526 research outputs found
Si/Ge hole-tunneling double-barrier resonant tunneling diodes formed on sputtered flat Ge layers
We have demonstrated Si/Ge hole-tunneling double-barrier resonant tunneling diodes (RTDs) formed on flat Ge layers with a relaxation rate of 89% by our proposed method; in this method, the flat Ge layers can be directly formed on highly B-doped Si(001) substrates using our proposed sputter epitaxy method. The RTDs exhibit clear negative differential resistance effects in the static currentâvoltage (IâV) curves at room temperature. The quantized energy level estimation suggests that resonance peaks that appeared in the IâV curves are attributed to hole tunneling through the first heavy- and light-hole energy levels
Numerical simulation code for self-gravitating Bose-Einstein condensates
We completed the development of simulation code that is designed to study the
behavior of a conjectured dark matter galactic halo that is in the form of a
Bose-Einstein Condensate (BEC). The BEC is described by the Gross-Pitaevskii
equation, which can be solved numerically using the Crank-Nicholson method. The
gravitational potential, in turn, is described by Poisson's equation, that can
be solved using the relaxation method. Our code combines these two methods to
study the time evolution of a self-gravitating BEC. The inefficiency of the
relaxation method is balanced by the fact that in subsequent time iterations,
previously computed values of the gravitational field serve as very good
initial estimates. The code is robust (as evidenced by its stability on coarse
grids) and efficient enough to simulate the evolution of a system over the
course of 1E9 years using a finer (100x100x100) spatial grid, in less than a
day of processor time on a contemporary desktop computer.Comment: 13 pages, 1 figure; updated to reflect changes in the published
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Decay Properties of Bh and Db Produced in the Cm + Na Reaction
Decay properties of an isotope Bh and its daughter nucleus Db
produced by the Cm(Na, 5\textit{n}) reaction were studied by
using a gas-filled recoil separator coupled with a position-sensitive
semiconductor detector. Bh was clearly identified from the correlation
of the known nuclide, Db. The obtained decay properties of Bh
and Db are consistent with those observed in the 113 chain,
which provided further confirmation of the discovery of 113.Comment: Accepted for publication in J. Phys. Soc. JPN., to be published in
Vol.78 No.
Vortices in multicomponent Bose-Einstein condensates
We review the topic of quantized vortices in multicomponent Bose-Einstein
condensates of dilute atomic gases, with an emphasis on that in two-component
condensates. First, we review the fundamental structure, stability and dynamics
of a single vortex state in a slowly rotating two-component condensates. To
understand recent experimental results, we use the coupled Gross-Pitaevskii
equations and the generalized nonlinear sigma model. An axisymmetric vortex
state, which was observed by the JILA group, can be regarded as a topologically
trivial skyrmion in the pseudospin representation. The internal, coherent
coupling between the two components breaks the axisymmetry of the vortex state,
resulting in a stable vortex molecule (a meron pair). We also mention
unconventional vortex states and monopole excitations in a spin-1 Bose-Einstein
condensate. Next, we discuss a rich variety of vortex states realized in
rapidly rotating two-component Bose-Einstein condensates. We introduce a phase
diagram with axes of rotation frequency and the intercomponent coupling
strength. This phase diagram reveals unconventional vortex states such as a
square lattice, a double-core lattice, vortex stripes and vortex sheets, all of
which are in an experimentally accessible parameter regime. The coherent
coupling leads to an effective attractive interaction between two components,
providing not only a promising candidate to tune the intercomponent interaction
to study the rich vortex phases but also a new regime to explore vortex states
consisting of vortex molecules characterized by anisotropic vorticity. A recent
experiment by the JILA group vindicated the formation of a square vortex
lattice in this system.Comment: 69 pages, 25 figures, Invited review article for International
Journal of Modern Physics
Experimental findings of soil particle movement in 2D seepage failure of soil using Particle Image Velocimetry
Seepage failure is one of the most important issues associated with the performance-based design of soil at high groundwater sites. We discuss the movement of soil particles with increase in the hydraulic head difference, H, in half 2D model tests on the seepage failure of soil in front of sheet piles using PIV analyses (Particle Image Velocimetry). The following conclusions were obtained: (1) At a certain value of Hpiv lower than Hy, the micro movement of soil particles is found around the bottom tip of a sheet pile wall, where Hpiv and Hy are the hydraulic head differences at the start of soil particle movement using PIV analysis, and at the onset of deformation of the soil surface, respectively. (2) The location of the micro movement of soil particles corresponds reasonably well with the net < 0 region, where net is the net body force exerted on a unit volume of soil. (3) Micro movement of soil particles occurs at a hydraulic head difference of 73 - 100% of Hy. (4) PIV analyses show the boundaries between regions where soil particles do or do not move as well as the movement of sand particles. (5) The region of soil particle movement proves the validity of the prism of failure for Terzaghiâs method and the prismatic failure concept
Oscillations of a rapidly rotating annular Bose-Einstein condensate
A time-dependent variational Lagrangian analysis based on the
Gross-Pitaevskii energy functional serves to study the dynamics of a metastable
giant vortex in a rapidly rotating Bose-Einstein condensate. The resulting
oscillation frequencies of the core radius reproduce the trends seen in recent
experiments [Engels et al., Phys. Rev. Lett. 90, 170405 (2003)], but the
theoretical values are smaller by a factor approximately 0.6-0.8.Comment: 7 pages, revtex
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