Interaction-induced negative mobility: realization in a system of two coupled Josephson junctions

An overdamped dynamical system, biased by an external constant force, does not exhibit negative mobility. However, when the system is coupled to its copy, negative mobility can arise. We show it by the example of an experimentally realizable system of two coupled resistively shunted Josephson junctions. The first junction is dc-biased by a constant current and ac-driven by an unbiased harmonic current. In the proposed setup one can control the transport properties of the second junction by manipulating the first junction only. We demonstrate that the second junction can exhibit both absolute negative resistance (ANR) near zero bias and negative resistance in the non-linear regimes (NNR). These anomalous transport features occur for restricted windows of the coupling constant.Comment: 4 pages, 4 figure

Families of twisted D\mathcal D-modules and arithmetic models of Harish-Chandra modules

We develop a theory of tdos and twisted $\mathcal D$-modules over general bases with an emphasis on functorial aspects. In particular, we establish a flat base change theorem as well as faithfully flat descent for twisted $\mathcal D$-modules. We define (derived) inverse and direct images of twisted $\mathcal D$-modules and investigate how these functors behave under base change. We also discuss forms of closed $K$-orbits attached to $\theta$-stable parabolic subgroups. These results imply the existence of models of (the dual of) cohomologically induced modules over general fields of characteristic 0 and even half-integer rings, whose study is motivated by potential applications to contraction families and number theory in the literature.Comment: Major revision of section 3.8 and 3.9. Section A.6 was adde

Product market competition, corporate governance and firm performance: an empirical analysis for Germany

Productivity growth has been slow in many continental European countries over the last few decades, especially in comparison with the United States. It has been argued that lack of product market competition and poor corporate governance are two of the main reasons for this phenomenon. However, predictions from theoretical models are far from unambiguous, and empirical evidence is sparse, in particular at the level of individual firms. In this paper, we aim to close this gap with an econometric analysis of firm performance in Germany. Based on a unique panel data set with detailed information on almost 400 manufacturing firms over the 1986-94 period, we find that firms operating in industries which are characterized by more intensive product market competition experience higher rates of productivity growth. We also find weak evidence for the notion that in Germany?s bank-based system of internal control, ownership concentration is harmful for productivity growth. --competition,corporate governance,productivity