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Full-Text Articles in Physics
Fluorescence Blinking Statistics From Cdse Core And Core/Shell Nanorods, S. Wang, C. Querner, Thomas B. Emmons , '08, M. Drndic, Catherine Hirshfeld Crouch
Fluorescence Blinking Statistics From Cdse Core And Core/Shell Nanorods, S. Wang, C. Querner, Thomas B. Emmons , '08, M. Drndic, Catherine Hirshfeld Crouch
Physics & Astronomy Faculty Works
We report fluorescence blinking statistics measured from single CdSe nanorods (NRs) of seven different sizes with aspect ratios ranging from 3 to 11. This study also included core/shell CdSe/ZnSe NRs and core NRs with two different surface ligands producing different degrees of surface passivation. We compare the findings for NRs to our measurements of blinking statistics from spherical CdSe core and CdSe/ZnS core/shell nanocrystals (NCs). We find that, for both NRs and spherical NCs, the off-time probability distributions are well described by a power law, while the on-time probability distributions are best described by a truncated power law, P(tau(on)) similar …
Dipole Trapped Spheromak In A Prolate Flux Conserver, Michael R. Brown, C. D. Cothran, Jerome Fung , '06, M. Chang, Jason Alexander Horwitz , '07, M. J. Schaffer, J. Leuer, E. V. Belova
Dipole Trapped Spheromak In A Prolate Flux Conserver, Michael R. Brown, C. D. Cothran, Jerome Fung , '06, M. Chang, Jason Alexander Horwitz , '07, M. J. Schaffer, J. Leuer, E. V. Belova
Physics & Astronomy Faculty Works
This paper reports the observation and characterization of a spheromak formed in the Swarthmore Spheromak Experiment (SSX, [M. R. Brown, Phys. Plasmas 6, 1717 (1999)]) and trapped in a simple dipole magnetic field. The spheromak is studied in a prolate (tilt unstable) 0.4 m diameter, 0.6 m length copper flux conserver in SSX. This plasma does not tilt, despite the prolate flux conserver. The spheromak is characterized by a suite of magnetic probe arrays for magnetic structure B(r,t), ion Doppler spectroscopy for T-i and flow, and interferometry for n(e). Three-dimensional magnetohydrodynamics simulations of this configuration verify its gross sta-bility. (c) …
An Off-Axis Rotating Atom Trap, J. Wu, Frank Mosacatelli, E. Oh
An Off-Axis Rotating Atom Trap, J. Wu, Frank Mosacatelli, E. Oh
Physics & Astronomy Faculty Works
We present a novel configuration of a magneto-optical trap for cold atoms. The trap is very simple in design, employing only a small permanent magnet and an external Helmholtz bias coil. The trap's principal advantage is that the entire volume of the overlapping laser beams can be used for atom guiding and manipulation. An especially interesting effect is the rotation of the trapped atoms in circular motion as the permanent magnet is rotated. Clouds containing on the order of 2*10⁶ atoms are rotated up to 60Hz forming a 5 mm diameter ring. This rotation can potentially be used in studying …
Fast High Resolution Echelle Spectroscopy Of A Laboratory Plasma, C. D. Cothran, Jerome Fung , '06, Michael R. Brown, M. J. Schaffer
Fast High Resolution Echelle Spectroscopy Of A Laboratory Plasma, C. D. Cothran, Jerome Fung , '06, Michael R. Brown, M. J. Schaffer
Physics & Astronomy Faculty Works
An echelle diffraction grating and a multianode photomultiplier tube are paired to construct a high resolution (R=lambda/delta lambda approximate to 2.5x10(4)) spectrograph with fast time response for use from the UV through the visible. This instrument has analyzed the line shape of C III impurity ion emission at 229.687 nm over the lifetime (approximate to 100 mu s) of the hydrogen plasmas produced at SSX. The ion temperature and line of sight average velocity are inferred from the observed thermal broadening and Doppler shift of the line. The time resolution of these measurements is about 1 mu s, sufficient to …
Two Fluid Effects On Three-Dimensional Reconnection In The Swarthmore Spheromak Experiment With Comparisons To Space Data, Michael R. Brown, C. D. Cothran, Jerome Fung , '06
Two Fluid Effects On Three-Dimensional Reconnection In The Swarthmore Spheromak Experiment With Comparisons To Space Data, Michael R. Brown, C. D. Cothran, Jerome Fung , '06
Physics & Astronomy Faculty Works
Several new experimental results are reported from spheromak merging studies at the Swarthmore SpheromakExperiment[M. R. Brown, Phys. Plasmas6, 1717 (1999)] with relevance to three-dimensional (3D) reconnection in laboratory and space plasmas. First, recent velocity measurements of impurity ions using ion Doppler spectroscopy are reported. Bidirectional outflow at nearly the Alfvén speed is clearly observed. Second, experimental measurements of the out-of-plane magnetic field in a reconnection volume showing a quadrupolar structure at the ion inertial scale are discussed. Third, a measurement of in-plane Hall electric field and nonideal terms of the generalized Ohm’s law in a reconnection volume of a weakly …
Path Integral Monte Carlo Simulations Of Positronium Annihilation: From Micropores To Mesopores, Amy Lisa Graves, P. A. Sterne
Path Integral Monte Carlo Simulations Of Positronium Annihilation: From Micropores To Mesopores, Amy Lisa Graves, P. A. Sterne
Physics & Astronomy Faculty Works
Path integral Monte Carlo (PIMC) can reproduce the results of simple analytical calculations in which a single quantum particle is used to represent positronium within an idealized spherical pore. Our calculations improve on this approach by explicitly treating the positronium as a two-particle e(-), e(+) system interacting via the Coulomb interaction. We study the lifetime and the internal contact density, kappa, which controls the self-annihilation behavior for positronium in model spherical pores as a function of temperature and pore size. We compare the results with both PIMC and analytical calculations for a single-particle model.
Reducing The Gender Gap In The Physics Classroom, M. Lorenzo, Catherine Hirshfeld Crouch, E. Mazur
Reducing The Gender Gap In The Physics Classroom, M. Lorenzo, Catherine Hirshfeld Crouch, E. Mazur
Physics & Astronomy Faculty Works
We investigate if the gender gap in conceptual understanding in an introductory university physics course can be reduced by using interactive engagement methods that promote in-class interaction, reduce competition, foster collaboration, and emphasize conceptual understanding. To this end we analyzed data from the introductory calculus-based physics course for non-majors at Harvard University taught traditionally or using different degrees of interactive engagement. Our results show that teaching with certain interactive strategies not only yields significantly increased understanding for both males and females, but also reduces the gender gap. In the most interactively taught courses, the pre-instruction gender gap was gone by …