The Cube Recurrence

We construct a combinatorial model that is described by the cube recurrence, a nonlinear recurrence relation introduced by Propp, which generates families of Laurent polynomials indexed by points in $\mathbb{Z}^3$. In the process, we prove several conjectures of Propp and of Fomin and Zelevinsky, and we obtain a combinatorial interpretation for the terms of Gale-Robinson sequences. We also indicate how the model might be used to obtain some interesting results about perfect matchings of certain bipartite planar graphs

Topological changes of two-dimensional magnetic textures

We investigate the interaction of magnetic vortices and skyrmions with a spin-polarized current. In a square lattice, fixed classical spins and quantum itinerant electrons, evolve according to the coupled Landau-Lifshitz and Schr\"odinger equations. Changes in the topology occur at microscopic time and length scales, and are shown to be triggered by the nucleation of a nontrivial electron-spin structure at the vortex core.Comment: See supplementary material (high resolution figures and movies) https://drive.google.com/folderview?id=0By4j_RJ9SKLpQ2R5UklXLURvbEE&usp=sharing --- v2: Extended versio

Airborne Fraunhofer Line Discriminator

Airborne Fraunhofer Line Discriminator enables prospecting for fluorescent materials, hydrography with fluorescent dyes, and plant studies based on fluorescence of chlorophyll. Optical unit design is the coincidence of Fraunhofer lines in the solar spectrum occurring at the characteristic wavelengths of some fluorescent materials

RURAL CREDIT RATIONING AND NATIONAL DEVELOPMENT BANKS IN DEVELOPING COUNTRIES

A common problem in agricultural credit markets in developing countries is the coexistence of a competitive market equilibrium interest rate and credit rationing. The literature typically explains the existence of credit rationing in competitive credit markets using adverse selection and moral hazard. Unfortunately these analyses are not consistent with the empirical reality that developing countries deal with in terms of subsidized credit, especially in the agricultural sector. This paper presents an alternative explanation for credit rationing in the agricultural sector in developing countries based on the fact that the requested loans are usually for small amounts, with many farmers making applications. As a result, the costs of operation increase with the number of loans given, so that inefficiencies in credit allocation occur when national development banks are present. It is shown that credit rationing can be reduced if shutting-down the national development bank is a feasible policy. Two other cases show that a national development bank is welfare-improving if an incentive compatible contract is used.Financial Economics,

Electrodynamics under a Possible Alternative to the Lorentz Transformation

A generalization of the classical electrodynamics for systems in absolute motion is presented using a possible alternative to the Lorentz transformation. The main hypothesis assumed in this work are: a) The inertial transformations relate two inertial frames: the privileged frame S and the moving frame S' with velocity v with respect to S. b) The transformation of the fields from S to the moving frame S' is given by H'=a(H - v D) and E'=a(E + v B) where a is a matrix whose elements depend of the absolute velocity of the system. c) The constitutive relations in the moving frame S' are given by D'= \epsilon E', B'= \mu H' and J'=\eta E'. It is found that Maxwell's equations, which are transformed to the moving frame, take a new form depending on the absolute velocity of the system. Moreover, differing from classical electrodynamics, it is proved that the electrodynamics proposed explains satisfactorily the Wilson effect.Comment: LaTeX, 15page

Asymmetry in self-assembled quantum dot-molecules made of identical InAs/GaAs quantum dots

We show that a diatomic dot molecule made of two identical, vertically stacked, strained InAs/GaAs self-assembled dots exhibits an asymmetry in its single-particle and may-particle wavefunctions. The single-particle wave function is asymmetric due to the inhomogeneous strain, while the asymmetry of the many-particle wavefunctions is caused by the correlation induced localization: the lowest singlet $^1\Sigma_g$ and triplet $^3\Sigma$ states show that the two electrons are each localized on different dots within the molecule, for the next singlet states $^1\Sigma_u$ both electrons are localized on the same (bottom) dot for interdot separation $d>$ 8 nm. The singlet-triplet splitting is found to be $\sim 0.1$ meV at inter-dot separation $d$=9 nm and as large as 100 meV for $d$=4 nm, orders of magnitude larger than the few meV found in the large (50 - 100 nm) electrostatically confined dots

Agency Costs and Investment Behaviour. ENEPRI Working Paper, No. 47, 3 February 2007

How do differences in the credit channel affect investment behavior in the U.S. and the Euro area? To analyze this question, we calibrate an agency cost model of business cycles. We focus on two key components of the lending channel, the default premium associated with bank loans and bankruptcy rates, to identify the differences in the U.S. and European financial sectors. Our results indicate that the differences in financial structures affect quantitatively the cyclical behavior in the two areas: the magnitude of the credit channel effects is amplified by the differences in the financial structures. We further demonstrate that the effects of minor differences in the credit market translate into large, persistent and asymmetric fluctuations in price of capital, bankruptcy rate and risk premium. The effects imply that the Euro Area's supply elasticities for capital are less elastic than the U.S

Micromagnetic Simulations of Ferromagnetic Rings

Thin nanomagnetic rings have generated interest for fundamental studies of magnetization reversal and also for their potential in various applications, particularly as magnetic memories. They are a rare example of a geometry in which an analytical solution for the rate of thermally induced magnetic reversal has been determined, in an approximation whose errors can be estimated and bounded. In this work, numerical simulations of soft ferromagnetic rings are used to explore aspects of the analytical solution. The evolution of the energy near the transition states confirms that, consistent with analytical predictions, thermally induced magnetization reversal can have one of two intermediate states: either constant or soliton-like saddle configurations, depending on ring size and externally applied magnetic field. The results confirm analytical predictions of a transition in thermally activated reversal behavior as magnetic field is varied at constant ring size. Simulations also show that the analytic one dimensional model continues to hold even for wide rings