Nonclassical dynamics of Bose condensates in an optical lattice in the superfluid regime

A condensate in an optical lattice, prepared in the ground state of the superfluid regime, is stimulated first by suddenly increasing the optical lattice amplitude and then, after a waiting time, by abruptly decreasing this amplitude to its initial value. Thus the system is first taken to the Mott regime and then back to the initial superfluid regime. We show that, as a consequence of this nonadiabatic process, the system falls into a configuration far from equilibrium whose superfluid order parameter is described in terms of a particular superposition of Glauber coherent states that we derive. We also show that the classical equations of motion describing the time evolution of this system are inequivalent to the standard discrete nonlinear Schreodinger equations. By numerically integrating such equations with several initial conditions, we show that the system loses coherence, becoming insulating.Comment: 5 pages, 4 figure

A Comparative Analysis of the Capacity-building Industries in Pittsburgh and Central Texas

Five years ago, The Forbes Funds provided support for a new research series exploring challenges and strategic opportunities in nonprofit management in the Pittsburgh region.The intention of this research was to determine what works in strengthening nonprofits' organizational capacity and management abilities, as well as what may be the barriers or service gaps in building nonprofit capacity. As part of this research series, in 2004,The Forbes Funds commissioned Judith L. Millesen, at Ohio University, and Angela L. Bies, at Texas A&M University, to conduct a comprehensive analysis of Pittsburgh's capacity-building "industry." This "Pittsburgh study" offered detailed findings about the degree to which Pittsburgh's "industry of consultants, firms, management support organizations, and academic centers offer accessible, quality services to the 1,600 nonprofit organizations in Allegheny County."1 With ongoing support from The Forbes Funds, Drs. Bies and Millesen also conducted continuing analyses during 2005, which explored the incentive to engage in capacity building (Millesen & Bies, 2005) and the role of 'learning' in building nonprofit performance (Bies & Millesen, 2005).During 2005-06, a replication study was conducted in and around Austin,Texas.2 A key purpose of the study was to help afford a comparative analysis of the nonprofit sectors in two metropolitan regions with differing environments, economies, and capacity-building industries. With support from The Forbes Funds, the Bremer Foundation, and the Minnesota Council on Nonprofits, a third replication study is planned for 2006-07 in the Minneapolis-St. Paul area.The Texas replication study shared the Pittsburgh study's focus on understanding the characteristics of effective capacity-building initiatives through an examination of a series of questions related to who (the capacity builders) is doing what (the kinds of support services provided) for whom (what types of nonprofits are engaging in capacity-building initiatives) and to what end (whether capacity-building initiatives produce desired organizational change).The core research purpose remained to describe and analyze several aspects of the capacity-building environment, including the quantity, accessibility, and quality of capacity building services, characteristics of effective capacity building, and challenges and barriers to implementing capacity-building interventions. Both the Austin study and the Pittsburgh study offered implications for practice and suggested directions for future research into capacity building's effectiveness and influence in the sector

Particle number fluctuations in a cloven trapped Bose gas at finite temperature

We study fluctuations in the atom number difference between two halves of a harmonically trapped Bose gas in three dimensions. We solve the problem analytically for non interacting atoms. In the interacting case we find an analytical solution in the Thomas-Fermi and high temperature limit in good agreement with classical field simulations. In the large system size limit, fluctuations in the number difference are maximal for a temperature $T\simeq 0.7 T_c$ where $T_c$ is the critical temperature, independently of the trap anisotropy. The occurrence of this maximum is due to an interference effect between the condensate and the non-condensed field.Comment: 8 pages, 4 figure

Landau-Khalatnikov phonon damping in strongly interacting Fermi gases

We derive the phonon damping rate due to the four-phonon Landau-Khalatnikov process in low temperature strongly interacting Fermi gases using quantum hydrodynamics, correcting and extending the original calculation of Landau and Khalatnikov [ZhETF, 19 (1949) 637]. Our predictions can be tested in state-of-the-art experiments with cold atomic gases in the collisionless regime.Comment: 7 pages, final versio

Networks of motifs from sequences of symbols

We introduce a method to convert an ensemble of sequences of symbols into a weighted directed network whose nodes are motifs, while the directed links and their weights are defined from statistically significant co-occurences of two motifs in the same sequence. The analysis of communities of networks of motifs is shown to be able to correlate sequences with functions in the human proteome database, to detect hot topics from online social dialogs, to characterize trajectories of dynamical systems, and might find other useful applications to process large amount of data in various fields.Comment: Accepted for publication in Phys. Rev. Lett. Main article 4 pages, 2 figure; supplementary material 4 pages, 1 figur

EPR-entangled Bose-Einstein condensates in state-dependent potentials: a dynamical study

We study generation of non-local correlations by atomic interactions in a pair of bi-modal Bose-Einstein Condensates in state-dependent potentials including spatial dynamics. The wave-functions of the four components are described by combining a Fock state expansion with a time-dependent Hartree-Fock Ansatz, so that both the spatial dynamics and the local and non-local quantum correlations are accounted for. We find that despite the spatial dynamics, our protocole generates enough non-local entanglement to perform an EPR steering experiment with two spatially separated con-densates of a few thousands of atoms

Social Diffusion and Global Drift on Networks

We study a mathematical model of social diffusion on a symmetric weighted network where individual nodes' states gradually assimilate to local social norms made by their neighbors' average states. Unlike physical diffusion, this process is not state conservational and thus the global state of the network (i.e., sum of node states) will drift. The asymptotic average node state will be the average of initial node states weighted by their strengths. Here we show that, while the global state is not conserved in this process, the inner product of strength and state vectors is conserved instead, and perfect positive correlation between node states and local averages of their self/neighbor strength ratios always results in upward (or at least neutral) global drift. We also show that the strength assortativity negatively affects the speed of homogenization. Based on these findings, we propose an adaptive link weight adjustment method to achieve the highest upward global drift by increasing the strength-state correlation. The effectiveness of the method was confirmed through numerical simulations and implications for real-world social applications are discussed.Comment: 7 pages, 3 figures; to appear in Phys. Rev.