2,507 research outputs found
Lessons learned applying CASE methods/tools to Ada software development projects
This paper describes the lessons learned from introducing CASE methods/tools into organizations and applying them to actual Ada software development projects. This paper will be useful to any organization planning to introduce a software engineering environment (SEE) or evolving an existing one. It contains management level lessons learned, as well as lessons learned in using specific SEE tools/methods. The experiences presented are from Alpha Test projects established under the STARS (Software Technology for Adaptable and Reliable Systems) project. They reflect the front end efforts by those projects to understand the tools/methods, initial experiences in their introduction and use, and later experiences in the use of specific tools/methods and the introduction of new ones
Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system
We study a hole-doped two-leg ladder system including metal ions, oxygen, and
electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}.
Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of
pressure by applying an unrestricted Hartree-Fock approximation to a multiband
Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase
transition between single-polaron and bi-polaron states. The electronic and
phononic excitations in those states, including distinctive local lattice
vibrational modes, are calculated by means of a direct-space Random Phase
approximation. Finally, as a function of pressure, we identify a transition
between site- and bond-centered bi-polarons, accompanied by a soft mode and a
low-energy charge-sliding mode. We suggest comparisons with available
experimented data
Nonmonotonic d_{x^2-y^2} Superconducting Order Parameter in Nd_{2-x}Ce_xCuO_4
Low energy polarized electronic Raman scattering of the electron doped
superconductor Nd_1.85Ce_0.15CuO_4 (T_c=22 K) has revealed a nonmonotonic
d_{x^2-y^2} superconducting order parameter. It has a maximum gap of 4.4 k_BT_c
at Fermi surface intersections with antiferromagnetic Brillouin zone (the ``hot
spots'') and a smaller gap of 3.3 k_BT_c at fermionic Brillouin zone
boundaries. The gap enhancement in the vicinity of the ``hot spots'' emphasizes
role of antiferromagnetic fluctuations and similarity in the origin of
superconductivity for electron- and hole-doped cuprates.Comment: 4 pages, 4 figure
Influence of oxygen ordering kinetics on Raman and optical response in YBa_2Cu_3O_{6.4}
Kinetics of the optical and Raman response in YBa_2Cu_3O_{6.4} were studied
during room temperature annealing following heat treatment. The superconducting
T_c, dc resistivity, and low-energy optical conductivity recover slowly,
implying a long relaxation time for the carrier density. Short relaxation times
are observed for the B_{1g} Raman scattering -- magnetic, continuum, and phonon
-- and the charge transfer band. Monte Carlo simulations suggest that these two
relaxation rates are related to two length scales corresponding to local oxygen
ordering (fast) and long chain and twin formation (slow).Comment: REVTeX, 3 pages + 4 PostScript (compressed) figure
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