682 research outputs found
Changes in the frequency distribution of energy deposited in short pathlengths as a function of energy degradation of the primary beam
Frequency distributions of event size in deposition of energy over small pathlengths measured after penetration of 44.3 MeV protons through thicknesses of tissue-like materia
Teaching and understanding of quantum interpretations in modern physics courses
Just as expert physicists vary in their personal stances on interpretation in
quantum mechanics, instructors vary on whether and how to teach interpretations
of quantum phenomena in introductory modern physics courses. In this paper, we
document variations in instructional approaches with respect to interpretation
in two similar modern physics courses recently taught at the University of
Colorado, and examine associated impacts on student perspectives regarding
quantum physics. We find students are more likely to prefer realist
interpretations of quantum-mechanical systems when instructors are less
explicit in addressing student ontologies. We also observe contextual
variations in student beliefs about quantum systems, indicating that
instructors who choose to address questions of ontology in quantum mechanics
should do so explicitly across a range of topics.Comment: 18 pages, references, plus 2 pages supplemental materials. 8 figures.
PACS: 01.40.Fk, 03.65.-
Development of quantum perspectives in modern physics
Introductory undergraduate courses in classical physics stress a perspective
that can be characterized as realist; from this perspective, all physical
properties of a classical system can be simultaneously specified and thus
determined at all future times. Such a perspective can be problematic for
introductory quantum physics students, who must develop new perspectives in
order to properly interpret what it means to have knowledge of quantum systems.
We document this evolution in student thinking in part through pre- and
post-instruction evaluations using the Colorado Learning Attitudes about
Science Survey. We further characterize variations in student epistemic and
ontological commitments by examining responses to two essay questions, coupled
with responses to supplemental quantum attitude statements. We find that, after
instruction in modern physics, many students are still exhibiting a realist
perspective in contexts where a quantum-mechanical perspective is needed. We
further find that this effect can be significantly influenced by instruction,
where we observe variations for courses with differing learning goals. We also
note that students generally do not employ either a realist or a quantum
perspective in a consistent manner.Comment: 18 pages, plus references; 3 figures; 9 tables. PACS: 01.40.Fk,
03.65._
The Volume of some Non-spherical Horizons and the AdS/CFT Correspondence
We calculate the volumes of a large class of Einstein manifolds, namely
Sasaki-Einstein manifolds which are the bases of Ricci-flat affine cones
described by polynomial embedding relations in C^n. These volumes are important
because they allow us to extend and test the AdS/CFT correspondence. We use
these volumes to extend the central charge calculation of Gubser (1998) to the
generalized conifolds of Gubser, Shatashvili, and Nekrasov (1999). These
volumes also allow one to quantize precisely the D-brane flux of the AdS
supergravity solution. We end by demonstrating a relationship between the
volumes of these Einstein spaces and the number of holomorphic polynomials
(which correspond to chiral primary operators in the field theory dual) on the
corresponding affine cone.Comment: 25 pp, LaTeX, 1 figure, v2: refs adde
Methacarn preserves mucus integrity and improves visualization of amoebae in gills of Atlantic salmon (Salmo salar L.)
Two aqueous fixation methods (modified Davidson's solution and modified Davidson's solution with 2% (w/v) Alcian blue) were compared against two nonâaqueous fixation methods (methacarn solution and methacarn solution with 2% (w/v) Alcian blue) along with the standard buffered formalin fixation method to (a) improve preservation of the mucous coat on Atlantic salmon, Salmo salar L., gills and (b) to examine the interaction between the amoebae and mucus on the gill during an infection with amoebic gill disease. Aqueous fixatives demonstrated excellent cytological preservation but failed to deliver the preservation of the mucus when compared to the nonâaqueousâbased fixatives; qualitative and semiâquantitative analysis revealed a greater preservation of the gill mucus using the nonâaqueous methacarn solution. A combination of this fixation method and an Alcian blue/Periodic acidâSchiff staining was tested in gills of Atlantic salmon infected with amoebic gill disease; lectin labelling was also used to confirm the mucus preservation in the methacarnâfixed tissue. Amoebae were observed closely associated with the mucus demonstrating that the techniques employed for preservation of the mucous coat can indeed avoid the loss of potential mucusâembedded parasites, thus providing a better understanding of the relationship between the mucus and parasite
Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions
We present a theoretical description of the thermopower due to
magnon-assisted tunneling in a mesoscopic tunnel junction between two
ferromagnetic metals. The thermopower is generated in the course of thermal
equilibration between two baths of magnons, mediated by electrons. For a
junction between two ferromagnets with antiparallel polarizations, the ability
of magnon-assisted tunneling to create thermopower depends on the
difference between the size of the majority and
minority band Fermi surfaces and it is proportional to a temperature dependent
factor where is the magnon Debye
energy. The latter factor reflects the fractional change in the net
magnetization of the reservoirs due to thermal magnons at temperature
(Bloch's law). In contrast, the contribution of magnon-assisted
tunneling to the thermopower of a junction with parallel polarizations is
negligible. As the relative polarizations of ferromagnetic layers can be
manipulated by an external magnetic field, a large difference results in a magnetothermopower effect. This
magnetothermopower effect becomes giant in the extreme case of a junction
between two half-metallic ferromagnets, .Comment: 9 pages, 4 eps figure
Special values of canonical Green's functions
We give a precise formula for the value of the canonical Green's function at
a pair of Weierstrass points on a hyperelliptic Riemann surface. Further we
express the 'energy' of the Weierstrass points in terms of a spectral invariant
recently introduced by N. Kawazumi and S. Zhang. It follows that the energy is
strictly larger than log 2. Our results generalize known formulas for elliptic
curves.Comment: 10 page
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Convergence of measures on compactifications of locally symmetric spaces
We conjecture that the set of homogeneous probability measures on the maximal Satake compactification of an arithmetic locally symmetric space S=ÎâG/K is compact. More precisely, given a sequence of homogeneous probability measures on S, we expect that any weak limit is homogeneous with support contained in precisely one of the boundary components (including S itself). We introduce several tools to study this conjecture and we prove it in a number of cases, including when G=SL3(R) and Î=SL3(Z)
Economists' Statement on U.S. Broadband Policy
In this statement, a group of economists assembled by the AEI-Brookings Joint Center makes the following two recommendations to improve the competitive provision of broadband services. First, Congress should eliminate local franchising regulations, which serve as a barrier to new entry. Second, Congress and the Federal Communications Commission should make more spectrum available to private parties and allow them to use it as they see fit or trade their licenses in the market, so that spectrum will go to its highest-valued uses.Technology and Industry
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