Self-energy and Self-force in the Space-time of a Thick Cosmic String

We calculate the self-energy and self-force for an electrically charged particle at rest in the background of Gott-Hiscock cosmic string space-time. We found the general expression for the self-energy which is expressed in terms of the $S$ matrix of the scattering problem. The self-energy continuously falls down outward from the string's center with maximum at the origin of the string. The self-force is repulsive for an arbitrary position of the particle. It tends to zero in the string's center and also far from the string and it has a maximum value at the string's surface. The plots of the numerical calculations of the self-energy and self-force are shown.Comment: 15 pages, 4 Postscript figures, ReVTe

Efeito da adição de uréia e sulfato de amônio sobre o pH e nitrificação em um solo ácido

The variation of pH and the production of nitrate were studied in a Dark Red Latosol, Guamium séries, in function of the addition of 200 and 400 ppm of N, as urea and ammonium sulphate in the presence and absence of Ca(0H)2, for a period of 30 days. The results obtained showed that the pH decreased with ammonium sulphate and increased with urea. The variations were observed even in the presence of Ca(0H)2. The production of nitrate increased with pH considering the same level and source of nitrogen.A variação do pH e a produção de nitrato foram estudados em um Latossolo Vermelho Escuro, Série Guamium, em função da adição de 200 e 400 ppm de N nas formas de uréia e sulfato de amônio, em presença e ausência de Ca(OH)2 por um período de 30 dias. Os resultados obtidos mostraram que o pH decresceu com o sulfato de amônio e aumentou com a uréia. As variações foram observadas mesmo empresença de Ca(0H)2. A produção de nitrato aumentou com o pH, considerando o mesmo nível e fonte de nitrogênio. Não foi observado no conjunto uma relação entre pH e produção de nitrato

Influência do pH e dos teores de fosfato solúvel e matéria orgânica sobre a fixação de zinco pelo solo

The purpose of this experiment was to verify the effects of some properties of the soil as pH, and the content of soluble phosphate and organic matter on the soil capacity to fix zinc. Ten grams each of 30 samples of different soils were placed in a 250 ml Erlenmeyer flask and 4 ml of solution containing 100 mg of inert zinc and 0.7 mcof radioactive 65Zn were added. After 20 days of incubation, Zn was extracted with 20 ml of 0.01 M EDTA solution made 1M respect to (NH4)2CO3. An aliquot of 5 ml of the extract was transferred to a test tub and radioactivity of 65 Zn in it was measured with a scintillation counter. Quantity of zinc fixed by the different soils was calculated from the data obtained and county made on the standard solution. It was concluded that the amount of zinc fixed by the soil was positively correlated with pH, soluble phosphate and organic matter content of the soils.No presente trabalho os autores apresentam um estudo dos efeitos do pH e dos teores de fosfato solúvel em H2SO4 0,05 N e de matéria orgânica do solo sobre a capacidade de fixação de Zn do mesmo. Na execução do ensaio utilizaram uma técnica traçadora sendo o 65Zn o elemento traçador. Foi concluído que as quantidades de Zn fixadas estão direta e positivamente correlacionadas com o pH, com o teor de fosfato solúvel e de matéria orgânica dos solos

Angle-resolved photoemission in doped charge-transfer Mott insulators

A theory of angle-resolved photoemission (ARPES) in doped cuprates and other charge-transfer Mott insulators is developed taking into account the realistic (LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random field potential. In most of these materials the first band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the non-crossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. Some unusual features of ARPES including the polarisation dependence and spectral shape in YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or small. The theory is compatible with the doping dependence of kinetic and thermodynamic properties of cuprates as well as with the d-wave symmetry of the superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.

Simulating maize yield in sub-tropical conditions of southern Brazil using Glam model

The objective of this work was to evaluate the feasibility of simulating maize yield in a sub‑tropical region of southern Brazil using the general large area model (Glam). A 16‑year time series of daily weather data were used. The model was adjusted and tested as an alternative for simulating maize yield at small and large spatial scales. Simulated and observed grain yields were highly correlated (r above 0.8; p<0.01) at large scales (greater than 100,000 km2), with variable and mostly lower correlations (r from 0.65 to 0.87; p<0.1) at small spatial scales (lower than 10,000 km2). Large area models can contribute to monitoring or forecasting regional patterns of variability in maize production in the region, providing a basis for agricultural decision making, and Glam‑Maize is one of the alternatives