10 research outputs found
The evolution of free wave packets
We discuss four general features of force-free evolution: (1) The spatial
spread of any packet changes with time in a very simple way. (2) Over
sufficiently short periods of time (whose duration is related to the spread in
momentum of the packet) the probability distribution moves but there is little
change in shape. (3) After a sufficiently long period (related to the initial
spatial spread) the packet settles into a simple form simply related to the
momentum distribution in the packet. In this asymptotic regime, the shape of
the probability distribution no longer changes except for its scale, which
increases linearly with the time. (4) There is an infinite denumerable set of
simple wave packets (the Hermite-Gauss packets) that do not change shape as
they evolve.Comment: 6 pages, 4 figures, didactic pape
The Design and Validation of the Quantum Mechanics Conceptual Survey
The Quantum Mechanics Conceptual Survey (QMCS) is a 12-question survey of
students' conceptual understanding of quantum mechanics. It is intended to be
used to measure the relative effectiveness of different instructional methods
in modern physics courses. In this paper we describe the design and validation
of the survey, a process that included observations of students, a review of
previous literature and textbooks and syllabi, faculty and student interviews,
and statistical analysis. We also discuss issues in the development of specific
questions, which may be useful both for instructors who wish to use the QMCS in
their classes and for researchers who wish to conduct further research of
student understanding of quantum mechanics. The QMCS has been most thoroughly
tested in, and is most appropriate for assessment of (as a posttest only),
sophomore-level modern physics courses. We also describe testing with students
in junior quantum courses and graduate quantum courses, from which we conclude
that the QMCS may be appropriate for assessing junior quantum courses, but is
not appropriate for assessing graduate courses. One surprising result of our
faculty interviews is a lack of faculty consensus on what topics should be
taught in modern physics, which has made designing a test that is valued by a
majority of physics faculty more difficult than expected.Comment: Submitted to Physical Review Special Topics: Physics Education
Researc
Quantum mechanics: classical results, modern systems, and visualized examples
`Quantum Mechanics'' is a comprehensive introduction to quantum mechanics for advanced undergraduate students in physics. It provides the reader with a strong conceptual background in the subject, extensive experience with the necessary mathematical background, as well as numerous visualizations of quantum concepts and phenomena. - ;Quantum Mechanics: Classical Results, Modern Systems, and Visualized Examples is a comprehensive introduction to non-relativistic quantum mechanics for advanced undergraduate students in physics and related fields. It provides students with a strong conceptual background in the most important theoretical aspects of quantum mechanics, extensive experience with the mathematical tools required to solve problems, the opportunity to use quantum ideas to confront modern experimental. realizations of quantum systems, and numerous visualizations of quantum concepts and phenomena. Changes from the First Edition include many new discussions of modern quantum systems (such as Bose-Einstein condensates, the quantum Hall effect, and wave packet revivals) all in the context of familiar. textbook level examples. The book continues to emphasize the many connections to classical mechanics and wave physics to help students use their existing intuition to better learn new quantum concepts.
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Forward-backward asymmetries in W and Z decays
The leptons emitted in decays of W and Z bosons produced in pp or anti pp collisions exhibit characteristic asymmetries with respect to the beam direction, as measured in the W or Z center-of-mass. The asymmetries appear in both pp and anti pp collisions. For anti pp collisions they appear to be approximately constant over the whole y range for values of M/..sqrt..s greater than or equal to 0.1. For smaller values of M/..sqrt..s, the asymmetries become more and more washed out in the central region as sea-sea collisions begin to play a larger role in gauge boson formation
Development of spirulina for the manufacture and oral delivery of protein therapeutics
The use of the edible photosynthetic cyanobacterium Arthrospira platensis (spirulina) as a biomanufacturing platform has been limited by a lack of genetic tools. Here we report genetic engineering methods for stable, high-level expression of bioactive proteins in spirulina, including large-scale, indoor cultivation and downstream processing methods. Following targeted integration of exogenous genes into the spirulina chromosome (chr), encoded protein biopharmaceuticals can represent as much as 15% of total biomass, require no purification before oral delivery and are stable without refrigeration and protected during gastric transit when encapsulated within dry spirulina. Oral delivery of a spirulina-expressed antibody targeting campylobacter—a major cause of infant mortality in the developing world—prevents disease in mice, and a phase 1 clinical trial demonstrated safety for human administration. Spirulina provides an advantageous system for the manufacture of orally delivered therapeutic proteins by combining the safety of a food-based production host with the accessible genetic manipulation and high productivity of microbial platforms
\u3ci\u3eDrosophila\u3c/i\u3e Muller F Elements Maintain a Distinct Set of Genomic Properties Over 40 Million Years of Evolution
The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu