564 research outputs found
Effect of Tensor Correlations on Gamow-Teller States in 90Zr and 208Pb
The tensor terms of the Skyrme effective interaction are included in the
self-consistent Hartree-Fock plus Random Phase Approximation (HF+RPA) model.
The Gamow-Teller (GT) strength function of 90Zr and 208Pb are calculated with
and without the tensor terms. The main peaks are moved downwards by about 2 MeV
when including the tensor contribution. About 10% of the non-energy weighted
sum rule is shifted to the excitation energy region above 30 MeV by the RPA
tensor correlations. The contribution of the tensor terms to the energy
weighted sum rule is given analytically, and compared to the outcome of RPA.Comment: 13 pages, 2 figures,2 table
Effective lattice actions for correlated electrons
We present an exact, unconstrained representation of the electron operators
in terms of operators of opposite statistics. We propose a path--integral
representation for the - model and introduce a parameter controlling the
semiclassical behaviour. We extend the functional approach to the Hubbard model
and show that the mean--field theory is equivalent to considering, at
Hamiltonian level, the Falikov--Kimball model. Connections with a bond-charge
model are also discussed.Comment: 12 pages, REVTeX 3.0, no figure
Generation of two-mode nonclassical states and a quantum phase gate operation in trapped ion cavity QED
We propose a scheme to generate nonclassical states of a quantum system,
which is composed of the one-dimensional trapped ion motion and a single cavity
field mode. We show that two-mode SU(2) Schr\"odinger-cat states, entangled
coherent states, two-mode squeezed vacuum states and their superposition can be
generated. If the vibration mode and the cavity mode are used to represent
separately a qubit, a quantum phase gate can be implemented.Comment: to appear in PR
Sources and transportation of organic carbon in the sediment from the Yellow River to the Bohai Sea: indicated by compound specific fatty acids
Spin-dependent transport in a Luttinger liquid
We develop a detailed theory for spin transport in a one-dimensional quantum
wire described by Luttinger liquid theory. A hydrodynamic description for the
quantum wire is supplemented by boundary conditions taking into account the
exchange coupling between the magnetization of ferromagnetic reservoirs and the
boundary magnetization in the wire. Spin-charge separation is shown to imply
drastic and qualitative consequences for spin-dependent transport. In
particular, the spin accumulation effect is quenched except for fine-tuned
parameter regimes. We propose several feasible setups involving an external
magnetic field to detect this phenomenon in transport experiments on
single-wall carbon nanotubes. In addition, electron-electron backscattering
processes, which do not have an important effect on thermodynamic properties or
charge transport, are shown to modify spin-dependent transport through long
quantum wires in a crucial way.Comment: 23 pages, 4 figure
Atomistic Studies of Defect Nucleation during Nanoindentation of Au (001)
Atomistic studies are carried out to investigate the formation and evolution
of defects during nanoindentation of a gold crystal. The results in this
theoretical study complement the experimental investigations [J. D. Kiely and
J. E. Houston, Phys. Rev. B, v57, 12588 (1998)] extremely well. The defects are
produced by a three step mechanism involving nucleation, glide and reaction of
Shockley partials on the {111} slip planes noncoplanar with the indented
surface. We have observed that slip is in the directions along which the
resolved shear stress has reached the critical value of approximately 2 GPa.
The first yield occurs when the shear stresses reach this critical value on all
the {111} planes involved in the formation of the defect. The phenomenon of
strain hardening is observed due to the sessile stair-rods produced by the
zipping of the partials. The dislocation locks produced during the second yield
give rise to permanent deformation after retraction.Comment: 11 pages, 13 figures, submitted to Physical Review
Generation of arbitrary two dimensional motional state of a trapped ion
We present a scheme to generate an arbitrary two-dimensional quantum state of
motion of a trapped ion. This proposal is based on a sequence of laser pulses,
which are tuned appropriately to control transitions on the sidebands of two
modes of vibration. Not more than laser pulses are needed to
generate a pure state with upper phonon number and in the and
direction respectively.Comment: to appear in PR
Hadron yields and spectra in Au+Au collisions at the AGS
Inclusive double differential multiplicities and rapidity density
distributions of hadrons are presented for 10.8 A GeV/c Au+Au collisions as
measured at the AGS by the E877 collaboration. The results indicate that large
amounts of stopping and collective transverse flow effects are present. The
data are also compared to the results from the lighter Si+Al system.Comment: 12 pages, latex, 10 figures, submitted to Nuclear Physics A (Quark
Matter 1996 Proceedings
Amorphous layer formation in Al86.0Co7.6Ce6.4 glass-forming alloy by large-area electron beam irradiation
Amorphous Al-Co-Ce alloys are of interest because of their resistance to corrosion, but high cooling rates are generally required to suppress the formation of crystalline phases. In this study, the surface of a bulk crystalline Al-Co-Ce alloy of a glass-forming composition was treated using large area electron beam (LAEB) irradiation. Scanning electron microscopy shows that, compared to the microstructure of the original crystalline material, the treated surface exhibits greatly improved microstructural and compositional uniformity. Glancing angle X-ray diffraction conducted on the surface of treated samples indicates the formation of the amorphous phase following 25 and 50 pulses at 35 kV cathode voltage. However, when the samples are treated with 100 and 150 pulses at 35 kV cathode voltage of electron beam irradiation, the treated layer comprises localised crystalline regions in an amorphous matrix. In addition, the formation of cracks in the treated layer is found to be localised around the Al8Co2Ce phase in the bulk material. Overall, crack length per unit area had no clear change with an increase in the number of pulses
Measurement of Pion Enhancement at Low Transverse Momentum and of the Delta-Resonance Abundance in Si-Nucleus Collisions at AGS Energy
We present measurements of the pion transverse momentum (p_t) spectra in
central Si-nucleus collisions in the rapidity range 2.0<y<5.0 for p_t down to
and including p_t=0. The data exhibit an enhanced pion yield at low p_t
compared to what is expected for a purely thermal spectral shape. This
enhancement is used to determine the Delta-resonance abundance at freeze-out.
The results are consistent with a direct measurement of the Delta-resonance
yield by reconstruction of proton-pion pairs and imply a temperature of the
system at freeze-out close to 140 MeV.Comment: 12 pages + 4 figures (uuencoded at end-of-file
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