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

Untangling Hope and Optimism: Implications for Counselors

Counselors often help clients gain insight that allows them to view the world through a new lens, cope with emotionally painful and complex issues, and change behaviors that are not effective in achieving desired life goals. However, counselors, as well as other mental health professionals, often respond to clients\u27 distress by relying on a medical model of psychopathology to reduce negative symptomology and increase quality of life. Positive psychology emerged as a new approach in the 1980s, focusing on clients’ strengths, rather than deficits, which seems to be more congruent with most counselors\u27 professional identity. Although relationships between positive psychology constructs such as hope, optimism, life satisfaction, and self-esteem have been investigated, questions remain regarding whether empirical evidence supports a distinction between them. More specifically, questions still remain regarding whether hope and optimism are the same fundamental human expression or distinct concepts, each adding unique value to learning more about clients\u27 outlook and worldview