Computational modelling of single crystals

The physical basis of computationally tractable models of crystalline plasticity is reviewed. A statistical mechanical model of dislocation motion through forest dislocations is formulated. Following Franciosi and co-workers (1980-88) the strength of the short-range obstacles introduced by the forest dislocations is allowed to depend on the mode of interaction. The kinetic equations governing dislocation motion are solved in closed form for monotonic loading, with transients in the density of forest dislocations accounted for. This solution, coupled with suitable equations of evolution for the dislocation densities, provides a complete description of the hardening of crystals under monotonic loading. Detailed comparisons with experiment demonstrate the predictive capabilities of the theory. An adaptive finite element formulation for the analysis of ductile single crystals is also developed. Calculations of the near-tip fields in Cu single crystals illustrate the versatility of the method

The endowment effect

The divergence between the willingness-to-pay (WTP) and willingness-to-accept (WTA) has resulted in two explanations. First, that this may be due to the manifestation of the endowment effect (Kahneman, Knetsch and Thaler, 1991). Second, the difference between WTA and WTP is directly related with the substitutability of the goods (Haneman, 1991). In this paper we show that one can observe undertrading in markets even if the WTA-WTP discrepancy is negligible. Due to underrevelation of intramarginal units very flat reported inverse supply and demand curves are obtained. As a result very small deviations in reported WTA and WTP can lead to undertrading

On varieties whose universal cover is a product of curves

We investigate a necessary condition for a compact complex manifold X of dimension n in order that its universal cover be the Cartesian product $C^n$ of a curve C = \PP^1 or \HH: the existence of a semispecial tensor $\omega$. A semispecial tensor is a non zero section $0 \neq \omega \in H^0(X, S^n\Omega^1_X (-K_X) \otimes \eta)$), where $\eta$ is an invertible sheaf of 2-torsion (i.e., \eta^2\cong \hol_X). We show that this condition works out nicely, as a sufficient condition, when coupled with some other simple hypothesis, in the case of dimension $n= 2$ or $n= 3$; but it is not sufficient alone, even in dimension 2. In the case of K\"ahler surfaces we use the above results in order to give a characterization of the surfaces whose universal cover is a product of two curves, distinguishing the 6 possible cases.Comment: 22 pages, dedicated to Sommese's 60-th birthday. Greatly improves, expands and supersedes arXiv:0803.3008, of which also corrects a mistak

Log-canonical pairs and Gorenstein stable surfaces with KX2=1K_X^2=1

We classify log-canonical pairs $(X, \Delta)$ of dimension two with $K_X+\Delta$ an ample Cartier divisor with $(K_X+\Delta)^2=1$, giving some applications to stable surfaces with $K^2=1$. A rough classification is also given in the case $\Delta=0$

Schottky barrier heights at polar metal/semiconductor interfaces

Using a first-principle pseudopotential approach, we have investigated the Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100) junctions, and their dependence on the semiconductor chemical composition and surface termination. A model based on linear-response theory is developed, which provides a simple, yet accurate description of the barrier-height variations with the chemical composition of the semiconductor. The larger barrier values found for the anion- than for the cation-terminated surfaces are explained in terms of the screened charge of the polar semiconductor surface and its image charge at the metal surface. Atomic scale computations show how the classical image charge concept, valid for charges placed at large distances from the metal, extends to distances shorter than the decay length of the metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure

What Have We Learned From Emissions Trading Experiments?

Emissions trading is a form of environmental regulation in which a regulatory body specifies the total allowable discharge of pollutants, divides this cap into individual permits assigned to individual polluters, and allows trading of the resulting permits. Laboratory experiments, in which paid subjects participate in controlled markets, can be used to test both proposals for emission trading and the theories on which they are based. This paper surveys the laboratory research that has investigated the efficiency of emission trading programs, role of alternative instruments and institutions, the effects of allowing firms to carry inventories of permits, and the extent to which market power can be exercised.

Clifford index for reduced curves

We extend the notion of Clifford index to reduced curves with planar singularities by considering rank 1 torsion free sheaves. We investigate the behaviour of the Clifford index with respect to the combinatorial properties of the curve and we show that Green's conjecture holds for certain classes of curves given by the union of two irreducible components.Comment: Prop. 3.7, prop. 4.2, Thm. 4.4 change