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Search Results: 1 - 10 of 402421 matches for " J. H. Huckans "
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Preparing a highly degenerate Fermi gas in an optical lattice
J. R. Williams,J. H. Huckans,R. W. Stites,E. L. Hazlett,K. M. O'Hara
Physics , 2008,
Abstract: We propose a method to prepare a sample of fermionic atoms in a three-dimensional (3D) optical lattice at unprecedentedly low temperatures and uniform filling factors. The process involves adiabatic loading of atoms into multiple energy bands of an optical lattice followed by a filtering stage whereby atoms from all but the ground band are removed. Of critical importance is the use of a non-harmonic trapping potential, taken here to be the radial profile of a high-order Laguerre-Gaussian laser beam, to provide external confinement for the atoms. For realistic experimental parameters, this procedure should produce samples with temperatures $\sim10^{-3}$ of the Fermi temperature. This would allow the investigation of the low-temperature phase diagram of the Fermi-Hubbard model as well as the initialization of a high-fidelity quantum register.
Three-body recombination in a three-state Fermi gas with widely tunable interactions
J. H. Huckans,J. R. Williams,E. L. Hazlett,R. W. Stites,K. M. O'Hara
Physics , 2008, DOI: 10.1103/PhysRevLett.102.165302
Abstract: We investigate the stability of a three spin state mixture of ultracold fermionic $^6$Li atoms over a range of magnetic fields encompassing three Feshbach resonances. For most field values, we attribute decay of the atomic population to three-body processes involving one atom from each spin state and find that the three-body loss coefficient varies by over four orders of magnitude. We observe high stability when at least two of the three scattering lengths are small, rapid loss near the Feshbach resonances, and two unexpected resonant loss features. At our highest fields, where all pairwise scattering lengths are approaching $a_t = -2140 a_0$, we measure a three-body loss coefficient $L_3 \simeq 5\times 10^{-22} \mathrm{cm}^6/\mathrm{s}$ and a trend toward lower decay rates for higher fields indicating that future studies of color superfluidity and trion formation in a SU(3) symmetric Fermi gas may be feasible.
Quantum and Classical Dynamics of a BEC in a Large-Period Optical Lattice
J. H. Huckans,I. B. Spielman,B. Laburthe Tolra,W. D. Phillips,J. V. Porto
Physics , 2009, DOI: 10.1103/PhysRevA.80.043609
Abstract: We experimentally investigate diffraction of a Rb-87 Bose-Einstein condensate from a 1D optical lattice. We use a range of lattice periods and timescales, including those beyond the Raman-Nath limit. We compare the results to quantum mechanical and classical simulations, with quantitative and qualitative agreement, respectively. The classical simulation predicts that the envelope of the time-evolving diffraction pattern is shaped by caustics: singularities in the phase space density of classical trajectories. This behavior becomes increasingly clear as the lattice period grows.
Acoustic Noise of MRI Scans of the Internal Auditory Canal and Potential for Intracochlear Physiological Changes
M. A. Busada,C. L. Eshleman,G. Ibrahim,J. H. Huckans
Physics , 2012,
Abstract: Magnetic resonance imaging (MRI) is a widely used medical imaging technique to assess the health of the auditory (vestibulocochlear) nerve. A well known problem with MRI machines is that the acoustic noise they generate during a scan can cause auditory temporary threshold shifts (TTS) in humans. In addition, studies have shown that excessive noise in general can cause rapid physiological changes of constituents of the auditory within the cochlea. Here, we report in-situ measurements of the acoustic noise from a 1.5 Tesla MRI machine (GE Signa) during scans specific to auditory nerve assessment. The measured average and maximum noise levels corroborate earlier investigations where TTS occurred. We briefly discuss the potential for physiological changes to the intracochlear branches of the auditory nerve as well as iatrogenic misdiagnoses of intralabyrinthine and intracochlear schwannomas due to hypertrophe of the auditory nerve within the cochlea during MRI assessment.
Evidence for Ground- and Excited-State Efimov Trimers in a Three-State Fermi Gas
J. R. Williams,E. L. Hazlett,J. H. Huckans,R. W. Stites,Y. Zhang,K. M. O'Hara
Physics , 2009, DOI: 10.1103/PhysRevLett.103.130404
Abstract: We observe enhanced three-body recombination in an ultracold three-component $^6$Li Fermi gas with large but unequal scattering lengths attributable to an excited Efimov trimer state near the three-atom scattering threshold. We find excellent agreement between the measured three-body recombination rate and the recombination rate calculated in the zero-range approximation where the only free parameters are the Efimov parameters $\kappa_*$ and $\eta_*$. The value of $\kappa_*$ determined by the location of the Efimov resonance we observe at 895 G also predicts the locations of loss features previously observed near 130 and 500 G \cite{Jochim08,OHara09} suggesting that all three features are associated with universal Efimov trimer states. We also report on the first realization of a quantum degenerate three-state Fermi gas with approximate SU(3) symmetry.
Strongly inhibited transport of a 1D Bose gas in a lattice
C. D. Fertig,K. M. O'Hara,J. H. Huckans,S. L. Rolston,W. D. Phillips,J. V. Porto
Physics , 2004, DOI: 10.1103/PhysRevLett.94.120403
Abstract: We report the observation of strongly damped dipole oscillations of a quantum degenerate 1D atomic Bose gas in a combined harmonic and optical lattice potential. Damping is significant for very shallow axial lattices (0.25 photon recoil energies), and increases dramatically with increasing lattice depth, such that the gas becomes nearly immobile for times an order of magnitude longer than the single-particle tunneling time. Surprisingly, we see no broadening of the atomic quasimomentum distribution after damped motion. Recent theoretical work suggests that quantum fluctuations can strongly damp dipole oscillations of 1D atomic Bose gas, providing a possible explanation for our observations.
Observation of Reduced Three-Body Recombination in a Fermionized 1D Bose Gas
B. Laburthe Tolra,K. M. O'Hara,J. H. Huckans,W. D. Phillips,S. L. Rolston,J. V. Porto
Physics , 2003,
Abstract: We investigate correlation properties of a one-dimensional interacting Bose gas by loading a magnetically trapped 87-Rb Bose-Einstein condensate into a deep two-dimensional optical lattice. We measure the three-body recombination rate for both the BEC in the magnetic trap and the BEC loaded into the optical lattice. The recombination rate coefficient is a factor of seven smaller in the lattice, which we interpret as a reduction in the local three-body correlation function in the 1D case. This is a signature of correlation intermediate between that of the uncorrelated phase coherent 1D mean-field regime and the strongly correlated Tonks-Girardeau regime.
Collisional de-excitation in a quasi-2D degenerate Bose gas
I. B. Spielman,P. R. Johnson,J. H. Huckans,C. D. Fertig,S. L. Rolston,W. D. Phillips,J. V. Porto
Physics , 2005, DOI: 10.1103/PhysRevA.73.020702
Abstract: We separate a Bose-Einstein condensate into an array of 2D sheets using a 1D optical lattice, and then excite quantized vibrational motion in the direction normal to the sheets. Collisions between atoms induce vibrational de-excitation, transferring the large excitation energy into back-to-back outgoing atoms, imaged as rings in the 2D plane. The ring diameters correspond to vibrational energy level differences, and edge-on imaging allows identification of the final vibrational states. Time dependence of these data provides a nearly complete characterization of the decay process including the energies, populations, and lifetimes of the lowest two excited vibrational levels. The measured decay rates represent a suppression of collisional de-excitation due to the reduced dimensionality, a matter wave analog to inhibited spontaneous emission.
Partial MHC/Neuroantigen Peptide Constructs: A Potential Neuroimmune-Based Treatment for Methamphetamine Addiction
Jennifer M. Loftis, Clare J. Wilhelm, Arthur A. Vandenbark, Marilyn Huckans
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056306
Abstract: Relapse rates following current methamphetamine abuse treatments are very high (~40–60%), and the neuropsychiatric impairments (e.g., cognitive deficits, mood disorders) that arise and persist during remission from methamphetamine addiction likely contribute to these high relapse rates. Pharmacotherapeutic development of medications to treat addiction has focused on neurotransmitter systems with only limited success, and there are no Food and Drug Administration approved pharmacotherapies for methamphetamine addiction. A growing literature shows that methamphetamine alters peripheral and central immune functions and that immune factors such as cytokines, chemokines, and adhesion molecules play a role in the development and persistence of methamphetamine induced neuronal injury and neuropsychiatric impairments. The objective of this study was to evaluate the efficacy of a new immunotherapy, partial MHC/neuroantigen peptide construct (RTL551; pI-Ab/mMOG-35-55), in treating learning and memory impairments induced by repeated methamphetamine exposure. C57BL/6J mice were exposed to two different methamphetamine treatment regimens (using repeated doses of 4 mg/kg or 10 mg/kg, s.c.). Cognitive performance was assessed using the Morris water maze and CNS cytokine levels were measured by multiplex assay. Immunotherapy with RTL551 improved the memory impairments induced by repeated methamphetamine exposure in both mouse models of chronic methamphetamine addiction. Treatment with RTL551 also attenuated the methamphetamine induced increases in hypothalamic interleukin-2 (IL-2) levels. Collectively, these initial results indicate that neuroimmune targeted therapies, and specifically RTL551, may have potential as treatments for methamphetamine-induced neuropsychiatric impairments.
A Wind Tunnel in Your Classroom: The Design and Implementation of a Portable Wind Tunnel for Use in the Science Classroom
John H. Huckans,Dean C. Walker,Carla Zembal-Saul,Nathan A. Kurz,Kimber H. Mitchell,Diane S. Reed,Milton W. Cole
Physics , 2002,
Abstract: This article describes a wind tunnel's ease of construction and its uses as a visualization tool that integrates concepts at the primary and secondary levels. An Appendix contains detailed building instructions. A web site (under construction) will provide sample lesson plans, visualization and application tips, animations and links to background
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