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

Concepciones de naturaleza de la ciencia en profesores ciencias de la ciudad de manizales (Colombia)

Se investigaron las concepciones de Naturaleza de la Ciencia de un grupo de 50 profesores de educación básica de la ciudad de Manizales (Colombia). Se siguió un diseño de investigación mixto en el que el análisis cuantitativo no arrojó diferencias significativas entre los diferentes énfasis en cuanto al concepto de naturaleza de la ciencia en los profesores. El análisis cualitativo permitió dar sentidos y significados a la concepciones de os profesores sobre naturaleza de la ciencia

Cannibalism in an Introduced Population of Cyclura nubila nubila on Isla Magueyes, Puerto Rico

In the mid-1960s, Cuban Iguanas (Cyclura nubila nubila) were introduced to Isla Magueyes, a 7.2-ha islet in southwestern Puerto Rico (Rivero 1978). Anecdotal information affirms that this population originated from a single pair of individuals

Seroprevalence of bovine viral diarrhea virus (BVDV) in cattle from Sotaquirá, Colombia

Worldwide distributed Bovine Viral Diarrhea Virus (BVDV) represents a high risk of infection in most bovine farms, in which it is associated with gastrointestinal, respiratory, and reproductive diseases. The purpose of this research was to establish the seroprevalence and the main risk factors associated with the presentation of BVDV in the municipality of Sotaquirá, Colombia. Samples were taken from 1000 cattle of Holstein, Ayrshire, Jersey, Normande Gyr and Holstein x Gyr. Epidemiological surveys were implemented, reproductive and management variables were taken into consideration. Indirect ELISA was performed to detect specific antibodies against BVDV using the commercial kit SERELISA® BVD p80 Ab Mono Blocking. The overall seroprevalence of antibodies against BVDV was 42.5% (425/1000), where the Gyr breed (59.1% apparent prevalence (AP); 60.3% real prevalence (PR)) and the age group > 4 years (53.0% PA; 54.4% PR) presented the highest seroprevalences. A significant statistical association was found for the breed, age, management practices evaluated and the presentation of PI3 (p ≤ 0.05). Age group > 4 years, Normande breed, presentation of PI3 and grazing lease were established as risk factors associated with BVDV in the herds. These infections are mainly associated with dairy cattle and herds with many animals, so it is important to consider vaccination plans as a preventive system and follow up on the most common diseases

Survival, dispersal and reproduction of headstarted Mona Island iguanas, Cyclura cornuta stejnegeri

The endemic Mona Island Iguana, Cyclura cornuta stejnegeri, is considered endangered, and exhibits relatively low population numbers and reduced recruitment of juveniles to adults. A headstarting program was initiated in 1999 to increase the effective population number. Two groups of headstarted iguanas were released in April and August 2002, after reaching a target size. Most of the released iguanas have since been observed to be active and in good health. Two females bred in 2004, the first certain record of reproduction by headstarted Cyclura iguanas in the wild. Eight radiotracked individuals had large dispersal ranges, with mean Minimum Convex Polygon (MCP) of 10.7 ha (range 2.6-22.2 ha) and mean distances covered of 288 m (range 471-6396 m).We discuss the future development of the headstarting program for Mona Island iguanas

Diagnóstico coproparasitológico de fascioliasis en ovinos y caprinos de Boavita, Boyacá (Colombia)

The aim of this study was to establish the prevalence of Fasciola hepatica through coprological analysis and to identify risk factors associated with the presentation of the parasite in sheep and goats in the municipality of Boavita, Boyacá. The study was observational, descriptive, cross-sectional with simple random sampling. Faecal samples were taken from 297 sheep and 337 goats to identify parasite eggs. The general prevalence was 8.0% (51/634), being 9.1% for sheep and 7.1% for goats. The prevalence in sheep was higher in males (14.8%) than in females (8.5%), likewise, sheep less than one year old (9.3%) and Criolla (11.1%) presented the highest prevalence. In goats, the prevalence was higher in females (7.3%) than in males (5.6%), and those less than one year old (10.5%) and the Alpine breed (8%) presented the greater prevalence. No significant statistical association was found between females and males. The Creole breed was established as a risk factor for sheep.El objetivo del estudio fue establecer la prevalencia de Fasciola hepatica mediante análisis coprológico e identificar factores de riesgo asociados a la presentación del parásito en ovinos y caprinos del municipio de Boavita, Boyacá. El estudio fue observacional, descriptivo de corte transversal con muestreo aleatorio simple. Se tomaron muestras de materia fecal a 297 ovinos y 337 caprinos para identificar los huevos del parásito. La prevalencia general fue de 8.0% (51/634), siendo de 9.1% para ovejas y de 7.1% para cabras. La prevalencia en ovinos fue mayor en machos (14.8%) que en hembras (8.5%); asimismo, los ovinos menores a un año (9.3%) y de Criolla (11.1%) presentaron las prevalencias más altas. En las cabras, la prevalencia fue mayor en hembras (7.3%) que en machos (5.6%), y los menores a un año (10.5%) y de la raza Alpina (8%) presentaron las prevalencias más altas. No se encontró asociación estadística significativa entre hembras y machos. La raza Criolla se estableció como factor de riesgo para los ovinos

“ESTANDARIZACION DEL METODO DE CAPTURA DE RADICALES LIBRES PARA LA EVALUACION DE LA ACTIVIDAD ANTIOXIDANTE DE EXTRACTOS VEGETALES”

La evaluación preliminar de la actividad antioxidante en extractos vegetales se realizó mediante el método de captura de radicales libres que utiliza el radical 1,1-difenil-2-picril-hidrazilo (DPPH). Con el fin de determinar las condiciones físicas, químicas y termodinámicas del ensayo fotométrico, se utilizaron los extractos metanólicos de plantas provenientes del Parque Regional Natural Ucumarí (PRNU) y Parque Natural Municipal La Nona (PNMN); extracto estandarizado de GingSeng (obtenido con el nombre comercial de GINGSANA) además de hidroquinona y ácido tánico. Los resultados permitieron establecer las condiciones óptimas las cuales corresponden a: 517 nm (longitud de onda), 30 minutos (tiempo de reacción) y temperatura ambiente (temperatura de reacción); adicionalmente, se indica la baja estabilidad de las soluciones del radical libre usado, hecho que implica inmediata utilización de las misma

“ESTANDARIZACION DEL METODO DE CAPTURA DE RADICALES LIBRES PARA LA EVALUACION DE LA ACTIVIDAD ANTIOXIDANTE DE EXTRACTOS VEGETALES”

La evaluación preliminar de la actividad antioxidante en extractos vegetales se realizó mediante el método de captura de radicales libres que utiliza el radical 1,1-difenil-2-picril-hidrazilo (DPPH). Con el fin de determinar las condiciones físicas, químicas y termodinámicas del ensayo fotométrico, se utilizaron los extractos metanólicos de plantas provenientes del Parque Regional Natural Ucumarí (PRNU) y Parque Natural Municipal La Nona (PNMN); extracto estandarizado de GingSeng (obtenido con el nombre comercial de GINGSANA) además de hidroquinona y ácido tánico. Los resultados permitieron establecer las condiciones óptimas las cuales corresponden a: 517 nm (longitud de onda), 30 minutos (tiempo de reacción) y temperatura ambiente (temperatura de reacción); adicionalmente, se indica la baja estabilidad de las soluciones del radical libre usado, hecho que implica inmediata utilización de las misma