170,170 research outputs found
Correction of dephasing oscillations in matter wave interferometry
Vibrations, electromagnetic oscillations and temperature drifts are among the
main reasons for dephasing in matter-wave interferometry. Sophisticated
interferometry experiments, e.g. with ions or heavy molecules, often require
integration times of several minutes due to the low source intensity or the
high velocity selection. Here we present a scheme to suppress the influence of
such dephasing mechanisms - especially in the low-frequency regime - by
analyzing temporal and spatial particle correlations available in modern
detectors. Such correlations can reveal interference properties that would
otherwise be washed out due to dephasing by external oscillating signals. The
method is shown experimentally in a biprism electron interferometer where a
perturbing oscillation is artificially introduced by a periodically varying
magnetic field. We provide a full theoretical description of the particle
correlations where the perturbing frequency and amplitude can be revealed from
the disturbed interferogram. The original spatial fringe pattern without the
perturbation can thereby be restored. The technique can be applied to lower the
general noise requirements in matter-wave interferometers. It allows for the
optimization of electromagnetic shielding and decreases the efforts for
vibrational or temperature stabilization
Horizontal Lloyd mirror patterns from straight and curved nonlinear internal waves
Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 1689-1700, doi:10.1121/1.3666004.Experimental observations and theoretical studies show that nonlinear internal waves occur widely in shallow water and cause acoustic propagation effects including ducting and mode coupling. Horizontal ducting results when acoustic modes travel between internal wave fronts that form waveguide boundaries. For small grazing angles between a mode trajectory and a front, an interference pattern may arise that is a horizontal Lloyd mirror pattern. An analytic description for this feature is provided along with comparisons between results from the formulated model predicting a horizontal Lloyd mirror pattern and an adiabatic mode parabolic equation. Different waveguide models are considered, including boxcar and jump sound speed profiles where change in sound speed is assumed 12 m/s. Modifications to the model are made to include multiple and moving fronts. The focus of this analysis is on different front locations relative to the source as well as on the number of fronts and their curvatures and speeds. Curvature influences mode incidence angles and thereby changes the interference patterns. For sources oriented so that the front appears concave, the areas with interference patterns shrink as curvature increases, while convexly oriented fronts cause patterns to expand.The authors thank the Office of Naval Research for
funding this work. Additionally, the first author is supported
through an ONR Ocean Acoustics Traineeship
Refined Characterization of Student Perspectives on Quantum Physics
The perspectives of introductory classical physics students can often
negatively influence how those students later interpret quantum phenomena when
taking an introductory course in modern physics. A detailed exploration of
student perspectives on the interpretation of quantum physics is needed, both
to characterize student understanding of physics concepts, and to inform how we
might teach traditional content. Our previous investigations of student
perspectives on quantum physics have indicated they can be highly nuanced, and
may vary both within and across contexts. In order to better understand the
contextual and often seemingly contradictory stances of students on matters of
interpretation, we interviewed 19 students from four introductory modern
physics courses taught at the University of Colorado. We find that students
have attitudes and opinions that often parallel the stances of expert
physicists when arguing for their favored interpretations of quantum mechanics,
allowing for more nuanced characterizations of student perspectives in terms of
three key interpretive themes. We present a framework for characterizing
student perspectives on quantum mechanics, and demonstrate its utility in
interpreting the sometimes-contradictory nature of student responses to
previous surveys. We further find that students most often vacillate in their
responses when what makes intuitive sense to them is not in agreement with what
they consider to be a correct response, underscoring the need to distinguish
between the personal and the public perspectives of introductory modern physics
students.Comment: 24 pages, 31 references, 1 Appendix (5 pages
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