Monte Carlo study of the critical temperature for the planar rotator model with nonmagnetic impurities

We performed Monte Carlo simulations to calculate the Berezinskii-Kosterlitz-Thouless (BKT) temperature $T_{BKT}$ for the two-dimensional planar rotator model in the presence of nonmagnetic impurity concentration $(\rho)$. As expected, our calculation shows that the BKT temperature decreases as the spin vacancies increase. There is a critical dilution $\rho_c \approx 0.3$ at which $T_{BKT} =0$. The effective interaction between a vortex-antivortex pair and a static nonmagnetic impurity is studied analytically. A simple phenomenological argument based on the pair-impurity interaction is proposed to justify the simulations.Comment: 5 pages, 5 figures, Revetex fil

The evaluation of student-centredness of teaching and learning: a new mixed-methods approach.

OBJECTIVE: The aim of the study was to develop and consider the usefulness of a new mixed-methods approach to evaluate the student-centredness of teaching and learning on undergraduate medical courses. An essential paradigm for the evaluation was the coherence between how teachers conceptualise their practice (espoused theories) and their actual practice (theories-in-use). METHODS: The context was a module within an integrated basic sciences course in an undergraduate medical degree programme. The programme had an explicit intention of providing a student-centred curriculum. A content analysis framework based on Weimer's dimensions of student-centred teaching was used to analyze data collected from individual interviews with seven teachers to identify espoused theories and 34h of classroom observations and one student focus group to identify theories-in-use. The interviewees were identified by purposeful sampling. The findings from the three methods were triangulated to evaluate the student-centredness of teaching and learning on the course. RESULTS: Different, but complementary, perspectives of the student-centredness of teaching and learning were identified by each method. The triangulation of the findings revealed coherence between the teachers' espoused theories and theories-in-use. CONCLUSIONS: A mixed-methods approach that combined classroom observations with interviews from a purposeful sample of teachers and students offered a useful evaluation of the extent of student-centredness of teaching and learning of this basic science course. Our case study suggests that this new approach is applicable to other courses in medical education

Analysis of pancreas histological images for glucose intolerance identificationusing ImageJ-preliminary results

The observation in microscopy of histological sections allows us to evaluate structural differences, in pancreatic cells, between rats with normal glucose tolerance and with glucose intolerance (pre-diabetic) situation. Nevertheless, this pre-diabetic condition implies subtle changes in islets of Langerhans structure. This and the normal variability among sampled cells makes difficult the task of identifying glucose intolerance (pre-diabetic situation) with a low level of error. This paper presents preliminary results in the processing of histological pancreas images with the goal of identifying pre-diabetic situation in Wistar rats. The immediate goal of this work is to evaluate the performance of a classifier based in a morphometric measurement of the histological images and to assess the potential for image based automatic processing and classification. A set of 90 images, were used (58 from rats with normal glucose tolerance, and 32 from pre-diabetic ones). These images were segmented manually using ImageJ. This segmentation and area measurements have been speedup by the application of ImageJ macros which were defined for this purpose. The ratio, between the area of -cells and the islets of Langerhans , was used has the indicator of the prediabetic situation. Considering this feature, a receiver operating characteristic analysis has been performed. True positive rate, vs. false positive rate shows the predicted performance of a binary classifier as its discrimination threshold is varied

Influence of taste sensitivity in diet choices and obesity among children.

Introduction: The prevalence of childhood overweight and obesity in Portugal is about 35% (Rito et al., 2012). Lifestyle and dietary habits are important risk factors for weight gain. Food choice and acceptance greatly relies on food perception. The evaluation of taste sensitivity in children and its relation to dietary choices and Body Mass Index (BMI) will be important in a context of obesity prevention. Nonetheless, methodologies for accessing taste sensitivity in children needs to be optimized and adjusted and in Portugal there is not an established protocol. Objectives: To test and optimize a protocol for sweet and bitter taste sensitivity, in Portuguese children, adapted from a protocol already used in German children (Knof et al., 2011). Methods: 20 children, 12 boys and 8 girls, with ages between 8 and 10 years old, were presented with 5 concentrations of sweet (3 – 16 g/L sucrose) and 5 concentrations of bitter taste solutions (0,05 – 0,25 g/L caffeine) and asked for selected the ones perceived as different from water. Results: Test conditions, both the type of presentation and time of tests, resulted for children with the ages tested. For sweet taste, the number and range of concentrations from test solutions appeared to be adequate in the age group between 8 and 10 years. For bitter taste in 80% of children the answers were not consensual with the range of concentrations. Conclusions: The results from the present work suggest that the concentrations used for access bitter taste sensitivity in children from other countries are not sensed by Portuguese children, showing the importance of adjusting adequate concentrations according to sociocultural habits. This may be possible being due to the complex pathway for bitter taste transduction

Evaluation of high-concentrate diets that vary in physically effective neutral detergent fibre for finishing lambs

The objective of this research was to evaluate lamb diets with a high proportion of concentrate and various levels of physically effective neutral detergent fibre (NDF) using tropical ingredients. Four diets were formulated: D1 with 16.5% physically effective NDF (peNDF), D2 with 21.4% peNDF, D3 with 23.3% peNDF, and D4 with 24.6% peNDF. Twenty male Santa Inês lambs at four months old with an average liveweight (LW) of 18.6 ± 3.4 kg were fed for 49 days. There were no differences (P >0.05) among the diets in dry matter (DM) intake. Crude protein (CP) intake, relative to either LW or metabolic live weight (LW0.75) or LW, was greater (P ≤0.05) for D2 and D3 than for D1 or D4. Lower (P ≤0.05) NDF intake, relative to LW0.75 or LW, was lower for D1 than for the other diets. Selection indexes (SIs) were similar (P >0.05) among diets. Animals that consumed D1 had less (P ≤0.05) rumination time per bolus. Meaningful variations were not observed in performance and efficiency of finishing lambs that were related to differences in peNDF among the diets. Santa Inês lambs were able to adapt to diets with low levels of peNDF by increasing rumination time as a consequence of increased fibre consumption and greater particle size selection

Vortex behavior near a spin vacancy in 2D XY-magnets

The dynamical behavior of anisotropic two dimensional Heisenberg models is still a matter of controversy. The existence of a central peak at all temperatures and a rich structure of magnon peaks are not yet understood. It seems that the central peaks are related, in some way, to structures like vortices. In order to contribute to the discussion of the dynamical behavior of the model we use Monte Carlo and spin dynamics simulations as well analytical calculations to study the behavior of vortices in the presence of nonmagnetic impurities. Our simulations show that vortices are attracted and trapped by the impurities. Using this result we show that if we suppose that vortices are not very much disturbed by the presence of the impurities, then they work as an attractive potential to the vortices explaining the observed behavior in our simulations.Comment: 4 pages, 6 figure

Adubação não radicular com duas fontes de zinco em Coffea arábica L. "mundo novo" (B.Rodr.) Choussy

A trial was carried out on an eight old coffee plantation with visible zinc problems. The plantation was situated nearly the city of Jaú (22º30'S, 48º30'W). State of São Paulo, Brazil. The soil is classified as medium texture Oxisol of low base saturation (Latossol Vermelho Amarelo - fase arenosa). The pulverization program started in november 1977, followed in march and July 1978 (heavy harvest) and ended in march and July 1979 (light harvest). Is should be mentioned that a well reconized characteristic of arábica coffe is its habit of biennial bearing, a very heavy harvest is most often followed by a light load the next year. The following treatments and amounts of chemicals per cova hole (4 trees) were tested in accordance with a random block design: 1. 1 g of zinc (zinc sulphate, 0.5%) 2. 3 g of nitrogen (urea, 1.3%) 3. 1 g of zinc + 3 g of nitrogen (zinc sulphate 0.5% + urea 1.3%) 4. 0.25 g, 0.50 g, 1.00 g, 2.00 g of zinc plus 0.75 g, 1.50 g, 3.00 g and 6.00 of nitrogen (correspondent to NZN* 15-0-0-5 as 0.75%, 1-5%, 3.0% and 6.0% by v/v). Foliar absorption data were obtained by collecting the 3rd and 4th pairs of the coffee leaves and analysed them for N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn. The main results may be summarized as follows: 1. The maximum calculated yields of clean coffee were obtained by the applications of 5.84 1 of NZN (1.13%) per hectare. 2. The applications of zinc sulphate (0.5%) and urea (1.3%) together or separate did not affected the coffee bean production. 3. The applications of 15.0 1 of NZN per hectare reduced the coffee yields. 4. Leaf damages and burning symptoms were observed by the applications of urea (1.3%) plus zinc sulphate (0.5%) and larger doses than 7.5 1 of NZN per hectare. 5. Leaf tissue analysis show that the concentrations of the elements were affecred by the age of the leaves and by the yields of the coffee trees. 6. The applications of increasing doses of NZN causes an increase in the concentration of zinc, manganese and boron in the leaves and decreased the concentration in calcium and potassium the leaves. 7. The concentration of zinc in the leaves associated with the heavy harvest, in July, was 70.0 ppm.Em cafezal com 8 anos de idade, com deficiência visível de zinco, situado em um Latossol Amarelo - fase arenosa, do município de Jaú, SP, procederam-se pulverizações em novembro, março e julho de 1978 (grande safra) e março e julho de 1979 (pequena safra), O delineamento experimental foi de blocos ao acaso e constou dos seguintes tratamentos, nas doses por planta: lg de zinco (sulfato de zinco 0,5%), 3g de nitrogênio (uréia 1,3%), lg de zinco + 3g de nitrogênio (sulfato de zinco 0,5% + uréia 1,3%) e 0,25g, 0,50g, 1 ,00g e 2,00g de zinco juntamente com 0,75g, l,50g, 3,00g e 6,00g de nitrogênio (respectivamente NZN 15-0-0-5 * a 0,75%, 3,00% e 6,00% v/v). Na época das pulverizaçoes foram coletadas amostras de 3º e 4º pares de folhas, e determinados os teores de nitrogênio, fósforo, potássio, cálcio, magnésio, boro, cobre, ferro, manganês e zinco. Os resultados mostraram que: a) a produção máxima calculada de café beneficiado foi 3-009,4 kg/ha, obtida com pulverizaçao de 5,84 1 de NZN por hectare (NZN 1 ,17%) ; b) o sulfato de zinco e a uréia, juntos ou isoladamente, não afetaram a produção; c) a dose de 15,0 1 de NZN por hectare diminuiu a produção; d) as aplicações de uréia (1,3%) + sulfato de zinco (0,5%) e de doses de NZN superiores a 7,51/ha provocaram injúrias visíveis nas folhas. Esse efeitos se agravaram com dosagens de 15 1 e 30 1 de NZN por hectare; e) as concentrações dos nutrientes nas folhas foram afetadas de maneira diferente pelas épocas de amostragem e pela produção do cafeeiro; f) a aplicação de doses crescentes de NZN provocou aumento nas concentrações de zinco, manganês e boro e diminuição nas de cálcio e potássio nas folhas, em determinadas épocas da grande ou pequena safra; g) a concentração de zinco em julho, relacionada com a maior produção do cafeeiro, foi 70 ppm

A kinetic approach to homogeneous Ziegler type polymerization. Transient state

In this paper we present a kinetic approach to the analysis of transient-state homogeneous Ziegler-Natta polymerization activity data. The main features of the experimental data are discussed and fitted to transient kinetic models.info:eu-repo/semantics/publishedVersio

Homogeneous Ziegler-Natta polymerisation: A kinetic approach .2. Transient-state kinetics

An integrated view is presented of several possible mechanisms applicable to the interpretation of homogeneous Ziegler-Natta polymerisation. In this paper, the transient aspects related to the kinetics of Ziegler-Natta polymerisation are investigated. Extensive data are used to construct kinetic profiles (rM vs. t) from a theoretical approach. Special attention is given to the duration of the transient period as a function of the different kinetic parameters. The kinetic models developed are fitted to experimental data, either directly obtained by the authors or published in the literature. These general models have a broad range of application.info:eu-repo/semantics/publishedVersio

On Phase Transition and Vortex Stability in the Generalized XY Models

We study a recent generalization proposed for the XY model in two and three dimensions. Using both, the continuum limit and discrete lattice, we obtained the vortex configuration and shown that out-of-plane vortex solutions are deeply jeopardized whenever the parameter of generalization, $L$, is increased. The critical temperature for such models is calculated using the self consistent harmonic approximation. In both, two- and three-dimensional cases, such a temperature decreases with raising $L$. Our results are also compared with other approximated methods available in the literature.Comment: 7 pages, 1 figur