Incommensurate antiferromagnetic fluctuations in the two-dimensional Hubbard model

Commensurate and incommensurate antiferromagnetic fluctuations in the two-dimensional repulsive t-t'-Hubbard model are investigated using functional renormalization group equations. For a sufficient deviation from half filling we establish the existence of local incommensurate order below a pseudocritical temperature T_{pc}. Fluctuations not accounted for in the mean field approximation are important--they lower T_{pc} by a factor \approx2.5.Comment: 7 pages, 8 figures, some changes due to referees' comments, equivalent to published versio

Diagnóstico nutricional de uma lavoura de soja a partir de informações georreferenciadas.

RESUMO: Neste trabalho, objetivou-se identificar os fatores relacionados à produtividade da soja, utilizando informações georreferenciadas sobre o estado nutricional das plantas, atributos do solo e produtividade da cultura. Uma área de 27,5 hectares foi dividida em grade amostral regular de 50 x 50m para coletas de folhas e do solo para análise. A colheita foi monitorada por meio de uma colhedora equipada com sensor de produtividade e DGPS. Os resultados das análises de solo e de folhas foram interpretados agronomicamente e correlacionados entre si e com a produtividade. Foram gerados mapas representando a espacialização das variáveis mais relevantes. Não foram obtidas correlações significativas dos teores foliares de nutrientes com as características do solo ou com a produtividade. Na lavoura estudada, os teores da matéria orgânica e potássio no solo e a saturação do potássio na CTC são os atributos mais relacionados com a produtividade da soja. ABSTRACT: The aim of this study was to identify yield conditioning factors of a soybean crop, based on georreferenced information concerning the plant nutritional status, soil attributes, and crop yield. An area of 27,5 ha was divided in a regular grid of 50 x 50m for colecting leaf and soil samples. The harvest was done using yield monitor and DGPS. Soil, plant, and yield data were interpreted on the agronomic basis, and submitted to correalation analysis. The spatial variation of the most important variables was mapped. It was not found any significant correlation among leaf nutrient concentrations and soil characteristics or yield. The soil organic matter and potassium contents, as well as the CEC potassium saturation, were the variables most correlated with the soybean yield.bitstream/CPAC-2009/27660/1/bolpd_145.pd

Dissolution of silicate minerals and nutrient availability for corn grown successively.

ABSTRACT - The objective of this work was to evaluate the nutrient availability for corn (Zea mays) grown successively in pure and ground biotite schist and biotite syenite rock samples. The rock powders were subjected to chemical, physical, and mineralogical characterization, and the availability of the elements released to the plants was determined. Plant and rock materials were evaluated at the end of seven successive growth cycles. Biotite schist and biotite syenite provided nutrients - as K, Ca, Mg, Fe, and Mn - to the corn plants. The nutrients accumulated in plant tissues came mostly from minerals containing oxidizable Fe and Mn in their structure, such as biotite, chlorite, and clinopyroxene. The congruent dissolution of some of the fine particles of these minerals, solubilize elements, which may, then, be available to the plants. RESUMO - O objetivo deste trabalho foi avaliar a disponibilidade de nutrientes para milho (Zea mays) cultivado sucessivamente em amostras das rochas puras e moídas biotita xisto e biotita sienito. Os pós das rochas foram submetidos à caracterização química, física e mineralógica, e a disponibilidade dos elementos liberados para as plantas foi determinada. Os materiais de planta e rocha foram avaliados no final de sete ciclos sucessivos de cultivo. A biotita xisto e a biotita sienito forneceram nutrientes - como K, Ca, Mg, Fe e Mn - para as plantas de milho. Os nutrientes acumulados no tecido das plantas vieram de minerais contendo Fe e Mn oxidáveis em sua estrutura, tais como biotita, chlorita e clinopiroxênio. A dissolução congruente de algumas partículas finas dos minerais, solubiliza elementos que podem, então, ser disponibilizados para as plantas.Título em português: Dissolução de minerais silicáticos e disponibilidade de nutrientes para milho cultivado sucessivamente

Impact of the Salt Concentration and Biophysical Cohesion on the Settling Behavior of Bentonites

The flocculation behavior of clay minerals in aquatic environments is an important process in estuarine and riverine dynamics, where strong gradients in salinity can locally occur. Various contradicting observations have been reported in the literature on the impact of salt concentration on the settling process of cohesive sediments. To address this issue in a systematic manner, we investigate the settling behavior of clay minerals as a function of the salt concentration of the ambient water. Specifically, we focus on montmorillonite as a prototype clay mineral with a high cation exchange capacity (CEC). To this end, we study suspensions of Wyoming bentonite (Volclay SPV) as a very important constituent for many constructional and industrial purposes. We perform an experimental campaign to study the settling behavior of moderately turbid montmorillonite concentrations in monovalent salt solutions with different salinities (sodium chloride) to represent different environments ranging from deionized to ocean water, respectively. The subsequent settling process was monitored by taking pictures by a camera in regular time intervals over a total observation time up to 48 h. In addition, a modified hydrometer analysis is conducted to determine the grain size distribution (in terms of an equivalent diameter) of the flocculated clay suspension in salt water. Despite the rather high cation exchange capacity of the investigated clay (CEC=88.1), our results show that the settling speed drastically increases within a range of 0.6–1.0 PSU and stays approximately constant for higher salinities. This critical salt concentration is defined here as the critical coagulation concentration (CCC) and lies well below the salinity of natural open water bodies. The hydrometer analysis revealed that 60% of the agglomerates exceed the equivalent grain size of 20 μm. Finally, the findings of this study are supplemented with experiments studying the effect of Extracellular Polymeric Substances (EPS) on the flocculation behavior of bentonite in salt water. Our results demonstrate that salinity is the original trigger for flocculation, whereas EPS allows for even larger floc size but it does not play a significant role for the settling processes of bentonite in estuarine environments

ARE MUSCLE FORCES RELEVANT IN THE AGE RELATED RISE OF INJURIES IN ADOLESCENT SOCCER PLAYERS?

The purpose of this study was the comparison of the kinematics and kinetics in soccer inside passes between three age groups (U12, U16, U23). Using 3D movement analysis and inverse dynamics, hip joint kinematics and adductor muscle forces were calculated. SPM analysis showed significant differences in adduction angle and velocity and in muscle forces of adductor longus and gracilis. Comparison of the muscle forces shows a rapid increase in muscle forces from the youngest children to the adolescents while the difference between the adolescents and adults is only minor. It seems reasonable, that the fast development of muscle forces in adolescents compared to the slower development of the tendons is a factor in the sudden rise in injury incidence at the beginning of puberty. Therefore, adolescent players should be trained with caution to avoid early injuries

HIP JOINT LOAD AND MUSCLE STRESS IN SOCCER INSIDE PASSlNG

Studies investigating the mechanisms of adductor injuries in soccer have concentrated on full effort kicks. Purpose of this study was a kinetic analysis of the inside pass. Using infrared cameras and inverse dynamics, hip joint moments and adductor muscle stress was calculated during the swing phase of the pass. Moments in the transverse plane were nearly as high as in full effort kicks reported previously. Muscle stress in the m. gracilis reached up to 450 kPa. Considering the repetitive nature of inside passes in modern sot; cer, adductor muscles undergo high loads in matches and training. This might contribute to the explanation of the high incidences of adductor injuries. Practitioners should therefore consider the load-recovery-relation even in inside pass training. Specific strength training programs for the adductor and abductor muscle groups should be developed

Increase in cation exchange capacity by the action of maize rhizosphere on Mg or Fe biotite-rich rocks.

O intemperismo de alguns minerais silicáticos em rochas moídas pode ocorrer em alguns dias de cultivo e gerar diferentes propriedades físico-químicas, com benefícios potenciais a solos tropicais. Objetivou-se investigar a influência da rizosfera do milho (Zea mays L.) nos produtos do intemperismo e na capacidade de troca de cátions da biotita-Mg da biotita xisto e biotita-Fe da biotita sienito. Um experimento em vasos foi conduzido de forma que plantas e rochas moídas foram avaliadas por sete ciclos de cultivo sucessivos. Os nutrientes ferro e potássio foram adquiridos da biotita xisto e da biotita sienito durante o cultivo. O intemperismo das biotitas promovido pela rizosfera causou mudanças mineralógicas. A mudança mais expressiva nos padrões da difração de raios-X ocorreu na fração com partículas < 53 &#956;m, mas as frações 53-300 &#956;m também mudaram. A alteração na biotita-Mg, que possui menor relação Fe/Mg nos sítios octaedrais que a biotita-Fe, foi responsável pelo maior aumento na capacidade de troca de cátions nas frações < 300 &#956;m. Entretanto, o processo de intemperismo da biotita-Fe, a qual apresenta alta relação Fe/Mg nos sítios octaedrais, não aumentou a capacidade de troca de cátion

Successive off take of elements by maize grown in pure basalt powder.

Abstract: Basalt powder wastes from mining activities have potential to be used as a natural fertilizer. Basalt minerals in agricultural soils may release plant nutrients and increase soil negative charge. In this work, the weathering of basalt promoted by maize rhizosphere was investigated. We studied the chemical and mineralogical composition of basalt, including cation exchange capacity, as well as the rate of elements offtake by maize grown in a pure basalt powder during seven successive growth cycles. A pot experiment was carried out under controlled environmental conditions; plant and rock materials were evaluated at the end of successive growth cycles. X-ray powder diffraction analysis showed diopside and andesine as main minerals of basalt, and smectite. Scanning electron microscopy images evidenced new amorphous components resulting from rhizosphere-induced weathering. The elements K, Ca, Mg, Al, B, Cu, Fe, Mn and Zn were measured in plant tissue, and related to the weathering of basalt minerals. The studied basalt, therefore, provides nutrients to plants and exhibits physicochemical properties, such as cation exchange capacity, especially important for highly weathered soils presenting low cation exchange capacity, such as Oxisols.Article Number - 9A4418A6291