ar X iv : 0 80 3 . 00 88 v 3 [ co nd - m at . s of t ] 6 J ul 2 00 8 Defect - mediated emulsification in two dimensions

ar X iv : 0 80 3 . 27 76 v 1 [ co nd - m at . s up r - co n ] 1 9 M ar 2 00 8 Negative conductance in driven Josephson junctions ∗

We investigate an optimal regime of negative-valued conductance, emerging in a resistively and capacitively shunted Josephson junction, which is driven simultaneously by both, a time-periodic (ac) and a constant (dc) current. We analyze the current-voltage characteristics in the regime of absolute negative conductance. We additionally explore the stability of the negative response with respect ...

ar X iv : 0 80 6 . 01 70 v 2 [ m at h . Q A ] 1 J ul 2 00 8 WEIGHT MULTIPLICITY POLYNOMIALS OF MULTI - VARIABLE WEYL MODULES

This paper is based on the observation that dimension of weight spaces of multi-variable Weyl modules depends polynomially on the highest weight (Conjecture 1). We support this conjecture by various explicit answers for up to three variable cases and discuss the underlying combinatorics.

ar X iv : 0 80 7 . 00 58 v 1 [ m at h . D G ] 1 J ul 2 00 8 EQUIVARIANT DIFFERENTIAL CHARACTERS AND SYMPLECTIC REDUCTION

We describe equivariant differential characters (classifying equi-variant circle bundles with connections), their prequantization, and reduction.

ar X iv : c on d - m at / 0 10 90 27 v 1 [ co nd - m at . s tr - e l ] 3 S ep 2 00 1 The Net Spin Model

We study a set of exactly soluble spin models in one and two dimensions for any spin S. Its ground state, the excitation spectrum, quantum phase transition points, as well as dimensional crossover are determined.

ar X iv : 0 80 1 . 25 00 v 1 [ co nd - m at . o th er ] 1 6 Ja n 20 08 Making , probing and understanding ultracold Fermi