Effects of Interactions on the Critical Temperature of a Trapped Bose Gas

We perform high-precision measurements of the condensation temperature of a harmonically-trapped atomic Bose gas with widely-tuneable interactions. For weak interactions we observe a negative shift of the critical temperature in excellent agreement with mean-field theory. However for sufficiently strong interactions we clearly observe an additional positive shift, characteristic of beyond-mean-field critical correlations. We also discuss non-equilibrium effects on the apparent critical temperature for both very weak and very strong interactions.Comment: 4 pages, 4 figure

Efficient Production of Large 39K Bose-Einstein Condensates

We describe an experimental setup and the cooling procedure for producing 39K Bose-Einstein condensates of over 4x10^5 atoms. Condensation is achieved via a combination of sympathetic cooling with 87Rb in a quadrupole-Ioffe-configuration (QUIC) magnetic trap, and direct evaporation in a large volume crossed optical dipole trap, where we exploit the broad Feshbach resonance at 402 G to tune the 39K interactions from weak and attractive to strong and repulsive. In the same apparatus we create quasi-pure 87Rb condensates of over 8x10^5 atoms.Comment: 7 pages, 5 figures; figure font compatibility improve

Can a Bose gas be saturated?

Bose-Einstein condensation is unique among phase transitions between different states of matter in the sense that it occurs even in the absence of interactions between particles. In Einstein's textbook picture of an ideal gas, purely statistical arguments set an upper bound on the number of particles occupying the excited states of the system, and condensation is driven by this saturation of the quantum vapour. Dilute ultracold atomic gases are celebrated as a realisation of Bose-Einstein condensation in close to its purely statistical form. Here we scrutinise this point of view using an ultracold gas of potassium (39K) atoms, in which the strength of interactions can be tuned via a Feshbach scattering resonance. We first show that under typical experi-mental conditions a partially condensed atomic gas strongly deviates from the textbook concept of a saturated vapour. We then use measurements at a range of interaction strengths and temperatures to extrapolate to the non-interacting limit, and prove that in this limit the behaviour of a Bose gas is consistent with the saturation picture. Finally, we provide evidence for the universality of our observations through additional measurements with a different atomic species, 87Rb. Our results suggest a new way of characterising condensation phenomena in different physical systems.Comment: 6 pages, 5 figure

Synthesis and assessment of catechol diether compounds as inhibitors of trypanosomal phosphodiesterase B1 (TbrPDEB1)

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Bioorganic & Medicinal Chemistry Letters 23 (2013): 5971-5974, doi:10.1016/j.bmcl.2013.08.057.Human African trypanosomiasis (HAT) is a parasitic neglected tropical disease that affects 10,000 patients each year. Current treatments are sub-optimal, and the disease is fatal if not treated. Herein, we report our continuing efforts to repurpose the human phosphodiesterase 4 (hPDE4) inhibitor piclamilast to target trypanosomal phosphodiesterase TbrPDEB1. We prepared a range of substituted heterocyclic replacements for the 4-amino-3,5-dichloro-pyridine head group of piclamilast, and found that these compounds exhibited weak inhibitory activity of TbrPDEB1.We acknowledge funding from the National Institutes of Health (R01AI082577)

Condensation dynamics in a quantum-quenched Bose gas

By quenching the strength of interactions in a partially condensed Bose gas we create a "super-saturated" vapor which has more thermal atoms than it can contain in equilibrium. Subsequently, the number of condensed atoms ($N_0$) grows even though the temperature ($T$) rises and the total atom number decays. We show that the non-equilibrium evolution of the system is isoenergetic and for small initial $N_0$ observe a clear separation between $T$ and $N_0$ dynamics, thus explicitly demonstrating the theoretically expected "two-step" picture of condensate growth. For increasing initial $N_0$ values we observe a crossover to classical relaxation dynamics. The size of the observed quench-induced effects can be explained using a simple equation of state for an interacting harmonically-trapped atomic gas.Comment: 4 pages, 4 figure

Rotorcraft Transmission Noise Path Model, Including Distributed Fluid Film Bearing Impedance Modeling

A computational approach for simulating the effects of rolling element and journal bearings on the vibration and sound transmission through gearboxes has been demonstrated. The approach, using ARL/Penn State s CHAMP methodology, uses Component Mode Synthesis of housing and shafting modes computed using Finite Element (FE) models to allow for rapid adjustment of bearing impedances in gearbox models. The approach has been demonstrated on NASA GRC s test gearbox with three different bearing configurations: in the first condition, traditional rolling element (ball and roller) bearings were installed, and in the second and third conditions, the traditional bearings were replaced with journal and wave bearings (wave bearings are journal bearings with a multi-lobed wave pattern on the bearing surface). A methodology for computing the stiffnesses and damping in journal and wave bearings has been presented, and demonstrated for the journal and wave bearings used in the NASA GRC test gearbox. The FE model of the gearbox, along with the rolling element bearing coupling impedances, was analyzed to compute dynamic transfer functions between forces applied to the meshing gears and accelerations on the gearbox housing, including several locations near the bearings. A Boundary Element (BE) acoustic model was used to compute the sound radiated by the gearbox. Measurements of the Gear Mesh Frequency (GMF) tones were made by NASA GRC at several operational speeds for the rolling element and journal bearing gearbox configurations. Both the measurements and the CHAMP numerical model indicate that the journal bearings reduce vibration and noise for the second harmonic of the gear meshing tones, but show no clear benefit to using journal bearings to reduce the amplitudes of the fundamental gear meshing tones. Also, the numerical model shows that the gearbox vibrations and radiated sound are similar for journal and wave bearing configurations

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

The electron-polarized-photon coincidence method is used to determine linear and circular polarization correlations in vacuum ultraviolet (VUV) for the differential electron-impact excitation of neon and argon resonance transitions at impact energies of 25 and 30 eV at small scattering angles up to 40. The circular polarization correlation is found to be positive in the case of Ne at 25 eV and supports the prediction of the present B-spline R-matrix theory concerning the violation of a long-established propensity rule regarding angular momentum transfer in electron-impact excitation of S→P transitions. Comparisons with the results from the present relativistic distorted-wave approximation and an earlier semirelativistic distorted-wave Born model are also made. For the case of Ar, at 25 and 30 eV, the circular polarization measurements remain in agreement with theory, but provide limited evidence as to whether or not the circular polarization at small scattering angles is also positive. For the linear polarizations, much better agreement with theory is obtained than in earlier measurements carried out by S. H. Zheng and K. Becker

2003 Manifesto on the California Electricity Crisis

The authors, an ad-hocgroup of professionals with experience in regulatory and energy economics, share a common concern with the continuing turmoil facing the electricity industry ("the industry") in California. Most ofthe authorsendorsed the first California Electricity Manifesto issued on January 25, 2001. Almost two years have passed since that first Manifesto. While wholesale electric prices have moderated and California no longer faces the risk of blackouts, in many ways the industry is in worse shape now than it was at the start of 2001. As a result, the group of signatories continues to have a deep concern with the conflicting policy directions being pursued for the industry at both the State and Federal levels of government and the impact the uncertainties associated with these conflicting policies will have, long term, on the economy of California. Theauthorshave once again convened under the auspices of the Institute of Management, Innovation and Organization at the University of California, Berkeley, to put forward ourtheir ideas on a basic set of necessary policies to move the industry forward for the benefit of all Californians and the nation. The authors point out that theydo not pretend to be "representative." They do bring, however, a very diverse range of backgrounds and expertise.Technology and Industry, Regulatory Reform