Stripes, Pseudogaps, and Van Hove Nesting in the Three-band tJ Model

Slave boson calculations have been carried out in the three-band tJ model for the high-T_c cuprates, with the inclusion of coupling to oxygen breathing mode phonons. Phonon-induced Van Hove nesting leads to a phase separation between a hole-doped domain and a (magnetic) domain near half filling, with long-range Coulomb forces limiting the separation to a nanoscopic scale. Strong correlation effects pin the Fermi level close to, but not precisely at the Van Hove singularity (VHS), which can enhance the tendency to phase separation. The resulting dispersions have been calculated, both in the uniform phases and in the phase separated regime. In the latter case, distinctly different dispersions are found for large, random domains and for regular (static) striped arrays, and a hypothetical form is presented for dynamic striped arrays. The doping dependence of the latter is found to provide an excellent description of photoemission and thermodynamic experiments on pseudogap formation in underdoped cuprates. In particular, the multiplicity of observed gaps is explained as a combination of flux phase plus charge density wave (CDW) gaps along with a superconducting gap. The largest gap is associated with VHS nesting. The apparent smooth evolution of this gap with doping masks a crossover from CDW-like effects near optimal doping to magnetic effects (flux phase) near half filling. A crossover from large Fermi surface to hole pockets with increased underdoping is found. In the weakly overdoped regime, the CDW undergoes a quantum phase transition ($T_{CDW}\to 0$), which could be obscured by phase separation.Comment: 15 pages, Latex, 18 PS figures Corrects a sign error: major changes, esp. in Sect. 3, Figs 1-4,6 replace

Neutron probe calibration correction by temporal stability parameters of soil water content probability distribution Correção da calibração de sondas de nêutrons por meio de parâmetros de estabilidade temporal da distribuição de probabilidade do conteúdo de água no solo

A neutron probe calibration correction is proposed in order to reduce soil water content variability, assumed to be a consequence of improper calibrations relations. The time stability of spatially measured soil water content data is used to correct the intercepts of linear calibration relations. This procedure reduced the coefficients of variation of soil water content data from 4 to less than 2% in a Rhodic Kanhapludalf.<br>É proposta uma correção para a calibração de sondas de nêutrons para reduzir a variabilidade de dados do conteúdo de água no solo, suposta como conseqüência de relações de calibração impróprias. A estabilidade temporal de dados espaciais de conteúdo de água no solo é usada para corrigir os coeficientes lineares de curvas de calibração. Esse procedimento reduziu coeficientes de variação de medidas de umidade do solo de 4 para valores menores que 2% em uma Terra Roxa Estruturada

Software process in practice: a grounded theory of the Irish software industry

This paper presents the results of a Grounded Theory study of how software process and software process improvement (SPI) is applied in the practice of software development. This study described in this paper focused on what is actually happening in practice in the software industry. Using the indigenous Irish software product industry as a test-bed, we examine the approaches used to develop software by companies at various stages of growth. The study used the grounded theory methodology and the results produce a picture of software process usage, with the outcome being a theory, grounded in the field data, that explains how software processes are formed and evolve, and when and why SPI is undertaken. The grounded theory is based on two conceptual themes, Process Formation and Process Evolution, and one core theoretical category, Cost of Process. Our research found that SPI programmes are implemented reactively and that many software managers reject SPI because of the associated implementation and maintenance costs and are reluctant to implement SPI models such as ISO 9000 and CMMI