Ab-initio determination of Bose-Hubbard parameters for two ultracold atoms in an optical lattice using a three-well potential

We calculate numerically the exact energy spectrum of the six dimensional problem of two interacting Bosons in a three-well optical lattice. The particles interact via a full Born-Oppenheimer potential which can be adapted to model the behavior of the s-wave scattering length at Feshbach resonances. By adjusting the parameters of the corresponding Bose-Hubbard (BH) Hamiltonian the deviation between the numerical energy spectrum and the BH spectrum is minimized. This defines the optimal BH parameter set which we compare to the standard parameters of the BH model. The range of validity of the BH model with these parameter sets is examined, and an improved analytical prediction of the interaction parameter is introduced. Furthermore, an extended BH model and implications due to the energy dependence of the scattering length and couplings to higher Bloch bands at a Feshbach resonance are discussed.Comment: 14 pages, 11 figures; typos and minor errors corrected, five references added, next-to-nearest neighbor hopping included in extended Bose-Hubbard mode

Nonperturbative Corrections to One Gluon Exchange Quark Potentials

The leading nonperturbative QCD corrections to the one gluon exchange quark-quark, quark-antiquark and $q \bar{q}$ pair-excitation potentials are derived by using a covariant form of nonlocal two-quark and two-gluon vacuum expectation values. Our numerical calculation indicates that the correction of quark and gluon condensates to the quark-antiquark potential improves the heavy quarkonium spectra to some degree.Comment: LaTex, 16 pages, three figures, to appear in Nucl. Phys.

Error matrices in quantum process tomography

We discuss characterization of experimental quantum gates by the error matrix, which is similar to the standard process matrix $\chi$ in the Pauli basis, except the desired unitary operation is factored out, by formally placing it either before or after the error process. The error matrix has only one large element, which is equal to the process fidelity, while other elements are small and indicate imperfections. The imaginary parts of the elements along the left column and/or top row directly indicate the unitary imperfection and can be used to find the needed correction. We discuss a relatively simple way to calculate the error matrix for a composition of quantum gates. Similarly, it is rather straightforward to find the first-order contribution to the error matrix due to the Lindblad-form decoherence. We also discuss a way to identify and subtract the tomography procedure errors due to imperfect state preparation and measurement. In appendices we consider several simple examples of the process tomography and also discuss an intuitive physical interpretation of the Lindblad-form decoherence.Comment: 21 pages (slightly revised version

Selection-bias correction based on the multinomial logit: An application to the Mexican labor market

In this presentation, we illustrate an application of a relatively new selection-bias correction methodology based on the multinomial logit model using the selmlog Stata command (Bourguignon, Fournier, and Gurgand, 2007, Journal of Economic Surveys 21: 174–205). selmlog allows for getting both consistent and efficient estimates of the selection process and a fairly good correction for the outcome equation, even when the independence of irrelevant alternatives (IIA) assumption is not achieved. The exercise depicts the current pattern of the occupational choices for the individuals in the Mexican labor market using a longitudinal panel with microdata from the Encuesta Nacional de Ocupación y Empleo (ENOE) during February 2008 to March 2009. We estimate an equation over an endogenously selected population. The command grants simplicity for both distributional and IIA assumptions for parametric models.

Volume changes during active shape fluctuations in cells

Cells modify their volume in response to changes in osmotic pressure but it is usually assumed that other active shape variations do not involve significant volume fluctuations. Here we report experiments demonstrating that water transport in and out of the cell is needed for the formation of blebs, commonly observed protrusions in the plasma membrane driven by cortex contraction. We develop and simulate a model of fluid mediated membrane-cortex deformations and show that a permeable membrane is necessary for bleb formation which is otherwise impaired. Taken together our experimental and theoretical results emphasize the subtle balance between hydrodynamics and elasticity in actively driven cell morphological changes.Comment: Phys. Rev. Lett. in press. 13 pages 4 figures, 9 supplementary figure

The Dynamics of School and Work in Rural Bangladesh

This paper investigates the causes underlying the poor school performance of children in rural Bangladesh, while focusing on the effect of work on school progress. To this end, a dynamic switching model is presented for the sequence of school and work outcomes up to the end of secondary school, where the switching in each school level considered is determined by the endogenous work sequence up to that level. This approach allow us to characterize the full sequence of school and work choices of children, and to evaluate the dynamic effects of work on schooling. We find that work has a negative and sizable effect on school progress for the entire population, as well as for all the subpopulations considered, including the different groups of working children. We are also able to identify at each school level the observable and unobservable characteristics of working children relative to those of non-working children. This characterization and the magnitude of the estimated effects of work have important policy implications.dynamics of school and work, dynamic evaluation, selection

STRUCTURAL CHANGES AND CONVERGENCE IN EU AND IN ADRIATIC-BALKANS REGION

Coming from standard economic growth theory and empirical evidences, we concentrated on the convergence process as a result of structural changes in economy. We investigate the differences among countries in EU in terms of the share in total economy of main sectors. Then, based on the spatial (empirical) distribution of such shares in EU we are proposing a model to estimate a typology of the convergence process in the European area. Taking into account the existing differences among sectors in matter of productivity, there are two versions of the model: considering the share of sectors in total employment and the share of sectors in GDP respectively. Moreover, we developed several modelling schemes that could be useful to improve the strategies oriented to achieve a real convergence in EU and further in Adriatic-Balkans region. In this way, we can obtain simulations from a country or group of countries (European Union, for example) on long term and quantifying the impact of structural changes on the convergence process. Indeed, the actual global crisis seems to influence negatively the convergence process in EU. As a rule, just new adhered countries were more affected by the actual crisis. Today all forecasts are suffering by uncertainty. Thus, further efforts must be allocated to evaluate the negative impact of actual crisis on the convergence process.