Physics Commons^™

Momentum-Space Engineering Of Gaseous Bose-Einstein Condensates, Mark Edwards, Brandon Benton, Jeffrey Heward, Charles W. Clark

Department of Physics and Astronomy Faculty Publications

We show how the momentum distribution of gaseous Bose-Einstein condensates can be shaped by applying a sequence of standing-wave laser pulses. We present a theory, whose validity was demonstrated in an earlier experiment [L. Denget al., Phys. Rev. Lett. 83, 5407 (1999)], of the effect of a two-pulse sequence on the condensate wavefunction in momentum space. We generalize the previous result to the case of N pulses of arbitrary intensity separated by arbitrary intervals and show how these parameters can be engineered to produce a desired final momentum distribution. We find that several momentum distributions, important in …

Vlt Observations Of Ngc 1097'S “Dog-Leg” Tidal Stream: Dwarf Spheroidals And Tidal Streams, P. Galianni, F. Patat, James L. Higdon, S. Mieske, P. Kroupa

Department of Physics and Astronomy Faculty Publications

Aims. We investigate the structure and stellar population of two large stellar condensations (knots A & B) along one of the faint optical “jet-like” tidal streams associated with the spiral NGC 1097, with the goal of establishing their physical association with the galaxy and their origin.

Methods. We use the VLT/FORS2 to get deep V-band imaging and low-resolution optical spectra of two knots along NGC 1097's northeast “dog-leg” tidal stream. With this data, we explore their morphology and stellar populations.

Results. Spectra were obtained for eleven sources in the field surrounding the tidal stream. The great …

The Energetics Of Molecular Gas In Ngc 891 From H2 And Far-Infrared Spectroscopy, G. J. Stacey, Vassilis Charmandaris, F. Boulanger, Yanling Wu, F. Combes, S. J. U. Higdon, J. D. T. Smith, T. Nikola

Department of Physics and Astronomy Faculty Publications

We have studied the molecular hydrogen energetics of the edge-on spiral galaxy NGC?891, using a 34 position map in the lowest three pure rotational H2 lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1), and S(2) lines are bright with an extinction-corrected total luminosity of ~2.8 × 107 L ?, or 0.09% of the total-infrared luminosity of NGC?891. The H2 line ratios are nearly constant along the plane of the galaxy?we do not observe the previously reported strong drop-off in the S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so …

Dark Matter Halos And Evolution Of Bars In Disk Galaxies: Varying Gas Fraction And Gas Spatial Resolution, Jorge Villa-Vargas, Isaac Shlosman, Clayton Heller

Department of Physics and Astronomy Faculty Publications

We conduct numerical experiments by evolving gaseous/stellar disks embedded in live dark matter halos aiming at quantifying the effect of gas spatial resolution and gas content on the bar evolution. Three model sequences have been constructed using different resolutions, and the gas fraction has been varied along each sequence within the range of f g = 0%-50%, but keeping the disk and halo properties unchanged. We find that the spatial resolution becomes important with an increase in the gas content. For the higher resolution model sequences, we observe a bimodal behavior in the bar evolution with respect to the gas …

Restructuring Introductory Physics By Adapting An Active Learning Studio Model, Delena Bell Gatch

Department of Physics and Astronomy Faculty Publications

Despite efforts to engage students in the traditional lecture environment, faculty in Georgia Southern University’s Physics Department became dissatisfied with lecture as the primary means of instruction. During the fall semester of 2006, our department began adapting the studio model to suit the needs of introductory calculus-based physics students at our institution. A studio course seamlessly integrates the lecture and laboratory courses into a single course, devoting much of the class time to active, collaborative, student-centered learning. An emphasis was placed on replacing traditional lectures with interactive, technology enriched class periods designed around the various learning styles. New teaching materials …

Why Are Ring Galaxies Interesting?, James L. Higdon, Sarah J.U. Higdon

Department of Physics and Astronomy Faculty Publications

Compared with ordinary spirals, the ISM in ring galaxies experiences markedly different physical conditions and evolution. As a result, ring galaxies provide interesting perspectives on the triggering/quenching of large scale star formation and the destructive effects of massive stars on molecular cloud complexes. We use high resolution radio, sub-millimeter, infrared, and optical data to investigate the role of gravitational stability in star formation regulation, factors influencing the ISM's molecular fraction, and evidence of peculiar star formation laws and efficiencies in two highly evolved ring galaxies: Cartwheel and the Lindsay-Shapley ring.

Stacking-Dependent Optical Conductivity Of Bilayer Graphene, Yingying Wang, Zhenhua Ni, Lei Liu, Yanhong Liu, Chunxiao Cong, Ting Yu, Xiao-Jun Wang, Dezhen Shen, Zexiang Shen

Department of Physics and Astronomy Faculty Publications

The optical conductivities of graphene layers are strongly dependent on their stacking orders. Our first-principle calculations show that, while the optical conductivities of single-layer graphene (SLG) and bilayer graphene (BLG) with Bernal stacking are almost frequency-independent in the visible region, the optical conductivity of twisted bilayer graphene (TBG) is frequency-dependent, giving rise to additional absorption features due to the band folding effect. Experimentally, we obtain from contrast spectra the optical conductivity profiles of BLG with different stacking geometries. Some TBG samples show additional features in their conductivity spectra, in full agreement with our calculation results, while a few samples give …

Interionic Energy Transfer In Y3Al5O12: Ce3+, Pr3+ Phosphor, Lei Wang, Xia Zhang, Zhendong Hao, Yongshi Luo, Jiahua Zhang, Xiao-Jun Wang

Department of Physics and Astronomy Faculty Publications

We present an investigation of dynamical processes of nonradiative energy transfer (ET)between Ce3+ and Pr3+ , and between Pr3+ ions in Y3Al5O12:Ce3+ , Pr3+ phosphor.Photoluminescence spectroscopy and fluorescence decay patterns are studied as a function ofPr3+ and Ce3+ concentrations. The analysis based on Inokuti–Hirayama model indicates that the ET from the lowest 5d state of Ce3+ to the D12 state of Pr3+ , and the quenching of theD12 state through a cross relaxation involving Pr3+ ions in the ground state are both governed by electric dipole–dipole interaction. An increase in the Ce3+–Pr3+ ET rate followed by the enhanced red emission …

Restructuring Introductory Physics By Adapting An Active Learning Studio Model, Delena Bell Gatch

Department of Physics and Astronomy Faculty Publications

Despite efforts to engage students in the traditional lecture environment, faculty in Georgia Southern University’s Physics Department became dissatisfied with lecture as the primary means of instruction. During the fall semester of 2006, our department began adapting the studio model to suit the needs of introductory calculus-based physics students at our institution. A studio course seamlessly integrates the lecture and laboratory courses into a single course, devoting much of the class time to active, collaborative, student-centered learning. An emphasis was placed on replacing traditional lectures with interactive, technology enriched class periods designed around the various learning styles. New teaching materials …

Long-Lasting Phosphorescence In Basi2O2N2:Eu2+ And Ba2Sio4:Eu2+ Phases For X-Ray And Cathode Ray Tubes, Meiyuan Wang, Xia Zhang, Zhendong Hao, Xinguang Ren, Yongshi Luo, Haifeng Zhao, Xiao-Jun Wang, Jiahua Zhang

Department of Physics and Astronomy Faculty Publications

We report the long-lasting bluish-green phosphorescence for X-ray or cathode ray tubes in the phosphors with compositions of either Ba2SiO4:0.01Eu2+–xSi3N4 (x=0–1) or 2BaCO3–ySi3N4:0.01Eu2+(y=1/6–1) synthesized by a solid-state reaction. By tuning the Si3N4content, the phosphorescence may originate from Eu2+ in BaSi2O2N2(peaking at 490 nm), Ba2SiO4 (505 nm), and Ba3SiO5 (590 nm) phases. The strong phosphorescence of the Ba2SiO4:Eu2+ phase in 2BaCO3–ySi3N4:0.01Eu2+ is attributed to N substitution for O to generate a shallow trap. In Ba2SiO4:0.01Eu2+–xSi3N4 , however, N prefers reacting with Ba2SiO4 to form BaSi2O2N2 , thereby exhibiting a strong phosphorescence of the BaSi2O2N2:Eu2+ phase but a weak phosphorescence of the …