3,859 research outputs found
Energy Loss from Reconnection with a Vortex Mesh
Experiments in superfluid 4He show that at low temperatures, energy
dissipation from moving vortices is many orders of magnitude larger than
expected from mutual friction. Here we investigate other mechanisms for energy
loss by a computational study of a vortex that moves through and reconnects
with a mesh of small vortices pinned to the container wall. We find that such
reconnections enhance energy loss from the moving vortex by a factor of up to
100 beyond that with no mesh. The enhancement occurs through two different
mechanisms, both involving the Kelvin oscillations generated along the vortex
by the reconnections. At relatively high temperatures the Kelvin waves increase
the vortex motion, leading to more energy loss through mutual friction. As the
temperature decreases, the vortex oscillations generate additional reconnection
events between the moving vortex and the wall, which decrease the energy of the
moving vortex by transfering portions of its length to the pinned mesh on the
wall.Comment: 9 pages, 10 figure
CMB Fluctuation Amplitude from Dark Energy Partitions
It is assumed that the dark energy observed today is frozen as a result of a
phase transition involving the source of that energy. Postulating that the dark
energy de-coherence which results from this phase transition drives statistical
variations in the energy density specifies a class of cosmological models in
which the cosmic microwave background (CMB) fluctuation amplitude at last
scattering is approximately .Comment: 7 Pages, Poster presented at Texas@Stanford conference, Dec. 2004,
minor clarification
Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties
Ferroelectric and dielectric properties of polydomain (twinned)
single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a
nonlinear thermodynamic theory, which has been developed recently for epitaxial
ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3
(PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit
strain-temperature" phase diagrams are calculated and compared with each other.
It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar
to the diagram of PbTiO3 films. They consist of only four different stability
ranges, which correspond to the paraelectric phase, single-domain tetragonal
ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at
x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of
stable polarization states, involving at least one monoclinic polydomain state.
Using the developed phase diagrams, the mean out-of-plane polarization of a
poled PZT film is calculated as a function of the misfit strain and
composition. Theoretical results are compared with the measured remanent
polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane
dielectric response of PZT films on the misfit strain in the heterostructure is
also reported.Comment: 23 pages, 4 figure
Teaching Innovation as Part of an Agribusiness Curriculum
Innovation is critical to the survival of agricultural businesses in the U.S. yet few universities have classes in their curricula that focus on innovation and innovation management. Innovation includes developing new processes and concepts and taking products based on those ideas to market. By its nature, innovation generally involves technical components, market assessment, business analysis, and implementation strategies that include marketing campaigns to a target market. As a result, if innovation is going to be experientially taught to students, the class will likely need to include concepts from multiple disciplines. The objectives of this paper are to present an outline of capstone/senior design classes designed to cause students to learn innovation by participating in interdisciplinary teams working with real companies on the development of new product innovation.Teaching/Communication/Extension/Profession,
The high-lying Li levels at excitation energy around 21 MeV
The H+He cluster structure in Li was investigated by the
H(,H He)n kinematically complete experiment at the incident
energy = 67.2 MeV. We have observed two resonances at =
21.30 and 21.90 MeV which are consistent with the He(H, )Li
analysis in the Ajzenberg-Selove compilation. Our data are compared with the
previous experimental data and the RGM and CSRGM calculations.Comment: 12 pages, 6 figures. Accepted for publication in J. Phys. Soc. Jp
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The tarantula toxin GxTx detains K+ channel gating charges in their resting conformation.
Allosteric ligands modulate protein activity by altering the energy landscape of conformational space in ligand-protein complexes. Here we investigate how ligand binding to a K+ channel's voltage sensor allosterically modulates opening of its K+-conductive pore. The tarantula venom peptide guangxitoxin-1E (GxTx) binds to the voltage sensors of the rat voltage-gated K+ (Kv) channel Kv2.1 and acts as a partial inverse agonist. When bound to GxTx, Kv2.1 activates more slowly, deactivates more rapidly, and requires more positive voltage to reach the same K+-conductance as the unbound channel. Further, activation kinetics are more sigmoidal, indicating that multiple conformational changes coupled to opening are modulated. Single-channel current amplitudes reveal that each channel opens to full conductance when GxTx is bound. Inhibition of Kv2.1 channels by GxTx results from decreased open probability due to increased occurrence of long-lived closed states; the time constant of the final pore opening step itself is not impacted by GxTx. When intracellular potential is less than 0 mV, GxTx traps the gating charges on Kv2.1's voltage sensors in their most intracellular position. Gating charges translocate at positive voltages, however, indicating that GxTx stabilizes the most intracellular conformation of the voltage sensors (their resting conformation). Kinetic modeling suggests a modulatory mechanism: GxTx reduces the probability of voltage sensors activating, giving the pore opening step less frequent opportunities to occur. This mechanism results in K+-conductance activation kinetics that are voltage-dependent, even if pore opening (the rate-limiting step) has no inherent voltage dependence. We conclude that GxTx stabilizes voltage sensors in a resting conformation, and inhibits K+ currents by limiting opportunities for the channel pore to open, but has little, if any, direct effect on the microscopic kinetics of pore opening. The impact of GxTx on channel gating suggests that Kv2.1's pore opening step does not involve movement of its voltage sensors
(Giant) Vortex - (anti) vortex interaction in bulk superconductors: The Ginzburg-Landau theory
The vortex-vortex interaction potential in bulk superconductors is calculated
within the Ginzburg-Landau (GL) theory and is obtained from a numerical
solution of a set of two coupled non-linear GL differential equations for the
vector potential and the superconducting order parameter, where the merger of
vortices into a giant vortex is allowed. Further, the interaction potentials
between a vortex and a giant vortex and between a vortex and an antivortex are
obtained for both type-I and type-II superconductors. Our numerical results
agree asymptotically with the analytical expressions for large inter-vortex
separations which are available in the literature. We propose new empirical
expressions valid over the full interaction range, which are fitted to our
numerical data for different values of the GL parameter
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