Strong Correlations Produce the Curie-Weiss Phase of Nax_{x}CoO2_2

Within the t-J model we study several experimentally accessible properties of the 2D-triangular lattice system Na$_x$CoO$_2$, using a numerically exact canonical ensemble study of 12 to 18 site triangular toroidal clusters as well as the icosahedron. Focusing on the doping regime of $x\sim0.7$, we study the temperature dependent chemical potential, specific heat, magnetic susceptibility and the dynamic Hall coefficient $R_H(T,\omega)$ as well as the magnetic field dependent thermopower. We find a crossover between two phases near $x \sim 0.75$ in susceptibility and field suppression of the thermopower arising from strong correlations. An interesting connection is found between the temperature dependence of the diamagnetic susceptibility and the Hall-coefficient. We predict a large thermopower enhancement, arising from {\em transport corrections} to the Heikes-Mott formula, in a model situation where the sign of hopping is reversed from that applicable to Na$_x$CoO$_2$.Comment: 5 pages, 4 figure

A South African review of harmonic emission level assessment as per IEC61000-3-6

Large-scale renewable power producing plants are being integrated into South African networks. Network operators need to ensure that Renewable Power Plants (RPP) do not negatively affect the power quality levels of their networks, as harmonics amongst others could become a concern. IEC 61000-3-6 details a method for allocating voltage harmonic emission limits for distorting loads. This method works well for the allocation of emission limits; however it does not address the management of harmonic emissions once a plant is connected to the network. The management of harmonic emissions requires that network operators measure or quantify the emissions from loads and generators to determine compliance. Post-connection quantification of harmonic levels and compliance is a challenge for network operators. The question asked is “How should a network operator measure/quantify the harmonic emissions of a load/generator to establish compliance with the calculated limits as per IEC 61000-3-6”. This paper reviews within a South African context methods of assessing harmonic emission levels and then evaluates these methods by means of field data. Opportunities for improvement are identified and operational requirements discussed

Using the Transtheoretical Model in Primary Care Weight management: Tipping the Decisional Balance Scale for Exercise

Changing or modifying a behavior that is addictive or potentially harmful is difficult for most people. The Transtheoretical Model (TM) (Prochaska, Norcross, & DiClemente, 1994) incorporates a compilation of previous theories, providing a framework for the stages of progression when deciding to change a problematic behavior. The stages include: Precontemplation, Contemplation, Preparation, Action, Maintenance, and Termination. Other constructs of the model, some adapted from previous models, include the Decisional Balance (Janis & Mann, 1977), Self-efficacy (Bandura, 1977) and the Processes of Change (Prochaska, Norcross, & DiClemente, 1994, Velicer, Prochaska, Fava, Norman, & Redding, 1998). Traditionally, examining the stages of change was in the domain of psychology; more recently it has been adapted for use in the primary care arena for various chronic conditions (Boudreaux, et al.,2003, Jimmy & Martin, 2005) as well as the basis for new models in primary care (Katz, 2001). One such chronic condition, leading to other co-morbidities and a factor in early death (LaViest, 2005), is overweight and/or obesity which leads to the challenge of weight management. Overweight patients desire direction with weight management issues (Potter, Vu, & Croughan-Minihane, 2001) yet primary care providers often express an inability to assist with meaningful treatment options other than eat less and move more (Bardia, Holton, Slezsak, & Thompson, 2007). The utility of the TM makes it well suited for use when tailoring healthy lifestyle information for patients during brief visits in primary care. Nurse Practitioners (NP) are trained to coach, teach, and support patients (Hayes & Kalmakis, 2007). Using the TM as a basis to determine the patient’s readiness to change and the construct of Decisional Balance, NPs, through coaching strategies, can be available to assist patients with behavior change

Managerialism and the care of older people: The Swedish example

In his dissertation Blomberg (2004) investigates into how the care manager reform is incorporated into organizational practice in the care of older people in Sweden. He shows that it is made through different lines of argumentations following one another. Through applying neo-institutional theory this can be understood as “solutions seeking problems to solve” rather than the other way around. In this paper we develop the idea that these findings can be associated with a broader development, i.e. globalization and modernization, which both pressure for reform along lines condensed in the reform agenda of New Public Management (NPM). NPM can be seen as part of globalization. Neo-liberals take up the NPM-agenda off-hand through emphasizing that the role of politics should be restricted. Their arguments are underpinned by neo-classical economics favouring market provision. The arguments in favour of change are centred on individualization and privatization. Modernization was originally brought forward through third way politics practiced by New Labour in Britain. Arguments are centred on opportunity and accountability (Le Grand 1998). It shows a resemblance with arguments filtered through NPM, though stressing elements creating a modernized society. Conclusion: While neo- liberalism uses ideology to shape practice, third way social democracy is letting administrative reform de-ideologize policy. The result is, that through two different lines, the two opposing major political forces in Europe end up with almost the same agenda for reform. Petersson (2006) has argued that taken together this forms a new logic of the welfare state, i.e. the substitution of a moral welfare state for an administrative one centred on managerialism

Maximal Cohen–Macaulay Modules and Gorenstein Algebras

AbstractLet B be a graded Cohen–Macaulay quotient of a Gorenstein ring, R. It is known that sections of the dual of the canonical module, KB, can be used to construct Gorenstein quotients of R. The purpose of this paper is to place this method of construction into a broader context. If M is a maximal Cohen–Macaulay B-module whose sheafified top exterior power is a twist of K̃B and if M satisfies certain additional homological conditions then regular sections of M* can again be used to construct Gorenstein quotients of R. On Cohen–Macaulay quotients, the normal module, the first Koszul homology module and several other associated modules all have sheafified top exterior power equal to a twist of K̃B. If additional restrictions are placed on the Cohen–Macaulay quotients then these modules will satisfy the required additional homological conditions. This places the canonical module within a broad family of easily manipulated maximal Cohen–Macaulay modules whose sections can be used to construct Gorenstein quotients of R

Towards early ice detection on wind turbine blades using acoustic waves

The study focuses on the early detection of ice using controlled acoustic waves propagating in the wind turbine blades. An experimental set-up with a cold climate chamber, a composite test object used in turbine blades and equipment for glaze and rime ice production has been developed. Controlled acoustic waves are generated by magnetostrictive Terfenol-D based actuator. The propagation of three orthogonally polarized acoustic waves was studied by means of 6 accelerometers positioned, 3 each, in 2 holders on the 8 m long composite test object. The results show that for the considered composite test object the formation of ice, the ice mass, icing areas and the temperature have a significant influence on controlled acoustic waves propagation w.r.t. Fourier transform, amplitude attenuation and RMS values as indicators concluding that the proposed acoustic wave technique is a promising approach for ice detection

Community Projects and the University Curriculum: Re-searching for a Civil Rights History Through Community Photographs

The following articles represent a collaborative process, as does the project that we will discuss. It is not within the scope of these articles to engage in an in depth examination of community photography. This practice and its relationship to high art, cultural production and representation has been the topic of other very interesting investigations. We will instead focus on a possible relationship between community photography and the higher education curriculum, wherein each project facilitates the other. The first article represents my view of the pedagogical foundations of this relationship as the instructor and a participant in this process. The second article will speak from a student/participant\u27s perspective, about the actual process and results of this particular class project

Chrysocolla flotation by the formation of insoluble surface chelates

Journal ArticlePure chrysocolla is floated with chelating agents that form insoluble complexes with copper at ambient temperature. Complete flotation is obtained with potassium octyl hydroxamate as collector at pH 6. Flotation response is enhanced with increased temperature when low additions of h ydroxamate are involved. A natural ore was floated with 0.4 lb per ton octyl hydroxamate at pH 6.5 and 58OC, and a flotation recovery of 76% was obtained with a concentrate grade of 31.6% copper

Finite temperature properties of the triangular lattice t-J model, applications to Nax_xCoO2_2

We present a finite temperature ($T$) study of the t-J model on the two-dimensional triangular lattice for the negative hopping $t$, as relevant for the electron-doped Na$_x$CoO$_2$ (NCO). To understand several aspects of this system, we study the $T$-dependent chemical potential, specific heat, magnetic susceptibility, and the dynamic Hall-coefficient across the entire doping range. We show systematically, how this simplest model for strongly correlated electrons describes a crossover as function of doping ($x$) from a Pauli-like weakly spin-correlated metal close to the band-limit (density $n=2$) to the Curie-Weiss metallic phase ($1.5<n<1.75$) with pronounced anti-ferromagnetic (AFM) correlations at low temperatures and Curie-Weiss type behavior in the high-temperature regime. Upon further reduction of the doping, a new energy scale, dominated by spin-interactions ($J$) emerges (apparent both in specific heat and susceptibility) and we identify an effective interaction $J_{eff}(x)$, valid across the entire doping range. This is distinct from Anderson's formula, as we choose here $t<0$, hence the opposite sign of the usual Nagaoka-ferromagnetic situation. This expression includes the subtle effect of weak kinetic AFM - as encountered in the infinitely correlated situation ($U=\infty$). By explicit computation of the Kubo-formulae, we address the question of practical relevance of the high-frequency expression for the Hall coefficient $R_H^*$. We hope to clarify some open questions concerning the applicability of the t-J model to real experimental situations through this study