Quantum magnons of the intermediate phase of half-doped manganite oxides

At half doping, the ground state of three-dimensional manganite perovskite oxides like R$_{1-x}$Ca$_x$MnO$_3$, where R is a trivalent ion such as La, Pr, etc, is still unclear. Many experimental findings agree better with the combined magnetic, charge, and orbital order characteristic of the "intermediate phase", introduced by Efremov et al. in 2004 [Nature Mats. 3, 853]. This phase consists of spin dimers (thus incorporating aspects of the Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine et al. [Phys. Rev. Lett. 89, 097205]), though formed by a pair of parallel Mn spins of different magnitude, in principle (thereby allowing for a degree of Mn charge disproportionation: not necessarily as large as that of Mn$^{3+}$-Mn$^{4+}$ in Goodenough's original CE phase [Phys. Rev. 100, 564 (1955)]). In the intermediate phase, consecutive spin dimers localed along the planar zig-zag chains are oriented at a constant relative angle $\Phi$ between them. Varying Mn-charge disproportionation and $\Phi$, the intermediate phase should allow to continuously interpolate between the two limiting cases of the CE phase and the dimer phase denoted as "orthogonal intermediate $\pi/2-$phase". It is not easy to find a microscopic model able to describe the phenomenological intermediate phase adequately for the spin, charge, and orbital degrees of freedom simultaneously. Here, we study the quantum spin excitations of a planar model of interacting localized spins, which we found can stabilize the intermediate phase classically. We compare the quantum magnons of the intermediate phase with those of the CE and orthogonal $\pi/2$ phases, in the context of recent experimental results.Comment: 5 pages, 8 figures Manuscript accepted 29 April 2013, by IEEE - Transactions on Magnetic

Effects of vertex corrections on diagrammatic approximations applied to the study of transport through a quantum dot

In the present work, we calculate the conductance through a single quantum dot weakly coupled to metallic contacts. We use the spin-1/2 Anderson model to describe the quantum dot, while considering a finite Coulomb repulsion. We solve the interacting system using the non-crossing-approximation (NCA) and the one-crossing approximation (OCA). We obtain the linear response conductance as a function of temperature and energy position of the localized level. From the comparison of both approximations we extract the role of the vertex corrections, which are introduced in the OCA calculations and neglected in the NCA scheme. As a function of the energy position, we observe that the diagrams omitted within NCA are really important for appropriately describing transport phenomena in Kondo systems as well as in the mixed valence regime. On the other hand, as a function of temperature, the corrections introduced by OCA partly recover the universal scaling properties known from numerical approaches such as the Numerical Renormalization Group(NRG).Comment: 5 pages, 5 figure

The moderator role of Gender in the Unified Theory of Acceptance and Use of Technology (UTAUT): A study on users of Electronic Document Management Systems

Venkatesh et al. [1] tried to integrate predictability capabilities from the different existing models of technology acceptance. This produced the Unified Theory of Acceptance and Use of Technology (UTAUT). This comprehensive model resulted in the identification of common aspects. It proposed several constructs with a greater explanatory power and analyzed moderating drivers, such as age, Gender, experience and voluntariness of use. By doing so, UTAUT identifies three major drivers of behavioral intention: performance expectancy, effort expectancy and social influence. On the other hand, facilitating conditions and behavioral intention were identified as determinant factors of actual use [1]. In addition to previous considerations about UTAUT, empirical research has scarcely analyzed the moderating role of Gender [2]. This is why this paper particularly aims to fill this gap. Hofstede [3] describes strength, competitiveness and guidance for material success as social roles linked to male values, whilst modesty, tenderness, sensitivity and concern for the quality of life are values associated with women. With respect to UTAUT, existing studies have shown that performance expectancy positively influences behavioral intention more strongly for men (cf. [4], [5], [6] and [7]). Moreover, it has been observed that effort expectancy positively influences behavioral intention more strongly for women (cf. [4], [5] and [6]), while social influence positively affects behavioral intention more strongly for women (cf. [5], [7] and [8]). In our research, with the aim of testing the moderating effects of Gender, a sample of 2,175 users of Electronic Document Management Systems (EDMS) in Portuguese municipalities was used. Taking into account that Gender is a categorical variable, we have adopted a multi-group or multi-sample analysis [9] -dividing the sample into two groups (male = 748; female = 1,427) and estimating each group of observations separately. Before comparing the groups, an analysis of the measurement invariance was carried out to make sure that the construct measures were invariant between both groups [10]. Once the metric invariance had been assessed, we carried out a set of multi-group analyses –interpreting statistically-significant differences in path coefficients as moderating effects. On the one hand, the parametric approach considering both equal variances and different variances has been used [11, 12]. On the other hand, we have applied non-parametric approaches exemplified by the permutation test [13], and Henseler’s PLS multi-group analysis [10, 12, 14]. This study notes slight differences in the results of the aforementioned methods. As a result, the moderating effect of Gender on the relation between performance expectancy and behavioral intention showed that this relationship is stronger among men than women. Finally, a discussion on the implications of Gender as a moderator for the UTAUT model is included

Determinants of User Acceptance of a Local eGovernment Electronic Document Management System (EDMS)

On numerous occasions the significant value of the investments involved in the development of eGovernment and the expectations of governmental information systems use do not correspond to the rate of effective use. This scenario makes it difficult to justify the development of electronic government by governments and local authorities among its citizens. It is therefore important to understand the factors that influence the employees' intention of using governmental information systems. With the aim of understanding the determining factors of using an Electronic Document Management System (EDMS) in the context of Portuguese municipalities, this study develops an empirical analysis using the Unified Theory of Acceptance and Use of Technology (UTAUT) model, (Venkatesh et al., 2003). This model's application for information systems research in the governmental context has a weak expression and is unique in EDMS research. This empirical research follows a realist and positivist approach. Data was collected from a survey answered by 2,175 employees of Portuguese municipalities (EDMS users). Partial Least Squares (PLS) was used to test the model proposed. The results showed that Intention to Use is positively affected by Performance Expectancy, Effort Expectancy, Social Influence and Facilitating Conditions. With respect to the EDMS Use, the results showed that it is positively influenced by Intention to Use and Facilitating Conditions. The main result indicates that EDMS users believe that the use of this information system will help them to obtain performance benefits in their work. However, the increasing use of EDMS is not very influenced by the system's perceived ease of use. In short, this study provides a contribution to the Information Systems Acceptance and Adoption literature in local eGovernmental contexts. In addition, our contribution empirically tests the model for implementation in governmental organizations and provides a better understanding of the adoption and use of an EDM

Rabbit Nutrition with Tropical Foliage and Sugar Cane.

The behavior of productive indicators was assessed in 45 growing Cuban Brown rabbits (498 g average mean weight), fed with tropical foliage and sugar cane stems. A completely random design was used, with three treatments and 15 repetitions: foliage of  Teramnus labialis+sugar cane stem; foliage of Ipomoea batata+sugar cane stem; and foliage of  Phyla nodiflora+sugar cane stem. The highest consumption of fresh foliage was observed in  Ipomoea ba-tata (269 g) and Teramnus labialis (205 g). Animal variants Phyla nodiflora+sugar cane had a basic consumption of sugar cane (144.87 g). The Teramnus labialis-sugar cane alternative produced the highest consumption levels of raw protein (9.32 g) and digestible energy (0.79 MJ). Live weight gains were observed between 10.46 and 16.96  g/d, and feed conversion between 4.06 and 5.23, similar in both indicators for Teramnus labialis-sugar cane and Ipomoea batata-sugar cane. Live weight gain was extremely low in the Phyla nodiflora-sugar cane variant, with the highest values observed for feed conversion. Teramnus labialis-sugar cane and Ipomoea batata-sugar cane may be used by rab-bit breeders with lands for tropical foliage, and sugar cane in Cuba. The opposite was observed for P hyla nodiflora-sugar cane, which turned out little attractive for rabbit fattening

La renta de la tierra; los precios del suelo y la especulación inmobiliaria en España

Si este país quiere mantenerse en la senda de la “modernización económica” que, después de 1975, se propuso transitar, parece impostergable un cambio en “el modelo económico”,dejando atrás el “imperio del ladrillo” y desarrollando un “modelo” similar a los países más avanzados de Europa. Desde el estudio de los “usos del suelo”, de los buenos o malos usos, nos proponemos investigar hasta qué punto el actual sistema de propiedad del suelo hipoteca la economía (y también la política, la sociedad y la intelectualidad) del país y hasta qué punto esa hipoteca puede entrabar, retrasar, e, incluso, llegar a impedir un cambio del “modelo de crecimiento económico”.Para ello planteamos las relaciones entre la ganancia (capitalista) y la renta del suelo (¿capitalista o semifeudal?), es decir, la apropiación del trabajo impago entre las clases sociales dueñas de los medios de producción, con el objetivo de comenzar a comprender las causas del estancamiento estructural de la economía española, en el que juega un papel fundamental los procesos especulativos ligados a la promoción inmobiliaria.If this country wants to be kept in the way of the “economic modernization” that, after 1975, it proposed to travel, a change seems to be ineluctable in “the economic model”, leaving behind the “empire of the brick” and developing a “model” similar to the Europa’s most advanced countries. From the study of the “land uses”, of the good or bad uses, we propose to investigate up to what point the property system of the land mortgages the economy (and also the politic,the society and the intellectuality) of the country and up to what point this mortgage can impede or be late a change of the “model of economic growth”. For it we raise the relations between the (capitalist) profi t and the land rent (capitalist or semifeudal?), that is to say, the appropriation of the unpaid work between the social classes owners of the means of production, with the aim to begin to understand the reasons of the structural stagnation of the Spanish economy, in which a fundamental paper plays the speculative processes tied to the real-estate promotion

Feeding Rabbits with tropical Foliage, Sugar Cane, and Sunflower Seeds.

The productive behavior of fattening rabbits was assessed using four feeding variants combining tropical foliage (Teramnus labiales,  Hibiscus rosas-sinensis,  Pyla nodiflora  and  Ipomoea batata)  with sugar cane and sunflower seeds. Sixty Cuban Brown rabbits weaned at 40 days of age were used, weighing an average 679 g, after 80 days of fattening. Three animals were placed in each cage, following a completely random design.  Each animal was consid-ered a replica for the following variables: initial  live  weight,  final live weight, and mean daily gain. For feed con-sumption and feed conversion variables, the means of the animals in every cage were considered.  Sugar cane foliage and stems were administered at will. The sunflower seeds were administered at a rate of 25 g/rabbit/day; water was supplied ad libitum. Variants  Teramnus labialis-sugar cane-sunflower, Ipomoea batata-sugar cane-sunflower and Phyla nodiflora-sugar cane-sunflower had the best  y  (100 % viability, live weigh gains between 19.28 and 22.78 g/rabbit/day, and cleaned meat production, between  785  and  972 g,  at a cost of  11.45, 16.94  and  12.52 CUP) for  Teramnus labialis-sugar cane-sunflower,  Ipomoea batata-sugar cane-sunflower and Phyla nodiflora-sugar cane-sunflower, respectively. Variant Hibiscus rosa-sinensis sugar cane-sunflower was the least efficient

How Do Methyl Groups Enhance the Triplet Chemiexcitation Yield of Dioxetane?

Chemiluminescence is the emission of light as a result of a nonadiabatic chemical reaction. The present work is concerned with understanding the yield of chemiluminescence, in particular how it dramatically increases upon methylation of 1,2-dioxetane. Both ground-state and nonadiabatic dynamics (including singlet excited states) of the decomposition reaction of various methyl-substituted dioxetanes have been simulated. Methyl-substitution leads to a significant increase in the dissociation time scale. The rotation around the O-C-C-O dihedral angle is slowed; thus, the molecular system stays longer in the "entropic trap" region. A simple kinetic model is proposed to explain how this leads to a higher chemiluminescence yield. These results have important implications for the design of efficient chemiluminescent systems in medical, environmental, and industrial applications

3D simulations of Einstein's equations: symmetric hyperbolicity, live gauges and dynamic control of the constraints

We present three-dimensional simulations of Einstein equations implementing a symmetric hyperbolic system of equations with dynamical lapse. The numerical implementation makes use of techniques that guarantee linear numerical stability for the associated initial-boundary value problem. The code is first tested with a gauge wave solution, where rather larger amplitudes and for significantly longer times are obtained with respect to other state of the art implementations. Additionally, by minimizing a suitably defined energy for the constraints in terms of free constraint-functions in the formulation one can dynamically single out preferred values of these functions for the problem at hand. We apply the technique to fully three-dimensional simulations of a stationary black hole spacetime with excision of the singularity, considerably extending the lifetime of the simulations.Comment: 21 pages. To appear in PR