Formal rules, informal rules, and economic performance

In this article the author tries consider a question important for economic development: what happens when formal rules and informal rules of economic behaviour are in conflict. Under such circumstances even the best, wealth creation-enhancing rules must bring about different outcomes if introduced in the different political, economic, and socio-cultural environments. These considerations begin with the overview of possible balances and imbalances in the relationships between formal and informal rules and potential conflicts that may arise in the latter cases. The next step is the selection of institutional characteristics that facilitate the explanation and prediction of outcomes of formal rulesŚinformal rules interactions. The third, and final, step considered in the article concerns the adjustment of rules (formal, informal, or both) over time and possible patterns of adjustment

Gyroscopic motion of superfluid trapped atomic condensates

The gyroscopic motion of a trapped Bose gas containing a vortex is studied. We model the system as a classical top, as a superposition of coherent hydrodynamic states, by solution of the Bogoliubov equations, and by integration of the time-dependent Gross-Pitaevskii equation. The frequency spectrum of Bogoliubov excitations, including quantum frequency shifts, is calculated and the quantal precession frequency is found to be consistent with experimental results, though a small discrepancy exists. The superfluid precession is found to be well described by the classical and hydrodynamic models. However the frequency shifts and helical oscillations associated with vortex bending and twisting require a quantal treatment. In gyroscopic precession, the vortex excitation modes $m=\pm 1$ are the dominant features giving a vortex kink or bend, while the $m=+2$ is found to be the dominant Kelvin wave associated with vortex twisting.Comment: 18 pages, 7 figures, 1 tabl

Measuring Learners’ Attitudes Toward Team Projects: Scale Development Through Exploratory And Confirmatory Factor Analyses

Team projects are increasingly used in engineering courses. Students may develop attitudes toward team projects from prior experience, and their attitudinal responses could influence their performance during team project-based learning in the future. Thus, instructors need to measure students’ attitudes toward team projects during their learner analysis to better understand students’ characteristics and be proactive in providing effective strategies to help students succeed in a team project environment. The purpose of our study was to develop a survey instrument that measures students’ attitudes toward team projects to be used as a learner analysis tool, derived from our local practical needs and due to the lack of appropriate existing instruments. The study was conducted at a mid-sized university in the northwestern United States during 2015-2016. After we generated an initial pool of 50 items, we administered the survey to 225 undergraduate engineering students, performed exploratory factor analysis on the data, and arrived at a four-factor solution of 20 items and a three-factor solution of 14 items. We tested the two competing solutions with another set of 330 undergraduate engineering students. Based on our confirmatory factor analysis results, we arrived at a three-factor model of 12 items as the finalized scale, which measures: (a) professional capacity building, (b) learning and problem-solving skills development, and (c) workload challenges. We call the scale, the Attitudes toward Team Projects Scale on Capacity, Learning, and Workload (ATPS-CLW). Suggestions for future research include continuous development, testing, and validation of the scale

Three-dimensional vortex dynamics in Bose-Einstein condensates

We simulate in the mean-field limit the effects of rotationally stirring a three-dimensional trapped Bose-Einstein condensate with a Gaussian laser beam. A single vortex cycling regime is found for a range of trap geometries, and is well described as coherent cycling between the ground and the first excited vortex states. The critical angular speed of stirring for vortex formation is quantitatively predicted by a simple model. We report preliminary results for the collisions of vortex lines, in which sections may be exchanged.Comment: 4 pages, 4 figures, REVTeX 3.1; Submitted to Physical Review A (6 March 2000

Generation of linear waves in the flow of Bose-Einstein condensate past an obstacle

The theory of linear wave structures generated in Bose-Einstein condensate flow past an obstacle is developed. The shape of wave crests and dependence of amplitude on coordinates far enough from the obstacle are calculated. The results are in good agreement with the results of numerical simulations obtained earlier. The theory gives a qualitative description of experiments with Bose-Einstein condensate flow past an obstacle after condensate's release from a trap.Comment: 11 pages, 3 figures, to be published in Zh. Eksp. Teor. Fi

Critical velocity in cylindrical Bose-Einstein condensates

We describe a dramatic decrease of the critical velocity in elongated cylindrical Bose-Einstein condensates which originates from the non-uniform character of the radial density profile. We discuss this mechanism with respect to recent measurements at MIT.Comment: 3 pages, 2 eps figures, revised according to referee's comment

Observation of Superfluid Flow in a Bose-Einstein Condensed Gas

We have studied the hydrodynamic flow in a Bose-Einstein condensate stirred by a macroscopic object, a blue detuned laser beam, using nondestructive {\em in situ} phase contrast imaging. A critical velocity for the onset of a pressure gradient has been observed, and shown to be density dependent. The technique has been compared to a calorimetric method used previously to measure the heating induced by the motion of the laser beam.Comment: 4 pages, 5 figure

Clustering and phase transitions in a 2D superfluid with immiscible active impurities

Phase transitions of a finite-size two-dimensional superfluid of bosons in presence of active impurities are studied by using the projected Gross–Pitaevskii model. Impurities are described with classical degrees of freedom. A spontaneous clustering of impurities during the thermalization is observed. Depending on the interaction among impurities, such clusters can break due to thermal fluctuations at temperatures where the condensed fraction is still significant. The emergence of clusters is found to increase the condensation transition temperature. The condensation and the Berezinskii–Kosterlitz–Thouless transition temperatures, determined numerically, are found to strongly depend on the volume occupied by the impurities: a relative increase up to a 20% of their respective values is observed, whereas their ratio remains approximately constant

Breakdown of superfluidity of an atom laser past an obstacle

The 1D flow of a continuous beam of Bose-Einstein condensed atoms in the presence of an obstacle is studied as a function of the beam velocity and of the type of perturbing potential (representing the interaction of the obstacle with the atoms of the beam). We identify the relevant regimes: stationary/time-dependent and superfluid/dissipative; the absence of drag is used as a criterion for superfluidity. There exists a critical velocity below which the flow is superfluid. For attractive obstacles, we show that this critical velocity can reach the value predicted by Landau's approach. For penetrable obstacles, it is shown that superfluidity is recovered at large beam velocity. Finally, enormous differences in drag occur when switching from repulsive to attractive potential.Comment: 15 pages, 6 figure

Generating vortex rings in Bose-Einstein condensates in the line-source approximation

We present a numerical method for generating vortex rings in Bose-Einstein condensates confined in axially symmetric traps. The vortex ring is generated using the line-source approximation for the vorticity, i.e., the rotational of the superfluid velocity field is different from zero only on a circumference of given radius located on a plane perpendicular to the symmetry axis and coaxial with it. The particle density is obtained by solving a modified Gross-Pitaevskii equation that incorporates the effect of the velocity field. We discuss the appearance of density profiles, the vortex core structure and the vortex nucleation energy, i.e., the energy difference between vortical and ground-state configurations. This is used to present a qualitative description of the vortex dynamics.Comment: Accepted for publication in Phys. Rev.