1,179 research outputs found
Transmission and Reflection of Collective Modes in Spin-1 Bose-Einstein Condensate
We study tunneling properties of collective excitations in spin-1
Bose-Einstein condensates. In the absence of magnetic fields, the total
transmission in the long wavelength limit occurs in all kinds of excitations
but the quadrupolar spin mode in the ferromagnetic state. The quadrupolar spin
mode alone shows the total reflection. A difference between those excitations
comes from whether the wavefunction of an excitation corresponds to that of the
condensate in the long wavelength limit. The correspondence results in the
total transmission as in the spinless BEC.Comment: 6 pages, 5 figure
Macroscopic resonant tunneling of magnetic flux
We have developed a quantitative theory of resonant tunneling of magnetic
flux between discrete macroscopically distinct quantum states in SQUID systems.
The theory is based on the standard density-matrix approach. Its new elements
include the discussion of the two different relaxation mechanisms that exist
for the double-well potential, and description of the ``photon-assisted''
tunneling driven by external rf radiation. It is shown that in the case of
coherent flux dynamics, rf radiation should lead to splitting of the peaks of
resonant flux tunneling, indicating that the resonant tunneling is a convenient
tool for studying macroscopic quantum coherence of flux.Comment: 11 pages, 8 figure
Low temperature atomic layer deposited ZnO photo thin film transistors
ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition technique. The growth temperature of ZnO channel layers are selected as 80, 100, 120, 130, and 250°C. Material characteristics of ZnO films are examined using x-ray photoelectron spectroscopy and x-ray diffraction methods. Stoichiometry analyses showed that the amount of both oxygen vacancies and interstitial zinc decrease with decreasing growth temperature. Electrical characteristics improve with decreasing growth temperature. Best results are obtained with ZnO channels deposited at 80°C; Ion/Ioff ratio is extracted as 7.8 × 109 and subthreshold slope is extracted as 0.116 V/dec. Flexible ZnO TFT devices are also fabricated using films grown at 80°C. ID-VGS characterization results showed that devices fabricated on different substrates (Si and polyethylene terephthalate) show similar electrical characteristics. Sub-bandgap photo sensing properties of ZnO based TFTs are investigated; it is shown that visible light absorption of ZnO based TFTs can be actively controlled by external gate bias. © 2014 American Vacuum Society
Peculiarities of sub-barrier fusion with quantum diffusion approach
With the quantum diffusion approach the unexpected behavior of fusion cross
section, angular momentum, and astrophysical S-factor at sub-barrier energies
has been revealed. Out of the region of short-range nuclear interaction and
action of friction at turning point the decrease rate of the cross section
under the barrier becomes smaller. The calculated results for the reactions
with spherical nuclei are in a good agreement with the existing experimental
data.Comment: 11 pages, 5 figure
Effect of the Surface on the Electron Quantum Size Levels and Electron g-Factor in Spherical Semiconductor Nanocrystals
The structure of the electron quantum size levels in spherical nanocrystals
is studied in the framework of an eight--band effective mass model at zero and
weak magnetic fields. The effect of the nanocrystal surface is modeled through
the boundary condition imposed on the envelope wave function at the surface. We
show that the spin--orbit splitting of the valence band leads to the
surface--induced spin--orbit splitting of the excited conduction band states
and to the additional surface--induced magnetic moment for electrons in bare
nanocrystals. This additional magnetic moment manifests itself in a nonzero
surface contribution to the linear Zeeman splitting of all quantum size energy
levels including the ground 1S electron state. The fitting of the size
dependence of the ground state electron g factor in CdSe nanocrystals has
allowed us to determine the appropriate surface parameter of the boundary
conditions. The structure of the excited electron states is considered in the
limits of weak and strong magnetic fields.Comment: 11 pages, 4 figures, submitted to Phys. Rev.
Coherent electron-phonon coupling and polaron-like transport in molecular wires
We present a technique to calculate the transport properties through
one-dimensional models of molecular wires. The calculations include inelastic
electron scattering due to electron-lattice interaction. The coupling between
the electron and the lattice is crucial to determine the transport properties
in one-dimensional systems subject to Peierls transition since it drives the
transition itself. The electron-phonon coupling is treated as a quantum
coherent process, in the sense that no random dephasing due to electron-phonon
interactions is introduced in the scattering wave functions. We show that
charge carrier injection, even in the tunneling regime, induces lattice
distortions localized around the tunneling electron. The transport in the
molecular wire is due to polaron-like propagation. We show typical examples of
the lattice distortions induced by charge injection into the wire. In the
tunneling regime, the electron transmission is strongly enhanced in comparison
with the case of elastic scattering through the undistorted molecular wire. We
also show that although lattice fluctuations modify the electron transmission
through the wire, the modifications are qualitatively different from those
obtained by the quantum electron-phonon inelastic scattering technique. Our
results should hold in principle for other one-dimensional atomic-scale wires
subject to Peierls transitions.Comment: 21 pages, 8 figures, accepted for publication in Phys. Rev. B (to
appear march 2001
Sub-barrier capture with quantum diffusion approach: actinide-based reactions
With the quantum diffusion approach the behavior of capture cross sections
and mean-square angular momenta of captured systems are revealed in the
reactions with deformed nuclei at subbarrier energies. The calculated results
are in a good agreement with existing experimental data. With decreasing
bombarding energy under the barrier the external turning point of the
nucleusnucleus potential leaves the region of short-range nuclear interaction
and action of friction. Because of this change of the regime of interaction, an
unexpected enhancement of the capture cross section is expected at bombarding
energies far below the Coulomb barrier. This effect is shown its worth in the
dependence of mean-square angular momentum of captured system on the bombarding
energy. From the comparison of calculated and experimental capture cross
sections, the importance of quasifission near the entrance channel is shown for
the actinide-based reactions leading to superheavy nuclei.Comment: 11 pages, 16 figures, Regular Articl
Global Analysis with SNO: Toward the Solution of the Solar Neutrino Problem
We perform a global analysis of the latest solar neutrino data including the
SNO result on the CC-event rate. This result further favors the LMA solution of
the solar neutrino problem. The best fit values of parameters we find are:
\Delta m^2 = (4.8 - 5.0)10^{-5} eV^2, tan^2 \theta = 0.35 - 0.38, f_B = 1.08 -
1.12, and f_{hep} = 1 - 4. With respect to this best fit the LOW solution is
accepted at 90% C.L.. The Vacuum oscillation solution with \Delta m^2 = 1.4
10^{-10} eV^2, gives good fit of the data provided that the boron neutrino flux
is substantially smaller than the SSM flux (f_B \sim 0.5). The SMA solution is
accepted only at 3\sigma level. We find that vacuum oscillations to sterile
neutrino, VAC(sterile), with f_B \sim 0.5 also give rather good global fit of
the data. All other sterile solutions are strongly disfavored. We check the
quality of the fit by constructing the pull-off diagrams of observables.
Predictions for the day-night asymmetry, spectrum distortion and NC/CC ratio at
SNO are calculated. In the best fit points of the global solutions we find:
A_{DN}^{CC} \approx (7 - 8)% for LMA, \sim 3% for LOW, and (2 - 3)% for SMA. It
will be difficult to see the distortion of the spectrum expected for LMA as
well as LOW solutions. However, future SNO spectral data can significantly
affect the VAC and SMA solutions. We also calculate expectations for the
BOREXINO rate.Comment: 35 pages, latex, 9 figures; results of analysis slightly changed due
to different treatment of the hep neutrino flux; predictions for NC/CC ratio
and Borexino rate adde
A Damage Mechanics Approach to Fatigue Assessment in Offshore Structures
This article is intended to describe the development of a fatigue damage model capable of assessing fatigue damage in offshore structures. This is achieved by for mulating a set of damage coupled constitutive and evolution equations which make the for mulation of a unified approach possible under both low and high cycle fatigue damage and consistent with the structural dynamic response of the changing/deteriorating material be haviors. The structural analysis for the whole designed period, say about 30 years, can be carried out with the aid of the proposed analytical procedure, in which the fundamental characteristics of sea wave statistics responsible for the structural dynamic response can be sufficiently considered. An offshore structure subject to complex ocean environment is described by a general stochastic system which embeds a group of stochastic subsystems, each characterizing a duty cycle. An effective analytical method is established by introduc ing the concept of duty strain range with a clear mathematical definition and its analytical solution which covers all possible spectral parameters. The history-dependent damage is also included in the damage model so that the overload effects can be analyzed. It should be pointed out that the whole procedure can be fully computerized such that the practical or engineering significance of varying design variables can be readily highlighted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67255/2/10.1177_105678959300200405.pd
Polyubiquitin-Photoactivatable Crosslinking Reagents for Mapping Ubiquitin Interactome Identify Rpn1 as a Proteasome Ubiquitin-Associating Subunit
Chemical Immunolog
- …