From collinear to vortex magnetic structures in Mn corrals on Pt(111)

We study the magnetic properties of small Mn ring shaped clusters on a Pt(111) surface in the framework of density functional theory. We find that the Mn atoms possess large magnetic moments, of the order of 4uB/atom, and have dominating antiferromagnetic interatomic exchange interactions. A quantum confinement effect within the ring like clusters was found, indicating that even very small clusters can be seen as quantum corrals. The antiferromagnetic exchange couplings lead to collinear magnetic arrangements in simple corrals, as well as complex non-collinear ordering, as vortex-like structures, for the case of corrals with particular geometry where antiferromagnetism becomes frustrated.Comment: Accepted for publication as a Regular Article in Physical Review B (2010

ANALYTICAL SOLUTION OF A 2D TRANSIENT HEAT CONDUCTION PROBLEM USING GREEN´S FUNCTIONS

Through the present work the authors determined the analytical solution of a transient two-dimensional heat conduction problem using Green’s Functions (GF). This method is very useful for solving cases where heat conduction is transient and whose boundary conditions vary with time. Boundary conditions of the problem in question, with rectangular geometry, are of the prescribed temperature type - prescribed flow in the direction x and prescribed flow - prescribed flow in the direction y, implying in the corresponding GF given by GX21Y22. The initial temperature of the space domain is assumed to be different from the prescribed temperature occurring at one of the boundaries along x. The temperature field solution of the two-dimensional problem was determined. The intrinsic verification of this solution was made by comparing the solution of a 1D problem. This was to consider the incident heat fluxes at y = 0 and y = 2b tending to zero, thus making the problem one-dimensional, with corresponding GF given by GX21. When comparing the results obtained in both cases, for a time of t = 1 s, it was seen that the temperature field of both was very similar, which validates the solution obtained for the 2D problem

Análise crítica da reconstrução da raiz da aorta com a preservação da valva aórtica: 11 anos de seguimento

INTRODUCTION: The composite mechanical valve conduit replacement is the standardized operation for aneurysms of the aortic root. The objective of this study is to evaluate the long-term surgical results of aortic valve-preserving procedures to the root reconstruction. METHODS: From 1996 to 2008, 54 consecutive patients underwent two different techniques of valve-sparing aortic root operation (40 Yacoub operations and 14 David operations). Mean age was 48 ± 14 years (range 17 to 74). 36 patients (66.7%) were male and 16 (29.6%) experienced Marfan's syndrome. The mean Euroscore was 4 ± 1.25. The mean follow up time was 4.1 years (from 49 days to 10.9 years). Clinical and echocardiographic parameters were analysed. T-Student paired test, the McNemar Non Parametric test and the Kaplan-Meyer Outcome Curves have been used. RESULTS: The hospital mortality was 5.6% and the average hospitalization time was 9±4 days. One non related late death (2%) was reported. The actuarial survival and freedom from reoperation were respectively 94.4% and 96% within 11 years of follow-up. There were benefits in reduction of functional class (P=0.002; 78% CF I), in reduction of aortic regurgitation (P<0.001; 78% with or without discrete reflux), in reduction of systolic and diastolic diameters, end-sytolic and end-diastolic volumes of left ventricle (respectively P=0.004; P<0.0001; P=0.036 and P<0.001). Two (3.9%) patients required aortic valve replacement due to severe aortic regurgitation during this same period. No thromboembolic, endocarditis or bleeding events were reported during the follow-up. CONCLUSION: The valve-sparing operation for aortic root aneurysms is an effective alternative to the use of a mechanical valve conduit replacement.INTRODUÇÃO: A utilização do tubo valvulado é a operação clássica para a reconstrução da raiz da aorta. O objetivo deste trabalho é avaliar a reconstrução da aorta ascendente com a preservação da valva aórtica. MÉTODOS: Entre 1996 e 2008, 54 pacientes consecutivos (66,7% do sexo masculino), com idade média de 48 ± 14 anos, foram submetidos à reconstrução da aorta ascendente e preservação da valva aórtica (40 remodelamentos e 14 reimplantes). O Euroscore médio foi de 4 ± 1,25 e 29,6% eram portadores de síndrome de Marfan. O tempo médio de seguimento foi de 4,1 anos (49 dias até 10,9 anos). Foram avaliados por parâmetros clínicos e ecocardiográficos. Para a análise dos dados foram utilizados os testes t de Student pareado, o não-paramétrico de McNemar e a curva de sobrevida de Kaplan-Meyer. RESULTADOS: A mortalidade hospitalar foi de 5,6%. O tempo médio de internação foi de 9 ± 4 dias. Houve um óbito tardio não relacionado (2%). A sobrevida e sobrevida livre de reoperação nos 11 anos de seguimento foram respectivamente de 94,4% e 96%. Houve melhora da classe funcional (P=0,002) (78% CF I), redução da insuficiência aórtica (P<0,001) (78% sem ou com refluxo discreto), redução dos diâmetros sistólico e diastólico, dos volumes sistólico final e diastólico final do ventrículo esquerdo, respectivamente P=0,004; P<0,001; P=0,036 e P<0,001. Dois pacientes foram submetidos à troca de valva aórtica (3,9%) com 4 e 10 anos da operação. Não foram observados fenômenos tromboembólicos, hemorrágicos ou endocardite durante o seguimento. CONCLUSÃO: A reconstrução da raiz da aorta com a preservação da valva aórtica é uma alternativa eficaz ao uso do tubo valvulado

Enamel and dentin mineralization in familial hypophosphatemic rickets: a micro-CT study

Objectives: The aim of the present study was to analyse the mineralization pattern of enamel and dentin in patients affected by X-linked hypophosphatemic rickets (XLHR) using micro-CT (µCT), and to associate enamel and dentin mineralization in primary and permanent teeth with tooth position, gender and the presence/absence of this disease. Methods: 19 teeth were collected from 5 individuals from the same family, 1 non-affected by XLHR and 4 affected by XLHR. Gender, age, tooth position (anterior/posterior) and tooth type (deciduous/permanent) were recorded for each patient. Following collection, teeth were placed in 0.1% thymol solution until µCT scan. Projection images were reconstructed and analysed. A plot profile describing the greyscale distance relationship in µCT images was achieved through a line bisecting each tooth in a region with the presence of enamel and dentin. The enamel and dentin mineralization densities were measured and compared. Univariate ANOVA and post hoc Tukey tests were used for all comparisons. Results: Teeth of all affected patients presented dentin with a different mineralization pattern compared with the teeth of healthy patients with dentin defects observed next to the pulp chambers. Highly significant differences were found for gray values between anterior and posterior teeth (p < 0.05), affected and non-affected (p < 0.05), as well as when position and disease status were considered (p < 0.05). Conclusions: In conclusion, the mineralization patterns of dentin differed when comparing teeth from patients with and without FHR, mainly next to pulp chambers where areas with porosity and consequently lower mineral density and dentin defects were found