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 non‐aqueous 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 non‐aqueous‐based fixatives; qualitative and semi‐quantitative analysis revealed a greater preservation of the gill mucus using the non‐aqueous methacarn solution. A combination of this fixation method and an Alcian blue/Periodic acid–Schiff 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 methacarn‐fixed 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 mucus‐embedded 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 $S_{AP}$ depends on the difference between the size $\Pi_{\uparrow, \downarrow}$ of the majority and minority band Fermi surfaces and it is proportional to a temperature dependent factor $(k_{B}T/\omega_{D})^{3/2}$ where $\omega_{D}$ 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 $T$ (Bloch's $T^{3/2}$ law). In contrast, the contribution of magnon-assisted tunneling to the thermopower $S_P$ 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 $\Delta S = S_{AP} - S_P \approx S_{AP} \sim - (k_B/e) f (\Pi_{\uparrow},\Pi_{\downarrow}) (k_BT/\omega_{D})^{3/2}$ results in a magnetothermopower effect. This magnetothermopower effect becomes giant in the extreme case of a junction between two half-metallic ferromagnets, $\Delta S \sim - k_B/e$.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

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=Γ∖G/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 Γ=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