Effect of grain refinement on enhancing critical current density and upper critical field in undoped MgB2 ex-situ tapes

Ex-situ Powder-In-Tube MgB2 tapes prepared with ball-milled, undoped powders showed a strong enhancement of the irreversibility field H*, the upper critical field Hc2 and the critical current density Jc(H) together with the suppression of the anisotropy of all of these quantities. Jc reached 104 A/cm2 at 4.2 K and 10 T, with an irreversibility field of about 14 T at 4.2 K, and Hc2 of 9 T at 25 K, high values for not-doped MgB2. The enhanced Jc and H* values are associated with significant grain refinement produced by milling of the MgB2 powder, which enhances grain boundary pinning, although at the same time also reducing the connectivity from about 12% to 8%. Although enhanced pinning and diminished connectivity are in opposition, the overall influence of ball milling on Jc is positive because the increased density of grains with a size comparable with the mean free path produces strong electron scattering that substantially increases Hc2, especially Hc2 perpendicular to the Mg and B planes.Comment: 26 pages, 9 figures, submitted to J. Appl. Phy

Aumento da resistência mecanica a penetração em função da perda natural de umidade no solo.

Nosso objetivo foi verificar a variação de umidade e sua interferência sobre a resistência mecânica a penetração em um latossolo amarelo disrófico (Lad) sobre relevo plano em área de pastagem, sob condições de clima Amazônico, através de modelo estatísticos de regressão polinomial de 2º grau

Low-field Instabilities in Nb3_{3}Sn Multifilamentary Wires: the Possible Role of Unreacted Nb

We report an experimental study aiming to demonstrate the not negligible role of unreacted Nb on the magnetic instabilities in superconducting Nb$_{3}$Sn multifilamentary wires, observable through partial flux jumps at magnetic field values below 0.5 T. The analysed wires were recently developed for use as dipoles required in future high-energy proton accelerators and are based on powder-in-tube technology. We studied both unreacted (only involving Nb filaments) and reacted wires, finding flux jump instabilities in both cases when performing magnetic measurements. The results can be interpreted on the basis of the critical state model and are coherent with the intrinsic stability criterion

UK Skills and Productivity in an International Context

A nation's prosperity depends largely on its ability to raise the level of its productivity. The education level of its workforce, and how effectively the skills are used in the production processes, are considered important factors in this process. In this report we investigate the extent to which skills have contributed to recent productivity performance in the UK. We do this within a cross-country framework, where we compare the UK's productivity trajectories with those of other close competitors. We quantify the role played by different types of certified skills, both academic and vocational, taking account of the influence of other factors, such as capital investment and technological change. Furthermore, we assess the influence of intangible investments, usually excluded from published data and traditional growth studies. We use a wide range of data sources, and employ growth accounting and panel data econometric techniques. The study begins with a comprehensive review of the literature on the role of human capital in productivity and growth, from both a theoretical and empirical point of view (section 1). We then provide a description of aggregate productivity and employment trends in section 2. Section 3 contains detailed results of the growth accounting decomposition and Section 4 summarises the econometric analysis. Sections 5 and 6 outline the key findings and conclusions emerging from this analysis. The main research questions addressed in this report are: • What have been the main sources of growth in the UK and other major economies since the recession? How have these differed relative to the previous periods? • What is the link between skills and productivity/growth? How have skills contributed to growth over recent years? • What is the contribution of different types of skills to growth? Where does the UK fare better and worse compared to international competitors? • What is the role of training and other intangible assets in explaining productivity and growth outcomes? Do they interact differently with different types of skilled workers

Quantification of aluminium in soil of the Solimões formation, Acre State, Brazil.

The variety of soils in the State of Acre is wide and their chemical profiles are still not fully understood. The nature of the material of origin of these soils is indicated by the high aluminium (Al) content, commonly associated with high calcium (Ca) and magnesium (Mg) contents. The study objective was to use different methods to quantify Al in soils from toposequences formed from material of a sedimentary nature originating from the Solimões Formation, in Acre, Brazil. Trenches were opened at three distinct points in the landscape: shoulder, backslope and footslope positions. Soil samples were collected for physical, chemical, mineralogical analyses. The Al content was quantified using different methods. High Al contents were found in most of these horizons, associated with high Ca and Mg levels, representing the predominant cations in the sum of exchangeable bases. The mineralogy indicates that the soils are still in a low weathering phase, with the presence of significant quantities of 2:1 minerals. Similar Al contents were determined by the methods of NaOH titration, xylenol orange spectrometry and inductively coupled plasma optical emission spectrometry. However, no consistent data were obtained by the pyrocatechol violet method. Extraction with KCl overestimated the exchangeable Al content due to its ability to extract the non-exchangeable Al present in the smectite interlayers. It was observed that high Al contents are related to the instability of the hydroxyl-Al smectite interlayers

Frações granulométricas e oxidáveis da matéria orgânica do solo em sucessão floresta - pastagem no Acre.

A conversão de floresta nativa em pastagem provoca mudanças no conteúdo das frações da matéria orgânica do solo (MOS). O objetivo deste trabalho foi avaliar as alterações ocorridas nas frações granulométricas e oxidáveis da MOS em Sucessão Floresta - Pastagem no Acre. Após a derrubada e queima da floresta, implantou-se a pastagem de braquiária. Nas duas áreas foram coletadas amostras de solo nas profundidades de 0-5 e 5-10 cm. Nestas, foram avaliados os conteúdos de carbono orgânico total (COT), carbono orgânico particulado (COp), carbono orgânico associado aos minerais (COam) e carbono das frações oxidáveis (F1, F2, F3 e F4). Verificou-se que, independente da profundidade, os maiores valores de COT, COp e carbono na F1 e F3 foram encontrados na área de floresta. A retirada da vegetação original para a implantação da pastagem diminuiu os teores de COT, COp e na F1, demonstrando a maior fragilidade desses ecossistemas.Edição dos Resumos do VI CBA e II CLAA

Taxonomia de solos desenvolvidos sobre depósitos sedimentares da Formação Solimões no Estado do Acre.

Os solos do Estado do Acre na maioria são formados sobre material de origem com grande influência da orogênese Andina, com elevados teores de Ca2+, Mg2+ e Al3+ concomitantemente, associado às combinações diferenciadas dos valores da CTC, V e m. O objetivo deste trabalho foi caracterizar e classificar os solos de uma topossequência sobre material sedimentar da Formação Solimões, no município de Feijó, Acre. Foram abertas trincheiras em três pontos de uma topossequência: terço superior (P1), terço médio (P2) e terço inferior (P3). Os solos foram analisados quanto a morfologia, granulometria (areia, silte e argila), complexo sortivo (Ca2+, Mg2+, Na+, K+ e Al3+), acidez potencial (H+Al), P assimilável, pH (água e KCl), superfície específica, ataque sulfúrico (óxidos de Fe, Al, Ti e Si), mineralogia (frações areia, silte e argila). Os solos foram classificados segundo o Sistema Brasileiro de Classificação de Solos (SiBCS, 2006) e apresentada uma proposta de classificação considerando as peculiaridades do solos da região. Os solos têm baixo grau de desenvolvimento pedogenético, com minerais da fração argila de alta atividade, além da presença de minerais primários, como feldspatos e plagioclásios, nas frações areia e silte. Os solos foram classificados segundo o SiBCS atual como Argissolo Vermelho Álitico plíntico (P1), Argissolo Acinzentado Distrófico plíntico (P2) e Cambissolo Háplico Ta Eutrófico típico (P3)

Alterations in vascular function in primary aldosteronism - a cardiovascular magnetic resonance imaging study

Introduction: Excess aldosterone is associated with increased cardiovascular risk. Aldosterone has a permissive effect on vascular fibrosis. Cardiovascular magnetic resonance imaging (CMR) allows study of vascular function by measuring aortic distensibility. We compared aortic distensibility in primary aldosteronism (PA), essential hypertension (EH) and normal controls and explored the relationship between aortic distensibility and pulse wave velocity (PWV).<p></p> Methods: We studied PA (n=14) and EH (n=33) subjects and age-matched healthy controls (n=17) with CMR, including measurement of aortic distensibility, and measured PWV using applanation tonometry. At recruitment, PA and EH patients had similar blood pressure and left ventricular mass.<p></p> Results: Subjects with PA had significantly lower aortic distensibilty and higher PWV compared to EH and healthy controls. These changes were independent of other factors associated with reduced aortic distensibility, including aging. There was a significant relationship between increasing aortic stiffness and age in keeping with physical and vascular aging. As expected, aortic distensibility and PWV were closely correlated.<p></p> Conclusion: These results demonstrate that PA patients display increased arterial stiffness compared to EH, independent of vascular aging. The implication is that aldosterone invokes functional impairment of arterial function. The long-term implications of arterial stiffening in aldosterone excess require further study.<p></p&gt