Properties of screw dislocation dynamics: time estimates on boundary and interior collisions

In this paper, the dynamics of a system of a finite number of screw dislocations is studied. Under the assumption of antiplane linear elasticity, the two-dimensional dynamics is determined by the renormalised energy. The interaction of one dislocation with the boundary and of two dislocations of opposite Burgers moduli are analysed in detail and estimates on the collision times are obtained. Some exactly solvable cases and numerical simulations show agreement with the estimates obtained.Comment: 25 pages, 4 figure

Banks as Catalysts for Industrialization

We provide a new theory of the role of banks as catalysts for industrialization. In their influential analysis of 19th century continental European industrialization, Gerschenkron and Schumpeter accorded banks a central role, arguing that they promoted the creation of new industries. We formalize this role of banks by introducing financial intermediaries into a 'big push' model. We show that banks may act as `catalysts' for industrialization provided that they are sufficiently large to mobilize a critical mass of firms, and that they possess sufficient market power to make profits from coordination. The theory provides simple conditions that help to explain why banks seem to play a creative role in some but not in other emerging markets. The model also shows that universal banking helps to reduce the cost of coordination. Finally, we show that one disadvantage of catalytic banks is that they may favor concentration in the industrial sector.http://deepblue.lib.umich.edu/bitstream/2027.42/39827/3/wp443.pd

Gamma ray tests of Minimal Dark Matter

We reconsider the model of Minimal Dark Matter (a fermionic, hypercharge-less quintuplet of the EW interactions) and compute its gamma ray signatures. We compare them with a number of gamma ray probes: the galactic halo diffuse measurements, the galactic center line searches and recent dwarf galaxies observations. We find that the original minimal model, whose mass is fixed at 9.4 TeV by the relic abundance requirement, is constrained by the line searches from the Galactic Center: it is ruled out if the Milky Way possesses a cuspy profile such as NFW but it is still allowed if it has a cored one. Observations of dwarf spheroidal galaxies are also relevant (in particular searches for lines), and ongoing astrophysical progresses on these systems have the potential to eventually rule out the model. We also explore a wider mass range, which applies to the case in which the relic abundance requirement is relaxed. Most of our results can be safely extended to the larger class of multi-TeV WIMP DM annihilating into massive gauge bosons.Comment: 25 pages, 8 figures. v2: a few comments and references added, matches version published on JCA

Corporate Income Taxation of Multinationals in a General Equilibrium Model

This paper contributes to the discussion on Separate Accounting versus Formula Apportionment in the corporate income taxation of multinational enterprises (MNEs). The innovation of the analysis is that we consider a general equilibrium tax competition model with an endogenously determined world interest rate. Under the principle of Separate Accounting, it turns out that corporate tax rates may be inefficiently low or high, while under Formula Apportionment corporate tax rates are always inefficiently low. These results are true independent of whether the number of countries is small or large. They reverse the insights obtained by previous studies under the assumption of an exogenously given world interest rate.corporate income tax, Separate Accounting, Formula Apportionment

Interjurisdictional Spillovers, Decentralized Policymaking and the Elasticity of Capital Supply

This paper points to the important role which the elasticity of aggregate capital supply with respect to the net rate of return to capital plays for the efficiency of policymaking in a decentralized economy with mobile capital and spillovers among jurisdictions. In accordance with previous studies, we show that under the assumption of a fixed capital supply (zero capital supply elasticity) the decentralized policy choice is optimal. If the capital supply elasticity is strictly positive, however, capital tax rates are inefficiently low in the decentralized equilibrium.decentralized policymaking, spillovers, capital supply elasticity

Complexity of Nested Circumscription and Nested Abnormality Theories

The need for a circumscriptive formalism that allows for simple yet elegant modular problem representation has led Lifschitz (AIJ, 1995) to introduce nested abnormality theories (NATs) as a tool for modular knowledge representation, tailored for applying circumscription to minimize exceptional circumstances. Abstracting from this particular objective, we propose L_{CIRC}, which is an extension of generic propositional circumscription by allowing propositional combinations and nesting of circumscriptive theories. As shown, NATs are naturally embedded into this language, and are in fact of equal expressive capability. We then analyze the complexity of L_{CIRC} and NATs, and in particular the effect of nesting. The latter is found to be a source of complexity, which climbs the Polynomial Hierarchy as the nesting depth increases and reaches PSPACE-completeness in the general case. We also identify meaningful syntactic fragments of NATs which have lower complexity. In particular, we show that the generalization of Horn circumscription in the NAT framework remains CONP-complete, and that Horn NATs without fixed letters can be efficiently transformed into an equivalent Horn CNF, which implies polynomial solvability of principal reasoning tasks. Finally, we also study extensions of NATs and briefly address the complexity in the first-order case. Our results give insight into the ``cost'' of using L_{CIRC} (resp. NATs) as a host language for expressing other formalisms such as action theories, narratives, or spatial theories.Comment: A preliminary abstract of this paper appeared in Proc. Seventeenth International Joint Conference on Artificial Intelligence (IJCAI-01), pages 169--174. Morgan Kaufmann, 200

Approximate controllability of the Schr\"{o}dinger Equation with a polarizability term in higher Sobolev norms

This analysis is concerned with the controllability of quantum systems in the case where the standard dipolar approximation, involving the permanent dipole moment of the system, is corrected with a polarizability term, involving the field induced dipole moment. Sufficient conditions for approximate controllability are given. For transfers between eigenstates of the free Hamiltonian, the control laws are explicitly given. The results apply also for unbounded or non-regular potentials

The Dynamics of Distributive Politics

We study dynamic committee bargaining over an infinite horizon with discounting. In each period a committee proposal is generated by a random recognition rule, the committee chooses between the proposal and a status quo by majority rule, and the voting outcome in period t becomes the status quo in period t+1. We study symmetric Markov equilibria of the resulting game and conduct an experiment to test hypotheses generated by the theory for pure distributional (divide-the-dollar) environments. In particular, we investigate the effects of concavity in the utility functions, the existence of a Condorcet winning alternative, and the discount factor (committee "impatience"). We report several new findings. Voting behavior is selfish and myopic. Status quo outcomes have great inertia. There are strong treatment effects, that are in the direction predicted by the Markov equilibrium. We find significant evidence of concave utility functions.Dynamic bargaining, voting, experiments, divide-the-dollar,committees