Conductivity in a symmetry broken phase: Spinless fermions with 1/d1/d corrections

The dynamic conductivity $\sigma(\omega)$ of strongly correlated electrons in a symmetry broken phase is investigated in the present work. The model considered consists of spinless fermions with repulsive interaction on a simple cubic lattice. The investigated symmetry broken phase is the charge density wave (CDW) with wave vector $Q=(\pi,\pi,\pi)^\dagger$ which occurs at half-filling. The calculations are based on the high dimensional approach, i.e. an expansion in the inverse dimension $1/d$ is used. The finite dimensionality is accounted for by the inclusion of linear terms in $1/d$ and the true finite dimensional DOS. Special care is paid to the setup of a conserving approximation in the sense of Baym/Kadanoff without inconsistencies. The resulting Bethe-Salpeter equation is solved for the dynamic conductivity in the non symmetry broken and in the symmetry broken phase (AB-CDW). The dc-conductivity is reduced drastically in the CDW. Yet it does not vanish in the limit $T \to 0$ due to a subtle cancellation of diverging mobility and vanishing DOS. In the dynamic conductivity $\sigma(\omega)$ the energy gap induced by the symmetry breaking is clearly discernible. In addition, the vertex corrections of order $1/d$ lead to an excitonic resonance lying within the gap.Comment: 23 pages, 19 figures included with psfig, Revtex; Physical Review B15, in press (October/November 1996) depending on the printer/screen driver, it might be necessary to comment out figures 3,4,5,10,11,12,19 and have them printed separatel

Self-propelled particles with fluctuating speed and direction of motion

We study general aspects of active motion with fluctuations in the speed and the direction of motion in two dimensions. We consider the case in which fluctuations in the speed are not correlated to fluctuations in the direction of motion, and assume that both processes can be described by independent characteristic time-scales. We show the occurrence of a complex transient that can exhibit a series of alternating regimes of motion, for two different angular dynamics which correspond to persistent and directed random walks. We also show additive corrections to the diffusion coefficient. The characteristic time-scales are also exposed in the velocity autocorrelation, which is a sum of exponential forms.Comment: to appear in Phys. Rev. Let

Finite-temperature properties of the two-orbital Anderson model

The metallic phase of the two-orbital Anderson lattice is study in the limit of infinite spatial dimensions, where a second order perturbation treatment is used to solve the single-site problem. Using this approximation, in the Kondo regime, we find that the finite temperature properties of the conduction electrons exhibit the same behaviour as observed in the metallic phase of the two-channel Kondo lattice. Possible connections between these two models are discussed.Comment: 4 pages, 2 figures, to appear in Journal of Physics: Condensed Matte

Study of the 12C+12C fusion reactions near the Gamow energy

The fusion reactions 12C(12C,a)20Ne and 12C(12C,p)23Na have been studied from E = 2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultra-low hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new resonances at E <= 3.0 MeV, in particular a strong resonance at E = 2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present non-resonant reaction rate of the alpha channel by a factor of 5 near T = 8x10^8 K. Due to the resonance structure, extrapolation to the Gamow energy E_G = 1.5 MeV is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full E_G energy range.Comment: 4 Pages, 4 figures, accepted for publication in Phys. Rev. Let

Goals Gone Wild: The Systematic Side Effects of Overprescribing Goal Setting

Goal setting is one of the most replicated and influential paradigms in the management literature. Hundreds of studies conducted in numerous countries and contexts have consistently demonstrated that setting specific, challenging goals can powerfully drive behavior and boost performance. Advocates of goal setting have had a substantial impact on research, management education, and management practice. In this article, we argue that the beneficial effects of goal setting have been overstated and that systematic harm caused by goal setting has been largely ignored. We identify specific side effects associated with goal setting, including a narrow focus that neglects nongoal areas, distorted risk preferences, a rise in unethical behavior, inhibited learning, corrosion of organizational culture, and reduced intrinsic motivation. Rather than dispensing goal setting as a benign, over-the-counter treatment for motivation, managers and scholars need to conceptualize goal setting as a prescription-strength medication that requires careful dosing, consideration of harmful side effects, and close supervision. We offer a warning label to accompany the practice of setting goals

On Good Scholarship, Goal Setting, and Scholars Gone Wild

In this article, we define good scholarship, highlight our points of disagreement with Locke and Latham (2009), and call for further academic research to examine the full range of goal setting\u27s effects. We reiterate our original claim that goal setting, like a potent medication, can produce both beneficial effects and systematic, negative outcomes (Ordóñez, Schweitzer, Galinsky,& Bazerman, 2009), and as a result, it should be carefully prescribed and closely monitored

Metacognitive approaches to the treatment of psychosis: a comparison of four approaches

In light of increasing interest in metacognition and its role in recovery from psychosis, a range of new treatments focused on addressing metacognitive deficits have emerged. These include Metacognitive Therapy, Metacognitive Training, metacognitive insight and reflection therapy, and metacognitive interpersonal therapy for psychosis. While each of these treatments uses the term metacognitive, each differs in terms of their epistemological underpinnings, their structure, format, presumed mechanisms of action, and primary outcomes. To clarify how these treatments converge and diverge, we first offer a brief history of metacognition as well as its potential role in an individual's response to and recovery from complicated mental health conditions including psychosis. We then review the background, practices, and supporting evidence for each treatment. Finally, we will offer a framework for thinking about how each of these approaches may ultimately complement rather than contradict one another and highlight areas for development. We suggest first that each is concerned with something beyond what people with psychosis think about themselves and their lives. Each of these four approaches is interested in how patients with severe mental illness think about themselves. Each looks at immediate reactions and ideas that frame the meaning of thoughts. Second, each of these approaches is more concerned with why people make dysfunctional decisions and take maladaptive actions rather than what comprised those decisions and actions. Third, despite their differences, each of these treatments is true to the larger construct of metacognition and is focused on person's relationships to their mental experiences, promoting various forms of self-understanding which allow for better self-management. Each can be distinguished from other cognitive and skills-based approaches to the treatment of psychosis in their emphasis on sense-making rather than learning a new specific thing to say, think, or do in a given situation

Schizophrenia and the progression of emotional expression in relation to others

Gaining an improved understanding of people diagnosed with schizophrenia has the potential to influence priorities for therapy. Psychosis is commonly understood through the perspective of the medical model. However, the experience of social context surrounding psychosis is not well understood. In this research project we used a phenomenological methodology with a longitudinal design to interview 7 participants across a 12-month period to understand the social experiences surrounding psychosis. Eleven themes were explicated and divided into two phases of the illness experience: (a) transition into emotional shutdown included the experiences of not being acknowledged, relational confusion, not being expressive, detachment, reliving the past, and having no sense of direction; and (b) recovery from emotional shutdown included the experiences of being acknowledged, expression, resolution, independence, and a sense of direction. The experiential themes provide clinicians with new insights to better assess vulnerability, and have the potential to inform goals for therapy

Levitation of the quantum Hall extended states in the B→B\to 0 limit

We investigate the fate of the quantum Hall extended states within a continuum model with spatially correlated disorder potentials. The model can be projected onto a couple of the lowest Landau bands. Levitation of the $n=0$ critical states is observed if at least the two lowest Landau bands are considered. The dependence on the magnetic length $l_B=(\hbar/(eB))^{1/2}$ and on the correlation length of the disorder potential $\eta$ is combined into a single dimensionless parameter $\hat\eta=\eta/l_B$. This enables us to study the behavior of the critical states for vanishing magnetic field. In the two Landau band limit, we find a disorder dependent saturation of the critical states' levitation which is in contrast to earlier propositions, but in accord with some experiments.Comment: 7 pages, 9 figures. Replaced with published versio