field $\phi(z)$ over a square $x$ of side $\tilde a$. The result for $S_{eff}$ is composed of the classical perfect action with a renormalized coupling constant $\beta_{eff}$, an augmented contribution from a Jacobian, and further genuine 1-loop correction terms. Our result extends Polyakov's calculation which had furnished those contributions to the effective action which are of order $\ln \tilde a /a$, where $a$ is the lattice spacing of the fundamental lattice. An analytic approximation for the background field which enters the classical perfect action will be presented elsewhere.Comment: 3 (2-column format) pages, 1 tex file heplat99.tex, 1 macro package Espcrc2.sty To appear in Nucl. Phys. B, Proceedings Supplements Lattice 9

Proceedings of the Conference on Globalization and Its Discontents

Analyzing two research projects on the industrial home-based work (HBW) in 2003 and 2006 in Istanbul, Turkey, this paper argues that two forms of rigidities shape the organizational characteristics of the HBW: limited physical mobility of the homeworkers and the in-built pressures within the labor process of the factory system. On one hand, the rigidities regarding the mobility of homeworkers determine the conditions of the labor process of the HBW. Among some dimensions of the labor process of HBW, mechanisms for the distribution of piecework, the training of homeworkers, or storage of the piecework are directly related with the physical mobility of homeworkers. On the other hand, the co-existence of labor- and capital-intensive processes in the factory system unavoidably creates management bottlenecks, which account for another form of rigidity. HBW appears as the solution for such management problems. These corresponding rigidities characterize the organizational variety of the HBW. Negative work conditions of the homeworkers such as low piece-wages and precariousness in the employment practices are accounted for by these rigidities. As much as the low piece-wages generally associated with the HBW in the literature. Thus, investigation of the HBW should go beyond the argument about the low piece-wages and start to analyze the actual conditions of organization resulting in the deteriorating conditions of work for homeworkers. The literature emphasizes the centrality of the low piece-wages turning this form of labor into an alternative for the factory system. Although the research projects analyzed in this paper verify this consensus, two forms of rigidities motivate both workers and employers to 'get into the HBW-nexus': Homeworkers shape the organizational arrangements significantly, given that HBW does not pertain to a formal form of employment. Thus, their conditions of physical mobility account for a key element in the organization of HBW. Since the state of mobility by homeworkers is rather one of rigidity than an advantage, their regarding condition should be the focus to understand the mindsets of the homeworkers.mobility of homeworkers, labor market rigidity

More about exactly massless quarks on the lattice

In a previous publication [hep-lat/9707022] I showed that the fermion determinant for strictly massless quarks can be written on the lattice as $\det D$, where $D$ is a certain finite square matrix explicitly constructed from the lattice gauge fields. Here I show that $D$ obeys the Ginsparg-Wilson relation $D\gamma_5 D = D\gamma_5 +\gamma_5 D$.Comment: 4 pages, plain Te

A Real-Time Solver For Time-Optimal Control Of Omnidirectional Robots with Bounded Acceleration

We are interested in the problem of time-optimal control of omnidirectional robots with bounded acceleration (TOC-ORBA). While there exist approximate solutions for such robots, and exact solutions with unbounded acceleration, exact solvers to the TOC-ORBA problem have remained elusive until now. In this paper, we present a real-time solver for true time-optimal control of omnidirectional robots with bounded acceleration. We first derive the general parameterized form of the solution to the TOC-ORBA problem by application of Pontryagin's maximum principle. We then frame the boundary value problem of TOC-ORBA as an optimization problem over the parametrized control space. To overcome local minima and poor initial guesses to the optimization problem, we introduce a two-stage optimal control solver (TSOCS): The first stage computes an upper bound to the total time for the TOC-ORBA problem and holds the time constant while optimizing the parameters of the trajectory to approach the boundary value conditions. The second stage uses the parameters found by the first stage, and relaxes the constraint on the total time to solve for the parameters of the complete TOC-ORBA problem. We further implement TSOCS as a closed loop controller to overcome actuation errors on real robots in real-time. We empirically demonstrate the effectiveness of TSOCS in simulation and on real robots, showing that 1) it runs in real time, generating solutions in less than 0.5ms on average; 2) it generates faster trajectories compared to an approximate solver; and 3) it is able to solve TOC-ORBA problems with non-zero final velocities that were previously unsolvable in real-time

Discrimination of low-frequency tones employs temporal fine structure

An auditory neuron can preserve the temporal fine structure of a low-frequency tone by phase-locking its response to the stimulus. Apart from sound localization, however, little is known about the role of this temporal information for signal processing in the brain. Through psychoacoustic studies we provide direct evidence that humans employ temporal fine structure to discriminate between frequencies. To this end we construct tones that are based on a single frequency but in which, through the concatenation of wavelets, the phase changes randomly every few cycles. We then test the frequency discrimination of these phase-changing tones, of control tones without phase changes, and of short tones that consist of a single wavelets. For carrier frequencies below a few kilohertz we find that phase changes systematically worsen frequency discrimination. No such effect appears for higher carrier frequencies at which temporal information is not available in the central auditory system.Comment: 12 pages, 3 figure

Clustering of fermionic truncated expectation values via functional integration

I give a simple proof that the correlation functions of many-fermion systems have a convergent functional Grassmann integral representation, and use this representation to show that the cumulants of fermionic quantum statistical mechanics satisfy l^1-clustering estimates